UBC Theses and Dissertations

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UBC Theses and Dissertations

Stress relaxation of paper plastic composites Chen, Chien-pin 1973

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STRESS RELAXATION OF PAPER PLASTIC COMPOSITES  by C h i e n - p i n Chen Bi.S. ( F o r . ) Taiwan P r o v i n c i a l U n i v . , 1964  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF MASTER OF SCIENCE i n t h e Department of Forestry  We a c c e p t t h i s t h e s i s a s conforming t o t h e required standard  THE UNIVERSITY OF BRITISH COLUMBIA May  1973  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the r e q u i r e m e n t s f o r  an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y  a v a i l a b l e f o r r e f e r e n c e and  I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e f o r s c h o l a r l y purposes may by h i s r e p r e s e n t a t i v e s .  study.  c o p y i n g of t h i s  be g r a n t e d by the Head of my  thesis  Department or  I t i s u n d e r s t o o d t h a t c o p y i n g or p u b l i c a t i o n  of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t written permission.  Department of The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada  my  - i -  ABSTRACT  F r a c t i o n a l s t r e s s r e l a x a t i o n ( S(t)/S(0|04 ) ) was  used t o compare time-dependent p r o p e r t i e s o f p a p e r s ,  p l a s t i c s and paper p l a s t i c composites  ( PPC ) . No  s i m i l a r o b s e r v a t i o n s appear i n t h e l i t e r a t u r e . L a b o r a t o r y handsheets  were p r e p a r e d  from  commercial w e s t e r n hemlock ( Tsuga h e t e r o p h y l l a (Raf.) S a r g . ) u n b r i g h t e n e d and b r i g h t e n e d groundwoods, as w e l l as unbleached  and b l e a c h e d k r a f t p u l p s .  Adjustments  were made t o p r o v i d e e q u i v a l e n t b a s i s w e i g h t s 30 g/m  ( 150 -  ) f o r m a t e r i a l s o f t h e s t u d y . Handsheets were  impregnated  w i t h m e t h y l m e t h a c r y l a t e ( MMA ) and  t e t r a e t h y l e n e g l y c o l d i m e t h a c r y l a t e ( TEGDMA ) (co)monomer systems. S a t u r a t e d handsheets  and p l a s t i c  f i l m s were c u r e d by ^°Co gamma i r r a d i a t i o n ( 1.4 - 0 . 9 Mrad ) . I t was f o u n d t h a t t h e s t a n d a r d l o g - t i m e e q u a t i o n , S(t)/S(0.04)  =  a  +  b In t ,  a p p l i e d t o d a t a c o l l e c t e d between 0.04 and 35 m i n f o l l o w i n g completion o f simulated step-loading ( r m o s t l y O.97 o r h i g h e r ) . A second q u a n t i t y , energy dissipation (  A s ) , AS  =  1 - S(35)/S(0.04),  - i i-  was used t o compare between t r e a t m e n t s . Some p l a s t i c s gave the h i g h e s t A S v a l u e s , w h i l e groundwoods gave l o w e s t v a l u e s and k r a f t papers were i n t e r m e d i a t e . P u l p d e l i g n i f i c a t i o n l e v e l appeared to r e l a t e d i r e c t l y t o &  S. W i t h i n l i m i t s o f the s t u d y i t seems t h a t  PPC  s t r e s s r e l a x a t i o n c u r v e s were i n f l u e n c e d by  polymer ( m a t r i x ) and f i b r e  both  ( substrate )  employed. The f o r m e r c o n t r i b u t e d i n minor ways, w h i l e t h e l a t t e r o p e r a t e d i n major ways.  *  •  •  - I l l -  TABLE OP CONTENTS  ABSTRACT  i  TABLE OF CONTENTS  i i i  L I S T OP TABLES  vi  L I S T OF FIGURES  v i i  ACKNOWLEDGEMENT  viii  1.0  INTRODUCTION  1  2.0  LITERATURE REVIEW  3  2.1  S t r e n g t h P r o p e r t i e s o f Paper P l a s t i c Composites  3  2.1.1  G r a f t i n g to pulps  3  2.1.2  G r a f t i n g t o papers  6  2.2  E f f e c t o f F i b r e C h e m i c a l C o n s t i t u e n t s on Grafting» E s p e c i a l l y L i g n i n  10  2.3  E f f e c t o f Gamma R a d i a t i o n on C e l l u l o s i c s and Polymers  12  R h e o l o g i c a l Behaviour o f S o l i d s  15  2.4  2.4.1  Stress r e l a x a t i o n of solids; general survey  16  2.4.2  R e l a x a t i o n o f polymers  20  2.4.3  R h e o l o g i c a l p r o p e r t i e s o f papers .. 27 2.4.3.1  2.4.4  Stress relaxation of papers  Time dependent b e h a v i o u r o f f i b r e p l a s t i c composites  29 32  - iv -  Page 3.0  4.0  5.0  MATERIALS AND METHODS  34  3.1  Pulps  34  3.2  Monomers and Comonomers  36  3.3  F o r m a t i o n and Treatment o f Paper Handsheets. 41  3.4  P r e p a r a t i o n o f Polymer Thd& F i l m s  42  3.5  Polymerization  43  3.6  Testing  44  RESULTS..  48  4.1  S t r e s s R e l a x a t i o n o f Papers  48  4.2  S t r e s s R e l a x a t i o n o f Polymer F i l m s  ......... 49  4.3  S t r e s s R e l a x a t i o n o f Paper P l a s t i c Composites ( PPC )  50  DISCUSSION  53  5.1  S h o r t Term S t r e s s Decay  53  5.2  S t r e s s R e l a x a t i o n o f Papers  56  5.2.1  E f f e c t o f l i g n i n on s t r e s s r e l a x a t i o n o f k r a f t papers  57  5.2.2  S t r e s s r e l a x a t i o n o f groundwood papers  58  5.2.3 5.3  Difference i n stress relaxation between k r a f t and groundwood papers . 59  S t r e s s R e l a x a t i o n o f Polymers 5.3.1  The c o n t r i b u t i o n o f c r o s s l i n k i n g t o polymer r h e o l o g i c a l p r o p e r t i e s ...  61 62  - V -  Page 5.4  Rheological Materials  Properties  o f Composite  66  5.4.1  I n f l u e n c e o f m a t r i x on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n . 6?  5.4.2  E f f e c t o f s u b s t r a t e s on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n . 70  5.4.3  E f f e c t o f paper c o p o l y m e r i z a t i o n w i t h (co)monomers on i n i t i a l material stress relaxation  71  5.4.4  E f f e c t o f l i g n i n on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n . 72  6.0  CONCLUSION  76  7.0  LITERATURE CITED  78  8.0  NOTATIONS  107  - vi-  LIST OF TABLES  Table  Page  I.  B a s i s w e i g h t ( g/m ) o f paper handsheets, paper p l a s t i c c o m p o s i t e s and polymer f i l m s . 109  II.  P r o p e r t i e s o f paper p l a s t i c composites ( PPC )  110  III.  Stress r e l a x a t i o n o f the d i f f e r e n t treatments s t u d i e d a t c o n s t a n t d e f o r m a t i o n ( n=5) 112  IV.  Regression analyses of stress r e l a x a t i o n curves according to S(t)/S(0.04) = a + b I n t ( n=30 ) 114  V.  T e s t f o r d i f f e r e n c e i n paper s t r e s s r e l a x a t i o n behaviours 116  VI.  T e s t f o r e f f e c t o f polymer f i l m c r o s s l i n k i n g on amount o f s t r e s s r e l a x a t i o n 117  Villi to VIIsiv.  T e s t f o r e f f e c t o f m a t r i x system on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n  VIIIii to VIIIiv.  T e s t f o r e f f e c t o f s u b s t r a t e on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n 122  118  I X i i to IX:x.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( k r a f t papers-polymer systems)  X t i to Xsx.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s o n paper s t r e s s r e l a x a t i o n ( groundwood papers-polymer systems) 137  127  - vii -  LIST OF FIGURES Figure  Page  1.  Polymer s t r e s s r e l a x a t i o n  2.  I m p r e g n a t i o n o f papers i n a w i t h monomers  3.  147 desiccator 145  G l a s s frame assembly f o r making polymer thin films  149  4.  S t r e s s r e l a x a t i o n o f papers  150  5.  S t r e s s r e l a x a t i o n o f polymer f i l m s  151  6.  E f f e c t o f m a t r i x systems on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n  152  7*1 t o 7- 5.  E f f e c t o f s u b s t r a t e s on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n  15^  8- 1 t o 8- 4.  C o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( k r a f t papers-polymer system ) .. 159  9- 1 t o 9-4.  C o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( groundwood papers-polymer system )  163  •  # *  - viii  -  ACKNOWLEDGEMENT  The  a u t h o r g r a t e f u l l y acknowledges Dr. J . W.  Wilson, Professor, F a c u l t y o f F o r e s t r y , U n i v e r s i t y o f B r i t i s h Columbia, f o r h i s k i n d g u i d a n c e i n t h e p l a n n i n g and e x p e r i m e n t a l  phases o f t h e s t u d y and p r e p a r a t i o n  o f the m a n u s c r i p t . A p p r e c i a t i o n i s a l s o due Dr. L . P a s z n e r , Research A s s o c i a t e , f o r h i s c o n s t r u c t i v e c r i t i c i s m o f this  thesis. S p e c i a l thanks a r e due t h e Department o f  Environement and t h e P u l p and Paper R e s e a r c h I n s t i t u t e o f Canada f o r f i n a n c i a l s u p p o r t . MacMillan study.  Thanks are a l s o due  Bloedel Ltd. f o r materials supplied f o r the  - 1 -  1.0  INTRODUCTION  Wood c e l l u l o s e i s an abundant and r e p r o d u c i b l e n a t u r a l polymer w i t h good m e c h a n i c a l p r o p e r t i e s and r e s i s t a n c e t o many s o l v e n t s and s w e l l i n g a g e n t s ( 9 )• I t i s used w i d e l y i n numerous ways. I t s weakness f o r some a p p l i c a t i o n s i s due t o s e n s i t i v i t y t o changing moisture content,  a c i d s , bases and oxygen ( 9i 35 ) •  In addition, c e l l u l o s i c materials are frequently  subject  to b i o l o g i c a l d e t e r i o r a t i o n . Paper p r o p e r t i e s may be enhanced by t r e a t m e n t o f f i b r e s o r p a p e r s w i t h c e r t a i n (co)monomers o r p o l y m e r s . I t i s n o t e d t h a t t h e s e t r e a t m e n t s may improve a v a r i e t y o f p r o p e r t i e s i n c l u d i n g t e n s i l e s t r e n g t h , wet s t r e n g t h , dye r e t e n t i o n and a d h e s i o n , as w e l l as r e s i s t a n c e t o b i o l o g i c a l d e g r a d a t i o n ,  abrasion,  a c i d s and bases ( 131 ) . On a weight b a s i s , paper p l a s t i c composites ( PPC ) c o s t l e s s t h a n plywood and s t e e l , and p o s s e s s s i g n i f i c a n t l y h i g h e r s t r e n g t h . The m a t e r i a l c a n be used a s o v e r l a y f o r plywood t o g i v e p r o d u c t s w i t h smooth p a i n t a b l e s u r f a c e s , o r as base f o r wood g r a i n p r i n t e d paper. A p p l i c a t i o n s as waterpoof, f i r e p r o o f p a c k a g i n g m a t e r i a l , as w e l l a s p a r t s o f t r a n s p o r t a t i o n f a c i l i t i e s suehsas r a i l r o a d b o x c a r s i d e s ,  containers,  t r a i l e r t r u c k b o d i e s and a u t o m o b i l e bumpers have been proposed ( 14, 123.  )• S u i t a b i l i t y f o r such uses depends  i n p a r t on m a t e r i a l f l o w p r o p e r t i e s . Stress r e l a x a t i o n i s a technique  a p p l i e d to  d e t e r m i n e f l o w p r o p e r t i e s o f s u b s t a n c e s . When specimens are h e l d a t c o n s t a n t d e f o r m a t i o n ,  s t r e s s e s may  be d i s s i p a t e d  r a p i d l y o r s l o w l y i n accordance w i t h f u n d a m e n t a l p r o p e r t i e s o f the m a t e r i a l s b e i n g  examined.  A l t h o u g h some PPC  product p r o p e r t i e s are  documented i n the l i t e r a t u r e , no i n f o r m a t i o n i s a v a i l a b l e on t h e i r s t r e s s r e l a x a t i o n b e h a v i o u r . present PPC  s t u d y was  The  d e s i g n e d about the hypotheses t h a t  f l o w p r o p e r t i e s are governed m a i n l y by paper  substrate properties.  - 3 -  2.0  2.1  LITERATURE REVIEW  Strength Properties  o f Paper P l a s t i c Composites  C e l l u l o s e i s a l i n e a r polymer, composed o f repeating  a n h y d r o g l u c o s e u n i t s which a r e l i n k e d  t o g e t h e r by 1 - 4 - p - D - g l u c o s i d i c bonds. Owing t o t h e numerous h y d r o x y l groups p r e s e n t , c e l l u l o s e i s h i g h l y s e n s i t i v e t o change i n m o i s t u r e c o n t e n t .  Cellulose  i s a l s o e a s i l y s u b j e c t e d t o d e t e r i o r a t i o n by l i g h t , h e a t , aqueous a c i d s and bases, oxygen, and m i c r o o r g a n i s m s ( 5. 35 ) .  R e d u c t i o n o f s e n s i t i v i t y t o w a t e r and d e t e r i o r a t i o n by e n v i r o n m e n t a l f a c t o r s , c a n be a c h i e v e d by c o p o l y m e r ! z a t i o n o f c e l l u l o s e and l i g n o c e l l u l o s e w i t h c e r t a i n monomers ( 9, 132 ) . I n a d d i t i o n , c o p o l y m e r i z a t i o n t e c h n i q u e s have been a p p l i e d ; o f t e n t o m o d i f y t h e s t r e n g t h o f c e l l u l o s e and i t s d e r i v a t i v e s . I n paper manufacture, g r a f t i n g o f monomers t o e i t h e r p u l p s o r p a p e r s has been performed and a l t e r a t i o n s o f paper  properties  have been a c h i e v e d .  2.1.1  Grafting to pulps  C o p o l y m e r i z a t i o n o f woodpulps w i t h monomers  - 4 -  improves t h e d r y and wet t e n s i l e s t r e n g t h s 67,  80, 93. 95. 100, 111,  113,  ( 1,  2,  15i  120 ) . B y C g r a f t i n g - a c f y i a i i d e  ( AA ) t o p a p e r p u l p by an o z o n i z a t i o n t e c h n i q u e ,  Neimo  e t a l . ( 80 ) r a i s e d wet b r e a k i n g l e n g t h 150$ above t h a t o f t h e i n i t i a l p u l p . K o b a y a s h i e t a l . ( 50 ) improved paper s t r e n g t h p r o p e r t i e s by b l e n d i n g ( AN ) and s t y r e n e  aerylonitrile  ( S ) g r a f t e d d i s s o l v i n g p u l p and  c o t t o n l i n t e r s w i t h high y i e l d pulps. Blends c o n t a i n i n g groundwood and g r a f t e d f i b r e s , however, gave p o o r e r p r o p e r t i e s than d i d ungrafted  b l e n d s . These r e s u l t s  i n d i c a t e d t h a t t h e g r a f t e d polymer was o n l y e f f e c t i v e when i t c o n t r i b u t e d t o i n t e r f i b r e b o n d i n g . I t ^ s u b t r a c t e d f r o m streng?th, however, when i t r e p l a c e d f i b r e t o f i b r e bonds. C h a r a c t e r i s t i c s o f p o l y v i n y l a l c o h o l ( PVA ) g r a f t e d p u l p s were s t u d i e d by Ogiwara e t a l . ( 93. 95 )• They f0und»  higher t e n s i l e strength properties f o r a i r - d r y  p a p e r s made from g r a f t e d p u l p s , b u t t h e amount o f i n c r e a s e was h i g h l y dependent on p u l p grade and b e a t i n g degree. G r a f t p e r c e n t i s a l s o known t o a f f e c t paper s t r e n g t h ( 26 )  .  I n most cases, g r a f t i n g onto woodpulp f i b r e s p r i o r t o s h e e t f o r m a t i o n has been f o u n d t o be d e t r i m e n t a l  - 5 -  t o paper p r o p e r t i e s ( 10, 41, 61, 79 ) . By use o f t h e Ce  method, Neimo e t a l . ( 7 9 ) g r a f t e d v a r i o u s monomers  onto ^ c e l l u l o s e f i b r e s and showed t h a t papermaking p r o p e r t i e s were enhanced o n l y w i t h AA o r v i n y l  acetate  ( VA ), p a r t i c u l a r l y when a p p l i e d t o l o w i n i t i a l o r damaged p u l p s . N e v e r t h e l e s s ,  strength  g r a f t i n g f i b r e s with  h y d r o p h o b i c monomers r e s u l t e d i n a d i s t i n c t o f most papermaking p r o p e r t i e s . Lee and F u j i i  lowering ( 63 )  d e c l a r e d t h a t b u t y l a c r y l a t e ( BA ) and e t h y l a c r y l a t e ( EA ), when g r a f t e d t o p u l p , h a d a d e l e t e r i o u s e f f e c t on subsequent paper p r o p e r t i e s . S i m i l a r r e s u l t s have been o b t a i n e d  when m e t h y l m e t h a c r y l a t e ( MMA ) , AN,  S, o r v i n y l c h l o r i d e ( VC ) were used ( 10, 23, 61, 62 ) .  C o n s e q u e n t l y , p r o p e r t i e s o f s h e e t s formed from g r a f t i n g depend upon polymers employed.  Adherence  o f a h y d r o p h o b i c polymer t o t h e f i b r e s e r i o u s l y b l o c k s n a t u r a l bonding s i t e s and i n h i b i t s s w e l l i n g , as w e l l as wet f i b r e f l e x i b i l i t y .  These b l o c k e d  sites  i n t e r f e r e w i t h s t r e n g t h development d u r i n g s h e e t formation  ( 23 ) . On t h e o t h e r hand, i f t h e g r a f t e d  polymer i s h y d r o p h i l i c , papermaking p r o p e r t i e s may  - 6 -  be enhanced due t o improved b o n d i n g c a p a b i l i t y ( 12, 15, 59, 110, 111,  120), The e f f e c t s ; o f g r a f t s w i t h h y d r o p h i l i c  and h y d r o p h o b i c monomers on paper p r o p e r t i e s o f g r a f t e d p u l p s were demonstrated by L e e and F u j i i  ( 61- 65 ) .  T h i s work showed t h a t h y d r o p h i l i c g r a f t s ( AA ) t o p u l p gave paper w i t h h i g h e r t e n s i l e s t r e n g t h and f o l d i n g endurance, b u t l o w t e a r i n g s t r e n g t h . A h y d r o p h o b i c g r a f t ( MMA ) , however, r e s u l t e d i n r e d u c e d t e n s i l e  strength  and t e a r i n g r e s i s t a n c e .  2.1.2  G r a f t i n g t o papers  Some d i s a d v a n t a g e s o f g r a f t i n g t o p u l p s c a n be r e d u c e d by d i r e c t i m p r e g n a t i o n and c o p o l y m e r i z a t i o n o f paper s h e e t s w i t h monomers. Lynch ( 68 ) g r a f t e d AA and MMA onto k r a f t , groundwood and f i l t e r papers by a f r e e r a d i c a l c a t a l y s i s method. The t e n s i l e s t r e n g t h o f t h e s e papers i n c r e a s e d w i t h i n c r e a s i n g polymer c o n t e n t . U s i n g t h e e e r i e i o n t e c h n i q u e t o g r a f t AN onto paper made from a l p h a - c e l l u l o s e p u l p s , a l a r g e improvement o f wet and d r y t e n s i l e s t r e n g t h s w i t h i n c r e a s e i n polymer c o n t e n t was n o t e d ( 26 ) . A t about 40%  -  7 -  r e t e n t i o n , t h e wet s t r e n g t h was e q u a l t o t h e c o n t r o l d r y s t r e n g t h . U s i n g t h e same method when g r a f t i n g d i f f e r e n t papers w i t h AN, AA, MMA,EA-AN, a c r y l i c a c i d and o t h e r monomers r e s u l t e d i n g r e a t improvement i n d r y and wet s t r e n g t h s ( 26, 43, 68, 105, 109, 120, 121  ).  