Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Compressive stress relaxation of wood pulps with particular reference to pulp chemistry Kirbach, Eberhard 1973

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1973_A1 K57.pdf [ 9.12MB ]
Metadata
JSON: 831-1.0101003.json
JSON-LD: 831-1.0101003-ld.json
RDF/XML (Pretty): 831-1.0101003-rdf.xml
RDF/JSON: 831-1.0101003-rdf.json
Turtle: 831-1.0101003-turtle.txt
N-Triples: 831-1.0101003-rdf-ntriples.txt
Original Record: 831-1.0101003-source.json
Full Text
831-1.0101003-fulltext.txt
Citation
831-1.0101003.ris

Full Text

\5\7S-  •'  COMPRESSIVE STRESS RELAXATION OF WOOD PULPS WITH PARTICULAR REFERENCE TO PULP CHEMISTRY  By EBERHARD KIRBACH Diplom-Holzwirt, University of Hamburg, 1966  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  i n the Department of Forestry  We accept this thesis as confirming to the required standard.  The University of British Columbia April 1973  i  In p r e s e n t i n g t h i s t h e s i s  in p a r t i a l  f u l f i l m e n t o f the  requirements 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 C o l u m b i a , I agree 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  study.  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 c o p y i n g o f t h i s 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 .  be g r a n t e d by  g a i n s h a l l not  permission.  Department o f The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada  Date  thesis  Department o r  I t i s u n d e r s t o o d that c o p y i n g o r  of t h i s thesis f o r f i n a n c i a l written  the Head of my  that  publication  be a l l o w e d w i t h o u t  my  ABSTRACT Stress relaxation responses in compression following steeping either in d i s t i l l e d water or 18.6% NaOH were examined on wood pulp mats with the objective to relate quantitative, physical, as well as structural features of pulp polymers to mat rheology. The study included 32 commercial and and laboratory prepared pulps (groundwood, holocellulose, paper grade, viscose, acetate and alpha-cellulose pulps) which provided wide variation in chemical characteristics. Rate of stress relaxation was found to differ considerably between individual pulps, indicating that each pulp possesses a different ability to dissipate stress.  The stress relaxation traces, following quasi steploading  (1.0 - 1.5 s e c ) , suggest that pulp mat relaxation i s governed by two mechanisms (Mj and M^).  M^, dominating between 0.0 to 1.0 min, i s believed to involve  primarily inter-fibre processes, while M^, controlling the response thereafter, comprises intra-fibre, essentially molecular processes. Swelling media were found to influence pulp mat  rheology.  Considerably higher rates of stress dissipation were observed with caustic (18.6% NaOH) than with water swollen mats. This indicates that intracrystalline swelling, in addition to inter-crystalline, enhances time dependent responses. rheology  The:effect of any swelling medium on pulp mat  appears to be highly dependent on length of swelling treatment,  since i t was observed that the capacity of pulps to dissipate stress changes inversely with length of steeping time.  This phenomenon suggests inter-  changeability of chemical and physical stress systems. Evidence presented in the study shows that pulp chemistry controls time dependent:  behavior of pulp mats. Quantitative and structural  characteristics of hemicelluloses appeared to be most important for rheological processes.  In the caustic swollen state, decrease in hemi-  cel lulose caused proportional changes in stress relaxation.  The same  observation was made for water swollen groundwood, holocellulose and paper pulps.  In water saturated low yield pulps, however, the viscoelastic  iii  effect  of h e m i c e l l u l o s e s was r e v e r s e d , due to d e g r a d a t i o n and  phenomena.  Here,  r e s i d u a l h e m i c e l l u l o s e s were found to r e t a r d s t r e s s d i s s i p a t i o n .  From these o b s e r v a t i o n s , i t f u n c t i o n s as an important systems of system.  redeposition  was deduced t h a t t h i s  linkage  group of wood polymers  in stress distribution  the undegraded o r o n l y s l i g h t l y  degraded  and d i s s i p a t i o n  lignin-carbohydrate  Low DP and h i g h degree of b r a n c h i n g make b e m i c e l l u l o s e s h i g h l y  s u i t e d to d i s s i p a t e  s t r e s s i n the wood of  living  trees,  as w e l l as g r o u n d -  woods and h o l o c e l l u l o s e p u l p s and to a l e s s e r e x t e n t i n o t h e r  pulp  types.  C e l l u l o s e was found to account f o r most o f the d i s s i p a t e d i n pulp polymeric rheology  systems.  Its  appeared to v a r y  degradation.  quantitative contribution  little  Severe d e g r a d a t i o n ,  between p u l p s o f no o r e.g.  enhanced the time dependent r e s p o n s e . relaxation  tests  compression, primarily  importance  pulp  limited  low y i e l d p u l p i n g ,  cellulose  however,  T h i s was demonstrated f u r t h e r  on v i s c o s e p u l p s degraded by r a d i a t i o n .  to be of o n l y s u b o r d i n a t e  the dominant  in  to  stress  L i g n i n appeared  f o r p u l p mat s t r e s s r e l a x a t i o n  a t t r i b u t a b l e to o r i e n t a t i o n  by  or l a y e r  effects  in and  to  r o l e of h e m i c e l l u l o s e s .  R e l a x a t i o n measurements on wood p u l p p r o d u c t s are useful tools for  p r e d i c t i n g and e s t i m a t i n g  as p r e s s i n g b e h a v i o r and a l k a l i response, runnability  solubility  and p r i n t a b i l i t y  of  suggested as  p u l p and paper p r o p e r t i e s , of v i s c o s e p u l p s , p u l p paper.  such  beating  iv  TABLE  OF  CONTENTS  TITLE PAGE  *  ABSTRACT  1 1  TABLE OF CONTENTS  iv  LIST OF TABLES  v i i  LIST OF FIGURES  viii  ACKNOWLEDGEMENTS  .. x i i  1.0' INTRODUCTION...... 2.0  1  '  BACKGROUND TO THE STUDY 2.1  3  Morphology and C o m p o s i t i o n o f Wood C e l l W a l l s . . . . .  3  2.1.1  Major wood c e l l t y p e s  2.1.2  C e l l wall o r g a n i s a t i o n  3  C h a r a c t e r i s t i c s o f wood c h e m i c a l c o n s t i t u e n t s . . . . . . . . . . . .  D  2.1.3  2.1.3.1  2.2  3  Cellulose  6  ;  2.1.3.1.1  Supermolecular  2.1.3.1.2  The c r y s t a l  2.1.3.2  Hemicelluloses  2.1.3.3  Lignin  7  arrangement  8  structure  9  1 0  *2  C h a r a c t e r i s a t i o n o f V a r i o u s P u l p Types 2.2.1  Mechanical pulps  *3  2.2.2  H o l o c e l l u l o s e pulps  2.2.3  Sulphite pulps  2.2.4  Sulphate pulps  1 7  2.2.5  Bleached pulps  2 0  2.2.6  Alpha-cellulose pulps..  2 1  t.  ^ ^  V  Page 2.3  Time Dependent M e c h a n i c a l P r o p e r t i e s o f High  Polymers,  such as Wood and C e l l u l o s i c s  2.A  2.3.1  M o l e c u l a r approach t o v i s c o e l a s t i c i t y .  23  2.3.2  Phenomenological  26  2.3.3  V i s c o e l a s t i c b e h a v i o r o f c e l l u l o s e f i b r e mats  study o f v i s c o e l a s t i c i t y e  2.4.2  Rheology  o f paper  29  2.3.3.2  Rheology  o f wet f i b r e mats i n compression  32  Mechanisms i n compression o f wet c e l l u l o s i c  35 f i b r e mats....  36  2.4.1.1  F i b r e bending.....  36  2.4.1.2  Fibre repositioning  37  2.4.1.3  Compression  38  at points of contact  F a c t o r s d e t e r m i n i n g compression c h a r a c t e r i s t i c s o f c e l l u l o s e f i b r e mats  38  2.4.2.1  F i b r e morphology.  38  2.4.2.2  Fibre properties  40  2.4.2.3  S t r u c t u r e o f f i b r e mats  42  MATERIALS AND METHODS  3.1  29  2.3.3.1  C o m p r e s s i b i l i t y o f C e l l u l o s i c F i b r e Mats 2.4.1  3.0  22  P u l p Samples  43  43  3.1.1  Holocellulose pulps....  43  3.1.2  Alpha-celluloses  44  3.2  Physical Testing  3.3  Determination of Pulp Constituents  4  6  47  3.3.1  Carbohydrates  47  3.3.2  Lignin  50  3.3.3  Other measurements  50  vi  4.0  52  RESULTS AND DISCUSSION..... 4.1  Fractional Stress Relaxation Tests  52  4.2  Effect of Steeping Media (Water vs. Caustic)  56  4.3  Effect of Residual Chemical Constituents  61 6 2  4.3.1  Lignin  4.3.2  Hemicelluloses  ^4.3.3  65  •  4.3.2.1  Mechanical pulps  67  4.3.2.2  Holocellulose pulps...  69  4.3.2.3  Sulphite and sulphate paper pulps  71  4.3.2.4  Viscose and acetate pulps  74  4.3.2.5  Alpha-cellulose pulps  7  7 6  Cellulose  4.4  Interchangeability of Stress Systems  4.5  Application of Stress Relaxation Measurements for  5  8 0  8  Characterising Pulps  ^  4.5.1  Estimation of viscose pulp alkali solubility  S3  4.5.2  Predicting viscose pulp pressing characteristics  8  ^  4.5.3  Predicting fibre response to machining  8  ^  4.5.4  Predicting paper printability.  8  5  5.0  CONCLUSIONS  6.0  LITERATURE CITED  ,  8 7  90  vii  LIST Table 1.  OF TABLES  "  Page  The chemical composition of woods from three angiosperms and three conifers  124  2.  Description of pulps used in the study  125  3.  Summative data (in per cent of extractive-free wood) for chemical composition of pulps tested in the study  4.  127  Summary of fractional stress relaxation results on pulps tested in the study as read after 35 min relaxation time (1 -£"(35 min)/^"(o)) following steeping in water or caustic  5.  Properties of viscose pulps treated with various doses of gamma-radiation  6.  135  141  Multiple curvilinear covariance analysis for the relationship between 10% NaOH solubility and fractional stress relaxation of irradiated and untreated viscose pulps  142  viii  LIST  OF  FIGURES  Figure 1.  Page Schematic representation of the c e l l wall organisation in a coniferous tracheid and/or angiospermous wood f i b r e , with respective microfibril orientation  144  2.  The, unit c e l l as proposed by Meyer and Misch  145  3.  Stress relaxation under constant strain  146  A.  Steeped pulp specimen mounted between glass plates for testing of relaxation in compression.......... 147  5.  Gas chromatogram of the acetylated hydrolysates of western hemlock groundwood pulp No.  10-2  (brightened).... 6.  148  Gas chromatogram of the acetylated hydrolysates of western cottonwood groundwood pulp No.  10-4  (brightened) 7.  149  Gas chromatogram of the acetylated hydrolysates of western cottonwood peracetic acid holocellulose No. 9-4  8.  Gas chromatogram of the acetylated hydrolysates of unbleached coniferous sulphate pulp No. 7-1  9.  151  Gas chromatogram of the acetylated hydrolysates of bleached coniferous sulphate pulp No. 7-2..  10.  150  152  Gas chromatogram of the acetylated hydrolysates of bleached predominantly angiospermous sulphate pulp No. 8-2  153  Figure 11.  . Page Gas chromatogram of the acetylated hydrolysates of coniferous viscose pulp No. 1-2....................  12.  Gas chromatogram of the acetylated hydrolysates of alpha-cellulose pulp No. 0-3  13.  155  Gas chromatogram of the acetylated hydrolysates of bleached coniferous sulphite pulp No. 6-1  14.  or caustic steeping  (n=5)  157  Typical fractional stress relaxation curves for holocellulose pulps following water  or caustic  steeping (n=5)... 16.  156  Fractional stress relaxation curves for eroundwood pulps following water  15.  154  158  Fractional stress relaxation curves for paper pulps following water or caustic steeping (n=5)  17.  159  Fractional stress relaxation curves for acetate and alpha-cellulose pulps following water or caustic steeping (n=5)..  18.  160  Typical fractional stress relaxation curves for three viscose pulps following water or caustic steeping (n=5)  19.  161  Correlation between fractional stress relaxation of 14 viscose pulps read after 35 min relaxation time following steeping in water or caustic and pulp bemicellulose content............................... 162  R e l a t i o n s h i p between f r a c t i o n a l s t r e s s (n=5)  and l i g n i n c o n t e n t s as observed  relaxation on water  steeped samples o f v a r i o u s p u l p types a f t e r 35 min relaxation  time...  ..•  R e l a t i o n s h i p between f r a c t i o n a l s t r e s s (n=5)  and l i g n i n c o n t e n t s as observed  steeped  relaxation on c a u s t i c  (18.6% NaOH) samples o f v a r i o u s p u l p  types a f t e r 35 min r e l a x a t i o n  time  R e l a t i o n s h i p between f r a c t i o n a l s t r e s s (n=5)  relaxation  and h e m i c e l l u l o s e c o n t e n t s as observed on  water and c a u s t i c  (18.6% NaOH) steeped  samples  of v a r i o u s pulp types a f t e r 35 min r e l a x a t i o n t ime R e l a t i o n s h i p between f r a c t i o n a l s t r e s s (n=5)  relaxation  and c e l l u l o s e c o n t e n t s as observed  steeped  samples o f v a r i o u s p u l p types a f t e r 35 min  relaxation  time.  R e l a t i o n s h i p between f r a c t i o n a l s t r e s s (n=5)  on water  relaxation  and c e l l u l o s e c o n t e n t s as observed  35 min r e l a x a t i o n  time on c a u s t i c  after  steeped  (18.6% NaOH) samples o f v a r i o u s p u l p t y p e s . . . . . . . . S h o r t and long time response relaxation  i n fractional stress  (n=5) o f two v i s c o s e p u l p s exposed  ( a i r - d r y ) to d i f f e r e n t gamma-radiation and  then steeped  i n 18.6%. NaOH (30 s e c , 22°C)  C o r r e l a t i o n between f r a c t i o n a l s t r e s s (n=5)  levels  relaxation  o f i r r a d i a t e d and u n t r e a t e d . v i s c o s e p u l p s  r e a d a f t e r 35 min r e l a x a t i o n  time  s t e e p i n g i n 18.6% NaOH and p u l p solubility  following  caustic  xi  Figure 27.  . Page Relationship between caustic solubility and relative amount of hemicelluloses of 14 viscose pulps.....  28.  170  Fractional stress relaxation results (n=5)  on  seven viscose pulps as read after 35 min relaxation time following short and long time steeping in water or caustic............. 29.  Effect of steeping time in 18.6%  171  NaOh (22°C)  on residual stress relaxation (n=5) of viscose pulp No. 3-2 30.  172  Correlation between fractional stress relaxation (n=5) of 14 viscose pulps read after 35 min relaxation time following steeping in water or caustic (18.6% NaOH) and caustic solubility  173  xii  ACKNOWLEDGMENTS  The author wishes to express his most sincere thanks to Dr. J.W. Wilson, Faculty of Forestry, University of British Columbia, for introducing him to the fields of wood and pulp rheology, and for his constructive criticisms and understanding guidance throughout the study. The author would also like to acknowledge with gratitude his appreciation to Dr. L. Bach, Department of C i v i l Engineering, Technical University, Copenhagen, Dr. G.G.S. Dutton, Department of Chemistry, Dr. F.E. Murray, Department of Chemical Engineering, Dr. L. Paszner and Dr. R.W. Wellwood, Faculty of Forestry, for their generous counsel, helpful advice and reading of the manuscript.  Special acknowledgement  must be extended to Dr. A. Kozak, Faculty of Forestry, for his advice on statistical analysis and computer programming. Grateful appreciation is also due to the National Research Council of Canada and to the University of British Columbia for the financial support extended through the academic program.  INTRODUCTION  1.0  When mechanical and chemical e x c i t a t i o n systems are applied to wood' or wood derived c e l l u l o s i c materials the l i g n o - c e l l u l o s i c polymer systems undergo e l a s t i c , v l a c o e l a s t i c and viscose deformation.  These r h e o l o g i c a l  processes are known or can be expected to depend on the molecular structure and compositional  c h a r a c t e r i s t i c s of wood polymers, as well as on other f a c t o r s  such as magnitude and nature of the external force, stress or s t r a i n h i s t o r y , temperature and degree o f swelling. Stress relaxation studies i n tension on wood tissues using infrared p o l a r i s a t i o n techniques provided  evidence that wood r h e o l o g i c a l behavior  i s a combined response of the three s t r u c t u r a l polymers: c e l l u l o s e , hemicellulose and l i g n i n (48).  It was shown that the o r i g i n a l response i s  disturbed by removing wood constituents.  Thereby v i s c o e l a s t i c behavior  of the remaining complex was d r a s t i c a l l y changed. Based on t h i s observation and other studies (95,273,283) showing dependence of mechanical properties on compositional postulate was put forward.  characteristics a  In t h i s , r h e o l o g i c a l properties of wood derived  materials, such as mechanical and chemical pulps, must be related to quantitative and s t r u c t u r a l features of r e s i d u a l wood polymers. Since compression treatments are frequently involved i n pulp processing, i t appeared appropriate pulp mats subjected  to constant  to examine water and caustic  compressive s t r a i n .  experimental evidence on r e l a t i o n s h i p s between properties and chemical-physical  swollen  It i s thought that  mechanical-rheological  features of f i b r e s may be of p r a c t i c a l ,  as well as t h e o r e t i c a l value. The study was designed around f i v e main objectives. F i r s t , to extend r h e o l o g i c a l techniques to wood based c e l l u l o s i c materials prepared mechanically  or by removal and/or reproportioning of wood  constituents i n i n d u s t r i a l and laboratory  processes.  Second, to determine to what extent change wood and pulp r h e o l o g i c a l properties.  such manipulations a f f e c t or The study included  materials  -  ' representing  2 -  the whole p u l p spectrum (groundwoods, h o l o c e l l u l o s e s , b l e a c h e d  s u l p h i t e , unbleached -and b l e a c h e d s u l p h a t e , v i s c o s e , a c e t a t e , cellulose  pulps). Third,  to examine r h e o l o g i c a l e f f e c t s  as i n t e r - c r y s t a l l i n e swelling  and a l p h a -  (steeping  in  (steeping  following  i n d i s t i l l e d , w a t e r ) and  treatments,  such  intra-crystalline  18.6% NaOH) and p u r p o s e f u l d e g r a d a t i o n by gamma-  irradiation. F o u r t h , to e l u c i d a t e properties  the e f f e c t  of  stress history  by s u b j e c t i n g p u l p samples to v a r i o u s p e r i o d s of  on r h e o l o g i c a l swelling  stresses. Fifth, procedure f o r for  to examine  stress relaxation  characterising pulps, i . e . ,  as a p h y s i c a l - m e c h a n i c a l  development  p r e d i c t i n g c h e m i c a l and m e c h a n i c a l p r o p e r t i e s  of  of r h e o l o g i c a l pulps.  indices  - 3 -  2.0 2.1  BACKGROUND TO THE STUDY  Morphology and Composition Woody c e l l s  of Wood C e l l  Walls  o f C o n i f e r a l e s (gymnosperms) and some D i c o t y l e d o n s  (angiosperms) a r e the p r i n c i p a l  sources of commercial p u l p s .  Numerous  s t u d i e s over the l a s t c e n t u r y have c e n t e r e d on m o r p h o l o g i c a l and c h e m i c a l s t r u c t u r e s of v a r i o u s c e l l  types from these s o u r c e s .  been t o i n c r e a s e u t i l i s a t i o n  O f t e n the purpose has  of wood as a f i b r e s o u r c e , o r t o improve the  p r o p e r t i e s o f f i b r o u s p r o d u c t s a l r e a d y b e i n g manufactured.  In s p i t e of  i n t e n s e r e s e a r c h a c t i v i t i e s , which have lead t o an ever i n c r e a s i n g of  i n f o r m a t i o n on the s u b j e c t , many q u e s t i o n s on wood c e l l  accumulation  w a l l s remain  unanswered. 2.1.1  Major wood c e l l  types  T r e e cambiums produce f o u r d i s t i n c t (i)  parenchyma c e l l s ;  elements. of  types of x y l a r y  elements:  ( i i ) t r a c h e i d s ; ( i i i ) f i b r e s ; and ( i v ) v e s s e l  Parenchyma c e l l s  are present  i n a l l woody s p e c i e s , whereas any  the o t h e r s t r u c t u r a l elements may be wanting.  In c o n i f e r s  longitudinal  t r a c h e i d s a r e dominant, w i t h few i f any f i b r e s and no v e s s e l s p r e s e n t , but i n angiosperms t r a c h e i d s a r e s c a r c e , w h i l e f i b r e s and v e s s e l s a r e o f t e n dominant c e l l  types  (103,121,128,182,226,251,301).  Longitudinal sylvestris  t r a c h e i d s i n stem woods of Scotch p i n e  L. ) and European spruce  (Pinus  ( P i c e a a b i e s K a r s t . ) have been found t o  amount t o 95% and 93% of the wood volume and 99% and 98% o f the wood In  comparison,  l i b r i f o r m f i b r e s i n European b i r c h  occupy 65% of the wood volume and account  weight.  ( B e t u l a v e r r u c o s a L. )  f o r 86% o f the wood weight  (232,251).  For a more complete d e s c r i p t i o n o f the v a r i o u s wood elements, t h e reader i s r e f e r r e d years 2.1.2  t o a number of e x c e l l e n t reviews  published w i t h i n recent  (103,226,251). Cell wall organisation Characteristic  t o a l l types of wood c e l l  they a r e composed of t h r e e groups of s u b s t a n c e s .  w a l l s i s the f a c t  that  Wardrop (316) has c l a s s i f i e d  - 4 -  t h e s e a s : ( i ) framework s u b s t a n c e s ;  ( i i ) matrix  encrusting  t h e predominant r o l e of t r a c h e i d s and  fibres  substances.  Considering  i n wood s t r u c t u r e , the f o l l o w i n g r e v i e w of c e l l  limited  t o these two c e l l  types.  Since  u l t r a s t r u c t u r e , they may be c o n s i d e r e d The  Hemicelluloses  are c o n s t i t u e n t s of the m a t r i x  e x t e r n a l and t h r e e  wall  and other  n o n - c e l l u l o s i c carbohydrates  D i s t r i b u t i o n and o r i e n t a t i o n  w a l l and between a d j a c e n t  internal  ( P ) ; outer  layers.  cells  three  ( S ^ ) , main ( S ) and i n n e r 2  wall  schematic p i c t u r e s f o r accepted Since  there a r e a great  produces  These a r e known as m i d d l e  l a y e r s ; and sometimes an i n n e r warty l a y e r (187,301,316).  architecture. cell  to f i v e  (M); primary w a l l  presents  wall  together.  (19,82,316).  of these m a t e r i a l s w i t h i n the c e l l  lamella  similar cell  is  s u b s t a n c e s , whereas l i g n i n s a r e c o n s i d e r e d t o  t h e main e n c r u s t i n g m a t e r i a l s  one  they show v e r y  w a l l composition  framework substance i s c e l l u l o s e which i s aggregated i n the  form of m i c r o f i b r i l s .  be  s u b s t a n c e s ; and ( i i i )  t h e o r i e s on c e l l  (S^) secondary Figure 1 wall  number of d e t a i l e d reviews on woody  l a y e r s (12,41,64,79,82,157,158,167,188,314), o n l y a few p o i n t s  p e r t i n e n t t o t h i s study w i l l be d i s c u s s e d . The  middle l a m e l l a (M) f u n c t i o n s as an i n t e r c e l l u l a r  l a y e r between a d j o i n i n g c e l l s (approximately  and i s c h a r a c t e r i s e d by i t s h i g h  70%) and n o n - c e l l u l o s i c c a r b o h y d r a t e s  c e l l u l o s e m i c r o f i b r i l s a r e p o s s i b l y absent with  the t h i n outermost  (12).  adhesive lignin  content  (14,156); whereas  I t (M) i s c l o s e l y a s s o c i a t e d  (P) l a y e r found i n f i b r e s o r t r a c h e i d s .  I t (P)  a l s o c o n s i s t s m a i n l y of s o - c a l l e d amorphous m a t e r i a l s , l i s n i n and noncellulosic  carbohydrates;  m i c r o f i b r i l s having or  but c o n t a i n s  only a loose aggregation  no d e f i n i t e o r i e n t a t i o n on t h e o u t e r  of c e l l u l o s i c  s u r f a c e , but a more  l e s s t r a n s v e r s e alignment t o the f i b r e a x i s on the i n n e r s u r f a c e  According  to Bucher ( 4 1 ) , the h i g h  l i g n i n content,  fibrillar  t e x t u r e , g i v e s the primary w a l l a v e r y  which causes i t t o b u r s t when t r e a t e d w i t h  It  i s g e n e r a l l y accepted  comprise the secondary w a l l S^ and S^, a r e arranged It has been found  (148,316).  as w e l l as the woven  limited  swelling capacity,  s w e l l i n g agents.  t h a t the a d j o i n i n g t h r e e  l a y e r s which  ( S ^ , S^ and S ^ ) , and a l s o l a m e l l a e w i t h i n the  i n cross-layered constructions  (72,101,148,311,316).  i n experiments u s i n g a p o l a r i z i n g microscope t h a t  microfibril  -  orientation 10°  in  l i e s between 50°  to 35° depending on  ranges i n fibrils  5  between 60°  form l a m e l l a e  species  (148).  thin  t h i s t h i n l a m e l l a r system can  be  Dunning (60) observed w i t h  l a y e r of  l o n g l e a f pine  l e a s t three  tracheids.  vary  from 30 to 40  w a l l mechanical and  Jayme and  These showed t h a t  only  3 to 4%  It has  outer  Fengel the  been observed  are o r i e n t e d  lamellae  The  nearly  towards  S^,  s i m i l a r to the  by  relative  non-alternating  f o r earlywood  (131)  S^,  thickness  only  7 t o 14%;  t o the  fibre axis.  e x h i b i t a gradual  when p r e s e n t , p r o b a b l y not  t h i n l a y e r (W)  lumen l i n i n g when the  o r i g i n a t e s from d e p o s i t s improve the It  The  of the  the  cell  5 to  11%;  i n most  S  2  Microfibrils  change from  in  and  body. i s a t h i n l a y e r of f l a t  helical  e x c e e d i n g f i v e to s i x l a m e l l a e  (148,316).  developed or wanting i n some genera and The  bulk,  measurements,  74 to 84%  (101,102) t h a t m i c r o f i b r i l s  and  and  on European s p r u c e earlywood  Liese  (166)  reported  i s somewhat t h i c k e r i n c o n i f e r s than i n pored woods and  cell  (251).  w a l l volume.  parallel  with a l t e r n a t i n g o r i e n t a t i o n s  may  stresses  physical properties.  layer occupied  to the c e l l  o r i e n t a t i o n s to t h a t of the main  or  which  swelling  Cote (148), the number of  w a l l ; whereas, the p r i m a r y w a l l c o n t r i b u t e d  lamellae  lamellae,  to high  the  (Pinus p a l u s t r i s  r e a d i l y t o r n from the b u l k y  layer i s also revealed  example those by  the  micro-  more f o r latewood, thus c o n t r i b u t i n g most t o the c e l l w a l l  r o l e of the  and  between  layers.  i n the main secondary w a l l may  and  axis; in  i n d i c a t e d i n F i g . 1, the  When s u b j e c t e d  to Kollmann and  as w e l l as d o m i n a t i n g c e i l  for  As  i s comprised of a t  exhibit alternating orientations.  t o 150  from the c e l l  p o s i t i o n i n the growth zone; and i t  i n the v a r i o n s  M i l l . ) latewood f i b r e s  lamellae  to 70°  and  to 90°  e l e c t r o n m i c r o s c o p e t h a t the  According  -  that  i n compression wood  of t o n o p l a s t  in  thickness  that  the  i t i s poorly tracheids.  c o n t a i n i n g warty s t r u c t u r e s may i s wanting.  pattern  cover  the  It i s g e n e r a l l y accepted that W  residues  (167,316).  Functionally, i t  chemical r e s i s t a n c e .  i s apparent from the above d e s c r i p t i o n s that  w a l l s are a m u l t i - p l y  t r a c h e i d or  l a m i n a t e of c e l l u l o s e m i c r o f i b r i l s which  fibre  differ  -  6  -  c o n s i d e r a b l y i n o r i e n t a t i o n between and w i t h i n r e s p e c t i v e p l i e s .  As Mark  (182) s u g g e s t s , such v a r i a t i o n s i n m i c r o f i b r i l o r g a n i s a t i o n c a n be e x p e c t e d to i n f l u e n c e t h e p h y s i c a l and m e c h a n i c a l and a l s o t h e r h e o l o g i c a l p r o p e r t i e s of f i b r o u s c e l l u l o s i c m a t e r i a l s .  There a r e s e v e r a l p u b l i s h e d works w h i c h  have i n v e s t i g a t e d m i c r o f i b r i l o r i e n t a t i o n - m e c h a n i c a l i n wood and i n i n d i v i d u a l f i b r e s 2.1.3  property r e l a t i o n s h i p s  (83,115,136).  C h a r a c t e r i s t i c s o f wood c h e m i c a l  constituents  C o m p o s i t i o n s t u d i e s on many c o n i f e r o u s woods have shown t h a t on a v e r a g e c e l l u l o s e amounts t o 4 3 % , h e m i c e l l u l o s e s 28% and l i g n i n 29% o f t h e e x t r a c t i v e - and m o i s t u r e - f r e e c e l l w a l l s u b s t a n c e ( 4 5 ) . for  pored woods a r e 4 3 % , 35% and 22% ( 4 5 ) .  Respective  From t h i s i t i s a p p a r e n t t h a t  w a l l s i n c o n i f e r o u s woods c o n t a i n c o n s i d e r a b l y l e s s m a t r i x  f o r a few N o r t h American c o m m e r c i a l l y  cell  hemicelluloses  and more e n c r u s t i n g l i g n i n s u b s t a n c e s t h a n t h o s e i n pored woods. compositions  values  Chemical  i m p o r t a n t woods a r e g i v e n  i n Table 1 (294). ' 2.1.3.1  Cellulose C e l l u l o s e i s c o m p r i s e d o f jft-D-glucopyranose  r e s i d u e s which are  bonded t o g e t h e r as l i n e a r c h a i n s by ( l - * " 4 ) - g l y c o s i d i c l i n k a g e s The  glucose residues are present  i n *C^ c h a i r c o n f o r m a t i o n  with  (119,218). identical  bond a n g l e s o f about 110° and w i t h h y d r o x y l groups a l l e q u a t o r i a l ( 1 1 9 , 2 9 4 ) . L i g h t s c a t t e r i n g measurements on n i t r a t e d c e l l u l o s e c a r r i e d o u t by G o r i n g and T i m e l l ( 9 0 ) i n d i c a t e d t h a t a t l e a s t 8,000 t o 10,000 g l u c o s e u n i t s p a r t i c i p a t e i n f o r m a t i o n o f a wood c e l l u l o s e According  strand.  t o M u t t o n (203) and Rydholro (251), c e l l u l o s e i s c a p a b l e  of u n d e r g o i n g r e a c t i o n s a t i t s h y d r o x y l  ( a d d i t i o n , s u b s t i t u t i o n and o x i d a t i o n  r e a c t i o n s ) and a c e t a l ( a c i d i c and a l k a l i n e h y d r o l y s i s ) g r o u p s .  Furthermore,  the a l d e h y d e end groups c a n be o x i d i z e d , r e d u c e d o r r e a r r a n g e d .  It i s well  known t h a t a l d e h y d e end groups a r e r e s p o n s i b l e f o r d e g r a d a t i o n a l k a l i n e pulping  (251).  reactions i n  - 7 -  2. 1.3.1.1  S u p e r m o l e c u l a r arrangement  fibrillar  S u p e r m o l e c u l a r arrangement of the c e l l u l o s e c h a i n m o l e c u l e s  within  and  of  sub-fibrillar cell  many t h e o r i e s .  Various  m i c r o s c o p y and  X-ray and  t h a t c e l l u l o s e - the  wall  c h e m i c a l and  s t r u c t u r e s has  been the s u b j e c t  p h y s i c a l methods, i n p a r t i c u l a r e l e c t r o n  e l e c t r o n d i f f r a c t i o n measurements, have  sole constituent  of m i c r o f i b r i l s  - i s at  packed i n t o c r y s t a l l i n e r e g i o n s , known as c r y s t a l l i t e s . e x i s t s i n the  ( i i ) paracrystalline; ( i i i ) c r y s t a l defect; fringed-fibril;  and  (vi) lamellar.  the most w i d e l y d i s c u s s e d The  regions  and  and  The  last  t h r e e models are  then i n the amorphous zone the c h a i n s  introduced  According  30 A* t h i c k (238,312), and  c r y s t a l l i t e s a r e arranged at r e g u l a r  the c r y s t a l l i t e s a r e  the  crystal; (v)  by Hermann  separate.  (177)  to F r e y - W y s s l i n g  (80),  randomly i n the  supported t h i s h y p o t h e s i s and  they there  l e a s t 600 A*  amorphous r e g i o n s .  i n t e r v a l s but  s e g r e g a t e d as f i b r i l s  crystalline  Thereafter  t r a n s i t i o n between c r y s t a l l i t e s which are at  Marchessault  Thus,  presently  s t a t e s t h a t c e l l u l o s e c h a i n m o l e c u l e s pass through  A* wide and  direction.  ( i ) perfect  (iv) fringed micelle;  fringed m i c e l l a r hypothesis,as f i r s t  e x i s t s a gradual 100  within  adopted.  r e a l i g n to form another c r y s t a l l i t e .  long,  controversy  s t r u c t u r e s , which are assumed t o form  m i c r o f i b r i l s , have been proposed as models, such a s :  a_l.(112),  Much  partially  (109,110,113,141,198,199,238,240,246,249,270).  s e v e r a l systems of f i n e l a t t i c e  et  least  l i t e r a t u r e on whether or not a l l c e l l u l o s e l i e s  c r y s t a l l i n e regions  revealed  The chain  proposed  that  which are embedded i n o r i e n t e d  hemicelluloses. More r e c e n t l y , H e a r l e fringed-fibril fibrils  and  (108-110) developed a c o n c e p t , known as  model, which c o n s i d e r s  the almost  the phenomenon of p o l y m o l e c u l a r  In t h i s model m i c r o f i b r i l s are d e s c r i b e d arranged  in spiral-form within  amorphous zones.  The  it fails,  as  shown by  l e n g t h of micro-  spherulitic  arrangement.  imperfectly c r y s t a l l i n e ,  s t r u c t u r e and  separated  This  several  hypothesis  the b e h a v i o r of c o t t o n c e l l u l o s e  Mark (182)  and  Cowdrey and  Preston  and  by  run a l t e r n a t e l y through  through amorphous r e g i o n s .  been found t o e x p l a i n s u f f i c i e n t l y  ( 5 2 ) , but  long,  c e l l u l o s e m o l e c u l e s may  c r y s t a l l i n e zones, as w e l l as has  growth by  as  the f i b r i l  infinite  the  (52),  to  - 8 -  'describe  satisfactorily  the mechanical b e h a v i o r of c o n i f e r o u s  L a m e l l a r or f o l d e d m o l e c u l e s are  folded  in-plane  helix  (58,59,185,297).  (176)  was  able  chain  By  theories  advocate t h a t c e l l u l o s e  t o form a f l a t  using  tracheids.  ribbon,  which i s wound as  c e l l u l o s e from s e v e r a l  Investigations coniferous  and  c a r r i e d out  f o l d i n g theory.  model i s not  c a p a b l e of s a t i s f a c t o r i l y e x p l a i n i n g of  However, as  the c e l l  by  Mark (182)  of  S u l l i v a n (284)  deciduous s p e c i e s  t o the c h a i n  mechanical p r o p e r t i e s  a  e l e c t r o n d i f f r a c t i o n t e c h n i q u e s , Manley  to show t h a t c e l l u l o s e d e r i v a t i v e s e x h i b i t t h i s type  s t r u c t u r a l arrangement.  chain  also  pointed  on  lend  support  out,  this  observed p h y s i c a l  and  wall.  From the above, i t i s apparent t h a t  none of the proposed t h e o r i e s  seems  to r e p r e s e n t a l l c a s e s of c e l l u l o s e m o l e c u l a r arrangement i n m i c r o f i b r i l s . Possibly  some new  or  improved p h y s i c a l methods of e x a m i n a t i o n couLd h e l p  elucidate m i c r o f i b r i l l a r 2.1.3.1.2  The The  crystal  structure  of  cellulosics.  structure  detailed structure  of c e l l u l o s e c r y s t a l l i n e zones has  deduced from X-ray d i f f r a c t i o n measurements. and  Preston  (237)  described  cellulose crystallites, clinic and  system.  Mark (196)  i n F i g . 2,  the  c o r n e r s of the  The and  the  the  smallest  H a r t s h o r n e and  g r o u p i n g of  l a t e r m o d i f i e d by consists  parallelepiped  and  Meyer and  was  and  first  Misch  (107)  the  of the mono-  proposed by  (197).  As  a f i f t h cellobiose unit  Meyer  indicated  of f o u r c e l l o b i o s e u n i t s a r r a n g e d  i n t e r s e c t i o n of the d i a g o n a l s w i t h  been  Stuart  subunits i n  u n i t c e l l , as p a r a l l e l e p i p e d  crystallographic unit c e l l  unit c e l l  passed through the  to  turned  in  180°  the and  a d i f f e r e n c e of  %-unit  spacing. A c h a r a c t e r i s t i c feature between the axes a and i n F i g . 2,  c which has  of c e l l u l o s e u n i t c e l l s been found to be  As  indicated  in  the;.formation of t h r e e p l a n e s , known as  i s assumed t h a t c r y s t a l l i t e , and  the  101  the arrangement of the  planes are  consequently  A c c o r d i n g to F r e y - W y s s l i n g  parallel  l i e parallel  (77,78), the  101  the  84°  i s the  for native c e l l u l o s e .  c h a i n s i n the 101,  to the to the  101  and  crystal results 002  planes.  larger surface cell  angle  wall  of  surface  It  the (237,315).  p l a n e , which i s p a r t i c u l a r l y  - 9 -  rich  i n hydroxyl  groups, i s the plane  which the f i b r i l s  tend  of l a m i n a t i o n ;  that  i s , the plane  to aggregate l a t e r a l l y w i t h i n c e l l  wall  in  lamellae  (81,315). F o r c e s which keep the g l u c o s e to  Honeyman and  fairly  Parsons ( 1 2 0 ) :  be  important  resist  plane.  i n determining  The to  ( i ) covalent  s t r o n g hydrogen bonds i n the a-b  Waal's f o r c e s i n the a-c  residues  plane;  A l l of these  Aqueous p o l a r compounds, such as  to Rydholm (251)  t h i s process  dimensional  changes of the u n i t c e l l  i n c r e a s e i n the  101  are s u f f i c i e n t l y  s t r o n g l y a l k a l i n e or alter  the c e l l u l o s e  involves f i r s t  and  hydroxyl  acid lattice.  the b r e a k i n g  t h e r e a f t e r the groups.  This  of formation  leads  i n transverse d i r e c t i o n , c h i e f l y 002  to because  spacings  '251).  Hemicelluloses  carbohydrates,  p h y s i c a l p r o p e r t i e s of the n o n - c e l l u l o s i c wood  or h e m i c e l l u l o s e s , have been c r i t i c a l l y  148,169,251,258,293,295). w a l l s of c o n i f e r o u s and  reviewed  A l t h o u g h r e l a t e d , the h e m i c e l l u l o s e s  pored woods d i f f e r  to some e x t e n t .  the 0 - a c e t y l - 4 - O - m e t h y l g l u c u r o n o - x y l a n appears to be hemicellulose.  According  r e s i d u e s , l i n k e d together stituted  to Meier (190), by  ( l - > 4 ) - g l y c o s i d i c bonds.  from b i r c h showed t h a t  i n only  or C^.  The  l i m i t e d amounts (294,295).  been found t o c o n t a i n  (1-—1*-4) - l i n k e d  r e s i d u e s m o s t l y i n a r a t i o of 1:2  (295).  i n the  cell  In pored woods, the dominant  It i s p a r t i a l l y  a c e t y l groups.  a 4-0-methyl-c^-D-glucuronic a c i d at the x y l a n  10 c a r r y an a c e t y l group at  (2,99,116,  t h i s x y l a n c o n s i s t s of yS-D-xylopyranose  by 4-0-methyl-c<-D-glucuronic a c i d and  (27) s t u d y i n g g l u c u r o n o - x y l a n  occurs  strong  zones, i n  i n t e r p l a n a r d i s t a n c e , whereas l O l and  o n l y minor changes  Chemical and  has  to  (212,300).  c e l l u l o s e h y d r o x y I s and  hydrogen bonds between reagent  2.1.3.2  considered  der  the s w e l l i n g caused by a d d i n g water to amorphous r e g i o n s  hydrogen bonds between two  exhibit  ( i i i ) much weaker van  f o r c e s a r e now  cellulose properties  s o l u t i o n s , however, a r e known to a t t a c k and  of an  and  according  plane; ( i i )  the p e n e t r a t i o n of water m o l e c u l e s i n t o c r y s t a l l i n e  (206,251).  of new  bonds i n the b-c  i n t e r m o l e c u l a r f o r c e s i n the u n i t c e l l  o t h e r words, l i m i t  According  i n p o s i t i o n are,  sub-  Bouveng et a l .  