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UBC Theses and Dissertations

Microscopical aspects of hardwood refiner pulps Cisneros, Hector A. 1991

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M I C R O S C O P I C A L A S P E C T S OF HARDWOOD R E F I N E R P U L P S by HECTOR A . CISNEROS B. Sc. F . , U n i v e r s i d a d N a c i o n a l A g r a r i a , L ima, 1981 M. Sc.. F . ,' U n i v e r s i t y of Toronto , 1983 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR T H E DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES FORESTRY We accept t h i s t h e s i s as conforming to the r e q u i r e d s tandard THE UNIVERSITY OF BRITISH COLUMBIA January, 1991 (c) Hector A . C i s n e r o s , COPYRIGHT 1991 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Forestr The University of British Columbia Vancouver, Canada Date DE-6 (2/88) ABSTRACT I n o r d e r t o g a i n i n s i g h t s i n t o u l t r a s t r u c t u r a l c h a n g e s t a k i n g p l a c e d u r i n g t h e c o n v e r s i o n o f h a r d w o o d s i n t o m e c h a n i c a l p u l p s , r e f i n e r p u l p f i b r e s were s t u d i e d i n d e t a i l u s i n g s e v e r a l m i c r o s c o p i c a l t e c h n i q u e s . A s p e n (Populus tremuloides M i c h x . ) and w h i t e b i r c h (Betula papyrifera M a r s h . ) wood c h i p s were u s e d t o p r o d u c e t h e r m o m e c h a n i c a l (TMP), c h e m i t h e r m o m e c h a n i c a l (CTMP) and c h e m i m e c h a n i c a l (CMP) p u l p s . F o l l o w i n g t h e h y p o t h e s i s t h a t t h e r e a r e f u n d a m e n t a l d i f f e r e n c e s i n t h e - s u r f a c e a n d s t a t e o f t h e f i b r e s due t o s p e c i e s and p r o c e s s i n g c o n d i t i o n s , f o u r p u l p s f o r e a c h s p e c i e s a n d p r o c e s s were a n a l y z e d . T r e n d s i n f i b r e c h a r a c t e r i s t i c d e v e l o p m e n t were o b t a i n e d w i t h i n e a c h g r o u p , b a s e d on t h e d e t a i l e d o p t i c a l a n a l y s i s o f 300 f i b r e c r o s s -s e c t i o n s f o r e a c h p u l p . F i b r e s u r f a c e q u a l i t y was t h e most i m p o r t a n t a s p e c t o f t h i s s t u d y . R e t e n t i o n o f m i d d l e l a m e l l a and o f t h e l a y e r , as w e l l as t h e e x t e n t o f e x p o s u r e o f t h e S2 l a y e r were e v a l u a t e d . I t was f o u n d t h a t TMP p r o c e s s i n g o f wood c h i p s p r o d u c e d f i b r e s w i t h more e x p o s u r e o f t h e S2 l a y e r . C h e m i c a l p r e t r e a t m e n t d i d n o t i m p r o v e t h e e x t e n t o f S2 l a y e r e x p o s u r e n o r t h e e x t e n t o f f i b r i l l a t i o n . However, t h e TMP f i b r e s r e m a i n e d s t i f f , p r o d u c i n g p u l p s h e e t s o f l o w d e n s i t y a n d s t r e n g t h . B i r c h f i b r e s showed a m a r k e d t e n d e n c y t o p r o d u c e s e p a r a t i o n a t o r n e a r t h e S1/S2 b o u n d a r y . T h i s r e s u l t e d i n h i g h e x p o s u r e o f S2 l a y e r s i n TMP f i b r e s , b u t p r o d u c e d a s h e a t h i i i of S]_ and ML around f i b r e s from c h e m i c a l l y - t r e a t e d c h i p s . T h i s sheath was sometimes r o l l e d back, exposing the f i b r e S 2 l a y e r . Aspen TMP pulps showed high p r o p o r t i o n s of f i b r e s with p a r t i a l l y exposed S 2 l a y e r . The a p p l i c a t i o n of chemical pretreatments to aspen c h i p s r e s u l t e d i n f i b r e s of s i m i l a r l e v e l s of S 2 exposure than those achieved by TMP p r o c e s s i n g of t h i s s p e c i e s , but only a f t e r r e a c h i n g f r e e n e s s l e v e l s of about 1 0 0 mL CSF. F i b r e s t h a t showed r a d i a l f a i l u r e were frequent i n TMP but not i n CTMP nor CMP pulps. The breakdown p a t t e r n of t e n s i o n wood f i b r e s (G-fibres) was a l s o s t u d i e d . TMP p r o c e s s i n g showed p r e f e r e n t i a l breakdown of G - f i b r e s , from which the G-l a y e r s were f r e e d . This was not the case i n the G - f i b r e s from c h e m i c a l l y - t r e a t e d c h i p s , i n which- the G-layer g e n e r a l l y remained i n s i d e the f i b r e s . Other c a t e g o r i e s d i s c u s s e d i n the a n a l y s i s of f i b r e c r o s s s e c t i o n s i n c l u d e d f i b r e s with delamination of the S 2 l a y e r and p r o p o r t i o n of f i b r e s d i s t o r t e d due to chemical impregnation. The breakdown of v e s s e l elements (VE) was s t u d i e d by comparing VE s i z e frequency d i s t r i b u t i o n s and the p r o p o r t i o n of whole VE that s u r v i v e d r e f i n i n g . TMP reduced VE i n t o s m a l l fragments showing v i r t u a l l y no whole VE, while wood s o f t e n i n g due to chemical pretreatment was r e s p o n s i b l e f o r a high p r o p o r t i o n of whole VE i n CTMP and CMP p u l p s . The VE from b i r c h tend to be destroyed more e a s i l y than those from aspen, due to the i n t e r v e s s e l p i t t i n g arrangement of the former. i v I t i s concluded that d e s p i t e s u p e r i o r bonding p o t e n t i a l of TMP f i b r e s due t o : - l a r g e S2 exposure i n f i b r e s on account of s e p a r a t i o n at or near the S^/52 boundary, - i n c r e a s e d f i b r i l l a t i o n , - longer f i b r i l s i n f i n e s , and - r e l e a s e and exposure of h i g h l y c e l l u l o s i c G - l ayers from t e n s i o n wood i n the case of aspen, the l a c k of c o n f o r m a b i l i t y of TMP f i b r e s , which t r a n s l a t e s i n t o low sheet d e n s i t y , negates the promising b e n e f i t s t h a t otherwise would be obtained. V TABLE OF CONTENTS Page ABSTRACT . . . . i i TABLE OF CONTENTS v LIST OF TABLES v i i i LIST OF FIGURES ,. ....x ACKNOWLEDGEMENTS xv INTRODUCTION 1 LITERATURE REVIEW 9 2.1. Importance o f Hardwoods ....9 2.2. R e f i n e r M e c h a n i c a l P u l p i n g . . . . 11 2.3. C h a r a c t e r i z a t i o n of M e c h a n i c a l P u l p s 15 2.4. E f f e c t o f Wood and F i b r e C h a r a c t e r i s t i c s i n M e c h a n i c a l P u l p i n g ...20 2.5. M e c h a n i c a l P u l p i n g o f Hardwoods 24 2.6. T e n s i o n Wood i n P u l p 29 2.7. The R o l e o f V e s s e l Elements i n P u l p 32 METHODOLOGY 36 3.1. Wood Procurement 36 3.2. P r o d u c t i o n and C h a r a c t e r i z a t i o n o f C h i p s 38 3.3. P r e p a r a t i o n o f P u l p s 40 3.3.1. P r o d u c t i o n o f Thermomechanical P u l p s 41 3.3.2. P r o d u c t i o n o f Chemithermomechanical P u l p s . . 4 3 3.3.3. P r o d u c t i o n o f Chemimechanical P u l p s 44 3.3.4. P r o d u c t i o n o f K r a f t P u l p s 45 3.4. P u l p p r o c e s s i n g 47 3.5. P u l p T e s t i n g . 48 v i 3 . 6 . M i c r o s c o p y 4 9 3 . 6 . 1 . Pu lp S l i d e s 49 3 . 6 . 2 . Study, o f F i b r e C r o s s S e c t i o n s 50 3 . 6 . 2 . 1 . P r e p a r a t i o n o f F i b r e C r o s s S e c t i o n s . . . 52 3 . 6 . 2 . 2 . D e f i n i t i o n o f C a t e g o r i e s S t u d i e d 55 3 . 6 . 2 . 3 . R e p e a t a b i l i t y 64 3 . 7 . Scanning E l e c t r o n M i c r o s c o p y 64 3 . 8 . T r a n s m i s s i o n E l e c t r o n M i c r o s c o p y 65 3 . 9 . V e s s e l Element Breakdown 66 RESULTS 69 4 . 1 . A n a l y s i s o f F i b r e Cross S e c t i o n s 69 4 . 1 . 1 . R e t e n t i o n o f Compound M i d d l e L a m e l l a and S]_ Layer 69 4 . 1 . 2 . Exposure of the S 2 l a y e r -.70 4 . 1 . 3 . C e l l W a l l Damage 70 4 . 1 . 4 . D i s t o r t e d F i b r e s 71 4 . 1 . 5 . T e n s i o n Wood F i b r e s 71 4 . 2 . P u l p P r o p e r t i e s . . . 71 4 . 3 . Breakdown of V e s s e l Elements 73 4 . 4 . F i b r e Length and Wood S p e c i f i c G r a v i t y . 74 DISCUSSION 93 5 . 1 . A n a l y s i s o f F i b r e C r o s s S e c t i o n s 93 5 . 1 . 1 . R e t e n t i o n o f Compound M i d d l e L a m e l l a and S-L Layer 93 5 . 1 . 2 . Exposure and D e l a m i n a t i o n o f the S 2 l a y e r 119 5 . 1 . 3 . D i s t o r t e d F i b r e s 126 5 . 1 . 4 . R a d i a l F a i l u r e 130 5 . 1 . 5 . Breakdown of T e n s i o n Wood F i b r e s 134 v i i 5 . 2 . Breakdown o f V e s s e l Elements 144 5 . 3 . P u l p P r o p e r t i e s .156 5 . 4 . S i g n i f i c a n c e o f F i n d i n g s 160 SUMMARY 170 CONCLUSIONS 174 SUGGESTIONS FOR FURTHER RESEARCH 178 LITERATURE CITED 182 APPENDICES 193 Appendix A . Hardwood f i b r e s t r u c t u r e a c c o r d i n g to Jayme and A z z o l a (1965) 193 Appendix B . C h a r t used f o r r e c o r d i n g c a t e g o r i e s o f f i b r e s i n c r o s s s e c t i o n 194 Appendix C . R e s u l t s and d i s c u s s i o n on r e p e a t a b i l i t y o f the a n a l y s i s o f f i b r e c r o s s s e c t i o n s 195 Appendix D. V a r i a t i o n o f wood s p e c i f i c g r a v i t y from p i t h to bark at d i f f e r e n t h e i g h t s o f the t r e e stem 202 Appendix E . C a l c u l a t i o n s i n v o l v e d i n the e s t i m a t i o n of the o r i g i n of the m a t e r i a l i n the P100 f r a c t i o n 205 Appendix F . A b b r e v i a t i o n s 207 v i i i LIST OF TABLES 3 . 1 . A c c e p t c h i p t h i c k n e s s c l a s s i f i c a t i o n 39 4 . 1 . Percentage o f f i b r e s under the c a t e g o r i e s d e f i n e d f o r ML and r e t e n t i o n 75 4 . 2 . Dependancy of M L r , and S-^r or S 2 e , on energy i n p u t . C h i - s q u a r e v a l u e s compared to a c r i t i c a l v a l u e o f 16.92 ( d=0.05, 9 d . f ) 76 4 . 3 . Percentage o f f i b r e s showing mode of s e p a r a t i o n o f the o u t e r l a y e r 77 4 . 4 . Percentage o f f i b r e s under c a t e g o r i e s d e f i n e d f o r the exposure o f the S 2 l a y e r 78 4 . 5 . Percentage o f f i b r e s showing c e l l w a l l damage 7 9 4 . 6 . Percentage o f d i s t o r t e d f i b r e s i n r e f i n e r p u l p s from c h e m i c a l l y - t r e a t e d wood c h i p s 80 4 . 7 . Percentage o f t e n s i o n wood f i b r e s i n aspen by a n a l y s i s o f c r o s s s e c t i o n s o f k r a f t p u l p f i b r e s 81 4 . 8 . Percentage o f t e n s i o n wood f i b r e s i n aspen r e f i n e r R48 p u l p f r a c t i o n s 82 4 . 9 . Aspen and b i r c h r e f i n e r p u l p c h a r a c t e r i s t i c s and f i b r e s i z e c l a s s i f i c a t i o n 83 4 .10 . P h y s i c a l p r o p e r t i e s of p u l p handsheets 84 4 . 1 1 . S u r f a c e and o p t i c a l p r o p e r t i e s o f p u l p handsheets 85 4 .12 . S i z e o f v e s s e l e lements from k r a f t p u l p s 86 4 .13 . Aspen v e s s e l element s i z e frequency a n a l y s i s (N=50) 87 4 .14 . B i r c h v e s s e l element s i z e frequency a n a l y s i s (N=50) .88 4 .15 . C h i - s q u a r e t e s t s on v e s s e l element s i z e d i s t r i b u t i o n ( d = 0.05) 89 4 . 1 6 . S u r v i v a l o f whole v e s s e l e lements i n r e f i n e r p u l p s . . 90 i x 4.17. Aspen and b i r c h f i b r e l e n g t h measurements 91 5.1. Percentage of f i b r e s with t o t a l S 2 l a y e r exposure from among the f i b r e s showing d e l a m i n a t i o n 124 X LIST OF FIGURES 2 . 1 . M e c h a n i c a l p u l p i n g p r o c e s s e s a c c o r d i n g to F r a n z e n (1986) 14 2 . 2 . Schematic r e p r e s e n t a t i o n o f the p a r t i c l e s p r e s e n t i n pure mechan ica l p u l p s (Mohl in 1982a) 16 2 . 3 . I n f l u e n c e o f d i f f e r e n t mechan ica l p u l p p a r t i c l e s on some important p u l p p r o p e r t i e s (Mohl in 1982b) 17 3 . 1 . . G e n e r a l o u t l i n e o f e x p e r i m e n t a l p r o c e d u r e s . V E : v e s s e l e lements ; TW: t e n s i o n wood f i b r e s ; SEM: s c a n n i n g e l e c t r o n m i c r o s c o p e ; TEM: t r a n s m i s s i o n e l e c t r o n microscope 3 7 3 . 2 . R e l a t i o n s h i p between s p e c i f i c energy consumption and unscreened f reeness f o r the hardwood r e f i n e r p u l p s produced 41 3 . 3 . C r o s s s e c t i o n o f aspen t e n s i o n wood. A H e r z b e r g reagent s t a i n e d p u r p l e the G - l a y e r s , w h i l e the l i g n i f i e d m a t e r i a l t u r n e d y e l l o w 46 3 . 4 . Aspen k r a f t p u l p f i b r e s s t a i n e d w i t h T o l u i d i n e B l u e 0, showing . G - l a y e r s i n c r o s s s e c t i o n 46 3 . 5 . R e l a t i o n s h i p between f reeness and the p e r c e n t o f f i b r e s r e t a i n e d on a 48 mesh s c r e e n 51 3 . 6 . Hardwood r e f i n e r p u l p f i b r e s i n c r o s s s e c t i o n showing: (a) ML r e t a i n e d , (b) d e l a m i n a t i o n o f the S 2 l a y e r , (c) r a d i a l f a i l u r e , and (d) s e p a r a t i o n of the o u t e r c e l l w a l l or " o u t / i n " e f f e c t 58 3 . 7 . R e t e n t i o n o f S^ l a y e r s shown as b r i g h t l i n e s around f i b r e s i n c r o s s s e c t i o n under p o l a r i z e d l i g h t 59 3 . 8 . (a) P e e l i n g o f the ML 59 3 . 9 . Aspen p u l p f i b r e s showing (a) G - l a y e r s t r i p p e d from the l i g n i f i e d c e l l w a l l , (b) G - l a y e r i n s i d e the f i b r e 59 3 . 1 0 . P u l p produced from c h e m i c a l l y - t r e a t e d c h i p s showing (a) N o n - d i s t o r t e d f i b r e , and (b) d i s t o r t e d f i b r e 59 4 . 1 . Wood s p e c i f i c g r a v i t y v a r i a t i o n at DBH f o r the t r e e s used i n t h i s s tudy 92 x i 5 . 1 . Bauer McNett f r a c t i o n a t i o n p a t t e r n s f o r a l l hardwood r e f i n e r p u l p s under s t u d y . S o l i d l i n e s : h i g h f r e e n e s s p u l p s ; dashed l i n e s : low f r e e n e s s ; d o t t e d l i n e s : i n t e r m e d i a t e f r e e n e s s 96 5 . 2 . P l o t o f ML r e t e n t i o n index a g a i n s t p u l p f r e e n e s s 98 5 . 3 . P l o t o f percentage o f f i b r e s w i t h t o t a l ML r e t e n t i o n a g a i n s t p u l p f reenes s .98 5 . 4 . SEM photograph of aspen TMP f i b r e showing uneven exposure o f c e l l w a l l l a y e r s (pulp A-TMP4) 102 5 . 5 . C r o s s s e c t i o n o f aspen TMP f i b r e s showing p a r t i a l r e t e n t i o n o f ML (pulp A-TMP3) 102 5 . 6 . TEM photograph o f b i r c h TMP f i b r e i n c r o s s s e c t i o n o f showing s e p a r a t i o n o f the l a y e r (pulp B-TMP1) 104 5 . 7 . TEM photograph, o f aspen TMP f i b r e bundle i n c r o s s s e c t i o n showing s e p a r a t i o n o f the S^ l a y e r near the S-L/S2 boundary (pulp A-TMP1) 104 5 . 8 . D i s t r i b u t i o n p a t t e r n o f ML and S^ l a y e r r e t e n t i o n i n aspen and b i r c h TMP p u l p s o f s i m i l a r f reeness (pulps A-TMP3 and B-TMP3) 106 5 . 9 . TEM photograph of aspen TMP f i b r e i n c r o s s s e c t i o n showing d e t a i l o f r e t e n t i o n and exposure o f the S - L l a y e r (pulp A-TMP1) 106 5 .10 . D i s t r i b u t i o n p a t t e r n o f ML and S^ r e t e n t i o n f o r aspen and b i r c h CTMP p u l p s o f s i m i l a r f r e e n e s s (pulps A-CTMP2 and B-CTMP4) 107 5 . 1 1 . D i s t r i b u t i o n p a t t e r n o f ML and S^ r e t e n t i o n f o r aspen and b i r c h CMP p u l p s o f s i m i l a r f r e e n e s s (pulps A-CMP3 and B-CMP3) . . . . . . 1 0 7 5 . 1 2 a . Unbeaten b i r c h k r a f t p u l p f i b r e s i n c r o s s s e c t i o n showing gaps between the S^ and S 2 l a y e r s i n b r i g h t f i e l d i l l u m i n a t i o n 109 5 .12b . Same f i e l d under p a r t i a l p o l a r i z e d l i g h t 109 5 . 1 3 . TEM photograph showing d e t a i l o f the gap p r o d u c e d between the S1 and S 2 l a y e r s . The S± l a y e r had s e p a r a t e d but remained s u r r o u n d i n g the f i b r e (pulp B-CMP4) I l l 5 .14 . B i r c h CMP p u l p f i b r e s i n c r o s s s e c t i o n . Note the f i b r e s i n which the S^ l a y e r has c o m p l e t e l y s e p a r a t e d but surrounds the f i b r e (pulp B-CMP4) . . . . 111 x i i 5.15. B i r c h CMP f i b r e s showing " s k i n n i n g " or " s l e e v e -r o l l i n g " (pulp B-CMP3) 114 5.16. B i r c h CMP f i b r e s e c t i o n e d at the p o i n t where s k i n n i n g o c c u r r e d along the Si l a y e r . Photograph taken under p a r t i a l p o l a r i z e d l i g h t (pulp B-CMP4) 114 5.17. Whole aspen TMP pulp showing extent of f i b r i l l a t i o n under phase c o n t r a s t i l l u m i n a t i o n (pulp A-TMP1) 117 5.18. Whole aspen CTMP pulp . Note l e s s e r f i b r i l l a t i o n compared t o TMP pulp (pulp A-CTMP1) 117 5.19. SEM photograph of f r e e z e - d r i e d aspen TMP f i b r e s (R48 f r a c t i o n ) . The f i b r e s are s t r a i g h t , s t i f f and f i b r i l l a t e d (pulp A-TMP4) 118 5.20. Aspen CTMP R48 f r a c t i o n . F i b r e s appeared t o be more f l e x i b l e than i n TMP (pulp A-CTMP4) 118 5.21. P l o t of S2 exposure index a g a i n s t pulp freeness....120 5.22. P l o t of percentage of f i b r e s with t o t a l S2 l a y e r exposure a g a i n s t pulp f r e e n e s s 120 5.23. Percentage of f i b r e s showing d e l a m i n a t i o n i n aspen r e f i n e r pulps 122 5.24. Percentage of f i b r e s showing d e l a m i n a t i o n i n b i r c h r e f i n e r pulps 122 5.25. TEM photograph of b i r c h CMP f i b r e i n c r o s s s e c t i o n showing d e l a m i n a t i o n of the S2 l a y e r (pulp B-CMP4) . 125 5.26. TEM photograph of b i r c h CMP f i b r e i n c r o s s s e c t i o n showing d e t a i l of d e l a m i n a t i o n of the S x l a y e r (pulp B-CMP4) .127 5.27. Another example of S-j_ l a y e r d e l a m i n a t i o n (pulp B-CMP4) 127 5.28. Percentage of f i b r e s showing d i s t o r t i o n i n aspen CTMP and CMP pulps 129 5.29. Percentage of f i b r e s showing d i s t o r t i o n i n b i r c h CTMP and CMP pulps 129 5.30. Percentage of f i b r e s showing r a d i a l f a i l u r e i n aspen r e f i n e r pulps 132 x i i i 5 . 3 1 . Percentage o f f i b r e s showing r a d i a l f a i l u r e i n b i r c h r e f i n e r p u l p s 132 5 .32 . SEM photograph o f G - f i b r e s i n aspen wood c r o s s s e c t i o n showing t h i n G - l a y e r s 136 5 . 3 3 . SEM photograph of G - f i b r e s i n aspen wood c r o s s s e c t i o n showing t h i c k G - l a y e r s 136 5 .34 . Percentage o f G - f i b r e s i n the R48 f r a c t i o n o f aspen r e f i n e r pu lps 137 5 . 3 5 . SEM photograph of G - f i b r e showing p a r t i a l u n r a v e l l i n g o f the c e l l w a l l t o expose the G - l a y e r i n s i d e (pulp A-TMP4) 138 5 .36 . SEM photograph i n which the f i b r e w a l l has been r i p p e d , l e a v i n g an exposed G - l a y e r (pulp A - T M P 4 ) . . . 1 3 8 5 . 3 7 . Presence o f G - l a y e r s t h a t were de tached from t h e i r p a r e n t f i b r e s i n the R48 f r a c t i o n o f p u l p A-TMP3 140 5 .38 . I s o l a t e d G - l a y e r showing f i n e c e l l u l o s i c f i l a m e n t s d e t a c h i n g from the s u r f a c e . F r a c t i o n 48/100 of p u l p A-TMP3. 140 5 .39 . G - l a y e r fragments i n the 100/150 f r a c t i o n o f p u l p A-TMP3 141 5 .40 . G - l a y e r f i l a m e n t s i n the P200 f r a c t i o n o f p u l p A-TMP3 141 5 . 4 1 . G - l a y e r i n aspen CTMP R48 f r a c t i o n . Note the t h i n - w a l l e d s k i n l e f t b e h i n d (pulp A-CTMP4) 143 5 .42 . G - l a y e r exposed at the c e n t r e o f a f i b r e w h i l e c o v e r e d by the f i b r e w a l l s at the extremes (pulp A-CTMP4) 143 5 . 4 3 . Frequency po lygons f o r VE s i z e i n aspen r e f i n e r p u l p s o f s i m i l a r f reenes se s 146 5 .44 . Frequency po lygons f o r VE s i z e i n b i r c h r e f i n e r p u l p s o f s i m i l a r f reenes se s • 146 5 . 4 5 . Percentage o f whole VE t h a t s u r v i v e d d u r i n g the r e f i n i n g o f aspen c h i p s 148 5 .46 . Percentage o f whole VE t h a t s u r v i v e d d u r i n g the r e f i n i n g o f b i r c h c h i p s 148 5 . 4 7 . B i r c h VE fragment showing s p i t t i n g a l o n g the l i n e o f i n t e r v e s s e l p i t t i n g (pulp B-CTMP3) 155 x i v 5 .48 . S i n g l e - w a l l e d VE fragment showing s e p a r a t i o n i n the d i r e c t i o n o f i n t e r v e s s e l p i t t i n g (pulp B-CTMP3) 155 5 .49 . 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 sheet d e n s i t y f o r a l l hardwood r e f i n e r p u l p s s t u d i e d 158 5 .50 . R e l a t i o n s h i p between t e n s i l e index and degree o f exposure o f the S2 l a y e r f o r a l l hardwood r e f i n e r p u l p s s t u d i e d 161 5 . 5 1 . SEM photograph o f a handsheet s u r f a c e f o r p u l p A-TMP1 162 5 .52 . SEM photograph o f a handsheet s u r f a c e f o r p u l p A-CTMP1 162 5.53 SEM photograph of a handsheet s u r f a c e f o r p u l p A-TMP4 163 5 .54 . SEM photograph of a handsheet s u r f a c e f o r p u l p A-CTMP4 163 5 .55 . SEM photograph of a handsheet i n c r o s s s e c t i o n O f p u l p A-TMP4 164 5 .56 . SEM photograph of a handsheet i n c r o s s s e c t i o n o f p u l p A-CTMP4. Note the d i f f e r e n c e i n f i b r e c o l l a p s i b i l i t y and b u l k compared t o TMP 164 5 .57 . P200 f r a c t i o n o f aspen TMP p u l p under phase c o n t r a s t i l l u m i n a t i o n (pulp A-TMP3) 166 5 .58 . P200 f r a c t i o n o f aspen CMP p u l p o f s i m i l a r f r e e n e s s than t h a t i n F i g . 5.57 (pulp A-CMP3) 166 5 .59 . P200 f r a c t i o n o f b i r c h TMP p u l p under phase c o n t r a s t i l l u m i n a t i o n (pulp B-TMP3) 167 5 .60 . P200 f r a c t i o n o f b i r c h CMP p u l p o f s i m i l a r f r e e n e s s than t h a t i n F i g . 5.59 (pulp B-CMP3) 167 5 . 6 1 . E s t i m a t e d c o m p o s i t i o n o f the P100 f r a c t i o n f o r aspen r e f i n e r p u l p s a c c o r d i n g to the o r i g i n o f the f i n e m a t e r i a l 169 5 .62 . E s t i m a t e d c o m p o s i t i o n o f the P100 f r a c t i o n f o r b i r c h r e f i n e r p u l p s a c c o r d i n g t o the o r i g i n o f the f i n e m a t e r i a l 169 XV ACKNOWLEDGEMENTS I am i n d e b t e d t o my r e s e a r c h s u p e r v i s o r , D r . J . V . H a t t o n , PAPRICAN, and t o my academic a d v i s o r , D r . L . P a s z n e r , Wood S c i e n c e , U . B . C . , f o r t h e i r i n t e r e s t , s u p p o r t and g u i d a n c e throughout the c o u r s e o f t h i s s t u d y . I am a l s o v e r y g r a t e f u l to the members o f s u p e r v i s o r y committe.e, D r s . R. W. Kennedy, R . J . Kerekes and A . Kozak f o r t h e i r c o n s t r u c t i v e c r i t i c i s m . S p e c i a l thanks are due to PAPRICAN f o r p r o v i d i n g a c c e s s t o t h e i r t e c h n i c a l s e r v i c e s and f a c i l i t i e s . I want t o e x p r e s s my s p e c i a l g r a t i t u d e t o G. W i l l i a m s , Head o f M i c r o s c o p y , PAPRICAN, f o r s h a r i n g w i t h me h i s b r o a d t e c h n i c a l knowledge, p a r t i c u l a r l y w i t h r e g a r d s to m i c r o s c o p i c a l t e c h n i q u e s . H i s a d v i c e , t i m e , p a t i e n c e and f r i e n d s h i p are a p p r e c i a t e d . To S. J o h a l and W. Gee, and many o t h e r s at PAPRICAN who w i t h t h e i r k i n d h e l p , work o r a d v i c e , a s s i s t e d me i n c o m p l e t i n g t h i s s t u d y . I am a l s o i n d e b t e d t o M. Weis , B i o l o g i c a l S c i e n c e s , U . B . C . , f o r p r o v i d i n g t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y s e r v i c e s . - Many thanks are due t o B . C . F o r e s t P r o d u c t s f o r a l l o w i n g me access to t h e i r aspen s tands and t o Ken Day, f o r e s t manager, A l e x F r a s e r R e s e a r c h F o r e s t , f o r s u p p l y i n g t r e e sample s . I ex t end my g r a t i t u d e to L . J o z s a , FORINTEK, and h i s team f o r t h e i r h e l p i n measur ing wood d e n s i t y v i a X - r a y d e n s i t o m e t r y . My g r a t i t u d e to a l l o t h e r s which i n one way o r a n o t h e r h e l p e d me d u r i n g the c o u r s e o f t h i s i n v e s t i g a t i o n . The f i n a n c i a l s u p p o r t r e c e i v e d from the C a n a d i a n I n t e r n a t i o n a l Development Agency (CIDA) i s t h a n k f u l l y x v i acknowledged. I want to thank my f a m i l y , i n p a r t i c u l a r my w i f e M a r c e l a f o r her l o v e , encouragement, and endurance throughout my y e a r s as a s t u d e n t . 1 I. INTRODUCTION The use of hardwoods f o r pulp and paper products has i n c r e a s e d c o n s i d e r a b l y i n recent years, p r i m a r i l y because of the d e c r e a s i n g a v a i l a b i l i t y of t r a d i t i o n a l old-growth c o n i f e r o u s raw m a t e r i a l s , and a l s o because of recent developments i n demonstrating the s u i t a b i l i t y of hardwoods f o r the manufacture of p r i n t i n g and w r i t i n g papers. For example, the world's t o t a l c a p a c i t y f o r the manufacture of hardwood pulps f o r t h e i r c o n v e r s i o n i n t o paper and paperboard products has i n c r e a s e d from 32.6 m i l l i o n a i r - d r y m e t r i c tonnes per year i n 1982 to 39.3 m i l l i o n adt/year i n 1988. I t i s estimated t h a t by 1993 the c a p a c i t y w i l l grow to 47.4 m i l l i o n adt/year (Anon. 1983, 1989a). P r i n t i n g papers are o f t e n manufactured with a h i g h - y i e l d mechanical pulp as the major pulp component. T h i s p r o v i d e s a f u r n i s h with the proper balance of o p t i c a l and s t r e n g t h p r o p e r t i e s . Hardwood mechanical pulps, and a l t e r n a t i v e f u r n i s h e s o f f e r e d by a p l e t h o r a of r e f i n e r mechanical p u l p i n g systems, are becoming important members of the f a m i l y of mechanical pulps a v a i l a b l e today. I t i s a n t i c i p a t e d t h a t t h e i r use w i l l continue t o grow i n Canada and elsewhere. The manufacture of h i g h - y i e l d pulps r e q u i r e s the a p p l i c a t i o n of mechanical energy to separate the f i b r e s from the wood. Due to the nature of the process, these pulps c o n t a i n a v a r i e t y of p a r t i c l e s i z e s and shapes. These p a r t i c l e s can 2 range from f i b r e bundles to very f i n e fragments o f the c e l l w a l l . The p a t t e r n o f breakdown of the wood i n t o f i b r e s and, i n t u r n , i n t o s m a l l fragments and f i n e s , i s i m p o r t a n t from the s t a n d p o i n t o f the u l t i m a t e q u a l i t y o f the p u l p . F i b r e s or t r a c h e i d s are the major component i n the wood m a t e r i a l so t h a t a l a r g e p o r t i o n o f the s m a l l e r f r a c t i o n s w i l l o r i g i n a t e from t h e s e . The q u a l i t y o f the d i f f e r e n t f i b r e f r a c t i o n s i s de termined by the s t r u c t u r e o f the f i b r e s themse lves which , i n t u r n , may be m o d i f i e d by the c o n d i t i o n s o f p u l p i n g . I t i s a n t i c i p a t e d , t h e n , t h a t examinat ion o f the l o n g f i b r e component o f a p u l p w i l l p r o v i d e an i n d i c a t i o n , not o n l y o f the breakdown p a t t e r n , but a l s o o f the q u a l i t y o f the s m a l l e r f r a c t i o n s , and the o v e r a l l q u a l i t y o f the p u l p . Almost any t r e e s p e c i e s can be reduced to m e c h a n i c a l p u l p by the r e f i n e r p r o c e s s (Sugden 1967). In g e n e r a l , the r e s u l t i n g s t r e n g t h p r o p e r t i e s o f hardwoods p u l p s are low and not g e n e r a l l y s a t i s f a c t o r y f o r i n c l u s i o n i n p r i n t i n g p a p e r s , u n l e s s some type o f c h e m i c a l t reatment i s a p p l i e d d u r i n g the p u l p i n g p r o c e s s (Atack and H e i t n e r 1982, Marton et al 1979) . Hardwood f i b r e s appear to have a more r i g i d s t r u c t u r e and a r e l a t i v e l y t h i c k e r l a y e r than softwood t r a c h e i d s . T h i s i s thought t o prevent the p e e l i n g - o f f o f the l a y e r and f i b r i l l a t i o n o f the S 2 l a y e r (Marton et al 1979) d u r i n g m e c h a n i c a l p u l p i n g . The l a y e r i s c o n s i d e r e d to impede f l e x i b i l i t y o f hardwood f i b r e s (Law et al 1985) . However, upon a p p l i c a t i o n o f a m i l d c h e m i c a l t reatment to the c h i p s , the wood i s s o f t e n e d , the f i b r e s become more f l e x i b l e , and 3 the p r i m a r y w a l l and l a y e r are p e e l e d o f f i n a manner s i m i l a r t o what i s observed i n spruce TMP f i b r e s ( G i e r t z 1977) . The i m p l i c a t i o n i s t h a t , i n o r d e r t o access the S 2 l a y e r i n hardwood f i b r e s and to promote f i b r i l l a t i o n and p r o d u c t i o n o f f i b r i l l a r f i n e s , a c h e m i c a l t rea tment i s n e c e s s a r y . Thus , the r e t e n t i o n o f the l a y e r appears to be d e t r i m e n t a l to p u l p s t r e n g t h . The exposure o f the S 2 l a y e r i s d e s i r a b l e because of i t s h i g h e r r a t i o o f c e l l u l o s e to l i g n i n content compared to the l a y e r s e x t e r n a l t o i t . T h e r e f o r e , i t possesses the h i g h e s t i n t e r f i b r e bond ing p o t e n t i a l . T h i s i s p a r t i c u l a r l y t r u e i n the case o f hardwoods, i n which the r e l a t i v e c o n c e n t r a t i o n o f c a r b o h y d r a t e s i n the secondary w a l l i s h i g h e r than i n the case o f softwoods (Rydholm 1965). However, the extent o f r e t e n t i o n o f the l a y e r - - w i t h or wi thout the compound middle l a m e l l a - - , and the r e s u l t i n g exposure o f the S 2 l a y e r has not been s t u d i e d i n a q u a n t i t a t i v e manner f o r a l a r g e number o f i s o l a t e d hardwood f i b r e s a f t e r t h e i r s e p a r a t i o n from the wood m a t r i x . Of s p e c i f i c i n t e r e s t are the e f f e c t s o f m e c h a n i c a l p u l p i n g a l t e r n a t i v e s , wood s p e c i e s and r e f i n i n g energy consumption l e v e l s on the p a t t e r n o f removal o f the o u t e r l a y e r s o f the c e l l w a l l . T h i s can be b e s t s t u d i e d by e x a m i n a t i o n o f f i b r e s i n c r o s s s e c t i o n . One t e c h n i q u e f o r a s s e s s i n g the s u r f a c e q u a l i t y o f a f i b r e was d e v e l o p e d to s tudy l i g n i n d i s t r i b u t i o n p a t t e r n s a f t e r a c e r t a i n p u l p i n g t r e a t m e n t . The p r o c e s s uses u l t r a - v i o l e t 4 l i g h t microscopy of f i b r e c r o s s s e c t i o n s (Wardrop et al 1961, K e r r and Goring 1976, Gadda et al 1981, Bruum and L i n d r o o s 1983). A n a l y s i s of middle l a m e l l a r e t e n t i o n has a l s o been done u s i n g s t a i n i n g techniques f o r softwood mechanical pulp f i b r e s i n c r o s s s e c t i o n (Kibblewhite 1983, W i l l i a m s 1989). A second technique examines the exposed f i b r e s u r f a c e under a t r a n s m i s s i o n e l e c t r o n microscope. For t h i s technique the sample p r e p a r a t i o n i s l a b o r i o u s , and the number of f i b r e s which can be analyzed i s l i m i t e d (Iwamida et al 1980a, Wardrop et al 1961) . The method makes use of the o r i e n t a t i o n of m i c r o f i b r i l s on the f i b r e s u r f a c e to d e f i n e the i d e n t i t y of the exposed l a y e r . The a n a l y s i s of f i b r e c r o s s - s e c t i o n s , although not an e n t i r e l y new t o o l , has not been used f o r the q u a n t i t a t i v e a n a l y s i s of hardwood mechanical p u l p s . The use of t h i s technique c o u l d p o t e n t i a l l y p r o v i d e answers t o q u e s t i o n s of f i b r e s u r f a c e q u a l i t y , and a l s o of other fundamental f e a t u r e s u s e f u l i n e l u c i d a t i n g aspects of hardwood r e f i n e r p u l p i n g . The p o s s i b i l i t i e s o f f e r e d by the examination of f i b r e c r o s s - s e c t i o n s i n terms of f i b r e q u a l i t y and f i b r e breakdown appear to be worth e x p l o r i n g . Examination of f i b r e s i n c r o s s - s e c t i o n , i n a d d i t i o n to those f e a t u r e s a l r e a d y mentioned r e g a r d i n g e l u c i d a t i o n of f i b r e s u r f a c e development, can p r o v i d e i n f o r m a t i o n on the manner i n which the outer l a y e r s separate from the f i b r e ; on the extent of damage to f i b r e s , i n c l u d i n g c e l l w a l l d e l a m i n a t i o n and r a d i a l f a i l u r e ; on the p r o p o r t i o n of c h e m i c a l l y - t r e a t e d 5 f i b r e s i n a r e f i n e r p u l p produced from c h e m i c a l l y - t r e a t e d wood c h i p s , as w e l l as the extent o f the t rea tment i t s e l f ; and on the presence and breakdown p a t t e r n o f t e n s i o n wood f i b r e s commonly p r e s e n t i n some hardwood s p e c i e s . These f e a t u r e s , combined w i t h the use o f o t h e r microscopy t e c h n i q u e s , s h o u l d p r o v i d e r e l i a b l e e x p l a n a t i o n s f o r the b e h a v i o r o f hardwoods i n r e f i n e r p u l p i n g and se t the b a s i s f o r p r o c e s s improvements l e a d i n g t o b e t t e r u t i l i z a t i o n o f these s p e c i e s . The amount o f m i c r o s c o p i c a l d e t a i l p r o v i d e d by such a s tudy i s expec ted to c o n t r i b u t e 'to the u n d e r s t a n d i n g o f the b e h a v i o r o f hardwood mechan ica l p u l p f i b r e s under i n t e n s e m e c h a n i c a l shear s t r e s s e s which , u l t i m a t e l y , de termine the p r o p e r t i e s o f these f i b r e s . Another aspec t o f i n t e r e s t i n the m e c h a n i c a l p u l p i n g o f hardwoods i s the breakdown of v e s s e l e lements (VE) . V e s s e l e lements are c o n d u c t i n g c e l l s , c h a r a c t e r i s t i c o f the wood of angiosperm t r e e s , g e n e r a l l y s h o r t e r and much wider than the f i b r e s o f the parent wood. Thus, t h e i r shape i s not c o n d u c i v e to bonding w i t h i n a paper sheet and can cause s e r i o u s problems d u r i n g the p r i n t i n g p r o c e s s by p i c k i n g i n the p r i n t i n g p r e s s (Marton et al 1979, C o l l e y 1973). T h i s i s p a r t i c u l a r l y troublesome i n o f f s e t p r i n t i n g which ' c o n s i s t s o f the a p p l i c a t i o n o f h i g h - v i s c o s i t y i n k s t o the paper s u r f a c e . Thus , f a s t p r i n t i n g r e q u i r e s papers o f h i g h s u r f a c e s t r e n g t h and i n t e g r i t y , and good r e s i s t a n c e t o p i c k i n g . P r e v i o u s l y , about 50% of the whole v e s s e l e lements p r e s e n t 6 i n the wood have been e s t i m a t e d t o s u r v i v e m e c h a n i c a l p u l p i n g d e s p i t e the r e f i n i n g a c t i o n (Marton et al 1979) . S i n c e the f i b r e s and, presumably , the VE of h i g h y i e l d p u l p s are more r i g i d i n nature than those o f c h e m i c a l p u l p s , VE can be a problem when i n c r e a s i n g p r o p o r t i o n s o f these p u l p s are used i n the manufacture o f p r i n t i n g p a p e r s . The s i z e - d i s t r i b u t i o n o f VE i n hardwood m e c h a n i c a l p u l p s under d i f f e r e n t mechanica l p u l p i n g c o n d i t i o n s , and t h e i r s u r v i v a l as e n t i r e e n t i t i e s upon r e f i n i n g , can p r o v i d e b a s i c i n f o r m a t i o n of the p o t e n t i a l p i c k i n g problems when l a r g e components of hardwood mechanica l p u l p s are u s e d . V e s s e l e lement s i z e m o d i f i c a t i o n a f t e r m e c h a n i c a l p u l p i n g i s an i m p o r t a n t t a s k i n e l i m i n a t i n g the p i c k i n g problem a s s o c i a t e d w i t h p r i n t i n g papers made of hardwood m e c h a n i c a l p u l p s . Wi th these q u e s t i o n s i n mind, the f o l l o w i n g o b j e c t i v e s were e s t a b l i s h e d i n t h i s t h e s i s : a) To i n v e s t i g a t e the response o f two impor tant N o r t h Amer ican hardwoods to r e f i n e r m e c h a n i c a l p u l p i n g c o n d i t i o n s , b) To c h a r a c t e r i z e such hardwood r e f i n e r m e c h a n i c a l p u l p s by d e t a i l e d examinat ion of the f i b r e c r o s s - s e c t i o n s as to the s t a t e o f t h e i r c e l l w a l l s , c) To s tudy the breakdown of v e s s e l e lements upon r e f i n i n g . 7 In o r d e r to a c h i e v e these o b j e c t i v e s , the f o l l o w i n g hypotheses were t e s t e d i n t h i s s t u d y : a) D i f f e r e n t hardwoods respond d i f f e r e n t l y t o m e c h a n i c a l d e f i b e r i z a t i o n . b) The o p t i c a l a n a l y s i s o f f i b r e c r o s s - s e c t i o n s can r e v e a l fundamental s p e c i e s ' r e sponses , and p r o v i d e q u a n t i t a t i v e d i f f e r e n c e s on f i b r e s t r u c t u r a l changes as a r e s u l t o f d i f f e r e n c e s i n s p e c i e s and a p p l i c a t i o n o f d i f f e r e n t p r o c e s s e s and r e f i n i n g energy l e v e l s . S u r f a c e p r o p e r t i e s o f the f i b r e s s h o u l d prove to be dependent on s p e c i e s as w e l l as on c h i p p r o c e s s i n g c o n d i t i o n s . Other r e l e v a n t f i b r e c r o s s - s e c t i o n a l c a t e g o r i e s may be e x p l o r e d and deve loped based on the o p t i c a l o b s e r v a t i o n s . These i n c l u d e , but are not l i m i t e d t o , f i b r e damage, the p r o p o r t i o n o f f i b r e s c h e m i c a l l y a f f e c t e d by l i q u o r p e n e t r a t i o n , and the breakdown c h a r a c t e r i s t i c s of t e n s i o n wood f i b r e s ( G - f i b r e s ) . c) A wide range o f f e a t u r e s c o u l d be r e c o r d e d by f i b r e c r o s s - s e c t i o n a l a n a l y s i s , and the s t a t i s t i c a l a n a l y s i s o f the da ta c o l l e c t e d i s expec ted t o uncover some r e l a t i o n s h i p s w i t h p r o p e r t i e s o f the p u l p . In p a r t i c u l a r , q u a n t i t a t i v e s u r f a c e p r o p e r t i e s observed f o r the f i b r e s are expec ted t o r e l a t e t o the s t r e n g t h p r o p e r t i e s o f the p u l p . d) The breakdown p a t t e r n o f v e s s e l e lements and the number of whole v e s s e l e lements t h a t s u r v i v e the r e f i n i n g o f 8 wood chips i s largely dependent on chip processing conditions. However, due to species differences i n the dimensions and structure of the vessel elements, a species e f f e c t may also be important. 