I n c r e a s e d bonding has been c i t e d t o e x p l a i n increased strength p r o p e r t i e s o f g r a f t e d papers. D a n i e l e t a l . ( 26 ) assumed t h a t t h e enhanced s t r e n g t h from AN g r a f t e d t o f i b r e s u b s t r a t e s was due t o p o l a r bonds between n e i g h b o u r i n g  p o l y ( AN ) c h a i n s . Putnam ( 105 )  concluded t h a t s t r e n g t h reinforcement  on AN p o l y m e r i z a t i o n  r e s u l t s f r o m a d d i t i o n o f hydrogen bonds between t h e polymer and t h e c e l l u l o s e f i b r e m a t r i x . AN and AA appear t o be p a r t i c u l a r l y b e n e f i c i a l w i t h r e s p e c t t o d r y paper s t r e n g t h p r o p e r t i e s ( 10, 69» 78, 80, 105, 112, 121, 130 ) . Such i n c r e a s e s were a t t r i b u t e d t o g r e a t l y i n c r e a s e d number o f i n t e r f i b r e bonds ( 26 ) . Some f i n d i n g s o f Neimo and S i h t o l a ( 78 ) i n d i c a t e d t h a t f i r m hydrogen bonds p r o b a b l y e x i s t between amide groups o f g r a f t e d p o l y ( AA ) c h a i n s and t h e c e l l u l o s e  - 8 -  h y d r o x y l s . T h i s may  g i v e r i s e to a s h e l l type s t r u c t u r e  w i t h c e l l u l o s e . " e n c a p s u l a t e d " i n p o l y ( AA  ) coils.  C o n t r a s t i n g w i t h the above r e s u l t s , Ogiwara et a l . ( 9 5  ) i n d i c a t e d t h a t g r a f t i n g commercial p r i n t i n g  papers w i t h AN i n a i r , w i t h e e r i e s a l t as  initiator,  l e d t o d e c r e a s e d b r e a k i n g l e n g t h and d i m e n s i o n a l MMA  and m e t h y l a c r y l a t e ( MA  the s t r e n g t h o f papers ( 79»  stability.  ) have been f o u n d to l o w e r 96, 121  ). Oraby e t a l .  ( 97 )» as w e l l as Crook e t a l . ( 25 ), s t u d i e d the r a d i a t i o n - i n d u c e d g r a f t i n g o f S t o paper s h e e t s . They found t h a t breaking  l e n g t h , b u r s t and f o l d i n g endurance  a l l decreased a f t e r g r a f t i n g , w i t h strength d e t e r i o r a t i o n p r o p o r t i o n a l t o the amount o f polymer g r a f t e d . R e i n f o r c e m e n t o f paper s t r e n g t h was  also  a t t e m p t e d by c o p o l y m e r i z a t i o n w i t h formed polymers p a r t i a l p o l y m e r s . B e r g e r and G e l b e r t  and  ( 11 ) i n d i c a t e d t h a t  t r e a t m e n t w i t h urethane e m u l s i o n s i n c r e a s e d paper d r y and wet  s t r e n g t h s , p a r t i c u l a r l y a t low l e v e l s o f  s a t u r a t i o n . A s m a l l amount o f u r e t h a n e produced a l a r g e i n c r e a s e i n s t r e n g t h . P a s z n e r ( 100  )  polymerized  a h y d r o c a r b o n d r y i n g o i l w i t h i n handsheets made f r o m c h e m i c a l p u l p s , groundwood and groundwood-chemical p u l p c o m b i n a t i o n s . I n t e r f i b r e bonding was  strengthened  without  -  9  -  n o t i c e a b l e e f f e c t on i n t r i n s i c f i b r e s t r e n g t h . The a d d i t i o n o f b u t a d i e n e - s t y r e n e  copolymers  ( Gr-S r u b b e r ) t o paper s h e e t s improved wet and d r y t e n s i l e strengths ( 3 9  ). S t r e s s - s t r a i n curves f o r  l a t e x - t r e a t e d papers i n d i c a t e d t h a t , w i t h few e x c e p t i o n s , a d d i t i o n o f the 60%  3  to paper m a i n l y improved  and  40$ \" a c r y l a t e e l a s t o m e r  the paper " p o s t - y i e l d  e x t e n s i b i l i t y ". L i t t l e v a r i a t i o n i n modulus o f e l a s t i c i t y , i . e . , e a r l y s t r e s s - s t r a i n behaviour, o b s e r v e d . S t r e s s - s t r a i n c u r v e s a t a number o f  was  Gr-S  r u b b e r a d d i t i o n l e v e l s showed t h a t e l o n g a t i o n a t f i n a l y i e l d i n c r e a s e d w i t h i n c r e a s i n g l a t e x c o n t e n t , but t h a t t e n s i l e s t r e n g t h a t f i n a l y i e l d remained f a i r l y c o n s t a n t . Heyse e t a l . ( 39 ) c o n c l u d e d t h a t i m p r e g n a t i o n by an e l a s t o m e r i n t r o d u c e d two i m p o r t a n t f a c t o r s which c o u l d g r e a t l y a f f e c t paper s t r e s s - s t r a i n p r o p e r t i e s « i.  the s t r e s s - s t r a i n and  adhesive  p r o p e r t i e s o f the Gr-S f i l m ; ii.  and  t h e f i l m f o r m i n g temperature o f the l a t e x , i . e . , the Gr-S f i l m would n o t be formed i f the i s below a c r i t i c a l  Thommen and S t a n n e t t ( 139  temperature point.  ) found t h a t the i n i t i a l polymer  - 10  -  a d d i t i o n brought about a s h a r p i n c r e a s e i n s t r e n g t h , f o l l o w e d by g r a d u a l l y d i m i n i s h e d  increases of b e n e f i c i a l  e f f e c t s w i t h f u r t h e r a d d i t i o n s , u n t i l the curve became n e a r l y f l a t . T h i s was  a t t r i b u t e d t o the q u a n t i t y o f  s i t e s a v a i l a b l e f o r reinforcement,  making f u r t h e r a d d i t i o n s  less effective. I t can be c o n c l u d e d t h a t a l t e r a t i o n o f paper s h e e t p r o p e r t i e s by c o p o l y m e r i z a t i o n  methods  r e s u l t s f r o m c h o i c e o f monomer, amount o f g r a f t i n g , t e c h n i q u e empolyed and the o r i g i n a l paper m a t e r i a l used. I n a d d i t i o n , f i b r e c h e m i c a l c o m p o s i t i o n environmental conditions during processing  and  have  significant effects.  2.2  E f f e c t o f F i b r e Chemical C o n s t i t u e n t s Grafting j Especially Lignin  on  S u i t a b i l i t y o f woodpulps f o r g r a f t i n g depends on f i b r e c h e m i c a l c o n s t i t u e n t s and  swelling characteristics.  Wood i s a complex s u b s t a n c e w h i c h i i s composed o f c e l l u l o s e , h e m i c e l l u l o s e s , l i g n i n s and compounds. The  extraneous  term " l i g n i n s " r e f e r s to a m i x t u r e  -  11  -  o f s u b s t a n c e s t h a t have s i m i l a r c h e m i c a l c o m p o s i t i o n but may have s t r u c t u r a l d i f f e r e n c e s . The a r o m a t i c s t r u c t u r e o f l i g n i n has been proven by i t s c h a r a c t e r i s t i c u l t r a v i o l e t a b s o r p t i o n spectrum,  which  i s v e r y s i m i l a r t o t h a t o f some g u a i a c y l p r o p a n e compounds ( 16, 82 ) . L i g n i n s appear t o be amorphous s u b s t a n c e s . I t s h o u l d be n o t e d t h a t c o n i f e r o u s wood lignins contain exclusively guaiacylpropyl units, whereas d e c i d u o u s wood l i g n i n s c o n t a i n b o t h g u a i a c y l and s y r i n g y l p r o p y l m o i e t i e s ( 16 ) . The n a t u r e o f t h e bond between l i g n i n s and c a r b o h y d r a t e s i n n o t c l e a r . I t seems, however, t h a t some p a r t o f l i g n i n i s c h e m i c a l l y bound t o c a r b o h y d r a t e s ( 82 ) . The presence o f l i g n i n i n f i b r e s may a c t as a r e t a r d e r t o g r a f t i n g r e a c t i o n s ( 79. 83, 103 ) . The d e l e t e r i o u s e f f e c t o f l i g n i n on g r a f t i n g by t h e e e r i e i o n t e c h n i q u e has been r e p o r t e d ( 83 ). w h e r e i n g r a f t i n g y i e l d s varied according to r e s i d u a l  lignin  c o n t e n t o f t h e p u l p s ( 10 ) . Increased r e s i d u a l l i g n i n decreased g r a f t i n g r a t e c o n s i d e r a b l y ( 10 ) . By u s i n g t h e e e r i e i o n  -  12 -  t e c h n i q u e , Kubota and Ogiwara ( 56, 94 ) s t u d i e d t h e e f f e c t o f l i g n i n i n a s e r i e s o f c o n i f e r o u s p u l p s on MMA g r a f t i n g . . T h e y  showed t h a t g r a f t i n g o c c u r r e d  only  a f t e r an i n d u c t i o n p e r i o d . L e n g t h o f the p e r i o d i n c r e a s e d w i t h i n c r e a s i n g p u l p l i g n i n c o n t e n t . I t was c o n c l u d e d t h a t the e e r i e i o n r e a c t e d a t a much f a s t e r r a t e w i t h l i g n i n t h a n w i t h c e l l u l o s e i n wood p u l p .  Coniferous  l i g n i n was n o t as severe a r e t a r d e r a s pored wood l i g n i n ( 103 ) . The  s u i t a b i l i t y o f l i g n i n - c o n t a i n i n g pulps  f o r g r a f t i n g i s dependent i n par-t on the  particular  monomer used. P h i l l i p s e t a l . ( 103 ) r e v e a l e d t h a t t h e g r a f t y i e l d o f S t o wood p u l p s i n c r e a s e d w i t h l i g n i n c o n t e n t , w h i l e the g r a f t i n g o f AA was s t r o n g l y i n h i b i t e d by o n l y a f e w per cent  2.3  lignin.  E f f e c t o f Gamma R a d i a t i o n o n C e l l u l o s i c s and Polymers  Gamma r a y s are h i g h energy photons and a s such c a r r y no charge o r r e s t mass. These r a y s r e s u l t from nuclear processes,  such a s r e l e a s e i n f i s s i o n and  decay o f r a d i o a c t i v e i s o t o p e s ( 48 ) .  - 13  -  I t has been o b s e r v e d t h a t r a d i a t i o n a f f e c t s polymers by c a u s i n g e i t h e r c r o s s l i n k i n g o r d e g r a d a t i o n . C r o s s l i n k i n g l e a d s t o . i n c r e a s e d m o l e c u l a r w e i g h t and eventually to formation of insoluble three-dimensional networks ( 20, 21 ). D e g r a d a t i o n i s r e v e a l e d by f r a c t u r e o f polymer m o l e c u l e s , l e a d i n g t o d e c r e a s e d average m o l e c u l a r w e i g h t ( 20, 21 ) . Even i n systems showing  initial  c r o s s l i n k i n g , d e g r a d a t i o n b e g i n s t o predominate a t s u f f i c i e n t l y h i g h r a d i a t i o n d o s e s . Both r e a c t i o n s a r e f o u n d t o be p r o p o r t i o n a l t o dose and r a t h e r independent o f r a d i a t i o n i n t e n s i t y ( 48 ) . I f o n l y c h a i n s c i s s i o n t a k e s p l a c e and t h e r a t e o f b r e a k i n g l i n k s i s a l i n e a r f u n c t i o n o f r a d i a t i o n dose, an e q u a t i o n  i s obtained  as i ( 1/ M  n  ) - ( 1/ ^  ) = r/E N d  where j f i n a l number average m o l e c u l a r weight, iio  i n i t i a l number average m o l e c u l a r weight,  r  r a d i a t i o n dose,  E  average energy absorbed by t h e system f o r each m a i n s c i s s i o n , and  - 14  N  =  -  Avogadro's number.  C o n v e r s e l y , i f o n l y random c r o s s l i n k i n g t a k e s p l a c e and  the r a t e o f c r o s s l i n k i n g i s a l i n e a r  f u n c t i o n o f the r a d i a t i o n dose, t h e m  { 2 J  q  =  q  q  =  r a t e of  q  =  the c r o s s l i n k i n g d e n s i t y produced per u n i t r a d i a t i o n dose, and  r  =  r a d i a t i o n dose.  0  r  where i crosslinking,  The  t o t a l dose absorbed to i n i t i a t e damage i n p l a s t i c s  and  e l a s t o m e r s i s i n the range o f 2.1  10  1 0  ergs g ~  1 0  ( 48  x 10^  to 7.3  ).  Depolymerization of c e l l u l o s e chains i n i t i a t e d by gamma r a d i a t i o n , o c c u r s m a i n l y by o f the 1-4-  x  p-D-glucosidic linkage.  as breaking  C a r b o n y l and  carboxyl  groups are formed i n b o t h amorphous and c r y s t a l l i n e r e g i o n s , but n e g l i g i b l e c r y s t a l l i n i t y i s l o s t ( 7, 101  ). P a s z n e r ( 101  d e g r a d a t i o n under Ng  ) indicated that  cellulose  i s a f u n c t i o n of t o t a l i r r a d i a t i o n  dose, whereby the l o g DP a l m o s t l i n e a r . No  8,  - l o g dose r e l a t i o n s h i p i s  changes o f paper m e c h a n i c a l p r o p e r t i e s 6 o r b r i g h t n e s s were n o t e d w i t h doses up t o 10 r a d .  - 15  -  F u r t h e r i r r a d i a t i o n l e d t o a marked d e t e r i o r a t i o n i n b o t h s t r e n g t h and b r i g h t n e s s (55). Loos(66) f o u n d t h a t i r r a d i a t i o n l e v e l s o f lo'' r a d o r g r e a t e r d e f i n i t e l y degraded wood and decreased i t s  t o u g h n e s s . I t has been f o u n d a l s o t h a t 6  dosages below 10  r a d s l i g h t l y i n c r e a s e some s t r e n g t h  p r o p e r t i e s ( 1 8 ) . Wood i s more r e s i s t a n t t o r a d i a t i o n degradation  t h a n c e l l u l o s e , p r o b a b l y due t o t h e presence  o f l i g n i n and e x t r a c t i v e s a s s o c i a t e d w i t h i t s l a t t i c e s t r u c t u r e (124). The f r a g m e n t a t i o n  of cellulose  chains  under i r r a d i a t i o n e f f e c t s t a k e s p l a c e randomly, t h u s r e d u c i n g p o l y d i s p e r s i t y . T h i s p r o c e s s , however, c a n a l s o be accompanied'by c r o s s l i n k i n g and e n d l i n k i n g , p r o v i d i n g i r r a d i a t i o n o c c u r s under s u i t a b l e c o n d i t i o n s ( 9 9 ) . 2.4  R h e o l o g i c a l Behaviour o f S o l i d s  Rheology i s t h e s c i e n c e concerned w i t h of deformation  study  and f l o w o f m a t e r i a l s , e s p e c i a l l y t h e  i n t e r r e l a t i o n s h i p o f s t r e s s , s t r a i n and t i m e . I n i t s broadest  sense t h e s u b j e c t r a n g e s f r o m f l o w o f gases  and l i q u i d s t o e l a s t i c d e f o r m a t i o n  of c r y s t a l l i n e  solids.  I n p r a c t i c e t h e term g e n e r a l l y r e f e r s t o t h e s t u d y o f m a t e r i a l s h a v i n g e l a s t i c and f l o w p r o p e r t i e s i n t e r m e d i a t e between t h o s e o f i d e a l s o l i d s and o r d i n a r y Wood, wood p r o d u c t s  liquids.  and p l a s t i c s a r e o f t h i s  type.  - 16 -  Two approaches  have been developed t o d e s c r i b e  v i s c o e l a s t i c p r o p e r t i e s o f m a t e r i a l s . One i s c h a r a c t e r i z a t i o n o f t h e m a t e r i a l by a  complete  d e s c r i p t i o n of i t s behaviour, while the other i s e l u c i d a t i o n o f the a t o m i c o r m o l e c u l a r s t r u c t u r e o f t h e m a t e r i a l and assignment o f mechanisms r e s p o n s i b l e f o r r h e o l o g i c a l phenomena. The f i r s t i s g e n e r a l l y r e f e r r e d to as phenomenological  r h e o l o g y , w h i l e t h e second  may  be c a l l e d m o l e c u l a r r h e o l o g y C 102 ) . N e v e r t h e l e s s , b o t h approaches  a r e concerned w i t h a n a l y s i s o f s t r e s s -  s t r a i n - t i m e r e l a t i o n s h i p s as r e s p o n s e s o f m a t e r i a l s t o various excitations.  2.4.1  S t r e s s r e l a x a t i o n o f s o l i d s j general survey  S t r e s s r e l a x a t i o n , as an a s p e c t o f v i s c o e l a s t i c b e h a v i o u r o f m a t e r i a l s , i s o b s e r v e d when a m a t e r i a l i s s u b j e c t e d t o s t r a i n t h a t i s h e l d c o n s t a n t . The s t r e s s i s found to decrease w i t h time. A c c o r d i n g to l i n e a r v i s c o e l a s t i c theory, r e l a x a t i o n curves o f s o l i d s a r e e x p r e s s e d by a s i n g l e M a x w e l l i a n model which i n v o l v e s an i d e a l s p r i n g and dashpot i n s e r i e s ( 3,  17  -  30,  71.  72, 81, 129,  -  141, 143 ) . The model, however,  i s d e s c r i b e d by E(t)  =  E exp ( - t / x ) s t e p s ( 71.  as d e r i v e d i n t h e f o l l o w i n g i.  the  142 )«  stress-strain relationship  f o r the..spring i s S  =  E&»  where j S  =  s t r e s s measured a c r o s s t h e e n t i r e model,  E  =  Young's modulus, and  £, = ii.  deformation o f the springj  the s t r e s s - s t r a i n r e l a t i o n s h i p f o r the dashpot i s S  =  IJ ( d f c i / d t )  where ; n -  =  Newtonian v i s c o s i t y of the l i q u i d ,  =  deformation of l i q u i d i n 5 Ithe dashpo t , and  ^rT>=  rate of 'defamation i  £  t  - 18 -  iii.  since t o t a l deformation ( % ) o f t h e model i s  t  =  e, + £ *  / 5 /  the s t r e s s - s t r a i n r e l a t i o n s h i p f o r t h e e n t i r e s e r i e s can be o b t a i n e d by s u b s t i t u t i n g { 4 J and i n t e g r a t i n g [ 3 / i n t o [ 5 J* thus« dfc/ dt  = (1/E) dS/dt + S/f)../"6 /  where ; d £ / dt iv.  =  strain rate;  during r e l a x a t i o n , macroscopic d e f o r m a t i o n o f t h e specimen i s h e l d c o n s t a n t so t h a t d f c / d t = 0, which a l t e r s { 6 J 0  =  to  (1/E ) ( dS/dt ) + S/  I J . . . /  7a/  or ; dS/S v.  = ( - d t / (Q /E) )  / 7b /  a f t e r i n t e g r a t i o n under t h e boundary c o n d i t i o n S = S  Q  « E  ( S  Q  t h a t t =0,  = i n i t i a l s t r e s s ),  - 19 -  f 7 J  becomes  S(t)  =  E t  { 8a /  E(t)  =  E exp ( - t / r )  S(t)  =  time dependent s t r e s s ,  E(t)  =  time dependent r e l a x a t i o n modulus, and  =  IJ /E  exp ( - t / t )  or; /"8b J  where \  ^  =  r e l a x a t i o n time.  In the m a j o r i t y o f cases, s t r e s s r e l a x a t i o n o c c u r s more s l o w l y t h a n p r e d i c t e d by t h e s i m p l e M a x w e l l i a n model ( 44, 51,  54, 116, 132-134, 142, 145 ) .  A f e a t u r e of s t r e s s p l o t t e d against the logarithm of t i m e i s t h e c o m p a r a t i v e l y b r o a d i n f l e c t i o n range which t h e c u r v e s a r e l i n e a r ( t h e l i n e a r i t y  over  inflection  r e g i o n ) . The r e g i o n u s u a l l y extends o v e r about two decades o f t i m e . T h i s l i n e a r i t y has been c a l l e d t h e l o g a r i t h m i c t i m e l a w ( 146 ), which may be f o r m u l a t e d a s i S  =  S  Q  - F log t  where % S  =  S„ = o  s t r e s s a t time t , i n i t i a l s t r e s s , and  {9  /  - 20 -  F  =  inflection  slope.  E x p e r i m e n t a l r e s u l t s o f r e l a x a t i o n may be  fitted  by t h e M a x w e l l - W e i e h e r t model ( 3t 30, 81, 142 ), w h i c h c o n t a i n s a s u f f i c i e n t number o f M a x w e l l i a n elements i n p a r a l l e l arrangement, such t h a t « E(t)  E1  =  exp ( - t / , ) + E r  .+  + E  n  2  exp ( - t  / ) t x  exp ( - t / r ) n  n  =£ E. exp ( - t / . ) r  or?  ^ E(t)  = )0  E(C ) exp ( - t / r ) d t  E(t)  =  H ( t l n v r ) exp ( . - t / r ) d ( l n C )  .../10a/  orj /"10b/ where j H( I n C ) = H ( r ) = t E ( T ) ( H( l n t ) ) = d i s t r i b u t i o n of r e l a x a t i o n times.  