1 i n 10 x y l a n p o s i t i o n and  residues about  7 of  second h e m i c e l l u l o s e , a glucomannan, It i s claimed  to be  j3-D-glucopyranose and  l i n e a r and  has  |3-D-mannopyranose  - 10 -  In most c o n i f e r o u s woods, a c c o r d i n g  t o Abdurahman e t a l . (1)  Meier ( 1 9 0 ) , two t y p e s o f h e m i c e l l u l o s e s - g l u c u r o n o a r a b i n o x y l a n galactoglucomannan - appear t o be dominant. |3-D-xylopyranose r e s i d u e s , l i n k e d t o g e t h e r  The by  and  and  former type c o n s i s t s of  (l-*-4 )-g l y c o s i d i c bonds.  Some of the x y l o s e r e s i d u e s c a r r y 4-0-methyl-<X-D-glucuronic a c i d groups at C^.  and  some a r e s u b s t i t u t e d by L - a r a b i n o f u r a n o s e  u n i t s a t C^.  glucomannan i s composed of  (1—»4) - l i n k e d f3-D-glucopyranose  ^-D-mannopyranose r e s i d u e s  (1:3.5 r a t i o ) w i t h  molecule.  o t h e r s have r e p o r t e d  Meier (190)  residues are attached  and  two  The and  or t h r e e branches  t h a t a c e t y l and  per  galactose  to mannose u n i t s of the backbone.  A c h a r a c t e r i s t i c f e a t u r e of n o n - c e l l u l o s i c c a r b o h y d r a t e s i s the r a t h e r low degree of p o l y m e r i s a t i o n .  i n wood  T i m e l l (294,295) r e p o r t e d  that  t h e i s o l a t e d h e m i c e l l u l o s e s mentioned above seldom have more t h a n 150  to  200  of  sugar r e s i d u e s . T h i s may  p a r t l y e x p l a i n the h i g h e r e x t r a e t a b i l i t y  h e m i c e l l u l o s e s i n comparison w i t h Berlyn  (251).  (19) c o n s i d e r s h e m i c e l l u l o s e s  of the c e l l w a l l m a t r i x . for  cellulose  Marchessault  (178)  to be  and  the main c o n s t i t u e n t s  Wardrop (316)  i n s t a n c e , n a t i v e x y l a n surrounds c e l l u l o s e f i b r i l s by  amorphous m a t r i x ,  and  t h e r e i s evidence  t h a t i t may  reported  forming  a somewhat  be o r i e n t e d i n wood  (70,165).Due to a h i g h l y branched s t r u c t u r e , however, i t i s d o u b t f u l n a t i v e xylan occurs by N e l s o n (205) with  i n c r y s t a l l i n e form (205).  present  evidence  c e l l u l o s e m i c r o f i b r i l s and  I t appears from s t u d i e s of L i n d b e r g  on European spruce  h o l o c e l l u l o s e preparations  2.1.3.3  or o n l y s l i g h t l y  be c l o s e l y  out  associated  a r e even p o s i t i o n e d between  c e l l u l o s e chains.  ordered  that  X-ray s t u d i e s c a r r i e d  t h a t glucomannans may probably  that,  and  Meier  (170)  t h a t glucomannans may  be  un-  ordered.  Lignin Lignin i s considered  as  the major e n c r u s t i n g s u b s t a n c e between  w i t h i n wood c e l l w a l l s .  The  complete due  t h a t i t i s a complex, t h r e e - d i m e n s i o n a l  to the f a c t  which i s d i f f i c u l t  knowledge of i t s s t r u c t u r e i s s t i l l  to i s o l a t e from the framework and m a t r i x  H y p o t h e t i c a l models of i t s c h e m i c a l  structure, in particular  and  f a r from polymer  substances  (19).  l i n k a g e s between  the main s t r u c t u r a l u n i t s , phenylpropane g r o u p s , have been proposed  by  - 11 -  Freudenberg  (74,75) and A d l e r  Due t o the aromatic  (3) among o t h e r s . nature and f u n c t i o n a l groups on the a l i p h a t i c  s i d e - c h a i n and r i n g of the phenylpropane u n i t , the l i g n i n macromolecule, a c c o r d i n g t o Rydholm (251), can undergo s e v e r a l r e a c t i o n s . s u l p h o n a t i o n , h y d r o l y s i s and c o n d e n s a t i o n as w e l l as m e r c a p t a t i o n , oxidation. processes,  i n a c i d i c and a l k a l i n e medium,  h a l o g e n a t i o n , d e g r a d a t i v e and  These r e a c t i o n s a r e most important such as p u l p i n g and b l e a c h i n g .  These i n c l u d e  non-degradative  i n many d e l i g n i n i f i c a t i o n  E x c e l l e n t reviews  on the s u b j e c t  have been p u b l i s h e d r e c e n t l y (47,57,230,251,309). The  p h y s i c a l nature o f the l i g n i n polymer system, p o s i t i o n i n g i n  the c e l l w a l l and i t s a s s o c i a t i o n w i t h c a r b o h y d r a t e s much argument.  I t "is o f t e n assumed t h a t l i g n i n  branched n a t u r e , i s p r e s e n t  character, particularly  i t s preventing e f f e c t  h e m i c e l l u l o s e s has been mentioned Goring and  i n wood, due t o i t s h i g h l y  i n an amorphous.state.  t h a t wood l i g n i n does not e x h i b i t a c r y s t a l l i n e  (89) reviewed  have been s u b j e c t o f  Frey  (76) p r e s e n t e d  structure.  evidence  I t s hydrophobic  on e x c e s s i v e s w e l l i n g of  earlier.  the l i t e r a t u r e on l i g n i n polymer p r o p e r t i e s  summarized f o u r proposed hypotheses on the p h y s i c a l s t a t e of l i g n i n  polymeric  systems i n wood.  These i n c l u d e network t h e o r y ,  small-molecule  t h e o r y , l i g n i n - c a r b o h y d r a t e bonds and p o s s i b l e "snake c a g e " t h e o r y , and t h e o r y on a g g r e g a t i o n by secondary According  bonds.  t o the network t h e o r y , the l i g n i n s t r u c t u r e i s t r e a t e d  as c o n s i s t i n g of s h o r t l i n e a r c h a i n s c r o s s - l i n k e d by v a r i o u s types o f c o v a l e n t bonds thus forming supported  t h i s hypothesis  p o s i t i o n by s t r o n g bonds.  a three-dimensional  by s u g g e s t i n g  Yean and G o r i n g molecular  The s m a l l - m o l e c u l e  theory  tries  theory c o n s i d e r s n a t i v e  which tend t o p o l y m e r i z e  lignin  during  T h i s t h e o r y appears t o be q u e s t i o n a b l e , however, s i n c e  (324), s t u d y i n g the e f f e c t  o f s u l p h o n a t i o n on l i g n i n  weight d u r i n g e x t r a c t i o n , observed The  Schuerch (257)  t h a t n a t i v e l i g n i n must be kept i n  as c o n s i s t i n g of s m a l l , r e a c t i v e m o l e c u l e s i s o l a t i o n processes.  structure.  l i g n i n - c a r b o h y d r a t e bond,  only i n s i g n i f i c a n t  changes.  and p o s s i b l e "snake cage" e f f e c t  t o e x p l a i n the u n i v e r s a l p r o t o l i g n i n  insolubility  of low-  - 12 -  m o l e c u l a r weight. compounds.  Such bonds might a t t a c h the l i g n i n  (254).  and Weyna (234), who  be surrounded they may  Another  stated  be h e l d i n the g e l - l i k e  that  limited  l i n e a r carbohydrate molecules  lignin  to  may  In o t h e r words,  substance by m o l e c u l a r entanglement  structures.  Various i n v e s t i g a t i o n s must i n f i l t r a t e  carbohydrate  a l t e r n a t i v e concept was. proposed  by the t h r e e - d i m e n s i o n a l l i g n i n network.  o r "snake cage"  (310,314,317) p r o v i d e e v i d e n c e t h a t  the c a r b o h y d r a t e complex.  Wardrop (310,314) and Wardrop and  found  lignin  Based on X-ray measurements,  P r e s t o n (317) c a l c u l a t e d  and h o l o c e l l u l o s e c r y s t a l l i t e s and 18.8%  to  However, the number of bonds i s p r o b a b l y s m a l l and  " o c c a s i o n a l spot welds" by Pew  slightly  the s i z e of wood  f o r h o l o c e l l u l o s e an i n c r e a s e of  i n c r y s t a l l i n i t y , which i s i n agreement w i t h v a l u e s determined  hydrolysed c e l l u l o s e c r y s t a l s .  Furthermore,  that h y d r o l y s i s during d e l i g n i f i c a t i o n of h o l o c e l l u l o s e caused the m i c r o s c o p e .  microfibrils  Wardrop (313,314.) observed,  t r e a t m e n t s and  to aggregate  Wardrop (314) a t t r i b u t e d  from  subsequent  hydrolysis  i n clumps v i s i b l e  under  t h i s phenomenon to c r y s t a l l i s a t i o n  of l e s s o r d e r e d r e g i o n s s u r r o u n d i n g the m i c r o f i b r i l s , f o r m e r l y prevented c r y s t a l l i s a t i o n by  infiltrated  lignin.  A g g r e g a t i o n by secondary mechanism f o r k e e p i n g  bonds appears  l i e n i n molecules  t o be an  important  i n p o s i t i o n w i t h i n the c e l l  Benko (17) r e p o r t e d a c o n s i d e r a b l e i n c r e a s e i n m o l e c u l a r weight .kraft  l i g n i n s by d e c r e a s i n g the pH from  t i o n s Benko suggested  11.5  to 7.0.  wall.  of  soluble  Based on these  t h a t a s s o c i a t i o n s of l i g n i n m o l e c u l e s  bonds, p r o b a b l y through  observa-  through weak c h e m i c a l  s o l v e n t dependent hydrogen and hydrophobic  bonds,  i n f l u e n c e markedly the a c t u a l m o l e c u l a r s i z e of l i g n o s u l p h o n a t e s and lignin materials.  Other  from  s t u d i e s (34,93) on k r a f t  other  l i g n i n a l s o support  the  b l e a c h i n g o r p u r i f i c a t i o n treatments  are  aggregation hypothesis. 2.2  C h a r a c t e r i s a t i o n of V a r i o u s Pulp Types P u l p i n g and  subsequent  known t o change d r a s t i c a l l y  the c h e m i c a l and c o n s e q u e n t l y the  n a t u r e of l i g n i n , h e m i c e l l u l o s e s and i n most p u l p t y p e s . on the mechanical  c e l l u l o s e and  Such changes undoubtedly  p r o p e r t i e s of p u l p mats.  physical  their relative  composition  must e x e r t a profound  For u n d e r s t a n d i n g  pulp  influence mat  - 13 -  responses to mechanical excitations i t seems useful to elucidate the chemical, physical and compositional modifications which carbohydrate and lignin fractions undergo in pulping. In the following section the present knowledge and understanding of these modifications will be reviewed in a somewhat summary way, with particular reference to pulp types examined in the present study. 2.2.1  Mechanical pulps Fibrous materials produced in conventional groundwood processes  are obtained by applying mechanical energy to wet wood. The absence of chemical treatments before and during manufacture maintains an almost quantitative yield from wood (95 to 98%).  Rydholm (251) suggested that  high temperatures developed during the grinding process may have three distinct effects on the lignin-carbohydrate complex: ( i ) softening of the lignin polymer; ( i i ) weakening of hydrogen bonds; and ( i i i ) probably hydrolysis of carbohydrates. The last effect probably accounts for most of the 2 to 5% yield loss.  Brecht and Klemm (30) considered alteration of  chemical nature of wood during the grinding process to be below the degree needed to significantly affect physical and chemical responses of c e l l wal Brightening treatments with oxidative reagents, such as sodium dithionite or hydrogen peroxide, are considered as having only a minor influence on groundwood mechanical properties, in spite of some structural changes imparted to lignin and, under certain circumstances, also to , carbohydrates.  The oxidative transformation of lignin chromophores to  colourless compounds (251) in peroxide brightening may be accompanied by condensation reactions.  This is evidenced by the work of Katuscak e_t a l .  (142), who observed that peroxide oxidation of methanol lignins caused an increase in cross-linkage without changing lignin molecular weight; in other words,increased intramolecular covalent bonding.  Because these  reactions do not seem to lead to enlargements of the lignin network, their effect on the mechanical behavior may be subordinate. The carbohydrates, according to Stobo and Russel (280), are apparently not affected in cold peroxide treatments, but hot treatments cause definite degradation as indicated by decreased viscosity and increased carboxyl content (168).  - 14 -  '2,2.2  Holocellulose Two  pulps  w i d e l y used  procedures  f o r h o l o c e l l u l o s e preparation are  p e r a c e t i c a c i d method as m o d i f i e d by Leopold method o r i g i n a l l y proposed r e c i p e by Wise e t al. No proposed  (164); and  by Jayme (129), but developed  the a c i d  Goring  (323). method produces h o l o c e l l u l o s e s w i t h o u t  some l o s s o f  Recently, Ahlgren  (4) c a r r i e d out a study on t h i s s u b j e c t and observed  d e l i g n i f i c a t i o n of b l a c k spruce holocellulose  i n 70% y i e l d  g a l a c t a n , 127. x y l a n and d e l i g n i f i c a t i o n was  ( P i c e a mariana  that  ( M i l l . ) BSP. ) wood  c o n t a i n i n g 40% c e l l u l o s e ,  o t h e r c a r b o h y d r a t e s and  found  mannose and g a l a c t o s e .  5%  chlorite  produced  13% glucomannan and  lignin.  Further  t o cause c o n s i d e r a b l e c a r b o h y d r a t e  loss,  mainly  A h l g r e n and G o r i n g ' s o b s e r v a t i o n s a r e i n r e a s o n a b l e  agreement w i t h e a r l i e r f i n d i n g s  (38,39,44,189,290).  Timell  (292) r e p o r t e d  t h a t a c i d c h l o r i t e d e l i g n i f i c a t i o n a t t a c k s the c a r b o h y d r a t e  p o r t i o n , as  i n d i c a t e d by d e c r e a s e i n DP w i t h p r o g r e s s i v e d e l i g n i f i c a t i o n . e x p l a i n the l o s s o f p o l y o s e s i n l a t e r s t a g e s of P o l j a k (236), who delignification  chlorite  as the p r e s e n t  n o n - c e l l u l o s i c c a r b o h y d r a t e s a t complete l i g n i n removal. and  the  first  T h i s may  well  delignification.  i n t r o d u c e d p e r a c e t i c a c i d f o r wood  (235), r e p o r t e d t h a t t h i s method c o m p l e t e l y removes the  l i g n i n w i t h o u t h y d r o l y s i n g the c a r b o h y d r a t e s  t o simple sugar u n i t s .  In  l a t e r comprehensive s t u d i e s on the s u b j e c t , which l e a d to a m o d i f i c a t i o n of P o l j a k s method, Leopold 1  c a t i o n does not  (164) was  a b l e t o show t h a t p e r a c i d d e l i g n i f i -  l e a v e the wood c a r b o h y d r a t e p o r t i o n e n t i r e l y  i n t a c t . Some  l o s s of the glucomannan, a r a b i n o s a l a c t a n and x y l a n p o l y o s e s , and  decrease  i n c e l l u l o s e DP  Furthermore,  (164), indicated-carbohydrate c h a i n d e g r a d a t i o n .  the h o l o c e l l u l o s e p r e p a r a t i o n s were found lignin.  2.2.3  c o n t a i n between 2 and  Evidence r e g a r d i n g the d e g r a d i n g e f f e c t of p e r a c e t i c a c i d  carbohydrates that  to s t i l l  i s a l s o g i v e n by work of Shimada and  increase in chip size  lowered y i e l d  Kondo (264), who  on observed  i n peracid cooking.  S u l p h i t e pulps Dependent on c o o k i n g v a r i a b l e s employed, such as  c o o k i n g time and  temperature,  l i q u o r c h a r a c t e r i s t i c s , s u l p h i t e p u l p i n g may  3%  be used  to  - 15 -  produce a whole s e r i e s of p u l p s . r i c h greaseproof  These range from t y p i c a l  paper p u l p s at 52% y i e l d  heraicellulose-  (86) through v a r i o u s types of  o r d i n a r y paper making pulps to h i g h a l p h a - t y p e d i s s o l v i n g grade p u l p at 35% y i e l d  (86). it  Jorgensen p u l p types and x y l o s e 4.4% raw  (139) a n a l y s e d  the c a r b o h y d r a t e  r e p o r t e d t h a t g l u c o s e accounted  of the c a r b o h y d r a t e  p u l p of 47.2%  y i e l d w i t h Roe  portion No.  c o m p o s i t i o n of v a r i o u s  f o r 90.2%, mannose 5.4%  and  i n an o r d i n a r y c o n i f e r o u s s u l p h i t e  of 1.6  (1.3% l i g n i n ) .  c a r b o h y d r a t e s were removed d u r i n g the c o o k i n g p r o c e s s .  Other wood  These o b s e r v a t i o n s  a r e i n r e a s o n a b l e agreement w i t h d a t a p u b l i s h e d by Thompson e_t a l . (291) f o r b l a c k spruce  s u l p h i t e pulps cooked a t pH v a l u e s below  7.  In d i s s o l v i n g grade p u l p s , the h e m i c e l l u l o s e p o r t i o n reduced a few  through  a d d i t i o n a l p u r i f i c a t i o n s t e p s and  per cent of a l l p u l p c a r b o h y d r a t e s .  p u l p was  found  x y l o s e , 3.3%  r e s i d u e s amount to o n l y  For i n s t a n c e , a s u l p h i t e  by Croon et a_l. (55) t o ^be comprised  mannose and  0.1%  i s even more  o f 95% g l u c o s e ,  spruce 1.7%  arabinose.  During s u l p h i t e p u l p i n g , l i g n i n undergoes t h r e e r e a c t i o n s which a r e significant  to b o t h  with pulp f i b r e s . sation  (321).  i t s removal and  the p h y s i c a l n a t u r e of r e s i d u e s  These a r e s u l p h o n a t i o n , h y d r o l y s i s and  Dependent on how  the l i g n i n c o n t e n t  sometimes conden-  f a r these r e a c t i o n s a r e a l l o w e d  i n unbleached p u l p s  l i e s between 1 and  remaining  4%  to  proceed,  (86).  The  v a r i o u s f a c t o r s and mechanisms r e s p o n s i b l e f o r l i g n i n r e a c t i o n s i n s u l p h i t e c o o k i n g a r e d i s c u s s e d i n s e v e r a l reviews  (86,88,251,321).  As i n o t h e r t e c h n i c a l p u l p i n g p r o c e s s e s , d e l i g n i f i c a t i o n i n s u l p h i t e cooking  i s very c l o s e l y  i n t e r r e l a t e d w i t h d e g r a d a t i o n of  both  c e l l u l o s e and h e m i c e l l u l o s e s and a t l e a s t w i t h a p a r t i a l d i s s o l u t i o n of latter. wall  Degree of p o l y m e r i s a t i o n (DP) d e t e r m i n a t i o n s on v a r i o u s  l a y e r s c a r r i e d out by Luce (171)  d e g r a d a t i o n due  by  Tayme and von  48% y i e l d  low as 300.  Koppen ( 1 3 4 ) .  tracheid  showed t h a t c e l l u l o s e undergoes s e r i o u s  to a c i d h y d r o l y s i s , i n p a r t i c u l a r  where DP reaches v a l u e s as  the  i n the o u t e r w a l l  layers  T h i s c o n f i r m s e a r l i e r p r o p o s a l s made  A c c o r d i n g t o Rydholm ( 2 5 1 ) , c o o k i n g  causes such s e r i o u s d e g r a d a t i o n  below  t h a t p a r t o f the c e l l u l o s e goes  - 16 -  i n t o s o l u t i o n and  even f i b r e f r a g m e n t a t i o n may  Hamilton  (97) sugeested  o r d e r e d zones i n m i c r o f i b r i l s  occur.  t h a t under a c i d i c p u l p i n g c o n d i t i o n s l e s s  are more s u s c e p t i b l e t o a t t a c k and  c e l l u l o s e chains are cleaved p r e f e r e n t i a l l y  thereby  i n amorphous r e g i o n s .  l o s e d e g r a d a t i o n by a c i d i c h y d r o l y s i s seems to be enhanced by  be e x p l a i n e d by  the f a c t  stages i s p a r t i a l l y  from damaged f i b r e s  caused  in early  may cooking  that h y d r o l y t i c chain degradation i n low y i e l d  s t r u c t u r a l changes d u r i n g  by a c i d i c h y d r o l y s i s of bonds between u n i t s  the main c h a i n and between backbone and  polyoses  This  lost.  s u l p h i t e cooking, mainly  especially  lower  (106).  t h a t the p r o t e c t i v e a c t i o n of l i p n i n  The h e m i c e l l u l o s e s undergo profound  of  cellu-  mechanical  damage of the f i b r e w a l l d u r i n g c h i p p r e p a r a t i o n , a s i n d i c a t e d by s t r e n g t h p r o p e r t i e s of pulps prepared  The  side-branches.  l e a d s to c o n s i d e r a b l e h e m i c e l l u l o s e l o s s ,  p u l p i n g which l e a v e s o n l y a few  i n pulp f i b r e s  I t i s w e l l known  per cent of  residual  (160). II  S t u d y i n g h e m i c e l l u l o s e s i n b i r c h p u l p s , Ohrn and 217)  observed  coworkers  t h a t d e g r a d a t i o n e f f e c t s on p o l y o s e s , as i n d i c a t e d by DP v a l u e s ,  a r e c o n s i d e r a b l y h i g h e r f o r s u l p h i t e than f o r k r a f t p u l p s . former  were found  t o be about 70 and  s u l p h i t e experiments r u b r a Bong. ), and  carried  western  f o r the l a t t e r  out by Hamilton  130  DP v a l u e s . f o r the  to 160.  Acid  ( 9 7 ) , w i t h r e d a l d e r (Alnus  hemlock (Tsuga h e t e r o p h y l l a (Raf. ) S a r g . ) showed  t h a t x y l a n s a r e somewhat more s u s c e p t i b l e t o h y d r o l y t i c c l e a v a g e medium than the mannan f a m i l y of c a r b o h y d r a t e s . P e t t e r s o n and  to II  (251).  by  pulps.  f o r r e s i d u a l xylans i n s u l p h i t e pulps  abundance of g l u c u r o n i c a c i d  in acidic  T h i s has been c o n f i r m e d  Rydholm (233) on European b i r c h s u l p h i t e  Characteristic  hydrolysis  (174,  groups which appear to be f a i r l y  is a relative s t a b l e to a c i d  S i m i l a r l y , some of the a c e t y l groups tend to remain a t t a c h e d  the x y l a n backbone.  T h i s presence  of a c e t y l groups has been proven  by  Ohrn and Croon (216) on i s o l a t e d b i r c h s u l p h i t e x y l a n s . However, o t h e r l i n k a g e s w i t h s i d e - b r a n c h e s As proven  by H a m i l t o n  backbone and  (97), arabinofuranose  seem to be  is readily  split  acid-labile.  from  the x y l a n  t h e r e f o r e s u l p h i t e x y l a n s c o n t a i n o n l y t r a c e s of a r a b i n o s e  (55).  - 17 -  Likewise,  the g a l a c t o s e branches a r e e n t i r e l y removed i n a c i d i c  pulping  the former galactoglucomannan polymer i s reduced to glucomannan. supported  by  E r i k s s o n and  of g a l a c t o s e  i n spent  Samuelson ( 6 6 ) , who  r e p o r t e d c o n s i d e r a b l e amounts  to a s u l p h i t e cook, Annergren and  linters  ( 1 0 ) demonstrated t h a t p r o b a b l y  a deacetylated  to the f i b r e s u r f a c e .  mannan i s d i s s o l v e d i n the e a r l y stage concluded  glucomannan was  This  and  t h a t t h i s rearrangement of glucomannan on  a d s o r p t i o n may  T i m e l l and even o c c u r  Tyminski  absorbed  l a t e r adsorbed.  the s u r f a c e and  l i n e a r molecular  c e l l u l o s e m i c r o f i b r i l s , or a t l e a s t a b e t t e r o r d e r e d surface.  s t r u c t u r e on  (296) postulated  i n s i d e the m i c r o f i b r i l s .  xylan content 2.2.A  surface.  T h i s may  not compete f o r the  p r o v i d e s y i e l d s of  a t l e a s t p a r t l y e x p l a i n the r e l a t i v e l y  AO  v a r i a b l e s employed, the k r a f t  55%  to  that h i g h l y d e l i g n i f i e d  based on oven-dry wood bleachable  A % l i g n i n , whereas h i g h - l i g n i n k r a f t pulps  pulps  may  analysed  the c a r b o h y d r a t e  been confirmed composition  by  was  arabinose.  Thompson ejt al_. ( 2 9 1 ) r e p o r t e d  has  comprised of 8 5 % g l u c o s e ,  a l s o contained  Jorgenson  of s u l p h a t e  A7.6% yield  similar yield  p r e h y d r o l y s i s stage. kraft  for  95.27o  and  arabinose  For  (0.1%)  He  i . e . , a pulp  The  pine  A.8%.  pulps  also of  (Pinus  of  hemicellulose portion  cook i s preceded by  ( 5 5 ) found t h a t i n a  present, while  t o t a l e d only  than a c i d s u l p h i t e  t h a t pored wood k r a f t  i n s t a n c e , Croon e t aJL.  of a l l c a r b o h y d r a t e s  1 0 % lignin.  6 % mannose, 8 . 2 % x y l o s e and 0 . 8 %  about 0 . 3 5 % g a l a c t o s e .  pulp made from s o u t h e r n  (215)  c o n t a i n 3 to  (139).  pulps,  been found to be markedly reduced when the k r a f t  hydrolysed  low  process  Nolan  c o n t a i n as much as  c o n t a i n c o n s i d e r a b l y more r e s i d u a l l i g n i n  of s i m i l a r y i e l d has  pulping  (251).  paper grade p u l p s  II  pulps  limited  pulps  Depending on cooking  That k r a f t  chains  i n s u l p h i t e pulps.  Sulphate  reported  to  Rydholm ( 2 5 1 ) p o i n t e d  liberated  microfibrillar  within  t h a t some glucomannan  are  t h e r e f o r e can  They  the micro-  t h a t glucomannan i s p r e f e r e n t i a l l y a d s o r b e d , s i n c e l i n e a r x y l a n i n the cook and  to  fragments on  out  later  Rydholm  i n d i c a t e s t h a t some g l u c o -  of c o o k i n g  the f i b r e p o s s i b l y causes c r y s t a l l i s a t i o n of  fibril  This i s  sulphite liquor.  By adding c o t t o n  a c e r t a i n degree on  and  spp.), glucose  xylose  a  pre-  accounted  (2.6%),  mannose  (2  - 18 -  As i n s u l p h i t e p u l p i n g , d e l i g n i f i c a t i o n a l s o accompanied by c o n d e n s a t i o n s e r i o u s i n a l k a l i n e media.  i n a l k a l i n e processes i s  r e a c t i o n s (251).  As G i e r t z  ^hese seem t o be more  (86) s u g g e s t e d , the i m p o s s i b i l i t y .of  d e l i g n i f y i n g k r a f t pulps to the l e v e l a c h i e v a b l e i n s u l p h i t e p u l p i n g to be e n t i r e l y a t t r i b u t e d  to e x t e n s i v e l i g n i n c o n d e n s a t i o n .  The  has  distribution II  of r e s i d u a l who  found  l i g n i n w i t h i n the f i b r e w a l l has been s t u d i e d by von  t h a t l i g n i n was  k r a f t pulp f i b r e s .  almost e v e n l y d i s t r i b u t e d  A c c o r d i n g to Hamilton c e l l u l o s e DP by two  over the e n t i r e w a l l of  fibres.  ( 9 7 ) , a l k a l i n e p u l p i n g c o n s i d e r a b l y reduces  major r e a c t i o n s :  ( i i ) hydrolytic chain cleavage.  ( i ) stepwise end-group d e g r a d a t i o n ;  Thompson et a_l. (291) demonstrated t h a t these d e g r a d a t i o n r e a c t i o n s  But d i s a d v a n t a g e s  sulphite  of c o m p a r a t i v e l y h i g h e r d e g r a d a t i o n are a t  o f f s e t by b e t t e r u n i f o r m i t y of c h a i n l e n g t h of a l k a l i degraded as proved  by Luce ( 1 7 1 ) .  T h i s phenomenon may  be a t t r i b u t e d  more u n i f o r m p e n e t r a t i o n o f a l k a l i n e p u l p i n g l i q u o r s . and  to f a s t e r  T h i s i s due  as o t h e r commercial c h e m i c a l p u l p i n g p r o c e s s e s :  of d i s s o l v e d compounds.  as has been observed  been found  to be  molecular  reprecipitation  T h i s can be a t t r i b u t e d  to d i s s o l v e r a t h e r e a s i l y  twice t h a t o f  sulphite  t o the tendency of i n a l k a l i n e cooking  low liquors  by A x e l s s o n et a_l. ( 1 3 ) .  It appears from s e v e r a l s t u d i e s on c a r b o h y d r a t e v a r i o u s p u l p types  (281),  R e s i d u a l s u l p h a t e p u l p h e m i c e l l u l o s e s are  (174,233).  molecular carbohydrates  inter-  i n the same  ( i ) change of  ( i i ) r e p o s i t i o n i n g by p a r t i a l  c h a r a c t e r i s e d by h i g h DP, which has hemicelluloses  to  and  system.  A l k a l i n e pulping a f f e c t s hemicelluloses p r i n c i p a l l y  s t r u c t u r e s by h y d r o l y s i s ; and  least  celluloses  i n t r a - c r y s t a l l i n e a l k a l i n e s w e l l i n g w h i c h , a c c o r d i n g to Stone  e n l a r g e s the f i b r e w a l l c a p i l l a r y  way  and  Based on v i s c o s i t y measurements, H a r t l e r  reduce c e l l u l o s e DP more than c o r r e s p o n d i n g r e a c t i o n s i n a c i d pulping.  (149),  In c o n t r a s t , i t appeared t o form a c o n s i d e r a b l e accumula-  t i o n i n the o u t e r l a y e r s o f s u l p h i t e p u l p  (104) and  Koppen  composition  of  (97,139,174,291) t h a t glucomannans a r e more s e r i o u s l y  degraded and d i s s o l v e d  i n a l k a l i n e p u l p i n g than are x y l a n s .  at l e a s t p a r t l y e x p l a i n e d by  T h i s can  be  the g r e a t e r s u s c e p t i b i l i t y of glucomannans to  a l k a l i n e p e e l i n g r e a c t i o n s as shown by  R i c h t z e n h a i n and  Abrahamson  (247).  - 19 -  R e s i d u a l glucomannans i n k r a f t glucomannan; and  pulps  occur  i n two  forms a s : ( i )  ( i i ) a system of galacto-glucomannans (54,97).  The  former  o r i g i n a t e from n a t i v e glucomannan, but have c o n s i d e r a b l y reduced DP.  The  l a t t e r a r i s e from O - a c e t y l - g a l a c t o - g l u c o m a n n a n which undergoes d e a c e t y l a t i o n and  partial  only in  chain degradation  during  l i n e a r glucomannans remain due  the p r e h y d r o l y s i s s t a g e The  pulps  pulping.  linkage.  T h i s i s due  (216),  wood k r a f t p u l p s c o n s i s t s o n l y of x y l o s e u n i t s .  furanose kraft  pulps  o f f during  DP of o n l y 22 to 60  Of  special  of h e m i c e l l u l o s e s  i s the f a c t  i n pored  In c o n i f e r o u s p u l p s  the  process.  But  (98).  arabino-  in  prehydrolysed  and  liquor.  the c e l l u l o s e  (326).  T h e r e a f t e r , the unbranched  on  be r e d e p o s i t e d  (86)  longer  or  in solution,  to c e l l u l o s e s u r f a c e s .  Meller  i n t h r e e d i f f e r e n t forms: ( i )  l o o s e l y p r e c i p i t a t e d or adsorbed on to the s u r f a c e ; c r y s t a l l i n e form on c e l l u l o s e ; or  Giertz  sulphate  of s i d e - c h a i n s a f t e r the branched  s i d e - c h a i n f r e e x y l a n m o l e c u l e i s h e l d no  proposed t h a t x y l a n may  with  physical characteristics  t h a t a p a r t of the x y l a n d i s s o l v e d i n  i n s t e a d i s adsorbed by or c r y s t a l l i z e d  (193)  and  (98).  i r r e v e r s i b l y by  x y l a n d i s s o l v e d i n the p u l p i n g  but  the c o o k i n g  t h i s phenomenon t o c l e a v a g e  essentially  residual xylan  10% of the o r i g i n a l  importance to c h e m i c a l  i s readsorbed  attributed  of the (l-*"2)  a l l x y l a n m o l e c u l e s a r e degraded t o l i n e a r x y l a n fragments  an e v e n t u a l  liquors  sulphate  been found t o be reduced to an a r a b i n o x y l a n  Enstrom (54) have shown t h a t o n l y u n i t s are s p l i t  units  (53,54,191) of 4-0-methyl-c<-D-  to high a l k a l i l a b i l i t y  a c e t y l groups a r e l i k e w i s e e a s i l y c l e a v e d  Croon and  in  S i n c e e s t e r bonds between the x y l a n backbone  o r i g i n a l x y l a n polymer has  fibres,  '97,160,269).  most c h a r a c t e r i s t i c f e a t u r e of r e s i d u a l x y l a n s  glucuronic acid residues.  pulp  t o removal of the g a l a c t o p y r a n o s e  i s the absence (97,291) or i n f r e q u e n c y  -glycosidic  In p r e h y d r o l y s e d  ( i i ) precipitated in  ( i i i ) c h e m i c a l l y combined w i t h  the  c e l l u l o s e by t r a n s g l u c o s i d a t i o n . C l a y t o n and for  as much as  already evidence  Stone (51) have shown t h a t t h i s r e d e p o s i t i o n can  3% of pulp w e i g h t , r e g a r d l e s s of the amount of  i n the f i b r e s .  Recent s t u d i e s c a r r i e d  out by  Simonson  t h a t even x y l a n - l i g n i n compounds found i n p u l p i n g  are redeposited  on to c e l l u l o s e .  account  hemicelluloses (266)  liquors  I t appears from s t u d i e s of M e l l e r  provide (265) (193)  - 20 -  t h a t p r e h y d r o l y s e d x y l a n from b i r c h and  straw shows much l e s s  toward  r e d e p o s i t i o n on to c o t t o n c e l l u l o s e when heated  2.2.5  Bleached  tendency  i n a l k a l i n e medium.  pulps  An e x c e l l e n t  survey on the s u b j e c t of wood p u l p b l e a c h i n g has  been g i v e n by Rydholm (251) and f o r t h i s r e a s o n o n l y a l i m i t e d publications related  to the p r e s e n t study w i l l be reviewed  Depending on f i n a l  number of  here.  use, most raw c h e m i c a l p u l p s a r e s u b j e c t e d t o  f u r t h e r d e l i g n i f i c a t i o n or l i g n i n m o d i f i c a t i o n by b l e a c h i n g t r e a t m e n t s . a d d i t i o n , d i s s o l v i n g grade  p u l p s are s u b j e c t e d to a d d i t i o n a l  carbohydrate-  removing p r o c e s s e s t o f u r t h e r reduce h e m i c e l l u l o s e p o r t i o n s . and  S p r i n g e r ejt a_l. (274) determined  and  reported that approximately  mainly  overall yield  Rydholm  (251)  loss i n pulp bleaching  1 to 5% of the f i b r e c e l l  wall components,  l i g n i n and h e m i c e l l u l o s e s are removed i n b l e a c h i n g of s u l p h i t e  k r a f t p u l p s cooked  to 38 ' t o 51%  In  and  yield.  In m u l t i - s t a g e b l e a c h i n g , which i s g e n e r a l l y employed i n b l e a c h i n g of c h e m i c a l p u l p s , r e s i d u a l it  II  l i g n i n i s d r a s t i c a l l y reduced  t o t r a c e amounts,  II  S j o s t r o m and  Enstrom  (268), f o r i n s t a n c e , r e p o r t e d t h a t a seven  stage  b l e a c h i n g sequence i n v o l v i n g c h l o r i n a t i o n , a l k a l i n e e x t r a c t i o n , h y p o c h l o r i t e and from  c h l o r i n e d i o x i d e reduced 2.42%  l i g n i n c o n t e n t of a c o n i f e r o u s s u l p h a t e p u l p  to l e s s than 0.05%.  In a t h r e e stage p r o c e s s c o n s i s t i n g  c h l o r i n a t i o n , a l k a l i n e e x t r a c t i o n and and H i g g i n s decreased  (143) observed  from  2.13  that  to 0.51%  and  of  sodium h y p o c h l o r i t e t r e a t m e n t ,  l i g n i n c o n t e n t of two from 4.59  Kayama  coniferous kraft  to 1.11%.  Most l i g n i n a b s t r a c t i n g s t a g e s i n b l e a c h i n g have been found a f f e c t a l s o the c a r b o h y d r a t e components.  to  A c c o r d i n g t o M e l l e r (194), both  c e l l u l o s e and h e m i c e l l u l o s e s undergo h y d r o l y s i s and  subsequent  oxidation  r e a c t i o n s i n the c h l o r i n a t i o n s t a g e c a u s i n g some l o s s i n c a r b o h y d r a t e s Subsequent a l k a l i e x t r a c t i o n has been found p r o b a b l y due  pulps  t o reduce  the y i e l d  (143).  (143),  to i n t r o d u c e d c a r b o x y l i c groups (194) which r e n d e r p a r t of the  low m o l e c u l a r c a r b o h y d r a t e  portion soluble in alkaline extraction  S i m i l a r l y , h y p o c h l o r i t e treatments and  subsequent  treatments.  alkaline  - 21 -  extraction lead also to a yield loss due to oxidation and hydrolytic cleavage of glycosidic bonds (143,159,194). Viscosity measurements on hypochlorite bleached pulps have indicated that severe chain degradation can occur during this bleaching stage (243,245). At low to medium pH chlorine dioxide does not react with aldehydes or ketones (244) and, consequently, no degradation or noticeable losses of carbohydrates occur in this bleaching stage (251). The work of Springer e_t a_l. (274) indicates that the extraction of lignin in bleaching without alkali purification appears to be the major factor responsible for differences in physical and mechanical properties between bleached and unbleached pulps.  In such practice the removal of  carbohydrates is comparatively low and these slight losses seem to be insignificant for the development of bleached pulp properties.  In the case  of cold or hot alkali purification, however, the low molecular carbohydrate portions, mainly as hemicelluloses and to some extent short chain cellulose, . are drastically reduced (251). According to Meller e_t a k  (195), cold alkali extractions have  considerably higher selective dissolving action on non-alpha cellulose components than do extractions with dilute, hot alkali solutions.  The  former method produces pulps with up to 98% alpha-cellulose content (195), while the latter gives maximum alpha-cellulose contents at 96 to 97% (251). Croon et a k  (55) reported that a prehydrolysed kraft pulp purified in cold  alkali s t i l l contained 0.3% mannose, 1.1% xylose and 0.1% arabinose. They attributed the high content of resistant xylan to stabilization during the sulphate cook. The presence of considerable residual mannan and xylan fractions in pulps extracted with hot alkali has been observed.  For instance,  a bleached standard sulphite pulp with 2.5% xylan and 2.4% mannan was found to s t i l l contain 0.5% xylan and 0.4% mannan after hot alkaline extraction (55). 2.2.6  Alpha-cellulose pulps Alpha-cellulose is generally regarded as pure cellulose, but-  several analytical investigations of alpha-cellulose preparations have shown that even exhaustive and repeated alkaline extractions leave non-cellulosic  - ll  c a r b o h y d r a t e f r a c t i o n s i n the p u l p . d a t a on a l p h a - c e l l u l o s e o b t a i n e d c h l o r i t e h o l o c e l l u l o s e by  0.3%  arabinose.  ( 8 7 ) , who  t r e a t i n g the p u l p w i t h  such as 8.8%  exhaustive  considerable  amounts of mannose and  rhamnose.  preparations but  The  17.5%  mannose. 2.3%  Don)  NaOH a c c o r d i n g  galactose,  a l k a l i n e e x t r a c t i o n with  from v i s c o s e p u l p s  to  hemicelluloses  1.3%  x y l o s e and  aqueous KOH  the  xylose and  and  Timell  holo-  still  contained  t r a c e s of g a l a c t o s e ,  arabinose  i n d i c a t e d that a l p h a - c e l l u l o s e  l i k e w i s e c o n t a i n mannan and  xylan  residues,  extent.  Time Dependent M e c h a n i c a l P r o p e r t i e s of H i g h Polymers, such as Wood Cellulosics Rheology has  an u l t i m a t e o b j e c t i v e of d i s c o v e r i n g  descriptions f o r materials  and  t h e i r behavior  time dependent mechanical b e h a v i o r  under s p e c i f i e d  behavior.  the phenomenological a p p r o a c h , i s based on  main approaches i n s t u d i e s of m a t e r i a l s  time w i t h  s t r e s s and  strain  samples.  An  i s made to d i s c o v e r g e n e r a l  attempt  ( l o a d and  deformation),  o f these parameters, so t h a t b e h a v i o r a l r a t e of e l o n g a t i o n , can be deduced. majority  gross  and  reported  as averaged  linking  macro-  such as  l o a d i n g r a t e or  superficial.  Such s t u d i e s  the body i n i t s macro form i r r e s p e c t i v e In o t h e r  a p p l i c a t i o n of e x t e r n a l f o r c e s  words,  are  values.  Another a p p r o a c h , known as m o l e c u l a r rheology  studies  u s u a l l y with  i n t e r r e l a t i o n s of s t r u c t u r a l components.  complex changes caused by  viscoelastic  T h i s a p p r o a c h , as employed i n the  the whole body, or w i t h  of the b e h a v i o r a l  There  equations covering v a r i a t i o n s  patterns,  of r h e o l o g i c a l s t u d i e s , i s e s s e n t i a l l y  deal only with  generalized  e x c i t a t i o n patterns.  