9 I I . LITERATURE REVIEW 2 . 1 . Importance o f Hardwoods Canada ' s p u l p and paper economy i s p r i m a r i l y based on softwood market p u l p s and n e w s p r i n t . U t i l i z a t i o n o f hardwoods i s o n l y on a r e l a t i v e l y s m a l l s c a l e . T h i s i s p a r t i c u l a r l y t r u e f o r medium to h i g h d e n s i t y hardwoods, not o n l y i n Canada and o t h e r temperate zones but a l s o i n the t r o p i c s . Today, however, w i t h the i n c r e a s i n g acceptance o f hardwoods, o p p o r t u n i t i e s abound f o r the u t i l i z a t i o n o f t h i s r e s o u r c e . Hardwoods i n Canada comprise 5.32 b i l l i o n m 3 o f merchantable t i m b e r (Anon. 1989b) of which Populus s p e c i e s comprise 56%. Aspen (Populus tremuloides M i c h x . ) i s the major s p e c i e s , growing throughout the f o r e s t e d areas o f Canada (Hosie 1979). In B . C . , aspen f o r e s t s account f o r a t o t a l net volume o f over 220 m i l l i o n m^, a r e s o u r c e s t i l l v i r t u a l l y untapped (Zak 1989) . B i r c h i s the , second most abundant hardwood i n Canada, w i t h a merchantable volume o f over one b i l l i o n m^ d i s t r i b u t e d throughout most o f Canada. In n o r t h e r n A l b e r t a , t h e r e i s much c u r r e n t a c t i v i t y w i t h new p r o j e c t s t h a t w i l l make use o f the l a r g e a v a i l a b l e hardwood r e s o u r c e (Sims 1989) . In e a s t e r n Canada, where s u b s t a n t i a l l o s s e s o f softwood f i b r e have r e s u l t e d i n the 70s and 80s from spruce budworm i n f e s t a t i o n , a raw m a t e r i a l s u p p l y gap i s f o r e s e e n f o r the p u l p and paper i n d u s t r y between the h a r v e s t o f sound o l d - g r o w t h t i m b e r and t h a t o f second-growth 10 t i m b e r ( B i r d 1985). Hardwoods have the p o t e n t i a l t o f i l l t h i s s u p p l y gap p r o v i d e d they can be p r o c e s s e d s a t i s f a c t o r i l y . These f a c t o r s are s t i m u l a t i n g i n t e r e s t and i n c e n t i v e i n the p r o d u c t i o n o f m e c h a n i c a l p u l p s from hardwoods. The s u c c e s s f u l c o n v e r s i o n o f hardwood s p e c i e s i n t o m e c h a n i c a l p u l p r e q u i r e s somewhat d i f f e r e n t p r o c e s s i n g c o n d i t i o n s than those used f o r sof twoods . Hardwood p u l p s are s u i t a b l e f o r the manufacture of p r i n t i n g and w r i t i n g papers f o r which the demand c o n t i n u e s to grow at an approximate r a t e o f 3% per annum. I t i s e s t i m a t e d t h a t the t o t a l w o r l d c a p a c i t y f o r newspr int and o t h e r p r i n t i n g and w r i t i n g papers w i l l i n c r e a s e from 100.9 m i l l i o n a d t / y e a r i n 1988 to 112.5 m i l l i o n a d t / y e a r by 1992 (Anon. 1989a). . Hardwood p u l p s can impart good o p a c i t y , and p r o v i d e good f o r m a t i o n and s u r f a c e f i n i s h to the f i n a l paper p r o d u c t . I t i s , t h e r e f o r e , a n t i c i p a t e d t h a t the u t i l i z a t i o n o f hardwoods i n p u l p and paper p r o d u c t s w i l l c o n t i n u e to i n c r e a s e i n the near f u t u r e . S p e c i f i c a l l y f o r m e c h a n i c a l p u l p s an i n c r e a s e i n the u t i l i z a t i o n o f hardwood p u l p s has a l r e a d y been m a n i f e s t e d . In the l a s t mechan ica l p u l p i n g s u r v e y s . (Leask 1989, 1990) i t was r e p o r t e d t h a t f o u r new systems w i l l be i n s t a l l e d i n Canada f o r the manufacture o f m e c h a n i c a l p u l p s from hardwoods, add ing 2120 a d t / d a y o f p u l p t o the w o r l d ' s m e c h a n i c a l p u l p c a p a c i t y . F u r t h e r m o r e , the p r o d u c t i o n o f hardwood mechan ica l p u l p s f o r the manufacture o f p r i n t i n g papers i s l i k e l y to c o n t i n u e to i n c r e a s e (Wood and K a r n i s 11 1989, M o l d e n i u s and Jackson 1989). 2 . 2 . R e f i n e r M e c h a n i c a l P u l p i n g In the 1930's , A s p l u n d , i n Sweden, d e v e l o p e d a method f o r the p r o d u c t i o n o f c o a r s e grades o f m e c h a n i c a l p u l p f o r use i n the manufacture o f r e s i n - b o n d e d h a r d b o a r d (Atack 1985) . The method i n v o l v e d the steaming o f wood c h i p s f o r a few minutes at a p r e s s u r e o f about 800 kPa and a t emperature o f 170 ° C , f o l l o w e d by d e f i b e r i z a t i o n i n a p r e s s u r i z e d s i n g l e -r o t a t i n g d i s c r e f i n e r . Then, i n the l a t e 1940's , a tmospher ic d i s c h a r g e d i s c r e f i n e r s were used to produce s e m i c h e m i c a l p u l p s and to t r e a t r e j e c t s from m e c h a n i c a l p u l p s p r o d u c e d by s tone g r i n d i n g . The s m a l l a d d i t i o n a l s t ep r e q u i r e d to d i s c r e f i n e wood c h i p s and r e s i d u a l s was taken i n the e a r l y 1950's and, i n 1962, t h i s system, known today as r e f i n e r m e c h a n i c a l p u l p i n g (RMP), was f i r s t used c o m m e r c i a l l y to produce n e w s p r i n t - g r a d e p u l p s . In the r e f i n e r m e c h a n i c a l p u l p i n g p r o c e s s , wood c h i p s are f e d between two meta l d i s k s w i t h at l e a s t one o f them r o t a t i n g . D e f i b r a t i o n o c c u r s by m e c h a n i c a l a c t i o n as the c h i p s are f i r s t broken by the l a r g e b r e a k e r b a r s l o c a t e d near the eye o f the r e f i n e r . The c o a r s e p u l p p r o d u c e d i n t h i s manner i s f u r t h e r r e f i n e d as i t passes through the middle zone and r e f i n i n g zone o f the p l a t e towards the p e r i p h e r y o f the r e f i n e r . In 1964, the f i r s t commercia l p r e s s u r i z e d r e f i n i n g system was i n s t a l l e d i n e a s t e r n Canada. C h i p s were steamed f o r a few seconds p r i o r to b e i n g f e d i n t o a p r e s s u r i s e d r e f i n e r . A f t e r 1968, s e v e r a l new p r e s s u r i s e d systems were i n s t a l l e d i n Sweden and the U n i t e d S t a t e s based on the o r i g i n a l d e s i g n o f the A s p l u n d D e f i b r a t o r system. P u l p s produced i n t h i s type of system were named thermomechanica l p u l p s (TMP). T h i s system i n v o l v e s s teaming wood- c h i p s under p r e s s u r e i n a s teaming v e s s e l f o r 1-3 minutes , at a t emperature between 105 and 1 3 0 ° C , f o l l o w e d by p r e s s u r i z e d r e f i n i n g . The c a s i n g of the r e f i n e r i s m a i n t a i n e d at a p r e s s u r e between 200 and 300 k P a . The p u l p i s then r e f i n e d to i t s f i n a l s t a t e i n an a tmospher ic d i s c h a r g e r e f i n e r . Today, many r e f i n e r p u l p i n g systems have added an i m p r e g n a t i o n s tage t o the p r o c e s s , so t h a t the c h i p s are c h e m i c a l l y t r e a t e d p r i o r to r e f i n i n g . The o v e r a l l p r o d u c t i o n of r e f i n e r p u l p s has now s u r p a s s e d t h a t by the c o n v e n t i o n a l s tone g r i n d i n g p r o c e s s . The m o d i f i c a t i o n o f some of the impor tant v a r i a b l e s i n the d i s c r e f i n i n g system have r e s u l t e d i n the c u r r e n t major p r o c e s s e s f o r the p r o d u c t i o n o f r e f i n e r m e c h a n i c a l p u l p s a c c o r d i n g to Atack et a l (1980): a) RMP: r e f i n e r mechan ica l p u l p i n g ; a tmospher ic d i s c h a r g e r e f i n i n g o f u n t r e a t e d c h i p s , b) TMP: thermomechanica l p u l p i n g ; p r e s t e a m i n g and p r e s s u r i z e d r e f i n i n g o f u n t r e a t e d c h i p s , c) CTMP: chemithermomechanical p u l p i n g ; p r e s t e a m i n g and p r e s s u r i z e d r e f i n i n g o f t r e a t e d c h i p s , and d) CMP: chemimechanica l p u l p i n g ; a tmospher ic 13 d i s c h a r g e r e f i n i n g o f t r e a t e d c h i p s . There a r e , however, many v a r i a t i o n s o f these methods s i n c e r e f i n i n g can be, and u s u a l l y i s , done i n more than one s t a g e . M i l d c h e m i c a l t rea tments can be a p p l i e d t o the c h i p s , t o the f i r s t - s t a g e p u l p , or to the f i n i s h e d p u l p . Thus , a l t e r n a t i v e s i n c l u d e c h i p treatment (Jackson 1988, Prusas et al 1987), i n t e r - s t a g e treatment (Barnet et al 1980), p o s t -t r e a t m e n t , and r e f i n i n g of p u l p r e j e c t s (Leask 1987) . There are s e v e r a l p a t e n t s i n e x i s t e n c e r e l a t e d t o the s p e c i f i c p r o c e s s i n g c o n d i t i o n s o f these s o - c a l l e d "alphabet" p u l p s (Mackie and T a y l o r 1988). F i g u r e 2.1 shows a more d e t a i l e d c l a s s i f i c a t i o n o f most m e c h a n i c a l p u l p i n g p r o c e s s e s . Reasons f o r the r a p i d expans ion o f m e c h a n i c a l p u l p s manufac tured from c h i p s , as opposed to s tone g r i n d i n g o f b o l t s , i n c l u d e the p o s s i b i l i t y o f u s i n g wood waste, such as r e s i d u a l c h i p s and lower q u a l i t y raw m a t e r i a l l i k e sawdust and s h a v i n g s (Leask 1977); p r o d u c t i o n o f a s u b s t a n t i a l l y s t r o n g e r p u l p ; s i m p l e r and more e f f e c t i v e r e f i n e r and p u l p q u a l i t y c o n t r o l ; and the p o t e n t i a l o f u s i n g l o w - l e v e l c h e m i c a l t rea tments to produce p u l p s which can approach the s t r e n g t h o f c h e m i c a l p u l p s (White 1969). The main c r i t i c i s m of d i s k r e f i n i n g has been i t s r e l a t i v e l y high, s p e c i f i c energy consumption (White 1969) . There a r e , however, s e v e r a l ways o f r e d u c i n g energy usage i n r e f i n i n g such as the a p p l i c a t i o n o f c h e m i c a l p r e t r e a t m e n t to the wood c h i p s , c h i p d e s t r u c t u r i n g , u n i f o r m r e f i n i n g c o n s i s t e n c y , 14 cu o z M H z P-( H Z w U l O O PM P<S - J O D b P i S5 M W CO ,J P-. o z o s: SGW PGW RMP TRMP PRMP TMP LFCMP CTLF TCMP CRMP CTMP OPCO SCMP BCMP IJHYBS U H Y S JPUR TMEC E ECHANICAL HEAVY FRACnONALl LIGHT HEAVY CHEMICALLY MODIFIED M O N O PULP: Pulp that, because of i t s combination of optical and strength properties, can constitute 100% of a newsprint furnish. PRINTING PULP: Pulp that constitutes the bulk of a newsprint furnish but requires a strong pulp for reinforcement. REINFORCEMENT PULP: Strong high-yield pulp that can replace chemical pulps in a newsprint furnish. SGW STONE GR0UNDW00D PGW PRESSURIZED GR0UNDW00D RMP REFINER MECHANICAL PULP TRMP THERMO REFINER MECHANICAL PULP PRMP PRESSURIZED REFINER MECHANICAL PULP TMP THERMO MECHANICAL PULP LFCMP LONG FIBRE CHEMIMECHANICAL PULP CTFL CHEMICAL TREATMENT LONG FIBRE TCMP THERMO CHEMI MECHANICAL PULP CRMP CHEMIMECHANICAL PULP (ALSO AS CMP) CTMP CHEMI THERMO MECHANICAL PULP OPCO ONTARIO PAPER COMPANY PROCESS SCMP SULFONATED CMP (CIP PROCESS) BCMP BISULPHITE CMP UHYBS ULTRA HIGH YIELD BISULPHITE UHYS ULTRA HIGH YIELD SULPHITE Figure 2.1. Mechanical pulping processes according to Franzen (1986). 15 improved p l a t e d e s i g n , and c o m p u t e r i z e d c o n t r o l systems ( A l l a n et al 1968, A t a c k 1980, G a v e l i n 1982b, H a r t l e r 1980). The most impor tant means to o f f s e t energy consumption i s p r o b a b l y by heat r e c o v e r y when r e f i n i n g under p r e s s u r e ( G a v e l i n 1982b). A l t h o u g h most o f the mechan ica l p u l p s p r o d u c e d are used i n newspr in t manufacture , a l a r g e v a r i e t y o f p r o d u c t s c o n t a i n s u b s t a n t i a l amounts o f m e c h a n i c a l p u l p s i n c l u d i n g p r i n t i n g and w r i t i n g p a p e r s , t i s s u e s and t o w e l l i n g , d i a p e r s , l i q u i d -p a c k a g i n g b o a r d s , w a l l p a p e r , c o a t e d paper and o t h e r s p e c i a l t y papers (Leask 1982). 2 . 3 . C h a r a c t e r i z a t i o n o f M e c h a n i c a l P u l p s A model o f the l a y e r e d s t r u c t u r e o f a f i b r e i s g i v e n i n Appendix A f o r a b e t t e r u n d e r s t a n d i n g o f the t r a n f o r m a t i o n of a wood c h i p i n t o f i b r e s and f i b r e p a r t i c l e s t h a t t akes p l a c e d u r i n g r e f i n e r mechan ica l p u l p i n g . When wood i s s u b j e c t e d to m e c h a n i c a l a t t r i t i o n , the r e s u l t i n g p u l p i s composed o f p a r t i c l e s o f d i f f e r e n t shapes and s i z e s . The d i f f e r e n t p a r t i c l e s can be c l a s s i f i e d i n t o f i v e c a t e g o r i e s as shown i n F i g u r e 2 .2 , a c c o r d i n g t o M o h l i n (1982a). Today ' s f r a c t i o n a t i o n t e c h n i q u e s are unable to s e p a r a t e c o m p l e t e l y the p a r t i c l e s a c c o r d i n g to F i g u r e 2 . 2 . When u s i n g a Bauer-McNet t C l a s s i f i e r , f o r example, s h i v e s and f i b r e bundles are found i n the c o a r s e f i b r e f r a c t i o n (R50 mesh), f i b r e fragments and r i b b o n - l i k e l a m e l l a e m a i n l y i n the 16 Shives Fibres Fibre fragments Ribbon-like particles Fines F i g u r e 2.2. Schematic r e p r e s e n t a t i o n o f the p a r t i c l e s p resent i n pure mechanical pulps (Mohlin 1982a). j middle f r a c t i o n (50/200 mesh), and f i n e p a r t i c l e s i n the f i n e f r a c t i o n (P200 mesh). The r e l a t i v e amounts and q u a l i t y of t he d i f f e r e n t p a r t i c l e types are the most important c h a r a c t e r i s t i c s of mechanical p u l p s . As an i n d i c a t i o n of the bonding a b i l i t y of these p a r t i c l e s , t e n s i l e index of handsheets of separate f r a c t i o n s has been used as a c r i t e r i o n . Each type o f p a r t i c l e c o n t r i b u t e s t o the p r o p e r t i e s and performance o f a mechanical pulp i n a n o n - a d d i t i v e way (Mohlin 1982a). The i n f l u e n c e of the d i f f e r e n t p a r t i c l e s on some important pulp p r o p e r t i e s i s summarized i n F i g u r e 2.3. In g e n e r a l , t h e r e are two fundamentally d i f f e r e n t approaches t o mechanical pulp c h a r a c t e r i z a t i o n . One i s t o i m i t a t e the papermaking process i n the l a b o r a t o r y and, based on t e s t 17 Strength Properties (Tensile Index) Optical Properties (Light scatt. Coefficient) Surface Properties (Smooth-ness) Runnability (Drainage) S hives - -Fibres . + Reinforcing bars - - + Fibre fragments -Ribbons + Bonding + + -Fines + Bonding + + + -F i g u r e 2.3. I n f l u e n c e of d i f f e r e n t mechanical pulp p a r t i c l e s on some important pulp p r o p e r t i e s . (Mohlin 1982b). r e s u l t s o b t a i n e d from handsheets, e v a l u a t e the pulp q u a l i t y f o r a c e r t a i n a p p l i c a t i o n . The other i s t o measure a few b a s i c p ulp p r o p e r t i e s and, from experience, t r a n s l a t e these r e s u l t s i n t o r e l e v a n t i n f o r m a t i o n about the expected q u a l i t y and s u i t a b i l i t y of the pulp t e s t e d f o r c e r t a i n paper a p p l i c a t i o n s (Mohlin 1982a). A combination of these two approaches w i l l probably render the most i n f o r m a t i o n about a pulp, p a r t i c u l a r l y when a s s e s s i n g new raw m a t e r i a l s or proc e s s a l t e r n a t i v e s f o r which experience might be i n s u f f i c i e n t t o p r e d i c t pulp q u a l i t y . 18 Among the methods used to c h a r a c t e r i z e m e c h a n i c a l p u l p s , the s p e c i f i c s u r f a c e o f a p u l p or o f i t s f r a c t i o n s has been used t o determine the bonding p o t e n t i a l , s i n c e i t measures the ex tent o f f i b r e s u r f a c e development . Apparent d e n s i t y o f handshee t s , on the o t h e r hand, p r o v i d e s a u s e f u l measure o f the a b i l i t y o f the wet-formed web to c o n s o l i d a t e under an a p p l i e d l o a d . T h i s p r o p e r t y r e p r e s e n t s a complex index o f f i b r e f l e x i b i l i t y , degree o f f i b r e p a c k i n g and ex tent of i n t e r f i b r e bonding between the f i b r e s a f t e r d r y i n g (Jackson and W i l l i a m s 1 9 7 9 ) . These authors a l s o used the s w o l l e n volume o f f r a c t i o n s as a measure o f the degree o f d i m e n s i o n a l s w e l l i n g o f the f i b r e s as i t r e l a t e d to f i b r e f l e x i b i l i t y . The f i n e s , w i t h a l a r g e s p e c i f i c s u r f a c e as compared to the l o n g f i b r e f r a c t i o n , have an impor tant r o l e i n p r o d u c i n g paper w i t h good s t r e n g t h , o p t i c a l p r o p e r t i e s and p r i n t a b i l i t y . These p a r t i c l e s c o u l d be d i v i d e d i n t o c e l l u l o s e - c o n t a i n i n g f i n e s w i t h good bond ing a b i l i t y ( s l imy , s w o l l e n f i b r i l s and l a m e l l a e ) and a l i g n i n - c o n t a i n i n g f l o u r -l i k e f r a c t i o n c o n s i s t i n g o f n o n - s w e l l i n g f i n e s w i t h poor bond ing p o t e n t i a l (Honkasalo et al 1 9 8 3 ) . I t i s d i f f i c u l t and l a b o r i o u s , however, t o p r e p a r e handsheets from t h i s m a t e r i a l and the d i r e c t p e r m e a b i l i t y method does not work f o r f i n e s . P u l p f r e e n e s s i s perhaps the most impor tant t e s t used to c h a r a c t e r i z e m e c h a n i c a l p u l p s . Freenes s measurement enjoys w idespread use i n s p i t e o f c r i t i c i s m o f t h i s t e s t • as an 19 i n d i c a t i o n o f p u l p q u a l i t y . Freenes s t e s t i n g i s done b o t h t o a s ses s dewater ing c h a r a c t e r i s t i c s o f the p u l p and t o e s t i m a t e the s t r e n g t h o f the paper to be made. However, f o r b o t h p u r p o s e s , the t e s t i s l e s s than i d e a l ( G a v e l i n 1982a) . F o r a g i v e n m i l l , f r eenes s can be a v e r y u s e f u l i n d i c a t o r o f p u l p s t r e n g t h , but one cannot use f r e e n e s s a lone to c a l c u l a t e s t r e n g t h a c c u r a t e l y . The t e s t i s b e s t used i n a r e s t r i c t e d s i t u a t i o n where the wood supp ly i s u n i f o r m . P u l p s produced by d i f f e r e n t p r o c e s s e s at the same f reenes s can show v e r y d i f f e r e n t p r o p e r t i e s (Fahey 1987). F r e e n e s s i s a f f e c t e d d i f f e r e n t l y by the d i f f e r e n t p u l p f r a c t i o n s . F i n e s , f o r i n s t a n c e , a f f e c t f r e e n e s s much more than s t r e n g t h , whereas f i b r e l e n g t h has c o m p a r a t i v e l y l i t t l e e f f e c t on f r e e n e s s . Thus, a t e s t v a l u e o f f r e e n e s s f o r one p u l p may not mean the same f o r ano ther , p a r t i c u l a r l y i f s p e c i e s or p r o c e s s i n g c o n d i t i o n s are changed. A f u l l c h a r a c t e r i z a t i o n o f a m e c h a n i c a l p u l p w i l l p r o b a b l y never be complete wi thout a m i c r o s c o p i c s t u d y . M i c r o s c o p y p r o v i d e s an o p p o r t u n i t y to v i s u a l l y examine the whole p u l p or each i n d i v i d u a l f r a c t i o n , and to determine the s u r f a c e q u a l i t y o f f i b r e s , the ex tent o f f i b r e c u t t i n g and u n r a v e l l i n g , and the degree o f f i b r i l l a t i o n . ' I t a l s o p r o v i d e s an o p p o r t u n i t y to a p p l y c o u n t i n g t e c h n i q u e s t o de termine frequency of v a r i o u s s t r u c t u r a l m o d i f i c a t i o n s on f i b r e s , e s p e c i a l l y i n the l o n g - f i b r e f r a c t i o n (Laamanen 1983). F u r t h e r m o r e , microscopy can be a p p l i e d to p u l p samples and to bonded paper sheets t o v i s u a l l y assess t h e i r 20 papermaking p o t e n t i a l . With r e g a r d to s t u d i e s on c r o s s s e c t i o n s o f f i b r e s , microscopy c o u p l e d w i t h u l t r a v i o l e t i l l u m i n a t i o n has been used to assess l i g n i n d i s t r i b u t i o n on f i b r e s a f t e r d i f f e r e n t p u l p i n g or p r e t r e a t m e n t a l t e r n a t i v e s (Wardrop et al- 1961, Bruun and L i n d r o o s 1983, K e r r and G o r i n g 1976) . K i b b l e w h i t e (1983) has used s t a i n i n g t e c h n i q u e s on c r o s s s e c t i o n s o f softwood f i b r e s to e v a l u a t e f i b r e damage and r e t e n t i o n o f middle l a m e l l a e . 2 . 4 . E f f e c t o f Wood and F i b r e C h a r a c t e r i s t i c s i n M e c h a n i c a l  P u l p i n g The i n f l u e n c e o f wood s p e c i f i c g r a v i t y (SG) and morphology on the p h y s i c a l p r o p e r t i e s o f p u l p s i n g e n e r a l , has been the s u b j e c t o f numerous i n v e s t i g a t i o n s . In g e n e r a l t erms , SG depends upon (1) the d iameter o f the c e l l s and (2) the t h i c k n e s s o f the c e l l w a l l s , and the r e l a t i o n s h i p between the number o f c e l l s o f v a r i o u s k i n d s i n terms of (1) and (2) (Panshin and de Zeeuw 1980). The r e l a t i o n s h i p s o b t a i n e d between wood c h a r a c t e r i s t i c s and p u l p p r o p e r t i e s have been d e r i v e d mos t ly from c h e m i c a l p u l p s , and o f t e n on a r e l a t i v e l y s m a l l number o f softwood s p e c i e s . On the o t h e r hand, the g r e a t e r v a r i a b i l i t y i n morphology f o r hardwoods, b o t h w i t h i n and between s p e c i e s ( p a r t i c u l a r l y when t r o p i c a l hardwoods are c o n s i d e r e d ) , makes i t d i f f i c u l t t o d e v e l o p r e l a t i o n s h i p s between wood parameters and p u l p q u a l i t y , even f o r c h e m i c a l p u l p s . S p e c i f i c g r a v i t y has p r o b a b l y been the wood p r o p e r t y most 21 w i d e l y used t o e x p l a i n or p r e d i c t p u l p s t r e n g t h . G e n e r a l l y , i t has been c o n s i d e r e d t h a t woods o f h i g h SG, produce p u l p s w i t h low b o n d i n g a b i l i t y . A l t h o u g h SG may p r o v i d e a g e n e r a l i n d i c a t i o n o f p u l p a b i l i t y f o r a c e r t a i n raw m a t e r i a l , i t may not s e r v e as a good p r e d i c t o r o f p u l p q u a l i t y s i n c e i t p r o v i d e s l i t t l e c l u e as to the r e l a t i v e numbers, form, s t r u c t u r e and d i s t r i b u t i o n o f the v a r i o u s c e l l types t h a t make up the wood of d i f f e r e n t s p e c i e s ( S c u r f i e l d 1976). F o r m e c h a n i c a l p u l p p r o p e r t i e s , t h e r e i s no d i r e c t r e l a t i o n s h i p p e r se between wood SG and p u l p s t r e n g t h p r o p e r t i e s (Bueno 1978, De Montmorency 1965, Marton et a l 1979) . R e l a t i o n s h i p s between wood SG and p u l p bonding s t r e n g t h t h a t appear to be c l e a r f o r c h e m i c a l p u l p s , may not a p p l y to m e c h a n i c a l p u l p s . In f a c t , some woods r e s u l t i n g i n s t r o n g m e c h a n i c a l p u l p s can y i e l d c h e m i c a l p u l p s r a n k i n g low i n t e n s i l e and b u r s t s t r e n g t h (De Montmorency 1965). F o r example, b l a c k spruce w i t h a h i g h e r d e n s i t y than balsam f i r p r o d u c e d m e c h a n i c a l p u l p s o f much g r e a t e r s t r e n g t h , but c h e m i c a l p u l p s o f lower s t r e n g t h , than d i d balsam f i r . F o r hardwoods, Marton et a l (1979) showed t h a t white b i r c h (SG=0.472) produced a much b e t t e r r e f i n e r m e c h a n i c a l p u l p i n terms o f t e n s i l e s t r e n g t h than d i d Eucalyptus v i m i n a l i s L a b i l l . (SG=0.465). S i m i l a r l y , sugar maple (SG=0.607) gave s t r o n g e r p u l p than r e d oak (SG=0.548) even at h i g h e r y i e l d v a l u e s o f the former . Thus, the statement by G i e r t z (1977) t h a t p u l p y i e l d s h o u l d be lower f o r h i g h e r d e n s i t y s p e c i e s to produce a c c e p t a b l e mechan ica l p u l p s t r e n g t h , does not 22 u n i v e r s a l l y a p p l y . S i n c e a g r e a t d e a l o f c u t t i n g and f r a g m e n t a t i o n takes p l a c e d u r i n g m e c h a n i c a l p u l p i n g , i n i t i a l f i b r e l e n g t h o f the wood m a t e r i a l has not been c o n s i d e r e d an impor tant l i m i t i n g f a c t o r ( G i e r t z 1977, Marton et al 1965) . In f a c t , the midd le and f i n e s f r a c t i o n have h i g h e r bonding a b i l i t y than the l o n g f i b r e f r a c t i o n . F o r example, f o r a softwood TMP p u l p , Jackson and W i l l i a m s (1979) r e p o r t e d t h a t the 100/200 f r a c t i o n had 8 t imes the t e n s i l e s t r e n g t h o f the R14 f r a c t i o n , and twice t h a t o f the 48/100 f r a c t i o n . However, l o n g f i b r e s are important to d i s t r i b u t e s t r e s s e s , and most s t r e n g t h p r o p e r t i e s c o r r e l a t e w i t h the s i z e o f the l o n g f i b r e f r a c t i o n i . e . , p u l p s t r e n g t h p r o p e r t i e s depend on the added l e n g t h o f the f i b r e s i n the p u l p , not on the l e n g t h o f i n d i v i d u a l f i b r e s (Forgacs 1963, M o h l i n 1982b). G i e r t z (1981) i n d i c a t e d t h a t a paramount t a s k i n m e c h a n i c a l p u l p i n g must be to remove the s u r f a c e l a y e r s q u a n t i t a t i v e l y wi thout u n n e c e s s a r i l y s h o r t e n i n g the f i b r e s . On the o t h e r hand, i t i s e s s e n t i a l t h a t the f i n e s p r o d u c e d i n m e c h a n i c a l p u l p i n g be o f good q u a l i t y , i . e . f i b r i l l a r f i n e s capab le o f i m p r o v i n g bonding and sheet c o n s o l i d a t i o n , r a t h e r than chop. In f a c t , the bonding l e v e l o f a p u l p depends l a r g e l y on the f i n e m a t e r i a l ( f ines and r i b b o n - l i k e p a r t i c l e s ) because i t a c t s l i k e b r i d g e s between the s t i f f f i b r e s . These f i b r e s , however, at the same t ime become more f l e x i b l e as the f i b r e s u r f a c e l a y e r s are removed, i n d i c a t i n g t h a t one cannot v a r y the f i n e s content wi thout a l s o i n f l u e n c i n g the f i b r e 23 c h a r a c t e r i s t i c s ( G a v e l i n 1982a) . I t i s c l e a r t h a t b o t h f i b r e s and f i n e s are important f o r m e c h a n i c a l p u l p q u a l i t y . The q u a l i t y o f these f i n e s w i l l l a r g e l y depend on the way i n which the f i b r e l o s e s i t s s u r f a c e l a y e r s d u r i n g r e f i n i n g . In g e n e r a l , the bonding a b i l i t y o f bo th f r a c t i o n s w i l l improve as r e f i n i n g proceeds ( G i e r t z 1977, Simmonds and H y t t i n e n 1964) s i n c e more o f the c e l l u l o s e - r i c h S 2 l a y e r o f the f i b r e s i s exposed, and the f i n e s f r a c t i o n w i l l a l s o have a h i g h e r p r o p o r t i o n o f f i b r i l l a r - t y p e f i n e s o r i g i n a t i n g from the S 2 l a y e r . Acces s to t h i s l a y e r o f the f i b r e w a l l seems to be a v e r y impor tant c o n s i d e r a t i o n i n m e c h a n i c a l p u l p i n g . On the o t h e r hand, f o r m a t i o n of r i b b o n - l i k e p a r t i c l e s i s o f s i g n i f i c a n c e f o r the q u a l i t y o f a m e c h a n i c a l p u l p . F o r g a c s (1963) sugges ted t h a t the success o f m e c h a n i c a l l y p u l p i n g a p a r t i c u l a r s p e c i e s might be a s s o c i a t e d w i t h the a b i l i t y to promote u n r a v e l l i n g o f the f i b r e s . He showed how development o f i n i t i a l s p l i t s or c r a c k s on the S 2 l a y e r t u r n e d i n t o f i b r e u n r a v e l l i n g and r i b b o n f o r m a t i o n . Because of the l a r g e s p e c i f i c s u r f a c e o f these r i b b o n s , p a r t i c u l a r l y when f i b r i l l a t e d , they had i n c r e a s e d bonding a b i l i t y . The pr ime l i m i t a t i o n o f raw m a t e r i a l s f o r mechan ica l p u l p s appears t o be the a b i l i t y o f t h e i r f i b r e s to u n r a v e l and produce good q u a l i t y f i n e s . Thus, i t seems t h a t the i n t e r n a l f i b r e morphology, r a t h e r than s p e c i f i c g r a v i t y or f i b r e l e n g t h , a f f e c t s the s t r e n g t h and bonding c h a r a c t e r i s t i c s o f m e c h a n i c a l p u l p s . The i n t e r n a l f i b r e morphology r e f e r s not o n l y t o the r e l a t i v e t h i c k n e s s e s o f the c e l l w a l l l a y e r s , 24 p a r t i c u l a r l y the l a y e r t h a t may r e s t r i c t acces s t o the S 2 l a y e r , but t o t h e i r s t r u c t u r e and c h e m i c a l c o m p o s i t i o n . 2 . 5 . M e c h a n i c a l P u l p i n g of Hardwoods Tn g e n e r a l , hardwoods have a more heterogeneous wood anatomy than so f twoods . A g r e a t e r number o f c e l l t ypes i s found i n hardwoods. V e s s e l e lements are c h a r a c t e r i s t i c o f t h i s group o f s p e c i e s . These c e l l s are s h o r t , n o n f i b r o u s and are j o i n e d e n d - t o - e n d i n a v e r t i c a l s e r i e s to form t u b e - l i k e s t r u c t u r e s (vesse l s ) which are seen as pores on the wood c r o s s s e c t i o n . The arrangement o f pores i n the wood can v a r y c o n s i d e r a b l y between s p e c i e s , , w i t h both d i f f u s e - p o r o u s and r i n g - p o r o u s s p e c i e s b e i n g r e p r e s e n t e d i n N o r t h A m e r i c a . Hardwoods have l i t t l e or no r a d i a l a l ignment o f the f i b r e s or v e s s e l s , except f o r s h o r t r a d i a l c h a i n s o f v e s s e l s i n a few s p e c i e s (Parham 1983) . The rays bend around the p o r e s , and l a r g e v e s s e l e lements crowd o t h e r c e l l s out o f l i n e . A l s o , i n hardwoods, r a y s are more v a r i a b l e i n w i d t h , w i t h most s p e c i e s h a v i n g m u l t i s e r i a t e rays w i t h or w i thout u n i s e r i a t e r a y s . F u r t h e r , hardwoods u s u a l l y c o n t a i n more s t r a n d parenchyma w i t h a l a r g e v a r i e t y o f arrangements . Thus , i t i s not s u r p r i s i n g t h a t many hardwood s p e c i e s p r e s e n t d i f f i c u l t i e s i n t h e i r c o n v e r s i o n i n t o m e c h a n i c a l p u l p s o f a c c e p t a b l e q u a l i t y . C o n s e q u e n t l y , the r e s u l t i n g p u l p i s o f t e n low i n s t r e n g t h and not g e n e r a l l y s a t i s f a c t o r y f o r i t s i n c l u s i o n i n p r i n t i n g p a p e r s . F o r most s p e c i e s , the a p p l i c a t i o n o f a chemica l p r e t r e a t m e n t i s e s s e n t i a l f o r the 25 s u c c e s s f u l r e f i n i n g o f wood i n t o f i b r e s and f i b r e bund le s w i thout s e r i o u s f i b r e damage (Marton et al 1979, Leask 1982) . A l t h o u g h t h i s i s p a r t i c u l a r l y t r u e f o r h i g h e r d e n s i t y hardwoods, even low d e n s i t y , l i g h t c o l o u r e d s p e c i e s may a l s o r e q u i r e pre trea tment (Atack . and H e i t n e r 1982) . The improvement i n s t r e n g t h and b r i g h t n e s s w i t h d i f f e r e n t c o m b i n a t i o n s o f chemica l s i s s u b s t a n t i a l . The use o f a m i x t u r e o f NaOH and Na2SC>3 i s common and e f f e c t i v e as p r e t r e a t m e n t f o r hardwood c h i p s . Whi le the NaOH a d d i t i o n i s r e l a t e d m a i n l y to p u l p s t r e n g t h , Na2S03 improves b r i g h t n e s s (Higg ins et al 1977) . A l t h o u g h i t has a n e g a t i v e e f f e c t on p u l p b r i g h t n e s s , a l k a l i consumption i n c r e a s e s s w e l l i n g o f the f i b r e w a l l s w i th accompanying p l a s t i c i z a t i o n t h a t enhances the a b i l i t y o f the f i b r e s to conform and bond to one another d u r i n g sheet making (Katz et al 1981) . In many c a s e s , hardwood mechanica l p u l p s can be upgraded to a l e v e l where they can be s u b s t i t u t e d f o r softwood m e c h a n i c a l p u l p , or p a r t i a l l y r e p l a c e c h e m i c a l p u l p s i n p r i n t i n g p a p e r s . Hardwood f i b r e s appear to have a more r i g i d s t r u c t u r e than softwood t r a c h e i d s , making the p e e l i n g o f f o f the l a y e r and f i b r i l l a t i o n of the S 2 l a y e r d i f f i c u l t , i f not i m p o s s i b l e (Marton et al 1979). I t has a l s o been found t h a t the l a y e r o f many hardwoods i s d i s p r o p o r t i o n a l l y t h i c k , r e s u l t i n g i n poor response to f i b r i l l a t i o n upon r e f i n i n g . They sugges ted t h a t the t h i c k e r the l a y e r , the more d i f f i c u l t i t would be to remove i t . The t h i n n e r l a y e r was a s s o c i a t e d w i t h good f i b r i l l a t i o n upon r e f i n i n g . 26 However, when c h e m i c a l t rea tments are a p p l i e d and the wood i s s o f t e n e d r e s u l t i n g i n more f l e x i b l e f i b r e s , the p r i m a r y w a l l and l a y e r are s a i d to be p e e l e d o f f i n a manner s i m i l a r t o what was observed w i t h spruce TMP f i b r e s ( G i e r t z 1977). F o r these softwood f i b r e s , G i e r t z p r o p o s e d t h a t t h e r e was a p o s s i b l e weak bonding between the and S 2 l a y e r s and, upon r e f i n i n g , the p r i m a r y w a l l and l a y e r r o l l e d b a c k . At the same t ime the. l a y e r c r a c k e d and f i b r i l l a t e d to g i v e access to the S 2 l a y e r . By m i x i n g f i n e s from spruce TMP and b i r c h h i g h y i e l d b i s u l p h i t e p u l p s w i t h spruce TMP f i b r e s and measuring the s t r e n g t h p r o p e r t i e s o f the r e s u l t i n g p u l p shee t s , G i e r t z c o n c l u d e d t h a t the q u a l i t y o f the f i n e s o f hardwood mechan ica l p u l p s was i n f e r i o r to t h a t o f so f twoods . A l t h o u g h t h i s c o n c l u s i o n may s t i l l h o l d , i t s h o u l d be mentioned t h a t the f i n e s i n v o l v e d i n the exper iment were removed from spruce and b i r c h p u l p s which had d i f f e r e n t f r eenes s v a l u e s (57 ° S R or about 125 mL CSF f o r spruce and 44 ° S R or over 200 mL CSF f o r b i r c h ) . T h i s f r e e n e s s d i f f e r e n c e may account f o r p a r t o f the d i f f e r e n c e i n the f i n e s q u a l i t y r e p o r t e d . On the o t h e r hand, the f a c t t h a t hardwoods c o n t a i n abundant ray c e l l s and v e s s e l e l ements , which produce poor q u a l i t y f i n e s i n terms o f bond ing (Marton et al 1979) , may be the cause o f t h i s q u a l i t y d i f f e r e n c e . A d i f f e r e n t c o n c l u s i o n was a r r i v e d at by L e v i n a et al (1987). They r e p o r t e d an improvement i n the p u l p s t r e n g t h o f c o t t o n s u l p h i t e p u l p when aspen CTMP f i n e s (removed from a p u l p o f 26 ° S R or about 400 mL CSF) were 27 added. I t i s c l e a r t h a t more work needs to be done to u n d e r s t a n d the r o l e o f f i n e s i n hardwood mechan ica l p u l p s . F o r example, the q u a l i t y o f the f i n e s from d i f f e r e n t m e c h a n i c a l p u l p i n g a l t e r n a t i v e s r e q u i r e s s t u d y . Presumably , i f the S 2 l a y e r i s exposed, the f i b r e s w i l l have more bond ing p o t e n t i a l because o f t h e i r h i g h p e r c e n t a g e o f c a r b o h y d r a t e s compared to the compound midd le l a m e l l a (CML), which i s r i c h i n l i g n i n and r e l a t i v e l y poor i n c e l l u l o s e and h e m i c e l l u l o s e s . C e l l u l o s e , the main c a r b o h y d r a t e i n wood, has at l e a s t 3 t imes the bonding p o t e n t i a l o f l i g n i n (Rydholm 1965). Hardwoods have lower c o n c e n t r a t i o n s o f l i g n i n i n the secondary w a l l compared to sof twoods , and the e f f e c t o f CML removal s h o u l d be even more b e n e f i c i a l i n terms o f bonding than i n the case o f softwood f i b r e s . In o r d e r t o access the S 2 l a y e r , the l i g n i n - r i c h l a y e r s e x t e r n a l t o i t have to be removed. In sof twoods , the Sj_ l a y e r i s removed and at the same t ime i t f i b r i l l a t e s ( G i e r t z 1977) . In hardwoods, however, i t seems t h a t i n o r d e r to remove the l a y e r , a l k a l i n e t reatment i s r e q u i r e d . F o r E u c a l y p t u s s p e c i e s , i t was r e p o r t e d t h a t the and p r i m a r y w a l l s e p a r a t e d as a l i g n i f i e d m o r p h o l o g i c a l complex under c o l d soda p u l p i n g c o n d i t i o n s (Wardrop et a l 1961) . S u l p h o n a t i o n o f l i g n i n i s a common p r a c t i c e i n the p r e t r e a t m e n t o f c h i p s f o r p r o d u c t i o n o f m e c h a n i c a l p u l p s from sof twoods . I t r e s u l t s i n lower s h i v e c o n t e n t , a l a r g e r l o n g f i b r e f r a c t i o n and more f l e x i b l e f i b e r s , t h e r e b y 28 i n d i r e c t l y i n c r e a s i n g p u l p s t r e n g t h . However, the ex t en t o f s u l p h o n a t i o n o f hardwood l i g n i n i s g e n e r a l l y lower than t h a t f o r c o n i f e r s (Beatson et al 1985) . The b a s i c c h e m i c a l s t r u c t u r e o f l i g n i n c o n s i s t s o f pheny lpropane u n i t s . The a d d i t i o n o f one methoxyl group to the p h e n o l r i n g produces a guaiacyl u n i t , w h i l e the a d d i t i o n o f two methoxyl groups r e s u l t s i n a s y r i n g y l u n i t . Almost a l l gymnosperms c o n t a i n g u a i a c y l l i g n i n , and a l l hardwoods have a g u a i a c y l - s y r i n g y l l i g n i n , which i s a copolymer of g u a i a c y l and s y r i n g y l r e s i d u e s (Panshin and de Zeeuw 1980) . E v i d e n c e has been found t h a t d u r i n g chemimechanica l s u l f i t e p u l p i n g o f aspen, the s y r i n g y l l i g n i n u n i t s do not s u l p h o n a t e . Thus, the d i s t r i b u t i o n o f s u l p h u r f o l l o w e d the d i s t r i b u t i o n o f g u a i a c y l u n i t s (Beatson 1986). I t was a l s o found t h a t the middle l a m e l l a c e l l c o r n e r r e g i o n and the v e s s e l w a l l were g u a i a c y l r i c h , whereas most o f the s y r i n g y l u n i t s are l o c a t e d i n the f i b r e w a l l . T h i s s tatement a l s o a p p l i e s i n the case o f b i r c h wood (Fergus and G o r i n g 1970). On the o t h e r hand, Beatson et al (1985) r e p o r t e d t h a t the degree o f s u l p h o n a t i o n o f aspen l i g n i n was o n l y 50 per cent t h a t o f spruce l i g n 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 the low degree o f s u l p h o n a t i o n o f the f i b r e w a l l l i g n i n of hardwood chemimechanica l p u l p s r e s u l t s i n a lower s t r e n g t h g a i n r e l a t i v e to t h a t u s u a l l y observed f o r softwoods . I t i s a c t u a l l y the a l k a l i n i t y o f the t rea tment which i s l a r g e l y r e s p o n s i b l e f o r the i n c r e a s e i n s t r e n g t h f o r hardwood m e c h a n i c a l p u l p s . 