2.4.2  R e l a x a t i o n o f polymers  The r e l a x a t i o n modulus ( E ( t ) , { 8b J  ) can be  used t o d e s c r i b e s t r e s s r e l a x a t i o n b e h a v i o u r o f h i g h polymers by p l o t t i n g  l o g E(t) against l o g time. I n  - 21 -  amorphous polymers f o u r s t a t e s , such as g l a s s y ,  transition,  r u b b e r y , and Newtonian f l o w a r e r e a d i l y o b s e r v e d i n such diagrams as shown i n F i g . 1 ( 36, 60, 118, 140, 142 ). A t v e r y s h o r t t i m e s amorphous polymers behave l i k e an e l a s t i c s o l i d . The h i g h modulus o b s e r v e d a t short times i s c h a r a c t e r i s t i c of glassy, b r i t t l e  solids  and i s a s s o c i a t e d w i t h r i g i d i t y o f t h e m o l e c u l a r c h a i n backbone. of  The modulus, E ( t ) , i s e s s e n t i a l l y  independent  time and temperature ( 40, 118 ) . The m o t i o n o f m o l e c u l a r  segments i s r e s t r i c t e d p r i m a r i l y t o v i b r a t i o n s ,  and  l a r g e s t r e s s e s a r e r e q u i r e d t o cause d e f o r m a t i o n o f s t i f f molecules. As t i m e p r o g r e s s e s , t h e t r a n s i t i o n range i s e n t e r e d , w h e r e i n polymers a c t l e s s g l a s s y and t h e modulus d e c r e a s e s s h a r p l y . A d d i t i o n a l modes o f m o t i o n , which might a l l o w i n c r e a s e d r e l a x a t i o n , a r e r o t a t i o n o f segments about t h e i r main c h a i n backbone and o t h e r segmental a d j u s t m e n t s w i t h r e s p e c t t o n e i g h b o u r i n g segments ( 40, 118 ). At s t i l l longer times, the rubbery p l a t e a u r e g i o n i s r e a c h e d . I n t h e r e g i o n E ( t ) approaches c o n s t a n t v a l u e and t h e m a t e r i a l d i s p l a y s l a r g e  a  elastic  - 22 -  deformation,  which i s m o s t l y r e c o v e r a b l e .  Relaxation  e f f e c t s are absent. Since E ( t ) i s c h a r a c t e r i s t i c of the v a l u e encountered i n r u b b e r e l a s t i c i t y , and i s r e l a t i v e l y independent o f t e m p e r a t u r e o r t i m e , t h i s r u b b e r y p l a t e a u has been a s s o c i a t e d w i t h entanglements between and among l o n g c h a i n m o l e c u l e s .  I n t h e Newtonian r e g i o n ,  the modulus f a l l s o f f r a p i d l y , i n d i c a t i n g t h a t a s t a t e o f l i q u i d f l o w has been r e a c h e d . P l o w b e h a v i o u r i s c h a r a c t e r i z e d by even g r e a t e r l o o s e n i n g o f t h e m o l e c u l a r s t r u c t u r e and g r e a t e r m o l e c u l a r m o b i l i t y . Among c r o s s l i n k e d polymer m a t e r i a l s a r e s t r i c t i o n i s p l a c e d on l o o s e n e s s  of the structure,  and t h e modulus l e v e l s o f f t o a r a t h e r c o n s t a n t  value  i n t h e f i n a l Newtonian r e g i o n ( 81 ) . A s u i t a b l e mode r e p r e s e n t i n g E ( t ) f o r these m a t e r i a l s i s i E(t)  = j** E( T ) exp ( - t / ) d t + E o c c  -..../• or; =  Le  H  <  l  n  t  )  e x  P (-*/r ) d ( l n t )  + Eoc D i f f e r e n c e s appear between p o l y e r y s t a l l i n e and amorphous p o l y m e r s . The ehange i n E ( t ) f o r  /'lib J  -  23  -  p o l y c r y s t a l l i n e t y p e s i s much s m a l l e r , and the  transition  r e g i o n extends o v e r a much w i d e r temperature range t h a n f o r amorphous polymers ( 4 0 ,  142  ), s i n c e o n l y d i s o r d e r e d  r e g i o n s t a k e p a r t i n t h e t r a n s i t i o n . I n the r u b b e r y p l a t e a u r e g i o n , t h e d i s o r d e r e d r e g i o n s are r u b b e r y i n nature.  The  modulus i s h i g h e r t h a n w i t h amorphous  polymers s i n c e c r y s t a l l i n e r e g i o n s are r i g i d and a c t as c r o s s l i n k s f o r the d i s o r d e r e d r e g i o n s . Molecules  pass  t h r o u g h b o t h o r d e r e d and d i s o r d e r e d r e g i o n s and o n l y s h o r t molecular may  l e n g t h s are r u b b e r y .  I n t h i s r e g i o n the m a t e r i a l  be compared t o a h i g h l y c r o s s l i n k e d r u b b e r w h i c h a l s o  c o n t a i n s r i g i d f i l l e r p a r t i c l e s . Where the Newtonian r e g i o n o c c u r s the c r y s t a l s m e l t , the modulus f a l l s d r a s t i c a l l y and the polymer shows v i s c o u s l i q u i d f l o w . The  t r a n s i t i o n region of p l a s t i c material  i s u s u a l l y c h a r a c t e r i z e d by a r e l a x a t i o n time. g i v e s r i s e to a f a m i l y of r e l a x a t i o n curves  C»  which  having  d i f f e r e n t t values. Stress r e l a x a t i o n curves f o r m a t e r i a l s w i t h low Z v a l u e s show r e l a t i v e l y r a p i d decay and  are  i n d i c a t i v e o f l i q u i d - l i k e behaviour,whereas those f o r  - 24 -  materials with higher r values cmaintain relativelyh i g h s t r e s s v a l u e s f o r l a r g e r time p e r i o d s and a r e i n d i c a t i v e o f s o l i d - l i k e b e h a v i o u r . W i t h i n l i m i t s , as X approaches^zerosto c  approaches © c , c o m p l e t e l y  v i s c o u s to completely e l a s t i c behaviour i s expected ( 72, 8 1 , 142 ) . Since r  depends on v i s c o s i t y , fj , ( T  and fj i s temperature s e n s i t i v e , t h e e f f e c t o f temperature on v i s c o e l a s t i c p r o p e r t i e s o f p l a s t i c m a t e r i a l s i s n o t a b l e . I n c r e a s e i n temperature d e c r e a s e s b o t h TJ and x p r o v i d e s ^ a f l u i d - l i k e s t a t e w i t h i n c r e a s i n g temperature, i n contrast to the s o l i d - l i k e state with decreasing temperature. Smith ( 125-127; ) , T o b o l s k y ( 140 ) , and o t h e r s ( 69» 84 ) have proposed t h a t t h e e f f e c t s o f time and t e m p e r a t u r e on v i s c o e l a s t i c p r o p e r t i e s o f n o n - c r y s t a l l i n e polymers c a n be i n t e r c o n v e r t e d above t h e g l a s s t r a n s i t i o n t e m p e r a t u r e and w i t h i n l i n e a r v i s c o e l a s t i c Williams et a l .  limits.  ( 150 ) c o n v e r t e d t h e m o d u l i o b t a i n e d  from d i f f e r e n t t e m p e r a t u r e s by u s i n g a s h i f t f a c t o r ( A ( t ) ) t o make a master curve ( WLF e q u a t i o n ) d e s c r i b i n g the m o d u l i o v e r s e v e r a l time decades ass  -  25  log A(t)  -  =  log t / t  = CJ( T - T  g  Q  ) / ( C  2  + T - T  g  )  /"12/ where j C  l* 2 C  T  constants,  =  =  and  the g l a s s t r a n s i t i o n t e m p e r a t u r e .  Time- temperature e q u i v a l e n c e when an amorphous polymer i s s u b j e c t e d  becomes a p p a r e n t to h e a t above  i t s T . aThe^molecular "chains- t e n d to r e a r r a n g e and  take  on the most p r o b a b l e c o n f i g u r a t i o n s commensurate w i t h the s t a t e o f s t r e s s o r s t r a i n b e i n g  endured.  The r a t e o f rearrangement depends on l o c a l r e s i s t a n c e e n c o u n t e r e d by any  chain. This r e s i s t a n c e  can be e x p r e s s e d by a v i s c o u s f r i c t i o n  coefficient  which i s d e r i v e d as the f o r c e r e q u i r e d t o move a t h r o u g h the s u r r o u n d i n g  chain  medium a t u n i t v e l o c i t y ( 127  ).  Thus, the f a s t e r the c h a i n i s r e q u i r e d to move, the g r e a t e r i s the f o r c e which must be a p p l i e d .  Likewise,  the r e q u i r e d f o r c e becomes g r e a t e r as temperautre i s d e c r e a s e d . Consequently, i t appears l o g i c a l t h a t some relationship  should  e x i s t between t i m e - and  temperature-  dependence o f amorphous polymer v i s c o e l a s t i c p r o p e r t i e s ( 128  )  - 26 -  The t i m e - t e m p e r a t u r e s u p e r p o s i t i o n  theory,  h o w e v e r , i s n o t v a l i d f o r c r y s t a l l i n e polymers ( 6, 81, 141, 142, 145 )• T h i s i s due t o changes i n m i c r o c r y s t a l l i n e s t r u c t u r e and i t s s t r e s s - b e a r i n g mechanisms a t v a r i o u s t e m p e r a t u r e s ( 127 ) . I t was found  127 ) w i t h  tensile  s t r e s s r e l a x a t i o n o f PVA d e r i v a t i v e s t h a t no s i n g l e t i m e - t e m p e r a t u r e s u p e r p o s i t i o n was v a l i d o v e r a l l s t a t e s , i n c l u d i n g the T  and r u b b e r y r e g i o n s . Changes from  s e m i c r y s t a l l i n e t o amorphous s t r u c t u r e were o b s e r v e d w i t h such m a t e r i a l s a t v a r i o u s t e m p e r a t u r e s above T^ . These a n o m a l i e s were a t t r i b u t e d t o e x i s t e n c e o f an i n t e r - m o l e c u l a r r e l a x a t i o n mechanism, c h a r a c t e r i z e d by l o o s e n i n g o f t h e c r y s t a l s t r u c t u r e t h r o u g h breakage o f s t r o n g secondary v a l e n c e bonds ( 32 ) . The s u p e r p o s i t i o n p r i n c i p l e has been examined w i t h copolymer systems. F u j i n o e t a l . ( 31 ) examined s t r e s s r e l a x a t i o n o f MMA-MA copolymers, as w e l l as poly(MMA) and p o l y (MA), a t v a r i o u s t e m p e r a t u r e s and f o u n d t h a t t h e s e c o u l d be s h i f t e d t o g i v e master c u r v e s c o v e r i n g numerous time decades. I n summary, polymer s t r e s s r e l a x a t i o n depends upon t h e c h a r a c t e r i s t i c s o f m a t e r i a l s and t h e  - 27 -  t e s t environment, i n c l u d i n g temperature and t i m e . E f f e c t s o f temperature and t i m e may be superimposed i n some c a s e s , such as w i t h amorphous polymer  2.4.3  systems.  R h e o l o g i c a l p r o p e r t i e s o f papers  E a r l y u n d e r s t a n d i n g o f paper v i s c o e l a s t i c b e h a v i o u r was drawn from s i m p l e i n v e s t i g a t i o n s o f l o a d d e f o r m a t i o n . I t i s noted here t h a t t h e i n i t i a l  response  i n a l o a d - d e f o r m a t i o n t e s t i s l a r g e l y e l a s t i c , and a t h i g h e r l o a d s paper does deform i n a manner i n d i c a t i n g f l o w . T h i s d e f o r m a t i o n caused by m a t e r i a l f l o w i s l a r g e l y n o n - r e c o v e r a b l e . When specimens a r e s u b j e c t e d t o l o a d i n g unloading cycles, deformation a f t e r the f i r s t  cycles  i s a l m o s t e n t i r e l y r e c o v e r a b l e . A marked h y s t e r e s i s i n t h e l o a d i n g ^ u n l o a d i n g c u r v e s has been o b s e r v e d . S t u d i e s by S t e e n b e r g and a s s o c i a t e ( 132-134 ) on paper load-deformation p r o p e r t i e s , i n d i c a t e d t h a t these r e s u l t s depend on numerous f a c t o r s r e l a t i n g t o t h e manner o f sheet preparation, e x t e r n a l t e s t c o n d i t i o n s , r a t e o f t e s t i n g and p r e v i o u s m e c h a n i c a l h i s t o r y o f t h e specimen. S u p e r f i c i a l i n v i s i b l e creep o f f i b r e s , macroscopic  - 28 -  u n k i n k i n g and f i b r e u n c u r l i n g i n the s h e e t were c o n s i d e r e d t o be r e s p o n s i b l e f o r n o n - r e c o v e r a b l e ( 71  deformation  ).  Attempts have been made t o d e s c r i b e viscoelastic  p r o p e r t i e s o f papers by m e c h a n i c a l  spring  and dashpot c o m b i n a t i o n s . Anders son ( 4 ) aKdQSt.©enberg,iand c  coworker  ( 132-  134  ) employed E y r i n g ' s t h e o r y o f r a t e  p r o c e s s e s ( 34 ) and the s p r i n g and dashpot  combination  developed f o r t e x t i l e s by H a l s e y and coworkers to d e s c r i b e paper s t r e s s - s t r a i n  (37.  38 )  curves according to a  t h r e e s element model. The model elements c o n s i s t e d o f a s p r i n g p a r a l l e l t o a H a x w e l l i a n body. Mason ( 71  )  suggested a f o u r element model w i t h a M a x w e l l i a n body i n s e r i e s w i t h a body c o n s i s t i n g o f a s p r i n g and dashpot i n p a r a l l e l , t o e x p l a i n paper  stress-strain  phenomena. I n the m o l e c u l a r approach, t h a t H-bonds p l a y an i m p o r t a n t r o l e  i t i s believed in  viscoelastic  b e h a v i o u r o f c e l l u l o s i c m a t e r i a l s ( 85-92, 135, Ranee ( 106, 107  ) proposed t h a t d e l a y e d e l a s t i c  136  ).  and  p l a s t i c cmoponents o f paper e l o n g a t i o n a r e due t o t h e breakage o f f i b r e t o f i b r e bonds. F o r c e s a c t i n g between  - 29 -  two f i b r e s were a t t r i b u t e d t o H-bonds o r van d e r Waal's f o r c e s , which c o n t r i b u t e t o the f l o w o f m a t e r i a l s . F u r t h e r , N i s s a n ( 85-90 ) and coworker.  ( 92; 135, \  136 ) p o s t u l a t e d t h a t paper v i s c o e l a s t i c p r o p e r t i e s a r e s t r o n g l y a f f e c t e d , o r even governed, by H-bonds.  The  f o r m a t i o n o f i n t e r - f i b r e bonds a t d i f f e r e n t s t a g e s d u r i n g s h e e t d r y i n g was f o u n d t o be i m p o r t a n t t o paper r e l a x a t i o n b e h a v i o u r ( 29 ) . I n a d d i t i o n , Page ( 98 ) argued t h a t r h e o l o g i c a l p r o p e r t i e s o f f i b r o u s n e t w o r k s , such as paper, were a l s o dependent upon s t r u c t u r e a t the s u p e r m o l e c u l a r l e v e l . I n c o n c l u s i o n , i t seems t h a t paper r h e o l o g i c a l p r o p e r t i e s have been a t t r i b u t e d t o v a l e n c e bond l e n g t h , bond d e f o r m a t i o n a n g l e , secondary bond d e f o r m a t i o n , r e o r i e n t a t i o n o f macromolecules i n amorphous r e g i o n s , r e o r i e n t a t i o n o f c r y s t a l l i n e r e g i o n s and c o n f i g u r a t i o n a l e n t r o p y e f f e c t s , as w e l l as d r y i n g c o n d i t i o n s and paper m a c r o - s t r u c t u r a l e f f e c t s ( 24, 92 ) .  2.4.3.1  S t r e s s r e l a x a t i o n o f papers  S t u d i e s on paper s t r e s s r e l a x a t i o n have been  -  30  -  l i m i t e d m o s t l y to p h e n o m e n o l o g i c a l d e s c r i p t i o n o f v e r s u s t i m e r e l a t i o n s h i p s and  stress  e f f e c t s o f t e s t i n g environment  on t h e s e measurements. P l o t t i n g o f s t r e s s decay a g a i n s t "between 0.01  and  10  sec by Anderson and  p r o v i d e d s i g m o i d shaped c u r v e s i m p l y i n g r e l a x a t i o n . Mason ( 71  time  scales  Sjoberg ( 5 ) Maxwellian  ) showed, w i t h e x c e p t i o n o f v e r y  e a r l y p a r t s , l i n e a r r e l a t i o n s h i p s f o r l o g s t r e s s decay against  t i m e . Kubat ( 52,  53  ) postulated  r e l a t i o n s h i p f o r stress ( S ) against  a linear  l o g dS/dt a c c o r d i n g  to» =  b ( exp a S - 1 )  =  s t r e s s at time t ,  dS/dt  =  s t r e s s decay,  a, b  =  . dS/dt  / 13  where ? S  Ranee . ~ ( 107  constants.  ) ' " r e p o r t e d l ^ o n c i paper s t r e s s  f o l l o w i n g constant elongation sec and  1%  i n 10  r a t e s between 1%  sec. L i k e Kubat, he has  the p l o t o f S a g a i n s t such t h a t t  and  log t followed  relaxation i n 23  recorded  that  a straight line,  /  -  S  31  -  / 14 J  = x - y log t  where ? x,y  =  c o n s t a n t s , dependent on amount of p r e l o a d i n g .  R e c e n t l y , Kubat ( 54 ) d e s c r i b e d r e l a x a t i o n k i n e t i c s i n s o l i d m a t e r i a l s , i n c l u d i n g paper, as not complying w i t h the s i m p l e M a x w e l l i a n model. The  c u r v e s extend,  however,  o v e r a p p r e c i a b l y l o n g e r i n t e r v a l s t h a n would be c o n s i s t e n t w i t h e x p o n e n t i a l decay. I t has been n o t e d ( 44 ) t h a t P, i n f l e x i o n s l o p e o f s t r e s s , v e r s u s I n t f o r paper and t o t a l s t r e s s d i s s i p a t i o n are r e l a t e d b y i P  =  0.1  f 15  As  where j A S = stress dissipation. I n t h i s r e s p e c t , paper conforms to the g e n e r a l o f o t h e r t y p e s o f s o l i d s as i n t e r p r e t e d by { 10  behaviour /.  Shape o f the r e l a x a t i o n curve i s a f f e c t e d by the t e s t i n g environment and t e s t c o n d i t i o n s . I t has been n o t e d t h a t an i n c r e a s e s i n m o i s t u r e  content  i n s u b s t a n t i a l i n c r e a s e i n r e l a x a t i o n r a t e ( 71  results )•  Increase i n i n i t i a l s t r e s s , i n analogy w i t h promotion  /  - 32 -  by t e m p e r a t u r e , a l t e r e d c u r v e s toward s h o r t e r r e l a x a t i o n time ( 44 ) . By i n c r e a s i n g s t r a i n i n g time a t c o n s t a n t i n i t i a l s t r e s s , e f f e c t i v e w i d t h o f t h e <£^distribution was d e c r e a s e d ( 5^ )• I n a d d i t i o n , Craven ( 24 ) r e p o r t e d t h a t i n f l u e n c e o f d r i e d - i n s t r e s s e s waso s i g n i f i c a n t on t h e r e l a x a t i o n - c u r v e . The e f f e c t o f b e a t i n g on shape and p o s i t i o n o f t h e c u r v e s was r a t h e r l i m i t e d ( 44 ) .  2.4.4  Time dependent b e h a v i o u r o f f i b r e composites  plastic  Composite m a t e r i a l s a r e i m p o r t a n t  t o development  o f h i g h s t r e n g t h s t r u c t u r e s . P r o p e r t i e s o f composites v a r y w i t h d i f f e r e n t s u b s t r a t e and m a t r i x  ( binder )  systems used . I t has been found ( 108 ) t h a t f i b r o u s composite c h a r a c t e r i s t i c s a r e s t r o n g l y a f f e c t e d by f i b r e length, f i b r e concentration, f i b r e o r i e n t a t i o n , f i b r e d i a m e t e r , f i b r e shape and component b e h a v i o u r s , w e l l as c o m p o s i t i o n  as  o f s u b s t r a t e and m a t r i x .  