two  One.  and  which permit p r e d i c t i o n of  are, b a s i c a l l y ,  and  r a d i a t a D.  have been made by G i l l h a m  work of Croon et a_l. (55)  t o a much lower  2.3  (Pinus  analytical  t h a t an a l p h a - c e l l u l o s e p u l p p r e p a r e d from w h i t e b i r c h  c e l l u l o s e by  and  published  S u r p r i s i n g l y h i g h amounts of  Similar observations  report  (304)  from Monterey p i n e  usual a l p h a - c e l l u l o s e procedure. remained i n the p u l p ;  Uprichard  rheology,  attempts to  use  as a t o o l f o r e l u c i d a t i n g the fundamental s t r u c t u r e of a m a t e r i a l  p a r t i c i p a t i o n of i t s components i n r h e o l o g i c a l phenomena. Considering  anatomical  the complex m o l e c u l a r  and  sometimes a l s o complex  s t r u c t u r e of many n a t u r a l polymers, such as c e l l u l o s i c s and  ligno-  - 23 -  eellulosics,  i t i s not s u r p r i s i n g  t h a t the m a j o r i t y of s t u d i e s on these  m a t e r i a l s have been phenomenological. viscoelasticity  is still  P r e s e n t l y , the s u b j e c t o f polymer  a t the stage o f development.  theory o f l i n e a r v i s c o e l a s t i c i t y  phenomenological  i s now e s s e n t i a l l y complete.  has a l s o been g i v e n to e s t a b l i s h i n g new o r improving non-linear v i s c o e l a s t i c i t y .  The  Much a t t e n t i o n  existing  Many e x c e l l e n t s u r v e y s a r e now  theories  of  available  (5,18,22,24,42,49,71,92,117). D i f f i c u l t i e s a r e e x p e r i e n c e d w i t h i n development o f a complete molecular  theory f o r c e l l u l o s i c s .  Even w i t h s i m p l e polymers,  o r i g i n of some a s p e c t s o f v i s c o e l a s t i c b e h a v i o r molecular weight, other f a c t o r s .  temperature,  i s c o m p l i c a t e d g r e a t l y by  c o n c e n t r a t i o n (e.g. moisture ;  T h i s becomes even more c o m p l i c a t e d  a molecular  c o n t e n t ) and  f o r wood and wood d e r i v e d  m a t e r i a l s due t o the complex and i n c o m p l e t e l y understood of the l i g n i n - c a r b o h y d r a t e polymer m i x t u r e .  the m o l e c u l a r  chemical s t r u c t u r e  I n d i c a t i o n s a r e , however, t h a t  approach t o polymer r h e o l o g y , c e l l u l o s i c s  i n p a r t i c u l a r , may be  feasible eventually. 2.3.1  M o l e c u l a r approach to v i s c o e l a s t i c i t y V i s c o e l a s t i c b e h a v i o r of c e l l u l o s i c m a t e r i a l s , such as wood and  c e l l u l o s e f i b r e networks, i s the product of many f a c t o r s i n t e r a c t i n g i n a complicated  and o n l y p a r t l y understood  way.  T h i s causes  great  difficulty  i n d e r i v i n g q u a n t i t a t i v e and u s e f u l e x p r e s s i o n s f o r d e s c r i b i n g macroscopic effects  i n terms of m o l e c u l a r  parameters.  A c c o r d i n g to Nis san and S t e r n s t e i n (214,279), the f o l l o w i n g f a c t o r s a r e expected of c e l l u l o s i c s :  t o be important  i n d e t e r m i n i n g mechanical  ( i ) i n t e r - c h a i n c o v a l e n t bonds;  properties  ( i i ) i o n i c bonds between  groups which were formed i n o x i d a t i o n and o t h e r d e g r a d a t i o n  processes;  ( i i i ) hydrogen bonds between and w i t h i n c e l l u l o s e and h e m i c e l l u l o s e c h a i n s ; ( i v ) i n t e r - c h a i n van d e r Waal's bonds; ( v ) DP; ( v i ) degree o f o r d e r and disorder;  ( v i i ) o r i e n t a t i o n o f m o l e c u l a r c h a i n s ; ( v i i i ) s i z e of p a r a c r y s t a l l i n e  or c r y s t a l l i n e r e g i o n s ; ( i x ) morphological c o m p o s i t i o n and presence factors attempts  of polar l i q u i d s .  s t r u c t u r e ; and ( x ) c h e m i c a l The r e p r e s e n t a t i o n o f these  i s by no means e x h a u s t i v e but i t shows w e l l the c o m p l e x i t y  facing  aimed a t development o f f o r m u l a t i o n s which d e s c r i b e a c c u r a t e l y the  - 24 -  mechanical character and behavior of cellulosic materials. During the last two decades some attempt has been made to give molecular interpretations to cellulosic viscoelastic behavior and to deveio a f i r s t set of molecular theories based on known properties of hydrogen bonded materials (48,207-214,220,278,279). , It is presently accepted that cellulose subjected to macroscopic deformation will show the following submicroscopic deformations (202,214, 298-300): ( i ) valence bond length and angle deformation (intra-molecular); ( i i ) secondary bond deformation; and ( i i i ) reorientation of macro-molecules in amorphous regions (inter-molecular).  It can be said, therefore, that  while ultrastructure is of significance to ultimate fibre property levels, the inter-molecular and intra-molecular bonds are responsible for viscoelastic properties (259). Particularly important in cellulosic viscoelastic processes are inter-molecular forces which arise from the separation of macromolecules that are joined by covalent links, ionic bonds and van der Waal' forces. It is now advanced by one group that the hydrogen bond system dominates viscoelastic processes in cellulosic materials (210,214,220,278). Since each anhydroglucose unit can form three hydrogen bonds, and, as shown by Marrinan and Mann (183), oven-dry cellulose possesses no free hydroxyl groups, the postulation has been made that viscoelastic phenomena are accompanied by breakdown, rearrangement, bending and stretching of these hydrogen bonds (214). The primary importance of the hydrogen bond on mechanical properties is underlined by a number of investigations undertaken by Nissan and Sternstein (214).  They observed that dry regenerated cellulose  (with high amorphous ratio) and strong papers show more significant hydrogen bond effects than weak papers.  In the latter, van der Waal^s  forces dominate, while in crystalline or oriented celluloses, such as cotton, flax and ramie, valence bonds appear to be more important. Based on postulated hydrogen bond behavior under stress or strain Nissan and coworkers (208-211,213,278) developed several quantitative  - 25 -  t h e o r i e s to e x p l a i n the r h e o l o g i c a l b e h a v i o r of c e l l u l o s i c m a t e r i a l s a t the molecular  level.  They were a b l e to demonstrate t h a t s t r e s s r e l a x a t i o n as a  f e a t u r e of v i s c o e l a s t i c b e h a v i o r can be hydrogen bond adjustment:'.  s t u d i e d by f o l l o w i n g p r o c e s s e s  A c c o r d i n g to t h i s  theory, stress d i s s i p a t i o n i n  a . c e l l u l o s i c m a t e r i a l under c o n s t a n t s t r a i n r e s u l t s from an change i n the e f f e c t i v e number of hydrogen bonds. and fact  f o r m a t i o n of new  N i s s a n and  independent  T h i s o c c u r s by  bonds i n a s t a t e of l e s s e n e d s t r e s s .  that t h e i r experimental  o b s e r v a t i o n s agree w i t h t h e i r  t o the t r u e time dependent b e h a v i o r of  In c o n t e m p l a t i o n  rupture  In s p i t e of  the  postulation,  S t e r n s t e i n (214) c o n s i d e r t h i s t h e o r y to be o n l y a  approximation  of  first  cellulosics.  of the v i s c o e l a s t i c b e h a v i o r of  cellulosic  m a t e r i a l s o t h e r s i g n i f i c a n t f a c t s have to be c o n s i d e r e d , such as s t r u c t u r e of the m a t e r i a l .  Page (220) p o i n t e d out  f i b r o u s networks, such as paper, super-molecular  level.  He  that r h e o l o g i c a l  p r o p e r t i e s of  a r e a l s o c o n t r o l l e d by s t r u c t u r e a t  the  s t a t e d t h a t from knowledge of the e x c e e d i n g l y  complex s t r u c t u r e of paper i t would seem u n l i k e l y t h a t i t s r h e o l o g i c a l b e h a v i o r can be e x p l a i n e d d i r e c t l y  i n terms of m o l e c u l a r d a t a .  c o u r s e , p a r t l y r e f u t e s N i s s a n ' s t h e o r y which t r e a t s c e l l u l o s i c as a m o l e c u l a r assemblage. a r e of c o n s i d e r a b l e and  T h i s , of networks o n l y  Page (220) a g r e e s , however, t h a t hydrogen bonds  perhaps primary  importance  i n g o v e r n i n g paper  sheet  properties. More r e c e n t l y , Chow (48) r e p o r t e d t h a t r h e o l o g i c a l p r o c e s s e s i n c o n i f e r o u s wood t i s s u e s i n v o l v e a two  stage m o l e c u l a r motion of a l l t h r e e  major wood components; c e l l u l o s e , h e m i c e l l u l o s e and polarisation  t e c h n i q u e s he  showed t h a t c a r b o h y d r a t e s  lignin. and  Using  infrared  l i g n i n move i n  o p p o s i t e d i r e c t i o n s on r e c e i v i n g e x t e r n a l e x c i t a t i o n ^ whereby the wood macro-molecular s t r u c t u r e m a i n t a i n s an i n t e r n a l e q u i l i b r i u m . the s t r e s s might be t r a n s m i t t e d u n i f o r m l y through  In t h i s  way,  the whole l i g n i n - c a r b o h y d r a t e  matrix. It may important  be  theorized that c e l l u l o s i c r h e o l o g i c a l  processes i n v o l v e  c o n f o r m a t i o n a l changes i n a d d i t i o n to s t r e t c h i n g , b r e a k i n g and r e -  f o r m a t i o n of hydrogen bonds, s t r e t c h i n g of c o v a l e n t bonds and deformation  bond  angle  (145), p r o v i d e d t h a t the degree of s w e l l i n g i s s u f f i c i e n t l y  high.  In dry cellulosic materials hydrogen bonds are abundant and probably prevent glucose units from rotating about glucosidic links as required to change conformation0  However, with increasing moisture content the glucose units  should be capable of such rotations and thereby undergo conformational changes in response to excitation.  It i s known that inter-molecular  hydrogen bonds within amorphous regions are widely destroyed by absorption of water (251). According to Lambert (154), six-member ring compounds prefer the more stable chair conformation.  Therefore, hydroxyl groups on C^, C^ and  the CH OH group on C  can be expected to l i e in the equatorial position. 1 The arrangement is known as C^ conformation. External energy applied in form of stress could cause these groups to switch to axial positions which changes the ring shape and thereby other conformational isomers are obtained (145')0  These conformers are characterized by higher energy levels and,  consequently, lower stability (154).  Under suitable conditions removal of  external forces or rebalance of stresses internally may result in reversion to the lower energy level ^C^ conformation.  In addition to providing an  instant response mechanism, the process could well explain the viscoelastic memory behavior of cellulosic materials (145). 2.3.2  Phenomenological study of viscoelasticity In general, phenomenological treatments of viscoelasticity are  characterized by two factors: ( i ) methods employed for describing observed responses; and ( i i ) phenomena of viscoelastic behavior.  Since both factors  are to some extent related to this study they are briefly discussed in the following section. According to Scott-Blair (260) there are two approaches for dealing with phenomenological data: ( i ) integrative; and ( i i ) analytical.  The f i r s t  is the purer phenomenological method, for i t takes the totality of experimenta data as applied to one simple generalized equation with the objective of describing a material behavior under a l l conditions of deformation.  An  equation employed in the integrative approach is the Nutting equation (242) as:  -  where;  £  I  -  f  =  stress,  e  =  strain,  t  =  time, fb  V, The In  c o n s t a n t s merely  and and  k  are constants.  serve to d e s c r i b e b e h a v i o r of the m a t e r i a l as a whole.  o t h e r words, c o n s t a n t s do not have any  s t r u c t u r a l or  theoretical  significance. The a n a l y t i c a l method a l s o attempts d a t a by e q u a t i o n s , but based  to represent  i t employs an assemblage of c e r t a i n  on the v e r y fundamental assumption  phenomenological ideal  t h a t the m a t e r i a l i s s t r u c t u r a l l y  comparable to these elements (5,135,147,162,163,231,263,325). elements commonly used elastic  theory  been found be used  are i d e a l  The  (161) and dashpots  containing ideal viscous l i q u i d s .  t o produce e q u a t i o n s which a p p r o x i m a t e l y  d e s c r i b e time dependent  m a t e r i a l , which can be c h a r a c t e r i s e d by s u i t a b l e combinations Newtonian l i q u i d s , i s s a i d t o d i s p l a y  (18,24,49).  principle  I t has  of these s i m p l e models can  b e h a v i o r of many p o l y m e r i c m a t e r i a l s , i n c l u d i n g d r y c e l l u l o s i c s  behavior  two  s p r i n g s which behave a c c o r d i n g to Hookean  t h a t more or l e s s complex combinations  s p r i n g s and  elements  linear  (255).  Any  of Hookean  viscoelastic  T h i s i m p l i e s t h a t such m a t e r i a l s obey the s u p e r p o s i t i o n  (263). More comprehensive s t u d i e s on v a r i o u s types of polymers have shown  t h a t numerous p o l y m e r i c m a t e r i a l s d i s p l a y n o n - l i n e a r b e h a v i o r , and  for this  reason  rheological  n o n - l i n e a r elements have been used  behavior  a l s o t o d e s c r i b e polymer  (96,228,239,325). The use of models has been w i d e l y d i s c u s s e d i n the g e n e r a l  of  rheology.  I t i s obvious  t h a t they have c o n s i d e r a b l e e d u c a t i v e v a l u e .  Whether or not they p r o v i d e any  o t h e r advantages i s much debated,  d e s c r i p t i v e e q u a t i o n s o b t a i n e d by d e r i v e d and  since  i n t e g r a t i v e methods are more simply  a r e j u s t as e f f e c t i v e i n use.  Furthermore,  p o i n t e d o u t , the use of models does not account for  field  the v i s c o e l a s t i c b e h a v i o r of c e l l u l o s i c s .  as Ranee (241,242)  f o r a l l mechanisms r e s p o n s i b l e Ranee m a i n t a i n s  that  irreversible  f l o w , which l e a d s t o permanent s e t , i s not " v i s c o u s " i n n a t u r e , but  i s the  effect  l e a d s to  of a c o n t i n u o u s  f i n a l break. important  s e r i e s of i n t e r n a l r u p t u r e s which u l t i m a t e l y  He a l s o m a i n t a i n s  t h a t such models do  not d e a l w i t h t h i s most  a s p e c t of break nor are they l i n k e d w i t h the s t r u c t u r e of  f i b r e mats.  Ranee (242) developed  described with s u f f i c i e n t  accuracy  a simplified  cellulose  s t r u c t u r a l t h e o r y which  time dependent b e h a v i o r as the r e s u l t  of  - progressive d i s r u p t i o n of an e l a s t i c network. For the reason of studying and understanding the nature of v i s c o e l a s t i c behavior, polymeric materials are subjected to d i f f e r e n t types of s t r a i n and stress patterns.  In general, three types of e x c i t a t i o n  h i s t o r i e s may be employed to study r h e o l o g i c a l responses to mechanical excitations:  ( i ) "creep", which i s time dependent s t r a i n (AL(t):L) a t constant s t r e s s (P:A).  The constant s t r e s s l e v e l .can be reached  i n a step, a ramp or a f t e r other e x c i t a t i o n programs, ( i i ) " s t r e s s r e l a x a t i o n " , which i s time dependent s t r e s s decay a t constant l e v e l of s t r a i n ( A L i L ) . The constant s t r a i n l e v e l can be reached i n a step, a ramp or a f t e r other e x c i t a t i o n programs, ^ i i i ) "dynamic damping", which i s normally observation of the mechanical response to s i n u s o d i a l e x c i t a t i o n i n s t r e s s . •or s t r a i n .  The frequencies, can be v a r i e d but during each  t e s t i t i s normally kept constant.  r Stress r e l a x a t i o n phenomena occur when a constant deformation i s imposed on a v i s c o e l a s t i c material and the force required to maintain t h i s continuing deformation i s measured as a f u n c t i o n of time (62,263),  This can  be expressed by the r e l a t i o n s h i p :  where:  [2]  ^(t)  =  G(t) €  G?(t)  «=  s t r e s s at time t ,  G(t)  =  r e l a x a t i o n modulus, and  t£  -  instantaneous s t r a i n ,  o  c  Figure 3 represents diagrammatically the curve G ( t ) £  p l o t t e d against time,  i n d i c a t i n g a time dependent decrease of stress i n v i s c o e l a s t i c m a t e r i a l s . The r e l a x a t i o n modulus (G(t)) as a monotomically decreasing f u n c t i o n of time can be expressed a l s o as:  G ( t )  where:  G  =  G  e  +  G  d(tr-  0  e  =  e q u i l i b r i u m modulus, and  d(t)  =  r e l a x a t i o n f u n c t i o n having i n i t i a l and f i n a l values of d(o) = 1 and d(oo) = 0 .  G  at time t  B  0 the equation reduces to  - 29 -  where:  G(t)  =  G o  =  ( O ^ . D -  Go  [4]  g l a s s modulus, °  The b e s t way 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 r , as e x h i b i t e d by h i g h p o l y m e r s , i s by a d i a g r a m r e l a t i n g r e l a x a t i o n modulus G ( t ) t o t h e l o g a r i t h m o f t i m e , t . As i n t h e c a s e o f c r e e p , polymers under c o n s t a n t s t r a i n behave l i k e i d e a l e l a s t i c s u b s t a n c e s a t v e r y s h o r t t i m e s .  Thereafter,  t h e y c a n be d e s c r i b e d by an o p e r a t o r e q u a t i o n t h a t r e l a t e s s t r e s s , s t r a i n and t i m e .  F o r l i n e a r s o l i d s t h e v a r i o u s methods o f r e p r e s e n t a t i o n a r e  e q u i v a l e n t t o each o t h e r and one c a n be o b t a i n e d from t h e o t h e r 2.3.3  (263).  V i s c o e l a s t i c b e h a v i o r o f c e l l u l o s e f i b r e mats Most p u b l i s h e d s t u d i e s on c e l l u l o s e f i b r e mat v i s c o e l a s t i c  p r o p e r t i e s have been based on a n a l y s i s o f c r e e p and s t r e s s r e l a x a t i o n  curves  o b t a i n e d from m o i s t u r e c o n d i t i o n e d p a p e r s under c o n s t a n t t e n s i l e l o a d o r deformation. of  U n f o r t u n a t e l y , l i t t l e i s known about t h e v i s c o e l a s t i c  f i b r e networks i n c o m p r e s s i o n  behavior  and even l e s s i s known about wet systems  under any c o n d i t i o n s . V a r i o u s t y p e s o f c e l l u l o s e networks such a s paper and p u l p mats have s e v e r a l f e a t u r e s i n common, i m p o r t a n t o f w h i c h i s t h e f a c t t h a t a l l a r e made from f i l t e r e d s u s p e n s i o n s o f c e l l u l o s i c f i b r e s i n w a t e r , pressed  and u s u a l l y d r y i e d w h i c h g i v e s c o h e r e n t s h e e t s .  Due t o t h e s e  i d e n t i c a l p r e p a r a t i o n p r o c e d u r e s , f i b r e networks may a l s o p r e s e n t common r h e o l o g i c a l f e a t u r e s , ,  subsequently  certain  For t h i s reason the f o l l o w i n g d i s c u s s i o n of  f i b r e network v i s c o e l a s t i c b e h a v i o r w i l l  i n c l u d e b o t h p a p e r s and p u l p m a t s .  A g a i n , o n l y s t u d i e s r e l e v a n t t o t h i s work w i l l be r e v i e w e d . 2.3.3.1  Rheology o f paper The f i r s t comprehensive s t u d i e s on time dependent s t r e s s - s t r a i n  b e h a v i o r o f c e l l u l o s e s h e e t s (papeis) were c a r r i e d o u t by S t e e n b e r g and c o w o r k e r s (125,276,277) as e a r l y as 1947.  They showed t h a t t h e l o a d -  d e f o r m a t i o n p r o p e r t i e s o f paper depend on numerous f a c t o r s , such as manner of  sheet p r e p a r a t i o n , 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 t h e  previous mechanical h i s t o r y of the specimen. Subsequent i n v e s t i g a t i o n s have c e n t e r e d p a r t l y on mechanisms o f paper r h e o l o g y , p a r t i c u l a r l y under t e n s i l e e x c i t a t i o n  (33,145,186,219,224,225,  J V  227,259,260,307,308).  It i s now  -  generally  agreed that both i n t e r - and  i n t r a - f i b r e mechanisms determine the time, dependent behavior of papers. Other studies have attempted to describe  the time dependent 11  response of paper mathematically.  Thus, Andersson and  Sjoberg (7)  studied  short time relaxation a f t e r rapid stretching at constant rates between 1% i n 0.01  sec and  1% i n 5 sec.  dependent on the i n i t i a l  They found that rate of stress decay i s highly  s t r a i n r a t e , i . e . , high s t r a i n i n g rate i s followed  by high stress decay r a t e , and vice versa . r e l a x a t i o n C ' U ) / ^ ( O ) against  By p l o t t i n g f r a c t i o n a l stress  the logarithum of time sigmoid shaped curves  were obtained, which indicated a Maxwellian delayed e l a s t i c type of r e l a x a t i o n . In h i s e a r l i e r publications on paper r e l a x a t i o n , Kubat (151,152) presented r e s u l t s of stress relaxation measurements following t e n s i l e s t r a i n i n g at low rates (1% i n 100  sec).  r e l a t i o n s h i p between r e s i d u a l stress and  He was log t.  able to demonstrate a l i n e a r Nevertheless, he pointed  out that t h i s r e l a t i o n s h i p must be regarded only as a temporary approximation. Such curves must, according to t h i s theory, ultimately conform to an ideal Maxwellian trend at long periods of stress d i s s i p a t i o n .  In other words, the  plot o f C a g a i n s t log t becomes asymptotic to a l i n e p a r a l l e l to the time a x i s . In paper stress relaxation following constant rates of (1% i n 23 sec to  1% i n  between stress (£>) and r e l a t i o n s h i p was  10 s e c ) a y  straight l i n e r e l a t i o n s h i p was  =  where: x and  also found  log t f o r the test period of 4 hr (242).  expressed by the following £  elongation  x  -  y  log  The  equation: c....[5j  t  y are constants which depend on preloading  history.  In a recent study on t e n s i l e stress relaxation of paper, Johanson and  Kubat (137)  determined the e f f e c t of  strain rate, i n i t i a l  s t r e s s , moisture  content  and beating on the v i s c o e l a s t i c behavior of paper under constant  strain.  They found that the following equation related i n f l e x i o n slope of  stress - log t curves and  t o t a l d i s s i p a t e d stress  Gi^ = ^(t 0 ) — ^(t^))  applied also to paper:  DO  - 31 -  Furthermore, results of their study indicated that activation energy for the stress relaxation process i s stress dependent. The viscoelastic response of air-dry newsprint subjected to constant load and deformation in compression was investigated by Gavelin (85). He observed increased viscoelasticity at higher moisture content and he also found very good correlation between stock freeness and the irreversible compressibility.  This showed that beating makes paper less compressible.  He also indicated that recovery response (which i s the instantaneous and time dependent "spring back" following removal of compressive deformation) i s related to the quality of the wood used in making the pulp. Other studies on behavior of air-dry paper under compression were II  carried out by Brecht and Schadler (31,32). They observed that increased basis weight reduced relative compression and increased relative expansion. Furthermore, addition of a small percentage of groundwood to a basic Scotch  pine sulphite stock caused a substantial increase in relative  2 Creep was found to be unimportant at low loads (20 kp/cm ), 2 but occurred at higher loads (200 kp/cm ). compression.  II  In a more recent study, Jackson and Ekstrom (127) investigated compressibility characteristics of air-dry sheets prepared from various pulp types. They reported that the recovery response following compression treatments was higher for unbleached than bleached pine sulphate pulp. Experiments with unbleached sulphate and bleached sulphite European birch pulps indicated higher recovery response for the f i r s t pulp type.  In general,  i t appeared that sulphate pulps show a higher degree of recovery response than sulphite pulps and unbleached pulps exhibit higher recovery than II  bleached pulps. Jackson and Ekstrom observed also a "species effect". Coniferous pulps were found to compress better than hardwood pulps, but the latter group showed higher relaxation responses than the f i r s t . Mardon et a l . (180,181) observed in their investigations on the dynamic and static compressibility of"papers made from various pulp types that compressibility is greatly influenced by moisture content (below the fibre saturation point), caliper, bulk, void volume and.previous stress  - 32 -  treatments.  Degree of deformation was found to increase with increasing  values of the f i r s t four variables and to decrease towards a constant value with increasing previous peak pressure. Their observation with respect to bulk effects, however, is not in agreement with the findings of Brecht and •  II  Schadler (31,32), who found that mat response i s indirectly proportional to bulk. Similar studies were carried out recently by Bliesner (25), who observed the viscoelastic behavior of two air-dry coniferous kraft pulps and one groundwood pulp under dynamic excitation in compression. It was found 3 that the effect of sheet bulk (cm /g) on compressibility differed widely between these two pulp types. The permanent set (non-recoverable deformation) increased with increase in bulk for kraft pulps but remained constant for the groundwood pulp.  Both pulp types showed an increase in relative compression,  but responded differently in relative recovery.  Increase in bulk improved  relative recovery in groundwood, but resulted in lower recovery in kraft pulps.  Repeated stressing up to three cycles was found to change the  compressive response of pulps, but thereafter no significant changes were noted. 2,3.3.2  Rheology of wet fibre mats in compression According to Brecht and Erfurt (29) and Lyne and Gallay (172), a  wet cellulose fibre network consists of fibres arranged in a manner similar to that in dry networks. But considerable differences arise from: ( i ) distance between the fibres; ( i i ) the degrees of fibre plasticity and e l a s t i c i t y ; and ( i i i ) degree of fibre association.  Interfibre bonding, a  controlling factor for mechanical properties in dry and partly dry fibre webs, does not play a significant role in the mechanical behavior of wet cellulose networks, i.e., below 20% solids.  Therefore, rheological behavior  of wet pulps is considered only as a function of wood fibre viscoelastic properties and characteristics of the network structure formed as result of fibre-to-fibre contacts. The rheology of wet fibre mats was f i r s t studied by Seborg et al_. (262). They compressed cylindrical small pulp sheets in wet condition at 2 a maximum pressure of 8.5 kg/cm » After no further deformation was noted they  - 33 -  removed the load and observed recovery.  It was found that recovery figures  were affected by mat caliper, where thicker mats gave less recovery for a given load. Experimental data indicated also a difference in recovery response between unbeaten and beaten pulps, with recovery higher for pulps without beating treatments.  In a later publication on the same subject  Seborg et a_l„ (261), presented data which indicated that sulphate pulps show higher recovery than comparable sulphite pulps and that groundwood exhibited less recovery than the chemical pulps. A comprehensive study on the effect of moisture content, degree of beating and caliper of pulp mats on their recovery response as derived from compressive deformation was carried out by Ivarsson (124). He observed that absolute compression and permanent set increased with increasing moisture content up to the fibre saturation point, whereas the recovery response decreased with moisture.  Further, increasing moisture contents changed  insignificantly the mechanical behavior of pulp mats under compression. I^varsson's observations on effects of beating and caliper are in general agreement with those made by Seborg et al_. (262). The relative permanent set was found to decrease slowly with increasing caliper.  In addition,  I^varsson examined the effect of caliper on relative compression.  His data  showed that more relative compression is obtained for thinner sheets. Other studies (122,138) reported that beating over wide ranges did not change the nature of wet pulp compressibility for bleached pulps, but they did observe some change for unbleached pulps. Several workers have developed mathematical expressions describing the behavior of wet fibre networks under compressive stress.  Campbell (43)  was the f i r s t to use a mathematical expression which he derived empirically, to describe the relationship between mat consistency (C) and stress (p): C  -  Mp N  [7]  where: N and M are constants which depend on nature of the pulp. Ingmanson and Whitney (123), studied the f i l t r a t i o n resistance of pulp slurries and pointed out the need to include a small but f i n i t e constant (C ) in the r o equation to satisfy conditions required for establishing f i n i t e consistency  - 34 -  at zero pressure: C  =  C  +  M  pN  c  [8]  o  Both equations, however, have to be considered as f i r s t approximations for describing the stress-pad concentration relationship, since time, known as a highly important variable in mat deformation processes, has been ignored. Wilder (322) studied wet fibre mat creep and creep recovery over long periods and for successive cycles and modified Ingmanson and Whitney's equation by replacing M with the new term (M = A + B log t) which includes time dependent effects.  Thereby, the stress - mat consistency relationship  became: C where:  C q + (A + B log t) p N  =  A,  B  =  constants, and  t  =  time.  •'••H  However, as Wilder (322) pointed out, the equation does not apply to extremely short time intervals during which f i l t r a t i o n resistance controls the mat response.  His experimental data also indicated that the equation constants  change for each compression and relaxation phase during the f i r s t 5 to 6 cycles.  Thereafter, the mat becomes conditioned and the constants remain  unchanged, one set for compression and another for recovery. As mentioned e a r l i e r , Wilder found his equation insufficient to describe the early phase of mat compression (up to 5 sec). He attributed this deviation to mat permeability and fractional drag of the water being pressed out.  Jones (138) carried out compressibility studies on various  types of wet fibre mats, and examined effects of fibre length and diameter and elastic modulus on compression recovery response.  The purpose of this  investigation was to obtain more information on fibre interaction mechanisms, such as fibre bending, fibre slippage and compression of fibres in overall mat deformation during rheological processes. The compression-recovery  was  found to be highly dependent on fibre length-to-diameter ratio and modulus of e l a s t i c i t y .  Fibre diameter alone, however, did not affect significantly  the recovery response.  Furthermore, fibre repositioning appeared to be very  - 35 -  important in early compression cycles, but fibre bending was the controlling factor in compression of mechanically conditioned mats. In a comprehensive study on specific permeability and compressib i l i t y of mats prepared with synthetic and natural pulp fibres, Higgins and De Yong (114) investigated the relationship between mat solids concentration and applied stress.  Their experimental data were obtained from two series  of coniferous sulphate and pored wood NSSC pulps, with each series covering a wide range of lignin contents. They found that compressibility and consolidation of wet mats was highly influenced by f l e x i b i l i t y and lateral conformation of the. wet fibres.  These two factors might not only contribute  to capacity for elastic deformation but also to the extent to which irreversible processes may occur. Similar investigations were carried out by Kayama and Higgins (143), who examined the'effect of bleaching on wet web compressibility of coniferous kraft pulps. They observed that pulp sedimentation volume decreased as lignin was removed, and as bleaching proceeded the compressibility decreased.  This  behavior has been attributed also to changes in f l e x i b i l i t y and lateral conformability with lignin removal. 2.4  Compressibility of Cellulosic Fibre Mats The behavior of cellulosic fibre mats under compressive deformation  can be considered as the combined response of rheological and non-rheological mechanisms. They are probably highly interrelated, particularly in early stages of mat deforming processes.  It is the purpose of this section to  review information on fibre mat compressibility as related to this work. The behavior of cellulosic networks under compressive stress or strain is. a function of numerous factors interacting in complex and not fully understood ways. In spite of several investigations (100,138) on the subject during the last 15 years, much research is s t i l l required for more complete elucidation of mechanisms and factors determining response of wet cellulosic mats subjected to compressive excitations.  It is rather surprising that so  l i t t l e emphasis has been placed on the subject, since industrial manufacturing processes frequently involve compression treatments of wet and dry fibre mats.  - 36 -  Fortunately, the knowledge and theories of air-dry paper response to tensile excitations in particular are rather advanced and, therefore, can offer some help for interpretating observations made on wet fibre mats. The following discussion also includes observations and theories of paper rheology so far as they are relevant to this study. For a comprehensive review i t i s convenient to subdivide the discussion into two sections; one dealing with the mechanisms which are involved in processes.of compressive deformation, and the other with factors determining the magnitude of instantaneous and time-dependent deformation of cellulosic networks. 2.4.1  Mechanisms in compression of wet cellulosic fibre mats A wet cellulose fibre mat can be defined as a fibre network  comprised of elements1 mostly lying loosely over each other and forming many sites of contact and potential contact. The fibres are limited to an approximately planar orientation, where within plane their position and orientation have a degree of randomness arising from the essentially disordered state of suspension from which mats are formed.  In the majority of  cases, however, the fibres l i e in-plane and consequently the regions of contact also l i e in the plane of the mat.  Complete randomness may be  adjusted somewhat by formation of mats on production wires. When a wet mat is subjected to compressive deformation three compressibility mechanisms can be expected to occur during deformation processes (100,138): ( i ) fibre bending; ( i i ) fibre slippage; and ( i i i ) fibre compression at regions of fibre-to-fibre contact.  In the following these  potential mechanisms are discussed separately in spite of the fact that they probably interact during compaction. 2.4.1.1 Fibre bending According to Han (100), application of external stresses to a mat will be followed by stress transmittance through fibre-to-fibre contacts and stress distribution along fibres.  This is accompanied by bending of  fibre segments between two points of support which causes formation of additional contact areas between neighboring fibres and thus increases mat  - 37 -  density.  If cellulosic fibres were entirely e l a s t i c , deformation within  the fibre would be expected to be entirely recoverable.  Due to the visco-  elastic nature of cellulosic fibres, however, both recoverable and nonrecoverable bending deformations, as well as time dependent bending deformations, take place (138).  Since a l l three mechanisms cause permanent  deformation in a very complex interaction,no exact information has been obtained as to what extent fibre bending contributes to the total mat response. Elias (63) studied the compression response of mats prepared from various fibre types and was able to show for glass fibres that bending i s the dominant mechanism during compaction.  Increasing load was found to  increase the glass fibre inflection points.  A comparison between glass  and synthetic fibres indicated that more flexible fibres, such as dacron filaments, give more contacts during bending.  Elias (63) also observed  that the number of contacts per unit length increased with fibre length for a given load.  -  Behavior of cellulose fibres as found in wet pulp mats w i l l differ somewhat from Elias' (63) observation on mats formed by non-cellulosic fibres.  Bending of pulp fibres in a wet mat is expected to be accompanied  by stretching and shearing processes (140), which may be particularly intensive for swollen fibres. 2.4.1.2  Fibre repositioning It is well known that the majority of fibres in a fibre bed obtained  from suspensions l i e flat in the horizontal plane.  There are always a number  of fibres, however, which are oriented at appreciable angles with the z-axis (perpendicular to mat direction).  Elias (63) observed on non-cellulosic  networks that a mat consisting of short fibres contains a higher number of individual fibres out of plane than a mat formed by long-fibre material. During compaction fibres out of plane were found to become nearly horizontal, which implies that those fibres change position relative to their neighbours. This phenomenon is known as slippage or fibre repositioning (63). It might contribute considerably to the non-recoverable deformation of wet cellulose fibre mats, since the forces needed to restore a wet pulp fibre  - 38 -  to i t s original position are rather low.  Resident restoring forces in the  fibre might provide at least partial recovery upon relief of the deformation stress, thereby contributing a component of recoverable fibre slippage. 2.4.1.3  Compression at points of contact Compressive excitations applied to cellulose networks are known  to cause stress concentrations at contact areas which induce contacting fibres to conform. The conformation process i s essentially characterized by changes in fibre cross-sectional shape, enlargement of contact areas, and increased fibre flattening (100). These phenomena, of course, are accompanied by deswelling processes when the fibre material is saturated with a swelling fluid such as water (100). 2.4.2  Factors determining compression characteristics of cellulose fibre mats The behavior of cellulose fibre mats under compressive stress or  strain has to be regarded as the result of numerous factors, most closely interrelated and, therefore, d i f f i c u l t to estimate.  