29 2.6. Tension Wood i n Pulp Tension wood (TW) i s a form of r e a c t i o n wood i n angiosperms. I t i s thought t o be formed as a mechanism f o r r e s t o r i n g l e a n i n g t r e e stems t o t h e i r normal v e r t i c a l o r i e n t a t i o n , or f o r maintenance of a p r e f e r r e d angular o r i e n t a t i o n of branches (Panshin and de Zeeuw 1980). Thus, i t forms t y p i c a l l y on the upper s i d e of l e a n i n g t r u n k s or branches, although i t may occur i n a d i f f u s e arrangement i n the stem c r o s s - s e c t i o n , or be present with l i t t l e evidence of stem e c c e n t r i c i t y , p a r t i c u l a r l y i n s p e c i e s of Populus. Tension wood i s c h a r a c t e r i z e d by the presence of a s i n g u l a r type of f i b r e known as g e l a t i n o u s f i b r e (or G - f i b r e ) . These G - f i b r e s d i f f e r from normal wood f i b r e s i n t h a t the i n n e r p o r t i o n of the c e l l w a l l c o n s i s t s of a unique l a y e r , known as the g e l a t i n o u s l a y e r (or G - l a y e r ) , which i s composed of over 98% c e l l u l o s e (Norberg and Meir 1966) and i s l o o s e l y a t t a c h e d t o the inne r secondary w a l l . Thus, c o n t r a r y t o the r e a c t i o n wood i n softwoods, TW i s low i n l i g n i n and pentosans compared t o normal wood, but has u s u a l l y h i g h e r d e n s i t y due to the presence of G - f i b r e s . D e s p i t e i t being l a b e l e d g e l a t i n o u s , the G-layer c o n t a i n s no p e c t i n s . The c e l l u l o s e i n the G-layer i s h i g h l y c r y s t a l l i n e ; the m i c r o f i b r i l o r i e n t a t i o n i s n e a r l y p a r a l l e l t o the f i b r e a x i s and has a b e t t e r developed m i c r o c a p i l l a r y system than the c e l l w a l l s of normal wood. I t has a l s o been shown t h a t the G-layer has a l a m e l l a r s t r u c t u r e with weak l a t e r a l bonds 30 (Cote and Day 1965, Norberg and M e i e r 1966) . The t h i c k n e s s o f t h i s G - l a y e r v a r i e s c o n s i d e r a b l y depending on the s p e c i e s and degree o f development o f t e n s i o n wood (Panshin and de Zeeuw 1980) . Even w i t h i n a s i n g l e f i b r e , the G - l a y e r i s much t h i c k e r at the c e n t r e a l o n g the f i b r e l e n g t h than toward the t i p s (Okumura et a l 1977). The amount o f TW i s a l s o v a r i a b l e depending on s p e c i e s and growth c o n d i t i o n s . I sebrands and Parham (1974) r e p o r t e d up to 40 % G - f i b r e s i n s h o r t r o t a t i o n Populus, and more than 70 % has been i n d i c a t e d f o r o t h e r s p e c i e s (Rao et al 1983) . The p r e s e n c e o f G - f i b r e s a f f e c t s not o n l y wood s p e c i f i c g r a v i t y , but a l s o the s i z e and number o f o t h e r wood e l e m e n t s . K a e i s e r and Boyce (1965) i n d i c a t e d t h a t n o n - G -f i b r e s o f reduced d iameter and i n c r e a s e d c e l l w a l l t h i c k n e s s were p r e s e n t i n TW, and t h a t the d iameter o f VE d e c r e a s e d , a l t h o u g h t h e i r frequency i n c r e a s e d . F i b r e l e n g t h remained unchanged i n TW compared to normal wood, a l t h o u g h wood s p e c i f i c g r a v i t y had i n c r e a s e d (Scaramuzzi and V e c c h i 1968). H i g h p r o p o r t i o n s o f TW are u n d e s i r a b l e f o r lumber and veneer p r o d u c t s . Wool ly s u r f a c e appearance , b u c k l i n g problems and d u l l i n g o f the c u t t i n g t o o l s are a l l caused by TW.' C h e m i c a l p u l p s p r e p a r e d from TW have much lower s t r e n g t h t h a n those from normal wood. T h i s has been a t t r i b u t e d t o the lower h e m i c e l l u l o s e content o f TW f i b r e s , thus a f f e c t i n g a d v e r s e l y the s w e l l i n g and b e a t i n g c h a r a c t e r i s t i c s (Perem and Clermont 1961). More r e c e n t l y , weak sheets from TW have •been r e l a t e d to the minimal c o n f o r m a b i l i t y o f the G - f i b r e s 31 and t h e i r l a c k o f c o l l a p s e (Robinson 1977, I sebrands and Parham 1974), as shown by h i g h e r b u l k v a l u e s and c r o s s s e c t i o n s o f p u l p handsheet s . N e u t r a l s u l p h i t e semichemica l (NSSC) p u l p i n g o f aspen showed t h a t p u l p s produced from TW r e q u i r e d more b e a t i n g t o r e a c h the same f reenes s l e v e l compared t o those from normal wood. F o r the same b e a t i n g t imes , however, TW p u l p s e x h i b i t e d lower d e n s i t y , lower t e n s i l e s t r e n g t h and h i g h e r t e a r index (Clermont and Bender 1958). T h i s suggests b e t t e r p r e s e r v a t i o n of f i b r e l e n g t h i n TW NSSC p u l p s compared to those from normal wood. However, the lower sheet d e n s i t y and h i g h e r t e a r index i n d i c a t e a lower degree o f c o l l a p s e o f the G - f i b r e s . L i t t l e i n f o r m a t i o n i s a v a i l a b l e on the e f f e c t o f t e n s i o n wood on mechanica l p u l p p r o p e r t i e s . Dadswel l et a l (1957) found t h a t the h i g h e s t TW content s were a s s o c i a t e d w i t h the h i g h e s t p u l p s t r e n g t h when r e f i n i n g Eucalyptus nitens and E. regnans c h i p s under RMP c o n d i t i o n s . The ease o f f i b r e s e p a r a t i o n r e p o r t e d was a t t r i b u t e d to the lower l i g n i n content and a more "rubbery" n a t u r e o f G - f i b r e s . Work done on c h i p r e f i n i n g o f Populus deltoides t e n s i o n wood showed t h a t r e d u c t i o n o f f reeness o c c u r e d more q u i c k l y f o r t e n s i o n wood than f o r normal wood. Handsheets p r e p a r e d from TW RMP showed a s i g n i f i c a n t i n c r e a s e i n d e n s i t y and s t r e n g t h p r o p e r t i e s . The p u l p p r e s e n t e d i n d i v i d u a l i z e d and l o n g e lements accompanied by abundant r i b b o n - s h a p e d and f i b r i l l a r m a t e r i a l (Scaramuzzi and V e c c h i 1968). E v i d e n c e o f exposure 32 o f G - l a y e r s s e p a r a t e d from the p a r e n t f i b r e s was a l s o p r e s e n t e d f o r t h i s p u l p . C o n v e r s e l y , a d j a c e n t wood p r e s e n t e d p r e d o m i n a n t l y bundles o f f i b r e s and c h i p p y m a t e r i a l , and p r o d u c e d p u l p s o f low s t r e n g t h . I t i s i n t e r e s t i n g to n o t e t h a t p u l p i n g p r o c e s s e s o f a c h e m i c a l n a t u r e had d e t r i m e n t a l e f f e c t s on TW p u l p s t r e n g t h . On the o t h e r hand, pure m e c h a n i c a l p u l p s from TW are s t r o n g e r t h a n those from normal wood. The i n c r e a s e d d e n s i t y o f these p u l p s i n d i c a t e s t h a t the s t r i p p i n g o f G - l a y e r s out o f the i n s i d e o f the f i b r e s might be the cause f o r s t r o n g e r m e c h a n i c a l p u l p s from TW. Assessment o f the breakdown p a t t e r n o f G - f i b r e s can p r o v i d e fundamental d e t a i l s o f the b e n e f i c i a l or d e t r i m e n t a l e f f e c t s o f t e n s i o n wood on pure m e c h a n i c a l p u l p i n g and o t h e r c h e m i c a l m o d i f i c a t i o n s o f t h i s p r o c e s s . N o t h i n g has been r e p o r t e d on the e f f e c t o f TW i n chemimechanica l p u l p s . 2 . 7 . The Ro le o f V e s s e l Elements i n P u l p V e s s e l s are t u b e - l i k e s t r u c t u r e s o f undetermined l e n g t h , composed o f i n d i v i d u a l c e l l s c a l l e d v e s s e l e lements (VE) . These c e l l s , p r e s e n t on ly i n wood o f dec iduous t r e e s , are s p e c i a l i z e d f o r c o n d u c t i o n and are g e n e r a l l y much l a r g e r i n d i a m e t e r , s h o r t e r i n l e n g t h and have t h i n n e r w a l l s than the a s s o c i a t e d f i b r e s (Haygreen and Bowyer 1982) . In the manufacture o f p r i n t i n g paper p r o d u c t s , VE can cause d i f f i c u l t y w i t h r e s p e c t to the s u r f a c e q u a l i t y o f the paper s i n c e t h e i r shape i s not conduc ive to development o f s t r o n g 33 bonds between p u l p e l ements . The c h e m i c a l c o m p o s i t i o n o f VE d i f f e r s from t h a t o f the f i b r e s . W h i l e the l i g n i n i n the secondary w a l l o f f i b r e s i s r i c h i n s y r i n g y l u n i t s , t h a t o f the VE i s mos t ly o f the g u a i a c y l type (Fergus and G o r i n g 1970, H a r d e l l et al 1980) . The b o n d i n g a b i l i t y o f VE i s g e n e r a l l y lower than t h a t o f f i b r e s . Handsheets formed from u n r e f i n e d VE o f k r a f t p u l p s gave s t r e n g t h p r o p e r t i e s i n f e r i o r to those o f the f i b r e s (Marton and Agarwal 1965) . However, when VE are p r e s e n t i n q u a n t i t i e s not exceed ing those found i n n a t u r e , they c o n t r i b u t e to the s t r e n g t h o f hardwood k r a f t p u l p s . The p o t e n t i a l adverse i n f l u e n c e o f VE i n a paper sheet t h e r e f o r e a r i s e s not from a r e d u c t i o n o f bonding between e lements , as measured by c o n v e n t i o n a l p u l p s t r e n g t h t e s t s , but because of t h e i r presence i n the paper s u r f a c e . V e s s e l e lements p r e s e n t on the s u r f a c e of a p r i n t i n g paper sheet may reduce i t s s u r f a c e r e s i s t a n c e . T h i s can cause problems d u r i n g the p r i n t i n g p r o c e s s . D u r i n g o f f s e t p r i n t i n g , v e s s e l p i c k i n g or l i f t - o f f can o c c u r , c a u s i n g the d e p o s i t i o n o f these e lements on the p r i n t i n g s u r f a c e . T h i s w i l l reduce the q u a l i t y o f p r i n t i n g and can l e a d to p e r i o d i c shutdowns o f the p r e s s t o c l e a n the p r i n t i n g b l a n k e t s (Smook 1982). V e s s e l p i c k i n g has been s t u d i e d f o r a number o f hardwood s p e c i e s , i n c l u d i n g t r o p i c a l woods, but always f o r c h e m i c a l p u l p s . From experiments c a r r i e d out by C o l l e y ( C o l l e y 1973, C o l l e y 1975 and C o l l e y and Ward 1976), i t was found t h a t 34 b o t h f i b r e and v e s s e l element morphology a f f e c t e d v e s s e l p i c k i n g . F o r a g i v e n s p e c i e s , a r e d u c t i o n o f v e s s e l / f i b r e r a t i o , an i n c r e a s e i n b e a t i n g t ime , and the r e d u c t i o n o f v e s s e l element s i z e , a l l caused a r e d u c t i o n o f v e s s e l p i c k i n g t endency . Nanko et al (1988) r e p o r t e d t h a t h i g h c o n s i s t e n c y r e f i n i n g c o u l d reduce v e s s e l element s i z e . However, t h i s was o n l y e f f e c t i v e b e f o r e a f r e e n e s s l e v e l o f 400 mL CSF was reached , beyond which f u r t h e r r e f i n i n g gave o n l y s m a l l changes i n s i z e and numbers o f V E , r e g a r d l e s s o f the method of r e f i n i n g . Mukoyoshi et al (1986) found t h a t a b l e a c h e d p u l p p r e p a r e d by k r a f t c o o k i n g o f c h e m i m e c h a n i c a l l y p r e f i b e r i z e d c h i p s had lower v e s s e l p i c k i n g tendency than c o n v e n t i o n a l l y b l e a c h e d k r a f t p u l p . T h i s i n d i c a t e s t h a t t h e r e might be a r e d u c t i o n o f VE s i z e upon c h i p r e f i n i n g . S e v e r a l o t h e r means o f s u p p r e s i n g v e s s e l p i c k i n g have a l s o been r e p o r t e d . Perhaps the most common one i s the a p p l i c a t i o n o f p r o p e r s u r f a c e s i z i n g (McGovern 1977, C o l l e y and Ward 1976) . A l s o , p a r t i a l removal o f l a r g e VE from the p u l p u s i n g h y d r o c y c l o n e s (Ohsawa 1987) was i n d i c a t e d as u s e f u l , a l t h o u g h i t was not as e f f e c t i v e as u s i n g s t r a t i f i e d sheet f o r m a t i o n t e c h n i q u e s to cover the VE i n the paper s u r f a c e w i t h a very t h i n l a y e r o f f i b r e s (Nanko et al 1987) . A l t h o u g h v e s s e l p i c k i n g has not been r e p o r t e d f o r m e c h a n i c a l p u l p s , i t i s a p o t e n t i a l prob lem, p a r t i c u l a r l y i f the use o f hardwood m e c h a n i c a l p u l p s i n c r e a s e s f o r the p r o d u c t i o n o f p r i n t i n g p a p e r s . Marton et al (1979) noted the e x i s t e n c e o f whole VE i n TMP p u l p s , and even more so i n CTMP p u l p s . S i n c e 35 these m e c h a n i c a l p u l p f i b r e s do not have the b o n d i n g p o t e n t i a l o f k r a f t p u l p s , and the v e s s e l e lements are p o s s i b l y more r i g i d and l e s s conformable i n m e c h a n i c a l p u l p s , v e s s e l p i c k i n g i s l i k e l y to o c c u r . I t i s a n t i c i p a t e d , however, t h a t mechan ica l d e f i b r a t i o n w i l l cause c o n s i d e r a b l e r e d u c t i o n o f v e s s e l element s i z e . The e f f e c t o f d i f f e r e n t m e c h a n i c a l p u l p i n g p r o c e s s e s on the breakdown p a t t e r n o f v e s s e l e lements has not been r e p o r t e d i n the l i t e r a t u r e so f a r . However, Marton et al (1979) e s t i m a t e d t h a t about one-h a l f o f the whole v e s s e l e lements p r e s e n t i n the wood were d i s i n t e g r a t e d i n t o f i n e s d u r i n g TMP p u l p i n g . Under a l k a l i n e s u l p h i t e CTMP r e f i n i n g c o n d i t i o n s , the number o f whole VE p e r gram of p u l p almost doub led f o r whi te b i r c h , but s u r p r i s i n g l y d e c r e a s e d f o r E u c a l y p t u s . The number o f VE fragments was a l s o counted , but the minimum p a r t i c l e s i z e was not s p e c i f i e d . One would expec t , however, t h a t v e r y s m a l l p a r t i c l e s would be i n c r e a s i n g l y d i f f i c u l t t o i d e n t i f y . C o n t r a r y t o these f i n d i n g s , G i e r t z (1977) i n d i c a t e d t h a t VE were reduced to f i n e m a t e r i a l which mos t ly ended up i n the 100/200 f r a c t i o n o f . a Bauer McNett C l a s s i f i e r . The q u e s t i o n o f the way i n which VE breakdown o c c u r s i n c h i p and p u l p r e f i n i n g has not been s o l v e d . E s t i m a t i o n o f the s u r v i v a l o f whole VE as w e l l as p a r t i c l e s i z e d i s t r i b u t i o n upon r e f i n i n g would p r o v i d e b a s i c i n f o r m a t i o n o f the p a t t e r n o f breakdown o f V E . Of s p e c i f i c i n t e r e s t i s the s tudy o f VE breakdown under c o n d i t i o n s o f wood s o f t e n i n g and r e f i n i n g . 36 I I I . METHODOLOGY T h i s c h a p t e r d e s c r i b e s the methods f o l l o w e d t o c h a r a c t e r i z e the wood s p e c i e s used f o r p u l p i n g , t o produce and e v a l u a t e the p u l p s , and the m i c r o s c o p i c t e c h n i q u e s i n v o l v e d i n t h e a n a l y s i s o f f i b r e s and v e s s e l element breakdown d u r i n g m e c h a n i c a l p u l p i n g . A g e n e r a l o u t l i n e o f the e x p e r i m e n t a l p r o c e d u r e s used i s p r e s e n t e d i n F i g u r e 3 . 1 . S p e c i f i c a l l y , the e f f e c t s o f t h r e e m e c h a n i c a l p u l p i n g p r o c e s s e s (TMP, CTMP and CMP) were s t u d i e d on the d e f i b r a t i o n c h a r a c t e r i s t i c s o f aspen and b i r c h woods. Four p u l p s were produced by each o f these p r o c e s s e s f o r each s p e c i e s , over a b r o a d range o f r e f i n i n g energy consumption l e v e l s . A t o t a l of 24 p u l p s was a n a l y s e d f o r the two s p e c i e s s e l e c t e d . • P u l p i d e n t i f i c a t i o n codes and p r o p e r t i e s are p r e s e n t e d i n T a b l e 4 . 9 . 3 . 1 . Wood Procurement Two hardwood s p e c i e s were s e l e c t e d f o r t h i s s tudy because o f t h e i r importance to Canada: aspen (Populus tremuloides M i c h x . ) and white b i r c h (Betul'a papyrifera M a r s h . ) . One t r e e o f each s p e c i e s was f e l l e d at the A l e x F r a s e r F o r e s t at W i l l i a m s L a k e , B . C . Both t r e e s were 110 y e a r s o f age and had a d i a m e t e r o f 22 cm at b r e a s t h e i g h t (DBH) . The t r e e s were cut i n t o l o g s o f about 1.20 m i n l e n g t h and debarked by hand. Any v i s i b l e decay was removed from the l o g s by s p l i t t i n g them i n 4 q u a r t e r s a l o n g the g r a i n and c u t t i n g out 37 WOOD PROCUREMENT I DEBARKING X-RAY DENSITOMETRY CHIPPING & SCREENING CHIP MIXING KRAFT PULPING FIBRE LENGTH VE SIZE % TW REFINER PULPING: TMP, CTMP, CMP LATENCY REMOVAL & SCREENING FRACTIONATION R48 X-SECTION HANDSHEETS VE SIZE PULP SLIDES LIGHT MICROSCOPY LIGHT MICROSCOPY TEM PAPER TESTING gure 3 . 1 . G e n e r a l O u t l i n e o f E x p e r i m e n t a l P r o c e d u r e s . V E : v e s s e l e lements ; TW:tens ion wood f i b r e s ; SEM:scanning e l e c t r o n m i c r o s c o p e ; T E M : t r a n s m i s s i o n e l e c t r o n m i c r o s c o p e . 38 the a f f e c t e d areas w i t h a band-saw b e f o r e c h i p p i n g . S i n c e a c o n s i d e r a b l e p o r t i o n of the aspen t r e e was a f f e c t e d , and t h e r e f o r e removed, a second aspen t r e e (80 years o f age, DBH=30 cm) was taken from an area near L y t t o n , B . C . , i n o r d e r to ensure a s u f f i c i e n t amount o f m a t e r i a l t o c a r r y out t h i s i n v e s t i g a t i o n . The t r e e s were c h a r a c t e r i z e d i n terms o f wood d e n s i t y by means o f d i r e c t r e a d i n g X - r a y d e n s i t o m e t r y as d e s c r i b e d by J o z s a and Myronuk (1986) . Wood d i s k s 1 i n (25 mm) t h i c k at DBH, and at h e i g h t s o f 20, 40, 60 and 80% up the t r e e stem l e n g t h were cut and p r o c e s s e d . The e x t r a c t e d t h i n c r o s s s e c t i o n s a n a l y s e d by d e n s i t o m e t r y p r o v i d e d wood d e n s i t y v a l u e s t h a t corresponded to b a s i c r e l a t i v e d e n s i t y (oven d r i e d weight per green volume) a c c o r d i n g to the c a l i b r a t i o n p r o c e d u r e deve loped by J o z s a et al (1987) . 3 . 2 . P r o d u c t i o n and C h a r a c t e r i z a t i o n o f C h i p s Only sound wood p i e c e s were used i n the p r o d u c t i o n o f c h i p s . Some of the l ogs had to be s p l i t f u r t h e r a l o n g the g r a i n to comply w i t h a maximum of 9x9 i n (23x23 cm) c r o s s - s e c t i o n r e q u i r e d by the shape and s i z e o f the c h i p p e r s p o u t . The wood p i e c e s o f each s p e c i e s were c h i p p e d i n a 60 H . P . , s i x -k n i f e d i s k c h i p p e r . The c h i p s were c o l l e c t e d i n p l a s t i c bags and s t o r e d i n a f r e e z e r at about -7 ° C b e f o r e f u r t h e r use . In o r d e r t o remove o v e r s i z e d m a t e r i a l and f i n e s , the c h i p s were then screened i n a c o n t i n u o u s Burnaby M i l l and Machinery Equipment L t d p i l o t s c a l e c h i p s c r e e n w i t h two 39 decks: an upper deck with 1.2 5 i n (32 mm) h o l e s and a lower deck with h o l e s of 0.25 i n (6 mm). The s o l i d s c ontents of the aspen and b i r c h c h i p s were 61.1% and 59.4%, r e s p e c t i v e l y . Accept aspen c h i p s from the two t r e e s c u t were thoroughly mixed. T h i s was done, by forming a p i l e of c h i p s and s h o v e l l i n g them i n t o a doughnut-shape arrangement. The c h i p s were then s h o v e l l e d back i n t o the c e n t r e t o form a new p i l e . T h i s o p e r a t i o n was repeated 5 times. The p r o p o r t i o n of c h i p s from W i l l i a m s Lake and L y t t o n i n the mix was approximately 0.625:1 . B i r c h accept c h i p s were a l s o mixed t o g e t h e r to p r o v i d e a uniform c h i p f u r n i s h . A r e p r e s e n t a t i v e sample of accept c h i p s from each s p e c i e s was c h a r a c t e r i z e d by t h i c k n e s s c l a s s i f i c a t i o n (Table 3.1) u s i n g a Wennberg Chip C l a s s i f i e r . TABLE 3.1. Accept c h i p t h i c k n e s s c l a s s i f i c a t i o n SPECIES THICKNESS ASPEN BIRCH < 2 mm 0.8% 2 .8% 2-6 mm 94 .1 95.5% > 6 mm 5.2% 1.7% 40 These c h i p s were used i n t h e manufacture o f thermomechanical p u l p s (TMP) and chemithermomechanical p u l p s (CTMP). F o r t h e manufacture of chemimechanical p u l p s (CMP), a p o r t i o n o f t h e s e c h i p s was s c r e e n e d by t h i c k n e s s and o n l y t h e 2-6 mm t h i c k a c c e p t s were used f o r p u l p i n g . K r a f t p u l p i n g t r i a l s were a l s o done u s i n g t h i s m a t e r i a l . F i b r e l e n g t h was measured from t h e c h i p s produced f o r t h e two s p e c i e s . M a t c h s t i c k - l i k e p i e c e s were c u t from randomly s e l e c t e d c h i p s , macerated i n a m i x t u r e o f hydrogen p e r o x i d e and a c e t i c a c i d (50/50) and g e n t l y b o i l e d u n t i l f i b r e s e p a r a t i o n o c c u r r e d , as d e s c r i b e d i n CPPA S t a n d a r d B.2P. F i b r e l e n g t h was t h e n measured by p r o j e c t i n g s l i d e s o f f i b r e s s t a i n e d w i t h t o l u i d i n e b l u e , and t r a c i n g t h e s e w i t h a probe o f an NEA F i b r e Length Counter. Each l e n g t h measured was a u t o m a t i c a l l y e n t e r e d i n t o a c o r r e s p o n d i n g c l a s s i n t e r v a l . These i n t e r v a l s were 80 um a p a r t . 3.3. P r e p a r a t i o n o f P u l p s T h i s s t u d y i s based on t w e n t y - f o u r hardwood r e f i n e r p u l p s s e l e c t e d from s e v e r a l p u l p r u n s . Twelve p u l p s were p r e p a r e d f o r each s p e c i e s . The p r o c e s s e s by which t h e s e p u l p s were produced encompassed TMP, CTMP and CMP c o n d i t i o n s and each c o v e r e d f o u r p o i n t s over a wide range of r e f i n i n g energy l e v e l s and p u l p f r e e n e s s , as shown i n F i g u r e 3.2. The p u l p s p r o d u c e d a r e g i v e n an i d e n t i f i c a t i o n code i n T a b l e 4.9, and t h e i r c o r r e s p o n d i n g p u l p p r o p e r t i e s a r e p r e s e n t e d i n T a b l e s 4.9 t h r o u g h 4.11. 41 550 Refining Energy, MJ/kg F i g u r e 3 . 2 . R e l a t i o n s h i p between s p e c i f i c energy consumption and unscreened freeness f o r the hardwood r e f i n e r pulps produced. Before any p u l p i n g took p l a c e , the f r o z e n c h i p s were thawed t o room temperature. The r e f i n i n g energy consumption was c a l c u l a t e d from c h a r t s r e c o r d i n g a watt meter output attached t o the r e f i n e r . The pulps produced were t e s t e d f o r unscreened f r e e n e s s a f t e r hot d i s i n t e g r a t i o n as d e s c r i b e d i n S e c t i o n 5 . 4 . The pulps were s t o r e d i n s e a l e d p l a s t i c bags a t about - 7 °C i f not processed immediately. 42 3 . 3 . 1 . P r o d u c t i o n o f Thermomechanical P u l p s (TMP) In the p r i m a r y r e f i n e r p u l p i n g , a Sunds D e f i b r a t o r TMP 300 p r e s s u r i z e d l a b o r a t o r y r e f i n e r (300 mm diameter) was used f o r the p r o d u c t i o n o f TMP from aspen and b i r c h , under the f o l l o w i n g c o n d i t i o n s : - Atmospher ic Pres teaming: 15 min - P r e h e a t i n g : Temperature: 125 ° C P r e s s u r e : 16 p s i (110 kPa) Time: 5 min - R e f i n e r Hous ing: Temperature: 128 ° C P r e s s u r e : 18 p s i (124 kPa) - Prex Impregnator Compression R a t i o : 1:3 - R e f i n e r P l a t e P a t t e r n : Rotor R3809 S t a t o r S3804 - R e f i n i n g c o n s i s t e n c y : approx . 20% These c o n d i t i o n s were s i m i l a r to those r e p o r t e d i n the l i t e r a t u r e f o r the p r o d u c t i o n o f hardwood TMP (Jackson 1982, Marton et al 1979, Law et al 1985, Koran 1988) . The gap between the p l a t e s was d e c r e a s e d s t epwise d u r i n g a r e f i n i n g run to i n c r e a s e the r e f i n i n g e n e r g y . In t h i s manner, a number o f p u l p s w i t h d i f f e r e n t f r e e n e s s v a l u e s was c o l l e c t e d at the o u t l e t o f the r e f i n e r sys tem. However, o n l y one p u l p was s e l e c t e d from each s p e c i e s f o r secondary r e f i n i n g . The p u l p o b t a i n e d from the p r i m a r y system was f u r t h e r r e f i n e d i n a 12 i n (300 mm) d i a m e t e r S p r o u t - W a l d r o n 43 l a b o r a t o r y r e f i n e r w i t h a tmospher ic d i s c h a r g e . To o b t a i n d i f f e r e n t l e v e l s o f r e f i n i n g energy, the number o f passes was i n c r e a s e d a n d / o r the gap between the r e f i n e r p l a t e s was d e c r e a s e d . The r e f i n i n g c o n s i s t e n c y was kept between 15 to 20 % and the r e f i n i n g temperature was c o n t r o l l e d a t 8 5 ° C . R e f i n e r p l a t e s w i t h a d e s i g n a t e d D2A507 p a t t e r n were u s e d . In an e f f o r t to measure p u l p y i e l d , a l l the p u l p m a t e r i a l was c o l l e c t e d d u r i n g the r e f i n i n g p r o c e s s . However, because o f the l a r g e amount o f p u l p produced i n any s i n g l e t r i a l and the d i f f e r e n c e i n c o n s i s t e n c y w i t h i n t h i s m a t e r i a l , the v a l u e s o b t a i n e d were not c o n s i d e r e d to be a c c u r a t e . 3 . 3 . 2 . P r o d u c t i o n of Chemithermomechanical P u l p s (CTMP) The same p r i m a r y system which was used f o r TMP p r o d u c t i o n was a l s o used f o r the CTMP r u n s . The same c o n d i t i o n s o f p r e -s teaming , compress ion r a t i o , p r e - h e a t i n g , r e f i n e r h o u s i n g and r e f i n e r p l a t e p a t t e r n were m a i n t a i n e d , as b e f o r e . The c h e m i c a l p r e - t r e a t m e n t o f the c h i p s was c a r r i e d out as f o l l o w s . A f t e r p r e - s t e a m i n g , the compressed c h i p s were a l l o w e d to expand i n a s o l u t i o n o f sodium h y d r o x i d e and sodium s u l f i t e o f known c o n c e n t r a t i o n w i t h i n the p r e - h e a t i n g v e s s e l . The c o n c e n t r a t i o n o f these reagents was a d j u s t e d to p r o v i d e a l i q u o r consumption by the c h i p s o f 2% Na2S03 and 3% NaOH based on the amount of o v e n - d r i e d c h i p s . The l i q u o r pH was 13.6 f o r both s p e c i e s . The s e l e c t e d p r e - t r e a t m e n t r e p r e s e n t e d t y p i c a l c o n d i t i o n s used to o p t i m i z e hardwood CTMP q u a l i t y (Higg ins et al 1978, 44 S inkey and C h a r t e r s 1977, Jackson 1982, 1987, Law et al 1985, V a l a d e and Law 1988). F o r aspen, i t was p o s s i b l e to o b t a i n low l e v e l s o f p u l p f r e e n e s s by d e c r e a s i n g the p l a t e gap. T h i s a l l o w e d p u l p s t o be made w i t h i n the d e s i r e d range o f 100-300 mL CSF f r e e n e s s . In the case o f b i r c h , energy i n p u t c o u l d not be i n c r e a s e d beyond a c e r t a i n v a l u e , wi thout c a u s i n g e x c e s s i v e d a r k e n i n g o f the p u l p . Thus, o n l y pulp's at h i g h f r e e n e s s l e v e l s (above 400 mL CSF) were produced , and a d d i t i o n a l passes t h rou gh the a tmospher i c d i s c h a r g e r e f i n e r were r e q u i r e d i n o r d e r t o o b t a i n b i r c h p u l p s o f lower f r e e n e s s . The c o n d i t i o n s used f o r the secondary r e f i n i n g o f b i r c h CTMP were s i m i l a r to those f o r TMP. As i n the case o f TMP, y i e l d d e t e r m i n a t i o n was a l s o at tempted f o r CTMP. 3 . 3 . 3 . P r o d u c t i o n o f Chemimechanical P u l p s (CMP) A more severe p r e - t r e a t m e n t o f the wood c h i p s was c a r r i e d out to assess d i f f e r e n c e s i n f i b r e development upon r e f i n i n g . F o r the p r o d u c t i o n o f p u l p w i t h t h i s p r o c e s s , the c h i p s were p r e - t r e a t e d under the f o l l o w i n g c o n d i t i o n s : - A tmospher i c P r e - s t e a m i n g : 15 min - C h e m i c a l charge : 2% Na2SC>3 based on o v e n - d r i e d c h i p s 5% NaOH based on o v e n - d r i e d c h i p s - I n i t i a l pH of l i q u o r : 13.0 - L i q u o r to Wood R a t i o : 5:1 - Maximum Temperature: 135 °C - Time t o Maximum Temperature: 50 min - Time at Maximum Temperature: 30 min These c o n d i t i o n s are more severe than those g e n e r a l l y r e p o r t e d i n the l i t e r a t u r e , p a r t i c u l a r l y i n terms o f the t ime and temperature o f p r e - c o o k i n g (Higg ins et al 1977, 1978, S inkey and C h a r t e r s 1977, A l l a n et al 1968, Marton et al 1979, V a l a d e and Law 1988, Leask 1968). More d r a s t i c c o n d i t i o n s were used here to see i f the p r e - t r e a t m e n t c o u l d cause complete r e m o v a l . o f the compound middle l a m e l l a and l a y e r s from CMP f i b r e s , and i f the c e l l w a l l was weakened enough to produce f i b r e s t h a t f a i l e d r a d i a l l y . A known weight o f c h i p s was p l a c e d i n a basket i n s i d e the d i g e s t e r f o r y i e l d e v a l u a t i o n . A f t e r the cook, these c h i p s were soaked i n water f o r 5 days w i th f r e q u e n t water changes . Washing was complete when no f u r t h e r change i n the c o l o r o f the water was o b s e r v e d . Immediately a f t e r the cook, the t r e a t e d c h i p s were r e f i n e d i n the Sprout Waldron atmospher ic d i s c h a r g e r e f i n e r . Four batches from s e v e r a l p u l p s , produced from each s p e c i e s by a d j u s t i n g energy i n p u t l e v e l s , were s e l e c t e d f o r e v a l u a t i o n . 3 . 3 . 4 . P r o d u c t i o n o f K r a f t Pu lps I n i t i a l l y , c o n v e n t i o n a l k r a f t p u l p s were p r o d u c e d to as ses s the presence o f t e n s i o n wood (TW) f i b r e s by a n a l y s i s o f f i b r e c r o s s s e c t i o n s . The presence o f t e n s i o n wood f i b r e s i s i l l u s t r a t e d i n F i g u r e 3 . 3 . The p r o p o r t i o n o f TW f i b r e s was measured from k r a f t f i b r e c r o s s s e c t i o n s , as shown i n F i g u r e 46 (OOAU* H % D B I F i g u r e 3 . 3 . Cross s e c t i o n o f aspen t e n s i o n wood. A Herzberg reagent s t a i n e d p u r p l e the G - l a y e r s , w h i l e the l i g n i f i e d m a t e r i a l t u r n e d y e l l o w . F i g u r e 3 . 4 . Aspen k r a f t p u l p f i b r e s s t a i n e d w i t h T o l u i d i n e Blue 0, showing G - f i b r e s i n c r o s s s e c t i o n . 47 3 . 4 . K r a f t p u l p s were a l s o used to g a i n i n f o r m a t i o n on the s e p a r a t i o n o f c e l l w a l l l a y e r s f o l l o w i n g p u l p i n g f o r the two s p e c i e s under s t u d y . F u r t h e r , these p u l p s were a l s o used i n measur ing the o r i g i n a l s i z e o f v e s s e l e lements f o r d e t e r m i n i n g the p o s s i b l e v e s s e l element breakdown d u r i n g m e c h a n i c a l p u l p i n g . R e p r e s e n t a t i v e samples o f aspen and b i r c h c h i p f u r n i s h e s were p u l p e d to Kappa Numbers o f 15.8 and 15 .5 , r e s p e c t i v e l y (approximate y i e l d s o f 56 and 52%) , f o r which H f a c t o r s o f 955 and 1110 were r e q u i r e d . The p u l p s were then washed and s c r e e n e d through an 0 . 008 i n (0.2 mm) s l o t f l a t s c r e e n b e f o r e f u r t h e r p r o c e s s i n g . 3.4. P u l p P r o c e s s i n g L a t e n c y was removed by hot d i s i n t e g r a t i o n b e f o r e the r e f i n e r p u l p s produced were e v a l u a t e d . I t i s i m p o r t a n t to remove l a t e n c y p r i o r to the c h a r a c t e r i z a t i o n o f m e c h a n i c a l p u l p s . L a t e n c y i s a s t r e s s c o n d i t i o n w i t h i n the f i b r e w a l l and i s l a r g e l y caused by m e c h a n i c a l p u l p i n g . In l a t e n c y removal , the l i g n i n - h e m i c e l l u l o s e m a t r i x o f the m e c h a n i c a l p u l p f i b r e s o f t e n s and the c e l l u l o s e i s r e l e a s e d from i t s s t r e s s e d c o n d i t i o n . T h i s r e s u l t s i n a p u l p showing lower f r e e n e s s and h i g h e r s t r e n g t h v a l u e s than the u n t r e a t e d f i b r e (Fahey 1987) . La tency removal was done by d i s i n t e g r a t i n g the p u l p s w i t h b o i l i n g water f o r 5 minutes (1500 r e v o l u t i o n s ) at a c o n s i s t e n c y of 1.2% i n a B r i t i s h S tandard D i s i n t e g r a t o r . The 48 p u l p was then f u r t h e r d i l u t e d with c o l d water and screened a c c o r d i n g t o PPRIC Standard T e s t i n g Procedure PS-3 (Method B) i n a f l a t screen with s l o t s 0.006 i n (0.15 mm) wide. F i n e s were r e c i r c u l a t e d and e v e n t u a l l y c o l l e c t e d with the r e s t of the p u l p . 3.5. Pulp T e s t i n g The f o l l o w i n g t e s t s were performed on the wet mechanical p u l p s : - Canadian Standard Freeness: CPPA Standard C . l - Shive Content: Pulmac Shive A n a l y s e r - Bauer-McNett C l a s s i f i c a t i o n (28, 48, 100, 150 and 200 mesh s c r e e n s ) : TAPPI Standard 233 cm-82 Pulp handsheets were prepared a c c o r d i n g t o CPPA Standard C.4, with f i n e s r e c i r c u l a t i o n . The f i n e s m a t e r i a l i s a very important p a r t of mechanical pulps i n terms of bonding, l i g h t s c a t t e r i n g a b i l i t y and s u r f a c e q u a l i t y of the sheet (Mohlin 1982b). F i v e handsheets were d i s c a r d e d b e f o r e a t e s t specimen was prepared i n order to reach a constant p r o p o r t i o n of f i n e m a t e r i a l r e t e n t i o n f o r a l l subsequent handsheets. The prepared handsheets were c o n d i t i o n e d a c c o r d i n g t o CPPA Standard A. 4 b e f o r e the f o l l o w i n g t e s t s were performed: - B a s i s Weight: CPPA Standard D.12 - Bulk: CPPA Standard D.5H - D e n s i t y : CPPA Standard D.5H 49 CPPA S t a n d a r d E . 2 CPPA S tandard E . 2 CPPA S t a n d a r d E . l CPPA S t a n d a r d D.9 CPPA S t a n d a r d D.8 CPPA S t a n d a r d D34.P CPPA S t a n d a r d D.34P CPPA S t a n d a r d D.34P CPPA U s e f u l Method 524 CPPA S t a n d a r d D.2 9P 3 . 6 . M i c r o s c o p y A r e p e a t se t o f Bauer-McNett f r a c t i o n a t i o n s was per formed on the p u l p s so t h a t the f r a c t i o n s c o u l d be c o l l e c t e d . F o r the c o l l e c t i o n o f the P200 f r a c t i o n , a sample o f about 15 L of s u s p e n s i o n p a s s i n g the 200 mesh s c r e e n was c o l l e c t e d between the t h i r d and s i x t h minute a f t e r the t e s t had s t a r t e d . The p u l p m a t e r i a l was then dewatered by f i l t r a t i o n t h rou gh a c l o t h , but not a l l owed to. d r y . L i g h t microscopy was c a r r i e d out i n a N ikon M i c r o p h o t - F X U n i v e r s a l M i c r o s c o p e , wh i l e s c a n n i n g e l e c t r o n microscopy was done u s i n g a JEOL JSM-840A s c a n n i n g m i c r o s c o p e . A ZEISS High r e s o l u t i o n e l e c t r o n microscope EM-10C was used , f o r t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y . - B r i g h t n e s s : - L i g h t S c a t t e r i n g : - O p a c i t y : - T e a r S t r e n g t h : - B u r s t S t r e n g t h : - T e n s i l e S t r e n g t h : - T e n s i l e Energy A b s o r p t i o n : - S t r e t c h : - P o r o s i t y : - Smoothness: 3 . 6 . 