Rauch e t a l . ( 108 ) e x p r e s s e d t h e b e l i e f t h a t f i b r e composite s t r e n g t h depends on«  -  33  -  i.  f i b r e s strength}  ii.  degree t o which a l l f i b r e s w i t h i n the m a t r i x are  S t u d i e s on wood p l a s t i c composites; ( WPC  and  stressed. ) indicate  t h a t u l t i m a t e p r o p e r t i e s seem t o be more stronglyi n f l u e n c e d by wood s p e c i e s t h a n by c h e m i c a l n a t u r e o f t h e i m p r e g n a t i n g monomer ( 131  ). P h y s i c a l p r o p e r t i e s o f  g r a f t e d papers a r e d e c i d e d by the n a t u r e o f f i b r e s , c h a r a c t e r i s t i c s o f monomers ( o r polymers ) and g r a f t i n g t e c h n i q u e s used. Little  work has been done on time dependent  p r o p e r t i e s o f wood f i b r e c o m p o s i t e s . Heyse e t a l . ( 39  )  o b s e r v e d t h a t when paper s u b s t r a t e s were formed w i t h s o f t , e x t e n s i b l e polymer m a t r i c e s ,  increases  occurred*  i n t e n s i l e s t r e n g t h and e l o n g a t i o n w i t h i n c r e a s i n g r a t f i o f s t r a i n . However, the p r o d u c t behaved l i k e paper i f s t i f f e r  copolymers and PVA  untreated  were a p p l i e d .  I n summary, t h e r e seems t o be a s c a r c i t y o f observations  on time-dependent b e h a v i o u r o f composite  m a t e r i a l s . Among t h e s e needs, i t seems e s p e c i a l l y c h a l l e n g i n g and u s e f u l t o d e s c r i b e s t r e s s r e s p o n s e s o f s u b s t r a t e and " m a t r i x composites ( PPC  ).  complexes as f o u n d i n paper p l a s t i c  -  3.0  3^  -  MATERIALS AND METHODS  M a t e r i a l s w i t h v e r y d i f f e r e n t p r o p e r t i e s were s e l e c t e d f o r s t u d y . These i n c l u d e d b l e a c h e d and  unbleached  k r a f t , as w e l l as b r i g h t e n e d and u n b r i g h t e n e d groundwood p u l p s , w i t h and w i t h o u t monomer and comonomer l o a d i n g . I n a d d i t i o n , a s s o c i a t e d polymer and copolymer f i l m s were p r e p a r e d and  3.1  tested.  Pulps  K r a f t and groundwood w e s t e r n hemlock ( Tsuga h e t e r o p h y l l a ( Raf. ) S a r g . ) p u l p s were o b t a i n e d from the P o w e l l R i v e r m i l l o f M a c M i l l a n B l o e d e l , L t d . The p u l p s were a t about 300?S m o i s t u r e c o n t e n t ( based on ovend r y „ w e i g h t . )1  as c o l l e c t e d . These were s t o r e d i n  p l a s t i c bags a t 2°C  i n a c o l d room p r i o r t o handsheet  preparation. Groundwood p u l p i s formed by  mechanical  s e p a r a t i o n o f f i b r e s from wood. The p r o d u c t r e p r e s e n t s a l m o s t t h e t o t a l wood f r a c t i o n s u b j e c t e d t o the s e p a r a t i o n a c t i o n and i s o b t a i n e d a t h i g h y i e l d ( a l m o s t 98$ ) i n c o n v e n t i o n a l o p e r a t i o n s ( 28 ). The p u l p i s composed m a i n l y o f f i b r e bundles and  fibre  fragments w i t h some whole i n d i v i d u a l f i b r e s . Groundwood  - 35  -  p u l p s a r e r i g i d due t o t h e i r h i g h l i g n i n c o n t e n t ,  whereby  t h e y do n o t c o l l a p s e on l o s s o f water and do n o t conform w e l l d u r i n g d r y i n g o r p r e s s i n g o f f i b r e webs.  Therefore,  webs p r e p a r e d f r o m groundwoods a r e b u l k y and show good o p a c i t y but low s t r e n g t h . Groundwood b r i g h t e n i n g , such as done w i t h one o f t h e p r e s e n t samples, is:a" n o n - l i g n i n a b s t r a c t i o n techniques.  The mechanisms o f groundwood b r i g h t e n i n g  may be c l a s s i f i e d e i t h e r as o x i d a t i o n o r r e d u c t i o n ( 49 ) . The b r i g h t e n i n g a c t i o n o f r e d u c i n g agents i s most p r o b a b l y r e l a t e d t o a d d i t i o n o f d i s s o c i a t i o n p r o d u c t s t o t h e c o l o r i n g m a t e r i a l s i n t h e wood, o r i t may be due t o changes o f these m a t e r i a l s . On the o t h e r hand, o x i d i z i n g t y p e b r i g h t e n i n g a g e n t s d i s s o c i a t e i n water by f o r m i n g H0~  ions. I t i s believed that t h i s  i o n s e l e c t i v e l y o x i d i z e s and/or h y d r o l y s e s  coloured  o r g a n i c compounds i n wood. Some c o n d e n s a t i o n may  occur,  but t h i s does tiSt a f f e c t a p p r e c i a b l y t h e b a s i c p h y s i c a l s t a t e o f the l i g n i n and c e l l u l o s e . K r a f t p u l p s , such as used i n t h i s s t u d y  differ  f r o m groundwood i n p r o c e s s i n g f i b r e s e p a r a t i o n . T h i s i s accomplished through expenditure  of chemical  energy  - 36 -  p r e c e d i n g a g i t a t i o n , which m a i n t a i n s i n d i v i d u a l s i b r e skeletons.  The v a r i o u s  pulping  steps involve d i s s o l v i n g  l i g n i n and a t t h e same time h e m i c e l l u l o s e s and  p a r t l y removed. H i g h h e m i e e l l u l o s e  a r e degraded  solubility i n  the a l k a l i c o o k i n g medium u s u a l l y l e a d s t o l o w e r hemieellulose  r e t e n t i o n ( 73 )» whereby s w e l l i n g  capacity  o f t h e f i b r e s i s f u r t h e r r e d u c e d . K r a f t p u l p s show good strength  p r o p e r t i e s , as t h e name i m p l i e s . Unbeaten k r a f t  p u l p i s known t o p r o v i d e mats w i t h open s t r u c t u r e and p o o r l y c o n f o r m i n g f i b r e s which do n o t c o l l a p s e on r e m o v a l o f water from the s h e e t , as w e l l as v i r t u a l absence o f f i b r i l l a t i o n  ( 17 ) . F a i l u r e o f papers made  f r o m unbeaten k r a f t f i b r e s i s due m a i n l y t o f i b r e p u l l - o u t o v e r a deep f r a c t u r e zone ( 17 ) .  3.2  Monomers and Comonomers  M e t h y l m e t h a e r y l a t e ( MMA  ) and  tetraethylene  g l y c o l d i m e t h a c r y l a t e ( TEGDMA ) were s e l e c t e d as monomers f o r t h e s t u d y . These were s u p p l i e d , r e s p e c t i v e l y , by Lortech  S e r v i c e s , L t d . , Burnaby, B r i t i s h Columbia and  Monomer- Polymer Lab, Borden Chemicals D i v . , Philadelphia.  Borden, I n c . ,  - 37 -  The i n h i b i t o r was removed from MMA by s h a k i n g approximately  250 ml o f monomer i n a s t o p p e r e d  separatory  f u n n e l w i t h 25 ml o f an aqueous s o l u t i o n c o n t a i n i n g 2g NaOH and l O g NaCl p e r 100 m l . The aqueous l a y e r was a l l o w e d , t o s e p a r a t e ^ and r u n o f f . The procedure was r e p e a t e d u n t i l t h e aqueous l a y e r remained c o l o u r l e s s . The monomer was t h e n washed w i t h s u c c e s s i v e 10 ml p o r t i o n s o f w a t e r u n t i l t h i s gave no a l k a l i n e r e a c t i o n . The o r g a n i c l a y e r was t h e n d i s t i l l e d t o remove w a t e r . S i n c e TEGDMA i s cured by gamma r a d i a t i o n w i t h dose a s l o w as 0.2 Mrad, no i n h i b i t o r removal was c o n s i d e r e d  necessary.  Some i n f o r m a t i o n on these two monomers and t h e i r uses followsrr;cc* „ MMA i s u s u a l l y prepared  from acetone,  hydrocyanide,  and o x i d a t i o n o f i s o b u t y l e n e w i t h n i t r i c a c i d ( 45, 114 ) . The monomer i s a c o l o u r l e s s l i q u i d w i t h  molecular  weight 100.11, b o i l i n g p o i n t 100.6 t o 101.1 °C, and w i t h i n f i n i t e s o l u b i l i t y i n a l c o h o l and e t h e r ( 14, 114 ) . MMA p o l y m e r i z a t i o n o c c u r s e a s i l y , and i s q u i t e s e n s i t i v e t o a v a r i e t y o f c a t a l y s t s and i n h i b i t o r s ( 46 ) . M o l e c u l a r oxygen i n h i b t s t h e p o l y m e r i z a t i o n . P o l y m e r i z a t i o n o f MMA i s e x o t h e r m i c t o t h e e x t e n t t h a t 13,000  calories  - 38 -  per gram-monomer u n i t a r e r e l e a s e d . The energy r e l e a s e d d u r i n g p o l y m e r i z a t i o n r a i s e s t h e system temperature, a c c e l e r a t i n g t h e r e a c t i o n somewhat d u r i n g e a r l y p o l y m e r i z a t i o n and f u r t h e r i n c r e a s i n g r a t e o f energy r e l e a s e ( 45 ) . Poly(MMA) i s s o l u b l e i n i t s own monomer, i n aromatic  and most c h l o r i n a t e d h y d r o c a r b o n s , e s t e r s ,  k e t o n e s , and t e t r a h y d r o f u r a n s o l v e n t s ( 114 ) . The s p e c i f i c g r a v i t y o f poly(MMA) i s 1.18 t o 1.19. The polymer i s temperature s e n s i t i v e , u n d e r g o i n g a second o r d e r t r a n s i t i o n when warmednto 60 °C t t h a t i s , t h e r e i s a t r a n s f o r m a t i o n a t t h a t temperature w i t h o u t an accompanying l a t e n t heat e f f e c t . Above t h i s  transition  t e m p e r a t u r e , t h e polymer becomes r u b b e r - l i k e . On f u r t h e r warming t o 138 t o 156 °C poly(MMA) m e l t s t o give a viscous l i q u i d . I t i s a b r i t t l e ,  transparent  polymer w i t h good s t r e n g t h p r o p e r t i e s , such as t e n s i l e 2 s t r e n g t h o f 2.1 k g / mm 2.4 t o 4.0 k g / mm  2  and c o m p r e s s i o n s t r e n g t h s o f  ( 45 ) .  Poly(MMA) shows a pronounced  delayed  p s e u d o - e l a s t i c o r memory e f f e c t . T h i s i s u s u a l l y something o f a d i s a d v a n t a g e because i t may l e a d t o d i m e n s i o n a l  -  39 -  i n s t a b i l i t y . I t a l s o i n d i c a t e s t h e presence o f l o c k e d - i n s t r e s s e s which may l e a d t o s u r f a c e c r a c k i n g . A network o f c r a c k s causes l o s s i n t r a n s p a r e n c y and s t r e n g t h . The c h e m i c a l b e h a v i o u r o f poly(MMA) i s t h a t o f a s t a b l e m a t e r i a l . Thus, i t has no c h l o r i n e , which might make i t s e n s i t i v e t o u l t r a v i o l e t exposure, and no u n s a t u r a t i o n which might make i t s e n s i t i v e o t h e r w i s e to a t m o s p h e r i c oxygen  ( 45 ) .  TEGDMA i s a h y d r o p h i l i c , d i v i n y l monomer w i t h b o i l i n g p o i n t g r e a t e r t h a n 160 °C and v i s c o s i t y o f 12 c.p.. I t i s i n s o l u b l e i n water, b u t h a s good s o l u b i l i t y i n MMA, S, VA, p o l y e s t e r s , a c r y l i c d i a l l y l maleate and a r o m a t i c s , b u t l i m i t e d  acid,  solubility  i n a l i p h a t i c hydrocarbons. TEGDMA hardens i n t o a g l a s s y s o l i d a t -55 t o -60 °C, which i s a l s o t h e l o w e s t temperature a t which p o l y m e r i z a t i o n c a n be  e f f e c t e d ( 117 )« The  TEGDMA monomer p o l y m e r i z e s much more r e a d i l y t h a n monomers w i t h o n l y one double bond. I t was f o u n d t o produce 18 5.4 x 10  f r e e r a d i c a l s p e r Mrep. I t s p e r o x i d e c a t a l i z e d  p o l y m e r i z a t i o n i s i n h i b i t e d by b o t h benzoquinone and oxygen  ( 119 ) . P o l y m e r i z a t i o n by h i g h energy r a d i a t i o n  - 40 -  was found t o be d i m e n s i o n a l l y s p e c i f i c and t h i s c a n be used t o form o b j e c t s o f p r e d e t e r m i n e d  shape ( 119 ) •  Eoly(TEGDMA) i s a t r a n s p a r e n t c r o s s l i n k e d  polymer.  A c c o r d i n g t o Micleo ( 76 ) , y i e l d s t r e s s i n compression o f t h e polymer i s 5.7 k g / mm 2  w i t h r u p t u r e s t r e s s o f 19  kg / mm 7 The s h e a r modulus o f poly(TEGDMA) i s d i f f e r e n t from t h a t o f  p o l y (MMA)' ^s„ s i n c e i t l e v e l s o f f w i t h >r  a h i g h modulus i n t h e r u b b e r y p l a t e a u ( 144 ) . P o l y m e r i z a t i o n o f two o r mareLcomanomersccan p r o v i d e a w i d e r v a r i e t y o f p h y s i c a l and c h e m i c a l p r o p e r t i e s t h a n when s i n g l e monomers a r e p o l y m e r i z e d , ! . As example, i n t r o d u c t i o n o f TEGDMA i n t o MMA s u p p r e s s e s t h e r e g i o n s o f r u b b e r y f l o w and l i q u i d f l o w , and i n c r e a s e s t h e " r u b b e r y p l a t e a u modulus ( 144 ) . Comonomer m i x t u r e s f o r i m p r e g n a t i n g paper handsheets and f o r m i n g t h i n f i l m s were p r e p a r e d by m i n i n g volumes o f MMA and TEGDMA t o giu>e t h r e e m i x t u r e s t o be d e s c r i b e d . These m i x t u r e s were chosen t o represen1?Gpartial;lyj t o f u l l y r : c r o s s l i n k e d polymer  systems.  - 41 -  3.3  F o r m a t i o n and Treatment o f Paper Handsheets  Handsheets were p r e p a r e d on a B r i t i s h  Sheet  Machine f o l l o w i n g t h e recommended p u l p d i s i n t e g r a t i o n and d i l u t i o n s t e p s o f TAPPI Standard T-205-M58 ( 138 ) . o The handsheets  were t h e n p r e s s e d t w i c e a t 0.325 k g / mm  w i t h s t a n d a r d p r e s s - p l a t e and d r y b l o t t e r s i n p i l e s o f seven handsheets.  P r e s s d w e l l t i m e s were 5 and 2 min,  r e s p e c t i v e l y . The handsheets  were t h e n c o n d i t i o n e d i n  p r e s s r i n g s f o r a minimum o f 2 days a t $0%'JR®M'L aftd 21?;C. The handsheets  were made up i n two c a t e g o r i e s .  Sheets w i t h t h e s t a n d a r d n o m i n a l 1.2 g m o i s t u r e f f r e e w e i g h t were employed t o p r e p a r e paper p l a s t i c  composites  ( PPC ) . I n o r d e r t o m a i n t a i n c o n s t a n t b a s i s w e i g h t s between paper handsheets  and PPC, h e a v i e r handsheets  were  p r e p a r e d by d r a i n i n g e x t r a amounts o f t h e p r e p a r e d s t o c k ( T a b l e I ). Paper p l a s t i c composites by p o l y m e r i z a t i o n o f impregnated  ( PPC ) were p r e p a r e d  (co)monomer  systems  i n s t a n d a r d paper handsheets. B l e a c h e d and unbleached k r a f t , as w e l l as b r i g h t e n e d and u n b r i g h t e n e d groundwood w e s t e r n hemlock p u l p s were t r e a t e d w i t h MMA  » TEGDMA  - 42 -  (co)monomer m i x t u r e s as 100 j 0, 95 « 5. 85 « 15» 60  : 40; and 0 : 100. I n p r a c t i c e , l a b o r a t o r y handsheets were c u t  i n t o r e c t a n g l e s 15.2 x 12.7 cm which were evacuated f o r 24 h r i n a d e s i c c a t o r a t 10 t o r r . The monomer m i x t u r e was then introduced funnel  through the d e s i c c a t o r l i d v i a a  ( F i g . 2 ) . Vacuum was m a i n t a i n e d  separatory  continuously  u n t i l no more b u b b l e s were a p p a r e n t on t h e paper s u r f a c e , i . e . , a p p r o x i m a t e l y 48 h r . S a t u r a t e d i n smooth aluminum f o i l  ( s h i n y s i d e inward ) and p r e s s e d  between g l a s s p l a t e s b e f o r e  3.4.  papers were wrapped  c u r i n g i n t h e Gammacell.  P r e p a r a t i o n o f T h i n Polymer F i l m s  F i l m s were p r e p a r e d i n t h e l a b o r a t o r y f r o m the f i v e  (co)monomer systems d e s c r i b e d  above. A f t e r some  p r a c t i c e , f i l m t h i c k n e s s was c o n t r o l l e d a t 10 - 1 m i l . T h i n f i l m s were made by f l o w i n g monomer f r o m a micro-pipette along three  between two spaced g l a s s p l a t e s  sealed  edges ( F i g . 3 ) . To e l i m i n a t e s t i c k i n g o f  cured f i l m s to the g l a s s p l a t e s , a l a y e r o f s i l i c o n e mold r e l e a s e agent was a p p l i e d t o both i n t e r n a l  surfaces.  - 43  -  The whole assembly was h e l d t o g e t h e r by s e v e r a l p i n c h clamps. Upon s e a l i n g o f the f o u r t h edge, t h e samples were c u r e d i n the  3.5  Gammacell.  Polymerization  P o l y m e r i z a t i o n o f s a t u r a t e d handsheets and pure (co)monomer systems was done i n a Gammacell 220 a t dose r a t e o f 0.762 Mrad/hr. A p p r o p r i a t e dose r e q u i r e m e n t f o r each i n d i v i d u a l t r e a t m e n t was determined f r o m exothermic temperature-time r e c o r d s run simultaneously on b u l k (co)monomer samples p l a c e d i n the Gammacell d u r i n g i r r a d i a t i o n . Sample i n i t i a l t e m p e r a t u r e s were around 3^ °C. Dose f o r each t r e a t m e n t i s g i v e n i n Table I I . M o i s t u r e c o n t e n t s ( M.C.  ), i n c l u d i n g paper  handsheets and PPC, were measured by d r y i n g samples i n an oven a t 95 t o 105 °C f o r 24 h r  and c a l c u l a t i n g  according t o i M.C.*  = 1  Sample a i r - d r y w e i g h t  ±  Sample oven-dry w e i g h t x 10©  {  16  J  - 44 -  Polymer l o a d i n g s i n PPC were c a l c u l a t e d according to f  17 / based on oven-dry weight ( o.d.  wt. ) o f m a t e r i a l s , which were o b t a i n e d by f  Loading, %  =  18 J\  PPG o l d . wt. - Paper o.d. wt. Paper o.d. wt. x 100  /  17  a i r - d r y w e i g h t x ( 1 + M.C.  )  where ; o.d. wt.t  \  3.6  =  f^J  Testing  S t r e s s r e l a x a t i o n t e s t s i n t e n s i o n were performed on PPC and c o r r e s p o n d i n g paper handsheets and polymer f i l m s o f c o m p a r a t i v e b a s i s w e i g h t . Ten specimens f o r each t r e a t m e n t were p r e p a r e d ; h a l f o f t h e s e were used f o r u l t i m a t e s t r e n g t h d e t e r m i n a t i o n and h a l f f o r stress relaxation tests. The 15.2 x 12.7 1.5  x 1.5  cm PPC s h e e t s were c u t i n t o  cm s t r i p s . These were used t o d e t e r m i n e  u l t i m a t e s t r e s s and r e l a x a t i o n b e h a v i o u r o f t h e  /  - 45 -  m a t e r i a l s . Paper and polymer s t r i p s were comparable i n b a s i s w e i g h t and d i m e n s i o n s t o t h e c o r r e s p o n d i n g PPC  ( Table I ) . A l l specimens were c o n d i t i o n e d i n a CTH room  a t 50% R.H. and 21 °C f o r two weeks p r i o r t o t e s t i n g . S i n c e s t r e s s r e l a x a t i o n c u r v e s may be a f f e c t e d by r a t e o f s t r a i n and t h e s t r e s s l e v e l s e t , u l t i m a t e t e n s i l e s t r e n g t h f o r each sample was determined p r i o r to r e l a x a t i o n t e s t s . Tests, i n c l u d i n g ultimate t e n s i l e s t r e n g t h and s t r e s s r e l a x a t i o n , were done on a f l o o r model I n s t r o n housed i n t h e CTH^ room. Headspeed was  5 cm/min, t h e maximum machine s e t t i n g . T h i s  provided  s i m u l a t e d s t e p ^ l o a d i n g L o f LspecimeiTs 'InCo£o§  t o 0.06 min.  