It seems reasonable,  however, to distinguish between three categories of factors: ( i ) fibre morphology; ( i i ) fibre properties; and ( i i i ) structure of fibre mats. 2.4.2.1  Fibre morphology There are three fibre characteristics which have been found, or  are expected, to influence the response of cellulose fibre mats to compressive excitations; ( i ) fibre length; ( i i ) fibre length/diameter ratio; and ( i i i ) c e l l wall thickness. The average dimensions of typical pored and coniferous wood fibres differ widely, wherein the latter show the greater dimensions (91).. It is also known that latewood fibres are somewhat longer than those of associated earlywood (40,320). Other differences in fibre dimensions arise from machining processes in pulping. In particular, mechanical pulping produces fibre materials characterised by considerable dimensional variations between fibre fragments.  Groundwood pulps are known to contain components as: ( i )  fibre bundles; ( i i ) separate f i b r i l l a t e d fibres; ( i i i ) broken fibres; and  - 39 -  (iv) fine wood flour (16).  In contrast, chemical pulps consist almost  entirely of single fibre skeletons often mechanically damaged in varying amounts during processing. Due to the absence of interfibre hydrogen bonding in wet cellulose fibre mats, fibre length has to be considered important to mat response under compressive stress and strain.  It i s well known that long fibres  cause a high degree of mechanical entanglement (56), which strengthens both air-dry and wet cellulosic networks. Brecht and Erfurt (29) investigated the wet-web strength of mechanical and chemical pulps and pointed out that fibre length, in addition to consideration of f l e x i b i l i t y and surface area, has to be considered as the dominant factor in determining wet-web mechanical properties.  This concept has been confirmed by experiments of  Forgacs e_t al_. (73) with mats formed at low fibre consistencies, such as 0.8%.  Further evidence for this can be derived from several studies on  paper, which have shown, for instance, that tearing strength is highly influenced by fibre length (28,50). Fibre length can also influence the general fibre mat structure. Watson e_t aJU (3 J. 9) were able to demonstrate this effect on sulphate pulps prepared from Monterey pine fibres of 1.7 mm and 3.0 mm length, but similar in morphological and chemical properties.  It was found that the longer  fibres gave sheets with much more open structure; in other words, longer fibres produced sheets of higher bulk. Fibre length/diameter ratio was found to have at least some bearing on mat response to mechanical excitation.  Hentschel (111), working  with synthetic fibres, showed that this ratio influences the strength properties of fibrous networks. Jones (138) also reported a "ratio effect". By studying this effect on synthetic fibre and pulp mats under compression excitation he observed that an increase in length/diameter ratio up to a certain value enhanced the compression recovery response of fibre mats. Cn the other hand, Dadswell and Watson (56) provide evidence that this ratio has very l i t t l e or no influence on mechanical properties of air-dry fibre networks (papers).  - 40 -  The  importance o f c e l l  to paper p r o p e r t i e s 250,286,318). i n c e l l wall  wall  thickness  has been r e c o g n i s e d  f o r many y e a r s  Most d i f f e r e n c e s w i t h c o n i f e r o u s thickness  and degree o f f i b r e  collapse  (65,118,132,150,225,  p u l p s a r i s e from v a r i a t i o n s  between,earlywood and latewood t r a c h e i d s .  Thin  cell  w a l l s , as those i n earlywood, c o l l a p s e more r e a d i l y and produce a dense and h i g h l y packed network; whereas t h i c k - w a l l e d collapse  l e s s and g i v e open and b u l k y networks.  appears t o be t w o - f o l d : contact  cells,  ( i ) increased  such as those i n latewood,  The e f f e c t o f f i b r e  f i b r e f l a t t e n i n g provides  collapse  larger  a r e a s between f i b r e s ; and ( i i ) f i b r e c o l l a p s e e n t a i l s g r e a t e r  flexibility 2.4.2.2  or conformability  Fibre  (248).  properties  Variations a r i s i n g during  i n c h e m i c a l and p h y s i c a l c h a r a c t e r i s t i c s o f pulps  pulping,  bleaching  and subsequent t r e a t m e n t s a r e expected  to i n f l u e n c e p u l p mat response to compressive e x c i t a t i o n . are m a n i f e s t e d i n f i b r e c o l l a p s i b i l i t y fibre f l e x i b i l i t y hemicelluloses)  These v a r i a t i o n s  ( i n f l u e n c e d by r e s i d u a l  and f i b r e  strength  linkage with hemicelluloses  ( r e l a t e d t o c e l l u l o s e DP). as w e l l  as i t s p r o b a b l e  (23,35), the whole l i g n i n - h e m i c e l l u l o s e  i s made p a r t l y hydrophobic and i s r e s t r a i n e d from e x c e s s i v e Moreover, the t h r e e - d i m e n s i o n a l  lignin structure  of f i b r e c o l l a p s e and f l e x i b i l i t y . fibre properties  from e x c e s s i v e  lignin),  ( a f f e c t e d by s t r u c t u r a l c h a r a c t e r i s t i c s o f r e s i d u a l  Due t o the h y d r o p h o b i c nature o f l i g n i n ,  influences  fibre  For instance,  swelling (86).  i s known to l i m i t high  complex  lignin  i n two ways a s : ( i ) p r e v e n t i n g  the degree  content hemicelluloses  s w e l l i n g and p l a s t i c i s a t i o n ; and ( i i ) g i v i n g f i b r e s a h i g h  degree o f s t i f f n e s s which impedes c o l l a p s i b i l i t y  (40,86,105,133,184,221,306).  Other comprehensive i n v e s t i g a t i o n s on f i b r e p r o p e r t i e s and c o m p r e s s i b i l i t y of f i b r e mats have been p u b l i s h e d Page and coworkers (221,223) s t u d i e d o f p u l p f i b r e s , and observed drying  increased  collapsed  that  extent  (105,221,223).  paper s t r u c t u r e and c o l l a p s e  the percentage o f c o l l a p s e d  i n v e r s e l y t o the p u l p y i e l d  to a g r e a t e r  recently  and t h a t  than s u l p h a t e f i b r e s .  were made l a t e r by H a r t l e r and Nyren  behavior  fibres after  sulphite fibres Similar  (105), who i n v e s t i g a t e d  observations the t r a n s v e r s e  - 41  c o m p r e s s i b i l i t y of pulp f i b r e s . was  l i g n i n and  phobic and exhibited  hemicellulose  rigid low  character  were a b l e  lower c o l l a p s i b i l i t y  contents.  of  The  i n v e s t i g a t e d by  having  Kayma and  lignin  contents  f i b r e mats Higgins  reduces mat  (248).  (143),  d e l i g n i f i c a t i o n of s u l p h a t e  volume and  numerous s h o r t  high  t h e r e f o r e produced b u l k y  to show t h a t p r o g r e s s i v e  fibres  As a consequence of the hydro-  l i g n i n , f i b r e s possessing  been t h o r o u g h l y  produces lower s e d i m e n t a t i o n  of k r a f t  c r o s s l i n k i n g i n those f i b r e p a r t s  c o n f o r m a b i l i t y and  T h i s e f f e c t has who  The  a t t r i b u t e d to more f r e q u e n t  high  -  pulps  compressibility.  s i d e c h a i n s , c h a r a c t e r i s t i c of many h e m i c e l l u l o s e s ,  are r e s p o n s i b l e f o r the amorphous s t a t e of n a t i v e h e m i c e l l u l o s i c m a t e r i a l s . Therefore,  water p e n e t r a t e s  more e a s i l y between h e m i c e l l u l o s e  a f t e r d e l i g n i f i c a t i o n causes c o n s i d e r a b l e  swelling.  This  of g e l s i n s i d e f i b r e w a l l s , such as  in i n t e r - f i b r i l l a r  surfaces  (45).  branching  chemical  p u l p i n g and  In a d d i t i o n , DP bleaching  and  treatments  chains  leads  to  spaces and  are considerably  (174,217,233).  pulps  enhance g r e a t l y f i b r e and  (95,201,233,282).  lateral  under s t r e s s c o n d i t i o n s  s w e l l i n g by  they are  promoting f i b r e s l i p p a g e and The particularly chemical  inter-fibrillar  These changes  sheet  processes  "internal positioned  produced by  (86).  mechanical p r o p e r t i e s i s  chemical  treatments.  In  carbohydrate  a l l c e l l u l o s e m o l e c u l e s are degraded to some e x t e n t .  e n t a i l s weakening of the f i b r e u l t r a - s t r u c t u r e and  pulping  swelling  p u l p i n g , as w e l l as subsequent d e l i g n i f i c a t i o n and  strength.  hemicelluloses  to f u n c t i o n as an e x t e r n a l l u b r i c a n t  r e p o s i t i o n i n g w i t h i n mats  important f o r pulps  the  papers  S i m i l a r l y , hemicelluloses  e f f e c t of f i b r e s t r e n g t h on  removal p r o c e s s e s ,  fibre  fibres  fibril  reduced i n  thought to a c t as a k i n d of  l u b r i c a n t " improving f i b r e f l e x i b i l i t y . on f i b r e s u r f a c e s are c o n s i d e r e d  In wet  formation on  are known to have a pronounced e f f e c t on m e c h a n i c a l p r o p e r t i e s of made from c h e m i c a l  and  Many s t u d i e s on  thereby r e d u c t i o n  paper have shown t h a t s u l p h a t e  produces f i b r e m a t e r i a l s which d i f f e r w i d e l y  (11,84,104,144,233), whereby s u l p h a t e  pulp  i n strength  f i b r e s u s u a l l y are o f  and  This  i n whole sulphite  properties superior  II  strength.  It has  been suggested by Jayme and  t h a t the cause f o r lower s t r e n g t h sulphate  pulp  lies  von  observed w i t h  Koppen (134),  instance,  s u l p h i t e pulp compared  i n weaker i n t e r f i b r e bonding i n the  r e s u l t s i n t u r n from lower c a r b o h y d r a t e DP,  for  s u l p h i t e sheet.  i n p a r t i c u l a r of the  with This  cellulose,  - 42 -  a t the f i b r e s u r f a c e .  D i f f e r e n c e s in'carbohydrate degradation at the outer  p a r t s o f f i b r e s may a l s o e x p l a i n i n p a r t t h e o b s e r v a t i o n made by Seborg and Simmonds (261) i n compression  o f wet p u l p mats, wherein s u l p h a t e  showed h i g h e r r e c o v e r y f i g u r e s than s u l p h i t e p u l p s . g i v i n g some i n d i c a t i o n  Another  pulps  investigation  t h a t c e l l u l o s e d e g r a d a t i o n and c o n s e q u e n t l y  weaker  f i b r e s e f f e c t f i b r e mat c o m p r e s s i b i l i t y was c a r r i e d out by P e t t e r s o n and Rydholm ( 2 3 3 ) .  They found  t h a t overcooked and o v e r b l e a c h e d  denser papers than would be expected 2.4.2.3  p u l p s form  from o p a c i t y measurements.  S t r u c t u r e o f f i b r e mats The  s t r u c t u r e o f f i b r e mats i s determined by d i s t r i b u t i o n and  o r i e n t a t i o n o f f i b r e s , which i n t u r n depends on p r o c e s s e s o f mat f o r m a t i o n (8,175).  A c c o r d i n g t o f i b r e arrangement the mat s t r u c t u r e can be c h a r a c t e r -  i z e d by: ( i ) the degree o f s e p a r a t i o n o f the f i b r e s a c r o s s the mat t h i c k n e s s ; ( i i ) orientation'of fibres flocculation; and  i n the t h r e e - d i m e n s i o n a l network; ( i i i ) degree o f  ( i v ) extent of c o i l i n g or w r i n k l i n g of i n d i v i d u a l  ( v ) d i s t r i b u t i o n o f f i n e m a t e r i a l (84,175,306).  fibres;  Evidence e x i s t s , i n  p a r t i c u l a r from s t u d i e s on p a p e r , t h a t these mat c h a r a c t e r i s t i c s can have an important b e a r i n g on mechanical In f i b r e mat compression  factors  p r o p e r t i e s o f f i b r e networks  ( i ) and ( i i ) a r e expected  (8,15,84).  t o p l a y major  r o l e s , as they p r o b a b l y determine the e x t e n t t o which the t h r e e mechanisms are i n v o l v e d d u r i n g the compaction p r o c e s s . (100)  T h i s agrees w i t h Han's statement  t h a t r e s i s t a n c e o f wet f i b r e mats to compression  increasing i n i t i a l f r a c t i o n at a given  solid fraction. compression.  increases with  T h i s r e s u l t s i n a lower f i n a l  solid  3„0 3<>1  MATERIALS AND  METHODS  P u l p Samples P u l p s were chosen  to b r o a d l y r e p r e s e n t . t h e wood p u l p  thus p r o v i d i n g a wide q u a n t i t i v e range  spectrum,  f o r r e s i d u a l carbohydrates  and  l i g n i n s and h o p e f u l l y l a r g e d i f f e r e n c e i n p h y s i c a l and r h e o l o g i c a l Consequently, study.  The  24 commercial  and  eight  l a b o r a t o r y p u l p s were used  responses.  i n the  sample c o l l e c t i o n i n c l u d e d f o u r groundwood p u l p s , f o u r  "holocellulose" pulps, four kraft d i s s o l v i n g grade  p u l p s , one  sulphite pulp,  fifteen  p u l p s and f o u r a l p h a - c e l l u l o s e p r e p a r a t i o n s .  Other  s o u r c e s of v a r i a t i o n were i n t r o d u c e d to the study by i n c l u d i n g both and  unbleached  p u l p s and by c h o o s i n g p u l p s prepared from both c o n i f e r o u s  and pored woods.  The v a r i o u s p u l p s employed and  i s t i c s are l i s t e d  i n Table  The  bleached  eight  some o f t h e i r c h a r a c t e r -  2.  l a b o r a t o r y p u l p s i n c l u d e d i n the study were h o l o -  c e l l u l o s e and a l p h a - c e l l u l o s e p r e p a r a t i o n s of wood f i b r e  s k e l e t o n s as  o b t a i n e d by s t a n d a r d methods. 3.1.1  Holocellulose  pulps  The wood m a t e r i a l s used f o r p r e p a r i n g h o l o c e l l u l o s e p u l p s were taken from one mature stem each of western ( R a f . ) S a r g . ) and western S p e c i a l c a r e was  damage to f i b r e s .  and  0.3  x 1.0 x 4.0  cm  i n o r d e r to minimize  size mechanical  A f t e r a i r - d r y i n g f o r t h r e e days the c h i p s were e x h a u s t i v e -  l y e x t r a c t e d w i t h 2:1 i n t o two  (Populus t r i c h o c a r p a T o r r & G r a y ) .  e x e r c i s e d i n d i s s e c t i n g wood b l o c k s i n t o s m a l l  p i e c e s of a p p r o x i m a t e l y  divided  cottonwood  hemlock (Tsuga h e t e r o p h i l l a  ethanol-benzene.  p a r t s , one  the o t h e r i n a c i d i f i e d  p a r t was  The  a i r - d r y e x t r a c t e d c h i p s were  used f o r p u l p i n g i n p e r a c e t i c  sodium c h l o r i t e  acid  solution.  P e r a c e t i c a c i d c o o k i n g accompanied by a l t e r n a t e sodium b o r o h y d r i d e r e d u c t i o n s t a g e s , was Leopold was  (164).  Due  carried  out a c c o r d i n g t o the method proposed  to r a t h e r l a r g e c h i p d i m e n s i o n s ,  r e q u i r e d f o r complete  defiberisation.  Chemical  a total  by  of s i x c y c l e s  a n a l y s e s of these p u l p  preparations indicated a higher loss i n n o n - c e l l u l o s i c carbohydrates  (Table  -  44  -  3g)than reported i n the l i t e r a t u r e (295).  This discrepancy can be attributed  to overcooking of the outer portion of the chips which obviously caused serious degradation and subsequent d i s s o l u t i o n of hemicelluloses. for t h i s occurred also i n work of Shimada and Kondo (264), who  Evidence  observed a  decrease i n pulp y i e l d with increasing chip thickness. C h l o r i t e h o l o c e l l u l o s e pulps were obtained by d e l i g n i f y i n g wood chips i n a solution of sodium c h l o r i t e and a c e t i c acid at 70° C. of the method are reported elsewhere  (323).  Approximately  Details  eight hours  c h l o r i t i n g time was required to produce a completely d e f i b r i s e d m a t e r i a l . Similar to peratic acid pulps, the c h l o r i t e h o l o c e l l u l o s e pulps contained less hemicelluloses than expected based on values published i n the l i t e r a t u r e . This can be explained by overcooking e f f e c t s i n outer portions of the r e l a t i v e l y large chips.  An i n v e s t i g a t i o n by Eriksson (67) on several factors  influencing q u a l i t y and quantity of c h l o r i t e holocelluloses supports t h i s assumption.  He observed also that increasing wood p a r t i c l e size and  ment time lowered holocellulose y i e l d s .  treat-  In the present study, both factors  exceeded considerably the values proposed by Wise et a l . (323). The f r e s h l y prepared h o l o c e l l u l o s e s were a i r - d r i e d as small flakes f o r two days at room temperature i n mechanical  i n order to eliminate or minimize  differences  properties between commercial and laboratory pulps due to  moisture h i s t o r y , which has been found to a f f e c t pulp mat properties (29). This procedure was necessary as commercial pulps were supplied i n a i r - d r y condition following unknown drying h i s t o r i e s . 3.1.2  Alpha-celluloses One alpha-cellulose pulp was  prepared from each of a commercial  viscose and acetate pulp and the two c h l o r i t e h o l o c e l l u l o s e preparations as obtained from western hemlock and western cottonwood.  The a l k a l i n e  extraction with 17.5% NaOH at 20°C was carried out i n accordance TAPPI T203 os-61  (289).  with  Alpha-cellulose residues were teased into small  flakes and a i r - d r i e d before further processing f o r sample sheets preparation. Since part of a preliminary study on viscose pulps i s included in t h i s work and specimens used i n the e a r l i e r i n v e s t i g a t i o n were cut from  - 45 -  commercial pulp sheets, i t was decided to prepare other fibre mats as close as possible in basis weight and thickness to those supplied commercially. Mats were prepared essentially according to TAPPI Standard T205m-58 (287). Following weighing, disintegration, and sheet formation in the standard sheet machine, 10 wet handsheets of each pulp type were prepared.  Prior to pressing these 10 standard wet sheets (each weighing  1.2 - 0.1 g oven-dry basis) were carefully laid over each other.  In this  way a wet pulp mat was obtained which, after wet-pressing and air-drying, yielded a sample sheet of desired basis weight and thickness.  Both  pressing stages were performed at 80 psi for time periods according to TAPPI Standard T205m-58. Conditioning of sample sheets was done between drying rings at controlled temperature - humidity conditions (22 C and 50 to 52% R.H.) for at least three days before further processing. The preparation of sample mats by means of assembling handsheets was found by preliminary experiments to produce more uniform structures than when thicker sheets were prepared from higher consistency stock, which gave high  flocculation.  Thus, serious density variations across mats  were avoided with the intention of minimizing variability due to this cause. Test specimens of viscose pulps (1-1 to 4-2) were prepared from commercial sheets, while specimens representing other pulp types were obtained from laboratory made mats as described.  Actual test specimens  were punched randomly from sample mats by using a carefully honed mechanical cork borer of 1.45 cm diameter. Specimens were either steeped i n d i s t i l l e d water or aqueous sodium hydroxide for varying times, or were subjected to gamma-radiation before further treatment.  Thereafter, the stress relaxation was performed  by methods to be described. The specimens used for studying stress decay on pulps i n wet condition were steeped approximately "one minute in d i s t i l l e d water. This was found to be the minimum time required for assuring complete swelling.  - 46 -  Those specimens exposed to caustic steeping were kept f o r 25 * 2 sec i n 18.6% NaOH, a concentration used i n commercial steeping. treatments were performed at a temperature of 22°C.  Both steeping  Immediately a f t e r  steeping, the pulp specimens were examined i n stress r e l a x a t i o n . specimens were kept i n corresponding solutions during t e s t i n g .  The In one  experiment, which dealt with the e f f e c t of steeping time on stress r e l a x a t i o n , the caustic steeping period was varied from 0.1 to 14400 minutes (more than f i v e time cycles of 10). Sample i r r a d i a t i o n treatments were done i n a Gamma-Cell 220 at ambient r a d i a t i o n chamber temperature of 34°C.  Air-dry pulp samples were  exposed i n an a i r atmosphere from 0.5 to 6 Mrad dosages at a dose rate of 0.829 Mrad/hr. 3.2  Physical Testing A l l stress r e l a x a t i o n measurements were performed with a Floor  Model TT Type C Instron t e s t i n g machine.  The specimens were placed between  a 1.0 mm thick microslide glass and a 5.0 mm thick glass plate i n order to protect the Instron load heads from corrosion i n tests involving caustic steeped specimens.  The glass assembly was found not to relax i n any  measurable way under conditions used i n this experiment.  A t y p i c a l test  assembly i s shown i n F i g . 4. Five r e p l i c a t i o n s were done f o r each pulp treatment combination. Since i t i s not possible to determine ultimate strength values i n pulp compression due to the collapsed state of the fibrous material i n the mat, 2 an a r b i t r a r y load of 3,5 kg/2.1 cm  was applied i n a l l t e s t s .  It can be  assumed that a stress of t h i s magnitude does not cause complete compression of the mat, although i n i t i a l c a l i p e r was reduced 60 to. 80%. S t r a i n (&L:L) was not used, since each pulp showed c h a r a c t e r i s t i c swelling. The desired stress was applied i n a l l tests at the rapid loading speed of 2 cm/min f o r water treated and 5 cm/min f o r a l k a l i steeped specimens.  These were the highest speeds possible f o r accurate setting  of stress levels with the test engine used.  Consequently, the loading  process was completed i n approximately 1 to 1.5 sec, which i s the l i m i t of approximation to step-function e x c i t a t i o n of the present study.  - 47 -  S t r e s s r e l a x a t i o n was except f o r experiments relaxation  t e s t s were stopped a f t e r  set a t c h a r t  speed  (0 to 15 s e c ) , and  100 min.  an X - Y - r e c o r d e r  of 2 i n / s e c was  1 in/min f o r t r a c i n g  of 35  min,  d e a l i n g w i t h the e f f e c t of s t e e p i n g time where  f o r o b s e r v i n g s t r e s s decay;  decay  observed over a time range  Two  (Mosely Autograph  used f o r r e c o r d i n g e a r l y  the I n s t r o n r e c o r d e r was  s t r e s s decay  r e c o r d e r s were employed  from  Model 7000-A)  stages of  stress  run a t a c h a r t speed  15 sec onward.  of  Both r e c o r d e r s were  f e d the same I n s t r o n s i g n a l . Data o b t a i n e d from c h a r t  t r a c e s were transformed i n t o  fractional  stress r e l a x a t i o n values according to: £(t)/£(o), where: cL, . i s the i n i t i a l Xo) was  completed,  such as 1.0  s t r e s s a t time t , i . e . , when the l o a d i n g p r o c e s s o to 1.5  d i f f e r s from much of the e a r l i e r t  sec a f t e r e x c i t a t i o n was  commenced.  l i t e r a t u r e where, f o r mathematical  has been taken as 1 min f o l l o w i n g c o m p l e t i o n o f l o a d i n g , and  f o l l o w i n g e x t e n s i v e but seldom d e s c r i b e d ramp-loading 3.3  This  convenience,  this  often  times.  Determination of Pulp C o n s t i t u e n t s In o r d e r t o o b t a i n i n f o r m a t i o n on the c o n t r i b u t i o n of v a r i o u s  wood and p u l p c o n s t i t u e n t s to p u l p v i s c o e l a s t i c i t y , s e v e r a l methods were employed  including:  ( i ) d e t e r m i n a t i o n of the c a r b o h y d r a t e  components; ( i i ) e s t i m a t i o n of r e s i d u a l 3.3.1  l i g n i n ; and  ( i i i ) o t h e r measurements.  Carbohydrates S e v e r a l q u a n t i t a t i v e gas chromatographic  of wood and  methods f o r a n a l y s i s  p u l p c a r b o h y d r a t e c o m p o s i t i o n s have been d e v e l o p e d  These have proven t o be earlier  analytical  traditional  l e s s time consuming and e a s i e r to o p e r a t e  paper chromatographic  methods, monosaccharides  recently.  procedures.  A c c o r d i n g to these  in neutralised hydrolysates originating  c e l l u l o s i c m a t e r i a l s can be a n a l y s e d a f t e r c o n v e r s i o n to d e r i v a t i v e s . (21,302), a c e t y l a t e d a l d o n i t r i l e s  than  from  trimethylsilyl  (61) o r a l d i t o l a c e t a t e s  (26,94,267,269). T r i m e t h y l s i l y l d e r i v a t i v e s a r e q u i c k l y p r e p a r e d b u t , due  to the  - 40 -  m u l t i p l i c i t y o f peaks a r i s i n g f r o m each a l d o s e by anomeric and r i n g - f o r m s , peak i n t e r p r e t a t i o n s a r e d i f f i c u l t t o make.  different  For t h i s  reason,  the a l d i t o l a c e t a t e methods which g i v e s o n l y a s i n g l e peak f o r . e a c h m o n o s a c c h a r i d e seems t o be more a c c u r a t e f o r q u a n t i t a t i v e d e t e r m i n a t i o n o f wood and p u l p p o l y s a c h a r i d e m i x t u r e s . d e v e l o p e d by B o r c h a r d t •acetate procedures, a l l known wood  I t was  t o a p p l y the method  and P i p e r ( 2 6 ) , w h i c h , compared w i t h o t h e r  i s l e s s t i m e consuming  and i s known t o  alditol  separate  sugars.  A 300 me  sample (oven-dry b a s i s ) was  p u l p mats used f o r r h e o l o g i c a l t e s t i n g . i n t h e s t u d y was  decided  represented  t a k e n f r o m each o f the  32  T h u s , each p u l p type i n v e s t i g a t e d  by one c o m p o s i t e s a m p l e .  A f t e r shredding  and  w e i g h i n g , the p u l p s were h y d r o l y s e d f o l l o w i n g the method of Saeman et^ a l . (253).  E x a c t l y O.lOO g o f m y o - i n o s i t o l as i n t e r n a l s t a n d a r d was  t h e aqueous h y d r o l y s a t e b e f o r e i t was  n e u t r a l i s e d and  a c c o r d i n g t o t h e p r o c e d u r e o u t l i n e d by B o r c h a r d t  further  added t o  processed  and P i p e r ( 2 6 ) .  In the  f i n a l s t e p o f t h i s p r o c e d u r e the a l d i t o l and m y o - i n o s i t o l a c e t a t e s were d i s s o l v e d i n m e t h y l e n e c h l o r i d e and  stored i n t i g h t l y sealed v i a l s ,  i n j e c t i o n i n t o the gas c h r o m a t o g r a p h .  Three i n j e c t i o n s o f 0.7  before  p i each were  done f o r a n a l y s i s o f each s a m p l e . S e p a r a t i o n s were c a r r i e d out w i t h a i d o f a M i c r o T e k 150  gas  chromatograph equipped w i t h a f l a m e i o n i s a t i o n d e t e c t o r and a Moseley 7100  B stripchart recorder.  A 6 f t x 1/8-In g l a s s ( a n a l y t i c a l ) column  packed w i t h 3% ECNSS - M on Gas  Chrom Q 80-100 mesh was  i n s t a l l e d f o r on  column i n j e c t i o n . H e l i u m was  used as c a r r i e r gas w i t h a f l o w r a t e o f 33 m l / m i n .  A l l o p e r a t i o n s were i s o t h e r m a l w i t h the column oven a t 195°C, the p o r t a t 210°C, and  the d e t e c t o r a t 240°C.  a c e t a t e s were e l u t e d i n a p p r o x i m a t e l y  The  myo-inositol  40 min w i t h s a t i s f a c t o r y  o f each component as can be seen i n F i g s . 5 t o The  a l d i t o l and  injection  resolution  13.  r e l a t i v e amounts o f i n d i v i d u a l components were c a l c u l a t e d  according to ( 2 6 ) :  - ty -  % Polysaccharide = C x I x F x 100 R x S x H x. k where:  [10]  C  =  chromatographic area of the component peak,  R  =  chromatographic area of the myo-inositol peak,  I  =  myo-inositol weight,  S  =  oven-dry sample weight,  F  =  factor converting monosaccharide weight to polysaccharide (0.88 pentose; 0.90 hexose),  H  =  hydrolysis survival factor, and  k  =  calibration factor for the individual component.  Peak area measurements were done manually by cutting and weighing chromatograms, since the Disc Chart Integrator was not in working order and the counter did not work satisfactorily for carbohydrate peaks.  The hydrol-  ysis survival factors of individual sugars used for this equation were determined by Saeman et al_. (253) and k-values were based on slopes of calibration curves which were obtained by plotting chromatographic peak area ratios (monosaccharide area/myo-inositol area) vs. weight ratios (monosaccharide weight/myo-inositol weight) for known samples. Uronic acid residues were determined commercially by Schwarzkoff Microanalytical Laboratory, Woodside, N.J., f o i l owing the method of Anderson et al_. (6). The quantitative analysis of acetyl groups was carried n  out by the same company using a modified method developed by Schoniger et a_l. (256). Data on acetyl and uronic acid groups are presented in Table 3. Hydrolysis of wood hemicelluloses according to the procedure of Saeman ejt al.(253) is not without shortcomings. Meier and Wilkie (192) and Zinbo and Timell (327) observed that aldobiouronic acids formed during hydrolysis were rather stable to further hydrolytic degradation.  Only  one-third of 4-0-methyl-D-glucopyranuronide linkages were found to undergo further hydrolysis under conditions provided by the method of Saeman (192, 327).  Since the xylose fraction which is present in non-hydrolysed aldo-  biouronic acid residues does not appear in the gas chromatographic analysis, some correction regarding xylose content was undertaken. This was done by multiplying the relative amount of glucuronic acid residues with a factor .  of 0.66 (which relates to non-hydrolysed aldobiouronic acid).  The value  obtained was added to xylose as determined by the gas chromatographic procedure (Table 3). Since the chromatographic analysis gave only information on the total amount of glucose present in pulp, i t was useful to estimate those portions of glucose originating from cellulose and glucomannans. This was done according to known ratios between glucose and mannose residues in isolates from coniferous (1:3) and pored (1:2) wood glucomannans (293). The corresponding values are presented in Table 3. 3.3.2  Lignin Lignin determinations were carried out according to the Klason  lignin method as described by Browning (37) on groundwoods (10-1 to 10-4), holocelluloses (9-1 to 9-4) and paper grade, pulps (6-1 to 8-2). presented as Klason lignin in Table 3.  Data are  Only groundwood pulps were subjected  to ethanol-benzene extraction treatments prior to acidification, since chemical pulps are known to contain no or only traces of extraneous compounds. No lignin determinations were undertaken on viscose, acetate and alpha-cellulose pulps,due to their extremely low lignin contents which are not measurable by the Klason lignin method. Their lignin contents were estimated to be ^ 0. l7o. 3.3.3  Other measurements Viscosity measurements were done for characterising pulps and for  determining degree of cellulose degradation by irradiation treatments.  They  were carried out in a modified FeTNa (EWNN, alkaline iron tartaric acid sodium complex)solution prepared according to Valtasaari (305), but with an additional 10 g/1 sodium tartrate used as stabilizer. of 0.015  Oven-dry sample weights  to 0.25 g pulp per 100 ml solution were used according to the method  of Paszner (229), with amount adjusted to the degradation level.  First,  specific viscosity Ctfsp) was determined with an Ubbelohde viscosimeter No. + o r- -1 la at 20 - 0.02  equation (305):  C.  Intrinsic viscosity (\_K>j)  w a s  then calculated by the  - 51 -  M l  where:  -  "CJ C  =  [nJ L  C (140.339 ^sp) amount of moisture-free pulp, g/100  J  ml.  TAPPI Standard method T293 os-6l (289) was followed in determining alpha-cellulose contents.  This particular method was scaled to accommodate  micro-amounts of material. The solubility determinations were performed according to TAPPI Standard T 235 m - 60 (288) with 107o NaOH solution at a constant temperature of 20°C.  Special care was exercised to keep the temperature at 20 - 0.02°C  for a l l tests, since i t has been found that even slight changes in temperature influence results of alkali solubility measurements (126).  - 52 -  4.0 4.1  RESULTS AND DISCUSSION  Fractional Stress Relaxation Tests As described e a r l i e r , five replicates were used in a l l pulp treat-  ment combinations.  Table 4 presents fractional stress relaxation data  (1.000 - ^ ( 3 5 min)) as obtained from individual measurements after 35 min i  o (o) relaxation time, mean values and standard deviations for each of the pulps tested for both water and caustic steeped conditions. Standard deviations show relatively l i t t l e variation between measurements at 35 min relaxation time as taken from individual pulps given the same steeping treatment.  This means that the results are consistent,  which is a strong point of the experiments.  Degree of variation was  approximately the same for a l l pulp types with comparable steeping treatments, but differed considerably between water and caustic steeped specimens of the same pulp. On average, caustic treated samples exhibited less variability in rate of stress decay, as compared with water saturated specimens.after 35 min relaxation.  As will be shown later, the reproducibility of stress  relaxation data, particularly when obtained from caustic treated samples, appears to be sufficiently high to employ relaxation measurements for characterising pulps. Characteristic of a l l viscoelastic materials is their ability to dissipate stress when subjected to deformation.  It is well known that  stress relaxation of viscoelastic solids occurs at the highest rate immediately after a constant deformation is applied, and thereafter decreases gradually with time.  A similar type of response can be expected also from pulp mats  placed under constant compressive strain. Two-dimensional £(t )/€T(o) vs. log time plots of typical fractional stress relaxation curves, as obtained from pulps steeped either in d i s t i l l e d water or 18.6% NaOH prior to relaxation tests, are shown in Figs. 14 to 18. The curves represent average values of five measurements.  It appears from  each set of plots that rate of stress dissipation in pulp compression follows patterns similar to those observed in woods or other cellulosics examined under constant compressive or tensile strains (137,145,146). Wet or caustic  -  53  -  s t e e p e d p u l p mats e x h i b i t e d the h i g h e s t  r a t e of s t r e s s decay  immediately  a f t e r s t r a i n a p p l i c a t i o n , which i s c h a r a c t e r i s t i c f o r r e l a x a t i o n p r o c e s s e s of  ligno-cellulosic  materials  and  o f t e n e x p r e s s e d as  l o g time r e l a t i o n s h i p s .  t  A more d e t a i l e d a n a l y s i s of the ^ ( t )/Sto) v s .  l o g time p l o t s r e v e a l s  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 take p l a c e as two  distinct  i n d i c a t e d as  two  The the  short  cation.  s l o p e s w i t h i n each f r a c t i o n a l  time range of 35 min  followed  by a h i g h  affect significantly  the  s t r e s s decay.  a l s o by Anderson and  first  and  non-linear  been found to i n v o l v e r a t h e r  p u l p s (0.00  to 0.03  min);  c h e m i c a l paper p u l p s longer  history.  this did  (7) who  (0.00  explain  superposition  Such o b s e r v a t i o n  show t h a t  s t r e s s r e l a x a t i o n responses.  It varies i n duration  log t p l o t  ( F i g s . 14-18) and  times f o r v i s c o s e and  often intermediate  min).  high  alpha-  times f o r h o l o c e l l u l o s e  to a p p r o x i m a t e l y 0.10  The  pulp-water or p u l p - c a u s t i c between ^ ( t )/g£(o) v s . n A n d e r s o n and S j o b e r g  rain);  and  and  comparatively (to  common c h a r a c t e r i s t i c s i n Phase I f o r a l l  t r e a t m e n t s i s the  log t .  not  Similar  p e r i o d of t h e ^ ( t ) / ^ t o ) v s .  short  studied  times f o r groundwoods, p a r t i c u l a r l y when steeped i n c a u s t i c  a p p r o x i m a t e l y 1.00  for  (145)  immediate consequence of the Boltzmann  w i l l be c a l l e d Phase I r e l a x a t i o n . has  that  Sjoberg  i s needed f o r i n t e r p r e t i n g i n i t i a l  The  appli-  observed t h a t a h i g h s t r a i n i n g  s t r e s s decay, but  p r i n c i p l e or as dependent on p r e v i o u s s p e c i a l care  Kirbach  l a t e r p r o c e s s of s t r e s s d i s s i p a t i o n .  were r e p o r t e d  t h i s phenomenon as an  initial  over  been found t o e x e r t a profound  s t r e s s decay i n wood microspecimens and  observations  are  stress relaxation trace.  f o l l o w i n g almost i n s t a n t a n e o u s s t r a i n  In p a r t i c u l a r , r a t e of s t r a i n has  r a t e was  These  w r i t e r emphasizes t h a t r e s p o n s e s have been observed o n l y  i n f l u e n c e on the magnitude of i n i t i a l the  phases.  that  sigmoid type r e l a t i o n s h i p  Such r e l a t i o n s h i p s have been found a l s o  ( 7 ) , and  to some e x t e n t  paper t e n s i l e s t r e s s r e l a x a t i o n .  by  Johanson and  Kubat  They a l s o used e x t r e m e l y s h o r t  by (137), periods  II  for  load or s t r a i n a p p l i c a t i o n .  100 mm  long specimens a t c o n s t a n t  5 sec and sec  Johanson and  * i n the m a j o r i t y  earlier, this  Anderson  1,0  study.  to 1.5  Kubat (137)  and  (7) s t r a i n e d  r a t e s between 1% i n 0.01  the e l a p s e d  long  strips.  1.25 As  time f o r c o m p l e t i o n of  their 17, i n  sec and  employed a s t r a i n r a t e of  of experiments-on 10 mm  sec was  Sjoberg  x  10  mentioned loading  in  - 54 -  The "linear" period, which w i l l be termed Phase II relaxation, characterises the.remaining part of the 35 min response of pulp mats steeped in either water or 18.6%  NaOH. A straight line relationship between  ^(t)/£>to) vs. log t has been reported also for other cellulosic materials, such as wood at micro- and macro-levels (145,146) and papers (137,242), while several equations have been developed to describe this linear inflection region.  For instance, Johanson and Kubat (137) used the following  equation to describe rate of stress decay (Phase II) mathematically as: • where:  F  =  <^0-F  log t  [li]  slope of the main inflection of C(log t ) .  A similar equation was derived empirically by Kitazawa  (146)  earlier and was used to describe wood stress relaxation: ^(t)/eto) where: m  =  -  1  -  m log t  [l4J  constant relaxation coefficient which takes into account factors such as species variations.  Kitazawa reported that his equation covered the total stress relaxation process as observed after 1 min.  