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Curing of drying oil in wood fibre webs by gamma-irradiation Paszner, Laszlo 1966

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CURING OF DRYING OIL I N WOOD FIBRE WEBS BY GAMMA-IRRADIATION by LASZLO PASZNER B.S.F. ( S o p r o n D i v i s i o n ) U n i v e r s i t y o f , B r i t i s h C o l u m b i a 1959 M.F. U n i v e r s i t y o f B r i t i s h C o l u m b i a 1963 A THESIS SUBMITTED I N PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n t h e Department o f F o r e s t r y We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA March, 1966 "In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the require-ments for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I further agree that permission f o r extensive copying of th i s thesis for scholarly purposes may be granted by the Head of my Department or by his representative. I t i s understood that copying or p u b l i c a t i o n of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission." Copyright by Laszlo Paszner March 29, 1966 The University of B r i t i s h Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR. OF PHILOSOPHY OF LASZLO PASZNER B.S.F., The University of B r i t i s h Columbia (Sopron D i v i s i o n ) , 1958 M„F.., The University of B r i t i s h Columbia, 1.963 TUESDAY, MARCH. 29, 1966 at: 10:30 A.M.„ IN ROOM. 239:. FORESTRY AND GEOLOGY BUILDING COMMITTEE IN CHARGE Chairman: I. McT. Cowan J . A, F. Gardner J „ H. G. Smith P, Go Haddock. R. Wo Wellwood 1... D„ Hayward J . W.. Wilson External Examiner: B. Leopold Empire State Paper Research I n s t i t u t e State University College of Forestry Syracuse,, New York. Research Supervi sor: J . Wo Wilson CURING OF DRYING OIL IN FIBRE WEBS BY GAMMA-IRRADIATION ABSTRACT Means are described for improving mechanical properties of wood f i b r e webs made from high y i e l d acid sulfite., k r a f t and groundwood pulps, as well as blends of both chemical pulps with groundwood= The procedure includes saturation of dried f i b r e webs with hydrocarbon drying o i l and subsequent: polymeriz-ation of the o i l by prolonged high temperature curing or by use of ^ 0QO gamma-ray i r r a d i a t i o n as energy source. The treatment was shown to strengthen i n t e r -f i b r e bonding. No e f f e c t s on i n t r i n s i c f i b r e , s t r e n g t h were noted. Tensi l e strength, parameters (maximum stress, ultimate s t r a i n , e l a s t i c modulus and t e n s i l e energy absorption) were used for sorting treatment e f f e c t s on paper handsheets prepared from the various materials. Wood f i b r e s a r i s i n g from the d i s s i m i l a r pulping pro-cesses were shown to behave i n the same manner observed previously as thermal " o i l tempering" of highly l i g n i -f i e d mechanical pulps. Mathematical models were used to describe mechanical property adjustments as rela t e d to treatments. B r i e f l y , thermal polymerization raised maximum t e n s i l e strength by 50-80% for the high y i e l d chemical pulps and 120% for groundwood. Gamma-irradia-t i o n induced curing provided up to 70%, of values had by thermal treatment. Thermal, after-treatment of ir r a d i a t e d samples provided maximum values, suggesting s i m i l a r mechanism for the two methods. Maximum e f f i c i e n c y of gamma-irradiation, induced curing occurred between lO^-lO^ rad i n t e g r a l dosage. This i s below the c r i t i c a l l e v e l causing serious degra-dation of wood f i b r e carbohydrates. The technique provides some advantages over thermal curing, such as more rapid polymerization rate, lower e l a s t i c moduli, and much less d i s c o l o r a t i o n with highly l i g n i f i e d pulps. Residual l i g n i n i n pulp f i b r e s appears to be an important v a r i a b l e c o n t r o l l i n g extra strength development by o i l polymerization treatments. Evidence was sought for d i s t i n g u i s h i n g between homopolymer and o i l - l i g n i r i g r a f t copolymer formation through, assessment of basic mechanical strength parameters and f i b r e fracture patterns and by use of organic solvent techniques. In a d d i t i o n l t o the main materials of the study, h i g h l y . p u r i f i e d pulps and glass f i b r e were examined i n t h i s regard. The presence of an o i l - l i g n i n . g r a f t copolymer.was not shown conclusively. GRADUATE STUDIES F i e l d s of Study- : Wood Technology (Forestry) and Chemistry Research i n Wood Properties Research i n Wood Anatomy Physical and Chemical Properite-s of Wood General. Forestry Seminar Modern A n a l y t i c a l Methods i n Chemistry Advanced Organic Chemistry D i g i t a l Computer Programming J. W. Wilson R, W. Wellwood J.. W, Wilson J, W. Wilson P. G. Haddock J. B. Farmer D. E. McGreer C. Froese PUBLICATION Paszner s 1.. and J . W. Wilson. 1965= Influence of Fiber Chemical Constituents on Oil-Tempering of Hardboardo Forest Prod. J . 15: 206-214= S u p e r v i s o r : P r o f e s s o r J a c k W. W i l s o n ABSTRACT A t e c h n i q u e i s d e s c r i b e d f o r i m p r o v i n g wood f i b r e web s t r e n g t h by c o p o l y m e r i z a t i o n o f a h y d r o c a r b o n d r y i n g o i l (CTLA P o l y m e r ) w i t h i n hand-s h e e t s made from pure and admixed forms o f h i g h y i e l d c h e m i c a l ( s u l f i t e and s u l f a t e ) and groundwood f i b r e s . O i l p o l y m e r i z a t i o n can be i n i t i a t e d s u c c e s s -f u l l y by p r o l o n g e d t h e r m a l t r e a t m e n t a t 145°C, as w e l l as by t h e n o v e l method of low dosage gamma-ray i r r a d i a t i o n . The t r e a t m e n t s t r e n g t h e n s i n t e r -f i b r e b o n d i n g . E v i d e n c e f o r c o p o l y m e r i z a t i o n was sought t h r o u g h assessment o f t e n s i l e and r e l a t e d s t r e n g t h d a t a on v a r i o u s l y t r e a t e d s t a n d a r d h a n d s h e e t s . E f f e c t i v e n e s s o f t h e p o l y m e r i z a t i o n on p u l p t y p e s i n v e s t i g a t e d as i n i t i a t e d by h e a t and low dosage i r r a d i a t i o n i s s t r o n g l y r e l a t e d t o s u r f a c e c o l l o i d a l and b a s i c p h y s i c a l and m e c h a n i c a l p r o p e r t i e s o f the f i b r e s . Maximum s t r e n g t h p a r a m e t e r s were o b t a i n e d w i t h o i l s a t u r a t e d s u l f i t e and groundwood h a n d s h e e t s f o l l o w i n g p o l y m e r i z a t i o n by t h e r m a l t r e a t m e n t . C o p o l y m e r i z a t i o n e f f i c i e n c y by i r r a d i a t i o n , on t h e o t h e r hand, i s e s t i m a t e d as 73 "L f o r s u l f i t e , 65 % f o r groundwood and 50 % f o r k r a f t h a n d s h e e t s . E f f e c t i v e n e s s o f o i l polymer-i z a t i o n by i r r a d i a t i o n was found t o be p r o p o r t i o n a l t o dosages up t o 10^ r a d . As a n t i c i p a t e d , l i m i t o f s t r e n g t h improvement was not s e t e n t i r e l y by . i n t r i n s i c f i b r e s t r e n g t h , b u t was a l s o i n f l u e n c e d by s u r f a c e c o l l o i d a l I p r o p e r t i e s o f the f i b r e s . B l e n d s made from chemical-groundwood f i b r e m i x t u r e s behaved more or l e s s p r o p o r t i o n a l t o i n d i v i d u a l p u l p s t r e n g t h s and e x t e n t o f b l e n d i n g . C o p o l y m e r i z e d s u l f i t e - g r o u n d w o o d b l e n d s a t e q u a l p r o p o r t i o n s a p p r o x i m a t e d t h e t e n s i l e s t r e n g t h o f s i m i l a r k r a f t papers s u g g e s t i n g b e t t e r economy w i t h k r a f t f i b r e s when papers o f l i m i t e d s t r e n g t h a r e produced. A l l o t h e r s t r e n g t h p a r a m e t e r s ( e l a s t i c modulus, t e n s i l e s t r a i n and t e n s i l e e n ergy a b s o r p t i o n ) f o l l o w e d s i m i l a r t r e n d s , o r i f d i f f e r e n t were o f a i d i n e x p l a i n i n g c e r t a i n phenomena c h a r a c t e r i s t i c t o t r e a t e d f i b r e webs. The p r e s e n c e o f g r a f t c o polymer c o u l d n o t be c o n c l u s i v e l y p r o v e n , s i n c e b o t h t h e copolymer"and o i l homopolymer a r e i n s o l u b l e i n t h e u s u a l o r g a n i c s o l v e n t s . A d u a l c h a r a c t e r o f the o i l p olymer was d e m o n s t r a t e d w i t h g l a s s f i l t e r p a p e r and h i g h l y p u r i f i e d c o m m e r c i a l c e l l u l o s e : f i b r e s * E f f e c t i v e n e s s o f o i l p o l y m e r i z a t i o n i n h i g h l y l i g n i f i e d m e c h a n i c a l p u l p s was g r e a t l y d e p r e s s e d by m i l d sodium c h l o r i t e t r e a t m e n t , a l t h o u g h t h e s t r e n g t h and b o n d i n g c a p a c i t y o f su c h f i b r e s i n c r e a s e d c o n s i d e r a b l y . T h i s was t a k e n as d i r e c t e v i d e n c e f o r t h e p o s s i b i l i t y o f a l i g n i n - C T L A P o l y m e r copolymer system. S i t e o f c h e m i c a l r e a c t i o n has n o t been d e s c r i b e d , a l t h o u g h means f o r assessment o f s u c h i n f o r m a t i o n a r e s u g g e s t e d . The s t u d y p r o v e s t h e u s e f u l n e s s o f gavma»^E^M^M'M'n:' as energy s o u r c e f o r t h e c o p o l y e r i z a t i o n o f d r y i n g o i l s i n h a n d s h e e t s as r e p l a c e m e n t f o r t h e p r o l o n g e d t h e r m a l t r e a t m e n t h i t h e r t o used by the h a r d b o a r d i n d u s t r y . Added advantages o f i r r a d i a t i o n p r o c e s s e d c o p o l y m e r i z e d p a p e r s a r e l e s s d i s c o l o r a t i o n , e s p e c i a l l y w i t h " h i g h l i g n i n c o n t e n t p u l p s , and l o w e r e l a s t i c modulus, a f a c t o r c l e a r l y o b j e c t i o n a b l e f o r some paper u s e s . i v . TABLE OF CONTENTS Page TITLE PAGE i ABSTRACT I I TABLE OF CONTENTS . i i i LIST OF TABLES v i i i L I ST OF FIGURES * ACKNOWLEDGEMENT x i i i INTRODUCTION 1 LITERATURE REVIEW 6 I . RESIDUAL LIGNIN IN WOOD PULPS 6 1. P u l p s from M e c h a n i c a l and S e m i - c h e m i c a l P r o c e s s i n g 7 2. P u l p s f r o m C h e m i c a l P r o c e s s i n g ... 11 a. R e s i d u a l l i g n i n i n a c i d s u l f i t e p u l p s 12 b. R e s i d u a l l i g n i n i n s u l f a t e p u l p s 15 3. D i f f e r e n c e s i n R e s i d u a l L i g n i n as R e s u l t o f P r o c e s s i n g 18 I I . THERMAL TREATMENT OF WOOD AND WOOD FIBRE PRODUCTS 20 1. H i g h Temperature Treatment o f Wood 21 2. Thermal Treatment o f Wood F i b r e P r o d u c t s 22 a. Heat t r e a t m e n t o f wood f i b r e b o a r d s 22 b. Heat t r e a t m e n t o f papers 25 3. Summary o f Thermal E f f e c t s 29 I I I . GAMMA-RADIATION AS ENERGY SOURCE IN CHEMICAL REACTIONS 30 1. G e n e r a l D e s c r i p t i o n o f Gamma-Rays 30 V. Page 2. Mechanism of R a d i a t i o n I o n i z a t i o n 31 3. D e g r a d a t i o n v e r s u s C r o s s - L i n k i n g o f P o l y m e r s 38 4. Fundamentals o f R a d i a t i o n G r a f t i n g 40 IV. EFFECT OF IONIZING RADIATION ON THE PHYSICAL AND CHEMICAL PROPERTIES OF WOOD AND WOOD HIGH POLYMERS 45 1. E f f e c t s w i t h Wood 45 2. E f f e c t s w i t h I s o l a t e d Wood C a r b o h y d r a t e F r a c t i o n s 47 3. E f f e c t s w i t h Wood A r o m a t i c Compounds and R a d i o p r o t e c t i o n o f P o l y m e r i c C a r b o h y d r a t e s 54 V. INFLUENCE OF RADIATION ON ORGANIC HYDROCARBON POLYMERS 61 V I . RADIATION GRAFTING ONTO WOOD AND WOOD CONSTITUENTS 63 1. G r a f t i n g onto Wood 63 2. G r a f t i n g o n t o C e l l u l o s e 64 3. G r a f t i n g o n t o L i g n i n 70 4. Summary S e c t i o n 72 MATERIALS AND METHODS 74 I . MATERIALS 75 1. P u l p Types 75 a. Groundwood p u l p 76 b. A c i d s u l f i t e p u l p 78 c. K r a f t p u l p 80 d. Other f i b r e m a t e r i a l s 82 2. Wood Microtome S e c t i o n s 82 3. D r y i n g O i l 83 I I . METHODS 85 1. P r e p a r a t i o n o f Handsheets 85 v i . Page 2. P a p e r T r e a t m e n t s 87 A. U n t r e a t e d c o n t r o l s 87 B. Heat t r e a t e d c o n t r o l s 89 C. I r r a d i a t e d c o n t r o l s 89 D. O i l d i p p e d c o n t r o l s 90 E. T h e r m a l l y p o l y m e r i z e d 92 F. R a d i a t i o n p o l y m e r i z e d 93 G. R a d i a t i o n p l u s t h e r m a l l y p o l y m e r i z e d 93 3. T e n s i o n T e s t Methods 94 4. S t a t i s t i c a l A n a l y s e s 95 a. Curve f i t t i n g 96 b. A n a l y s i s o f v a r i a n c e 97 c. R e l a t i o n s h i p between dependent v a r i a b l e s 97 RESULTS 99 DISCUSSION 101 I . THERMAL POLYMERIZATION WITH THIN WOOD SECTIONS 102 I I . THERMAL AND IRRADIATION INDUCED POLYMERIZATION WITH PULP HANDSHEETS 104 1. Mechanism o f B o n d i n g i n Paper 105 2. S t r e s s - S t r a i n P r o p e r t i e s o f Paper Webs 108" a. F i b r e s t r e n g t h 110 b. Bond s t r e n g t h 110 c. Degree o f f i b r e b o n d i n g I l l 3. P o l y m e r i z a t i o n w i t h Groundwood Handsheets 113 a. Thermal t r e a t m e n t 114 v i i . Page b. Gamma-ray i r r a d i a t i o n t r e a t m e n t 115 4. P o l y m e r i z a t i o n w i t h S u l f i t e Handsheets 119 a. Thermal t r e a t m e n t 120 b. Gamma-ray i r r a d i a t i o n t r e a t m e n t 121 c. O t h e r m a t e r i a l s 123 5. P o l y m e r i z a t i o n w i t h K r a f t Handsheets 124 a. Thermal t r e a t m e n t 125 b. Gamma-ray i r r a d i a t i o n t r e a t m e n t 126 6. P o l y m e r i z a t i o n w i t h Handsheets P r e p a r e d from P u l p F i b r e B l e n d s . 131 a. Thermal t r e a t m e n t 136 b. Gamma-ray i r r a d i a t i o n t r e a t m e n t 138 SUMMARY 146 CONCLUSIONS 153 REFERENCES 154 APPENDIX 171 TABLES AND FIGURES ,. 172 LIST OF TABLES v i i i . Page T a b l e I . P r o d u c t i o n o f f r e e r a d i c a l s by g a m m a - i r r a d i a t i o n o f o r g a n i c l i q u i d s (2$) 37 T a b l e I I . D e g r a d a t i o n o f c e l l u l o s e b y g a m m a - i r r a d i a t i o n (84) .... 52 T a b l e I I I . C a l c u l a t e d maximum d i s t a n c e between b e n z o y l groups as a f u n c t i o n o f degree o f s u b s t i t u t i o n (25) 57 T a b l e IV. E f f e c t o f h i g h dosage i r r a d i a t i o n on t e n s i l e s t r e n g t h and DP of Douglas f i r wood, zones' (86) 59 T a b l e V. Wood s p e c i e s c o m p o s i t i o n o f p u l p s 75 T a b l e V I . Summary o f p e r t i n e n t d a t a on p u l p s 81 T a b l e V I I . S p e c i f i c a t i o n s and some p r o p e r t i e s o f CTLA Polymer (61) 84 T a b l e V I I I . B a s i s w e i g h t o f handsheets made from v a r i o u s b l e n d s o f s u l f i t e - g r o u n d w o o d (SG) and k r a f t - g r o u n d w o o d (KG) p u l p s 86 T a b l e I X . N e c e s s a r y number o f t e n s i l e t e s t r e p l i c a t e s f o r groundwood, s u l f i t e and k r a f t h a n d s h e e t s 88 T a b l e X. E x t r a c t i o n o f o i l polymer f o l l o w i n g normal paper t r e a t m e n t s as e x p r e s s e d i n per c e n t o f sample w e i g h t l o s s 94 T a b l e X I . A n a l y s i s o f v a r i a n c e f o r t e n s i l e s t r e n g t h o f handsheets made from s u l f i t e - and k r a f t - g r o u n d w o o d p u l p b l e n d s ... 97 T a b l e X I I . Mean u l t i m a t e t e n s i l e s t r e n g t h ( p s i ) ( Y , ) v a l u e s f o r han d s h e e t s made from s u l f i t e - g r o u n d w o o d b l e n d s T a b l e X I I I . Mean e l a s t i c i t y ( p s i / 1 0 0 ) ( Y 2 ) v a l u e s f o r h a n d s h e e t s made from s u l f i t e - g r o u n d w o o d p u l p b l e n d s 174 T a b l e XIV. Mean v a l u e s o f u l t i m a t e t e n s i l e s t r a i n ( i n . / i n . ) . 1 0 ) ( Y j ) f o r handsheets made from s u l f i t e - g r o u n d w o o d p u l p b l e n d s 175 T a b l e XV. Mean v a l u e s o f maximum t e n s i l e e nergy a b s o r p t i o n ( i n . l b / c u i n . ) ( Y ^ ) f o r h a n d s h e e t s made from s u l f i t e -groundwood p u l p b l e n d s 176 i x . Page T a b l e X V I . Mean u l t i m a t e t e n s i l e s t r e n g t h ( p s i ) (Y-^) v a l u e f o r ha n d s h e e t s made fr o m k r a f t - g r o u n d w o o d p u l p b l e n d s 177 T a b l e X V I I . Mean e l s a t i c i t y ( p s i / 1 0 0 ) ( Y 2 ) v a l u e s f o r h a n d s h e e t s made from k r a f t-groundwood p u l p b l e n d s 178 T a b l e X V I I I . M e a n v a l u e s o f u l t i m a t e t e n s i l e s t r a i n ( i n . / i n . ) . 1 0 ) (Yg) f o r ha n d s h e e t s made from k r a f t - g r o u n d w o o d p u l p b l e n d s 179 T a b l e X IX. Mean v a l u e s o f maximum t e n s i l e e nergy a b s o r p t i o n ( i n . l b / c u i n . ) (Y4) f o r h a n d s h e e t s made from k r a f t -groundwood p u l p b l e n d s , . . . 180 T a b l e XX. E q u a t i o n s f o r c a l c u l a t e d r e s p o n s e s u r f a c e s 181 T a b l e X X I . E f f e c t o f t h e r m a l and i r r a d i a t i o n g r a f t i n g on s t r e n g t h p r o p e r t i e s o f h a n d s h e e t s made from t h e t h r e e b a s i c p u l p s 188 T a b l e X X I I . P e r c e n t t e n s i l e s t r e n g t h i n c r e a s e on some p u r i f i e d p u l p s b e f o r e and a f t e r sodium c h l o r i t e and o i l p o l y m e r i z a t i o n t r e a t m e n t s 189 T a b l e X X I I I . E q u a t i o n s f o r c a l c u l a t e d dependent v a r i a b l e c o r r e l a t i o n s 190 L I S T OF FIGURES Page F i g u r e 1. F r e e r a d i c a l c o n c e n t r a t i o n s i n i r r a d i a t e d wood and wood p r o d u c t s . Decay a t 25°C. R a d i a t i o n dosage c a . 10 Mrads (186) 34 F i g u r e 2. E f f e c t o f h e a t i n g on f r e e r a d i c a l c o n c e n t r a t i o n . (a) ESR.spectrum i m m e d i a t e l y a f t e r i r r a d i a t i o n ; (b) ESR s p e c t r u m a f t e r h e a t i n g t h e sample f o r 2 h r a t 105°C (186) 35 6n F i g u r e 3. D e g r a d a t i o n o f c e l l u l o s e by g a m m a - i r r a d i a t i o n ( Co s o u r c e c e n t r a l i n t e n s i t y 1.3x10 r a d / h r ) (84) 52 F i g u r e 4. E f f e c t o f g a m m a - i r r a d i a t i o n on t h e c a l c u l a t e d d i s t a n c e between m o l e c u l a r c l e a v a g e s o f f i b r o u s b e n z o y l a t e d c o t t o n c e l l u l o ^ | as a f u n c t i o n o f degree o f s u b s t i t u t i o n . Dosage: 1.3x10 e.v./g c e l l u l o s e (15) 58 F i g u r e 5. Change o f p u l p m e t h o x y l c o n t e n t as a f u n c t i o n o f i r r a d i a t i o n dosage 91 F i g u r e 6. S c a n n i n g e l e c t r o n p h o t o m i c r o g r a p h s o f wood t e n s i l e f r a c t u r e s b e f o r e and a f t e r i r r a d i a t i o n and t h e r m a l g r a f t i n g 191 F i g u r e 7. S c a n n i n g e l e c t r o n p h o t o m i c r o g r a p h s o f paper t e n s i l e f r a c t u r e s b e f o r e and a f t e r g r a f t i n g 192 F i g u r e 8. Deep t e n s i l e f r a c t u r e o f k r a f t paper 193 F i g u r e 9. S u l f i t e - g r o u n d w o o d handsheet t e n s i l e s t r e n g t h (Y^) as a f u n c t i o n o f b l e n d i n g and p o s t - s h e e t f o r m a t i o n t r e a t m e n t s 194 F i g u r e 10. K r a f t - g r o u n d w o o d handsheet t e n s i l e s t r e n g t h (Y^) as a f u n c t i o n p u l p b l e n d i n g and p o s t - s h e e t f o r m a t i o n t r e a t -ments 194 F i g u r e 11. Change of s u l f i t e - g r o u n d w o o d handsheet e l a s t i c i t y (Y2) as a f u n c t i o n o f b l e n d i n g and p o s t - s h e e t f o r m a t i o n t r e a t m e n t s 195 F i g u r e 12. Change o f k r a f t - g r o u n d w o o d handsheet e l a s t i c i t y ( Y 2 ) as a f u n c t i o n o f p u l p b l e n d i n g and p o s t - s h e e t t r e a t m e n t s 195 x i . Page F i g u r e 13. E f f e c t o f p u l p b l e n d i n g and p o s t - s h e e t f o r m a t i o n t r e a t m e n t s on u l t i m a t e t e n s i l e s t r a i n (Y3) o f s u l f i t e - g r o u n d w o o d h a ndsheets 196 F i g u r e 14. E f f e c t o f p u l p b l e n d i n g and p o s t - s h e e t f o r m a t i o n t r e a t m e n t s on u l t i m a t e t e n s i l e s t r a i n (Y^) o f k r a f t-groundwood h a n d s h e e t s 196 F i g u r e 15. Maximum t e n s i l e e n e r g y a b s o r p t i o n (Y4) o f s u l f i t e -groundwood h a n d s h e e t s as a f u n c t i o n o f p u l p b l e n d i n g and p o s t - s h e e t f o r m a t i o n t r e a t m e n t s 197 F i g u r e 16. Maximum t e n s i l e e n ergy a b s o r p t i o n (Y^) o f k r a f t -groundwood handsheets as a f u n c t i o n o f p u l p b l e n d i n g and p o s t - s h e e t f o r m a t i o n t r e a t m e n t s 197 F i g u r e 17. A b s o l u t e s t r e n g t h i n c r e a s e due t o t h e r m a l and i r r a d i a t i o n g r a f t i n g . o n t o s u l f i t e - and k r a f t - g r o u n d w o o d h a n d s h e e t s . 198 F i g u r e 18. E f f e c t o f e x t r a c t a b l e monomer r e s i d u e s and homopolymer f r a c t i o n s ( e x p r e s s e d as p e r c e n t a g e o f sample w e i g h t ) on i n i t i a l t e n s i l e s t r e n g t h o f o i l d i p p e d (D) specimens f o l l o w i n g t h e r m a l (E) and g a m m a - i r r a d i a t i o n g r a f t i n g (F,G) 199 F i g u r e 19. T e n s i l e s t r e n g t h o f s u l f i t e - and k r a f t - g r o u n d w o o d hand-s h e e t s as c a l c u l a t e d from t h e s i g n i f i c a n t i n t e r a c t i o n between p u l p t y p e and l e v e l o f p u l p b l e n d i n g 200 F i g u r e 20. R e l a t i o n s h i p between u l t i m a t e t e n s i l e s t r e n g t h (Y-^) and modulus o f e l a s t i c i t y ( Y 2 ) f o r handsheets made from s u l f i t e - and k r a f t - g r o u n d w o o d b l e n d s 201 F i g u r e 21. R e l a t i o n s h i p between u l t i m a t e t e n s i l e s t r e n g t h (Y^) and u l t i m a t e t e n s i l e s t r a i n (Y3) f o r h a n d s h e e t s made from s u l f i t e - and k r a f t - g r o u n d w o o d b l e n d s 202 F i g u r e 22. R e l a t i o n s h i p between u l t i m a t e t e n s i l e s t r e n g t h (Y^) and t e n s i l e energy a b s o r p t i o n (Y,) f o r h a n d s h e e t s made from s u l f i t e - and k r a f t - g r o u n d w o o d b l e n d s 203 F i g u r e 23. R e l a t i o n s h i p between modulus o f e l a s t i c i t y ( Y 2 ) and u l t i m a t e t e n s i l e s t r a i n (Y3) f o r handsheet made from s u l f i t e - and k r a f t - g r o u n d w o o d b l e n d s 204 F i g u r e 24. R e l a t i o n s h i p between modulus o f e l a s t i c i t y ( Y 2 ) and t e n s i l e energy a b s o r p t i o n (Y^) f o r h a n d s h e e t s made from s u l f i t e - and k r a f t - g r o u n d w o o d b l e n d s 205 x i i . Page F i g u r e 25. Scheme f o r s e l e c t i v e m e t h y l a t i o n o f l i g n i n i n wood .... 206 F i g u r e 26. D i s c o l o r a t i o n o f groundwood, s u l f i t e and k r a f t p apers due t o i r r a d i a t i o n and t h e r m a l g r a f t i n g 207 F i g u r e 27, C h a r a c t e r i s t i c s t r e s s - e l o n g a t i o n c u r v e s f o r 50:50 s u l f i t e - g r o u n d w o o d b l e n d s 208 x i i i . ACKNOWLEDGMENT The a u t h o r acknowledges w i t h g r a t i t u d e h i s a p p r e c i a t i o n t o D r . J . W. W i l s o n , P r o f e s s o r , F a c u l t y o f F o r e s t r y , f o r h i s v a l u a b l e p r o f e s s i o n a l a s s i s t a n c e i n p l a n n i n g and e x p e r i m e n t a l phases and p r e p a r i n g t he t h e s i s , as w e l l as f o r h i s c o n s c i e n t i o u s and u n d e r s t a n d i n g g u i d a n c e o v e r the p a s t f o u r y e a r s a t t h i s U n i v e r s i t y ; t o D r . R.W. Wellwood, P r o f e s s o r , F a c u l t y o f F o r e s t r y and D r . L.D. Hayward, A s s o c i a t e P r o f e s s o r , Department o f C h e m i s t r y , f o r h e l p f u l s u g g e s t i o n s and c r i t i c i s m ; t o D r . A. Kozak, A s s i s t a n t P r o f e s s o r , F a c u l t y o f F o r e s t r y , f o r t h e s t a t i s t i c a l a n a l y s i s and computer programming; t o D r . J.A.F. G a r d n e r , Dean, and D r . J.H.G. S m i t h , P r o f e s s o r , F a c u l t y o f F o r e s t r y , f o r t h e i r a d v i s o r y h e l p ; and t o Dr. B. L e o p o l d , D i r e c t o r , E m p ire S t a t e P a p e r R e s e a r c h " I n s t i t u t e ;• S t a t e / E o ' l l e g e o f ^ F o r e s t r y Syracuse,••; ••% •>.*... U n i v e r s i t y , f o r s e r v i n g as E x t e r n a l Examiner o f t h e t h e s i s ; t o M a c M i l l a n , B l o e d e l and P o w e l l R i v e r , . L i m i t e d , f o r t h e e x p e r i m e n t a l p u l p m a t e r i a l and p r o -v i d i n g f a c i l i t i e s f o r h a n dsheet p r e p a r a t i o n ; t o Mr. A.G. D a v i e s o f A t o m i c Energy o f Canada, L i m i t e d , f o r t h e gamma-ray i r r a d i a t i o n t r e a t m e n t s ; t o Mr. H. Green, P u l p and Paper R e s e a r c h I n s t i t u t e o f Canada, f o r p r e p a r a t i o n . o f t h e s c a n n i n g e l e c t r o n p h o t o m i c r o g r a p h s ; t o M i s s . J . E t h r i d g e and Mr. U. Rumma, T e c h n i c i a n , F a c u l t y o f F o r e s t r y , f o r t h e i r h e l p i n p r e p a r i n g t h e h a n d s h e e t s ; to t h e N a t i o n a l R e s e a r c h C o u n c i l o f Canada, f o r r e p e a t e d f i n a n c i a l s u p p o r t d u r i n g t h e t h r e e - y e a r academic programme; t o t h e P u l p and Paper R e s e a r c h I n s t i t u t e o f Canada f o r a s s i s t a n c e ; and l a s t , b u t . n o t • l e a s t t o Mrs. M. P a s z n e r f o r h e r p a t i e n c e , d e v o t i o n and k i n d u n d e r s t a n d i n g t h r o u g h o u t t h e s e memorable y e a r s . -1-INTRODUCTION \-D u r i n g t h e p a s t decade i n t e n s e c o m p e t i t i o n has d e v e l o p e d between c e l l u l o s i c m a t e r i a l s and v a r i o u s s y n t h e t i c p o l y m e r s . Some t r a d i t i o n a l c e l l u l o s e markets have p a r t l y o r e n t i r e l y g i v e n way t o man-made f i b r e s and f i l m s . The e f f e c t has been t o promote new r e s e a r c h e f f o r t s d i r e c t e d a t improvement o f wood and wood p r o d u c t p r o p e r t i e s by m o d i f y i n g b o t h t h e i r p h y s i c a l and c h e m i c a l s t r u c t u r e . P a r t o f t h e answer i s b e i n g found by b l e n d i n g n a t i v e wood p r o p e r t i e s w i t h t h o s e o f q u i t e d i s s i m i l a r m a t e r i a l s . T h i s has l e d i n r e c e n t y e a r s t o development o f methods f o r g r a f t i n g and c o p o l y m e r i z a t i o n o f v a r i o u s polymers o n t o wood base c o n s t i t u e n t s namely, c e l l u l o s e and l i g n i n . An a t t r a c t i v e energy s o u r c e f o r f o r m i n g such c o m p o s i t e s has been found i n t h e form o f gamma-rays. E a r l y o b s e r v a t i o n s o f i r r a d i a t i o n e f f e c t s on v a r i o u s s y n t h e t i c s has s t i r r e d g r e a t hopes r e g a r d i n g a d j u s t m e n t o f polymer p r o p e r t i e s . Expo-s u r e o f n a t u r a l r u b b e r t o i o n i z i n g r a d i a t i o n i s known t o d e c r e a s e i t s v i s c o s i t y , i o d i n e number, m o l e c u l a r w e i g h t , and s o f t e n i n g p o i n t . S h o r t , i n t e n s e b u r s t s o f e l e c t r i c a l d i s c h a r g e cause r u b b e r v u l c a n i z a t i o n . E i t h e r c h a i n s c i s s i o n o r c r o s s - l i n k i n g r e s u l t s from i o n i z a t i o n o f a v a r i e t y o f n a t u r a l and s y n t h e t i c polymers (9, 29, 47, 125, 177, 2 2 2 ) . W i t h wood t h e major e f f e c t o f i r r a d i a t i o n i s d e g r a d a t i o n . Below 105 r a d i n t e g r a l dosage d e g r a d a t i o n i s s m a l l (86) and h a r d l y d e t e c t a b l e on m e c h a n i c a l s t r e n g t h (21, 3 9 ) . However, i r r a d i a t i o n dosages i n excess o f 10^ -2-r a d r e s u l t i n d e p o l y m e r i z a t i o n o f c e l l u l o s e (26, 48, 70, 76, 86, 179, 2 0 0 ) . D e p o l y m e r i z a t i o n i s thought t o be a random p r o c e s s a f f e c t i n g b o t h c e l l u l o s e c r y s t a l l i n e and amorphous r e g i o n s e q u a l l y , so t h a t a c i d h y d r o l y s i s and enzyme a c t i v i t y i s g r e a t l y enhanced (123, 180). A t h i g h e r i r r a d i a t i o n dosages, such as a t 10 t o 15 Mrad, c e l l u l o s e d e g r a d a t i o n i s advanced ( 8 6 ) , w h i l e t r e a t m e n t w i t h 3 x 10^ r a d dosage g i v e s a w a t e r - s o l u b l e c e l l u l o s e . G r e a t e r r e s i s t a n c e o f l i g n i n t o i r r a d i a t i o n e f f e c t s i n c o m p a r i -son t o p o l y s a c c h a r i d e s has been s u g g e s t e d by S m i t h and M i x e r ( 2 0 4 ) , F r e i d i n and co-workers £(.7,0$jfOfb) and R o l l i n s e t a l . - (184) and has been e x p l a i n e d on t h e b a s i s o f i t s a r o m a t i c c h a r a c t e r . I t i s f u r t h e r s u g g e s t e d t h a t l i g n i n i n i n t i m a t e c h e m i c a l a d m i x t u r e w i t h wood c a r b o h y d r a t e s may e x e r t a p r o t e c t i v e e f f e c t as shown by d e c r e a s e d amounts o f w a t e r - s o l u b l e c a r b o h y d r a t e p r o d u c t s , c a r b o x y l c o n t e n t and per c e n t o f decomposed c a r b o h y d r a t e s ( 7 0 ) . I t i s n o t e d .in-; t h i s r e g a r d t h a t condensed l i g n i n p r e p a r a t i o n s , i s o l a t e d w i t h s t r o n g a c i d s , a r e more s t a b l e t o i r r a d i a t i o n t h a n p r e p a r a t i o n s i s o l a t e d by n e u t r a l s o l v e n t s , s u g g e s t i n g t h a t l i g n i n h i s t o r y i s an i m p o r t a n t f a c t o r w i t h r e g a r d , t o i t s d e g r e e o f p o l y m e r i z a t i o n and c o n s e q u e n t l y i t s s t a t e o f c h e m i c a l r e a c t i v i t y . The g r e a t i n t e r e s t and e n t h u s i a s m a r o u s e d i n t h e f i e l d o f wood i r r a d i a t i o n i s m a i n l y due t o d i s c o v e r i e s t h a t s t r e n g t h , h e a t r e s i s t a n c e and d i m e n s i o n a l s t a b i l i t y may be improved by s u i t a b l e roonQmetisaturLatipn-folio^ed by i r r a d i a t i o n . . A p p l i c a t i o n o f v a r i o u s known c a t a l y s t - h e a t g r a f t i n g t e c h n i q u e s can now be e x t e n d e d t o i r r a d i a t i o n c o p o l y m e r i z a t i o n as a f a s t e r and b e t t e r c o n t r o l l e d energy s o u r c e . A t t e m p t s to improve wood s t r e n g t h and h y g r o -s c o p i c i t y by g r a f t i n g o f v i n y l t y p e monomers i n wood a r e r e p o r t e d w i t h ( - 3 -v a r i o u s l e v e l s o f s u c c e s s , and i n f o r m a t i o n i n t h i s f i e l d i s g r o w i n g r a p i d l y . C o n c e n t r a t i o n o f r a d i o a c t i v e w a s t e s i n l a r g e q u a n t i t i e s has l e d t o numerous p r a c t i c a l a p p l i c a t i o n s o f i r r a d i a t i o n p r o c e s s e s i n o t h e r f i e l d s , . . /^V" T h e r e has been v e r y l i m i t e d e x t e n s i o n o f wood and c e l l u l o s e r a d i a t i o n t e c h n o l o g y t o t r e a t m e n t o f wood f i b r e webs . The low s t r e n g t h o f m e c h a n i c a l wood p u l p s has always been one s e r i o u s l i m i t a t i o n t o t h e i r a p p l i c a t i o n as f u r n i s h f o r many paper g r a d e s , and much i n t e r e s t has con-t i n u e d i n s e a r c h f o r means to improve t h i s p r o p e r t y . W i t h c o n t i n u a l l y r i s i n g wood c o s t s , t h e a dvantage o f h i g h y i e l d had w i t h m e c h a n i c a l p u l p s has become a s t r o n g i n c e n t i v e t o f i n d i n g methods f o r i n c r e a s i n g a l l o w a b l e p r o p o r t i o n s o f m e c h a n i c a l p u l p s f o r v a r i o u s t y p e s o f p a p e r s . The improvement o f c e r t a i n p r o p e r t i e s o f c e l l u l o s i c m a t e r i a l s used i n o r d n a n c e p a c k a g i n g i s c o n s i d e r e d h i g h l y d e s i r a b l e . F o r s i m i l a r r e a s o n s h i g h y i e l d c h e m i c a l p u l p s a r e r e c e i v -i n g new a t t e n t i o n . F o r most paper uses i t i s d e s i r a b l e t o have c a p a c i t y f o r a b s o r b i n g l a r g e amounts o f energy b e f o r e f a i l u r e . The o b j e c t i v e can be a c c o m p l i s h e d i n two ways, by m a x i m i z i n g t h e s u r f a c e a r e a r e s i s t i n g t h e s t r e s s e s o r by m a x i m i z i n g t h e s t r e s s r e s i s t i n g bond s t r e n g t h . The f o r m e r p r o c e d u r e i s c h i e f l y c o n t r o l l e d by s t r u c t u r a l c o n s i d e r a t i o n s w h i l e t h e l a t t e r i s i n f l u e n c e d by t h e c h e m i s t r y o f the s y s t e m . I t i s t h e l a t t e r avenue t h a t i s p u r s u e d i n t h i s s t u d y w i t h systems new t o the paper i n d u s t r y , b u t known i n p a r t f o r some ti m e f o r improvement o f f l e x u r a l p r o p e r t i e s o f p a p e r b o a r d s p o s s e s s i n g h i g h amounts o f r e s i d u a l l i g n i n ( 1 7 8 ) . A l t h o u g h t h e e v i d e n c e c o l l e c t e d so f a r does n o t a l l o w f o r c l e a r d e s c r i p t i o n o f t h e o i l t e m p e r i n g mechanism,since i t i s s t i l l c o n s i d e r e d as e x t r e m e l y q u a l i t a t i v e , b e n e f i c i a l e f f e c t s accompanying o i l p o l y m e r i z a t i o n w i t h i n iW.ood:fibre p r o d u c t s has s u f f i c i e n t s i g n i f i c a n c e and p r a c t i c a l meaning t o w a r r a n t f u r t h e r i n v e s t i g a t i o n . The p r e s e n t s t u d y i s c o n c e r n e d w i t h the c u r i n g o f d r y i n g o i l i n wood'-'"fibre': webs and has been d e s i g n e d a r o u n d f o u r main o b j e c t i v e s . F i r s t , t o d e t e r m i n e i f wood f i b r e s a r i s i n g f rom q u i t e d i s s i m i l a r p r o c e s s e s behave i n the same manner as observed, w i t h c h e m i c a l pulps,. S i n c e e a r l i e r r e s u l t s w i t h A s p l u n d f i b r e (179) and n e w s p r i n t (178) s u g g e s t l i g n i n q u a l i t y as the most i m p o r t a n t s i n g l e v a r i a b l e c o n t r o l l i n g e x t r a s t r e n g t h development i n o i l p o l y m e r i z a t i o n t r e a t m e n t s , emphasis i s p l a c e d on new m a t e r i a l s d e m o n s t r a t i n g q u a l i t a t i v e and q u a n t i t a t i v e d i f f e r e n c e s i n l i g n i n c o n t e n t . T h e r e b y , w e s t e r n hemlock groundwood, h i g h y i e l d a c i d s u l f i t e and u n b l e a c h e d k r a f t p u l p s a r e i n c l u d e d i n the c o m p a r i s o n , as i s the e n t i r e range o f b l e n d s between groundwood and the two c h e m i c a l p u l p s . As a f u r t h e r f e a t u r e , h i g h l y p u r i f i e d s u l f i t e and s u l f a t e c o m m e r c i a l p u l p s and g l a s s f i b r e webs a r e used t o r e p r e s e n t t h e l o w e r end o f the l i g n i n s c a l e . The m a t e r i a l s c o n t a i n a t l e a s t t h r e e t y p e s o f l i g n i n i n amounts from 0 t o 28.9 % and show o t h e r major d i f f e r e n c e s i n f i b r e s t r e n g t h , f i b r e geometry and f i b r e c o n f o r m i t y . Second, t o e x p l o r e t h e p r o s p e c t o f u s i n g g a m m a - i r r a d i a t i o n as e n ergy s o u r c e f o r c u r i n g d r y i n g o i l i n woocl f i b r e webs. T h i s new t e c h n i q u e c o u l d show some advan t a g e s o v e r the e s t a b l i s h e d p r a c t i c e o f t h e r m a l c u r i n g used w i t h some wood: f i b r e , p r o d u c t s . T h i r d , t o d e s c r i b e the range o f p h y s i c a l p r o p e r t i e s t h a t can be had by t h e r m a l and i r r a d i a t i o n p o l y m e r i z a t i o n o f d r y i n g o i l i n w o o d f . f i b r e webs. A n a l y s e s o f t e n s i l e s t r e s s - s t r a i n c u r v e s a r e e s p e c i a l l y s u i t e d f o r -5-e v a l u a t i n g t h e s e e f f e c t s . F o u r t h , t o f u r t h e r d e v e l o p u n d e r s t a n d i n g o f the p o l y m e r i z a t i o n mechanism(s) w i t h wood: f i b r e webs. Through assessment o f b a s i c m e c h a n i c a l s t r e n g t h p a r a m e t e r s , o b s e r v a t i o n o f f i b r e f r a c t u r e systems and by use o f o r g a n i c s o l v e n t t e c h n i q u e s e v i d e n c e i s sought f o r p a r t i t i o n o f o i l homopolynier and o i l - l i g n i n g r a f t copolymer e f f e c t s . I n t h i s r e g a r d , e v i d e n c e f o r g r a f t copolymer was p r o v i d e d r e c e n t l y f o r i s o l a t e d h y d r o c h l o r i c a c i d l i g n i n and m e t h y l m e t h a c r y l a t e ( 1 1 6 , 117). -6-LITERATURE REVIEW I . RESIDUAL LIGNIN IN WOOD PULPS The g r e a t d i v e r s i t y o f paper p r o p e r t i e s o b t a i n e d w i t h p u l p s made from t h e same wood s o u r c e by v a r i o u s p r o c e s s e s r e f l e c t s t h e b r o a d s p e c t r u m o f changes t a k i n g p l a c e i n t h e p r e p a r a t i o n o f wood f i b r e . The changes may be p h y s i c a l , c h e m i c a l o r p h y s i c o - c h e m i c a l i n n a t u r e (23, 36, 115, 194, 197, 2 2 0 ) . A l t h o u g h t h e d i f f e r e n c e s i n wood c h a r a c t e r i s t i c s may w e l l e x p l a i n some o f t h e v a r i a t i o n i n f i n a l paper p r o p e r t i e s , t h e y a r e n o t s u f f i c i e n t l y l a r g e t o a c c o u n t f o r major d i f f e r e n c e s found between s u l f i t e , k r a f t and h i g h y i e l d A s p l u n d p u l p s . E x p l a n a t i o n s o f such d i f f e r e n c e s , though o f t e n s o u g h t , have n o t been e a s i l y f o u n d . A t l e a s t one v a r i a b l e , t h e amount, d i s t r i b u t i o n and s t a t e o f r e s i d u a l l i g n i n w i t h i n t h e f i b r e w a l l s appears t o i n f l u e n c e i n t r i n s i c f i b r e s t r e n g t h and i n t e r f i b r e b o n d i n g o f v a r i o u s papers and r e c o n -s t i t u t e d wood f i b r e p r o d u c t s (25, 36, 94, 95, 96, 104, 106, 115, 132, 179, 189, 194) . S i n c e l i g n i n i s e s s e n t i a l l y h y d r o p h o b i c i n n a t u r e , i t s p r e s e n c e may be e x p e c t e d t o d e c r e a s e t h e d e g r e e o f i n t e r f i b r e b o n d i n g i n p a p e r . Thus, i t was s u g g e s t e d by Jayme and v o n Koeppen (94) t h a t t h e lower a c i d i t y o f k r a f t p u l p s and, t h e r e b y , t h e lower i o n b o n d i n g c a p a c i t y i s cause o f t h e lower s t r e n g t h o f k r a f t p u l p s as compared t o s u l f i t e p u l p s o f the same l i g n i n c o n t e n t . The p r e s e n c e o f l a r g e r amounts o f r e s i d u a l l i g n i n i n a p u l p may -7-r e s t r i c t s w e l l i n g and d e c r e a s e a d h e s i o n between f i b r e s due t o i t s hydropho-b i c n a t u r e and predominant l o c a t i o n a t t h e f i b r e s u r f a c e (108, 115) . F u r t h e r , i t was shown (59, 66) t h a t l i g n i n t h r o u g h i t s s t i f f e n i n g e f f e c t a c t s as i n h i b i t o r t o f i b r e c o n f o r m i t y , i . e . , f i b r e c o n f o r m i t y i s i n v e r s e l y p r o p o r t i o n a l t o l i g n i n c o n t e n t . I n some t r e a t m e n t s , however, h i g h y i e l d p u l p s such as A s p l u n d and M a s o n i t e a r e r e c o n s t i t u t e d i n t o h i g h d e n s i t y s t r u c t u r a l b oards by a p p l i c a t i o n o f h e a t and p r e s s u r e i n t h e p r e s e n c e o f m o i s t u r e . L i g n i n p l a s t i c i z a t i o n and r e c o n d e n s a t i o n has been c r e d i t e d w i t h f o r m a t i o n o f s t r o n g i n t e r f i b r e bonds i n t h e s e m a t e r i a l s ( 1 9 2 ) . 1. P u l p s from M e c h a n i c a l and S e m i - c h e m i c a l " P r o c e s s i n g S i n c e groundwood p u l p r e p r e s e n t s a l m o s t t h e e n t i r e wood s u b s t a n c e d e l i v e r e d t o t h e g r i n d e r , i t s c h e m i c a l c o m p o s i t i o n i s a t l e a s t as complex as t h a t o f wood. Whether, o r t o what e x t e n t c h e m i c a l changes o c c u r d u r i n g t h e g r i n d i n g p r o c e s s has not been w e l l e s t a b l i s h e d . A t any r a t e , t h e n e t m e c h a n i c a l e f f e c t s o f g r i n d i n g and subsequent r e f i n i n g a r e r e a l i z e d i n a t r e m e n d o u s l y i n c r e a s e d s u r f a c e a r e a o f exposed f i b r e w a l l s f o r c h e m i c a l r e -a c t i o n s , as compared t o a r e a s r e a l i z e d w i t h c h e m i c a l p u l p s . T h i s m e c h a n i c a l f r a g m e n t a t i o n i s due t o a b r a s i o n , f i b r i l l a t i o n and c u t t i n g o f t h e f i b r e s ( 3 2 ) . O b s e r v a t i o n s on groundwood p u l p s show t h a t much o f t h e e x t r a a r e a exposed i s f i b r e lumen, q u i t e d i f f e r e n t f r o m e x t e r n a l f i b r e s u r f a c e exposed by c h e m i c a l d i g e s t i o n (32,, 6 6 ) . The d e c r e a s e o f wood i n t e r f i b r e bond s t r e n g t h w i t h i n c r e a s e o f t e m p e r a t u r e may be u t i l i z e d - i n groundwood p r o c e s s i n g . A c t u a l t e m p e r a t u r e s a t t h e wood-stone i n t e r f a c e a r e d i f f i c u l t t o measure, but may a t t h e moment of f i b e r i z i n g r e a c h t h e s o f t e n i n g r a n g e o f l i g n i n (140) . Such h i g h -8-t e m p e r a t u r e s (170 t o 180°C) i n t h e p r e s e n c e o f w a t e r c o u l d l e a d t o e x t e n s i v e t h e r m a l c r o s s - l i n k i n g o r p o l y m e r i z a t i o n o f l i g n i n . E x p e r i m e n t s (109, 110) show t h a t , w i t h t e m p e r a t u r e s above the s o f t e n i n g p o i n t o f l i g n i n , h o t w a t e r -s o l u b l e c a r b o h y d r a t e s a r e removed from a s s o c i a t i o n w i t h l i g n i n , and t h i s i s t h e p r i m a r y f a c t o r i n r e d u c t i o n o f t h e l i g n i n i n t e r f a c i a l a r e a by c a u s i n g l i g n i n c o a l e s c e n c e a t t h e v a c a t e d s i t e s . The r e d u c t i o n i n l i g n i n i n t e r f a c e has been f o l l o w e d by S O 2 and p h e n o l s o r p t i o n on p r e h y d r o l y s i s o f t h e wood (109,.110, 1 1 1 ) . The d i f f i c u l t y i n c h e m i c a l p u l p i n g o f A s p l u n d f i b r e and even i n l i g n i n d e t e r m i n a t i o n o f t h e m a t e r i a l a l s o s u g g e s t s a change o f l i g n i n c o n s t i t u t i o n due t o h i g h t e m p e r a t u r e t r e a t m e n t i n t h e p r e s e n c e o f w a t e r . F u r t h e r e v i d e n c e o f l i g n i n c o n d e n s a t i o n w i t h i n wood, t h e r m a l l y t r e a t e d i n t h e p r e s e n c e o f w a t e r , was shown by L e o p o l d (129, 130, 131) as r e d u c t i o n i n t h e y i e l d : ; o f a r o m a t i c a l d e h y d e s ( v a n i l l i n and s y r i n g i c a l d e h y d e ) o b t a i n e d by a l k a l i n e n i t r o b e n z e n e o x i d a t i o n . I t seems t h a t l i g n i n c o n d e n s a t i o n r e a c t i o n s o c c u r r e d whether o r n o t t h e r e was i n i t i a l c h e m i c a l l i n k a g e between the c a r b o -h y d r a t e s ( m a i n l y h e m i c e l l u l o s e ) and l i g n i n ( 1 0 9 ) . I n t e r e s t i n g l y , t h e e x t e n t o f l i g n i n c o a l e s c e n c e was l e s s pronounced when s u p e r s a t u r a t e d steam was s u b s t i t u t e d f o r h o t w a t e r ( 1 0 9 ) , s u g g e s t i n g t h a t K l e i n e r t (109) i s c o r r e c t i n h i s o b s e r v a t i o n on e f f e c t o f f r e e space caused by " l e a c h i n g " o f h e m i c e l l u l o s e s . L i t e r a t u r e d e s c r i p t i o n s o f r e s i d u a l l i g n i n i n groundwood p u l p s a r e s c a r c e . Most o f t h e s e d e a l w i t h some s p e c i f i c p r o b l e m r e l a t e d t o improvement o f p u l p q u a l i t y ( f r e q u e n t l y b o n d i n g and b r i g h t n e s s ) and t h e r e b y r a r e l y t r e a t t h e b a s i c phenomena. The h i g h ; l i g n i n c o n t e n t o f groundwood has been c o n s i d e r e d as the p r i m a r y s o u r c e o f c o l o r i n t h e s e p u l p s ( 2 2 9 ) . -9-B r i g h t e n i n g i s b r o u g h t about by o x i d a t i o n o f c h r o m o p h o r i c g r o u p s , p r e f e r a b l y w i t h o u t a d d i t i o n a l y i e l d l o s s (189, 2 2 9 ) . The mechanism o f t h e s e o x i d a t i o n r e a c t i o n s i s : l a r g e l y unknown. I t has been s u g g e s t e d (7) t h a t p e r o x i d e o x i d a t i o n o f m e c h a n i c a l p u l p s i s s e l e c t i v e f o r s u c h chromophores,. and i n v o l v e s t h e t o t a l p u l p l i g n i n . The p r i m a r y s i t e s o f a t t a c k a r e b e l i e v e d t o be c a r b o n y l groups and p o s s i b l y p h e n o l i c h y d r o x y l s i n t h e l i g n i n s t r u c t u r e ( 9 8 ) . Rapson and co-workers (229) showed t h a t t h e permanganate number and c h l o r i n e demand o f p e r a c e t i c a c i d b l e a c h e d groundwood a r e v e r y l i t t l e a f f e c t e d . I t w o u l d seem t h a t s i t e s on t h e l i g n i n m o l e c u l e w h i c h a r e s u s c e p t i b l e t o a t t a c k by c h l o r i n e a r e n o t a f f e c t e d by t h i s b l e a c h i n g r e a c t i o n . F u r t h e r m o r e , the r e l a t i v e l y s m a l l d e c r e a s e i n permanganate number by p e r a c e t i c a c i d b l e a c h -i n g s u g g e s t s t h a t t h e a c t u a l amount o f o x i d a t i o n must be v e r y s m a l l . Reeves and P e a r l (189) s o r t e d r e l a t i o n s h i p s between v a r i o u s l i g n i n f u n c t i o n a l groups and e f f e c t i v e n e s s o f a l k a l i n e p e r o x i d e b l e a c h i n g o f l i g n i n -r e l a t e d model compounds and came t o the c o n c l u s i o n t h a t o n l y t h o s e compounds r e a c t e d w h i c h p o s s e s s e d c a r b o n y l ( f o r m y l ) groups on t h e a l i p h a t i c s i d e - c h a i n . S i n c e compounds w i t h o u t t h i s c a r b o n y l group ( f e r u l i c a c i d ) d i d n o t r e a c t , i t was s u g g e s t e d t h a t t h e i n i t i a l p o i n t o f a t t a c k i s p r o b a b l y a t an oxygen-c o n t a i n i n g f u n c t i o n a l g r o u p . A l t h o u g h p r e s e n c e o f t h e c a r b o n y l was mandatory f o r t h e o x i d a t i o n r e a c t i o n , i t was n o t t h e o n l y r e q u i r e m e n t . I n a d d i t i o n t o t h e c a r b o n y l , a f r e e p h e n o l i c h y d r o x y l seemed t o be n e c e s s a r y , as has been s u g g e s t e d by Jones ( 9 8 ) . However, an i n d e p e n d e n t c a r b o n y l r e a c t i o n was shown w i t h t h e model compound (3,4-dimethoxy p h e n y l ) - 2 propanone. The i s o l a t e d r e a c t i o n p r o d u c t i n d i c a t e d e n o l i z a t i o n and subsequent c l e a v a g e o f the d o u b l e bond. I n . a l k a l i n e n i t r o b e n z e n e o x i d a t i o n o f l i g n i n , Wacek and -10-K r a t z l (224) f o u n d t h a t t h e p r e s e n c e o f a f r e e p h e n o l i c h y d r o x y l group i n pa r a p o s i t i o n t o t h e s i d e - c h a i n f a v o u r e d o x i d a t i o n o f t h e s i d e - c h a i n . On the o t h e r hand, K o s h i j i m a and M u r a k i (117) have r e p o r t e d a marked e f f e c t o f f r e e p h e n o l i c h y d r o x y l on t h e degree o f m e t h y l m e t h a c r y l a t e g r a f t i n g o n t o h y d r o c h l o r i c a c i d l i g n i n . I n a r e c e n t i n v e s t i g a t i o n by P a s z n e r and W i l s o n (179) t h e r e a c t i v i t y o f v a r i o u s A s p l u n d p u l p components toward c o n d e n s a t i o n r e a c t i o n s i n v o l v e d i n o i l - t e m p e r i n g o f h a r d b o a r d w i t h CTLA Polymer was r e d u c e d by m i l d o x i d a t i v e d e l i g n i f i c a t i o n o f t h e f i b r e w i t h sodium c h l o r i t e . I t was a l s o shown t h a t p r e c o n d e n s a t i o n w i t h c a t e c h i n t a n n i n l o w e r e d f i b r e r e a c t i v i t y on h e a t t r e a t m e n t . I n degrada'tion s t u d i e s o f l i g n i n - m e t h y l m e t h a c r y l a t e g r a f t c o p o l y m e r s , r e p o r t e d by K o s h i j i m a and M u r a k i ( 1 1 6 ) , t h e p o l y m e t h y l m e t h a c r y l a t e became s o l u b l e from t h e copolymer upon m i l d o x i d a t i o n w i t h sodium c h l o r i t e . Thereby, i t i s e v i d e n t t h a t w h a t e v e r l i g n i n s i t e i s i n v o l v e d i n t h e p o l y m e r i z a t i o n p r o c e s s , i t i s p r e f e r e n t i a l l y d e a c t i v a t e d o r d e s t r o y e d by the o x i d i z i n g a c t i o n o f sodium c h l o r i t e o r may be o t h e r w i s e complexed ( 1 7 9 ) . T h i s a l s o s u g g e s t s t h a t two mechanisms, i . e . , p o l y m e r i z a -t i o n by t h e r m a l t r e a t m e n t o r i o n i z i n g i r r a d i a t i o n , i n v o l v e t h e same r e a c t i o n s i t e s on t h e l i g n i n m o l e c u l e and may v e r y w e l l be t h e same. The d i f f e r e n c e i n speed between p o l y m e r i z a t i o n s c o u l d be due t o d i f f e r e n c e s i n t h e a p p l i e d energy, as w e l l as t o the e f f i c i e n c y o f f r e e r a d i c a l f o r m a t i o n by t h e two p r o c e s s e s . I n summary, i t i s s a f e t o c o n j e c t u r e t h a t l i g n i n a c c e s s i b i l i t y may be i n c r e a s e d by i n v e s t m e n t o f m e c h a n i c a l energy i n a m e c h a n i c a l p u l p . A c c o r d i n g t o t h e a v a i l a b l e e v i d e n c e , r e a c t i o n s w i t h l i g n i n appear t o depend - l i -on t h e s i d e - c h a i n s t r u c t u r e and a r e enhanced by t h e p r e s e n c e o f f r e e p h e n o l i c h y d r o x y l s . N a t i v e l i g n i n i n s i t u p r o b a b l y has l e s s a c c e s s i b l e o r exposed m o l e c u l a r s t r u c t u r e and t h e r e b y r e a c t s l e s s r e a d i l y . 2. P u l p s f r o m C h e m i c a l P r o c e s s i n g Many of t h e q u e s t i o n s r a i s e d more t h a n a decade ago by B l a n d and Stamp (158) on t h e c o n s t i t u t i o n and c h a r a c t e r o f r e s i d u a l l i g n i n i n c h e m i c a l p u l p s a r e s t i l l unanswered. F o r example, does t h e r e s i d u a l l i g n i n i n p u l p d i f f e r from t h a t found i n o r i g i n a l wood; has i t been a l t e r e d d u r i n g t h e p u l p i n g p r o c e s s , o r was i t d i f f e r e n t o r i g i n a l l y ? These a r e q u e s t i o n s o f major i m p o r t a n c e , w i t h answers t h a t w o u l d s e r v e as good b a s i s f o r a t t e m p t i n g problems o f p u l p and paper improvements i n v o l v i n g l i g n i n r e a c t i o n s . Numerous i n v e s t i g a t o r s have co n c e r n e d t h e m s e l v e s w i t h q u a n t i t a -t i v e e s t i m a t i o n s o f r e s i d u a l l i g n i n s i n v a r i o u s p u l p s and a t t e m p t e d e x p l a n a t i o n o f p u l p b e h a v i o r by t h e amount o f r e s i d u a l l i g n i n t h e r e i n . I t i s g e n e r a l l y a c c e p t e d t h a t s u l f i t e p u l p s b l e a c h much more r e a d i l y t h a n k r a f t p u l p s f r o m t h e same wood o r i g i n and a t t h e same r e s i d u a l l i g n i n l e v e l . ( 2 3 , 36, 115, 2 3 2 ) . O t h e r major e v i d e n c e on s u l f i t e - s u l f a t e l i g n i n d i f f e r e n c e o c c u r s from c o m m e r c i a l c h l o r i n a t i o n . S u l f i t e c h l o r o l i g n i n s a r e m o s t l y ( b u t not e n t i r e l y ) w a t e r s o l u b l e . S u l f a t e c h l o r o l i g n i n s r e q u i r e a l k a l i t r e a t m e n t . Thus G i e r t z (75) found t h a t b l e a c h a b i l i t y depends n o t o n l y on t h e amount b u t a l s o on t h e s t a t e o f t h e l i g n i n p r e s e n t . C h e m i c a l p u l p i n g p r o c e s s e s a r e found t o a f f e c t t h e c h e m i c a l and p h y s i c a l n a t u r e o f l i g n o - c e l l u l o s i c m a t e r i a l s i n d i f f e r e n t ways, t h e r e b y p r o -v i d i n g p u l p s w i t h d i f f e r e n t r e a c t i v i t y and s t r e n g t h . A l t h o u g h n o t much -12-d i f f e r e n c e i s shown by c o n v e n t i o n a l c e l l u l o s e p arameters i n i n d i c a t i n g f i b r e damage by e i t h e r p r o c e s s ( 9 4 ) , t h e d e f i n i t e e f f e c t s on s w e l l i n g and s u r f a c e c o l l o i d a l p r o p e r t i e s must r e l a t e t o o v e r a l l q u a l i t a t i v e d i f f e r e n c e s o f some r e s i d u a l f i b r e c o n s t i t u e n t s , such as t h e h e m i c e l l u l o s e and l i g n i n (23, 94, 96,. 