U l t i m a t e s t r e n g t h s f o r v a r i o u s samples  t e s t e d under t h e s e conditions. 'axe .ilitfte'd ' i n UtiS&Mm !'SfI. S t r e s s r e l a x a t i o n t e s t s were c a r r i e d o u t by d e f o r m i n g samples t o a f i x e d s t r a i n and m e a s u r i n g s t r e s s required to maintain  t h i s s t r a i n as a f u n c t i o n o f t i m e .  An e x c i t a t i o n energy o f 50% o f t h e u l t i m a t e  tensile  s t r e n g t h was used. The s t r e s s - t i m e r e l a t i o n s h i p f o r a t e s t e d specimen was r e a d from t h e I n s t r o n  strip  chart r e c o r d e r . Data i n Table I I I represent  internal  - 46  -  energy d i s s i p a t i o n ( s t r e s s decay, o r s t r e s s r e t e n t i o n ) as the average o f f i v e r e p l i c a t i o n s f o r each sample o v e r p e r i o d s up t o 35 min.  observations e x c i t a t i o n was  r e a d between 0.04  s u b j e c t e d to r e g r e s s i o n viscoelastic!L  The  stress after  35 min  and  and  a n a l y s i s according to l i n e a r  behaviour; S  a  / 0.04 S  + b In t  where j s s  s t r e s s a t time t , following  a  intercept,  b  slope,  t Results  stress at t  0.04  Q  Q  ^  min  loading,  and  time.  of these r e g r e s s i o n  analyses  are  g i v e n i n Table IV.. Energy d i s s i p a t i o n ( 33 was  c a l c u l a t e d a c c o r d i n g to £  Duncan's New  20 J  ) f o r each and  subjected to  M u l t i p l e Range T e s t i n o r d e r to compare  energy f l o w b e h a v i o u r s between m a t e r i a l s to X )  as»  material  ( TablesvV  - 47 -  = 1 - S ( 3 5 ) / S(0.04>... { 20 J  AS where ; AS  = amount o f energy d i s s i p a t i o n i f stress at t , i s r e g a r d e d as 1. * QQl  ^(35) s  (0  =  04)  =  s  3  *  ^  r  e  s  r e s s  s  a  a - t  t  35 ^ » and m  n  °»°4 i » m  n  - 48 -  4.0  RESULTS  As d e t e r m i n e d by r e g r e s s i o n a n a l y s i s , r e l a x a t i o n curves f o r a l l three types o f m a t e r i a l s 7 *  were f o u n d t o f o l l o w s t r a i g h t l i n e s a c c o r d i n g t o R e g r e s s i o n c o e f f i c i e n t s ranged from 0 . 9 5 7 t o 0 . 9 9 7 f o r p a p e r s , 0 . 9 4 6 t o 0 . 9 9 7 f o r polymer f i l m s , and 0 . 9 7 6 t o 0 . 9 9 7 f o r PPC ( Table I V ) . T h i s means t h a t l i n e a r v i s c o e l a s t i c t h e o r y c a n be a p p l i e d t o e x p l a i n t h e  r e l a x a t i o n obehaviour o f t h e m a t e r i a l s i n v e s t i g a t e d o v e r o b s e r v a t i o n t i m e s up t o 3 5 m i n .  4.1  S t r e s s R e l a x a t i o n o f Papers  As d e s c r i b e d , v i s c o e l a s t i c b e h a v i o u r i s u s u a l l y c h a r a c t e r i z e d by a r e l a x a t i o n time ( :t'j ) which g i v e s r i s e t o a f a m i l y o f curves r e l a t i n g r e l a x a t i o n behaviour f o r d i f f e r e n t m a t e r i a l s . Curves w i t h l o w t v a l u e s d e s c r i b e a r e l a t i v e l y r a p i d decay and a r e i n d i c a t i v e o f f l u i d - l i k e b e h a v i o u r . Samples g i v i n g h i g h e r x  values  maintain r e l a t i v e l y high stress l e v e l s f o r longer periods, which i n d i c a t e s s o l i d - l i k e b e h a v i o u r . Among papers o f the p r e s e n t s t u d y , i t was f o u n d t h a t t h o s e p r e p a r e d from t h e bleached k r a f t pulp r e l a x e d s t r e s s f a s t e r than those  - 49 -  from t h e unbleached c o u n t e r p a r t . I n c o n t r a s t , no d i f f e r e n c e s were o b s e r v e d i n s t r e s s r e l a x a t i o n between paperscmade from b r i g h t e d e d and u n b r i g h t e n e d groundwood p u l p s . R e l a x a t i o n between papjers from k r a f t and groundwood were s i g n i f i c a n t l y d i f f e r e n t . Even  unbleached k r a f t papers  r e l a x e d f a s t e r t h a n t h o s e from e i t h e r groundwood p u l p ( T a b l e V, and F i g . 4 ) .  4.2  S t r e s s R e l a x a t i o n o f Polymer F i l m s  The s e r i e s demonstrated t h e e f f e c t o f c r o s s l i n k i n g on r e l a x a t i o n b e h a v i o u r . S i n c e TEGDMA s e r v e d as t h e c r o s s l i n k i n g agent, i t s g r a d u a l i n c r e a s e i n MMA l e d t o r e d u c i n g t h e r e l a x a t i o n amounts. Some unexpected r e s u l t s were o b t a i n e d . The polymer f i l m s a r r a n g e d i n o r d e r o f d e c r e a s i n g s t r e s s decay were M 9 5 , TEGDMA, M«5, M60, MMA ( F i g . 5 )• A g a i n d a t a were s u b j e c t e d t o Duncan's New M u l t i p l e T e s t , which r e v e a l e d t h a t t h e r e were no s i g n i f i c a n e e : i n energy d i s s i p a t i o n among t h e group M85, M60, and MMA ( Table V I ) .  -  4.3  50  -  S t r e s s R e l a x a t i o n o f Paper P l a s t i c ( PPC)  Composites  The p h y s i c a l p r o p e r t i e s o f composite m a t e r i a l s depended on t h e i r r e s p e c t i v e components. S t u d i e s on r e l a x a t i o n b e h a v i o u r o f composites showed t h a t treated with and MMA  comonomers i n r a t i o s o f 85 » 15.  handsheets 60 i 40,  were more e l a s t i c t h a n those from 95 « 5 and  TEGDMA, d e s p i t e o b v i o u s l y d i f f e r e n t p r o p e r t i e s o f the v a r i o u s p u l p s ( T a b l e s V I I «i t o V I I t i x , and P i g . 6 ) . T h i s meant t h a t d i s t r i b u t i o n o f the r e l a x a t i o n c u r v e s was more o r l e s s a f f e c t e d by p r o p e r t i e s o f the m a t r i c e s used ( compare P i g . 6 w i t h F i g . 5 ) . The e f f e c t o f p u l p i n g p r o c e s s on s t r e s s r e l a x a t i o n was n o t l o s t a f t e r f o r m a t i o n o f c o m p o s i t e s . A l t h o u g h d i s t r i b u t i o n o f r e l a x a t i o n c u r v e s was by the m a t r i c e s used, energy^  affected  d i s s i p a t i o n s . wjer&;  more dependent on c h a r a c t e r i s t i c s o f s u b s t r a t e s . I t was found t h a t papers from k r a f t p u l p s r e l a x e d f a s t e r t h a n t h o s e from groundwood p u l p s ( T a b l e s V I I I l i t o V I I I i v , and F i g s . 7-1  t o 7-5  ).  Comparing r e l a x a t i o n c u r v e s o f c e r t a i n  -  51  -  composites w i t h r e s p e c t t o t h e i r c o r r e s p o n d i n g components, t h e s t r e s s decays f o r k r a f t - p o l y m e r systems were commonly l e s s t h a n t h o s e f o r e i t h e r paper handsheets o r p l a s t i c f i l m s ( T a b l e s I X i i To I X : x , F i g s . 8-1 t o 8- 4 ) .  The amount o f r e l a x a t i o n f o r groundwoodpolymer systems, however, was s i m i l a r t o t h a t f o r those p a p e r s . Both papers and composites r e l a x e d r e l a t i v e l y more s l o w l y t h a n o b s e r v e d f o r t h e c o r r e s p o n d i n g pure ( c o p o l y m e r f i l m s ( T a b l e s X : i t o X i x , and F i g s . 9- 1 t o 9-4  ).  S t r e s s r e t e n t i o n between unbleached- and b l e a c h e d - k r a f t papers t r e a t e d w i t h e i t h e r MMA  ( linear  polymer ), o r TEGDMA ( c r o s s l i n k e d polymer ), o r t h e 95 » 5 comonomer m i x t u r e ( s l i g h t l y c r o s s l i n k e d polymer ) were n o t s i g n i f i c a n t l y d i f f e r e n t ( T a b l e s V i l l i i , Vllliii,  and V I I I i v ) . o n t h e o t h e r hand, b l e a c h e d  k r a f t papers r e l a x e d f a s t e r t h a n unbleached papers when t h e y were impregnated w i t h e i t h e r t h e 85 : 15 o r 60 : 40 comonomer m i x t u r e s ( Table VIII»iii, V l l l i i v , and F i g s . 7-3. 7-4 )• N e v e r t h e l e s s , amount o f r e l a x a t i o n a f t e r t r e a t m e n t was n o t s i g n i f i c a n t l y  - 52 -  d i f f e r e n t between b r i g h t e n e d and u n b r i g h t e n e d groundwoods ( T a b l e s V I I I : i t o VIII»iii and V I I I : v ), except f o r s u b s t r a t e s t r e a t e d w i t h t h e 95 » 5 comonomer ( Table V I I I l i i ) .  -  5.0  53  -  DISCUSSION  S t r e s s r e l a x a t i o n i s concerned w i t h the i n v e s t i g a t i o n o f d e f o r m a t i o n and f l o w b e h a v i o u r o f r m a t e r i a l s . I n t h i s regard, polymeric molecules,  including  p l a s t i c s and c e l l u l o s i c s , a r e s i m i l a r t o s i m p l e monomer m o l e c u l e s . The m o l e c u l e s a r e h e l d t o g e t h e r by c o v a l e n t , i o n i c and hydrogen bonds, as w e l l as d i p o l e i n t e r a c t i o n s . A p p l i c a t i o n of s t r e s s to these m a t e r i a l s may  cause d e f o r m a t i o n , s l i p p a g e , breakage o f m o l e c u l a r  bonds and p o s s i b l y changes i n m o l e c u l a r c o n f o r m a t i o n . Thereby, the r e l a x a t i o n b e h a v i o u r o f m a t e r i a l s can be e l u c i d a t e d i n terms o f m o l e c u l a r s t r u c t u r e s which p a r t i c i p a t e i n mechanisms r e s p o n s i b l e f o r the r e l a x a t i o n phenomenon.  3.1  S h o r t Term S t r e s s Decay  A t c o n s t a n t specimen d e f o r m a t i o n , s t r e s s decay w i t h i n t h e f i r s t m i l l i s e c o n d s a f t e r e x c i t a t i o n has been s t u d i e d by s e v e r a l workers  ( 46, 47, 74, 115,  149 ).  Watson e t a l . ( 149 ) measured s t r e s s r e l a x a t i o n on d i f f e r e n t polymers o v e r the approximate 0.01  t o 2.5  time range  sec and r e p o r t e d t h a t h a r d , s t i f f ,  b r i t t l e m a t e r i a l s were c h a r a c t e r i z e d by l i t t l e w i t h i n such time r a n g e .  of  and relaxation  S t r a i n s which t h e s e m a t e r i a l s  - 54 -  c o u l d s u s t a i n w i t h o u t f r a c t u r e , however, were s m a l l . S o f t e r , more d u c t i l e p l a s t i c s , on t h e o t h e r hand, showed f a s t e r r e l a x a t i o n r a t e s and were c o n s i d e r a b l y more e x t e n s i b l e than b r i t t l e  plastics.  Working w i t h c e l l u l o s e f i b r e s , M e r e d i t h ( 74 ) demonstrated t h a t t h e f a s t e r t h e e x t e n s i o n ,  the f a s t e r  the subsequent decay o f s t r e s s w i t h i n a f r a c t i o n o f a second a f t e r r e a c h i n g  a g i v e n e x c i t a t i o n . T h i s was  i n f e r r e d as t h e f a s t e r t h e i n i t i a l e x t e n s i o n , t h e l e s s time t h e r e was f o r i n t e r n a l r e o r g a n i z a t i o n o f the s t r u c t u r e , w i t h t h e r e s u l t t h a t more damage was done. P o s s i b l e damage o f the s t r u c t u r e s was a l s o o b s e r v e d w i t h polymer s u b s t a n c e s (.115 )• I n v e s t i g a t i o n o f some wood t i s s u e s and v i s c o s e p u l p s by K i r b a c h that conformational  ( 46, 47 ) l e d t o a p o s t u l a t i o n  changes o f h e m i c e l l u l o s e s and  g l u c o s e may c o n t r i b u t e t o h i g h s t r e s s decay i n e a r l y s t a g e s o f wood p r o d u c t : r h e o l o g " i c a l p r o c e s s e s .  As  r e g a r d s mechanism, e x t e r n a l energy a p p l i e d as s t r e s s m i g h t cause t h e a n h y d r o g l u c o s e "'"C^ c o n f o r m a t i o n t o 4 s w i t c h t o C-L c o n f o r m a t i o n , which i s c h a r a c t e r i z e d  -  55  -  by h i g h e r energy c o n t e n t and l o w e r  stability.  Removal o f e x t e r n a l f o r c e s o r p r o c e s s e s o f i n t e r n a l accomodation might r e s u l t i n r e v e r s i o n to the "^C^ conformation with release of stored  energy.  I n polymer t e s t i n g , Schmitz and Brown ( l i b ) h i g h l y recommend t h a t d a t a s h o u l d be t a k e n from  one  time decade a f t e r t h e i n i t i a l s t r a i n was a c h i e v e d f o r m e a n i n g f u l measurements. U n f o r t u n a t e l y , no e x p l a n a t i o n was  suggested. A sharp drop i n i n i t i a l s t r e s s was  w i t h i n the f i r s t 0.04 ( Table I I I  observed  min o f the p r e s e n t s t u d y  There i s ho s t r o n g t h e o r e t i c a l e v i d e n c e  s u p p o r t i n g such e x t e n s i v e s t r e s s l o s s o v e r s h o r t time. At t h i s stage i t i s a d v i s i b l e to f o l l o w Bergen's a d v i c e , i n which a n a l y s i s o f s t r e s s - l o g time c u r v e s i s s t a r t e d o n l y a f t e r a c e r t a i n p e r i o d o f r e l a x a t i o n ( l i b ). Consequently, e a r l y p a r t s o f r e l a x a t i o n c u r v e s are l e f t a l o n e u n t i l e v i d e n c e i s o b t a i n e d as t o t h e i r  further  significance.  -  5.2  56  -  S t r e s s R e l a x a t i o n o f Papers  Paper r h e o l o g i c a l p r o p e r t i e s r e l a t e d i r e c t l y to p r e s s i n g , m a c h i n i n g and p r i n t i n g p r o p e r t i e s . I t i s n o t e d t h a t paper r h e o l o g i c a l b e h a v i o u r has been the s u b j e c t o f i n v e s t i g a t i o n s s i n c e the 1920's. I n e a r l y , days, the mechanism o f s t r e s s / e l o n g a t i o n was  explained  by s i m p l e models o f s p r i n g - d a s h p o t c o m b i n a t i o n s (171, 132-134 ), and l a t e r by hydrogen bonding t h e o r y ( 8592, 106, 107, 135.  1 3 6 ? ) . The most a c c e p t a b l e  i n t e r p r e t a t i o n s o f paper m e c h a n i c a l p r o p e r t i e s i.  considers  sheet s t r u c t u r e parameters, i n c l u d i n g such f a c t o r s as f i b r e l e n g t h d i s t r b u t i o n , n a t u r e and e x t e n t o f f i b r e t o f i b r e bonding, and o t h e r d i s t r i b u t i o n f u n c t i o n s ;  ii.  i n s t r i n s i c strength of f i b r e to f i b r e bonds; and  iii.  t e n s i l e strength of i n d i v i d u a l f i b r e s ( 147 ).  B e s i d e s t h e s e s t r u c t u r a l parameters, such o t h e r f e a t u r e s as d r y i n g c o n d i t i o n s , t e s t environment  - 57 -  ( t e m p e r a t u r e , h u m i d i t y , s t r e s s o r s t r a i n l e v e l s ), i n f l u e n c e o f l i g n i n and p u l p i n g  p r o c e s s have been  studied.  5.2.1  E f f e c t o f l i g n i n on s t r e s s r e l a x a t i o n o f k r a f t papers  L i g n i n i s c h a r a c t e r i s t i c a l l y a threed i m e n s i o n a l s u b s t a n c e . The p a r t i c i p a t i o n o f l i g n i n i n r e l a x a t i o n o f wood s u b s t a n c e s d i f f e r s from c e l l u l o s e . The  highly crosslinked l i g n i n structure could  restrict  c e l l u l o s e c h a i n movement, t h e r e b y d e c r e a s i n g energy d i s s i p a t i o n . S t u d i e s on d e l i g n i f i e d wood t i s s u e s ( 29 ) r e v e a l e d  that the f u n c t i o n of l i g n i n i n r e l a x a t i o n  was t o r e d u c e c a r b o h y d r a t e m o b i l i t y .  Likewise,  magnitude and r a t e o f s t r e s s decrement  increased  r a p i d l y a s specimen l i g n i n c o n t e n t d e c r e a s e d ( 22, 33 ) . S i n c e l i ' g n i n a f f e c t s r a t e o f wood s t r e s s r e l a x a t i o n , the d i f f e r e n t r e l a x a t i o n behaviours between unbleached and b l e a c h e d k r a f t papers o b s e r v e d i n t h e p r e s e n t s t u d y may be a t t r i b u t e d l i k e w i s e to v a r i o u s  amounts o f l i g n i n i n t h e m a t e r i a l s .  -  58  -  The l a r g e r q u a n t i t y o f l i g n i n i n unbleached  kraft  papers may have l e d t o energy s t o r a g e , d e l a y e d  energy  t r a n s m i s s i o n and, t h e r e b y , t h e h i g h e r s t r e s s r e t e n t i o n observed  5.2.2  ( Table V, F i g . 4 ) .  S t r e s s r e l a x a t i o n o f groundwood  papers  R e l a x a t i o n o f groundwood papers was found t o d i f f e r from t h a t o f k r a f t p a p e r s . Not o n l y were v a l u e s much l o w e r , b u t no s i g n i f i c a n t d i f f e r e n c e s i n energy d i s s i p a t i o n were found between b r i g h t e n e d and u n b r i g h t e n e d groundwoods. The r e s u l t s can be a t t r i b u t e d to t h e i r s i m i l a r c h e m i c a l s t r u c t u r e s . S i n c e t h e r e i s no r e a l l o s s o f s u b s t a n c e s d u r i n g t h e t y p i c a l groundwood b r i g h t e n i n g p r o c e s s ( 49 ), t h e c h e m i c a l components between b r i g h t e n e d and u n b r i g h t e n e d p u l p s a r e a l m o s t i d e n t i c a l . T h e r e f o r e , t h e y a r e expected t o a f f e c t t h e amount o f energy d i s s i p a t i o n i n a s i m i l a r manner. The p r e s e n t r e s u l t s a r e c o n s i s t e n t w i t h t h e s e s p e c u l a t i o n s ( Table V, F i g . 4 ) .  -  5.2.3  59  -  D i f f e r e n c e s i n s t r e s s r e l a x a t i o n between k r a f t and groundwood papers  The r h e o l o g i c a l b e h v i o u r o f d i f f e r e n t  papers  i n response t o s t r e s s e x c i t a t i o n i s a t t r i b u t e d t o v a r i a t i o n i n f i b r e n a t u r e and paper s t r u c t u r e . R e s u l t s from p r e s e n t s t u d y r e v e a l r e l a t i v e l y l e s s amount o f  the  energy  d i s s i p a t i o n f o r groundwoods as opposed t o t h e k r a f t papers. This c o n f l i c t s with p r e v i o u s l y e s t a b l i s h e d p a t t e r n s by J a c k s o n and Ekstrom  ( 42 ), as w e l l as  Seborg and Simmonds ( 122 ). They have shown t h a t groundwood p u l p mats have. l o w e r «.recovery value's f r o m %  compressive  d e f o r m a t i o n t h a n s u l p h a t e and  sulphite  p u l p s . T h i s was a t t r i b u t e d t o a l a r g e r percentage f i n e s i n groundwood p u l p s ( 122  ). The  of  relative  e x p a n s i o n r e c o v e r y a f t e r p r e s s u r e removal was  used  to c h a r a c e r i z e these m a t e r i a l s . For a p e r f e c t l y e l a s t i c substance the e x p a n s i o n would be e q u a l t o 100%,  and f o r a p e r f e c t l y p l a s t i c m a t e r i a l i t would-be  e q u a l to u%. Paper c o m p r e s s i b i l i t y was v a r i e d by unbleached  adding  s u l p h i t e p u l p t o a b a s i c groundwood s t o c k .  