1 . P u l p S l i d e s A p o r t i o n o f each f r a c t i o n and each whole p u l p was sampled 50 t o p r e p a r e m i c r o s c o p i c s l i d e s . A suspens ion o f the m a t e r i a l was u n i f o r m l y spread and d r i e d onto a warm s l i d e . The p u l p m a t e r i a l was subsequent ly s t a i n e d w i t h T o l u i d i n e B l u e 0, a dye which has been e x t e n s i v e l y used i n b i o l o g i c a l s t u d i e s ( C l a r k 1981, Green 1978). Permount was a p p l i e d as mount ing medium b e f o r e a f f i x i n g the cover s l i p . A few s l i d e s were l e f t u n s t a i n e d so t h a t they c o u l d be used w i t h a s o l u t i o n o f an a p p r o p r i a t e r e f r a c t i v e index f o r o b s e r v a t i o n under phase c o n t r a s t . Because o f the presence o f t e n s i o n wood f i b r e s i n aspen, o t h e r reagents were a l s o used to d i s t i n g u i s h the h i g h l y c e l l u l o s i c G - l a y e r from the r e s t o f the f i b r e w a l l . These i n c l u d e d B a s i c Green (TAPPI Rout ine C o n t r o l Method R C - 2 2 1 ) , which s t a i n e d the G - l a y e r y e l l o w and the l i g n i f i e d f i b r e w a l l green i n c h e m i c a l l y t r e a t e d f i b r e s , and the H e r z b e r g S t a i n (CPPA S tandard B.3P) which produced a p u r p l e c o l o r on the G - l a y e r and g o l d f o r the l i g n i f i e d m a t e r i a l . 3 . 6 . 2 . Study of F i b r e C r o s s S e c t i o n s F i b r e c r o s s - s e c t i o n a l a n a l y s i s i s a t e c h n i q u e t h a t a l l o w s the s tudy of d i f f e r e n t f e a t u r e s o f p u l p f i b r e s based on t h e i r c r o s s s e c t i o n s . Of 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 tudy were the f i b r e s produced by m e c h a n i c a l p u l p i n g p r o c e s s e s ; t h e i r e x a m i n a t i o n i n c l u d e d the assessment o f f i b r e s u r f a c e q u a l i t y , and c e l l w a l l damage. The Bauer-McNet t R48 f r a c t i o n ( f i b r e s r e t a i n e d on the 48 mesh screen) was p r e p a r e d f o r a n a l y s i s o f f i b r e c r o s s s e c t i o n s . The R28 f r a c t i o n was 51 considered too small to provide information over the entire pulp. On the other hand, fractions passing the 48 mesh screen were considered to be large l y a t t r i t i o n products of the long f i b r e f r a c t i o n . The R48 f r a c t i o n always accounted for a large portion of a screened pulp, as shown i n Figure 3.5. Twenty-four mechanical pulps were studied and, for each pulp, two samples, consisting of 150 f i b r e s each, were analyzed. Figure 3.5. Relationship between freeness and the percent of fib r e s retained on a 48 mesh screen. 52 3 . 6 . 2 . 1 . P r e p a r a t i o n o f f i b r e c r o s s s e c t i o n s The f o l l o w i n g s teps were completed i n the p r e p a r a t i o n o f f i b r e c r o s s s e c t i o n s : a) S t a n d a r d Bauer-McNett t e s t s were per formed on the 24 p u l p s s e l e c t e d ; the R48 f r a c t i o n s were c o l l e c t e d and not a l l o w e d t o d r y . b) The samples were p l a c e d i n a c o n t i n u o u s s o l v e n t exchange a p p a r a t u s . So lvent exchange was done f o r about one hr u n t i l the f i b r e s were g r a d u a l l y embedded i n 100% t e r t -b u t a n o l , f o l l o w i n g the method by G o l d f a r b et a l (1977) . c) The f i b r e s suspended i n b u t a n o l were p l a c e d i n a s p e c i a l f l a s k and t h i s , i n t u r n , i n t r o d u c e d i n t o methanol at about -45 °C i n a Nes lab C r y o b a t h CB-60 a p p a r a t u s . By s l o w l y r o t a t i n g the f l a s k , the m a t e r i a l f r o z e . d) The f i b r e s were d r i e d under vacuum at a t emperature o f -55 ° C i n an Edwards F r e e z e D r y e r Super Modulyo a p p a r a t u s . e) The d r y , f l u f f y f i b r e m a t e r i a l was kept under vacuum i n a d e s i c c a t o r i n s m a l l l a b e l l e d v i a l s t o a v o i d h y d r a t i o n . f) A p o r t i o n o f these f i b r e s was p l a c e d over a g l a s s s l i d e w i t h a few drops of Spurr embedding medium p r e v i o u s l y p r e p a r e d . Spurr r e s i n was chosen f o r i t s low v i s c o s i t y and c l e a r c o l o r . The s t a n d a r d S p u r r p r e p a r a t i o n f o r m u l a was used a c c o r d i n g to a J . B . E M S e r v i c e s P r o d u c t Note (Anon. 1988b). To ensure good p e n e t r a t i o n o f the r e s i n i n t o the f i b r e s , the f i b r e s were s u b j e c t e d to s e v e r a l 53 c y c l e s o f g e n t l e vacuum to remove a i r i n the f i b r e s . g) The impregnated f i b r e s were then c a r e f u l l y a l i g n e d w i t h f i n e tweezers i n t o f i b r e bundles o f at l e a s t 200 f i b r e s . A l i g n m e n t was done f o r a few f i b r e s at a t ime u n t i l a bundle o f enough m a t e r i a l was p r o d u c e d . Each bundle was then p i c k e d up and r o l l e d g e n t l y between f i n g e r s . P l a s t i c g loves were used to p r e v e n t s k i n c o n t a c t w i t h the r e s i n . h) Wi th f i n e tweezers , the r o l l o f f i b r e s was p l a c e d i n t o the t i p o f a s i l i c o n e c a p s u l e . H e m i - h y p e r b o l o i d t i p JBS #301A BEEM embedding c a p s u l e s were u s e d . The c a p s u l e s c o n t a i n e d a drop of Spurr r e s i n and had to be p r e v i o u s l y evacuated t o remove the a i r bubble u s u a l l y t r a p p e d i n the t i p . When the f i b r e r o l l was i n s i d e the t i p o f the c a p s u l e , i t was f i l l e d w i t h r e s i n and s u b j e c t e d to s e v e r a l c y c l e s o f g e n t l e vacuum u n t i l no bubbles were o b s e r v e d . i ) F i n a l l y , the c a p s u l e s were l a b e l l e d , c l o s e d and p l a c e d i n a c o n s t a n t temperature oven (TAAB Embedding Oven MK-11) m a i n t a i n e d at 70 ° C . The r e s i n was c u r e d f o r at l e a s t 16 h . j) S i x c a p s u l e s were p r e p a r e d f o r each p u l p sample . However, on ly two of them were s e l e c t e d f o r the a c t u a l a n a l y s i s o f f i b r e c r o s s s e c t i o n s . The b l o c k s , a f t e r s t r i p p i n g the s i l i c o n e c a p s u l e s , c o n t a i n i n g the b e s t f i b r e bundle a l ignment were s e l e c t e d a f t e r o b s e r v a t i o n under a s t e r e o m i c r o s c o p e . 54 k) The c u r e d b l o c k s were trimmed down t o j u s t above the m i d d l e o f the f i b r e r o l l l e n g t h . T h i s was done w i t h a Dremel M o t o - t o o l 395 w i t h v a r i a b l e speed under a s t e r e o m i c r o s c o p e . A subsequent cut w i t h a sharp r a z o r b l a d e p r o v i d e d the f i n a l b l o c k s u r f a c e b e f o r e s e c t i o n i n g w i t h g l a s s k n i v e s . 1) A LKB 2178 Knifemaker II was used t o p r e p a r e g l a s s k n i v e s f o l l o w i n g the i n s t r u c t i o n s i n the c o r r e s p o n d i n g manual . m) U s i n g f r e s h l y p r e p a r e d g l a s s k n i v e s , the b l o c k s were cut i n a microtome i n t o s e c t i o n s o f 1.5 um i n t h i c k n e s s . E i t h e r a S o r v a l P o r t e r - B l u m U l t r a m i c r o t o m e MT-2 or a R e i c h e r t - J u n g 2050 Supercut were used f o r c u t t i n g at v e r y slow speeds . n) The s e c t i o n s were p i c k e d up and p l a c e d i n a watch g l a s s c o n t a i n i n g the s t a i n i n g s o l u t i o n . A JBS #197 t i s s u e s t a i n (Anon. 1988a) was s e l e c t e d f o r s t a i n i n g a f t e r t r y i n g s e v e r a l o t h e r o p t i o n s . I t c o n t a i n e d a mix o f T o l u i d i n e B lue 0 and B a s i c F u c h s i n . T o l u i d i n e B l u e 0 i s known t o s e l e c t i v e l y s t a i n l i g n i n and t o g i v e good c o n t r a s t between middle l a m e l l a and secondary w a l l i n a s i n g l e f i b r e ( O ' B r i e n et al 1964, Green 1978, C l a r k 1981) . However, optimum s t a i n i n g c o n t r a s t d i f f e r e d from softwoods i n which pH i s kept at around 10 ( W i l l i a m s 1988) . On the o t h e r hand, B a s i c F u s h i n was found t o s t a i n the G - l a y e r o f t e n s i o n wood f i b r e s w i t h a p i n k i s h c o l o r s i n c e i t has a f f i n i t y f o r c e l l u l o s e ( C l a r k 1981) . 55 The commerc ia l s t a i n i n g s o l u t i o n was d i l u t e d 10 t imes b e f o r e i t was used to s t a i n the s e c t i o n s f o r an approximate t ime o f f i v e m i n u t e s . The pH o f the s t a i n i n g s o l u t i o n was n e u t r a l . o) The s t a i n e d s e c t i o n s were then p i c k e d up w i t h a s m a l l l o o p , immersed b r i e f l y i n d i s t i l l e d water f o r washing and p l a c e d on a b l o c k of T e f l o n to p r e v e n t a d h e s i o n , w h i l e removing the r e s t o f the dye w i t h the c o r n e r o f an absorbent p a p e r . p) Once the s e c t i o n s were d r y , they were c a r e f u l l y p i c k e d up w i t h f i n e tweezers and p l a c e d on a g l a s s s l i d e on top o f a drop of P o l y b e d embedding medium (Anon. 1987) p r e v i o u s l y p r e p a r e d . P o l y b e d was used here as a mounting medium because i t does not cause r e t i c u l a t i o n w i t h S p u r r r e s i n and does not b l e a c h the s t a i n out o f the s t a i n e d f i b r e s (Wi l l i ams 1988). B e f o r e p l a c i n g the cover s l i p , the s e c t i o n s were t o t a l l y submerged i n P o l y b e d t o a v o i d f o r m a t i o n o f a i r b u b b l e s . q) The s l i d e s p r e p a r e d i n t h i s way were clamped o v e r n i g h t to ensure s e c t i o n f l a t n e s s . E v e r y s l i d e c o n t a i n e d s e v e r a l s e c t i o n s , but o n l y one was s e l e c t e d f o r the a n a l y s i s o f f i b r e c r o s s s e c t i o n s a f t e r i n s p e c t i o n under the l i g h t m i c r o s c o p e . The s e c t i o n s chosen p r o v i d e d the b e s t combinat ion o f s t a i n c o n t r a s t and f l a t n e s s . 3.6.2.2. D e f i n i t i o n o f C a t e g o r i e s S t u d i e d W i t h the o b j e c t i v e s i n mind and a f t e r c a r e f u l o b s e r v a t i o n o f 56 s e v e r a l s e c t i o n s , i t was d e c i d e d to c o n f i n e the a n a l y s i s o f f i b r e c r o s s s e c t i o n s to the f o l l o w i n g c a t e g o r i e s : a) R e t e n t i o n o f Compound M i d d l e L a m e l l a , b) R e t e n t i o n o f S-t l a y e r , c) Exposure o f S 2 l a y e r , d) Mode o f s e p a r a t i o n o f o u t e r l a y e r , e) R a d i a l f a i l u r e , f) D e l a m i n a t i o n of the S 2 l a y e r , g) Breakdown of t e n s i o n wood f i b r e s , and h) P r o p o r t i o n o f d i s t o r t e d f i b r e s . Only c o m p l e t e l y s e p a r a t e d f i b r e s were c o n s i d e r e d f o r every one o f these c a t e g o r i e s , i . e . , no f i b r e s w i t h i n a f i b r e bundle o r s h i v e were a n a l y s e d . A l s o , s i n c e i t was not p o s s i b l e t o cu t a l l the f i b r e s at the exact c e n t r e o f t h e i r l e n g t h , no r e s t r i c t i o n was p l a c e d on minimum f i b r e d i a m e t e r , except t h a t the lumen be v i s i b l e . A sample c h a r t used f o r r e c o r d i n g the above-mentioned c a t e g o r i e s i s p r e s e n t e d i n Appendix B . The a b b r e v i a t i o n s used to i d e n t i f y f i b r e s u r f a c e c a t e g o r i e s are l i s t e d i n Appendix F . F i g u r e s 3.6 to 3.10 show examples o f the f i b r e c r o s s s e c t i o n a l f e a t u r e s r e c o r d e d . Data was o b t a i n e d f o r each: c a t e g o r y by c o u n t i n g the number o f f i b r e s t h a t p r e s e n t e d the f e a t u r e o f i n t e r e s t . The c a t e g o r i e s were e s t a b l i s h e d and d e f i n e d as f o l l o w s : a) R e t e n t i o n o f Compound M i d d l e L a m e l l a (MLr) : F i b r e s i n c r o s s s e c t i o n c o u l d be c l a s s i f i e d as h a v i n g or 57 l a c k i n g a middle l a m e l l a around i t . T h i s i s d e f i n e d by the sharp c o n t r a s t between compound midd le l a m e l l a and secondary w a l l due to t h e i r d i f f e r e n c e i n l i g n i n c o n c e n t r a t i o n . T o l u i d i n e B l u e 0 has g r e a t a f f i n i t y f o r l i g n i n and does not s t a i n p o l y s a c c h a r i d e s such as c e l l u l o s e (O ' B r i e n et al 1964, Green 1978) . Because o f the d i f f i c u l t y o f d i s t i n g u i s h i n g the t r u e m i d d l e l a m e l l a from the p r i m a r y w a l l , the term midd le l a m e l l a (ML) i s c o n s i d e r e d here to i n c l u d e the p r i m a r y w a l l . Thus ML was t r e a t e d as the compound midd le l a m e l l a , which a c t u a l l y i n c l u d e s the p r i m a r y w a l l . W i t h i n t h i s c a t e g o r y , s e v e r a l s u b d i v i s i o n s were c o n s i d e r e d : - No r e t e n t i o n o f middle l a m e l l a (ML(r=0)}: when no l i g h t a b s o r p t i o n was e v i d e n t around the f i b r e c r o s s s e c t i o n , i . e . , zero r e t e n t i o n . - Less than 50% R e t e n t i o n {ML(r<50)}: when t h e r e was some r e t e n t i o n o f the ML but i t was l e s s than 50% o f the p e r i m e t e r of the f i b r e c r o s s s e c t i o n . - More than 50% R e t e n t i o n (ML(r>50)}: when the r e t e n t i o n was not t o t a l , but was g r e a t e r than 50% o f the p e r i m e t e r of the f i b r e c r o s s s e c t i o n . - T o t a l R e t e n t i o n (ML(r=100)}: when the ML was p r e s e n t a l o n g the e n t i r e p e r i m e t e r of the f i b r e c r o s s s e c t i o n , i . e . , 100% r e t e n t i o n . 58 F i g u r e 3 . 6 . Hardwood r e f i n e r p u l p f i b r e s i n c r o s s s e c t i o n showing: (a) ML r e t a i n e d , (b) d e l a m i n a t i o n o f the S2 l a y e r , (c) r a d i a l f a i l u r e , and (d) s e p a r a t i o n o f the o u t e r c e l l w a l l or " o u t / i n " e f f e c t . 59 ' ' O r . 0 F i g u r e 3 . 7 . R e t e n t i o n o f l a y e r s shown as b r i g h t l i n e s around f i b r e s i n c r o s s s e c t i o n under p o l a r i z e d l i g h t . F i g u r e 3 . 8 . (a) P e e l i n g o f the ML. F i g u r e 3 . 9 . Aspen p u l p f i b r e s showing (a) G - l a y e r s t r i p p e d from the l i g n i f i e d c e l l w a l l , (b) G - l a y e r i n s i d e the f i b r e . F i g u r e 3.10. Pu lp produced from c h e m i c a l l y - t r e a t e d c h i p s showing (a) N o n - d i s t o r t e d f i b r e , and (b) d i s t o r t e d . 60 An I n d e x f o r ML r e t e n t i o n . ( M L r l ) was c o n c e i v e d . I t p r o v i d e d an i n d i c a t i o n o f ML r e t e n t i o n f o r an a v e r a g e f i b r e o f a p a r t i c u l a r p u l p , a c c o r d i n g t o t h e f o l l o w i n g f o r m u l a : M L r l = ML(r<50) x0.25 + ML (r>50) xO . 75 +• ML(r=100) R e t e n t i o n o f t h e l a y e r ( S ^ r ) : U n d e r t r a n s m i t t e d l i g h t m i c r o s c o p y u s i n g p o l a r i z e d f i l t e r s , t h e c h a n g e i n f i b r i l a n g l e o f t h e S-j_ w i t h r e s p e c t t o t h e S 2 l a y e r p r o v i d e s an e x c e l l e n t means o f e s t a b l i s h i n g t h e p r e s e n c e o r a b s e n c e o f t h e f o r m e r . The S - L l a y e r h a s a l a r g e f i b r i l a n g l e w i t h r e s p e c t t o t h e a x i s o f t h e f i b r e . Thus, t h e c e l l u l o s e m i c r o f i b r i l s a r e a r r a n g e d a l m o s t p e r p e n d i c u l a r t o t h e l i g h t p a t h when a f i b r e i s v i e w e d i n c r o s s s e c t i o n . Due t o t h i s p a r t i c u l a r a r r a n g e m e n t a nd t o t h e c r y s t a l l i n e n a t u r e of- c e l l u l o s e , l i g h t i s p o l a r i z e d b y t h e l a y e r a n d i t a p p e a r s , when p r e s e n t , as a b r i g h t l i n e a r o u n d t h e f i b r e ( C o t e 1981) . By r o t a t i n g t h e s t a g e i n t h e l i g h t m i c r o s c o p e , t h e b e s t p o l a r i z a t i o n f o r a p a r t i c u l a r p o r t i o n o f t h e f i b r e c r o s s s e c t i o n p e r i m e t e r c o u l d be o b t a i n e d . As i n t h e c a s e o f ML r e t e n t i o n , t h e f o l l o w i n g s u b d i v i s i o n s were c o n s i d e r e d i n t h i s c a t e g o r y : - No r e t e n t i o n o f l a y e r { S ^ ( r = 0 ) } : when t h e r e i s no e v i d e n c e o f ML r e t e n t i o n a n d no l i g h t p o l a r i z a t i o n due > . . . 61 t o the l a y e r , i . e . , zero S± r e t e n t i o n . - Less than 50% Reten t i o n {S]_ (x<50) } : when t h e r e i s r e t e n t i o n of the l a y e r but t h i s i s l e s s than 50% of the perimeter of the f i b r e c r o s s s e c t i o n . - More than 50% Reten t i o n { ( r > 5 0 ) } : when r e t e n t i o n i s not t o t a l but i s more than 50% of the perimeter of the f i b r e c r o s s s e c t i o n . - T o t a l Retention (S 1(r=100)}: when the S - L l a y e r i s pre s e n t along the e n t i r e perimeter of the f i b r e c r o s s s e c t i o n , i . e . , 100% r e t e n t i o n . The S - L r e t e n t i o n Index ( S ^ r l ) was c a l c u l a t e d i n accordance with the equation t o p r o v i d e i n d i c a t i o n of S ] _ l a y e r r e t e n t i o n f o r an average f i b r e : S 1 r l = S 1(r<50)x0.25 + S X (r>50)xO.75•+ S±(r=100) I t i s c l e a r t h a t when the ML was present, the in n e r S ^ l a y e r was a l s o p r e s e n t . However, when the ML had been removed, the S ^ l a y e r may or may not have been l e f t b ehind s t i l l a t tached to the r e s t of the f i b r e w a l l . Exposure of the S 2 l a y e r ( S 2 e ) : Example of S 2 l a y e r exposure can be seen i n F i g u r e s 3.6 through 3.10. However, o b s e r v a t i o n through c r o s s e d N i c o l s i s e s s e n t i a l f o r a s s e s s i n g the p o s s i b l e presence of the Si l a y e r on top of S 2 (Figure 3.7). T h i s category i s 62 a c t u a l l y d e f i n e d by the p r e v i o u s one, i . e . , r e t e n t i o n o f the S-L l a y e r . F o r i n s t a n c e , when t h e r e i s no r e t e n t i o n o f S - L , t h e r e i s t o t a l exposure o f the S 2 l a y e r and v i c e versa. More than 5 0 % r e t e n t i o n o f the S^ l a y e r means l e s s than 5 0 % exposure o f the S 2 l a y e r . T h i s c a t e g o r y was s u b d i v i d e d i n a s i m i l a r manner than the p r e v i o u s two: No exposure ( S 2 ( e = 0 ) } , l e s s than 50% exposure (S 2 (e<50)} , more than 50% exposure (S 2 (e>50)} and t o t a l exposure {S 2 (e=100)} . The S 2 exposure Index ( S 2 e l ) was c a l c u l a t e d as f o l l o w s : S 2 e l = S 2 (e<50)xO.25 + S 2 (e>50)xO.75 + S 2 (e=100) Mode o f S e p a r a t i o n o f the Outer L a y e r : When the compound middle l a m e l l a , w i t h o r w i thout the S± l a y e r a t t a c h e d to i t , was removed from the r e s t o f the f i b r e w a l l , s e p a r a t i o n was observed to o c c u r i n t h r e e d i f f e r e n t modes: - ML P e e l i n g : when t h e r e was ML s t i l l a t t a c h e d t o the f i b r e s u r f a c e , but p a r t o f i t was a c t u a l l y hang ing l o o s e at one end, as shown i n F i g u r e 3 . 8 . . - ML s e p a r a t e d but not b r o k e n : when at l e a s t a p o r t i o n o f ML, w i t h or wi thout the S^ l a y e r a t t a c h e d , s e p a r a t e s from the p e r i m e t e r o f the f i b r e . The ends o f t h i s p o r t i o n , however, remain a t t a c h e d to the f i b r e , i . e . , p o r t i o n s o f the o u t e r l a y e r are s e p a r a t e d but not 63 removed. T h i s ca t egory has been d e s i g n a t e d here as the " o u t / i n e f f e c t " . F i g u r e 3.6 i l l u s t r a t e s some t y p i c a l s i t u a t i o n s found under t h i s c a t e g o r y . e) R a d i a l F a i l u r e : T h i s o c c u r r e d when the f i b r e c r o s s s e c t i o n was r u p t u r e d r a d i a l l y . Examples o f t h i s ca t egory are p r e s e n t e d i n F i g u r e 3.6. f) D e l a m i n a t i o n o f the S 2 l a y e r : When t h e r e was ev idence o f s e p a r a t i o n or d e l a m i n a t i o n w i t h i n the S 2 l a y e r , whether or not t h i s l a y e r was exposed, as shown i n F i g u r e 3 . 6 . g) Breakdown of T e n s i o n Wood F i b r e s : Because o f the . r e l a t i v e l y h i g h p r o p o r t i o n o f TW f i b r e s found i n aspen, i t was d e c i d e d to i n c l u d e these i n the a n a l y s i s o f c r o s s s e c t i o n s . G - l a y e r s can be d i f f e r e n t i a t e d even i f they are no l o n g e r i n s i d e the f i b r e w a l l , i . e . , when the G - l a y e r has been s t r i p p e d from an opened f i b r e . Two d i s t i n c t s u b d i v i s i o n s were made f o r t h i s c a t e g o r y : - G - l a y e r i n s i d e a f i b r e : when TW f i b r e s appeared w i t h the G - l a y e r i n s i d e , as i n the wood f i b r e s . - G - l a y e r exposed: when the G - l a y e r has been s t r i p p e d from the s u r r o u n d i n g f i b r e w a l l . 64 Both s u b d i v i s i o n s are i l l u s t r a t e d w i t h examples i n F i g u r e 3 . 9 . h) P r o p o r t i o n o f D i s t o r t e d F i b r e s : Whi l e examining f i b r e c r o s s s e c t i o n s o f CTMP and CMP f i b r e s , i t was observed t h a t many o f these f i b r e s were s w o l l e n , more rounded, and even c o l o u r e d d i f f e r e n t l y from the r e s t of them, p a r t i c u l a r l y when compared w i t h TMP f i b r e s . Thus, these were c a l l e d d i s t o r t e d or "d" f i b r e s . Such f i b r e s e x i s t e d w i t h i n CTMP or CMP p u l p s . ' E x a m p l e s of d i s t o r t e d i n comparison w i t h n o n - d i s t o r t e d f i b r e s are shown i n F i g u r e 3 .10 . 3 . 6 . 2 . 3 . R e p e a t a b i l i t y Two d i f f e r e n t samples o f 150 f i b r e s each were p r o c e s s e d f o r each p u l p . A Z - t e s t f o r d i f f e r e n c e o f p r o p o r t i o n s was per formed f o r each ca tegory f o r every p u l p , a c c o r d i n g to p r o c e d u r e s o u t l i n e d by Walpole (1982). 3 . 7 . Scanning E l e c t r o n M i c r o s c o p y (SEM) The SEM was used as a complement o f the l i g h t m i c r o s c o p e . I t was v e r y u s e f u l f o r q u a l i t a t i v e e x a m i n a t i o n o f s u r f a c e s o f f r e e z e d r i e d f i b r e s or f r a c t i o n s , a n a l y s i s o f paper s u r f a c e c o m p o s i t i o n and paper c r o s s s e c t i o n s . S i n c e samples i n SEM can be viewed at v e r y h i g h m a g n i f i c a t i o n s , an attempt was made to p r e p a r e samples o f f i b r e s i n c r o s s s e c t i o n f o r SEM o b s e r v a t i o n . The t e c h n i q u e 65 i n v o l v e d a t t a c h i n g a s e c t i o n to a g l a s s s l i d e and then d i s s o l v i n g away the Spurr r e s i n , f o l l o w i n g a t e c h n i q u e c o n c e i v e d by Maxwell (1978), b e f o r e normal p r e p a r a t i o n o f SEM samples . A s i m i l a r p r i n c i p l e was a p p l i e d i n the p r e p a r a t i o n o f c r o s s s e c t i o n s o f handshee t s , where the sheets were embedded and c u r e d i n c y a n o a c r y l a t e g l u e , cut w i t h a sharp r a z o r b l a d e and f i n a l l y the g l u e was d i s s o l v e d w i t h a m i x t u r e o f s o l v e n t s (Wi l l iams 1989). B e f o r e a sample c o u l d be observed under the SEM, i t had to be c o a t e d w i t h g o l d - p a l l a d i u m under a HUMMER IV S p u t t e r i n g System f o r 5 min . 3 . 8 . T r a n s m i s s i o n E l e c t r o n M i c r o s c o p y (TEM) TEM was used i n t h i s s tudy not o n l y to c o n f i r m the o b s e r v a t i o n s made on f i b r e c r o s s s e c t i o n s i n the l i g h t m i c r o s c o p e , but a l s o to g a i n a d d i t i o n a l i n f o r m a t i o n i n terms o f d e t a i l s i n the s e p a r a t i o n o f c e l l w a l l l a y e r s upon m e c h a n i c a l p u l p i n g . Only f o u r samples were chosen f o r o b s e r v a t i o n under the TEM. These were the h i g h f reeness TMP (ATMP-1 and BTMP-1) and low f r e e n e s s CMP (ACMP-4 and BCMP-4) p u l p s from b o t h s p e c i e s . B l o c k s o f Spurr embedded f i b r e s were cut i n t o t h i n s e c t i o n s o f 900 A u s i n g an u l t r a m i c r o t o m e equipped w i t h a diamond k n i f e . The s e c t i o n s were s t a i n e d i n a s o l u t i o n o f 1% KMnO^ f o r 40 minutes b e f o r e washing i n d i s t i l l e d water (Parham 1974) . The permanganate r e a c t s w i t h the l i g n i n , thus p r o v i d i n g the h i g h e l e c t r o n d e n s i t y c o n t r a s t means f o r 66 d i f f e r e n t i a t i n g the l a y e r s o f the c e l l w a l l . Because o f the d i f f e r e n c e s i n f i b r i l angle between the and S 2 l a y e r s , a d i f f e r e n c e i n shade and the p e r c e p t i o n o f a d i f f e r e n t t e x t u r e i s e v i d e n t between these two l a y e r s , as shown by P a n s h i n and de Zeeuw (1980) . S e v e r a l photomicrographs were taken f o r each sample. 3 . 9 . V e s s e l Element Breakdown The s tudy o f VE breakdown d u r i n g m e c h a n i c a l p u l p i n g was done by measur ing element p a r t i c l e s i z e i n the s l i d e s p r e p a r e d from whole p u l p s . A f t e r measur ing VE fragments from each p u l p w i t h a 10X o b j e c t i v e , s t a r t i n g at a minimum s i z e o f 50 um , i t was d e c i d e d to i n c r e a s e the minimum p a r t i c l e s i z e measured to 125 um and to s w i t c h to a 4X o b j e c t i v e . T h i s i s a s i z e range i n which the VE fragments c o u l d be i d e n t i f i e d w i t h more c e r t a i n t y . A l s o , the s i z e d i s t r i b u t i o n i n t h i s case i n c l u d e d a l a r g e r percentage o f r e l a t i v e l y l a r g e fragments ; these r e p r e s e n t a p o t e n t i a l c o n c e r n f o r p r i n t i n g papers i n terms of s u r f a c e s t r e n g t h and p i c k i n g tendency d u r i n g p r i n t i n g . To i n v e s t i g a t e t h i s , a t tempts were made to p r o c e s s these samples by Image A n a l y s i s . T h i s system would have p r o v i d e d not o n l y the l i n e a r d imens ions o f v e s s e l fragments but a l s o area v a l u e s o f each p a r t i c l e . I n s u f f i c i e n t c o n t r a s t was a c h i e v e d f o r a s u c c e s s f u l a n a l y s i s because some fragments r e t a i n e d o n l y one c e l l w a l l l a y e r and the s t a i n i n g d e n s i t y was not s u f f i c i e n t even a f t e r e x t e n s i v e s t a i n i n g . 67 Comparisons o f s i z e d i s t r i b u t i o n were c a r r i e d out u s i n g C o n t i n g e n c y T a b l e s f o l l o w i n g the C h i - S q u a r e t e s t c r i t e r i o n ( S t e e l , and T o r r i e 1980). D i f f e r e n c e s due to s p e c i e s , p r o c e s s e s and r e f i n i n g energy were t e s t e d . Whole VE s i z e from k r a f t p u l p s was a l s o measured f o r c o m p a r i s o n . The knowledge p r o v i d e d by the s i z e d i s t r i b u t i o n o f VE fragments was complemented by d a t a on the number o f whole v e s s e l e lements per gram o f p u l p , which s u p p l i e d • i n f o r m a t i o n on the s u r v i v a l o f these' elements upon r e f i n e r p u l p i n g . The number o f whole VE was measured as f o l l o w s : one handsheet was taken from, each o f the 24 p u l p s under s tudy and a l s o from the k r a f t p u l p s p r e p a r e d from each s p e c i e s . E i g h t c i r c l e s o f one cm i n d iameter were punched out randomly from each shee t . S i x o f these c i r c l e s were s e l e c t e d at random, o v e n - d r i e d , and weighed. The o t h e r two c i r c l e s were soaked i n water o v e r n i g h t , s t a i n e d w i t h t o l u i d i n e b l u e and d i s i n t e g r a t e d a c c o r d i n g to p r o c e d u r e s o u t l i n e d i n T a p p i S t a n d a r d T401, but e n s u r i n g t h a t no p u l p p a r t i c l e s were l o s t i n the p r o c e s s . The d i s i n t e g r a t e d m a t e r i a l was taken to 50 mL and, from t h i s u n i f o r m suspens ion i n mot ion , 2 mL were drawn w i t h a p l a s t i c p i p e t t e . The p u l p m a t e r i a l was enough t o p r e p a r e two 75x25 mm p u l p s l i d e s . The number o f whole VE were counted under a l i g h t microscope a c r o s s the e n t i r e a r e a o f each s l i d e w i t h the a i d o f a t a l l y c o u n t e r . The weight p r o v i d e d by 6 c i r c l e s a l l o w e d these r e s u l t s to be t a k e n to r e p r e s e n t the number o f VE i n one gram o f p u l p . Then, by u s i n g the measured y i e l d v a l u e s , or assuming a p p r o p r i a t e 68 y i e l d s f o r those p u l p s from which y i e l d v a l u e s c o u l d not be measured a c c u r a t e l y , the number o f whole VE per gram o f wood was c a l c u l a t e d . S e p a r a t i o n o f l a r g e VE fragments was attempted, f o l l o w i n g the t e c h n i q u e s deve loped by J a c q u e l i n (1966). H i s t e c h n i q u e i s based on f i b r e f l o c c u l a t i o n . T h i s p r i n c i p l e was f u r t h e r a p p l i e d by C o l l e y (1973) f o r s e p a r a t i o n o f VE i n hardwood c h e m i c a l p u l p s . S e v e r a l s tock c o n c e n t r a t i o n s and speeds were t r i e d i n the' J a c q u e l i n Apparatus f o r r e f i n e r p u l p s produced from c h e m i c a l l y t r e a t e d c h i p s . Even w i t h the s o l e use o f f r a c t i o n s r i c h i n l a r g e VE fragments , coherent f l o e s d i d not form i n q u a n t i t i e s l a r g e enough t o a l l o w s e p a r a t i o n . The method o f Marton and Agarwal (1965), a l s o a p p l i e d to hardwood c h e m i c a l p u l p s , was a t tempted . However, due to the n a t u r e o f the m e c h a n i c a l p u l p s and the r e l a t i v e l y s m a l l a spec t r a t i o o f hardwood f i b r e s , no s a t i s f a c t o r y r e s u l t s were o b t a i n e d . The i n f l u e n c e o f whole VE on p r i n t i n g p r o p e r t i e s c o u l d have o therwise been t e s t e d , p r o v i d e d t h a t handsheets c o u l d be produced at s i m i l i a r l e v e l s o f s u r f a c e smoothness . S u r f a c e s t r e n g t h and VE p i c k i n g measurements c o u l d have then been at tempted b e f o r e and a f t e r ' removal o f whole V E . 69 IV . RESULTS 4 . 1 . A n a l y s i s o f F i b r e Cross S e c t i o n s The r e s u l t s and d i s c u s s i o n on the r e p e a t a b i l i t y o f the t e c h n i q u e s employed i n t h i s s tudy f o r each c a t e g o r y o f the a n a l y s i s o f f i b r e c r o s s s e c t i o n s , are p r e s e n t e d i n Appendix C . 4 . 1 . 1 . R e t e n t i o n o f Compound M i d d l e L a m e l l a and1 S ^ L a y e r T a b l e 4.1 shows the percentage o f f i b r e s w i t h d i f f e r e n t degrees o f ML and S ^ r e t e n t i o n , i n c l u d i n g t h e i r MLr and S ^ r i n d i c e s , f o r every p u l p s t u d i e d . The r e s u l t s i n d i c a t e t h a t the ML and S ^ l a y e r f o l l o w e d s i m i l a r p a t t e r n s o f removal from the r e s t o f the f i b r e w a l l i n r e f i n e r p u l p i n g . TMP p u l p s p r e s e n t e d more f i b r e s w i t h ML or S ^ removed than d i d e i t h e r CTMP or CMP p u l p s . R e t e n t i o n was g e n e r a l l y more pronounced i n the f i b r e s o f CTMP and CMP p u l p s , but a d d i t i o n a l removal o f the outer l a y e r s was a c c o m p l i s h e d w i t h s m a l l e r r e d u c t i o n s i n f reeness than i n the case o f TMP p u l p s . T a b l e 4.2 d i s p l a y s the r e s u l t s o f C h i - s q u a r e t e s t s (Cont ingency Tables ) performed to determine d i f f e r e n c e s i n d i s t r i b u t i o n p a t t e r n s o f ML and S-L r e m o v a l . The d a t a r e v e a l t h a t the d i s t r i b u t i o n p a t t e r n s o f removal changed s i g n i f i c a n t l y f o r any g i v e n r e f i n e r p u l p i n g p r o c e s s or s p e c i e s as the r e f i n i n g proceeded . f T a b l e 4.3 compi l e s data f o r the percentage o f f i b r e s which show p e e l i n g o f the outer l a y e r and t h a t o f f i b r e s showing 70 p a r t i a l s e p a r a t i o n o f the o u t e r l a y e r (des ignated as the o u t / i n e f f e c t ) . TMP f i b r e s p r e s e n t e d a l a r g e r percentage o f f i b r e s w i t h o u t e r - l a y e r p e e l i n g . The o u t / i n e f f e c t was m a i n l y a c h a r a c t e r i s t i c o f b i r c h r e f i n e r p u l p f i b r e s and i t appeared o n l y o c c a s i o n a l l y i n aspen p u l p f i b r e s . 4 . 1 . 2 . Exposure o f the S 2 Layer • T a b l e 4.4 p r e s e n t s the p r o p o r t i o n o f f i b r e s t h a t were c l a s s i f i e d under the d i f f e r e n t c a t e g o r i e s o f exposure o f the S 2 l a y e r , as w e l l as t h e i r index o f exposure . TMP f i b r e s showed h i g h e r S 2 l a y e r exposure than CMP or CTMP f i b r e s . However, upon r e f i n i n g , the S 2 l a y e r o f the c h e m i c a l l y -t r e a t e d f i b r e s became exposed more q u i c k l y , p a r t i c u l a r l y i n the case o f aspen f i b r e s . S i n c e the S 2 e d i s t r i b u t i o n p a t t e r n , when i n v e r t e d , i s i d e n t i c a l t o the one f o r the S^ l a y e r , the r e s u l t s from T a b l e 4.2 a l s o a p p l y , i n d i c a t i n g t h a t the S 2 e p a t t e r n changed s i g n i f i c a n t l y upon r e f i n i n g . 4 . 1 . 3 . C e l l W a l l Damage The p e r c e n t a g e s o f f i b r e s p r e s e n t i n g r a d i a l f a i l u r e as w e l l as o f those showing d e l a m i n a t i o n o f the S 2 l a y e r , are summarized i n Tab le 4 . 5 . R a d i a l f a i l u r e o c c u r r e d more f r e q u e n t l y i n TMP than i n e i t h e r CTMP or CMP f i b r e s , whereas d e l a m i n a t i o n was g e n e r a l l y more pronounced i n the f i b r e s from c h e m i c a l l y - t r e a t e d wood c h i p s and more pronounced f o r aspen t h a n f o r b i r c h . 71 4 . 1 . 4 . D i s t o r t e d F i b r e s T a b l e 4.6 l i s t s the percentage o f d i s t o r t e d f i b r e s from CTMP and CMP p u l p s . CMP p u l p s c o n t a i n e d a l a r g e r p r o p o r t i o n o f d i s t o r t e d f i b r e s than d i d CTMP p u l p s , and aspen, i n g e n e r a l , appeared t o produce more d i s t o r t e d f i b r e s than d i d b i r c h . 4 . 1 . 5 . T e n s i o n Wood F i b r e s The p r o p o r t i o n o f aspen t e n s i o n wood f i b r e s ( G - f i b r e s ) i n the c h i p s u p p l y , as measured from k r a f t p u l p , averaged 31% as p r e s e n t e d i n T a b l e 4 . 7 . T a b l e 4.8 shows the presence o f G - l a y e r s i n the R48 f r a c t i o n o f aspen r e f i n e r p u l p f i b r e s , whether i n i s o l a t i o n ( G - l a y e r s t r i p p e d from the r e s t o f the f i b r e w a l l , i . e . , "G ONLY") or i n s i d e the f i b r e , as i n the o r i g i n a l wood f i b r e . TMP p u l p s not o n l y showed a h i g h p e r c e n t a g e o f G ONLY f i b r e s compared to CTMP and CMP, but a l s o a much lower o v e r a l l percentage o f G - f i b r e s i n the R48 f r a c t i o n . 4 . 2 . P u l p P r o p e r t i e s The p u l p c h a r a c t e r i s t i c s e v a l u a t e d b e f o r e handsheets were p r e p a r e d are p r e s e n t e d i n T a b l e 4 . 9 . I n c l u d e d are r e s u l t s on r e f i n i n g energy , f r e e n e s s , s h i v e content and Bauer -McNet t f r a c t i o n a t i o n . In g e n e r a l , i n c r e a s i n g r e f i n i n g energy was accompanied by r e d u c t i o n s i n f r e e n e s s , s h i v e c o n t e n t , and l o n g - f i b r e f r a c t i o n (a l so shown i n F i g u r e 3 . 5 ) , and i n c r e a s e s i n f i n e s c o n t e n t . TMP p u l p s consumed more energy 72 t o a g i v e n f reenes s l e v e l (a l so shown i n F i g u r e 3.2) than d i d p u l p s from CTMP and CMP p r o c e s s e s , and p r o d u c e d h i g h e r c o n t e n t s o f f i n e s . Handsheet p r o p e r t i e s are p r e s e n t e d i n T a b l e s 4.10 and 4 . 1 1 . Sheet b u l k , d e n s i t y and s t r e n g t h p r o p e r t i e s are shown i n T a b l e 4 .10 . F o r any g i v e n p u l p , r e f i n i n g caused i n c r e a s e s i n sheet d e n s i t y and s t r e n g t h p r o p e r t i e s , except f o r t e a r s t r e n g t h i n CTMP and CMP p u l p s where i t f o l l o w e d a more complex t r e n d . The e f f e c t o f c h e m i c a l p r e t r e a t m e n t s on s t r e n g t h p r o p e r t i e s i s e v i d e n t . CMP sheets were denser and s t r o n g e r than those from CTMP and b o t h , i n t u r n , had much h i g h e r s t r e n g t h than those from TMP. T a b l e 4.11 shows p o r o s i t y , sheet s u r f a c e and o p t i c a l p r o p e r t i e s . P o r o s i t y was reduced d r a m a t i c a l l y as a r e s u l t o f c h e m i c a l p r e t r e a t m e n t and i n c r e a s e d r e f i n i n g energy . The e f f e c t o f s p e c i e s i s a l s o e v i d e n t w i t h b i r c h g i v i n g h i g h e r p o r o s i t y v a l u e s than aspen . S u r f a c e roughness , on the o t h e r hand, d i d not show l a r g e v a r i a t i o n s due to r e f i n i n g energy nor c h e m i c a l p r e t r e a t m e n t when the t e s t was performed on the rough s u r f a c e o f the s h e e t . However, roughness as measured on the g l a z e d s i d e of the shee t , d e c r e a s e d c o n s i d e r a b l y due t o c h e m i c a l p r e t r e a t m e n t and h i g h e r r e f i n i n g energy a p p l i c a t i o n . B i r c h p r o d u c e d rougher sheets t h a n . d i d aspen p u l p s . As e x p e c t e d , p u l p b r i g h t n e s s d e c r e a s e d w i t h i n c r e a s i n g a l k a l i c o n c e n t r a t i o n i n the c h e m i c a l p r e t r e a t m e n t , as d i d the l i g h t s c a t t e r i n g c o e f f i c i e n t . At comparable a l k a l i c o n c e n t r a t i o n , aspen always gave b r i g h t e r p u l p s than b i r c h . 