115, 197). Knowledge o f t h e s e d i f f e r e n c e s i s v e r y l i m i t e d , i n d e e d . a« R e s i d u a l l i g n i n i n a c i d s u l f i t e p u l p s I n a c i d s u l f i t e p u l p i n g t h e d e l i g n i f i c a t i o n i s b e l i e v e d t o s t a r t a t t h e m i d d l e l a m e l l a ( 1 6 ) , whereas i n t h e case o f a l k a l i n e p u l p i n g a more s e l e c t i v e d e l i g n i f i c a t i o n i s s a i d t o o p e r a t e ( 2 4 ) . T h i s was d e m o n s t r a t e d by Jayme and v o n Koeppen (94) who o b t a i n e d a s t r u c t u r e l e s s , amorphous l i g n i n powder from k r a f t p u l p by s t r o n g a c i d h y d r o l y s i s o f f i b r e c a r b o h y d r a t e s , whereas s u l f i t e f i b r e s g i v e n t h e same t r e a t m e n t r e t a i n e d t h e i r o r i g i n a l shape as a l i g n i n s k e l e t o n . I t i s b e l i e v e d (92) t h a t d i f f e r e n c e i n r e s i d u a l l i g n i n s w i t h i n s u l f i t e and k r a f t c h e m i c a l p u l p s i s due t o d i f f e r e n t r e a c t i o n mechanisms d u r i n g p u l p i n g . I n t h e s u l f i t e p r o c e s s t h e c h e m i c a l a t t a c k on wood l i g n i n has been found t o p r o c e e d t o p o c h e m i c a l l y (92, 156) s t a r t i n g f r o m th e r a d i a l m i d d l e l a m e l l a e ( t h e a t t a c k may be a i d e d by t h e numerous b o a r d e r e d p i t s on t h i s s u r f a c e ) , whereas t a n g e n t i a l w a l l s a r e i n i t i a l l y r e l a t i v e l y unchanged. S o l u t i o n o f l i g n i n p r oceeds s i m u l t a n e o u s l y i n b o t h i n t e r - and i n t r a f i b r e zones a l t h o u g h the deeper p a r t s o f t h e f i b r e w a l l s a r e r e l a t i v e l y u ntouched ( 9 2 ) . T h u s , m i c r o f i b r i l s w i t h i n t h e s e c o n d a r y l a y e r can r e m a i n more o r l e s s " c o a t e d " w i t h p r o t e c t i v e s u b s t a n c e s , s u c h as h e m i c e l l u l o s e and l i g n i n . I n a d d i t i o n , t h e r e l a t i v e l y h i g h l i g n i n c o n t e n t on t h e s u l f i t e f i b r e -13-s u r f a c e g i v e s some degree o f r i g i d i t y t o t h e f i b r e s . A c c e p t i n g t h a t some o f the p a r t i a l l y s u l f o n a t e d l i g n i n i s s t i l l r e t a i n e d w i t h i n and on t h e f i b r e , G i e r t z (74) e x p l a i n e d t h e b e t t e r h y d r a t i o n c a p a c i t y o f s u l f i t e f i b r e s by t h e improved h y g r o s c o p i c i t y o f l i g n i n . I n h i s o p i n i o n , l i g n o s u l p h o n i c a c i d s , as s t r o n g a c i d s , s w e l l more r e a d i l y i n w a t e r and t h e r e b y a l l o w a h i g h e r d e g r e e o f h y d r a t i o n t h e n do k r a f t r e s i d u a l l i g n i n s . The p r o m i n e n t r o l e o f hemi-c e l l u l o s e s w e l l i n g , however, i s n o t m e n t i o n e d . R e a c t i v i t y o f s u l f i t e p u l p r e s i d u a l l i g n i n can be e s t i m a t e d from th e r a t h e r f a c i l e b l e a c h i n g c h a r a c t e r i s t i c s o f such p u l p s . T h i s has been a t t r i b u t e d t o the lower degree o f condensed l i g n i n w i t h i n t h e s u l f i t e f i b r e w a l l ( 1 9 4 ) . The ready c h l o r i n a t i o n and w a t e r s o l u b i l i t y o f c h l o r o l i g n i n s i n v o l v e d h i g h - m o l e c u l a r w e i g h t l i g n o s u l f o n i c a c i d fragments ( p a r t i a l s u l f o n a t i o n o f r e s i d u a l l i g n i n was d e t e r m i n e d as 0.2 t o 0 . 3 S / O C H 3 ) whereby a p p r o x i m a t e l y 807° o f t h e r e s i d u a l l i g n i n was found a c c e s s i b l e t o t h e b l e a c h -i n g a g e n t s . The r a t h e r r e ady r e a c t i o n s o f s u l f i t e p u l p s t o w a r d s a c e t y l a t i o n (23, 151) and m e t h y l a t i o n (151) i n c o n t r a s t t o k r a f t p u l p s , i s a l s o an i n d i c a t i o n o f h i g h e r r e a c t i v i t y and l e s s condensed n a t u r e o f s u l f i t e p u l p r e s i d u a l l i g n i n . I t has been shown (141) t h a t m e t h y l a t i o n w i t h diazomethane or m e t h a n o l - h y d r o c h l o r i c a c i d d e c o l o r i z e d b o t h n a t i v e a n d . p u l p l i g n i n s by e l i m i n a t i o n o f a l m o s t a l l groups c a p a b l e o f r e d u c t i o n ( c a r b o n y l s ) . T h i s r e s u l t s u g g e s t s r e a c t i o n o f 1 , 2 - d i c a r b o n y l g r o u p s , such as o - q u i n o n e s , as w e l l as 1 , 4 - c o n f i g u r a t i o n s o f t h e qu i n o n e methide t y p e . A c e t y l a t i o n was shown t o produce s i m i l a r r e s u l t s , p o s s i b l y f o r t h e same r e a s o n s , a l t h o u g h t h i s t r e a t m e n t i s accompanied by a r e d u c t i o n i n p u l p s t r e n g t h due t o r e d u c e d hydrogen b o n d i n g o f the c e l l u l o s e (151) . -14-A c c o r d i n g t o A d l e r (3) some c a r b o n y l groups i n t h e l i g n i n mole-c u l e a r e p r o t e c t e d by t h e f o r m a t i o n o f l o o s e l y bound b i s u l f i t e i o n s as a l p h a -h y d r o x y l s u l p h o n a t e s , b u t s i n c e such i o n s were shown t o d i s a p p e a r towards t h e end o f l o n g cooks, d a r k e n i n g o f p u l p c o l o r i s p o s s i b l y due t o c o n d e n s a t i o n o f c a r b o n y l groups i n the l i g n i n . The r a t h e r l i g h t c o l o r o f s u l f i t e p u l p s i s a t t r i b u t e d t o t h e above p r o t e c t i v e e f f e c t . The r e d d e n i n g o f u n b l e a c h e d s u l f i t e p u l p s t o a s t a b l e brown c o l o r has been r e l a t e d t o p r e s e n c e o f q u i n o n e and q u i n o n e m e t h i d e groups by A d l e r and H a g g r o t h ( 4 ) . These r e a c t i o n s a r e thought t o o p e r a t e t h r o u g h a i r o x i d a t i o n , i n v o l v i n g t h e f r e e p h e n o l i c h y d r o x y l i n p a r a p o s i t i o n t o t h e s i d e - c h a i n . Such o x i d a t i o n i s u s u a l l y c a t a l i y i z e i b y t h e p r e s e n c e o f m e t a l i o n s , , m a i n l y i r o n and c o p p e r . S i m i l a r effects were shown t o be due t o t h e f o r m a t i o n o f p y r o c a t e c h o l - t y p e s t r u c t u r e s i n l i g n i n as a r e s u l t o f d e m e t h y l a t i o n d u r i n g t h e c o o k i n g p r o c e s s (112) . A n o t h e r s i m i l a r e f f e c t o c c u r s when m i l l p r o c e s s w a t e r c o n t a i n i n g a p p r e c i a b l e amounts o f c h l o r i n e i s u s e d f o r d i l u t i o n or w a s h i n g s u l f i t e raw s t o c k , p a r t -i c u l a r l y w e s t e r n hemlock. The condensed systems i n v o l v i n g a l p h a - c a r b o n y l groups u s u a l l y c o n t a i n f r e e p h e n o l i c h y d r o x y l s w h i c h s t r o n g l y r e s e m b l e t h e c a r b i n o l bases o f t r i p h e n y l methane d y e s t u f f s . Such systems a r e c o n d e n s a t i o n p r o d u c t s o f a l p h a - c a r b o n atoms on one m o l e c u l e w i t h t h e C^-atom o f t h e n e x t . The p r e s e n c e o f d i h y d r o x y - b e n z y l a l c o h o l (and thus q u i n o n e methide) s t r u c t u r e s have been shown f o l l o w i n g a c i d h y d r o l y s i s (194) . -15-b. R e s i d u a l l i g n i n i n s u l f a t e ( k r a f t ) p u l p s As mentioned e a r l i e r , d e l i g n i f i c a t i o n d u r i n g t h e s u l f a t e cook proceeds a t a more u n i f o r m r a t e t h r o u g h o u t t h e f i b r e w a l l and a t g r e a t e r speed o f r e a c t i o n i n a l k a l i n e media (17, 23, 53, 59, 107, 232) . Through s w e l l i n g caused by t h e a l k a l i g r e a t e r l i g n i n a c c e s s i b i l i t y i s o b t a i n e d and t h e r e b y a more homogeneous d e l i g n i f i c a t i o n i s g u a r a n t e e d . A c c o r d i n g t o K l e i n e r t (108) l i g n i n and c e l l u l o s e b o t h s u f f e r f r a g m e n t a t i o n by f o r m i n g f r e e r a d i c a l s d u r i n g a l k a l i n e p u l p i n g o f wood. I t i s e a s i l y i m a g i n e d t h a t t h e s e f r e e r a d i c a l s combine i n a s e r i e s o f s e c o n d a r y r e a c t i o n s i n w h i c h l i g n i n m a c romolecules m ight become g r a f t e d by c o v a l e n t b o n d i n g o n t o t h e c e l l u l o s e p u l p . A s i m i l a r v i e w was e x p r e s s e d by B l a n d and Stamp ( 2 5 ) . Such g r a f t i n g ( w h i c h was d i s t i n g u i s h e d from r e d e p o s i t i o n ) was shown t o depend on t h e p r e s e n c e o f f r e e p h e n o l i c h y d r o x y I s , as w e l l as on t h e p r e s e n c e o f r e d u c e -a b l e groups such as a l d e h y d e s . The p r e s e n c e o f condensed l i g n i n i s a l s o shown i n h i g h l y b l e a c h e d s u l f i t e p u l p f o l l o w i n g s t r o n g a l k a l i t r e a t m e n t above 140°C by t h e p r e s e n c e o f m i c r o s c o p i c d a r k s p o t s . D i s t r i b u t i o n o f r e s i d u a l l i g n i n i n k r a f t p u l p was shown by Jayme and von Koeppen (94, 115) t o be a l m o s t u n i f o r m a c r o s s t h e f i b r e w a l l . I t was a l s o d e m o n s t r a t e d t h a t r e s i d u a l l i g n i n c o n c e n t r a t i o n w i t h i n the f i b r e w a l l i s n e v e r h i g h enough t o r e t a i n t h e o r i g i n a l f i b r e s k e l e t o n a f t e r c a r e f u l h y d r o l y s i s o f the c a r b o h y d r a t e p o r t i o n . Such l i g n i n s a r e always r e c o v e r e d as a powder, n o t a f a c s i m i l e o f t h e f i b r e . I n s p i t e o f i n c r e a s e d a c c e s s i b i l i t y and more u n i f o r m l i g n i n d i s t r i b u t i o n w i t h i n f i b r e w a l l s , k r a f t p u l p s a r e d e c i d e d l y more d i f f i c u l t t o b l e a c h t h a n s u l f i t e p u l p s c o n t a i n i n g t h e same amount o f l i g n i n (23, 194).--16-O n e . l i k e l y e x p l a n a t i o n f o r t h i s phenomenon i s t h e h i g h e r d e g r e e o f l i g n i n c o n d e n s a t i o n o c c u r r i n g d u r i n g t h e h i g h - t e m p e r a t u r e (160-170°C) k r a f t cook (23, 53, 7 2 ) . I n a d d i t i o n , c o n d e n s a t i o n i n a l k a l i n e c o o k i n g i s f a v o u r e d by t h e f o r m a t i o n o f a d d i t i o n a l p h e n o l i c groups i n s p l i t t i n g o f a l k y l - a r y l e t h e r l i n k a g e s (72,. 194) w i t h e l i m i n a t i o n o f m e t h o x y l groups (52, 194) . A conden-s a t i o n p r o d u c t i s u s u a l l y formed between b e n z y l a l c o h o l g r o u p s , a c t i v a t e d by f r e e p h e n o l i c h y d r o x y l s , and an u n o c c u p i e d C t j p o s i t i o n o r by f o r m a t i o n o f d i b e n z y l methane s t r u c t u r e s upon e l i m i n a t i o n o f one o f t h e s i d e ^ c h a i n s . Con-d e n s a t i o n s o f t h e above t y p e a r e u s u a l l y c o u n t e r a c t e d by t h e f o r m a t i o n o f lower m o l e c u l a r w e i g h t c o n d e n s a t i o n p r o d u c t s w i t h f o r m a l d e h y d e on e l i m i n a t i o n ( c l e a v a g e ) from t h e s i d e - c h a i n ( 1 9 4 ) . D i s c o l o r a t i o n o f t h e p u l p o c c u r s a t an e a r l y s t a g e i n t h e k r a f t p r o c e s s ( 1 0 ) . T h i s d i s c o l o r a t i o n i s t a k e n as t h e f i r s t s i g n o f l i g n i n c o n d e n s a t i o n , r e s u l t i n g from i n i t i a l s p l i t t i n g o f a l k y l - a r y l e t h e r l i k a g e s ( a l p h a - a r y l , b e t a - a r y l e t h e r s ) by t h e a l k a l i w i t h subsequent f o r m a t i o n o f q u i n o n e m e t h i d e t y p e i n t e r m e d i a t e s ( 7 2 ) . The accompanying r e a c t i o n i s a l k a l i n e h y d r o l y s i s as i n d i c a t e d by t h e c o m p a r a t i v e l y low m o l e c u l a r w e i g h t o f t h e s o l u b i l i z e d l i g n i n , as w e l l as t h e l o s s of m e t h o x y l groups from t h e m o l e c u l e . As a r e s u l t o f t h e s e competing r e a c t i o n s o n l y few o f t h e i n i t i a l c a r b o n y l , b e n z y l a l c o h o l o r a l k y l e t h e r groups a r e found i n t h e r e s i d u a l p u l p l i g n i n (160) . As consequence o f e x t e n s i v e s p l i t t i n g o f a l k y l - a r y l e t h e r groups the number o f f r e e p h e n o l i c h y d r o x y l s i s i n c r e a s e d t o a l m o s t 1.0 per monomer i n t h e r e s i d u a l l i g n i n ( 6 2 ) , as compared to 0.3 i n m i l l e d - w o o d l i g n i n and 0.29 i n b o r o h y d r i d e t r e a t e d l i g n i n f o l l o w i n g two hours c o o k i n g i n 2N NaOH a t 170°C, as d e t e r m i n e d by G i e r e r _et (72) . As w i t h a c i d c o n d e n s a t i o n , t h e C5 p o s i t i o n o f the a r o m a t i c n u c l e u s i s t h e most r e a c t i v e s i t e o f c o n d e n s a t i o n (43, 190) and t h e f o r m a t i o n o f f r e e p h e n o l i c h y d r o x y 1 groups d u r i n g t h e cook i s l i k e l y t o i n c r e a s e i t s r e a c t i v i t y . P r o b a b l y the h i g h e r p r o p o r t i o n o f condensed l i g n i n i s a l s o t h e cause o f r e l a t i v e l y low k r a f t p u l p r e a c t i v i t y i n a c e t y l a t i o n (23, 151) and m e t h y l a t i o n (3) t r e a t m e n t s . The lower m e t h o x y l c o n t e n t o f k r a f t p u l p s , as compared t o s u l f i t e p u l p s o f t h e same a p p a r e n t K l a s o n l i g n i n c o n t e n t , has been d e m o n s t r a t e d by K l e i n e r t and Roberge ( 1 1 2 ) , a l t h o u g h a p o s s i b l e r e l a t i o n -s h i p between c o o k i n g degree ( l i g n i n c o n t e n t ) and bromine consumption was n o t s i g n i f i c a n t . S t a b i l i t y o f m e t h o x y l groups t o p e r i o d a t e o x i d a t i o n was i n v e s t i g a t e d by G i e r e r jet a _ l . ( 7 2 ) , who found t h e a r o m a t i c m e t h o x y l s were more s t a b l e t h a n b e n z y l m e t h y l e t h e r s . M e t h y l a t i o n o f m i l l e d - w o o d l i g n i n p h e n o l i c h y d r o x y l s w i t h diazomethane p r e v e n t e d c l e a v a g e o f the a l k y l - a r y l e t h e r , whereas m e t h y l a t i o n . o f a l c o h o l i c h y d r o x y l s i n a l p h a p o s i t i o n w i t h m e t h a n o l - h y d r o c h l o r i c a c i d m e t h y l a t i n g agent p r e v e n t e d e p o x i d e f o r m a t i o n and subsequent c l e a v a g e o f t h e b e t a - a r y l e t h e r l i n k a g e , even when f r e e p h e n o l i c h y d r o x y l s were p r e s e n t . A l k a l i n e n i t r o b e n z e n e o x i d a t i o n p r o d u c t s from k r a f t r e s i d u a l l i g n i n d e g r a d a t i o n s u g g e s t e d t h a t t h e e s s e n t i a l framework o f t h i s l i g n i n i s s i m i l a r t o t h a t found i n wood, a l t h o u g h t h e a l d e h y d e y i e l d was g r e a t l y r e d u c e d ( 1 5 8 ) . The f a c t t h a t a c e t o g u a i a c o n e was i s o l a t e d t o a g r e a t e r e x t e n t from t h e wood p u l p t h a n from wood l i g n i n i n d i c a t e d t h e p r e s e n c e o f a m o d i f i e d p h e n y l p r o p a n e group. The g e n e r a l p a t t e r n o f u l t r a v i o l e t a b s o r p t i o n s p e c t r a from k r a f t r e s i d u a l l i g n i n was p r a c t i c a l l y t h e same as t h a t o b t a i n e d f o r wood l i g n i n . The f a c t t h a t methods f o r d e t e r m i n i n g wood l i g n i n a r e more o r - 1 8 -l e s s a p p l i c a b l e t o p u l p l i g n i n d e t e r m i n a t i o n s s u p p o r t s t h e s e s t a t e m e n t s . 3. D i f f e r e n c e s i n R e s i d u a l L i g n i n as R e s u l t o f P r o c e s s i n g I n summary, t h e r e a r e o b v i o u s d i f f e r e n c e s between t h e t h r e e t y p e s o f f i b r e s and t h e i r r e s i d u a l l i g n i n s . These d i f f e r e n c e s a r e m a i n l y q u a l i -t a t i v e and q u a n t i t a t i v e w i t h r e g a r d t o r e s p e c t i v e p o s i t i o n w i t h i n t h e c e l l w a l l . W h i l e r e s i d u a l l i g n i n i n groundwood f i b r e s i s t h o u g h t t o be o n l y s l i g h t l y m o d i f i e d due t o c o a l e s c e n c e , i t s d i s t r i b u t i o n w i t h i n the f i b r e w a l l s h o u l d n o t be much d i f f e r e n t t h a n t h a t o f normal wood. On the o t h e r hand, e f f e c t s o f c h e m i c a l c o o k i n g seem t o a l t e r n o t o n l y t y p e s o f l i g n i n r e s i d u e s , b u t a l s o the amounts and r e l a t i v e d i s t r i b u t i o n w i t h i n v a r i o u s l a y e r s o f t h e f i b r e w a l l . These changes i n l i g n i n c h e m i c a l c o m p o s i t i o n and p o s i t i o n a r e r e f l e c t e d i n a l t e r e d f u n c t i o n a l g r o u p s , as w e l l as p h y s i c a l c o n s i d e r a t i o n s o f l i g n i n a c c e s s i b i l i t y . T h i s must have b e a r i n g on r e a c t i v i t y toward f u r t h e r m o d i f i c a -t i o n s such as b l e a c h i n g , s i z i n g , c h e m i c a l d e r i v a t i v e f o r m a t i o n and m o d i f i c a -t i o n s r e l a t i n g t o c o p o l y m e r i z a t i o n w i t h s u i t a b l e monomers. I t i s known t h a t b e t t e r i n t e r f i b r e b o n d i n g o f p u l p s i s o b t a i n e d by i n c r e a s i n g the d e g r e e o f d e l i g n i f i c a t i o n ( 1 0 , 1 0 5 , 1 7 9 ) . O b v i o u s l y , d i f f e r e n c e s i n r e s i d u a l s u l f i t e and k r a f t p u l p l i g n i n s a r e o f more i m p o r t a n c e w i t h l i g n i n - r i c h p u l p s . Thus i t i s a c c e p t e d ( 1 0 , 9 5 , 9 6 ) t h a t a l l p u l p i n g p r o c e s s e s d i s p l a y an o p t i m a l l i g n i n c o n t e n t below w h i c h no f u r t h e r improve-ment i i n f i b r e b o n d i n g i s e x p e r i e n c e d w i t h o u t m o d i f i c a t i o n subsequent t o d e l i g n i f i c a t i o n . The a b s o l u t e l e v e l o f t h i s optimum l i g n i n c o n t e n t i s i n t h e o r d e r o f 5 t o 107o b a s e d on the o r i g i n a l wood w e i g h t depending on t y p e o f -19-wood and p r o c e s s c h a r a c t e r i s t i c s . T h i s l e v e l o f r e s i d u a l l i g n i f i c a t i o n i s e s t i m a t e d as o n l y s l i g h t l y below t h e p o i n t o f f i b r e l i b e r a t i o n from w h o l e wood (194) . The f a c t t h a t such r e l a t i v e l y h i g h l i g n i n c o n t e n t s a r e t o l e r a -t e d w i t h i n p u l p f i b r e s w i t h o u t s e r i o u s d e t r i m e n t t o p h y s i c a l and m e c h a n i c a l p r o p e r t i e s o f r e s u l t a n t papers has economic i m p o r t a n c e , as w e l l as o f f e r i n g o p p o r t u n i t y f o r f u r t h e r p r o c e s s i n g i n v o l v i n g improvements by l i g n i n copolyme s y s t e m s . -20-I I . THERMAL TREATMENT OF WOOD AND WOOD: FIBRE PRODUCTS Water i s h e l d w i t h i n t he c e l l w a l l o f c e l l u l o s i c m a t e r i a l s i n t h r e e d i s t i n c t ways namely, w a t e r o f c o n s t i t u t i o n , s u r f a c e bound w a t e r and c a p i l l a r y condensed w a t e r (234) . I n normal a i r d r y i n g o f wood i t i s the r e l a t i v e l y l o o s e l y bound c a p i l l a r y condensed w a t e r t h a t i s removed f i r s t . T h i s p r o c e s s o f w a t e r removal i s r e v e r s i b l e and i s n o t accompanied by a p p r e c i a b l e change w i t h i n the s t r u c t u r a l network o f wood. E v a p o r a t i o n o f c a p i l l a r y condensed w a t e r i s f o l l o w e d by l o s s o f s u r f a c e bound w a t e r t h r o u g h d i f f u s i o n and r e - c o n d e n s a t i o n mechanisms u n t i l an e q u i l i b r i u m i s s e t up between the wood s u b s t a n c e and the r e l a t i v e h u m i d i t y o f the s u r r o u n d i n g e n v i r o n m e n t . Removal of s u r f a c e bound w a t e r i s accompanied by major dimen-s i o n a l changes i n the f o r m o f s h r i n k a g e ( 2 0 7 ) . On a c c e l e r a t e d d r y i n g o f wood t h r o u g h removal o f the s u r f a c e bound w a t e r , d i f f u s i o n of m o i s t u r e f r o m i n s i d e the wood i s much s l o w e r t h a n e v a p o r a t i o n f r o m the s u r f a c e . Due t o d i f f e r e n t i a l s h r i n k a g e r a t e s the s m a l l e r s h e l l can no l o n g e r accommodate the l a r g e i n t e r i o r , l e a d i n g t o d r y i n g s t r e s s e s o f t e n g r e a t enough t o cause r u p t u r e o f the f i b r e n e twork. The d i m e n s i o n a l changes, i f w a t e r removal i s n o t c a r r i e d t o extreme, a r e more o r l e s s r e v e r s i b l e on m o i s t u r e r e a b s o r p t i o n and s w e l l i n g . I t i s removal o f the f i n a l s m a l l amount o f w a t e r , the w a t e r o f c o n s t i t u t i o n , u s u a l l y by h i g h - t e m p e r a t u r e h e a t i n g (above the b o i l i n g p o i n t o f w a t e r ) t h a t b r i n g s about, d r a s t i c and i r r e v e r s i b l e changes w i t h i n wood p r o d u c t s . -21-1. High-Temperature Treatment of Wood The e f f e c t of p r o l o n g e d h e a t t r e a t m e n t of wood a t t e m p e r a t u r e s below t h o s e r e q u i r e d t o i n i t i a t e c o m b u s t i o n and p y r o l y s i s , i . e . , 228°C ( 2 0 7 ) , p roduces s l o w d e g r a d a t i v e changes, a l o s s of s t r e n g t h (195) and d e c r e a s e d h y g r o s c o p i c i t y ( 2 1 3 ) . The r a t e of change has been f o u n d t o be a f u n c t i o n of t e m p e r a t u r e and t i m e , a l l o w i n g c a l c u l a t i o n of wood d u r a b i l i t y a t o r d i n a r y t e m p e r a t u r e s (210) . When wood i s exposed t o v a r i o u s l e v e l s of t h e r m a l t r e a t m e n t f o r l o n g e r p e r i o d s of time the l o g a r i t h m of r e s i d u a l wood w e i g h t v a r i e s d i r e c t l y w i t h t i m e (207) . The i n i t i a l w e i g h t l o s s i s u s u a l l y due t o l o s s of the v a r i o u s forms of w a t e r . As d r y i n g c o n d i t i o n s become more s e v e r e c a r b o n d i o x i d e and c a r b o n monoxide, t o g e t h e r w i t h l a r g e amounts o f v o l a t i l e o r g a n i c compounds, a r e l o s t as d i s t i l l a t e and f l u e g a s e s . Among th e s e a r e a c e t i c and f o r m i c a c i d s , e s t e r s and a l d e h y d e s , m e t h y l a l c o h o l and v a r i o u s p h e n o l i c compounds. These a r e a s c r i b e d t o d e g r a d a t i o n o f v a r i o u s wood components (58) . As d e m o n s t r a t e d by Stamm (207) wood h e m i c e l l u l o s e i s de-graded by f a r the most r a p i d l y , f o l l o w e d by the c e l l u l o s e and l a s t l y by the l i g n i n . I n h e a t i n g wood t o the e x t e n t where l o s s i n oven-dry w e i g h t o c c u r s , a s i g n i f i c a n t change i n h y g r o s c o p i c i t y i s o b s e r v e d w i t h r e s u l t a n t r e d u c t i o n i n the e x t e n t t o w h i c h i t w i l l s w e l l and s h r i n k . The degree o f such d i m e n s i o n a l s t a b i l i z a t i o n was shown to be s i g n i f i c a n t l y g r e a t e r p e r u n i t w e i g h t l o s s when h e a t i n g was p e r f o r m e d i n the absence of a i r ( 1 6 6 ) . U n f o r t u n a t e l y , l a r g e g a i n s i n d i m e n s i o n a l s t a b i l i t y a r e accompanied by e x t e n s i v e l o s s i n s t r e n g t h p r o p e r t i e s , m a i n l y toughness and t e n s i l e s t r e n g t h . -22-Much more e f f e c t i v e methods have been found r e c e n t l y f o r i n c r e a s i n g d i m e n s i o n a l s t a b i l i t y by i m p r e g n a t i n g wood w i t h b u l k i n g agents ( s u g a r , wax, r e s i n , p o l y e t h y l e n e g l y c o l ( 2 0 7 ) ) , by c h e m i c a l m o d i f i c a t i o n of wood t h r o u g h a c e t y l a t i o n ( 2 1 4 ) , f o r m a l d e h y d e c r o s s r l i n k i n g ( 6 0 , 209) and by numerous g r a f t i n g t e c h n i q u e s w i t h the c e l l u l o s e f r a c t i o n w i t h o r w i t h o u t c a t a l y s t s i n a d d i t i o n t o t h e r m a l t r e a t m e n t s (63,.147, 1 6 1 ) . The advantages a r e i n most ca s e s q u i t e c o n s i d e r a b l e as f a r as d i m e n s i o n a l s t a b i l i t y i s c o n c e r n e d , a l t h o u g h a d v e r s e e f f e c t s on m e c h a n i c a l s t r e n g t h p r o p e r t i e s may accompany the t r e a t m e n t s (209) . 2. Thermal Treatment o f WoodxFibre P r o d u c t s T h i s group o f c e l l u l o s i c m a t e r i a l s i n c l u d e s wood f i b r e b o a r d s p u l p s and v a r i o u s paper p r o d u c t s . Thereby, two b a s i c s u b d i v i s i o n s may be made based on r e s i d u a l l i g n i n c o n t e n t i n the s t a r t i n g m a t e r i a l . I t i s e x p e c t e d t h a t p r e s e n c e o f l i g n i n i n f l u e n c e s e f f e c t i v e n e s s o f h e a t t r e a t m e n t w i t h t h e s e two types o f wood p r o d u c t s . a. Heat t r e a t m e n t o f w o o d - f i b r e b o a r d s Heat t r e a t m e n t has become common p r a c t i c e f o r i n c r e a s i n g dimen-s i o n a l s t a b i l i t y and t o some e x t e n t i m p r o v i n g f l e x u r a l p r o p e r t i e s o f h a r d -boards ( 7 8 , 101, 2 2 1 ) . The c h e m i c a l c o m p o s i t i o n o f hard b o a r d s made f r o m c o a r s e wood f i b r e s i s changed somewhat by removing the w a t e r o f c o n s t i t u t i o n , w h i c h r e s u l t s i n h i g h e r s t r e n g t h and d i m e n s i o n a l s t a b i l i t y . R e c e n t l y , K l i n g a and Back (113) i n t r o d u c e d the co n c e p t o f c r o s s - l i n k i n g s t r e s s e s i n h a r d b o a r d s w h i c h c o u n t e r b a l a n c e the permanent d r y i n g s t r e s s e s a l r e a d y e x i s t i n g i n wet--23-p r o c e s s h a r d b o a r d s . The c r o s s - l i n k s a r e b e l i e v e d t o be of the h e m i - a c e t a l t y p e and a r e formed between the c e l l u l o s e and h e m i c e l l u l o s e a t v e r y l o w h u m i d i t y c o n d i t i o n s . C r o s s - l i n k i n g i s c l a i m e d t o produce permanent s h r i n k a g e i n the p l a n e and t h i c k n e s s of the s h e e t . A s t r e n g t h i n c r e a s e of 507> f o l l o w e d h e a t i n g a t 160°C f o r 3 h r , w h i l e d i m e n s i o n a l s t a b i l i t y i n c r e a s e d 807, by h e a t i n g a t 160°C f o r 8 h r . I n t e r e s t i n g l y , the times r e q u i r e d f o r maximum development o f s t r e n g t h and d i m e n s i o n a l s t a b i l i t y do n o t c o i n c i d e , s i n c e c o n s i d e r a b l e s t r e n g t h l o s s was r e p o r t e d f o l l o w i n g an 8 h r t r e a t m e n t a t the same t e m p e r a t u r e . F u r t h e r c o n s i d e r a t i o n s h o u l d be g i v e n t o the e f f e c t of l i g n i n i n h a r d b o a r d s . The o p p o s i n g t h e o r i e s o f l i g n i n r e c o n d e n s a t i o n and c o m p lete d e h y d r a t i o n . of h e m i c e l l u l o s e a r e c u r r e n t l y d e b a t e d i n the l i t e r a t u r e . The s t r e n g t h i n c r e a s e of h a r d b o a r d s on h e a t t r e a t m e n t can h a r d l y be due t o i n c r e a s e o f i n t r i n s i c f i b r e s t r e n g t h , b u t must r e s u l t f r o m improved f i b r e b o n d i n g i n w h i c h h e m i c e l l u l o s e and l i g n i n may b o t h have some s h a r e . The f a c t t h a t l i g n i n p l a s t i c i z a t i o n can o c c u r a t h i g h t e m p e r a t u r e s and w i t h p r o l o n g e d h e a t i n g (77) s h o u l d n o t be w i t h o u t e f f e c t . However, the e f f e c t of h e a t t r e a t m e n t on i n t e r f i b r e b o n d i n g cannot be f u l l y r e a l i z e d as i n c r e a s e d s t r e n g t h s i n c e the i n d i v i d u a l f i b r e ! s t r e n g t h i s a l r e a d y u t i l i z e d up t o 70 t o 807,, as e v i d e n c e d by the n a t u r e o f m e c h a n i c a l t e s t f a i l u r e s . The l i m i t o f p r o p o r t i o n a l i t y i s i n c r e a s e d p r a c t i c a l l y t o the p o i n t o f f a i l u r e , i n d i c a t i n g l e s s r e l a x a t i o n and a h i g h e r degree o f o r d e r w i t h i n the b o a r d . M cKnight and Mason (145) a t t r i b u t e the improved h y g r o s c o p i c p r o p e r t i e s of t h e s e m a t e r i a l s t o l o w e r w a t e r s o r p t i o n of the h e a t t r e a t e d l i g n i n . F u r t h e r improvement i n h a r d b o a r d f l e x u r a l and d i m e n s i o n a l - 2 4 -p r o p e r t i e s i s o b t a i n e d by c o p o l y m e r i z i n g u n s a t u r a t e d d r y i n g o i l s on h e a t t r e a t m e n t w i t h h i g h q u a l i t y h a r d b o a r d s ( 1 2 2 , 1 7 9 ) . I n v e s t i g a t i o n o f the u n d e r l y i n g mechanism (1 .75 . ) showed t h a t Douglas f i r A s p l u n d p u l p l i g n i n q u a l i t y was more i m p o r t a n t t h a n l i g n i n q u a n t i t y , and t h a t the c o n d e n s a t i o n r e a c t i o n depended m o s t l y on r e a c t i v e s i t e s w i t h i n t h e l i g n i n m o l e c u l e . The f i b r e m a t e r i a l c o u l d be i n a c t i v a t e d by m i l d sodium c h l o r i t e t r e a t m e n t , r p o s s i b l y by o x i d i z i n g l i g n i n a l d e h y d e groups o r by t a n n i n c o n d e n s a t i o n . L i g n i n was t h o u g h t t o be r e s p o n s i b l e f o r 807o of the s t r e n g t h i n c r e a s e ( 1 1 0 7 o ) t h a t was o b t a i n e d by o i l t e m p e r i n g over t h a t o b t a i n e d by h e a t t r e a t m e n t o n l y . S i n c e the d e t a i l e d s t r u c t u r e o f the l i g n i n m a c r omolecule i s s t i l l unknown, the s i t e o f c o p o l y m e r i z a t i o n c o u l d be o n l y s u r m i s e d / ' I n l i g n i n c o n d e n s a t i o n s w i t h f o r m a l d e h y d e i n a c i d s o l u t i o n ( 6 0 ) s e v e r a l r e a c t i o n s o c c u r whereby s o l u b l e f o r m a l d e h y d e l i g n i n s a r e o b t a i n e d . I n the p r o p o s e d l i g n i n m o l e c u l e , e t h e r l i n k a g e s a r e a s s i g n e d between p h e n y l p r o p a n e u n i t s a t a r b i t r a r y p o s i t i o n s . F u r t h e r , c r o s s - l i n k i n g m a r k e d l y l o w e r s l i g n i n s o l u b i l i t y . Such l i n k a g e s a r e a p p a r e n t l y n o t numerous enough to p r e v e n t s w e l l i n g . I n c o n d e n s a t i o n r e a c t i o n s , even w i t h s e l f c o n d e n s a t i o n and c r o s s - l i n k i n g , l o s s of w a t e r p r o b a b l y o c c u r s . Perhaps the a l p h a p o s i t i o n i n the s i d e - c h a i n and t h e C f j - p o s i t i o n i n t h e a r o m a t i c n u c l e i a r e i n v o l v e d i n such c o n d e n s a t i o n s , because the f o r m e r i s e a s i l y s u l p h o n a t e d when l i g n i n i s h e a t e d i n aqueous sodium b i s u l f i t e and t h e l a t t e r can be c h l o r i n a t e d . A c i d s o l u b i l i t y o f fo r m a l d e h y d e l i g n i n s u g g e s t s t h a t t h e f o r m a l d e h y d e has condensed a t a c t i v a t e d l i g n i n c e n t e r s w h i c h n o r m a l l y c r o s s - l i n k w i t h each o t h e r t o form i n s o l u b l e K l a s o n l i g n i n ( 6 0 ) . O n l y moderate s t r e n g t h i n c r e a s e (7 t o 1 0 7 , ) was r e p o r t e d r e c e n t l y -25-by K l i n g a and Tarkow (114) on v apour phase a c e t y l a t i o n of h a r d b o a r d . On t h e o t h e r hand, d i m e n s i o n a l s t a b i l i t y i n c r e a s e d by 30%. b. Heat t r e a t m e n t o f paper. I t i s w e l l r e c o g n i z e d t h a t the h e a t i n g of c e l l u l o s i c f i b r e s and f i b r e webs a t e l e v a t e d t e m p e r a t u r e , b u t b e l o w the i g n i t i o n p o i n t , has pronounced d e g r a d i n g e f f e c t upon t h e i r p h y s i c a l and m e c h a n i c a l p r o p e r t i e s (35, 2 0 8 ) . O t t and S p u r l i n (175) r e p o r t e d l o w e r s t r e n g t h d a t a f o l l o w i n g s e v e r a l hours h e a t t r e a t m e n t o f c o t t o n t i r e c o r d . Murphy (162) s t u d i e d the t h e r m a l d e c o m p o s i t i o n of n a t u r a l c e l l u l o s e i n vacuo and f o u n d t h a t w a t e r , c a r b o n d i o x i d e and c a r b o n monoxide were the main d e g r a d a t i o n p r o d u c t s . The amount of d e c o m p o s i t i o n p r o d u c t s was r e l a t e d t o the s t a t e o f d e g r a d a t i o n . Above a c e r t a i n t e m p e r a t u r e the s w e l l i n g c a p a c i t y of t h e c e l l u l o s e f i b r e i s i r r e v e r s i b l y r e d u c e d . E x p e r i m e n t s w i t h Whatman No. 1. f i l t e r p a p e r by B r i t t and Y i a h n o s (35) showed t h a t the z e r o span t e n s i l e s t r e n g t h , t e a r r e s i s t a n c e and f o l d i n g e ndurance, a f t e r an i n i t i a l s l i g h t i n c r e a s e , d e c r e a s e d s i g n i f i c a n t l y a f t e r p r o l o n g e d h e a t t r e a t m e n t , whereas s t i f f n e s s was c o n s i d e r a b l y i n c r e a s e d . T h i s was e x p l a i n e d by d e p b l y m e r i z a t i o n of the c e l l u l o s e and e m b r i t t l e m e n t o f the f i b r e s t r u c t u r e . I n t e r e s t i n g l y , even v e r y l o w t e m p e r a t u r e and i n i t i a l pulpwood d r y i n g i s r e p o r t e d t o have a v e r y d e t r i m e n t a l e f f e c t on r e s u l t i n g paper p r o p e r t i e s . I n t h i s r e g a r d , Jayme (90) showed t h a t the w a t e r r e t e n t i o n v a l u e (WRV) of p u l p s i s c o n s i d e r a b l y l o w e r e d and t h a t the o r i g i n a l s t a t e o f s w e l l i n g can n e v e r be r e s t o r e d even by v e r y p r o l o n g e d s o a k i n g . The s t r e n g t h of p a p e r p r e p a r e d from p r e - d r i e d wood o r p u l p s was shown t o be i n f e r i o r t o -26-t h a t produced f r o m n e v e r - d r i e d m a t e r i a l s by G i e r t z ( 7 3 ) , Jayme ( 9 0 ) , Teder (218) and Teder and Stockman ( 2 1 6 ) . The a l k a l i s o l u b i l i t y d e c r e a s e d and v i s c o s i t y o f t h e p u l p s i n c r e a s e d i f t h e a i r t e m p e r a t u r e exceeded 120°C d u r i n g the p u l p d r y i n g . The f a c t t h a t some s t r e n g t h p r o p e r t i e s a r e o n l y s l i g h t l y r e d u c e d i s due t o t h e predominant r o l e t h a t i n t e r f i b r e b o n d i n g p l a y s i n n ormal t e n s i l e s t r e n g t h development o f paper. Only a f t e r c o n s i d e r a b l e l o s s i n i n d i v i d u a l f i b r e s t r e n g t h i s normal t e n s i l e s t r e n g t h a p p r e c i a b l y a f f e c t e d . I n h i g h l y bonded paper s h e e t s , t h e r e f o r e , a l o s s i n f i b r e s t r e n g t h would be r e f l e c t e d t o a g r e a t e r degree. Oddly enough, b l e a c h e d k r a f t p u l p s t r e n g t h i s more i n f l u e n c e d by h e a t - t r e a t m e n t t h a n t h a t o f b l e a c h e d s u l f i t e p u l p s ( 2 1 6 ) . D e t e r i o r a t i o n i n b l e a c h e d k r a f t p u l p was so e x t e n s i v e t h a t t h e con-c e p t o f c o n s t a n t t e a r f a c t o r a t c o n s t a n t b r e a k i n g l e n g t h o f f i b r e mats d i d not h o l d ( 2 1 6 ) . D r i e d p u l p s , however, showed l e s s d e g r a d a t i o n under s i m i l a r c o n d i t i o n s , i n d i c a t i n g t h e e f f e c t o f m o i s t u r e on the d e g r a t i o n o f b l e a c h e d p u l p s d u r i n g h i g h - t e m p e r a t u r e t r e a t m e n t . The u n b l e a c h e d p u l p s t r e n g t h was o n l y m o d e r a t e l y i n f l u e n c e d by comparable heat t r e a t m e n t (216.) •i%9&-.r" I t seems t h a t s t r e t c h i n g i n t r o d u c e d by t h e " d r i e d - i n " s t r e s s e s w i t h r e s t r a i n e d p u l p s h e e t s i n c r e a s e s t h e a p p a r e n t c r y s t a l l i n i t y o f the s t r u c t u r e ( s i m i l a r t o some s y n t h e t i c h i g h - p o l y m e r s ) i n v o l v i n g f o r m a t i o n o f h i g h l y bonded a r e a s , and t h e r e b y r e s t r i c t i n g f r e e m o b i l i t y o f t h e m a c r o m o l e c u l e s ( 7 3 ) . P a p e r s d r i e d w i t h o u t s h r i n k a g e by f r e e z e d r y i n g and s o l v e n t exchange methods were f o u n d t o be w i t h o u t wet s t r e n g t h ( 2 1 6 ) . Re-h y d r a t i o n o f " d e n a t u r e d " ( 9 0 ) p u l p s c a n be a i d e d by b r e a k i n g t h e c r i t i c a l bonds w i t h s t r o n g e r s w e l l i n g a g e n t s t h a t w a t e r ( a l k a l i ) o r by m e c h a n i c a l a c t i o n ( b e a t i n g o r u l t r a s o n i c t r e a t m e n t ) . -27-Most r e m a r k a b l e , i s the e f f e c t o f h e a t t r e a t m e n t on the wet-s t r e n g t h o f b o t h s u l f i t e and s u l f a t e p apers ( 1 8 , 1 9 , 5 1 ) w i t h e f f e c t s a p p r o a c h i n g t h o s e had w i t h a d d i t i o n o f 5 t o 107o w e t - s t r e n g t h r e s i n t o the f u r n i s h . A c c o r d i n g t o Back and K l i n g a ( 1 9 ) , who s t r e s s the f o r m a t i o n o f i n t e r n a l c r o s s - l i n k s as a r e s u l t o f h e a t t r e a t m e n t , t h i s i mproved w e t - s t r e n g t h can be t a k e n as e v i d e n c e f o r p r e s e n c e o f c r o s s - l i n k s i n paper as i n t r o d u c e d by h e a t t r e a t m e n t . I t appears t h a t t h e i n t e n s i t y o f h e a t t r e a t m e n t s h o u l d be r e l a t e d t o b a s i s w e i g h t o f the paper p r o d u c t t o a v o i d s i g n i f i c a n t d r y - s t r e n g t h l o s s e s on p r o l o n g e d h e a t i n g . The o v e r a l l c h e m i c a l r e a c t i o n s i n d u c e d by h e a t t r e a t m e n t a r e d e s c r i b e d as c r o s s - l i n k i n g ( 1 8 , 1 9 ) o r f o r m a t i o n o f h y d r o p h o b i c f u r f u r a l t y p e r e s i d u e s f r o m h e m i c e l l u l o s e d e g r a d a t i o n p r o d u c t s ( 2 0 7 ) . The a d d i t i o n o f a l d e h y d e s has been shown t o promote c r o s s - l i n k i n g , whereas b o r o h y d r i d e a d d i t i o n d e l a y e d i t ( 1 9 ) . The f a c t t h a t k r a f t l i g n i n e x i s t s i n a more degraded and condensed s t a t e w i t h i n the f i b r e ( 2 3 , 5 3 ) makes u n b l e a c h e d k r a f t p u l p s more h e a t r e s i s t a n t . The l o w e r p r o p o r t i o n o f h e m i c e l l u l o s e s i s a l s o shown t o be a c o n t r i b u t i n g f a c t o r ( 9 1 ) . Formaldehyde has been f o u n d i n the v o l a t i l e d e g r a d a t i o n p r o d u c t s of h a r d b o a r d s ( 1 1 3 ) . T h i s would be e x p e c t e d t o a r i s e a l s o f r o m r e s i d u a l l i g n i n o f o t h e r h i g h y i e l d p u l p s , b u t t o a l e s s e r e x t e n t . I t m i g h t c o n t r i b u t e t o c r o s s - l i n k i n g as a l s o m i g h t f u r f u r a l d e h y d e as formed by the t h e r m a l d e g r a d a t i o n o f h e m i c e l l u l o s e ( 1 9 ) . On e x t e n s i v e h e a t i n g , a h y d r o l y t i c d e g r a d a t i o n o f c e l l u l o s e and h e m i c e l l u l o s e o c c u r s as u s u a l l y i n d i c a t e d by the t i t r a t a b l e a c i d i c m a t e r i a l and i n c r e a s e i n w a t e r s o l u b l e f r a c t i o n ( 1 9 ) . The p r o c e s s i s e v i d e n t l y an -28-o x i d a t i v e bond c l e a v a g e . I t i s i m p o r t a n t t o p o i n t o u t t h a t the h y d r o l y t i c d e g r a d a t i o n r e a c t i o n s a r e e n d o t h e r m i c , w h i l e r e a c t i o n s l e a d i n g t o c r o s s -l i n k i n g a r e e x o t h e r m i c . T h e r e f o r e , i t i s e x p e c t e d t h a t w i t h i n c r e a s e i n c u r i n g t e m p e r a t u r e t h e e q u i l i b r i u m between bond f o r m a t i o n and c l e a v a g e i n the c e l l u l o s e m a t e r i a l would s h i f t toward i n c r e a s e d bond c l e a v a g e . I n t e r n a l c r o s s - l i n k i n g r e a c t i o n s may be c a t a l y s e d by p o l y v a l e n t m e t a l s a l t s , a c i d s and hydrogen i o n s ( 5 1 , 208) . The n e t e f f e c t of i n c l u s i o n o f such s a l t s o r a c i d s i s the r e d u c t i o n of t e m p e r a t u r e l e v e l f o r o b t a i n i n g a c e r t a i n degree o f d i m e n s i o n a l s t a b i l i t y , however, the d r y - s t r e n g t h o f t h e s e m a t e r i a l s i s a d v e r s e l y a f f e c t e d . C o n s e q u e n t l y , i t was s u g g e s t e d by Stamm (208) t h a t b e t t e r r e s u l t s a r e o b t a i n e d w i t h o u t i n c l u s i o n of such c a t a l y s t s i n the p r o c e s s . D i m e n s i o n a l s t a b i l i z a t i o n o f paper has been a t t e m p t e d w i t h v a r i o u s systems of c h e m i c a l b u l k i n g r e a c t i o n s i n v o l v i n g c y a n o e t h y l a t i o n w i t h a c r y l o n i t r i l e (142, 212) a c e t y l a t i o n w i t h a c e t i c a n h y d r i d e ( 2 1 1 , 212) and by c r o s s - l i n k i n g w i t h f o r m a l d e h y d e (208, 2 1 2 ) . The numerous methods f o r g r a f t i n g monomers on t o c e l l u l o s e by c h a i n t r a n s f e r , r e d o x s y s t e m s , h e a t t r e a t m e n t and i r r a d i a t i o n and a d d i t i o n p o l y m e r i z a t i o n t e c h n i q u e s u s i n g a c r y l o n i t r i l e , s t y r e n e , m e t h y l m e t h a c r y l a t e and a c r y l a m i d e are, summarized by Schwab, S t a n n e t t and Hermans (199) . The works o f Lynch ( 1 4 2 ) , P a s z n e r (178, 179) and o t h e r s , have shown t h a t r e s u l t s o f c a t a l y s e d (167) and n o n - c a t a l y s e d p o l y m e r i z a t i o n r e a c t i o n s g i v e improvements i n p r o p e r t i e s comparable to t h o s e o b t a i n e d by i r r a d i a t i o n , b u t c o n s i d e r a b l y h i g h e r t h a n o b t a i n a b l e w i t h t h e r m a l t r e a t m e n t a l o n e . No m e n t i o n has been f o u n d i n the l i t e r a t u r e , o t h e r t h a n p o s s i b l e -29-c o n d e n s a t i o n o f l i g n i n w i t h f o r m a l d e h y d e (113) and t h a t o f c o p o l y m e r i z a t i o n of d r y i n g o i l s i n h a r d b o a r d ( 1 7 9 ) , o f c a s e s where the r e a c t i v i t y o f r e s i d u a l p u l p l i g n i n was used f o r the p u r p o s e o f g r a f t copolymer f o r m a t i o n w i t h monomeric i m p r e g n a n t s , n o r has the p o s s i b i l i t y been m e n t i o n e d t h a t some v i n y l monomer impregnants m i g h t have condensed w i t h a v a i l a b l e r e a c t i v e c e n t e r s o f r e s i d u a l l i g n i n s i n p u l p s . 3. Summary o f Thermal E f f e c t s P r o l o n g e d h e a t t r e a t m e n t a t h i g h t e m p e r a t u r e has been shown t o cause d e g r a d a t i o n o f b o t h wood (210) and wood" p u l p s ( 7 3 , 90, 216, 218) p r e p a r e d t h e r e f r o m . D e g r a d a t i v e e f f e c t s a r e m a n i f e s t e d i n l o s s o f dr.y-w e i g h t and change of h y g r o s c o p i c and m e c h a n i c a l p r o p e r t i e s . L a r g e g a i n s i n d i m e n s i o n a l s t a b i l i t y a r e p a r a l l e l e d by c o n s i d e r a b l e l o s s o f m e c h a n i c a l p r o p e r t i e s , m a i n l y toughness and t e n s i l e s t r e n g t h ( 2 0 7 ) . Heat t r e a t m e n t o f wood f i b r e p r o d u c t s , such as h a r d b o a r d and paper (113) r e s u l t s i n i n c r e a s e d d i m e n s i o n a l s t a b i l i t y and t o some e x t e n t improved m e c h a n i c a l p r o p e r t i e s . The e f f e c t i s a s c r i b e d t o f o r m a t i o n o f c r o s s - l i n k s between the c e l l u l o s e and h e m i c e l l u l o s e a t v e r y l ow h u m i d i t y c o n d i t i o n s . C h e m i c a l changes i n v o l v e f u r f u r a l t y p e r e s i n f o r m a t i o n f r o m h e m i c e l l u l o s e and c r o s s - l i n k i n g w i t h i n the l i g n i n m o l e c u l e ( 2 0 7 ) . S u b s t a n t i a l l y l a r g e r p r o p e r t y g a i n s a r e r e p o r t e d by newer t e c h n i q u e s i n v o l v i n g g r a f t i n g o f v i n y l t y p e monomers ont o c e l l u l o s e ( 1 9 9 ) . Gamma i r r a d i a t i o n has been s u c c e s s f u l l y a p p l i e d as energy s o u r c e i n t h e s e c o p o l y m e r i z a t i o n p r o c e s s e s . -30-I I I . GAMMA. RADIATION AS ENERGY SOURCE IN CHEMICAL REACTIONS 1. G e n e r a l D e s c r i p t i o n o f Gamma-Rays A l t h o u g h about f i f t y y e a r s have p a s s e d s i n c e i o n i z i n g r a d i a t i o n s were f i r s t o b s e r v e d , s y s t e m a t i c i n v e s t i g a t i o n i n t h e f i e l d has t a k e n p l a c e o n l y w i t h i n t h e l a s t decade. T h i s r e c e n t advance r e s u l t s m a i n l y from the' l a r g e r ange o f r a d i a t i o n s o u r c e s t h a t have become a v a i l a b l e . F e a t u r e s a s s o c i a t e d w i t h use o f h i g h - e n e r g y i r r a d i a t i o n f o r i n i t i a t i o n o f c h e m i c a l r e a c t i o n s a r e : 1. t h e enormous s u r f e i t o f energy i n t h e p h o t o n ; 2. the non-s p e c i f i c c h a r a c t e r o f r a d i o l y s i s ; and 3. t h e c o m p l e x i t y o f changes, b o t h p h y s i c a l and c h e m i c a l , t h a t o c c u r . N e a r l y a l l known elements e x i s t i n s e v e r a l i s o t o p i c forms w h i c h e i t h e r o c c u r n a t u r a l l y o r a r e formed a r t i f i c i a l l y i n n u c l e a r r e a c t o r s ( 6 4 ) . Many o f t h e s e i s o t o p e s a r e u n s t a b l e as c h a r a c t e r i z e d by t h e i r c o n s t a n t l y d i s i n t e g r a t i n g n u c l e i e j e c t i n g e n e r g i z e d p a r t i c l e s and/or by e m i s s i o n o f e l e c t r o m a g n e t i c r a d i a t i o n i n t h e form o f gamma-rays (46, 6 4 ) . Gamma-rays h a v i n g no mass a t r e s t a r e u n d e f l e c t e d by e l e c t r i c and m a g n e t i c f i e l d s and p o s s e s s e x t r e m e l y h i g h p e n e t r a t i n g power. The energy quantum, or energy per photon, of gamma-rays i s i n v e r s e l y p r o p o r t i o n a l to t h e w a v e l e n g t h (46) . The p e n e t r a t i n g power o f gamma-rays i n c r e a s e s w i t h d e c r e a s i n g w a v e l e n g t h . The gamma-ray w a v e l e n g t h s p e c t r u m i s d e f i n e d as t h a t -9 -11 between 3x10 t o 3x10 cm, or 40 kev t o 4 Mev ( 4 6 ) . The i s o t o p e w h i c h has r e c e i v e d g r e a t e s t a t t e n t i o n , as a s o u r c e -31-o f r a d i a t i o n energy, i s u n d o u b t e d l y C o b a l t - 60 (^Co) . I t i s p r e p a r e d from 59 Co by n e u t r o n c a p t u r e v i a two c a p t u r e r e a c t i o n s t h a t produce i s o t o p e s h a v i n g h a l f - l i f e t i m e s o f 10 min and 5.27 y r . The 10 min i s o t o p e decays by an 60 i s o m e r i c t r a n s i t i o n t o t h e 5.27 y r i s o t o p e . The p r e f e r r e d u s e o f Co i s due t o i t s r e a d y a v a i l a b i l i t y , r e l a t i v e l y u n i f o r m h i g h - e n e r g y r a d i a t i o n (1.173 t o 1.33 Mev) and t h e l o n g h a l f - l i f e (5.27 y e a r ) . Gamma-rays a r e a l s o p r e f e r r e d f o r i n d u s t r i a l a p p l i c a t i o n s b e c a u s e t h e y l e a v e no r e s i d u a l r a d i o -a c t i v i t y i n t r e a t e d m a t e r i a l s . 2. Mechanism o f R a d i a t i o n I o n i z a t i o n I n t h e p r o c e s s o f i r r a d i a t i o n by gamma-rays energy d e p o s i t i o n o c c u r s a l o n g the r a y t r a j e c t o r y i n t h e m a t e r i a l due t o e l a s t i c and i n e l a s t i c c o l l i s i o n s - . ^ I n s p i t e o f numerous s t u d i e s , t h e b a s i c phenomenon o f energy d e p o s i t i o n i s n o t r e a l l y u n d e r s t o o d f o r compressed and condensed systems ( 1 4 9 ) . I t i s known t h a t t h e energy c o n t e n t o f gamma-rays i s much g r e a t e r t h a n t h a t r e q u i r e d t o e x c i t e m o l e c u l e s o r t o b r e a k c h e m i c a l bonds ( 2 0 ) . A p p a r e n t l y , o n l y a minor f r a c t i o n o f t h e t o t a l energy d e p o s i t i o n i s i n v o l v e d i n s u c h p r o c e s s e s . Most o f t h e energy, i n t h i s v i e w , goes i n t o c o l l e c t i v e e x c i t a t i o n (40) . Gamma-rays tend t o losjse. t h e i r energy t h r o u g h a s i n g l e i n t e r a c t i o n , whereby a p o r t i o n i s a b s o r b e d and t h e o t h e r p a r t i s t r a n s m i t t e d w i t h f u l l i n i t i a l e n e r g y . I t i s t h o u g h t t h a t c o l l i s i o n s r e s u l t i n i o n i z a -t i o n by a t r a n s f e r o f energy between t h e h i g h - e n e r g y quanta and atoms o f t h e medium t h r o u g h w h i c h t h e y p a s s . The c h e m i c a l changes f o l l o w i n g s u c h c o l l i s i o n s a r e m a i n l y due t o t h e e j e c t i o n o f h i g h - s p e e d e l e c t r o n s . D i s p l a c e -ment o f e l e c t r o n s i n c h e m i c a l bonds comes about by energy t r a n s f e r from t h e -32-charged p a r t i c l e and i f t h e d i s p l a c e m e n t i s s u f f i c i e n t f o r s t r i p p i n g an e l e c t r o n from t h e p a r e n t m o l e c u l e , i o n i z a t i o n o c c u r s . A t low l e v e l s o f d i s -p lacement o n l y m o l e c u l a r e x c i t a t i o n s o c c u r . I n cases where an e l e c t r o n i s e j e c t e d from i t s o r b i t w i t h s u f f i c i e n t k i n e t i c energy i t , t o o , can cause e x c i t a t i o n and i o n i z a t i o n . Such an e f f e c t i s c a l l e d s e c o n d a r y e x c i t a t i o n o r s e c o n d a r y i o n i z a t i o n . C o n s e q u e n t l y , a t each p o i n t o f i n i t i a l i o n i z a t i o n groups o f i o n - p a i r s a r e formed (161, 182, 226) . The d e n s i t y o f w a t e r 60 P i o n i z a t i o n s by | Co r a y s on t h e a v e r a g e i s one per 1000A, as e s t i m a t e d by P h i l l i p s ( 1 8 2 ) . The number o f f r e e r a d i c a l s formed was found t o be one per 4 5 10 t o 10 g l u c o s e u n i t s i n c e l l u l o s e ( 1 7 7 ) . I n i o n i z e d and e x c i t e d m o l e c u l e s a v a r i e t y o f s e c o n d a r y p r o c e s s e s may o c c u r b e f o r e t h e f i n a l c h e m i c a l change t a k e s p l a c e . I n t h e c o u r s e o f e x c i t a t i o n and i o n i z a t i o n the a f f e c t e d m o l e c u l e may b r e a k i n t o f ragments by r u p t u r i n g weak bonds (226) . R u p t u r e may o c c u r i n c a r b o n - h y d r o g e n bonds, f o r m i n g h y d r o g e n atoms and a l k y l r a d i c a l s ; R - H R. + H-o r i n c a r b o n - c a r b o n bonds i n a polymer c h a i n , f o r m i n g two p o l y m e r i c r a d i c a l s w i t h u n p a i r e d e l e c t r o n s ; IT R^ - R 2 R^ + R 2" The e x t e n t t o w h i c h t h e s e r e a c t i o n s o c c u r , o t h e r t h i n g s b e i n g e q u a l , w i l l depend upon a c t i v a t i o n e n e r g i e s . Thus, a l a r g e number o f the m o l e c u l a r fragments become f r e e t o r e a c t w i t h each o t h e r and w i t h r e a c t i v e m o l e c u l e s i n t h e s u r r o u n d i n g e n v i r o n m e n t . The p r e s e n c e and number o f f r e e - r a d i c a l s was a c t u a l l y d e t e r m i n e d -33-t h r o u g h s t u d y o f e l e c t r o n p a r a m a g n e t i c r e s o n a n c e s p e c t r a (ESR)^ by Abraham and W h i f f e n ( 2 ) , G l e g g and K e r t e s z ( 7 6 ) , P a r k (177) and by Rapson and co-w o r k e r s ( 8 4 ) i n c e l l u l o s e and by Ramalingam, Werezak and Hodgins (186) i n c e l l u l o s e , c e l l u l o s e p u l p i m p r e g n a t e s , wood p u l p i m p r e g n a t e s and l i g n i n . A q u a n t i t a t i v e e s t i m a t i o n o f f r e e r a d i c a l s i n t h e f o r e g o i n g m a t e r i a l s i s p r e -s e n t e d i n F i g . 