Sheet e x p a n s i o n i n c r e a s e d as c h e m i c a l p u l p c o n t e n t  was  - 60 -  i n c r e a s e d . Up t o 60% a d d i t i o n o f c h e m i c a l p u l p , however, had l i t t l e e f f e c t o n r e l a t i v e  expansion.  The p r e s e n t r e s u l t s , on t h e o t h e r hand, seem to agree w i t h work done by Drummond and Parsons ( 2b ) . They r e p o r t e d t h a t b u l k i n e s s gave a c u s h i o n i n g  effect  i n groundwood s h e e t s , s i n c e t h e f i b r e s tended t o r e g a i n t h e i r shape f o l l o w i n g r e l e a s e a f t e r compression. T h i s c u s h i o n e f f e c t may c o n t r i b u t e t o e l a s t i c p r o p e r t i e s o f paper. B e s i d e s , f i b r e s t i f f n e s s may a l s o be used to e x p l a i n t h e r e s u l t s . S t i f f n e s s i s d e f i n e d as t h e product  o f t h e modulus o f e l a s t i c i t y o f t h e f i b r e  m a t e r i a l and t h e moment o f i n e r t i a o f t h e f i b r e c r o s s s e c t i o n ( 116 ) . S t i f f n e s s i s , t h e r e b y ,  influenced  by f i b r e w a l l m a t e r i a l s and t h e d i m e n s 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 . Paper s t i f f n e s s i s r e l a t e d t o these i n d i v i d u a l f i b r e p r o p e r t i e s . Papers made f r o m p u l p s high!  i n h e m i e e l l u l o s e c o n t e n t a r e s t i f f e r t h a n papers  made f r o m p u l p s l o w i n h e m i e e l l u l o s e c o n t e n t . made from s h o r t - f i b r e d p u l p s , e.g., straw,  Papers  chestnut  and groundwood a r e g e n e r a l l y s t i f f e r t h a n papers made  - 61 -  from l o n g e r - f i b r e d p u l p s , e.g.,  fiouglas-fir.  Groundwood  produces v e r y h i g h s t i f f n e s s p a p e r s , but r e s u l t s i n t h i c k e r s h e e t s a t t h e same b a s i s weight t h a n s h e e t s p r e p a r e d from o t h e r p u l p s * ( 19 ) The s t i f f n e s s o f f i b r e s a f f e c t s m e c h a n i c a l p r o p e r t i e s o f t h e f i b r e network. Shear modulus o f f i b r e networks i s d i r e c t l y r e l a t e d t o f i b r e ( 75  stiffness  ).  S i n c e groundwood f i b r e i s more s t i f f t h a n k r a f t p u l p f i b r e , the r e l a t i v e l y l e s s amount o f s t r e s s d i s s i pation!©;;: f o r groundwoods seems r e a s o n a b l e ( Table V, F i g . 4 ).  5.3  S t r e s s R e l a x a t i o n o f Polymers  Polymer s t r e s s r e l a x a t i o n p r o c e s s e s can be t h o u g h t o f i n terms o f t h e r m a l m o t i o n a f f e c t i n g polymer m o l e c u l e o r i e n t a t i o n . I n t h i s , m e c h a n i c a l s t r e s s a p p l i e d t o a polymer i n c r e a s e s f r e e energy o f the system. I f the sample i s k e p t i n deformed  state,  -  62  -  s t r e s s r e l a x a t i o n t a k e s p l a c e as r e s u l t o f t h e r m a l motion o f t h e c h a i n s , m o l e c u l a r d e f o r m a t i o n s a r e o b l i t e r a t e d , and excess f r e e energy i s d i s s i p a t e d a s h e a t . D e t a i l s o f such a s t r e s s r e l a x a t i o n p r o c e s s u s u a l l y depend upon t h e m u l t i p l i c i t y o f ways i n which polymer m o l e c u l e s can r e g a i n t h e i r most s t a b l e through thermal motion  5.3.1  conformations  ( 74 ) .  The c o n t r i b u t i o n o f c r o s s l i n k i n g t o polymer rheological properties  Polymer m o l e c u l e s c o n s i s t o f many u n i t s c h e m i c a l l y l i n k e d t o g e t h e r . Some atoms i n these u n i t s form t h e polymer c h a i n backbone w h i l e o t h e r s a r e c h e m i c a l s u b s t i t u e n t s a t t a c h e d t o t h e backbone. I f backbone atoms form a l i n e a r sequence, t h e polymer i s c a l l e d l i n e a r . I n some cases t h e c h a i n atoms which a r e s e p a r a t e d by m a c r o s c o p i c d i s t a n c e s may be l i n k e d t h r o u g h backbone atoms i n t h e mode o f a t h r e e - d i m e n s i o n a l network. These a r e c a l l e d c r o s s l i n k e d polymers. As r e s u l t o f c r o s s l i n k i n g many c h a i n s become, i n f a c t , one c h a i n . Although c h a i n fragmental motion i s p o s s i b l e , the  - 63 -  s l i d i n g o f one c h a i n p a s t a n o t h e r and l o o s e n i n g  of the  s t r u c t u r e i s no l o n g e r p o s s i b l e . Polymer s t r e s s r e l a x a t i o n t e s t s i n t h e p r e s e n t study involved  t h e l i n e a r poly(MMA), as w e l l as a s e r i e s  o f polymer p r o d u c t s p r e p a r e d t o i n c l u d e v a r y i n g o f c r o s s l i n k i n g . I t was a n t i c i p a t e d t h a t  degrees  introduction  o f p r i m a r y - v a l e n c e c r o s s l i n k s would i n v a r i a b l y  increase  c r e e p r e s i s t a n c e and d e c r e a s e r e l a x a t i o n r a t e ( 3, 141, 14-2,  145 ) . I n t r o d u c t i o n o f s a m i l amounts o f TEGDMA  s h o u l d s u p p r e s s r u b b e r y and l i q u i d f l o w r e g i o n s and enhance t h e g l a s s y ,  t r a n s i t i o n and r u b b e r  regions.  t h e amounts o f TEGDMA i n poly(MMA)  Increasing  should increase  plateau  t h e time a t o n s e t o f t h e t r a n s i t i o n  r e g i o n and a l s o i n c r e a s e  t h e r u b b e r y p l a t e a u modulus  ( 144 ) . However, somewhat  o p p o s i t e r e s u l t s were o b t a i n e d  !C Table V I , F i g . 5 ) . I t was f o u n d t h a t t h e amounts o f s t r e s s r e t e n t i o n "did n o t s y s t e m a t i c a l l y d e c r e a s e the p l a n n e d i n c r e a s e  with  i n c r o s s l i n k i n g agent ( TEGDMA ) { c  p o s s i b l y t h e s e r e s u l t s may be i n t e r p r e t e d as f o l l o w s . O b s e r v a t i o n time was n o t l o n g enough. A t room t e m p e r a t u r e poly(MMA) i s f a r below i t s T  o (110 C ) .  - 64 -  As a m a t t e r o f f a c t , c r o s s l i n k i n g o f MMA w i t h TEGDMA increases T  o f t h e b a s i c polymer. Low degree o f  c r o s s l i n k i n g i s expected t o cause a s m a l l s h i f t i n T , hut a t h i g h c r o s s l i n k i n g degrees t h e s h i f t . i s l a r g e . I t i s n o t e d t h a t "below T  very  these polymers a r e  c h a r a c t e r i z e d as hard, b r i t t l e s o l i d s , w i t h s t r u c t u r e s s i m i l a r to supercooled  l i q u i d s i n which t h e r m a l m o t i o n  i s e x c e e d i n g l y slow. S i n c e c r o s s l i n k i n g has no major e f f e c t on time dependent b e h a v i o u r temperatures; w e l l below t h e i r T  o f polymers a t  r e g i o n o r over very  s h o r t o b s e r v a t i o n p e r i o d s ( 80 ), t h e m o t i o n o f molecular  segments below T  i s r e s t r i c t e d p r i m a r i l y to  V i b r a t i o n s w i t h o u t f l o w phenomena. Thus, time dependent behaviours  among t h e s e polymers any n o t be c l e a r l y  separated. The polymer s t r u c t u r e s may have been damaged d u r i n g p r e p a r a t o r y s t e p l o a d i n g . Rogovian and S l o n i m s k i i ( 115 ) conducted s t r e s s r e l a x a t i o n e x p e r i m e n t s w i t h p o l y e t h l e n e t e r e p h t h a l a t e ( PETP ) and r e p o r t e d  that  s t r e c h i n g i n t h e g l a s s y r e g i o n was accompanied by f o r m a t i o n o f t r a n s v e r s e f i s s u r e s . These f i s s u r e s  arose  i n specimens s u b j e c t e d t o e l a s t i c d e f o r m a t i o n ,  and  -  65 -  began a t l o w e x t e n s i o n l e v e l s o f 0 . 5 $ . The growth o f f i s s u r e s l e d t o g r e a t e r s t r e s s l o s s . When r a t e o f e x t e n s i o n was  l o w t h e s t r e s s produced was a l s o s m a l l ; c o n s e q u e n t l y ,  f i s s u r e s were f o u n d t o be s m a l l e r and t h e i r e f f e c t was less  significant. P o s s i b l e damage t o polymer s t r u c t u r e s m i g h t  be s u s p e c t e d i n t h i s s t u d y , s i n c e specimens were deformed a t c a t e s a s h i g h as 5 cm/ m i n w h i l e below t h e i r T temperatures. D e g r a d a t i o n m i g h t have been i n d u c e d by gamma r a d i a t i o n . P r e c i s e c h e m i c a l r e a c t i o n s which l e a d t o degradation  under i r r a d i a t i o n have been s u b j e c t t o much  d i s c u s s i o n . Indeed, i t c o u l d be argued t h a t r a d i a t i o n i n d u c e d i o n i z a t i o n and e x c i t a t i o n produce r a d i c a l s which a r e r e l a t i v e l y s t a b l e and o n l y cause main c h a i n s c i s s i o n . I t i s n o t e d , however, t h a t t h e change i n m e c h a n i c a l p r o p e r t i e s o f an i r r a d i a t e d poly(MMA) sample m i g h t w e l l depend on t h e time l a p s e between i r r a d i a t i o n and  t e s t i n g ( 20, 21 ) . I n a d d i t i o n t o main c h a i n  s c i s s i o n , i r r a d i a t e d poiy(MMA) may a l s o show changes i n m e c h a n i c a l p r o p e r t i e s due t o t r a p p e d g a s e s . I t i s known t h a t t h e s i d e g r o u p C00CH., decomposes and,  -  66 -  t o g e t h e r w i t h hydrogen from;, another: p a r t e o f may g i v e r i s e t o G, CO, C 0 , CH^ 2  or H  2  the?^hain  t  ( 20, 21 ) .  When i r r a d i a t e d poly(MMA) i s a l l o w e d tot s t a n d f o r l o n g p e r i o d s o f time f i s s u r e s can be o b s e r v e d w i t h i n t h e b u l k o f t h e specimen. The r h e o l o g i c a l p r o p e r t i e s o f p l a s t i c  film  d i f f e r e d f r o m those o f p a p e r s . The former showed more f l u i d - l i k e behaviour.  The 95 J 5 comonomer and TEGDMA  r e l a x e d a l m o s t t w i c e a s much as groundwood ( Tables V, V I , F i g s . 4 , 5 ) . These may r e s u l t from d i f f e r e n t molecular  s t r u c t u r e , cidegisees o f c r y s t a l l i n i t y and s t r u c t u r a l  v a r i a t i o n s between the  5.4  twocmaterials.  R h e o l o g i c a l P r o p e r t i e s o f Composite M a t e r i a l s  Composites a r e c o m b i n a t i o n s n o f  materials  d i f f e r i n g i n form on a m a c r o - s c a l e . C o n s i t u e n t s more or l e s s r e t a i n i n d i v i d u a l i d e n t i t i e s i n composites. The  c o n s i t u e n t s o f a composite may assume v a r i o u s  f o r m s . I n some, d i s c r e t e u n i t s o f t h e s u b s t r a t e a r e embeded i n and bonded t o g e t h e r by a c o n t i n u o u s  matrix,  w h i l e i n o t h e r s , t h e bonding phase may be d i s c o n t i n u o u s  - 67 -  o r i t may be absent a l t o g e t h e r i f t h e d i s c r e t u n i t s a r e bonded o r i n t e r l o c k e d d i r e c t l y . Composite  properties  are s t r o n g l y i n f l u e n c e d by m a t e r i a l s o f which t h e y a r e composed, d i s t r i b u t i o n o f t h e s e c o n s t i t u e n t s and i n t e r a c t i o n s among them. P r o p e r t i e s may be t h e sumcof c o n s t i t u e n t p r o p e r t i e s , o r t h e c o n s t i t u e n t s may i n t e r a c t i n such ways as t o p r o v i d e e s s e n t i a l l y new p r o p e r t i e s i n t h e composite which were n o t p r e s e n t i n i n d i v i d u a l constituents. The v i s c o e l a s t i c b e h a v i o u r o f composites i s a l s o a f f e c t e d by t h e c o n s t i t u e n t s .  Time-temperature  s u p e r p o s i t i o n p r i n c i p l e s , and t h u s t h e WLF e q u a t i o n , have been a p p l i e d t o i n v e s t i g a t e some time-dependent p r o p e r t i e s o f composites ( 27, 57, 5», 70, 104 ) .  5.4.1  I n f l u e n c e o f m a t r i x on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n  S t r e s s r e l a x a t i o n m o d u l i o f composites a r e c h a r a c t e r i z e d by t h e i r c o n s t i t u e n t s . I n p r a c t i c e t h e m o d u l i a r e d e r i v e d by e x t r a p o l a t i o n s i n which t h e s h i f t f a c t o r A ( t ) i s obtained f o r d i f f e r e n t temperatures.  - 6b -  T h i s modulus can he superimposed "by a h o r i z o n t a l t r a n s l a t i o n o f temperature sequence r e l a t i v e t o a base r e f e r e n c e t e m p e r a t u r e . R e s u l t s i n t h e s o - c a l l e d master curve, a t a g i v e n temperature, cover a s e r i e s o f time decades. I n a l m o s t e v e r y system i n v e s t i g a t e d t h e b i n d e r ( m a t r i x ) has been f o u n d t o c o n t r o l shape o f t h e A ( t ) versus  temperature c u r v e . As examples, an i n v e s t i g a t i o n  by P i s t e r and Monsmith ( 104 ) showed e x c e l l e n t agreement between A ( t ) f o r pure a s p h a l t and t h a t f o r b i t u m i n o u s c o n c r e t e , when n o r m a l i z e d c o n s t a n t r a t e s o f compression d a t a were s h i f t e d . Very l i t t l e d i f f e r e n c e was f o u n d ' ( 27 ) i n t h e c o n s t a n t v a l u e s f o r t h e WLF e q u a t i o n a p p l i e d t o u n f i l l e d and f i l l e d p o l y - i s o b u t y l e n e  systems,  when dynamic shear s t o r a g e and l o s s c o m p l i a n c e s were s h i f t e d . S i m i l a r r e s u l t s were a l s o r e p o r t e d f o r p r o p e l l a n t systems by Lander, and CSmith ( 58 ) "and Mar t i n (' 70  f.  I n t h e p r e s e n t s t u d y , composite s t r e s s r e l a x a t i o n c u r v e s were a f f e c t e d by t h e v a r i o u s m a t r i x systems employed. A gradual increase of c r o s s l i n k i n g density d i d not s y s t e m a t i c a l l y decrease the siopesoof r e l a x a t i o n curves f o r t r e a t e d p a p e r s . Slo/pes were, howeverr,i s i m i l a r t o  -  69 -  t h o s e d e s c r i b e d f o r pure polymers, i . e . , pure TEGDMA and 95 » 5 coraonomer f i l m s , as w e l l as c o r r e s p o n d i n g  composites  showing s m a l l e r s t r e s s r e t e n t i o n t h a n o t h e r samples ( T a b l e s V I , V I I s i t o V I I s i x , F i g s . 5. 6 ) . These o b s e r v a t i o n s  s u p p o r t r e s u l t s from  Heyse e t a l . ( 39 ), who p r o c l a i m e d  that matrix  systems  a f f e c t e d time dependent b e h a v i o u r o f lajfcex t r e a t e d p a p e r s . Papers t r e a t e d w i t h s o f t e x t e n s i b l e polymers were f o u n d to g i v e i n c r e a s e d t e n s i l e s t r e n g t h and e l o n g a t i o n  with  i n c r e a s i n g r a t e s o f s t r a i n , ©n t h e o t h e r hand, papers t r e a t e d w i t h s t i f f e r polymers d i s p l a y e d a b e h a v i o u r s i m i l a r to untreated  papers. This  meant t h a t t e n s i l e  s t r e n g t h and modulus f o r s t i f f e r polymer t r e a t e d paper were somewhat h i g h e r and t h a t e l o n g a t i o n was about t h e same f o r h i g h r a t e s o f s t r a i n i n g . The  p o s s i b l e e f f e c t o f polymer o n composite  s t r e s s r e l a x a t i o n may be s i m i l a r t o t h a t employed t o e x p l a i n l t h e t e n s i l e s t r e n g t h increment f o r g r a f t e d c e l l u l o s i c s u b s t r a t e s . When f i b r e by g r a f t  ( paper ) i s m o d i f i e d  p o l y m e r i z a t i o n the observed increase i n  s t r e n g t h r e s u l t s from pendant g r a f t c h a i n i n domains t h a t a c t a s secondary v a l e n c e  aggregations c r o s s l i n k s ( 131 ) .  -  70  -  A d d i t i o n a l bonds produced by p o l y m e r i z a t i o n r e s t r i c t f i b r e m o t i o n i n the composite. B e s i d e s , the  increased  f a c i l i t y f o r energy t r a n s f e r from f i b r e to f i b r e v a r i o u s polymer m a t r i c e s may  by  a f f e c t ; t h e composite energy  dissipation.  5.4.2  E f f e c t o f s u b s t r a t e on paper p l a s t i c composite (PPC) s t r e s s r e l a x a t i o n  The  e f f e c t o f s u b s t r a t e on composite  v i s c o e l a s t i c p r o p e r t i e s depends on p e r c e n t a g e , shape, s i z e and d i s t r i b u t i o n o f s u b s t r a t e p a r t i c l e s , and n a t u r e o f bonding between the s u b s t r a t e and The  matrix.  e f f e c t o f s u b s t r a t e c o n t e n t has been  d i s c u s s e d i n s e v e r a l p u b l i c a t i o n s . L a n d e l and ( 57.  the  coworker  58 ) r e p o r t e d t h a t i n c r e a s e i n s u b s t r a t e  content  l e d to d e c r e a s e d dynamic s h e a r c o m p l i a n c e s f o r poly-isobutylene-binder-glass-bead  systems.  Increased  shear m o d u l i were f o u n d by D a v i s and K r o k o s k y ( 27 f o r asphalt-aggregate  )  systems w i t h i n c r e a s i n g s u b s t r a t e  contents. D e s p i t e m a t r i x systems used i n the  present  - 71  -  s t u d y , groundwood paper-polymer-composites  always  d i s p l a y e d l o w e r r e l a x a t i o n t h a n f o u n d f o r k r a f t paperpolymer- c o m p o s i t e s . T h i s c o n f i r m s t h a t s t r e n g t h p r o p e r t i e s o f c o m p o s i t e s depend m a i n l y upon c h a r a c t e r i s t i c s o f t h e s u b s t r a t e ( 108 ) . T h i s a l s o p r o v i d e s e v i d e n c e s u p p o r t i n g the p o i n t t h a t WPC s t r e n g t h p r o p e r t i e s a r e governed by c h a r a c t e r i s t i c s o f t h e wood used ( 131 ) . F u r t h e r , t h e p r e s e n t d a t a a l s o s u p p o r t Heyse e t a l . t h a t t h e time dependent  ( 39 ) i n  b e h a v i o u r o f papers t r e a t e d  w i t h s t i f f e r polymers i s s i m i l a r t o t h a t o f u n t r e a t e d paper. I n summary, PPC r e l a x a t i o n b e h a v i o u r was a f f e c t e d is'ubgrdi'nat(glyGcc' by t h e polymer employed,  b u t governed,-mainiyy  ( m a t r i x ) system by f i b r e  ( substrate )  characteristics.  5.4.3  E f f e c t o f paper c o p o l y m e r i z a t i o n w i t h (co)monomers on i n i t i a l m a t e r i a l s t r e s s r e l a x a t i o n  C o p o l y m e r i z a t i o n o f paper w i t h  (co)monomers  may have i n c r e a s e d secondary v a l e n c e c r o s s l i n k s among  - 72 -  the f i b r e s ( 131 ) . As a r e s u l t o f c r o s s l i n k i n g , t h e s l i d i n g o f f i b r e s p a s t one a n o t h e r and l o o s e n i n g o f entanglements among f i b r e s may be r e s t r i c t e d .  