In contrast to other studies  in stress relaxation (7,137,145), Kitazawa's work ignored stress relaxation in the 1 min period and therefore does not report existence of a non-linear Phase I relationship. Since the constants F and m in the two equations above may  be  replaced by any number representing a certain slope, both equations can be employed to describe pulp mat stress relaxation following water or caustic steeping.  Such application, of course, is limited to the linear (Phase II)  inflection region. The steep slopes observed in Phase I, compared with Phase I I , for other cellulosics suggests profound differences in mechanisms responsible for i n i t i a l stress decay, especially in the water and caustic swollen state of pulp mats and other cellulosic materials.  This includes observations by  Johanson and Kubat (137) for paper 3tress relaxation i n tension and Xirbach  - 55 -  (H5)  f o r wood microspecimens  i n compression  t h a t r a t e o f s t r a i n i n g e f f e c t s may  have induced  e x c l u d e d , s i n c e f o r a l l experiments stress dissipation  (Phase  in i n i t i a l  possibility  these d i f f e r e n c e s can  i n v e s t i g a t i n g s h o r t term  I ) s t r a i n was  Dissimilarities  and t e n s i o n . The  or  applied at high  rates.  stress dissipation  (Phase  initial  I ) between  v a r i o u s c e l l u l o s i c s a r e a t t r i b u t e d m a i n l y to f a c t o r s which determine r e l a t i o n s between i n d i v i d u a l such as type and  s t r u c t u r a l u n i t s i n wood and  c a u s t i c s a t u r a t e d p u l p mats the randomly arranged rather limited bonding  interaction.  expected middle and  surfaces.  cellulosics,  In water and  f i b r e s can e x e r t o n l y  of a i r - d r y f i b r o u s m a t e r i a l s , a r e l a c k i n g and  fibre  Consequently,  to r e p o s i t i o n e a s i l y  to m e c h a n i c a l  the o n l y  individual fibres.  interacting  entanglement o r  e x t e r n a l mechanical  l a m e l l a h o l d s v a r i o u s s t r u c t u r a l elements  excitations  a l o n g c o n t a c t a r e a s , mechanical  friction  are  In woods, where the s t r o n g in spacial  arrangement  i n d r y papers which o b t a i n s t r e n g t h from i n t e r - f i b r e hydrogen e x c i t a t i o n s encounter  bonding  considerably higher  r e s i s t a n c e b e f o r e s t r u c t u r a l u n i t s a r e s e p a r a t e d from each o t h e r o r D u r i n g , and mat of  response  immediately  i s expected  inter-  Hydrogen bonds, c h a r a c t e r i s t i c f o r i n t e r f i b r e  f o r c e s i n s a t u r a t e d p u l p mats a r e due at  fibrous  i n t e n s i t y of f i b r e a s s o c i a t i o n and o r d e r .  be  following  repositioned.  load a p p l i c a t i o n , s a t u r a t e d p u l p  t o i n c l u d e both i n i t i a l  f i b r e rearrangements  c o u r s e , i n t r a - f i b r e p r o c e s s e s c a u s i n g m o l e c u l a r rearrangements.  the e a r l y s t a g e s o f s t r e s s decay (Phase two  f u n d a m e n t a l l y d i f f e r e n t mechanisms.  M^,  can be a t t r i b u t e d  and, Consequently,  I ) would seem to be c o n t r o l l e d One  of t h e s e , which may  to i n t e r - f i b r e p r o c e s s e s .  be  by  called  These p r o c e s s e s might  l a r g e l y c o n t r o l r a t e of Phase I s t r e s s decay. The  o t h e r mechanism, which may  be c a l l e d  M^,  i n t r a - f i b r e p r o c e s s e s t a k i n g p l a c e a t the m o l e c u l a r d i s c u s s e d below, these may  be o f i n t e r - and  on s l o p e s of c u r v e s i n F i g s .  i s a s s o c i a t e d with  level.  As w i l l  intramolecular nature.  14 to 18, i t can be c o n c l u d e d  that M  l e s s important mechanism i n Phase I, but seems to c o n t r o l almost Phase I I , i . e . , a f t e r The in  be  2  Based i s the  entirely  i n t e r f i b r e p r o c e s s e s a r e a t a minimum.  i n t e r f i b r e p r o c e s s e s which a r e thought  Phase I s t r e s s decay i n v o l v e e s s e n t i a l l y  t o p l a y the major r o l e  f i b r e movements, such as  bending  - 56 -  slippage, deswelling effects at points of contact and, to a lesser extent, movement of fluids in the saturated mat.  Certainly, most fibre slippage  occurs during the loading process, but some fibre repositioning can be expected in early stages of the stress relaxation process. This might contribute significantly to Phase 1 stress decay. The rather long periods of Phase I observed for groundwood pulps support this assumption. The low length/diameter ratio of groundwood fibres, together with presence of a considerable amount of fines, provides a mat of low coherence.  Therefore,  some fibre movement in particular toward the sample edge can be expected. The consequence is decreasing stress. o  Changes in fibre bending, which according to Jones (138) are time dependent, may be also of great importance to stress relaxation in Phase I. Deswelling processes at points of contact are, according to Han (100), a significant feature of water saturated mat compression.  Removal  of internal fluids from areas under compression requires time, therefore, these processes will continue beyond conclusion of strain application (t )» adding to the high rate of Phase I stress dissipation. It i s not believed that f i l t r a t i o n resistance plays more than a subordinate role in i n i t i a l stress relaxation processes.  Slopes of the  loading curves indicate that only low stresses (less than 5% o f ^ a t t ) develop during early periods of the straining process. This holds even when a high degree of straining (approximately 90% of total mat  deformation)  is employed. It appears from this that almost a l l free liquid is removed from the mat before the desired i n i t i a l stress level i s attained. The conclusion can be drawn that i n i t i a l stress relaxation (Phase I) in saturated pulp mats involves mechanisms at least partly different from those responsible for stress decay in dry fibrous webs or in dry or saturated woods. This is due mainly to the fact that associations between structural units of saturated fibre mats are profoundly different from those, existing in wood and papers. 4.2  Effect of Steeping Media (Water vs. Caustic) It is known from studies on wood and other cellulosic materials  - 57 -  that  steeping  and  treatments w i t h s t r o n g  alkaline solutions  i n t r a - c r y s t a l l i n e s w e l l i n g , whereas s t e e p i n g  i n water e n t a i l s  e x t e n s i o n o f i n t e r - c r y s t a l l i n e r e g i o n s (251,275). on c a u s t i c (46)  steeping  mechanical  exert  profound i n f l u e n c e s  rheological  on the response o f c e l l u l o s i c s t o  t o undertake r e l a x a t i o n  stress relaxation  NaOH, a r e p r e s e n t e d i n F i g s .  traces  as averages of f i v e  i n p u l p mats t r e a t e d  mats.  14 t o 18; whereas T a b l e 4 c o n t a i n s  with c a u s t i c  In o t h e r words, c a u s t i c  i n water r e s u l t e d  i n reduction  higher rates  solutions  steeping  o r c a r b o h y d r a t e complex.  (Phase I ) o f r e l a x a t i o n  14 to 18 i n d i c a t e c l e a r l y t h a t d i f f e r e n c e s  amount o f s t r e s s decay between water o r c a u s t i c e s s e n t i a l l y during  the f i r s t  from t h i s o b s e r v a t i o n  that  e f f e c t s of caustic  stress d i s s i p a t i o n processes.  treated  in relative  pulps are set  0.01 t o 0.1 min o f r e l a x a t i o n .  f i b r e s t r u c t u r a l polymer complex i s o n l y  swelling within  a c t i v e during  I t appears the p u l p  e a r l y s t a g e s o f the  I t can be c o n c l u d e d t h a t c a u s t i c  swelling  some mechanisms w h i c h , a f t e r d i s s i p a t i n g c o n s i d e r a b l e  s t r e s s , exhaust q u i c k l y .  quantitatively  between 10 and 54% a t  of loading.  S l o p e s of t h e q u i c k l y d e s c e n d i n g p o r t i o n  must a c t i v a t e  than i n water  i n comparison w i t h  can be seen, r a t e o f s t r e s s d i s s i p a t i o n i n c r e a s e d  curves i n F i g s .  of s t r e s s  o f the e l a s t i c and enhancement of  p l a s t i c b e h a v i o r o f the l i g n i n - c a r b o h y d r a t e  35 min a f t e r c o n c l u s i o n  of  trials  s t r e s s r e l a x a t i o n d a t a f o r a l l p u l p s as observed a t 35 min.  dissipation  As  studies  p u l p types steeped i n w a t e r , and i n  Each p l o t and the T a b l e 4 d a t a show c o n s i d e r a b l y  the  o f the  samples.  i n 35 min t e s t s o f v a r i o u s  individual  and because a major o b j e c t i v e  p r o c e s s e s , i t appeared u s e f u l  Fractional  steeping  differences  the r o l e o f r e s i d u a l wood p u l p polymers i n  on both c a u s t i c and water steeped  saturated  properties  excitations.  p r e s e n t study was t o e l u c i d a t e  18.6%  only  investigations  (204) p r o v i d e e v i d e n c e t h a t  Based on t h i s i n f o r m a t i o n ,  obtained  Former  f o r adjustment o f c e l l u l o s e f i b r e m e c h a n i c a l  and c r e e p b e h a v i o r o f wood  in swelling  cause both i n t e r -  The c o n t r i b u t i o n  l a r g e but l i m i t e d i n d u r a t i o n .  amounts  t o r h e o l o g i c a l response i s  - 58 -  As noted above, differences in stress decay over 35 min, as caused by various steeping treatments, ranged between 10 and 54%.  It can be seen in  Figs. 14 to 18 and Table 4 that the "steeping" effect is essentially independent of pulp type tested, in spite of wide variations in lignin and hemicellulose contents (see Table 3). This proves that the higher rate of stress decay observed following caustic steeping is mainly caused by (M ) processes at inter- and intra-molecular levels of cellulose organisation, in particular within highly oriented regions. It is generally accepted that strong alkaline solutions, of at least 8 to 9% NaOH, penetrate cellulose crystalline regions by f i r s t breaking H-bonds and thereafter forming new H-bonds between the reagent and cellulose hydroxyl groups (173,251,275). This causes dimensional changes in the unit c e l l , in particular an increase in the 101 inter-planar distance (179).  The former strong inter-molecular bonds in c r y s t a l l i t e s , H-bonds in  the a-b plane and van der Waal's forces in the a-c plane (120, see Fig. 3), are replaced by weak H-bonds which have been found to be associated with decreased crystallinity (153). The higher stress decay in intra-crystalline swollen pulps under compressive strain may involve any of several processes. (i)  These may include:  conformational changes of cellulose; ( i i ) sliding effects within the  cellulose crystallites; ( i i i ) enhanced molecular motion of cellulose chains on the cellulose crystallite surface, and ( i v ) , in the case of chemical pulps, possibly enhanced mobility of formerly crystalline hemicelluloses. Since the swelling power of water is limited to amorphous zones of the lignin-carbohydrate complex, no short term viscoelastic processes probably take place within crystalline portions of cellulose or  redeposited  crystalline xylan and glucomannan in water treated samples. These components may undergo elastic deformation when subjected to stresses, which would mean storage but not dissipation of energy. That elastic deformations of the cellulose lattice can occur has been shown by X-ray measurements on Hinoki (Cupressus obtusa, Koch) wood specimens subjected to tensile strains (285). It has been proposed (145) that the *"C. conformation in unstressed  - 59 -  cellulosic material can be expected to switch by mechanical excitations to the less stable (higher energy level) abrupt means for energy storage.  conformation, thus providing an  The reduction of inter- and intra-  crystalline forces by caustic solutions, which converts the cellulose from a three-dimensional body to a more or less two-dimensional form, may allow glucose units to switch conformations more easily by mechanical excitation. The fact that capacity of glucose units to absorb energy is limited, and that glucose units in alkaline swollen celluloses are rather f l e x i b l e , can be used to explain the high but limited rate of stress decay observed immediately after application of straining. At the same time, converting transition zones between crystalline and amorphous regions, and part of cellulose crystallites (153) into amorphous zones, may also contribute to i n i t i a l stress relaxation.  Such  changes can be expected to increase molecular movement around the crystalline cores.  The changes in cellulose crystalline l a t t i c e , particularly increase  in 101 interplanar distance (179) provides a further system for redistributing or dissipating stress through less tight  bonding.  In addition, the  deposition of water and hydroxyl ions with counter ions between 101 planes (153) can be expected to act as lubricants promoting sliding along 101 planes when the lattice system is stressed above a c r i t i c a l value.  This,  of course, is accompanied by breaking and reforming the rather weak H-bonds between reagents and cellulose hydroxyl groups. That sliding phenomena are involved only in i n i t i a l stress relaxation can be explained by a c r i t i c a l stress level below which no further intra-crystalline sliding occurs.  At beginning of the stress  relaxation process, the strain level used in this work may have exceeded such a c r i t i c a l level.  With progressive relaxation, however, the residual  stress would soon f a l l below that level.  Thereby, intra-crystalline  processes would be excluded from further involvement in the rheological behavior of pulp mats maintained at constant strain. Stress relaxation differences between caustic and water steeped chemical pulp samples (with the exception of holocellulose preparations) can be attributed also to some extent to crystalline (redeposited) hemi-  - 60 -  celluloses. and  xylans  Observations  on wood glucomannans i n s u l p h i t e p u l p i n g ( 1 0 ) ,  i n sulphate pulping  (51,326), show t h a t these h e m i c e l l u l o s e s can  be r e d e p o s i t e d  o r adsorbed d u r i n g  process  p r e f e r e n t i a l l y on the f i b r e s u r f a c e o r , more a c c u r a t e l y ,  occurs  l a t e r cooking  stages.  The r e d e p o s i t i o n  on t h e s u r f a c e o f m i c r o f i b r i l s on the o u t e r p a r t o f the f i b r e s . i s formation The in  these  but y i e l d  The r e s u l t  of c r y s t a l l i n e layers. abundant H-bonds between i n d i v i d u a l x y l a n o r glucomannan  layers are s u f f i c i e n t l y strong to r e s i s t t o a t t a c k by s t r o n g a l k a l i n e s o l u t i o n s .  chains  t h e p e n e t r a t i o n o f water, C o n s e q u e n t l y , the s h o r t  c h a i n and i n t e r - and i n t r a - c r y s t a l l i n e s w o l l e n h e m i c e l l u l o s e s may p r o v i d e a l u b r i c a n t l a y e r between f i b r i l s  o f t h e same f i b r e o r ad}acent  fibres.  T h i s might promote r e p o s i t i o n i n g o f f i b r e s w i t h i n the mat which, as d e s c r i b e d e a r l i e r , i s thought t o be p a r t l y r e s p o n s i b l e f o r h i g h r a t e o f i n i t i a l I ) stress relaxation.  (Phase  Such l u b r i c a n t e f f e c t s may be expected a l s o t o enhance  s l i p p a g e of m i c r o f i b r i l s w i t h i n  fibres.  F i g u r e 19, which shows c o r r e l a t i o n between 1 - ^ ( 3 5 min)/Ca(o) and  h e m i c e l l u l o s e content  18,6%  f o r 14 v i s c o s e pulps  NaOH, lends e v i d e n c e  t o t h i s assumption.  steeped  e i t h e r i n water o r  The i n v e r s e r e l a t i o n s h i p f o r  water and c a u s t i c treatments i n d i c a t e s t h a t an i n c r e a s e i n e s s e n t i a l l y h e m i c e l l u l o s e s reduces the v i s c o e l a s t i c response o f water s w o l l e n but  enhances the time dependent response i n c a u s t i c s w o l l e n  effect  i s rather short, i . e . , limited  which shows t y p i c a l s t r e s s r e l a x a t i o n t r a c e s o f t h r e e v i s c o s e The  h e m i c e l l u l o s e content  ranged from 2.2 t o 6.1%. xylan adsorption  pulp mats,  pulps.  t o Phase I , i s e v i d e n c e d  crystall  That  this  by F i g . 18 pulps.  o f v i s c o s e p u l p s examined i n the study  As the work o f C l a y t o n and Stone (51) showed,  i n raw paper p u l p s c a n reach v a l u e s up t o 3% o f t h e pulp  weight and 10.2% o f t h i s redeposited x y l a n was found to r e s i s t a 90 min e x t r a c t i o n with  10% NaOH a t room temperature.  t h a t , i n s p i t e o f severe  Therefore,  p u r i f i c a t i o n treatments,  i t c a n be expected  a c e r t a i n p o r t i o n of the  adsorbed h e m i c e l l u l o s e s a r e r e t a i n e d . F u r t h e r , F i g . 19 a l s o i n d i c a t e s t h a t the h e m i c e l l u l o s e s , removal o f s i d e branches and r e d e p o s i t i o n , have l o s t most o f t h e i r  after otiginal  s t r e s s d i s s i p a t i o n f u n c t i o n i n the l i g n i n - c a r b o h y d r a t e complex o f wet p u l p s .  - bl  This function seems to be partly regained, however, when caustic solutions "soften" the layer of highly oriented hemicellulose on the f i b r i l surface, A more detailed discussion on this particular subject appears in a following paragraph. 4.3  Effect of Residual Chemical Constituents Stress relaxation data obtained from a l l water and caustic steeped  pulps at 35 min relaxation time (Table 4)  indicate wide variations in stress  decay between various pulps given the same steeping treatment.  These  variations, however, were less pronounced between pulps of the same type (for instance within groundwood pulps, holocellulose preparations, bleached sulphate and viscose pulps) than between different pulp types.  It i s also  apparent that stress decay variations seem to be somewhat higher for pulps steeped in caustic. It is further evident from Table 4 that the highest rates in stress relaxation following caustic steeping occurred in groundwoods, wherein the cottonwood pulps exhibited slightly higher rates.  In this respect, ground-  wood pulps were followed in order by holocellulose preparations, sulphite, bleached sulphate, unbleached sulphate, acetate and viscose pulps and, f i n a l l y , by alpha-cellulose preparations (with the exception of 0-1 and 0-2). In water saturated pulp mats differences were less distinct and the sequence for stress dissipation i s not identical with results from caustic treated samples.  It appears that water saturated groundwood pulps  and holocellulose preparations exhibited approximately the same rate of stress decay, followed by unbleached sulphate pulp, bleached sulphate pulps, sulphite pulp; then viscose, acetate and alpha-cellulose pulps which showed the lowest rates of stress relaxation. Experimental variables such as sample preparation and testing conditions were carefully controlled throughout the experiments.  Therefore,  the above differences must be attributed to inherent variations in chemistry of the pulp samples. The analytical data presented in Table 3 exhibit large differences in chemical composition for the various materials. contents were estimated to vary between ^0.1  Lignin  and 30.5%, total hemicelluloses  - 62 -  .between 0.8  to 31.9%, w h i l e the c e l l u l o s e p o r t i o n ranged from 42.2  Some e v i d e n c e t h a t mat  such broad v a r i a t i o n s can  be  expected  to i n f l u e n c e  r h e o l o g i c a l p r o p e r t i e s appears i n s e v e r a l works showing t h a t  changes of  l i g n i n and  hemicelluloses  mechanical-rheological  p r o p e r t i e s of  The  to 99.3%.  quantitative  r e s u l t i n profound v a r i a t i o n s of ligno-cellulosics  (200,201,283).  f o l l o w i n g d i s c u s s i o n r e l a t e s these v a r i a t i o n s i n p u l p c h e m i s t r y  w i t h r h e o l o g i c a l r e s p o n s e s observed i n r e l a x a t i o n t e s t s on water and swollen  samples.  For c o n v e n i e n c e , i n d i v i d u a l e f f e c t s of the  l i g n i n , hemicelluloses  and  components, various  separately.  Lignin The  most c h a r a c t e r i s t i c f e a t u r e s of  supposedly amorphous s t r u c t u r e , formed by  l i g n i n are  swelling  (3,74-76,86).  between c e l l s stances  and  (316).  In the n a t i v e  especially  state l i g n i n  It i s apparent from the  i n the water s a t u r a t e d  The  r e s t r i c t s absorption  lignin  deposited sub-  s t r u c t u r e , p h y s i c a l nature that  i t may  play  wood d e r i v e d  work of Murakami and  Yamada (200)  of water i n p l a n t c e l l w a l l s .  (68,69) s t u d i e d  an  materials,  expected to r e s i s t m e c h a n i c a l e x c i t a t i o n both  l i g n i n must e x e r t a l s o an  and  s t a t e , to mechanical e x c i t a t i o n .  a c o n t r o l l i n g f a c t o r i n s w e l l i n g p r o c e s s e s and  explained  excessive  w i t h i n amorphous p a r t s of c e l l w a l l s as e n c r u s t i n g  L i g n i n can be  Eriksson  its  i s thought to be  r o l e i n g o v e r n i n g the response of wood and  indirectly.  three-dimensional  c a r b o h y d r a t e s from  p o s i t i o n , as w e l l as a s s o c i a t i o n w i t h h e m i c e l l u l o s e s , outstanding  its  p h e n y l p r o p a n o i d u n i t s , and  h y d r o p h o b i c n a t u r e which r e s t r a i n s a s s o c i a t e d  and  three  caustic  c e l l u l o s e , on time dependent b e h a v i o r of  p u l p t y p e s , w i l l be d i s c u s s e d 4.3.1  pulp  indirect  leads  showed t h a t  lignin  T h i s proves l i g n i n to to the c o n c l u s i o n  i n f l u e n c e on m e c h a n i c a l  h i s data according  to i n d i r e c t  It i s unquestioned  t h a t the a r o m a t i c c h a r a c t e r  be  that  properties.  the e f f e c t of d e l i g n i f i c a t i o n on wood c r e e p e f f e c t s of  directly  and  l i g n i n on the r h e o l o g i c a l  response.  s t r u c t u r e of the and  l i g n i n polymeric  r h e o l o g i c a l behavior.  for instance  by an  system  T h i s has  and  three  (3) i n f l u e n c e s d i r e c t l y  been e v i d e n c e d f o r s t r e n g t h  i n v e s t i g a t i o n c a r r i e d out  by  Stone and  dimensional  mechanical properties,  Kallmes  (283).  - 63 -  They showed t h a t p r o g r e s s i v e its  shear s t r e n g t h .  the h i g h  rigidity  The  d e l i g n i f i c a t i o n of wood reduced  ability  provided  by  of a r o m a t i c systems to s t o r e energy,  the  three-dimensional  i s expected to e x e r t a s i m i l a r d i s t i n c t of  ligno-cellulosics.  It can  e f f e c t on  be assumed t h a t the  r e t a r d v i s c o e l a s t i c p r o c e s s e s i n wood. an e f f e c t was  not  As  observed f o r water and  low  l i g n i n content.  groundwoods and and  viscose  dissipated  rheological  properties  l i g n i n component  shown i n F i g s . 20  observation.  Altogether,  only  two  Both f i g u r e s i n d i c a t e , independent l i g n i n content  (groundof  acetate  preparations  groundwoods when  water.  Firstly,  may  account f o r t h i s unexpected  perhaps no r e t a r d i n g e f f e c t of  compressive s t r e s s r e l a x a t i o n of p u l p . l i g n i n e x h i b i t s only  of the h o l o c e l l u l o s e  r a t e than the.  a l t e r n a t i v e explanations  l i g n i n occurs i n  S e c o n d l y , the more l i k e l y case  that  a modest r e t a r d i n g e f f e c t which i s much s u b o r d i n a t e to  a more dominant r o l e of h e m i c e l l u l o s e s . i n the complex t o t a l  i n t h i s experiment v a r i e d no d i r e c t i n f o r m a t i o n r e l a x a t i o n was  such  subjected  p u l p s such as a l p h a - c e l l u l o s e s ,  s t r e s s at s l i g h t l y h i g h e r  Two  21,  r a t e s of s t r e s s r e l a x a t i o n than most m a t e r i a l s  highly delignified  pulps.  and  will  T h e r e were s u r p r i s i n g l y l a r g e d i f f e r e n c e s between  steeped i n d i s t i l l e d  recognized  structure,  t r e a t m e n t , t h a t p u l p s with the h i g h e s t  woods) e x h i b i t e d h i g h e r  and  polymeric  NaOH steeped p u l p mats  to compressive s t r e s s r e l a x a t i o n t e s t i n g . of s t e e p i n g  drastically  Thereby, the  response.  obtained.  Unfortunately,  i n both h e m i c e l l u l o s e  on c o n t r i b u t i o n of  lignin  However, i t can  of n a t i v e or r e s i d u a l l i g n i n s  l i g n i n e f f e c t i s not  i n f i b r e mat  be  and  the p u l p s used  l i g n i n c o n t e n t s so  to compressive p u l p  that  mat  concluded that p a r t i c i p a t i o n  r h e o l o g i c a l p r o p e r t i e s does  not  reach a c o n t r o l l i n g l e v e l . These unexpected r e s u l t s may Thus, the r e s i s t a n t b e h a v i o r of partly  l o s t due  process.  lignin  be  r e l a t e d a l s o to o t h e r  i n the case of groundwood c o u l d  to the h i g h m e c h a n i c a l damage imparted d u r i n g  M e c h a n i c a l damage c o u l d  cause a  loosening  of the  s t r u c t u r e i n such ways t h a t p a r t i a l weakening of the c l o s e a s s o c i a t i o n may l i g n i n on  occur.  s w e l l i n g and  T h i s , i n t u r n , may c o n s e q u e n t l y on  c a r b o h y d r a t e s to s t r a i n i n g .  factors.  the  reduce the  the  be  grinding  inter-fibrillar lignin-carbohydrate  r e t a r d i n g e f f e c t of  time dependent response of  Support to t h i s assumption i s l e n t by  the  - 64 -  observation  t h a t unbeaten wet  p u l p s e x h i b i t a h i g h e r degree of  recovery  from compressive c r e e p , i n o t h e r words,showed l e s s v i s c o e l a s t i c i t y , than beaten wet  pulps  (261).  B e a t i n g i s known to cause f i b r i l l a t i o n  d e l a m i n a t i o n of the f i b r e w a l l s w e l l i n g of f i b r e s and expected to be  ( 2 2 2 ) , which has  i n h i b i t i o n of  liquids  s i m i l a r to those o c c u r r i n g  (251),.  i n comnressive p u l p mat  lamellation effect.  to the the  living  applied  to t h i s a x i s .  to a k i n d  One  of the  by a l i g n i n - r i c h  layered.  layered  (20)  An  o r i e n t a t i o n might be i n p a r t i c u l a r high  l e s s to c o u n t e r a c t  to the f i b r e a x i s . system at two  The  l a y e r (M and The  P) and  other  stresses  in  excitation, therefore,  the  compressed i n t r a n s v e r s e  direction.  compressive s t r e s s e s a p p l i e d p a r a l l e l  I t i s formed  layer predominately  l a y e r type of s t r u c t u r e which i s  between m i c r o f i b r i l s . to c a r r y the  structure.  related  stresses  s y s t e m s o c c u r s a t the m i c r o l e v e l .  carbohydrates are forced  d e f o r m a t i o n w i l l be  lignin  levels.  found a t the u l t r a - s t r u c t u r a l l e v e l , i s caused by hemicelluloses  (130,155,  In t h i s experiment the f i b r e s were loaded  of l a y e r e d  o c c u p i e d by c a r b o h y d r a t e s .  and  an o r i e n t a t i o n and/or  i n the f i b r e r w a l l t h a t  l i g n i n which i s to r e s i s t  p r e f e r e n t i a l l y perpendicular was  lignin  t r e e a l o n g the f i b r e a x i s , and  perpendicular  s u b o r d i n a t e r o l e of  There e x i s t s e v i d e n c e from s e v e r a l s t u d i e s  l e a s t p a r t l y o r i e n t e d and f u n c t i o n of  The^se e f f e c t s are  f o r the  r e l a x a t i o n might be  200,252) i n v e s t i g a t i n g the s t a t u s of i s at  facilitate  i n g r i n d i n g of wood.  Another f a c t o r p o s s i b l y r e s p o n s i b l e lignin  been found to  and  the d e p o s i t i o n  In such l a y e r e d  same loads as  the  of  systems  lignin  the  l i e n i n complex when  T h i s seems to be d i f f e r e n t f o r to the g r a i n where the r e s i s t a n c e  p r e d o m i n a n t l y c o n t r o l l e d by  the more r i g i d  to  lignin  C o n s e q u e n t l y , i t can be b e l i e v e d "that compressive s t r a i n i n g  of f i b r e s p e r p e n d i c u l a r  to t h e i r a x i s l e s s e n s  r a t e of s t r e s s d e c a y , but  The  only  the  i n f l u e n c e of  enhances v i s c o e l a s t i c response of the  i n d i c a t i o n that  l i g n i n may  exert  lignin  on  carbohydrates.  some i n d i r e c t  influence  on r a t e of s t r e s s decay of c h e m i c a l paper p u l p s can be deduced from the  fact  t h a t the unbleached s u l p h a t e p u l p ( 7 - 1 ) ^ when steeped i n w a t e r , d i s s i p a t e d s t r e s s at a somewhat h i g h e r r a t e than the b l e a c h e d s u l p h a t e paper p u l p s (7-2,8-1,3-2) ( F i g . 2 0 ) .  When the  same p u l p s were steeped i n c a u s t i c , however,  - 65 -  the response level was reversed (Fig. 21).  Since hemicellulose content did  not vary greatly between these pulps (Table 3) the observation has to be attributed to increased cellulose crystallinity by removal of lignin through purification treatments. That cellulose crystallinity increases as delignification progresses has been proven by Wardrop (310,314), Wardrop and Preston (317) and Murakami and Yamada (200) with holocellulose preparations. In water steeping, the relatively larger crystalline portion in bleached pulp cellulose caused' a somewhat lower degree of swelling and, consequently, less viscoelasticity than in unbleached pulps. However, by steeping in 18.6% NaOH this crystallinity effect seemed to be lost or of subordinate importance in rheological processes, due to intra-crystalline swelling phenomena in strong alkaline media. 4,3.2  Hemicelluloses It is well known that hemicelluloses contribute to mechanical  properties of cellulosics, such as strength of individual fibres and papers and pulp beating behavior (95,173,201,272,273). In pulping, most chemical treatments have been found to cause profound changes, in particular in the molecular structure of non-cellulosic carbohydrates. Such changes certainly must affect pulp mat viscoelasticity. In this study an attempt was made to relate pulp viscoelastic behavior, under constant compressive strain, to residual hemicelluloses in the pulp material.  Emphasis is placed on'establishing an interrelationship  between quantitative features and rheological response.  The discussion i s  also concerned with structural characteristics of residual hemicelluloses as they may relate to viscoelastic behavior. Experimental data obtained from stress relaxation measurements at 35 min relaxation time (Table 4), and from carbohydrate analyses (Table 3), are presented in Fig. 22 as plots showing 1 -(^>(35 min)/<o(o) as a function of hemicellulose content. The points show average values of five relaxation measurements. It i s apparent from the two regression lines, and evidenced by statistical calculations, that rate of stress decay in pulp mats under  -  0 0  -  constant strain is highly correlated with the amount of hemicelluloses present in the pulp materials. As indicated by slope changes, the relationships are characterized by two distinct stages.  In the case of  water steeped pulps, the slope descends from 0 to approximately 6% hemicelluloses, which shows that pulp viscoelasticity was lowered by increasing contents up to the 6% level.  Further increases in hemicelluloses reversed  this relationship and lead to a considerable enhancement of stress relaxation. The positive slope from approximately 5 to 32% hemicelluloses confirms this. In respect to caustic steeped pulps, slope variation was less distinct.  The slope covering the range from 0 to 6% hemicelluloses  exhibits a somewhat steeper ascent than that for the range above 6%. Consequently, changes in hemicellulose content below 6% appear to have a more pronounced effect on rate of stress decay than variations above this level. In the range from 6 to 32% hemicellulose similar slopes for both water and caustic treatment groups are evident.  This indicates that effect  of hemicellulose variation above 6% becomes independent of the steeping medium. As mentioned above, distance between the two regression lines originates primarily from phenomena which are inherent in alkaline swelling effects of cellulose. Somewhat unexpected is the reverse relationship for water and 18.6% NaOH steeping in the range below 6%.  It is obvious that hemicelluloses  at such low contents resist stress relaxation when the .pulp is soaked in d i s t i l l e d water, but contribute to stress dissipation when alkaline steeping is applied. This behavior, can be attributed particularly to qualitative features of residual hemicelluloses, in other words, to structural changes of hemicellulose molecules. It seems reasonable to base the following discussion about the stress relaxation - hemicellulose relationship on a detailed analysis of characteristic features of pulp types or individual pulps, such as amount and molecular structure of hemicelluloses. This facilitates a better understanding of the hemicellulose contribution to rheological processes in the  fibre wall and, consequently, to the pulp mat.  The discussion on this  particular subject is subdivided according to pulp types. 4.3.2,1  Mechanical pulps In the caustic swollen state groundwood pulps, which were found  to contain the largest hemicellulose quantities (Table 3), exhibited the highest stress dissipation rates (Fig.22). This differs to some extent from observations made on water steeped samples. Here, the Cottonwood holocelluloses appeared to dissipate energy at the highest rate, slightly more than groundwood pulps and hemlock holocelluloses.  The superiority of  groundwoods in stress dissipation, compared with low hemicellulose pulps, can be considered as strong evidence for involvement of hemicelluloses in rheological processes. In groundwood, the wood polymers are more or less present in the native state (30).  It means that the hemicelluloses - as in the undamaged  wood fibres - are fully branched, amorphous and deposited on the f i b r i l surface as matrix substance which surrounds the microfibrils (19.178.316). These polyoses are believed to form connecting layers between microfibrils and the encrusting lignin polymer system. It i s well known that lignin and cellulose vary widely in physical and mechanical properties. Consequently, in the stressed state, hemicelluloses acting as connecting links have to function as a stress adjusting system.  Low DP, high degree of branching and hygroscopic nature  make the hemicelluloses well suited to dissipate or distribute stresses uniformly in the c e l l wall.  In wet condition, their strong tendency to  swell, provides a gel system which, as a lubricant-like layer, allows a t least some gliding along the f i b r i l surface. An excessive gliding, however, may be hindered particularly by covalent bonds connecting them t o the rigid three-dimensional lignin polymer system. The existence o f such bonds has been proposed by several workers (36,272). The low DP is expected to contribute to gliding or flow processes. Due to the gel-like state and numerous side branches, the strength and density o f H-bonds is f a i r l y low,  This possibly facilitates flow between  - 68 -  adjacent  h e m i c e l l u l o s e or h e m i c e l l u l o s e and  t h e r e f o r e , a i d s i n d i s s i p a t i o n of s t r e s s . may  c e l l u l o s e molecules The  numerous s i d e branches  not o n l y c o n t r i b u t e to the f l o w response^but may  stress distribution On  l i g n i n may  hinder  the f l o w p r o c e s s e s  l i g n i n - c a r b o h y d r a t e complex.  Both m i c r o s c o p i c may  deformation  layers  (148), may  i n microscopic  complex, i n t u r n , storage  i n h e m i c e l l u l o s e m o l e c u l e s and  In the case of compressive or t e n s i l e a x i s , the m i c r o f i b r i l  The  d i s t r i b u t i o n and  be p a r t of the v i s c o e l a s t i c memory  and  between h e m i c e l l u l o s e s  but c e r t a i n l y r e s u l t  be adapted b e t t e r to p r o v i d e u n i f o r m  processes  involved i n  the o t h e r hand, p o s s i b l e l i g n i h - h e m i c e l l u l o s e bonds  d e f o r m a t i o n s of the may  a l s o be  processes.  m e c h a n i c a l entanglement w i t h i n h e m i c e l l u l o s e s and and  and.  of energy.  gliding  behavior. s t r a i n s along  the  fibre  a n g l e , which i s known to change between c e l l  exert a considerable  i n f l u e n c e on  wall  the r h e o l o g i c a l  processes  between m i c r o f i b r i l s  angle has  been found to a f f e c t m e c h a n i c a l p r o p e r t i e s of wood p a r a l l e l  grain  i n the h e m i c e l l u l o s e m a t r i x .  microfibril to  the  (83). I n t e r e s t i n g l y , the c o n t r i b u t i o n of h e m i c e l l u l o s e s  response does not The  The  seem to depend on any  s i n g l e h e m i c e l l u l o s i c component.  f u n c t i o n of v a r i o u s h e m i c e l l u l o s e types  v e r y much the differences  same.  T h i s i s evidenced  to the r e l a x a t i o n  by  i n h e m i c e l l u l o s e composition  i n t h i s regard  appears to  the f a c t t h a t , although  be  profound  e x i s t between angiospermous  and  c o n i f e r o u s groundwoods ( T a b l e 3 ) , s i m i l a r r a t e s of s t r e s s r e l a x a t i o n were observed f o r a l l groundwood p u l p s .  The  s l i g h t d i f f e r e n c e s i n s t r e s s decay  a r e caused by v a r i a t i o n s i n t o t a l amount of h e m i c e l l u l o s e s shown i n F i g . The  fibres. be  c o n c l u s i o n can be drawn t h a t wood h e m i c e l l u l o s e s  M r e o v e r , they may n  It can be assumed  present  tree.  The  as  22.  s t a t e , and/or even a f t e r chemical systems.  i n the pulp  i n the c e l l validity  i n the  native  adjustment, f u n c t i o n i n s t r e s s a d j u s t i n g  c o n t r o l the r h e o l o g i c a l p r o p e r t i e s of wood that a minimum p o r t i o n of h e m i c e l l u l o s e s must  w a l l to w i t h s t a n d  sudden e x c i t a t i o n s i n the  of t h i s assumption i s supported  by  the f a c t  living  t h a t wood  - 69 -  h e m i c e l l u l o s e content to pored woods.  i n c r e a s e d c o n s i d e r a b l y d u r i n g e v o l u t i o n from  These changes may  system i n woody c e l l  have o c c u r r e d  to enhance the energy t r a n s f  walls.  P r e v i o u s l y , the f u n c t i o n of h e m i c e l l u l o s e s t r e e has  been r a t h e r o b s c u r e .  