1 ( 1 8 6 ) . F o r t h e p r o c e d u r e d i p h e n y l p i c r y l h y d r a z y l was used as p r i m a r y s t a n d a r d (0.1 mg o f t h e s t a n d a r d r e p r e s e n t e d 1 . 5 x 1 0 ^ s p i n s ) . The a b s o r p t i o n c u r v e s were o b t a i n e d by g r a p h i c a l i n t e g r a t i o n o f t h e d e r i v a -t i v e c u r v e s and t h e r a d i c a l c o n c e n t r a t i o n s were c a l c u l a t e d from comparisons o f i n t e g r a t e d a r e a s . The e f f e c t o f h e a t i n g on f r e e r a d i c a l c o n c e n t r a t i o n i s shown i n F i g . 2 (186) . Such changes in vacuo a r e b e l i e v e d due t o s e c o n d a r y c h e m i c a l mechanisms, such as c r o s s - l i n k i n g . The decay o f f r e e r a d i c a l c o n c e n t r a t i o n was a l s o f o l l o w e d by A r t h u r and co-workers (14, 26) who found t h a t f r e e r a d i c a l s o f i r r a d i a t e d c e l l u l o s e i n t e r a c t e d w i t h the f r e e oxygen o f t h e a i r , whereby f u r t h e r c h a i n s c i s s i o n s were pr o d u c e d . The e x i s t e n c e o f such l o n g - l i v e d f r e e r a d i c a l s was shown t o o r i g i n a t e from t h e c e l l u l o s e i n c e l l u l o s e - m o n o m e r - s o l v e n t mix-t u r e s (186) and was f o l l o w e d o v e r a p e r i o d o f 20 days (85, 1 8 6 ) . These p o s t - i r r a d i a t i o n e f f e c t s r e s u l t e d i n c o n t i n u o u s d e c r e a s e i n c e l l u l o s e v i s c o s i t y (26, 85) and an i n c r e a s e i n g r a f t y i e l d (85) w i t h t i m e from d a t e o f 1 E l e c t r o n p a r a m a g n e t i c r e s o n a n c e s p e c t r o m e t r y i s based on r e s o n a n c e a b s o r p -t i o n o f e l e c t r o - m a g n e t i c energy by u n p a i r e d e l e c t r o n s i n s u b s t a n c e s exposed t o an e x t e r n a l m a g n e t i c f i e l d . S i n c e f r e e r a d i c a l s a r e c h a r a c t e r i z e d by t h e p r e s e n c e o f one or more u n p a i r e d e l e c t r o n s t h e y a r e e x p e c t e d t o e x h i b i t e l e c t r o n p a r a m a g n e t i c r e s o n a n c e a b s o r p t i o n (76, 186). -34-i r r a d i a t i o n . S i m i l a r o b s e r v a t i o n s were made by Majumdar and Rapson ( 1 5 0 ) . The r a p i d decay o f f r e e r a d i c a l s o b s e r v e d on a d m i t t i n g a i r t o t h e i r r a d i a t e d sample i s due t o oxygen w h i c h a c t s as a r a d i c a l s c a v e n g e r ( 1 8 6 ) . 10 2 0 3 0 4 0 5 0 6 0 7 0 Time after Irradiation, Hours F i g u r e i . F r e e r a d i c a l c o n c e n t r a t i o n s i n i r r a d i a t e d wood and wood p r o d u c t s . Decay a t 25°C . R a d i a t i o n dosage c a . 10 Mrad (186) . -35-Figure 2. E f f e c t of heating on free r a d i c a l concentration. (a) ESR spectrum immediately a f t e r i r r a d i a t i o n , (b) ESR spectrum a f t e r heating the same sample for 2 hr. at 105°C (186) . The c h e m i c a l r e a c t i o n s and r e a r r a n g e m e n t s w h i c h t a k e p l a c e a f t e r i n i t i a l i o n i z a t i o n and e x c i t a t i o n a r e dependent on t h e p h y s i c a l s t r u c t u r e o f t h e i r r a d i a t e d m a t e r i a l ( 2 6 ) . W i t h p o l y m e r i c m a t e r i a l s , i r r a d i a t e d i n t h e s o l i d s t a t e , t h e r a d i c a l s and e x c i t e d m o l e c u l e s a r e r e l a t i v e l y i m m o b i l i z e d and cannot r e a d i l y i n t e r a c t w i t h o t h e r a c t i v a t e d s p e c i e s by s i m p l e c o l l i s i o n as i n gaseous and l i q u i d s t a t e s . E q u i l i b r i u m i s a t t a i n e d by i n t e r a c t i o n w i t h o t h e r a c t i v a t e d s p e c i e s t h a t have c l o s e enough p r o x i m i t y t h r o u g h i n t r a m o l e -c u l a r r e a r r a n g e m e n t , energy t r a n s f e r i n t e r a c t i o n s w i t h more m o b i l e m o l e c u l e s , o r by a c t i v a t e d s p e c i e s i n i t i a l l y p r e s e n t or p r o duced by i r r a d i a t i o n (150) . The u n d e r s t a n d i n g ''of energy t r a n s f e r i n p o l y m e r i c systems s t i l l poses some p r o b l e m s . Mechanisms t h a t have been p r o p o s e d a r e s i m i l a r t o t h o s e o b s e r v e d i n gaseous and l i q u i d systems (29,.149) . These mechanisms d e s c r i b e energy t r a n s f e r p r i m a r i l y as an e l e c t r o n i c e x c i t a t i o n (149) o f photons -36-o r i g i n a t i n g from r e c o m b i n a t i o n o f e j e c t e d e l e c t r o n s w i t h i o n s i n t h e s y s t e m (22, 29, 4 7 ) . The main e v i d e n c e p o i n t i n g towards an e x c i t a t i o n t r a n s f e r o f energy i s s c i n t i l l a t i o n o f f l u o r e s c e n t s o l u t e s i n n o n - f l u o r e s c i n g s o l v e n t s under r a d i a t i o n (120) . I n t e r m o l e c u l a r t r a n s f e r o f r a d i a t i o n - i n d u c e d i o n i z a t i o n energy has a l s o been o b s e r v e d i n condensed systems (120, 235) . Some o r g a n i c and o r g a n o - m e t a l l i c compounds a r e c a p a b l e o f e x e r t i n g a p r o t e c t i v e e f f e c t , as w e l l as a r e t a r d i n g e f f e c t on d e g r a d a t i o n s e n s i t i v e compounds. Thus a r o m a t i c compounds have been shown t o be much more s t a b l e t h a n c y c l i c h y d r o c a r b o n s ( s u c h as c y c l o h e x a n e ) towards r a d i o l y s i s e f f e c t s (31,,41, 120, 235). The a r o m a t i c r i n g was o b s e r v e d to a b s o r b w i t h o u t c h e m i c a l change no t o n l y t h e energy i t r e c e i v e d d i r e c t l y , b u t a l s o t h a t w h i c h was i n t e r m o l e c u l a r l y t r a n s -f e r r e d t o i t . A r o m a t i c r i n g s t e n d t o s t a b i l i z e t h e m o l e c u l e w i t h a r e s u l t i n g low e f f i c i e n c y o f r a d i c a l p r o d u c t i o n (41) . I n s u c h compounds most o f t h e energy i s t r a n s f e r r e d i n t o t h e benzene r i n g as a w h o l e w i t h o u t r e s i d e n c e a t any one bond l o n g enough to b r e a k i t (41) . T h i s d i r e c t i n t e r m o l e c u l a r energy t r a n s f e r s h o u l d be a t l e a s t f o l l o w e d by an e q u a l l y p o w e r f u l i n t r a m o l e c u l a r e f f e c t and t h e r e b y e f f e c t i v e l y p r o t e c t more s u s c e p t i b l e m o l e c u l e s from d e g r a d a t i o n . Thus, a r o m a t i c r i n g s a t t a c h e d t o polymer c h a i n s may i n c r e a s e t h e r e s i s t a n c e t o r a d i a t i o n damage by s e r v i n g as "energy s i n k s " , i . e . , t h e y draw energy away from more r a d i o s e n s i t i v e bonds and d i s s i p a t e i t non-d e s t r u c t i v e l y . The p r o t e c t i v e e f f e c t s o f some b e n z e n e - r i n g compounds as compared to some s i m p l e h y d r o c a r b o n s and t h e i r h a l o g e n d e r i v a t i v e s a r e d e m o n s t r a t e d i n T a b l e I ( 2 9 ) . -37-The s t r i k i n g e f f e c t o f e l e c t r o n e g a t i v e h a l o g e n s u b s t i t u e n t s i s a l s o e v i d e n t . Such p r o t e c t i v e a r o m a t i c compounds were found t o e x e r t e f f e c t s s i m i l a r t o a n t i - o x i d a n t s ( 8 ) . T a b l e I . P r o d u c t i o n o f f r e e r a d i c a l s by gamma i r r a d i a t i o n o f o r g a n i c l i q u i d s ( 2 9 ) . F r e e r a d i c a l s Compound produced per Energy Y i e l d , 100 ev. % Benzene 1.8 3.0 S t y r e n e 1.6 2.8 m-Xylene 6.3 11.0 E t h y l benzene 9.0 15.0 C h l o r o b e n z e n e 17.3 26.0 n-Heptane 9.9 17.0 C y c l o h e x a n e 14.3 24.5 D i o x a n e 20.0 34.0 M e t h a n o l 24.0 41.5 P r o p a n o l 30.0 51.5 V i n y l a c e t a t e 33.0 57 .0 A c e t o n e 50.0 87 .0 E t h y l bromide 28.0 39.0 C h l o r o f o r m 59.5 88.4 I n t h e copolymer s y s t e m o f b u t a d i e n e and s t y r e n e (235) t h e s t y r e n e n o t o n l y a b s o r b e d t h e r a d i a t i o n energy t h a t i t r e c e i v e d d i r e c t l y , b u t -38-was a b l e t o absorb and d i s s i p a t e n o n - d e s t f u c t i v e l y t h e energy t r a n s f e r r e d t o i t f rom n e i g h b o r i n g b u t a d i e n e u n i t s . I n p h y s i c a l m i x t u r e s , t h e s t y r e n e was found t o d i s s i p a t e h a r m l e s s l y t h e energy i t r e c e i v e d , b u t s i n c e no energy t r a n s f e r was p o s s i b l e b u t a d i e n e d e g r a d a t i o n and c r o s s - l i n k i n g was e v i d e n t . The s t y r e n e u n i t s i n p h y s i c a l m i x t u r e s can p r o t e c t b u t a d i e n e o n l y by d e c r e a s -i n g t h e g r o s s amount o f i n c i d e n t r a d i a t i o n e n e r g y . T h i s i m p l i e s t h a t a p r o t e c t i v e agent must be an i n t e g r a l p a r t o f , o r p o s s i b l y i n homogeneous s o l u t i o n w i t h , t h e polymer c h a i n s t o e x e r t p r o t e c t i v e e f f e c t s (8, 2 3 5 ) . Such a s i t u a t i o n may o r may n o t e x i s t or may e x i s t o n l y t o a l i m i t e d e x t e n t i n l i g n o - c e l l u l o s i c s . 3 . D e g r a d a t i o n v e r s u s C r o s s - L i n k i n g o f Polymers The e f f e c t s o f r a d i a t i o n on a s i n g l e p o l y m e r i c s y s t e m a r e u s u a l l y r e a l i z e d i n two t y p e s o f r e a c t i o n s : 1. s c i s s i o n o f t h e m o l e c u l a r c h a i n r e s u l t i n g i n d e g r a d a t i o n , i . e . , d e c r e a s e d a v e r a g e m o l e c u l a r w e i g h t , and i n c r e a s e d s o l u b i l i t y i n s o l v e n t s ; and 2. c r o s s - l i n k i n g o f polymer c h a i n s t o f o r m an i n s o l u b l e n e t w o r k . B o t h p r o c e s s e s have been found t o o c c u r s i m u l t a n e o u s l y i n such a s y s tem; t h e i n i t i a l e f f e c t b e i n g i o n i c and c o v a l e n t bond b r e a k i n g . The r e s u l t i n g r a d i c a l s can r e a c t t h e n i n a number o f ways. R e a c t i o n s o f degrad-a t i o n ( d e p o l y m e r i z a t i o n ) and c r o s s - l i n k i n g a r e c h a r a c t e r i s t i c o f p a r t i c u l a r p o l y m e r s . I t has been shown, f o r i n s t a n c e , t h a t w h i l e p o l y e t h y l e n e m a i n l y undergoes c r o s s - l i n k i n g ( 1 8 6 ) , p u r e c e l l u l o s e i s s e v e r e l y d e p o l y m e r i z e d (84, 1 82) . V i n y l polymers b e a r i n g a l p h a s u b s t i t u e n t s ( s u c h as CH-, C I , e t c . ) -39-i n s t e a d o f a l p h a hydrogens undergo s c i s s i o n on i r r a d i a t i o n . T h i s e f f e c t i s b e l i e v e d t o be due t o s t e r i c s t r a i n s w h i c h weaken the c a r b o n - c a r b o n bond o f the main c h a i n . W a l l (225) a l s o r e l a t e d . l o w h e a t s o f p o l y m e r i z a t i o n o f c e r t a i n compounds t o predominant s c i s s i o n r e a c t i o n s . However, p r e s e n t e x p l a n a t i o n s o f t h e s e phenomena a r e n o t s a t i s f a c t o r y . Mechanisms such as r e a r r a n g e m e n t i n t h e p r e s e n c e o f a l p h a - m e t h y l groups t o d o u b l e bonds and f a c t o r s i n v o l v i n g r e l a t i v e tendency o f r a d i c a l s t o p roduce c h a i n s c i s s i o n a r e d e s c r i b e d i n the l i t e r a t u r e ( 2 2 5 ) . I t has been shown,however, t h a t t h e p r e s e n c e o f oxygen tends t o encourage s c i s s i o n (26, 150) and c e r t a i n polymers may show predominant s c i s s i o n o r c r o s s - l i n k i n g d epending on w h e t h e r oxygen ife p r e s e n t o r a b s e n t (29, 103, 186, 2 2 2 ) . The p o s s i b i l i t y o f c r o s s - l i n k i n g between l o n g - c h a i n . p o l y m e r s by c h e m i c a l means o f f e r s many i n t e r e s t i n g p o s s i b i l i t i e s . I n t h e f i r s t p l a c e , i t p r o v i d e s means f o r p r o d u c i n g m a t e r i a l s w i t h any r e q u i r e d degree o f c r o s s -l i n k i n g . T h i s can be a c c o m p l i s h e d i n many cases w i t h o u t h e a t t r e a t m e n t , w h i c h m i g h t , a f f e c t o t h e r p r o p e r t i e s o f t h e m a t e r i a l s ( s u c h as s t r e n g t h and c o l o r ) , and w i t h o u t t h e i n t r o d u c t i o n o f f o r e i g n atoms (139) . S i n c e the mechanism o f c r o s s - l i n k i n g i s q u i t e d i f f e r e n t from t h a t r e a l i s e d i n c o n v e n t i o n a l c h e m i s t r y (49) a w i d e r a n g e o f new p l a s t i c s can be •.j^^^^0'tzed-i The method a l s o a l l o w s m e c h a n i c a l and p h y s i c a l p r o p e r t i e s t o be s t u d i e d as f u n c t i o n s o f t h e d e g r e e o f c r o s s - l i n k i n g . O c c u r r e n c e o f c r o s s - l i n k i n g i s u s u a l l y a t t r i b u t e d t o t h e forma-t i o n o f polymer r a d i c a l s on a d j a c e n t s i t e s o f n e i g h b o r i n g c h a i n s (22, 29, 4 9 ) . I f t h e r a d i c a l s a r e produced a t random s i t e s , c l o s e r a d i c a l p a i r s do n o t o c c u r o f t e n enough t o a c c o u n t f o r any o b s e r v a b l e c r o s s - l i n k i n g . R e a c t i o n s -40-accompanying c r o s s - l i n k i n g and a l s o o f c h a i n s c i s s i o n a r e m a i n l y the s p l i t t i n g o f f o f hydrogen, methane, ethane, c a r b o n monoxide and c a r b o n d i o x i d e , i n i n c r e a s i n g o r d e r . C o n s e q u e n t l y , c r o s s - l i n k a g e s a p p a r e n t l y form between n e i g h b o r i n g c h a i n s w i t h e l i m i n a t i o n i n h o m o p o l y m e r i z a t i o n (47) . The amount o f e l i m i n a t i o n p r o d u c t s formed a r e n o t always i n d i c a t i v e o f t h e number o f c r o s s - l i n k a g e s formed b u t may a r i s e a l s o from d o u b l e bond forma-t i o n , a l e s s common r e s u l t o f i r r a d i a t i o n (139) . 4. Fundamentals o f R a d i a t i o n G r a f t i n g I n r e c e n t y e a r s c o n s i d e r a b l e a t t e n t i o n has been g i v e n t o m o d i f i c a -t i o n o f s y n t h e t i c and n a t u r a l h i g h - p o l y m e r s by c o m b i n i n g p o l y m e r i c s i d e -c h a i n s w i t h t he main polymer under v a r i o u s c o n d i t i o n s t o form g r a f t co-polymers . G r a f t i n g i s a s p e c i a l r e a c t i o n o f c r o s s - l i n k f o r m a t i o n between an a l r e a d y e x i s t i n g p o l y m e r i c s t r u c t u r e and s p e c i a l l y p o s i t i o n e d r e a c t i v e monomer (34, 153). I r r a d i a t i o n g r a f t i n g o f polymers may be d i v i d e d i n t o two b r o a d c l a s s i f i c a t i o n s ( 1 5 3 ) : A. S i m u l t a n e o u s i r r a d i a t i o n o r m u t u a l t e c h n i q u e , i n w h i c h t h e s u b s t r a t e t o be g r a f t e d upon i s i m p r e g n a t e d w i t h t h e monomer f o l l o w e d by i r r a d i a t i o n . The c h e m i c a l r e a c t i o n i s s a i d t o r e l y on c h a i n t r a n s f e r mechanisms (202) . S u c c e s s o f such r a d i a t i o n p o l y m e r i z a t i o n i s dependent on the number o f s t r o n g c h a i n t r a n s f e r r i n g a c t i v e groups w h i c h i n t u r n a r e a c t i v a t e d by f r e e r a d i c a l s (230) . I n a d d i t i o n t o c o m p l e t e c o m p a t i b i l i t y o f such systems, s u f f i c i e n t p o l a r i n t e r a c t i o n between t h e f r e e r a d i c a l s and monomer a c t i v e c e n t e r s i s r e q u i r e d . F u r t h e r , n e g l i g i b l e c h a i n t r a n s f e r -41-r e s u l t i n g i n t h e f o r m a t i o n o f a homopolymer must be assumed ( 2 3 0 ) . B. P r e - i r r a d i a t i o n o f t h e s u b s t r a t e , whereby f r e e r a d i c a l t y p e c e n t e r s a r e p l a n t e d on t h e e x i s t i n g p o l y m e r i c s y s t e m and t h e monomer i s impreg n a t e d a f t e r p r e - a c t i v a t i o n (202, 226, 230) . Normal copolymers o f two o r more monomers can be l i n e a r o r bran c h e d (153) and t h e o r i g i n a l c h e m i c a l e n t i t i e s may be combined i n e i t h e r r e g u l a r o r i r r e g u l a r f a s h i o n . I n t h e l a t t e r c a s e , t h e components a r e i n t i m a t e l y mixed i n t h e copolymer m o l e c u l e w i t h o u t a p a r t i c u l a r s y s t e m a t i c o r d e r . The r e s u l t i n g polymer p r o p e r t i e s , t h e r e f o r e , a r e w e i g h t e d averages o f t h e p r o p e r t i e s o f the p o l y m e r i c components (49, 119, 1 5 3 ) . I n systems where u n i f o r m c h e m i c a l components e x i s t i n l a r g e r s t r e t c h e s o r segments, b l o c k copolymers a r e o b t a i n e d . A l t e r n a t e p o s i t i o n s o f p o l y m e r i c components w i t h o n l y a s e c o n d a r y degree o f l a t e r a l b o n d i n g r e s u l t i n ; l i n e a r c o p o l y m e r s . I t was o b s e r v e d (230) t h a t w i t h polymers w h i c h p r e d o m i n a n t l y c r o s s - l i n k on i r r a d i a t i o n , a monomer ( u s u a l l y o f t h e v i n y l t y p e ) adds t o a c t i v e c e n t e r s b e f o r e t h e y can combine t o form c r o s s - l i n k s . I n polymers t h a t m a i n l y undergo d e g r a d a t i o n , the monomer may add t o b r o k e n c h a i n ends and t h e r e b y form b l o c k c o p o l y m e r s . A l t e r n a t i v e l y , r a d i c a l s formed by e l i m i n a t i o n r e a c t i o n s o f atoms o r s i d e - g r o u p s may add monomers and form g r a f t c o p o l y m e r s . D i s r u p t i o n o f s i d e - c h a i n r a d i c a l s , i n t h e absence o f monomer, i s p o s s i b l e . T h i s p r o v i d e s c h a i n s c i s s i o n s . Most e a r l y s t u d i e s o f g r a f t i n g i n d u c e d by h i g h - e n e r g y r a d i a t i o n i n c l u d e d d e t e r m i n a t i o n o f w e i g h t g a i n s a f t e r t h o r o u g h homopolymer e x t r a c t i o n (13, 85, 103, 150, 230), as w e l l as measurement o f m e c h a n i c a l s t r e n g t h i n -c r e a s e (38, 69, 79, 103, 148, 185, 202, 2 3 8 ) . These have been used as -42-measures o f a p p a r e n t g r a f t i n g r a t e , l e a v i n g open the q u e s t i o n o f r e l a t i v e amount o f t r u e c o v a l e n t g r a f t i n g and caged homopolymer. I n o t h e r cases (13, 38, 84, 185, 230, 238), changed s o l u b i l i t y c h a r a c t e r i s t i c s o f t h e b a s i c polymer have been a c c e p t e d as e v i d e n c e f o r e x t e n t o f g r a f t c o p o l y m e r i z a t i o n . Most o f t e n , h o w e v e r , s o l u b i l i t y d i f f e r e n c e s between g r a f t copolymers and homo-polymers a r e n o t l a r g e enough t o a l l o w adequate s e p a r a t i o n . T h e r e f o r e , e x a c t amounts and c o m p o s i t i o n o f such copolymers a r e i n f r e q u e n t l y known. T h i s i s a s e r i o u s l i m i t a t i o n , s i n c e many g r a f t polymers a r e produced by he t e r o g e n e o u s r e a c t i o n s and r e a c t i o n s such as c h a i n t r a n s f e r , where c o n s i d e r -a b l e homopolymer f o r m a t i o n can be a n t i c i p a t e d (238) . T h i s i s p a r t i c u l a r l y t r u e o f methods where t h e degr e e o f g r a f t i n g . i s o b t a i n e d from t h e i n c r e a s e i n w e i g h t a f t e r homopolymer e x t r a c t i o n . I n p a r t i c u l a r , t h e p r o p o r t i o n o f o r i g i n a l p o l y m e r i c s u b s t r a t e p o s s e s s i n g g r a f t e d s i d e - c h a i n s i s n o t known a t a l l . F u r t h e r m o r e , d i f f i c u l t y i n removing t h e o c c l u d e d homopolymer l e a d s a t b e s t t o o n l y a maximum f i g u r e f o r t h e amount o f g r a f t i n g . Such l a c k o f know-l e d g e has p r e v e n t e d the e s t a b l i s h m e n t o f any a c c u r a t e p i c t u r e on k i n e t i c s and mechanism o f g r a f t i n g . Most g r a f t i n g methods y i e l d p r o d u c t s t h a t a r e m i x t u r e s o f g r a f t and homopolymer (84, 85, 103, 119, 150, 226, 2 3 8 ) . I n many cases t h e number aver a g e g r a f t y i e l d s a r e low because o n l y a l i m i t e d number o f o f t e n r e l a t i v e -l y l o n g s i d e - c h a i n s i s a t t a c h e d t o t h e backbone o f t h e p r e - e x i s t i n g polymer (13, 84, 119, 153, 215, 230, 2 3 8 ) . M o l e c u l a r w e i g h t o f t h e s i d e - c h a i n i s always many t i m e s l a r g e r t h a n t h a t o f t h e homopolymer c o n c u r r e n t l y produced i n t h e monomer s o l u t i o n (215) . Such i s t h e case w i t h h e t e r o g e n e o u s systems (84, 215, 230, 238) as e x p l a i n e d by g e l e f f e c t s . -43-The y i e l d o f g r a f t copolymer i n c r e a s e s s t e a d i l y w i t h r a d i a t i o n dosage, b u t d e c r e a s e s a t h i g h e r dose r a t e s . Due t o t h e d i f f u s i o n : c o n t r o l l e d growth m e c h a n i s m , g r a f t i n g r a t e s a t h i g h dose r a t e s a r e ne v e r as h i g h as t h o s e w i t h l o w e r dosages (215) . T h i s l a t t e r e f f e c t i s p r o b a b l y due t o de-c r e a s e d a v a i l a b i l i t y o f monomer m o l e c u l e s i n t h e immediate n e i g h b o r h o o d o f a c t i v e s i t e s o f g r o w i n g c h a i n s . I f t h e dose r a t e i s h i g h , s u f f i c i e n t monomer cannot d i f f u s e i n t o t h e i n t e r i o r o f t h e polymer and t e r m i n a t i o n o f a c t i v e r a d i c a l s o c c u r s w i t h o u t c o p o l y m e r i z a t i o n . However, by i n c r e a s e d s w e l l i n g o f the p a r e n t polymer and w i t h a p p r o p r i a t e s o l v e n t s a t f i x e d . p a r e n t polymer t h i c k n e s s e s , p e n e t r a t i o n becomes l e s s o f a problem, and,thereby, g r a f t i n g r a t e can be i n c r e a s e d w i t h s i m u l t a n e o u s r e d u c t i o n i n g r a f t m o l e c u l a r w e i g h t (215) . A t low dose r a t e s , on t h e o t h e r hand, no t h i c k n e s s e f f e c t s s h o u l d be o b s e r v e d . However, t h e presence, o f w e t t i n g a g e n t s s t i l l r e mains a p r e -r e q u i s i t e f o r s u c c e s s f u l g r a f t i n g (84, 103, 186, 2 3 8 ) . Long and Thompson (136) o b s e r v e d t h a t t h e r a t e o f o r g a n i c vapour d i f f u s i o n i n t o p l a s t i c i z e d h y d r o p h i l i c f i l m s was f a s t e r t h a n i n t o n o n - p l a s t i c i z e d f i l m s . T h i s e f f e c t i s b e l i e v e d t o be caused by t h e b r e a k i n g o f h y d r o g e n bonds w i t h w a t e r , o r any good s w e l l i n g a gent f o r t h a t m a t t e r , thus p r o v i d i n g g r e a t e r segment m o b i l i t y o f t h e polymer m o l e c u l e s and f a c i l i t a t i n g improved d i f f u s i o n o f monomers. Enhancement o f d i f f u s i o n by s w e l l i n g o c c u r s even i n systems where t h e pene-t r a n t m o l e c u l e s a r e not m i s c i b l e w i t h t h e s w e l l i n g agent (85) . Huang and Rapson (85) a t t r i b u t e t h e i n d i r e c t e f f e c t s o f s o l v e n t s on r a d i o c h e m i c a l g r a f t y i e l d s t o t h e i n t e r a c t i o n o f s o l v e n t w i t h b o t h t h e monomer and p a r e n t polymer t o i n c r e a s e t h e a c c e s s i b i l i t y o f a c t i v a t e d s i t e s t o t h e monomer. Per c e n t h o m o p o l y m e r i z a t i o n i n h e t e r o g e n e o u s systems was found -44-to i n c r e a s e a l m o s t l i n e a r l y w i t h i r r a d i a t i o n dosage, i r r e s p e c t i v e o f whether o r n o t s i m u l t a n e o u s or p o s t - i r r a d i a t i o n g r a f t i n g t e c h n i q u e s were u s e d i n t h e p r e s e n c e o r absence o f a s u i t a b l e s w e l l i n g agent (150) . H o m o p o l y m e r i z a t i o n a l s o i n c r e a s e d w i t h i n c r e a s i n g g r a f t , y i e l d , p o s s i b l y due t o t h e f a c t t h a t f r e e r a d i c a l s a r e produced i n p a i r s ; one f i x e d and one m o b i l e . Each o f t h e s e two f r e e r a d i c a l s may i n i t i a t e p o l y m e r i z a t i o n . The f i x e d , f r e e r a d i c a l i n i t i a t e s g r a f t i n g ( o r c h a i n s c i s s i o n i n t h e absence o f monomer), whereas t h e m o b i l e one causes h o m o p o l y m e r i z a t i o n . I n case o f s h o r t - l i v e d f r e e r a d i c a l s i n c a p a b l e o f p o l y m e r i z a t i o n , D a l t o n et al. (54) r e p o r t e d marked i n c r e a s e i n p o l y m e r i z a t i o n by a d d i t i o n o f some s o l i d s c a p a b l e o f t r a p p i n g e l e c t r o n s . A s t u d y o f t h e mechanism s u g g e s t s t h a t i n t h e absence o f a d d i t i v e no p o l y m e r i z a t i o n c o u l d o c c u r . A p p a r e n t l y , t h e s u r f a c e a r e a o f such c a t a l y s t s i s o f g r e a t i m p o r t a n c e ( 2 9 ) . From t h e f o r e g o i n g s e c t i o n s i t s h o u l d be u n d e r s t o o d , t h a t a l l t h r e e major e f f e c t s o f i r r a d i a t i o n , namely c h a i n s c i s s i o n , c r o s s - l i n k i n g and g r a f t i n g accompanied by h o m o p o l y m e r i z a t i o n , a r e s i m u l t a n e o u s r a d i o c h e m i c a l r e a c t i o n s . Predominance o f any one, or t h e i r c o m b i n a t i o n , i s m a i n l y dependent on c o n d i t i o n s o f i r r a d i a t i o n and i s t h e r e b y s u b j e c t t o some c o n t r o l . -45-I V . EFFECT OF IONIZING RADIATION ON THE PHYSICAL AND CHEMICAL PROPERTIES OF  WOOD AND WOOD HIGH POLYMERS Much work has been r e p o r t e d on use o f h i g h speed e l e c t r o n and g a m m a - r a d i a t i o n f r o m ^ C o s o u r c e s as p o l y m e r i z a t i o n i n i t i a t o r f o r c r o s s -l i n k i n g ( 3 8 , 47, 124, 125, 127, 184, 2 3 5 ) , g r a f t i n g r e a c t i o n s ( 1 3 , 76, 84, 85, 103, 119, 153, 186, 202, 203, 223, 226, 230, 238) and as means o f random d e p o l y m e r i z a t i o n f o r c e l l u l o s i c wood m a t e r i a l s ( 86, 1 6 5 ) . I n t h i s e a r l y s t a g e o f i n v e s t i g a t i o n , most p u b l i s h e d works have been c o n c e r n e d w i t h changes i n m e c h a n i c a l and p h y s i c a l p r o p e r t i e s as measured a t room t e m p e r a t u r e . A wide v a r i e t y o f m i s c e l l a n e o u s wood-polymer c o m b i n a t i o n s have been a l s o i n v e s t i g a t e d on a s e m i q u a n t i t a t i v e b a s i s w i t h l i t t l e a t t e m p t t o s t u d y the c h e m i c a l p r o c e s s e s t h a t t a k e p l a c e . Due t o l a r g e d i f f i c u l t i e s s t i l l e x i s t i n g i n l i g n i n c h e m i s t r y , most c h e m i s t r y s t u d i e s on i r r a d i a t e d wood d e a l w i t h the c a r b o h y d r a t e f r a c t i o n , whereas works on l i g n i n a r e s c a r c e and h i g h l y s p e c u l a t i v e i n n a t u r e . S i m i l a r l y , much has been done w i t h wood and c e l l u l o s e b e h a v i o r i n g r a f t c o p o l y m e r i z a t i o n , b u t l i t t l e Is known about r e a c t i o n w i t h the l i g n i n c o n s t i t u e n t a l o n e . 1. E f f e c t s w i t h Wood I n v e s t i g a t i o n s on wood exposed t o th e a c t i o n o f i o n i z i n g r a d i a t i o n show c o l l e c t i v e l y d e g r a d a t i o n w i t h l i t t l e c r o s s - l i n k i n g , e s p e c i a l l y f o l l o w i n g h i g h dosage i r r a d i a t i o n ( 2 1 , 39, 70, 70/b, 123, 124, 183, 2 0 0 ) . A t -46-h i g h dosage l e v e l s (above 10 r a d ) the r a d i a t i o n i n d u c e d d e g r a d a t i o n seems to be i n d e p e n d e n t o f dosage r a t e . G a r n e t t and Merewather (71) r e p o r t e d 7 c h e m i c a l changes i n i r r a d i a t e d wood f o l l o w i n g 10 r a d t r e a t m e n t w h i c h showed an i n c r e a s e i n p h e n o l i c h y d r o x y l s and degraded c a r b o h y d r a t e bonds. A s t r e n g t h d e c r e a s e i n wood c o m p r e s s i o n and i m p a c t b e n d i n g f o r p i n e , s p r u c e and beech wood was r e p o r t e d by B e c k e r and Bu r m e s t e r (21) when the wood was exposed t o 1 0 7 r a d dosage. T e n s i l e and c o m p r e s s i o n s t r e n g t h t e s t s o f i r r a d i a t e d woods gave s i m i l a r r e s u l t s , as d e m o n s t r a t e d by I f j u (86) and Bur m e s t e r (39), r e s p e c t i v e l y . A marked r e d u c t i o n i n toughness was r e p o r t e d by Loos:: (138) above 10^ r a d dosage. Kenaga and C o w l i n g (102) r e p o r t e d o n l y s l i g h t l y i n c r e a s e d h y g r o s c o p i c i t y f o l l o w i n g 4 x l 0 7 r a d dosage, a l t h o u g h the t o t a l amount o f a b s o r b e d w a t e r was p r a c t i c a l l y t he same as had w i t h non-i r r a d i a t e d wood. F u r t h e r t o changes i n p h y s i c a l and m e c h a n i c a l p r o p e r t i e s a s l i g h t d a r k e n i n g o f wood and e m b r i t t l e m e n t accompanied >by c h a r a c t e r i s t i c odor may be o b s e r v e d a f t e r i r r a d i a t i o n t o 1 0 7 r a d dosage ( 1 8 3 ) . Such e m b r i t t l e m e n t becomes more o b v i o u s when i r r a d i a t i o n i s f o l l o w e d by s w e l l i n g ( 6 9 ) , m e c h a n i c a l d i s i n t e g r a t i o n o r u l t r a s o n i c b e a t i n g ( 1 8 3 ) . S i m i l a r l y , t he decay r e s i s t a n c e o f wood was f o u n d t o be d e c r e a s e d o n l y by i r r a d i a t i o n dosages l a r g e r t h a n 3.2x10"* r a d as r e p o r t e d by S c h e f f e r ( 1 9 6 ) . F i n a l l y , wood exposed to h i g h dosage i r r a d i a t i o n was more s u s c e p t i b l e t o a c i d h y d r o l y s i s as e v i d e n c e d by h i g h e r s u g a r y i e l d on f e r m e n t a t i o n o f i r r a d i a t e d sawdust ( 1 6 5 ) . Low dosage i r r a d i a t i o n , on t h e o t h e r hand, has been f o u n d t o be b e n e f i c i a l t o some m e c h a n i c a l and p h y s i c a l wood p r o p e r t i e s . Though s t r e n g t h i n c r e a s e s were n o t always s t a t i s t i c a l l y s i g n i f i c a n t (21) th e y were c h a r a c t e r -i s t i c . A s l i g h t i n i t i a l s t r e n g t h i n c r e a s e was f o u n d f o r i m p a c t b e n d i n g , -47-c o m p r e s s i o n , t e n s i l e s t r e n g t h p a r a l l e l and p e r p e n d i c u l a r t o g r a i n and toughness as r e p o r t e d by B e c k e r and Bu r m e s t e r (21) and Burmester (39) f o r p i n e , s p r u c e and beech and by Kenaga and C o w l i n g (102) f o r p o n d e r o s a p i n e . W i t h i n c r e a s e o f i r r a d i a t i o n dosage t e n s i l e s t r e n g t h showed the f i r s t s i g n of d e t e r i o r a t i o n , whereas c o m p r e s s i o n s t r e n g t h was r e l a t i v e l y u n a f f e c t e d ( 3 9 ) . H y g r o s c o p i c i t y and s w e l l i n g c h a r a c t e r i s t i c s o f wood v a r i e d o n l y s l i g h t l y ( 1 0 2 ) . Such e f f e c t s may be e v e n t u a l l y e x p l a i n e d by d i f f e r e n t r a d i o s u s c e p t i b i l i t y o f the v a r i o u s wood c o n s t i t u e n t s c o n t r o l l i n g t h e s e wood p r o p e r t i e s . 2. E f f e c t s w i t h I s o l a t e d Wood C a r b o h y d r a t e F r a c t i o n s The e a r l i e r i n v e s t i g a t i o n s o f Lawton and c o - w o r k e r s ( 1 2 3 , 124, 200) on i r r a d i a t e d wood and c e l l u l o s e showed t h a t the n e t e f f e c t o f i r r a d i a t i o n i s d e g r a d a t i o n o f the wood s u b s t a n c e . (.11^201), e s p e c i a l l y the hemi-c e l l u l o s e and c e l l u l o s e . E x t e n t o f d e g r a d a t i o n was a l m o s t d i r e c t l y p r o p o r t i o n a l t o the i r r a d i a t i o n dosage f o r t h e c e l l u l o s e p o r t i o n , i n c r e a s i n g s u b s t a n t i a l l y above 1 0 6 r a d dosage ( 2 7 , 4 8 , 76, 86, 100, 180, 183, 2 0 0 ) . S i n c e r e s i s t a n c e o f wood t o d i l u t e a c i d h y d r o l y s i s i s c o n s i d e r -a b l y d i m i n i s h e d by r a d i o l y t i c d i s t u r b a n c e o f the c e l l u l o s e macro-m o l e c u l e , the s o l u b i l i t y o f wood p o l y s a c c h a r i d e s i n c r e a s e s w i t h i n c r e a s i n g dose r a t e s . A p p a r e n t l y h e m i c e l l u l o s e i s more a f f e c t e d t h a n c e l l u l o s e (70/b, 165).. W i t h dosages above 1 Mrad s e v e r e d e g r a d a t i o n o f h e m i c e l l u l o s e g and c e l l u l o s e o c c u r s and a t 2x10 r a d dosage w a t e r s o l u b l e c e l l u l o s e i s o b t a i n e d . Such d e g r a d a t i o n m a i n l y a f f e c t s 1,4 - b e t a - g l u c o s y l bonds ( 1 3 9 ) . r48-The s o l u b l e p o r t i o n i s made up o f mono-, d i - , and o l i g o s a c c h a r i d e s i n a d d i t i o n t o a c i d s . L a r g e q u a n t i t i e s o f gases ( h y d r o g e n , c a r b o n monoxide and c a r b o n d i o x i d e ) a r e a l s o e v o l v e d d u r i n g t r e a t m e n t . F r e i d i n and c o - w o r k e r s (70 , 70/b) s t u d i e d the d e g r a d a t i o n p r o d u c t s o f wood c e l l u l o s e , l i g n i n - f r e e h e m i c e l l u l o s e , d i o x a n e l i g n i n and l i g n i n p r e p a r a t i o n s . An i r r a d i a t i o n dosage f r o m z e r o t o 500 Mrad ( w i t h an average dose r a t e o f 0.7-0.9 Mrad p e r h o u r ) i n c r e a s e d i o d i n e number o f i n v e r t e d h e m i c e l l u l o s e s f r o m 10.6 t o 78.0%>, c e l l u l o s e s o l u b i l i t y i n NaOH f r o m 4.1 t o 36.2% and t h a t o f c o t t o n c e l l u l o s e f r o m 0.0 t o 50.8%. A l l components o f t h e l i g n i n - c a r b o h y d r a t e complex were found t o be s u b j e c t t o changes on r a d i o l y s i s , b u t g r e a t e s t change o c c u r r e d i n the h e m i c e l l u l o s e . L i g n i n e l e m e n t a l c o m p o s i t i o n was changed (C=62.3, H= 5.95, OCH 3=14.26% vs.C=61.05, H- 5.83, 0CH 3»13.35%) by 200 Mrad dosage. D i o x a n e l i g n i n showed s l i g h t l o s s i n m e t h o x y l (0CH 3=12.7% Y£.11.5% a t 500 M r a d ) . The l a r g e s t volume o f gas was c o l l e c t e d f r o m t h e c o t t o n c e l l u l o s e sample (2.42 ml/100 g ) , f o l l o w e d by t h e l i g n i n - f r e e h e m i c e l l u l o s e (1.2 ml/100 g) and wood (0.99 ml/100 g ) . T h e r e b y , i t c o u l d be shown t h a t d e g r a d i n g e f f e c t s o f e q u i v a l e n t i r r a d i a t i o n dosages were somewhat l o w e r f o r the wood c e l l u l o s e t h a n f o r p u r e c o t t o n c e l l u l o s e . G l e g g and K e r t e s z ((76) have r e p o r t e d t h a t m o i s t u r e c o n t e n t has no s i g n i f i c a n t e f f e c t on c e l l u l o s e d e g r a d a t i o n a t comparable i r r a d i a t i o n d o s a g e s . A t 0.3%. m o i s t u r e c o n t e n t c e l l u l o s e was shown a t l e a s t as s u s c e p t i b l e t o d e g r a d a t i o n as a t h i g h e r m o i s t u r e c o n t e n t . C o t t o n samples w i t h e x c e s s w a t e r gave the same degree o f d e g r a d a t i o n as the sample w i t h o n l y 3.5% m o i s t u r e c o n t e n t . T h i s i s i n l i n e w i t h e x p e c t a t i o n s r e g a r d i n g aqueous s o l u t i o n s and the l a r g e a b i l i t y o f w a t e r to c a p t u r e e l e c t r o n s , as shown by Magee ( 1 4 9 ) . T h e r e b y , i t was c o n c l u d e d -49-t h a t w a t e r d i d n o t a c c e n t u a t e c e l l u l o s e d e g r a d a t i o n by i r r a d i a t i o n . Lawton and co-workers (200) c a r r i e d out t e s t s t o d e t e r m i n e t h e e f f e c t o f h i g h - e n e r g y , h i g h - i n t e n s i t y r a d i a t i o n (0.14 Mrad/sec) on pur e c e l l u l o s e . They f o u n d l i t t l e d e g r a d a t i o n b e l o w 10"* r a d , b u t a c o n s i d e r a b l e e f f e c t above 10^ r a d and complete d e g r a d a t i o n t o w a t e r s o l u b l e m a t e r i a l s a t g 2x10 r a d i r r a d i a t i o n dosage. I r r a d i a t i o n o f d r y m e t h y l c e l l u l o s e by A r t h u r and co-workers (28) p r o d u c e d a d e c r e a s e i n i t s s p e c i f i c v i s c o s i t y . I n aqueous s o l u t i o n s o f m e t h y l c e l l u l o s e i n s o l u b l e g e l s were o b t a i n e d w i t h con-com m i t t a n t l o s s of m e t h o x y l c o n t e n t . The g e l f o r m a t i o n i n aqueous s o l u t i o n was s a i d t o be due t o c r o s s - l i n k i n g i n the i r r a d i a t e d m a t e r i a l . C o t t o n and wood c e l l u l o s e i s a u n i q u e p o l y m e r i c s p e c i e s . I t c o n s i s t s o f l o n g l i n e a r c h a i n s w h i c h pass t h r o u g h h i g h l y c r y s t a l l i n e and amorphous r e g i o n s ( 1 5 7 ) . The c r y s t a l l i n e r e g i o n s o f c e l l u l o s e a r e a l m o s t impermeable t o l i q u i d s and even t o gases ( 3 6 ) . Temperature e l e v a t i o n u s u a l l y does n o t improve c h a i n m o b i l i t y . These p r o p e r t i e s o f c e l l u l o s e a r e a r e s u l t o f l i n e a r c l o s e l y p a c k e d c h a i n s , a s t e r i c r e q u i r e m e n t o f the b a s i c b u i l d i n g u n i t s and e s p e c i a l l y o f s t r o n g hydrogen b o n d i n g between h y d r o x y l groups of n e i g h b o r i n g c h a i n s t h a t a r e i n p e r f e c t a l i g n m e n t (36, 86, 2 3 4 ) . Due t o reduced a c c e s s i b i l i t y i m p a r t e d by such h i g h m o l e c u l a r o r d e r , c h e m i c a l a t t a c k on the b u l k o f the c e l l u l o s i c m a t e r i a l i s r e s t r i c t e d t o t h e s u r f a c e o f c r y s t a l l i t e s and the more a c c e s s i b l e amorphous r e g i o n s ( 8 5 , 1 6 5 ) . The c h e m i c a l r e a c t i v i t y o f c e l l u l o s e can be g r e a t l y enhanced by e x t e n s i v e m o d i f i c a t i o n o f i t s c r y s t a l l i n e f i n e s t r u c t u r e t h r o u g h some c h e m i c a l o r p h y s i c a l p r e - t r e a t m e n t ( 8 4 , 127, 165, 1 8 2 ) . The p e n e t r a t i n g power o f h i g h - e n e r g y r a d i a t i o n i s n o t i n f l u e n c e d -50-by the c r y s t a l l i n e - a m o r p h o u s n a t u r e o f the c e l l u l o s e ( 2 6 ) . Each a n h y d r o g l u c o s e u n i t has an e q u a l p r o b a b i l i t y o f b e i n g r i o n i z e d . I n d e e d , f r e e r a d i c a l a c t i v i t y was shown i n b o t h g r a f t e d and n o n - g r a f t e d c e l l u l o s e l o n g a f t e r i r r a d i a t i o n by c o m p a r a t i v e ESR s p e c t r a as e v i d e n c e o f i o n i z a t i o n and t r a p p e d f r e e r a d i c a l s ( 7 6 , 1 8 6 ) . The n a t u r e o f changes t h a t t a k e p l a c e i n c e l l u l o s e a f t e r h i g h -energy i r r a d i a t i o n a r e dependent upon the p a r t i c u l a r c a r b o n atom i o n i z e d , o r t h e p a r t i c u l a r c a r b o n atom t o w h i c h the i o n i z e d atom i s bound; the c h e m i c a l n a t u r e o r p o s i t i o n o f t h e c a r b o n atom i n t h e b a s i c u n i t w i t h r e g a r d t o i t s s u b s t i t u e n t s ( p r i m a r y o r s e c o n d a r y h y d r o x y l s , p o t e n t i a l a l d e h y d e g r o u p ) ; o r the atmosphere d u r i n g i r r a d i a t i o n (26) . D e s c r i p t i o n o f mechanisms i n c e l l u l o s e i r r a d i a t i o n c h e m i s t r y r e q u i r e s c o n s i d e r a t i o n o f b o t h c h e m i c a l and p h y s i c a l p r o p e r t i e s o f the c e l l u l o s e m a t e r i a l , as w e l l as f e a t u r e s o f the i r r a d i a t i o n t r e a t m e n t i t s e l f . F r e e r a d i c a l s f o r m i n b o t h amorphous and c r y s t a l l i n e c e l l u l o s e a r e a s (76, 1 8 6 ) . Exposure t o oxygen produces f r e e r a d i c a l d i s s i p a t i o n i n t h e more a c c e s s i b l e r e g i o n s . I n t e r a c t i o n of f r e e r a d i c a l s w i t h oxygen r e s u l t s i n c h a i n c l e a v a g e (26, 28, 84, 1 8 2 ) . I r r a d i a t i o n i n a n i t r o g e n atmosphere s l i g h t l y r e d u c e d t h e e x t e n t o f d e g r a d a t i o n a t low dosage l e v e l s ( 1 8 2 ) , i n d i c a t i n g t h a t oxygen i s i n v o l v e d o n l y i n a s e c o n d a r y p r o c e s s . F r e e r a d i c a l c o n c e n t r a t i o n s as e s t i m a t e d f r o m p o s t - i r r a d i a t i o n changes i n c e l l u l o s e v i s c o s i t y (84, 186) and ESR s p e c t r a were shown t o d e c r e a s e r a p i d l y w i t h i n the f i r s t 4 t o 5 h r b u t were c o n s i d e r a b l e even a f t e r 20 d a y s . Such p o s t - i r r a d i a t i o n changes i n v i s c o s i t y were n o t accompanied by s t r e n g t h l o s s ( 2 6 ) , i n d i c a t i n g t h a t even though p o s t - i r r a d i a t i o n c l e a v a g e of c e l l u l o s e does t a k e p l a c e on e x p o s u r e to a i r , no p r o d u c t d e t e r i o r a t i o n would be -51-expected following r a d i a t i o n dosage l e v e l s studied. No p o s t - i r r a d i a t i o n changes i n v i s c o s i t y were observed with pure cotton (12, 26) or methyl c e l l u l o s e s (28) as compared to those found with wood c e l l u l o s e i t s e l f . Long-lived free r a d i c a l s were also detected i n the above two c e l l u l o s e species (186) . These re s u l t s suggest that energy d i s s i p a t i o n occurred v i a another mechanism i n these systems. Indeed, a loss i n y i e l d of acid and carbonyl groups was observed with i r r a d i a t e d methyl c e l l u l o s e . C e l l u l o s e and i t s derivatives are polymers which are degraded by d i r e c t i r r a d i a t i o n and cross-linked under s u i t a b l e conditions (126). Degradation proceeds at a well defined rate by a series of dehydration mechanisms (165) . The process r e s u l t s i n a random degradation and a f f e c t s both the c r y s t a l l i n e and amorphous regions (26, 69, 85, 177, 182). An almost l i n e a r r e l a t i o n s h i p was obtained when c e l l u l o s e degree of polymeriza-t i o n (DP) was p l o t t e d against i r r a d i a t i o n dosage, as reported by Huang and Rapson (84), and shown i n Table II and F i g . 3. Such data support the work of Blouin and Arthur (23) showing that c e l l u l o s e degradation i s a function of t o t a l r a d i a t i o n dosage, but i s independent of the source i n t e n s i t y (84) . At high i n t e n s i t y a larger proportion of primary r a d i c a l s i s formed (84) which favour cross-termination rather than polymerization or degradation. Such cross-termination r e s u l t s i n cross-linkages, a closer coherence of the fragmented c e l l u l o s e chains. Due to close packing within ordered regions of the c e l l u l o s e i t i s suggested (177) that c r o s s - l i n k i n g occurs only i n the amorphous c e l l u l o s e . Thereby, d i s s o l u t i o n on hydrolysis or s o l v o l y s i s w i l l occur p r i m a r i l y i n regions -52-T a b l e I I . D e g r a d a t i o n o f c e l l u l o s e by g a m m a - i r r a d i a t i o n ( 8 4 ) . T o t a l r a d i a t i o n d o s e , x 1 0 " 6 r I n t r i n s i c v i s c o s i t y (CED), 100 ml /g DP 0 11.10 1676 0.1 8.45 1252 0.5 5.78 823 1.0 4.06 557 2.0 2.92 387 5.0 1.82 202 10.0 0.98 116 50.0 0.33 35 100.0 0.18 18 Total Radiation Dose (Megaroentgens) F i g u r e 3. D e g r a d a t i o n o f c e l l u l o s e by g a m m a - i r r a d i a t i o n ( 6 0 C o s o u r c e c e n t r a l i n t e n s i t y 1.3 x 1 0 6 r / h r ) ( 8 4 ) . -53-f r e e o f c r o s s - l i n k a g e s and i f t h e s e a r e the c r y s t a l l i n e r e g i o n s (183) an amorphous c e l l u l o s e s h o u l d r e s u l t . I n d e e d , i t has been shown by x - r a y d i f f r a c t i o n p a t t e r n s (177) t h a t m a i n l y the c r y s t a l l i n e p o r t i o n s a r e r e n d e r e d s o l u b l e a f t e r i r r a d i a t i o n c r o s s - l i n k i n g o f r e g e n e r a t e d c e l l u l o s e as e v i d e n c e by absence o f d i f f r a c t i o n a r c s . I t was shown (177), however, t h a t t h e s t a b l e r a d i c a l s formed i n c e l l u l o s e by h i g h - e n e r g y r a d i a t i o n a r e l o c a t e d i n the h i g h l y o r d e r e d o r c r y s t a l l i n e p o r t i o n o f t h e m a t e r i a l . E x t r a c t i o n w i t h cuprammonium h y d r o x i d e removed a l l f r e e r a d i c a l s . . T h i s d e m o n s t r a t e s the s e l e c t i v e removal o f o r d e r e d r e g i o n s o f c e l l u l o s e f o l l o w i n g i r r a d i a t i o n . Such p r e f e r e n t i a l attack on o r d e r e d r e g i o n s i s a d i f f e r e n t e f f e c t t h a n v o b t a i n e d by o t h e r means such as h y d r o l y t i c and e n z y m a t i c r e a g e n t s . H i g h energy i r r a d i a t i o n o f c e l l u l o s e has been r e p o r t e d as p r o d u c i n g an e f f e c t s i m i l a r t o o x i d a t i v e d e g r a d a t i o n (28) . The r e s u l t i s e x t e n s i v e d e p o l y m e r i z a t i o n a t h i g h i r r a d i a t i o n dosage l e v e l s w i t h i n t r o d u c -t i o n o f c a r b o x y l and c a r b o n y l groups ( 26, 28, 8 4 ) . I n i t i a t i o n o r i o n i z a t i o n o c c u r s e i t h e r a t o r on and p o s i t i o n s i n the a n h y d r o g l u c o s e u n i t ( 2 8 , 139) r e s u l t i n g i n c h a i n c l e a v a g e when the p o s i t i o n i s a f f e c t e d . On c l e a v a g e , 2 - k e t o - g l u c o n i c a c i d i s formed on the r e d u c i n g end by u t i l i z i n g one mole of oxygen. An u n a l t e r e d g l u c o s e u n i t i s l e f t on the o t h e r end of the c h a i n . I n t e r a c t i o n a t r e s u l t s i n c h a i n c l e a v a g e and l i b e r a t i o n o f t h r e d u c i n g end o f the c h a i n as an u n a l t e r e d g l u c o s e u n i t by p r o d u c i n g a k e t o n e group i n the p o s i t i o n on the n o n - r e d u c i n g end o f the m o l e c u l e . T h e r e b y , o n l y o n e - h a l f mole o f oxygen i s consumed. A c t i v a t i o n o f o t h e r c a r b o n atoms tha n and (C2 , , and C^)c o f the a n h y d r o g l u c o s e u n i t y i e l d s h ydrogen and new r e d u c i n g g r o u p s , e i t h e r k e t o n e s o r a l d e h y d e s ( 2 8 ) . -54-The a c t u a l l o s s of m o l e c u l a r w e i g h t has been found t o be l e s s than the a p p a r e n t d e g r a d a t i o n as i n d i c a t e d by end-group a n a l y s i s methods. By 18 c o m p a r i s o n i t was shown t h a t 2x10 r a d i c a l s a r e formed p e r gram of c e l l u l o s e s u b s t a n c e (186) w h i c h i s a p p r o x i m a t e l y 1 t o 2 f r e e r a d i c a l s p e r c e l l u l o s e m o l e c u l a r u n i t ( assuming a DP of 1500 t o 3000). T h i s s u g g e s t s t h a t the un-p a i r e d e l e c t r o n l o c a t i o n i s a t the end of the m o l e c u l e . I n d e e d , w i t h up t o 6x10^ rep dosage t h e r e a r e on the average 2.1 end groups formed p e r i o n p a i r . Thus the end r e s u l t of each i o n i z a t i o n , w herever i t o c c u r s i n the m o l e c u l e , i s p r o d u c t i o n o f two end-groups (182) . I n d e x t r i n , w i t h f u r t h e r d e g r a d a t i o n d u r i n g i r r a d i a t i o n an i n c r e a s e i n b r a n c h i n g was o b s e r v e d . F o r a twenty f o l d d e c r e a s e i n m o l e c u l a r w e i g h t the b r a n c h i n g p e r m o l e c u l e dropped o n l y by a f a c t o r o f two, s u g g e s t i n g t h a t a l l the b r a n c h p o i n t s a r e p r o b a b l y t e t r a -f u n c t i o n a l ( 1 8 2 ) . Out o f the f i v e i o n p a i r s p r o d u c e d by i r r a d i a t i o n , one p r o v i d e s a t e t r a f u n c t i o n a l b r a n c h , 1.1 p r o v i d e a b r e a k i n the c h a i n and the r e s t l e a d t o r u p t u r e i n the D - g l u c o s e r i n g w i t h o u t o c c u r r e n c e o f e i t h e r d e g r a d a t i o n o r e v e n t u a l b r a n c h i n g . 3. E f f e c t s w i t h Wood.Aromatic Compounds and R a d i o - p r o t e c t i o n of P o l y m e r i c  C a r b o h y d r a t e s F i n d i n g s of A l e x a n d e r and C h a r l e s b y ( 2 0 4 ) , A r t h u r and Mares ( 1 5 ) , F r e i d i n , e t a l . (70/b) , Lueck and D e l l ( 1 3 9 ) , Manion and B u r t o n (152) and Smith and M i x e r (204) show t h a t t h e r e i s e v i d e n c e f o r r a d i o - p r o t e c t i o n of c a r b o h y d r a t e s i n m i x t u r e s w i t h a r o m a t i c r i n g c o n t a i n i n g compounds. A r o m a t i c groups a r e r e p o r t e d t o e x e r t a p r o t e c t i v e e f f e c t by i n t e r m o l e c u l a r energy t r a n s f e r mechanisms, and by a c t i n g as energy d i s s i p a t o r s o r "energy s i n k s " . I n the r a d i a t i o n c h e m i s t r y o f s o l i d m a t t e r , energy t r a n s f e r -55-e f f e c t s depend on the mechanism o f e nergy l o s s t o m o l e c u l e s by i n c i d e n t r a d i a t i o n , the i n i t i a l random n o n - l o c a l i z e d e nergy d e p o s i t i o n w i t h i n t h e m o l e c u l e and f i n a l l y on the r a p i d r a t e o f energy l o c a l i z a t i o n w i t h i n the m o l e c u l e ( 1 5 ) . Energy l o c a l i z a t i o n w i t h i n the m o l e c u l e r e s u l t s i n c h e m i c a l changes such as d e h y d r o g e n a t i o n ( 1 6 5 ) , a c t i v a t i o n by l o n g - l i v e d e x i t e d s i t e s ( 1 8 6 ) , d e g r a d a t i o n of the m o l e c u l e o r d e p o l y m e r i z a t i o n ( 8 4 ) . Time r e q u i r e d -13 f o r t h i s presumed l o c a l i z a t i o n p r o c e s s was e s t i m a t e d as n o t e x c e e d i n g 10 s e c ( 4 0 ) , F u r t h e r m o r e , i t has been s u g g e s t e d by B u r t o n (40) t h a t the e f f e c t s o f n o n - l o c a l i z e d h i g h - e n e r g y d e p o s i t i o n s can e x t e n d o v e r d i s t a n c e s r a n g i n g o t o 100 A. I n t e r - and i n t r a m o l e c u l a r t r a n s f e r s o f energy i n the l o c a l i z a t i o n p r o c e s s w i t h c a r b o h y d r a t e s has been shown t o depend on p h y s i c a l s t r u c t u r e , complex f o r m a t i o n w i t h o t h e r m o l e c u l e s and c h e m i c a l s u b s t i t u t i o n o f m o l e c u l e s (18 1 , 1 8 2 ) . A r t h u r and Mares (15) i n v e s t i g a t e d the p r o t e c t i v e e f f e c t s by b e n z o y l a t i o n of c o t t o n c e l l u l o s e t o v a r i o u s l e v e l s of s u b s t i t u t i o n . E f f e c t i v e r a d i o - p r o t e c t i o n was o b s e r v e d even a t v e r y low s u b s t i t u t i o n l e v e l s and low 21 i r r a d i a t i o n dosages. However, a t the h i g h e r dosage l e v e l (1.3x10 e.v./g) the r a d i o - p r o t e c t i o n was n e g l i g i b l e A t an i n t e r m e d i a t e degree o f s u b s t i t u -t i o n (D.S.1.1) much g r e a t e r r a d i o - p r o t e c t i o n was o b t a i n e d . F u r t h e r e v i d e n c e f o r r a d i o - p r o t e c t i o n was o b t a i n e d by c omparing ESR s p e c t r a o f s u b s t i t u t e d and n o n - s u b s t i t u t e d i r r a d i a t e d s amples. W i t h i n c r e a s i n g degree o f s u b s t i t u t i o n of b e n z o y l g r o u p s , t h e r e l a t i v e s i g n a l s t r e n g t h o f s p e c t r a f r o m i r r a d i a t e d samples d e c r e a s e d . On e n l a r g e d a t t e n u a t i o n o f t h e r e s o n a n c e s p e c t r a o f h i g h l y s u b s t i t u t e d (D.S. 1.5) samples i t was found t h a t t h e s p e c t r u m s t r u c t u r e was s i m i l a r t o t h a t had w i t h i r r a d i a t e d p u r i f i e d c e l l u l o s e . T h i s s i m i l a r i t y o f s p e c t r a s u g g e s t s t h a t a l t h o u g h b e n z o y l groups r a d i o - p r o t e c t -56-e e l l u l o s e t o a c o n s i d e r a b l e e x t e n t , the l o c a l i z a t i o n of n o n - d i s s i p a t e d r a d i a t i o n i n d u c e d r e s o n a n c e i n the c e l l u l o s e m o l e c u l e i s n o t s u b s t a n t i a l l y a l t e r e d on s u b s t i t u t i o n . I t i s d e m o n s t r a t e d , t h a t the r e l a t i v e f r e e r a d i c a l c o n c e n t r a t i o n o f i r r a d i a t e d b e n z o y l a t e d c e l l u l o s e d i m i n i s h e s r a p i d l y a t even low degree o f s u b s t i t u t i o n and r e a c h e s a c o n s t a n t v a l u e a t D.S. 1.0 t o 1.1. T h ereby, the l o s s o f f r e e r a d i c a l s i n b e n z o y l a t e d c e l l u l o s e i s r e s p o n s i b l e f o r the h i g h e r s t r e n g t h r e t e n t i o n f o l l o w i n g i r r a d i a t i o n . By assuming t h a t b e n z o y l groups a r e randomly d i s t r i b u t e d on the c e l l u l o s e backbone and each h y d r o x y l group i s e q u a l l y a c c e s s i b l e f o r r e a c t i o n , the minimum d i s t a n c e between b e n z o y l groups a l o n g the c e l l u l o s e m o l e c u l e can be c a l c u l a t e d as a f u n c t i o n of degree of s u b s t i t u t i o n . Such c a l c u l a t i o n s by A r t h u r and Mares (15) a r e p r e s e n t e d i n T a b l e I I I . The e f f e c t o f gamma i r r a d i a t i o n on the c a l c u l a t e d d i s t a n c e i ' between m o l e c u l a r c l e a v a g e s o r v i s c o s i t y o f b e n z o y l a t e d c e l l u l o s e as a f u n c t i o n of degree o f s u b s t i t u t i o n i s p r e s e n t e d i n F i g . 