This  r e s u l t s i n a material with d i f f e r e n t rate of stress decay. C o p o l y m e r i z a t i o n o f k r a f t papers w i t h (co)monomers may have g i v e n r i s e t o s t r o n g bonds between f i b r e and polymer c h a i n s , l e a d i n g t o t h e o b s e r v a t i o n t h a t composites r e l a x i n t e r n a l s t r e s s s l o w e r t h a n e i t h e r c o n s t i t u e n t ( 51 ) . On t h e o t h e r hand, some t r e a t e d groundwood papers r e l a x e d more r a p i d l y t h a n t h e u n t r e a t e d p a p e r s . The tendency f o r c r o s s l i n k i n g between f i b r e and polymer c h a i n s may be governed b y f f i t o x e p r o p e r t i e s , especially lignin  5.4.4  content.  E f f e c t o f l i g n i n on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n  As mentioned e a r l i e r , PPC s t r e s s r e l a x a t i o n depended on t h e c o n s t i t u e n t s used. T h i s p r o p e r t y was a l s o a f f e c t e d by bonding o f s u b s t r a t e t o m a t r i x . S u b s t r a t e s which d e v e l o p good a d h e s i o n w i t h t h e  -  73  -  binder ( matrix ) could r a i s e m o d u l i and  l o w e r c r e e p and  shear-and-stress-relaxation  dynamic c o m p l i a n c e . However,  i n i t i a t i o n o f d e w e t t i n g between components may t h i s b e h a v i o u r ( 51 may  PPC  r e l a t e to e f f e c t i v e n e s s  p u l p s and of  ).The  reverse  s t r e s s r e l a x a t i o n behaviour  o f bonding between the  polymer c h a i n s and  r e f e r to g r a f t  various  copolymerization  (co)monomers t o p a p e r s . As n o t e d , g r a f t i n g e f f i c i e n c y depends on  c h a r a c t e r i s t i c s of m a t e r i a l s  used, as w e l l as  t e c h n i q u e . I t i s shown i n e a r l i e r r e p o r t s of  grafting  that  presence  l i g n i n i n wood p u l p s d e l e t e r i o u s l y a f f e c t e d  o f most monomers ( 103 Bergem e t a l . ( 10  ). By u s i n g Ce - as an  grafting  initiator,  ) indicated that g r a f t i n g y i e l d s  v a r i e d a c c o r d i n g to p u l p r e s i d u a l l i g n i n c o n t e n t . I t e s t a b l i s h e d ^ -.1 t h a t w i t h  increased^oresiduali§ai'gnin  t h e t r a t e of g r a f t i n g decreased c o n s i d e r a b l y (  83).  R e s i d u a l l i g n i n i n wood p u l p a c t s as an i n h i b i t o r r e t a r d s r d u r i n g the g r a f t i n g r e a c t i o n . I t was r e c e n t l y t h a t i n h i b i t i o n and transfer reactions ( 137  was-  retardation  and  found  r e s u l t e d from  o f polymer r a d i c a l s w i t h  lignin  ). T h i s p r e v e n t s f o r m a t i o n o f m a c r o r a d i c a l s  n e c e s s a r y f o r the g r a f t i n g r e a c t i o n to g e t under way  ( 83  ).  - 74 -  K o b a y a s h i e t a l . ( j>® ) Jb.lended g r a f t e d c o t t o n l i n t e r s and d i s s o l v i n g p u l p s i n v a r i o u s  proportions  w i t h unbleached k r a f t and groundwood p u l p s . They showed t h a t when even s m a l l amounts o f g r a f t e d f i b r e s were p r e s e n t , a s i g n i f i c a n t i n c r e a s e i n paper d r y - s t r e n g t h c o u l d be a c h i e v e d  i f the p u l p c o n t a i n e d s m a l l amounts  o f l i g n i n . The advantage o f g r a f t i n g became l e s s as  lignin  c o n t e n t o f the b l e n d e d p u l p i n c r e a s e d . When groundwood p u l p was  b l e n d e d , s t r e n g t h p r o p e r t i e s were worse t h a n  those f o r the c o r r e s p o n d i n g  ungrafted  blend.  Because groundwood p u l p s c o n t a i n a g r e a t d e a l o f l i g n i n and h e m i c e l l u l o s e s , tooth o f which deieteriously  affect grafting  to assume t h a t bonding may  ( 103  )t  i t is  reasonable  n o t o c c u r between groundwoods  and polymer c h a i n s . Such composites are s i m p l y p h y s i c a l m i x t u r e s w i t h c h a r a c t e r i s t i c s s i m i l a r t o paper p r o p e r t i e s . Conversely,  most l i g n i n and p a r t o f the  had been removed by k r a f t p u l p i n g .  hemicelluloses  Bondiformation  between k r a f t f i b r e s and polymer c h a i n s seems more l i k e l y . Thereby, c r o s s l i n k s might e x i s t , g i v i n g  papers  - 75  -  w i t h more compacted s t r u c t u r e . More energy, t h e r f o r e , would he r e q u i r e d t o cause m a t e r i a l f l o w . The s t r e s s r e l a x a t i o n i n t r e a t e d k r a f t papers was  r e l a t i v e l y slower  t h a n t h a t i n u n t r e a t e d papers ( T a b l e s IX »i t o IX i x , F i g s . 6-1 to  ).  The e f f e c t o f d e i i g n i f c i a t i o n upon paper s t r e s s r e l a x a t i o n was d i s c u s s e d e a r l i e r . As n o t e d , l i g n i n a v a i l a b l e i n unbleached k r a f t papers l e d t o lower s t r e s s r e l a x t i o n than f o r bleached pulp conterparts. This r e l a t i o n s h i p d i d not continue with PPC p r e p a r e d w i t h MMA,  95 » 5 comonomer, o r TEGDMA.  T h i s r e s u l t demonstrates g r e a t e r i n t e r a c t i o n between f i b r e and polymer, t h a n caused by s m a l l d i f f e r e n c e s i n l i g n i n content.  - ?6 -  6.0  CONCLUSION  S t r e s s r e l a x a t i o n t e s t s i n t e n s i o n were conducted on groundwood and k r a f t p a p e r s , p l a s t i c s and t h e i r composites  ( PPC ) o v e r time between 0.04  and 3 5 min. R e s u l t s were as f o l l o w s i 1.  The l i n e a r v i s c o e l a s t i c i t y e q u a t i o n c o u l d  be employed t o d e c r i b e r e l a x a t i o n b e h a v i o u r o f a l l materials investigated. 2.  Papers p r e p a r e d from groundwood p u l p s  r e l a x e d i n t e r n a l s t r e s s much s l o w e r t h a n those made from k r a f t p u l p s . 3.  L i g n i n a f f e c t e d r e l a x a t i o n o f k r a f t papers.  Paper made from unbleached p u l p seemed t o p a r t i c i p a t e d i f f e r e n t l y i n energy s t o r a g e and t r a n s m i s s i o n , r e s u l t i n g i n l a r g e r s t r e s s r e t e n t i o n . C o n v e r s e l y , b r i g h t e n e d and u n b r i g h t e n e d groundwood gave almost i d e n t i c a l r e s u l t s . 4.  Energy d i s s i p a t i o n i n p l a s t i c s d i d n o t  s y s t e m a t i c a l l y decrease a c c o r d i n g t o t h e amount o f c r o s s l i n k i n g o i n t e n d e d by c h o i c e o f p r e p a r a t i o n s . 5.  PPC s t r e s s r e l a x a t i o n c u r v e s were i n f l u e n c e d  by b o t h polymer ( m a t r i x ) and f i b r e ( s u b s t r a t e ) employed. The f o r m e r c o n t r i b u t e d i n minor ways, w h i l e the l a t t e r , o p e r a t e d ' i n " m a j o r ways.  - 77 -  6. PPC and u n t r e a t e d paper handsheets d i s s i p a t e d i n t e r n a l s t r e s s e s i n r e l a t i v e l y s m a l l amount compared t o some polymer t h i n f i l m s . PPC made from k r a f t papers displayed r e l a t i v e l y l a r g e r s t r e s s d i s s i p a t i o n than u n t r e a t e d k r a f t p a p e r s , h u t no such d i f f e r e n c e s were f o u n d between t r e a t e d and u n t r e a t e d groundwoods.  - 70 -  7.0 1.  LITERATURE CITED  Adams, J.W. and H.W. H o f t e z e r . 1 9 6 5 . D e p o s i t i o n o f h y d r o l y z e d polymers on c e l l u l o s i c m a t e r i a l . U.S. P a t e n t 3 , 1 9 4 , 7 2 7 . (not seen, from C.A. 6 3 I 1 1 8 6 1 ) .  2.  . 1966. M o d i f i e d cellulose f i l t e r material. U.S. P a t e n t 3 . 2 5 6 , 3 7 2 . ( n o t  seen, from C.A. 6 5 T 7 4 4 8 ) . 3.  A l f r e y , T. 1 9 4 8 . M e c h a n i c a l B e h a v i o u r o f High Polymers. I n t e r s c i e n c e Publ., I n c . , New York. 5 8 1 pp.  4.  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Soc. 7 7 » 3 7 0 1 - 3 7 0 7 .  - 107 -  b.O  1.  BK, UK  NOTATIONS  = Bleached k r a f t ,  unbleached  k r a f t hemlock p u l p s . 2.  BG, UG  = B r i g h t e n e d groundwood,  unbrightened  groundwood hemlock p u l p s . 3. 4. 5.  MMA TEGDMA  (  M95  = Methyl  methacrylate.  = Tetraethylene g l y c o l  dimethacrylate.  = MMA » TEGDMA i n volume p r o p o r t i o n s o f 95 « 5»  6.  Mb 5  = MMA < TEGDMA i n volume p r o p o r t i o n s o f b5 « 1 5 .  7.  M60  = MMA i TEGDMA i n volume p r o p o r t i o n s o f 60 j 40.  b.  MBK, MUK, MBG, MUG = BK, UK, BG, UG t r e a t e d w i t h MMA .  9.  9BK, 9UK, 9BG, 9UG = BK, UK, BG, UG t r e a t e d with M95.  10.  bBk, bUK, bBG, bUG, = BK, UK, BG, UG t r e a t e d w i t h Mb5.  11.  6Bk, 6UK, 6BG, f;6UG = BK, UK, BG, UG t r e a t e d w i t h M60.  -  12.  PBK,  PUK,  lob  PBG,  -  PUG,  = BK,  UK,  BG,  UG,  w i t h TEGDMA, 13.  r  = Correlation  14.  r  = Square o f r = r e g r e s s i o n  coefficient.  d i v i d e d by t o t a l 15.  S  W1?  = Standard e r r o r of  SS  SS. estimate.  treated  Table I .  B a s i s weight ( g/m 2 ) o f paper handsheets,  paper  p l a s t i c composites and polymer f i l m s .  Samples  BK UK BG UG  (a) Standard handsheets  Treated papers  56.87 5 « . 63 59.00 58.90  (b)  Matched (a) papers  122.20  141.25  W.37  164.47  171.20  171.13  173.01  185.51  Polymer^ films  o  MMA  120.06  M95  142.60  M85 M60  161.37  TEGDMA  177.99  132.74 (a) = Average r e a d i n g o f 5 s h e e t s (b) = Average r e a d i n g from Table I I c  Table I I .  P r o p e r t i e s o f paper p l a s t i c c o m p o s i t e s ( PPC ) .  Monomer System MMA Paper Dose sample Mrad.  Loading  B.W.  Dose  M95 Loading  fo  g/m  Mrad.  fo  2  M»5 B.W.  Dose  Loading  • B.W.  g/m  Mrad.  *  g/m  2  2  BK  2.3  87  111.06  2.1  85  110.00  1.5  199  116.59  UK  2.3  136  148.62  2.1  221  132.59  1.5  127  136.11  BG  2.3  160  167.37  2.1  261  135.52  1.5  274  169.19  UG  2.3  159  163.57  2.1  270  155.67  1.5  273  164.64  Table I I .  Continued.  Monomer System M60  TEGDMA  Paper sample  Dose  Loading  B.W.  Dose  Loading  Mrad.  %  g/m*  Mrad.  %  BK  1.1  105  117.35  0.5  161  155.89  UK  1.1  133  137.76  0.5  204  191.77  BG  1.1  188  175.32  0.5  227  £208.61  UG  1.1  279  174..88  0.5  222  206.27  B.W, g/m*  Table I I I .  S t r e s s , r e l a x a t i o n of" the d i f f e r e n t t r e a t m e n t s s t u d i e d a t c o n s t a n t d e f o r m a t i o n ( n=5).  Ultimate (a) 0 .004 Treatment s t r e n g t h , kg 7.76 16.70 BK 8.35 14.54 6.74 Paper UK 7.27 5.00 4.46 10.00 BG 4.64 10.41 5.21 UG PPC (MMA)  PPC (M95)  .01  Time, min .02 .04  1  10  20  30  35  7.56  7.47  7.37  6.65  6.04  5.88  5.77  5.74  6.54  6.48  6.42  5.85  5.39  5.24  5.15  5.12  4.27  4.20  4.17  3.88  3.50  4.37  4.32  4.03  3.57 3.72  3.53  4.43  3.64 3.80  3.67  3.65  5.85  5.75  5.69  5.27  4.90  4.77  4.71  4.67  7.85  7.77  7.69  7.12  6.65  6.48  6.39  6.33  7.77  7.69  7.12  6.65  6.39  6.33  5.65  5.58  5.20  4.92  6.48 4.81  4.75  4.73  BK UK  13.00  6.50  16.50  8.25  6.02 8.00  BG UG  12.91 12.94  6.46  8.00  6.47  6.15  7.85 5.81  BK UK  13.16 16.42  6.58  6.35  6.17  6.09  6.02  5.51  5.17  5.00  4.91  4.88  8.21  7.71  7.63  7.54  6.91  6.43  6.21  6.11  6.07  BG UG  12.34 11.45  6.17  7.87 5.72  5.55  5.48  5.42  5.01  4.70  4.59  4.51  4.48  5.73  5.25  5.09  5.02  4.96  4.62  4.35  4.25  4.19  4.17  Table I I I .  Treatment  PPC (M85)  PPC (M60)  PPC (TEGDMA)  Ultimate strength kg  0  (a)  .004  .01  Time, m i n .04 .02  1  10  20  30  35  14.03 16.20 11.84 12.68  7.01 8.10  6.63 7.78  6.47  6.40  6.32  5.79  5.36  5.23  5.14  5.11  7.65  7.59  7.49  6.43  6.15  5.51  5.29  5.24  4.61  4.47  4.44  6.34  5.95  5.36 5.80  6.31 4.51  6.20  5.92  6.91 4.88  5.73  5.66  5.28  4.97  4.88  4.82  4.80  BK UK  13.01  6.51  5.78  5.33  4.97  4.83  4.75  4.71  7.53  5.91 7.04  5.85  15.05  6.07 7.18  6.97  6.90  6.39  5.98  5.85  5.74  BG UG  11.89 10.62  5.95  5.40  5.32  5.27  4.92  4.66  4.58  4.52  5.81  5.54 5.42  5.77 4.54  5.25  5.19  5.13  4.80  4.54  4.44  4.3b  4.36  1 H>  BK  12.97 10.16  6.49  6.00  5.84  5.76  5.68  5.20  4.80  4.68  4.61  4.57  5.08  4.50  4.09  4.03  3.30  3.25  3.23  11.77 12.49  5.89 6.49  5.46  5.30  5.23  5.17  3.67 4.78  3.38  1  4.23  4.47  4.37  4.32  4.29  5.83  5.67  5.60  5.54  5.14  4.83  4.72  4.63  4.60  10.23 8.40  5.12  4.63  4.34  4.22  4.14  3.76  3.49  3.40  3.34  3.32  4.70  4.28  4.05  2.78  2.40  4.47  4.22  3.61  3.30  2.57 3.20  2.44  4.99  3.83 4.02  3.29  9.98  3.93 4.11  3.14  3.11  7.69  3.84  3.61 2.18  3.23  2.98  2.o9  2.83  2.01  2.59  3.65 2.24  3.50  5.19  3.73 2.34  2.14  1.87  1.65  1.59  1.55  1.53  BK UK BG UG  UK BG UG MMA  Polymer  ............ C o n t i n u e d . -  M95  M85 M60 TEGDMA  (a) t ( o ) i s d e f i n e d as time f o l l o w i n g ( 0.05 t o 0.06 min )..  i n i t i a l stress excitation  1—1  - 114 -  Table IV.  Regression analyses of s t r e s s r e l a x a t i o n curves a c c o r d i n g t o S ( t ) / S (0.04) = a + b I n t ( n = 3 0 )  Sample  a  b  r  2  r  (a)  S  EE  BK  .896201  -.0330223  .993485  -.996737  .00670831  UK  .906553  -.0300249  .990802  -.995390  .00725706  BG  .927076  -.0234806  .990690  -.995334  .00571015  UG  .932837  -.0236880  .915262  -.956693  .0180804  MBK  .919441  -.0263299  .979323  -.989608  .00959731  MUK  .920735  -.0258323  .980188  -.990045  .00921264  MBG  .925464  -.0240163  .990479  -.995228  .00590659  MUG  .929332  -.0224682  .980830  -.990369  .00787951  9BK  .913846  -.0276479  .967385  -.983557  .0127347  9UK  .911670  -.0286777  .977678  -.988776  .0108699  9BG  .921399  -.0253904  .989752  -.994863  .00648123  9UG  .926548  -.0236242  .983108  -.991518  .00776823  8BK  .911352  -.0282873  .994659  -.997326  .00519992  8 UK  .917915  -.0263141  .992718  -.996352  .00565358  8BG  .929525  -.0222995  .979172  -.989531  .00815838  8UG  .929622  -.0224843  .988718  -.994343  .00602506  6BK  .916739  -.0271276  .979745  -.989821  .00978446  6UK  .922244  -.0248270  .993607  -.996799  .00499573  6BG  .932821  -.0210792  .987797  -.993880  .00587733  t  - 115  Table IV  Sample  -  Continued.  a  b  r  2  r  (a)  6UG  .931970  -.0220568  ^951641  -.975521  EE .0124727  PBK  .910471  -.0287440  .985148  -.992546  .00885337  PUK  .906519  -.0295265  .989351  -.994661  .00768447  PBG  .921407  -.0251466  .987505  -.993733  .00709584  PUG  .92377?  -.0247468  .983903  -.991919  .00794060  MMA  .907496  -.0290840  .993107  -.996548  .006078553  M95  .835979  -.0553927  .985690  -.992819  .0167423  M85  .895049  -.0553927  .985690  -.992819  .0167423  M60  .905316  -.0304165  .987857  -.993910  .00845967  TEGDMA  .868065  -.0420076  .894819  -.945949  .0361277  S  (a) i m p l i e s t h a t a l l r v a l u e s a r e s i g n i f i c a n t a t t h e 0.01 p r o b a b i l i t y l e v e l .with degree o f freedom o f 1 and 28.  - 116 -  Table  V.  T e s t f o r d i f f e r e n c e i n paper r e l a x a t i o n behaviours. „  a.  Analysis of Variance Source  DP  Treatment  3  SS  stress  MS  P  .016241  .0054138  62.14  .000087126  Error  16  .0013940  Total  19  .017635  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan s New M u l t i p l e 1  Treatment Amount o f energy dissipation  UG  .1551  Range T e s t  BG  UK  BK  .1591  .2024  .2221  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t t h e 0.05 p r o b a b i l i t y l e v e l .  - 117 -  Table V I .  T e s t f o r e f f e c t o f polymer f i l m on amount o f s t r e s s  a.  crosslinking  relaxation.  A n a l y s i s of Variance  Source Treatment  DP 4  SS  MS  .10743  .02685b .0005181b*  Error  20  .010364  Total  24  .11779  P 51.»3  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  MMA  M60  Mb5  TEGDMA  M95  Amountsof energy dissipation  .19b6  .2069  .2272  .2b67  .3745  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t t h e 0.05 probability l e v e l .  - 118 -  Table V I I t i  a.  T e s t f o r e f f e c t o f m a t r i x system o n paper p l a s t i c composite (PPC) s t r e s s r e l a x a t i o n ( b l e a c h e d k r a f t paper-polymer system) .  Analysis o f Variance Source Treatment  DF  SS  MS  4  .00082781  .00020695 .000096365  Error  20  .0019273  Total  24  .0027551  n.s.  b.  F  2.15  not s i g n i f i c a n t .  Duncan's New M u l t i p l e Range T e s t  (a) '  Treatment  9BK  MBK  Amount o f energy dissipation  „ „ n. s.  .1786  6BK  .1848  .1897  8BK  PBK  .1917  .1951  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t t h e 0.05 probability level. (a)  the t a b l e i s s e t f o r reference only.  - 119  Table  -  V I I t i i T e s t f o r e f f e c t o f m a t r i x system on paper p l a s t i c composite (PPC) s t r e s s  relaxation  (unbleached k r a f t paper-polymer s y s t e m ) . a.  Analysis of Variance Source Treatment  Error Total  DP  SS  MS  P  4  .0034212  .00085530  20 24  .0018010 .0052222  .000090051  9.50  ** s i g n i f i c a n t a t t h e 0.01 p r o b a b i l i t y level. b.  Duncan's New M u l t i p l e Treatment  Range T e s t  6 UK  MUK  Amount o f energy dissipation .1681  .1758  8 UK .1791  9 UK  PUK  .1941  .1995  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i n f i c a n t l y a t t h e 0.05 probability level.  - 120 -  Table V l l i i i i .  a.  T e s t f o r e f f e c t o f m a t r i x system on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n ( b r i g h t e n e d groundwood paperpolymer system ) .  Analysis of Variance Source Treatment  DP  SS  4  .0033822  Error  20  .0014805  Total  24  .0048672  MS .00084555 .000074025  P 11.42'  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  6BG  8BG  MBG  PBG  9BG  Amount o f energy dissipation  .1425  .1513  .1631  .1700  .1736 '  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y at. the 0.05 p r o b a b i l i t y l e v e l .  - 121 -  Table V I I l i v .  