consider hemicelluloses formation.  According  lignification.  coniferous  i n wood of the  living  Kollmann and. Cote (148), f o r i n s t a n c e ,  i n wood c e l l w a l l s as p o s s i b l e r e l i c t s o f c e l l  to them, these  Hopefully,  serve as a temporary m a t r i x  the f i n d i n g s of the present  study  wall  preceeding  will  cause  r e c o n s i d e r a t i o n of the r o l e of wood h e m i c e l l u l o s e s , which appear to have been u n d e r r a t e d 4.3.2.2  i n importance or m i s i n t e r p r e t e d  h o l o c e l l u l o s e preparations  r a t e s than groundwoods when steeped  q u i t e i n accordance w i t h  pulp  d i s s i p a t e d s t r e s s a t somewhat lower  i n 18.6%  s t r e s s decay i n the water s a t u r a t e d  would be  The "overcooking"  state.  expected r e s u l t s .  e x h i b i t e d more or  This observation  i s not  N o r m a l l y , the removal of  r a t e of s t r e s s decay would seem  somewhat unexpected r e s u l t s must be effects.  s i m i l a r to those  Shimada and  able hemicellulose  lignin  compared w i t h  reported  that  large chips, i n outer  expected to r e s u l t  p o s s i b l y , i n severe degradation  low h e m i c e l l u l o s e c o n t e n t s obtained  f o r t h i s assumption.  p o r t i o n s of x y l a n and l o s s e s were so h i g h  p r i m a r i l y a t t r i b u t e d to  f o r these  of the r e -  f o r groundwoods of the  preparations,  same s p e c i e s ,  I t i s apparent from T a b l e  glucomannan were l o s t d u r i n g p u l p p r e p a r a t i o n .  t h a t , d e s p i t e d e l i g n i f i c a t i o n which n o r m a l l y  c e l l u l o s e p o r t i o n was  provide  3 that s u b s t a n t i a l  the r e l a t i v e amount of n o n - c e l l u l o s i c c a r b o h y d r a t e s ,  On  in consider-  portion.  rather those  likely.  cause f i b r e o v e r c o o k i n g  T h i s , i n t u r n , can be  l o s s e s and,  maining c a r b o h y d r a t e The  Kondo (264)  used i n t h i s study,  p o r t i o n s of the c h i p s .  increased  NaOH, but  expected to i n c r e a s e the r e l a t i v e amount of h e m i c e l l u l o s e i n the  so t h a t a h i g h e r  evidence  past.  H o l o c e l l u l o s e pulps The  equal  i n the  considerably  below v a l u e s  the o t h e r hand, o v e r c o o k i n g  e f f e c t on s i d e b r a n c h e s .  As T a b l e  obtained  must have had  3 suggests,  The  would have  the hemi-  f o r groundwoods.  a rather  degree of b r a n c h i n g  limited was  still  - 70 -  fairly  high.  It lower  rate  compared  that  observed  losses.  f o r the important  This  role  residual hemicelluloses  function essentially  wood  data  i n Tables  3 and 4 t h a t t h e  swollen h o l o c e l l u l o s e s ,  observation  c a n be  of hemicelluloses  pulps.  exerted  a particular  Unfortunately, behavior  change.  i n wood a n d  changed  t o some e x t e n t  any c o n c l u s i o n  during  the rather  limited  decrease  pulping  that  is difficult  makes i t e x t r e m e l y  t o draw.  to evaluate  both  It  c a n be assumed  by  loss of hemicelluloses  on  both  cellulose  the decrease  discussed  i s t o some e x t e n t  Consequently, extent swollen  the degradation  reduced  reactions  by  degradation  Pulping  i n both  effects  acid  chlorite  to cause decreased  DP f o r a l l  experiments, which  will  i n DP e n h a n c e s  the c o n t r i b u t i o n of remaining  the v i s c o e l a s t i c  c a n be e x p e c t e d  hemicelluloses  be  response.  to increase  i n both  water  t o some  and c a u s t i c  pulps.  With was f o u n d  respect  to the water  to exhibit the highest  t h e lower h e m i c e l l u l o s e  phenomenon  process.  xylan  swollen  rate  content  seems t o b e r a t h e r  the branched  cation  reported  As i r r a d i a t i o n  below,show, a d e c r e a s e  mechanism  i n s t r e s s r e l a x a t i o n caused  and r e s i d u a l h e m i c e l l u l o s e s .  (4,164.292).  effect  pulps.  p e r a c e t i c a c i d media has been  carbohydrates  on  that  lignin.  The l o s s i n  in  steeped  of  the r h e o l o g i c a l  l i g n i n - h e m i c e l l u l o s e a s s o c i a t i o n on t h e s t r e s s d i s s i p a t i o n c a u s t i c and w a t e r  branching  the effect of  affects  difficult  f o r groundin  due t o t h e removal  o n how d e l i g n i f i c a t i o n complex  earlier  of  of  considered  swollen h o l o c e l l u l o s e s  B u t i t c a n be e x p e c t e d  of the hemicellulose  hemicellulose  i n caustic  i n t h e same way a s d e s c r i b e d  It i s u n l i k e l y that  branches might have  and  was  rheology.  The may  analytical  o n g r o u n d w o o d s o f t h e same t r e a t m e n t ,  due t o h e m i c e l l u l o s e  a f u r t h e r proof  pulp  from  o f s t r e s s r e l a x a t i o n e x h i b i t e d by c a u s t i c  with  primarily as  i s conclusive  o f s t r e s s decay  a s compared  complex.  molecules  s t a t e , cottonwood h o l o c e l l u l o s e  may h a v e  ( F i g . 22) i n s p i t e  t o groundwood  pulps.  P o s s i b l y , an " a c t i v a t i n g taken  place  during  the  This  effect" delienifi-  -  71 -  As Table 3 indicates, no severe loss of glucuronic acid side chains occurred during pulping treatments.  It can be assumed that these  side chains were closely associated with lignin and consequently exerted a,retarding effect on swelling or viscoelastic behavior. By removing lignin this effect was eliminated and f l e x i b i l i t y of the xylan molecule was considerably enhanced, possibly by the swelling tendency of the now unhindered glucuronic acid groups. This assumption i s supported by Pew and Weyna (234) who proposed that carbohydrate molecules are surrounded by lignin.  In other words, they  may be held in the gel-like lignin substance by molecular entanglement ("snake cage" structures). The considerably lower relaxation of water steeped hemlock holocelluloses, compared with cottonwood pulps, can be attributed to the lower content of acidic xylans in coniferous wood. Due to this quantitative difference the "activating effect" of acidic xylans, as caused by delignification . may contribute less to the total viscoelastic response of hemlock pulps.  In 'addition, some removal of galactose side branches from glucomannans  may have reduced to some extent the viscoelastic contribution of hemicelluloses. 4.3.2.3  Sulphite and sulphate paper pulps As indicated by Table 4 and Fig. 22 the group of paper pulps ranked  third with respect to hemicellulose content, which explains the lower rate of stress decay compared with that exhibited by groundwoods and holocelluloses. Again, the amount of residual hemicelluloses appeared to dominate the viscoelastic behavior of these pulps under compressive straining. As indicated by Fig. 22, however, the corresponding data are rather scattered around the two regression lines showing that pulping method exerts an influence on paper pulp viscoelasticity.  The variations between  individual pulps within this group seem to be less due to quantitative, but more due to structural  differences of the remaining carbohydrate  complex. The rather similar hemicellulose content of these pulps (Table 3) confirms this.  In addition, relative amount of lignin seems to be of some  - 72  -  importance f o r unbleached p u l p s t r e s s The  r e l a x a t i o n response of  swollen state  i s characterised  by  relaxation. s u l p h i t e p u l p s i n water and  a number of f a c t o r s i n h e r e n t  to t h i s  p a r t i c u l a r p u l p type.  It i s apparent, from F i g . 22  that  l o s s of h e m i c e l l u l o s e s  during  the major f a c t o r  responsible  s u l p h i t e pulping  f o r the g e n e r a l l y  w i t h groundwoods and  lower r a t e s of  holocelluloses.  was  Other f a c t o r s which may  i n the  outer part  residual hemicelluloses; abundance of g l u c u r o n i c  of the f i b r e ;  (iii)  lignin  amorphous  low  and  of  (v) r e l a t i v e  groups.  That severe d e g r a d a t i o n of c e l l u l o s e i n s u l p h i t e p u l p i n g , by  Luce (171), may  influence  in a later section. low  average DP  The  considerably  shorter and  water and  swollen  The believed  highly  also contribute  so t h a t  ordered  s w o l l e n samples.  the  structure  of r e d e p o s i t e d  It may  rather response.  The  p u l p , but  glucomannan  (10)  is  I t p r o b a b l y r e g a r d e d s t r e s s decay e x e r t e d no  e f f e c t on  relaxation  r e l a t i v e l y h i g h amount of g l u c u r o n i c  s t r e s s decay p r o c e s s i n a s i m i l a r way  holocelluloses.  discussed  "lubrication effect"  3 ) , i n d i c a t i n g a h i g h degree of r e s i d u a l x y l a n  influenced  swollen  relaxation  proven  states.  to some e x t e n t i n water s a t u r a t e d  (Table  to the  as  r a t e of s t r e s s decay i s enhanced i n both  to have p l a y e d a s u b o r d i n a t e r o l e .  in caustic  d e g r a d a t i o n to a  c h a i n s might improve the  of h e m i c e l l u l o s e s caustic  s u l p h i t e pulp v i s c o e l a s t i c i t y w i l l be  S i m i l a r l y , hemicellulose  (174,217) may  to  regions,  average DP  ( i v ) glucomannan r e d e p o s i t i o n ; acid  have enhanced  ( i ) removal of  ( i i ) h i g h degree of c e l l u l o s e d e g r a d a t i o n w i t h i n  particularly  substantial  s t r e s s decay i n comparison  or reduced s u l p h i t e p u l p s t r e s s r e l a x a t i o n a r e : 0,7%;  the  caustic  b r a n c h i n g , may  acid have  to t h a t d e s c r i b e d  have enhanced r e l a x a t i o n p a r t i c u l a r l y i n the  for caustic  state. In the  changes of  steeping,  s u l p h i t e pulp h e m i c e l l u l o s e s  overshadowed by Similar rates celluloses  case of c a u s t i c  these p h y s i c a l  (factors i i i  ( F i g . 22)  chemical  to v ) appear to  c e l l u l o s e d e g r a d a t i o n e f f e c t s caused by  of s t r e s s decay f o r c a u s t i c  and  sulphite  pulping.  s w o l l e n s u l p h i t e pulp and  provide t h i s evidence.  be  holo-  It seems t h a t a r e d u c t i o n  in  - 73 -  relaxation due to hemicellulose losses is at least partly compensated for by the cellulose degradation.phenomena. In the case of sulphate pulps, the following pulp characteristics, in addition to quantitative changes in hemicelluloses, are believed to have influenced stress decay: (i) removal of lignin; ( i i ) hemicellulose degradation; and ( i i i ) xylan redeposition.  This i s confirmed by the scattered distribution  of sulphate pulps around the regression lines which indicates considerable variation  between individual pulps. Figure 22 shows that pulps 7-1 and 8-2 in the caustic swollen state  dissipated less stress than predicted from residual total hemicellulose contents. It i s d i f f i c u l t to attribute this deviation to any particular factor.- It seems l i k e l y , however, that in the case of pulp 7-1 the relatively high lignin content (9.1%) and probably lignin condensation are responsible for the comparatively low rate of stress decay. Hemicellulose degradation effects may account most for the comparatively low relaxation rate observed for angiospermous pulp 8-2.  It i s known  that the susceptibility of glucuronic acid and acetyl groups to loss in alkaline pulping media leaves the pored wood xylan without or with only few residues of side chains (53,54,97,191,216,291). This essentially linear xylan, which is the dominant hemicellulose in this hardwood pulp (Table 3), was substantially reduced in i t s capability to assist in stress dissipation. In the water swollen state, the xylan degradation effect seems to play only a subordinate role in viscoelasticity of the same pulp. Further, the close location of this pulp to the lower regression line in Fig. 22 indicates also that effect of xylan redeposition, which could be expected to be particularly high for this pulp species, may not reach a significant level. The considerably lower relaxation rate of bleached pulps in comparison with unbleached sulphate pulp 7-1 when steeped in water has to be considered as an indirect effect of lignin.  It can be expected that  removal of lignin and subsequent drying of pulp increased considerably the number of H-bonds in the remaining carbohydrate portion of the c e l l wall.  - 74 -  A c e r t a i n p o r t i o n of newly formed H-bonds i n the c l o s e v i c i n i t y o f  crystal-  l i t e s may  This in  t u r n may  have been s u f f i c i e n t l y s t r o n g to r e s i s t water s w e l l i n g . have reduced the v i s c o e l a s t i c response of the b l e a c h e d  sulphate  pulps. 4.3.2.4  V i s c o s e and  acetate  In v i s c o s e and  acetate  i s reduced to l e s s than 7%. evidenced  by F i g . 22,  regression  pulps pulps  the r e s i d u a l h e m i c e l l u l o s e  In the c a u s t i c s w o l l e n  to l e s s s t r e s s r e l a x a t i o n .  l i n e i n the range of v i s c o s e and  t h a t of the remaining  state, this  The  steeper  acetate pulps,  portion  leads,  s l o p e of  to be  the r e s u l t o f two  c e l l u l o s e degradation.  The  comparatively  high  and ( i i )  s t r e s s r e l a x a t i o n values  l y i n g above the r e g r e s s i o n l i n e ) o b t a i n e d latter  from s u l p h i t e  suggestion.  In the water s w o l l e n  s t a t e , r a t e of v i s c o s e and  acetate  pulp  s t r e s s r e l a x a t i o n i s i n v e r s e l y r e l a t e d to r e s i d u a l h e m i c e l l u l o s e s The  unexpected b e h a v i o r  and  r e d e p o s i t i o n phenomena of h e m i c e l l u l o s e s .  and  x y l a n to r e p r e c i p i t a t e as h i g h l y ordered  has  been noted above.  i s b e l i e v e d to o r i g i n a t e p r i m a r i l y from  It i s l i k e l y  it  i s also likely  l e s s severe  The  particularly  i n p u l p s of  lower  t h a t p a r t of the h e m i c e l l u l o s e s remained i n t h e i r  original  with adjacent  sufficiently  acetate  pulps  l i n e a r chains  c e l l u l o s e chains.  a s s i s t , or o n l y a s s i s t s to r a t h e r  s m a l l amount of h e m i c e l l u l o s e s  limited extent,  side  formed H-bonds  These bonds can  i s not a c c e s s i b l e to water and,  relatively  (removal of  s t r o n g to r e s i s t water p e n e t r a t i o n .  a l a r g e p o r t i o n of the r e l a t i v e l y  Since pulps with  hemi-  Further,  between themselves and  v i s c o s e and  fibrils  p u r i f i c a t i o n t r e a t m e n t s were employed.  Durine p u l p d r y i n g the e s s e n t i a l l y  e x p e c t e d to be  degradation  d e p o s i t s on c e l l u l o s e  p o s i t i o n i n the f i b r e w a l l , but were s u b j e c t to d e g r a d a t i o n chains).  ( F i e . 22).  tendency of glucomannan  t h a t a p o r t i o n of r e d e p o s i t e d  c e l l u l o s e s survived p u r i f i c a t i o n treatments, p u r i t y f o r which  This  f a c t o r s : ( i ) increased  v i s c o e l a s t i c c o n t r i b u t i o n of h e m i c e l l u l o s e s - a t lower c o n t e n t s ;  the  with  range, i n d i c a t e s t h a t h e m i c e l l u l o s e v a r i a t i o n s below  phenomenon i s c o n s i d e r e d  pulps confirm  the  i n comparison  6% cause c o n s i d e r a b l y g r e a t e r changes i n r a t e o f s t r e s s r e l a x a t i o n .  (groups of p u l p s  as  be  Consequently, in  t h e r e f o r e , does not  in stress dissipation.  l a r g e p o r t i o n s of h e m i c e l l u l o s e  residues  75  exhibited  -  the lowest r e l a x a t i o n response  celluloses  seem  ( F i g . 22), the i n a c c e s s i b l e hemi-  to be d i r e c t l y p r o p o r t i o n a l  to t o t a l amount o f  residual  hemicelluloses. In c a u s t i c broken  and  the t o t a l  s t e e p i n g , however, the newly formed H-bonds a r e remaining h e m i c e l l u l o s e p o r t i o n e x i s t s  s t a t e which f a c i l i t a t e s and  stress dissipation.  T h i s e x p l a i n s why  p h y s i c a l changes of p o l y o s e s do not a f f e c t  caustic  in a  t h a t the o r i g i n a l  or s w o l l e n wood f i b r e s was treatments.  these  chemical  the v i s c o e l a s t i c response  of  almost  entirely  f u n c t i o n of polyoses i n green, l o s t d u r i n g p u l p i n g and  T h i s o b s e r v a t i o n u n d e r l i n e s a g a i n the importance  d i s s i p a t i o n and 4.3.2.5  s t o r a g e systems of wood  purification  of side  i n n a t i v e h e m i c e l l u l o s e s f o r m a i n t a i n i n g the h i g h l y e f f i c i e n t  branches  energy  fibres.  A l p h a - c e l l u l o s e pulps No  polyoses.  a l p h a - c e l l u l o s e p r e p a r a t i o n was  As i n d i c a t e d  i n T a b l e 4 and  a l p h a - c e l l u l o s e s from wood pulps s t i l l The  content.  to account  found  to be f r e e of r e s i d u a l ,  supported by o t h e r work (55,87,304) c o n t a i n v a r i o u s amounts of h e m i c e l l u -  r e s i d u a l q u a n t i t y seems to depend on the o r i g i n a l h e m i c e l l u l o s e  The h e m i c e l l u l o s e p o r t i o n s i n the two  which were prepared from v i s c o s e p u l p 1-3 f o r 0.8  and  1.5%  It i s apparent contribute very l i t t l e  and  a c e t a t e pulp 5-1,  from F i g . 22 t h a t  such  and  0-4,  were found  low c o n t e n t s as the above  to s t r e s s decay i n both water and  i n t e r s e c t i o n s o f the two  c a u s t i c steeped mats.  l o c a t i o n of the c o r r e s p o n d i n g p o i n t s to the  r e g r e s s i o n l i n e s with the Y - a x i s .  p o i n t s i n d i c a t e s t r e s s decay f o l l o w i n g complete the response  a l p h a - p u l p s 0-3  of p u l p c o m p o s i t i o n .  T h i s i s e v i d e n c e d by the c l o s e  i.e.,  gel-like  swollen pulps. I t i s obvious  loses.  readily  removal  The  intersection  of h e m i c e l l u l o s e s ,  c o n t r i b u t e d by pure c e l l u l o s e as o b t a i n e d by p u l p i n g  and a l k a l i n e e x t r a c t i o n  treatments.  As i n the case of v i s c o s e and a c e t a t e p u l p s the r e s i d u a l hemic e l l u l o s e s are e s s e n t i a l l y cellulose.  linear  (degraded)  It i s assumed t h a t t h i s r e s i d u a l  from degraded  c h a i n s c l o s e l y a s s o c i a t e d with portion originates  primarily  but n o n - r e d e p o s i t e d h e m i c e l l u l o s e s t i g h t l y embedded between  -  cellulose micro-fibrils. sufficient  -  Even s t r o n g l y  alkaline extractions  to remove t h i s r e s i d u a l p o r t i o n  contribution identical  76  of these h e m i c e l l u l o s e s  from the f i b r e w a l l .  and  acetate pulps.  s t r e s s decay i n water steeped a l p h a - c e l l u l o s e d i s s i p a t i o n of s t r e s s i n the c a u s t i c  still This  swollen  p u l p s , but  The  They r e d u c e d enhanced  the  state.  a l p h a - p u l p s prepared from cottonwood and  contained considerable  not  to p u l p v i s c o e l a s t i c i t y i s b e l i e v e d  to t h a t observed f o r v i s c o s e  The  are  hemlock  holocelluloses  amounts of r e s i d u a l h e m i c e l l u l o s e s  (Table  i s r e f l e c t e d i n t h e i r s u b s t a n t i a l l y d i f f e r e n t v i s c o e l a s t i c responses  compared w i t h those observed on  the  saturated  less stress,but  state  they d i s s i p a t e d  r a t e when steeped i n c a u s t i c .  As  o t h e r two  can be  alpha-pulps. exhibited  seen i n F i g . 22,  In the a higher  p u l p s of  low  purity.  I t appears t h a t r e s i d u a l h e m i c e l l u l o s e s  r e l a x a t i o n response of these two proposed i n e a r l i e r d i s c u s s i o n s 4.3.3  a l p h a - p u l p s i n a way dealing  22  i n t e r s e c t i o n of  the  two  regression  provides e v i d e n c e t h a t c e l l u l o s e p l a y s  e l a s t i c b e h a v i o r of both water and c e l l u l o s e accounts f o r at  observed f o r the v a r i o u s and  i t s contribution  the  intersection  viscose  the  that  pulps.  l i n e s with the Y - a x i s i n  the dominant r o l e i n v i s c o -  caustic treated  l e a s t more than 50%  pulp types.  to r e l a x a t i o n  pulps.  be  stress dissipation  I t s independent v i s c o e l a s t i c b e h a v i o r  in highly  p u r i f i e d pulps i s obtained  assumed t h a t ,  groundwood p u l p s  of c e l l u l o s e i s more d i f f i c u l t  i s b a s i c a l l y the  however, i s made on to s e r i o u s  to  estimate.  i n s p i t e of complex i n t e r a c t i o n s between  t h r e e wood s t r u c t u r a l polymers i n r h e o l o g i c a l p r o c e s s e s , the contribution  from  point.  the v i s c o e l a s t i c c o n t r i b u t i o n i t can  I t i s apparent  of t o t a l  In the c a s e of paper grade, h o l o c e l l u l o s e and  But  viscose  Cellulose The  that  relaxation  affect  s i m i l a r to  w i t h paper and  water  t h e i r response  i s e s s e n t i a l l y i d e n t i c a l w i t h t h a t observed on b l e a c h e d paper and  Fig.  3).  same f o r a l l pulp t y p e s .  the assumption t h a t  d e g r a d a t i o n or does not  This  the c e l l u l o s e has  contain  degraded s h o r t  not  the  cellulose conclusion, been  chain  subjected  fractions.  - 77 -  V a r i a t i o n s i n DP above 1000 the p u l p mechanical fall  below 1000  expected  are known to not  p r o p e r t i e s , which are d r a s t i c a l l y  (251).  Consequently,  influence significantly lowered  as DP  values  c e l l u l o s e r h e o l o g i c a l p r o p e r t i e s can  be  not to be changed s i g n i f i c a n t l y by pulp p r o c e s s e s which degrade  c e l l u l o s e u n i f o r m l y to a DP  l e v e l not  lower  than 1000.  c e l l u l o s e s of groundwoods, h o l o c e l l u l o s e s and bleached  paper grade k r a f t  T h i s i m p l i e s that  a l s o of unbleached  and  pulps show e s s e n t i a l l y the same v i s c o e l a s t i c  response. In s u l p h a t e p u l p i n g the c e l l u l o s e d e g r a d a t i o n i s u n i f o r m usually results  i n DP v a l u e s above 1000  s t r e n g t h p r o p e r t i e s of unbleached  This i s reflected  Based  t h i s o b s e r v a t i o n , i t seems u n l i k e l y t h a t c e l l u l o s e v i s c o e l a s t i c i t y  i n un-  and b l e a c h e d  kraft  pulps i n p a r t i c u l a r  i n the h i g h  (104).  bleached  kraft  (171).  and  pulps d i f f e r s  s i g n i f i c a n t l y from  groundwoods and h o l o c e l l u l o s e s . Consequently, the s u b s t a n t i a l q u a n t i t a t i v e and  that i n  not c e l l u l o s e but i n s t e a d  s t r u c t u r a l changes of h e m i c e l l u l o s e s and  possibly  l i g n i n must be r e s p o n s i b l e f o r the profound  observed  between groundwoods, h o l o c e l l u l o s e s and  kraft  on  viscoelastic  unbleached  and  differences  bleached  pulps. T h i s l e a d s to the c o n c l u s i o n t h a t the h i g h c o r r e l a t i o n between  c e l l u l o s e and as a secondary  r a t e of s t r e s s r e l a x a t i o n phenomenon.  ( F i g s . 23 and  24) has  decrease and  two  The  (except f o r c a u s t i c  a l p h a - p u l p s ) which i s r e f l e c t e d s t r e s s r e l a x a t i o n and As noted  treated v i s c o s e , acetate  i n the n e g a t i v e r e l a t i o n s h i p between  c e l l u l o s e content  ( F i g s . 23 and  t h a t the c e l l u l o s e response  i s based  i s e s s e n t i a l l y the same.  on m o l e c u l a r  rearrangements of c e l l u l o s e c h a i n s or p a r t s t h e r e o f found regions.  24).  above, the c o n t r i b u t i o n of c e l l u l o s e to v i s c o e l a s t i c  i n p u l p s of no or s l i g h t c e l l u l o s e d e g r a d a t i o n appears  increase in  l o s s of h e m i c e l l u l o s e s i s accompanied by a p r o p o r t i o n a l  in viscoelasticity  fractional  considered  Thus,the d e c r e a s i n g o r d e r of h e m i c e l l u l o s e c o n t e n t  i n groundwood to a l p h a - p u l p p r e p a r a t i o n s a l l o w s f o r a r e l a t i v e c e l l u l o s e content.  to be  In the c a u s t i c  processes  s t r u c t u r e may  be  It  or  i n the amorphous  swollen s t a t e , molecular displacement  the s w o l l e n c e l l u l o s e c r y s t a l  behavior  i n p a r t s of  involved i n v i s c o e l a s t i c  processes.  - 78 -  In d r a s t i c b l e a c h i n g procedures  pulping treatments,  such as s u l p h i t e p u l p i n g or  which cause o x i d a t i v e d e g r a d a t i o n , e.g.  b l e a c h i n g , c e l l u l o s e i s s u b j e c t to c o n s i d e r a b l e d e g r a d a t i o n T h i s i s known to reduce  certain  hypochlorite (171,243,245).  p u l p s t r e n g t h p r o p e r t i e s e x t e n s i v e l y (104).  s u l p h i t e p u l p i n g , the c l e a v a g e of the ( 1 — > 4 ) g l u c o s i d i c  In  l i n k a e e between  |*J-D-glucopyranose r e s i d u e s o c c u r s p r e f e r e n t i a l l y i n the amorphous r e g i o n s thus c r e a t i n g weak areas i n m i c r o f i b r i l s .  S i n c e a g r e a t number, of  c h a i n s i n amorphous r e g i o n s , a c t i n g as c o n n e c t i n g  l i n k s between  cellulose  crystallites  i n the m i c r o f i b r i l s , a r e c l e a v e d , the former h i g h r e s i s t a n c e of the amorphouscrystalline  system to s t r a i n i n g  i s s u b s t a n t i a l l y reduced.  c r y s t a l l i t e s , which can be c o n s i d e r e d as c e n t r e s of energy  Thus the storage  r e s i s t a n c e to s t r a i n i n g , become more or l e s s i n e f f e c t i v e without number of c o n n e c t i n g c e l l u l o s e c h a i n s .  They y i e l d  r e a d i l y to  e x c i t a t i o n when c h a i n d e g r a d a t i o n exceeds the c r i t i c a l It appears e f f e c t s may pulps  from  F i g s . 2 2 and  24 t h a t some c e l l u l o s e  paper p u l p s )  steeped  a  sufficient*  mechanical  level.  have c o n t r i b u t e d to r a t e of s t r e s s r e l a x a t i o n .  ( v i s c o s e , a c e t a t e and  and  in caustic  degradation A l l sulphite dissipated  s t r e s s a t h i g h e r r a t e s than p r e h y d r o l i z e d s u l p h a t e pulps of s i m i l a r hemicellulose content. regression  residual  A l l v i s c o s e and a c e t a t e p u l p s l o c a t e d above the  l i n e , r e p r e s e n t i n g the d a t a o b t a i n e d from c a u s t i c t r e a t e d pulps  ( F i g s . 2 2 and  24) and  p u l p 6-1,  are s u l p h i t e  pulps.  S i n c e c e l l u l o s e d e g r a d a t i o n appears of low y i e l d  p u l p s , i t was  demonstrating  decided  to p r o v i d e more e x p e r i m e n t a l  r e l e v a n c e of c e l l u l o s e  reason, gamma-irradiation employed on two  treatments  v i s c o s e pulps  DP  to p u l p v i s c o e l a s t i c i t y .  a t v a r i o u s dose l e v e l s  (3-2 and  i n both h e m i c e l l u l o s e c o n t e n t and  3-4).  r a t e of s t r e s s r e l a x a t i o n .  i n a l p h a - c e l l u l o s e , i n t r i n s i c v i s c o s i t y and  relaxation  evidence For  this  ( F i g . 25) were  These pulps were found  d e g r a d a t i o n e f f e c t s on c e l l u l o s e s of these two  shown i n T a b l e  to r e l a t e to s t r e s s  to d i f f e r  Radiation  pulps as f o l l o w e d by changes  107. NaOH s o l u b i l i t y  are  5.  It i s e v i d e n t from F i g . 25, which p r e s e n t s the l-££t )/,€>(o) - Mrad dose r e l a t i o n s h i p at 6 sec and changed r e l a x a t i o n responses  35 min  r e l a x a t i o n times, that  of the c e l l u l o s e .  gamma-irradiation  As the p o s i t i v e  s l o p e s show, •  - 79 -  the time dependent r e s i s t a n c e of pulps i n c r e a s i n g dose l e v e l .  Since  t h i s experiment was  removing or r e p o r t i o n i n g i n i t i a l unequivocally chains  leads  increased  to s t r a i n i n g d e c r e a s e d s t e a d i l y with  or s h o r t e n i n g  As d i s c u s s e d  prove  of c e l l u l o s e  p l a s t i c i s a t i o n o f . m i c r o f i b r i l s and  stress relaxation.  without  c a r b o h y d r a t e s the a s c e n d i n g s l o p e s  that progressive degradation to i n c r e a s e d  c a r r i e d out  i n turn  above, the a c t u a l mechanism  r e s p o n s i b l e f o r enhanced v i s c o e l a s t i c i t y of c e l l u l o s e i s i n c r e a s e d of c r y s t a l l i t e s caused by c h a i n d e g r a d a t i o n It i s apparent t h a t i n pulps of c a r b o h y d r a t e s the v i s c o e l a s t i c hemicellulose  p o r t i o n and  c e l l u l o s e m o l e c u l e s i n low y i e l d and  i n amorphous  response changes a c c o r d i n g  pulps  to both  i n the c a u s t i c s w o l l e n  hemicelluloses  respect  state.  to s t r e s s  T h i s means t h a t  changes i n v i s c o e l a s t i c r e s p o n s e s of p u l p s ,  such as v i s c o s e , a c e t a t e  s u l p h i t e paper p u l p s , have to be c o n s i d e r e d  as  in total  short chain material  suggestion  1 - G£(35')/£"(o) on  As F i g . 27  statistical  hemicelluloses.  ( F i g . 26)  (Table 6) showed no  l e v e l s of the t h r e e r e g r e s s i o n  lines  this  of  untreated  viscose  i n Table  6.  of n o n - i r r a d i a t e d  content.  Consequently,  caustic solubility  i s b e l i e v e d to be  T e s t i n g of p a r a l l e l i s m and  curvilinear regression and  the r e g r e s s i o n  i n d i c a t e s , the c a u s t i c s o l u b i l i t y  p r i m a r i l y dependent on h e m i c e l l u l o s e  pulps  v a l i d i t y of  c a l c u l a t i o n s given  h i g h c o r r e l a t i o n between 1 -€J35' )/e""(o) and irradiated  The  10% NaOH s o l u b i l i t y of i r r a d i a t e d and  pulps,and the c o r r e s p o n d i n g  p u l p s was  illustrating  and  the r e s u l t of v a r i a t i o n s  i n the f i b r e w a l l .  i s supported by F i g . 26  the  S i n c e hemi-  linear,  c e l l u l o s e can be assumed to f u n c t i o n s i m i l a r l y with  dissipation particularly  degradation  DP c e l l u l o s e i n d u c e d . are e s s e n t i a l l y  mobility  regions.  undergoing p r o g r e s s i v e  amount of low  to  of  the  non-  e s s e n t i a l l y caused by r e s i d u a l coincidence  for multiple  significant differences in  i n F i g . 26.  This provides  t h a t s t r e s s r e l a x a t i o n i n h i g h l y degraded pulps  seems to be  of t o t a l amount of low  of a s p e c i f i c  DP c a r b o h y d r a t e s arid not  slopes  evidence  solely a function carbohydrate  component. This observation chain  length  l e n g t h and  i s u s e f u l i n e x p l a i n i n g the r e l a t i v e l y  of n a t i v e h e m i c e l l u l o s e s .  h i g h degree of b r a n c h i n g  As proposed e a r l i e r ,  small  limited chain  appear u s e f u l to v i s c o e l a s t i c  processes  in the undamaged or slightly degraded fibre wall.  In the water swollen  state, severe chain degradation, particularly in low yield pulping, changes profoundly the original mechanical function of carbohydrates in the fibre wall. Highly degraded cellulose appeared to behave similarly to native hemicelluloses,whereas  that part of the degradated hemicelluloses, which i s  redeposited in highly ordered form or remains after degradation (removal of side chains) in close association with cellulose, responded like crystalline cellulose. 4.4. Interchangeability of Stress Systems When dry cellulosic materials are steeped in water or alkaline solutions, swelling takes place. This phenomenon is known to cause enormous swelling stresses which, in turn, can be assumed  to induce rheological  processes in the lignin-carbohydrate complex. Weakening, breaking and reformation of hydrogen bonds, bond angle changes, stretching of primary bonds, or even conformational changes can be expected to occur in cellulosics under swelling stresses. Therefore, i t was hypothesized that time of steeping in swelling reagents, i.e, the time period over which the sample is subjected to swelling stress, may significantly affeet'rheological behavior of ligno-cellulosics under subsequent mechanical excitation. Two experiments were carried out to study the effect of steeping (swelling) period on viscose pulp relaxation.  In the f i r s t experiment this  effect was investigated on samples steeped in water and 18.6% NaOH for short (1 min and 25 sec) and long periods (48 h r ) . For a more complete study of this interaction a second experiment with a sequence of tests following steeping periods in 18.6% NaOH ranging from 0.1 to 14400 min was undertaken. The data are shown in Figs.28 and 29.  Figure 28^ in which fractional stress  relaxation at 35 min is plotted against steeping time, compares stress dissipation in viscose pulps following short(one minute or less) and long (48 hr) term steeping in water or caustic.  Figure 29 represents the data  obtained from pulps steeped between 0.1 and 14400 min in 18.6% NaOH. It appears from both figures that steeping time influenced residual stress dissipation.  Extension of steeping time unequivocally resulted i n  reduced ability of. the cellulosic material to absorb or dissipate energy.  -  This  VI  -  i s t r u e f o r both water and c a u s t i c s t e e p i n g t r e a t m e n t s .  i n F i g . 28, a p p r o x i m a t e l y specimens steeped steeped  10% l e s s s t r e s s r e l a x a t i o n was observed  with  48 h r i n water o r i n 18.6% NaOH, compared t o specimens  one minute i n water o r 25 sec i n 18.6% NaOH.  occurred  As e x h i b i t e d  w i t h water s t e e p i n g , a l t h o u g h  S i n c e the e f f e c t  to a l e s s e r extent  than  with  c a u s t i c , i t i s assumed t h a t p o s s i b l e e x t r a c t i o n s o f s o l u b l e f r a c t i o n s during  s t e e p i n g c o u l d not e n t i r e l y cause t h e change.  f r a c t i o n f o l l o w i n g prolonged  s t e e p i n g was not examined i n the p r e s e n t  In F i g , 29 a l o g - l o g p l o t specimens t r e a t e d over v e r y  The r e s i d u a l s o l u b l e s study.  i s used f o r p r e s e n t i n g d a t a o b t a i n e d  s h o r t t o long s t e e p i n g p e r i o d s .  with  The two l i n e s  show the r e l a t i o n s h i p s between <^( t )/(^(o) observed a t 6 sec and 100 min after pulp  t  and s t e e p i n g  time.  Again,  t o d i s s i p a t e energy decreased  i t can be seen t h a t the c a p a b i l i t y o f considerably with  increased  treatment  time. The best The  dependence of s t r e s s r e l a x a t i o n on s t e e p i n g p e r i o d can be  expressed  by a c u r v i l i n e a r r e l a t i o n s h i p as i n d i c a t e d i n F i g . 29.  slope r e v e a l s that short steeping periods  l a r g e d i f f e r e n c e s i n s t r e s s decay. did  not o c c u r  (below one min) do not show  This implies that s w e l l i n g stresses  over a s h o r t time p e r i o d o r were l e s s than the s e n s i t i v i t y  of the t e s t method.  I t appears to take a t l e a s t f i v e minutes s t e e p i n g to  observe t h e s t e e p i n g e f f e c t a t the temperature employed. curves  i n F i g . 29 show, f u r t h e r m o r e ,  approximately  that increased  5 minutes reduced both s h o r t  (above 6 s e c ) r a t e s o f s t r e s s d i s s i p a t i o n - . indicating  that a f t e r i n f i n i t e l y  c l o s e to ^ ( 1 0 0 period  t h e pulp  min).  steeping periods  (below 6 s e c ) and long Both c u r v e s  above  time  approach each  other,  long s t e e p i n g p e r i o d s <^(6 s e c ) w i l l  I t may be proposed t h a t a f t e r  such a long  fall  steeping  i s " c o n d i t i o n e d " or " s e t " i n a way t h a t l i m i t s f u r t h e r  chemical  adjustment under t e m p e r a t u r e - c o n c e n t r a t i o n  system.  Such s e t t i n g o r p r e s t r e s s i n g s i m u l t a n e o u s l y  dependent  physical-mechanical  relaxation  periods.  It i s e v i d e n t cellulosics  The s l o p e s o f the  c o n d i t i o n s o f the reduces the time  p r o p e r t i e s , a t l e a s t as measured over  from t h e d a t a  presented  short  i n F i g . 29_, t h a t a b i l i t y o f  to d i s s i p a t e s t r e s s can be d i m i n i s h e d  by two types o f e x c i t a t i o n :  - 82 -  ( i ) by an i n f i n i t e l y  long  steeping  time; ( i i ) by an i n f i n i t e l y  of m e c h a n i c a l e x c i t a t i o n ; and t h a t e x h a u s t i o n should  long  period  o c c u r through a  combination of both. The  i n v e r s e r e l a t i o n s h i p between s t r e s s d i s s i p a t i o n and s t e e p i n g  time i n s w e l l i n g s o l u t i o n s may be e x p l a i n e d  i n t h e f o l l o w i n g way:  assumption can be made t h a t c e l l u l o s i c m a t e r i a l s for absorption  p o s s e s s a maximum c a p a c i t y  o r d i s s i p a t i o n o f s t r e s s under s e t c o n d i t i o n s  to t h e i r h i s t o r y .  Steeping  the enormous s w e l l i n g f o r c e s  these k i n d s  " i n t e r n a l chemical s t r e s s r e l a x a t i o n " .  o f s t r a i n s may produce  The longer  t h e pulp i s kept  s w e l l i n g environment, the l a r g e r i s t h i s component. to e x t e r n a l  f r a c t i o n of the i n i t i a l  swelling solutions,  induce r h e o l o g i c a l p r o c e s s e s w i t h i n t h e f i b r e  Under s u i t a b l e c o n d i t i o n s  subsequently subjected  and a c c o r d i n g  time adds a new component t o t h a t h i s t o r y .  When, f o r i n s t a n c e , p u l p s a r e steeped i n water o r o t h e r  walls.  capacity  during  physical-mechanical  s t r a i n only a  f o r r e l a x a t i o n can be o b s e r v e d .  the c h e m i c a l  treatment, i . e . c a u s t i c s  T h i s phenomenon, as observed on v i s c o s e primarily The  high  i n the  When t h e m a t e r i a l i s  assumes t h a t adjustments i n c h e m i c a l components, such as a l k a l i have not o c c u r r e d  The  This solubles,  steeping.  p u l p s , has t o be a t t r i b u t e d  to m o l e c u l a r p r o c e s s e s i n the amorphous r e g i o n s  of c e l l u l o s e .  s w e l l i n g s t r e s s e s may cause m o l e c u l a r motion of c e l l u l o s e , p r o b a b l y  involving  the mechanisms mentioned a t the b e g i n n i n g of the s e c t i o n .  