73 W h i l e b r i g h t n e s s s t a y e d cons tant on f u r t h e r r e f i n i n g , s c a t t e r i n g showed an i n c r e a s e f o r TMP p u l p s but r e l a t i v e l y l i t t l e change i n CTMP or CMP p u l p s . O p a c i t y showed l i t t l e v a r i a t i o n due to r e f i n i n g . F o r b o t h s p e c i e s TMP and CMP p u l p s p r o v i d e d the most opaque s h e e t s , a l t h o u g h b i r c h e x h i b i t e d h i g h e r o p a c i t y v a l u e s than aspen . 4 . 3 . Breakdown of V e s s e l Elements T a b l e 4.12 p r e s e n t s the average s i z e o f VE from aspen and b i r c h k r a f t p u l p s . B i r c h VE were found to be s i g n i f i c a n t l y l o n g e r than aspen VE wi th an average o f 904 um. The average VE s i z e f o r aspen was 625 um. T a b l e s 4.13 and 4.14 show VE s i z e f requency d i s t r i b u t i o n s i n aspen and b i r c h p u l p s , r e s p e c t i v e l y . F o r both s p e c i e s , TMP p u l p s had the l a r g e r c o n c e n t r a t i o n o f s m a l l VE fragments , whereas b o t h CTMP and CMP c o n t a i n e d fragments o f l a r g e r s i z e s , as w e l l as whole V E . C h i - s q u a r e t e s t r e s u l t s f o r d i s t r i b u t i o n p a t t e r n d i f f e r e n c e s i n VE s i z e are shown i n T a b l e 4 .15 . I t i n d i c a t e s s i g n i f i c a n t d i f f e r e n c e s among r e f i n e r p u l p s f o r a g i v e n s p e c i e s . These d i f f e r e n c e s were l a r g e l y due to the d i f f e r e n t r e f i n e r p r o c e s s e s under s t u d y . When comparing s p e c i e s under the same p r o c e s s , TMP and CMP d i d not show s i g n i f i c a n t VE s i z e d i s t r i b u t i o n p a t t e r n d i f f e r e n c e . R e s u l t s on the number o f whole VE per gram o f p u l p , and e s t i m a t e s f o r VE per gram of o r i g i n a l wood, are p r e s e n t e d i n T a b l e 4 . 1 6 . TMP produced v i r t u a l l y no whole V E , whereas t h e i r s t r u c t u r e was p r e s e r v e d to a l a r g e ex ten t i n CTMP and 74 even more so i n CMP p u l p s . W i t h i n these l a s t two p r o c e s s e s , f u r t h e r r e f i n i n g reduced the number o f whole V E . 4 . 4 . F i b r e Length and Wood S p e c i f i c G r a v i t y T a b l e 4.17 d i s p l a y s the r e s u l t s o f f i b r e l e n g t h measurements f o r aspen and b i r c h p u l p s , showing an average o f 1.33 mm f o r b i r c h . T h i s i s s i g n i f i c a n t l y h i g h e r than the 0.90 mm f o r aspen f i b r e s . Wood s p e c i f i c g r a v i t y v a r i a t i o n s from p i t h t o bark at b r e a s t h e i g h t are p r e s e n t e d i n F i g u r e 4.1 f o r the t h r e e t r e e s i n v o l v e d . Aspen showed a wide range o f d e n s i t y v a l u e s , w i t h an average o f approx imate ly 0 .45 . B i r c h gave d e n s i t y v a l u e s which were n a r r o w l y d i s t r i b u t e d around 0.55 w i t h no d e f i n i t e t r e n d i n d e n s i t y v a r i a t i o n from p i t h to b a r k . Appendix D shows the v a r i a t i o n o f wood d e n s i t y from p i t h to ba rk at d i f f e r e n t h e i g h t s up a t r e e f o r each of the t h r e e t r e e s p u l p e d . Table 4.1. Percentage of f i b r e s under the c a t e g o r i e s d e f i n e d f o r M L and S-L r e t e n t i o n . %ML RETENTION %S1 RETENTION MLr Sir PULP ID MLr=0 MLr<50 MLr>50 MLr=100 INDEX Slr=0 Slr<50 Slf>50 Slr=100 INDE A-TMP1 33 32 21 14 38 28 17 27 28 52 A-TMP2 40 24 22 14 37 36 22 19 24 43 A-TMP3 37 33 16 14 34 30 25 19 26 47 A-TMP4 47 26 19 8 29 41 13 28 18 42 A-CTMP1 5 15 22 58 78 4 8 22 66 84 A-CTMP2 29 17 19 35 54 24 16 17 43 60 A-CTMP3 39 10 21 31 49 37 6 18 38 54 A-CTMP4 40 23 17 20 39 37 17 17 29 46 A-CMP1 17 20 14 49 65 14 14 15 56 71 A-CMP2 40 19 17 23 41 32 21 14 33 49 A-CMP3 51 14 9 26 36 46 11 11 31 43 A-CMP4 46 21 19 14 33 42 14 17 27 43 B-TMP1 40 11 11 38 49 35 10 14 40 53 B-TMP2 44 12 12 32 44 43 9 13 35 47 B-TMP3 51 7 8 34 41 49 7 7 38 44 B-TMP4 63 9 10 18 28 60 7 9 24 33 B-CTMP1 16 5 5 74 79 16 3 3 78 81 B-CTMP2 33 5 12 50 60 30 4 7 59 65 B-CTMP3 32 8 8 52 60 28 5 6 61 66 B-CTMP4 37 6 12 45 55 35 4 6 55 61 B-CMP1 22 6 9 63 71 22 2 6 70 75 B-CMP2 36 9 9 46 55 31 6 4 59 63 B-CMP3 30 7 10 53 62 26 5 7 62 69 B-CMP4 43 7 1 48 51 31 6 5 58 63 76 Table 4.2. Dependency of MLr, and S2_r or S 2e, on energy input. Chi-square values compared to a c r i t i c a l value of 16.92 (a=0.05, 9 d . f . ) . MLr Sir or S2e PULP TYPE ASPEN BIRCH ASPEN BIRCH TMPs •23.1 46.1 37.9 47.0 CTMPs 164.6 66.8 159.0 42.7 CMPs 144.2 52.9 109.9 20.2 CONCLUSION: Distribution pattern depends on energy input in all cases 77 Table 4.3. Percentage of f i b r e s showing mode of separation of the outer layer. SEPARATION OF OUTER LAYER PULP ID PEELING OUT/IN A-TMP1 25 2 A-TMP2 22 3 A-TMP3 22 5 A-TMP4 19 4 A-CTMP1 10 3 A-CTMP2 11 8 A-CTMP3 17 4 A-CTMP4 13 6 A-CMP1 14 8 A-CMP2 14 5 A-CMP3 9 5 A-CMP4 11 8 B-TMP1 14 19 B-TMP2 11 20 B-TMP3 21 10 B-TMP4 11 3 B-CTMP1 8 17 B-CTMP2 7 ' 24 B-CTMP3 9 24 B-CTMP4 11 25 B-CMP1 8 24 B-CMP2 8 18 B-CMP3 7 19 B-CMP4 4 13 78 Table 4.4. Percentage of f i b r e s under categories defined for the exposure of the S 2 layer. %S2 EXPOSED S2e PULP ID S2e=0 S2e<50 S2e>50 S2e=100 INDEX A-TMP1 28 27 17 28 v 48 A-TMP2 24 19 22 36 57 A-TMP3 26 19 25 30 ... 54 A-TMP4 18 28 13 41 58 A-CTMP1 66 22 8 4 16 A-CTMP2 43 17 16 24 40 A-CTMP3 38 18 6 37 46 A-CTMP4 29 17 17 37 54 A-CMP1 56 15 14 14 29 A-CMP2 33 14 21 32 51 A-CMP3 31 11 11 46 57 A-CMP4 27 17 14 42 57 B-TMP1 40 14 10 35 47 B-TMP2 35 13 9 43 53 B-TMP3 38 7 7 49 56 B-TMP4 24 9 7 60 67 B-CTMP1 78 3 3 16 19 B-CTMP2 59 7 4 30 35 B-CTMP3 61 6 5 28 34 B-CTMP4 55 6 4 35 39 B-CMP1 70 6 2 22 • 25 B-CMP2 59 4 6 31 • 37 B-CMP3 62 7 5 26 31 B-CMP4 58 5 6 31 37 79 Table 4 .5 . Percentage of f i b r e s showing c e l l w a l l damage. CELL WALL DAMAGE RADIAL PULP ID FAILURE DELAMINATION A-TMP1 17 3 A-TMP2 19 9 A-TMP3 20 3 A-TMP4 19 16 A-CTMP1 3 10 A-CTMP2 5 21 A-CTMP3 5 21 A-CTMP4 9 28 A-CMP1 4 14 A-CMP2 2 22 A-CMP3 2 20 A-CMP4 5 32 B-TMP1 12 3 B-TMP2 11 5 B-TMP3 21 3 B-TMP4 22 4 B-CTMP1 3 3 B-CTMP2 3 14 B-CTMP3 3 15 B-CTMP4 4 7 B-CMP1 3 4 B-CMP2 3 15 B-CMP3 2 9 B-CMP4 3 10 80 Table 4 . 6 . Percentage of distorted fibres in refiner pulps from chemically-treated wood chips. P U L P I D A S P E N B I R C H C T M P 1 6 9 6 4 C T M P 2 6 5 5 6 C T M P 3 5 4 6 2 C T M P 4 6 4 4 9 C M P 1 7 8 8 0 C M P 2 9 0 8 1 C M P 3 8 9 7 7 C M P 4 8 4 7 8 81 Table 4 . 7 . Percentage of tension wood f i b r e s i n aspen by analysis of cross sections of kraf t pulp f i b r e s B L O C K T O T A L FIBRES N U M B E R OF PERCENT No. COUNTED TENSION WOOD TENSION FIBRES WOOD FIBRES 319 100 31 299 92 31 401 123 31 T O T A L 1019 315 31 82 Table 4.8. Percentage of tension wood f i b r e s i n aspen , r e f i n e r R48 pulp f r a c t i o n s . PULP ID INSIDE G - L A Y E R O N L Y T O T A L A-TMP1 13 * 6 19 * A-TMP2 13 * 6 19 * A-TMP3 11 * 5 16 * A-TMP4 11 * 4 15 * A-CTMP1 33 NS 1 34 NS A-CTMP2 29 NS 1 30 NS A-CTMP3 27 NS 2 29 NS A-CTMP4 26 NS 4 30 NS A-CMP1 32 NS 1 33 NS A-CMP2 32 NS 1 33 NS A-CMP3 30 NS 1 31 NS A-CMP4 25 * 3 28 NS * : significantly different from G-layer content in wood (level of significance d=0.05) NS: not significantly different T a b l e 4 . 9 . Aspen and b i r c h r e f i n e r p u l p c h a r a c t e r i s t i c s and f i b r e s i z e c l a s s i f i c a t i o n . REFINING UNSCREENED SCREENED PULMAC PULP ID ENERGY FREENESS FREENESS SHIVES R28 28/48 R48 48/100 100/150 150/200 P200 MJ/ke mL mL % % % % % % % % A-TMP1 5.5 373 380 0.76 11.3 37.0 48.3 26.3 2.6 2.7 20.1 A-TMP2 7.8 200 220 0.10 6.1 37.4 43.5 26.5 2.3 2.6 25.1 A-TMP3 9.7 142 161 0.04 4.9 36.6 41.5 27.0 2.3 2.5 26.7 A-TMP4 11.3 106 125 0.02 3.8 36.0 39.8 27.2 2.6 2.7 27.7 A-CTMP1 2.5 285 300 0.10 5.2 40.4 45.6 33.9 3.1 2.0 15.4 A-CTMP2 4.3 159 164 0.05 3.3 39.2 42.5 33.5 3.2 2.8 18.0 A-CTMP3 5.9 112 122 0.05 2.3 36.4 38.7 33.5 3.7 3.5 20.6 A-CTMP4 7.2 71 67 0.00 0.6 22.9 23.5 35.1 5.4 5.6 30.4 A-CMP1 6.8 312 298 0:25 17.1 42.5 59.6 27.1 1.9 0.9 10.5 A-CMP2 7.7 220 214 0.10 17.1 39.0 56.1 26.9 2.6 1.2 13.2 A-CMP3 8.7 154 156 0.00 16.0 37.8 53.8 27.9 2.7 1.2 14.4 A-CMP4 9.7 101 98 0.00 12.2 37.4 49.6 28.7 3.1 1.3 17.3 B-TMP1 5.6 514 552 1.35 13.2 36.9 50.1 21.0 2.3 2.4 24.2 B-TMP2 9.9 205 240 0.02 5.0 36.7 41.7 23.6 3.0 3.0 28.7 B-TMP3 12.3 165 180 0.00 4.6 36.3 40.9 22.5 2.5 2.8 31.3 B-TMP4 14.5 105 116 0.02 2.9 32.5 35.4 25.2 3.2 3.5 32.7 B-CTMP1 3.9 460 507 0.24 21.8 43.6 64.8 15.5 2.2 2.1 15.4 B-CTMP2 5.3 225 254 0.05 20.3 40.4 60.7 15.5 2.3 2.0 19.5 B-CTMP3 5.7 165 203 0.01 24.3 38.1 62.4 15.2 2.2 2.3 17.9 B-CTMP4 6.1 107 143 0.01 23.8 36.9 60.7 15.0 2.3 2.7 19.3 B-CMP1 5.3 317 323 0.30 44.6 25.8 59.2 10.7 1.8 1.2 15.9 B-CMP2 6.8 240 206 0.10 42.4 25.2 67.2 11.4 2.1 1.4 17.5 B-CMP3 6.8 160 150 0.05 43.4 24.4 67.8 10.8 1.7 1.3 18.4 B-CMP4 8.4 90 76 0.00 43.5 21.7 65.2 10.3 2.0 1.7 20.8 84 Table 4 . 1 0 . P h y s i c a l p r o p e r t i e s o f pulp handsheets. B U L K DENSITY TEAR BURST TENSILE TEA * STRETC PULP ID INDEX INDEX INDEX INDEX cm3/g g/cm3 mN.m2/g kPa.m2/g N.m/g mJ/g % A-TMP1 3.15 0.317 2.4 0.5 14 75 1.08 A-TMP2 2.90 0.345 2.5 0.8 17 95 1.12 A-TMP3 2.64 0.379 2.6 0.9 20 95 1.00 A-TMP4 2.52 0.397 3.2 .. 1.1 24 150, . 1.23 A-CTMP1 1.91 0.524 5.7 2.0 40 450 1.78 A-CTMP2 1.91 0.524 5.6 2.4 40 395 • 1.59 A-CTMP3 1.98 0.505 5.4 2.4 44 490 1.79 A-CTMP4 1.68 0.595 4.9 2.7 48 635 2.04 A-CMP1 1.87 0.536 6.0 2.2 37 310 1.32 A - C M P 2 1.80 0.556 6.0 2.5 44 475- 1.64 A-CMP3 1.71 0.583 6.3 2.8 47 505 1.65 A-CMP4 1.66 0.603" 6.6 3.1 49 555 1.71 B-TMP1 3.61 0.277 1.7 0.3 8 25 0.74 B-TMP2 3.10 0.323 2.4 0.6 15 100 1.12 B-TMP3 2.92 0.342 2.7 0.8 19 70 0.91 B-TMP4 2.86 0.350 2.7 0.9 20 ' 105 1.05 B-CTMP1 2.61 0.383 6.3 1.7 35 325- • 1.53 B-CTMP2 2.46 0.406 7.4 2.2 43 415 1.56 B-CTMP3 2.39 0.419 7.0 2.5 46 450 1.64 B-CTMP4 2.25 . 0.445 7.7 2.8 52 610 1.90 B-CMP1 2.20 0.454 8.3 2.8 45 480 1.64 B-CMP2 2.10 0.475 9.7 3.1 49 515 1.66 B-CMP3 2.03 0.494 8.3 3.5 55 670 1.90 B-CMP4 1.92 0.522 8.3 3.7 59 745 1.93 (*): Tensile Energy Absorption Table 4.11. Surface and o p t i c a l properties of pulp handsheets. PULP ID POROSITY Sheffield ROUGHNESS R O U G H Sheffield ROUGHNESS SCATTERING OPACITY BRIGHTNESS G L A Z E D COEFFICIENT Sheffield m 2/kg % % . A-TMP1 A-TMP2 A-TMP3 A-TMP4 A-CTMP1 A-CTMP2 A-CTMP3 A-CTMP4 A-CMP1 A-CMP2 A-CMP3 A-CMP4 172 81 45 29 33 11 8 5 14 6 3 2 385 373 369 369 366 358 355 349 398 390 384 375 332 253 211 168 160 100 122 60 140 101 87 71 58 64 65 67 37 40 44 45 35 36 35 35 92.4 94.2 94.7 94.9 89.7 89.7 90.3 90.9 94.1 94.0 94.1 94.0 64 64 64 65 50 56 59 59 41 42 41 41 oo Cn B-TMP1 B-TMP2 B-TMP3 B-TMP4 B-CTMP1 B-CTMP2 B-CTMP3 B-CTMP4 B-CMP1 B-CMP2 B-CMP3 B-CMP4 400 130 92 63 204 38 20 7 19 7 4 3 402 385 378 372 398 396 398 396 416 408 411 402 387 323 320 258 345 255 164 126 182 142 146 164 49 61 62 68 34 35 34 34 32 35 33 33 96.3 97.1 97.6 98.3 92.3 93.5 93.3 93.0 96.1 96.9 96.2 96.4 51 55 54 55 46 46 45 46 36 37 37 37 86 Table 4.12. Size of vessel elements from kraf t pulps. SPECIES N U M B E R V E A V E R A G E STANDARD S T A N D A R D COEFFICIENT M E A S U R E D L E N G T H DEVIATION ERROR OF V A R I A T O N ym ym ym % ASPEN 50 625 128 18 20.6 BIRCH 50 ' 904 189 27 20.9 Table 4.13. Aspen vessel element size frequency analysis (N=50) . L A S S B O U N D A R I E S pm K R A F T T M P 1 T M P 2 T M P 3 T M P 4 C T M P 1 C T M P 2 C T M P 3 C T M P 4 C M P 1 C M P 2 C M P 3 C M F 112.5 162.5 0 25 32 34 37 11 8 11 18 6 13 10 13 162.5 212.5 0 14 7 6 8 7 11 11 12 7 7 7 6 212.5 262.5 0 6 5 3 3 6 8 6 8 4 6 6 5 262.5 312.5 0 0 2 4 1 4 9 10 6 4 2 4 5 312.5 362.5 0 1 2 1 0 4 2 2 1 0 1 3 1 362.5 412.5 3 3 1 1 1 6 3 1 1 2 1 1 2 412.5 462.5 4 0 1 1 0 3 0 0 1 5 2 0 2 462.5 512.5 4 1 0 0 0 3 1 1 0 1 2 4 3 512.5 562.5 6 0 0 0 0 3 2 2 2 2 2 1 2 562.5 612.5 4 0 0 0 0 0 2 2 0 7 4 1 2 612.5 662.5 6 0 . 0 0 0 0 3 0 1 5 2 3 5 662.5 712.5 8 0 0 0 0 1 0 4 6 2 3 2 3 712.5 762.5 9 0 0 0 0 1 0 0 0 3 5 5 0 762.5 812.5 5 0 0 0 0 1 1 0 0 1 0 2 0 812.5 862.5 0 0 0 0 0 0 0 0 0 0 0 1 0 862.5 912.5 1 0 0 0 0 0 0 0 0 0 0 0 0 912.5 962.5 0 0 0 0 0 0 0 0 0 1 0 0 0 962.5 (+) 0 0 0 0 0 0 0 0 0 0 0 0 1 Table 4.14. Birch vessel element size frequency analysis (N=50). :LASS BOUNDARIES Um KRAFT TMP1 TMP2 TMP3 TMP4 CTMP1 CTMP2 CTMP3 CTMP4 CMP1 CMP2 CMP3 CMF 112.5 162.5 0 22 29 34 25 8 7 14 19 13 14 16 23 162.5 212.5 0 12 10 4 13 8 7 9 6 10 7 11 4 212.5 262.5 0 8 9 5 6 5 9 7 9 5 8 3 2 262.5 312.5 0 5 1 4 5 5 7 6 2 5 6 4 8 312.5 362.5 0 0 1 1 0 2 1 3 2 0 3 3 4 362.5 412.5 0 0 0 1 . 0 2 4 2 2 2 1 3 1 412.5 462.5 0 1 0 0 1 1 1 0 1 1 1 1 0 462.5 512.5 0 1 0 0 0 1 1 2 1 1 3 0 0 512.5 562.5 1 0 0 0 0 5 2 2 2 2 1 1 1 562.5 612.5 1 0 0 0 6 2 1 0 0 2 1 0 0 612.5 662.5 5 1 0 0 0 2 1 1 3 1 6 0 0 662.5 712.5 3 0 0 0 0 1 1 1 1 1 0 2 2 712.5 762.5 3 0 0 0 0 1 3 0 1 1 1 2 1 762.5 812.5 4 0 0 1 0 1 0 1 1 0 0 0 0 812.5 862.5 3 0 0 0 0 3 0 2 0 0 0 1 0 862.5 912.5 • 6 0 0 6 0 0 0 0 6 1 1 0 1 912.5 962.5 5 0 0 0 0 0 1 0 0 6 0 2 0 962.5 1012.5 7 . 0 0 0 6 0 2 0 0 3 0 0 0 1012.5 1062.5 3 0 0 0 6 2 0 0 0 0 1 0 2 1062.5 1112.5 2 0 0 0 0 1 0 0 0 0 1 0 0 1112.5 1162.5 2 0 0 0 0 0 2 0 0 1 1 0 0 1162.5 1212.5 0 0 0 0 0 0 0 6 •0 0 0 1 0 1212.5 1262.5 4 0 0 0 0 0 0 0 0 1 0 0 0 1262.5 (+) 1 0 0 0 0 0 0 0 0 0 0 0 1 89 Table 4.15. Chi-square tests on vessel element size d i s t r i b u t i o n (a=0.05). PULPS NUMBER DEGREES OF CHI-SQUARE CHI-SQUARE RESULT TESTED PULPS IN FREEDOM CALCULATED CRITICAL TEST  A) ASPEN REFINER PULPS 12 55 221.5 73.3 * BIRCH REFINER PULPS 12 44 131.7 60.5 * B) ASPEN TMPs 4 6 9.5 12.6 NS ASPEN CTMPs 4 15 21.1 25.0 NS ASPEN CMPs 4 18 12.9 28.9 NS C) BIRCH TMPs 4 9 13.0 16.9 NS BIRCH CTMPs 4 18 20.4 28.9 NS BIRCH CMPs 4 12 13.4 21.0 NS D) ASPEN TMPs vs CTMPs 8 28 110.4 41.3 * ASPEN TMPs vs CMPs 8 28 136.8 41.3 * ASPEN CTMPs vs CMPs 8 42 65.1 58.1 * E) BIRCH TMPs vs CTMPs 8 28 108.4 41.3 * BIRCH TMPs vs CMPs 8 28 85.9 41.3 * BIRCH CTMPs vs CMPs 8 42 46.7 58.1 NS F) ASPEN vs BIRCH TMPs 8 21 28.7 32.7 NS ASPEN vs BIRCH CTMPs 8 35 53.4 49.8 * ASPEN vs BIRCH CMPs 8 35 41.1 49.8 NS * : Significantly Different NS: Not Significantly Different 90 Table 4.16. Survival of whole vessel elements i n r e f i n e r pulps. W H O L E V E W H O L E V E PER PER P U L P ID G R A M G R A M OF PULP OF WOOD (xlOOO) (xlOOO) W H O L E V E S U R V I V A L AS % V E IN WOOD A - K R A F T A-TMP1 A-TMP2 A-TMP3 A-TMP4 A-CTMP1 A-CTMP2 A-CTMP3 A-CTMP4 A-CMP1 A - C M P 2 A-CMP3 A-CMP4 860 8 3 0 0 202 167 142 59 439 389 325 294 482 7 3 0 0 186 153 131 54 386 342 286 259 100 2 1 0 0 39 32 27 11 80 71 59 54 B - K R A F T B-TMP1 B-TMP2 B-TMP3 B-TMP4 B-CTMP1 B-CTMP2 B-CTMP3 B-CTMP4 B-CMP1 B-CMP2 B-CMP3 B-CMP4 261 0 0 0 0 37 36 24 23 91 73 69 69 136 0 0 0 0 34 33 22 21 82 66 62 62 100 0 0 0 0 25 24 16 16 60 48 46 46 91 Table 4.17. Aspen and b i r c h f i b r e length measurements. SPECIES N U M B E R OF A V E R A G E STANDARD COEFFICIENT FIBRES FIBRE DEVIATION OF M E A S U R E D L E N G T H VARIATION ym ym % A S P E N 169 897 181 20.2 BIRCH 220 1326 266 20.1 92 0.3-0 2 4 6 8 10 12 DISTANCE FROM PITH, cm ASPEN (W.LAKE) BIRCH (W.LAKE) — — ASPEN (LYTTON) Figure 4 . 1 . Wood s p e c i f i c gravity v a r i a t i o n at DBH for the trees used i n t h i s study. 93 V . DISCUSSION 5 . 1 . A n a l y s i s o f F i b r e Cross S e c t i o n s T h i s s e c t i o n i s d i v i d e d i n t o t o p i c s t h a t w i l l be d i s c u s s e d s e p a r a t e l y . The d i s c u s s i o n o f the r e p e a t a b i l i t y o f the r e s u l t s o b t a i n e d by the a n a l y s i s o f f i b r e c r o s s s e c t i o n s i s g i v e n i n Appendix C . 5 . 1 . 1 . R e t e n t i o n o f Compound M i d d l e L a m e l l a and S^ L a y e r When wood i s r u p t u r e d i n the l o n g i t u d i n a l p l a n e , s e p a r a t i o n can take p l a c e i n a v a r i e t y o f modes depending on m a t e r i a l and t e s t i n g c o n d i t i o n s . I n t r a w a l l f a i l u r e r e s u l t s i n the s e p a r a t i o n w i t h i n the compound middle l a m e l l a , S i / S 2 boundary and w i t h i n the S 2 l a y e r . T r a n s w a l l f a i l u r e , on the o t h e r hand, i s r e s p o n s i b l e f o r f a i l u r e a c r o s s the c e l l w a l l , e . g . , broken f i b r e s (Koran 1967, 1968). In the p r e s e n t s tudy , however, these types o f wood f a i l u r e do not a p p l y d i r e c t l y s i n c e o n l y i s o l a t e d f i b r e s were a n a l y z e d , i . e . , f i b r e s t h a t were not p a r t o f a s h i v e or f i b r e b u n d l e . The f i b r e s i n the a n a l y s i s , c o n s e q u e n t l y , had a l r e a d y s e p a r a t e d from the wood m a t r i x and undergone some degree o f r e f i n i n g . The average s u r f a c e o f f i b r e s i n i t i a l l y s e p a r a t e d from the wood can thus d i f f e r from t h a t o f the f i b r e s a n a l y z e d i n t h i s s t u d y . The o b j e c t i v e was not to s tudy wood f a i l u r e , but r a t h e r the exposed s u r f a c e o f the f i b r e s p r o d u c e d under d i f f e r e n t r e f i n i n g p r o c e s s e s and a f t e r c e r t a i n degree o f r e f i n i n g . Y e t , i t i s r e c o g n i z e d t h a t the i n i t i a l mode o f 9 4 s e p a r a t i o n can p l a y an important r o l e i n f i b r e s u r f a c e q u a l i t y upon r e f i n i n g . I t s h o u l d be emphasized t h a t an a n a l y s i s o f f i b r e c r o s s s e c t i o n s had not been c a r r i e d out b e f o r e f o r hardwood r e f i n e r p u l p s . In f a c t , p u b l i s h e d i n f o r m a t i o n on the a n a l y s i s o f m e c h a n i c a l p u l p f i b r e s i n c r o s s s e c t i o n has been based on softwood f i b r e s so f a r ( K i b b l e w h i t e 1983). The use o f p o l a r i z i n g f i l t e r s to view the presence or absence o f the Si l a y e r and, at the same t ime , to make use o f s t a i n i n g t e c h n i q u e s to v i s u a l l y assess the presence or absence o f the ML, i s a new t e c h n i q u e and p r o v i d e s a d e f i n i t e advantage i n e v a l u a t i n g f i b r e s u r f a c e q u a l i t y . A l t h o u g h p o l a r i z i n g f i l t e r s had been used to observe the presence o f the S^ l a y e r i n wood and wood f a i l u r e s t u d i e s , t o t h i s a u t h o r ' s knowledge i t has never been used f o r q u a n t i t a t i v e e v a l u a t i o n o f S]_ l a y e r r e t e n t i o n i n i s o l a t e d f i b r e s from hardwood r e f i n e r p u l p s . A l t h o u g h the t e c h n i q u e s i n v o l v e d i n . d i s s o l v i n g r e s i n from f i b r e s e c t i o n s to observe f i b r e c r o s s s e c t i o n s under the SEM were p r a c t i c a l , the SEM o b s e r v a t i o n f a i l e d to p r o v i d e a d d i t i o n a l i n f o r m a t i o n to t h a t o b t a i n e d from l i g h t m i c r o s c o p y . S ince s t a i n i n g t e c h n i q u e s cannot be a p p l i e d to SEM samples , i t was hoped t h a t changes o f t e x t u r e between f i b r e w a l l l a y e r s i n c r o s s s e c t i o n c o u l d be o b s e r v e d under SEM. However, the c e l l w a l l l a y e r s a l l o w e d no d i f f e r e n t i a t i o n by means o f t h i s t e c h n i q u e . B e f o r e d i s c u s s i n g the r e s u l t s p r e s e n t e d i n T a b l e 4.1 on ML 95 and r e t e n t i o n , i t i s c o n s i d e r e d impor tant t o e s t a b l i s h t h a t , a f t e r the p o i n t o f f i b r e l i b e r a t i o n was r e a c h e d , which o c c u r s at f r e e n e s s l e v e l s of around 700 mL CSF a c c o r d i n g t o C o r s o n (198 9) , no s e r i o u s f i b r e s h o r t e n i n g took p l a c e i n the p u l p s f o r the r e f i n e r p u l p i n g p r o c e s s e s under s t u d y . I n s t e a d , more f i n e s (P200 f r a c t i o n ) were p r o d u c e d as r e f i n i n g energy i n c r e a s e d . T h i s i s shown i n F i g u r e 5 . 1 , which i n d i c a t e s t h a t . l i t t l e change had o c c u r r e d i n the midd le f r a c t i o n (48/100) and the s h o r t e r f r a c t i o n s 100/150 and 150/200. The r e d u c t i o n i n the R48 f r a c t i o n o f the h i g h f r e e n e s s p u l p s , r e s u l t e d e s s e n t i a l l y i n an i n c r e a s e i n the P200 f r a c t i o n i n the lower f reenes s p u l p s . T h i s c o n f i r m s o b s e r v a t i o n s by G a v e l i n (1982a) t h a t one cannot v a r y the f i n e s f r a c t i o n wi thout a l s o i n f l u e n c i n g the f i b r e c h a r a c t e r i s t i c s . A l t h o u g h the g e n e r a l shape o f these curves were se t l a r g e l y by pre trea tment c o n d i t i o n s , w i t h i n any of the s i x groups o f p u l p (same p r o c e s s and s p e c i e s , but d i f f e r e n t f r eenes s l e v e l s ) , i t i s c l e a r t h a t r e f i n i n g a c t e d upon the f i b r e s m a i n l y by removing s u r f a c e l a y e r s r a t h e r than by r e d u c i n g t h e i r l e n g t h , w i t h the e x c e p t i o n o f the low f r e e n e s s aspen CTMP p u l p (A-CTMP4) , i n which some f i b r e s h o r t e n i n g was e v i d e n t from these c u r v e s . The r e s u l t s p r e s e n t e d i n T a b l e 4 . 1 . and those o f T a b l e 4.2 f o r C h i - s q u a r e t e s t s on d i s t r i b u t i o n p a t t e r n d i f f e r e n c e s o f ML and S^ r e t e n t i o n due t o r e f i n i n g , e s t a b l i s h the f a c t t h a t t h e r e was q u a n t i t a t i v e removal o f f i b r e s u r f a c e l a y e r s . As e x p e c t e d , i n a l l p u l p groups the p e r c e n t a g e o f f i b r e s w i t h 96 A S P E N TMPs BIRCH TMPs EH a cu fu En o w o EH S3 W O w {U R28 2^48 4*100 100/150 150/200 P200 A S P E N CTMPs R28 28/48 48/100 100/150 150/200 P200 45-A S P E N CMPs 40+ 35 30--25" 20--15 10+ 5 0 f r T £i \ A / / 1 r - / • / • " R28 28/48 48/100 100/150 150/200 P200 BIRCH CTMPs R28 28/48 48/100 100/150 150/200 P200 BIRCH CMPs R28 28/48 48/100 100/150150/200 P200 R28 28/48 487100 100/150150/200 P200 BAUER McNETT FRACTIONS F i g u r e 5 . 1 . Bauer McNett f r a c t i o n a t i o n p a t t e r n s f o r a l l hardwood r e f i n e r p u l p s under s t u d y . S o l i d l i n e s : h i g h f reeness p u l p s ; dashed l i n e s : low f r e e n e s s ; d o t t e d l i n e s : i n t e r m e d i a t e f r e e n e s s . 97 t o t a l ML r e t e n t i o n , ML(r=100), and o f MLr index ( M L r l ) , was h i g h e s t f o r the p u l p s w i t h h i g h e s t f r eenes s v a l u e s w i t h i n each g r o u p , i . e . , f o r those p u l p s f o r which the r e f i n i n g energy a p p l i e d was a l s o the lowest f o r the g r o u p . In these p u l p s , the work done on f i b r e s u r f a c e development was r e l a t i v e l y s m a l l compared to t h a t f o r low f r e e n e s s p u l p s . There were, however, important d i f f e r e n c e s between these pulp, g r o u p s . The t r e n d of ML removal depended on the p r o c e s s and s p e c i e s and was d i f f e r e n t a l s o w i t h r e s p e c t to -pulp f r e e n e s s . There were a l s o important d i f f e r e n c e s i n the i n i t i a l r e t e n t i o n o f ML and i n the d i s t r i b u t i o n p a t t e r n o f ML r e t e n t i o n . F i g u r e s 5.2 and 5.3 d e p i c t the t r e n d s f o l l o w e d by the d i f f e r e n t groups i n terms of MLr index and f i b r e s w i t h t o t a l r e t e n t i o n o f ML. Only the g e n e r a l t r e n d s are d e l i n e a t e d here to s i m p l i f y the more complex v a r i a t i o n w i t h i n each group of f o u r p u l p s . The degree o f ML r e t e n t i o n was g e n e r a l l y lower f o r TMP p u l p s than f o r f i b r e s from c h e m i c a l l y - t r e a t e d c h i p s . Presumably , i n TMP p r o c e s s i n g , the l i g n i n p r e s e n t i n h i g h c o n c e n t r a t i o n s i n the ML was not s u f f i c i e n t l y s o f t e n e d by the p r e s t e a m i n g , p r e h e a t i n g or r e f i n i n g c o n d i t i o n s to a l l o w f i b r e s e p a r a t i o n at the ML zone. T h i s i s suppor ted by the lower p e r c e n t a g e o f R48 f r a c t i o n s found i n these p u l p s compared t o CTMP or CMP. Thus , these r e s u l t s i n d i c a t e t h a t some t r a n s w a l l f a i l u r e had p r o b a b l y o c c u r r e d . T h i s agrees w i t h s t u d i e s by C a r l s s o n and L a g e r g r e n (1957) who showed t h a t b i r c h wood f a i l e d m a i n l y a c r o s s the c e l l w a l l i n t e n s i l e t e s t i n g o f hea ted w a t e r -98 0-| , 1 1 . 1 1 0 100 200 300 400 500 600 C.S.F., mL Figure 5 . 3 . Plot of percentage of f i b r e s with t o t a l -ML retention against pulp freeness. 99 s w o l l e n specimens . I t i s a n t i c i p a t e d t h a t a tmospher ic r e f i n i n g o f u n t r e a t e d c h i p s , an i n c r e a s e i n the removal of ML w i l l o c c u r . T h i s a l s o enhances f r a c t i o n a t i o n o f the f i b r e s . S t u d i e s on Pinus radiata ( K i b b l e w h i t e 1983) c o n f i r m t h i s o b s e r v a t i o n when RMP and TMP p u l p s were compared. As r e f i n i n g under TMP c o n d i t i o n s c o n t i n u e d , ML removal p r o c e e d e d s l o w l y , and l i t t l e change o c c u r r e d u n t i l the f r e e n e s s l e v e l s were c l o s e to 150 mL C S F . Then, a r a t h e r abrupt r e d u c t i o n o f ML r e t e n t i o n was r e c o r d e d . F o r b i r c h , the MLr index was reduced from 49% t o 28%, whereas i n aspen i t d e c r e a s e d from 38% to 29%. The exposed s u r f a c e o f TMP f i b r e s appears to be l a r g e l y se t by the i n i t i a l s e p a r a t i o n o f f i b r e s from the wood m a t r i x , s i n c e r e f i n i n g does not e a s i l y a l l o w the removal of the ML from the f i b r e s u r f a c e u n l e s s f r eenes s va lues o f about 100 mL CSF are r e a c h e d . The g e n e r a l t r ends o f ML removal f o r p u l p s produced from c h e m i c a l l y - p r e t r e a t e d c h i p s were q u i t e d i f f e r e n t from those o f TMP p u l p s . At h i g h l e v e l s o f p u l p f r e e n e s s , the v a l u e s f o r r e t e n t i o n of ML were much h i g h e r than those f o r TMP f i b r e s . F i b r e s e p a r a t i o n had o c c u r r e d l a r g e l y at the ML and, when f r e e n e s s va lues o f about 300 mL CSF were r e a c h e d , the l e v e l s o f ML r e t e n t i o n were s t i l l w e l l over 50%. T h i s smooth s e p a r a t i o n a l ong the ML was accompanied by the expec ted r e d u c t i o n o f sh ive s i n these p u l p s (Table 4.9) compared to TMP p u l p s . The c h e m i c a l pr e t r e a tm e nt s chosen i n t h i s s tudy s h o u l d cause s w e l l i n g o f the f i b r e w a l l , as w e l l as l i g n i n s u l p h o n a t i o n 100 ( G i e r t z 1977) . Wood then tends t o f a i l w i t h i n the ML, and l i b e r a t e d f i b r e s w i l l show h i g h ML r e t e n t i o n at h i g h l e v e l s of p u l p f r e e n e s s . T h i s was a l s o shown to be the case f o r b i r c h c o a r s e p u l p f i b r e s u r f a c e s produced under h i g h y i e l d s u l p h i t e p u l p i n g c o n d i t i o n s (Iwamida et a l 1980a) . I t i s i n t e r e s t i n g to note t h a t ML s e p a r a t i o n was not the main mode o f f a i l u r e f o r c o l d soda p u l p s . In t h a t case , wood f i b r e s s e p a r a t e d m a i n l y between the and S 2 l a y e r (Wardrop and D a d s w e l l 1958) . However, under those c o n d i t i o n s l i t t l e l i g n i n d e g r a d a t i o n was a c h i e v e d and the aim was to s w e l l the f i b r e w a l l r a t h e r than to degrade the ML l i g n i n . I t i s shown i n t h i s s tudy , i n which p r e t r e a t m e n t t empera tures ranged from 125 °C to 135 ° C , t h a t ML r e t e n t i o n ranged between 65 and 80%, expres sed i n terms of the MLr i n d e x , f o r b i r c h and aspen CTMP and CMP f i b r e s at f r e e n e s s l e v e l s h i g h e r than 300 mL CSF, r e s p e c t i v e l y . The p e r c e n t a g e o f f i b r e s h a v i n g t o t a l r e t e n t i o n o f ML was a l s o v e r y h i g h , s i n c e i t was the major c o n t r i b u t o r to the MLr i n d e x . I t i s c l e a r t h a t , from the p o i n t o f f i b r e l i b e r a t i o n , which presumably o c c u r r e d at the ML, to the p o i n t at which f u r t h e r r e f i n i n g r e n d e r e d freeness v a l u e s o f a p p r o x i m a t e l y 300 mL CSF, c h e m i c a l pre trea tment had f a i l e d to a c h i e v e the same l e v e l s o f ML removal as those f o r TMP p u l p f i b r e s . Wi th f u r t h e r r e f i n i n g , however, CTMP and CMP f i b r e s l o s t t h e i r ML much q u i c k e r than d i d TMP f i b r e s ( F i g u r e s 5.2 and 5 . 3 ) . Aspen f i b r e s , i n t u r n , showed a q u i c k e r response than b i r c h i n removing ML, as shown by the s l o p e s o f the c u r v e s 101 i n these f i g u r e s . They reached lower l e v e l s o f MLr at s i m i l a r , f r e e n e s s . On the o t h e r hand, CTMP and CMP f i b r e s f o l l o w e d a s i m i l a r t r e n d w i t h i n each s p e c i e s . F o r b i r c h , the MLr index seemed to d e c r e a s e at an e q u i v a l e n t r a t e f o l l o w i n g v a l u e s t h a t were s i m i l a r f o r CTMP and CMP. F o r aspen, the d i f f e r e n c e -between CMP and CTMP was more e v i d e n t . A l t h o u g h they showed s i m i l a r t r e n d s f o r ML removal , CMP f i b r e s gave lower v a l u e s o f r e t e n t i o n than CTMP at s i m i l a r p u l p d r a i n a g e . T h i s i m p l i e s t h a t , f o r aspen r e l a t i v e to b i r c h , the CMP p r o c e s s i s more e f f e c t i v e i n removing the f i b r e ML than the CTMP p r o c e s s . An o v e r a l l d i f f e r e n c e between the two s p e c i e s was the r e l a t i v e c o n t r i b u t i o n o f f i b r e s w i t h t o t a l ML r e t e n t i o n to the MLr i n d e x . T h i s was much h i g h e r f o r b i r c h t h a n f o r aspen . The index i n d i c a t e d a v a l u e r e f l e c t i n g the MLr o f an average f i b r e , thereby a l s o a c c o u n t i n g f o r f i b r e s w i t h p a r t i a l r e t e n t i o n o f ML. From T a b l e 4.1 i t i s seen t h a t the b i r c h v a l u e s o f ML(r=100) were c l o s e r to those o f the MLr index than those f o r the same c a t e g o r i e s i n a spen . T h i s shows t h a t aspen, i n g e n e r a l , c o n t a i n e d a h i g h p e r c e n t a g e o f f i b r e s w i t h p a r t i a l r e t e n t i o n o f ML compared t o b i r c h . T h i s was p a r t i c u l a r l y n o t i c e a b l e f o r aspen TMP, where f i b r e s w i t h p a r t i a l l y r e t a i n e d ML c o n t r i b u t e d more than t w i c e as much to the MLr index than f i b r e s w i t h ML(r=100) . In g e n e r a l , t h e n , aspen r e f i n e r p u l p s c o n t a i n e d a l a r g e p r o p o r t i o n o f f i b r e s w i t h "patched" s u r f a c e p a t t e r n s o f ML r e t e n t i o n . Examples o f these are g i v e n i n F i g u r e s 5.4 and 5 . 5 . 102 F i g u r e 5.4. SEM photograph o f an aspen TMP f i b r e showing uneven exposure of c e l l w a l l l a y e r s ( P u l p A-TMP4). F i g u r e 5.5. C r o s s s e c t i o n o f aspen TMP f i b r e s showing p a r t i a l r e t e n t i o n o f ML ( p u l p A-TMP3). 103 I t i s important to note t h a t f o r a g i v e n s p e c i e s , the l e v e l s of MLr e x h i b i t e d by TMP f i b r e s were not exceeded by e i t h e r of the processes with chemical pretreatment. Aspen CMP and CTMP f i b r e s , however, came c l o s e r t o the MLr l e v e l s of t h e i r TMP. c o u n t e r p a r t s at low freeness v a l u e s than d i d the c o r r e s p o n d i n g b i r c h p u l p s . I t can be concluded t h a t even the more severe chemical pretreatments of the type used i n t h i s study, c o u l d not improve ML removal beyond t h a t achieved by TMP p r o c e s s i n g . R e t e n t i o n of ML was found to be c l o s e l y a s s o c i a t e d with the presence or absence of the l a y e r . I t should be mentioned t h a t i t was b a s i c a l l y the bulk of the l a y e r whose presence was recorded i n t h i s study. The u l t i m a t e exposed l a y e r of the f i b r e w a l l would probably be b e t t e r assessed by o b s e r v a t i o n of the f i b r e s u r f a c e under TEM. T h i s technique,. however, not only r e q u i r e s p r e p a r a t i o n of s u r f a c e r e p l i c a s , but does not p r o v i d e i n f o r m a t i o n as to what happens t o the bulk of the l a y e r . The r e t e n t i o n of the -S^ l a y e r was found to be the main cause f o r the r e t e n t i o n of ML. When ML was removed from the f i b r e s u r f a c e , i t was l a r g e l y because the l a y e r had separated from the S 2 l a y e r . T h i s was found to be the case not only f o r f i b r e s from c h e m i c a l l y - t r e a t e d c h i p s but a l s o f o r TMP f i b r e s . F i g u r e s 5 .6 and 5 .7 are examples of s e p a r a t i o n along or near the f i b r e S^ /S2 boundary f o r b i r c h and aspen TMP f i b r e s . The d i f f e r e n c e s i n l a y e r r e t e n t i o n between processes or s p e c i e s f o l l o w e d the same g e n e r a l p a t t e r n as f o r ML 104 F i g u r e 5.7. TEM photograph o f aspen TMP f i b r e bundle i n c r o s s s e c t i o n showing s e p a r a t i o n o f the S± l a y e r near the S1/S2 boundary (pulp A-TMP1). 105 r e t e n t i o n . There were important d i f f e r e n c e s due t o s p e c i e s . For i n s t a n c e , when no chemical pretreatment was a p p l i e d , t h e r e was a l a r g e r d i f f e r e n c e between v a l u e s of MLr and S ^ r f o r aspen than there was f o r b i r c h f i b r e s (Figure 5.8). T h i s i n d i c a t e s t h a t f o r aspen TMP f i b r e s , ML removal d i d not f o l l o w S-L removal as c l o s e l y as i t d i d i n b i r c h . Thus, aspen f i b r e s u r f a c e s had more areas with exposed S-j_ l a y e r . T h i s was i n p a r t supported by the f a c t t h a t many aspen f i b r e s p r e s e n t e d p a r t i a l ML r e t e n t i o n . The exposed s u r f a c e s ranging from ML t o the S 2 l a y e r w i l l have t o have a t r a n s i t i o n a l area i n which the i s exposed. An example of the l a y e r b e i n g r e t a i n e d . a n d exposed i n an aspen TMP f i b r e i s d e p i c t e d i n F i g u r e 5 . 9 . ' B a s i c a l l y , the d i s p a r i t y between MLr and S-^r values was sm a l l f o r the f i b r e s of any b i r c h r e f i n e r pulp, as i l l u s t r a t e d i n F i g u r e s 5.8, 5.10 and 5.11, i n d i c a t i n g t h a t ML removal i s a consequence of S - j y s 2 s e p a r a t i o n . For aspen, these l a s t two f i g u r e s show t h a t the a p p l i c a t i o n of a chemical pretreatment not only reduced the number of f i b r e s with p a r t i a l r e t e n t i o n of ML or r e l a t i v e t o TMP pulps, but a l s o .tends t o cause a r e d u c t i o n of the d i f f e r e n c e between MLr and S-^r va l u e s . T h i s suggests t h a t f o r aspen, chemical pretreatments of the type used i n t h i s study are r e s p o n s i b l e f o r weakening the boundary between the and S 2 l a y e r s , ' c a u s i n g i n c r e a s e d s e p a r a t i o n o f the l a y e r . The d i f f e r e n c e i n the s e v e r i t y of the chemical pretreatment appeared t o p l a y a comparatively s m a l l e r r o l e than the 106 F i g u r e 5 . 8 ASPEN MLr --Q--• ASPEN S i r BIRCH MLr BIRCH S i r D i s t r i b u t i o n p a t t e r n of ML and l a y e r r e t e n t i o n i n aspen and b i r c h TMP pulps o f s i m i l a r freeness (pulps A-TMP3 and B-TMP3) 107 >50 =100 ASPEN MLr - -E3--ASPEN S i r BIRCH MLr — K — BIRCH S1 r F i g u r e 5 .10 . D i s t r i b u t i o n p a t t e r n o f ML and r e t e n t i o n f o r aspen and b i r c h CTMP p u l p s o f s i m i l a r f r eenes s (pulps A-CTMP2 and B-CTMP4) . <50 >50 =100 ASPEN MLr - - E 3 - -ASPEN S i r BIRCH MLr — K — BIRCH S i r F i g u r e 5.11. D i s t r i b u t i o n p a t t e r n o f ML and r e t e n t i o n f o r aspen and b i r c h CMP p u l p s o f s i m i l a r f r e e n e s s (pulps A-CMP3 and B-CMP3) . 108 t rea tment i t s e l f , s i n c e the MLr o r S^r p a t t e r n s were s i m i l a r f o r CTMP and CMP f i b r e s f o r p u l p s o f s i m i l a r f r e e n e s s e s . I t i s e v i d e n t from F i g u r e s 5 .8 , 5.10 and 5 .11 , t h a t r e f i n i n g caused a d i f f e r e n t response i n f i b r e s u r f a c e q u a l i t y depending on the p r o c e s s i n g c o n d i t i o n s and on the s p e c i e s . F o r example, a C h i - s q u a r e v a l u e c a l c u l a t e d f o r the MLr d i s t r i b u t i o n p a t t e r n (88.16) f o r the TMP p u l p s o f F i g u r e 5 .8 , was s i g n i f i c a n t l y l a r g e r than the c r i t i c a l v a l u e o f 7 .82 . T h i s was a l s o t r u e f o r the CTMP and CMP c u r v e s shown i n F i g u r e s 5.10 and 5 .11 , r e s p e c t i v e l y . Thus , i t i s c l e a r t h a t the d i s t r i b u t i o n p a t t e r n o f f i b r e s u r f a c e q u a l i t y depends h e a v i l y on the type o f wood b e i n g p r o c e s s e d . F o r b i r c h r e f i n e r p u l p f i b r e s , t h e r e was ev idence o f an i n i t i a l s e p a r a t i o n between the and S 2 l a y e r s , even when the S ] _ l a y e r had not been removed. T h i s v i s i b l e s e p a r a t i o n o f the S-L from the S 2 l a y e r was p r e s e n t even at low l e v e l s of f i b r e development (high f r e e n e s s l e v e l s ) and was a s t a r t i n g p o i n t f o r f u r t h e r p r e f e r e n t i a l detachment o f the l a y e r a l o n g or near the S 1 / S 2 boundary . T h i s was r e f e r r e d to as the " o u t / i n " e f f e c t p r e s e n t e d i n T a b l e 4 . 