4 ( 1 5 ) . M o l e c u l a r w e i g h t v a l u e s were o b t a i n e d f r o m changes i n b r e a k i n g s t r e n g t h on the a s s u m p t i o n t h a t the b r e a k i n g s t r e n g t h o f p u r i f i e d c o t t o n c e l l u l o s e d e c r e a s e s l i n e a r l y w i t h i n c r e a s i n g number of m o l e c u l a r c l e a v a g e s . 21 A t a dosage of 1.3x10 e.v./g c e l l u l o s e the r e t e n t i o n of b r e a k i n g s t r e n g t h of i r r a d i a t e d s u b s t i t u t e d c e l l u l o s e (D.S. 1.1 t o 1.50) was as h i g h as 60%. The c o r r e s p o n d i n g c a l c u l a t e d s p a c i n g of b e n z o y l a t e d groups was 10 t o 20 A*. A t the same i r r a d i a t i o n dosage the a verage e s t i m a t e d d i s t a n c e between o m o l e c u l a r c l e a v a g e s was i n c r e a s e d f r o m about 50 c e l l o b i o s e u n i t s o r 515A (one c e l l o b i o s e u n i t i n c o t t o n i s about 10.3 A* i n l e n g t h (76)) f o r unsub-s t i t u t e d c e l l u l o s e t o about 300 c e l l o b i o s e u n i t s (3400 X) f o r b e n z o y l a t e d -57-c e l l u l o s e (D.S. 2 . 0 ) . A p p a r e n t l y , t h e i n t r a m o l e c u l a r energy t r a n s f e r can be a f f e c t e d by the p r e s e n c e o f b e n z o y l groups a t l e a s t s e v e r a l c e l l o b i o s e u n i t s away f r o m the p l a c e o f i n i t i a l e nergy d e p o s i t i o n . T a b l e I I I . C a l c u l a t e d maximum d i s t a n c e between b e n z o y l groups as a f u n c t i o n o f degree o f s u b s t i t u t i o n 3 ( 1 5 ) . Degree o f s u b s t i t u t i o n Maximum number o f c e l l o b i o s e u n i t s p e r b e n z o y l group Maximum d i s t a n c e between b e n z o y l g r o u p s , A° 0 CO CO 0.2 7-8 72-82 0.5 3-4 31-41 1.1 1-2 10-21 1.5 1 10 2.0 1 10 C a l c u l a t e d as a b i n o m i a l d i s t r i b u t i o n o f b e n z o y l groups w i t h a p r o b a b i l i t y o f r e a c t i o n > 0.95. Assuming t h a t b e n z o y l groups a r e randomly s u b s t i t u t e d on the c e l l u l o s e m o l e c u l e and t h a t each h y d r o x y l group i s e q u a l l y a c c e s s i b l e f o r r e a c t i o n . I n an e x p e r i m e n t a l case f o r the same l e v e l o f p r o b a b i l i t y o f r e a c t i o n the maximum d i s t a n c e between b e n z o y l groups w i l l be g r e a t e r t h a n t h a t assumed i n case b. -58-3 5 0 3 5 0 0 . 3 0 0 - 5 0 0 1500 1000 0 ' i i i i 1 1 1 1 — J o 0-2 0-4 0-6 0-8 1 0 1-2 1-4 1-6 1-8 2 0 Degree of Substitution F i g u r e 4. E f f e c t s o f ga m m a - r a d i a t i o n on t h e c a l c u l a t e d d i s t a n c e between m o l e c u l a r c l e a v a g e s o f f i b r o u s b e n z o y l a t e d c o t t o n c e l l u l o s e as a f u n c t i o n o f degree o f s u b s t i t u t i o n . Dosage: 1.3 x 1 0 ^ e.g./g. c e l l u l o s e , ( 1 5 ) . I n d i c a t i o n s f o r r a d i o - p r o t e c t i o n were a l s o f o u n d f o r wood c e l l u l o s e , a l t h o u g h the e x t e n t i s n o t e x a c t l y known. F r e i d i n and co-workers (70/b) r e p o r t e d a p r o t e c t i v e e f f e c t o f l i g n i n o v e r c e l l u l o s e when wood c e l l u l o s e and c o t t o n c e l l u l o s e s o l u b i l i t i e s were compared f o l l o w i n g s e v e r e d e g r a d a t i o n . W h i l e sodium hy d r o x y d e s o l u b i l i t y o f wood c e l l u l o s e i n c r e a s e d from 4.1 t o 36.27. a f t e r e x p o s u r e t o dosages o f z e r o t o 500 Mrad, t h e same dosage i n c r e a s e d the s o l u b i l i t y o f p u r i f i e d c e l l u l o s e f r o m z e r o t o 50.87,. T h i s r e p r e s e n t s n e a r l y 167, d i f f e r e n c e i n s o l u b i l i t y o f c o t t o n c e l l u l o s e . S i m i l a r e f f e c t s o f l i g n i n p r o t e c t i n g o f c e l l u l o s e were o b s e r v e d by Smith and M i x e r (204) and S e i f e r t ( 2 0 1 ) . Comparable s t r e n g t h v a l u e s and a p p r o p r i a t e DP v a l u e s were p r e s e n t e d by I f j u (86) and a r e summarized i n T a b l e IV. -59-T a b l e IV. E f f e c t of h i g h dosage i r r a d i a t i o n on t e n s i l e s t r e n g t h and DP of Douglas f i r wood zones ( 8 6 ) . Wood Zone P r o p e r t y I n t e i g r a l I r r a d i a t i o n Dosage,Mrad DP and T.S. r e t e n t i o n , % 0-15 Mrad 0 0.1 1.0 10.0 15.0 E a r l y w o o d DP 5246 4899 2470 584 159 3 T.S.* 4680 4929 4060 3385 1403 30 Latewood DP 5660 5313 2499 664 157 3 T.S. 19198 17273 17899 12959 8540 43 * U l t i m a t e m i c r o t e n s i l e s t r e n g t h , p s i . I t i s r a t h e r i n t e r e s t i n g t o n o t e t h a t a l t h o u g h DP r e t e n t i o n was the same f o r b o t h wood z o n e s , l a t e w o o d s t r e n g t h r e t e n t i o n was h i g h e r ( 8 6 ) . T h i s i s i n a way c o n t r a d i c t o r y t o some e a r l i e r d i s c u s s i o n s on mechanism of c e l l u l o s e d e g r a d a t i o n and r a d i o - p r o t e c t i o n by l i g n i n . By a c c e p t i n g the f i n d i n g s of Wu (236) t h a t e a r l y w o o d c o n t a i n s on a w e i g h t b a s i s more l i g n i n than l a t e w o o d , (2-37«) a r e v e r s e d e f f e c t would be e x p e c t e d . I t i s n o t known, however, whether i n t e g r a l r a d i a t i o n dosages were c a l c u l a t e d on the b a s i s o f a p p a r e n t wood w e i g h t of growth zone samples o r by some c o n v e n t i o n a l d o s i m e t r y . T h e r e f o r e , b a s e d on a c t u a l r a d / g wood s u b s t a n c e b a s i s ( o r a v a i l a b l e c e l l u l o s e s u b s t a n c e b a s i s ) the e a r l y w o o d s e c t i o n s may have r e c e i v e d much l a r g e r r a d i a t i o n dosages t h a n i n d i c a t e d . A f a c t o r of 2.5 t o 3 ( r a t i o o f l a t e w o o d - e a r l y w o o d s p e c i f i c g r a v i t y ) c o u l d be e a s i l y a p p l i e d . I n l i g h t o f such c o n s i d e r a t i o n s an improvement i n e a r l y w o o d DP and s t r e n g t h r e t e n t i o n c o u l d be e x p e c t e d , b u t i t i s n o t known a t t h i s time whether o r n o t any p r e c a u t i o n s were made d u r i n g i r r a d i a t i o n t o compensate f o r the h i g h e r s p e c i f i c g r a v i t y of l a t e w o o d . I n v i e w of t h i s f a c t no v a l i d c o n c l u s i o n s c o u l d be drawn from the d a t a p r e s e n t e d above. On the o t h e r hand, B u t l e r (42) showed t h a t s p e c i f i c g r a v i t y had a marked e f f e c t on t e n s i l e -60-s t r e n g t h l o s s of wood a f t e r i r r a d i a t i o n . H i g h s p e c i f i c g r a v i t y s e c t i o n s were more s e v e r e l y degraded. R o l l i n s and co-workers (184) r e p o r t e d on an i n t e r e s t i n g phenomena whi c h i s d i r e c t l y r e l a t e d t o r e s i s t a n c e o f l i g n i n a g a i n s t r a d i o l y t i c d e g r a d a t i o n and p o s s i b l y r a d i o - p r o t e c t i o n on c e l l u l o s e . Upon exposure of g t h i n wood c r o s s - s e c t i o n s t o h i g h i r r a d i a t i o n dosage (1.5x10 r a d ) and r i n s i n g the i r r a d i a t e d wood s e c t i o n s w i t h w a t e r on a m i c r o s c o p e s l i d e , t h e s e c o n d a r y w a l l s were f o u n d t o d i s s o l v e c o m p l e t e l y , a l t h o u g h the p r i m a r y w a l l r emained i n t a c t . T h i s a p p a r e n t r e s i s t a n c e o f the p r i m a r y w a l l was a t t r i b u t e d t o the h i g h c o n c e n t r a t i o n o f n o n - c e l l u l o s i c m a t e r i a l s , s u c h as l i g n i n , w h i c h were no t c o n v e r t e d t o w a t e r - s o l u b l e p r o d u c t s on i r r a d i a t i o n . ' -61-V. INFLUENCE OF RADIATION ON ORGANIC HYDROCARBON POLYMERS I r r a d i a t i o n o f o r g a n i c h y d r o c a r b o n s has been e x t e n s i v e l y s t u d i e d by r e s e a r c h e r s o f the p e t r o l e u m and f o o d p r o c e s s i n g i n d u s t r i e s . T h e i r f i n d i n g s a r e m a i n l y a v a i l a b l e i n t h e p a t e n t l i t e r a t u r e t h r o u g h d e s c r i p t i o n s o f t h e e f f e c t s n o t e d w h i c h r a r e l y t r e a t t h e b a s i c phenomena. I r r a d i a t i o n o f p o l y e t h y l e n e p r e d o m i n a n t l y causes c r o s s - l i n k i n g as found by C h a r l e s b y ( 5 0 ) , Lawton et a l . (124) and L i t t l e ( 1 3 5 ) . Such p r o d u c t s show r u b b e r - l i k e e l a s t i c i t y when h e a t e d , and r e d u c t i o n o f w e i g h t due t o h y d r o g e n l o s s . C r o s s - l i n k i n g i n n - p a r a f f i n s was i n v e s t i g a t e d by C h a r l e s b y ( 4 9 ) . He found t h a t t h e c r i t i c a l dosage v a r i e d i n v e r s e l y w i t h i n c r e a s e i n m o l e c u l a r w e i g h t . On i r r a d i a t i o n . o f h y d r o c a r b o n s t h e c o m p o s i t i o n o f gases e v o l v e d was shown to be a p p r o x i m a t e l y 98 "L hydrogen w i t h the r e m a i n i n g 2 "L made up o f methane, ethane,, propane and b u t a n e ( 4 9 ) . These v o l a t i l e s a r e n o t t a k e n as e v i d e n c e o f d i r e c t c h a i n s c i s s i o n , b u t r a t h e r as o r i g i n a t i n g from s c i s s i o n o f c h a i n ends and b r a n c h ends. T h i s has l i t t l e e f f e c t on m e c h a n i c a l p r o p e r t i e s o r s o l u b i l i t y o f t h e r e s u l t a n t polymers ( 2 9 ) . U n s a t u r a t i o n i n c e r t a i n h y d r o c a r b o n s has been found t o d i s a p p e a r a t about 15 t o 20 Mrad dosage. Measurements made on s a t u r a t i o n r a t e s i n d i c a t e r a p i d and p r e f e r e n t i a l r e a c t i o n a t the u n s a t u r a t e d c e n t e r s ( 1 3 3 , 163). P o l y - i s o b u t y l e n e (used as s o u r c e f o r polymers and c o p o l y m e r s ) has a marked tendency t o undergo t h e r m a l d e g r a d a t i o n by " u n z i p p i n g " to t h e monomer l e v e l (29) . T h i s i s due t o t h e s t e r i c s t r a i n w i t h i n t h e m o l e c u l e as -62-r e f l e c t e d by t h e low h e a t o f p o l y m e r i z a t i o n (10 to 13 K c a l / m o l e o f monomer). Because o f such low main c h a i n bond s t r e n g t h , p o l y - i s o b u t y l e n e m a i n l y undergoes s c i s s i o n when s u b j e c t e d t o i o n i z i n g r a d i a t i o n ( 1 2 4 ) . P o l y s t y r e n e , . p r e d o m i n a n t l y a s t r a i g h t c h a i n polymer, i s p r e f e r e n t -i a l l y c r o s s - l i n k e d by g a m m a - r a d i a t i o n i n absence o f oxygen (8, 103, 119, 153). The e f f i c i e n c y o f c r o s s - l i n k i n g i s low because o f t h e p r o t e c t i v e e f f e c t e x e r t e d by t h e a r o m a t i c r i n g (8, 31, 4 1 ) . The e f f e c t o f r a d i a t i o n on n a t u r a l r u b b e r and s y n t h e t i c d i o l e f i n s ( d i e n e polymers and c o p o l y m e r s ) has been s u b j e c t . t o much s t u d y . I t i s c l e a r t h a t t h e e f f e c t i s p r e d o m i n a n t l y c r o s s - l i n k i n g u n l e s s t h e p r o p o r t i o n o f o l e f i n i s v e r y low (222, 237) . H e i s i g (81, 82) f ound t h a t i r r a d i a t i o n o f a l i p h a t i c , a l i c y c l i c and o l e f i n i c h y d r o c a r b o n s w i t h d o u b l e bonds produced good y i e l d s o f p o l y m e r i c p r o d u c t s . Polymer y i e l d s i n r e a c t i o n s i n i t i a t e d by g a m m a - i r r a d i a t i o n were found to depend l a r g e l y on p r e s s u r e a p p l i e d f o r d u r a t i o n o f t h e i r r a d i a t i o n t r e a t m e n t ( 1 3 3 ) . Gas y i e l d s were c o n s i d e r a b l y lower t h a n f r o m p o l y e t h y l e n e , p r o b a b l y due t o enhanced r e a c t i v i t y a t d o u b l e bonds combined w i t h a g e n e r a l p r o t e c t i o n o f a l l o t h e r p o s s i b l e s i t e s f o r c r o s s - l i n k i n g r e a c t i o n s . The s i t e s o f c r o s s - l i n k i n g have n o t been d e t e r m i n e d as y e t . A c c o r d i n g t o Kuzminsky and co-workers as c i t e d by T u r n e r ( 2 2 2 ) , u n s a t u r a t e d compounds undergo marked changes on i r r a d i a t i o n . N a t u r a l r u b b e r was r e p o r t e d t o have l o s t 50 % o f i t s u n s a t u r a t i o n f o l l o w i n g an i r r a d i a t i o n dose o f 240 Mrad. O t h e r w o r k e r s have found t h i s e f f e c t r e l a t i v e l y s m a l l ( 2 9 ) . P r o t e c t i v e e f f e c t s o f a r o m a t i c compounds i n l i q u i d h y d r o c a r b o n m i x t u r e s were shown by A l e x a n d e r and C h a r l e s b y ( 8 ) , Manian and B u r t o n (152) and W i t t ( 2 3 5 ) . -63-V I . RADIATION GRAFTING ONTO WOOD AND WOOD CONSTITUENTS 1. G r a f t i n g onto Wood S t u d i e s o f v a r i o u s m e c h a n i c a l and p h y s i c a l p r o p e r t i e s o f i r r a d i a t e d wood i n d i c a t e b e h a v i o r s i m i l a r t o and q u i t e c o n s i s t e n t w i t h t h a t o f s y n t h e t i c h i g h p o l y m e r s , a l t h o u g h t h e r e appears to be a w i d e r a n g e o f dosages where t h e s e e f f e c t s may have been o b s e r v e d . The r a t h e r modest improve-ments i n wood p r o p e r t i e s on i r r a d i a t i o n have been shown t o be g r e a t l y enhanced by f o r m i n g c o m p o s i t e s o f wood w i t h v a r i o u s v i n y l monomers ( 1 0 3 ) . By c o n t i n u e d r e s e a r c h on wood and polymer c o m p o s i t e s t h e r e a r e good i n d i c a -t i o n s t h a t wood and wood p r o d u c t s can be t a i l o r e d t o g i v e d e s i r e d p r o p e r t i e s by s e l e c t i n g the t y p e o f monomer, degree o f i m p r e g n a t i o n and t o t a l e x p o s u r e to r a d i a t i o n . Wood p r o p e r t i e s such as d i m e n s i o n a l s t a b i l i t y (79, 103, 186, 202, 203), w a t e r a b s o r p t i o n (79, 148), s t r e n g t h (38, 79, 150, 186, 226) and har d n e s s (79, 100) can be improved w i t h h i g h polymer l o a d i n g and t r e a t m e n t a t r e l a t i v e l y low i r r a d i a t i o n d o s a g e s . As an example, w o r k i n g w i t h w h o l e wood Kenaga e t aJL. (102, 103) imp r e g n a t e d ponderosa p i n e c r o s s - s e c t i o n s w i t h w a t e r - s a t u r a t e d d i o x a n e s o l u t i o n s o f s t y r e n e and exposed t h e s e t o ^ C o i r r a d i a t i o n . They found t h a t polymer r e t e n t i o n i n c r e a s e d w i t h dose r a t e , showing t h e i m p o r t a n c e o f monomer d i f f u s i o n t o f r e e r a d i c a l s i t e s i n d e t e r m i n i n g r a t e o f g r a f t c o p o l y m e r i z a t i o n . Thereby, i t has been shown t h a t means o f p r o p e r monomer p o s i t i o n i n g i s v e r y c r i t i c a l i n g r a f t i n g p r o c e s s e s . -64-2. G r a f t i n g o n t o C e l l u l o s e One i n t r i g u i n g p o s s i b i l i t y p r e s e n t e d by i r r a d i a t i o n g r a f t i n g i s p r e p a r a t i o n o f polymers c o m b i n i n g c e l l u l o s i c p r o p e r t i e s as base s t r u c t u r e w i t h h y d r o p h o b i c p r o p e r t i e s o f s e l e c t e d v i n y l monomers g r a f t e d onto t h e c e l l u l o s e t r u n k . A d i f f i c u l t f e a t u r e i n c a r r y i n g o u t g r a f t c o p o l y m e r i z a t i o n o f c e l l u l o s e w i t h monomers i s t h e r e l a t i v e . u n r e a c t i v i t y o f t h e c e l l u l o s e c h a i n and d i f f i c u l t y o f g r a f t i n i t i a t i o n (223) . S i n c e : m o d i f i c a t i o n o f t h e c e l l u l o s e s t r u c t u r e i s d i f f i c u l t t o c h a r a c t e r i z e . b a s i c s t r u c t u r e o f many c e l l u l o s e g r a f t copolymers i s l a r g e l y unknown. The r e s u l t s o f c e l l u l o s i c h i g h - p o l y m e r p o l y m e r i z a t i o n s w i t h v a r i o u s v i n y l and r e l a t e d monomers by g a m m a - i r r a d i a t i o n has been e x t e n s i v e l y i n v e s t i g a t e d . Among t h e g r a f t copolymers w h i c h have r e c e i v e d d e t a i l e d a t t e n t i o n a r e t h o s e o f pure c e l l u l o s e w i t h s t y r e n e (13, 84, 85, 103, 186,202, 203, 206, 215, 230, 2 3 8 ) , m e t h y l m e t h a c r y l a t e (103, 127, 185, 186, 2 2 6 ) , a c r y l o n i t r i l e (14) and o t h e r monomers ( 2 , 42, 178, 2 2 6 ) . When d r y c e l l u l o s e i s i r r a d i a t e d i n t h e p r e s e n c e o f pur e s t y r e n e no g r a f t i n g i s o b s e r v e d and o n l y homopolymer has been i s o l a t e d (84, 150, 202, 203, 206, 2 1 5 ) . C h a p i r o and S t a n n e t t (45) r e p o r t e d on p o l y m e r i z i n g v i n y l monomers w i t h f i l m s o f p o l y v i n y l a l c o h o l , c e l l o p h a n e and c o t t o n . I r r a d i a t i o n i n t h e d r y s t a t e l e d o n l y t o s u r f a c e g r a f t i n g , whereas c o n s i d e r -a b l e g r a f t i n g d e p t h was a c h i e v e d . o n l y i n t h e p r e s e n c e o f w a t e r . Huang _et a l . (14, 84) g r a f t e d s t y r e n e o n t o c e l l u l o s e by u s i n g a s o l v e n t exchange t e c h n i q u e to i n t r o d u c e s t y r e n e onto c o t t o n c e l l u l o s e p r i o r t o i r r a d i a t i o n . Huang and Rapson (85) s t u d i e d t h e e f f e c t o f v a r i o u s s w e l l i n g a g e n t s on r a d i a t i o n g r a f t i n g o f s t y r e n e o n t o c e l l u l o s e . I n c r e a s e d s w e l l i n g -65-l e d to i n c r e a s e d d i f f u s i o n o f monomers t o r e a c t i o n s i t e s and r e s u l t e d i n i n c r e a s e d amounts o f i s o l a t e d g r a f t y i e l d s . Anhydrous s w e l l i n g a g e n t s were a l s o used w i t h s u c c e s s , showing t h a t w a t e r i s n o t a b s o l u t e l y n e c e s s a r y . Magee (149) i c o n s i d e r s t h e p r e s e n c e o f w a t e r o n l y from t h e s t a n d p o i n t o f an e l e c t r o n c a p t u r e medium, whereby s e c o n d a r y e f f e c t s accompanying i r r a d i a t i o n such as d e g r a d a t i o n a r e g r e a t l y r e d u c e d . B l o u i n and A r t h u r (12) r e p o r t e d t h a t r a d i o - c h e m i c a l y i e l d o f s t y r e n e g r a f t was z e r o when pur e monomer was u s ed, b u t was h i g h w i t h a mix-t u r e o f 98 7, s t y r e n e and 2 7. m e t h a n o l . T e r n i a r y s o l u t i o n s o f s t y r e n e , m ethanol and w a t e r were a l s o used w i t h good s u c c e s s (29, 1 8 6 ) . G r a f t i n g r a t e d e t e r m i n a t i o n s o f Sobne et al. (206) showed a d e c r e a s e o f g r a f t w i t h i n c r e a s i n g amount o f methanol and r e d u c e d amounts o f s t y r e n e . Below 60 7, s t y r e n e t h e p o l y s t y r e n e s e p a r a t e d as a p r e c i p i t a t e and t h e c e l l u l o s e a c e t a t e f i l m s t u r n e d opaque. Number a v e r a g e d e g r e e o f p o l y m e r i z a t i o n was t h e same f o r b o t h t h e g r a f t e d c o p o l y s t y r e n e and h o m o p o l y s t y r e n e . The h i g h DP v a l u e o f p o l y s t y r e n e i n d i c a t e d a r e d u c t i o n i n t e r m i n a t i o n r a t e a r i s i n g from l o w e r e d m o b i l i t y of p r o p a g a t i n g polymer r a d i c a l s i n t h e f i l m s . Good g r a f t ; y i e l d s were o b t a i n e d i n t h e range o f 25 t o 50 7. s t y r e n e c o n c e n t r a t i o n , w h i c h may be due t o r e d u c t i o n i n h o m o p o l y m e r i z a t i o n . A c c o r d i n g t o B l o u i n and A r t h u r (12) the i n d i r e c t e f f e c t o f s o l v e n t s i n t h e m u t u a l i r r a d i a t i o n t e c h n i q u e a r e p r o b a b l y due t o i n t e r a c t i o n o f s o l v e n t s w i t h b o t h t h e monomer and a c t i v a t e d c e l l u l o s e t o i n c r e a s e a c c e s s i b i l i t y o f a c t i v a t e d s i t e s t o t h e monomer. Usmanov and c o - w o r k e r s (223) found t h a t g r a f t i n g o f a c r y l o n i t r i l e w i t h c e l l u l o s e can be o b s e r v e d o n l y i f t h e s o l v e n t f o r a c r y l o n i t r i l e i s a -66-p o l a r compound. W i t h pure a c r y l o n i t r i l e , f o r m a t i o n o f a g r a f t copolymer was i n s i g n i f i c a n t a l t h o u g h l a r g e amounts o f h o m o p o l y a c r y l o n i t r i l e were formed. I n the p r e s e n c e o f benzene as s o l v e n t no g r a f t polymer was i s o l a t e d . T h i s i s due t o t h e f a c t , t h a t w e t t a b i l i t y o f c e l l u l o s e by benzene i s s m a l l , and t h e r e b y benzene e v i d e n t l y does no t f u r t h e r p e n e t r a t i o n o f a c r y l o n i t r i l e i n t o the i n t e r m o l e c u l a r spaces o f c e l l u l o s e . I t was c o n c l u d e d t h a t g r a f t copolymer f o r m a t i o n o n l y t a k e s p l a c e i n cases where th e c e l l u l o s e i s w e t t e d by the a c r y l o n i t r i l e and where t h e s o l v e n t i s s o r b e d by t h e c e l l u l o s e . Some s o l v e n t s such as m e t h anol and N,N-dimethyIformamide were found t o i n c r e a s e t h e e f f i c i e n c y o f a c t i v a t i o n between c o t t o n c e l l u l o s e and s t y r e n e (12, 1 4 ) . D i r e c t r a d i a t i o n g r a f t i n g o f s t y r e n e onto c e l l u l o s e i s t h o u g h t t o be a h e t e r o g e n e o u s r e a c t i o n (85, 165, 215) i n w h i c h p e n e t r a t i o n o f t h e monomer i n t o t h e f i b r e i s n e c e s s a r y f o r g r a f t i n g t o o c c u r . The p a r t i c i p a t i o n o f c e l l u l o s e and i t s d e r i v a t i v e s i n g r a f t i n g i s m a i n l y due t o low degree o f a c c e s s i b i l i t y even on s w e l l i n g . N o r m a l l y , i t i s e x t r e m e l y d i f f i c u l t t o f o l l o w t h e changes i n c e l l u l o s e c o n s t i t u t i o n d u r i n g t h e r a d i a t i o n g r a f t i n g p r o c e s s due t o c o m p l e x i t i e s i n t r o d u c e d by s i m u l t a n e o u s h o m o p o l y m e r i z a t i o n . The g r a f t copolymer can be s e p a r a t e d from t h e homopolymer by s i m p l e e x t r a c t i o n p r o c e d u r e s (85, 222, 225, 226) . F u r t h e r m o r e , t h e r e i s an a d d i t i o n a l s o l u -b i l i t y d i f f e r e n c e between t h e c e l l u l o s e t r u n k and g r a f t polymer (230, 238), thus t h e c e l l u l o s i c backbone can be h y d r o l y s e d away whereby m o l e c u l a r w e i g h t and m o l e c u l a r w e i g h t d i s t r i b u t i o n c u r v e s o f t h e g r a f t copolymer can be o b t a i n e d (84, 230, 2 3 8 ) . T h i s method, however, p r o v i d e s l i t t l e i n f o r m a t i o n about th e c e l l u l o s e t r u n k i t s e l f as i t has t o be d e s t r o y e d , u s u a l l y by a c i d -67-h y d r o l y s i s , d u r i n g i s o l a t i o n o f t h e g r a f t s i d e - c h a i n . I t was found t h a t even when most o f t h e p o l y m e r i z a t i o n a r i s e s by g r a f t i n g mechanism o n l y a s m a l l f r a c t i o n o f t h e c e l l u l o s e s u b s t r a t e p a r t i c i p a t e s i n t h e g r a f t i n g p r o c e s s . The r e a s o n f o r t h i s i s m a i n l y t h e i n a c c e s s i b i l i t y o f c e l l u l o s e t o t h e monomer under h e t e r o g e n e o u s r e a c t i o n c o n d i t i o n s (84, 2 3 0 ) . Many d i s a p p o i n t i n g p e rformances w i t h p h y s i c a l c h a r a c t e r i s t i c s o f g r a f t c opolymers a r e e v i d e n t l y due t o g r o s s h e t e r o g e n e i t y and' to 1'f ;a it?:?'gi ,eater l e n g t h o f t h e g r a f t e d s i d e - c h a i n . The p r o o f f o r g r a f t f o r m a t i o n has r e s t e d upon th e f a c t t h a t t h e polymer cannot be e x t r a c t e d q u a n t i t a t i v e l y and i s u s u a l l y i n s o l u b l e i n o r g a n i c s o l v e n t s (84, 85, 150, 185, 2 3 8 ) . One a d d i t i v e f e a t u r e o f g r a f t polymers i s t h a t t h e a v e r a g e m o l e c u l a r w e i g h t d i s t r i b u t i o n c u r v e , o b t a i n e d by f r a c t i o n a l p r e c i p i t a t i o n , d i f f e r s from s i m i l a r c u r v e s d e t e r m i n e d f o r p h y s i c a l m i x t u r e s (185) . By e x t r a c t i n g t h e g r a f t polymer o f a c r y l o n i t r i l e from h i g h l y p u r i f i e d paper (Whatman No. 2 f i l t e r paper) Putnam (185) o b s e r v e d l o s s o f s t r e n g t h r e i n f o r c e m e n t o b t a i n e d .on g r a f t i n g . S i n c e t h e polymer was e x t r a c t -a b l e , r u p t u r e o f p r i m a r y v a l e n c e f o r c e s was assumed. The IR s p e c t r a o f t h e g r a f t , p o l y a c r y l o n i t r i l e and h o m o p o l y a c r y l o n i t r i l e were i d e n t i c a l s u g g e s t i n g t h a t t h e major p o r t i o n o f t h e p o l y a c r y l o n i t r i l e "add-on" was n o t g r a f t e d t o t h e c e l l u l o s e t r u n k . Thus, o t h e r e x p l a n a t i o n s had t o be found f o r s u b s t a n t -i a l s t r e n g t h r e i n f o r c e m e n t o f t h e t r e a t e d p a p e r . The p o s s i b i l i t y o f s i m p l e m e c h a n i c a l r e i n f o r c e m e n t by t h e i n t e r v e n i n g polymer r e s u l t i n g from s e c o n d a r y v a l e n c e f o r c e s f o r m i n g a d d i t i o n a l h ydrogen bonds s h o u l d be a l s o c o n s i d e r e d . The n o n - l i n e a r e l a s t i c i t y o f paper i n l o a d e l o n g a t i o n c u r v e s -68-has been e x p l a i n e d as e x t e n s i b l e h y d r o g e n bonds by N i s s a n (169, 170,. 1.71). N o n - l i n e a r i t y o f t h e l o a d e l o n g a t i o n c u r v e i s due t o v a r i a t i o n o f f o r c e a p p l i c a t i o n w i t h s t r e t c h i n g o f hydrogen bonds,,whereby e l a s t i c d e f o r m a t i o n i s t h e n a r e s u l t o f s t r e t c h i n g , b r e a k i n g and r e f o r m i n g o f h y d r o g e n bonds. Runce ( 1 8 7 ) , on t h e o t h e r hand, c o n s i d e r s t h e n o n - l i n e a r n a t u r e of t h e paper e l a s t i c i t y c u r v e as due t o p r o g r e s s i v e s t r a i n c o n c e n t r a t i o n w i t h i n t h e s t r e s s e d m a t e r i a l r a t h e r t h a n to n o n - l i n e a r e l a s t i c i t y o f t h e s e c o n d a r y bonds. T h e r e f o r e , e l o n g a t i o n o f paper i s v i s u a l i z e d as t h e s t r a i g h t e n i n g o f b e n t and c u r v e d f i b r e s f i r m l y f i x e d a t p o i n t s o f i n t e r f i b r e b o n d i n g . O n l y a t c o n c l u s i o n o f t h e s t r a i g h t e n i n g p r o c e s s can t e n s i l e e l o n g a t i o n o f t h e f i b r e b e g i n . The e f f e c t i s t e r m i n a t e d by r u p t u r e o f h y d r o g e n bonds l i n k i n g t h e f i b r e s t o one a n o t h e r . S i m p l e d e p o s i t i o n o f a polymer w i t h i n f i b r e networks s h o u l d g i v e l i n e a r , n o n - e l a s t i c d e f o r m a t i o n as v i e w e d by N i s s a n ' s f i b r e model. A s i m i l a r d e p o s i t i o n i n t o Runce's network might cause a s m a l l i n c r e a s e i n e l a s t i c i t y due t o t h e b e n d i n g f o r c e o f t h e polymer m o l e c u l e s a t low l o a d s . But s i n c e " f r i c t i o n a l " f o r c e s must be l e s s t h a n t h e energy c o n t e n t o f a v a i l a b l e h y d r o -gen bonds, t h e m a j o r c o n t r i b u t i o n w o u l d be due t o s l i p p a g e and t h e r e b y w o u l d be i n e l a s t i c i n c h a r a c t e r . Putnam (185) found t h a t g r a f t e d and u n t r e a t e d paper d e f o r m a t i o n was i d e n t i c a l and t h e r e b y the s t r e n g t h c o n t r i b u t i o n c o u l d n o t be due t o s l i p p a g e . Based on some e x p e r i m e n t a l e v i d e n c e ( l o g o f paper d e n s i t y v s . l o g o f modulus o f e l a s t i c i t y g i v i n g a s t r a i g h t l i n e ) t h e s t r e n g t h i n c r e a s e was a t t r i b u t e d to h y d r o g e n b o n d i n g w i t h i n t h e paper n e t w o r k . I f p o l y m e r i z a t i o n o f a c r y l o n i t r i l e i n n o n - s w e l l i n g s o l v e n t s -69-(50 % m i x t u r e w i t h e t h y l a l c o h o l , a c e t o n e and benzene t r e a t e d a t 10^ r a d dosage) i n the p r e s e n c e o f c e l l u l o s e r e s u l t s i n s e c o n d a r y bond f o r m a t i o n between t h e polymer and f i b r e e x t e r i o r i t i s d i f f i c u l t t o u n d e r s t a n d r e a s o n s f o r p r i m a r y bond f o r m a t i o n o r g r a f t c o p o l y m e r i z a t i o n w i t h i n t h e f i b r e n e t -work. Usmanov e_t a l . (223) showed t h a t degree o f c e l l u l o s e s w e l l i n g i s r e l a t e d t o t h e amount o f n o n - e x t r a c t a b l e polymer r e m a i n i n g i n t h e c e l l u l o s e . I n t e r c r y s t a l l i n e s w e l l i n g o f c e l l u l o s e was shown by Huang and Rapson (85) t o t a k e p l a c e w i t h i n t h e more a c c e s s i b l e amorphous r e g i o n s . G r a f t polymer f o r m a t i o n w i t h a c r y l o n i t r i l e o c c u r s o n l y i n t h o s e cases where th e c e l l u l o s e i s w e l l w e t t e d by t h e s o l v e n t and where th e s o l v e n t i s s o r b e d by t h e c e l l u -l o s e . The amount o f s t y r e n e g r a f t under p r o p e r c o n d i t i o n s was found t o i n c r e a s e w i t h i n c r e a s i n g dose r a t e (13, 85) even o v e r s e v e r a l days f o l l o w i n g i r r a d i a t i o n . The e f f e c t was a t t r i b u t e d t o s l o w d i f f u s i o n o f n o n p o l y m e r i z e d monomer towards t r a p p e d l o n g - l i v e d f r e e r a d i c a l s (84, 150, 186) . A t h i g h r a d i a t i o n dosage r a t e s t h e p r e s e n c e o f a i r appeared t o enhance r a t h e r t h a n i n h i b i t g r a f t i n g (14) whereby, i n a d d i t i o n t o r a d i a t i o n i n d u c e d f r e e r a d i c a l s , , d e c o m p o s i t i o n o f p e r o x i d e i n t e r m e d i a t e s may have a i d e d f u r t h e r g r a f t i n g . I t was shown by Huang _et al. (84) t h a t d e s p i t e t h e l a r g e w e i g h t r a t i o o f p o l y -s t y r e n e g r a f t e d t o c e l l u l o s e o n l y one i n e v e r y 20 c e l l u l o s e c h a i n s had}a g r a f t e d s t y r e n e s i d e - c h a i n , o r o n l y one g r a f t e d p o l y s t y r e n e s i d e - c h a i n e x i s t e d per 4,000 t o 10,000 a n h y d r o g l u c o s e u n i t s . M o l e c u l a r w e i g h t o f b r a n c h e d c h a i n s was a p p r o x i m a t e l y 26,000 ( 8 4 ) . From t h e v i e w p o i n t o f p h y s i c a l p r o p e r t i e s i t may be d e s i r a b l e t o produce c e l l u l o s e g r a f t copolymers h a v i n g a l a r g e r number o f g r a f t e d b r a n c h e s o f l o w e r m o l e c u l a r w e i g h t . -70-Good r e s u l t s c o u l d be e x p e c t e d w i t h t h e p r e - i r r a d i a t i o n t e c h n i q u e s i f a p o l a r monomer c o u l d be found t h a t i s a l s o a good s w e l l i n g a gent f o r wood (202) . 3. G r a f t i n g o n t o L i g n i n L i t t l e i s known about g r a f t p o l y m e r i z a t i o n o n t o l i g n i n e i t h e r i n wood o r i n i s o l a t e d form. There i s no r e a s o n why such systems c o u l d not o c c u r . Based on c o n s i d e r a t i o n t h a t t h e l i g n i n m a c r o m o l e c u l e c o n t a i n s numer-ous f u n c t i o n a l groups and p o t e n t i a l s i t e s f o r i o n i z a t i o n , shows a t h r e e -d i m e n s i o n a l random s t r u c t u r e (31) and i s a c c e s s i b l e t o v a r i o u s s o l v e n t systems ( b o t h o r g a n i c and i n o r g a n i c ) makes i t e s p e c i a l l y s u i t a b l e f o r g r a f t c o p o l y m e r i z a t i o n . I t i s p o s s i b l y t h e g r e a t c o m p l e x i t y and d i v e r s i t y o f r e -a c t i o n s t h a t b o t h n a t u r a l and i s o l a t e d l i g n i n s e x h i b i t t h a t has made c h e m i s t s r e t r e a t from t h i s v a s t s o u r c e o f n a t u r a l h i g h - p o l y m e r . L i g n i n i s the second l a r g e s t c o n s t i t u e n t i n wood, and i s m o s t l y c o n s i d e r e d as a contam-i n a n t o f c e l l u l o s e r e q u i r i n g s e p a r a t i o n and d i s p o s a l . A t t e m p t s t o d e m o n s t r a t e the u s e f u l n e s s o f l i g n i n i n p o l y m e r i z a t i o n have been o n l y p a r t i a l l y s u c c e s s f u l . Through m i l d o x i d a t i v e t r e a t m e n t w i t h sodium c h l o r i t e P a s z n e r and W i l s o n (179) were a b l e t o m a r k e d l y lower s t r e n g t h r e i n f o r c e m e n t i n o i l - t e m p e r i n g , o f h a r d b o a r d s made from Douglas f i r A s p l u n d p u l p . S u g g e s t i o n i n t h i s i s t h a t l i g n i n q u a l i t y was most a f f e c t e d and t h a t t h i s f a c t o r was r e s p o n s i b l e f o r a t l e a s t 80 % o f t h e e x t r a s t r e n g t h t h r o u g h c o n d e n s a t i o n - p o l y m e r i z a t i o n w i t h t h e u n s a t u r a t e d h y d r o c a r b o n o i l u s e d . I n an extended s t u d y (178) the c u r i n g r e a c t i o n was i n d u c e d by g a m m a - i r r a d i a t i o n . T h i s s t u d y i n c l u d e d h i g h l i g n i n c o n t e n t groundwood. paper as a second m a t e r i a l -71-f o r e x a m i n a t i o n of e f f e c t s o f r e l a t i v e l y u n m o d i f i e d l i g n i n on the p o l y m e r -i z a t i o n mechanism. I t was shown t h a t gamma i r r a d i a t i o n i n d u c e d p r o p e r t y changes i n b o t h types o f f i b r e s o n l y t o o n e - h a l f the e x t e n t had w i t h t h e r m a l p o l y m e r i z a t i o n . D e s c r i p t i o n of the mechanism has n o t been a t t e m p t e d . R e c e n t l y B u t l e r (42) a t t e m p t e d i n s i t u g r a f t c o p o l y m e r i z a t i o n of l i g n i n w i t h CTLA o i l polymer as i n i t i a t e d by gamma i r r a d i a t i o n . Microtome t a n g e n t i a l s e c t i o n s f r o m s e v e r a l s p e c i e s , r e p r e s e n t i n g a l a r g e s p e c i f i c g r a v i t y range (0.2 t o 0.7 g/cm3), were s a t u r a t e d w i t h the p o l y m e r i c o i l and i r r a d i a t e d t o v a r i o u s dosage l e v e l s i n a n t i c i p a t i o n o f s t r e n g t h i n c r e a s e . However, no changes o c c u r r e d i n m i c r o t e n s i l e s t r e n g t h o r r e l a t e d work f u n c t i o n s -- f o l l o w i n g e i t h e r g a m m a - i r r a d i a t i o n o r c o n v e n t i o n a l t h e r m a l t r e a t m e n t . No e x p l a n a t i o n f o r the f a i l u r e was o f f e r e d . R e s u l t s on s e p a r a t e d h y d r o c h l o r i c a c i d l i g n i n p o l y m e r i z a t i o n s by g a m m a - i r r a d i a t i o n w i t h m e t h y l m e t h a c r y l a t e , s t y r e n e and v i n y l a c e t a t e were p u b l i s h e d by K o s h i j i m a and M u r a k i (116, 117). They showed t h r o u g h s t e p by s t e p s u b s t i t u t i o n of the l i g n i n h y d r o x y l groups t h a t the r a t e o f m e t h y l m e t h a c r y l a t e g r a f t p o l y m e r i z a t i o n was g r e a t l y enhanced when s u b s t i t u t i o n was made on the p h e n o l i c h y d r o x y l group. Benzene, d i m e t h y l s u l f o x i d e and c h l o r o f o r m were used as s o l v e n t s . I t was found (117) t h a t the y i e l d of g r a f t p olymer on l i g n i n was 1317 0 a t 10^ r a d dosage f o r the l i g n i n sample on w h i c h o n l y the p h e n o l i c h y d r o x y l was s u b s t i t u t e d . A g e n e r a l s u b s t i t u t i o n o f a l l p o t e n t i a l h y d r o x y l s r e d u c e d the g r a f t t o 387o. The l i g n i n - m e t h y l m e t h a c r y l a t e copolymer was fo u n d t o be i n s o l u b l e i n o r g a n i c s o l v e n t s . A t r u e g r a f t p olymer w i t h l i g n i n 4 5 was f ound o n l y w i t h m e t h y l m e t h a c r y l a t e a t 10 t o 10 r a d dosage, whereas -72-v i n y l a c e t a t e and s t y r e n e formed o n l y s u r f a c e g e l s and were found u n s u i t a b l e f o r g r a f t i n g w i t h l i g n i n . On o x i d a t i o n o f l i g n i n m e t h y l m e t h a c r y l a t e copolymer w i t h sodium c h l o r i t e ( 1 1 6 ) , the g r a f t p o lymer was i s o l a t e d w i t h o u t d e g r a d a t i o n . The a verage m o l e c u l a r w e i g h t of the s i d e - c h a i n was l a r g e r t h a n t h a t of the homopolymer. Based on the a s s u m p t i o n t h a t m o l e c u l a r w e i g h t of h y d r o c h l o r i c a c i d l i g n i n i s a p p r o x i m a t e l y the same as t h a t of s u l p h o n i c a c i d l i g n i n ( i . e . , 10,000 t o 120,000) the g r a f t polymer m o l e c u l a r w e i g h t was a t l e a s t 10 t o 100 time t h a t of the t r u n k p o l y m e r . Through d e g r a d a t i o n of the b r a n c h polymer i t was shown t h a t the p o l y m e t h y l m e t h a c r y l a t e was a t r u e g r a f t p o lymer to l i g n i n . 4. Summary S e c t i o n R e c o g n i t i o n o f p o t e n t i a l i n g r a f t c o p o l y m e r i z a t i o n p r o c e d u r e s has r e s u l t e d i n two major c o n t r a c t s o r i g i n a t i n g f r o m the U.S.. A t o m i c Energy Commission t o make r a d i a t i o n p r o c e s s e d c o m p o s i t e s o f wood and p l a s t i c s ( 1 ) . D i f f i c u l t i e s e x p e r i e n c e d w i t h e f f i c i e n c y of i r r a d i a t i o n i n d u c e d g r a f t i n g t o c e l l u l o s e and l i g n i n prompts f u r t h e r r e s e a r c h f o r c l a r i f i c a t i o n of b a s i c r e a c t i o n mechanisms. The need f o r such s t u d i e s i s w e l l d e m o n s t r a t e d by the f a c t t h a t e x p l a n a t i o n s o f most f a i l u r e s cannot be d e m o n s t r a t e d e x p e r i m e n t a l l y and, t h e r e b y , r e m a i n o n l y ad hoc a s s u m p t i o n s w i t h o u t r e a l v a l u e t o f u r t h e r s t u d i e s . -73-The f a c t t h a t f r e e r a d i c a l s have been shown t o e x i s t i n i r r a d i a t e d wood and i s o l a t e d wood c o n s t i t u e n t s i s enc o u r a g i n g . A n e x t s t e p i n s u c c e s s f u l a p p l i c a t i o n o f r a d i a t i o n t r e a t m e n t s i s t o f i n d ways f o r m a x i m i z i n g use of t h e s e a v a i l a b l e r e a c t i v e s i t e s . I t i s i n t e r e s t i n g t o n o t e t h a t p o t e n t i a l w i t h the l i g n i n com-ponent o f wood has been l i t t l e s t u d i e d , a l t h o u g h the p r e s e n c e o f l i g n i n f r e e r a d i c a l s has been shown by Ramalingam e t a l . (186) t h r o u g h c a r e f u l examina-t i o n of ESR s p e c t r a from i r r a d i a t e d wood, as w e l l as p e r i o d a t e , d i o x a n e and Brauns' n a t i v e l i g n i n s . L i g n i n has been o b s e r v e d t o y i e l d a f r e e r a d i c a l s p e c t r u m on i r r a d i a t i o n w h i c h has n o t been s p e c i f i c a l l y i d e n t i f i e d . 1 _74-MATERIALS AND METHODS I t was d e s i r a b l e t o i n c l u d e b o t h a wide q u a n t i t a t i v e range o f l i g n i n j , a s w e l l as n o m i n a l l y d i f f e r e n t ( m o d i f i e d ) l i g n i n s i n the f i b r e m a t e r i a l s under s t u d y , w i t h the common f e a t u r e o f o r i g i n f r o m an i m p o r t a n t s i n g l e wood s p e c i e s . The c h o i c e was r e s t r i c t e d t o t h r e e major p u l p t y p e s namely, m e c h a n i c a l and c h e m i c a l f i b r e s i n the fo r m o f groundwood, s u l f a t e and a c i d s u l f i t e p u l p s . A s p l u n d p u l p was fo u n d t o be u n s u i t a b l e f o r making good q u a l i t y h andsheets and t h e r e f o r e was n o t i n c l u d e d i n t h i s s t u d y . T h i s imposed no l i m i t a t i o n on the s t u d y , s i n c e e f f e c t s o f g a m m a - i r r a d i a t i o n w i t h t h i n (0.03 cm n o m i n a l t h i c k n e s s ) e x p e r i m e n t a l h a r d b o a r d s made fr o m Douglas f i r A s p l u n d f i b r e had been i n v e s t i g a t e d i n a p r e l i m i n a r y s t u d y (178) . Thus, t h r e e p u l p samples were s e l e c t e d so as t o s a t i s f y the two b a s i c r e q u i r e m e n t s . O r i g i n a l l y , i t was i n t e n d e d to i n c l u d e and p a r t l y r e p e a t the s t u d y o f i r r a d i a t i o n g r a f t i n g w i t h t h i n , g reen Douglas f i r microtome wood s e c t i o n s (42). w i t h the o b j e c t i v e o f t r e a t i n g a l i g n i n s p e c i e s w h i c h had n o t been exposed t o c o n d i t i o n i n g t r e a t m e n t s o t h e r t h a n normal a i r d r y i n g . P r e -l i m i n a r y i n v e s t i g a t i o n o f t h i s a p p roach showed t h a t r e p l i c a t i o n of the above i n v e s t i g a t i o n would r e s u l t i n c o n t i n u e d l i m i t e d s u c c e s s , s i n c e t r e a t m e n t e f f e c t s a r e c o m p l e t e l y overshadowed by i n h e r e n t s t r u c t u r a l l i m i t a t i o n s of t h i n wood s e c t i o n s . E x p l a n a t i o n s o f f a i l u r e w i t h the p r o c e s s a p p l i e d t o whole wood i s o f f e r e d i n a l a t e r s e c t i o n . -75-I . MATERIALS 1. P u l p Types The p u l p m a t e r i a l s were o b t a i n e d from M a c M i l l a n , B l o e d e l and P o w e l l R i v e r , L t d . as c o m m e r c i a l s t o c k f u r n i s h . These c l o s e l y c o m p l i e d w i t h t h e r e q u i r e m e n t s as s t a t e d . Thus, c o m m e r c i a l groundwood r e p r e s e n t e d a h i g h l i g n i n c o n t e n t m e c h a n i c a l p u l p , w h i l e c o m m e r c i a l h i g h y i e l d s u l f a t e ( h e r e a f t e r c a l l e d k r a f t f o r b e t t e r d i s t i n c t i o n from t h e s i m i l a r l y s o u n d i n g , b u t d i f f e r e n t a c i d s u l f i t e ) and a c i d s u l f i t e p u l p s r e p r e s e n t e d two l i g n i n s p e c i e s h a v i n g c h a r a c t e r i s t i c m o d i f i c a t i o n s i n d u c e d by p r o c e s s i n g . The p u l p s were o b t a i n e d as wet s t o c k t h a t had n e v e r been d r i e d . I n a d d i t i o n , an unbeaten, b l e a c h e d hemlock k r a f t , a TAPPI S t a n d a r d p u l p , h i g h a l p h a - c e l l u l o s e " v i s c o s e " p u l p s and g l a s s f i l t e r p a p e r were i n c l u d e d as r e p r e s e n t a t i v e s o f v a r i o u s t y p e s o f l i g n i n - f r e e m a t e r i a l s . O r i g i n o f major p u l p s w i t h r e g a r d s t o wood c o m p o s i t i o n i s d e s c r i b e d i n T a b l e V. The p u l p s were s t o r e d i n p o l y -e t h y l e n e bags a t 5°C u n t i l f u r t h e r p r o c e s s e d . T a b l e V Wood s p e c i e s c o m p o s i t i o n o f p u l p s . P u l p Types Wood S p e c i e s , % Groundwood W. hemlock: 50%, S p r u c e : 20%, M i x e d O t h e r : 1% (Douglas f i r , p i n e ) . t r u e f i r : 20%,, A c i d s u l f i t e W. hemlock: 7370, M i x e d t r u e f i r s : 27% K r a f t W. hemlock: 100% - 7 6 -l a. Groundwood p u l p U n b l e a c h e d groundwood p u l p s a r e used e x t e n s i v e l y as p a r t i a l f u r n i s h i n m a n u f a c t u r e o f n e w s p r i n t , book, magazine, w r i t i n g , a b s o r b e n t t o w e l and o t h e r i n e x p e n s i v e p a p e r s . I n 1962 9,200,000 t o n s , r e p r e s e n t i n g 237, of w o r l d p u l p p r o d u c t i o n , were produced on t h i s c o n t i n e n t (229) . F o r n e w s p r i n t , groundwood i s mixed w i t h 20 t o 357> of i t s w e i g h t w i t h u n b l e a c h e d s u l f i t e p u l p , o r 15 t o 307, s e m i - b l e a c h e d k r a f t p u l p . There i s good p r o s p e c t t h a t the i n t r o d u c t i o n of h i g h e r s t r e n g t h groundwood w i l l i n c r e a s e demand and t h a t f a c t o r s t h e n l i m i t i n g the amount of c h e m i c a l p u l p w h i c h can be r e p l a c e d by groundwood i n papers where b r i g h t n e s s i s of l e s s e r i m p o r t a n c e , w i l l be the s t r e n g t h t h a t can be a t t a i n e d o v e r t h e r e g u l a r b l e n d e d p u l p s t r e n g t h . Groundwood p u l p s r e p r e s e n t a l m o s t the t o t a l wood f r a c t i o n d e l i v e r e d t o the g r i n d e r s and a r e o b t a i n e d i n 977,.or b e t t e r y i e l d i n con-v e n t i o n a l o p e r a t i o n s ( 3 3 , 6 6 ) . M e c h a n i c a l p u l p s a r e r i g i d due t o t h e i r h i g h l i g n i n c o n t e n t , whereby they do n o t c o l l a p s e on d r y i n g and do n o t c o n f o r m w e l l i n d r i e d p a p e r webs. They a r e made up of a wide range of f r a g m e n t e d wood i n c l u d i n g a l a r g e p r o p o r t i o n of f i n e s and f i b r e b u n d l e s , but o n l y a s m a l l f r a c t i o n of i n t a c t , i n d i v i d u a l f i b r e s . S t r e n g t h of groundwood papers has been shown t o depend l a r g e l y on the r a t i o o f f i n e s t o c o a r s e f r a c t i o n s as shown by B r e c h t and. E r f u r t ( 3 2 ) , F o r g a c s (66, 6 8 ) , and M a rton and A l e x a n d e r ( 1 5 5 ) • Shape of the l a r g e r p a r t i c l e s i s symptomatic of wholewood p u l p s , whereby they e x h i b i t l i t t l e f i b r i l l a t i o n w i t h o u t any p r e f e r r e d p l a n e of r u p t u r e d u r i n g f i b r e s e p a r a t i o n ( 6 6 ) . R i g i d i t y of groundwood f i b r e s , t o g e t h e r w i t h t h e i r i r r e g u l a r shapes i s i m p o r t a n t because the s p e c i f i c bonded a r e a o r combined c l o s e f i b r e c o n t a c t between any two such f i b r e s i n a paper -77-network i s s m a l l , g i v i n g h i g h b u l k t o the r e s u l t a n t p a p e r s . The low b o n d i n g p o t e n t i a l o f the l o n g f i b r e i n m e c h a n i c a l p u l p s ( i n c l u d i n g A s p l u n d p u l p s ) i s r e f l e c t e d i n low t e n s i l e s t r e n g t h o f handsheets made fr o m such f r a c t i o n s . I t was shown r e c e n t l y by F o r g a c s (66) t h a t c e r t a i n d i s k - r e f i n e d groundwood p u l p s d e v e l o p h i g h e r s h e e t s t r e n g t h due t o f o r m a t i o n o f r i b b o n l i k e s t r u c t u r e s as a c o n t i n u a t i o n of l o n g i t u d i n a l c r a c k s o b s e r v e d o n . " i n t a c t " s t o n e - g r o u n d f i b r e s . Such r i b b o n - l i k e p a r t i c l e s were shown t o o r i g i n a t e f r o m u n r a v e l i n g o f the c r a c k e d f i b r e s u r f a c e d u r i n g t h e r e f i n i n g p r o c e s s . These a r e e x t r e m e l y s c a r c e i n co m m e r c i a l groundwood p u l p s . The i n c r e a s e d p a p e r s t r e n g t h had by a d d i t i o n o f l o n g c h e m i c a l p u l p f i b r e s t o groundwood i s due t o b e t t e r c o n f o r m i t y o f the r i b b o n - l i k e c h e m i c a l f i b r e s ( 3 2 , 66, 1 5 5 ) . I n such m i x t u r e s F o r g a c s a n d . A t t a c k (68) fou n d 1.4 times more groundwood on the w i r e s i d e and showed t h a t u n i f o r m f i b r e d i s t r i b u t i o n was v e r y d i f f i c u l t t o m a i n t a i n due t o d i f f e r e n c e i n b u l k c h a r a c t e r i s t i c s o f the f i b r e s . S t r e n g t h of paper made fr o m groundwood was shown t o i n c r e a s e c o n s i d e r a b l y f o l l o w i n g s t o c k d e l i g n i f i c a t i o n . Thus, Jahn and Holmberg (89) and Watson ( 2 2 7 ) r e p o r t e d t h a t a g e n e r a l i n c r e a s e i n s t r e n g t h p r o p e r t i e s accompanied p r o g r e s s i v e d e l i g n i f i c a t i o n o f groundwood by a c i d i c sodium c h l o r i t e . However, y i e l d l o s s e s were r e l a t i v e l y h i g h f o l l o w i n g such t r e a t -ments s i n c e s u b s t a n t i a l g a i n s i n s t r e n g t h were o b t a i n e d o n l y a f t e r 50 t o 75% of the l i g n i n had been removed (227) . The groundwood used f o r t h i s i n v e s t i g a t i o n was c o m m e r c i a l l y r e f i n e d and s c r e e n e d and had Ca n a d i a n S t a n d a r d F r e e n e s s (TAPPI T 227-m58 method) a t 109 CSF. M o i s t u r e c o n t e n t o f the p u l p was 239% (2 9 . 