However, i t can be assumed t h a t c e l l u l o s e a r e not o f i n f i n i t e l e a v e and e n t e r  these m o l e c u l a r rearrangements o f amorphous  extent  c r y s t a l l i n e zones.  c e l l u l o s e chains  from  due t o the f a c t Such dichotomy  u n r e s t r i c t e d motion.  that c e l l u l o s e c h a i n s  limits  the l i n e a r  T h i s means, t h a t  energy  d i s s i p a t i o n by r e o r i e n t a t i o n of amorphous c e l l u l o s e i s o f l i m i t e d In t h e s w o l l e n  state the swelling stresses w i l l  e n t a i l molecular  extent. rearrange-  ments w h i c h , i n t u r n , reduce t h e c a p a b i l i t y of c e l l u l o s e t o d i s s i p a t e s t r e s s . Under subsequent e x t e r n a l be  s t r a i n i n g t h e magnitude o f c e l l u l o s e reponse  will  s o l e l y dependent on " r e s i d u a l " m o l e c u l a r rearrangements of amorphous  eellulose. These o b s e r v a t i o n s  on i n t e r c h a n g e a b i l i t y o f c h e m i c a l and p h y s i c a l  s t r e s s systems c a r r y the profound s u g g e s t i o n  o f a u n i f y i n g concept f o r  - 83  adjudicating translate  r e s u l t s of mixed systems.  i n to the  amorphous zones. i.e., 4.5  -  same b a s i c  Difference  " i n t e r n a l " or Application  Both, as has  function:  been d i s c u s s e d ,  re-orientation  of c e l l u l o s e i n  l i e s o n l y i n the ways e x c i t a t i o n  of S t r e s s  R e l a x a t i o n Measurements f o r C h a r a c t e r i s i n g  of c e l l u l o s i c m a t e r i a l s  b e h a v i o r by  estimating  uses of  In the  4.5.1  following,  stress relaxation  properties  relaxation  and  highly alkali  importance.  solubility  solubility The  i n 10%  inverse  alkali  NaOH as  The  reproducibly,  and  F i g . 30. conditions  be  mechanical  may  on  of  pulp  samples  time consuming.  suitable for replacing be  be  multi-step  p u l p q u a l i t i e s are  S o l u b i l i t y values could  stress  c h e m i c a l methods  estimated  by  or o t h e r c a u s t i c  concentrations.  ( F i g . 30)  suggests t h a t measurements done on  used a l s o  to p r e d i c t  r e l a t i o n of  could  in predicting  p u l p t y p e s , the  s o l u b i l i t y by  any  be much lower.  a c c u r a c y of  i n d i c a t e ^ by  the  using  water  the stress  From t h i s  t h i s new  method  study, was  standard e r r o r values i n  s i n g l e p u l p type under c o n t r o l l e d The  and  solubility.  t h i s to a c c e p t i b i l i t y c r i t e r i a .  r e a s o n a b l y good, as  Variation within  alkali  f a c t o r r e m a i n i n g f o r a p p l i c a t i o n of  s i z e of e r r o r  numerous v i s c o s e  found to be  ( F i g . 30)  whereas customary  shown i n F i g . 30,  only uncertain  t e c h n i q u e i s the  including  potential  r e l a t i o n s h i p of 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 between water  p u l p s might be  relaxation  a few  great  l i n e r e l a t i o n s h i p , such as between l-£(t)/^(o) and  steeped m a t e r i a l s  saturated  pulps  D e t e r m i n a t i o n of s t r e s s r e l a x a t i o n  tests f o r determining viscose  straight  employed w i t h  solubility  s o l u b i l i t y of v i s c o s e  t e s t s may  material  papers.  pulp a l k a l i  with l e s s c o s t l y procedures. u s i n g the  are  s i g n i f i c a n t c o r r e l a t i o n between f r a c t i o n a l  Consequently, r e l a x a t i o n  mechanical  as a t o o l f o r d e t e r m i n i n g c h e m i c a l and  i s done r a p i d l y , e a s i l y and  Pulps  Many c a s e s are known where  characterisations  of v a r i o u s wood p u l p s and  The  and  used f o r p r e d i c t i n g  an attempt i s made to d e s c r i b e  E s t i m a t i o n of v i s c o s e  practical  i s frequently  related characteristics.  such i n d i r e c t methods of m a t e r i a l success.  applied,  "external".  I n t e r r e l a t i o n s h i p between many c h e m i c a l , p h y s i c a l properties  is  importance h e r e c o u l d  be  manufacturing  the u t i l i z a t i o n •  - 84 -  of r h e o l o g y dynamics f o r "on machine" t e s t i n g , thereby  introducing a point  of p u l p p r o c e s s c o n t r o l not p r e s e n t l y e x e r c i s e d . V i s c o s e pulp a l k a l i as r e g a r d s y i e l d  and  that other u s e f u l  s o l u b i l i t y has meaning to v i s c o s e  manufacturers  p o s s i b l y other v i s c o s e processing f a c t o r s .  It i s l i k e l y  parameters,  as w e l l as t h i s , a r e a s s o c i a t e d with  stress  relaxation.  4.5.2  P r e d i c t i n g v i s c o s e pulp pressing c h a r a c t e r i s t i c s The  important  response  of f i b r o u s s t r u c t u r e s to c o m p r e s s i b i l i t y has  b e a r i n g on a number of f i b r e p r o c e s s i n g o p e r a t i o n s .  r a t e of water or a l k a l i n e s o l u t i o n f l o w from a f i b r o u s mat to a l a r g e e x t e n t upon i t s r h e o l o g y i n Compressibility importance observed  an  Thus, the  should depend  compression.  of f i b r e mats or s h r e d d i n g s  i s of  particular  to the p r e s s i n g of steeped v i s c o s e p u l p s , where i t has  been  t h a t time o r p r e s s u r e r e q u i r e d to o b t a i n the d e s i r e d " p r e s s  v a r i e s with i n d i v i d u a l pulps.  The  v a r i a t i o n s are r e l a t e d d i r e c t l y absorb  fractional  and  to some i n t r i n s i c a b i l i t y  d i s s i p a t e s t r e s s e s , s i n c e i t i s found  differences behavior.  p r e s e n t work suggests  that  ratio"  these  of the p u l p to  t h a t v i s c o s e pulps  exhibit  i n r a t e of s t r e s s decay c o r r e s p o n d i n g t o r e p o r t e d p r e s s i n g Thus, high i n i t i a l  d i s s i p a t i o n , which may  r a t e of s t r e s s decay shows r a p i d  i n d i c a t e ease i n p r e s s i n g .  to be done f o r examining  energy  A f u r t h e r study  needs  t h i s r e l a t i o n s h i p as r e g a r d s i t s p r a c t i c a l  implications. . 4.5.3  P r e d i c t i n g f i b r e response  to  machining  In p u l p b e a t i n g , the d e f o r m a t i o n b e i n g of the r e l a x a t i o n to deform r e a d i l y and, (272).  I t appears  type  (271).  of f i b r e s can be c o n s i d e r e d  P u l p f i b r e s of h i g h p l a s t i c i t y a r e  t h e r e f o r e , respond  easily  t h a t a c e r t a i n minimum low m o l e c u l a r f r a c t i o n  p a r t i c u l a r l y of h e m i c e l l u l o s e s , i s necessax-y It i s b e l i e v e d t h a t new when some energy  to the b e a t i n g  level c r i t i c a l  as said  treatment content,  f o r good b e a t i n g performance.  s u r f a c e s a r e formed i n p u l p machining  to a g i v e n p u l p i s exceeded.  T h i s may  only be  - 85 -  a c c o m p l i s h e d by f u r t h e r l o a d i n g of the m o l e c u l a r by  s w e l l i n g processes  i n the  system a l r e a d y s t r a i n e d  l i g n i n - c a r b o h y d r a t e complex which, of  course,  reduces the energy a b s o r p t i o n / d i s s i p a t i o n r a t i o . Based on should  t h i s work, the s u g g e s t i o n  e x i s t between b e a t i n g response and  demonstrated by  the h i g h  low  I t would be of p a r t i c u l a r  t h i s r e l a t i o n s h i p , s i n c e the  r a t e of s t r e s s decay.  P r e d i c t i n g paper Among o t h e r  interest  to examine the c o n t e n t s  response.  printability  f i b r e machining o p e r a t i o n s , the p o s s i b i l i t y of  to I v a r s s o n  a paper product with  other  (124)  and  Steenberg  c o r r e l a t e s with  (277),  softness/hardness  i t s compression b e h a v i o r  T h i s i m p l i e s t h a t i f paper i s s o f t and  deforming r a d i l y under p r e s s u r e , between the f i b r e s and s u r f a c e smoothness. i n steploaded  and,  of  together  capable  required intimate contact w i l l  affect of  be  assured  the p r i n t i n g p l a t e , even at some v a r i a t i o n s i n  It can be  supposed that h i g h r a t e of s t r e s s d i s s i p a t i o n  o p e r a t i o n s would i n d i c a t e a h i g h degree of s o f t n e s s  t h e r e f o r e , good  and,  printability.  E x i s t i n g methods f o r a s s e s s i n g p r i n t i n g q u a l i t y of v a r i o u s products  a r e not  em-  is attractive.  f a c t o r s , the compression p r o p e r t i e s of a paper or board  printing results.  of  s t r e s s r e l a x a t i o n t e s t c o u l d be a p p l i e d as a  p l o y i n g s t r e s s r e l a x a t i o n f o r p r e d i c t i n g paper p r i n t a b i l i t y According  This i s  DP c e l l u l o s e , and r e l a x a t i o n  dynamic system f o r "on machine" p r e d i c t i o n of pulp b e a t i n g 4.5.4  correlation  c o r r e l a t i o n found between r e s i d u a l low-molecular  f r a c t i o n s , i . e . h e m i c e l l u l o s e s and response.  i s made t h a t a h i g h  always s a t i s f a c t o r y  (9,302).  According  to Ullman  paper (303),  c u r r e n t measurements can d i s t i n g u i s h r e l i a b l y o n l y between papers of considerable differences.  I t i s o b v i o u s from the e r e a t number of v a r i a b l e s ,  which have been found to i n f l u e n c e paper p r i n t a b i l i t y , method alone  i s not  sufficient  to supply  accurate  t h a t one  testing  information.  For i n s t a n c e , c u r r e n t smoothness measurements of paper widely  p r a c t i s e d f o r e v a l u a t i n g h e a v i l y coated  some good i n d i c a t i o n r e g a r d i n g  paper s u r f a c e s  printing quality.  surface,  (127),  However, due  t h a t t h i s e v a l u a t i o n c o n s i d e r s o n l y s u r f a c e c h a r a c t e r i s t i c s and  to the  give fact  neglects  - 86 -  the compressibility value.  behavior of the paper, the information i s of limited  It appears f e a s i b l e to obtain accurate information by combining  physical and mechanical testing methods, such as smoothness and stress relaxation measurements.  Such a pair of measurements could be c a r r i e d  out simultaneously on the paper machine. The  same stress relaxation data may also furnish information about  runnability of paper, a property extremely important i n high speed p r i n t i n g . It i s well known that the modulus of e l a s t i c i t y (E) i s c l o s e l y related to frequency of breaks and bagginess (303).  Low E indicates an extensible  paper which adapts smoothly to the printing r o l l s , thus l i m i t i n g the number of breaks.  Since v i s c o e l a s t i c and e l a s t i c properties  are highly  interrelated,  stress relaxation measurements would be expected to be useful i n predicting the runnability of various p*per grades.  0 /  -  5.0 CONCLUSIONS 1. Rate of stress relaxation varied widely between individual pulps or pulp types. However, the relaxation measurements obtained from individual pulps, in particular when steeped in caustic, appeared to be highly consistent indicating good reproducibility. 2.  Stress dissipation in water or caustic steeped pulp mats  followed a similar pattern observed on wood and other ligno-cellulosics under constant compressive or tensile strain. 3.  Two different mechanisms (M^ and  appeared to be involved  in pulp mat stress relaxation following quasi steploading (1.0 to 1.5 sec). One dominated the i n i t i a l short period (0.0 to approximately 1.0 min), while the other featured longer time response 'from approximately 1.0 min to 35 min). whereas M  It i s thought that  is mainly caused by inter-fibre processes,  comprises intra-fibre, essentially molecular processes. 4.  Pulps dissipate stress at substantially higher rates in the  caustic than in the water swollen state.  This underlines the importances  of inter-(in water and 18.6% NaOH) and intra-(in 18.6% NaOH) crystalline swelling phenomena which determine the molecular forces between individual molecules of the pulp polymeric system. These forces, in turn, control the relaxation response. 5.  Pulp chemistry exerts a profound influence on stress relaxation  of both water and caustic (18.6% NaOH) steeped pulp mats. 6.  Lignin appeared to make no or only an insignificant contribution  to pulp mat stress relaxation in compression.  This i s probably due to a  "layer-effect" causing discontinued stress communication in the lienin(carbohydrate  complex and due to the dominant role of hemicelluloses which  seem to obscure a moderate contribution of lignin. 7. The hemicelluloses were found to be of extreme importance for stress dissipation or redistribution processes in water and caustic swollen pulp mats. Both quantitative and structural features of degraded or nondegraded residual hemicelluloses appeared to play an outstanding role in the  - 88 -  r e l a x a t i o n response.  High h e m i c e l l u l o s e c o n t e n t s  i n s i g n i f i c a n t degradation elastic  redeposited  they r e t a r d e d 8.  no  or  a c o n s i d e r a b l y h i g h e r degree of v i s c o -  c a p a c i t y than extremely low c o n t e n t s  hemicellulose residues. and  provide  i n a s s o c i a t i o n with  In water s w o l l e n  of h i g h l y degraded and  low y i e l d  pulps,the  redeposited  h i g h l y degraded  r e s i d u e s were found to e x e r t even a r e v e r s e e f f e c t , i . e .  s t r e s s decay. It i s apparent from t h e i r r h e o l o g i c a l b e h a v i o r  i n p u l p mats  t h a t h e m i c e l l u l o s e s must f u n c t i o n as an e x t r a o r d i n a r y p a r t i n the s t r e s s dissipating  system i n l i v i n g wood.  h i g h degree of b r a n c h i n g 9.  and  It i s evident  s t r e s s i n p u l p mats steeped  the  T h i s f u n c t i o n i s f a c i l i t a t e d by  low  DP.  t h a t c e l l u l o s e accounts f o r most of the d i s s i p a t e d i n water or c a u s t i c .  In the n a t i v e or  s l i g b t l y degraded s t a t e i t s c o n t r i b u t i o n to- pulp mat o n l y i n s i g n i f i c a n t l y between pulps However, p r o g r e s s i v e c h a i n c l e a v a g e changes the r h e o l o g i c a l b e h a v i o r .  seems to  vary  contents. drastically  T h i s i s i n d i c a t e d by c o n s i d e r a b l y  increased  degraded  High degree of c e l l u l o s e d e g r a d a t i o n  carbohydrates  only  l e a d i n g to DP v a l u e s below 1000  r e d e p o s i t i o n phenomena of h e m i c e l l u l o s e s r e v e r s e these  rheology  of v a r i o u s h e m i c e l l u l o s e  r a t e s of s t r e s s r e l a x a t i o n of g a m m a - i r r a d i a t i o n 10.  the  i n r h e o l o g i c a l processes  pulps.  and d e g r a d a t i o n  and  the o r i g i n a l f u n c t i o n of  i n the. water s w o l l e n  p u l p mats.  Degraded c e l l u l o s e d i s s i p a t e d s t r e s s a t i n c r e a s e d r a t e s , whereas degraded and  redeposited hemicelluloses retard r h e o l o g i c a l processes. 11.  controlled  In the c a u s t i c steeped  s o l e l y by the s h o r t c h a i n m a t e r i a l p r e s e n t  i m p l i e s t h a t i t does not depend on any 12. caustic  suggests the  two  a c o m b i n a t i o n of  both.  i n the p u l p .  This  component.  time, observed on water  and  and  p h y s i c a l s t r e s s systems.  to d i s s i p a t e or r e d i s t r i b u t e s t r e s s can  types of e x c i t a t i o n :  ( i i ) an i n f i n i t e l y  appeared.-to be  v i s c o s e p u l p s , on r e s i d u a l s t r e s s r e l a x a t i o n  i n t e r c h a n g e a b i l i t y of chemical  by  rheology  s p e c i f i c carbohydrate  profound e f f e c t of s t e e p i n g  the c a p a b i l i t y of pulps  be d i m i n i s h e d time;  The  (18.6% NaOH) steeped  Therefore,  s t a t e , pulp mat  ( i ) an  infinitely  long  long p e r i o d of mechanical e x c i t a t i o n ; and  steeping  ov  13. are suggested properties, viscose and  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 measurements on p u l p s and as u s e f u l  t o o l s f o r d e t e r m i n i n g c h e m i c a l and m e c h a n i c a l  such as p r e s s i n g  14,  response  of r u n n a b i l i t y and p r i n t a b i l i t y Further studies  to machining  (beating)  of paper.  need to be done f o r examining  the r e l a t i o n s h i p  between s t r e s s r e l a x a t i o n and pulp mat c h a r a c t e r i s t i c s as r e g a r d s i t s practical  implications.  pulp  c h a r a c t e r i s t i c s and a l k a l i s o l u b i l i t y o f  p u l p s , e s t i m a t i o n of pulp f i b r e  evaluation  papers  - 90 -  6.0  LITERATURE  CITED  Abdurahman, N. , Dutton, G.G.S., McLardy, D.M. , P i e r r e , K.E. and  B . I . Stephenson. 1964.  H e m i c e l l u l o s e s of  b l a c k s p r u c e , S i t k a s p r u c e , ponderosa pine and  Douglas f i r ,  Adams, G.A. 1964.  T a p p i 47: 812.  Wood c a r b o h y d r a t e s .  P u l p Paper Mag. Can.  65: T13-T24. A d l e r , E. 1957. 40:  Newer views o f l i g n i n f o r m a t i o n .  Tappi  294-301.  A h l g r e n , P.A. and D.A.I. G o r i n g .  1971.  Removal o f wood  components d u r i n g c h l o r i t e d e l i g n i f i c a t i o n of black spruce. A l f r e y , T. 1948.  Can. J . Chem. 49: 1272-1275.  Mechanical  Behavior  of High  Polymers.  I n t e r s c i e n c e P u b l . I n c . , New York. 570 pp. Anderson, D.M.W., G a r b u t t , S. and S.S. Z a i d i . on u r o n i c a c i d m a t e r i a l s . simultaneous  1963.  Studies  P a r t IX. The  d e t e r m i n a t i o n o f u r o n i c a c i d and  a l k o x y l groups i n p o l y s a c c h a r i d e s by r e f l u x hydriodic acid.  with  A n a l . Chim. A c t a . 29: 39-45.  it  Anderson, 0. and L. S j o b e r g . 1953.  T e n s i l e s t u d i e s o f paper  at d i f f e r e n t r a t e s of e l o n g a t i o n .  Svensk  P a p p e r s t i d n . 56: 615-624. and  I. Steen.  non-uniformity (Ed. ).  1962. on sheet  Formation  Influence of suspension structure.  In F. B o l a m  and S t r u c t u r e of Paper.  Tech.  Sec. B.P. and B.M.A., London, pp. 772-782. A n e l i u n a s , A.E. and L.S. Campbell. paperboard.  1969.  P r i n t a b i l i t y of  Pulp Paper Mag. Can. 70: T487-T498.  - 91 -  10.  Annergren, G.E. and S.A. Rydholm. 1959.  On the b e h a v i o r  of the h e m i c e l l u l o s e s d u r i n g s u l f i t e  pulping.  Svensk P a p p e r s t i d n . 62: 737-746. 11.  and S. Vardheim. 1963. I n f l u e n c e of raw m a t e r i a l and p u l p i n g on the c h e m i c a l  composition  process  and p h y s i c a l  p r o p e r t i e s o f paper p u l p s . Svensk P a p p e r s t i d n . 66: 12.  196-210.  Asunraaa, S. 1957.  Die M i t t e l l a m e l l e .  In E. T r e i b e r ( E d . ) .  Die Chemie d e r P f l a n z e n z e l l w a n d . Berlin, 13.  Springer Verlag,  pp. 181-187.  A x e l s s o n , S., Croon, J . and B. Enstrom. 1962. D i s s o l u t i o n of h e m i c e l l u l o s e s d u r i n g s u l p h a t e p u l p i n g . Svensk P a p p e r s t i d n .  14.  B a i l e y , A . J . 1936.  65: 693-697.  Lignin i n Douglas-fir:  of t h e middle  lamella.  composition  Ind. Eng. Chem. ( A n a l .  Ed. ) 8: 52-55. 15.  B a l o d i s , V., McKenzie, A.W.  and K.J. H a r r i n g t o n . 1966.  E f f e c t s of h y d r o p h i l i c c o l l o i d s and o t h e r nonf i b r o u s m a t e r i a l s on f i b r e f l o c c u l a t i o n and network c o n s o l i d a t i o n , _In F. Bolam ( E d . ) . C o n s o l i d a t i o n of the Paper Web. and 16.  Bearce,  B.M.A., London,  G.D. 1962. (Ed. ). Vol. pp.  17.  Mechanical  Tech. Sec. B.P.  pp. 639-686. pulping.  In C.E. L i b b y  Pulp and Paper S c i e n c e and Technology.  I. McGraw - H i l l  Book Co., New York,  141-159.  Benko, J . 1964.  The measurement o f m o l e c u l a r weight of  l i g n o s u l f o n i c a c i d s and r e l a t e d m a t e r i a l s by diffusion.  T a p p i 47: 508-514.  - 92 -  Bergen, J.T. I960.  Viscoelasticity.  Academic Press, New York.  150 pp. Berlyn, G.P. 1964. Recent advances in wood anatomy. Forest Prod. J . 14: 467-476. and R.E. Mark. 1965. Lignin distribution in c e l l walls.  Forest Prod. J . 15: 140-141. II  Bethge, P.O., Holmstrom, C. and S. Juhlin. 1966. Quantitative gas chromatography of mixtures of simple sugars. Svensk Papperstidn. 69: 60-63. Biot, M.A. 1965. Mechanics of Incremental Deformations. Interscience Publ. Inc., New York. 504 pp. II  Bjorkman, A. 1957. Studies on finely divided wood. Svensk Papperstidn. 60: 243-251. Bland, D.R. 1960. Theory of Linear Viscoelasticity.  Pergamon  Press, New York. 125 pp. Bliesner, W.C. 1970. Dynamic smoothness and compressibility measurements on coated papers. Tappi 53: 1871-1879. Borchardt, L.G. and C.V. Piper.  1970. A gas chromatographic  method for carbohydrates as alditol acetates. Tappi 53: 257-260. Bouveng, H., Garegg, P. and B. Lindberg. I960. Position of 0-acetyl groups in birch xylan.  Acta Chem. Scand.  14: 742-748. Brainerd, F.W. 1939. A new fibre classifier and its application. Paper Trade J . 108(16): 33-40. Brecht, W. and H„ Erfurt. 1959. Wet-web strength of mechanical and chemical pulps of different form composition. Tappi 42: 959-968.  - 93 -  30.  B r e c h t , W. and K. Klemm. 1953. mechanical  The m i x t u r e of s t r u c t u r e s i n a  pulp as a key t o the knowledge of i t s  technological properties.  P u l p Paper Mag. Can. 54:  72-80. II  31.  and M. S c h a d l e r . 1961.  Die Zusammendruckbarkeit II  von P a p i e r e n i n i h r e r A b h a n g i g k e i t von e i n i g e n Festigkeitsbedingungen. 32.  . 1963.  Das P a p i e r 15: 695-703. Ueber neue Messungen d e r  n  K o m p r e s s i b i l i t a t von P a p i e r e n .  Das P a p i e r 17:  626-634. 33.  B r e z i n s k i , J.P. 1956.  Creep  p r o p e r t i e s of paper.  T a p p i 39:  116-128. 34.  Brown, W.  1967.  S o l u t i o n p r o p e r t i e s of l i g n i n .  p r o p e r t i e s and m o l e c u l a r weight  Thermodynamic  determinations. J.  A p p l . Polym. S c i . 11: 2381-2396. 35.  B r o w n e l l , H.H.  1965.  I s o l a t i o n of m i l l e d wood l i g n i n and  c a r b o h y d r a t e complex. 36.  P a r t I I . T a p p i 48: 513-519.  and K. L. West. 1961. carbohydrate  lignin-  The n a t u r e o f the l i g n i n -  l i n k a g e i n wood.  P u l p Paper Mag. Can.  62: T374-T384. 37.  Browning, B.L. 1967.  Methods of Wood C h e m i s t r y .  I n t e r s c i e n c e P u b l . I n c . , New York. 38.  \  and L.O. B u b l i t z . h o l o c e l l u l o s e from wood.  39.  B u b l i t z , J.W.  1951.  1953.  II.  pp. 726-727.  The i s o l a t i o n of  T a p p i 36: 452-458.  An i n v e s t i g a t i o n o f the c a r b o h y d r a t e  f r a c t i o n of spruce c h l o r i t e 427-432.  Vol.  liquors.  Tappi  34:  - 94 -  Buchanan, J.G. and O.V. Washburn. 1962. The surface and tensile fractures of chemical fibre handsheets as observed with the scanning electron microscope. Pulp Paper Mag. Can. 63: T485-T493. Bucher, H. 1958. Discontinuities in the microscopic structure of wood fibres.  In F. Bolam (Ed.).  Papermaking Fibres.  Fundamentals of  Tech. Sect. B.P. and B.M.A.,  Kenley. pp. 7-34. Bueche, F. 1962. Physical Properties of Polymers.  Interscience  Publ. Inc., New York. 354 pp. Campbell, W.G. 1947. The physics of water removal. Pulp Paper Mag. Can. 48: T103-T109. and I.R.C. McDonald. 1952. The chemistry of the wood c e l l wall.  Part I I . The isolation of beech  and spruce acid soluble and modified lignins.  J. Chem.  Soc. 3180-3183. Casey, J.P. 1960. Pulp and Paper.  Vol. I I . Papermaking.  Interscience Publ. Inc., New York, pp 795-1405. Centola, G. and R. Rifa.  1965. Properties and some regenerated  cellulose fibres. cold a l k a l i .  Variations caused by treatment with  Ric. Doc. Tessile 2-17.  Chang, H.M. and G.G. Allan. 1971. Oxidation (of lignin ). In K. V. Sarkanen and C.H. Ludwig (Ed.). Interscience Publ. Inc., New York.  Lignins.  pp. 433-385.  Chow, S.-Z. 1969. Molecular Rheology of Coniferous Wood Tissues. Unpub. PhD Thesis, Fac. For., Univ. B.C., Vancouver. 142 pp. Christensen, R.M. 1971. Theory of Viscoelasticity. Press, New York. 245 pp.  Academic  - 95 -  Clark, J. d'A. 1943.  Factors influencing apparent density  and i t s effect on paper properties. Paper Trade J. 116 (1): 31-38. Clayton, D.W.  and J.E. Stone. 1963.  The redeposition of hemi-  celluloses during pulping.  Pulp Paper Mag. Can. 64:  T459-T468. Cowdrey, D.R. and R.D. Preston. 1965.  The mechanical properties  of plant c e l l walls: helical structure and Young's modulus of air-dried xylem in Picea sitchensis. W.A.  Cote, Jr. (Ed.).  Woody Plants.  In  Cellular Ultrastructure of  Syracuse Univ. Press, Syracuse, pp.  473-492. n  Croon, I. and B.F. Enstrom. 1961.  The 4-0-methyl-D-glucuronic  acid groups of birch xylan during sulfate pulping. Tappi 44: 870-874. . 1962. pulps from scots pine.  The hemicelluloses in sulphate Svensk Papperstidn. 65: 595-  599. , Jonsen, H. and H-G. Olofsson. 1968. in pulp, viscose and yarn.  Hemicelluloses  Svensk Papperstidn. 71:  40-45. Dadswell, H.E. and A.J. Watson. 1962.  Influence of the  morphology of woodpulp fibers on paper properties. In F. Bolam (Ed. ).  Formation and Structure of  Paper. Tech, Sec. B.P. and B.M.A., London, pp.537-564. Dence, C.W.  1971.  Halogenation and nitration (of lignin ). In  K.V. Sarkanen and C.H. Ludwig (Ed. ).  Lignins.  Interscience Publ. Inc., New York. pp. 373-432. Dolmetsch, H. 1961.  II  Anzeichen fur eine Kettenfaltung in der  Feinstruktur der Cellulose.  Kolloid - Z. 176: 63-64.  - 96 -  59.  Dolmetsch, H. 1963. Uber d i e Entstehung d e r C e l l u l o s e . Papier  60.  Dunning,  61.  17: 710-721.  C.E. 1968. C e l l - w a l l morphology wood.  Easterwood,  V.M. and B.J.L. H u f f . 1969. C a r b o h y d r a t e  Svensk  of acetylated  analysis  aldonitriles.  E i r i c h , F.R. 1958. Rheology, Theory and A p p l i c a t i o n s .  V o l . 2.  591 pp.  E l i a s , C.T. 1967. I n v e s t i g a t i o n o f t h e compression r e s p o n s e o f i d e a l unbonded f i b r o u s s t r u c t u r e s .  64.  late-  P a p p e r s t i d n . 72: 768-772.  Academic P r e s s , New York. 63.  of l o n g l e a f pine  Wood S c i . 1: 65-76.  by gas chromatography  62.  Das  Emerton,  H.W.  T a p p i 50: 125-132.  1958. The o u t e r secondary w a l l .  In F. Bolam (Ed. ).  Fundamentals  I.  Its structure.  o f Papermaking  Fibres.  Tech. Sec. B.P. and B.M.A., Kenley. pp. 35-54. 1  65.  , Page, D.H. and W.H. H a l e . 1962. The s t r u c t u r e of papers as seen i n t h e i r s u r f a c e s . (Ed.).  F o r m a t i o n and S t r u c t u r e o f Paper.  B.P. and B.M.A., London, 66.  In F. Bolam Tech. Sec.  pp. 53-99.  E r i k s s o n , E. and 0. Samuelson. 1962. I s o l a t i o n o f h e m i c e l l u l o s e from s u l f i t e c o o k i n g l i q u o r s .  Svensk P a p p e r s t i d n .  65: 600-605. 67.  E r i k s s o n , H.D.  1962. Some a s p e c t s o f method i n d e t e r m i n i n g  c e l l u l o s e i n wood. 68.  T a p p i 45: 710-719.  E r i k s s o n , L. 1967. On t h e p h y s i c a l and mechanical p r o p e r t i e s o f d e l i g n i f i e d wood.  Meddeiande 150B.  Svenska  T r a f o r s k n i n g s i n s t i t u t e t T r a t e k n i k , Stockholm.  23.pp.  E r i k s s o n , L. 1968. In R.E.  M e c h a n i c a l p r o p e r t i e s o f d e l i g n i f i e d wood. Wetton and R.W.  Systems-Deformation pp. F e n g e l , D.  Whorlow ( E d . ) .  and Flow.  Polymer  M a c M i l l a n Co.,  London,  141-152.  1969.  The u l t r a s t r u c t u r e of c e l l u l o s e from wood.  Wood S c i . Tech. 3: 203-217. F e r r y , J.D.  1970.  V i s c o e l a s t i c P r o p e r t i e s of Polymers.  I n t e r s c i e n c e Pub. F o r g a c s , O.L.  1963.  I n c . , New  York.  671  Can.  _, Robertson, A.A.  pp.  64  ( C ) : T89-T118.  and S.G.  Mason. 1958.  dynamic b e h a v i o r of paper making f i b r e s .  Freudenberg,  K.  Can.  The  hydro-  Pulp  Paper  59: T117-T128.  1961.  B i o g e n e s i s and c o n s t i t u t i o n of  P r o c . Wood Chem. Symposium, M o n t r e a l , pp. .1964.  1928.  The  lignin.  9-20.  Entwurf e i n e s K o n s t i t u t i o n s s c h e m a s f u r das  L i g n i n der F i c h t e . F r e y , A.  H o l z f o r s c h . 18:  intermicellar  3-9.  spaces o f c e l l u l a r membranes.  Ber. Deutsch. Bot. Ges. 46: 444-456 ( O r i g i n a l seen, B i o . A b s t r . 4: F r e y - W y s s l i n g , A.  1954.  fibrils.  17332).  S c i e n c e 119:  80-82.  On the c r y s t a l  s t r u c t u r e of c e l l u l o s e .  I. Biochem. e t B i o p h y s . A c t a . 18: 1959.  1968.  Tech. 2: 73-83.  166-168.  Die P f a n z l i c h e Z e l l w a n d .  V e r l a g , B e r l i n . 367 .  not  The f i n e s t r u c t u r e of c e l l u l o s e m i c r o -  . 1955.  .  ed.  The c h a r a c t e r i s a t i o n o f m e c h a n i c a l p u l p s .  P u l p Paper Mag.  Mag.  2nd  Springer  pp.  The u l t r a s t r u c t u r e o f wood.  Wood S c i .  - 98 -  81.  ii  Frey-Wyssling, A. and K. Muhlethaler. f i b r i l l e n der Cellulose.  . 1965. Plant Cytology. Fujisaki, K. 1962.  Die Elementar-  Makrom. Chera. 62: 25-30.  82.  83.  1963.  Ultrastructural  Elsevier Publ. Co., Amsterdam. 377 pp.  Studies of factors affecting the modulus of  elasticity of wood. B u l l . Ehime Univ. Forest. 1: 3437.  Transl. No. 30, Fac. For., Univ. B.C., Vancouver.  4 pp. 84.  Gallay, W. 1962.  The interdependence of paper properties. In  F. Bolam (Ed. ).  Formation and Structure of Paper.  Tech. Sec. B.P. and B.M.A., London, pp. 491-532. 85.  Gavelin, G. 1949.  The compressibility of newsprint.  Svensk  Papperstidn. 52: 413-419. 86.  Giertz, H.W.  1962.  Effect of pulping processes on fibre proper-  ties and paper structure. In F. Bolam (Ed.). Formation and Structure of Paper. Tech. Sec. B.P. and B.M.A., London, pp. 597-620. 87.  Gillham, J. K. and T.E. Timell. 1958.  The polysaccharides o f  white birch (Betula papyrifera).  Part 7. Carbohydrates  associated with the alpha-cellulose component. Svensk Papperstidn. 61: 540-544. 88.  Glennie, D.W.  1971.  Reactions in sulphite pulping.  In  K.V, Sarkanen and C.H. Ludwig (Ed.). Lignins. Interscience Pub. Inc., New York, pp. 597-637. 89.  Goring, D.A.I. 1971.  Polymer properties of lignin and lignin  derivatives. Lignins. 90.  JLn K.V. Sarkanen and C.H. Ludwig (Ed,).  Interscience Pub. Inc., New York. pp. 695-768.  and T.E. Timell. 1962. celluloses.  Molecular weight of native  Tappi. 45: 454-460.  - 99 -  G r a n t , J . 1962. paper  I n f l u e n c e o f f i b e r t y p e s , s i z e and shape on p r o p e r t i e s f o r p u l p s o t h e r than wood p u l p s .  In F. Bolam ( E d . ) . Tech.  Formation  and S t r u c t u r e o f Paper.  Sec. B.P. and B.M.A., London,  G r o s s , B. 1947.  pp. 573-591.  On c r e e p and r e l a x a t i o n . J . A p p l . Phys. 18:  212-221. G r o s s , S.K., Sarkanen, K.V, and C. Schuerch. of m o l e c u l a r weight t h r e e methods.  1958.  Determinations  o f l i g n i n d e g r a d a t i o n p r o d u c t s by  A n a l . Chem. 30: 518-521.  G r o w e l l , E.P. and B.B. B u r n e t t . 1967.  D e t e r m i n a t i o n o f the  c a r b o h y d r a t e c o m p o s i t i o n o f wood p u l p s by gas chromatography of the a l d i t o l a c e t a t e s . 39:  121-124.  Guha, S.R.D. and P.C. Pant.  1970.  p r o p e r t i e s of paper. H a l s e y , G.J. 1947. model. Hamilton,  A n a l . Chem.  Effect  o f h e m i c e l l u l o s e s on  I n d i a n P u l p Paper 25: 385-388.  N o n - l i n e a r e l a s t i c i t y and t h e E y r i n g shear  J . A p p l . Phys. 18: 1072-1097.  J.K. 1961.  The b e h a v i o r of wood c a r b o h y d r a t e s i n  technical pulping processes.  P r o c . Wood Chem.  Symposium, M o n t r e a l , pp. 197-217. , P a r t l o w , E.V. and N.S. Thompson.  1958. The  b e h a v i o r o f wood h e m i c e l l u l o s e s d u r i n g p u l p i n g . 41:  Tappi  803-816. and  N.S. Thompson.  1959.  A comparison  c a r b o h y d r a t e s of hardwoods and softwoods.  o f the  T a p p i 42  752-760. Han, S.T. 1969.  C o m p r e s s i b i l i t y and p e r m e a b i l i t y o f f i b r e mats.  P u l p Paper Mag. Can. 70: 65-77.  - 100 -  Harada, H. 1965.  infrastructure and organisation of gymnosperm  c e l l walls.  In W.A.  Cote, Jr. (Ed.). Cellular  Ultrastructure of Woody Plants.  Syracuse Univ.  Press, Syracuse, pp. 215-233. , Miyazaki, Y. and T. Wakashima. 1958.  Electron-  microscopic investigation of the c e l l wall structure of wood. Bull. No. 104, Govt. Forest Exp. Sta. (Japan). 115 Harlow, W.M.  1970.  pp.  Inside Wood. The American Forestry  Association, Washington. 120 Hartler, N. 1962.  pp.  Comparison between kraft and sulphite pulps.  Svensk Papperstidn. 65: 535-544. and J. Nyren. 1970. pulp fibers. II.  Transverse compressibility of  Influence of cooking method, y i e l d ,  beating, and drying.  Tappi 53: 820-823.  and 0. Sundberg. 1960.  Strength loss due to chip  damage in acid b i s u l f i t e , bisulfite and sulfate pulps. Svensk Papperstidn. 63: 263-271. Hartshorne, N.H. and A. Stuart. 1960. . Crystals and the Polarising Microscope. 557  Edward Arnold, Ltd., London.  pp.  Hearle, J.W.S. 1958.  A fringed f i b r i l theory of structure in  crystalline polymers. J. Polymer S c i . 28: 432-435. . 1963. polymers.  The fine structure of fibers and c r y s t a l l i I.  Fringed f i b r i l structure. J. Appl.  Polymer Sci. 7: 1175-1192. . 1967.  The structural mechanics of fibers.  Polymer Sci. 20 (C): 215-251.  J.  - 101 -  Hentschel, P.A.A. 1959.  Structure - property relationship in  synthetic fiber papers.  Tappi 42: 979-982.  Hermann, H.G. , Stewart, CM. and K.J. Abitz. 1930.  Zur  rontgenographischen Structurforschung des Gelatinemic e l l s . Z. Physik. Chem. 10: 371-394. Hermans, P.H. 1951.  X-ray investigations on the crystallinity  of cellulose.  Makromol. Chem. 6: 25-29.  Higgins, H.G. and J. De Yong. 1966.  Viscoelasticity and  consolidation of the fibre network during free water drainage.  In F. Bolam (Ed. ).  Paper Web.  Consolidation of the  Tech. Sec. B.P. and B.M.A., London,  pp. 242-267. H i l l , R.L. 1967.  The creep behavior of individual pulp fibers  under tensile stress. Hirst, F.R.S. 1958. group.  Tappi 50: 432-440.  Chemical structure in the hemicellulose  In F. Bolam (Ed.).  Making Fibres.  Fundamentals of Paper  Tech. Sec. B.P. and B.M.A., Kenley.  pp. 93-105. Hoff, N.J. 1960.  Creep in Structures.  Colloquium held at  Stanford Univ..Berkeley. 375 pp. Holzer, W.F. and H.F. Lewis. 1950.  The characteristics of un-  bleached kraft pulps from western hemlock, Douglas f i r , western red cedar, loblolly pine and black spruce. VII.  Comparison of springwood and summerwood fibers  of Douglas f i r . Honeyman, J . 1959.  Tappi 33: 110-112.  Recent Advances in the Chemistry of Cellulose  and Starch. Heywood and Company, London. 366 pp.  - 102 -  Honeyman, J . and M.A. Parsons.1959. c e l l u l o s e and s t a r c h .  Molecular  In J . Honeyman (Ed. ).  Recent Advances i n the Chemistry Starch.  s t r u c t u r e of  of C e l l u l o s e and  I n t e r s c i e n c e P u b l . I n c . , New York. pp. 49-74.  Hunt, G.M. and G.A. G a r r a t t . 1967.  Wood P r e s e r v a t i o n .  3rd ed.  McGraw-Hill Book Co., New York. 433 pp. Ingmanson, W.L. and B.D. Andrews. 1959.  The e f f e c t  of b e a t i n g  on f i l t r a t i o n r e s i s t a n c e and i t s components of s p e c i f i c s u r f a c e and s p e c i f i c volume. and  R.P. Whitney. 1954.  of p u l p s l u r r i e s , I v a r s s o n , B.W.  1956.  Tappi  T a p p i 42: 29-35. The f i l t r a t i o n r e s i s t a n c e  t a p p i 37: 523-534.  Compression o f c e l l u l o s e f i b e r  sheets.  39: 97-104.  and body.  B. Steenberg.  1947.  III. Applicability  Paper as a v i s c o - e l a s t i c  of E y r i n g ' s and H a l s e y ' s  t h e o r y t o s t r e s s s t r a i n diagram o f paper.  Svensk  P a p p e r s t i d n . 50: 419-432. Iwanow, I . and R„ Hahn. I960.  On the a l k a l i  s o l u b i l i t y o f pulps,  Z e l l s t o f f P a p i e r 8: 451-454, 9: 4-9. II  Jackson,  M. and L. Ekstrom. 1964. c o m p r e s s i b i l i t y of paper.  S t u d i e s c o n c e r n i n g the Svensk P a p p e r s t i d n . 67:  807-821. Jane, F.W.  1970.  The S t r u c t u r e o f Wood. 2nd ed., Adam & C h a r l e s  B l a c k , London. 427 pp. Jayme, G. 1942.  P r e p a r a t i o n o f h o l o c e l l u l o s e and c e l l u l o s e w i t h  sod ium c h l o r i t e . not  C e l l u l o s e Chem. 20: 43-49.  seen, Chem. A b s t r . 37: 7663).  (Orig.  - 103 -  Jayme, G. and D. F e n g e l . 1961.  B e i t r a g z u r K e n n t n i s des  Feinbaus der F i c h t e n h o l z t r a c h e i d e n . i l .  Beobachtungen  II  an U l t r a d u n n s c h n i t t e n von d e l i g n i f i z i e r t e m H o l z und II  Ligningerusten. .  H o l z f o r s c h . 15: 97-102. 1961.  C o n t r i b u t i o n towards the  knowledge of the m i c r o s t r u c t u r e of springwood tracheids.  Examination o f u l t r a - t h i n  Roh-Werkstoff  s e c t i o n . Holz  19: 50-55.  and H. Hunger. 1962.  E l e c t r o n microscope  2-and 3-  d i m e n s i o n a l c l a s s i f i c a t i o n o f f i b r e bonding. F, Bolam  In  ( E d . ) . Formation and S t r u c t u r e o f Paper.  Tech. Sec. B.P„ and B.M.A., London, and W. Mohrberg. 1949.  pp. 135-170.  Quellungsmessungen  an l i g n i n -  haltigen Holocellulosen.  Das P a p i e r 3: 153-159.  n and A. von Koppen. 1950.  S t r u c t u r a l and c h e m i c a l  d i f f e r e n c e s between s u l f i t e and s u l f a t e pulps..  Das  P a p i e r 4: 373-378, 415-420, 455-462. ( o r i g i n a l not seen, B u l l . Jayne, B.A. 1962. (Ed.).  I n s t . Paper Chem. 21: 394).  M e c h a n i c a l t e s t s f o r wood.  I_n A.P. Schniewind  The M e c h a n i c a l B e h a v i o r o f Wood. Univ.  Calif.,  B e r k e l e y , pp. 105-118. J e n t z e n , C.A. 1964.  The e f f e c t  of s t r e s s applied during  d r y i n g on some of the p r o p e r t i e s o f i n d i v i d u a l fibres. Johanson,  T a p p i 47: 412-418.  F. and J . Kubat.  1964.  r e l a x a t i o n i n paper. Jones, R.L. 1963.  pulp  Measurements o f s t r e s s  Svensk P a p p e r s t i d n . 67: 822-832.  The e f f e c t o f f i b e r s t r u c t u r a l  compression  response o f f i b e r beds.  p r o p e r t i e s on  T a p p i 46: 20-27.  - 104 -  139.  J o r g e n s e n , L. 1958. The c h e m i s t r y F. Bolam ( E d . ) .  of pulp f i b r e s .  