3 . C l e a r l y , b i r c h f i b r e s showed t h i s f e a t u r e more f r e q u e n t l y than d i d aspen f i b r e s . B i r c h f i b r e s showed t h i s tendency o f p r o d u c i n g p a r t i a l s e p a r a t i o n s between the and S 2 l a y e r s even i n unbeaten k r a f t p u l p s , as i s d e p i c t e d i n F i g u r e 5 .12 . Presumably , d e l i g n i f i c a t i o n o f b i r c h f i b r e s had caused s e p a r a t i o n between the S]_ and S 2 l a y e r s i n segments o f the 109 F i g u r e 5.12a. U n b e a t e n b i r c h k r a f t p u l p f i b r e s i n c r o s s s e c t i o n s h o w i n g g a p s b e t w e e n t h e a n d S2 l a y e r s i n b r i g h t f i e l d i l l u m i n a t i o n . F i g u r e 12b. Same f i e l d u n d e r p a r t i a l p o l a r i z e d l i g h t . 110 f i b r e . By comparison, the unbeaten aspen k r a f t f i b r e s d i d not produce these separations (Figure 3.4). Thus, the chemical composition and bond strength at or near the S-jys2 i n t e r f a c e of the b i r c h f i b r e s appear to be d i f f e r e n t than those of the aspen f i b r e s . The separation of and S 2 i n b i r c h f i b r e s i s thought to be caused by mechanical and/or chemical a c t i o n s since they were not observed i n f i b r e s on wood cross s e c t i o n s . •At freeness l e v e l s higher than 300 mL CSF, about 20% of b i r c h TMP f i b r e s demonstrated t h i s o u t / i n e f f e c t . At freeness values c l o s e r t o 100 mL CSF, t h i s f e a t u r e appeared i n only 3% of the f i b r e s . Therefore, most of the S-^/^ p a r t i a l separations had r e s u l t e d i n t o t a l s e paration of the S-j_ l a y e r , l e a v i n g the S 2 l a y e r exposed. This marked t r e n d was not observed f o r b i r c h CTMP nor CMP f i b r e s . Instead, the f i b r e s produced from c h e m i c a l l y - t r e a t e d wood chips showed high l e v e l s of o u t / i n e f f e c t even at low pulp freeness l e v e l s . For these f i b r e s , i t i s evident that the p a r t i a l separations d i d not always r e s u l t i n removal of the S^ from the c e l l w a l l . Rather, the S 1/S 2 gaps became longer, to the p o i n t where the S^ had t o t a l l y separated from the S 2 l a y e r but remained surrounding the f i b r e s , as i s shown i n the example i n Figure 5.13. An extreme case of an unattached S^ l a y e r i s shown i n Figure 5.14. These f i g u r e s i n d i c a t e t h a t these b i r c h f i b r e s are, at l e a s t i n p a r t , covered by a sheath of S^ and ML l a y e r s t h a t had separated from the S 2 l a y e r , but were not removed during the mechanical I l l F i g u r e 5.13. TEM photograph showing d e t a i l of the gap produced between the and S 2 l a y e r s . The l a y e r had separated but remained surrounding the f i b r e (pulp B-CMP4). F i g u r e 5.14. B i r c h CMP pulp f i b r e s i n c r o s s s e c t i o n . Note the f i b r e s i n which the l a y e r has completely separated but surrounds the f i b r e (pulp B-CMP4). 112 d e f i b r a t i o n p r o c e s s . The s o f t e n i n g of the f i b r e s due to chemical pretreatment seems t o be r e s p o n s i b l e f o r the i n c r e a s e d number of o u t / i n f e a t u r e s i n b i r c h f i b r e s upon r e f i n i n g , and a l s o f o r the extended gap between the and S 2 l a y e r s . The l a y e r has expanded d u r i n g the process without a memory to r e t a i n i t s o r i g i n a l s i z e . Presumably, as f i b r e s go through c y c l e s of compression and decompression s t r e s s e s i n r e f i n i n g (Pearson 1989) as w e l l as l o n g i t u d i n a l shear f o r c e s (Hoglund et al 1976), the r e l a t i v e l a c k of r i g i d i t y causes the f i b r e s t o deform momentarily. Layers with h i g h e l a s t i c i t y , such as the high h e m i c e l l u l o s e -c o n t a i n i n g S 1 (Meier 1962) , elongate i n s t e a d of b r e a k i n g away from the f i b r e s u r f a c e i n r i g i d f a i l u r e , as i s more l i k e l y the case with TMP f i b r e s . The i n c r e a s e d removal of ML and S 1 l a y e r s i n TMP f i b r e s compared to CTMP and CMP f i b r e s supports t h i s i n t e r p r e t a t i o n . G i e r t z (1977) r e p o r t e d a " r o l l i n g s l e e v e " mechanism observable on the f i b r e s u r f a c e to e x p l a i n the removal of the Si l a y e r and the exposure of the S 2 l a y e r f o r hardwood r e f i n e r p u l p s produced a f t e r chemical pretreatment of c h i p s . He i n d i c a t e d t h a t i f hardwood ch i p s were c h e m i c a l l y p r e t r e a t e d , the wood was s o f t e n e d i n such a way t h a t the primary w a l l and the l a y e r were pe e l e d o f f i n the same manner as had o c c u r r e d with spruce TMP pulp f i b r e s . T h i s was a l s o r e p o r t e d as " s k i n n i n g s " by Law et a l (1985) . The suggested mechanism f o r removal of spruce TMP s u r f a c e l a y e r s c o n s i s t e d of the primary w a l l being r o l l e d back along the 113 f i b r e as a s l e e v e and, simultaneously, the h e l i x of the l a y e r c r a c k i n g and f i b r i l s and la m e l l a e b e i n g p e e l e d o f f . T h i s r o l l i n g s l e e v e mechanism was based on o b s e r v a t i o n s of pulp s l i d e s under the l i g h t microscope and not on f i b r e c r o s s s e c t i o n s . In the present study based on aspen and b i r c h r e f i n e r pulps, f i b r e s k i n n i n g s were not noted with any frequency i n aspen CTMP or CMP p u l p s . I t should a l s o be s t a t e d t h a t the number of f i b r e s p r e s e n t i n g the o u t / i n e f f e c t was r e l a t i v e l y small f o r aspen r e f i n e r pulps, the h i g h e s t b e i n g 8% of the f i b r e s analyzed i n a sample. In b i r c h CTMP and CMP pulps, however, f i b r e s k i n n i n g s were fr e q u e n t . F i g u r e 5.15 shows examples of these. The mechanism of r o l l i n g s l e e v e observed i n t h i s study was not the one suggested by G i e r t z (1977). I t appears as i f the s k i n n i n g s are due to s e p a r a t i o n and r o l l i n g of the l a y e r r a t h e r than t o the primary w a l l . F i g u r e 5.16 shows a case i n which the l a y e r had been r o l l e d back i n d i c a t i n g t h a t the f i b r e was s e c t i o n e d at the p o i n t at which the s k i n n i n g appeared. The r o l l i n g back seems to be caused by the i n i t i a l s e p a r a t i o n of the l a y e r and not the primary w a l l e x t e r n a l to i t . T h i s view i s supported by the tendency of hardwoods to f a i l at the S^/S2 boundary f o r a l k a l i soaked wood (Wardrop et a l 1961, C a r l s s o n and Lagergren 1957) . I t should be noted, however, t h a t the mechanism proposed by G i e r t z was based on b i r c h b i s u l f i t e chemimechanical pulp, and not f o r the a l k a l i n e pretreatment c o n d i t i o n s used i n t h i s i n v e s t i g a t i o n . Thus, i t i s p o s s i b l e t h a t these d i f f e r e n t 114 F i g u r e 5 .15 . B i r c h CMP f i b r e s showing " s k i n n i n g " o r "s leeve r o l l i n g " (pulp B-CMP3). F i g u r e 5 .16 . B i r c h CMP f i b r e s s e c t i o n e d a t the p o i n t where s k i n n i n g s o c c u r r e d a l o n g the l a y e r . Photograph taken under p a r t i a l p o l a r i z e d l i g h t (pulp B-CMP4). 115 c o n d i t i o n s might be r e s p o n s i b l e f o r c a u s i n g d i f f e r e n t s k i n n i n g mechanisms to be e f f e c t i v e . The mechanism proposed by G i e r t z f o r spruce TMP was a t t r i b u t e d to a p r o b a b l e weak t r a n s i t i o n between the and S 2 l a y e r s . I t was i n d i c a t e d t h a t hardwoods might need c h e m i c a l p r e t r e a t m e n t to undergo f i b r e s k i n n i n g and expose the S 2 l a y e r . However, i n t h i s s tudy b i r c h f i b r e s e v i d e n t l y p r e s e n t e d a weak S 1 / S 2 boundary, even when no c h e m i c a l p r e t r e a t m e n t was a p p l i e d . I t i s not then a mat ter t h a t s k i n n i n g and exposure o f the S 2 l a y e r i s p r e v e n t e d i n hardwood TMP due to a suggested s t r o n g e r S 1 / S 2 t r a n s i t i o n ( G i e r t z 1977). The f a c t i s t h a t , a l though s k i n n i n g s d i d not o c c u r i n hardwood TMP f i b r e s , the ML and S± l a y e r s were removed from the f i b r e s u r f a c e i n g r e a t e r p r o p o r t i o n s than from f i b r e s i n CTMP or CMP p u l p s , p r o b a b l y because o f weak S 1 / S 2 bonds . In a d d i t i o n to the o u t / i n e f f e c t r e c o r d e d as a mode of s e p a r a t i o n o f the outer l a y e r , f i b r e s were a l s o c l a s s i f i e d as e i t h e r h a v i n g or not h a v i n g the outer l a y e r p e e l e d away (Table 4 . 3 ) . T h i s p e e l i n g o f the ML a l s o o c c u r r e d l a r g e l y on or near the S - L / S 2 boundary . The major d i f f e r e n c e s found i n t h i s c a t e g o r y were between TMP f i b r e s and e i t h e r CTMP or CMP f i b r e s . TMP p u l p s not on ly showed a h i g h e r number o f f i b r e s p r e s e n t i n g obv ious ML p e e l i n g — m a i n l y a l o n g the l a y e r -but a l s o the l e n g t h o f the p e e l e d p o r t i o n a t t a c h e d t o the f i b r e s appeared somewhat l o n g e r . T h i s s u b s t a n t i a t e s the o b s e r v a t i o n t h a t f o r TMP f i b r e s , p e e l i n g a l o n g the S 1 / S 2 116 boundary was more e f f e c t i v e than f o r CTMP or CMP f i b r e s . An i m p l i c a t i o n o f the mechanism proposed by G i e r t z (1977) i s t h a t c h e m i c a l pre trea tment would cause i n c r e a s e d f i b r i l l a t i o n o f the f i b r e . T h i s was not observed t o be the case f o r the c o n d i t i o n s used i n t h i s i n v e s t i g a t i o n , as TMP p u l p f i b r e s from aspen and b i r c h appeared to be more f i b r i l l a t e d than those from CMP or CTMP p u l p s . F i g u r e s 5.17 and 5.18 compare the extent o f f i b r i l l a t i o n i n aspen TMP and CTMP p u l p s under phase c o n t r a s t i l l u m i n a t i o n . S i n c e t h e r e was a l a r g e d i f f e r e n c e i n the degree o f f i b r e ML and S]_ l a y e r r e t e n t i o n between these p u l p s (over 30%), i t i s e x p e c t e d t h a t f i b r i l l a t i o n o f the f i b r e w a l l i n t o l o n g f i l a m e n t s o r i g i n a t e s l a r g e l y from the S 2 l a y e r . SEM photomicrographs o f R48 p u l p f i b r e s i n F i g u r e s 5.19 and 5.20 show t h a t , at lower f reeness v a l u e s , the main d i f f e r e n c e i n the appearance o f TMP and CTMP f i b r e s i s due to s t i f f n e s s and not t o f i b r i l l a t i o n . Marton et al (1979) suggested t h a t the t h i c k n e s s o f the S-j_ l a y e r was r e s p o n s i b l e f o r the poor response o f hardwoods to TMP p u l p i n g . They r e p o r t e d t h i c k n e s s e s o f 0.12 um and 0.21 um f o r s p e c i e s o f Populus and B e t u l a , r e s p e c t i v e l y . In the p r e s e n t i n v e s t i g a t i o n , i t was shown t h a t i t was not the Sj_ l a y e r t h i c k n e s s t h a t r e s t r i c t e d access t o the S 2 l a y e r . In f a c t , b i r c h TMP f i b r e s w i t h t h i c k S^ l a y e r s p r e s e n t e d l e s s r e t e n t i o n o f t h i s l a y e r than d i d aspen because o f the i n i t i a l weak bond at the S ^ / S 2 boundary . I t seems t h a t i t i s the s t r e n g t h o f t h i s bond t h a t c o n t r o l s the s e p a r a t i o n o f 117 F i g u r e 5 .18 . Whole aspen CTMP p u l p . Note l e s s e r f i b r i l l a t i o n compared t o the TMP p u l p (pulp A-CTMP1) . 118 F i g u r e 5 .19 . SEM photograph o f f r e e z e - d r i e d aspen TMP f i b r e s (R48 f r a c t i o n ) . The f i b r e s are s t r a i g h t , s t i f f and f i b r i l l a t e d (pulp A-TMP4) . F i g u r e 5 .20 . Aspen CTMP R48 f r a c t i o n . F i b r e s appeared to be more f l e x i b l e than i n TMP (pulp A-CTMP4) . 119 the S-L l a y e r and, c o n s e q u e n t l y , the exposure o f the S 2 l a y e r . 5 . 1 . 2 . Exposure and D e l a m i n a t i o n o f the S2 L a y e r The exposure o f the S 2 l a y e r , o f c o u r s e , depends on the r e t e n t i o n o f the l a y e r . S 2 l a y e r exposure data are i n f a c t i n v e r s e l y r e l a t e d to those of S^r, as more r e t e n t i o n o f the Sj_ l a y e r a l l o w s l e s s exposure o f the S 2 and vice versa. The r e s u l t s f o r S 2 e are g i v e n i n T a b l e 4.4 and are a l s o shown, i n p a r t , i n F i g u r e s 5.21 and 5 .22, i n which p l o t s are p r e s e n t e d o f S 2 e index and S 2(e=100) a g a i n s t p u l p f r e e n e s s , r e s p e c t i v e l y . As expected from the low r e t e n t i o n v a l u e s o f ML and the l a y e r , TMP p u l p f i b r e s had h i g h e r S 2 e i n d i c e s t h a n CTMP or CMP p u l p s made from the same s p e c i e s . S i m i l a r l y , more f i b r e s had t o t a l exposure o f the S 2 l a y e r , S 2 ( e=100) , i n the TMP p u l p s . T h i s f i n d i n g shows t h a t c h e m i c a l t r e a t m e n t s , l i k e the ones used i n t h i s s tudy , are not r e q u i r e d to cause i n c r e a s e d exposure o f the S 2 l a y e r . B i r c h TMP f i b r e s showed the most S 2 exposure , p a r t i c u l a r l y at f r e e n e s s l e v e l s near 100 mL CSF, even though aspen showed a lower r e t e n t i o n o f ML. T h i s can be e x p l a i n e d as f o l l o w s . When the ML was removed i n aspen TMP f i b r e s , the h i g h e r r e t e n t i o n o f S^ l a y e r s r e s u l t e d i n f i b r e s u r f a c e s w i t h lower S 2 exposure than f o r b i r c h TMP. B i r c h TMP f i b r e s had the h i g h e s t S 2 e index and the h i g h e s t percentage o f f i b r e s w i t h t o t a l S 2 exposure . The r e l a t i v e c o n t r i b u t i o n o f S 2 (e=100) to the S 2 e index was much h i g h e r f o r b i r c h p u l p s , r e l a t i v e to 120 A-TMP jk. A-CTMP x A-CMP • B-TMP ® B-CTMP M B-CMP "0 100 200 300 400 500 600 C.S.F., mL Figure 5.21. Plot of S2 exposure index against pulp freeness. 0 100 200 300 400 500 600 C.S.F., mL Figure 5.22. Plot of percentage of f i b r e s with t o t a l S 2 layer exposure against pulp freeness. 121 aspen , which c a r r i e d h i g h p r o p o r t i o n o f f i b r e s w i t h p a r t i a l S 2 e x p o s u r e . The l a r g e p r o p o r t i o n o f f i b r e s i n b i r c h TMP p u l p s f e a t u r i n g a p a r t i a l s e p a r a t i o n between the and the S 2 l a y e r s ( o u t / i n e f f e c t ) seems to be r e s p o n s i b l e f o r the c o r r e s p o n d i n g l y l a r g e number o f f i b r e s w i t h t o t a l S 2 e x p o s u r e . The g e n e r a l t r e n d s o f S 2 e are the same as those f o r S^r, except t h a t they are i n v e r t e d . S i n c e , as has been shown e a r l i e r , r e t e n t i o n o f the S^ l a y e r l a r g e l y f o l l o w e d the b e h a v i o r o f MLr, the S 2 e f o l l o w e d the i n v e r t e d p a t t e r n o f M L r , i . e . , l e s s r e t e n t i o n o f ML r e s u l t i n g i n more exposure o f the S 2 l a y e r . F i g u r e s 5.21 and 5.22 show t h a t c h e m i c a l p r e t r e a t m e n t s were more e f f e c t i v e i n expos ing S 2 f o r aspen than f o r b i r c h , as aspen curves d i s p l a y e d s t e e p e r s l o p e s . D e l a m i n a t i o n o f the S 2 l a y e r was r e c o r d e d (Table 4.5 and F i g u r e s 5.23 and 5.24) to g a i n i n s i g h t s i n t o the damage and p o s s i b l e f i b r i l l a t i o n o r i g i n a t i n g from t h i s l a y e r . C o n c e n t r i c d e l a m i n a t i o n i s known to occur i n beaten c h e m i c a l p u l p f i b r e s (Wardrop 1963). In f a c t , the l a m e l l a r s t r u c t u r e o f the S 2 l a y e r i n the wood f i b r e was demonstrated e a r l i e r (Ruel et a l 1978, 1979) . Thus, some degree o f d e l a m i n a t i o n can be expec ted , at l e a s t f o r the f i b r e s s u b j e c t e d to c h e m i c a l t reatment p r i o r to r e f i n i n g , because o f the e x p e c t e d a c c e s s i b i l i t y w i t h i n c e l l u l o s e l a m e l l a e and s o f t e n i n g o f the S 2 l a y e r . In the p r e s e n t s tudy , hardwood r e f i n e r p u l p f i b r e s d i d show some degree o f d e l a m i n a t i o n . In g e n e r a l , more f i b r e s were d e l a m i n a t e d i n CTMP and CMP ASPEN REFINER PULPS F i g u r e 5 . 2 3 . Percentage o f f i b r e s showing d e l a m i n a t i o n i n aspen r e f i n e r p u l p s . BIRCH REFINER PULPS F i g u r e 5 .24 . Percentage o f f i b r e s showing d e l a m i n a t i o n i n b i r c h r e f i n e r p u l p s . 123 than i n TMP p u l p s . As expec ted , p u l p s from c h e m i c a l l y -t r e a t e d c h i p s p r e s e n t e d more f i b r e s showing d e l a m i n a t i o n s , even though TMP f i b r e s had more exposure o f the S 2 l a y e r . C h e m i c a l p r e t r e a t m e n t combined w i t h r e f i n i n g caused more e x t e n s i v e c o n c e n t r i c d e l a m i n a t i o n s than m e c h a n i c a l t r e a t m e n t s w i t h l i m i t e d f i b r e s o f t e n i n g , as i n the case o f TMP p u l p s . T h e r e f o r e , S 2 d e l a m i n a t i o n appears to be r e l a t e d to c h e m i c a l s o f t e n i n g of the c e l l w a l l . A l t h o u g h t h i s f e a t u r e was r e c o r d e d to p o i n t out the degree o f s e p a r a t i o n w i t h i n the S 2 l a y e r , as seen under the l i g h t m i c r o s c o p e , i t c o u l d be a n a l y z e d i n c o n j u n c t i o n w i t h o t h e r r e c o r d e d f e a t u r e s . T a b l e 5.1 i n d i c a t e s t h a t , f o r most p u l p s , the m a j o r i t y o f the f i b r e s which showed d e l a m i n a t i o n had t o t a l exposure o f the S 2 l a y e r . T h i s was p a r t i c u l a r l y t r u e f o r p u l p s at low f reenes s l e v e l s . The i m p l i c a t i o n i s t h a t once the S 2 i s exposed, e x t e r n a l d e l a m i n a t i o n takes p l a c e w i t h the p o s s i b l e p r o d u c t i o n o f f i n e s from t h i s l a y e r . However, and a l t h o u g h not q u a n t i t a t i v e l y measured, the degree and type o f d e l a m i n a t i o n r e c o r d e d d i f f e r e d somewhat between TMP and the o t h e r r e f i n e r p u l p s . In TMP f i b r e s , d e l a m i n a t i o n took p l a c e c l e a n l y , as s e p a r a t i o n o c c u r r e d w i t h i n the S 2 l a y e r (F igure 3 . 6 ) . F o r CTMP and CMP f i b r e s , d e l a m i n a t i o n appeared to be a g r a d u a l p e e l i n g o f the S 2 l a y e r d u r i n g m e c h a n i c a l t reatment from which f i n e s o f a f i b r i l l a r n a t u r e are p r o d u c e d . An example i s shown f o r b i r c h i n F i g u r e 5 .25 . D e l a m i n a t i o n o f the l a y e r was a l s o observed i n 124 Table 5.1. Percentage of fi b r e s with t o t a l S 2 layer exposure from among the fib r e s showing delamination. % OF S2(e=100) PULP ID OF D E L A M I N A T E D FIBRES A-TMP1 63 A-TMP2 64: A-TMP3 56 A-TMP4 69 A - C T M P l 7 A-CTMP2 45 A-CTMP3 79 A-CTMP4 66 A-CMP1 14 A-CMP2 54 A-CMP3 64 A-CMP4 64 B-TMP1 30 B-TMP2 50 B-TMP3 33 B-TMP4 67 B-CTMP1 63 B-CTMP2 77 B-CTMP3 96 B-CTMP4 75 B-CMP1 58 B-CMP2 89 B-CMP3 70 B-CMP4 66 125 F i g u r e 5 .25 . TEM photograph o f a b i r c h CMP f i b r e i n c r o s s s e c t i o n showing d e l a m i n a t i o n o f the S 2 l a y e r (pulp B-CMP4). 126 c h e m i c a l l y - t r e a t e d f i b r e s under TEM. I t i s known t h a t a l l l a y e r s o f the c e l l w a l l o f a wood f i b r e e x h i b i t l a m e l l a t i o n and - t h a t the l a y e r has a h i g h e r p o r o s i t y than the S 2 (Wardrop 1963). Thus , i t i s expected t h a t , when the remained a t t a c h e d to the S 2 , some degree o f d e l a m i n a t i o n s h o u l d o c c u r i n the Sj_ l a y e r i n f i b r e s t h a t have undergone c h e m i c a l and r e f i n i n g t r e a t m e n t s . F i g u r e s 5.26 and 5.27 show e v i d e n c e o f d e l a m i n a t i o n o f the l a y e r . I t i s expec ted t h a t , upon remova l , t h i s d e l a m i n a t e d m a t e r i a l w i l l produce f i n e s w i t h h i g h e r bonding a b i l i t y than i f the l a y e r were removed i n t a c t . A l t h o u g h not q u a n t i t a t i v e l y measured, d e l a m i n a t i o n o f the S i l a y e r can o c c u r i n c h e m i c a l l y - t r e a t e d f i b r e s . The p o s s i b l e breakdown o f the S^ i n t o f i b r i l s a f t e r s e p a r a t i o n and removal d e s e r v e s f u r t h e r s t u d y , as does i t s r o l e i n the f o r m a t i o n o f f i n e s f r a c t i o n s . 5 . 1 . 3 . D i s t o r t e d F i b r e s When examining c r o s s s e c t i o n s o f f i b r e s from c h e m i c a l l y -t r e a t e d c h i p s , i t became e v i d e n t t h a t the f i b r e s c o u l d be c l a s s i f i e d i n t o two c a t e g o r i e s : t r e a t e d and u n t r e a t e d f i b r e s . The appearance o f the u n t r e a t e d f i b r e s i n c r o s s s e c t i o n resembled t h a t o f TMP f i b r e s , w h i l e the t r e a t e d f i b r e s were d i s t o r t e d i n shape compared t o the f o r m e r , i . e . , more rounded and s w o l l e n , as was shown i n F i g u r e .3 .10 . I t was thus d e c i d e d to r e c o r d the p r o p o r t i o n o f d i s t o r t e d f i b r e s f o r CTMP and CMP p u l p s . A l t h o u g h the s e p a r a t i o n o f these types o f f i b r e would be b e t t e r done w i t h an image 127 128 a n a l y s i s system t h a t c o u l d d e t e c t d i f f e r e n c e s i n s t a i n i n g i n t e n s i t i e s and shape f a c t o r s , an e s t i m a t i o n of the number of d i s t o r t e d f i b r e s was done under simple l i g h t microscopy. Obviously, there were many f i b r e s t h a t c o u l d be c o n s i d e r e d t r a n s i t i o n a l between untreated and t r e a t e d . These f i b r e s were c l a s s i f i e d a c c o r d i n g t o t h e i r s i m i l a r i t y t o f i b r e s t h a t were o b v i o u s l y u n t r e a t e d or o b v i o u s l y d i s t o r t e d . The r e s u l t s (Table 4.6 and F i g u r e s 5.28 and 5.29) showed t h a t t h e r e was a l a r g e p r o p o r t i o n of d i s t o r t e d f i b r e s i n r e f i n e r pulps from c h e m i c a l l y - t r e a t e d c h i p s , approximately from 5 0 - 7 0 % f o r CTMP and from 75-90% f o r CMP pulps. There seems t o be a tendency f o r aspen t o produce more d i s t o r t e d f i b r e s than b i r c h , p o s s i b l y due t o b e t t e r l i q u o r p e n e t r a t i o n . S i n c e l i q u o r p e n e t r a t i o n i s l a r g e l y i n i t i a t e d through the v e s s e l s (Wardrop 1963), the hi g h e r v a l u e s f o r aspen are c o n s i s t e n t with i t s high e r number of VE per u n i t area of v e s s e l s i n wood and i t s t h i n n e r f i b r e w a l l s . On the other hand, the chemical pretreatments were markedly d i f f e r e n t . CMP treatments i n v o l v e d not onl y h i g h e r c o n c e n t r a t i o n of chemicals, but a l s o l o n g e r times and h i g h e r temperatures than CTMP. The r e s u l t s of the number of d i s t o r t e d f i b r e s showed t h i s d i f f e r e n c e . N e v ertheless, the l a r g e d i f f e r e n c e i n chemical treatment c o n d i t i o n s p r o v i d e d o n l y a compar a t i v e l y small d i f f e r e n c e i n the number of d i s t o r t e d f i b r e s between CMP and CTMP. Presumably, t h i s was due t o the CTMP screw press i n the impregnation system ASPEN REFINER PULPS 1 0 0 90 oo 80i W £ 70 Q w H 0 4 O 40 H oo 3 3 ° i 60 50 20 10 0 1 HTf 1 2 3 4 1 2 3 4 F i g u r e 5.28. Percentage of f i b r e s showing d i s t o r t i o n i n aspen CTMP and CMP pulps. BIRCH REFINER PULPS 100 ; 90-1 2 3 4 1 2 3 4 F i g u r e 5.29. Percentage of f i b r e s showing d i s t o r t i o n i n b i r c h CTMP and CMP pulps. 130 (compression r a t i o of 3:1) which caused c r a c k s i n the c h i p s through which l i q u o r penetrated. One e v i d e n t a p p l i c a t i o n o f the number of d i s t o r t e d f i b r e s i s the i n v e s t i g a t i o n of l i q u o r p e n e t r a t i o n and u n i f o r m i t y of f i b r e treatment. R e s u l t s i n t h i s study showed t h a t both CTMP and CMP pulps, produced under the c o n d i t i o n s used here, are mixtures of t r e a t e d and untreated f i b r e s , although most f i b r e s were c h e m i c a l l y t r e a t e d p a r t i c u l a r l y i n the case of CMP p u l p s . I t should be mentioned t h a t the degree of f i b r e d i s t o r t i o n between s p e c i e s or processes i s not known, only the p r o p o r t i o n s . The e f f e c t of r e f i n i n g on the number of d i s t o r t e d f i b r e s d i d not f o l l o w a d e f i n i t e t r e n d . More p r e c i s e i n f o r m a t i o n , p o s s i b l y p r o v i d e d w i t h the h e l p of an image a n a l y s i s system, would be needed t o draw c o n c l u s i o n s on the e f f e c t of r e f i n i n g on f i b r e shape changes. 5.1.4. R a d i a l F a i l u r e (RF) I t has been shown i n e a r l y s t u d i e s t h a t the formation of ribbons i s h i g h l y d e s i r a b l e f o r the p r o d u c t i o n of a good stone groundwood or r e f i n e r mechanical pulp (Forgacs 1963). These ribbons enhance bonding, l i g h t s c a t t e r i n g and smoothness of mechanical pulps (Mohlin 1982b). Although f i b r e r a d i a l f a i l u r e may o r i g i n a t e i n p a r t from i n i t i a l t r a n s w a l l f a i l u r e i n r e f i n i n g , i t c o u l d a l s o s t a r t from c r a c k development on i n t a c t f i b r e s . A c c o r d i n g t o Forgacs (1963), r i b b o n formation s t a r t s with the r a d i a l f a i l u r e 131 (cracks o r s p l i t s ) of the f i b r e and the subsequent u n r a v e l l i n g of the c e l l w a l l along the S 2 l a y e r . Thus, the number of f i b r e s i n which r a d i a l f a i l u r e occurs r e l a t e s t o the frequency of ribbons i n the pulp. Ribbon formation has been observed not only i n mechanical pulps from softwoods but a l s o from hardwoods (Vecchi 1969, Scaramuzzi and V e c c h i 1968). T h i s c h a r a c t e r i s t i c may appear i n g r e a t e r p r o p o r t i o n s i n the middle f r a c t i o n r a t h e r than i n the R48 t h a t was used i n t h i s study. However, the 48/100 resembled the R48 f r a c t i o n i n the pulps s t u d i e d , i n terms of f i b r e shapes. The R48 f r a c t i o n i s expected t o pr o v i d e r e l i a b l e i n f o r m a t i o n on the r e l a t i v e amounts of ribbons produced. The p r o p o r t i o n of f i b r e s t h a t f a i l e d r a d i a l l y a c r o s s the c e l l w a l l (Table 4.5 and F i g u r e s 5. 30 and 5.31) was c l e a r l y h i g h e r f o r TMP pulps and was only minor i n most CTMP or CMP f i b r e s , although i t approached 10% i n A-CTMP4. RF i n t h i s pulp might be a s s o c i a t e d with the f a c t t h a t t h i s p a r t i c u l a r pulp showed a reduced R48 f r a c t i o n i m p l y i n g t h a t f i b r e c u t t i n g may have been p r e v a l e n t d u r i n g r e f i n i n g ( F i g u r e s 3.5 and 5.1.). Otherwise, c h e m i c a l l y - t r e a t e d f i b r e s were sof t e n e d t o the p o i n t where r e f i n i n g d i d not c r a c k the f i b r e w a l l t o the same extent as i n TMP, but l i t t l e d i f f e r e n c e s i n RF were found between CTMP and CMP f i b r e s . I t i s a n t i c i p a t e d t h a t RMP w i l l produce even h i g h e r p r o p o r t i o n s of r a d i a l l y f a i l e d f i b r e s s i n c e r e f i n i n g i s done under atmospheric c o n d i t i o n s and the f i b r e s w i l l be s t i f f e r . Presumably, t h i s would cause more t r a n s w a l l f a i l u r e as w e l l ASPEN REFINER PULPS 1 2 3 4 1 2 3 4 1 2 3 4 Figure 5.30. Percentage of fi b r e s showing r a d i a l f a i l u r e i n aspen re f i n e r pulps. BIRCH REFINER PULPS 1 2 3 4 1 2 3 4 1 2 3 4 Figure 5.31. Percentage of fi b r e s showing r a d i a l f a i l u r e i n birch r e f i n e r pulps. 133 as more c r a c k s i n the f i b r e w a l l . Whereas l i t t l e change i n the number o f r a d i a l l y - f a i l e d f i b r e s due t o f u r t h e r r e f i n i n g was d e t e c t e d f o r aspen TMP p u l p s , b i r c h TMP p u l p s showed h igher ' p r o p o r t i o n s o f RF at low. f r e e n e s s . The low number o f f i b r e s w i t h ' RF at h i g h f r e e n e s s i n d i c a t e s t h a t b i r c h may need more r e f i n i n g than aspen t o produce and propagate c r a c k s a l o n g the S 2 w a l l . T h i s may be r e l a t e d to the t h i c k e r c e l l w a l l s o f b i r c h f i b r e s . The r e s u l t s f o r RF i n TMP f i b r e s i n t h i s i n v e s t i g a t i o n (RF i n a p p r o x i m a t e l y 20% of the f i b r e s ) are s i m i l a r to those r e p o r t e d f o r Pinus radiata TMP ( K i b b l e w h i t e 1983). He i n d i c a t e d t h a t 81% of the f i b r e c r o s s s e c t i o n s were i n t a c t , thus l e a v i n g 19% as R F . The i n c r e a s e d f i b r i l l a t i o n o f TMP p u l p s r e l a t i v e to CTMP o r CMP i s p o s s i b l y due not o n l y to f i b r i l l a t i o n o f the exposed S 2 l a y e r , but to the g r a d u a l c o n v e r s i o n o f some of the r i b b o n s i n t o l o n g f i b r i l s , as i s the case f o r softwood m e c h a n i c a l p u l p s (Forgacs 1963). To a c e r t a i n e x t e n t , the r i b b o n s p r e s e n t i n the p u l p w i l l expose the f i b r e S3 l a y e r , which s h o u l d p r o v i d e a good bonding s u r f a c e because o f i t s h i g h c a r b o h y d r a t e content (Lange 1959) . The f a c t t h a t r a d i a l l y - f a i l e d f i b r e s appeared i n s m a l l numbers o n l y i n CTMP and CMP p u l p s , and t h a t these p u l p s were much s t r o n g e r than those produced by the TMP p r o c e s s , i n d i c a t e s t h a t i n c r e a s e d f i b r e f l e x i b i l i t y due to the c h e m i c a l p r e t r e a t m e n t i s more important than p o t e n t i a l 134 b e n e f i t s which c o u l d a r i s e from r a d i a l f a i l u r e . 5.1.5. Breakdown o f Tens ion Wood F i b r e s The p r e s e n c e o f TW was f i r s t n o t i c e d w h i l e o b s e r v i n g the aspen r e f i n e r p u l p s l i d e s . S t r u c t u r e s t h a t d i d not resemble normal wood f i b r e s were i d e n t i f i e d . The presence o f TW was then c o n f i r m e d by examinat ion o f wood c r o s s s e c t i o n s from the two aspen t r e e s c h i p p e d . A l s o a t h i r d aspen wood sample was examined from the Peace R i v e r r e g i o n i n A l b e r t a . They a l l c o n t a i n e d n o t i c e a b l e amounts o f t e n s i o n wood. The b i r c h samples d i d not show presence o f t e n s i o n wood. E x a m i n a t i o n of wood c r o s s s e c t i o n s c o u l d g i v e i n d i c a t i o n of the ex tent o f G - f i b r e s i n the c h i p f u r n i s h . However, such work c o u l d not p r o v i d e a c c u r a t e e s t i m a t e s o f the G - f i b r e content u n l e s s a l l c e l l s are counted i n many s l i d e s e c t i o n s a c r o s s the d iameter of the t r e e and at d i f f e r e n t h e i g h t s . T h i s would have been an enormous t a s k and s t i l l i t would not have p r o v i d e d a c c u r a t e va lues to a l l o w comparisons w i t h v a l u e s o b t a i n e d from f i b r e c r o s s s e c t i o n s i n the r e f i n e r p u l p s p r o d u c e d . A c c u r a c y o f such e s t i m a t e s would have been low because some p a r t s o f the logs were removed b e f o r e c h i p p i n g due t o s t a i n i n g or decay . I t was, t h e r e f o r e , d e c i d e d to assess G - f i b r e s from the unbeaten k r a f t p u l p i n which the G - l a y e r would be i n t a c t i n s i d e the f i b r e . Due to the f i b r i l o r i e n t a t i o n and h i g h c r y s t a l l i n i t y , the G - l a y e r gave s t r o n g p o l a r i z a t i o n under c r o s s p o l a r s when observed i n p u l p s l i d e s . However, i t was 135 not p o s s i b l e to s e p a r a t e G - f i b r e s on t h i s b a s i s f o r two r e a s o n s : 1) the s u b s t a n t i a l v a r i a t i o n i n G - l a y e r t h i c k n e s s e n c o u n t e r e d ( F i g u r e s 5.32 and 5 .33 ) , and 2) because o f l i g h t p o l a r i z a t i o n due to the S 2 l a y e r . Based on c r o s s s e c t i o n s o f k r a f t f i b r e s , i t was then p o s s i b l e t o measure a c c u r a t e l y the p r o p o r t i o n o f G - f i b r e s i n the aspen raw m a t e r i a l used (Table 4.7 and F i g u r e 3.4) . An average o f 31% of the t o t a l amount o f f i b r e s were G - f i b r e s . Thus , t h i s v a l u e was taken as b e i n g i d e n t i c a l t o t h a t f o r the o r i g i n a l wood which was c h i p p e d and then c o n v e r t e d i n t o r e f i n e r p u l p . The c o n t e n t o f G - f i b r e s i n the R48 f r a c t i o n o f the aspen r e f i n e r p u l p s shown i n T a b l e 4.8 i s i l l u s t r a t e d i n F i g u r e 5 .34 . There was s i g n i f i c a n t breakdown o f the G - f i b r e s o n l y i n TMP p u l p s as e v i d e n c e d by t h e i r lower r e t e n t i o n i n the R48 f r a c t i o n compared to the G - f i b r e content o f the o r i g i n a l f u r n i s h . Even when f r e e G - l a y e r s were i n c l u d e d , the t o t a l G -l a y e r count was s i g n i f i c a n t l y below t h a t o f the wood. T h i s i n d i c a t e s t h a t t h e r e was a p r e f e r e n t i a l breakdown of G -f i b r e s under TMP p r o c e s s i n g c o n d i t i o n s . Presumably , the t h i n n e r w a l l s o f the G - f i b r e s (when e x c l u d i n g the G - l a y e r ) , as r e p o r t e d by K a e i s e r and Boyce (1965), promoted the f o r m a t i o n o f r i b b o n s from the G - f i b r e w a l l s ("sk ins") , t h e r e b y r e d u c i n g the weight o f the R48 f r a c t i o n and, at the same t i m e , expos ing G - l a y e r s , as can be o b s e r v e d i n F i g u r e s 5.35 and 5 .36 . T h i s i s c o n s i s t e n t w i t h e a r l i e r o b s e r v a t i o n s o f abundant exposed G - l a y e r s i n RMP p u l p s from Populus 136 F i g u r e 5 .32 . SEM photograph o f G - f i b r e s i n aspen wood c r o s s s e c t i o n showing t h i n G - l a y e r s . F i g u r e 5 .33 . SEM photograph o f G - f i b r e s i n aspen wood c r o s s s e c t i o n showing t h i c k G - l a y e r s . 137 1 2 3 4 1 2 3 4 1 2 3 4 F i g u r e 5.34. Percentage o f G - f i b r e s i n the R48 f r a c t i o n of aspen r e f i n e r p u l p s . 138 139 d e l t o i d e s (Scaramuzzi and V e c c h i 1968). The breakdown o f the f r e e G - l a y e r s , a l though not q u a n t i t a t i v e l y measured, can be m o n i t o r e d w i t h i n the d i f f e r e n t f r a c t i o n s o f . the p u l p , as seen i n F i g u r e s 5.37 through 5 .40 . I t can be seen t h a t f r e e G - l a y e r s are p r e s e n t i n every f r a c t i o n o f the aspen TMP p u l p s . These photomicrographs show t h a t the i n t e g r i t y o f the G - l a y e r i s l a r g e l y m a i n t a i n e d . The G - l a y e r s do not appear to break down e a s i l y , as p a r t i c u l a r l y e v i d e n t from f i b r e c r o s s s e c t i o n a n a l y s e s which shows the presence o f f r e e G - l a y e r s i n the R48 p u l p f r a c t i o n . I t seems t h a t the d i s t r i b u t i o n of G - l a y e r m a t e r i a l i n the d i f f e r e n t p u l p f r a c t i o n s i s se t at the i n i t i a l breakdown of the c h i p s i n t o p u l p . On the o t h e r hand, due to r e p o r t e d weak l a t e r a l bonding (Cote and Day 1965, N o r b e r g and Meier 1966), the G - l a y e r would be expec ted to produce a c e r t a i n extent of f i b r i l l a t i o n d u r i n g r e f i n i n g . Once the G - l a y e r s are i n i t i a l l y l i b e r a t e d , the r e f i n i n g a c t i o n s h o u l d be a b l e to produce some degree o f d e l a m i n a t i o n and f i b r i l l a t i o n o f t h i s l a y e r . F i g u r e s 5.38 and 5.40 suppor t t h i s h y p o t h e s i s . They show the presence o f p u r p l e f i l a m e n t s d e r i v e d from G - l a y e r m a t e r i a l . I t i s expec ted t h a t the exposed G - l a y e r or any f i b r i l l a r m a t e r i a l d e r i v e d from i t would c o n t r i b u t e to i n c r e a s i n g the i n t e r f i b r e b o n d i n g i n a sheet of p a p e r . There was no p r e f e r e n t i a l breakdown of G - f i b r e s i n CTMP or CMP p u l p s . The t o t a l amount o f G - l a y e r s i n the R48 p u l p f r a c t i o n was not s i g n i f i c a n t l y d i f f e r e n t from t h a t o f the p a r e n t wood. On the one hand, these two p r o c e s s e s p r e s e r v e d 140 F i g u r e 5.37. Presence of G-layers t h a t were detached from t h e i r parent f i b r e s i n the R48 f r a c t i o n of pulp A-TMP3. Fi g u r e 5.38. I s o l a t e d G-layer showing f i n e c e l l u l o s i c f i l a m e n t s d e taching from the s u r f a c e . F r a c t i o n 48/100 f r a c t i o n of pulp A-TMP3. 141 F i g u r e 5 .40 . G - l a y e r f i l a m e n t s i n the P200 f r a c t i o n o f p u l p A-TMP3. 