5 % b.d. s o l i d s ) -78-as r e c e i v e d . The f i b r e l e n g t h d i s t r i b u t i o n was n o t d e t e r m i n e d . R e p l i c a t e samples of K l a s o n l i g n i n (TAPPIT222-m54 method) gave 29.6 and 28.3% l i g n i n c o n t e n t (28.9%, average) as c o r r e c t e d f o r a l c o h o l - b e n z e n e s o l u b l e s (TAPPI T 6-m59 method). The m e t h o x y l c o n t e n t o f an a i r - d r y sample was f ound t o be 5.32%, on e x t r a c t i v e - f r e e , oven-dry p u l p b a s i s . b. A c i d s u l f i t e p u l p There i s v o l u m i n o u s l i t e r a t u r e on d i f f e r e n c e s between f i b r e c h a r a c t e r i s t i c s of s u l f i t e and k r a f t p u l p s , o f t e n w i t h s l i g h t l y c o n f l i c t i n g o b s e r v a t i o n s . B e s i d e s i n d i v i d u a l c o n t r i b u t i o n s ( 2 3 , 36, 37, 56, 59, 73, 88, 95, 96, 115, 144, 158, 194, 197, 219, 2 2 7 ) , two e x t e n s i v e summaries have been p u b l i s h e d by Jayme (91) and D i n w o o d i e (57) on p h y s i c a l and c h e m i c a l d i f f e r e n c e s and e f f e c t s o f v a r i o u s f a c t o r s on the s t r e n g t h p r o p e r t i e s of r e s u l t a n t p a p e r s . These summaries p r e s e n t a comprehensive r e v i e w of what i s known about paper p r o p e r t i e s , as w e l l as f a c t o r s and p r o c e s s i n g methods i n f l u e n c i n g them. The l o c a l i z e d a t t a c k of a c i d s a c r o s s the e n t i r e wood c e l l w a l l has been l o n g s u s p e c t e d as cause o f low s t r e n g t h w i t h a c i d s u l f i t e f i b r e s ( 1 9 4 ) . I t may be a c c e p t e d t h a t f i b r e s weakened by a c i d h y d r o l y s i s cannot be b e a t e n f o r f u r t h e r s t r e n g t h development t o the same e x t e n t as nonhydro-l i z e d f i b r e s b e f o r e f i b r e damage o c c u r s . The e x t e n t of a c i d h y d r o l y s i s a c r o s s the f i b r e w a l l has been measured by Jayme and von Koeppen (94) t h r o u g h DP c o m p a r i s o n s , However, q u a n t i t a t i v e d a t a r e l a t i n g the degree of a c i d h y d r o l y s i s and the s t r e n g t h of i n d i v i d u a l paper-making wood f i b r e s do n o t appear i n the l i t e r a t u r e . The h i g h e r s t r e n g t h of papers made fr o m -79-unbeaten o r s l i g h t l y b e a t e n s u l f i t e p u l p s , as compared t o unbeaten k r a f t p u l p s , i s i n c o n t r a d i c t i o n t o the a c i d damage t h e o r y , as p o i n t e d o u t by McKenzie and H i g g i n s ( 1 4 4 ) . Jayme and von Koeppen (94) have shown t h a t the l o w e r f l e x i b i l i t y o f s u l f i t e f i b r e s i s m a i n l y due t o the r e l a t i v e l y h i g h l i g n i n c o n c e n t r a t i o n i n the o u t e r l a y e r s o f the s u l f i t e f i b r e w a l l . Papers made o f h i g h y i e l d s u l f i t e p u l p had the appearance of an open network w i t h r e l a t i v e l y un-c o l l a p s e d f i b r e s ( 3 7 ) , b u t had l o w e r b u l k than k r a f t p a p e r s a t the same l i g n i n c o n t e n t . S i n c e paper s h e e t b u l k i s c o n t r o l l e d by such f a c t o r s as f i b r e l e n g t h , f i b r e f l e x i b i l i t y , t he f i l l i n g o f v o i d s by f i n e f i b r e s and degree o f b o n d i n g ( 1 5 4 ) , i t i s e x p e c t e d t h a t the l o w e r b u l k o f s u l f i t e p a p ers r e s u l t s from s l i g h t l y s h o r t e r , b e t t e r c o n f o r m i n g f i b r e s (194) and a l a r g e r p r o p o r t i o n . o f f i n e s . A l t h o u g h s h e e t s t r e n g t h has been shown t o i n c r e a s e w i t h f i b r e l e n g t h (59, 83, 88, 2 1 9 ) , t e n s i l e s t r e n g t h was shown t o i n c r e a s e t o a maximum w i t h a d d i t i o n o f up t o 4C7o f i n e s t o the s e p a r a t e d l o n g f r a c t i o n of s u l f i t e p u l p ( 1 5 4 ) . B o n d i n g s t r e n g t h due t o b e t t e r s w e l l i n g c a p a c i t y has been shown to be h i g h e r f o r s u l f i t e p u l p s ( 7 3 , 74, 91) as e v i d e n c e d by the l a r g e r p o r t i o n o f b r o k e n f i b r e s on c l o s e e x a m i n a t i o n o f t e n s i l e f a i l u r e s (37, 83, 88, 2 1 9 ) . P o s s i b l e cause f o r such i n c r e a s e i n f i b r e f a i l u r e was a t t r i b u t e d by F o r g a c s (67) t o weak s p o t s (nodes) on t h e f i b r e s . The h i g h y i e l d s u l f i t e p u l p u s e d i n t h i s i n v e s t i g a t i o n was measured a t 638 CSF and c o n t a i n e d 252% w a t e r (28.4%, b.d. s o l i d s ) . I t had a 40 ml permanganate number (K No.) a c c o r d i n g t o TAPPI T 236-m60. of 38.4, c o r r e s p o n d i n g t o 18.987° K l a s o n l i g n i n . The m e t h o x y l c o n t e n t o f the a i r - d r y -80-p u l p was f o u n d t o be 3.777., on e x t r a c t i v e - f r e e , oven-dry p u l p b a s i s , c. K r a f t p u l p K r a f t p u l p s d i f f e r f r o m s u l f i t e p u l p s i n b o t h q u a n t i t a t i v e and q u a l i t a t i v e d i s t r i b u t i o n of f i b r e c h e m i c a l c o n s t i t u e n t s w h i c h i s thought t o c o n t r o l p h y s i c a l p r o p e r t i e s ( 1 1 5 ) . I t has been r e p o r t e d e a r l i e r t h a t c o a l e s c e n c e of l i g n i n , d u r i n g the h i g h - t e m p e r a t u r e k r a f t d i g e s t i o n , l e a d s t o l o w e r r e a c t i v i t y and s t r o n g e r h y d r o p h o b i c p r o p e r t i e s w i t h i n the c e l l w a l l . H igh s o l u b i l i t y o f h e m i c e l l u l o s e i n the a l k a l i c o o k i n g medium i s s a i d t o r e s u l t i n l o w e r h e m i c e l l u l o s e r e t e n t i o n ( 1 5 9 ) , whereby s w e l l i n g c a p a c i t y o f t h e f i b r e s i s f u r t h e r r e d u c e d . U n i f o r m o v e r a l l l i g n i n d i s t r i b u t i o n a c r o s s the f i b r e w a l l was shown to i m p a r t b e t t e r f i b r e f l e x i b i l i t y t o the c e l l s t r u c t u r e t h a n w i t h s u l f i t e f i b r e s o f the same l i g n i n c o n t e n t ( 9 4 ) , a l t h o u g h e q u a l bond s t r e n g t h w i t h k r a f t p u l p s cannot be d e v e l o p e d w i t h o u t c o n s i d e r -a b l e b e a t i n g (57, 94, 115, 194) a t the expense o f i n c r e a s e d energy i n p u t ( 5 , 8 3 ) . Unbeaten k r a f t p u l p was shown to have an open s t r u c t u r e w i t h p o o r l y c o n f o r m i n g f i b r e s w h i c h have n o t c o l l a p s e d on removal of w a t e r f r o m the s h e e t , as w e l l as v i r t u a l absence of f i b r i l l a t i o n ( 3 7 ) . Thereby, k r a f t p a pers appear b u l k y and h i g h l y opaque. K r a f t f i b r e s a l s o show weak s p o t s (nodes) s i m i l a r t o s u l f i t e f i b r e s ( 6 7 ) . F a i l u r e o f paper made fr o m unbeaten k r a f t f i b r e s i s m a i n l y due t o f i b r e p u l l - o u t o v e r a deep f r a c t u r e zone ( 3 7 ) . C l o s e o b s e r v a t i o n of the bond a r e a a f t e r f r a c t u r e r e v e a l s no o r l i t t l e m a t e r i a l t r a n s f e r , an i n d i c a t i o n o f low i n t e r f i b r e bond s t r e n g t h i n such p a p e r s . However, the l a r g e r t e a r r e s i s t a n c e of k r a f t p apers was r e l a t e d by - 8 1 -van den Ak k e r and co-workers ( 6 ) t o the f a c t t h a t w i t h l o n g f i b r e d k r a f t p a p e r o n l y a s m a l l p e r c e n t a g e o f f i b r e s b r e a k i n s h e a r as compared t o p r e -dominant f i b r e f a i l u r e i n t e a r t e s t i n g o f s u l f i t e p a p e r s . T h i s was t a k e n as e v i d e n c e f o r l o w e r energy r e q u i r e m e n t i n b r e a k i n g f i b r e s i n s h e a r t h a n r u p t u r i n g i n t e r f i b r e bonds i n t e n s i o n . Numerous f i b r e c r o s s i n g s o v e r the l e n g t h o f a l o n g f i b r e may be the r e a s o n why k r a f t p a p e r s show h i g h e r t e a r as compared t o s u l f i t e p a p e r s h a v i n g the same b r e a k i n g l e n g t h ( 1 1 5 ) . T h e o r e t i c a l l y , t h e maximum mean p u l l e d o u t f i b r e l e n g t h when b r e a k i n g paper a l o n g a l i n e s h o u l d be L / 4 , where L i s the mean f i b r e l e n g t h . I n p r a c t i c e , however, 1 0 t o 157o h i g h e r v a l u e s a r e o b t a i n e d , w h i c h i s o b v i o u s l y due t o the wide f r a c t u r e zone found f o r u n beaten p u l p s as de m o n s t r a t e d by H e l l e ( 8 3 ) . Thereby, H e l l e ( 8 3 ) c o n c l u d e d t h a t the w i d t h o f the f r a c t u r e zone f o r c h e m i c a l handsheets i s an i n d i c a t i o n o f the degree o f b o n d i n g . The h i g h y i e l d k r a f t p u l p used i n t h i s s t u d y had 7 3 9 CSF f r e e n e s s and was r e c e i v e d a t 2637o m o i s t u r e c o n t e n t ( 2 7 . 5 7 > b.d. s o l i d s ) . I t c o n t a i n e d 9 . 6 0 7 o K l a s o n l i g n i n and gave a K No. of 3 2 . 6 ( 4 0 m l ) . The m e t h o x y l c o n t e n t , based on e x t r a c t i v e - f r e e , oven-dry p u l p was found t o be 1 . 6 2 7 > . A summary o f p e r t i n e n t p u l p p r o p e r t i e s and t h e i r method o f d e t e r m i n a t i o n i s p r e s e n t e d i n T a b l e V I . T a b l e V i . Summary, o f p e r t i n e n t d a t a on p u l p s . P u l p Types CSF T 227-m58 K l a s o n L i g n i n , 7o T 222-m-54 40 ml K No. T 2l4-m58 OMe, % Groundwood 109 28.90 5.55 A c i d S u l f i t e 638 18.98 38.4 3.77 K r a f t 739 9.60 32.6 1.62 -82-d. O t h e r f i b r e m a t e r i a l s E a r l i e r i n v e s t i g a t i o n s (178,. 179) s u g g e s t e d t h a t o i l p o l y m e r i z a -t i o n w i t h h a r d b o a r d s and n e w s p r i n t was m o s t l y s p e c i f i c f o r l i g n i n . O n ly o n e - f i f t h o f the e x t r a s t r e n g t h development was a t t r i b u t e d t o f i b r e con-s t i t u e n t s o t h e r t h a n l i g n i n , p o s s i b l y a s e c o n d a r y r e a c t i o n w i t h some c a r b o h y d r a t e f r a c t i o n , and m e c h a n i c a l a d h e s i o n a t the f i b r e - o i l polymer i n t e r -f a c e . To f u r t h e r examine t h e s e phenomena v a r i o u s p u r i f i e d p u l p s and a c h e m i c a l l y i n e r t web ( g l a s s f i b r e f i l t e r p a p e r ) were i n c l u d e d i n t h e p r e s e n t s t u d y . U n f o r t u n a t e l y , no s p e c i f i c d a t a a r e a v a i l a b l e f o r t h e t h r e e p u l p t y p e s w h i c h were an unb e a t e n , b l e a c h e d w e s t e r n hemlock k r a f t p u l p , a TAPPI S t a n d a r d p u l p (30) and a s u l f i t e v i s c o s e d i s s o l v i n g p u l p c o n t a i n i n g 50% w e s t e r n hemlock as wood f u r n i s h . 2. Wood M i c r o t o m e S e c t i o n s O n e - h u n d r e d - f i f t y - m i c r o n t h i c k t a n g e n t i a l microtome s e c t i o n s were c u t from a wood b l o c k t a k e n from t h e sapwood o f a f r e s h l y f e l l e d , s t r a i g h t g r a i n e d Douglas f i r grown a t t h e s o u t h s i d e o f the U n i v e r s i t y Endowment Lands, V a n c o u v e r , B.C. The s e c t i o n s were s t o r e d i n t h e sequence t a k e n between s t r i p s o f wet b l o t t i n g paper and k e p t wet i n a p o l y e t h y l e n e bag a t 3°C u n t i l f u r t h e r p r o c e s s e d . -83-3. D r y i n g O i l F r e s h commercial d r y i n g o i l (CTLA Polymer) was o b t a i n e d f r o m Van Waters and Rogers o f Canada,Ltd., a d i s t r i b u t o r o f the raw o i l m a n u f a c t u r e d by I m p e r i a l O i l , L t d . I n f o r m a t i o n as t o i n g r e d i e n t s and s p e c i a l a d d i t i v e s ( l i n s e e d o i l and 17« m a l e i c a n h y d r i d e ) was o b t a i n e d f r o m The C h e m i c a l P r o d u c t s Department, I m p e r i a l O i l , L t d . , T o r o n t o , Canada ( 5 5 , 6 1 ) . The d r y i n g o i l , i s a p r e - p o l y m e r o f a c r a c k e d naphtha g a s - o i l f r a c t i o n w h i c h c o n t a i n s s t r a i g h t , b r a n c h e d and c y c l i c mono- and d i - o l e f i n e s , n a p h t h a n e s , as w e l l as normal and i s o - p a r a f f i n s . I t i s h e a t r e a c t i v e and i s p r e p a r e d by p a r t i a l p o l y m e r i z a t i o n o f the f r a c t i o n o v e r h o t c l a y . The p o l y m e r , b e i n g h i g h l y u n s a t u r a t e d , d r i e s b o t h by o x i d a t i o n and p o l y m e r i z a t i o n . A c h a r a c t e r i s t i c p r o p e r t y o f the polymer i s i t s tendency f o r d e p o l y m e r i z a t i o n or r e a r r a n g e m e n t on e x t e n s i v e h e a t i n g . T h i s has been o b s e r v e d as an i n h e r e n t c h a r a c t e r i s t i c o f d i c y l c o p e n t a d i e n e s w i t h an endo-methylene b r i d g e i n the m o l e c u l e . To reduc e h e a t r e q u i r e m e n t f o r o i l p o l y m e r i z a t i o n , a 1% m a l e i c a n h y d r i d e a d d i t i o n i s made. T h i s p r o v i d e s a new p o l y m e r , w h i c h i s c l a i m e d to g i v e g r e a t e r s t r e n g t h and b e t t e r f l e x i b i l i t y t han can be had w i t h the i n i t i a l p o lymer a l o n e . The re d u c e d h e a t r e q u i r e m e n t a l s o l e s s e n s danger o f s e l f -i g n i t i d n i n the h a r d b o a r d t e m p e r i n g p r o c e s s . The tendency f o r d e p o l y m e r i z a -t i o n on p r o l o n g e d h e a t i n g i s f u r t h e r r e d u c e d by a d d i t i o n of c e r t a i n amounts of l i n s e e d o i l . The d r y i n g o i l i s s o l u b l e i n a r o m a t i c , , p a r a f f i n i c and c h l o r i n a t e d h y d r o c a r b o n s , a c e t a t e s , k e t o n e s and a l c o h o l s above b u t y l a l c o h o l . I t i s c o m p a t i b l e w i t h v a r i o u s o t h e r d r y i n g - o i l s , b o t h raw and b o d i e d , such as -84-l i n s e e d , tung,. soyabean, c a s t o r and f i s h o i l s . F u r t h e r m o r e , i t i s a l s o c o m p a t i b l e w i t h r o s i n , r o s i n e s t e r s , coumars, m o d i f i e d a l k y d s , m o d i f i e d p h e n o l i c s , n a t u r a l and s y n t h e t i c r u b b e r s and n i t r o c e l l u l o s e . B e s i d e s a p p l i c a t i o n t o h a r d b o a r d p r o c e s s i n g , CTLA Polymer i s used e x t e n s i v e l y i n o t h e r i n d u s t r i e s , such as c o r e o i l t e s t i n g where i t r e p l a c e s n a t u r a l d r y i n g - o i l s . S p e c i f i c a t i o n s and some t y p i c a l p r o p e r t i e s o f CTLA Polymer a r e g i v e n i n T a b l e V I I . T a b l e V I I . S p e c i f i c a t i o n s and some p r o p e r t i e s o f CTLA Polymer ( 6 1 ) . T e s t V a l u e T e s t Method G r a v i t y , A P I 6 . - 14 ; ASTM D 2 7 8 - 5 5 V i s c o s i t y , SSU a t 210° F. 100 - 250 ASTM D 88 - 53 N o n v o l a t i l e m a t t e r , Wt. % M i n . 80 ASTM D 154 - 53 I o d i n e No., c g . / g . , M i n . 240 ASTM D 555 - 54 Water V o l . , 7 . Max. 0.8 ASTM D 9 5 - 4 6 F l a s h , COC °F., M i n . 210 ASTM D 9 2 - 5 2 -85-I I . METHODS The g e n e r a l p l a n o f t h e i n v e s t i g a t i o n r e q u i r e d p r e p a r a t i o n o f han d s h e e t s from two s e r i e s o f p u l p b l e n d s made from s u l f i t e - g r o u n d w o o d and k r a f t - g r o u n d w o o d a t v a r i o u s l e v e l s o f m i x t u r e f o l l o w e d by t h e v a r i o u s t r e a t -ments . Thereby, groundwood became an i n t e r n a l s t a n d a r d . The two s e r i e s , i n c l u d e d 11 and 10 s e t s o f p u l p h a n d s h e e t s i n w h i c h t h e groundwood c o n t e n t r a n g e d from 0 to 100 7, a t 10 7, i n t e r v a l s . Such c l o s e e x a m i n a t i o n o f r a d i a -t i o n e f f e c t s w i t h b l e n d s was e x p e c t e d t o ext e n d t h e u s e f u l i n f o r m a t i o n o b t a i n e d , n o t w i t h s t a n d i n g t h e b a s i c p h y s i c a l c h a r a c t e r i s t i c s o f such b l e n d s . B l e n d i n g o f t h e v a r i o u s f i b r e s was c o n s i d e r e d t o have s u b s t a n t i a l p r a c t i c a l meaning, s i n c e i t i n c l u d e s the e n t i r e range o f s t o c k m i x t u r e s used by v a r i o u s i n d u s t r i e s . 1. P r e p a r a t i o n o f Handsheets F o l l o w i n g p r e - w e i g h i n g , d i l u t i o n and m i x i n g o f a p p r o p r i a t e p r o -p o r t i o n s o f the v a r i o u s p u l p s ( t o g i v e h a n d s h e e t s o f a n o m i n a l b a s i s w e i g h t 2 o f 60 g/m ) , 30 handsheets o f each b l e n d were p r e p a r e d on a B r i t i s h S h e e t Machine a c c o r d i n g t o TAPPI S t a n d a r d T 205-m58. A f t e r f o r m a t i o n o f s h e e t s , t h e y were couched w i t h two b l o t t e r s , a s h e e t m e t a l p l a t e and a r o l l , i n the s t a n d a r d manner. The ha n d s h e e t s were i n t e r l e a f e d between d r y b l o t t e r s and a p r e s s - p l a t e , and were w e t - p r e s s e d a t 60 p s i f o r 3.5 min. F o l l o w i n g the above p r e s s i n g c y c l e t h e ha n d s h e e t s were t r a n s f e r r e d w i t h t h e i r r e s p e c t i v e -86-p r e s s - p l a t e s t o d r y b l o t t e r s and r e - p r e s s e d f o r 2.5 min. C o n d i t i o n i n g o f the h a n d s h e e t s was done between d r y i n g r i n g s a t c o n t r o l l e d h u m i d i t y con-d i t i o n s (75°F and 50 7, R.H.) u n t i l a i r - d r y (3 t o 5 h r ) . The a i r - d r y hand-s h e e t s were t h e n o v e n - d r i e d between p o l i s h e d f e r r o p l a t e s a t 145°C f o r 10 min w i t h o u t p r e s s u r e , a f t e r w h i c h t h e y were s e a l e d i n p o l y e t h y l e n e bags u n t i l f u r t h e r t r e a t m e n t . B a s i s w e i g h t o f t h e v a r i o u s p r e p a r e d h a n d s h e e t s i s g i v e n i n T a b l e V I I I . T a b l e V I I I . B a s i s w e i g h t o f handsheets made from v a r i o u s b l e n d s o f s u l f i t e - g r o u n d w o o d (SG) and k r a f t - g r o u n d w o o d (KG) p u l p s . Groundwood S u l f i t e S e r i e s W e i ght, g per Handsheet B a s i s Weight, g/m* K r a f t S e r i e s W e i g h t , g per Handsheet Bas i s W e i g h t , g/m2 0 s* 1 .20 60.0 K** 1.20 60.0 10 S10G 1 .18 59.0 K10G 1.20 60.0 20 S20G 1 .21 60.5 K20G 1.21 60.5 30 S30G 1 .25 62.5 K30G 1.20 60.0 40 S40G 1 .29 64.5 K40G 1.20 60.0 50 S50G 1 .25 62.5 K50G 1.20 60.0 60 S60G 1 .23 61.5 K60G 1.15 57.5 70 S70G 1 .20 60.0 K70G 1.16 58.0 80 S80G 1 .15 57 .5 K80G 1.14 67.0 90 S90G 1 .13 56.5 K90G 1.18 59.0 100 G*** 1 .15 57.5 G 1.15 57.5 0 1.18 59.0 *S : A c i d s u l f i t e ; **K : K r a f t ; ***G : Groundwood; ****BK : B l e a c h e d k r a f t 2. Paper Treatments For purpose of c l a r i t y the various treatments used are l i s t e d as follows: Treatment Des ignation A. Untreated (control) S, G, K, S G, KG, BK B. Heat treated only SH, GH, KH, SGH, KGH C . Irradiated only SR, GR, KR, SGR, KGR D . O i l dipped SD, GD, KD, SGD, KGD, BKD E . Thermally polymerized SO, GO, KO, SGO, KGO, BKO F. Radiation polymerized SRT, GRT, KRT, SGRT, KGRT G. Radiation plus thermally polymerized SRTH, GRTH, KRTH, SGRTH, KGRTH A. Untreated controls The number of t e n s i l e specimens necessary for proper r e p l i c a t i o n was determined experimentally for each basic pulp type (groundwood, s u l f i t e and k r a f t ) from preliminary tests on standard t e n s i l e specimens. These specimens were prepared with a %-ton Arbor press, equipped with a cutting die of 1.5 cm width and 15.0 cm length. This device for sample preparation has been described e a r l i e r by I f j u (86) and Wellwood (231) for microtome wood sections and by Paszner (178) for paper. Pertinent data from which the necessary number of r e p l i c a t e s were calculated are presented i n Table IX. -88-T a b l e I X . N e c e s s a r y number o f t e n s i l e s t r e n g t h r e p l i c a t e s f o r groundwood, s u l f i t e and k r a f t h a n d s h e e t s . P u l p Number o f T e s t s Ave.Max. Tens. S t r e n g t h , p s i SD , ps i N a t t 0 > 0 5 Groundwood 10 1184 63.5 9 .37 S u l f i t e 10 4620 78.0 1.01 K r a f t 10 2213 72.0 2.66 From t h e s e c a l c u l a t i o n s i t was d e c i d e d t o use 10 specimens f o r r e p l i c a t i o n w i t h groundwood and 5 specimens per t r e a t m e n t f o r s u l f i t e and k r a f t p u l p s , as w e l l as a l l b l e n d s c o n t a i n i n g them. F i v e t e n s i l e specimens can be o b t a i n e d e a s i l y from each h a n d s h e e t , b u t t o m i n i m i z e e f f e c t s o f between handsheet v a r i a t i o n t e s t specimens f o r a l l t r e a t m e n t s w i t h o u t o i l d i p p i n g (Treatments A, B, C) were punched out a t t h e same t i m e , and t h e n e c e s s a r y number of specimens was a l l o t t e d t o t h e t r e a t m e n t s i n a random f a s h i o n . Thereby, a d o u b l e r a n d o m i z a t i o n was a c h i e v e d w i t h i n each b l e n d s e r i e s . F u r t h e r m o r e , each s e t o f handsheets was d i v i d e d i n t o l o t s o f 7 and 10 s h e e t s ( t h e l a t t e r t o p r o v i d e e x t r a s h e e t s f o r v a r i o u s l e v e l s o f i r r a d i a -t i o n t r e a t m e n t s ) and i n d i v i d u a l specimens were f u r t h e r r a n d o m i z e d and a l l o t t e d t o s h e e t t r e a t m e n t s . Each t e n s i l e specimen was p r o p e r l y l a b e l l e d and s e a l e d i n a t h i n p o l y e t h y l e n e bag, s p e c i a l l y made f o r t h i s p urpose, t o p r o t e c t t h e specimens from m o i s t u r e r e - a b s o r p t i o n . Specimens r e l a t e d by s i n g l e t r e a t m e n t s were s e a l e d i n t o l a r g e r b a gs. C o n t r o l specimens (Treatment A) were o v e n - d r i e d f o r 20 min a t 145°C b e f o r e b a g g i n g t o e n s u r e complete m o i s t u r e - f r e e c o n d i t i o n s . -89-B. Heat t r e a t e d c o n t r o l s The c u t t e n s i l e specimens, p r e p a r e d and s e l e c t e d i n the manner d e s c r i b e d , were exposed t o h e a t t r e a t m e n t i n a f o r c e d a i r c i r c u l a t i n g l a b o r a -t o r y oven a t 145°C 2°C) f o r 1.5 h r . The t e m p e r a t u r e and ti m e c o m b i n a t i o n was d e t e r m i n e d as opti m a f o r maximum s t r e n g t h development w i t h t h e s e m a t e r i a l s by methods to be d e s c r i b e d . Such h e a t t r e a t m e n t i s d e s i g n e d t o a c c o u n t f o r th e e f f e c t o f h e a t i n g v a r i o u s t y p e s o f papers w i t h o u t o i l a d d i t i v e and t h e r e b y a l l o w s c a l c u l a t i o n o f s t r e n g t h i n c r e a s e r e s u l t i n g from i n t e r a c t i o n o f a d d i t i v e and t h e r m a l t r e a t m e n t w i t h o u t t h e c o n f o u n d i n g e f f e c t o f h e a t a l o n e . F o l l o w i n g t h i s t r e a t m e n t t h e t e n s i l e specimens were q u i c k l y t r a n s f e r r e d i n t o s m a l l p o l y e t h y l e n e b a g s . The bags were p a r t i a l l y h e a t s e a l e d and, f o l l o w i n g c omplete e v a c u a t i o n and r e p l a c e m e n t o f vacuum by d r y n i t r o g e n gas, c o m p l e t e l y s e a l e d w i t h the a i d o f a s o l d e r i n g gun. C. I r r a d i a t e d c o n t r o l s The specimens d e s i g n e d as c o n t r o l s f o r t h e i r r a d i a t i o n treatment, were p r e p a r e d i n much t h e same way as samples f o r Treatment A. A c c o r d i n g t o the p l a n , 5 specimens were a l l o t t e d f o r each o f t h e 5 i r r a d i a t i o n dosage 2 3 5 7 l e v e l s namely, 10, 10 , 10 , 10 and 2x10 r a d . I r r a d i a t i o n o f t h e samples was done by A t o m i c Energy o f Canada., L t d . , C h e m i c a l P r o d u c t s D i v i s i o n , Ottawa, Canada. Samples w i t h low dosage 2 60 l e v e l s o f 10 and 10 r a d were Co i r r a d i a t e d i n a t h e r a p y u n i t a t 60 r a d / h r , whereas t h e h i g h e r dosages were a p p l i e d i n a "Gamma C e l l 200" a t 0.60 Mrad/hr dosage. F u r t h e r d e s c r i p t i o n o f t h e s e f a c i l i t i e s has been p r e s e n t e d by I f j u ( 8 6 ) , and P a s z n e r and W i l s o n ( 1 7 9 ) . -90-C h e m i c a l changes a t t h e v a r i o u s i r r a d i a t i o n l e v e l s were f o l l o w e d by d e t e r m i n a t i o n o f m e t h o x y l c o n t e n t s o f t h e wood p u l p s . A t l e a s t r e p l i c a t e d e t e r m i n a t i o n s were r u n f o r each o f t h e t h r e e p u l p s p e c i e s f o r each o f t h e r a d i a t i o n dosage l e v e l s . Two numbers were a c c e p t e d as t r u e r e p l i c a t e s o n l y i f t h e i r p e r c e n t a g e s a g r e e d w i t h i n "t 0.05 % about t h e i r mean. The e f f e c t o f r a d i a t i o n on a v e r a g e m e t h o x y l c o n t e n t o f t h e d i f f e r e n t p u l p s i s p r e s e n t e d i n F i g .5. D. O i l d i p p e d c o n t r o l s Handsheets r e s e r v e d f o r o i l t r e a t m e n t were f i r s t r e - d r i e d a t 145°C f o r 10 min, f o l l o w e d by 15 min c o o l i n g i n a p o l y e t h y l e n e bag, b e f o r e d i p p i n g i n t o t h e d r y i n g o i l . F o r good p e n e t r a t i o n and s w e l l i n g o f t h e l i g n i n t h e d r y i n g o i l was d i l u t e d w i t h benzene i n t h e r a t i o o f 1:3. Benzene has been shown t o p o s s e s s a t l e a s t i n t e r m e d i a t e s w e l l i n g power f o r l i g n i n (198) ( s w e l l i n g parameter d=9.15 ( c a l / c c ) . whereas s o l v e n t s w i t h s w e l l i n g p a r a -meters around 11 a r e good l i g n i n s o l v e n t s ) and was found to be f u l l y c o m p a t i b l e w i t h t h e d r y i n g o i l . As shown by M c L a u g h l i n ( 1 4 6 ) , t h e use o f f u g i t i v e c o a l e s c i n g agents ( s o l v e n t s ) , e s p e c i a l l y t h o s e w h i c h a r e c a p a b l e o f s w e l l i n g polymer n e t w o r k s , p e r m i t s a much b e t t e r s a t u r a n t p e n e t r a t i o n . E x c e s s o i l was removed from t h e handsheet s u r f a c e by b r i e f s t a c k i n g between b l o t t i n g p a p e r . D u r i n g subsequent p r e p a r a t i o n o f t e s t specimens t h e h a ndsheets c o u l d n o t be p r o t e c t e d from a i r m o i s t u r e . However, i t i s e x p e c t e d t h a t l i t t l e . i f a n y ; m o i s t u r e a b s o r p t i o n took p l a c e d u r i n g t h i s phase due t o c o n t i n u e d e v a p o r a t i o n o f e x c e s s benzene. -91-6 0 5 0 Groundwood (28-9% Klason Lignin) 4 0 c a> c o o >» 3 0 | X o "5 Sulfite (18-98% Klason Lignin) o 3 S 2 0 | o r Sulfate (9-60% Klason Lignin) OS 1 I I I I 0 10 2 0 3 0 5 0 7-3 Log- irradiation Dosage,rad F i g u r e 5. Change o f p u l p m e t h o x y l c o n t e n t as a f u n c t i o n o f i r r a d i a t i o n dosage. -92-S o l v e n t was removed from t h e specimens, f o l l o w i n g specimen c u t t i n g and b a g g i n g , by a p p l y i n g vacuum (100 t o 200yi)Hg)in a l a r g e d e s i c c a t o r a t room t e m p e r a t u r e . S i n c e the samples were s t o r e d o v e r phosphorus pento-x i d e i n the d e s i c c a t o r under vacuum f o r t h r e e days, i t i s e x p e c t e d t h a t t h e s e p r e c a u t i o n s r e e s t a b l i s h e d t h e ov e n - d r y c o n d i t i o n . Thereby, v a r i a b l e m o i s t u r e i n t h e samples d i d n o t i n f l u e n c e t h e s t r e n g t h t e s t s . The vacuum was r e -p l a c e d by d r y n i t r o g e n and t h e specimens were s e a l e d i n t h e i r r e s p e c t i v e b a gs. These p r e c a u t i o n s were n e c e s s a r y i n v i e w o f f i n d i n g s o f v a n den A k k e r and co-workers ( 2 3 3 ) , B r e c h t and E r f u r t ( 3 2 ) , Cohen, Stamm and Fahey ( 5 1 ) , Rieman and K u r a t h (191) and Thode and Ingmanson (219) who showed t h a t t e n s i l e s t r e n g t h i n c r e a s e s a l m o s t a s y m p t o t i c a l l y t o a maximum w i t h a d e c r e a s e i n m o i s t u r e c o n t e n t from 5 t o 0 %. A p p a r e n t l y , e l o n g a t i o n i s much l e s s s e n s i t i v e t o such s m a l l changes i n m o i s t u r e c o n t e n t ( 5 1 ) . E . T h e r m a l l y P o l y m e r i z e d T e s t specimens o f one s e t o f t h e above o i l d i p p e d samples were removed once more from t h e i r bags and were suspended i n an oven f o r t h e r m a l t r e a t m e n t a t 145°C over a p e r i o d o f 1.5 h r . Optima o f ti m e and t e m p e r a t u r e o f t h e r m a l t r e a t m e n t were d e t e r -mined i n a p r e l i m i n a r y s t u d y i n v o l v i n g t h e t h r e e b a s i c p u l p s . Thereby, i t was found t h a t t h e s t r e n g t h o f t e n s i l e specimens was p r a c t i c a l l y unchanged ( e x c e p t f o r some normal v a r i a t i o n n o t e x c e e d i n g t h e s t a n d a r d d e v i a t i o n v a l u e s g i v e n i n T a b l e IX) w i t h i n 140 t o 155°C range a p p l i e d o v e r a p e r i o d o f 1 t o 2 h r . Lower s t r e n g t h v a l u e s were o b t a i n e d o u t s i d e t h e s e ranges due t o i n c o m p l e t e o i l p o l y m e r i z a t i o n a t t h e lo w e r t e m p e r a t u r e s and s h o r t e r t i m e s - 9 3 -and p o s s i b l y t h e r m a l d e g r a d a t i o n on p r o l o n g e d h i g h - t e m p e r a t u r e h e a t i n g . The c o n d i t i o n s chosen as r e s u l t o f t h i s e x p e r i m e n t were somewhat a r b i t r a r y i n t h e sense t h a t any number of j u s t i f i a b l e c o m b i n a t i o n s o c c u r w i t h i n t h e above-mentioned r a n g e . The f a c t t h a t the specimens were s e v e r e l y d i s c o l o r e d a t h i g h e r t e m p e r a t u r e s and p r o l o n g e d t i m e s s u g g e s t s advantage by use of lower t e m p e r a t u r e and s h o r t e r t i m e . The t r e a t e d samples were c o o l e d , r e p l a c e d i n t h e i r r e s p e c t i v e bags w i t h a minimum o f c o n t a c t w i t h t h e atmosphere, and s t o r e d i n vacuum o v e r phosphorus p e n t o x i d e b e f o r e t h e f i n a l s e a l was a p p l i e d . F. R a d i a t i o n p o l y m e r i z e d E i g h t s e t s o f o i l d i p p e d samples were i r r a d i a t e d . C o n d i t i o n s and dosages d u r i n g i r r a d i a t i o n were t h e same as t h o s e d e s c r i b e d f o r Treatment C . G. R a d i a t i o n p l u s t h e r m a l l y p o l y m e r i z e d T h r e e s e t s o f samples were a l l o t t e d t o t h i s t r e a t m e n t . The t r e a t m e n t was d e s i g n e d t o r e v e a l c e r t a i n d i f f e r e n c e s i n p o l y m e r i z a t i o n mechanism between t h e two major methods under e x a m i n a t i o n . I t was e x p e c t e d t h a t s t r e n g t h r e c o v e r y on t h e r m a l t r e a t m e n t f o l l o w i n g i r r a d i a t i o n s h o u l d i n d i c a t e p o s s i b l e b l o c k i n g or d e s t r u c t i o n o f r e a c t i v e s i t e s a v a i l a b l e f o r g r a f t i n g on t h e r m a l t r e a t m e n t and t h e r e b y g i v e some i n d i c a t i o n o f e f f i c i e n c y and p o s s i b l e s i t e s o f g r a f t i n g . 2 O n l y t h r e e i r r a d i a t i o n l e v e l s were used, namely 10, 10 and 2 x 1 0 7 r a d d o s a g e s . Maximum e f f i c i e n c y i n s i m i l a r systems was shown -94-2 to occur e a r l i e r with about 10 rad dosage (134), whereas the e f f e c t of i n t r i n s i c strength loss due to gamma-ray degradation was expected to occur as r e s u l t of 2 x 10^ rad i r r a d i a t i o n dosage (86). A l l treatment procedures including o i l dipping, i r r a d i a t i o n and the subsequent thermal treatment were c a r r i e d out i n exactly the same manner as described for Treatments D, E, and F. Re-extraction of o i l polymer from o i l dipped samples of the three basic pulps (groundwood, s u l f i t e and k r a f t ) was attempted by Soxhlet extraction with a benzene:chloroform mixture (9:1). Results of these extractions together with i n i t i a l o i l absorption values are given i n Table X., Table X . E x t r a c t i o n of o i l polymer following normal paper treatments as expressed in per cent of sample weight l o s s . Pulp Sheet O i l Abs ,y % Weight Loss on E x t r a c t i o n following treatment, °L A D E _C_ F G 10 10 5 2xl0 7 10 lOT" 2xl0 7 10 2 x l 0 7 Groundwood 83 .64 67 7.5 0.0 0.0 0.5 29.9 23.6 20.7 3.5 5.5 S u l f i t e 42 .10 26 13.5 .50 .70 0.0 19.3 16.6 14.6 4.5 4.3 Kraft 61 .60 44 5.6 .10 .50 1.1 14.7 12.7 10.6 2.4 2.6 3 . Tension Test Methods Te n s i l e strength of paper sheets i s considered to r e s u l t from resistance of hydrogen bond chains to stresses by means.that w i l l be d i s -cussed i n a subsequent sec t i o n . The chains are quite independent and under t e n s i l e s t r a i n f a i l independently, each re q u i r i n g a c e r t a i n energy to -95-produce f a i l u r e . The sum o f t h e e n e r g i e s i s equated t o t h e r u p t u r e energy o f p a p e r . I n t h i s s t u d y t e n s i l e p r o p e r t i e s o f t h e e x p e r i m e n t a l papers were d e t e r m i n e d by use o f a t a b l e model I n s t r o n T e n s i l e T e s t e r . The e x t e r n a l s t r e s s was a p p l i e d w i t h c o n t i n u o u s m o t i o n o f t h e moving c r o s s - h e a d c a u s i n g a c o n s t a n t r a t e o f e l o n g a t i o n a t 0.05 in./min i n a l l t y p e s o f p a p e r s . The i n i t i a l d i s t a n c e between the g r i p s was s e t a t 10 cm. S t r e s s i n g t h e specimens under t h e s e c o n d i t i o n s caused 0.0127 in./min n o m i n a l r a t e o f s t r a i n . Load-e l o n g a t i o n c u r v e s were r e c o r d e d a u t o m a t i c a l l y w i t h t h e c h a r t moving a t con-s t a n t speed o f 1 in./min. F o l l o w i n g r u p t u r e o f specimens t h e t e s t d i a g r a m was e v a l u a t e d f o r u l t i m a t e t e n s i l e l o a d , l o a d t o u n i t s t r a i n w i t h i n t h e p r o p o r t i o n -a l l i m i t and u l t i m a t e e l o n g a t i o n . A p p r o p r i a t e s t r e n g t h v a l u e s ( u l t i m a t e t e n s i l e s t r e n g t h , modulus o f e l a s t i c i t y and u l t i m a t e s t r a i n ) were c a l c u l a t e d by r e l a t i n g t e s t d a t a t o t h e l o a d r e s i s t i n g c r o s s - s e c t i o n o f paper s t r i p s . The t o t a l a r e a under t h e l o a d e l o n g a t i o n c u r v e was measured, u s i n g a p l a n i -meter, from w h i c h maximum t e n s i l e energy a b s o r p t i o n (TEA) was c a l c u l a t e d . As m entioned above, i n d i v i d u a l specimens were t e s t e d i n o v en-dry c o n d i t i o n , s e a l e d i n p o l y e t h y l e n e bags . A t o t a l o f 1600 specimens were t e s t e d i n t e n s i o n f o r t h e s t u d y . 4. S t a t i s t i c a l A n a l y s e s The l a r g e amount o f d a t a a v a i l a b l e r e q u i r e d r e d u c t i o n t o s i m p l e a r i t h m e t i c means f o r t r e a t m e n t r e p l i c a t i o n s . These a v e r a g e v a l u e s were t a b -u l a t e d ( T a b l e 12-19, A p p e n d i x ) and p l o t t e d f o r the two i n d e p e n d e n t v a r i a b l e s (X-^ = 7o b l e n d , X 2 = l o g . i r r a d i a t i o n dosage, rad) to e v a l u a t e the n e c e s s a r y - 9 6 -d e g r e e o f t h e p o l y n o m i a l t h a t b e s t d e s c r i b e d t h e v a r i o u s s e t s o f d a t a i n t h e s e two d i m e n s i o n s . a. C u r v e f i t t i n g M u l t i p l e c u r v i l i n e a r r e g r e s s i o n (134) was used t o f i n d e q u a t i o n s o f r e s p o n s e s u r f a c e s f o r e v a l u a t i n g t h e main t r e a t m e n t e f f e c t s . Degree o f p o l y n o m i a l f o r i n i t i a l e q u a t i o n s was d e f i n e d by g r a p h i c a l methods. P l o t t i n g t h e v a r i o u s dependent v a r i a b l e s o v e r i n d e p e n d e n t v a r i a b l e s i n d i c a t e d t h a t a common t h i r d degree p o l y n o m i a l would be s u f f i c i e n t f o r d e s c r i b i n g e f f e c t s o f the i n d e p e n d e n t v a r i a b l e s . (X\ = b l e n d i n g i n %, X 2 = l o g . i r r a d i a t i o n dos-age, r a d ) , The i n i t i a l e q u a t i o n employed f o r a l l r e s p o n s e s u r f a c e s had the f o l l o w i n g g e n e r a l form: T h i s e q u a t i o n was e v a l u a t e d by a new r e g r e s s i o n programme p r o v i d e d by Kozak and S m i t h ( 1 1 8 ) . The program e l i m i n a t e s c o n t r i b u t i o n o f n o n s i g n i f i c a n t i ndependent v a r i a b l e s from t h e i n i t i a l model u s i n g t h e s o - c a l l e d , " M i l l e r ' s t - p r i m e " p r o c e d u r e (164) . A t each s t e p o f e l i m i n a t i o n a t e s t o f s i g n i f i c a n c e i n g v a r i a b l e components t o t h e m u l t i p l e r e g r e s s i o n . Thereby, an e q u a t i o n can be o b t a i n e d i n w h i c h a l l r e s i d u a l i n dependent v a r i a b l e s a r e s i g n i f i c a n t . (1) can be c a r r i e d o u t t o e s t i m a t e s i g n i f i c a n c e o f c o n t r i b u t i o n s o f the r e m a i n --97-b . A n a l y s i s o f v a r i a n c e A s i n g l e a n a l y s i s o f v a r i a n c e was d e s i g n e d t o t e s t s i g n i f i c a n c e f o r d i f f e r e n c e s between b e h a v i o r o b s e r v e d on t h e two t y p e s o f c h e m i c a l f i b r e s w i t h groundwood. The e f f e c t o f a d d i t i o n a l t r e a t m e n t s was e v a l u a t e d by t e s t -i n g t h e i n t e r a c t i o n between b a s i c p u l p r e s p o n s e and t r e a t m e n t s f o r b o t h t y p e s o f p u l p b l e n d s . The b a s i c model f o r a n a l y s i s o f v a r i a n c e i s p r e s e n t e d i n T a b l e XL, T a b l e X I . A n a l y s i s o f v a r i a n c e f o r t e n s i l e s t r e n g t h o f ha n d s h e e t s made . from s u l f i t e - and k r a f t -groundwood p u l p b l e n d s . S o u r c e DF Sum SQ Mean SQ F F.05 F.01 SVK 1 0.13463E 08 0.13463E 08 210.15** 4.03 7.17 TREAT 5 0.66060E 08 0.13212E 08 206.24** 2.40 3.41 PER. 10 0.74524E 08 0.74524E 07 116.33** 2.02 2.70 SXT 5 0.34908E 07 0.69815E 06 10.90** 2.40 3.41 SXP 10 0.85858E 07 0.85858E 06 13 .40** 2.02 2.70 TXP . 50 0.18358E 07 0.36716E 05 0.57 1.60 1.94 ERROR 50 0.32031E 07 0.64063E 05 TOTAL 131 0.17116E 09 Symbols: S : S u l f i t e K : K r a f t > P e r . : X_ ( b l e n d i n g i n p e r c e n t ) T r e a t : . Treatment A, B, D, E, F and G. c. R e l a t i o n s h i p between dependent v a r i a b l e s R e l a t i o n s h i p s between dependent v a r i a b l e s ( s t r e n g t h p a r a m e t e r s ) were f i r s t examined by v i s u a l i n s p e c t i o n o f p l o t s p r o duced by t h e computer. F o l l o w i n g i n s p e c t i o n o f r e s p e c t i v e p l o t s i t was found t h a t t h e d a t a grouped na.turally :-, i n t o , three:, p a r t s according! i :to . the, t h r e e major t y p e s o f t r e a t m e n t s . -98-S i m p l e l i n e a r r e g r e s s i o n s were c a l c u l a t e d f o r u l t i m a t e t e n s i l e s t r e n g t h (Y_) v e r s u s modulus o f e l a s t i c i t y ( Y 2 ) , u l t i m a t e t e n s i l e s t r a i n (Y3) and t e n s i l e energy a b s o r p t i o n ( Y ^ ) , Y 2 v s . Y3 and Y^ and Y^ v s . Y3 . C a l c u l a t e d p o i n t s were d e r i v e d from s i g n i f i c a n t e q u a t i o n s o f r e s p e c t i v e c o r r e l a t i o n s . -99-RESULTS Change i n p u l p m e t h o x y l c o n t e n t f o r t h e t h r e e b a s i c p u l p t y p e s as a f u n c t i o n o f i r r a d i a t i o n dosage i s p r e s e n t e d i n F i g . 5. P e r t i n e n t d a t a r e l a t i n g t o d i f f e r e n c e s i n o i l a b s o r p t i o n and r e - e x t r a c t a b l e o i l f r a c t i o n s b e f o r e and a f t e r o i l d i p p i n g and p o l y m e r i z a t i o n a r e t a b u l a t e d i n T a b l e X. R e s u l t s o f a n a l y s i s o f v a r i a n c e on p u l p t y p e , e x t e n t o f b l e n d i n g (Xj_, Treatment A) and paper t r e a t m e n t s ( h e a t t r e a t m e n t ( B ) , o i l d i p p i n g ( D ) , g r a f t i n g by g a m m a - i r r a d i a t i o n ( F ) , t h e r m a l ( E ) and combined i r r a d i a t i o n and t h e r m a l (G) t r e a t m e n t s ) and t h e i r i n t e r a c t i o n on t e n s i l e s t r e n g t h a r e p r e s e n t e d i n the u s u a l t a b u l a r f o r m i n T a b l e X I . T e n s i l e f r a c t u r e s w i t h p e r t i n e n t s t r e n g t h and o t h e r d a t a f o r t r e a t e d and n o n - t r e a t e d wood microtome s e c t i o n s a r e p r e s e n t e d i n F i g . 6 ( a t o f ) . S c a n n i n g e l e c t r o n p h o t o m i c r o g r a p h s t o g e t h e r w i t h c h a r a c t e r i s t i c .strength v a l u e s "are shown ''for pure groundwood i n F i g . 7 ( F i g . 7, g t o i ) , f o r s u l f i t e ( F i g . 7, j t o 1) and k r a f t ( F i g . 7, m t o o ) . I n a d d i t i o n a deep t e n s i l e f r a c t u r e c h a r a c t e r i s t i c o f k r a f t paper i s p r e s e n t e d as F i g . 8. Mean v a l u e s o f measured and c a l c u l a t e d s t r e n g t h p a r a m e t e r s f o r a l l p u l p b l e n d s a r e summarized i n T a b l e X I I t h r o u g h XV and i n F i g . 9 t h r o u g h 12 f o r s u l f i t e and i n T a b l e XVI t h r o u g h IXX and F i g . 13 t h r o u g h 16 f o r k r a f t p a p e r s . E q u a t i o n s f o r t h e c a l c u l a t e d r e s p o n s e s u r f a c e s a r e p r e s e n t e d i n T a b l e XX. E f f e c t o f t h e r m a l and i r r a d i a t i o n p o l y m e r i z a t i o n o f d r y i n g o i l on s t r e n g t h p r o p e r t i e s o f h a n d s h e e t s made f r o m t h e t h r e e b a s i c p u l p s i s summar-i z e d i n T a b l e XXI. V a l u e s f o r a b s o l u t e s t r e n g t h p a r ameter i n c r e a s e s a r e -100-p l o t t e d i n F i g . 17. F i g . 18 shows the e f f e c t o f e x t r a c t a b l e monomer r e s i d u e s and s o l u b l e homopolymer f r a c t i o n s on t e n s i l e s t r e n g t h . T e n s i l e s t r e n g t h v a r i a t i o n o f p u l p h a n d s h e e t s , c a l c u l a t e d from t h e s i g n i f i c a n t i n t e r a c t i o n between p u l p t y p e and l e v e l o f b l e n d i n g i s d e m o n s t r a t e d i n F i g . 19. T a b l e X X I I p r e s e n t s per c e n t s t r e n g t h i n c r e a s e v a l u e s o b t a i n e d : o n p u r i f i e d c e l l u l o s e p u l p s b e f o r e and a f t e r sodium c h l o r i t e t r e a t m e n t and o i l p o l y m e r i z a t i o n by t h e r m a l t r e a t m e n t . R e l a t i o n s h i p s between dependent v a r i a b l e s (Y-s) a r e p l o t t e d i n F i g . 20 t h r o u g h 24 f o r w h i c h t h e a p p r o p r i a t e e q u a t i o n s can be found i n T a b l e X X I I I . Based on recommendations made f o r f u r t h e r i n v e s t i g a t i o n o f o i l c o p o l y m e r i z a t i o n w i t h l i g n i n (and p o s s i b l y c e l l u l o s e ) a scheme f o r s e l e c t i v e l i g n i n m e t h y l a t i o n i s d e s c r i b e d i n F i g . 25. Compar i s o n between t h e r m a l and i r r a d i a t i o n t r e a t e d samples i s de m o n s t r a t e d by a c t u a l s p e c i m e n t s p r e s e n t e d as F i g . 26. -101-DISCUSSION D u r i n g t h e p a s t few y e a r s a g r e a t d e a l o f e f f o r t has been expended on i n v e s t i g a t i o n o f g r a f t c o p o l y m e r s . M o s t l y , t h e s e s t u d i e s have d e a l t w i t h development o f new t e c h n i q u e s and p r o v i d e l i m i t e d u n d e r s t a n d i n g o f r e a c t i o n mechanisms and a c t u a l g r a f t copolymer s t r u c t u r e s . Most r e a c t i o n s i n v o l v i n g g r a f t c o p o l y m e r i z a t i o n s u f f e r f r o m t h e d i s a d v a n t a g e o f c o n c o m i t a n t homopoly-m e r i z a t i o n o f t h e s a t u r a n t w i t h i n the copolymer network. Few, i f any, pure g r a f t copolymers have been c o n c l u s i v e l y p r o v e n so f a r . W i t h wood and wood components t h e s i t u a t i o n i s even more complex. I n f o r m a t i o n on s i t e s and s p e c i f i c i t y o f g r a f t s i s l i m i t e d i n d e e d , due t o t h e n a t u r e o f p a r e n t wood polymers such as c e l l u l o s e and l i g n i n . I n t h e p r e s e n t s t u d y p o l y m e r i z a t i o n phenomena between a c o m m e r c i a l u n s a t u r a t e d d r y i n g o i l (CTIA Polymer) and t h r e e wood p u l p t y p e s was i n v e s t i g a -t e d . P o l y m e r i z a t i o n r e a c t i o n s were i n i t i a t e d by g a m m a - i r r a d i a t i o n from a 60 Co s o u r c e and by p r o l o n g e d h i g h - t e m p e r a t u r e h e a t t r e a t m e n t . I n a l l i n s t a n c e s c o n s i d e r a b l e g a i n s were made i n paper s h e e t s t r e n g t h p r o p e r t i e s . The t r e a t m e n t may be o f i m p o r t a n c e where i n t e r f i b r e bond s t r e n g t h i s t h e l i m i t i n g f a c t o r on f i b r e web s t r e n g t h . F o r example, i t c o u l d be a p p l i e d t o a w i d e v a r i e t y o f s p e c i a l t y papers d e s i g n e d f o r uses w h e r e - s t r e n g t h improve-ment o f low c o s t , h i g h y i e l d f i b r e f u r n i s h i s d e s i r e d . F o l l o w i n g t h e t r e a t m e n t s , e v i d e n c e was sought t o d i s t i n g u i s h between h o m o p o l y m e r i z a t i o n and g r a f t c o p o l y m e r i z a t i o n t h r o u g h assessment o f b a s i c m e c h a n i c a l s t r e n g t h parameters and by use o f u s u a l o r g a n i c s o l v e n t -102-t e c h n i q u e s . I . THERMAL POLYMERIZATION WITH THIN WOOD SECTIONS E a r l i e r a t t e m p t s by B u t l e r (42) t o m o d i f y wood e l a s t i c i t y and work f u n c t i o n s by s o a k i n g a v a r i e t y o f wood s e c t i o n s i n CTLA Polymer f o l l o w e d by a p p l i c a t i o n o f t h e r m a l and i r r a d i a t i o n energy t o i n d u c e c o p o l y m e r i z a t i o n gave no c o n c l u s i v e r e s u l t s . Due t o t h e l i m i t e d scope o f t h e s t u d y no e v i d e n c e was sought f o r t h i s f a i l u r e . I t was s u g g e s t e d , however, t h a t cause o f f a i l u r e t o show p o l y m e r i z a t i o n e f f e c t s m i ght be due t o r e l a t i v e l y low r e -a c t i v i t y o f n a t u r a l l i g n i n _ i n s i t u , and t h a t p o s s i b l y h i g h - t e m p e r a t u r e t r e a t -ment i n t h e p r e s e n c e o f m o i s t u r e i s r e q u i r e d t o a c t i v a t e l i g n i n i n p r e p a r a t i o n f o r c o p o l y m e r i z a t i o n r e a c t i o n s . S i n c e t h e r e was no d i f f e r e n c e i n s t r e n g t h , between c o n t r o l and o i l d i p p e d wood s e c t i o n s , f o l l o w i n g i r r a d i a t i o n t r e a t -ments t h e d i s c u s s i o n was l i m i t e d m a i n l y t o e v a l u a t i o n o f i r r a d i a t i o n e f f e c t s as a f u n c t i o n o f wood d e n s i t y , t h e main independent v a r i a b l e o f t h e s t u d y . Such e x p l a n a t i o n may n o t a d e q u a t e l y d e s c r i b e e f f e c t s w i t h n a t u r a l l i g n i n . Through f u r t h e r e x p e r i m e n t a t i o n s t r e n g t h d a t a on matched specimens were o b t a i n e d f o r b o t h e a r l y w o o d and l a t e w o o d microtome s e c t i o n s w i t h and w i t h o u t t h e r m a l p o l y m e r i z a t i o n t r e a t m e n t . S u r p r i s i n g l y , a g a i n s t r e n g t h i n -c r e a s e o f t h e o i l t r e a t e d s e c t i o n s n e v e r exceeded 157o. The i n c r e a s e was found t o be lower, b u t more r e p r o d u c i b l e ^ f o r e a r l y w o o d s e c t i o n s t h a n f o r l a t e -wood. N e i t h e r t h e r m a l p r e t r e a t m e n t ( b o i l i n g i n w a t e r or h e a t t r e a t m e n t be-tween m o i s t paper t o w e l s a t 170°C), n o r m e t h y l a t i o n o f t h e wood s e c t i o n s i n a l k a l i n e d i m e t h y l s u l f a t e a t room t e m p e r a t u r e improved r e s u l t s . T h e r e f o r e , -103-i t was c o n c l u d e d t h a t f a i l u r e t o o b t a i n s t r e n g t h i n c r e a s e s , p r o p o r t i o n a l t o d i f f e r e n c e i n l i g n i n c o n t e n t o f e a r l y w o o d and l a t e w o o d t i s s u e s was not due t o i n s u f f i c i e n t l i g n i n r e a c t i v i t y toward c o p o l y m e r i z a t i o n . The answer i s c o n t a i n e d i n p a r t i n t e n s i l e f a i l u r e p a t t e r n s as p r e s e n t e d i n F i g . 6. O b s e r v a t i o n s on wood m i c r o - t e n s i l e f a i l u r e s were made by I f j u and Kennedy ( 8 7 ) . I t was shown t h a t e a r l y w o o d specimens always f a i l i n t e n s i o n a c r o s s f i b r e w a l l s , whereas l a t e w o o d s e c t i o n s f a i l between f i b r e s by s h e a r o f the m i d d l e l a m e l l a . F o l l o w i n g t h e r m a l p o l y m e r i z a t i o n w i t h t h e d r y i n g o i l b o t h e a r l y w o o d and l a t e w o o d s e c t i o n s f a i l e d i n t e n s i o n as e v i d e n c e d on t h e s c a n n i n g e l e c t r o n p h o t o m i c r o g r a p h s shown i n F i g . 6. T h e r e i s p r a c t i c a l l y no change i n e a r l y w o o d f r a c t u r e p a t t e r n ( F i g . 6, a, b and c) as one p r o g r e s s e s from u n t r e a t e d wood s e c t i o n s t o h i g h l y i r r a d i a t e d (10 7'"* r a d ) or t h e r m a l l y t r e a t e d o i l soaked s e c t i o n s . S t r e n g t h appears t o be l i m i t e d by i n t r i n s i c f i b r e s t r e n g t h i n e a r l y w o o d s e c t i o n s . On t h e o t h e r hand, a s u c c e s s i v e change i n f r a c t u r e p a t t e r n can be o b s e r v e d on i n s p e c t i o n o f l a t e w o o d p h o t o m i c r o g r a p h s ( F i g . 6, d, e and f ) . I n F i g . 6, d, a t y p i c a l s h e a r f a i l u r e between t h e m i d d l e l a m e l l a e o f a d j a c e n t f i b r e s i s shown. T h i s i n d i c a t e s h i g h i n t r i n s i c f i b r e s t r e n g t h . F o l l o w i n g h i g h - d o s a g e i r r a d i a t i o n ( F i g . 6, e) s t r e n g t h o f t h e latewood specimens was r e d u c e d to 437, o f t h e - o r i g i n a l , • p o s s i b l y due t o c e l l u l o s e d e p o l y m e r i z a t i o n and t h e r e b y l o s s o f i n t r i n s i c f i b r e s t r e n g t h . I n t h i s i n s t a n c e the f r a c t u r e changed from pure s h e a r to a c o m b i n a t i o n o f s h e a r and t e n s i l e f a i l u r e , an i n d i c a t i o n of unchanged i n t e r f i b r e b o n d i n g b u t de-c r e a s e d i n t r i n s i c f i b r e s t r e n g t h . Thermal p o l y m e r i z a t i o n w i t h t h e d r y i n g o i l works i n t h e o p p o s i t e d i r e c t i o n as d e m o n s t r a t e d by F i g . 6, f . By. o n l y 14.17, i n c r e a s e i n t e n s i l e s t r e n g t h t h e f r a c t u r e p a t t e r n changed from pure s h e a r t o -104-pure t e n s i l e f a i l u r e i n d i c a t i n g t h a t improvement i n i n t e r - f i b r e b o n d i n g d i d t a k e p l a c e . An u l t i m a t e l i m i t t o s t r e n g t h improvement seems t o be s e t by i n t r i n s i c f i b r e s t r e n g t h , s i m i l a r t o the case w i t h e a r l y w o o d t i s s u e . The above o b s e r v a t i o n s s u g g e s t t h a t wood f i b r e s t r e n g t h i s u t i l i z e d c l o s e t o i t s maximum t e n s i l e c a p a c i t y i n b o t h growth z o n e s . T h i s a l s o i m p l i e s t h a t s u b s t a n t i a l change i n wood s t r e n g t h cannot be e f f e c t e d w i t h -out r a i s i n g b o t h l i m i t i n g f a c t o r s , i .e . j i n t e r f i b r e b o n d i n g and i n t r i n s i c f i b r e s t r e n g t h . Indeed, t h e r e i s e x p e r i m e n t a l e v i d e n c e (1) showing t h a t s t r e n g t h p r o p e r t i e s o f monomer s a t u r a t e d wood were h i g h e r when a m i x t u r e o f s t y r e n e and m e t h y l m e t h a c r y l a t e were used, t h a n by e i t h e r one o f t h e monomers used a l o n e . T h i s o b s e r v a t i o n i s c o n s i s t e n t w i t h work o f K o s h i j i m a and M u r a k i ( 1 1 7 ) , who found t h a t l i g n i n p r e f e r e n t i a l l y p o l y m e r i z e d w i t h methy1-m e t h a c r y l a t e on i r r a d i a t i o n , whereas s t y r e n e gave v e r y low g r a f t , y i e l d s . S i m i l a r l y , Rapson and K v a s n i c k a (187/b) o b s e r v e d a s t r o n g s y n e r g i s t i c e f f e c t w i t h s t y r e n e and a c r y l o n i t r i l e when s i m u l t a n e o u s l y g r a f t e d o n t o c e l l u l o s e by gamma i r r a d i a t i o n . The e f f e c t showed not o n l y a h i g h e r s t r e n g t h i n c r e a s e , b u t p e r m i t t e d an e x t r e m e l y l a r g e r e d u c t i o n i n i r r a d i a t i o n dosage f o r a g i v e n w e i g h t o f polymer a d d i t i o n t o c e l l u l o s e . I I . THERMAL AND IRRADIATION INDUCED POLYMERIZATION WITH PULP HANDSHEETS S i n c e m e c h a n i c a l e v i d e n c e i s much used i n t h i s s t u d y f o r s o r t i n g t h e r m a l and i r r a d i a t i o n t r e a t m e n t e f f e c t s , i t i s a p p r o p r i a t e t o r e v i e w f a c t o r s i n f l u e n c i n g b a s i c r h e o l o g i c a l b e h a v i o r o f wood f i b r e webs. T h e o r e t i c a l l y , such m e c h a n i c a l comparisons a r e p e r m i s s i b l e s i n c e -105-b o n d i n g i n paper has been a c c e p t e d as m a i n l y dependent on s e c o n d a r y v a l e n c e f o r c e s between f i b r e c o n t a c t s (168i 176), as w e l l as on s u r f a c e c o l l o i d a l p r o p e r t i e s o f f i b r e s (91, 2 2 7 ) . S i n c e the s t r e s s - s t r a i n c u r v e o b t a i n e d by t e n s i l e t e s t i n g o f paper webs r e f l e c t s t he n a t u r e and o r g a n i z a t i o n o f t h e s h e e t components, i t i s w e l l s u i t e d f o r e v a l u a t i n g e f f e c t s o f f i b r e and paper s h e e t t r e a t m e n t s . 1. Mechanism o f Bonding i n paper The r e s i s t a n c e o f wood f i b r e webs t o r u p t u r e as a s s e s s e d by a c o n v e n t i o n a l p r o c e d u r e such as t e n s i l e t e s t i n g , i s b e l i e v e d t o depend on s e v e r a l f a c t o r s . S i n c e t h e f i b r e s form a t h r e e - d i m e n s i o n a l , a t t a c h e d network i n t h e paper s h e e t t h e s t r e n g t h o f t h e s t r u c t u r e i s i n p a r t due t o t h e s t r e n g t h o f s h e e t f o r m i n g elements ( f i b r e s ) and i n p a r t t o t h e j o i n t s o r bonds between them (5, 83, 109, 174, 197, 2 1 9 ) . The l a t t e r i s dependent upon the t o t a l a r e a o f such c o n t a c t s , as w e l l as on t h e q u a l i t y o f t h e bond a r e a o r t h e s t r e n g t h o f bonds. C o n s i d e r i n g t h a t paper s t r e n g t h i s measured as r u p t u r e s t r e n g t h i t s v a l u e a l s o depends on energy d i s t r i b u t i o n w i t h i n t h e f i b r e n etwork and, t h e r e b y , on t h e r e l a t i v e d e n s i t y o f bonded a r e a s a l o n g any p a r t i c u l a r c r o s s - s e c t i o n »of-!