T e s t f o r e f f e c t o f m a t r i x system on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n ( u n b r i g h t e n e d groundwood paper- polymer system ).  a.  Analysis of Variance  Source Treatment Error  DP 4 20  SS .0013068 .0024901  MS .00032670 .00012451  P 2.62  n , s  *  n.s. n o t s i g n i f i c a n t .  b.  (a.) Duncan's New M u l t i p l e Range T e s t ' x  Treatment  6UG  8UG  MUG  9UG  PUG  Amount o f energy dissipation  .1496  .1518  .1534  .1605  .1694  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t t h e O.05 p r o b a b i l i t y  level,  (a) t h e t a b l e i s s e t f o r r e f e r e n c e only.  - 122 -  T a b l e VIII«i  a.  T e s t f o r e f f e c t o f s u b s t r a t e on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n ( MMA-substrate system ) , 0  Analysis of Variance Source Treatment  DF 3  SS .0020508  MS .00068260  Error' Total  16 19  .0019314 .0039822  .00012071  5.66  ** s i g n i f i c a n t a t t h e 0.01 probility level.  b.  Duncan's New M u l t i p l e Range T e s t Treatment Amount o f energy dissipation  MUG  MBG  MUX  MBK  .1534  .1631  .1758  .1786  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0 . 0 5 p r o b a b i l i t y l e v e l .  - 123  Table V I I I s i i .  a.  -  T e s t f o r e f f e c t o f s u b s t r a t e on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n ( M 9 5 - s u b s t r a t e system ) .  Analysis of Variance  Source  DF  SS  MS  I  3  .0035642  .0011881  Error  16  .00006610.33  Total  19  .001057b* .0046220  Treatment  17.97  ** s i g n i f i c a n t a t t h e 0.01 probability  b.  Duncan's New M u l t i p l e  level.  Range T e s t  Treatment  9UG  9BG  9BK  9UK  Amount o f energy dissipation  .1605  .1736  .1897  .1941  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0 . 0 5 p r o b a b i l i t y l e v e l .  - 124 -  Table V I I I l i i i .  a.  T e s t f o r e f f e c t o f s u b s t r a t e on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n ( M 8 5 - s u b s t r a t e system ) .  Analysis of Variance  Source Treatment  DF 3  SS  MS  F  .0061283  .002042b .000061556  Error  16  .00098489  Total  19  .0071132  33.19  ** s i g n i f i c a n t a t t h e 0 . 0 1 probability  b.  Duncan's New M u l t i p l e  level.  Range T e s t  Treatment  8BG  8UG  8 UK  8BK  Amount o f energy dissipation  .1513  .1518  .1791 .1917  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0 . 0 5 p r o b a b i l i t y  level.  -  Table V l l l s i v .  a.  125  -  T e s t f o r e f f e c t o f s u b s t r a t e on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n ( M 6 0 - s u b s t r a t e system ) .  Analysis o f Variance  Source Treatment  DP  SS  3  .0054414  Error  16  .0022039  Total  19  .0076453  MS .0018138  F 13.17  .00013774 ,  ** s i g n i f i c a n t a t t h e 0.01 probability  b.  Duncan's New M u l t i p l e  level.  Range T e s t  Treatment  6BG  6UG  Amount o f energy dissipation  . 1 4 2 5 .1496  6UK  6BK  .1681 .1848  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0 . 0 5 p r o b a b i l i t y l e v e l .  -  Table V I I I : v .  a.  126  -  T e s t f o r e f f e c t o f s u b s t r a t e on paper p l a s t i c composite ( PPC ) s t r e s s r e l a x a t i o n ( TEGDMA- s u b s t r a t e system ) .  Analysis of Variance  Source Treatment  DF 3  SS .0038471  MS .0012824  Error Total  16 19  .0015208 .0053680  .000095058  13.49  ** s i g n i f i c a n t a t t h e 0.01 probability  b. Duncan's New M u l t i p l e  level.  Range T e s t  Treatment  PUG  PBG  PBK  Amount o f energy dissipation  .1694  .1700  .1951  PUK .1995  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0 . 0 5 p r o b a b i l i t y l e v e l .  - 127  Table IX»i  -  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b l e a c h e d k r a f t paperMMA system ) .  a. A n a l y s i s o f V a r i a n c e  Source Treatment  DF 2  SS  MS  .0047533  .0023767  Error  12  .00099245 .000082704  Total  14  .0057458  F 28.74  ** s i g n i f i c a n t a t t h e 0 . 0 1 probability level.  b. Duncan's New M u l t i p l e  Range T e s t  Treatment  MBK  MMA  Amount o f energy dissipation  .1786  .1986  BK .2221  Any two means d i f f e r s i g n i f i c a n t l y at the 0 . 0 5 p r o b a b i l i t y l e v e l .  - 128 -  Table I X i i i .  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b l e a c h e d k r a f t paperM95 system ) .  Analysis of Variance  Source Treatment  DF 2  SS  MS  .097407  .048703 .000068755  Error  12  .00082506  Total  14  .09823  F 708.36  ** s i g n i f i c a n t a t t h e 0X01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  9BK  BK  Amount o f energy dissipation  .1897  .2221  M95 .3745  Any two means d i f f e r s i g n i f i c a n t l y at the 0 . 0 5 p r o b a b i l i t y l e v e l .  - 129 -  Table I X j i i i .  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b l e a c h e d k r a f t paper-M85 system ) .  Analysis of Variance  Source Treatment  DF  SS  MS  2  .0036972  .0018486  Error  12  .0010524  .000067702  Total  14  .0047497  F 21.08  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  8BK  BK  M85  Amount o f energy dissipation  .1917  .2221  .2272  Me'ansB u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t t h e 0.05 p r o b a b i l i t y l e v e l .  - 130  Table I X t i v .  a.  -  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b l e a c h e d k r a f t paper-M60 system ) .  Analysis of Variance  Source Treatment  DF 2  SS  MS  .0035165  .0017583 .00010875  Error  12  .OOI3050  Total  14  .0048216  16.17  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range Test  Treatment  6BK  .M60  Amount o f energy dissipation  .1847  .2069  BK .2221  Any two means d i f f e r s i g n i f i c a n t l y a t t h e O.05 p r o b a b i l i t y l e v e l .  -  Table  IXJV.  a.  131  -  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b l e a c h e d k r a f t paperTEGDMA system ) .  Analysis of Variance  Source Treatment  DF  SS  2  MS  .022181  .011090  Error  Ik  .0097106 .00080922  Total  16  .031891  F 13.71  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  PBK  BK  Amount o f energy dissipation  .1951  .2221  TEGDMA .2867  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0.05 p r o b a b i l i t y l e v e l .  -  Table I X t v i .  132  -  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper r e l a x a t i o n ( unbleached k r a f t paperMMA system ) .  Analysis of Variance  Source  DP  SS  MS  2  .0020723  .0010361  Error  12  .0013506  .00011255  Total  14  .0034228  Treatment  9.21  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  MUK  MMA  UK  Amount o f energy dissipation  .1758  .1986  .2024  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0.05 p r o b a b i l i t y l e v e l .  - 133 -  Table I X i v i i .  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( unbleached k r a f t paperM 9 5 system ) .  A n a l y s i s of Variance  Source Treatment Error Total  DP 2 12  14  SS .10374  .0010971 .10484  MS .051871  F  **  567.35  .000091427  ** s i g n i f i c a n t a t t h e 0 . 0 1 probability level.  b.  Duncan's New M u l t i p l e Range T e s t  Treatment  9UK  UK  Amount o f energy dissipation  .1941  .2024  M95 .3745  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0 . 0 5 p r o b a b i l i t y l e v e l .  -  Table I X i v i i i .  a.  134  -  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( unbleached k r a f t p a p e r - M 8 5 system ) .  Analysis of Variance  Source Treatment  DF  SS  MS  2  .0057812  .0028906  Error  12  .0010185  .000084877  Total  14  .0067998  F 34.06  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  6UK  UK  Amount o f energy dissipation  .1791  .2024  M85 .2272  Any two means d i f f e r s i g n i f i c a n t l y at the 0 . 0 5 p r o b a b i l i t y l e v e l .  - 135  Table I X t i x .  a.  -  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( unbleached k r a f t paperM60 system ) .  Analysis of Variance  Source Treatment  DP  SS  2  MS  .0045076  ,002253b .000070854  Error  12  .00085024  Total  14  .0053579  F 31.bl  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  6UK  UK  M60  Amount o f energy dissipation  .1681  .2024  .2026  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the  0.05 p r o b a b i l i t y .  - 136 -  Table I X t x .  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b l e a c h e d k r a f t paperTEGDMA system ) .  Analysis o f Variance  Source Treatment  DP 2  SS  MS  .023560  .012280 .00079826  Error  12  .0095791  Total  14  .034139  F 15.38  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  PUK  UK  TEGDMA  Amount o f energy dissipation  .1995  .2024  .2867  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0.05 p r o b a b i l i t y l e v e l .  - 137  Table X $ i .  a.  -  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b r i g h t e n e d groundwood paper-MMA system ) .  Analysis of Variance  Source Treatment  DP 2  SS  MS  I  .0047412  .0023706  43.81  .000054108  Error  12  .00064929  Total  14  .0053905  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  BG  MBG  MMA  Amount o f energy dissipation  .1591  .1631  .1986  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0.05 p r o b a b i l i t y l e v e l .  - 138 -  Table X i i i .  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b r i g h t e n e d groundwood paper- M 9 5 system ) .  a. A n a l y s i s o f V a r i a n c e  Source Treatment  DF 2  Error  12  Total  14  SS  MS  .14502 .00075037  .072509  1159.57  .000062531  .14577  ** s i g n i f i c a n t a t t h e 0 . 0 1 probability level.  b. Duncan's New M u l t i p l e  Range T e s t  Treatment  BG  9BG M 9 5  Amount o f energy dissipation  .1591  .1736  .3745  Any two means d i f f e r s i g n i f i c a n t l y at the 0 . 0 5 p r o b a b i l i t y l e v e l .  - 139 -  Table X t i i i .  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b r i g h t e n e d groundwood paper-M85 system ).  Analysis of Variance  Source Treatment  DP  SS  2  MS  .17450  .0087249  Error  12  .0013176 .00010980  Total  14  .018767  P 79.46  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  8BG  BG  M85  Amount o f energy dissipation  .1513  .1591  .2272  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the  0.05 p r o b a b i l i t y l e v e l .  - 140 -  Table X i i v .  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b r i g h t e n e d groundwood paper-M60 system ) .  Analysis of Variance  Source Treatment  DF 2  SS  MS  .011169  .0055844 .000074635  Error  12  .00089562  Total  14  .012064  F 74.82  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan!s New M u l t i p l e Range T e s t  Treatment  6BG  BG  M60  Amount o f energy dissipation  .1425  .1591  .2069  Any two means d i f f e r s i g n i f i c a n t l y a t t h e 0.05 p r o b a b i l i t y l e v e l .  - 141 -  Table X J V .  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b r i g h t e n e d groundwood paper-TEGDMA system ) .  Analysis o f Variance  Source Treatment  DF  2  SS  MS  .050076  Error  12  .0094236  Total  14  .059500  .025038 .00078530  31.88  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  BG  PBG  TEGDMA  Amount o f energy dissipation  .1591  .1700  .2867  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t t h e 0.05 p r o b a b i l i t y l e v e l .  - 142 -  Table X : v i .  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( u n b r i g h t e n e d groundwood paper-MMA system ) ,  A n a l y s i s of Variance  Source Treatment Error Total  SS  DP 2 12 14  MS  .0065845  .0032923  .0012556  .00010463  31.47  .0078401  ** s i g n i f i c a n t a t t h e 0..XJ1 probability level.  b.  Duncan's New M u l t i p l e Range T e s t  Treatment  MUG  UG  MMA  Amount o f energy dissipation  .1534  .1551  .1986  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t t h e 0.05 p r o b a b i l i t y l e v e l .  - 143 -  Table X»vii.  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( u n b r i g h t e n e d groundwood p a p e r - M 9 5 system ) .  Analysis o f Variance  Source Treatment  DP  SS  2  MS  .15665  .078323 .000079441  Error  12  .00095330  Total  14  .15760  F 985.92  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  9UG  UG  Amount o f energy dissipation  .1551  .1605  M95 .3745  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0 . 0 5 p r o b a b i l i t y l e v e l .  - 144 -  Table X i v l i i .  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( u n b r i g h t e n e d groundwood paper-M85 system ) .  Analysis o f Variance  Source Treatment Error Total  DP 2 12 14  SS  MS  .018182  .009012  .0012963  .00010802  I 84.16  .019479  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e Range T e s t  Treatment  8UG  UG  M85  Amount o f energy dissipation  .1518  .1551  .2272  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0.05 p r o b a b i l i t y l e v e l .  - 145 -  Table X i i x .  a*  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( u n b r i g h t e n e d groundwood paper-M6G system ) .  Analysis of Variance  Source Treatment Error Total  DP  SS  MS  2  .0099748  .0049874  12  .0022100  .00018416  14  .012185  F  *#  27.08  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Range T e s t  Treatment  6UG  UG  M60  Amount o f energy dissipation  .1496  .1551  .2069  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t the 0.05 p r o b a b i l i t y l e v e l .  - 146 -  Table X i x .  a.  T e s t f o r c o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( u n b r i g h t e n e d groundwood paper-TEGDMA system ) .  Analysis of Variance  Source Treatment  DP 2  SS  MS  .52173  .026087 .00079920  Error  12  .0095905  Total  14  .061764  32.64  ** s i g n i f i c a n t a t t h e 0.01 probability level.  b.  Duncan's New M u l t i p l e  Test  Treatment  UG  PUG  TEGDMA  Amount o f energy dissipation  .1551  .1694  .2867  Means u n d e r l i n e d by t h e same l i n e do n o t d i f f e r s i g n i f i c a n t l y a t t h e 0.05 p r o b a b i l i t y l e v e l .  log  /  au) ^  i  log t F i g u r e 1.  Polymer s t r e s s r e l a x a t i o n ( 148  ).  - 148 -  - 149 -  F i g u r e 3.  G l a s s frame assembly f o r making polymer t h i n f i l m s .  - 150 -  -  -1.2  F i g u r e 5.  -1.0  0  151  -  1.0  1.3  1.5  I n t , min S t r e s s r e l a x a t i o n o f polymer f j i l m s .  -  152  -  I n t , min  I n t , min F i g u r e 6.  E f f e c t o f m a t r i x systems on paper p l a s t i c composite (PPC) s t r e s s r e l a x a t i o n .  - 153 -  I n t, min  -  l.o  w  154  -  ^  0.9  MUG MBG MUK MBK 03 03  2 -p  0.8  w  1  -j.2 Jl.o '  Figure 7-1.  6——Tto—i.b  1.^ I n t , min E f f e c t o f s u b s t r a t e s on paper p l a s t i c composite (PPC) s t r e s s r e l a x a t i o n 1 MMA-substrate system ). n  -  155  -  1.0  9UG 9BG 9BK 9UK  s -1.2  Pigure  7-2.  -1.0  0  1.0  1.3  1.5  I n t , min E f f e c t o f s u b s t r a t e s on paper p l a s t i c composite(PPC) s t r e s s r e l a x a t i o n ( M 9 5 - S u b s t r a t e system ).  -  156  -  I n t , min F i g u r e 7-3.  E f f e c t o f s u b s t r a t e s on paper p l a s t i c composite (PPC) s t r e s s ( M b 5 - s u b s t r a t e system ) .  relaxation  -  157  -  6BG 6UG 6UK 6BK  -1.2 Figure  7-4.  -1.0  1.0  1.3  1.5  I n t , min  E f f e c t o f s u b s t r a t e s on paper p l a s t i c composite (PPC) s t r e s s r e l a x a t i o n ( M 6 0 - s u b s t r a t e system ).  -  158  -  0  Figure  7-5.  ~ 1 . 0 1 . 3  1.5  I n t , min.  E f f e c t o f s u b s t r a t e s on paper p l a s t i c composite (PPC) s t r e s s r e l a x a t i o n ( TEGDMA-substrate system ) .  -  I  -1.2  F i g u r e b-1.  I  I  -1.0  159  <s»  -  »  0  RF>U  ~  I  I L  1 . 0 1 . 3  C o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( bleached k r a f t paper-polymer system ) .  1  1.5  I n t , min  160  -  I  S  -1.2  FTU  I  -1.0  -  I  t\f  I  I  1.0  0  1.3  I  I  1.5  I n t , min  1  I ' 1  - e a-2.  ,1. 2  '  -l.o  A  IJ  '•  o  l  ~u  .  o  1.3  C o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( bleached k r a f t paper-polymer system ).  1.5  I n t , min  -  *  1  -1.2  Figure b-3.  • -l.O  161  -  *u  -i O  • 1 7 0 1 . 3  . . . 1.5  I n t , min  C o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( unbleached k r a f t paper-polymer system ).  - 162 -  H  °  S to co to \  CO  PUK UK  CO  TEGDMA -1.2  -liO  1.3  1.5  I n t , min 1.0  o  0.9  H  IS!  0.85  u  3  03 CO ©  CO \  +>  to  6UK UK M60  +»  —. CO  0.75  -1.2  -1.0  TTo  1.3  1.5  I n t , min 1.0  o •H  0.9 >j3 °  X  co co CO  0.85  8 UK UK  CO  M85  0.75 -1.2 F i g u r e 8-4.  -1.0  0  T7G  1.3  1.5  I n t , min  C o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( unbleached k r a f t paper-polymer system ) .  -  I I -1.2 F i g u r e 9-1.  I  -L.O  163  -  KM  I  O  *m  ~  I  I  l.O173  I.  175 lrig t , min  C o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b r i g h t e n e d groundwood paper-polymer system ).  - 164 -  -1.2  -L.O  0  L.O  1.3  1.5  I n t , min  -1.2  -1.0  1.0  1.3  1.5  I n t , min  8BG BG  M85 -1.2  F i g u r e 9-2.  -1.0  0  1.0  1.3  1.5  I n t , min C o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( b r i g h t e n e d groundwood paper-polymer system ).  -  -1.2  Figure 9-3.  -l.O  165  -  O  l.O  1.3  1.5  I n t , min C o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( u n b r i g h t e n e d groundwood paper-polymer system ).  - 166 -  ° 1.0  n  0.9 o  •ri  • U) o }  OB  PUG  \  0.8  TEGDMA  -1.2  -1.0  T7o  1.3  I n t , min  1.0  o/  1.5  •H/  0.9  «!  \r+ O 0);  T/  o  a>  -  4  w  w  6UG UG 0.8 M60  -1.2  -1.0  0  1.0  (a  3-  CQ »  W \  1.5 I n t , min  1.0  /IS  1.3  0.9  O  -P  8UG UG 0.8 M85  -i.2 - l . O S Figure  9-4.  O  H  — — i t n t s  I n t , min C o p o l y m e r i z a t i o n e f f e c t s on paper s t r e s s r e l a x a t i o n ( u n b r i g h t e n e d groundwood paper-polymer system ) .  

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