1 4 2 f i b r e l e n g t h to a much g r e a t e r ex tent than d i d TMP p r o c e s s i n g , so t h a t the chance o f f i b r e s b r e a k i n g and l i b e r a t i n g G - l a y e r s was s m a l l . On the o t h e r hand, o n l y a s m a l l p o r t i o n o f the CMP or CTMP f i b r e s f a i l e d r a d i a l l y , as measured on f i b r e c r o s s s e c t i o n s , t h e r e b y m i n i m i z i n g the chance f o r G - l a y e r s to be s t r i p p e d o f f a f t e r the f i b r e s c r a c k e d and opened. I t i s i n f e r r e d t h a t , f o r CTMP and CMP p u l p s , the breakdown of the G - f i b r e s f o l l o w e d a p a t t e r n s i m i l a r t o t h a t f o r the r e s t o f the f i b r e s , at l e a s t i n i t i a l l y from the R48 i n t o the 48/100 f r a c t i o n . N e v e r t h e l e s s , at low freeness l e v e l s , the presence o f some G - f i b r e breakdown was e v i d e n t s i n c e the v a l u e f o r f r e e G -l a y e r s i n c r e a s e d . Examples of these are shown i n F i g u r e 5.41 and 5 .42 . An i m p o r t a n t c o n s i d e r a t i o n r e g a r d i n g the l i b e r a t i o n o f G -f i b r e s concerns the "skins" t h a t are l e f t b e h i n d when t h i s o c c u r s . In TMP pu lps these s k i n s are l i k e l y to be a source o f r i b b o n s , whereas i n CTMP these s k i n s appeared as p a r t l y r o l l e d and t w i s t e d f i b r e s , or as f r e e t h i n l a m e l l a e . O v e r a l l , the bonding p o t e n t i a l o f these s k i n s s h o u l d be h i g h compared t o normal f i b r e s , based on the apparent f l e x i b i l i t y and l a r g e s u r f a c e area shown. F i g u r e 5.41 shows examples o f these s k i n s . The l i t e r a t u r e had i n d i c a t e d some b e n e f i c i a l e f f e c t s o f TW on the s t r e n g t h of pure mechanica l p u l p s , but d e t r i m e n t a l e f f e c t s i n c h e m i c a l p u l p s . In TMP p u l p s , G - l a y e r s were not o n l y l i b e r a t e d i n l a r g e numbers, but they a l s o may be F i g u r e 5.42 G - l a y e r exposed a t the c e n t r e o f a f i b r e w h i l e covered by the f i b r e w a l l s a t the extremes (pulp A-CTMP4) . 144 r e s p o n s i b l e f o r p a r t o f the f o r m a t i o n o f r i b b o n s . The b e n e f i t s from the presence o f TW i n TMP p u l p s seem to be c l e a r . On the o t h e r hand, the e f f e c t o f TW i s unknown on CTMP and CMP p u l p s t r e n g t h s and an i n v e s t i g a t i o n d e s i g n e d to s tudy t h i s may be needed. However, from the r e s u l t s o b t a i n e d i n the p r e s e n t s tudy f o r the chemi -mechan ica l p u l p s , i t would seem t h a t the low p r o p o r t i o n o f l i b e r a t e d G - l a y e r s would produce fewer c o l l a p s e d f i b r e s , and thus b u l k i e r shee t s w i t h lower s t r e n g t h i f compared w i t h p u l p s from normal wood. The t e c h n i q u e deve loped f o r a s s e s s i n g the p r o p o r t i o n o f t e n s i o n wood f i b r e s has e x c e l l e n t p o t e n t i a l f o r use i n s t u d i e s i n which the p r o p o r t i o n o f TW (measured i n terms of G - f i b r e s ) i s r e l a t e d to s p e c i f i c c h e m i c a l components o f the wood, wood b e h a v i o r and p u l p p r o p e r t i e s . I t i s a r e l a t i v e l y s i m p l e method t h a t p r o v i d e s a c c u r a t e assessment o f the p r o p o r t i o n o f G - f i b r e s i n a wood sample . 5 . 2 . Breakdown of V e s s e l Elements Whole VE are presumably the ones w i t h h i g h e r p i c k i n g tendency d u r i n g p r i n t i n g . T h e r e f o r e , i t was c o n s i d e r e d i m p o r t a n t to assess t h e i r s u r v i v a l d u r i n g r e f i n i n g . The s tudy of the breakdown o f VE was done by measur ing the s i z e d i s t r i b u t i o n o f VE fragments i n the p u l p and by c o u n t i n g , i n each p u l p , the number o f whole VE t h a t s u r v i v e d r e f i n i n g . Because a minimum s i z e v a l u e had t o be se t i n o r d e r to p o s i t i v e l y i d e n t i f y VE fragments , the s i z e f requency 145 d i s t r i b u t i o n d i d not p r o v i d e i n f o r m a t i o n on the p r o d u c t i o n o f p a r t i c l e s s m a l l e r than 112.5 um. With t h i s i n f o r m a t i o n a l o n e , no c o n c l u s i o n c o u l d be drawn on the number o f whole VE t h a t were reduced t o fragments o f d i f f e r e n t s i z e s . The i n f o r m a t i o n p r o v i d e d by the c o u n t i n g t e c h n i q u e used to a s se s s s u r v i v a l o f whole V E , complemented the f i n d i n g s on p a r t i c l e s i z e d i s t r i b u t i o n . F o r example, i f two p u l p s show no d i f f e r e n c e i n VE s i z e d i s t r i b u t i o n , but do show d i f f e r e n t numbers o f whole VE per gram of wood (or o f p u l p i f t h e r e i s no y i e l d d i f f e r e n c e ) , i t can then be c o n c l u d e d t h a t the p u l p w i t h fewer whole VE has more f i n e p a r t i c l e s ( s m a l l e r than the minimum set value) t h a t o r i g i n a t e d from the breakdown of VE t h a t d i d not s u r v i v e the r e f i n i n g p r o c e s s . The r e s u l t s p r e s e n t e d i n T a b l e s 4.13 and 4.14 show t h a t c h i p r e f i n i n g under TMP c o n d i t i o n s e f f e c t i v e l y reduced the s i z e o f the VE t o f i n e p a r t i c l e s f o r both s p e c i e s . F i g u r e s 5.43 and 5.44 i l l u s t r a t e p a r t i c l e s i z e d i s t r i b u t i o n f o r d i f f e r e n t p u l p s o f s i m i l a r f reeness produced under the d i f f e r e n t r e f i n e r p u l p i n g proces se s s t u d i e d h e r e . I t s h o u l d be ment ioned t h a t the frequency po lygon was c l o s e d at zero i n the lower end, because of s i m p l i c i t y and c l a r i t y . I t i s a n t i c i p a t e d however, t h a t the frequency v a l u e s would i n c r e a s e w i t h d e c r e a s i n g p a r t i c l e s i z e . In TMP p u l p s , about 90% of the VE fragments measured were s m a l l e r than 250 um and about h a l f o f them were s m a l l e r than 150 um. T h i s i s the s i z e o f the openings i n a 100 mesh s c r e e n o f a Bauer-McNett C l a s s i f i e r . A l a r g e p r o p o r t i o n o f j . fi b 50 ASPEN f~w BH 1000 1200 V.E. SIZE, Mm F i g u r e 5 . 4 3 . Frequency po lygons f o r VE s i z e i n aspen r e f i n e r p u l p s o f s i m i l a r f r e e n e s s . 600 800 1000 V.E. SIZE, nm 1600 F i g u r e 5 . 4 4 . Frequency po lygons f o r VE s i z e i n b i r c h r e f i n e r p u l p s o f s i m i l a r f r e e n e s s . 147 s m a l l VE p a r t i c l e s was a l s o p r e s e n t i n CTMP and CMP p u l p s as the m a j o r i t y o f the fragments accumulated i n the s m a l l e r s i z e c a t e g o r i e s . Thus , i t i s not s u r p r i s i n g t h a t VE are s a i d t o be reduced to f i n e m a t e r i a l d u r i n g r e f i n i n g , and found mos t ly i n the 100/200 f r a c t i o n ( G i e r t z 1977). However, i n the P200 f r a c t i o n ( s i eve opening o f 74 um) , VE fragments were a l s o abundant f o r these p u l p s . I t can be c o n c l u d e d , t h e r e f o r e , t h a t s m a l l fragments o f VE are p r e s e n t i n l a r g e numbers i n the f i n e p u l p f r a c t i o n s (100/150,. 150/200 and P200) r e g a r d l e s s o f the r e f i n e r p r o c e s s used . T h e i r abundance by weight , however, w i l l depend not o n l y on the VE s i z e and frequency i n the o r i g i n a l wood, but a l s o on t h e i r r e l a t i v e s u r v i v a l upon r e f i n i n g , and the amount o f f i n e s p r o d u c e d by o t h e r wood e l ements . A l t h o u g h the e x p e r i m e n t a l ranges o f f r eenes s and r e f i n i n g energy v a l u e s were wide i n TMP p u l p s , no d i f f e r e n c e i n the VE s i z e d i s t r i b u t i o n o f these p u l p s was found due to r e f i n i n g , r e g a r d l e s s o f s p e c i e s (parts B and C of T a b l e 4.15) . A l s o , the number o f whole VE i n these p u l p s was almost n o n - e x i s t e n t (only h i g h f reenes s aspen TMP showed a m i n u s c u l e p r o p o r t i o n o f whole VE) . T h i s i n f o r m a t i o n , from T a b l e 4 .16 , i s i l l u s t r a t e d i n F i g u r e s 5.45 and 5 .46 . I t i s obv ious t h a t r e f i n i n g under TMP c o n d i t i o n s was e f f e c t i v e i n d e s t r o y i n g whole VE and c o n v e r t i n g them i n t o f i n e p a r t i c l e s , even when those p u l p s were o f a h i g h f r e e n e s s . In f a c t t h e r e were v i r t u a l l y no VE i n the R48 f r a c t i o n s o f any TMP p u l p . I t was the i n i t i a l breakdown of the wood c h i p s t h a t caused 148 ASPEN REFINER PULPS 100-Figure 5.45. Percentage of whole VE that survived during the r e f i n i n g of aspen chips. Figure 5.46. Percentage of whole VE that survived during the re f i n i n g of bir c h chips. 149 the VE f r a g m e n t a t i o n . F u r t h e r r e f i n i n g may have reduced these fragments i n t o even s m a l l e r p a r t i c l e s , but o n l y a f t e r the wood VE had a l r e a d y been broken down. The f a c t t h a t a lmost no o v e r l a p p i n g i s seen between the TMP and k r a f t p u l p c u r v e s ( F i g u r e s 5.43 and 5 .44 ) , conf i rms t h i s f i n d i n g . In s p i t e o f the f a c t t h a t t h e r e was a s i g n i f i c a n t d i f f e r e n c e i n the o r i g i n a l s i z e o f v e s s e l e lements (Table 4 . 1 2 ) , w i t h average l e n g t h s o f 625 and 904 um f o r aspen and b i r c h , r e s p e c t i v e l y , no d i f f e r e n c e was found between the VE s i z e d i s t r i b u t i o n o f t h e i r TMP p u l p s . The VE breakdown under TMP c o n d i t i o n s was so e f f e c t i v e t h a t even the l a r g e r VE o f b i r c h were reduced t o a s i z e d i s t r i b u t i o n p a t t e r n s i m i l a r t o t h a t f o r the aspen TMP p u l p s . Moreover , b i r c h VE appeared to break down even more r e a d i l y than the aspen VE as no whole VE were found i n a n y . o f the b i r c h TMP p u l p s . The g e n e r a l l y h i g h e r tendency o f b i r c h VE to break down compared to aspen w i l l be d i s c u s s e d l a t e r i n t h i s s e c t i o n . Presumably , the wood d e f i b r a t e d under TMP c o n d i t i o n s f o l l o w e d the i n i t i a l p a t t e r n o f f a i l u r e through VE as i n d i c a t e d by Ohsawa and Yoneda (1978) f o r h i g h shear c o n d i t i o n s , i . e . , d e f i b r a t i o n p r o d u c i n g t r a n s w a l l f a i l u r e i n c e l l s o f low Runkel R a t i o (double c e l l w a l l t h i c k n e s s over lumen d iameter) . T h i s c o n d i t i o n h o l d s f o r V E , even a f t e r water s a t u r a t i o n o f wood and temperatures up to 170 ° C . F u r t h e r m o r e , the l i g n i n i n the VE c e l l w a l l s , r i c h i n g u a i a c y l u n i t s (Fergus and G o r i n g 1970, H a r d e l l et a l 1980), i . e . , more c r o s s - l i n k e d and l e s s heat s e n s i t i v e than the 150 s y r i n g y l l i g n i n i n the f i b r e secondary w a l l , c o n t r i b u t e s t o the s t i f f n e s s o f V E . The low f l e x i b i l i t y o f VE seems to be r e s p o n s i b l e f o r t h e i r d e s t r u c t i o n d u r i n g r e f i n i n g . S i g n i f i c a n t l y d i f f e r e n t r e s u l t s were o b t a i n e d i n terms of VE breakdown when c h e m i c a l l y - t r e a t e d c h i p s were r e f i n e d . A g r e a t e r number o f l a r g e VE fragments c o u l d be found i n these p u l p s compared to the TMP p u l p s . R e s u l t s i n T a b l e 4.15 (par t s D and E) showed a l a r g e d i f f e r e n c e between v a l u e s o f C h i - s q u a r e c a l c u l a t e d and C h i - s q u a r e c r i t i c a l when comparisons were made between VE s i z e d i s t r i b u t i o n s o f TMP and e i t h e r CTMP or CMP p u l p s . T h i s i s a l s o shown g r a p h i c a l l y i n F i g u r e s 5.43 and 5 . 4 4 . , where in the curves of VE s i z e d i s t r i b u t i o n o f CTMP and CMP p u l p s o v e r l a p w i t h those o f k r a f t p u l p s o f the same s p e c i e s . T h i s o v e r l a p p i n g i n d i c a t e s the p r e s e r v a t i o n o f some whole VE i n these two r e f i n e r p u l p s . As i n the case o f TMP, n e i t h e r CTMP nor CMP VE s i z e d i s t r i b u t i o n p a t t e r n s showed a dependency on r e f i n i n g energy , when comparisons were made w i t h i n a s p e c i e s (part s B and C i n T a b l e 4 . 1 5 ) . A g a i n , the d i s t r i b u t i o n o f VE fragment s i z e s was se t at the i n i t i a l breakdown o f wood i n t o p u l p f o r a g i v e n p r o c e s s and s p e c i e s , and f u r t h e r r e f i n i n g d i d not change these p a t t e r n s . F o r a g i v e n s p e c i e s , the d i f f e r e n c e i n VE d i s t r i b u t i o n p a t t e r n s ( C h i - s q u a r e va lues ) was r a t h e r s m a l l when CTMP and CMP p u l p s were compared (parts D and E i n T a b l e 4 . 1 5 ) , a l t h o u g h s t i l l s i g n i f i c a n t i n the case o f aspen . The 151 r e l a t i v e l y s m a l l d i f f e r e n c e s between r e f i n e r p u l p s from c h e m i c a l l y - t r e a t e d wood, compared t o the l a r g e d i f f e r e n c e o f these compared a g a i n s t TMP p u l p s , i n d i c a t e t h a t wood s o f t e n i n g was r e s p o n s i b l e f o r the p r e s e r v a t i o n o f a l a r g e r p r o p o r t i o n o f whole VE i n CTMP and CMP p u l p s . Yet the d i s t r i b u t i o n o f VE s i z e d i d not v a r y much when the s e v e r i t y of the t rea tment i n c r e a s e d , s i n c e the i n i t i a l breakdown p a t t e r n s o f VE were s i m i l a r by the CTMP and CMP processes ' . The s i g n i f i c a n t d i f f e r e n c e r e p o r t e d i n VE s i z e d i s t r i b u t i o n between aspen CTMP and CMP may be i n p a r t due to the c u t t i n g e f f e c t as i n d i c a t e d f o r the p u l p A-CTMP4 on one hand, and a l s o t o the p r o d u c t i o n o f s l i g h t l y more f i n e p a r t i c l e s i n CTMP and. l e s s e lements o f l a r g e s i z e than i n CMP on the o t h e r . I t i s c l e a r , however, t h a t b o t h CTMP and CMP p u l p s , f o r b o t h b i r c h and aspen, p r e s e r v e d to some ex tent the i n t e g r i t y o f whole V E . Thereby , these p u l p s may be more prone to VE p i c k i n g . R e d u c t i o n o f l a r g e VE would r e q u i r e more e x t e n s i v e r e f i n i n g . I t i s i n t e r e s t i n g to note t h a t i n both CTMP and CMP curves ( F i g u r e s 5.43 and 5.44) t h e r e were e s s e n t i a l l y two p e a k s . The f i r s t peak appeared, at the lower end, as ment ioned e a r l i e r , t o c l o s e the p o l y g o n . But the second peak, p a r t i c u l a r l y f o r aspen, f o l l o w e d the d i s t r i b u t i o n p a t t e r n o f the whole VE s i z e se t by the k r a f t c u r v e . Breakdown appeared t o take p l a c e a f t e r a number o f VE had been i n i t i a l l y f ragmented , and f u r t h e r f r a g m e n t a t i o n proceeded from these f ragments . On the o t h e r hand, a number o f VE remained as 152 whole e n t i t i e s i n the p u l p . The r e s u l t s i n T a b l e 4.16 and F i g u r e s 5.45 and 5.4 6 p r o v i d e i n f o r m a t i o n on the number o f VE t h a t d i d not break down d u r i n g r e f i n i n g . I t i s p r i m a r i l y here where the d i f f e r e n c e between CTMP and CMP p u l p s (and a l s o between spec i e s ) becomes a p p a r e n t . In f a c t , these f i g u r e s a l s o show the e f f e c t o f r e f i n i n g on the r e d u c t i o n o f whole VE f o r a g i v e n p r o c e s s . I t i s c l e a r t h a t the s i z e d i s t r i b u t i o n a lone c o u l d not p r o v i d e complete i n f o r m a t i o n on the ex tent o f VE breakdown. Such graphs r e v e a l on ly the p a r t i c l e s i z e d i s t r i b u t i o n , but suggest n o t h i n g about the number o f VE t h a t s u r v i v e d r e f i n i n g . S i m i l a r VE s i z e d i s t r i b u t i o n s , w i t h a d i s p a r i t y i n whole VE c o n t e n t , i n d i c a t e s t h a t an i n c r e a s e d number o f VE are b r o k e n down i n t o very f i n e p a r t i c l e s , which are a c t u a l l y s m a l l e r than the minimum v a l u e measured. R e g a r d l e s s o f s p e c i e s , CMP p u l p i n g o b v i o u s l y p r e s e r v e d more whole VE than d i d the CTMP p r o c e s s . The h i g h e r c h e m i c a l a p p l i c a t i o n i n CMP p u l p i n g , combined w i t h h i g h e r c o o k i n g temperatures and l o n g e r c o o k i n g t imes , produced whole VE i n amounts t h a t , f o r h i g h f r e e n e s s CMP p u l p s , were c l o s e r to those o f k r a f t than to TMP p u l p s . F o r CTMP p u l p s , the amount o f whole VE l a y s somewhere between the TMP and CMP v a l u e s . T h i s shows t h a t the breakdown of V E , as i n the case o f f i b r e breakdown, depended on the s e v e r i t y of the c h e m i c a l t reatment b e f o r e m e c h a n i c a l d e f i b r a t i o n . F o r i n s t a n c e , k r a f t p u l p s p r e s e r v e the l e n g t h o f a l l f i b r e s and those o f V E . M e c h a n i c a l d e f i b r a t i o n i s o n l y neces sary f o r l i n e r b o a r d - g r a d e p u l p s . 153 CMP p u l p s have l a r g e r amounts o f l o n g f i b r e f r a c t i o n s than CTMP which i n t u r n , are l a r g e r than those o f TMP p u l p s . The same p a t t e r n a p p l i e s to V E . O b v i o u s l y , however, VE are l e s s p r e s e r v e d than f i b r e s due to t h e i r t h i n n e r w a l l s , l a r g e r d i a m e t e r s and h i g h e r r i g i d i t y . A l t h o u g h no i n f o r m a t i o n i s a v a i l a b l e on the p e e l i n g o f s u r f a c e l a y e r s o f VE d u r i n g r e f i n i n g , i t i s presumed t h a t p e e l i n g would b e ' u n l i k e l y as most damage w i l l be i n the form o f f r a g m e n t a t i o n o f the V E . When comparisons o f VE s i z e d i s t r i b u t i o n s were made between s p e c i e s , no d i f f e r e n c e s were found f o r TMP or CMP p u l p s (part F i n T a b l e 4 . 1 5 ) . Only i n CTMP p u l p s was a s i g n i f i c a n t d i f f e r e n c e found, which c o u l d be i n p a r t a t t r i b u t e d to the c u t t i n g e f f e c t i n the low f reenes s aspen CTMP p u l p s . The most i m p o r t a n t d i f f e r e n c e between s p e c i e s , however, was i n . the number o f whole VE t h a t s u r v i v e d r e f i n i n g ( F i g u r e s 5.45 and 5.4 6) . B i r c h VE were more r e a d i l y reduced to fragments than were those from aspen. A l t h o u g h VE c e l l w a l l t h i c k n e s s i s r e p o r t e d to be h i g h e r i n b i r c h (1 .8 -2 .3 um) than i n aspen ( 1 . 3 - 1 . 6 um) a c c o r d i n g to Musha and G o r i n g (1975), the d i f f e r e n c e i n i n t e r v e s s e l p i t t i n g appears t o be the cause o f s i z e r e d u c t i o n i n b i r c h V E . The f i b r i l ang le o f VE w a l l s f o l l o w the d i r e c t i o n o f the s l i t - l i k e a p e r t u r e s o f the b o r d e r e d p i t s i n the v e s s e l w a l l (Harada 1965). On one hand, b i r c h i n t e r v e s s e l p i t s are minute (2-4 um), w i t h c o a l e s c e n t a p e r t u r e s , i . e . , o r i f i c e s f r e q u e n t l y c o n f l u e n t (Panshin and de Zeeuw 1980). These s l i t - l i k e i n n e r a p e r t u r e s i n many cases u n i t e s e v e r a l p i t s t o form s p i r a l grooves t h a t , upon 154 r e f i n i n g , f a c i l i t a t e the u n r a v e l i n g o f the VE ( F i g u r e 5.47 and 5 . 4 8 ) . On the o t h e r hand, aspen has l a r g e i n t e r v e s s e l p i t s (8-12 um) and the s e p a r a t i o n between p i t a p e r t u r e s d i d not l e a d t o u n r a v e l i n g o f the V E . I n s t e a d , aspen VE were broken down i n a more random f a s h i o n . T h i s r e s u l t e d i n aspen r e f i n e r p u l p s h a v i n g a h i g h e r p r o p o r t i o n o f VE s u r v i v a l from the o r i g i n a l wood. Aspen has more VE i n wood than does b i r c h (Panshin and de Zeeuw 1980) . A l s o , the percentage o f whole VE s u r v i v a l upon r e f i n i n g i s h i g h e r f o r aspen. The l a r g e d i f f e r e n c e i n VE c o n t e n t between these two s p e c i e s i s a c c e n t u a t e d d u r i n g r e f i n i n g . I t would be reasonab le to expect t h a t aspen r e f i n e r p u l p s would have a h i g h e r tendency to v e s s e l p i c k i n g than b i r c h p u l p s , not on ly because o f more whole V E , but a l s o because o f the s u b s t a n t i a l d i f f e r e n c e i n f i b r e l e n g t h between them. Due to the l o n g e r f i b r e s , f e l t i n g i n b i r c h p u l p s i s more e x t e n s i v e , and the f i b r e s would h o l d VE from b e i n g p i c k e d d u r i n g p r i n t i n g . On the o t h e r hand, aspen f i b r e s are more c o l l a p s i b l e , and the number o f f i b r e s p e r gram o f p u l p t o h o l d VE d u r i n g p r i n t i n g i s a l s o l a r g e r than i n b i r c h ( G i e r t z 1977) . Thus, i t i s not easy to c l e a r l y a n t i c i p a t e the r e l a t i v e e f f e c t s o f these two s p e c i e s i n v e s s e l p i c k i n g . The e f f e c t s o f c h e m i c a l and mechan ica l t rea tment are s i g n i f i c a n t i n the s u r v i v a l o f V E . The more severe the c h e m i c a l p r e t r e a t m e n t , the h i g h e r the s u r v i v a l r a t e o f V E . F o l l o w i n g t h i s , a d d i t i o n a l r e f i n i n g causes f u r t h e r breakdown 155 F i g u r e 5 .47 . B i r c h VE fragment showing s p l i t t i n g a l o n g the l i n e o f i n t e r v e s s e l p i t t i n g (pulp B-CTMP3) . F i g u r e 5 .48 . S i n g l e - w a l l e d VE fragment showing s e p a r a t i o n i n the d i r e c t i o n o f i n t e r v e s s e l p i t t i n g (pulp B -CTMP3). 156 o f V E . However, as observed b e f o r e , the s t a r t i n g p o i n t was se t by the c o n d i t i o n s o f the c h e m i c a l pre t rea tment a p p l i e d to the c h i p s . N e v e r t h e l e s s , i t i s d i f f i c u l t aga in to p r e d i c t the r e l a t i v e e f f e c t s o f the pre trea tment c o n d i t i o n s on the VE p i c k i n g tendency d u r i n g p r i n t i n g . A l t h o u g h more severe t rea tment c o n d i t i o n s r e s u l t e d i n s u r v i v a l o f more whole V E , the p a r e n t f i b r e s (and presumably a l s o these VE) are more f l e x i b l e and conformable , and are thus a b l e to h o l d VE b e t t e r . 5 . 3 . P u l p P r o p e r t i e s The p r o p e r t i e s o b t a i n e d f o r the r e f i n e r p u l p s produced i n t h i s s tudy are i n g e n e r a l agreement w i t h those p u b l i s h e d i n the l i t e r a t u r e f o r these s p e c i e s . N e v e r t h e l e s s , s e v e r a l p o i n t s need to be s t r e s s e d . There were c o n s i d e r a b l e d i f f e r e n c e s i n the o p t i c a l p r o p e r t i e s o f the p u l p s . TMP p u l p s from b o t h s p e c i e s showed the t y p i c a l b e h a v i o r f o r mechanica l p u l p s , and the l i g h t s c a t t e r i n g c o e f f i c i e n t i n c r e a s e d w i t h i n c r e a s e d r e f i n i n g . Thus , h i g h e r d e n s i t y v a l u e s f o r TMP sheets were accompanied by l a r g e r unbonded areas per u n i t gram. In CTMP and CMP p u l p s the e f f e c t was l e s s pronounced, so much so t h a t o n l y aspen CTMP showed an i n c r e a s e i n l i g h t s c a t t e r i n g c o e f f i c i e n t upon r e f i n i n g due, p o s s i b l y , t o f i b r e s i z e r e d u c t i o n i n these p u l p s . The o t h e r p u l p s produced from c h e m i c a l l y - t r e a t e d c h i p s showed e s s e n t i a l l y no change, i n d i c a t i n g t h e i r chemimechanical n a t u r e . 157 B r i g h t n e s s v a l u e s were much h i g h e r f o r TMP p u l p s . The o r i g i n a l h i g h b r i g h t n e s s o f aspen wood p r o v i d e d h i g h e r b r i g h t n e s s v a l u e s than those found f o r b i r c h p u l p s . The a l k a l i n e c h i p p r e t r e a t m e n t s i n CTMP and CMP p u l p m a n u f a c t u r i n g r e s u l t e d , as expec ted , i n lower b r i g h t n e s s v a l u e s f o r b o t h p u l p s . The d a r k e n i n g e f f e c t o f the a l k a l i i n the t rea tment was pronounced and the s imul taneous a d d i t i o n o f s u l p h i t e a p p l i e d d i d l i t t l e to reduce the b r i g h t n e s s l o s s . P r i n t i n g o p a c i t y , on the o t h e r hand, was h i g h i n TMP p u l p s due t o the h i g h s c a t t e r i n g c o e f f i c i e n t , and a l s o h i g h i n CMP p u l p s due to t h e i r low b r i g h t n e s s which , i n t u r n , was caused by h i g h l i g h t a b s o r p t i o n c o e f f i c i e n t v a l u e s . The s i z e d i s t r i b u t i o n o f p u l p f r a c t i o n s was e s s e n t i a l l y se t at the i n i t i a l breakdown of c h i p s i n t o p u l p . F u r t h e r r e f i n i n g o n l y changed t h i s m a r g i n a l l y . Thus , i n o r d e r to modi fy t h i s d i s t r i b u t i o n i n f a v o r o f a l a r g e r l o n g - f i b r e f r a c t i o n , c h e m i c a l t reatment o f the c h i p s i s r e q u i r e d . T h i s t rea tment a l s o r e s u l t e d i n more f l e x i b l e f i b r e s as e v i d e n c e d by the h i g h sheet d e n s i t y v a l u e s o b s e r v e d . Thereby , the p u l p s t r e n g t h p r o p e r t i e s improved d r a m a t i c a l l y from TMP to CTMP o r CMP p u l p s . Consequent ly , the degree o f i n t e r f i b r e bonding can be a t t r i b u t a b l e b o t h t o c h e m i c a l p r e t r e a t m e n t as w e l l as t o the degree o f r e f i n i n g , w i t h c e r t a i n l i m i t a t i o n s . T h i s i s i l l u s t r a t e d i n F i g u r e 5 .49 . I t shows the s t r o n g i n f l u e n c e o f sheet d e n s i t y on t e n s i l e s t r e n g t h . As shown i n t h i s f i g u r e , the l e v e l o f sheet d e n s i t y was aga in set by the type o f t r e a t m e n t . F u r t h e r r e f i n i n g i n c r e a s e s sheet d e n s i t y . TMP 158 60 50" w td 20" 10-M r 0 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 SHEET DENSITY A-TMP o A-CTMP • A-CMP B-TMP B-CTMP H B-CMP 0.65 F i g u r e 5 . 4 9 . 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 sheet d e n s i t y f o r a l l hardwood r e f i n e r p u l p s s t u d i e d . p u l p s had v e r y low sheet d e n s i t i e s f o r both s p e c i e s . Aspen and b i r c h TMP p u l p s a l s o had s i m i l a r Bauer-McNett f r a c t i o n a t i o n p a t t e r n s ( F i g u r e 5 . 1 ) , so t h a t e f f e c t s due t o f i b r e l e n g t h appear t o be u n i m p o r t a n t . R a t h e r , the l e v e l s o f shee t d e n s i t y and, c o n s e q u e n t l y , o f t e n s i l e s t r e n g t h were s l i g h t l y h i g h e r f o r aspen TMP p u l p s . T h i s i s presumably due t o the l o w e r . Runkel R a t i o o f aspen f i b r e s which may render 159 them more c o l l a p s i b l e . There was a d r a s t i c change i n sheet d e n s i t y when p u l p s were p r o d u c e d from c h e m i c a l l y - t r e a t e d c h i p s . In aspen, CTMP and CMP p u l p s f o l l o w e d the same l i n e i n i t i a t e d by the TMP p u l p s . However, t h e r e seemed to be l i t t l e d i f f e r e n c e between aspen CTMP and CMP i n terms o f e i t h e r sheet d e n s i t y or t e n s i l e s t r e n g t h . The response to c h e m i c a l pre trea tment was more e v i d e n t i n b i r c h . A l t h o u g h sheet d e n s i t y d i d not a t t a i n l e v e l s comparable to aspen, the s h i f t t o h i g h e r t e n s i l e s t r e n g t h v a l u e s was s u b s t a n t i a l . The i n f l u e n c e o f a much l a r g e r l o n g -f i b r e f r a c t i o n i s suspec ted as the cause f o r t h i s change, but i t c o u l d a l s o be due to improved f i n e s q u a l i t y . The d i f f e r e n c e between b i r c h CTMP and CMP p u l p s shown i n F i g u r e 5.49 c o u l d a l s o be a t t r i b u t e d to a l a r g e r R48 f r a c t i o n i n CMP p u l p s . However, i t i s a l s o seen t h a t the CMP p u l p s had h i g h e r sheet d e n s i t i e s than those o f the CTMP p u l p s at e q u i v a l e n t l e v e l s o f t e n s i l e s t r e n g t h . On the o t h e r hand, CTMP p u l p s r e q u i r e d lower f r e e n e s s , i . e . , p r o b a b l y a h i g h e r p r o d u c t i o n o f f i n e s , t o ach ieve the same t e n s i l e s t r e n g t h o f CMP p u l p s . Thus , i t can be seen t h a t a c e r t a i n l e v e l o f i n t e r f i b r e bond ing can be o b t a i n e d by e i t h e r a p p l y i n g severe c h e m i c a l p r e t r e a t m e n t f o l l o w e d by r e f i n i n g to a h i g h f r e e n e s s l e v e l (as i n CMP), or by u s i n g m i l d e r t r e a t m e n t s f o l l o w e d by r e f i n i n g to a lower f reeness l e v e l (as i n CTMP). The d i f f e r e n c e i n p u l p t e n s i l e s t r e n g t h o f b i r c h , r e l a t i v e 160 t o aspen a t s i m i l a r sheet d e n s i t y l e v e l s , f o r p u l p s from c h e m i c a l l y - t r e a t e d c h i p s , may a l s o be due t o s u p e r i o r l e v e l s o f the l o n g - f i b r e f r a c t i o n i n b i r c h . I t i s c l e a r , however, t h a t h i g h wood d e n s i t y was not a l i m i t a t i o n i n t h i s case , s i n c e b i r c h , w i t h much h i g h e r wood d e n s i t y l e v e l s (0.55 compared to 0.45 f o r aspen) , r endered CTMP and CMP p u l p s of h i g h e r s t r e n g t h than aspen. 5 . 4 . S i g n i f i c a n c e o f F i n d i n g s D e s p i t e the f a c t t h a t the S 2 l a y e r was found to be more exposed i n TMP p u l p s than i n t h e i r CTMP or CMP c o u n t e r p a r t s , TMP p u l p s t r e n g t h s were much lower . The removal o f the S^ l a y e r was not s u f f i c i e n t to produce f i b r e f l e x i b i l i t y l e v e l s (as i n d i c a t e d by sheet d e n s i t y va lues ) comparable to those o b t a i n e d by the a p p l i c a t i o n o f c h e m i c a l t r ea tment s to the c h i p s p r i o r to r e f i n i n g . Thus, the f i b r e s w i t h t h e i r S 2 s u r f a c e s exposed are not capab le o f t a k i n g advantage o f t h e i r h i g h e r bonding c a p a c i t y u n l e s s the area o f c o n t a c t between them i s i n c r e a s e d . F i g u r e 5.50 shows a p l o t o f t e n s i l e index a g a i n s t the l e v e l o f S 2 exposure f o r the v a r i o u s p u l p s . I t i s e v i d e n t t h a t i n t e r f i b r e bonding d i d not f o l l o w the measure o f q u a l i t y o f f i b r e s u r f a c e . In f a c t , b i r c h TMP p u l p s , w i t h f i b r e s o f the h i g h e s t S 2 e index , p r o d u c e d the weakest p u l p s . Thus, TMP p u l p s even w i t h t h e i r h i g h p r o d u c t i o n o f r i b b o n s o f good bonding a b i l i t y and, i n 161 40 S2e INDEX F i g u r e 5.50 R e l a n t i o n s h i p between t e n s i l e index and degree of exposure of the S 2 l a y e r f o r a l l hardwood r e f i n e r pulps s t u d i e d . the case of aspen, with the presence of l i b e r a t e d h i g h l y c e l l u l o s i c m a t e r i a l from G-layers, c o u l d not compete i n s t r e n g t h with CTMP or CMP pulps. F i g u r e s 5.51 t o 5.54 show the d i f f e r e n c e i n s u r f a c e appearance of handsheets made from aspen TMP and CTMP pulps. Even a t low f r e e n e s s l e v e l s the r e l a t i v e f i b r e r i g i d i t y can be a p p r e c i a b l e i n TMP pu l p s . Despite the l a r g e amount of TMP f i n e s produced, i t seems as i f t h e i r bonding r o l e i n a c t i n g as b r i d g e s between f i b r e s i s l i m i t e d i n sharp c o n t r a s t t o the be h a v i o r i n CTMP 162 F i g u r e 5.52. SEM photograph of a handsheet s u r f a c e f o r pulp A-CTMP1. 163 F i g u r e 5.54. SEM photograph o f a handsheet s u r f a c e f o r p u l p A-CTMP4. 164 F i g u r e 5.56. SEM photograph o f handsheet i n c r o s s s e c t i o n o f p u l p A-CTMP4. Note the d i f f e r e n c e i n f i b r e c o l l a p s i b i l i t y and b u l k compared to TMP. 165 p u l p s . T h i s i s a l s o i l l u s t r a t e d i n c r o s s s e c t i o n s of handsheets (F igures 5.55 and 5 . 5 6 ) . These photographs show a l a c k o f c o n s o l i d a t i o n i n the sheet from TMP f i b r e s as opposed t o the more f l e x i b l e and w e l l c o l l a p s e d f i b r e s i n CTMP s h e e t s . I t i s c o n c l u d e d t h a t f i b r e f l e x i b i l i t y , as measured by sheet d e n s i t y , takes precedence over any b e n e f i t p r o v i d e d by f i b r e s u r f a c e s o f h i g h bonding p o t e n t i a l s . The importance o f the f i n e s f r a c t i o n o f m e c h a n i c a l p u l p s has been w i d e l y r e c o g n i z e d i n the l i t e r a t u r e . I t has been s a i d t h a t the main cause f o r the low s t r e n g t h o f hardwood m e c h a n i c a l p u l p i s due to the poor q u a l i t y o f f i n e s produced (almost c o m p l e t e l y l a c k i n g i n f i b r i l s ) , and t h a t c h e m i c a l p r e t r e a t m e n t improved the f i n e s q u a l i t y ( G i e r t z 1977, 1981) so t h a t paper o f a c c e p t a b l e s t r e n g t h c o u l d be p r o d u c e d . However, from the e x p e r i e n c e o b t a i n e d i n t h i s s tudy , i t was found t h a t f i n e s from TMP, as w e l l as from CTMP and CMP, c o n t a i n e d not o n l y ray c e l l s and VE fragments , but a l s o abundant f i b r i l l a r m a t e r i a l and l a m e l l a e . In f a c t , TMP f i n e s appeared to have l o n g e r f i b r i l s than those from e i t h e r CTMP or CMP, as i l l u s t r a t e d i n F i g u r e s 5.57 t o 5 .60 . A l t h o u g h i t i s not c l e a r what i s the i n f l u e n c e o f the shape and s i z e o f the m a t e r i a l i n the f i n e s f r a c t i o n on p u l p s t r e n g t h , the mat ter o f f i n e s q u a l i t y deserves f u r t h e r a t t e n t i o n . Thus, based on the r e s u l t s o f removal o f f i b r e s u r f a c e l a y e r s and on the breakdown of V E , an attempt was made to o b t a i n i n f o r m a t i o n about f i n e s q u a l i t y (P100 f r a c t i o n ) a c c o r d i n g to the o r i g i n o f the m a t e r i a l . The r e s u l t s are p r e s e n t e d i n 166 F i g u r e 5.58. P200 f r a c t i o n of aspen CMP pulp of s i m i l a r f reeness than t h a t i n F i g . 5.57 (pulp A-CMP3) 167 168 F i g u r e s 5.61 and 5.62, and the assumptions and c a l c u l a t i o n p r o c e d u r e s i n v o l v e d are l i s t e d i n Appendix E . The l a r g e amount o f m a t e r i a l o r i g i n a t i n g from the f i b r e S 2 l a y e r i n p u l p A-CTMP4 was mos t ly due to the c u t t i n g e f f e c t ment ioned e a r l i e r f o r t h i s p u l p and i s e v i d e n t from the c o m p a r a t i v e l y l a r g e v a l u e s o f the 100/150 and 150/200 f r a c t i o n s . Otherwise TMP f i n e s c o n t a i n e d , as expec ted , l a r g e amounts o f VE and ray c e l l s , as w e l l as c o n s i d e r a b l e amounts o f m a t e r i a l from the S 2 l a y e r o f the f i b r e w a l l . E x c l u d i n g aspen CTMP p u l p s , the c o m p o s i t i o n o f the f i n e s f r a c t i o n does not seem to d i f f e r much between p r o c e s s e s f o r the same s p e c i e s . I f a n y t h i n g , the p r o p o r t i o n o f f i n e s d e r i v e d from the S 2 l a y e r , t o those from VE and ray c e l l s , appears to be l a r g e r f o r the TMP p u l p s , p a r t i c u l a r l y f o r b i r c h r e f i n e r p u l p s . I f t h e r e i s a d i f f e r e n c e i n the bond ing c a p a c i t y o f the f i n e s f r a c t i o n due to the p r o c e s s used i n p r o d u c i n g the r e f i n e r p u l p , i t may be due more to the f l e x i b i l i t y o f these p a r t i c l e s than to the c h e m i c a l c o m p o s i t i o n or l e n g t h o f the p a r t i c l e s i n v o l v e d . 169 ASPEN REFINER PULPS OH — — i — '— >— *— T 1 — L - r — L - r — L r T - 1 — ' -H—' 1 2 3 4 1 2 3 4 1 2 3 4 F i g u r e 5 . 6 1 . E s t i m a t e d c o m p o s i t i o n o f the P100 f r a c t i o n f o r aspen r e f i n e r pu lps a c c o r d i n g to the o r i g i n o f the f i n e m a t e r i a l . 5" BIRCH REFINER PULPS TMPs CTMPs Ml CMPs H H pi 1 2 3 4 1 2 3 4 1 2 3 4 F i g u r e 5 .62 . E s t i m a t e d c o m p o s i t i o n o f the P100 f r a c t i o n f o r b i r c h r e f i n e r pu lps a c c o r d i n g to the o r i g i n o f the f i n e m a t e r i a l . 