|the'sheet b e i n g ^ s t r e s s e d . The s t r e n g t h o f paper i s g e n e r a l l y a t t r i b u t e d t o hyd r o g e n bond-i n g between f i b r e s ( 5 , 44, 83, 158, 168, 169, 170, 171, 172, 174, 176, 187, 205) , s u g g e s t i n g t h a t bond s t r e n g t h s h o u l d be u n i f o r m f o r a l l c e l l u l o s i c paper p r o d u c t s (173) . As t h e bond s t r e n g t h i s c a l c u l a t e d per u n i t o f bonded a r e a i n v a r i o u s papers i t i s found t h a t t h e number o f bonds per u n i t a r e a d i f f e r s f o r p u l p s o f v a r i o u s q u a l i t i e s . F a c t o r s a f f e c t i n g t h e bond s t r e n g t h -106-were examined by G i e r t z (74),. Jayme and L o c k m u e l l e r - K e r l e r (95, 96)and Nordman ( 1 7 4 ) , by i n v e s t i g a t i n g t h e e f f e c t s o f wood c o n s t i t u e n t s and by L e o p o l d (128, 132) and S c h n i e w i n d _et al.(197) by s t u d y i n g e f f e c t s o f s t r e n g t h and b o n d i n g c h a r a c t e r i s t i c s o f e a r l y w o o d and l a t e w o o d f i b r e s . F u r t h e r , E i n s p a h r ( 5 9 ) , H e l l e ( 8 3 ) , Ingmanson and Thode (88), M c i n t o s h ( 1 4 3 ) , M a r t o n (154) and Mayhood, K a l l m e s and C a u l e y (158) s t u d i e d t h e c o n t r i b u t i o n o f i n t r i n s i c f i b r e s t r e n g t h and s h e a r s t r e n g t h o f i n d i v i d u a l f i b r e - t o - f i b r e c o n t a c t s t o s t r e n g t h o f p a p e r s . The s t r e n g t h o f a bond between a d j a c e n t f i b r e s i s t h e p r o d u c t o f bond a r e a and s t r e n g t h o f t h e m a t e r i a l w i t h r e s p e c t t o i t s b o n d i n g c a p a c i t y . The a r e a o f t h e bond i s l a r g e l y d e t e r m i n e d by t h e f l e x i b i l i t y o f f i b r e s (132, 197, 219), t h e geometry o f f i b r e s u r f a c e s (59, 83,. 88, 154), t h e e x t e r n a l l y a p p l i e d p r e s s u r e used i n s h e e t f o r m a t i o n (154, 174, 205, 219) and i n t e r n a l t e n s i o n p r o c e s s e s d u r i n g d e w a t e r i n g and d r y i n g phases ( C a m p b e l l e f f e c t ) ( 4 4 ) . Paper f o r m a t i o n , from a d i l u t e f i b r e s u s p e n s i o n t o t h e f i n i s h e d s h e e t , r e p r e s e n t s a complex p h y s i c o - c h e m i c a l p r o c e s s i n w h i c h w a t e r -t o - w a t e r h y d r o g e n bonds a r e s u p e r s e d e d by c e l l u l o s e - t o - w a t e r h y d r o g e n bonds, and f i n a l l y as s u r f a c e t e n s i o n f o r c e s draw t h e f i b r e s i n t o i n t i m a t e c o n t a c t , by c e l l u l o s e - t o - c e l l u l o s e h y d r o g e n bonds (168) . T h e r e f o r e , t h e bond s t r e n g t h per u n i t a r e a o f f i b r e may be assumed t o be a f u n c t i o n o f f i b r e s u r f a c e c h e m i s t r y w h i c h i s d e f i n i t e l y i n f l u e n c e d by b o t a n i c a l o r i g i n and subsequent c h e m i c a l p r o c e s s i n g . The r h e o l o g i c a l b e h a v i o r o f paper depends t o a l a r g e e x t e n t on t h e h y d r o g e n bond s y s t e m w h i c h has been imposed upon t h e f i b r e assemblage and t h e r e s p o n s e o f t h a t s y s t e m to t h e t e s t e n v i r o n m e n t . Numerous t h e o r i e s have been advanced w h e r e i n b o n d i n g w i t h i n a . -107-s h e e t o f paper i s e x p l a i n e d i n terms o f m o l e c u l a r s t r u c t u r e (5, 44, 168, 169, 170, 171, 172, 176, 187, 2 0 5 ) . The o n l y p o i n t on w h i c h a l l t h e s e t h e o r i e s a g r e e i s t h e i m p o r t a n c e o f h y d r o g e n bonds as a p r i m a r y s o u r c e o f paper s t r e n g t h . I n f a c t , n u m e r i c a l c a l c u l a t i o n s have been advanced by N i s s a n ( 1 6 8 ) , based on a number o f a r b i t r a r y a s s u m p t i o n s as p o i n t e d out by Page (176), t o a c c o u n t f o r h y d r o g e n bond s t r e n g t h as measured by a b s o r p t i o n o f s t r a i n e n e r g y . N i s s a n (168) assumes the s t r a i n i n paper under s t r e s s i s d e r i v e d from t h e e x t e n t i o n o f h y d r o g e n bonds w h i c h a r e , i f a c c e p t e d , u b i q u i t o u s to c e l l u l o s i c m a t e r i a l s . D i f f i c u l t i e s i n o b s e r v i n g s t r a i n d i s t r i b u t i o n i n c e l l u l o s e webs i s m a i n l y due t o t h e f a c t t h a t c e l l u l o s e amorphous r e g i o n s a r e n o t a c c e s s i b l e to d i r e c t v i e w i n g by X - r a y . I t i s p o s t u l a t e d ( 1 6 8 ) , however, t h a t t h e a b s o r b e d s t r a i n energy i s t a k e n up e n t i r e l y by t h e amorphous r e g i o n , whereas t h e c r y s t a l l i n e p o r t i o n , o f c e l l u l o s e o n l y t r a n s m i t s e n e r g y . On t h e o t h e r handy Page (176) b e l i e v e s t h a t c a l c u l a t i o n of c e l l u l o s e e l a s t i c m o d u l i (191) must be based on a more d e t a i l e d a s s u m p t i o n , whereby t h e c h a i n m o l e c u l e s can be c o n s i d e r e d i n d i v i d u a l l y , and t h a t d e f o r m a t i o n a r i s e s f r o m b o t h s t r e t c h i n g and a n g u l a r d e f o r m a t i o n o f c o v a l e n t l i n k a g e s . 0 . D i s c r e p a n c i e s i n N i s s a n ' s t h e o r y (168) a r i s e from t h e f a c t t h a t s t r a i n w i t h i n a f i b r e h e l d i n a s h e e t can v a r y c o n s i d e r a b l y from.one l o c a l i t y t o a n o t h e r due t o n o n u n i f o r m s h e a r and b e n d i n g o f t h e randomly a r r a n g e d n e t -work. The m o l e c u l a r a p p r o a c h does n o t a l l o w p r e d i c t i o n o f s u c h a n o m a l i e s f o r paper (176) , Paper has been r e c o g n i z e d by K a l i m e s and B e r n i e r (99) as c o n s i s t -i n g o f a randomly a r r a n g e d , a p p r o x i m a t e l y t w o - d i m e n s i o n a l a r r a y o f f i b r e s bonded a t f i b r e c r o s s i n g s . On t h i s b a s i s s t r e n g t h was d e f i n e d as a r i s i n g -108-from t h e b e n d i n g , s t r e t c h i n g and s h e a r i n g o f f i b r e segments between bond s i t e s . The t h e o r y , however, f a i l s t o d e s c r i b e t h e s t r e n g t h and number o f bonds on a t r u l y q u a n t i t a t i v e b a s i s , s i n c e i t n e g l e c t s d e f o r m a t i o n o f t h e f i b r e s t h e m s e l v e s a t bond s i t e s . However, t h e p r i n c i p l e o f complex s h e e t d e f o r m a t i o n , i n c l u d i n g f i b r e b e n d i n g , s t r e t c h i n g and s h e a r i n g i s a c c e p t a b l e . 2. S t r e s s - S t r a i n P r o p e r t i e s o f Paper Webs The s t r e s s - s t r a i n c u r v e o f a s t r i p o f paper t e s t e d i n t e n s i o n i s an e x t r e m e l y s e n s i t i v e i n d e x o f t h e n a t u r e and. o r g a n i z a t i o n o f s h e e t compon-en t s (59, 88, 128,. 158, 174, 191), e f f e c t o f f i b r e t r e a t m e n t s (88, 90, .137,, 146, 176, 211, 219), s h e e t f o r m a t i o n (174, 228) and p r e v i o u s s t r e s s h i s t o r y o f t h e paper b o t h d u r i n g and a f t e r d r y i n g (18, 51,. 73, 2 1 6 ) . A t p r e s e n t t h e r e a r e s u f f i c i e n t d a t a a v a i l a b l e t o d e m o n s t r a t e t h a t b o t h m o l e c u l a r and i n t e r f i b r e m a c r o s c o p i c e f f e c t s p l a y an i m p o r t a n t r o l e i n d e t e r m i n i n g paper r e s i s t a n c e t o s t r e s s e s . F i b r e components w i t h i n a s h e e t a r e n o t f r e e t o t w i s t and change shape or s l i d e o v e r each o t h e r d u r i n g deform-a t i o n . As p o i n t e d o u t by Jayme ( 9 7 ) , the r e s p o n s e o f p u l p f i b r e s t o s t r e s s e s i s p r i m a r i l y , b u t not e n t i r e l y , e l a s t i c . D e f o r m a t i o n o f r e a l s o l i d s i s a lways accompanied by d i s s i p a t i o n o f a p a r t o f t h e a p p l i e d energy (121, 217) . The i r r e v e r s i b l e p r o c e s s e s r e s p o n s i b l e f o r energy d i s s i p a t i o n g e n e r a l l y show a r e l a x a t i o n s p e c t r u m w i t h t i m e w h i c h i s c h a r a c t e r i s t i c o f t h e s o l i d under i n v e s t i g a t i o n . A s m a l l p o r t i o n . o f t h e energy a b s o r b e d d u r i n g s t r a i n i n g i s l o s t due t o c r e a t i o n , o f new s u r f a c e f r e e energy w i t h c a r b o h y d r a t e s a t t h e i r a i r i n t e r f a c e s on r u p t u r e ( 2 1 7 ) . A second p o r t i o n i s l o s t i n v a r i o u s m o t i o n s d u r i n g bond b r e a k i n g , u l t i m a t e l y a p p e a r i n g as h e a t and sound but a l a r g e -109-p o r t i o n i s consumed f o r p l a s t i c d e f o r m a t i o n o f t h e f i b r e s ( 1 7 6 ) . I t i s t h e t o t a l energy i n p u t w h i c h r e s u l t s i n d i r e c t bond b r e a k i n g t h a t i s o f i n t e r e s t , b ecause i t r e f l e c t s t h e m e c h a n i c a l p r o p e r t i e s o f t h e v a r i o u s p a p e r s . Thus, th e o b s e r v e d n o n - l i n e a r i t y o f s t r e s s - s t r a i n c u r v e s ( 5 , 171, 173, 174, 176, 191, 217) i s d e r i v e d i n an a p p r e c i a b l e way f r o m t h e n o n - l i n e a r i t y o f i n t e r n a l energy o f t h e s y s t e m . The d e p a r t u r e f r o m . l i n e a r i t y i s a s s o c i a t e d w i t h b r e a k -age, o f bonds w i t h i n t h e paper s h e e t , as w e l l as energy d i s s i p a t i o n and o n s e t o f c r e e p (176, 193) . Bonds s t a r t t o f a i l a t v e r y low s t r a i n v a l u e s (158, 173, 187, 217) ( e l a s t i c r e g i o n ) w h i c h a c c o u n t s f o r n o n - l i n e a r i t y o f t h e i n i t i a l p o r t i o n o f t h e s t r e s s - s t r a i n c u r v e . Bond f a i l u r e becomes o f much g r e a t e r a m p l i t u d e as t h e " p l a s t i c " r e g i o n o f t h e c u r v e i s r e a c h e d . I t i s t h i s r e g i o n where me a s u r e a b l e energy i s consumed i n t h e p r o c e s s o f i r r e v e r s i b l e f i b r e s e p a r a -t i o n ( 1 5 8 ) . As t h e s t r a i n i s i n c r e a s e d , bond f a i l u r e s o c c u r randomly t h r o u g h -o u t the s h e e t u n t i l a weak s p o t has d e v e l o p e d ( 2 1 7 ) . F u r t h e r s t r e s s e s a r e c o n c e n t r a t e d w i t h i n t h i s a r e a u n t i l t h e s h e e t f a i l s c o m p l e t e l y . S i n c e i t i s m a i n l y c o n t a c t f a i l u r e s t h a t d i f f e r e n t i a t e i r r e v e r s i b l e f rom e l a s t i c r e g i o n s o f the curve,' extfeS&ion o f t h e t h e o r y t o r e g i o n s beyond t h e s t r a i g h t l i n e i s c o n t i n g e n t upon i n s i g h t i n t o the s t r e n g t h o f i n d i v i d u a l f i b r e s and f i b r e c o n t a c t s . The s t r a i n r e s i s t a n c e o f paper i s dependent on t h e q u a l i t y o f t h r e e p h y s i c a l f a c t o r s : 1. s t r e s s - s t r a i n p r o p e r t i e s o f i n d i v i d u a l f i b r e s (59, 132, 154); .,2. s h e a r r e s i s t a n c e o f o p t i c a l c o n t a c t . a r e a s between f i b r e s (158, 1 9 7 ) ; and '3 . degree o f i n t e r f i b r e b o n d i n g (37, 88, 172, 174, 2 0 5 ) . -110-a. F i b r e s t r e n g t h The f i b r e s t r e n g t h u s u a l l y depends on t h e i n t e r n a l f i b r e s t r u c t u r e (115, 128, 154, 197) and t h e e x t e n t o f m e c h a n i c a l damage (.83, 154) imposed upon t h e f i b r e s d u r i n g t h e p r o c e s s o f f i b r e s e p a r a t i o n , p r e p a r a t i o n and form-a t i o n o f t h e s h e e t . The e x t e n t o f f i b r e b r e a k a g e a t f a i l u r e o f t h e s h e e t (a measure o f f i b r e s t r e n g t h i n paper) i s c l o s e l y c o r r e l a t e d w i t h bond s t r e n g t h . I t has been f o u n d t h a t t h e number o f f i b r e p u l l - o u t s d e c r e a s e s w i t h i n c r e a s -i n g b r e a k i n g l e n g t h ( 8 3 ) . I n o r d e r t o compare f i b r e s t r e n g t h i n s u l f i t e and k r a f t papers t h e e x t e n t o f f i b r e b o n d i n g w o u l d have t o be t h e same. T e n s i l e s t r e n g t h o f i n d i v i d u a l l o b l o l l y p i n e f i b r e s from b o t h e a r l y - and latewood o r i g i n was t e s t e d by L e o p o l d ( 1 2 8 ) . and M c i n t o s h (143) who found t h a t t h e s e two f i b r e t y p e s c o n t r i b u t e d i f f e r e n t l y t o paper s t r e n g t h due t o d i f f e r e n c e s i n i n t r i n s i c f i b r e s t r e n g t h , b o n d i n g c a p a c i t y and f i b r e geometry. b. Bond s t r e n g t h Shear r e s i s t a n c e o f o p t i c a l c o n t a c t a r e a s between f i b r e s , o n t h e o t h e r h a n d , i s governed by t h e b o n d i n g p o t e n t i a l (143, 197) and s u r f a c e a r e a (83, 168, 173, 174, 219) o f the f i b r e s as r e l a t e d t o t h e i r f l e x i b i l i t y and p l a s t i c i t y , as w e l l as g e o m e t r i c arrangements w i t h i n t h e paper s h e e t (219) . On t h e o r e t i c a l g rounds, N i s s a n (168) e s t i m a t e d bond s t r e n g t h w i t h i n paper as 10 2 b e i n g e q u a l t o 2x10 dynes/cm w h i c h r e p r e s e n t s o n l y 17o o f t h e a v a i l a b l e h ydrogen bonds. c. Degree o f f i b r e b o n d i n g Bonded a r e a has been d e f i n e d by Nordman and G u s t a f s o n (174) as 2 t h e d i f f e r e n c e i n s u r f a c e a r e a o f the p u l p (cm /g) and t h e f r e e s u r f a c e a r e a o f t h e s h e e t s made t h e r e f r o m . S i n c e s t r e n g t h p r o p e r t i e s o f paper a r e c o n s i d e r -ed t o be i n t i m a t e l y r e l a t e d w i t h magnitude o f t h e bonded a r e a , numerous methods have been d e v i s e d f o r i t s d e t e r m i n a t i o n . The o p t i c a l method based on Kubelka-Munk t h e o r y has been d e v e l o p e d by R a t l i f f (188) and expanded to gas. a b s o r p t i o n by H a s e l t o n (80) . R e c e n t l y , a new method was d e v e l o p e d by S m i t h (205) i n v o l v i n g d i r e c t c u r r e n t e l e c t r i c a l c o n d u c t i v i t y measurements on p a p e r . The method t a k e s advantage o f t h e d i f f e r e n c e i n d i s s o c i a t i o n energy between m e t a l l i c c a t i o n s and h y d r o g e n i o n s , a l o n g t h e c e l l u l o s e m o l e c u l e s , i n c h e m i c a l b o n d i n g w i t h oxygen atoms o f p o t e n t i a l h y d r o x y l s as i o n g e n e r a t i n g s i t e s . On a p p l y i n g an e x t e r n a l p o t e n t i a l t o c e l l u l o s e t h e m e t a l l i c c a t i o n s s t r e a m towards t h e c a thode a l o n g a b s o r b e d (hydrogen bonded) w a t e r b r i d g e s o r s u c c e s s i v e i o n g e n e r a t i n g s i t e s . The p r o c e s s i s t e r m i n a t e d by t h e absence o f w a t e r m o l e c u l e s from t h e c e l l u l o s e c h a i n s . Due t o r e l a t i v e s i m p l i c i t y , d e t e r m i n a t i o n o f o p t i c a l bonded a r e a i s t h e most w i d e l y used measurement f o r t h i s p r o p e r t y (88) . However, Jayme and Hunger (93) have shown t h a t o p e r a t i v e f a c t o r s a r e n o t t h e s u r f a c e s t h a t come i n t o c o n t a c t as shown by t h e l i g h t m i c r o s c o p e , but r a t h e r m i c r o f i b r i l s as p r o v e n by e l e c t r o n m i c r o s c o p y . On the s h e a r s u r f a c e s the m i c r o f i b r i l s were t o r n f r o m each o t h e r and p a r t l y t o r n t h e m s e l v e s combined w i t h t h e b r e a k -i n g o f p r i m a r y v a l e n c e f o r c e s . F u r t h e r m o r e , i t was p o s s i b l e t o p r e s e n t a 2 3 4 5 s e r i e s o f p h o t o m i c r o g r a p h s w i t h m a g n i f i c a t i o n s o f 10, 10 , 10 , 10 and 10 times showing e s s e n t i a l l y t h e same p a t t e r n s r e c u r r i n g on t h e c e l l u l o s i c -112-f i b r e s , f i b r i l s , and m i c r o f i b r i l s . By e n l a r g i n g t h e o p t i c a l l y " i n t a c t " a r e a w i t h a l i g h t m i c r o s c o p e t o an e l e c t r o n i c a l l y o b s e r v e d a r e a o f lOOx m a g n i f i c a t -i o n t h e r e a l a r e a was o n l y 10 t o 20 "L. Thereby, t h e "law o f i n v a r i a n c e o f c e l l u l o s i c f i b r i l l a r p a t t e r n w i t h m a g n i f i c a t i o n " i s i n v o k e d and i t appears 3 3 t h a t t h e o p t i c a l l y i n t a c t a r e a i s i n f a c t o n l y (0.1) t o (0.2) w h i l e t h e r e s t i s v o i d . I t has been shown by Ingmanson and Thode (88, 219) t h a t a t a g i v e n t o t a l bonded a r e a t h e s t r e n g t h o f paper i s i n d e p e n d e n t o f t h e degree o f f i b r i l l a t i o n o r the amount o f f i n e s . F i b r i l l a t i o n and f i n e s a r e c o n s i d e r -ed t o p r o v i d e o n l y g r e a t e r s u r f a c e t e n s i o n f o r c e s d u r i n g d r y i n g . The t o t a l d r y f i b r e a r e a a v a i l a b l e f o r b o n d i n g i s t h e o r i g i n a l u n b e a t e n f i b r e s u r f a c e , i r r e s p e c t i v e o f the degree o f r e f i n i n g . The r a t i o o f b r e a k i n g l e n g t h t o bonded a r e a i n paper i s h i g h w i t h k r a f t papers ( 1 7 4 ) . W i t h s u l f i t e p a p e r s , on t h e o t h e r hand, a c o n s i d e r -a b l e degree o f f i b r e b r e a k a g e o c c u r s a t t h e expense o f i n c r e a s e d work a t h i g h b r e a k i n g l o a d s . W i t h k r a f t paper a p p r o a c h i n g s u l f i t e paper s t r e n g t h n e a r l y a l l f i b r e s p u l l away. T h i s happens even i n a d m i x t u r e s o f the two t y p e s o f f i b r e s , s u g g e s t i n g t h a t f o r a u n i t bonded a r e a h i g h e r s t r e n g t h v a l u e s a r e o b t a i n e d w i t h k r a f t t h a n s u l f i t e ( 1 7 4 ) . Thereby, i t seems p o s s i b l e t h a t t h e w h ole bonded a r e a o f t h e s h e e t does n o t c o n t r i b u t e e q u a l l y to the s t r e n g t h o f p a p e r . As p o i n t e d out by H e l l e ( 8 3 ) , L e o p o l d and M c i n t o s h (132) and Norman and G u s t a f s o n (174) optimum s h e e t s t r e n g t h i s o b t a i n e d by a c r i t i c a l b a l a n c e o f i n t r i n s i c f i b r e s t r e n g t h , f i b r e - t o - f i b r e b o n d i n g and bond d e n s i t y . U s u a l l y , the t y p e o f f a i l u r e g i v e s some answer to the r e l a t i o n s h i p of t h e s e -113-parameters and paper q u a l i t y . R u p t u r e w i t h e x c e s s i v e f i b r e p u l l - o u t a t h i g h s t r e n g t h can i n d i c a t e a low degree o f i n t e r f i b r e b o n d i n g and s t r o n g f i b r e s , whereas t e n s i l e f i b r e f r a c t u r e s u g g e s t s weaker f i b r e s and s t r o n g i n t e r f i b r e b o n d i n g . 3. P o l y m e r i z a t i o n w i t h Groundwood Handsheets E a r l i e r o b s e r v a t i o n s on low s t r e n g t h o f groundwood handsheets i n co m p a r i s o n t o papers made fr o m c h e m i c a l p u l p s a r e w e l l founded and can be f u r t h e r s u p p o r t e d w i t h r e s u l t s o f t h i s e x p e r i m e n t . T e n s i l e s t r e n g t h o f groundwood c o n t r o l specimens i s a p p r o x i m a t e l y o n e - f o u r t h t o o n e - f i f t h o f t h a t had w i t h c h e m i c a l p u l p s . T h i s low s t r e n g t h i s b e l i e v e d t o be due i n p a r t t o t h e l a r g e p r o p o r t i o n o f f i n e s ( 6 6 ) , but m o s t l y t o poor c o n f o r m i n g c a p a c i t y o f t h e h i g h - l i g n i n c o n t e n t f i b r e f r a g m e n t s . As a r e s u l t , b o n d i n g c a p a c i t y i n such f i b r e webs i s low. Treatments improv-i n g b o n d i n g o r c o n f o r m i t y o f groundwood f i b r e s s h o u l d y i e l d s i m u l t a n e o u s i n c r e a s e i n t e n s i l e p r o p e r t i e s . S u b s t a n t i a l s t r e n g t h improvements, however, do not n e c e s s a r i l y r e q u i r e i n c r e a s e i n i n t r i n s i c f i b r e s t r e n g t h (as i s t h e case w i t h s o l i d wood s e c t i o n s ) , s i n c e i n t e r f i b r e bond s t r e n g t h i n groundwood i s f a r below t h e l e v e l r e q u i r e d f o r f a i l i n g f i b r e s by t e n s i l e s t r e s s i n g . S u b s t a n t i a l s t r e n g t h i n c r e a s e s have been r e p o r t e d e a r l i e r by d e l i g n i f i c a t i o n o f m e c h a n i c a l p u l p s , such as A s p l u n d (179) and groundwood (98, 1 5 1 ) . I n t h i s s t u d y a 15 % w e i g h t l o s s f o l l o w i n g 1 h r t r e a t m e n t w i t h a c i d i c sodium c h l o r i t e ( c o r r e s p o n d i n g t o a p p r o x i m a t e l y 52 "L l i g n i n l o s s ) i n c r e a s e d t h e t e n s i l e s t r e n g t h from 1230 t o 7314 p s i o r by 495 °L. Such s t r e n g t h g a i n i s n o t approached by the o i l p o l y m e r i z a t i o n t e c h n i q u e under s t u d y . -114-T h i s e f f e c t c l e a r l y p o i n t s toward l i g n i n r e m o v a l as a most i m p o r t a n t means f o r i m p r o v i n g paper s t r e n g t h . a. Thermal t r e a t m e n t Somewhat more moderate b u t s t i l l s u b s t a n t i a l s t r e n g t h improvements can be o b t a i n e d by CTLA polymer s a t u r a t i o n and subsequent t h e r m a l i n d u c e d p o l y m e r i z a t i o n . The s t r e n g t h i n c r e a s e i s 110 t o 120 7, by p r o l o n g e d h e a t t r e a t m e n t o r about o n e - f o u r t h t o o n e - f i f t h t h a t o f d e l i g n i f i e d f i b r e s t r e n g t h . F u r t h e r e f f e c t s o f o i l p o l y m e r i z a t i o n w i t h groundwood handsheets i s e v i d e n t from T a b l e XXI and X X I I . O i l d i p p i n g o f handsheets" f o l l o w e d ' b y t h e r m a l t r e a t m e n t r a i s e d t e n s i l e s t r e n g t h t o a l e v e l c l o s e l y a p p r o a c h i n g t h a t o f h a n d s h e e t s made from unbeaten h i g h y i e l d k r a f t p u l p . I t i s i n t e r e s t i n g t o n o t e t h a t o i l d i p p i n g a l o n e d e c r e a s e d t e n s i l e s t r e n g t h by 21 % and t e n s i l e energy a b s o r p t i o n by 74 7o. I n c o m p a r i s o n , s t r e n g t h r e d u c t i o n by o i l d i p p i n g was even h i g h e r f o r t h e h i g h l y p u r i f i e d p u l p s ( T a b l e XXII). C o n s e q u e n t l y , s t r e n g t h r e d u c t i o n s seem to be i n v e r s e l y r e l a t e d t o t h e r e s i d u a l l i g n i n con-t e n t o f p a r e n t p u l p s . By c o m p a r i s o n w i t h c h e m i c a l p u l p s t h e s t r e n g t h r e d u c t i o n w i t h groundwood handsheets i s 30 t o 40 7<> h i g h e r t h a n t h a t found on s u l f i t e and k r a f t p u l p s a l t h o u g h the a b s o l u t e l e v e l o f s t r e n g t h r e d u c t i o n was t w i c e as h i g h i n t h e c h e m i c a l p u l p s . Such an e f f e c t i s e v i d e n t l y - d u e t o a s w e l l i n g of f i b r e s by e i t h e r t h e s o l v e n t (benzene) o r some o t h e r o i l i n g r e d i e n t , a p r o c e s s w h i c h w o u l d be e x p e c t e d to lower h y d r o g e n b o n d i n g c a p a c i t y o f groundwood f i b r e s . Thermal p o l y m e r i z a t i o n o f t h e o i l polymer w i t h i n hand-s h e e t s made o f sodium c h l o r i t e d e l i g n i f i e d groundwood p u l p r e s u l t e d i n 8930 p s i t e n s i l e s t r e n g t h w h i c h was o n l y 22 7» h i g h e r t h a n t h e s t r e n g t h o f h a n d s h e e t s -115-made from t h e same t y p e o f f i b r e w i t h o u t o i l s a t u r a t i o n . T h i s f i n d i n g i s e x a c t l y t h e same as r e p o r t e d p r e v i o u s l y f o r d e l i g n i f i e d A s p l u n d p u l p s ( 1 7 9 ) . I t seems t h a t sodium c h l o r i t e t r e a t m e n t o n l y a f f e c t s r e s i d u a l p u l p l i g n i n , t h e r e b y i m p a r t i n g an i n h i b i t i n g e f f e c t on h i g h l i g n i n c o n t e n t f i b r e s . Such b e h a v i o r i s n o t e v i d e n t , however, w i t h h i g h p u r i t y c e l l u l o s e f i b r e s , a l t h o u g h t h e sodium c h l o r i t e t r e a t m e n t r e d u c e d s h e e t s t r e n g t h f o r a l l t y p e s o f p u l p s i n v e s t i g a t e d . These e f f e c t s a r e shown i n T a b l e X X I I . The s t r e n g t h o f i n t e r f i b r e b o n d i n g \ was ., r a i s e d t o such an e x t e n t by t h e r m a l p o l y m e r i z a t i o n o f d r y i n g o i l w i t h i n t h e paper network t h a t c l e a r e v i d e n c e o f e x c l u s i v e f i b r e t e n s i l e f a i l u r e was o b t a i n e d . Depth o f t h e t e n s i l e f r a c t u r e zone was t h e r e b y g r e a t l y reduced; (compare F i g . 7 g t o i ) . The p r o c e s s i s always accompanied by an i n c r e a s e i n s t i f f n e s s ( i n t h i s c a s e the i n c r e a s e was 6 7 % ) , an e f f e c t c l e a r l y o b j e c t i o n a b l e f o r many paper uses r e q u i r i n g h i g h t e a r r e s i s t a n c e and f o l d i n g endurance. F u r t h e r m o r e , such t r e a t e d papers a r e h i g h l y d i s c o l o r e d due t o t h e r m a l o x i d a t i o n o f c o l o r chromophores such as l i g n i n w i t h i n t h e wood p u l p ( F i g . 2 6 ) . b. Gamma-ray i r r a d i a t i o n t r e a t m e n t s U s i n g g a m m a - i r r a d i a t i o n as energy s o u r c e f o r o i l p o l y m e r i z a t i o n w i t h i n t h e paper web gave a 76%, s t r e n g t h i n c r e a s e . T h i s s t r e n g t h i n c r e a s e was produced by a p p l y i n g up t o 10^ r a d i r r a d i a t i o n dosage f o r the p a r t i c u l a r groundwood samples s t u d i e d , a l t h o u g h maximum s t r e n g t h v a l u e s were o b t a i n e d a t lower i r r a d i a t i o n dosages f o r o t h e r p u l p samples and i n o t h e r e x p e r i m e n t s (178) . These r e s u l t s show t h e r a t h e r poor r e p r o d u c i b i l i t y o f -116-p o l y m e r i z a t i o n by i r r a d i a t i o n o f s u p p o s e d l y s i m i l a r m a t e r i a l s as a l s o r e p o r t e d by Rapson and co-workers (84) . Where e x t r a s t r e n g t h r e s u l t s from g r a f t c o p o l y m e r i z a t i o n such i n c o n s i s t e n c y i s m a i n l y a r e s u l t o f r e a c t i o n h e t e r o g e n i t y due t o problems e n c o u n t e r e d i n p e n e t r a t i o n and w e t t i n g o f t h e p a r e n t polymer by t h e s a t u r a n t . I t seems t h a t p e n e t r a t i o n problems a r e much more s e v e r e w i t h c e l l u l o s i c m a t e r i a l s h a v i n g h i g h r e s i d u a l l i g n i n c o n t e n t , p o s s i b l y due t o the h y d r o p h o b i c n a t u r e o f l i g n i n . I t i s a l s o p o s s i b l e t h a t a l i g n i n - o i l c opolymer, i n d u c e d by e i t h e r t h e r m a l o r i r r a d i a t i o n energy, d i s r u p t s c o n t i n u i t y o f t h e o i l polymer w i t h i n bond c o n t a c t a r e a s w i t h o u t r e a l l y c o n t r i b u t i n g t o bond s t r e n g t h . Such copolymer s i t e s may, t h e r e f o r e , a c t as weak l i n k s i n t h e bond i n c r e a s i n g p r o c e s s . Indeed, such s p e c u l a t i o n i s s u p p o r t e d by t h e f a c t t h a t t e n s i l e s t r a i n o f t h e r m a l l y p o l y m e r i z e d samples i n c r e a s e d by 20 "U w h i c h i s about t h e same amount found f o r i r r a d i a t e d o i l s a t u r a t e d s a m p l e s . The i n c r e a s e i n s t r a i n c o u l d be a r e s u l t o f n o n - u n i f o r m energy d i s t r i b u t i o n , i . e . , s t r e s s c o n c e n t r a t i o n s a t f i b r e t o f i b r e c o n t a c t s . A l l s t r e n g t h v a l u e s e v a l u a t e d show an i n c r e a s e w i t h i n c r e a s i n g i r r a d i a t i o n dosage between 10 t o 10"* r a d as e v i d e n c e d i n T a b l e X I I , X I I I , XIV and XV and F i g . 9, 11, 13 and 15. A t 2x10^ r a d i n t e g r a l dosage, however, s t r e n g t h l o s s e s a r e e v i d e n t . I t can be n o t e d , on t h e o t h e r hand, t h a t s t r e n g t h l o s s e s f o l l o w i n g h i g h dosage i r r a d i a t i o n a r e ne v e r as d r a s t i c w i t h groundwood samples as had w i t h c h e m i c a l p u l p s t r e a t e d t o t h e same l e v e l . As d i s c u s s e d e a r l i e r , s t r e n g t h l o s s e s f o l l o w i n g such i r r a d i a t i o n dosage may be due t o l o s s o f i n t r i n s i c f i b r e s t r e n g t h ( 8 6 ) , as r e g u l a t e d by the p r o t e c t i v e e f f e c t o f a r o m a t i c compounds such as l i g n i n on t h e c a r b o h y d r a t e s (70, 70/b, 123,",204) ., -117-As found w i t h wood (42, 86), modulus o f e l a s t i c i t y was a f f e c t e d o n l y by s u b s t a n t i a l i n c r e a s e i n i r r a d i a t i o n dosage. I r r a d i a t i o n o f o i l s a t u r a t e d h a n d s h e e t s , on t h e o t h e r hand, r e s u l t e d i n a 46 7« s t i f f n e s s i n c r e a s e a t 10"* r a d i n t e g r a l dosage. E x p l a n a t i o n s o f t h i s e f f e c t must be sought i n b a s i c s t r u c t u r a l c o n s i d e r a t i o n s o f papermaking wood f i b r e s and h a ndsheets made t h e r e f r o m . A change i n modulus o f e l a s t i c i t y can o n l y t a k e p l a c e i f t h e r e l a t i v e p r o p o r t i o n o f amorphous to c r y s t a l l i n e a r e a i s changed w i t h i n the b a s i c c e l l u l o s e network or i f t h e t o t a l number o f s e c o n d a r y v a l e n c e f o r c e s c o n n e c t i n g t h e c e l l u l o s e m o l e c u l e s and h o l d i n g t h e f i b r e s t o g e t h e r i n a s h e e t o f paper i s changed. S i n c e t h e r e l a t i v e p r o p o r t i o n o f c r y s t a l l i n e t o amorphous c e l l u l o s e i s b e l i e v e d t o r e m a i n unchanged (200) no a d j u s t m e n t i n o v e r a l l d e f o r m a t i o n would be e x p e c t e d . T h e r e f o r e , i f i t i s a c c e p t e d t h a t b o n d i n g i n o i l s a t u r a t e d h a ndsheets i s i n c r e a s e d by c o v a l e n t l i n k a g e s e i t h e r t o c e l l u l o s e or l i g n i n f r a c t i o n s , i t may be p r o j e c t e d t h a t paper s h e e t s made of s u c h r e i n f o r c e d f i b r e s w i l l have much g r e a t e r l o a d b e a r i n g c a p a c i t y and be c a p a b l e o f much g r e a t e r d e f o r m a t i o n w i t h o u t r u p t u r e . T h i s c o u l d be due t o i n c r e a s e d number o f bonds and more u n i f o r m energy d i s t r i b u t i o n w i t h i n t h e paper webs. N o n - l i n e a r i t y o f t h e s t r e s s - s t r a i n d i a g r a m i s t h e r e s u l t o f energy l o s s and f a i l u r e o f i n d i v i d u a l f i b r e t o f i b r e c o n t a c t s under s t r e s s c o n c e n t r a t i o n s due t o n o n - u n i f o r m s t r e s s d i s t r i b u t i o n and f o r m a t i o n o f weak s p o t s i n paper (83, 1 7 6 ) . As a consequence, i n c r e a s e i n paper e l a s t i c i t y s h o u l d be r e f l e c t e d as improved l i n e a r i t y o f the s t r e s s - s t r a i n c u r v e , s i n c e modulus o f e l a s t i c i t y i s c a l c u l a t e d as t h e s l o p e o f t h e i n i t i a l p a r t o f t h e s t r e s s - s t r a i n c u r v e . E q u a l r e s i s t a n c e o f a l l bonds w i t h i n a s h e e t o f paper -118-up to r e l a t i v e l y high external stresses should r e s u l t i n a longer and better defined s t r a i g h t portion in the s t r e s s - s t r a i n curve. The slope of the i n i t i a l s t r a i g h t portion is s t i l l defined by the load bearing capacity of the bonds and uniformity of strength d i s t r i b u t i o n within the f i b r e network. Indeed, i t has been found that the i n i t i a l s t r a i g h t portion of the s t r e s s - s t r a i n curves was greatly increased by i r r a d i a t i o n as o i l polymeriza-t i o n i n i t i a t i n g treatment. Further, this was extended almost to the point of f a i l u r e following further thermal treatment. The combined treatment effects of low dosage i r r a d i a t i o n followed by thermal a f t e r treatment gave p r a c t i c a l l y the same r e s u l t s as had with thermal treatment alone. Lower resultant strength values by i r r a d i a t i o n compared to thermal treatment are believed to be due to incomplete polymerization by i r r a d i a t i o n . This was demonstrated by: 1. r e l a t i o n s h i p between non-extract-able o i l following gamma-irradiation and t e n s i l e strength as shown i n F i g . 18;a "2 . the a d d i t i v e e f f e c t of polymerization by i r r a d i a t i o n followed by thermal treatment. The lower bond strength of i r r a d i a t i o n treated handsheets is demonstrated by a larger proportion of f i b r e pull-outs as compared to other fracture patterns ( F i g . 7, h _vs . i) . From the foregoing i t is clear that groundwood sheet strength can be considerably improved by o i l saturation followed by either i r r a d i a t i o n or thermal polymerization of the saturant within the paper sheet. With i r r a d i a t i o n treatment as energy source for o i l polymerization a dosage l e v e l 2 5 between 10 to 10 rad is required. In such case the strength increase i s more or less an exponential function of logarithm of i r r a d i a t i o n dosage up to 10^ rad i n t e g r a l dosage. - 1 1 9 -L i m i t s o f improvement a r e a p p a r e n t l y s e t by t h e lower e f f i c i e n c y o f i r r a d i a t i o n w i t h i n t h e u s e f u l i r r a d i a t i o n dosage range, as compared to p o l y m e r i z a t i o n by h e a t t r e a t m e n t , and by c h e m i c a l , p h y s i c a l and s t r u c t u r a l c o n s i d e r a t i o n s o f the papermaking f i b r e s . B l e a c h i n g o f groundwood by conven-t i o n a l methods f o l l o w e d by an o i l t r e a t m e n t as proposed w o u l d l e a d t o ground-wood papers o f v e r y h i g h s t r e n g t h and s t i f f n e s s p o s s i b l y c o u p l e d w i t h improved m o i s t u r e r e s i s t a n c e . A t l e a s t 75 "L of t h e maximum s t r e n g t h may be d e v e l o p e d by c o n t i n u o u s p r o c e s s i n g o f such papers w i t h i r r a d i a t i o n s o u r c e s o f h i g h i n t e n s i t y , s i n c e c e l l u l o s e d e g r a d a t i o n depends o n l y on t h e amount o f a b s o r b e d energy a b s o r b e d , but i s i n d e p e n d e n t o f s o u r c e i n t e n s i t y ( 8 4 ) . T h i s s u g g e s t s means f o r c o n t i n u o u s p r o c e s s i n g . Such i r r a d i a t i o n c u r e d o i l s a t u r a t e d groundwood papers have a p l e a s i n g l i g h t brown c o l o r as compared t o t h e l i f e l e s s , d a r k brown c o l o r o f samples c u r e d by p r o l o n g e d h e a t t r e a t m e n t ( F i g . 2 6 ) . 4. P o l y m e r i z a t i o n w i t h S u l f i t e Handsheets The h i g h y i e l d s u l f i t e p u l p used f o r t h i s i n v e s t i g a t i o n c o n t a i n e d 18.98 7„ K l a s o n l i g n i n . As such i t was c o n s i d e r e d t o be r e p r e s e n t a t i v e o f 2 h i g h y i e l d a c i d s u l f i t e p u l p . When formed i n t o s t a n d a r d h a n d s h e e t s o f 60 g/m n o m i n a l b a s i s w e i g h t i t gave a t e n s i l e s t r e n g t h o f 4185 p s i ( T a b l e XII and 3 F i g . 9 ) , a r e l a t i v e l y h i g h modulus o f e l a s t i c i t y a t 460 x 10 p s i ( T a b l e XIII and F i g . 11) and a h i g h t e n s i l e energy a b s o r p t i o n o f 144.2 i n . l b / c m i n . ( T a b l e XV and F i g . 1 5 ) . A l l s t r e n g t h v a l u e s , e x c e p t t e n s i l e s t r a i n ( T a b l e XIV and F i g . 13 ) , a r e t h r e e times h i g h e r t h a n had w i t h groundwood h a n d s h e e t s s u g g e s t i n g b e t t e r i n t e r f i b r e b o n d i n g . The u n t r e a t e d s h e e t s showed some -120-evidence of f i b r e t e n s i l e f a i l u r e s , although f i b r e p u l l - o u t was s t i l l pre-dominant w i t h i n the f r a c t u r e zone ( F i g . 7 j ) . Due to the longer f i b r e s the f r a c t u r e zone i s considerably deepened as compared to f r a c t u r e s observed w i t h groundwood paper. Furthermore, good conformity of f i b r e s i s a l s o evident as i n F i g . 7, j and 1, thereby p r o v i d i n g maximum f i b r e surface f o r i n t e r f i b r e bonding. In s p i t e of the unusually high Klason l i g n i n content of t h i s pulp i t showed higher strength than the high y i e l d k r a f t pulp, a feature contra-d i c t o r y to some e a r l i e r r e p o r t s . a. Thermal treatment O i l d ipping of oven-dry handsheets r e s u l t e d i n a 15 7o drop i n t e n s i l e s t r e n g t h , as w e l l as 23 % r e d u c t i o n i n t e n s i l e energy a b s o r p t i o n . O i l d ipping followed by heat treatment r e s u l t e d i n a 527<, strength increase on an absolute s t r e n g t h b a s i s , the increase being 2200 p s i , almost as much as i n i t i a l s t r e n g t h of the k r a f t paper and twice that of the groundwood paper used i n the study. The thermal p o l y m e r i z a t i o n treatment increased the strength of i n t e r f i b r e bonding to such an extent, that only t e n s i l e f i b r e f a i l u r e s occurred w i t h i n the f r a c t u r e zone. The f r a c t u r e zone was reduced to almost a s i n g l e plane across the t e s t specimen c r o s s - s e c t i o n . A t y p i c a l f r a c t u r e zone f o l l o w i n g thermal p o l y m e r i z a t i o n and t e n s i l e t e s t i n g i s pre-sented i n F i g . 7 1. The d i s c o l o r a t i o n due to o x i d a t i o n and o i l p o l y m e r i z a t i o n of f i b r e surfaces i s e s p e c i a l l y evident on t h i s photomicrograph as a non-lust r o u s appearance. The e f f e c t i s only p a r t i a l l y evident i n F i g . 7 k, where p o l y m e r i z a t i o n i s only p a r t i a l l y completed. I t i s considered that u l t i m a t e t e n s i l e s t r e n g t h i s also p r o p o r t i o n a l -121-t o maximum t e n s i l e s t r e n g t h o f t h e f i b r e s i n c o r p o r a t e d i n t o t h e s e p a p e r s . The h i g h t e n s i l e s t r e n g t h and c o r r e s p o n d i n g l y h i g h modulus o f e l a s t i c i t y i s i n d i c a t i v e o f t h e h i g h bond s t r e n g t h f o l l o w i n g o i l p o l y m e r i z a t i o n w i t h i n s u l f i t e f i b r e webs. There i s no t r e a t m e n t known w h i c h i n c r e a s e s f i b r e b o n d i n g w i t h o u t s e r i o u s l y a f f e c t i n g . i n t r i n s i c f i b r e s t r e n g t h . W i t h o u t this^maximum t e n s i l e s t r e n g t h o f s u l f i t e f i b r e s i n paper webs cannot be measured. b. Gamma-ray i r r a d i a t i o n t r e a t m e n t By u s i n g g a m m a - i r r a d i a t i o n as energy s o u r c e f o r i n i t i a t i n g o i l p o l y m e r i z a t i o n w i t h s u l f i t e papers a 38 % maximum s t r e n g t h i n c r e a s e was o b s e r v e d . T h i s i s a p p r o x i m a t e l y 73 % o f t h a t o b t a i n e d by t h e r m a l p o l y m e r i z a -t i o n ( T a b l e X X I ) . The accompanying i n c r e a s e i n modulus o f e l a s t i c i t y was 29 "L o r 88 7<> o f t h a t had w i t h t h e r m a l p o l y m e r i z a t i o n . I n s p i t e o f lower s t r e n g t h v a l u e s a c h i e v e d by i r r a d i a t i o n p o l y m e r i z a t i o n , t h e t e n s i l e energy a b s o r p t i o n r emained a t t h e same l e v e l as found f o r h i g h e r s t r e n g t h t h e r m a l l y p o l y m e r i z e d p a p e r . I t i s b e l i e v e d t h a t t h i s i s due t o a s l i g h t s w e l l i n g e f f e c t o f u n p o l y m e r i z e d o i l f r a c t i o n s w h i c h p r o v i d e s i n c r e a s e i n s t r a i n . A l t h o u g h s t r e n g t h r e a c h e d o n l y 73 °L o f t h e t h e r m a l maximum t h e r e i s e v i d e n c e o f major f i b r e p u l l - o u t i n f a i l u r e zones o f i r r a d i a t e d specimens ( F i g . 7 k ) . The f a i l u r e i n t h i s case c l o s e l y r e s e m b l e s t h a t found by o t h e r w o r k e r s f o r k r a f t p a p e r s , i . e . , f i b r e t i p s a r e b r o k e n o f f , w h i l e t h e r e s t o f t h e f i b r e i s p u l l e d away i n t e n s i l e r u p t u r e . T h i s may be e x p l a i n e d by con-s i d e r i n g t h a t f i b r e c o l l a p s e may n o t be u n i f o r m a l o n g t h e l e n g t h o f i n d i v i d u a l f i b r e s . The somewhat t h i c k e r f i b r e ends t h e r e f o r e t a k e up a l a r g e r p r o p o r t -i o n o f t h e p r e s s u r e on s h e e t d r y i n g o p e r a t i o n s and may d e v e l o p b e t t e r b o n d i n g -122-w i t h n e i g h b o r i n g f i b r e s . On f u r t h e r i n c r e a s e o f i n t e r f i b r e bond s t r e n g t h the f i b r e t i p s become a n c h o r e d so s t r o n g l y i n t h e paper network t h a t t h e y a r e c a p a b l e o f l a r g e r d e f o r m a t i o n s and d i s t r i b u t i o n o f s t r e s s e s , whereas s t r e s s c o n c e n t r a t i o n s a t such b o n d i n g s u r f a c e s w i l l b r e a k t h e f i b r e s due t o t h e t a p e r e d c r o s s - s e c t i o n . I t t a k e s l e s s energy t o b r e a k t h e f i b r e s i n t e n s i o n t h a n s h e a r a l l bonded a r e a s a l o n g t h e t o t a l f i b r e l e n g t h ( 6 ) . I t i s ex-p e c t e d t h a t i n a p r o c e s s where few f i b r e s f a i l i n t e n s i o n , b u t many f a i l by sh e a r o f f i b r e c o n t a c t s , t h e amount o f t e n s i l e energy a b s o r b e d s h o u l d be h i g h . On t h e o t h e r hand, t h e i n c r e a s e o f s t i f f n e s s may be a s c r i b e d t o d e c r e a s e d m o b i l i t y o f s t r u c t u r a l d e f e c t s . Any h i n d r a n c e t o the m o t i o n o f s t r u c t u r a l elements o r d e f e c t s w i l l r e s u l t i n l e s s dampening r e l a x a t i o n under s t r e s s e s and t h e r e b y i n g r e a t e r s t i f f n e s s . Such change may be l o o k e d upon as an i n c r e a s e i n t h e l e v e l o f i n t e r n a l s t r e s s e s . The modulus o f e l a s t i c i t y , t h e r e f o r e , w i l l r e a c h a maximum w i t h maximum i n t e r n a l s t r e s s e s , i . e . , o b t a i n s h i g h e s t v a l u e under c o n d i t i o n s where t h e number o f bonds b r o k e n i s e s p e c i a l l y h i g h . Thermal t r e a t m e n t f o l l o w i n g i r r a d i a t i o n d i d n o t y i e l d a d d i t i o n a l s t r e n g t h w i t h s u l f i t e p a p e r s , p o s s i b l y due t o t h e h i g h e r demand o f i n t r i n s i c f i b r e s t r e n g t h i n s u l f i t e papers f o l l o w i n g t h e r m a l p o l y m e r i z a t i o n . A l t h o u g h no measurements were c o n d u c t e d , i t i s e x p e c t e d t h a t c e l l u l o s e d e g r a d a t i o n may p r o c e e d a t a f a s t e r r a t e w i t h d e l i g n i f i e d o r p a r t i a l l y d e l i g n i f i e d t i s s u e s t h a n w i t h w h ole wood. The f a c t t h a t l i g n i n c o n t e n t i s minimum i n the s e c o n d a r y w a l l o f s u l f i t e f i b r e s may have a d i r e c t b e a r i n g on c a r b o h y d r a t e d e g r a d a t i o n by g a m m a - i r r a d i a t i o n even a t r e l a t i v e l y low i r r a d i a t i o n dosage -123-l e v e l s . I t i s f u r t h e r p o s s i b l e t h a t t h e g r e a t e r i o n g e n e r a t i n g e f f i c i e n c y o f i r r a d i a t i o n may have caused g r a f t i n g o f t h e o i l polymer t o e i t h e r c e l l u l o s e o r l i g n i n , a p r o c e s s t h a t was s u g g e s t e d e a r l i e r as d e t r i m e n t a l t o l i g n i n b o n d i n g e f f i c i e n c y w i t h t h e o i l p o l y m e r . A t t h e p r e s e n t s t a t e o f knowledge r e g a r d i n g mechanism o f e x t r a s t r e n g t h development by o i l p o l y m e r i z a t i o n w i t h i n paper s h e e t s , i t i s d i f f i -c u l t t o p o i n t out any f a c t o r o r f i b r e c o n s t i t u e n t t h a t d e f i n i t e l y i n f l u e n c e s t h e p r o c e s s . From t h e f o r e g o i n g d i s c u s s i o n i t i s c l e a r , however, t h a t s t r e n g t h g a i n o f o i l s a t u r a t e d paper s h e e t s t r e a t e d by i r r a d i a t i o n i s r e l a t e d t o s u r f a c e c o l l o i d a l p r o p e r t i e s o f t h e f i b r e s and i s l i m i t e d by i n t r i n s i c f i b r e s t r e n g t h . E f f i c i e n c y o f o i l p o l y m e r i z a t i o n by g a m m a - i r r a d i a t i o n seems t o be h i g h e s t on t h e ' s u l f i t e p u l p s w h i c h may be due t o h i g h e r r e a c t i v i t y and b e t t e r m e c h a n i c a l s t r e s s d i s t r i b u t i o n by t h e l o n g e r , b e t t e r c o n f o r m i n g s u l f i t e f i b r e s . c. O t h e r m a t e r i a l s On comparing the e f f i c i e n c y o f o i l p o l y m e r i z a t i o n i n v a r i o u s paper webs a t v a r i o u s l e v e l s , o f c e l l u l o s e p u r i t y , t h e r e seems t o be a r e l a -t i o n s h i p between i n i t i a l s t r e n g t h o f t h e paper and t h a t f o l l o w i n g t h e o i l s a t u r a t i o n and p o l y m e r i z a t i o n t r e a t m e n t ( T a b l e X X I I ) . I n t h i s s e r i e s r e l a t i n g t o s u l f i t e p u l p s s t u d i e s w i t h h i g h a l p h a v i s c o s e p u l p s h o u l d be m e n t i o n e d . S t r e n g t h o f t h e u n t r e a t e d paper made from t h i s p u l p was o n l y 565 p s i . Upon o i l s a t u r a t i o n f o l l o w e d by t h e r m a l p o l y -m e r i z a t i o n a 713 7» i n c r e a s e i n t e n s i l e s t r e n g t h was o b s e r v e d ( T a b l e X X I I ) . T reatment o f t h e i n i t i a l p u l p by a c i d i c sodium c h l o r i t e r e d u c e d t h e u n t r e a t e d -124-paper s t r e n g t h by 68 7«, b u t i n c r e a s e d e f f e c t i v e n e s s o f o i l p o l y m e r i z a t i o n w i t h i n t h e h a n d s h e e t s t o 860 "L. S i m i l a r o b s e r v a t i o n s were made on a TAPPI S t a n d a r d p u l p , r e s u l t s o f w h i c h a r e p r e s e n t e d i n T a b l e X X I I . I n a n o t h e r e x p e r i m e n t , c h e m i c a l l y i n e r t g l a s s f i b r e f i l t e r p a p e r gave low i n i t i a l t e n s i l e s t r e n g t h (6.5 p s i ) , b u t g r e a t l y improved p r o p e r t i e s f o l l o w i n g t h e o i l p o l y m e r i z a t i o n t r e a t m e n t . These r e s u l t s s u g g e s t t h a t t e n s i l e s t r e n g t h o f t h e s e p a r t i c u l a r g l a s s f i b r e s i s 52.% l o w e r t h a n t h a t o f t h e w e a k e s t , h i g h p u r i t y c e l l u l o s e f i b r e s , d i s r e g a r d i n g s h e e t d e n s i t y . S i n c e g l a s s paper f a i l u r e s o c c u r r e d m a i n l y a c r o s s f i b r e s the a b s o l u t e s h e a r s t r e n g t h o f t h e polymer bond c o u l d n o t be e s t i m a t e d . S i m i l a r f a i l u r e s have been o b s e r v e d f o r a l l paper s p e c i m e n s . Thereby, i t i s n o t p o s s i b l e t o t e l l w hether t h e h i g h e r s t r e n g t h v a l u e s o f c h e m i c a l p u l p s a r e due o n l y t o improved a d h e s i o n o f the f i b r e s o r p a r t l y t o a c e l l u l o s e o r l i g n i n g r a f t copolymer w i t h t h e o i l . 5 . P o l y m e r i z a t i o n w i t h K r a f t Handsheets The b e h a v i o r o f k r a f t p u l p i n t h e o i l s a t u r a t i o n and c u r i n g t r e a t -ment was o f p a r t i c u l a r i n t e r e s t i n t h i s s t u d y . The r e s u l t s may be o f i n t e r e s t t o t h e p a c k a g i n g i n d u s t r y , m a i n l y f o r c o n t a i n e r s where h i g h s t r e n g t h , r i g i d -i t y and m o i s t u r e r e s i s t a n c e a r e of p r i m a r y c o n c e r n . S u r f a c e c o l l o i d a l p r o p e r t i e s o f k r a f t f i b r e s have been shown to d i f f e r m a r k e d l y from t h o s e o f s u l f i t e f i b r e s , whereby b e h a v i o r o f k r a f t f i b r e s i n paper s h e e t s has been found to depend on t h e amount o f r e s i d u a l l i g n i n and more r e s i s t a n t h e m i c e l l u l o s e s W i t h i n c r e a s e i n r e s i d u a l l i g n i n t h e b o n d i n g c a p a c i t y o f f i b r e s u s u a l l y de-c r e a s e s , p o s s i b l y because o f the lower c o n f o r m i t y o f h i g h l i g n i n c o n t e n t f i b r e s . -125-On the o t h e r hand, r e t e n t i o n o f h e m i c e l l u l o s e s has been shown t o r a i s e s w e l l -i n g c a p a c i t y o f k r a f t f i b r e s and c o n s e q u e n t l y p r o v i d e l a r g e r d r a w i n g f o r c e s and c l o s e r f i b r e b o n d i n g f o l l o w i n g s h e e t d r y i n g . F o r c o n d e n s a t i o n r e a c t i o n s ( g r a f t i n g ) s p e c i f i c t o l i g n i n t h e r e seems to be good p o s s i b i l i t y f o r i n c r e a s -i n g b o t h i n t r i n s i c f i b r e s t r e n g t h and bond s t r e n g t h due t o r a t h e r u n i f o r m r e s i d u a l l i g n i n d i s t r i b u t i o n o v e r the e n t i r e f i b r e w a l l . Such t r e a t m e n t c o u l d p r o v i d e papers w i t h improved s t r e n g t h , s t i f f n e s s and d i m e n s i o n a l s t a b i l i t y . a. Thermal t r e a t m e n t I t was found t h a t handsheet s t r e n g t h w i t h u n b e a t e n k r a f t p u l p c o n t a i n i n g 9.607= r e s i d u a l K l a s o n l i g n i n c o u l d be i n c r e a s e d as much as 847o on s a t u r a t i o n w i t h CTLA Polymer f o l l o w e d by p r o l o n g e d h e a t t r e a t m e n t . T h i s d i d n o t t a k e f u l l a d vantage o f i n t r i n s i c f i b r e s t r e n g t h as shown i n F i g . 7 o . The f a c t t h a t f a i l u r e f o r the o i l t r e a t e d k r a f t paper was a c o m b i n a t i o n . o f f i b r e b r e a k a g e and i n t e r f i b r e bond s h e a r e x p l a i n s t h e h i g h t e n s i l e energy a b s o r p t i o n v a l u e s found by a n a l y s i s o f s t r e s s - e l o n g a t i o n c u r v e s and r e c o r d e d i n T a b l e XIX and X X I . I t i s c o n c l u d e d t h a t t h e t r e a t m e n t d i d not maximize k r a f t paper s t r e n g t h , p o s s i b l y due t o some s u r f a c e i n h i b i t i o n p r e v e n t i n g t h e . o i l f rom p r o v i d i n g maximum r e i n f o r c e m e n t o f i n t e r f i b r e bond a r e a s . From the f a i l u r e p a t t e r n , however, t h e r e i s s u g g e s t i o n t h a t f u r t h e r s t r e n g t h development might be o b t a i n e d , t o a p o i n t where a l l f a i l u r e w o u l d o c c u r a c r o s s t h e f i b r e s , s i m i l a r t o t h a t o b s e r v e d w i t h papers made from a c i d s u l f i t e p u l p . S t r e n g t h d a t a were o b t a i n e d w i t h paper made from b l e a c h e d k r a f t f i b r e s (Tablel':XX;l5L). T h i s has a d i f f e r e n t s o u r c e t h a n used f o r t h e u n b l e a c h e d k r a f t paper s h e e t s . Removal o f most o f the r e s i d u a l l i g n i n by c o n v e n t i o n a l - 1 2 6 -b l e a c h i n g t e c h n i q u e s may have i n c r e a s e d t e n s i l e s t r e n g t h by 1 0 - 2 0 % , . O i l p o l y m e r i z a t i o n w i t h s u c h papers by p r o l o n g e d h e a t t r e a t m e n t gave a 1387o s t r e n g t h i n c r e a s e w h i c h b r o u g h t a b s o l u t e s t r e n g t h t o a l e v e l n e a r l y 20% h i g h e r t h a n t h a t had w i t h t h e u n b l e a c h e d s u l f i t e paper ( T a b l e X X ) . M i c r o -s c o p i c e x a m i n a t i o n o f f r a c t u r e zones showed t h a t t h e f a i l u r e p a t t e r n was s i m i l a r t o t h a t shown i n F i g . 7 o. T h i s i n d i c a t e s t h a t b o t h f i b r e and bond s t r e n g t h i n k r a f t papers i s i n v e r s e l y a f f e c t e d by p r e s e n c e o f a l k a l i l i g n i n and t h a t t h i s i s d e t r i m e n t a l t o e x t r a s t r e n g t h development on o i l p o l y m e r i z a -t i o n . A l t h o u g h f u r t h e r t r e a t m e n t o f t h e b l e a c h e d k r a f t p u l p by sodium c h l o r i t e l o w e r e d i n i t i a l s h e e t s t r e n g t h by as much as 77%., t h e s t r e n g t h l o s s was r e c o v e r e d on o i l p o l y m e r i z a t i o n t h r o u g h p r o p o r t i o n a l l y h i g h e r s t r e n g t h g a i n s . b. Gamma-ray i r r a d i a t i o n t r e a t m e n t W h i l e s t r e n g t h i n c r e a s e by g a m m a - i r r a d i a t i o n o f o i l t r e a t e d s h e e t s was 73%, f o r s u l f i t e and 697, w i t h groundwood compared t o p o l y m e r i z a t i o n by p r o l o n g e d h e a t t r e a t m e n t , i t was o n l y 50%, f o r k r a f t h a n d s h e e t s . T h i s i s i n l i n e w i t h o b s e r v a t i o n s on t h e r m a l p o l y m e r i z a t i o n . The lower e f f i c i e n c y , however, seems t o be s p e c i f i c t o k r a f t p u l p s as e v i d e n c e d i n F i g . 1 8 . I t i s customary t o examine s u s p e c t e d g r a f t copolymers by s o l u -b i l i t y i n v a r i o u s o r g a n i c s o l v e n t s f o r p r o o f o f c o p o l y m e r i z a t i o n . S i n c e the amount o f g r a f t copolymer found i s u s u a l l y p r o p o r t i o n a l to i r r a d i a t i o n dosage (or amount o f energy a p p l i e d ) , the former i s a l s o f r e q u e n t l y p r o p o r t i o n a l to i n c r e a s e i n t h e p h y s i c a l p r o p e r t y b e i n g measured. S i n c e t h e o i l homopolymer o b t a i n e d on g l a s s f i b r e s was m o s t l y i n s o l u b l e i n o r g a n i c s o l v e n t s t h e r e c i p r o -c a l o f g r a f t i n g ( o r degree o f p o l y m e r i z a t i o n ) was d e t e r m i n e d by e x t r a c t i o n -127-as e x p r e s s e d i n p e r c e n t w e i g h t l o s s o f t h e s a t u r a t e d paper s a m p l e s . The e f f i c i e n c y o f p o l y m e r i z a t i o n t r e a t m e n t became o b v i o u s by r e l a t i n g w e i g h t l o s s e s on e x t r a c t i o n of v a r i o u s t r e a t e d papers t o t e n s i l e s t r e n g t h b e f o r e e x t r a c t i o n . A t t h e same degree o f polymer f o r m a t i o n as had w i t h s u l f i t e p apers the s t r e n g t h d e v e l o p e d w i t h t r e a t e d k r a f t papers was c o n s i d e r a b l y lower and d i d n o t show a s t r a i g h t l i n e r e l a t i o n s h i p ( F i g . 18) .as found f o r b o t h groundwood and s u l f i t e . I t i s i n t e r e s t i n g t o n o t e , t h a t w h i l e the a b s o r b e d , b u t uncured, o i l c o u l d be q u a n t i t a t i v e l y r e c o v e r e d f r o m the g l a s s f i l t e r p a p e r , under t h e e x p e r i m e n t a l c o n d i t i o n s used an i r r e v e r s i b l e a b s o r p t i o n was o b s e r v e d f o r a l l t y p e s o f p u l p f i b r e s as e v i d e n c e d i n T a b l e X. Such i r r e v e r s i b l e a b s o r p t i o n c o u l d n o t be due t o a s i m p l e c a g i n g e f f e c t w i t h i n t h e p a r e n t polymer a l t h o u g h t h e amounts r e t a i n e d were p r a c t i c a l l y t h e same f o r b o t h c h e m i c a l p u l p s , b u t somewhat lo w e r f o r groundwood. The r a t h e r low i n t e r f i b r e bond s t r e n g t h had w i t h t r e a t e d k r a f t p apers i s e v i d e n t from t h e e xtended f r a c t u r e zone as shown i n F i g . 8. I n s p i t e o f t h e 427° i n c r e a s e i n s t r e n g t h f o l l o w i n g o i l p o l y m e r i z a t i o n by i r r a d i a t i o n no change i n f r a c t u r e p a t t e r n was o b s e r v e d ( F i g . 7 n ) . The f u l l e x t e n t o f one h a l f o f a deep f r a c t u r e zone i s p r e s e n t e d i n F i g . 8. From t h e p h o t o m i c r o g r a p h i t i s e v i d e n t t h a t t h e zone extends f a r i n t o t h e paper web, a p p e a r i n g l o n g e r t h a n t h e a v e r a g e f i b r e l e n g t h . Such a p r o c e s s o f f a i l u r e w o u l d be e x p e c t e d t o i n v o l v e s h e a r i n g , o f a l a r g e number o f f i b r e c r o s s i n g s , t h e r e b y c o n t r i b u t i n g t o the r e l a t i v e l y h i g h t e n s i l e energy a b s o r p t i o n had i n c o m b i n a t i o n w i t h l o w e r u l t i m a t e t e n s i l e s t r e n g t h o f such p a p e r s . I n c r e a s e i n modulus o f e l a s t i c i t y on o i l p o l y m e r i z a t i o n s u g g e s t s a r e d u c t i o n i n t h e normal h i g h f o l d i n g endurance o f k r a f t p a p e r s . However, -128-i t was s t i l l o b s e r v e d , t h a t o i l t r e a t e d and c u r e d papers r e t a i n e d a f a i r amount o f p l i a b i l i t y even f o l l o w i n g t h e p r o l o n g e d h e a t t r e a t m e n t . W h i l e f a i l -u r e o f t e n s i l e specimens was a b r u p t f o r groundwood and s u l f i t e papers f o l l o w -i n g t r e a t m e n t , the k r a f t specimens showed more g r a d u a l f a i l u r e p o s s i b l y due t o t h e s low r e l e a s e o f i n t e r f i b r e bonds. S t r e s s - e l o n g a t i o n c u r v e s o b t a i n e d w i t h t r e a t e d k r a f t papers showed o n l y a s h o r t p o r t i o n o f d i r e c t p r o p o r t i o n -a l i t y , as w e l l as a rugged, j i t t e r y curve, i m m e d i a t e l y b e f o r e specimen f a i l -u r e . The l a t t e r p o r t i o n i s e v i d e n t l y due t o f i b r e p u l l - o u t t h r o u g h o u t t h e f r a c t u r e z one. From t h e f o r e g o i n g i t i s e v i d e n t t h a t e x t r a s t r e n g t h development by t r e a t m e n t o f specimens p r e p a r e d from groundwood, s u l f i t e and k r a f t p u l p s can be o b t a i n e d w i t h up t o 707o e f f i c i e n c y when g a m m a - i r r a d i a t i o n i s s u b s t i t u -t e d f o r p r o l o n g e d h i g h t e m p e r a t u r e t r e a t m e n t as energy s o u r c e f o r o i l p o l y m e r i z a t i o n . The e f f i c i e n c y seems t o be r e l a t e d t o b o t h b a s i c paper s t r e n g t h and s t a t e o f r e s i d u a l l i g n i n i n t h a t r e l a t i v e l y h i g h e r s t r e n g t h i n c r e a s e s were r e a l i z e d w i t h papers o f lower u n t r e a t e d s t r e n g t h i n i n c r e a s i n g o r d e r o f groundwood, k r a f t and s u l f i t e . On the o t h e r hand, a v a i l a b i l i t y o f l a r g e r amounts o f l i g n i n on t h e f i b r e s u r f a c e seemed t o a i d s t r e n g t h development f o l l o w i n g p o l y m e r i z a t i o n by g a m m a - i r r a d i a t i o n . Reasons f o r l o w e r p o l y m e r i z a -t i o n e f f i c i e n c y by t h e i r r a d i a t i o n t e c h n i q u e a r e unknown. A t any r a t e , d e g r e e o f p o l y m e r i z a t i o n ( s t r e n g t h i n c r e a s e ) has been shown t o be p r o p o r t i o n a l t o t h e i r r a d i a t i o n dosage ( F i g . 10, 18, T a b l e X V I ) and i s s t r o n g l y r e l a t e d t o b a s i c paper s t r e n g t h . Among o t h e r s t r e n g t h p a r a m e t e r s , modulus o f e l a s t i c i t y ( F i g . 12, T a b l e . X V I I ) and t e n s i l e energy a b s o r p t i o n ( F i g . 16, T a b l e X I X ) f o l l o w i n g p o l y m e r i z a t i o n i n c r e a s e d i n a manner s i m i l a r to t h a t w i t h t h e r m a l t r e a t m e n t . S i n c e t h e s e paramenters a r e more s e n s i t i v e i n d i c e s o f energy d i s t r i b u t i o n w i t h i n -129-s t r e s s e d papers they s u g g e s t c l o s e s i m i l a r i t y o f s i t e s i n v o l v e d i n t h e r e -i n f o r c i n g p r o c e s s as i n d u c e d by t h e two t y p e s o f t r e a t m e n t s . I t i s i n t e r e s t -i n g t o note., t h a t t o t a l a d d i t i v i t y o f p o l y m e r i z a t i o n e f f e c t s by combined t r e a t m e n t s was a c h i e v e d o n l y w i t h t h e h i g h l i g n i n - c o n t e n t groundwood paper, whereas c h e m i c a l p u l p s showed lower s t r e n g t h v a l u e s f o l l o w i n g t h e combined t r e a t m e n t . The r e l a t i v e l y l o w e r s t r e n g t h v a l u e s may be due t o more c e l l u l o s e d e g r a d a t i o n by i r r a d i a t i o n as i n d i c a t e d from r e d u c e d s t r a i n and t e n s i l e e nergy a b s o r p t i o n f o r samples d e s i g n a t e d G m a x . These r e s u l t s seem t o i n d i c a t e a l o w e r degree o f c a r b o h y d r a t e p r o t e c t i o n by r e s i d u a l l i g n i n s i n the c h e m i c a l p u l p s . Based on p r o j e c t i o n s r e g a r d i n g CTLA o i l p o l y m e r i z a t i o n w i t h i n paper webs made from h i g h y i e l d p u l p s , t h e r e l a t i v e l y h i g h s t r e n g t h i n c r e a s e s had w i t h h i g h p u r i t y c e l l u l o s e papers and i n e r t s h e e t s s u c h as g l a s s f i l t e r p a p e r cannot be s a t i s f a c t o r i l y e x p l a i n e d . A p p a r e n t l y , t h e o i l i s c a p a b l e o f homo-p o l y m e r i z a t i o n t o s t r o n g , b r i t t l e , r e s i n - l i k e s u b s t a n c e s w h i c h a r e i n s o l u b l e i n b e n z e n e , t o l u e n e , c h l o r o f o r m , p e t r o l e u m e t h e r and t e t r a h y d r o f u r a n . B o n d i n g between i n e r t g l a s s f i b r e s must e v i d e n t l y depend on s u f f i c i e n t w e t t i n g and a d h e s i o n a t the g l a s s - o i l polymer i n t e r f a c e . W i t h c h e m i c a l l y r e a c t i v e sub-s t a n c e s c o v a l e n t l i n k a g e f o r m a t i o n under f a v o u r a b l e c o n d i t i o n s must be con-s i d e r e d . W i t h h i g h l i g n i n c o n t e n t p u l p s t h e l e v e l o f e x t r a s t r e n g t h i n c r e a s e does n o t exceed 1507o, but i s somewhat l o w e r . A l t h o u g h d e l i g n i f i c a t i o n o f groundwood w i t h sodium c h l o r i t e t o a p p r o x i m a t e l y 157» w e i g h t l o s s i n c r e a s e d u n t r e a t e d paper s t r e n g t h a l m o s t f i v e t i m e s , f u r t h e r t r e a t m e n t by o i l s a t u r a -t i o n and h e a t p o l y m e r i z a t i o n gave o n l y an a d d i t i o n a l 227> s t r e n g t h i n c r e a s e . R e s u l t s o f sodium c h l o r i t e d e l i g n i f i c a t i o n o f A s p l u n d p u l p f o l l o w e d by s h e e t -130-f o r m a t i o n and o i l p o l y m e r i z a t i o n gave s i m i l a r v a l u e s ( 1 7 9 ) . I n f a c t , s u c h low s t r e n g t h i n c r e a s e s were o b s e r v e d qn p u l p s w i t h o n l y 57c w e i g h t l o s s had by m i l d o x i d a t i v e d e l i g n i f i c a t i o n . S i n c e c o m m e r c i a l l y p u r i f i e d p u l p s were no t t e s t e d a t t h a t t i m e , t h e above r e s u l t l e d t o t h e h y p o t h e s e s t h a t o i l p o l y m e r i z a t i o n w i t h i n l i g n i f i e d t i s s u e s i s c h e m i c a l i n n a t u r e and depends on l i g n i n q u a l i t y r a t h e r t h a n l i g n i n q u a n t i t y . F u r t h e r m o r e , the s t r e n g t h o f o i l - t e m p e r e d e x p e r i m e n t a l h a r d b o a r d s was s i g n i f i c a n t l y r e d u c e d when h o t w a t e r s o l u b l e hemlock b a r k t a n n i n s were p r e c i p i t a t e d o n t o t h e A s p l u n d f i b r e p r i o r t o t r e a t m e n t . E v i d e n c e o f a' l i g n i n - t a n n i n c o n d e n s a t i o n was i m m e d i a t e l y e v i d e n t on h o t - p r e s s i n g o f t h e f i b r e mat by development o f t h e c h a r a c t e r i s t i c p u r p l e c o l o r known f o r t h e complex. O t h e r f i b r e t r e a t m e n t s s u c h as h o t c a u s t i c and a l c o h o l - b e n z e n e e x t r a c t i o n s , as w e l l as c e l l u l o s e d e g r a d a t i o n by i r r a d i a t i o n d i d n o t i n f l u e n c e o i l c o n d e n s a t i o n w i t h i n t h e e x p e r i m e n t a l h a r d -b o a r d s t o any d e g r e e . The p r e s e n t s t u d y c o n t a i n e d t h r e e t y p e s o f r e s i d u a l l i g n i n i n f i b r e s . The a l k a l i l i g n i n o f t h e k r a f t p u l p showed l o w e s t r e a c t i v i t y as measured by i n c r e a s e i n t e n s i l e s t r e n g t h f o l l o w i n g t h e i r r a d i a t i o n t r e a t m e n t . W i t h t h i s p u l p t h e r e i s s t i l l room f o r s t r e n g t h improvement as e v i d e n c e d by t h e l a r g e p r o p o r t i o n o f f i b r e p u l l - o u t s w i t h i n t h e f r a c t u r e zone. On t h e o t h e r hand, o i l p o l y m e r i z a t i o n w i t h groundwood and s u l f i t e s h e e t s produced t e n s i l e s t r e n g t h v a l u e s o f "approx|mateily imaiximum s t r e n g t h ; c a p a c i t y ; ! o f t h e i . ' p a r t i c -u l a r f i b r e s . Thereby, i n t r i n s i c f i b r e s t r e n g t h became t h e l i m i t i n g f a c t o r w i t h s u c h paper s h e e t s . The i n c r e a s e d m e t h o x y l c o n t e n t o f i r r a d i a t e d , u n t r e a t e d p u l p s may be a competing mechanism f o r t h e v e r y s i t e o f o i l c o p o l y m e r i z a t i o n w i t h i n and between f i b r e s . R e a c t i v e s i t e s t e r m i n a t e d by a d d i t i o n of m e t h y l r a d i c a l s -131-c o u l d a c c o u n t f o r the lower e f f i c i e n c y o f i r r a d i a t i o n g r a f t i n g compared t o t h a t produced w i t h t h e r m a l c u r i n g . T h i s t h e o r y seems to be s u b s t a n t i a t e d by h i g h e r e x t r a c t a b i l i t y o f o i l r e s i d u e s f o l l o w i n g i r r a d i a t i o n t r e a t m e n t . F u r t h e r , maximum s t r e n g t h was not o b t a i n e d by h e a t t r e a t m e n t o f i r r a d i a t e d samples (Treatment G ) . T h i s i s t o say, t h a t t h e number o f s i t e s a v a i l a b l e f o r bond f o r m a t i o n c o u l d be r e d u c e d by some a s s o c i a t e d f a c t o r o f i r r a d i a t i o n . The e f f e c t appears t o be l e s s pronounced w i t h t h e k r a f t s h e e t s , whereas t h e i n -c r e a s e i n m e t h o x y l c o n t e n t i s h i g h e s t f o r t h i s p u l p (177„) . The i n c r e a s e o f m e t h o x y l c o n t e n t may be due t o f o r m a t i o n o f f o r m a l d e h y d e as d e g r a d a t i o n p r o d u c t from r e s i d u a l l i g n i n (T94) o r c a r b o h y d r a t e s and r e c o n d e n s a t i o n w i t h the same. 6. P o l y m e r i z a t i o n w i t h Handsheets P r e p a r e d from P u l p F i b r e B l e n d s Most p r e v i o u s work done o n e f f e c t o f f i b r e l e n g t h and s h e e t s t r e n g t h p r o p e r t i e s i s n o t a p p l i c a b l e when c h e m i c a l p u l p s a r e mixed w i t h groundwood. T h i s i s due t o the l a r g e d i f f e r e n c e i n b o n d i n g c a p a c i t i e s o f t h e two f i b r e i n g r e d i e n t s . W i t h s u l f i t e p u l p s r e m o v a l o f f i n e s had l i t t l e e f f e c t on r e g u l a r t e n s i l e s t r e n g t h , b u t r e d u c e d s t r e t c h and b u r s t s l i g h t l y as o b s e r v e d by Thode and Ingmanson ( 2 1 9 ) . I n s i m i l a r e x p e r i m e n t s w i t h k r a f t p u l p s , r e m o v a l o f f i n e s s h i f t e d t h e t e a r - t e n s i l e s t r e n g t h r e l a t i o n s h i p i n d i r e c t i o n o f h i g h e r t e a r f o r a g i v e n f i b r e b r e a k i n g l e n g t h . The change was r a t h e r s m a l l by a d d i n g more f i n e s , s i n c e b o n d i n g c a p a c i t y and f l e x i b i l i t y o f t h e f i b r e s was not a l t e r e d m a t e r i a l l y . B l e n d i n g c h e m i c a l f i b r e s w i t h groundwood i n v o l v e s a n o t h e r phenomenon. A l t h o u g h e f f e c t s o f b l e n d i n g have n o t been i n v e s t i g a t e d i n d e t a i l , -132-i n d i c a t i o n s (32) a r e t h a t s t r e n g t h o f t h e r e s u l t i n g p apers i s n o t a d i r e c t f u n c t i o n o f b l e n d i n g between t h e two e x t r e m e s . The b r e a k i n g l o a d o f f i b r e m i x t u r e s i s dependent upon t h e r a t i o o f l o n g f i b r e s t o f i n e s i n t h e m i x t u r e s , as w e l l as upon t h e b r e a k i n g l o a d o f each component. I f t h e s e were t h e o n l y e f f e c t s p r e s e n t w i t h such m i x t u r e s a l i n e a r r e l a t i o n s h i p between b r e a k i n g l o a d and groundwood c o n t e n t w o u l d be e x p e c t e d . The e f f e c t o f f i b r e b l e n d i n g i s examined i n t h e p r e s e n t s t u d y as shown i n F i g . 9 and 10 ( P l o t A ) . The r e l a t i o n s h i p between t e n s i l e s t r e n g t h and e x t e n t o f b l e n d i n g i s e x p o n e n t i a l f o r b o t h s u l f i t e and k r a f t m i x t u r e s . E q u a t i o n s a r e p r e s e n t e d i n T a b l e XX (Eq,;- 1 and 1 7 ) . Thus, t h e r e must be a d d i t i o n a l f a c t o r s i n f l u e n c i n g b r e a k i n g l o a d o f t h e b l e n d s . B r e c h t and E r f u r t (32) s u g g e s t s h e e t d e n s i t y as a c o n t r i b u t i n g f a c t o r , s i n c e d e n s i t y o f the s h e e t i n c r e a s e s w i t h a l a r g e r p r o p o r t i o n o f f i n e s . A l t h o u g h c u r v e s o b t a i n e d f o r t h e two t y p e s o f b l e n d s a r e m i r r o r images ( s u l f i t e ; convex - concave, k r a f t : concave - convex) t h e y b o t h have i n f l e c t i o n p o i n t s a t t h e 50% b l e n d l e v e l . These r e p r e s e n t q u i t e d i f f e r e n t t e n s i l e s t r e n g t h s ( F i g . 9 and 10) w i t h v a l u e s h i g h e r f o r the s u l f i t e - g r o u n d w o o d m i x t u r e . The same h o l d s f o r modulus o f e l a s t i c i t y ( F i g . 11 and 12)., S i m p l e p a r a b o l i c r e l a t i o n s h i p s were o b t a i n e d f o r u l t i m a t e t e n s i l e s t r a i n ( F i g . 13 and 1 4 ) j s i n c e s t r a i n i s g e n e r a l l y h i g h e r f o r t h e s h e e t s c o n t a i n i n g k r a f t f i b r e s . V a r i a t i o n o f t e n s i l e energy a b s o r p t i o n was l i n e a r w i t h i n c r e a s i n g amounts o f groundwood p u l p . S l o p e o f t h e s e r e g r e s s i o n s i s n e g a t i v e , g e n e r a l l y w i t h h i g h e r v a l u e s f o r t h e s u l f i t e - groundwood m i x t u r e s , A d d i t i o n o f s m a l l amounts o f groundwood l o w e r e d t h e s t r e n g t h o f s u l f i t e h a n d s h e e t s d r a s t i c a l l y , p o s s i b l y due t o t h e l a r g e d i f f e r e n c e i n t e n s i l e -133-s t r e n g t h o f the i n d i v i d u a l components. The s t r e n g t h d i f f e r e n c e i s n e a r l y f o u r f o l d f o r s u l f i t e vs.groundwood, whereas i t i s o n l y t w o f o l d f o r u n b e a t e n k r a f t . Thereby, groundwood a d d i t i o n r e d u c e d b o n d i n g o f s u l f i t e p u l p s much more t h a n w i t h k r a f t p u l p s . The g r e a t e r b o n d i n g c a p a c i t y o f s u l f i t e f i b r e s , however, was r e t a i n e d t h r o u g h o u t t h e w h o l e s e r i e s o f m i x t u r e s . I t i s p o s s i b l t h a t t h e h i g h e r t e n s i l e s t r e n g t h o f s u l f i t e papers i s d e r i v e d from f i b r e b r e a k a g e up t o t h e i n f l e c t i o n p o i n t , w h e r e a f t e r t h e s t r e n g t h i s d e t e r m i n e d by t h e s t r e n g t h o f i n t e r f i b r e bonds r a t h e r t h a n t h e f i b r e s t r e n g t h . A t the p o i n t o f 50% m i x t u r e B r e c h t and Klemm (33) found t h a t a l l l o n g f i b r e s were s u r r o u n d e d by f i n e s (groundwood) so t h a t t h e f i n e s a l o n e d e t e r m i n e d the b r e a k i n g l o a d o f t h e s e p a p e r s . They b e l i e v e d t h a t p r o p e r t i e s o f h i g h . y i e l d , l o n g - f i b r e d u n beaten p u l p s a r e , i n p r i n c i p l e , , s i m i l a r t o t h o s e o f groundwood s i n c e t h e l o n g f i b r e s a r e r e l a t i v e l y s t i f f o r b r i t t l e and l i t t l e f i b r i l l a t e d . A c c o r d i n g t o t h e s e f i n d i n g s t h e r e s h o u l d be a s h a r p drop i n t e n s i l e s t r e n g t h at the 50% b l e n d i n g r a t i o . No s u c h phenomena were,,Obseryed;*w;i^ s e r i e s p r e p a r e d f o r t h i s e x p e r i m e n t . S t r e n g t h o f s u l f i t e s h e e t s a t t h e 507= b l e n d l e v e l was about the same as t h a t f o u n d f o r pur e k r a f t h a n dsheets i n t h i s e x p e r i m e n t . I t appears t h a t l o n g f i b r e s c o n t r i b u t e c o n s i d e r a b l y t o paper s t r e n g t h t h r o u g h o u t the w h o l e b l e n d i n g r ange, w i t h l i m i t i n g f a c t o r b e i n g m o s t l y d e t e r m i n e d by the b o n d i n g c a p a c i t y and t o some e x t e n t t h e s t r e n g t h o f the p a r e n t c h e m i c a l p u l p . I t i s o f i n t e r e s t t h a t t h e same r e l a t i o n s h i p h o l d s f o r modulus o f e l a s t i c i t y ( F i g . 11 and 12), and t o some e x t e n t f o r t e n s i l e energy a b s o r p t i o n ( F i g . 15 and 1 6 ) . T e n s i l e s t r a i n p r o p e r t i e s , on the o t h e r hand, a r e q u i t e d i s s i m i l a The lower degree o f a l l o w a b l e d e f o r m a t i o n seems t o be i n d i c a t i v e o f b e t t e r -134-c o n f o r m i t y and more e f f e c t i v e s t r e s s d i s t r i b u t i o n w i t h i n paper webs made from s u l f i t e f i b r e s even i n m i x t u r e s w i t h groundwood ( F i g . 1 3 ) . T h i s i s a l s o e x p e c t e d from the s u b s t a n t i a l l y h i g h e r modulus o f e l a s t i c i t y v a l u e s i n d i c a t e d above. From an i n d u s t r i a l p o i n t o f v i e w t h e above f i n d i n g s have v e r y c r i t i c a l meaning. By t a k i n g t h e c a s e where c e r t a i n s t r e n g t h s t a n d a r d s have t o be met w i t h e i t h e r o f t h e two c h e m i c a l pulp; f u r n i s h e s i t w o u l d be e a s i e r to m a i n t a i n t h e d e s i r e d s t r e n g t h f e a t u r e w i t h k r a f t b l e n d s due t o t h e s m a l l change o v e r t h e 40 t o 707= r a n g e o f groundwood c o n t e n t used as b l e n d . On t h e o t h e r hand, b l e n d i n g p r o p o r t i o n s w o u l d have t o be more e x a c t l y metered w i t h s u l f i t e - groundwood p u l p m i x t u r e s i f p r o p e r t i e s a r e t o be c o n t r o l l e d , due t o t h e r a t h e r , l a r g e s t r e n g t h change ( a p p r o x i m a t e l y 400, p s i f o r every 107. i n c r e a s e i n s u l f i t e p u l p between 30 t o 1007. s u l f i t e p u l p c o n t e n t ) w i t h t h i s s e r i e s . I t s h o u l d be n o t e d , however, t h a t based, on p u l p b e h a v i o r s i m i l a r t o t h e one o b s e r v e d h e r e , i t c o u l d be s t i l l more e c o n o m i c a l t o produce a c e r t a i n paper s t r e n g t h w i t h s u l f i t e - g r o u n d w o o d m i x t u r e due to t h e s u b s t a n t i a l l y h i g h e r s t r e n g t h had f r o m s u c h m i x t u r e s . I n o t h e r words, r e l a t i v e l y s m a l l e r amounts o f e x p e n s i v e c h e m i c a l p u l p w o u l d be n e c e s s a r y t o a c h i e v e a d e s i r e d s t r e n g t h w i t h s u l f i t e - g r o u n d w o o d t h a n w i t h k r a f t - g r o u n d w o o d m i x t u r e s . W i t h i n the i r r a d i a t i o n dosage range i n v e s t i g a t e d no m e a s u r a b l e l o s s i n t e n s i l e s t r e n g t h o c c u r r e d up t o 10^ t o 10-> r a d dosage ( P l o t C, F i g . 9-16). A f t e r s l i g h t i n i t i a l s t r e n g t h i n c r e a s e t h e l o s s was a p p r o x i m a t e l y 21 t o 307, f o l l o w i n g a 2 x 1 0 7 r a d i n t e g r a l i r r a d i a t i o n dosage f o r the s u l f i t e -groundwood s e r i e s . T h i s d e c r e a s e d w i t h i n c r e a s i n g amounts o f groundwood. On t h e o t h e r hand, s t r e n g t h l o s s e s seemed t o have i n c r e a s e d f o r the k r a f t --135-groundwood s e r i e s from 17 t o 21% w i t h i n c r e a s i n g groundwood c o n t e n t . These o b s e r v a t i o n s may be i n l i n e w i t h t h e o r i e s on r a d i o p r o t e c t i o n o f wood c a r b o -h y d r a t e s by l i g n i n , s i n c e a more i n t i m a t e c h e m i c a l m i x t u r e o f wood c a r b o h y d r a t e s w i t h l i g n i n can be e x p e c t e d on l i g n i n g r a f t i n g o n t o c e l l u l o s e f o l l o w i n g a l k a l i n e p u l p i n g as o b s e r v e d by K l e i n e r t (108) . Modulus o f e l a s t i c i t y was r e l a t i v e l y u n a f f e c t e d w i t h i n t h e i r r a d i a t i o n range s t u d i e d . However, b o t h t e n s i l e s t r a i n and energy a b s o r p t i o n f o l l o w e d s i m i l a r p a t t e r n s as had w i t h u l t i m a t e t e n s i l e s t r e n g t h . The e q u a t i o n s c a l c u l a t e d f o r t e n s i l e s t r e n g t h change o f o i l d i p p e d s u l f i t e - and k r a f t - g r o u n d w o o d b l e n d s ( F i g . 9 and 10, P l o t D and E q . 5 and 21) p r e d i c t s t r a i g h t l i n e r e l a t i o n s h i p s f o r b o t h b l e n d s e r i e s a t a s l i g h t l y l o w e r l e v e l t h a n had f o r c o n t r o l specimens ( F i g . 9 and 10, P l o t A ) . R e d u c t i o n i n t e n s i l e s t r e n g t h was n o t f o l l o w e d by modulus o f e l a s t i c i t y ( F i g . 11 and 12), b u t i s e v i d e n c e d by a d e c r e a s e i n t e n s i l e s t r a i n ( F i g . 13 and 14) and t e n s i l e energy a b s o r p t i o n ( F i g . 15 and 1 6 ) . D e c r e a s e i n t e n s i l e s t r e n g t h due t o o i l a b s o r p t i o n has been a s c r i b e d by o t h e r s (146) t o l u b r i c a t i o n o f t h e f i b r e s p e r m i t t i n g e a s i e r d e f o r m a t i o n . I n c r e a s e d d e f o r m a t i o n , however, s h o u l d r e s u l t i n lower modulus o f e l a s t i c i t y and h i g h e r s t r a i n . The f a c t i s , t h a t n e i t h e r l u b r i c a t i o n n o r s w e l l i n g o f t h e polymer network can a c c o u n t f o r t h e h i g h e r modulus o f e l a s t i c i t y s i n c e t h e f i n a l e f f e c t s h o u l d be t h e same i n b o t h c a s e s . -136-a:.\ Thermal, t r e a t m e n t C o n s i d e r a b l e improvements i n a l l s t r e n g t h p r o p e r t i e s were o b s e r v e d f o l l o w i n g t h e r m a l t r e a t m e n t o f o i l d i p p e d h andsheets p r e p a r e d from the p u l p b l e n d s . B e h a v i o r o f the s a t u r a t e d papers were s t r o n g l y a f f e c t e d by p r o p e r t i e s o f the b a s i c p u l p s . T h e r e i s s t r o n g i n d i c a t i o n f rom t h i s t h a t o i l p o l y m e r i z a -t i o n by h e a t i s s t r o n g l y i n f l u e n c e d by l i g n i n q u a l i t y and f i b r e p r o p e r t i e s . As p o s t u l a t e d i n e a r l i e r s e c t i o n s , l i m i t a t i o n s t o o i l p o l y m e r i z a t i o n e f f e c t s appear t o be due t o i n t r i n s i c f i b r e s t r e n g t h i n case o f s u l f i t e f i b r e s , t o s u r f a c e c h e m i s t r y w i t h k r a f t f i b r e s and t o p h y s i c a l l i m i t a t i o n s f o r groundwood f i b r e f r a g m e n t s . The a c t u a l e f f e c t i v e n e s s o f p o l y m e r i z a t i o n i s d i f f i c u l t t o measure w i t h s u l f i t e papers s i n c e p r a c t i c a l l y no i n t e r f i b r e f a i l u r e s o c c u r on t e n s i l e t e s t i n g ( F i g . 7 1) . An e f f e c t i v e n e s s o f 80 t o 85%. i s e s t i m a t e d f o r k r a f t s h e e t s a c c e p t i n g e q u a l i n t r i n s i c f i b r e s t r e n g t h f o r • s u l f i t e arid k r a f t : f i b r e s . Under.! t h e i p r e s e n t c i r c u m s t a n c e s , more t h a n lOO7^'iee^§^E^'S0iit^ei£ft'i.-eticy was e s t i m a t e d f o r groundwood s h e e t s . Change i n t e n s i l e s t r e n g t h o f o i l t r e a t e d s u l f i t e - g r o u n d w o o d s h e e t s shows a s h a r p i n i t i a l d r o p ( F i g . 9 , P l o t E) f o l l o w i n g a d d i t i o n o f s m a l l amounts o f groundwood, p o s s i b l y due t o ease o f weak s p o t f o r m a t i o n i n paper w i t h h e t e r o g e n e o u s groundwood d i s t r i b u t i o n . T h i s l a r g e s e n s i t i v i t y o f t e n s i l e s t r e n g t h t o d i s t u r b a n c e s i n t h e paper network i s due t o t h e f i b r e s t r e n g t h dependence o f o i l p o l y m e r i z e d s u l f i t e papers t o a l e v e l where c h a r a c t e r i s t i c s o f o i l p o l y m e r i z e d groundwood become s t r e n g t h c o n t r o l l i n g f a c t o r s . T h i s o c c u r s between 40 t o 60%, groundwood i n p u l p b l e n d s c o m p r i s i n g t h e h a n d s h e e t s . The same p r o c e s s shows s u r p r i s i n g u n i f o r m i t y o f s t r e n g t h - 1 3 7 -improvement f o r t h e k r a f t-groundwood b l e n d s e r i e s ( F i g . 10> P l o t E . ) , a l m o s t as i f t r e a t e d s h e e t s t r e n g t h depends on f a c t o r s s i m i l a r t o those o f u n t r e a t e d s h e e t s . T h i s a l l o w s .more a c c u r a t e p r e d i c t i o n o f s t r e n g t h improvement due t o o i l p o l y m e r i z a t i o n w i t h i n t h e k r a f t - g r o u n d w o o d s e r i e s . Of i n t e r e s t w i t h r e g a r d t o o i l p o l y m e r i z a t i o n w i t h i n c h e m i c a l pulp-groundwood s h e e t s i s t h e f a c t t h a t a common s t r e n g t h l e v e l can be o b s e r v e d a t 5 0 7 , b l e n d r e g a r d l e s s o f whether s u l f i t e o r k r a f t p u l p i s used f o r b l e n d i n g . The s t r e n g t h i n c r e a s e a t t h i s p o i n t i s o n l y 3 7 7 . f o r s u l f i t e and 1107o f o r the k r a f t s e r i e s . I t i s b e l i e v e d t h a t t h i s r e s u l t i s due t o th e e f f e c t e x e r t e d by o i l polymer r e i n f o r c e m e n t o f i n t e r f i b r e b o n d i n g between l o n g and s h o r t f i b r e s c o m p r i s i n g t h e s e b l e n d s . I t i s a l s o p o s s i b l e t h a t t h e energy r e q u i r e d t o b r e a k a l l t h e f i b r e s i n t e n s i o n w i t h i n a s h e e t c o n t a i n i n g 507o groundwood s t r o n g l y w e l d e d t o t h e c h e m i c a l f i b r e s i s t h e same as t h a t r e q u i r e d f o r p u l l i n g o u t 507= o f k r a f t f i b r e s from the groundwood n e t w o r k . However, comparing r e s u l t s i n T a b l e X V and X I X and F i g . 1 5 and 16 ( P l o t E ) f o r t h e s e samples shows t h a t the t e n s i l e energy a b s o r p t i o n was some 5 0 7 . h i g h e r f o r t h e k r a f t - g r o u n d w o o d s e r i e s f o l l o w i n g o i l p o l y m e r i z a t i o n t h a n had w i t h t h e s u l f i t e -groundwood s e r i e s . F u l l e x p l a n a t i o n r e q u i r e s f u r t h e r t r e a t m e n t o f t h e s e phenomena. Modulus o f e l a s t i c i t y ( F i g . 1 1 and 1 2 , P l o t E ) changed s i g n i f i c a n t l y and i n s i m i l a r f a s h i o n t o t e n s i l e s t r e n g t h , w i t h l a r g e s t improvements o c c u r r i n g w i t h h i g h groundwood-content (up t o 5 0 7 » ) b l e n d s . I t s h o u l d be n o t e d a l s o t h a t w h i l e t e n s i l e s t r a i n d e c r e a s e d i n a r e g u l a r f a s h i o n f o r the k r a f t - g r o u n d w o o d s e r i e s ( F i g . 1 4 ) an i n c r e a s e i s n o t e d w i t h i n c r e a s i n g amounts o f groundwood i n the s u l f i t e b l e n d s e r i e s . ( F i g . 1 3 ) -138-b . Gamma-ray i r r a d i a t i o n t r e a t m e n t Much o f t h a t d i s c u s s e d i n t h e f o r e g o i n g s e c t i o n c o u l d be r e p e a t e d h e r e , s i n c e e f f e c t s had by i r r a d i a t i o n p o l y m e r i z a t i o n w i t h i n s h e e t s made o f b l e n d s between c h e m i c a l p u l p s and groundwood a r e much t h e same as t h o s e w i t h t h e r m a l t r e a t m e n t . Some r e s u l t s a r e more modest. N e v e r t h e l e s s , p r o p e r t i e s from i r r a d i a t i o n o i l p o l y m e r i z a t i o n a r e i n some cases d i r e c t l y comparable t o t h o s e had w i t h p r o l o n g e d h e a t t r e a t m e n t . I n F i g . 9 and 10 maximum t e n s i l e s t r e n g t h v a l u e s o b t a i n e d w i t h i n 10 t o 10^ r a d dosage a r e p l o t t e d ( P l o t F m ) f o r c o m p a r i s o n w i t h e f f e c t s had from t h e r m a l t r e a t m e n t . The same r e s u l t s e x p r e s s e d as per c e n t o f a b s o l u t e s t r e n g t h i n c r e a s e a r e p l o t t e d i n F i g . 17. These p l o t s show p o l y m e r i z a t i o n e f f i c i e n c y by g a m m a - i r r a d i a t i o n f o r b o t h p u l p b l e n d s e r i e s compared t o t h o s e had w i t h t h e r m a l t r e a t m e n t . Thereby, i t i s found t h a t based on a b s o l u t e s t r e n g t h i n c r e a s e o i l p o l y m e r i z a t i o n by i r r a d i a t i o n was l e a s t e f f e c t i v e ( f o r r e a s o n s a l r e a d y d i s c u s s e d ) on s u l f i t e h a n d s h e e t s and most e f f e c t i v e on handsheets made from pure groundwood p u l p . Handsheets p r e p a r e d from k r a f t - g r o u n d w o o d p u l p b l e n d s show an i n t e r m e d i a t e p o s i t i o n . On an a b s o l u t e s t r e n g t h b a s i s , o i l p o l y m e r i z a t i o n by i r r a d i a t i o n was most e f f e c t i v e f o r papers made from s u l f i t e groundwood b l e n d s . However, t h e s e r e q u i r e d h i g h e r l e v e l s o f i r r a d i a t i o n . F o r b o t h t y p e s o f p u l p b l e n d t h e i n c r e a s e i n t e n s i l e s t r e n g t h o f o i l d i p p e d handsheets i n c r e a s e d e x p o n e n t i a w i t h i n c r e a s e i n i n t e g r a l i r r a d i a t i o n dosage as d e s c r i b e d by e q u a t i o n 5 f o r s u l f i t e and e q u a t i o n 21 f o r t h e k r a f t b l e n d s e r i e s ( T a b l e XX ) . 7.)UnfortunateTy t h e r e i s no common b l e n d l e v e l a t w h i c h e f f e c t i v e n e s s o f p o l y m e r i z a t i o n by i r r a d i a t i o n w o u l d be the same f o r the two types o f p u l p m i x t u r e s . I n f a c t , e q u a t i o n 13 p r e d i c t s a 157., h i g h e r s t r e n g t h v a l u e f o r o i l t r e a t e d h a n d s h e e t s - 1 3 9 -made o f pur e groundwood p u l p , s u g g e s t i n g t h e i m p o r t a n c e o f s u l f i t e f i b r e s i n the h i g h groundwood c o n t e n t b l e n d s . Thereby,, on an a b s o l u t e s t r e n g t h b a s i s o i l p o l y m e r i z a t i o n by g a m m a - i r r a d i a t i o n f a v o u r s b l e n d i n g w i t h s u l f i t e p u l p s to such an e x t e n t t h a t a t 607o groundwood c o n t e n t t h e l e v e l o f t e n s i l e s t r e n g t h o b t a i n e d w i t h t h e r m a l t r e a t m e n t o f o i l d i p p e d h a n d s h e e t s i s s u r p a s s e d . T h i s r e s u l t s u g g e s t s t h a t l i g n i n q u a n t i t y may be o n l y o f s e c o n d a r y i m p o r t a n c e f o r t h e p r o p o s e d s t r e n g t h r e i n f o r c e m e n t by o i l c o n d e n s a t i o n . S i n c e s u l f i t e p u l p r e s i d u a l l i g n i n i s r e t a i n e d i n a l e s s degraded and condensed s t a t e t h a n k r a f t p u l p l i g n i n , s u c h r e s p o n s e was e x p e c t e d . S u p e r i o r b e h a v i o r o f r e s i d u a l s u l f i t e l i g n i n may be a s c r i b e d t o a more open s t r u c t u r e , as w e l l as improved h y d r o -p h i l i c p r o p e r t i e s a c q u i r e d d u r i n g p r o c e s s i n g . S i m i l a r p l o t s ( P l o t F m ) a r e produced f o r modulus o f e l a s t i c i t y (Eq. 1 4 and 2 6 ) and t e n s i l e energy a b s o r p t i o n ( Eq. 1 6 and 2 8 ) f o r b o t h t y p e s o f p u l p b l e n d s . P l o t s f o r t e n s i l e s t r a i n a r e not g i v e n , s i n c e c o r r e l a t i o n between t e n s i l e s t r a i n and p u l p b l e n d f o r t h e samples showing maximum t e n s i l e s t r e n g t h w i t h i n 1 0 t o 1 0 ^ r a d i n t e g r a l i r r a d i a t i o n dosage were n o n - s i g n i f i c a n t . S i g n i f i c a n c e o f t r e a t m e n t e f f e c t s on u l t i m a t e t e n s i l e s t r e n g t h was t e s t e d by a combined a n a l y s i s o f v a r i a n c e f o r t h e t h r e e p u l p s . R e s u l t s o f the a n a l y s i s a r e p r e s e n t e d i n T a b l e X I . B o t h t r e a t m e n t s ( b l e n d i n g = Per.} and i r r a d i a t i o n = T r e a t . ) and t h e i r i n t e r a c t i o n had a h i g h l y s i g n i f i c a n t e f f e c t on development o f u l t i m a t e t e n s i l e s t r e n g t h . I n c u r v i l i n e a r r e g r e s s i o n a n a l y s e s , on t h e o t h e r hand, i t was shown t h a t the independent v a r i a b l e s ( b l e n d p er c e n t and i r r a d i a t i o n ) a r e c o m p l e t e l y u n r e l a t e d . The t e n s i l e s t r e n g t h l e v e l r e s u l t i n g from i n t e r a c t i o n o f p u l p t y p e and e x t e n t o f b l e n d i n g was c a l c u l a t e d f r o m t h e a n a l y s i s o f v a r i a n c e f o r b o t h s u l f i t e - a n d k r a f t - groundwood s e r i e s and i s p l o t t e d i n F i g . 1 9 . The -140-h i g h l y s i g n i f i c a n t d i f f e r e n c e between t h e two b l e n d s i s due t o t h e o v e r a l l d i f f e r e n c e i n s l o p e s between any two l e v e l s o f b l e n d i n g . S i g n i f i c a n c e o f t h e s e d i f f e r e n c e s have been d i s c u s s e d i n t h e f o r e g o i n g s e c t i o n s . R e l a t i o n s h i p between dependent v a r i a b l e s i s d e t e r m i n e d by c a l c u l a -t i n g s i m p l e r e g r e s s i o n e q u a t i o n s f o r v a r i o u s groups o f t r e a t m e n t s t h a t appeared as c l o s e g r o u p s . Thus, i t was found t h a t c o n t r o l s ( A ) and i r r a d i a t e d c o n t r o l s (C) formed one group, o i l d i p p e d (D) and i r r a d i a t i o n p o l y m e r i z e d (F) samples formed a n o t h e r group and f i n a l l y t h e r m a l l y , p o l y m e r i z e d ( E ) land i r t a d J b a t i o n p l u s t h e r m a l l y rpo'lymeifi^ed'(G). samples::rep.resented a: t h i r d e d i s t i n c t i v e .grttu.pt. The v a r i o u s r e g r e s s i o n s f o r b o t h p u l p b l e n d s a r e p r e s e n t e d i n F i g , 20 t o 24. R e l a t i o n s h i p s were drawn f o r u l t i m a t e t e n s i l e s t r e n g t h (Y^) v s . modulus o f e l a s t i c i t y ( Y 2 ) , u l t i m a t e t e n s i l e s t r a i n (Y3) and t e n s i l e energy a b s o r p t i o n (Y4) and f o r Y 2 v s . Y3 and Y^. V a l u e s o b t a i n e d f o r t h e h i g h l y i r r a d i a t e d samples (2 x 107 r a d dosage) a r e o m i t t e d from t h e p l o t s s i n c e t h e y f e l l beyond t h e p r e d i c t i o n . Reasons f o r t h i s a r e found i n advanced c e l l u l o s e d e g r a d a t i o n , s i n c e the l o w e r t e n s i l e s t r e n g t h was n o t accompanied by s u b s t a n t i a l change i n modulus o f e l a s t i c i t y . I n t e r e s t i n g l y , t h e l e v e l o f s t r a i n w i t h i n t h e s e samples r e m a i n e d p r a c t i c a l l y c o n s t a n t as t e n s i l e s t r e n g t h i n c r e a s e d t o a maximum. G e n e r a l l y , t h e two t y p e s o f b l e n d s behaved s i m i l a r l y i n t h i s r e g a r d . A s i g n i f i c a n t r e l a t i o n s h i p was o b t a i n e d between t e n s i l e s t r e n g t h and modulus o f e l a s t i c i t y f o r the s u l f i t e - g r o u n d w o o d b l e n d as shown i n F i g . 20. T h i s r e l a t i o n s h i p i s i n d i c a t i v e o f the good b o n d i n g q u a l i t y o f s u l f i t e f i b r e s u sed f o r t h i s e x p e r i m e n t . I t was found t h a t improvement i n t e n s i l e s t r e n g t h on t h e r m a l g r a f t i n g i s p r o p o r t i o n a l t o f i b r e q u a l i t y . W i t h i r r a d i a -t i o n g r a f t i n g t h e r e was a d e f i n i t e i n c r e a s e i n modulus o f e l a s t i c i t y as -141-r e l a t e d t o t e n s i l e s t r e n g t h . T h i s e f f e c t g i v e s e v i d e n c e f o r l o s s i n t e n s i l e s t r e n g t h a t even i n t e r m e d i a t e i r r a d i a t i o n l e v e l s ( p o s s i b l y a t 10^ r a d ) , and has s i g n i f i c a n c e i n t h a t a t t h i s dosage l e v e l c e l l u l o s e d e g r a d a t i o n may have t a k e n p l a c e . R e l a t i o n s h i p s l i k e t h e s e may be o f some a s s i s t a n c e i n d e t e r m i n i n g t h e a l l o w a b l e d e g r a d a t i o n o f p r o d u c t s when exposed t o i r r a d i a t i o n t r e a t m e n t . Trends seem t o be s i m i l a r w i t h k r a f t b l e n d s a l t h o u g h n o t q u i t e as d e c i s i v e . Of i n t e r e s t h e r e i s t h e d i f f e r e n c e i n a v e r a g e s l o p e i n d i c a t i n g a much l a r g e r a l l o w a b l e d e f o r m a t i o n o f bonds w i t h i n t h e k r a f t p apers even a f t e r t h e r m a l p o l y -m e r i z a t i o n . F i g . 20 i s b e l i e v e d t o be a good d e m o n s t r a t i o n o f the w i d e range o f s t r e n g t h paramenters t h a t can be c o v e r e d by b l e n d i n g and t h e pro p o s e d copo"lym§jriza;ti6n p r o c e d u r e . The r a t h e r s t r o n g r e l a t i o n s h i p between Y^ and Y 2 can be o b s e r v e d w i t h a l l r e l a t i o n s h i p s t h e y e n t e r . The s i m i l a r i t y between F i g . 22 and F i g . 24 i s a l s o s t r i k i n g . R e l a t i o n s h i p s w i t h u l t i m a t e t e n s i l e s t r a i n ( F i g . 21 and 23) a r e d i f f i c u l t t o f o l l o w due t o l i m i t e d a c c u r a c y o f s t r a i n measurements. I t i s o b v i o u s , h o w e v e r , t h a t w h i l e t h e r e was l i t t l e change i n s t r a i n p a t t e r n w i t h i n c r e a s i n g t e n s i l e s t r e n g t h ( o r modulus o f e l a s t i c i t y ) f o r t h e s u l f i t e -groundwood samples i n any p a r t i c u l a r t r e a t m e n t , t h e r e was a d e f i n i t e i n c r e a s e i n s t r a i n i n t h e k r a f t - g r o u n d w o o d s a m p l e s . T h i s may be due t o weakened i n t e r f i b r e bonds caused by s w e l l i n g , i f s o l v e n t s w e l l i n g i s a c c e p t e d as more d e t r i m e n t a l t o k r a f t - g r o u n d w o o d i n t e r f i b r e b o n d i n g . I t can a l s o be o b s e r v e d t h a t s u c h s o l v e n t e f f e c t s must be permanent w i t h i n t h e s e t y p e s o f s h e e t s , s i n c e t h e r m a l t r e a t m e n t gave s i m i l a r l y i n c r e a s i n g s t r a i n t o t h a t o b s e r v e d w i t h i r r a -;.diIti%ifi:poiyifie'ri'i£exi s a m p l e s . I t seems t h a t s t r a i n f a l l s o f f r a p i d l y w i t h d e c r e a s e d amounts o f groundwood and i n c r e a s e d amounts o f i r r a d i a t i o n • -142-( F i g . 21, P l o t D and F ) . T e n s i l e energy a b s o r p t i o n i n r e l a t i o n t o t e n s i l e s t r e n g t h and modulus o f e l a s t i c i t y i s i n f l u e n c e d f a v o r a b l y f o r t h e t r e a t e d h i g h groundwood-c o n t e n t s u l f i t e p u l p s and f o r t h e t h e r m a l l y polymerized:tkraft'^pulp'isf.V.LrThi-.s; i s o b v i o u s l y due t o the e f f e c t i v e w e l d i n g e f f e c t by o i l p o l y m e r i z a t i o n . w i t h i n t h e h a n d s h e e t s . Lower r e l a t i v e e f f e c t i v e n e s s o f i r r a d i a t i o n on k r a f t b l e n d s i s a l s o e v i d e n t from F i g . 24. A t t h i s p o i n t i t seems a p p r o p r i a t e t o r e v i e w homopolymer v e r s u s g r a f t copolymer e f f e c t s as shown by t h e s t u d y . R e s u l t s from s o l v e n t e x t r a c t i o n s i n c l u d e d i n t h i s e x p e r i m e n t c e r t a i n l y do n o t p r o v e t h i s p o i n t e i t h e r way, s i n c e t h e homopolymer produced w i t h i n t h e web o f g l a s s f i l t e r p a p e r c o u l d n o t be d i s s o l v e d by u s u a l o r g a n i c s o l v e n t s . F u r t h e r , the l a r g e r s t r e n g t h i n c r e a s e s o b s e r v e d w i t h h a ndsheets made from h i g h p u r i t y c e l l u l o s e f i b r e s and w i t h g l a s s f i l t e r p a p e r s u g g e s t t h a t l i g n i n has d e t r i m e n t a l e f f e c t to e x t r a s t r e n g t h d evelopment. However, i t s h o u l d be remembered t h a t o i l p o l y m e r i z a t i o n i n t h e s e cases was c a r r i e d o u t w i t h h e a t a l o n e . I t i s a l s o p o i n t e d o u t , t h a t t h e o i l i s s u f f i c i e n t l y s t a b l e a t room t e m p e r a t u r e t o p r e v e n t h o m o p o l y m e r i z a -t i o n f o r l o n g p e r i o d s o f t i m e (perhaps one o r two y e a r s ) . E f f e c t s on p o l y m e r i z a t i o n by i r r a d i a t i o n must be due t o f o r m a t i o n o f e i t h e r homopolymer, g r a f t - c o p o l y m e r , o r to: a c o m b i n a t i o n o f t h e s e . 'OHowever ^ iythese cannot be p a r t i t i o n e d from t h e p r e s e n t d a t a . The e f f e c t o f l i g n i n o x i d a t i o n by sodium c h l o r i t e t r e a t m e n t i n A s p l u n d (175) and groundwood p u l p s p o i n t e d toward a c h e m i c a l r e a c t i o n between r e s i d u a l l i g n i n and the d r y i n g o i l . The f a c t t h a t t r e a t e d f i b r e s were s t r o n g l y i n h i b i t e d i n s t r e n g t h r e i n f o r c e m e n t s u g g e s t s l o w e r e d r e a c t i v i t y o f -143-t h e f i b r e s u r f a c e and p r e f e r e n t i a l d e s t r u c t i o n o f l i g n i n r e a c t i v e s i t e s , s i n c e the o x i d a t i o n t r e a t m e n t i s s p e c i f i c t o l i g n i n and when p r o p e r l y p r a c t i c e d has l i t t l e e f f e c t on c a r b o h y d r a t e s . The same was d e m o n s t r a t e d w i t h i n t h i s e x p e r i m e n t . U n f o r t u n a t e l y , p r e f e r e n t i a l a t t a c k o f o x i d i z i n g agent on l i g n i n may have caused an e r r o n e o u s c o n c l u s i o n by K o s h i j i m a and M u r a k i (116), who r e p o r t e d p r o o f f o r a m e t h y l m e t h a c y l a t e - I h y d r o c h l o r i c a c i d l i g n i n copolymer by a p p l i c a t i o n o f a m i l d sodium c h l o r i t e t r e a t m e n t t o t h e c o p o l y m e r . Thereby, t h e g r a f t p o l y m e t h y l m e t h a c r y l a t e was d i s s o l v e d from t h e co p o l y m e r . The s e p a r a t e d p o l y m e t h y l m e t h a c r y l a t e had a m o l e c u l a r w e i g h t a t l e a s t f i f t y - f o l d t h a t d e t e r m i n e d f o r t h e p a r e n t polymer, h y d r o c h l o r i c a c i d l i g n i n . T h u s , i t was c o n c l u d e d t h a t o n l y a few l o n g - c h a i n p o l y m e t h y l m e t h a c r y l a t e m o l e c u l e s were g r a f t e d . o n t o the p a r e n t p o l y m e r . However, f r a g m e n t a t i o n and d e g r a d a t i o n o f t h e p a r e n t polymer by sodium c h l o r i t e c o u l d a l s o l i b e r a t e t h e b r a n c h p o l y m e r . I t i s not known whether r e c o v e r y o f copolymers was q u a n t i t a t i v e o r i n v o l v e d t o t a l d e s t r u c t i o n o f h y d r o c h l o r i c a c i d l i g n i n by sodium c h l o r i t e . The p r e s e n t work c o u l d be expanded i n two main d i r e c t i o n s : 1. F u r t h e r i n v e s t i g a t i o n o f t h e b a s i c p o l y m e r i z a t i o n mechanism by b l o c k i n g c o n c e i v a b l e r e a c t i v e s i t e s on t h e l i g n o c e l l u l o s e i c f i b r e s t h r o u g h a c e t y l a t i o n o r s e l e c t i v e m e t h y l a t i o n , or b o t h . I t i s known (31) t h a t t h e s e t r e a t m e n t s p r o v i d e s u b s t i t u t e d l i g n o c e l l u l o s i c . c p u l p d e r i v a t i v e s , w h e r e i n hydrogens o f p o t e n t i a l p r i m a r y and s e c o n d a r y h y d r o x y l s , as w e l l as c a r b o n y l groups a r e r e p l a c e d by a c e t y l o r m e t h o x y l g r o u p s . P o s s i b l y m e t h y l a t i o n w o u l d be t h e more u s e f u l t r e a t m e n t due t o s e l e c t i v e c o n t r o l o f s i t e s by c h o o s i n g d i f f e r e n t m e t h y l a t i n g a g e n t s . A b r i e f summary o f s e l e c t i v e -144-m e t h y l a t i o n on t h e p h e n y l propane l i g n i n b u i l d i n g u n i t i s p r e s e n t e d i n F i g . 25. T h r e e m e t h y l a t i n g a g e n t s c o u l d be used, diazomethane, aqueous a l k a l i n e d i m e t h y l ;. s u l f a t e and m e t h a n o l - h y d r o c h l o r i c a c i d (17. by v o l u m e ) . Any combina-t i o n o f t h e s e c o u l d p r o v i d e the d e s i r e d d e g r e e o f s u b s t i t u t i o n . The m e t h y l a t i o n t r e a t m e n t s s h o u l d be c a r r i e d o u t on t h e p u l p s a t n o t g r e a t e r t h a n 107. con-s i s t e n c y . I t i s e x p e c t e d t h a t t h e anhydrous c o n d i t i o n s r e q u i r e d f o r diazomethane and m e t h a n o l - h y d r o c h l o r i c a c i d t r e a t m e n t s w o u l d cause p u l p s t r e n g t h l o s s , as w e l l as r e q u i r e e x t e n s i v e w a t e r s o a k i n g b e f o r e handsheet f o r m a t i o n . E f f e c t i v e n e s s o f m e t h y l a t i o n can be f o l l o w e d by d e t e r m i n a t i o n o f m e t h o x y l c o n t e n t o r d e t e r m i n a t i o n o f p h e n o l i c h y d r o x y l s by some s u i t a b l e method. K r a f t p u l p s h o u l d show l o w e r r e a c t i v i t y t h a n e i t h e r s u l f i t e o r groundwood p u l p . Handsheets p r e p a r e d from p u l p s t r e a t e d as d e s c r i b e d s h o u l d be f u r t h e r p r o c e s s e d i n t h e way d e s c r i b e d h e r e i n . Due t o poor r e p r o d u c i b i l i t y o f s t r e n g t h r e s u l t s by a s i n g l e i r r a d i a t i o n dosage, a t l e a s t t h r e e l e v e l s o f i r r a d i a t i o n dosages, i . e . , 10, 10^ and 10^ r a d , s h o u l d be u s e d . C o n t r o l s p e c i m e n s ( s i m i l a r t o Treatment A o f t h i s e x p e r i m e n t ) would be r e q u i r e d . 