170 V I . SUMMARY Fundamental a spec t s o f the breakdown o f hardwood elements i n t o m e c h a n i c a l p u l p s were s t u d i e d i n d e t a i l . The most i m p o r t a n t aspec t o f t h i s s tudy was the assessment o f the s u r f a c e q u a l i t y o f hardwood r e f i n e r p u l p f i b r e s . The i n v e s t i g a t i o n was based on the d e f i b e r i z a t i o n o f t r e m b l i n g aspen (Populus tremuloides Mich'x.) and white b i r c h (Be tu la papyrifera Marsh . ) c h i p s . These were r e f i n e d under TMP, CTMP and CMP c o n d i t i o n s , t o a b r o a d range o f p u l p f r e e n e s s l e v e l s ( g e n e r a l l y between 100 and 300 mL C S F ) . F o r each p u l p , t h i n c r o s s s e c t i o n s o f f i b r e s from the R48 f r a c t i o n were p r e p a r e d . T h r e e - h u n d r e d f i b r e s were a n a l y z e d f o r each p u l p . The f i b r e c r o s s s e c t i o n s were s t a i n e d to p r o v i d e d i f f e r e n t i a t i o n o f the compound midd le l a m e l l a and the secondary w a l l . In t h i s manner, and by u s i n g p o l a r i z e d l i g h t m i c r o s c o p y to assess the presence o f the l a y e r , the s u r f a c e q u a l i t y o f f i b r e s was e v a l u a t e d . In g e n e r a l , f i b r e s produced by TMP p r o c e s s i n g showed h i g h p r o p o r t i o n s o f S 2 l a y e r exposure when compared to those p r o d u c e d under CTMP or CMP c o n d i t i o n s , p a r t i c u l a r l y f o r b i r c h p u l p s . I t was shown t h a t the c h e m i c a l p r e t r e a t m e n t s used d i d not improve f i b r e s u r f a c e q u a l i t y i n terms o f S 2 l a y e r exposure or ex tent o f f i b r i l l a t i o n . In f a c t , f i b r e s from c h e m i c a l l y - t r e a t e d c h i p s p r e s e n t e d more r e t e n t i o n o f the compound middle l a m e l l a . When c h e m i c a l pre t rea tment was a p p l i e d t o the c h i p s , the 171 s p e c i e s response v a r i e d c o n s i d e r a b l y . B i r c h CTMP and CMP f i b r e s had h i g h middle lamella r e t e n t i o n (MLr i n d i c e s over 70% at p u l p f reenes s l e v e l s over 300 mL CSF) , and these v a l u e s d e c r e a s e d s l o w l y with f u r t h e r r e f i n i n g . Moreover the weak S^/32 boundary , a l o n g with the h i g h r e t e n t i o n o f ML, o f t e n p r o d u c e d b i r c h f i b r e s covered by a sheath o f S^/ML t h a t had s e p a r a t e d from the S 2 l a y e r , but was not removed. T h i s sheath was sometimes r o l l e d back, e x p o s i n g the S 2 l a y e r . Aspen responded d i f f e r e n t l y to the a p p l i c a t i o n o f c h e m i c a l p r e t r e a t m e n t . Although the r e t e n t i o n o f ML i n CTMP and CMP aspen f i b r e s was h i g h f o r p u l p s o f h i g h f r e e n e s s , i n c r e a s e d r e f i n i n g produced a q u i c k r e s p o n s e . ML r e t e n t i o n d e c r e a s e d f a s t e r than i t d i d f o r b i r c h p u l p f i b r e s . C o n s e q u e n t l y , at f r eenes s l e v e l s o f about 100 mL CSF, aspen CTMP and CMP p u l p s showed l e v e l s o f S 2 exposure , comparable t o those o b t a i n e d f o r aspen TMP f i b r e s . Other i m p o r t a n t fundamental d i f f e r e n c e s were found between TMP f i b r e s and those r e s u l t i n g from c h e m i c a l l y - t r e a t e d c h i p p r o c e s s i n g . R a d i a l l y - f a i l e d f i b r e s were f requent i n TMP but not i n CTMP nor CMP p u l p s . Format ion of r i b b o n - l i k e p a r t i c l e s , t h e r e f o r e , was common o n l y i n TMP p u l p s . These p u l p s a l s o showed p r e f e r e n t i a l breakdown of the G - f i b r e s p r e s e n t i n aspen c h i p s . Not o n l y were the G - f i b r e s broken down i n t o s m a l l e r f r a c t i o n s , but i n many cases the G - l a y e r s were denuded from the c e l l w a l l , expos ing t h e i r h i g h l y c e l l u l o s i c s u r f a c e . T h i s was not the case i n the G - f i b r e s from c h e m i c a l l y - t r e a t e d c h i p s , f o r which the G - l a y e r 172 g e n e r a l l y remained i n s i d e the f i b r e s . Other c a t e g o r i e s d i s c u s s e d i n the a n a l y s i s o f f i b r e c r o s s -s e c t i o n s i n c l u d e d d e l a m i n a t i o n o f the S 2 l a y e r and p r o p o r t i o n o f f i b r e s d i s t o r t e d due to c h e m i c a l i m p r e g n a t i o n . D e l a m i n a t i o n tends t o appear more f r e q u e n t l y i n c h e m i c a l l y -t r e a t e d f i b r e s , and more o f t e n i n aspen than i n b i r c h . D i s t o r t i o n o f the f i b r e c r o s s - s e c t i o n a l shape i s more common when the c h i p c h e m i c a l pre trea tment i s more s e v e r e . P u l p p r o p e r t i e s were measured. I t was found t h a t p u l p s t r e n g t h d i d not r e l a t e to the degree o f exposure o f the S 2 l a y e r , but r a t h e r c l o s e l y f o l l o w e d f i b r e f l e x i b i l i t y (as measured by sheet d e n s i t y ) . Thus, d e s p i t e the s u p e r i o r b o n d i n g p o t e n t i a l o f TMP f i b r e s due to t h e i r l a r g e exposure o f the S 2 l a y e r , the f i b r e s remained s t i f f t h e r e b y p r o d u c i n g sheets o f low d e n s i t y and s t r e n g t h . The breakdown of v e s s e l e lements (VE) was s t u d i e d by comparing VE s i z e frequency d i s t r i b u t i o n s and t h e . p r o p o r t i o n o f whole VE t h a t s u r v i v e d r e f i n i n g . Whi le T M P p r o c e s s i n g reduced VE i n t o s m a l l fragments , wood s o f t e n i n g due t o c h e m i c a l p r e t r e a t m e n t was r e s p o n s i b l e f o r the s u r v i v a l o f h i g h p r o p o r t i o n s o f whole VE i n CTMP and CMP p u l p s . F u r t h e r r e f i n i n g , however, reduced the amount o f whole VE i n these p u l p s . C o n s i d e r a b l e d i f f e r e n c e was observed between the r e l a t i v e s u r v i v a l o f VE i n aspen and b i r c h . B i r c h VE were d e s t r o y e d more e a s i l y , s i n c e f a i l u r e i n the VE w a l l s o c c u r r e d a l o n g the l i n e o f the f i n e i n t e r v e s s e l p i t t i n g . The breakdown of VE and the removal o f the s u r f a c e l a y e r s o f the f i b r e s a l l o w e d the e s t i m a t i o n o f the o r i g i n o f the f i n e s i n the P100 f r a c t i o n o f a Bauer McNett c l a s s i f i e r . A l t h o u g h TMP f i n e s c o n t a i n e d l a r g e r amounts o f VE compared t o CTMP or CMP p u l p s , the amount o f m a t e r i a l d e r i v e d from the f i b r e s ' S 2 l a y e r was a l s o l a r g e r . F u r t h e r m o r e , TMP f i n e s c o n t a i n e d l o n g e r f i l a m e n t s . F o r papermaking p u r p o s e s , however, the q u a l i t y o f the f i n e s may not be judged o n l y on t h e i r c o m p o s i t i o n . 1 7 4 V I I . CONCLUSIONS The f o l l o w i n g are c o n s i d e r e d the major c o n c l u s i o n s o f t h i s i n v e s t i g a t i o n : 1 . TMP p r o c e s s i n g o f b i r c h and aspen wood c h i p s produced f i b r e s w i t h h i g h e r exposure of the S 2 l a y e r than n o r m a l l y o b t a i n e d w i t h r e f i n e r p u l p s from c h e m i c a l l y - t r e a t e d wood c h i p s . F o r aspen CTMP or CMP p u l p s , a d d i t i o n a l r e f i n i n g t o f r e e n e s s v a l u e s o f about 1 0 0 mL CSF had to be a p p l i e d t o o b t a i n l e v e l s o f S 2 exposure e q u i v a l e n t to those o f t h e i r TMP c o u n t e r p a r t s . B i r c h showed a s lower response than aspen i n the removal of ML and S ^ l a y e r s upon the r e f i n i n g o f f i b r e s produced from c h e m i c a l l y - t r e a t e d c h i p s . Thus , i t can be c o n c l u d e d t h a t t h e r e was an e f f e c t due t o s p e c i e s and p r o c e s s i n g c o n d i t i o n s on the s u r f a c e c h a r a c t e r i s t i c s of the f i b r e s . 2 . Improvements i n p u l p sheet d e n s i t y due t o the removal o f the S-L l a y e r o f the f i b r e s were s m a l l compared to the e f f e c t s r e s u l t i n g from c h e m i c a l p r e t r e a t m e n t . F i b r e s w i th h i g h v a l u e s o f ML and S ^ l a y e r r e t e n t i o n , f o r example h i g h f r e e n e s s CTMP and CMP p u l p s , were much more f l e x i b l e (as measured by sheet d e n s i t y ) than low f reenes s . TMP f i b r e s w i t h h i g h exposure o f the S 2 l a y e r . T e n s i l e s t r e n g t h development f o l l o w e d sheet d e n s i t y l e v e l s r a t h e r than f i b r e s u r f a c e q u a l i t y . F i b r e s u r f a c e q u a l i t y d i d not have an important r o l e i n the s t r e n g t h development o f the 175 p u l p s . Thus , i t i s not the l a c k o f S 2 exposure t h a t g i v e s hardwood TMP low s t r e n g t h p r o p e r t i e s , but r a t h e r a l a c k o f f i b r e f l e x i b i l i t y . 3 . C h e m i c a l p r e t r e a t m e n t s used i n t h i s s tudy d i d not improve the f i b r e s u r f a c e i n terms of S 2 exposure . On the c o n t r a r y , c h e m i c a l l y - t r e a t e d f i b r e s had g e n e r a l l y more ML r e t e n t i o n at e q u i v a l e n t f reeness l e v e l s . F u r t h e r m o r e , c h e m i c a l p r e t r e a t m e n t s used i n t h i s s tudy d i d not improve f i b r i l l a t i o n o f the r e s u l t i n g f i b r e s . 4. B i r c h f i b r e s showed gaps between the and S 2 l a y e r s ( o u t / i n e f f e c t ) , i m p l y i n g a weak bond between these l a y e r s . In TMP p u l p f i b r e s , t h i s r e s u l t e d i n f a c i l e s e p a r a t i o n a l o n g or near the S 1 / S 2 boundary , g i v i n g f i b r e s w i t h the S 2 l a y e r l a r g e l y exposed. In f i b r e s made from c h e m i c a l l y - t r e a t e d c h i p s , t h i s i n i t i a l gap between Si and S 2 l a y e r s appeared to be r e s p o n s i b l e f o r the t o t a l s e p a r a t i o n o f the l a y e r and f o r p r o v o k i n g the s k i n n i n g e f f e c t . Thus , the t h i c k n e s s o f the l a y e r , known to be l a r g e r i n b i r c h than i n aspen, was not the l i m i t i n g f a c t o r t o ach i eve s e p a r a t i o n of t h i s l a y e r from the f i b r e s u r f a c e . 5. TMP p r o c e s s i n g o f wood c h i p s was e f f e c t i v e i n d e s t r o y i n g V E . Not o n l y d i d i t produce p u l p s w i t h v i r t u a l l y no whole V E , but most VE fragments produced were v e r y s m a l l i n d e e d . On the o t h e r hand, c h e m i c a l p r e t r e a t m e n t s p r e s e r v e d whole VE i n CTMP p u l p s and even more so i n CMP. At f r e e n e s s l e v e l s c l o s e to 300 mL CSF, aspen CMP 176 p r e s e r v e d about 80% o f the VE o r i g i n a l l y p r e s e n t i n the wood, w h i l e l e s s than 60% whole VE s u r v i v e d f o r b i r c h . In g e n e r a l , b i r c h VE were more r e a d i l y d e s t r o y e d because o f t h e i r p r e f e r e n t i a l breakdown a l o n g the i n t e r v e s s e l p i t t i n g arrangement i n t h e i r w a l l s . There was an e f f e c t o f s p e c i e s as w e l l as o f p u l p i n g c o n d i t i o n s i n the breakdown p a t t e r n o f V E . Other i m p o r t a n t f i n d i n g s o f t h i s s tudy are summarized below: 6. The presence o f t e n s i o n wood (presence o f G - f i b r e s ) a c c o u n t e d f o r a p p r o x i m a t e l y 31% of the aspen f i b r e s . The method deve loped to assess the p r o p o r t i o n o f G - f i b r e s i n wood o r p u l p p r o v i d e d a c c u r a t e r e s u l t s . TMP p r o c e s s i n g s i g n i f i c a n t l y reduced the amount o f G - f i b r e s i n the R4 8 f r a c t i o n o f the p u l p . A l s o , TMP p u l p s c o n t a i n e d abundant l i b e r a t e d G - l a y e r s t h a t were s t r i p p e d from t h e i r p a r e n t s h e l l s . M a t e r i a l d e r i v e d from the G - l a y e r s was p r e s e n t i n a l l TMP f i b r e f r a c t i o n s . CTMP and CMP p u l p s d i d not g e n e r a l l y show p r e f e r e n t i a l - breakdown of the G - f i b r e s . 7. R a d i a l f a i l u r e o f f i b r e s o c c u r r e d i n 20% of the TMP p u l p f i b r e s , w h i l e i t was g e n e r a l l y below 5% i n CTMP and CMP p u l p s . 8. D i s t o r t i o n and d e l a m i n a t i o n of f i b r e s were observed as a r e s u l t o f c h e m i c a l t reatment o f the c h i p s . However, c u r r e n t t e c h n i q u e s o f r e c o r d i n g such changes are not enough f o r d e s c r i b i n g and max imiz ing the e f f e c t s o f 177 r e f i n i n g . A measure o f the extent o f these changes needs t o be deve loped to f a c i l i t a t e the r e c o r d i n g o f shape change and ex tent o f d e l a m i n a t i o n . 9. The t e c h n i q u e s used i n the s tudy o f c r o s s - s e c t i o n a l c h a r a c t e r i s t i c s o f f i b r e s a l l o w e d the d e t a i l e d a n a l y s i s o f l a r g e numbers o f f i b r e s under the s t a n d a r d l i g h t m i c r o s c o p e . On the o t h e r hand, TEM p r o v i d e d more d e t a i l s on the c r o s s s e c t i o n s b u t , due t o the i n t e n s i t y o f sample p r e p a r a t i o n i n v o l v e d , o n l y a l i m i t e d number o f f i b r e s c o u l d be o b s e r v e d . 10. ' The f i n e s f r a c t i o n o f TMP p u l p s c o n t a i n e d abundant f i b r i l l a r m a t e r i a l i n a d d i t i o n to many VE fragments . The e f f e c t o f the f i n e s f r a c t i o n on the s t r e n g t h o f the r e s u l t i n g p u l p i s not c l e a r . 178 V I I I . SUGGESTIONS FOR FURTHER RESEARCH Based on the work done i n t h i s s tudy , the f o l l o w i n g s u g g e s t i o n s f o r f u r t h e r r e s e a r c h can be made: a . One obv ious t o p i c o f s tudy i s the i n f l u e n c e o f S 2 exposure on p u l p s t r e n g t h . T h i s can be a c h i e v e d by t e s t i n g handsheets o f f i b r e s o f known but d i f f e r e n t degrees o f S 2 exposure . Only the l o n g - f i b r e f r a c t i o n s h o u l d be used t o form the sheets to e l i m i n a t e the e f f e c t o f the o ther f r a c t i o n s . A l s o the sheets s h o u l d be p r o d u c e d at the same d e n s i t y , s i n c e sheet d e n s i t y has a s t r o n g e f f e c t on p u l p s t r e n g t h . b . The e f f e c t o f s u r f a c e q u a l i t y on f i b r e f l e x i b i l i t y c o u l d be s t u d i e d w i t h i n a g i v e n p u l p . F o r t h i s , f l e x i b i l i t y c o u l d be measured on i n d i v i d u a l f i b r e s which then c o u l d be a n a l y z e d f o r s u r f a c e q u a l i t y . c . Even w i t h the S 2 l a y e r l a r g e l y exposed and f i b r i l l a t e d , and w i t h the p r o d u c t i o n o f r i b b o n - l i k e p a r t i c l e s i n TMP p u l p s , these p u l p s were weak compared to the c o r r e s p o n d i n g CTMP or CMP p u l p s . In o r d e r to take advantage of the p o t e n t i a l l y b e n e f i c i a l c h a r a c t e r i s t i c s o f TMP f i b r e s , the e f f e c t o f an i n t e r s t a g e treatment t h a t f o c u s s e s on s w e l l i n g the f i b r e s s h o u l d be s t u d i e d . A h i g h degree o f f i b r e s w e l l i n g which may t r a n s l a t e i n t o f l e x i b i l i t y s h o u l d be a c h i e v e d which , upon d r y i n g , c o u l d p r o v i d e s t r o n g p u l p s . I f the r i g i d i t y o f f i b r e s i s the 179 main reason f o r the h i g h exposure o f the S 2 l a y e r i n TMP p u l p s , perhaps o t h e r medium and h i g h d e n s i t y hardwood s p e c i e s w i t h r i g i d f i b r e s w i l l produce h i g h S 2 l a y e r e x p o s u r e . These p u l p s may then be improved w i t h the p r o p e r i n t e r s t a g e or p o s t - c h e m i c a l t r e a t m e n t . d . The e f f e c t o f t e n s i o n wood p u l p q u a l i t y s h o u l d be s t u d i e d f o r d i f f e r e n t p r o p o r t i o n s o f G - f i b r e s i n the wood f u r n i s h . T h i s can be done by a n a l y s i s o f c r o s s s e c t i o n s o f c h e m i c a l p u l p s produced from the c h i p m a t e r i a l . S i n c e i t i s known now t h a t i n TMP p u l p s the G - l a y e r s can be s t r i p p e d o f f and produce c e l l u l o s i c f i l a m e n t s , the e f f e c t o f TW s h o u l d prove to be b e n e f i c i a l . The e f f e c t o f c h e m i c a l t rea tments b e f o r e the r e f i n i n g s h o u l d a l s o be a s s e s s e d . Of p a r t i c u l a r i n t e r e s t i s the use o f an i n t e r s t a g e p r o c e s s t h a t w i l l s w e l l and p o s s i b l y enhance f i b r i l l a t i o n o f the G - l a y e r s a f t e r t h e i r denuding from the p a r e n t f i b r e s . The p r o p o r t i o n o f t e n s i o n wood (measured as G - f i b r e s ) s h o u l d be de termined f o r g e o g r a p h i c a l areas i n which hardwoods are u t i l i z e d f o r p u l p i n g . e. L i t t l e i s known about the q u a l i t y o f the f i n e s from hardwood m e c h a n i c a l p u l p s . The b o n d i n g and l i g h t s c a t t e r i n g a b i l i t y o f these p a r t i c l e s s h o u l d be s t u d i e d f o r d i f f e r e n t r e f i n e r p u l p i n g p r o c e s s e s . T h i s c o u l d be done by m i x i n g a f i x e d percentage o f f i n e s w i t h a s t a n d a r d f u r n i s h . I t s h o u l d be mentioned t h a t the f i n e s c o m p o s i t i o n may v a r y w i t h the l e v e l o f r e f i n i n g . Thus, i t 180 i s recommended t h a t the f i n e m a t e r i a l be c o l l e c t e d at d i f f e r e n t l e v e l s o f r e f i n i n g . I t would be i n t e r e s t i n g to a s ses s the e f f e c t o f an i n t e r s t a g e t rea tment and of a p o s t - t r e a t m e n t i n the q u a l i t y o f TMP f i n e s . S w e l l i n g o f the . f ines p a r t i c l e s may prove to enhance bond ing on the paper s h e e t . The i n t e r a c t i o n o f f i b r e s and f i n e s o f d i f f e r e n t q u a l i t i e s might a l s o be i n v e s t i g a t e d . f . The use o f an image a n a l y s i s system c o u l d p r o v i d e i n f o r m a t i o n about the extent o f d i s t o r t i o n o f f i b r e s due to c h e m i c a l t rea tment and r e f i n i n g i n the a n a l y s i s o f f i b r e c r o s s s e c t i o n s . The a c t u a l r e s t r i c t i o n to f i b r e s w e l l i n g due to r e t e n t i o n o f the S^ c o u l d then be e f f e c t i v e l y measured. On the o t h e r hand, the s t a i n i n g t e c h n i q u e s c o u l d be m o d i f i e d to maximize the c o n t r a s t between c h e m i c a l l y a f f e c t e d and u n t r e a t e d f i b r e s . Other a p p l i c a t i o n s o f the q u a n t i t a t i v e a n a l y s i s o f d i s t o r t e d f i b r e s i n c r o s s s e c t i o n , i n c l u d e s t u d i e s o f l i q u o r p e n e t r a t i o n . The degree o f s w e l l i n g and the number o f s w o l l e n f i b r e s c o u l d be a s ses sed w i t h t h i s method f o r d i f f e r e n t p r e t r e a t m e n t c o n d i t i o n s . g . The e f f e c t o f the presence o f whole VE i n r e f i n e r p u l p s from c h e m i c a l l y - t r e a t e d c h i p s i s not known. T e s t s on s u r f a c e s t r e n g t h and p i c k i n g tendency are recommended. I f the presence o f whole VE proves to be a problem d u r i n g p r i n t i n g , s e v e r a l o p t i o n s are a v a i l a b l e f o r a t t e m p t i n g t h e i r s o l u t i o n . 181 On a more fundamental s tudy , the reasons f o r the i n i t i a l gap found f o r b i r c h f i b r e s between the and S 2 l a y e r s , can be i n v e s t i g a t e d . These i n c l u d e a p o s s i b l e abrupt change i n f i b r i l angle between these w a l l l a y e r s a n d / o r s u b s t a n t i a l changes i n t h e i r c h e m i c a l c o m p o s i t i o n . The apparent weak bond between the and S 2 l a y e r s , however, may o n l y be p r e s e n t i n f i b r e s o f b i r c h t r e e s grown under c e r t a i n c o n d i t i o n s . A weak S - L / S 2 boundary may a l s o e x i s t i n o t h e r hardwood s p e c i e s . 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Smook, G . A . 1982. Handbook f o r P u l p and Paper T e c h n o l o g i s t s . J o i n t Textbook Committee o f the Paper I n d u s t r y . 395 P-S t e e l , R . G . D . and J . H . T o r r i e . 1980. P r i n c i p l e s and P r o c e d u r e s o f S t a t i s t i c s , a B i o m e t r i c a l Approach (2nd E d i t i o n ) . M c G r a w - H i l l Book Company. 632 p . Sugden, E . A . N . 1967. M e c h a n i c a l p u l p i n g , a rev iew of s e l e c t e d r e f e r e n c e s : 1957-1967. O n t a r i o Research F o u n d a t i o n , Report ORF 67-3 . 44 p . V a l a d e , J . L . and K . N . Law. 1988 . Some p r o p e r t i e s o f whi te b i r c h u l t r a - h i g h y i e l d p u l p s . • C e l l u l o s e Chem. T e c h n o l . , 22:525-529. V e c c h i , E . 1969. Q u a l i t y c o n t r o l o f p o p l a r groundwood: f a c t o r s r e l a t e d to the s t r u c t u r a l c o m p o s i t i o n o f the p u l p . T a p p i 52(12): 2390-2399. W a l p o l e , R . E . . 1982. I n t r o d u c t i o n to S t a t i s t i c s (3rd e d i t i o n ) . M a c M i l l a n P u b l i s h i n g C o . , I n c . U . S . A . 521 P- ' Wardrop, A . B . 1963. M o r p h o l o g i c a l f a c t o r s i n v o l v e d i n the p u l p i n g and b e a t i n g o f wood f i b r e s . Svensk P a p p e r s t i d n i n g 66(7): 231-247. Wardrop, A . B . and H . E . D a d s w e l l , H . E . 1958. Changes i n wood and f i b r e s t r u c t u r e observed i n the p r e p a r a t i o n of c o l d soda p u l p s . J . I n s t . Wood S c i e n c e 2 ( N o v . ) : 8 - 2 1 . Wardrop, A . B . , H . E . Dadswel l and G.W. D a v i e s . 1961. A s p e c t s o f wood s t r u c t u r e i n f l u e n c i n g the p r e p a r a t i o n o f s e m i c h e m i c a l p u l p s . A p p i t a 14 (6) :185-202. Whi te , J . H . 1969. The manufacture o f m e c h a n i c a l p u l p . In.The P u l p i n g o f Wood, V o l I (2nd E d i t i o n ) . P u l p and Paper M a n u f a c t u r e . J o i n t Textbook Committee o f the Paper I n d u s t r y . M c G r a w - H i l l Book Company. 7 69 p . W i l l i a m s , G . P e r s o n a l Communicat ion. 1988-1989. 192 Wood, J.B. and A. K a r n i s . 1989. Future f u r n i s h requirements f o r newsprint and mechanical p r i n t i n g papers. In Proc. 1989 Newsprint Conference, p. 105-109. Zak, J.B. 1989. A.S.P.E.N. (Aspen Scotomas and Paranoia -E c o l o g i c a l N a i v i t y or Changing our Views on Aspen Acceptance. In Proc. 70th Annual Meeting CPPA Woodlands S e c t i o n . E105-E109. ***** (1965,9 * * « * « • «=ordi„ g t o J a y B e M d 2 ' S =" « * S 3 : o u t e r i »= warty l a y e r ° f the s e c o n d a r ^ U u ^ ^ r s . : j 194 Ui 7~ i O APPENDIX B: Chart used for recording categories of fibres in cross section. i i i . = i i j i • i • • o : i • — - -•" - 1 I z • H\ ; x • j -<5 i —J ' u) -J > u.-ft O u • : : '; ; • : • "><.' U i <\» o K : ! : ' •. ' ' : : : 1 t. «r i • i ' i r i 1 >-l : - : : ' ' ' : i ' if! (-! ; : i O in A V) V < _J o m A 1 ; : . . . : •. _.. O in . . . . . : : .-. . . . ; -o • i ! ' c J «n * V, ^ ^ : c o ^ - ^ •,. c . ; ^ ^ ^ ^ ^ «o ^ o - - ^ £ V> 195 APPENDIX C: Results and discussion on repeatability of the analysis of fibre cross sections. R e s u l t s T a b l e C . l . shows the c a t e g o r i e s o f f i b r e c r o s s - s e c t i o n a l a n a l y s i s under which t h e r e was no agreement between the two sub-samples (150 f i b r e s each) taken from every p u l p , as t e s t e d by d i f f e r e n c e s o f p r o p o r t i o n s , at a 95% c o n f i d e n c e l e v e l . From a t o t a l o f 328 t e s t s per formed , o n l y 30 were found t o g i v e s i g n i f i c a n t l y d i f f e r e n t r e s u l t s , i . e . over 90% o f the t e s t s per formed showed r e p e a t a b i l i t y w i t h i n the sample, as p r e s e n t e d i n a summary i n Tab le C.2. The cases i n which the d i f f e r e n c e s were found t o be s i g n i f i c a n t , d i d not f o l l o w any d e f i n i t e p a t t e r n and they appear to be d i s t r i b u t e d randomly i n T a b l e C . l . D i s c u s s i o n There i s no r e c o r d i n the l i t e r a t u r e o f q u a n t i t a t i v e m i c r o s c o p i c a l a n a l y s i s on c r o s s s e c t i o n s o f hardwood r e f i n e r p u l p s . T h e r e f o r e , the s t a t i s t i c a l e v a l u a t i o n o f the t e c h n i q u e s i n v o l v e d was p e r t i n e n t . From the r e s u l t s p r e s e n t e d i n T a b l e s C . l and C.2 i t was e s t a b l i s h e d t h a t over 90% o f the t e s t s were r e p e a t a b l e . A l t h o u g h t h e r e i s no p r e c e d e n t f o r comparison t h a t would i n d i c a t e the r e l a t i v e c o r r e c t n e s s o f t h i s work, the r e s u l t s o b t a i n e d i n terms of r e p e a t a b i l i t y were e n c o u r a g i n g . I t i s i n d i c a t e d t h a t when s i g n i f i c a n t d i f f e r e n c e s o c c u r r e d , the gap between the r e a l d i f f e r e n c e and the s t a t i s t i c a l l y a l l o w a b l e one was always Table C . l . Repeatability of tests i n the analysis of f i b r e cross sections, based on sub-samples of 150 f i b r e s at a 95% confidence l e v e l . ASPEN REFINER PULPS FIBRE CROSS TMP CTMP C M P SECTIONAL F E A T U R E 1 2 3 4 1 2 3 4 1 2 3 4 T O T A L MLr=0% * 1 MLr<50% 0 MLr>50% * 1 MLr=100% 0 Slr=0%,S2e=100% 0 Slr<50%,S2e>50% * 1 Slr>50%, S2e<50% 0 Slr=100%,S2e=0% 0 PEELING OUTER L A Y E R * 1 OUT/IN EFFECT *' * 2 R A D I A L F A I L U R E * 1 D E L A M I N A T I O N * * 2 DISTORTED FIBRES * 1 G L A Y E R INSIDE 0 G L A Y E R O N L Y * 1 11 BIRCH REFINER PULPS FIBRE CROSS TMP CTMP C M P SECTIONAL F E A T U R E 1 2 3 4 1 2 3 4 1 2 3 4 T O T A L MLr=0% . * * 2 MLr<50% * * * 3 MLr>50% 0 MLr=100% * * 2 Slr=0%, S2e=100% * * 2 Slr<50%,S2e>50% * * * * 4 Slr>50%,S2e<50% * * * 3 Slr=100%, S2e=0% * 1 PEELING OUTER L A Y E R * 1 OUT/IN EFFECT * 1 R A D I A L F A I L U R E 0 D E L A M I N A T I O N 0 DISTORTED FIBRES 0 * : S i g n i f i c a n t d i f f e r e n c e s between subsamples 19 197 T a b l e C . 2 . Summary o f r e p e a t a b l e c a t e g o r i e s on t h e a n a l y s i s o f f i b r e c r o s s s e c t i o n s . N U M B E R OF CATEGORIES FIBRE CROSS (TESTS) SECTIONAL A S P E N BIRCH T O T A L F E A T U R E M L r 48 48 96 S l ro rS2e 48 48 96 PEELING OUTER L A Y E R 12 12 24 OUT/IN EFFECT 12 12 24 R A D I A L F A I L U R E 12 12 24 D E L A M I N A T I O N 12 12 24 DISTORTED FIBRES 8 8 16 G L A Y E R INSIDE 12 - 12 G L A Y E R O N L Y 12 _ 12 T O T A L 176 152 328 CATEGORIES: Not repeatable 11 19 30 Repeatable 165 133 298 % Repeatable 94 88 91 198 l e s s than 7 f i b r e s and g e n e r a l l y l e s s than 3 f i b r e s f o r the subsamples o f 150 f i b r e s . In a l l case s , the average f o r the 300 f i b r e s i n each c a t e g o r y was taken as the v a l u e r e p r e s e n t i n g the f i b r e c r o s s s e c t i o n a l c h a r a c t e r i s t i c . The f a c t t h a t the cases ( l e s s than 10%) i n which s i g n i f i c a n t d i f f e r e n c e s o c c u r r e d , appeared t o be randomly spread i n T a b l e C . l , suggests t h a t i t may be p o s s i b l e t o improve the o v e r a l l r e p e a t a b i l i t y r a t h e r than to c o n c e n t r a t e on a p a r t i c u l a r c a t e g o r y . W h i l s t i t i s d i f f i c u l t t o e s t a b l i s h i f the l a c k o f r e p e a t a b i l i t y i n some c a t e g o r i e s was due to human e r r o r or a c t u a l v a r i a t i o n i n the p u l p , an examinat ion of the p o s s i b l e causes o f e r r o r i s i n o r d e r . These i n c l u d e : - V a r i a t i o n o f wood d e n s i t y - P r o d u c t i o n o f p u l p and sampl ing - Sample p r e p a r a t i o n - Human e r r o r The v a r i a t i o n o f wood s p e c i f i c g r a v i t y was l a r g e w i t h i n a t r e e , as shown i n Appendix D. Even i f a v a r i a t i o n o f t h i s magnitude a l s o a p p l i e d t o such c h a r a c t e r i s t i c s o f the f i b r e s which c o n t r o l t h e i r response t o r e f i n e r p u l p i n g (as measured by c r o s s s e c t i o n a l a n a l y s i s ) , i t i s u n l i k e l y t h a t t h i s e f f e c t would be s i g n i f i c a n t because the wood m a t e r i a l was t h o r o u g h l y mixed b e f o r e p u l p i n g t o min imize such v a r i a t i o n . I t was assumed then t h a t , w i t h i n a s p e c i e s , every p u l p subsample was p r o d u c e d from a r e p r e s e n t a t i v e sample of a 199 c h i p mix. D e n s i t y v a r i a t i o n , t h e r e f o r e , does not seem to be a probable cause f o r l a c k of r e p e a t a b i l i t y . Pulp p r o d u c t i o n as a source of e r r o r r e f e r s t o v a r i a t i o n s i n the r e f i n i n g c o n d i t i o n s while a pulp i s being produced. The exp e r i m e n t al pulps were obtained over a p e r i o d of time i n which s p e c i f i c energy was not p e r f e c t l y c onstant. Thus, "pockets" of f i b r e s with d i f f e r e n t c h a r a c t e r i s t i c s may form w i t h i n a g i v e n p u l p . However, the pulp i s subsequently mixed and sampled' f o r hot d i s i n t e g r a t i o n . T h i s sampling i s done from a w e l l mixed pulp by t a k i n g small amounts u n t i l the r e q u i r e d pulp weight f o r d i s i n t e g r a t i o n has been reached. A f t e r s c r e e n i n g and f r a c t i o n a t i o n , the R48 sample should be q u i t e uniform. Thus, any v a r i a t i o n d u r i n g the pulp p r o d u c t i o n process should have been m i t i g a t e d or e l i m i n a t e d by subsequent pulp h a n d l i n g . Methods used f o r sample p r e p a r a t i o n may have c o n t r i b u t e d as sources of e r r o r . • P r e p a r a t i o n was a long and t e d i o u s procedure c o n s i s t i n g of many d i f f e r e n t steps of which f i b r e alignment and s t a i n i n g of c r o s s s e c t i o n s were the most c r i t i c a l ones. F i b r e alignment' was important to i d e n t i f y p r o p e r l y the presence of the l a y e r . The technique used rendered s a t i s f a c t o r y r e s u l t s , and the a l t e r n a t i v e technique of a l i g n i n g f i b r e s one by one was c o n s i d e r e d i m p r a c t i c a l f o r a l a r g e number of hardwood f i b r e s . The s t a i n i n g methods a l s o p r o v i d e d s a t i s f a c t o r y i d e n t i f i c a t i o n of the ML. Thus, sample p r e p a r a t i o n does not appear to be a major source of e r r o r . The p o i n t at which the f i b r e s were s e c t i o n e d would have an 200 impact on t h e i r c r o s s - s e c t i o n a l f e a t u r e s . The assumption t h a t the c r o s s s e c t i o n o f a f i b r e at any p o i n t r e p r e s e n t s f e a t u r e s a l o n g the e n t i r e l e n g t h o f the f i b r e , i s c l e a r l y not e n t i r e l y c o r r e c t . However, i t i s r e a s o n a b l e to assume t h a t the f i b r e s cut at the middle may r e p r e s e n t b e t t e r the f e a t u r e s o f an e n t i r e f i b r e than of those f i b r e s s e c t i o n e d near t h e i r ends . I t may be p o s s i b l e t h a t the m a j o r i t y o f the f i b r e s i n one subsample were cut near t h e i r midd le w h i l e the s e c t i o n on the second subsample was made near the f i b r e ends , thus p r o d u c i n g a s i g n i f i c a n t d i f f e r e n c e i n some c a t e g o r i e s when t e s t i n g r e p e a t a b i l i t y . However, an average s e c t i o n p r o b a b l y c o n t a i n e d f i b r e s cut at d i f f e r e n t p l a c e s t h r o u g h o u t t h e i r l e n g t h s , so t h a t s e c t i o n i n g does not appear t o p l a y a s i g n i f i c a n t r o l e . There i s the p o s s i b i l i t y o f human e r r o r i n r e c o r d i n g c r o s s s e c t i o n a l f e a t u r e s o f f i b r e s under the l i g h t m i c r o s c o p e . A l t h o u g h the samples were a n a l y z e d i n a random f a s h i o n to m i n i m i z e o b s e r v e r b i a s , the p o s s i b i l i t y o f e r r o r c o u l d p r o b a b l y be f u r t h e r reduced i f a l l the f i b r e s were a n a l y z e d t h r o u g h a t r a n s m i s s i o n e l e c t r o n m i c r o s c o p e . I t i s f e l t t h a t the i d e a l a n a l y s i s o f f i b r e c r o s s s e c t i o n s would be c a r r i e d out on u l t r a t h i n s e c t i o n s , cut w i t h a diamond k n i f e , f o r o b s e r v a t i o n under a TEM. T h i s system a l l o w s the use o f s t a i n i n g t e c h n i q u e s combined w i t h v e r y h i g h r e s o l u t i o n , which m i n i m i z e s o b s e r v e r b i a s . The p r i n c i p a l l i m i t a t i o n , however, l i e s i n the s m a l l number of f i b r e s viewed i n one f i e l d , as w e l l as i n the d i f f i c u l t i e s encountered and t ime 201 r e q u i r e d f o r c u t t i n g l a r g e amounts o f u l t r a t h i n s e c t i o n s ; i n a d d i t i o n , t h e r e are h i g h c o s t s i n v o l v e d i n u s i n g a TEM sys tem. TEM was used i n t h i s s tudy t o c o n f i r m the o b s e r v a t i o n s made under the l i g h t microscope i n terms o f the r e t e n t i o n o f ML and l a y e r , the exposure o f the S 2 l a y e r , and t o observe a d d i t i o n a l d e t a i l s r e g a r d i n g f e a t u r e s o f the f i b r e s i n c r o s s s e c t i o n . In summary, no c l e a r c o n c l u s i o n c o u l d be drawn on the source o f l a c k o f r e p e a t a b i l i t y f o r a p p r o x i m a t e l y 10% of the t e s t s on d i f f e r e n c e s o f p r o p o r t i o n s between subsamples . I t i s p o s s i b l e , however, t h a t t h e r e c o u l d be s i g n i f i c a n t v a r i a t i o n o f the f i b r e c r o s s - s e c t i o n a l c h a r a c t e r i s t i c s w i t h i n p u l p samples . 202 APPENDIX D: Variation of wood specific gravity from pith to bark at different heights (as %) of the tree stem. SG DISTRIBUTION, ASPEN TREE FROM LYTTON, B.C. 0.6T 1 ° ' 3 0 2 4 6 8 10 12 0.& — 0.5-0.4 0 3 0 2 4 6 8 10 12 0.6-' 3 0 2 4 6 8 10 12 DISTANCE FROM PITH, cm 2 03 APPENDIX D (cont inued) SG DISTRIBUTION, ASPEN TREE FROM WILLIAMS LAKE, B.C. 0.6T 1 '•30 2 4 6 8 10 0:6-' 3 0 2 4 6 8 10 DISTANCE FROM PITH, cm APPENDIX D (cont inued) 204 SG DISTRIBUTION, BIRCH TREE FROM WILLIAMS LAKE, B.C. 0.6l : DISTANCE FROM PITH, cm 205 APPENDIX E: Calculations involved in the estimation of the origin of the material in the P100 fraction. A s s u m p t i o n s : 1. The v a l u e s p r e s e n t e d i n T a b l e s E . l and E . 2 f o r aspen and b i r c h are a p p l i c a b l e to the wood samples used i n t h i s s t u d y . 2. A l l the components o f e lements i n T a b l e E . l have the same d e n s i t y , so t h a t the v a l u e s can a l s o be taken as weight p e r c e n t a g e s . 3. Any l o s s o f m a t e r i a l a f f e c t s e v e n l y a l l the e lements . 4. Any m a t e r i a l removed from the f i b r e s u r f a c e ends up i n the P100 f r a c t i o n o f the p u l p . 5. The weight o f VE fragments from the f requency t a b l e s are p r o p o r t i o n a l t o t h e i r s i z e . 6. M a t e r i a l from the G - l a y e r s i s not taken i n t o a c c o u n t . P r o c e d u r e : 1. Ray c e l l s S i n c e the ray c e l l s were s m a l l e r than 150 um, i t i s taken t h a t a l l t h i s m a t e r i a l passed the 100 mesh s c r e e n o p e n i n g s . V a l u e s o f 4 and 10% of the wood weight were taken f o r aspen and b i r c h , r e s p e c t i v e l y . 2. V e s s e l e lements I t was c o n s i d e r e d t h a t a l l VE fragments l a r g e r than the lower c o n f i d e n c e l i m i t o f the mean from the k r a f t p u l p VE s i z e d i s t r i b u t i o n , c o u l d be r e g a r d e d as whole V E . The r e s t were c o n s i d e r e d VE fragments . From these fragments , the p o r t i o n i n c l u d e d i n the f i r s t c l a s s i n t e r v a l , was taken as the weight o f VE p a s s i n g the 100 mesh s c r e e n . T h i s p o r t i o n , m u l t i p l i e d by the percentage o f VE t h a t . were fragmented, t imes the v a l u e s f o r VE from T a b l e E . l , gave the weight o f VE i n the P100 f r a c t i o n . 3 . ML m a t e r i a l V a l u e s f o r ML p l u s MLcc , as d e f i n e d i n T a b l e E . l , were taken from t h i s t a b l e and m u l t i p l i e d by the p o r t i o n o f ML t h a t was removed from the f i b r e s . 4. S-j_ l a y e r m a t e r i a l The p r o p o r t i o n o f S-]_ l a y e r m a t e r i a l t o that , o f the secondary w a l l was c a l c u l a t e d from v a l u e s p r e s e n t e d i n T a b l e E . 2 , and m u l t i p l i e d by v a l u e s f o r f i b r e secondary w a l l i n T a b l e E . l . The r e s u l t s were then m u l t i p l i e d by 206 the portion of S i material that was removed from the f i b r e s . 5 . S2 layer material This was calculated by substracting the values obtained in points 1, 2, 3 and 4 (above) from the weight of the P100 pulp f r a c t i o n . Table E. l PERCENTAGE VOLUME OF COMPONENTS OF ELEMENTS (Source: Musha & Goring 1975) FIBRE VESSEL RAY S ML MLcc S ML* S ML* ASPEN ' 74.0 6.0 3.0 11.0 2.0 3.0 1.0 BIRCH 73.4 5.2 2.4 8.2 0.8 10.0 0.0 *: Assuming the middle lamella width found for fibres S: secondary wall; ML: middle lamella; cc: cell corner Table E.2 FIBRE DIMENSIONS IN CROSS SECTION (microns) DIAMETER TOTAL SI (1) SECONDARY LAYER WALL(l) (2) ASPEN 18.8 2.55 0.12 BIRCH 19.5 3.60 0.21 (1) : Musha & Goring (1975) (2) : Marton et al (1979) 207 APPENDIX F : ABBREVIATIONS ML Compound M i d d l e L a m e l l a MLr R e t e n t i o n o f Compound M i d d l e L a m e l l a M L r l Compound M i d d l e L a m e l l a R e t e n t i o n Index ML(r=0) No R e t e n t i o n o f Compound M i d d l e L a m e l l a ML(r<50) MLr on l e s s than 50%, but more than zero o f the f i b r e c r o s s s e c t i o n ML(r>50) MLr on more than 50%, but l e s s than 100% of the f i b r e c r o s s s e c t i o n ML(r=100) T o t a l R e t e n t i o n o f the Compound M i d d l e L a m e l l a S ^ r R e t e n t i o n o f the l a y e r S-^rl S-L l a y e r R e t e n t i o n Index S 1 ( r = 0 ) No R e t e n t i o n o f the l a y e r S 1 ( r < 5 0 ) S-jr on l e s s than 50%, but more than zero o f the f i b r e c r o s s s e c t i o n S 1 (r>50) S^r on more than 50%, but l e s s than 100% of the f i b r e c r o s s s e c t i o n S 1 (r=100) T o t a l R e t e n t i o n o f the S x l a y e r S 2 e Exposure o f the S 2 l a y e r S 2 e l S 2 l a y e r Exposure Index S 2 (e=0) Zero exposure o f the S 2 l a y e r S 2 (e<50) S 2 e on l e s s than 50%, but more than zero o f the f i b r e c r o s s s e c t i o n S 2 ( e > 5 0 ) S 2 e on more than 50%, but l e s s than 100% o f the f i b r e c r o s s s e c t i o n S 2 ( e=100) T o t a l Exposure o f the S 2 l a y e r RF R a d i a l F a i l u r e TW T e n s i o n Wood VE V e s s e l Element 

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