2. A second avenue o f i n v e s t i g a t i o n c o u l d i n c l u d e m a x i m i z i n g t h e e f f e c t o f s t r e n g t h i n c r e a s e by i r r a d i a t i o n p o l y m e r i z a t i o n o f t h e d r y i n g o i l . T h i s c o u l d i n c l u d e f o r m u l a t i o n o f a more s e l e c t i v e o i l ( p o s s i b l y by gas c h r o m a t o g r a p h i c d e t e r m i n a t i o n o f o i l components b e f o r e and a f t e r i r r a d i a -t i o n , a i d e d by I . R. s p e c t r a ) , r e m o v a l o f s t a b i l i z i n g a g e n t s and i n v e s t i g a -t i o n o f e f f e c t o f p e r o x i d e f o r m a t i o n on i r r a d i a t i o n . Each approach c o u l d c o m p r i s e t h e s u b j e c t o f a s e p a r a t e e x p e r i m e n t . I t w o u l d be hoped t h a t w i t h t h e a i d o f such i n f o r m a t i o n t h e o i l c o p o l y m e r i z a t i o n -145-mechanism c o u l d be a d e q u a t e l y d e s c r i b e d . E f f i c i e n c y o f o i l p o l y m e r i z a t i o n by t h e i r r a d i a t i o n t e c h n i q u e c o u l d be e s t i m a t e d by t h e use o f g l a s s f i l t e r -p aper as a s u b s t r a t e w h i c h r e s i s t s d e g r a d a t i o n by gamma-rays. -146-SUMMARY Means f o r i m p r o v i n g m e c h a n i c a l s t r e n g t h o f papers made from, h i g h y i e l d s u l f i t e , k r a f t and groundwood f i b r e s , as w e l l as b l e n d s o f t h e c h e m i c a l p u l p s w i t h groundwood, a r e d e s c r i b e d . The t r e a t m e n t i n v o l v e s s a t u r a t i o n o f handsheets w i t h CTIA Polymer (a c o m m e r c i a l h y d r o c a r b o n d r y i n g o i l ) and subsequent o i l p o l y m e r i z a t i o n w i t h i n t h e f i b r e webs by h i g h t e m p e r a t u r e h e a t i n g o r by t h e n o v e l method o f g a m m a - i r r a d i a t i o n . E f f e c t s w i t h t h e v a r i o u s t r e a t m e n t s examined i n t h e s t u d y a r e summarized as f o l l o w s : A. I n s p i t e o f t h e r e l a t i v e l y h i g h r e s i d u a l p u l p l i g n i n , hand-s h e e t s made fr o m h i g h y i e l d s u l f i t e f i b r e s gave h i g h e s t t e n s i l e s t r e n g t h and modulus o f e l a s t i c i t y . K r a f t s h e e t s t r e n g t h was s l i g h t l y more t h a n one-h a l f o f t h a t had w i t h s u l f i t e and t w i c e t h a t w i t h groundwood. Lower s t r e n g t h i s a t t r i b u t e d t o weaker i n t e r f i b r e b o n d i n g w i t h i n k r a f t papers and t o poor f i b r e c o n f o r m i t y and low a v e r a g e f i b r e l e n g t h w i t h groundwood. E v i d e n c e f o r lower bond s t r e n g t h i n k r a f t s h e e t s i s i n d i c a t e d by e x c e s s i v e f i b r e p u l l -o u t on f a i l u r e . S i g n i f i c a n t l y d i f f e r e n t e f f e c t s were e x p e r i e n c e d when b l e n d i n g s u l f i t e and k r a f t f i b r e s w i t h groundwood. The h i g h e r b o n d i n g c a p a c i t y o f s u l f i t e f i b r e s was c l e a r l y p r e s e r v e d , even w i t h h i g h groundwood c o n t e n t s h e e t s . B a s i c f i b r e s t r e n g t h was n o t t h e o n l y f a c t o r o p e r a t i n g i n c h e m i c a l p u l p m i x t u r e s w i t h groundwood. -147-B. P r o l o n g e d h e a t i n g (1.5 h r a t 145°C) o f n on-impregnated hand-s h e e t s gave 10 t o 157» i n c r e a s e i n t e n s i l e s t r e n g t h , as w e l l as s l i g h t l y i n c r e a s e d s t i f f n e s s and t e n s i l e energy a b s o r p t i o n . L a r g e s t improvements were o b t a i n e d w i t h t h e more h e a t r e s i s t a n t k r a f t p u l p s f o l l o w e d by s u l f i t e and groundwood. T h i s b e h a v i o r i s p r o b a b l y due t o improved h y d r o g e n b o n d i n g and a d d i t i o n a l c r o s s - l i n k f o r m a t i o n w i t h i n d r y f i b r e webs. C. E x p o s u r e o f n on-impregnated h a n d s h e e t s t o i n c r e a s i n g amounts o f gamma-ray i r r a d i a t i o n had l i t t l e e f f e c t on s h e e t s t r e n g t h p a r a m e t e r s up t o 10^ r a d i n t e g r a l dosage. A t 2 x l 0 7 r a d dosage o n l y s u l f i t e p u l p h a n d s h e e t s were a d v e r s e l y a f f e c t e d , p o s s i b l y due t o advanced c e l l u l o s e d e p o l y m e r i z a t i o n and d e c r e a s e d i n t r i n s i c f i b r e s t r e n g t h . D. O i l s a t u r a t i o n w i t h o u t c u r i n g r e d u c e d t e n s i l e s t r e n g t h by up t o 207,, but s l i g h t l y i n c r e a s e d modulus o f e l a s t i c i t y e s p e c i a l l y f o r t h e low groundwood c o n t e n t k r a f t b l e n d s . S l i g h t r e d u c t i o n s i n u l t i m a t e t e n s i l e s t r a i n and t e n s i l e energy a b s o r p t i o n were a l s o n o t e d . These e f f e c t s a r e b e l i e v e d t o r e s u l t from s w e l l i n g by t h e d i l u t e d o i l (benzene p l u s some o i l component) w h i c h i s c a p a b l e o f w e t t i n g c e l l u l o s e o r l i g n i n . A second f a c t o r , l u b r i c a t i o n o f i n t e r f i b r e bonds, may p e r m i t l a r g e r d e f o r m a t i o n b e f o r e t e n s i l e f a i l u r e . E. No c e l l u l o s e t r e a t m e n t known c o n f e r s a l l p r o p e r t i e s t h a t o c c u r as a r e s u l t o f o i l c o p o l y m e r i z a t i o n w i t h i n f i b r e webs. S u b s t a n t i a l s t r e n g t h i n c r e a s e s were r e c o r d e d f o r a l l t y p e s o f h a ndsheets f o l l o w i n g p r o -l o n g e d t h e r m a l t r e a t m e n t o f o i l s a t u r a t e d s a m p l e s . R e l a t i v e e f f e c t i v e n e s s o f t r e a t m e n t seems t o be l i m i t e d by: 1. s t a t e o f r e s i d u a l l i g n i n and 2. i n t r i n s i c f i b r e s t r e n g t h . Maximum s t r e n g t h was o b t a i n e d on s u l f i t e s h e e t s -148-as e v i d e n c e d by e x c l u s i v e f i b r e f a i l u r e s on t e n s i l e t e s t i n g . B o t h modulus o f e l a s t i c i t y and t e n s i l e energy a b s o r p t i o n were h i g h f o l l o w i n g such t r e a t m e n t . Maximum s t r e n g t h development was a l s o o b s e r v e d w i t h groundwood h a n d s h e e t s , a l t h o u g h o n l y o n e - t h i r d as h i g h as had w i t h u n t r e a t e d h a n d s h e e t s f o l l o w i n g sodium c h l o r i t e d e l i g n i f i c a t i o n o f t h e i n i t i a l p u l p . A l t h o u g h s t r e n g t h o f k r a f t h a n d s h e e t s was a l m o s t d o u b l e t h a t o f u n t r e a t e d s h e e t s , , o n l y p a r t i a l f i b r e f a i l u r e was o b s e r v e d . T h i s s u g g e s t s t h a t c h e m i c a l r e a c t i v i t y o f k r a f t r e s i d u a l l i g n i n i s n o t s u f f i c i e n t t o a l l o w a maximum i n c r e a s e o f bond s t r e n g t h w i t h i n such paper webs. N e v e r t h e l e s s , t h e s t r e n g t h improvements were s u b s t a n t i a l . A common t e n s i l e s t r e n g t h l e v e l was o b s e r v e d w i t h t h e s u l f i t e - and k r a f t-groundwood b l e n d s a t 507» groundwood a d d i t i o n . The p o i n t was r e a c h e d r a p i d l y by i n c r e a s i n g groundwood i n s u l f i t e s h e e t s , due t o the l a r g e d i f f e r e n c e i n b a s i c s h e e t s t r e n g t h s . The s t r e n g t h e q u i l i b r i u m between the two t y p e s o f b l e n d s must be due t o p h y s i c o - c h e m i c a l e f f e c t s a c c e n t u a t e d by t h e t r e a t m e n t and l i m i t e d by i n t r i n s i c f i b r e s t r e n g t h . R e i n f o r c e d bond s t r e n g t h w i t h i n f i b r e webs may a l s o c o n t r i b u t e a d d i t i o n a l s t r e n g t h . I n s u l f i t e - g r o u n d w o o d b l e n d s a l l f i b r e s were b r o k e n i n t e n s i o n . S i n c e groundwood f i b r e s may n o t c o n t r i b u t e more s t r e n g t h t h a n i n p u r e ground-wood s h e e t s , t h e i r p r e s e n c e must promote weak-spot development i n b l e n d e d p a p e r s . Development o f k r a f t - g r o u n d w o o d s h e e t s t r e n g t h was due t o comparable s t r e n g t h c o n t r i b u t i o n s o f i n d i v i d u a l p u l p components. F i b r e b r e a k i n g was found t o o c c u r more e x t e n s i v e l y i n s u l f i t e t h a n k r a f t p a p e r . S i n c e i n t r i n s i c f i b r e s t r e n g t h and bond s t r e n g t h cannot be s e p a r a t e d c o m p l e t e l y w i t h paper webs, o t h e r e v i d e n c e must be u s e d . The l a r g e r number o f f i b r e s b r o k e n i n t e n s i l e t e s t i n g o f t r e a t e d s u l f i t e papers i n d i c a t e d a l a r g e r number o f f i b r e s -149-t a k i n g p a r t i n the s t r e s s d i s t r i b u t i o n as compared t o k r a f t p a p e r s . Modulus o f e l a s t i c i t y o f t r e a t e d papers was r a i s e d t o a v e r y h i g h l e v e l . L i m i t o f p r o p o r t i o n a l i t y on t h e s t r e s s - e l o n g a t i o n c u r v e s was g r e a t l y e x tended f o r such f i b r e webs. F. G a m m a - i r r a d i a t i o n as energy s o u r c e f o r c o p o l y m e r i z a t i o n gave comparable r e s u l t s a l t h o u g h s l i g h t l y 1 ower (30-507,) t h a n p o l y m e r i z a t i o n by t h e r m a l t r e a t m e n t . T e n s i l e s t r e n g t h i n c r e a s e s by t h e r m a l t r e a t m e n t o f o i l i m p r e g n a t e d h a n d s h e e t s were 1187, f o r groundwood, 527. f o r s u l f i t e and 847, f o r k r a f t s h e e t s . V a l u e s were 767,, 387, and 427,, r e s p e c t i v e l y , by gamma-irr ad i a t i o n . E f f i c i e n c y w i t h s u l f i t e papers was d i f f i c u l t t o a s s e s s , s i n c e p r a c t i c a l l y no i n t e r f i b r e f a i l u r e o c c u r r e d on t e n s i l e t e s t i n g f o l l o w i n g o i l p o l y m e r i z a t i o n by t h e r m a l t r e a t m e n t . C o p o l y m e r i z a t i o n e f f i c i e n c y was e s t i m a t e d a t 657. w i t h groundwood, 737, w i t h s u l f i t e and 507. w i t h k r a f t paper s h e e t s i n d i c a t i n g some c o r r e l a t i o n w i t h r e a c t i v i t y o f r e s p e c t i v e f i b r e s u r f a c e s i n p a p e r . Maximum e f f i c i e n c y was o b s e r v e d w i t h an i r r a d i a t i o n dosage below t h a t known t o cause d e t e c t a b l e d e g r a d a t i o n o f wood c a r b o h y d r a t e s . The d i s c o n t i n u o u s s t r u c t u r e o f paper was r e t a i n e d , a l t h q u g h a s l i g h t s w e l l i n g was e v i d e n t w i t h i r r a d i a t i o n p o l y m e r i z e d p a p e r s . Whether no r m a l f i b r e b o n d i n g w i t h h y d r o x y l hydrogens i s d i s r u p t e d by t h e c o p o l y m e r i z a -t i o n t r e a t m e n t , i s n o t known. The i n i t i a l e f f e c t o f s w e l l i n g was e v i d e n t by d e c r e a s e d t e n s i l e s t r e n g t h , i n c r e a s e d e l a s t i c i t y , t e n s i l e s t r a i n and energy a b s o r p t i o n . I t i s p o s s i b l e t h a t t h e h i g h e r s t r e n g t h o f t h e r m a l l y p o l y m e r i z e d samples i s due t o a p a r t i a l f l o w o f CTLA Polymer and r e d u c e d p l a s t i c i z a t i o n t e m p e r a t u r e of the l i g n i n , as w e l l as t o a h i g h e r v a l u e of permanent s e t 'obtained on heating.. J u s t , t o what p r o p a r t i o n V c q v a l e f a t banding:, las - 1 5 0 -compared t o m e c h a n i c a l a d h e s i o n , between t h e l i g n i n - o i l copolymer d s r j f e e s p o n s i b l e f o r t h e i n c r e a s e d s t r e n g t h i n s h e e t s made from h i g h y i e l d p u l p s , was not i n v e s t i g a t e d . Based on e v i d e n c e from sodium c h l o r i t e o x i d a t i o n o f groundwood, a p p r o x i m a t e l y 8 0 7 , o f t h e s t r e n g t h , i n c r e a s e i s due t o c o v a l e n t b o n d i n g and i207o t o m e c h a n i c a l a d h e s i o n by homopolymer f o r m a t i o n between t h e wood f i b r e s , . G. The s y n e r g i s t i c e f f e c t o f o i l p o l y m e r i z a t i o n by g a m m a - i r r a d i a t i o n and t h e r m a l a f t e r - t r e a t m e n t s u g g e s t s a s i m i l a r i t y o f r e a c t i o n end p r o d u c t s a l t h o u g h k i n e t i c s and mechanism o f e x t r a s t r e n g t h development may i n v o l v e e n t i r e l y d i f f e r e n t p r i n c i p l e s . No e f f o r t s were made t o c h a r a c t e r i z e e i t h e r t y p e o f r e a c t i o n . A p p l i c a t i o n o f i r r a d i a t i o n as energy s o u r c e c o u l d r e p l a c e t h e r m a l t r e a t m e n t as b e i n g comparably e f f e c t i v e and f a s t e r , whereby i t i s more s u i t e d f o r c o n t i n u o u s p r o c e s s i n g o f l o n g paper webs. Added advantage o f i r r a d i a t i o n p r o c e s s e d o i l t r e a t e d papers i s l e s s d i s c o l o r a t i o n , e s p e c i a l l y w i t h h i g h l i g n i n c o n t e n t p a p e r s , and lower modulus o f e l a s t i c i t y , a f a c t o r c l e a r l y o b j e c t i o n a b l e f o r some paper u s e s . By use o f g l a s s f i l t e r p a p e r , h i g h l y p u r i f i e d c o m m e r c i a l c e l l u l o s e s and groundwood o x i d a t i o n , a d u a l r o l e o f t h e d r y i n g o i l was d e m o n s t r a t e d . I n th e i n e r t g l a s s f i l t e r p a p e r b o n d i n g i s e v i d e n t l y m e c h a n i c a l a d h e s i o n . I t i s a l s o p o s s i b l e t h a t t h e same t y p e o f bo n d i n g t a k e s p l a c e w i t h h i g h l y p u r i f i e d c e l l u l o s e f i b r e s . L a b o r a t o r y p u r i f i c a t i o n by sodium c h l o r i t e t r e a t m e n t , w h i c h m o s t l y a f f e c t s l i g n i n ( a p p r o x i m a t e l y 507= o f t h e l i g n i n was removed), improved groundwood s h e e t t e n s i l e s t r e n g t h t r e m e n d o u s l y , w h i l e o n l y 227> a d d i t i o n a l s t r e n g t h was o b s e r v e d on hand s h e e t s f o l l o w i n g o i l s a t u r a t i o n and t h e r m a l t r e a t m e n t . T h i s i s i n d i r e c t l i n e w i t h e a r l i e r o b s e r v a t i o n s made by - 151 -t h e a u t h o r (179) on A s p l u n d f i b r e . The same i n h i b i t i n g e f f e c t was n o t o b s e r v e d when h i g h p u r i t y c e l l u l o s e f i b r e s were c h l o r i t e d . As f u r t h e r work, t h e s u b s t i t u t i o n o f r e a c t i v e h y d r o x y l groups i n b o t h c e l l u l o s e a n d l i g n i n by s e l e c t i v e a c e t y l a t i o n and m e t h y l a t i o n and by r e d u c t i o n f o l l o w e d by m e t h y l a t i o n c o u l d b e t t e r r e v e a l i d e n t i t y o f r e a c t i v e s i t e s a n d r e s p e c t i v e r e a c t i v i t i e s o f c e l l u l o s e and l i g n i n towards c o p o l y m e r i z a t i o n w i t h h y d r o c a r b o n d r y i n g o i l s . I f no s i t e i s f ound by t h e s e o r o t h e r means t h e p o s s i b i l i t y o f pure m e c h a n i c a l b o n d i n g would be f a v o u r e d , a l t h o u g h t h e i n h i b i t i o n o b s e r v e d on o x i d a t i o n o f h i g h l i g n i n c o n t e n t m e c h a n i c a l p u l p s would s t i l l have t o be e x p l a i n e d . P a r t i a l s o l u b i l i t y o f t h e o i l s a t u r a n t f o l l o w i n g p o l y m e r i z a t i o n t r e a t m e n t s u g g e s t s c o v a l e n t b o n d i n g between some f i b r e c o n s t i t u e n t and d r y i n g o i l . An e s p e c i a l l y good r e l a t i o n s h i p was o b s e r v e d between o i l f r a c t i o n s r e s i s t i n g e x t r a c t i o n and t e n s i l e s t r e n g t h o f i r r a d i a t i o n p o l y m e r i z e d samples. S i n c e i r r a d i a t i o n has been shown t o r e d u c e u n s a t u r a t i o n o f o l e f i n s and p o l y m e r i z a t i o n r e q u i r e s l a r g e r i r r a d i a t i o n dosages, a r e d u c t i o n i n s o l u b i l i t y a t 10 r a d dosage c o u l d h a r d l y be due t o h o m o p o l y m e r i z a t i o n . However, e x t e n t o f t r u e g r a f t c o p o l y m e r i z a t i o n cannot be d e t e r m i n e d by s i m p l e e x t r a c t i o n t e c h n i q u e s s i n c e t h e homopolymer was a l s o i n s o l u b l e i n t h e u s u a l o r g a n i c s o l v e n t s . A p p l i c a -t i o n o f t h e sodium c h l o r i t e t r e a t m e n t and I.R. s p e c t r a s o f c o l l e c t e d p r e c i p i t a t e s m i g ht be e x p e c t e d t o r e v e a l p r e s e n c e o f l i g n i n f r a g m e n t s w i t h t h e l i b e r a t e d o i l polymer as d e m o n s t r a t e d by K o s h i j i m a and M u r a k i ( 1 1 6 ) . -1*52-CONCLUSIONS O i l p o l y m e r i z a t i o n w i t h i n h a n d s h e e t s made from c h e m i c a l p u l p s , groundwood and c h e m i c a l pulp-groudwood c o m b i n a t i o n s s t r e n g t h e n e d i n t e r -f i b r e b o n d i n g w i t h o u t n o t i c e a b l e e f f e c t on i n t r i n s i c f i b r e s t r e n g t h . W i t h wood f i b r e s e f f e c t i v e n e s s o f t h e t r e a t m e n t as i n i t i a t e d by heat or gamma-ray i r r a d i a t i o n was r e l a t e d t o s u r f a c e c o l l o i d a l and b a s i c f i b r e p r o p e r t i e s . Maximum s t r e n g t h parameters ( u l t i m a t e t e n s i l e s t r e n g t h , e l a s t i c i t y , u l t i m a t e t e n s i l e s t r a i n and t e n s i l e e n e r g y a b s o r p t i o n ) were o b s e r v e d o n l y w i t h s u l f i t e s h e e t s f o l l o w i n g c o p o l y m e r i z a t i o n as r e v e a l e d by t e n s i l e f a i l u r e s . The r e l a t i v e l y l o w e r e f f i c i e n c y i n e x t r a s t r e n g t h development w i t h k r a f t p u l p s 'could be a r e s u l t o f the more condensed n a t u r e o f a l k a l i l i g n i n , as w e l l as o f t h e p r e - e x i s t i n g l i g n i n -c e l l u l o s e g r a f t formed d u r i n g t h e a l k a l i n e p u l p i n g p r o c e s s . T h e r e b y , as a n t i c i p a t e d t h e l i m i t o f s t r e n g t h improvement was n o t s e t e n t i r e l y by i n t r i n s i c f i b r e s t r e n g t h . C o n s e q u e n t l y , the e x p e r i m e n t a l c o p o l y m e r i z e d s u l f i t e f i b r e s w i t h s t a n d 30% more s t r e s s t h a n t h e c o r r e s p o n d i n g k r a f t f i b r e s . T h i s phenomena may be r e l a t e d t o d i f f e r e n c e i n r e a c t i v i t y and s t r a t e g i c l o c a t i o n on o r w i t h i n the f i b r e w a l l r a t h e r t h a n t o d i f f e r e n c e i n the -tqfffA amount o f l i g n i n . Groundwood behaved d i f f e r e n t l y and cannot be compared d i r e c t l y t o c h e m i c a l p u l p s due t o the l i m i t a t i o n o f e x c e s s i v e s h o r t f i b r e f r agments o f low c o n f o r m i t y . 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Chem- Phy s . 42:3315-3319. 238. Y asuda, H., Wray,,J.A. and V. S t a n n e t t . 1963. P r e p a r a t i o n and c h a r a c t e r i z a t i o n of some c e l l u l o s e g r a f t c o p o l y m e r s . P a r t I . J . Polymer S c i . P t . C. 2:387-402. -171-APPENDIX -172-TABLES AND FIGURES T a b l e X I I , Mean u l t i m a t e t e n s i l e s t r e n g t h (psi)CYi) v a l u e s f o r handsheets made from s u l f i t e -groundwood p u l p b l e n d s . Per c e n t groundwood i n handsheet Treatment 0. 10. 20. 30. 40. 50. 60. 70. 80. 90. 100. A 4 1 8 5 1 4234 3600 3655 2899 2553 2229 1956 1457 1308 1230 B 4319 4065 3643 3374 2695 2661 2202 1966 1545 1364 1277 D 3730 3595 3300 2906 2232 2139 1830 1322 1361 1011 1011 CIO' r a d 4543 4079 3536 3616 2783 2611 2158 1987 1592 1344 1283 C l 0 2 r a d 4720 4169 3841 3706 2590 2546 2110 1805 1574 1432 1247 C l 0 3 r a d 4409 4256 3690 3678 2624 2626 2104 1832 1579 1406 1307 C l 0 5 r a d 4342 4151 3621 3418 3068 2343 2073 2105 1613 1379 1204 C 2 x l 0 7 r a d 3249 3300 2919 2831 2353 1992 1639 1554 1270 1125 1090 E 6352 4996 4603 3818 3553 3468 3529 3394 2957 3027 2691 F10 r a d 5239 4488 4153 4172 3185 3160 3147 2872 2387 2373 1987 F 1 0 2 r a d 5768* 4623 4030 4102 3338* 3410 3152* 2740 2535* 2260 2123 F 1 0 3 r a d 5748 5131* 4290 4142 3337 3253 3071 3010* 2316 2104 2085 F 1 0 5 r a d 5658 5014 4392* 4282* 3280 3435* 3015 2689 2419 2242 2166* F 2 x l 0 7 r a d 4270 3627 3253 2908 2537 2429 2671 2155 1907 1923 1881 G10 r a d 5082 4314 4108 4158 3265 2729 3365 3493 2965 2974 2749 G l 0 2 r a d 5335 4634 4356 3920 2988 2735 3207 3398 2854 2683 2518 G 2 x l 0 7 r a d 3877 3521 3278 2572 2237 2392 2375 2332 2051 2233 1850 1. Each v a l u e r e p r e s e n t s an a v e r a g e o f 5 measurements f o r p a r t i c u l a r (X_) b l e n d s . *. Maximum s t r e n g t h v a l u e f o r p a r t i c u l a r ( X i ) b l e n d f o l l o w i n g i r r a d i a t i o n g r a f t i n g ( F m ) . T r e a t m e n t . A. U n t r e a t e d c o n t r o l ; B. Heat t r e a t e d c o n t r o l ; C. I r r a d i a t e d c o n t r o l ; D. O i l d i p p e d c o n t r o l ; E. T h e r m a l l y g r a f t e d ; F. I r r a d i a t i o n g r a f t e d ; G. I r r a d i a t i o n p l u s t h e r m a l l y g r a f t e d . T a b l e X I I I . Mean e l a s t i c i t y ( p s i / 1 0 0 ) ( Y 2 ) v a l u e s f o r handsheets made from s u l f i t e -groundwood p u l p b l e n d s . Per c e n t groundwood i n handsheet (X^) Treatment 0. 10. 20. 30. 40. 50. 60. 70. 80. 90. 100. A 4 6 3 7 1 4562 3933 4124 3457 3035 2627 2259 2083 1619 1534 B .. 4776 4562 4205 3628 2987 2968 2897 2149 1861 1685 1469 D 4961 4718 4332 3717 2973 2754 2598 2019 2063 1495 1584 CIO r a d 4983 4741 4128 3912 3243 3098 2744 2281 2032 1810 1663 C l 0 2 r a d 5143 4631 4313 4314 3182 2906 2583 2283 2005 1851 1675 C l 0 3 r a d 4967 5024 4294 3964 3198 3040 2619 2326 1996 1792 1739 C l 0 5 r a d 4765 4779 4122 3928 3617 3008 2578 2527 2034 1763 1743 C 2 x l 0 ? r a d 5272 4962 4450 4105 3725 2967 2571 2537 2159 1707 1580 E 6184 5034 4447 3822 3356 3370 3339 3139 2705 2825 2566 F10 r a d 5882 5289* 4672 4613* 3622 3432 3171 2862 2414 2340* 2148 F 1 0 2 r a d 5218 5135 4732 4432 3575 3663* 3304* 2717 2500* 2289 2145 F 1 0 3 r a d 5905 5356* 4861* 4502 3767* 3396 3223 3037* 2408 2217 2154 F 1 0 5 r a d 5995* 5242 4807 4221 3717 3637 3164 2878 2405 2338 2242* F 2 x l 0 7 r a d 5840 5287 4887 4215 3334 3359 3438 2979 2563 2511 2290 G10 r a d 5797 4810 4147 4087 3113 3194 3351 3114 2905 2776 2377 G 1 0 2 r a d 5622 4884 4467 3930 3153 3269 3304 3275 2927 2614 2322 G 2 x l 0 7 r a d 6006 4629 4227 3603 3293 3285 2851 2844 2750 2502 2303 1. Each v a l u e r e p r e s e n t s an a v e r a g e o f 5 measurements f o r p a r t i c u l a r (X^) b l e n d s . *. Maximum s t r e n g t h v a l u e f o r p a r t i c u l a r ( X l ) b l e n d f o l l o w i n g i r r a d i a t i o n g r a f t i n g ( F m ) . Tr e a t m e n t : A. U n t r e a t e d c o n t r o l ; B. Heat t r e a t e d c o n t r o l ; C. I r r a d i a t e d c o n t r o l ; D. O i l d i p p e d c o n t r o l ; E. T h e r m a l l y g r a f t e d ; F. I r r a d i a t i o n g r a f t e d ; G. I r r a d i a t i o n p l u s t h e r m a l l y g r a f t e d . T a b l e XIV. Mean v a l u e s f o r u l t i m a t e t e n s i l e s t r a i n ( i n . / i n . ) ^ 1 0 ) (Y^) f o r handsheets made from s u l f i t e - g r o u n d w o o d p u l p b l e n d s . Per c e n t groundwood i n handsheet (X^) irea c m e n c 0. 10. 20. 30. 40. 50. 60. 70. 80. 90. 100. A • 1 7 2 1 .165 .160 .157 .173 .154 .148 .151 .136 .127 .133 B .161 .157 .153 .163 .169 .169 .153 .171 .148 .140 .147 D .162 .178 .173 .177 .169 .156 .147 .146 .120 .116 .106 CIO r a d .169 .170 .147 .165 .178 .170 .139 .160 .141 .115 .142 C 1 0 2 r a d .188 .158 .153 .152 .156 .159 .159 .133 .141 .133 .133 C 1 0 3 r a d .165 .157 .155 .169 .161 .162 .148 .142 .138 .128 .124 C l O ^ r a d .175 .160 .165 .155 .171 .146 .150 .145 .135 .134 .114 C 2 x l 0 7 r a d .087 .083 .090 .097 .090 .097 .095 .093 .087 .097 .086 E .177 .139 .154 .147 .172 .152 .152 .168 .164 .180 .159 F10 r a d .141 .144 .143 .151 .156 .160 .171 .178 .141 .178* .144 F 1 0 2 r a d .172 .148 .127 .158 .173* .167 .158 .174 .141 .159 .164 F l 0 3 r a d .189* .164 .146 .163 .166 .171 .177* .190* .179* .176 .176* F 1 0 5 r a d .168 .173* .158* .177* .172 .177* .174 .171 .169 .177 .174 F 2 x l 0 7 r a d .095 .088 .083 .093 .096 .090 .106 .094 .100 .109 .115 G10 r a d .107 .120 .130 .141 .142 • 123 • 130 .149 • 141 .149 .157 G 1 0 2 r a d .130 .121 .131 .130 .121 .105 .140 .156 .132 .141 .142 G 2 x l 0 7 r a d .077 .087 .094 .081 .080 .083 .100 .096 .088 .089 .101 1. Each v a l u e r e p r e s e n t s an a v e r a g e o f 5 measurements f o r p a r t i c u l a r (X^) b l e n d s . *. Maximum s t r e n g t h v a l u e f o r p a r t i c u l a r ( X i ) b l e n d f o l l o w i n g i r r a d i a t i o n g r a f t i n g ( F m ) . T r e a t m e n t : A. U n t r e a t e d c o n t r o l ; B. Heat t r e a t e d c o n t r o l ; C. I r r a d i a t e d c o n t r o l ; D. O i l d i p p e d c o n t r o l ; E. T h e r m a l l y g r a f t e d ; F. I r r a d i a t i o n g r a f t e d ; G. I r r a d i a t i o n p l u s t h e r m a l l y g r a f t e d . T a b l e XV. Mean v a l u e s o f maximum t e n s i l e energy a b s o r p t i o n ( i n . l b / c u i n . ) (Y_^) f o r handsheets made from s u l f i t e - g r o u n d w o o d p u l p b l e n d s . Per c e n t groundwood i n handsheet (X]_) Treatment 0. 10. 20. 30. 40. 50. 60. 70. 80. 90. 100. A 144.1 126.9 114.7 111.2 99.4 80.5 67.9 53.9 39.7 34.3 33.0 B 131.9 121.0 107 .7 105.5 90.0 83.8 64.2 66.0 40.7 36.4 36.9 D 117 .4 130.4 121.3 107.3 79.7 70.8 55.1 35 .6 35 .3 23.4 18.9 CIO r a d 147.9 135 .0 99.2 111.6 101.9 88.6 59.1 64.7 44.4 30.0 35.2 C 1 0 2 r a d 166.9 143.5 116.2 108.1 80.0 80.1 65.8 46.6 40.9 37 .3 32.8 C 1 0 3 r a d 146.5 121.3 113.8 123.4 82.5 92.1 59.5 51.8 46.3 25.5 33.1 C l O ^ r a d 153.9 130.1 118.1 102.2 107 .5 59.5 53.7 60.7 38.5 36 .9 25 .9 C 2 x l 0 7 r a d 52.1 44.3 47.9 50.6 37.9 35.0 27.6 26.7 31.2 20.8 14.4 E 220.1 125.4 126.4 103.7 110.5 95.5 103 .1 100.8 80.9 97 .4 82.2 F10 r a d 146 .2 125.3 114.7 110.5 103.3 99.2 108.0* 100.2 81.1 89 .0* 53.7 F 1 0 2 r a d 150.2 110.6 95.8 127 .4 121.0* 109.1 98.2 93.0 91.8* 73.5 70.0 F 1 0 3 r a d 220.9* 161.9 121.1 123.6 103.8 118.5 105.7 103 .6* 76.0 77.2 75.6* F 1 0 5 r a d 181.2 168.9* 133.2* 139.8* 112.2 126.0* 103.4 87 .9 69.0 76 .9 74.5 F 2 x l 0 7 r a d 73.7 53.7 46.9 45 .6 43.8 38.3 49.9 37.3 41.9 36.4 38.8 G10 r a d 90.5 96 .4 84.4 91.8 81.1 65 .1 73.5 96.8 61.3 72.3 74.0 G 1 0 2 r a d 121.6 92.5 98.4 84.5 60.5 50.8 79.4 89.5 50.3 52.4 58.1 G 2 x l 0 7 r a d 50.9 46.9 48.3 33.6 29.0 33.5 33.2 33.3 27 .0 27 .9 32.1 1. Each v a l u e r e p r e s e n t s an a v e r a g e o f 5 measurements f o r p a r t i c u l a r (X^) b l e n d s . *. Maximum s t r e n g t h v a l u e f o r p a r t i c u l a r b l e n d f o l l o w i n g i r r a d i a t i o n g r a f t i n g ( F m ) . T r e a t m e n t : A. U n t r e a t e d c o n t r o l ; B. Heat t r e a t e d c o n t r o l ; C. I r r a d i a t e d c o n t r o l ; D. O i l d i p p e d c o n t r o l ; E. T h e r m a l l y g r a f t e d ; F. I r r a d i a t i o n g r a f t e d ; G. I r r a d i a t i o n p l u s . t h e r m a l l y g r a f t e d . T a b l e X V I . Mean u l t i m a t e t e n s i l e s t r e n g t h ( p s i ) (Y^) v a l u e s f o r handsheets made from k r a f t - g r o u n d w o o d p u l p b l e n d s . Per c e n t groundwood i n handsheet (X^) 1 11 "V *"\ 4— m s~\ 4— i r ea ttneiix 0. 10. 20. 30. 40. 50. 60. 70. 80. 90. 100. A 2 6 8 0 1 2214 1951 1919 1705 1661 1678 1605 1138 1203 1230 B 2953 2398 2179 1983 1815 1835 1689 1659 1268 1178 1277 D 2354 1763 1712 1595 1410 1351 1347 1259 1083 1117 1011 CIO r a d 2663 2207 2060 1939 1739 1699 1654 1625 1207 1232 1283 C 1 0 2 r a d 2734 2282 1983 1962 1688 1635 1564 1744 1309 1154 1247 C l 0 3 r a d 2650 2142 1964 1904 1733 1680 1463 1713 1103 1097 1307 C 1 0 5 r a d 2720 2305 1955 1902 1666 1629 1520 1557 1207 1081 1204 C 2 x l 0 7 r a d 2297 1890 1651 1485 1366 1417 1290 1245 945 958 1090 E 4935 4416 4059 3818 3510 3646 3625 3405 2690 2872 2691 F10 r a d 3454 3331 3129 3050 2867* 2607 2453 2466 2136 1952 1987 F 1 0 2 r a d 3817* 3445* 3332* 3300* 2715 2683 2467 2202 1968 1910 2123 F 1 0 3 r a d 3668 3216 3087 3159 2819 2914* 2350 2578* 2219* 2120 2085 F 1 0 5 r a d 3767 3325 3284 3011 2852 2797 2522* 2567 2090 2133* 2166* F 2 x l 0 7 r a d 3175 2747 2557 2466 2235 2206 2248 2090 1744 1784 1881 G10 r a d 4716 4219 3893 3749 3550 3599 3141 3217 2649 2758 2748 G 1 0 2 r a d 4601 3993. 4021 3872 3677 3339 2959 2918 2768 2500 2517 G 2 x l 0 7 r a d 3008 2661 2328 2633 2511 2401 2136 2174 1941 1824 1850 1. Each v a l u e r e p r e s e n t s an a v e r a g e o f 5 measurements f o r p a r t i c u l a r (X].) b l e n d s . *. Maximum s t r e n g t h v a l u e f o r p a r t i c u l a r (X\) b l e n d f o l l o w i n g i r r a d i a t i o n g r a f t i n g ( F m ) . Treatment: A. U n t r e a t e d c o n t r o l ; B. Heat t r e a t e d c o n t r o l ; C. I r r a d i a t e d c o n t r o l ; D. O i l d i p p e d c o n t r o l ; E. T h e r m a l l y g r a f t e d ; F. I r r a d i a t i o n g r a f t e d ; G. I f r a d i a t i o n w p - l u s t h e r m a l l y g r a f t e d . Table XVII. Mean e l a s t i c i t y (psi/100) (Y 2) values for handsheets made from kraft-groundwood pulp blends . Per cent groundwood i n handsheet (X^) Treatment 0. 10. 20. 30. 40. 50. 60. 70. 80. 90. 100. A 2702 1 2623 2162 2154 2113 1926 1915 1848 1530 1406 1534 B 3463 2967 2588 2370 2264 2227 2062 2200 1529 1456 1469 D 3278 2626 2500 2277 2133 2001 2010 2147 1808 1763 1584 CIO rad 3274 2757 2449 2385 2220 2086 2012 2152 1626 1669 1663 C l 0 2 r a d 3292 2766 2450 2423 2053 2032 1867 2166 1725 1576 1675 C10 3rad 3281 2673 2487 2287 2175 2085' 1729 2272 1544 1439 1739 C l 0 5 r a d 3473 2847 2404 2335 2071 2051 1940 1999 1582 1362 1743 C2xl0 7rad 3487 2746 2469 2255 2198 2220 1948 1988 1427 1511 1580 E 4240 3589 3480 3281 2991 3169 3145 2921 2584 2600 2566 F10 rad 3604 3467 3132 2957 2816 2554 2552 2579 2182 2052 2148 F10 2rad 3874 3588* 3340* 3207 2668 2679 2532 2398 2055 1925 2145 F l 0 3 r a d 3850 3319 3258 3210* 2821* 2862* 2904* 2848* 2337* 2242* 2154 F l 0 5 r a d 4035* 3268 3183 2867 2677 2765 2140 2593 2142 2192 2242* F2xl0 7rad 4319 3864 3501 3288 2975 2942 2977 2881 1396 2277 2290 G10 rad 3961 3714 3428 3458 3383 3372 3130 3272 2756" 2664 2377 G10 2rad 3890 3556 3506 3569 3484 3241 3102 3048 2817 2552 2322 G2xl0 7rad 4145 3710 3193 3523 3195 3359 2985 3220 2723 2579 2303 1. Each value represents an average of 5 measurements for p a r t i c u l a r (X^) blends. *. Maximum strength value for p a r t i c u l a r (X^) blend following i r r a d i a t i o n g r a f t i n g ( F m ) . Treatment: A. Untreated co n t r o l ; B. Heat treated control; C. Irradiated control; D. O i l dipped c o n t r o l ; E. Thermally grafted; F. I r r a d i a t i o n grafted; G. Irradiation.plus.:thermally, grafted. T a b l e X V I I I . Mean v a l u e s o f u l t i m a t e t e n s i l e s t r a i n ( i n . / i n . ^ 1 0 ) (Y3) f o r handsheets made from k r a f t - g r o u n d w o o d p u l p b l e n d s . Per cent groundwood i n handsheet (X^) Treatment 0. 10. 20. 30. 40. 50. 60. 70. 80. 90. - 100. A .210 1 .208 .217 .216 .194 .206 .200 .188 .161 .158 .133 B .218 .218 .201 .208 .189 .204 .191 .161 .174 .146 .147 D .192 .181 .190 .199 .177 .179 .155 .140 .135 .135 .106 CIO r a d .204 .189 .198 .204 .198 .190 .174 .160 .151 .147 .142 C l 0 2 r a d .203 .199 .191 .186 .187 .193 .190 .163 .158 .145 .133 C 1 0 3 r a d .175 .186 .195 .205 .184 .193 .185 .159 .157 .139 .124 C l 0 5 r a d .192 .184 .198 .207 .184 .170 .174 .169 .167 .156 .114 C 2 x l 0 7 r a d .117 .116 .116 .111 .105 .115 .110 .098 .105 .100 .086 E .260 .260 .250 .228 .228 .208 .206 .201 .177 .182 .159 F10 r a d .206 .227 .233 .257 .242 .207 .202 .182 .200 .169 . 144 F l 0 2 r a d .255* .256 .288* .298* .253 .264* .233 .197 .216 .192 .164 F 1 0 3 r a d .253 .259 .237 .273 .267* .257 .215 .207 .208 .207* .176* F l O ^ r a d .250 .276* .288 .277 .256 .252 .237* .217* .224* .203 .174 F 2 x l 0 7 r a d .132 .127 .130 .128 .121 .117 .117 .112 .102 .112 .115 G10 r a d .220 .206 .200 .205 .182 .169 .154 .143 .141 .143 .157 G 1 0 2 r a d .212 .207 .210 .189 .178 .165 .144 .139 .138 .138 .142 G 2 x l 0 7 r a d .097 .095 .093 .100 .095 .089 .090 .080 .085 .084 .101 1. Each v a l u e r e p r e s e n t s an a v e r a g e o f 5 measurements f o r p a r t i c u l a r (X]_) b l e n d s . *. Maximum s t r e n g t h v a l u e f o r p a r t i c u l a r ( X i ) b l e n d f o l l o w i n g i r r a d i a t i o n g r a f t i n g ( F m ) . T r e a t m e n t : A. U n t r e a t e d c o n t r o l ; B. Heat t r e a t e d c o n t r o l ; C. I r r a d i a t e d c o n t r o l ; D. O i l d i p p e d c o n t r o l ; E. T h e r m a l l y g r a f t e d ; F. I r r a d i a t i o n g r a f t e d ; G . I r r a d i a t i b t t a p l u s ^ t h e r m a l l y g rafted_. T a b l e X I X . Mean v a l u e s o f maximum t e n s i l e energy a b s o r p t i o n ( i n . l b / c u . i n . ) (Y4) f o r handsheets made from k r a f t - g r o u n d w o o d p u l p b l e n d s . Per cent groundwood i n handsheet Treatment --0. 10. 20. 30. 40. 50. 60. 70. 80. 90. 100. A 117.6 1 103 .3 92.1 92.4 72.6 75 .0 74.3 64.1 39.2 38.2 33.0 B 124.5 110.4 94.7 88.1 73.7 82.9 67.1 57.9 44.6 27.9 36.9 D 101.8 73 .0 73.7 73.1 61.5 56.3 45.6 38.8 32.5 31.6 18.9 CIO rad. 107.2 89.5 96.0 87 .5 78.5 71.6 62.7 54.2 38.2 37.3 35 .2 C 1 0 2 r a d 116.5 100.6 82.0 78.1 65.3 69.0 65 .4 68.9 43.9 34.0 32.8 C l 0 3 r a d 105.9 86 .6 82.5 87 .0 72.9 80.0 66.2 57.1 34.1 36.9 33.2 C l O ^ r a d 114.5 90.9 83.0 83.8 67 .8 58.8 57.4 56.3 40.7 35.3 25.9 C 2 x l 0 7 r a d 50.4 72.8 38.1 32.2 28.3 33.8 27.4 22.6 22.5 20.3 14.5 E 251.9 217 .0 196.8 168.0 154.8 142.0 144.5 125.5 87.4 94.1 82.2 F10 r a d 150.2 158.9 155.1 166.2 147 .8 110.0 109.0 88.9 89.6 68.1 53.7 F l 0 2 r a d 205.7* 214.2* 213.2* 214.7* 154.8 146.5 125.7 91.4 91.2 73.4 70.0 F l O ^ r a d 201.5 178.3 175.9 186.4 160.6* 165.0* 144.8* 112.9 93.8 88. 1* 75.6* F l 0 5 r a d 198.7 202.2 210.7 181.0 158.8 143.1 97 .2 116.4* 99.3* 87.1 74.5 F 2 x l 0 7 r a d 80.2 71.7 69.0 61.7 51.8 49.1 53.4 40.9 34.6 37.3 38.8 G10 r a d 191.7 168.0 150.6 150.9 121.1 112.9 91.5 83.7 69.6 75.0 74.0 G 1 0 2 r a d 180.0 165 .7 174.1 139.7 125.3 106 .1 80.9 73.1 66.5 62.8 58.1 G 2 x l 0 7 r a d 53.3 45.7 39.3 47.9 39.6 40.4 33.6 31.2 30.5 27.5 32.1 1. Each v a l u e r e p r e s e n t s an a v e r a g e o f 5 measurements f o r p a r t i c u l a r (X^) b l e n d s . •*. Maximum s t r e n g t h v a l u e f o r p a r t i c u l a r (X^) b l e n d f o l l o w i n g i r r a d i a t i o n g r a f t i n g ( F m ) . Treatment: A. U n t r e a t e d c o n t r o l ; B. Heat t r e a t e d c o n t r o l ; C. I r r a d i a t e d c o n t r o l ; D, O i l d i p p e d c o n t r o l ; E. T h e r m a l l y g r a f t e d ; F. I r r a d i a t i o n g r a f t e d ; G, I r r a d i a t i o n : p l u s t h e r m a l l y g r a f t e d . -181-Table XX; Equations for calculated response surfaces. Symbols: Y^= Ultimate t e n s i l e strength, p s i . ^2= Modulus of e l a s t i c i t y , psi/100. Y^= Ultimate t e n s i l e s t r a i n , (in/in).10. Y^= Te n s i l e energy absorption, in.lb/eu i n . X x= Pulp blend, %. Log. Radiation dosage, rad. (X )= X]_ vs. Y n plane; (X,.= (Z)= Z.vs. Y n plane. Series: G--SG--S QL ), GR--SGR--SR (X )-(Z.), N= 66. 2 2 1. Y x= 4507.86 - 28.4606X2 - .3631X2 + .1766X^X2 -- 2.6048xJ + .003179X2 • SEE= 156.35 p s i , R = .99028, R 2= .98066. 2. Y 2 = 4973.80 - 28.5883X2 - .36347X2 + .350389X^ + + .0031514X2-SEE = 153.15 psi/100, R = .99171, R 2 • = .98349. 3. Y 3 = .163472 + .0030322X2 - .000003244X2 - .00007458X^2" - .00061297XJ + .000002278X^X2. SEE = .00902 (i n . / i r i . ) . 1 0 , R = .94783, R 2 = .89838 -182-S e r i e s : G--SG--S ( X ^ ; GR--SGR--SR ( X 2 ) = (Z) C o n t i n u e d : 4. Y. = 141.959 - 1.13543X. + 2.3156X 2 - . ^ g g x ^ . + 4 2 1 1 / + , 0 3464Xp : 2 - . 53524XJ . SEE = 9.64 i n . l b / c u i n . . , R = 97414, R 2 - .94894. S e r i e s : GD--SGD--SD ( X ^ , GRT--SGRT--SRT ( X 2 ) = (Z) . N=66. 5. Yl" 3826.36 + 883.615X 1 - 28.0439X 2 = 114.593xJ -- 3 . 0 7 2 9 4 X ^ 2 + .00074254X^X 2 . SEE = 300.76 p s i , R = 96693, R 2 = 93494. 6. Y 2 = 5257.31 + 261.834X 1 - 48.5655X 2 - 27.3388X 2 + + .0013174X 2. SEE = 220.77 p s i / 1 0 0 , R = 98424, R 2 = 96872 7. Y 3 = .15675 + .003979X 2 - .000002575X 2 + .0000007858X^2 - .0007256X 3. SEE = .0135339 '{inV/in ;. ) .,10, R.= .89499, R 2 = .80100. 8. Y 4 = 112.677 + 7.1469X 2 - .010735X 2 + .00579X^2 - 1.1329X 3 + . 0 0 0 2 2 5 9 X ^ - •002274X 2X 2. SEE = 17.871 i n . l b / c u in.., R = .90679, . R 2 = .82226 . -183-S e r i e s : GO--SGO--SO ( x p , GRTH - - SGRTH - - SRTH ( X 2 ) = (Z) .. N=44 . 9. Yx = 5622.90 - 164.311X 1 - 88.4973X 2 + 1.23041X 2 -- .006216X 2. SEE = 287 .29 p s i , R = .9585 R 2 = .91862. 10. Y 2 • 5950.86 - 27.00990^ - 110.196X 2 + 1.5556X 2 . 0 0 8 0 4 7 X 2 < SEE = 164.15 p s i / 1 0 0 , R = .98822, R 2 = .97659. 11. Y 3 = .15333 - .038808X' + .01537X 2 + .00000201X 2 - .001561X^. SEE = .010668 ( i n / . / i n . ). 10, R = .93548, R 2 = .87513. 12. Y. = 168.08 - 114.14X- - 1.6364X 0 + 55.118X 2 + .00772X 2 + 4 1 2 1 Z-+ 1.2696XjX - .7013X 2X 2 - 5.69-lX^. SEE = 15.08 i n . l b / c u i n . , R = .92564 R 2 = .85682. S e r i e s : GRT.--SGRT --SRT ( X . ) ; N= 11. m m m l ' 2 13. Y x = 5655.87 - 57.942X 1 + .23989X^, SEE = 195.58 p s i , R = .9773, R 2 = .9545. -184-S e r i e s : GRT --SGRT --SRT ( X , ) : C o n t i n u e d : m m m l 14. Y 2= 5951.61 - 57.204X 1 + .19655X 2. SEE= 116 .28 p s i / 1 0 0 , R= .9932, R 2 = .9865, 15. Y.j = N o n - s i g n i f i c a n t r e g r e s s i o n , 16. Y, = 213.66 - 4.56778X. + 7.2108X 2 - 406.69X? 4 1 1 1 SEE = 9.61 i n , . l b / c u i n . , R = .9615, R 2 = .9253. S e r i e s : G--KG--K ( X ^ , GR--KGR--KR ( X 2 ) = (Z) . N=66 17. Y x = 2629.12 - 3 5 . 2 3 3 7 X 2 + .4148X 2 - .80955X^ • - .002062X 2-SEE = 120.49 p s i , R = .96648, „ R 2 = .93408. 18. Y 2 = 3056.09 + 40.0408X 1 - 41.4928X 2 + .52704X 2 - .56911X^2 - .002603X 2. SEE = 168 .27 p s i / 1 0 0 , R = .94968, R 2 = .90189. 19. Y 3 = .215269 - •02023X 1 + .00793X 2 - .000007028X 2 - .0009497X^4- .000 000 000 107X^X 2. SEE = .008889 ( i n . / i r i . ) . 10, R = .97026, R 2 + .94141. -185-S e r i e s : G--KG--K ( X ^ , GR--KGR--KR (X 2> = (Z) . C o n t i n u e d ; 20. Y 4 = 110.57 - .7991X 2 - .1242X^+ .00006370X 2X 2. SEE = 7.364 i n . l b / c u i n . , R = .96465, . R 2 = .93055. S e r i e s : GD--KGD--KD ( X ^ , GRT - - KGRT - - KRT ( X 2 ) = (Z) . N=66 21. Y L = 2318.97 + 1 0 3 8 . 5 ^ - 14.864LX 2 - 243.06X 2 + + 15 .696 X 3 . SEE = 231.71 p s i , R = .94548, R 2 = .89394. 22. Y 2 = 3155.96 + 156-.573X - 17.1211X 2 + 4.8819X^2 - 2 . 1 9 6 7 X 2 X 2 + .1474X 3X 2 + .003861X 2X 2. SEE = 251.983 p s i / 1 0 0 , R = .92458, R 2 = .85484. 23. Y 3 = .2030+ .03117X 1 - .00000968X 2 - .000769X 3 + + .ooo ooo m s x ^ 2 . SEE = 0164 ( i n . / i n . ) . 1 0 , R = .95684 R 2 = .91555 24. Y. = 101.28 + 69.703X, - .7819X„ - 9.9704X? 4 1 2 1 - .004643X^2 + .0007023X 2X 2. SEE = 14.74. , i n . l b / c u i n . , R.= .96873, R 2 = .93843. - 1 8 6 -S e r i e s : G R T — K G R T - - K R T ( X . . ) . N = l l . m m m l 2 5 . Yl = 3 6 9 1 . 6 7 - 1 6 . 9 3 8 X 1 SEE = 1 2 2 . 1 5 p s i , R = . 9 5 9 1 8 , R 2 = . 9 1 9 8 . 2 6 . Y 2 = 3 7 1 5 . 5 0 - 1 5 . 6 3 2 X 1 SEE = 1 5 1 . 1 1 p s i / 1 0 0 , R = . 9 2 8 7 , R 2 = . 8 6 4 6 . 2 7 . Y 3 = Non s i g n i f i c a n t r e g r e s s i o n 2 8 . Y 4 = 2 1 8 . 2 1 - 3 . 2 2 9 X 2 + 1 7 8 . 6 4 5 X ^ J.l.SEE = 1 1 / 2 8 i n , l b / c u i n , , R = . 9 6 4 4 8 , R 2 = . 9 3 0 2 . S e r i e s : G 0 - - K G 0 - - K 0 ( X 1 ) , G R T H - - K G R T H - - K R T H ( X 2 ) = ( Z ) . N = 4 4 . 2 9 . Yl = 4 8 1 8 . 9 2 - 2 5 0 . 7 8 2 X 1 - 2 7 . 7 5 9 6 X 2 + . 0 6 5 8 4 X 2 + + 1 . 3 8 6 2 X ^ 2 . SEE = 1 7 1 . 4 6 2 p s i , R = . 9 7 8 6 3 , R 2 = . 9 5 7 7 1 . 3 0 . Y 2 = 3 9 9 0 . 0 6 - 3 8 . 5 3 4 5 X 2 + . 0 5 8 6 6 9 X 2 + 7 . 1 2 6 6 X ^ 2 -. 0 6 7 8 9 X ^ 2 - . 8 7 2 6 X 2 X 2 r . 0 0 3 5 8 3 X 2 + . O O l l O l X ^ X 2 R SEE = 1 3 8 . 1 3 p s i / 1 0 0 , = . 9 6 4 3 3 , R 2 = . 9 2 9 9 4 . -187-S e r i e s : . GO--KGO--KO ( X ^ , GRTH--KGRTH--KRTH ( X ^ = (Z) . C o n t i n u e d 31. Y 3 = .26028 - .06238X 1 - .00091662X 2 + .02453X 2 -- .002576X 3 + .000 000 1 4 9 1 X 2 X 2 . SEE = .00932 f(inO / i iriv)).,10, R = .98582, R 2 = .97185. 32. Y, = 235.964 - 31.571X. - 2.2018X o + 1.02377X 2 + 4 1 2 1 + .006165X 2 + .1834 8 X ^ 2 . SEE = 17.5832 i n . l b / c u i n . , R = . 9451 , R 2 = .8938 . Table XXI. E f f e c t of thermal and i r r a d i a t i o n g r a f t i n g on strength properties of handsheets made from the three basic pulp types. Sample Max. Tens i l e Strength Strength Increase from A B D Modulus of E l a s t i c i t y Strength Increase from A B D U l t . Tens . St r a i n Strength Increase from A B D Max.Tens. Energy Lbs . Strength Increase from A B D ps i 7= 7c 7c 100 p s i 7c 7c 7, i n / i n 7c 7c 7, i n lb/cu in 7= 7c 7„ A B D G C max E F max G max 1230 1277 1012 1307 2691 2166 2749 + 4 -- 21 + 6 + 118 +110 +165 +76 - +114 + 124 +116 +172 1534 1469 1584 1743 2566 2242 2377 _ 4 + 3 -+ 14 +67 +74 +62 +46 - +42 +55 +61 +50 .133 .147 .106 .142 .159 .176 .157 + 10 +25 + 6 -+20 + 8 +50 +32 - +66 + 18 + 7 +48 33.0 36.9 18.9 35 .2 82.2 75.6 74.1 + 9 - -74 + 6 -+ 149 +123 +335 +129 - +300 +125 +201 +292 A B D S C max E F max G max 4185 4319 3730 4720 6353 5768 5335 + 3 -- 15 + 13 -+ 5 2 + 4 7 + 7 0 +38 - + 55 + 27 + 1 3 + 4 3 4637 4776 4961 5143 6184 5995 5797 + 3 + 7 + 11 +33 +30 +25 +29 - +20 +25 +21 +16 .172 .161 .162 .188 .177 .189 .130 - 7 -- 6 -+ 9 -+ 3 +10 + 9 +10 - +17 -31 -24 -25 144.2 131.9 117.4 166.9 220.1 220.9 121.6 - 9 -23 + 15 +52 + 6 7 + 8 7 +53 - + 88 -18 - 7 + 3 A B D K C max E F max G max 2680 2953 2353 2733 4935 3816 4716 + 10 - 14 + 2 + 84 + 67 +110 +42 - + 62 + 76 + 60 +100 2702 3463 3278 3473 4240 4035 3961 +28 +21 +28 +57 +22 +29 +50 - +23 +46 +14 +21 .210 .218 .192 .204 .260 .255 .220 + 4 -- 9 -_ 3 +24 +19 +35 +21 - +33 + 4 + 1 +14 117 .6 124.5 101.8 116.5 251.9 205.7 191.7 + 6 -16 - 1 +114 +106 +147 + 75 - +102 +63 + 5 4 + 8 8 A: Control; B: Heat treated co n t r o l ; D: O i l dipped c o n t r o l ; C max: Irradiated control; E: Thermally grafted; F: I r r a d i a t i o n grafted; G: I r r a d i a t i o n plus thermally grafted. -189-Table XXII. Per cent t e n s i l e strength increase on some p u r i f i e d pulps before and a f t e r sodium c h l o r i t e and o i l polymerization treatments. Fibre Type Treat-ment Tens i l e Strength Strength Increase, "L, from A B D H HD p s i Glass Paper A 6.5 - - - - -E 2446 3490 - - - -Bleached Kr a f t A 3257 - - - - -B 3527 +8.3 - - - -D 2788 -16.8 -26 .5 - - -E 7752 +138 + 120 + 178 - -H 1838 -77 - - - -HD 1720 - - - - -HE 7442 + 128 - - - 305 TAPPI Standard A 1025 - - - - -B 1101 +7 .4 - - - -D 784 -30 -40 - - -E 4423 +332 +302 +464 - -H 1037 0 - - - -HD 973 - - - -6 -HE 5316 415 - - - +446 High-Alpha Viscose A 565 - - - - -D 512 -10 - - - -E 5336 713 - - - -H 389 -68 - - - -HD 394 - - - -1 -HE 3734 468 - - - +860 - - - - - - -Ground-wood A 1230 - - - _ B 1277 +4 - - - _ D 1011 -21 - - - -E 2691 + 118 + 110 + 165 - -H 7314 +495 - - - -HD 7080 - - - -3 -r HE 8929 +545 - - +22 +26 Treatment: A: Control; B: Heat Treated Control; D: O i l dipped cont r o l ; E: Thermally grafted; H: D e l i g n i f i e d by a c i d i c sodium c h l o r i t e (NaCI0 2), HD: NaCi:02 + o i l dip, HE: NaCI 0 2 + o i l dip + heat. Table XXIII. Equations for calculated dependent va r i a b l e correlations, (Y =a+bX+cX +dX ). Scaling Yi= 10-2, Y2=10"3) n Pulp Type Treat-- Relatioi a P a r t i a l Regression C o e f f i c i e n t s R 2 SEE ment X Y a b c d A&C Y l Y 2 Y 3 Y 4 .405081E 01 .963353E-02 -.138710E 02 .102481E 01 .138578E-01 .358926E 01 - .430658E-03 .449922E-05 .991 .766 .969 1.067 1.008 7.109 S u l f i t e D&F Y l Y 2 Y 3 Y4 .112834E 02 - .234758E-01 -.841417E 02 .177597E-01 .123534E 02 .355944E-01 - .5.17580E-03 -.285869E 00 - .372549E-03 .467889E-05 .264009E-02 .937 .564 .902 3.119 0.012 12.075 E&G Y l Y 2 Y 3 Y 4 .100280E 02 -.407120E 00 -.590065E 03 .430217E-01 .489423E 02 .287778E-01 - .107329E-02 -.117595E 01 - .243420E-03 .851421E-05 .953875E-02 .943 .298 .840 2.499 0.016 13.030 A&C Y l Y 2 Y 3 Y4 .950476E 01 .176124E-01 -.106661E 02 .119918E-01 .536208E-01 .462314E 00 - .829633E-03 -.744509E-05 -..108990E-01 .951 .660 .939 1.142 0.015 6.304 Kraft D&F Y l Y2 Y 3 Y 4 .193166E 02 .986479E-01 -.551625E 00 ?372603E-03 .275567E 00 .386121E-03 - .686448E-05 - .324718E-02 .876 .754 .907 2.076 0.022 17.299 E&G Y l Y 2 Y 3 Y4 .882553E 01 .105421E 00 .273798E 01 .660966E 00 .64046 IE-04 .985267E-01 .890 .709 .906 1.581 0.020 15.532 A&C Y 2 Y 3 Y 4 .754817E-01 -.266251E 02 .394757E-02 .345685E 01 - .431.346E-04 .684 .953 0.009 8.844 S u l f i t e D&F Y 2 Y 4 -.120605E 00 -.247804E 03 .235007E-01 .253993E 02 -.604628E-03 -.623623E 00 .490023E-05 .535305E-02 .419 .848 0.014 15.021 E&G Y 2 Y 3 Y 4 .182215E 00 .655369E 02 -.686980E-04 .968981E-06 .407485E-03 .167 .532 0.017 21.537 A&C Y2 Y 3 Y 4 - .402559E-01 -.197138E 02 .170023E-01 -.300743E-03 .345977E 00 - .685650E-02 .513 .842 0.018 10.154 Kraft D&F Y 2 Y 3 Y 4 -.237208E 00 -.92816IE 02 .285824E-01 -.414494E-03 .571183E 00 - .972120E-02 .641 .822 0.027 23 .906 E&G Y 2 V 3 Y4 .994513E-01 -.202088E 02 .835212E-04 .141754E 00 .467 .727 0.027 26.558 E a r l y w o o d : F i g u r e 6. S c a n n i n g e l e c t r o n p h o t o m i c r o g r a p h s o f wood t e n s i l e f r a c t u r e s b e f o r e and a f t e r i r r a d i a t i o n and t h e r m a l g r a f t i n g (150 X ) . Latewood: C o n t r o l I r r a d i a t e d , 10 r a d T h e r m a l l y g r a f t e d T e n s i l e s t r e n g t h p r o p e r t i e s o f Douglas f i r wood s e c t i o n s b e f o r e and a f t e r t h e r m a l g r a f t i n g . P o s i t i o n Sp. Number Sample U l t i m a t e S t r e n g t h Sample Treatment i n G r . o f T e n s i l e I n crement R e p l i c a t e s T h i c k n e s s S t r e n g t h I n c r e a s e 1 g/cm 3 -- cm p s i % E a r l y w o o d C o n t r o l 7.5 .275 10 .137 7330 9.0 Therma1 G r a f t i n g 10 .135 7970 Latewood C o n t r o l 88.3 .682 10 .125 17,660 14.1 Thermal G r a f t i n g 10 .128 20,150 F i g u r e 7. S c a n n i n g e l e c t r o n p h o t o m i c r o g r a p h s o f paper t e n s i l e f r a c t u r e s b e f o r e and a f t e r g r a f t i n g < 1 5 0 X ) . Sample Treatment Photo-m i c r o -graph T e n s i l e S t r e n g t h Modulus o f E l a s t i c i t y T e n s i l e S t r a i n T e n s i l e E n e r g y A b s o r p t i o n p s i 1,000 p s i ( i n / i n ) . 1 0 " 1 i n . l b / c u i n Groundwood A F E m g h i 1230 2166 2691 153.4 224.2 256.6 .133 .176 .159 33.0 75.6 82.2 S u l f i t e A F E m j k 1 4185 5768 6353 463.7 599.5 618.4 .172 .189 .177 144.2 220.9 220.1 K r a f t A F E m m n o 2680 3816 4935 270.2 403.5 424.0 .210 .255 .260 117 .6 191.7 251.9 A: C o n t r o l , F : Gamma-m •ray i r r a d i a t i o n g r a f t e d , E: T h e r m a l l y g r a f t e d • -193-F i g u r e 8. Deep t e n s i l e f r a c t u r e o f k r a f t paper (150 X ) . (0 10 20 30 40 50 60 70 80 90 100 G 100 90 80 70 60 50 4 0 30 20 10 0 S Pulp Blend,% F i g u r e 9 . S u l f i t e - g r o u n d w o o d h a n d s h e e t t e n s i l e s t r e n g t h ( Y l ) a s a f u n c t i o n o f b l e n d i n g a n d p o s t - s h e e t f o r m a t i o n t r e a t m e n t s . vo •P-0 10 20 30 40 50 60 70 80 90 100 6 100 90 80 70 60 50 40 30 20 10 O K Pulp Blends,% F i g u r e 1 0 . K r a f t - g r o u n d w o o d h a n d s h e e t t e n s i l e s t r e n g t h ( Y ] J a s a f u n c t i o n o f p u l p b l e n d i n g a n d p o s t - s h e e t f o r m a t i o n t r e a t m e n t s . O 10 20 30 4 0 50 60 70 8 0 90 100 G 100 90 80 70 60 50 40 30 20 10 0 S Pulp Blend,% Figure 11. Change of sulfite-groundwood handsheet elasticity (Y2) as a function of blending and post-sheet formation treatments. Figure 12. Change of kraft-groundwood handsheet elasticity (Y2) as a function of pulp blending and post-sheet formation treatments. vO I 0 10 20 30 40 50 60 70 80 90 100 G 100 90 80 70 60 50 4 0 30 20 10 O S 0 10 20 30 40 50 60 70 80 90 100 90 80 70 60 50 4 0 30 20 10 100 G 0 K Pulp Blend,% Pulp Blend,% F i g u r e 1 3 . E f f e c t o f p u l p b l e n d i n g a n d p o s t - s h e e t t r e a t m e n t s o n u l t i m a t e t e n s i l e s t r a i n (Y3) o f s u l f i t e - g r o u n d w o o d h a n d s h e e t s . F i g u r e 1 4 . E f f e c t o f p u l p b l e n d i n g a n d p o s t - s h e e t f o r m a t i o n t r e a t m e n t s o n u l t i m a t e t e n s i l e s t r a i n (Y-j) o f k r a f t - g r o u n d w o o d h a n d s h e e t s . 0 10 20 30 4 0 50 60 70 60 90 100 G 0 10 20 30 40 50 60 70 80 90 100 G 100 90 80 70 60 50 4 0 30 20 10 O S |00 90 80 70 60 50 40 30 20 10 O K Pulp Blend,% Pulp Blend,% F i g u r e 1 5 . Max imum t e n s i l e e n e r g y a b s o r p t i o n (Y4) o f s u l f i t e - g r o u n d w o o d h a n d s h e e t s a s a f u n c t i o n o f p u l p b l e n d i n g a n d p o s t - s h e e t f o r m a t i o n t r e a t m e n t s . F i g u r e 1 6 . Maximum t e n s i l e e n e r g y a b s o r p t i o n (Y4) o f k r a f t - g r o u n d w o o d h a n d s h e e t s a s a f u n c t i o n o f p u l p b l e n d i n g a n d p o s t - s h e e t f o r m a t i o n t r e a t m e n t s . -198-+40 Q) O £ 0 0 20 40 60 80 TOO 80 60 40 20 0 G 100 80 60 40 20 0 0 0 0 0 O S 0 0 0 0 0 0 ;20 40 60 80 100 K Pulp Blends,% F i g u r e 17. A b s o l u t e s t r e n g t h i n c r e a s e due t o t h e r m a l and i r r a d i a t i o n g r a f t i n g onto s u l f i t e - and k r a f t - g r o u n d w o o d h a n d s h e e t s . ' ' I I 1— 10 20 30 40 50 F i g u r e 18. E f f e c t o f samp Sample Weight L o s s , % of e x t r a c t a b l e monomer r e s i d u e s and homopolymer f r a c t i o n s ( e x p r e s s e d as percentage „ ^ l e w e i g h t ) on i n i t i a l t e n s i l e s t r e n g t h of o i l d i p p e d (D) specimens f o l l o w i n g t h e r m a l (E) and g a m m a - i r r a d i a t i o n g r a f t i n g (F,G). -200-3 4 5 6 7 8 9 1 0 11 Level of Pulp Blend Interaction F i g u r e 19. T e n s i l e s t r e n g t h o f s u l f i t e - and k r a f t - g r o u n d w o o d h a n d s h e e t s as c a l c u l a t e d from t h e s i g n i f i c a n t i n t e r a c t i o n between p u l p t y p e and l e v e l o f b l e n d i n g . 75 Sulfite-Groundwood Blend Control Irradiated Control Oil Dipped Control Irradiation Graft Thermal Graft Irradiation plus Thermal Graft 15 20 25 30 35 4 0 45 50 55 Ultimate Tensile Strength ( Y j ) , l 0 0 p s i • 60 a. O O q_ o" ^T45 CM > » 30 o LU **~ o co o Kraft-Groundwood Blend A = Control C- Irradiated Control D : Oil Dipped Control F : Irradiation Graft E : Therma l Graft G : Irradiation plus Thermal Graft 15 20 25 30 35 4 0 4 5 50 55 Ultimate Tensile Strength (Y|),IOO ps i F i g u r e 20. R e l a t i o n s h i p between u l t i m a t e t e n s i l e s t r e n g t h (Y^) and modulus o f e l a s t i c i t y ( Y 2 ) f o r h a n dsheets made from s u l f i t e - and k r a f t - g r o u n d w o o d b l e n d s . Sulfite - Groundwood Blend D B F J. Control Irradiated Control Oil Dipped Control Irradiation Graft Thermal Graft Irradiation plus Thermal Graft 15 20 25 30 35 40 45 50 Ultimate Tensile Strength (Y,), 100 psi 55 •20 ro i . is o 1 0 co CO c CP 10 | 0 5 Kraft-Groundwood Blend to O Control Irradiated Control Oil Dipped Control Irradiation Graft Thermal Graft Irradiation plus Thermal Graft 15 20 25 30 35 40 45 50 Ultimate Tensile Strength (Y|),IOO psi 55 F i g u r e 21. R e l a t i o n s h i p between u l t i m a t e t e n s i l e s t r e n g t h (Y-^) and u l t i m a t e t e n s i l e s t r a i n (Y3) f o r h andsheets made from s u l f i t e - and k r a f t - g r o u n d w o o d b l e n d s . , 4 0 0 o \ -a ^ 3 0 0 § 2 0 0 < w 100 — c <D Sulfite-Groundvrood Blend Control Irradiated Control Oil Dipped Control Irradiation Graft Thermal Graft Irradiation plus Thermal Graft 15 F i - 4 0 0 3 O ~ 3 0 0 | 2 0 0 .a < >> CO <P £ 100 © c « 20 25 30 35 40 45 50 55 Ultimate Tensile Strength (Y|), 100 psi Kraft-Groundwood Blend Control Irradiated Control Oil Dipped Control Irradiation Graft Thermal Graft Irradiation plus Thermal Graft O c o JL 15 20 25 30 35 4 0 45 50 Ultimate Tensile Strength (Y|),IOO psi 55 gure 22. R e l a t i o n s h i p between u l t i m a t e t e n s i l e s t r e n g t h (Y.) and t e n s i l e energy a b s o r p t i o n (Y^) f o r h a n d s h e e t s made from s u l f i t e - and k r a f t - g r o u n d w o o d b l e n d s . Sulfite - Groundwood Blend D B F A Control C Irradiated Control D Oil Dipped Control F Irradiation Graft E Thermal Graft G Irradiation plus Thermal Graft 15 20 25 30 35 40 45 50 55 Modulus of Elasticity ( Y 2 ) , 10,000 psi •20 g X J>I5 c o co .-= 1 0 co c CD E 0 5 Control Irradiated Control Oil Dipped Control Irradiation Graft Thermal Graft Irradiation plus Thermal Graft Kraft-Groundwood Blend 15 20 25 30 35 40 45 50 55 Modulus of Elasticity ( Y 2 ) , 10,000 psi F i g u r e 23. R e l a t i o n s h i p between modulus of e l a s t i c i t y (Y2) and u l t i m a t e t e n s i l e s t r a i n (Y3) f o r h a n dsheets made from s u l f i t e - and k r a f t - g r o u n d w o o d b l e n d s . Sulfite-Groundwood Blend Control Irradiated Control Oil Oipped Control Irradiation Graft Thermal Graft Irradiation plus Thermal Graft :400 ^ 3 0 0 c o Q. t-O (0 <200 >» cn a> c UJ = 100 (0 c a> Kraft-Groundwood Blend 15 20 25 30 35 40 45 50 55 Modulus of Elasticity ( Y 2 ) , 10,000 psi Control Irradiated Control Oil Dipped Control Irradiation Graft Thermal Graft Irradiation plus Thermal Graft N3 O 15 20 25 30 35 40 45 50 55 Modulus of Elasticity ( Y 2 ) , 10,000 ps i F i g u r e 24. R e l a t i o n s h i p between modulus of f o r h a n d s h e e t s made from s u l f i t e l a s t i c i t y ( Y 2 ) and t e n s i l e energy a b s o r p t i o n (Y^) e- and k r a f t - g r o u n d w o o d b l e n d s . -206-H - C - O C H o O C H 3 OH m o n o - s u b s t i t u t i o n F i g u r e 25. Scheme f o r s e l e c t i v e m e t h y l a t i o n o f l i g n i n i n wood. -207-F i g u r e 26. D i s c o l o r a t i o n o f groundwood, s u l f i t e and k r a f t papers due t o i r r a d i a t i o n and t h e r m a l g r a f t i n g . Groundwood P u l p : C o n t r o l I r r a d i a t e d C. 2 x l 0 7 r a d dose R a d i a t i o n Copolymer 105 r a d dose Thermal Copolymer 1450C, 1.5 h r S u l f i t e P u l p : C o n t r o l S u l f a t e P u l p : I r r a d i a t e d C. 2 x l 0 7 r a d dose R a d i a t i o n Copolymer 105 r a d dose Thermal Copolymer 145°C, 1.5 h r C o n t r o l I r r a d i a t e d C. 2x10? r a d dose R a d i a t i o n Copolymer 105 r a d dose Therma1 Copolymer 145°C, 1.5 h r C o n t r o l (A) -208-C h a r t speed: 1 i n . / m i n . Head speed: 0.05 i n . / m i n . Gauge l e n g t h : 10 cm. I r r a d i a t e d , 2 x 1 0 7 r a d (C) I r r a d i a t i o n (10 r a d ) p l u s t h e r m a l l y g r a f t e d (G) Load, k g . F i g u r e 27. C h a r a c t e r i s t i c s t r e s s - e l o n g a t i o n c u r v e s f o r 50:50 s u l f i t e - g r o u n d w o o d b l e n d . 

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