Fundamentals o f Paper Making F i b r e s .  T e c h . S e c . B.P. and B.M.A., K e n l e y . 140.  I_n  pp.. 107-128.  K a l l m e s , 0 „ J „ and G.A. B e r n i e r . 1962. M e c h a n i c a l p r o p e r t i e s of paper.  In F . Bolam ( E d . ) .  of P a p e r .  F o r m a t i o n and S t r u c t u r e  T e c h . S e c . B.P. and B.M.A., London,  pp.  369-388. 141.  K a r g i n , V.A. 1958. S t r u c t u r e and phase s t a t e o f p o l y m e r s . J . Polymer S c i . 30: 247-258.  142.  K a t u s c a k , S., H o r s k y , K. and M. M a h d a l i k . 1971. O x i d a t i o n o f l i g n i n w i t h oxygen and p e r o x i d e s . 53  143.  P a p e r i j a Puu.  ( 4 a ) : 197-202.  Kayama, T. and H.G. H i g g i n s . 1966. E f f e c t on f i b r e and paper p r o p e r t i e s o f bleaching treatments a p p l i e d t o Pinus r a d i a t a sulphate pulps.  144.  A p p i t a 19: 86-94.  K e l l o g g , R.M. and F.F. Wangaard. 1964. I n f l u e n c e o f f i b e r s t r e n g t h on sheet p r o p e r t i e s o f hardwood  pulps.  T a p p i 4 7 : 361-367. 145.  K i r b a c h , E . 1 9 7 1 . T e n s i l e and Compressive S t r e s s R e l a x a t i o n i n C o n i f e r o u s Wood T i s s u e s .  Unpub. R e p t , , F a c . F o r . ,  U n i v . B.C., Vancouver. 99 p p . 146.  K i t a z a w a , G. 1947. R e l a x a t i o n o f wood under c o n s t a n t  strain. .  T e c h . B u l l . No. 6 7 . , S t a t e U n i v . New Y o r k , C o l l e g e o f F o r e s t r y , S y r a c u s e . 12 p p . 147.  K o l l m a n n , F„ 1 9 6 1 . R h e o l o g i e und S t r u k t u r f e s t i g k e i t v o n H o l z . H o l z Roh-Werkstoff  148.  19: 73-80.  and W.A. C o t e . 1968. P r i n c i p l e s o f Wood S c i e n c e and Technology.  S p r i n g e r V e r l a g I n c . , New Y o r k . 592 p p .  -  von  K o p p e n , A.  1964.  between  Kress,  0.  105  -  Structural  sulfite  and  F.T.  and  northern  and  Ratcliff. kraft  and  kraft  1943.  chemical pulps.  differences  Tappi  47:  A comparison  of  Paper Trade  J.  pulps.  589-595.  southern 117  (17):  31-35. II  Kubat,  J.  1952.  Uber r h e o l o g i s c h e  Zeit.  129:  Relaxationsprozesse.  Koll.  73-77. II  .  1953.  Studien  Papier.  uber das  Svensk  plastische  Papperstidn.  56:  Fliessen  von  670-675.  II  Kurschner,  K. der  Lambert,  J.B.  1962.  Chemie des  Wissenschaften, 1970.  Scientific  L a n g e , P.W.  1945.  . of  shapes  Am.  68:  1954.  The  normal  1958.  distribution  the  mentals  Papermaking  B.M.A., K e n l e y .  1959.  of  r e a c t i o n wood  The  cell  pp.  Verlag  pp. molecules.  fast  lignin.  241-245.  lignin from  Svensk P a p p e r s t i d n .  The  Deutscher  a b s o r p t i o n av  48:  throughout  .  173  organic  distribution  and  of  of  VEB  58-69.  Ultraviolett  hardwoods.  .  Berlin.  The  Svensk P a p p e r s t i d n .  Holzes.  of  spruce 57:  the  In  wall.  cell  and  a  wall  few  525-537.  chemical  F.  Fibres.  i n the  Bolam Tech.  constituents  (Ed.). Sec  Funda-  . B.P.  and  147-185.  morphology  o f hardwood  fibres.  Tappi  42:  786-792.  Larsen,  L.E.  1970.  (Ed.). Nostrand  Bleaching-hypochlorite stage. Handbook o f Reinhold  Pulp Co.,  and New  In  K.W.  Paper Technology. York.  pp.  269-274.  Britt Van  - 106  160.  L a r s s o n , L . J . and  -  0. Samuelson. 1968.  Automatic  d e t e r m i n a t i o n of the c a r b o h y d r a t e p u l p , a l k a l i c e l l u l o s e and  chromatographic  composition  rayon.  i n rayon  Svensk P a p p e r s t i d n .  71: 432-435. 161.  Leaderraan, H.  1943.  E l a s t i c and  M a t e r i a l s and  Other High  of Washington, D.C. 162.  . 1958.  systems.  Theory and  163.  164.  Rheology,  V o l . I I . Academic P r e s s ,  Some a s p e c t s of the mechanical  Univ. C a l i f . , B e r k e l e y ,  of Wood.  1961.  Chemical  B a s s e t , K.H.,  composition T a p p i 44:  and  (Ed.).  Mechanical pp.  43-83.  physical properties  230-232.  McGinnes, E.A.  and  R.H.  Marchessault.  I n f r a r e d s p e c t r a of c r y s t a l l i n e p o l y s a c c h a r i d e s .  T a p p i 43: 1963.  Schniewind  properties  Behavior  L i a n g , C.Y.,  L i e s e , W.  (Ed.).  In A.P.  1960.  166.  Eirich  of h i g h polymers.  L e o p o l d , B.  Foundation  1-61.  of wood f i b r e s . 165.  Textile  pp.  In F.R.  Application.  York. pp. . 1962,  278  Polymers.  Filamentous  V i s c o e l a s t i c phenomena i n amorphous h i g h  polymeric  New  Creep P r o p e r t i e s of  1017-1024.  T e r t i a r y w a l l and warty l a y e r i n wood  cells.  J . Polymer S c i . 2 ( C ) : 213-219. 167.  . 1965.  The warty l a y e r .  In W.A.  Cote,  J r . (Ed.).  C e l l u l a r U l t r a s t r u c t u r e of Woody P l a n t s . Univ. P r e s s , S y r a c u s e , 168.  L i n d a h l , E., Moberg, C.-G.  and  pp.  251-269.  L. Stockman. 1959.  Del 2. S l u t b l e k n i n g av S u l f a t m a s s a med P a p p e r s t i d n . 62: 169.  L i n d g e r g , B. 61:  1958.  Peroxideblekning p e r o x i d . Svensk  308-317.  H e m i c e l l u l o s a n i ved.  675-679.  Syracuse  Svensk P a p p e r s t i d n .  - 107 -  L i n d b e r g , B. and H. Meier.  1957.  Norwegian s p r u c e . Luce, J . E . 1964.  S t u d i e s on glucomannans from  Svensk P a p p e r s t i d n .  60: 785-790.  R a d i a l d i s t r i b u t i o n o f p r o p e r t i e s through the  c e l l wall.  Pulp Paper Mag. Can. 65: T419-T423.  Lyne, L.M. and W. G a l l a y . 1954.  F i b r e p r o p e r t i e s and f i b r e -  water r e l a t i o n s h i p i n r e l a t i o n t o t h e s t r e n g t h and rheology  o f wet webs.  Pulp Paper Mag. Can. 55:  159-171. McKenzie, A.W.  and H.G. H i g g i n s .  p r o p e r t i e s of paper. alkali  1958. Part  on the i n f r a - r e d  b e a t i n g response  The s t r u c t u r e and  II.  The i n f l u e n c e o f  s p e c t r a , bonding c a p a c i t y and  of,wood and c o t t o n f i b r e s .  Svensk  P a p p e r s t i d n . 61: 893-901. McPherson, J . and O.E. Ohrn. 1960. p r o p e r t i e s of b i r c h pulps. 63:  Part  I. Svensk P a p p e r s t i d n .  762-768.  Majewski, Z.J. 1962. structure. of  H e m i c e l l u l o s e s and paper  Paper.  E f f e c t o f forming  processes  In F. Bolam (Ed. ).  on sheet  Formation  and S t r u c t u r e  Tech. Sec. B.P. and B.M.A., London, pp.  749-764. Manley, R.S.J. 1963. of  New i n v e s t i g a t i o n s on the f i n e s t r u c t u r e  cellulose.  Proceed.  Symposium, T o r o n t o , Marchessault, to  R.H. 1962.  First  Can. Wood Chem.  pp. 247-249.  A p p l i c a t i o n of i n f r a r e d  c e l l u l o s e and wood p o l y s a c c h a r i d e s .  spectroscopy Pure A p p l .  Chem. 5: 107-129. . 1964..  T e x t u r e and morphology o f x y l a n .  Actes du Symposium I n t e r n a t i o n a l , Grenoble,  Proc.  pp. 287-301.  179.  M a r c h e s s a u l t , R.H.  and  B.G.  Ranby. 1959.  H y d r o l y s i s of  c e l l u l o s e i n phosphoric a c i d s o l u t i o n - i n d u c t i v e effects. 180.  Svensk P a p p e r s t i d n . 62:  Mardon, J . , Monahan, R.E.,  C a r t e r , R.A.  and  230-240. J.E. Wilder.  1966.  Dynamic c o n s o l i d a t i o n o f paper d u r i n g c a l e n d e r i n g . In F . Bolam ( E d . ) .  C o n s o l i d a t i o n o f the Paper  T e c h . S e c . B.P.  B.M.A., London, pp. 576-623.  181.  and  , Q u i n t , R.J., W i l d e r , J . E . and Howe. 1964.  The change o f paper p r o p e r t i e s  machine c a l e n d e r s t a c k s .  Part I I .  Web.  B.I.  through  P u l p Paper  Mag.  Can. 65: T481-T498. 182.  Mark, R.E.  1967.  C e l l W a l l Mechanics of T r a c h e i d s .  U n i v e r s i t y P r e s s , New 183.  M a r r i n a n , H.J. and  Haven. 310  J . Mann. 1954.  Yale  pp.  A study o f i n f r a r e d s p e c t r o -  scopy o f hydrogen b o n d i n g ^ i n c e l l u l o s e .  J . Appl.  Chem. 4: 204-211. 184.  M a r t o n , R.  1959.  F i b e r geometry a s . r e l a t e d  T a p p i 42: 185.  to paper  bonding.  948-953.  M a r x - F i g i n i , M. and G.V.  S c h u l z . 1966.  Uber d i e K i n e t i k  und  den Mechanismus der B i o s y n t h e s e der C e l l u l o s e i n II  den hoheren P f l a n z e n .  Biochim. Biophys. Acta  112:  81-101. 186.  Mason, S.G.  1948.  49:  The r h e o l o g y o f p a p e r .  P u l p Paper Mag.  Can.  207-214. II  187.  M e i e r , H. 1955.  Uber den  Zellwandabbau durch  und d i e s u b m i k r o s k o p i s c h e und 188.  Birkenholzfasern.  .. 1957.  Holzvermorschungspilze  S t r u k t u r von F i c h t e n t r a c h e i d e n  H o l z Roh-Werkstoff 13:  Die T e r t i a r w a n d .  In E . T r e i b e r  (Ed.).  323-338. Die  Chemie der P f l a n z e n z e l l w a n d . S p r i n g e r V e r l a g , B e r l i n , pp. 213-223.  - 109 -  Meier,  H. 1960.  S t u d i e s on glucomannans from Norwegian s p r u c e .  III.  Partial hydrolysis.  A c t a . Chem. Scand. 14:  749-756. . 1961.  The d i s t r i b u t i o n o f p o l y s a c c h a r i d e s  fibres. . 1962.  J . Polymer S c i . 51: 11-18. On the b e h a v i o r  different 65: and  of wood h e m i c e l l u l o s e s under.  pulping conditions.  Svensk P a p p e r s t i d n .  589-594. K.C.B. W i l k i e . 1959.  saccharides (Pinus  L . ) . H o l z f o r s c h . 13: 177-182.  The r e t a k e of x y l a n d u r i n g a l k a l i n e  a critical 19:  The d i s t r i b u t i o n of p o l y -  i n the c e l l w a l l o f t r a c h e i d s of p i n e  silvestris  M e l l e r , A. 1965.  .  i n wood  a p p r a i s a l o f the l i t e r a t u r e .  Holzforsch.  118-124.  1965.  The c h e m i s t r y  saccharides  o f the r e a c t i o n s w i t h  , Britt,  K.W.  extraction.  poly-  i n the a l k a l i n e e x t r a c t i o n s t a g e of  b l e a c h i n g of wood p u l p s .  and  pulping:  T a p p i 48: 231-238.  and R.P. S i n g h . In"K.W. B r i t t  Paper Technology.  1970.  (Ed.).  Bleaching-alkaline Handbook of Pulp  Van Nostrand R e i n h o l d  Co.,  New York. pp. 249-262. II  Meyer, K.H. and H. Mark. 1929.  Uber den Bau des k r i s t a l l i s i e r t e n  A n t e i l s der C e l l u l o s e I I .  Z. P h y s i k . Chem. B 2:  115-145. and  L. Misch.  1937.  P o s i t i o n des atomes dans l e  nouveau modele s p a t i a l de l a c e l l u l o s e .  Helv.  Chim.  A c t a . 20: 232-244. Mikchailow,  N.V.  1958.  On the phase s t r u c t u r e of c e l l u l o s e .  J. Polymer S c i . 30: 259-269.  - 110 -  M u h l e t h a l e r , K. 1965. microfibril.  The f i n e s t r u c t u r e o f the c e l l u l o s e In W.A.  Cote, J r . ( E d . ) .  U l t r a s t r u c t u r e o f Woody P l a n t s .  Cellular  Syracuse  Univ.  P r e s s , S y r a c u s e , pp. 191-198. Murakami, R. and H. Yamada. 1971.' The dynamic v i s c o e l a s t i c i t y o f hardboard treatment.  s h e e t s . IV. E f f e c t o f d e l i g n i f y i n g  J . Jap. Wood Res. Soc. 17: 288-291. and  K. M o r i . 1971.  p r o p e r t i e s o f p u l p s h e e t s by removal  The change o f some of h e m i c e l l u l o s e .  J . Jap. Wood Res. Soc. 17: 341-345. Murphey, W.K.  1963.  C e l l w a l l c r y s t a l l i n i t y as a f u n c t i o n o f  t e n s i l e s t r a i n . F o r e s t Prod. J . 13: 151-155. Mutton, D.B. 1964.  Cellulose chemistry.  P u l p Paper Mag. Can. 65  T41-T51. Narayanamurti,  D., V i c t o r , V . J . and S.F. X a v i e r . 1970.  Einfluss  v e r s c h i e d e n e r C h e m i k a l i e n auf das K r i e c h e n und andere E i g e n s c h a f t e n des H o l z e s . N e l s o n , R. 1961.  H o l z t e c h n . 11: 161-167.  The use o f h o l o c e l l u l o s e s t o study  cellulose  super m o l e c u l a r s t r u c t u r e . J . Polymer S c i . 51: 27-58. N i k i t i n , N.I. 1962.  The Chemistry  o f C e l l u l o s e and Wood.  I s r a e l Program f o r S c i e n t i f i c T r a n s l . , New York. 1966. 691 pp. N i s s a n , A.H. 1955.  A m o l e c u l a r approach  viscoelasticity. .  1955.  Nature  t o the problem o f  175: 424.  The r o l e o f the hydrogen bond i n the  r h e o l o g i c a l behavior of c e l l u l o s e sheets. Res. _.  Textile  J . 25: 780-788.  1956.  The r h e o l o g i c a l p r o p e r t i e s o f c e l l u l o s e  s h e e t s : r e t r o s p e c t and s y n t h e s i s .  T a p p i 39: 93-97.  N i s s a n , A.H.  1957.  The  r h e o l o g i c a l behavior  bonded s o l i d s . . 1959.  The  T r a n s . Faraday S o c . 53:  700-721.  r h e o l o g i c a l b e h a v i o r o f hydrogen-  bonded s o l i d s . . 1962.  of hydrogen-  T r a n s . Faraday Soc. 55:  General  2048-2053.  p r i n c i p l e s of adhesion  with  p a r t i c u l a r r e f e r e n c e to the hydrogen bond. F . Bolam ( E d . ) . T e c h . S e c . B.P. and H.G.  F o r m a t i o n and and  S t r u c t u r e of P a p e r .  B.M.A., London, pp.  H i g g i n s . 1959.  A molecular  the problem o f v i s c o e l a s t i c i t y . and  S.S.  S t e r n s t e i n . 1962.  elastic material. N o l a n , W.J.  1970. (Ed. ).  Co.,  New  approach t o 1477-1478.  C e l l u l o s e as a v i s c o -  Alkaline pulping chemistry.  Nostrand Reinhold  119-134.  Nature 184:  Pure A p p l . Chem. 5:  Handbook of P u l p and  Jjn  131-145. In K.W.  Britt  Paper T e c h n o l o g y .  Y o r k . pp.  Van  135-143.  II  Ohrn, O.E.  and  J . C r o o n . 1960.The o c c u r r e n c e  of  partially  a c e t y l a t e d 4-0-methyl-glucuronoxylans i n o r d i n a r y birch  sulphite pulps.  Svensk P a p p e r s t i d n . 63:  601-605.  ti and B.F. Enstrom. 1960. H e m i c e l l u l o s e s and paper p r o p e r t i e s of b i r c h p u l p s . P a r t I I . Svensk P a p p e r s t i d n . 63: Ott,  E., S p u r l i n , H.M.  and  817-822. M.W.  Grafflin.  Cellulose Derivatives. New Page, D.H.  Y o r k . 510  1960. their  structure.  and  Inc.,  pp.  direct observation. The  Cellulose  Interscience Publ.  Fibre-to-fibre.bonds.  ^.1963.  1954.  rheology T a p p i 46:  P a r t 1. A method f o r  Paper T e c h n o l .  1: 407-411.  of paper i n terms of i t s m o l e c u l a r 750-756.  - 112 -  221.  Page, D.H. 1967. 50:  222.  The collapse behavior of pulp fibers.  449-455.  and J.H. DeGrace. 1967.  The delamination of fiber  walls by beating and refining. 223.  Tappi  Tappi 50: 489-495.  , Sargent, J.W. and R. Nelson. 1966. paper in the cross-section.  Structure of  In F. Bolam (Ed.).  Consolidation of the Paper Web.  Tech. Sec. B.P. and  B.M.A., London, pp. 313-352. 224.  and P.A. Tydeman. 1960. 2.  Fibre-to-fibre bonds. Part  A preliminary study of their properties in paper  sheets. 225.  Paper Technol. 1: 519-530. and M. Hunt. 1962.  The behavior of  fibre-to-fibre bonds in sheets under dynamic conditions. In F. Bolam (Ed.).  Formation and Structure of Paper.  Tech. Sec. B.P. and B.M.A., London, pp. 249-263. 226.  Panshin, A.J., de Zeeuw, C. and H.P. Brown. 1964. of Wood Technology.  Textbook  Vol. 1. 2nd ed. McGraw-Hill Book  Co., New York. 643 pp. 227.  Parker, J.L. 1962.  The effects of ethylamine decrystallisation  of cellulose fibers on the viscoelastic properties of paper. 228.  Tappi 45: 936-943.  Passaglia, E. and H.P. Koppehele. 1958.  The strain dependence  of stress relaxation in cellulose monofilaments. J. Polymer Sci. 33: 281-289. 229.  Paszner, L. 1968.  Effect of inter- and intra- crystalline  swelling on cellulose degradation by gamma-rays. Svensk Papperstidn. 71: 822-828. 230.  Pearl, I.A. 1967.  The Chemistry of Lignin.  Inc., New York. 339 pp.  Marcel Dekker  Pentoney, R.E. and R.W. Davidson. 1962. Rheology and the study of wood. Forest Prod. J . 12: 243-248. . II  Perila, 0. 1961. The chemical composition of carbohydrates of wood c e l l s .  J . Polymer Sci. 51: 19-26.  Petterson, S.E. and S.A. Rydholm. 1961. Hemicelluloses and paper properties of birch pulps.  Part III. Svensk  Papperstidn. 64: 4-17. Pew, J.C. and P. Weyna. 1962. Fine grinding, enzyme digestion, and the lignin-cellulose bond in wood. Tappi 45: 247-256. II  Poljak, A. 1948. Holzaufschluss mit Peressigsaure.  Angew.  Chemie 60 (A): 45-46. it  . 1951. Holzaufschluss mit Peressigsaure I I . II  Cellulosebestimmung mit Peressigsaure. Holzforsch. 5: 31-33. Preston, R.D. 1952. The Molecular Architecture of Plant Cell Walls.  Interscience Publ. Inc., New York.211 pp.  . 1962. The electron microscopy and electron diffraction analysis of natural cellulose. In R.J.C. Harris (Ed.). The Interpretation of Ultrastructure.  Academic Press, New York. pp. 325-348. II  Raczkowski, J . 1969. Der Einfluss von Feuchtigkeitsanderungen auf das Kriechen des Holzes.  Holz Roh-Werkstoff 27:  232-237. Ranby, B.G. 1958. The fine structure of cellulose f i b r i l s . In F. Bolam (Ed. ). Fibres.  Fundamentals of Paper making  Tech. Sec. B.P. and B.M.A., Keriley.  pp. 55-82.  - 114 -  Ranee, H.F. 1953.  Mechanical properties of paper.  Meredith (Ed. ).  In  R.  Mechanical Properties of Wood and  Paper. North Holland Publ. Co., Amsterdam, pp. 99-289. . 1956.  The formulation of methods and objectives  appropriate to the rheological study of paper. Tappi 39: 104-115. Rapson, W.H.  1956.  The role of pH in bleaching pulp.  Tappi  39: 284-285. . 1970. (Ed.).  Bleaching-chlorine dioxide.  In K.W.  Britt  Handbook of Pulp and Paper Technology.  Van  Nostrand Reinhold Co., New York. pp. 275-286. , Anderson, C.B. and G.F. King. 1958.  Carbonyl  groups in cellulose and color reversion. Tappi 41: 442-447. Rebenfeld, L. 1965.  Morphological foundations of fiber proper-  t i e s . J . Polymer S c i . 9 (C): 91-112. II  Richtzenhain, H. and B. Abrahamson. 1954. Abbau von Polysacchariden. Hemicellulose.  II. M i t t e i l . : Abbau von  Svensk Papperstidn. 57: 538-541.  Robertson, A.A. and S.G. Mason. 1962. in papermaking.  Uber den alkalischen  The role of fibre collapse  In F. Bolam (Ed. ).  Formation and  Structure of Paper. Tech. Sec. B.P, and B.M.A., London, pp. 639-647. Roelofson, P.A. 1959.  The Plant Cell Wall.  Springer Verlag,  Berlin. 335 pp. n  Runkel, R.O.H. 1949.  Uber die Herstellung von Zellstoff aus  Holz aus der Gattung Eucalyptus und Versuche mit zwei unterschiedlichen Eucalyptusarten. 3: 476-490.  Das Papier  Rydholm, S.A, 1965.  Pulping Processes.  Interscience Publ.  Inc., New York. 1269 pp. Sachs, I., Clark, I.T. and J.C. Pew. 1963.  Investigation of  lignin distribution in the c e l l wall of certain woods. J. Polymer Sci. 2 (C): 203-212. Saeman, J.F., Moore, W.E., Mitchell, R.L. and M.A. M i l l e t . 1954.  Techniques for the determination of pulp  constituents by quantitative paper chromatography. Tappi 37: 336-343. Sarkanen, K.V. and C.H. Ludwig. 1971.  Lignins.  Interscience  Pub. Inc., New York. pp. 695-768. Schniewind, A.P. 1968.  Recent progress in the study of the  rheology of wood. Wood S c i . Tech. 2: 188-206. II  Schoniger, W., Lieb, H. and M.G. El Din Ibrahim. 1954.  Rapid  microanalytical determination of acetyl and C-methyl groups. Mikrochim. Acta. pp. 96-103. Schuerch, C. 1952.  The solvent properties of liquids and their  relation to the s o l u b i l i t y , swelling, isolation, and fractionation of l i g n i n . J. Am. Chem. Soc. 74: 5061-5067. . 1963. (Ed.),  The hemicelluloses.  Ln B.L. Browning  The Chemistry of Wood. Interscience Pub.  Inc., New York. pp. 191-243. Schulz, J.H. 1961.  The effect of straining during drying on  the mechanical and viscoelastic behavior of paper. Tappi 44: 736-744. Scott-Blair, G.W. 1953.  Theoretical approaches in rheology.  B u l l . B r i t . Soc. Rheology 39: 2-6.  - 116 -  Seborg, C.O. and F.A. Simraonds. 1947. Additional data on the recovery of wet pulp mats from compressive deformation. Paper Trade J. 125 (15): 63-67. and P.K. Baird. 1939. Properties of wet fiber mats: relation of recovery from compressive deformation to sheet properties.  Paper Trade J .  109 (8): 35-42. Sharma, M.G. 1965. Viscoelasticity and Mechanical Properties of Polymers. Penn. State Univ., Univ. Park. 331 pp. Shimada, I. and T. Kondo. 1968. Studies on peracid cooking. (2).  Influence of chip dimensions and pH of cooking  liquor.  J . Jap. Tappi 22: 258-264.  Simonson, R. 1971. The hemicellulose in the sulfate pulping process.  Part 7. Crystallised xylan-lignin compounds.  Svensk Papperstidn. 74: 268-270. . 1971. Sorption of hemicellulose-lignin compounds on cotton. Svensk Papperstidn. 74: 519-520. II  II  Sjostrom, E. 1971. Gas chromatographic determinations of carbohydrates in wood and pulp.  Cellulose Chem. Tech.  5: 139-145. II  and B. Enstrom. 1966. Spectrophotometric  determina-  tion of residual lignin in pulp after dissolution in cadoxen. Svensk Papperstidn. 69: 469-476. II  , Haglund, P. and J . Janson. 1966. Quantitative determination of carbohydrates in cellulosic materials by gas-liquid chromatography. Svensk Papperstidn. 69: 381-385.  Smith, J.K., Kitchen, W.J. and D.B. Mutton. 1963. The structural study of cellulosic fibres.  J . Polymer  S c i . 2 (C): 499-513. Solechnik, N. and V.P. Alikin. 1959. The problem of deformation and beating of technical cellulose.  Bumazh. Prom.  34: 7-8. I960.  The effect of poly-  disparity on viscoelastic properties of pulp and i t s beatability.  Nauch. Trudy, Leningrad. 91: 49-64.  Spiegelberg, H.L. 1966. Effect of hemicelluloses on mechanical properties of individual pulp fibers. Tappi 49: 388396. Springer, E.L., Nordman, L. and N-L. Virkola. 1964. Factors influencing the dynamic strength of pine sulfate pulp.  Tappi 47: 463-467.  Stamm, J.A. 1964. Wood and Cellulose Science. Press Company, New York.  The Ronald  549 pp.  Steenberg, B. 1947. Paper as a visco-elastic body. I. General survey.  Svensk Papperstidn. 50: 128-140.  . 1947. Paper as a visco-elastic body. I I . Importance of stress relaxation in paper. Svensk Papperstidn. 50: 346-350. Sternstein, S.S. and A.H. Nissan. 1962. A molecular theory of the viscoelasticity of a three-dimensional hydrogenbonded network.  In F. Bolam (Ed.). Formation and  Structure of Paper. Tech. Sec. B.P. and B.M.A., London, pp. 319-337. . 1964. Cellulose - f i b e r bonding. Tappi 47: 1-6.  - 118 -  Stobo, W.E. and J.K. Russel. 1947. The effect of certain variables in the bleaching of groundwood with sodium peroxide.  Pulp Paper Mag. Can. 48 (C): 224-232.  Stone, J.E. 1957. The effective capillary cross-sectional area of wood as a function of pH. Tappi 40: 539-541. . 1963. Bond strength in paper.  Pulp Paper Mag.  Can. 64: T528-T532. and 0. Kallmes. 1957. The rheology of cooked wood. III.  Effect of mild delignifying agents.  Pulp Paper  Mag. Can. 58: T191-T196. Sullivan, J.D. 1968. Wood cellulose protofibrils.  Tappi 51:  501-507. Suzuki, M. 1968. Mechanical deformation of crystal lattice of cellulose in Hinoki wood. J . Jap. Wood Res, Soc. 14: 268-275. Tamolang, F.N. and F.F. Wangaard. 1961. Relationships between fiber characteristics and pulp sheet properties. Tappi 44: 201-216. TAPPI. 1958. Forming handsheets for physical tests of pulp. T205-m-58. Tech. Assoc. Pulp and Paper Ind., New York. TAPPI. 1960. Solubility of pulp in sodium hydroxide at 20°C. T235 m-60. Tech. Assoc. Pulp and Paper Ind., New York. TAPPI. 1961. Alpha-,beta-, and gamma-cellulose in pulp. T203 os-61.  Tech. Assoc. Pulp and Paper Ind., New York.  Thompson, N.S., Kremers, R.E. and O.A. Kaustinen. 1968. Effects of alkali on mature and immature jack pine holocelluloses.  Tappi 51: 123-131.  - 119 -  Thompson, N.S., Peckham, J.R. and E.F. Thode. 1962. in f u l l and  chemical pulping.  related  T i m e l l , T.E. 1959.  .  I I . Carbohydrate changes  physical effects.  T a p p i 45: 433-442.  I s o l a t i o n . o f h o l o c e l l u l o s e from  (Pinus banksiana). 1964.  Studies  jack pine  P u l p Paper Mag. Can. 60: T26-T28.  Wood h e m i c e l l u l o s e s .  Advan.  Carbohydrate  Chem. 19: 247-302; 20: 409-483. . 1965. Jr.  (Ed.).  Syracuse .  Wood and bark p o l y s a c c h a r i d e s .  1967.  Cote  C e l l u l a r S t r u c t u r e o f Woody P l a n t s .  Univ. P r e s s , S y r a c u s e , pp. 127-156. Recent  hemicelluloses.  p r o g r e s s i n the c h e m i s t r y o f wood Wood S c i . Tech.  and A. T y m i n s k i . mannan from white  1957. spruce.  T^nnesen, B.A. and 0. E l l e f s e n . possibility  T r e l o a r , L.P.G. 1960.  1: 45-70.  The s t r u c t u r e o f a g l u c o T a p p i 40: 519-522.  1960.  Chain-folding  - a  t o be c o n s i d e r e d i n c o n n e c t i o n w i t h t h e  c e l l u l o s e molecule?  crystals:  J-n W.A.  Norsk Skog Ind. 14: 266-269.  C a l c u l a t i o n s o f e l a s t i c moduli o f polymer  I. P o l y e t h y l e n e and n y l o n 66.  Polymer 1:  95-103. . 1960. crystals:  C a l c u l a t i o n s o f e l a s t i c moduli  II.  Terylene.  Polymer 1: 279-289.  . 1961. C a l c u l a t i o n s o f e l a s t i c moduli crystals:  III. Cellulose.  o f polymer  Polymer 1: 290-303.  Tsoumis, G. 1968. Wood as Raw M a t e r i a l . 276 pp.  o f polymer  Pergamon P r e s s , Oxford  - 120  Turunen, K.,  Arvinen,  -  A. and  J . Turunen. 1971.  Improved  chromatographic method f o r the d e t e r m i n a t i o n c a r b o h y d r a t e c o m p o s i t i o n s of h i g h a l p h a Paperi Ullman, U.  1971. Can.  Uprichard,  j a Puu.  53:  J.M.  The  1957.  Appita  S t u d i e s based on  c e l l u l o s e s o l v e n t s based on  van  den  j a Puu  Akker, J.A. Tappi  pulps.  Pulp Paper  a l p h a - c e l l u l o s e content  the c h l o r i t e p r o c e d u r e .  Paperi  39:  1959.  42:  the  19:  of wood by  36-39.  improvement  iron tartaric  of  a c i d complex.  245-252. S t r u c t u r a l aspects  of b o n d i n g .  1962.  Some t h e o r e t i c a l c o n s i d e r a t i o n s on  m e c h a n i c a l p r o p e r t i e s of f i b r o u s s t r u c t u r e s . F. Bolam  (Ed. ).  Tech. Sec.  B.P.  The and  , Lathrop,  Tappi  41:  W a l l i s , A.F.A, 1971.  Voelker,  S o l v o l y s i s by  Sarkanen and  1949.  J_n  S t r u c t u r e of Paper.  B.M.A., London, pp.  A.L.,  M.H.  205-239.  and  L.R.  to sheet  Dearth. strength.  C.H.  a c i d s and  bases  Ludwig ( E d . ) .  Inc., New  York. pp.  (of  lignin).  Lignins. 345-372.  M i c e l l a r o r g a n i s a t i o n i n primary c e l l  walls.  Nature 164:366. .  1951.  the  416-425.  I n t e r s c i e n c e Publ. Wardrop, A.B.  Formation and  Importance of f i b e r s t r e n g t h  In K.V,  Mag.  940-947.  .  1958.  the  T151-T157.  1965.  V a l t a s a a r i , L.  of  189-194.  Newsprint q u a l i t y c o n t r o l .  72:  gas  C e l l w a l l o r g a n i s a t i o n and  o f the x y l a n .  A u s t r a l . J . S c i . Res.  the B 4:  properties 391-414.  Wardrop, A.B. 1954. Fine structure of conifer tracheids. Holzforsch. 8: 12-29. .1954. The raicellar system in cellulose fibres. Biochem. Biophys. Acta 13: 306-307. . 1957. The phase of lignification in the differentiation of wood fibres.  Tappi 40: 225-243.  . 1963. Morphological factors involved in the pulping and beating of wood fibres.  Svensk Papperstidn.  66: 1-17. . 1964. The structure and formation of the c e l l wall in xylem.  In M.H. Zimmermann (Ed. ). The  Formation of Wood in Forest Trees. Inc., New York.  Academic Press  pp. 87-134.  and R.D. Preston. 1951. The submicroscopic organisation of the c e l l wall in conifer tracheids and wood fibres.  J . Exp. Botany 11: 20-22.  Watson, A.J. and J.G. Hodder. 1954. Relationship between fibre structure and handsheet properties in Pinus taeda . Appita 8: 290-307. , Wardrop, A.B., Dadswell, H.E. and W.E. Cohen. 1952. Influence of fibre structure on pulp and paper properties.  Appita 6: 243-269.  Wellwood, R.W. 1962. Tensile testing of small wood samples. Pulp Paper Mag. Can. 63: T61-T67. Wenzl, H.F.J. 1970. The Chemical Technology of Wood. Academic Press, New York. 692 pp.  - 122 -  Wilder, H.D. I960. The compression creep properties of wet pulp mats. Tappi A3: 715-720. Wise, L.E., Murphy, M. and A.A. D'Addieco. 19A6. Chlorite holocellulose, i t s fractionation and bearing on summative wood analysis.  Paper Trade J . 122 (2):  35-A3. Yean, W.Q. and D.A.I. Goring. 196A. Simultaneous sulphonation and fractionation of spruce wood by a continuous flow method. Pulp Paper Mag. Can. 65: T127-T132. II  II  Ylinen, A, 1965. Uber die Bestimmung der zeitabhangigen elastischen und Festkeitseigenschaften des Holzes mit Hilfe eines allgemeinen nichtlinear viskoelastischen rheologischen Modells.  Holz Roh-Werkstoff  23: 193-196. n  Yllner, S. and B. Enstrom.  1956. Studies of the adsorption  of xylan on cellulose fibres during the sulphate cook.  Svensk Papperstidn. 59: 229-232.  Zinbo, M. and T.E. Timell. 1965. The degree of branching of hardwood xylans.  Svensk Papperstidn. 68: 6A7-662.  TABLES  - 124 -  All values in per cent of extractive-free wood.  Component  Red mople (Acer rubrum L.)  Cellulose Lignin Glucuronpxy Ian Glucomannan Pectin, starch  45 24 25 4 2  White birch (Befu/a papyri fera Marsh.) 42 19 35 3 1  Component  Balsam fir (Abies bolsameo [L.] Mill)  Cellulose Li gnin Arabinoglucuronoxylan Galoctoglucomannan Pectin, starch  42 29 9 18 2  T a b l e 1.  Trembling aspen (Populus tremuloides Michx.) 48 21 24 3 4  White spruce (Piceo g louco Eastern white pine tMoen chl Voss) (Pinus strobus L.) 41 27 13 18 1  41 29 9 18 3  The c h e m i c a l c o m p o s i t i o n o f woods from t h r e e angiosperms and t h r e e c o n i f e r s ( a f t e r T i m e l l (294)).  -125 -  T a b l e 2 / a . D e s c r i p t i o n o f p u l p s used i n t h e s t u d y .  Product Code No.  Wood source  0-1(9-1)°)  C  0-2(9-2)  A  0-3(5-1)  C  0-4(1-3)  C  )  Pulp type  Alphacellulose  Pulping process Additional or method o f pulping p r e p a r a t i o n (and treatments s t a r t i n g experi-. mental m a t e r i a l ) )  (W)  —  TAPPI  CW)  —  standard  (s)  T.203 os— 61 7  +  (S)  -  Sulphate  (S)  ' C  Sulphate  (S)  1-3  c  Sulphate  (S)  1-4  c  Sulphate  (S)  -  2-1  c  Sulphite  (S)  _  2-2  c  Sulphite  (S)  2-3  A  Sulphate  Cs)  2-4  C+A  Sulphate  (S)  3-1  C  Sulphite  (S)  3-2  C  Sulphite  (s)  3-3  C  Sulphate  (s)  -  3-4  C  Sulphate  (s)  -  4-1  C  Sulphite  (S)  Sulphite  (S)  1-1  C  1-2  4-2 a  )  k) c  )  L  Viscose pulps  1  i  f  -  C o n i f e r o u s ( C ) , Angiospermous ( A ) . S t a r t i n g e x p e r i m e n t a l m a t e r i a l as wood (W), p u l p s l u r r y (P) o r p u l p sheet ( S ) .  fibre  Numbers i n b r a c k e t s r e f e r t o code No. o f p u l p s used for alpha-cellulose preparations.  - 126 -  Table 2/b. Product Code No.  Wood source  5-1  C  6-1  )  Pulp type  Sulphite  (S)  —  c  Sulphite  Cs)  Bleached.  7-1  c  Sulphate  (P)  Unbleached  7-2  c  Sulphate  (P)  Bleached  8-1  c  Sulphate  (s)  Bleached  Sulphate  (s)  Bleached  Chlorite  (w)  —  Chlorite  (W)  —  Peracetic acid (W) Peracetic (W) acid Mechanical ( P )  —  Unbleached  Mechanical ( P )  Bleached  Mechanical (P)  Unbleached  Mechanical ( P )  Bleached  8-2 9-1  10% c+  90% A  Acetate  Pulping process Additional or method of pulping preparation (and treatments s t a r t i n g experi-. mental material ))  Paper grade  r  C  9-2  A  9-3  C  9-4  A  10-1  C  10-2  C  10-3  A  10-4  A  Holocellulose r .  Grc>undwood r  - 127 -  T a b l e 3/a. Summative d a t a ( i n p e r cent o f e x t r a c t i v e - f r e e wood) f o r c h e m i c a l c o m p o s i t i o n o f . p u l p s t e s t e d i n the s t u d y . Values f o r c e l l u l o s e and t o t a l amount o f h e m i c e l l u l o s e s have been a d j u s t e d a c c o r d i n g to r a t i o s : o f glucose-mannose i n i s o l a t e d wood.glucomannans ( i n c o n i f e r s 1:3, and i n pored wood 1 : 2 ( 2 9 5 ) ) .  Component  Alpha-cellulose 0-1  Acetyl Uronic  0-2  —  anhydride  Residues o f : Galactose  -  -  -  -  preparations 0-3  -  0-4  —  -  -  -  -  Glucose  92.9  97.1  99.5  99.2  Mannose  6.2  2.0  0.5  40.1  0.1  -  0.8  Xylose  0.6  1.3  0.2  0.5  Rhamnose  . -  90.8  96.1  99.3  99.0  8.9  4.4  0.9  1.5  100.5  100.2  100.5  Arabinose  ; Cellulose ! Hemicelluloses ! Lignin  -  -  —  —  -  -  i  | Total  99.7  I  -  Table  128 -  3/b.  Component  1-1  -  Acetyl Uronic  anhydride  Residues o f : Galactose Glucose Mannose Arabinose Xylose Rhamnose Cellulose Hemicelluloses Lignin  -  95.1  ;  Viscose  pulps  1-2  1-3  1-4  -  -  ; :  97.0'  -  —  -  -  96.6  97.5  2.4  2.0  1.8  2.0  ^0.1  0.1  /.0.1  <0.1  1.9  2.4  0.8  0.7  -  -  —  94.3  96.3  96.0  96.8  5.1  5.2  3.2  3.4  —  —  -  -  i.  Total  99.4  j 101.5  j i  99.2  100.2  - 129 -  l i a b l e 3/c.  Viscose pulps  Component 2-1  2-2  2-3  2-4  -  -  -  -  Acetyl Uronic  -  anhydride  Residues o f :  -  Galactose  -  mm*  -  -  Glucose  92.5  97.3  94.2  96.3  Mannose  2.3  1.5  1.0  0.7  <0.1  ^0.1  0.1  ^0.1  Xylose  1.8  1.9  2.6  1.2  Rhamnose  '  Arabinose  Cellulose Hemicelluloses Lignin  Total  —  -  —  91.7  96.8  93.7  96.1  4.9  3.9  4.2  2.2  —  96.6  — •  100.7  —  97.9  —•  98.3  |  - 130 -  Table  3/d.  Viscose pulps  Component  3-1 Acetyl Tronic  anhydride  -  3-2  3-3  3-4  -  -  -  -  -  -  -  Residues o f : Galactose  -  mm-  Glucose  93.1  92.4  96.1  96.5  Mannose  1.8  3.5  1.6  1.6  ^0.1  -:0.1  40.1  Xylose  1.7  1.4  1.9  Rhamnose  .-  -  -  Cellulose  92.5  91.2  95.6  96.0  4.1  6.1  4.0  2.7  97.3  | 99.6  98.7  Arabinose  Hemicelluloses Lignin  Total  —  96.6  -  40.1.  0.6  -  -  - 131 -  Table  3/e. •  1  Viscose pulps  Component  Acetate Bleached pulp s u l p h i t e pulp  4-1  4-2  5-1  6-1  -  -  -  3.1 0.9  -  -  -  0.2  Glucose  97.0  93.9  97.0  86.5  Mannose  2.3  2.2  2.2  7.2  ZO.l  *0.1  ^0.1  0.3  1.5  1.5  1.2  96.2  93.2  96.3  84.1  4.6  4.4  4.1  17.9  Acetyl Uironic  anhydride  R e s i d u e s of:. Galactose  Arabinose Xylose  —  Rhamnose  Cellulose Hemicelluloses Lignin  Total *)  —  100.8  —  97.6  -  100.4  0.7  102.7  v a l u e s i n d i c a t e t o t a l x y l o s e r e s i d u e s as o b t a i n e d from gas- l i q u i d chromatography measurements ( i n b r a c k e t s ) and c o r r e c t e d f o r x y l o s e r e s i d u e s i n a l d o b i o u r o n i c a c i d groups which r e s i s t e d a c i d h y d r o l y s i s ( a c c o r d i n g to Meier and W i l k i e (192} and Zinbo . and T i m e l l (327)' ) ,  -  132 -  T a b l e 3/f.  Component  Unbleacheds u l p h a t e pulpsi  \  7-1  anhydride  1.1  0.7  0.7  1.6  0.3  0.3.  0.2  0.2  Acetyl Uronic  Bleached; s u l p h a t e p u l p s  / 7-2  -  8-1  8-2  -  -  Residues o f r •Galactose Glucose  74.6  83.4  83.1  83.0  Mannose  7.5  8.4  7.2  1.5  Arabinose  0.5  0.5  0.3  0.5  6.0 (5.3)*)  6.0 (5.5)*)  7.4 (6.9)*)  Cellulose  72.1  80.6  80.7  82.2  Hemicelluloses  17.9  18.7  18.2  19.3  9.1  1.0  0.3  0.5  100.3  99.2  Xylose Rhamnose  Lignin  Total  -  99.1  -  -  14.7 (13.6)*)  -  • " ! 102.0 j  - 133 -  Table 3/g.  H o l o c e l l u l o s e pulps  Component 9-1  9-2  9-3  9-4  Acetyl  5.1  6.0  3.8  5.6  "(Ironic anhydride  3.0  3.0  2.6  2.2  0.9  0.6"'  1.1  0.7  Residues of: Galactose Glucose  72.4  75.1  71.7  73.8  Mannose  11.9  4.3  12.0  4.6  0.4  0.3  0.5  0.3  Arabinose Xylose Rhamnose  5.4 13.3 (3.4)*] (11.3)*) 0.1  Cellulose  68.5  73.0  67.7  71.5  Hemicelluloses  30.6  29.7  29.7  28.1  0.3  0.4  0.3  0.4  99.4  103.1  Lignin Total  -  j  5.7 (4.0)*)  12.3 (10.8)*)  -  0.1  100.0  97.7 t  j  T a b l e 3/h.  Groundwoods Component  10-1  10-2  10-3  10-4  3.7  3.8  4.7  4.7  2.8  2.8  4.0  4.0  1.2  1.1  1.0  1.2  Glucose  47.0  46.5'  50.5  50.8  Mannose  12.4  12.7  2.9  2.9  0.5  0.6  0.7  0.6  Acetyl llronic  anhydride  R e s i d u e s oft. Galactose  Arabinose  5.4 (3.6)*)  Xylose  16.4 5.7 (13.8)*) (3.9)*) 0.1 0.3  16.8 (14.2)*)  Rhamnose  0.1  Cellulose  42.9  42.2  49.0  49.3  Hemicelluloses  30.1  31.0  31.5  31.9  Lignin  30.5  30.3  21.7  21.6  | 103.5  103.5  102.2  ; 102.8  r  ! Total i  0.2  f  J  j i  - 135 T a b l e 4/a.  Summary o f 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 r e s u l t s on p u l p s t e s t e d i n the study as r e a d a f t e r 35 min r e l a x a t i o n time (1 - £ ( 3 5 m i n ) / £ ( 0 ) ) f o l l o w i n g s t e e p i n g i n water o r c a u s t i c . 1 - £ ( 3 5 min) £ ( o )  Product H20 , distilled  Code No.  Single Measur.  >iean  Value  18.6% NaOH Single Mean i-ieasur. Value  Std. Dev.  .026  .667 .655 .652 .661 .648  .657  .008  .017  .702 .705 .693 .699 .702  .701  .003  .010  .625 .618 .628 .638 .639  .630  .009  .015  .582 .576 .579 .580 .577  .579  .002  .020  .648 .634 .642 .673 .668  .653  .017  .017  .654 .615 .659 .669 .649  .649  .021  Std. ' 3?ev.  r-.cellulose pulps 0-1  0-2  0-3  0-4  .495 .480 .479 .592 .487 .510 .498 .492 .494 .464 .534 .543 .550 .537 .523 .527 .546 .515 .541 .513  .497  .492  .537  .528  Viscose Pulps 1-1  1-2  .436 .443 .477 .470 .477 .481 .456 .470 .435 .461  .461  .461  - 136 -  T a b l e 4/b. 1 -  <^>(35 min)  £ (o )  Product  18.6% I-;aOH  distilled  Code No.  Single lieasur.  Mean Value  Std. 3>ev.  Single Measur.  Mean Value  Std. Bev.  Viscose Pulps 1-3  .485 .485 .506 .500 .486  1-4  .509 .482 .512 .497 .496  2-1  .468 .487 .400 .467 .443  2-2  .503 .448 .487 .422 .514  2-3 •  2-4.  3-1  .484 .482 .530 .520 .500 .532 .554 .534 .549 .562 .533 .506 .496 .470 .497  .492  .499  .453  .475  .503  .546  .500  .010  .610 .616 .622 .618 .621  .617  .005  .012  .576 .611 .619 .618 .614  .608  .018  .034  .720 .730 .714 .725 .734  .725  .008  .039  .683 .702 .702 .716 .759  .712  .029  .021  .677 .682 .679 .676 .690  .681  .006  .013  .599 .569 .594 .593 .601  .591  .013  .023  .642 .644 .647 .643 .628  .641  .007  -  IM  -  T a b l e 4/c. 1 - £ ( 3 5 rain) (o)  Product ,  Code No.  Single Heasur.  J  distilled Mean Value  18.(5% NaOH Single Measur.  Std.  Uev.  Lean Value  Std. J>ev.  Viscose Pulps  3-2  3-3  3-4  4-1  4-2  .474 .461 .428 .461 .465 .508 .527 .511 .505 .496 .517 .520 .524 .537 .529 .466 .497 .512 .498 .491 .486 .456 .416 .458 .485  .458  .509  .525  .018  .695 .690 .716 .699 .706  .701  .010  .011  .617 .613 .615 .622 .622  .618  .004  .008  .600 .590 .608 .617 .610  .605  .010  .017  .704 .709 .727 .725 .746  .722  .017  .029  .707 .741 .713 .724 .751  .727  .019  .010  .682 .633 .673 .701 .701  .678  .028  •  .493  .460  Acetate Pulp  5-1  • 527 .529 .543 .525 .547  .535  -  138 -  T a b l e 4/d. 1 - <o(35 rain) £» (o )  Product Code No.  fl  18.6% NaOH-  2°» distilled  Single Measur.  Std. Dev.  Single Measur.  .021  .795 .807 .797 .809 .798  .801  .006  .007  .735 .723 .731 .724 .734  .729  .006  .534  .782 .769 .781 .775 .785  .778  .006  .523  .012  .811 .804 .810 .802 .808  .807  .004  .021  .741 .744 .735 .748 .735  .741  .006  Mean Value  Mean - Value  Std. Dev.  Sulphite Pulp 6-1  .506 .559 .519 .518 .513  .523  Unbleached Sulphate Pulp 7-1  .574 .572 .533 .570 .536  .577  Bleached Sulphate Pulps 7-2  8-1  8-2  .533 .533 .548 .532 .526 .510 .530 .545 .506 .524 .539 .538 .506 .496 .538  .524  - 139 T a b l e 4/e. 1 - £ ( 3 5 min) <Z (o)  Product Code No.  13.6% NaOH.  H20, d i s t i l l e d Single Measur.  Mean Value  Std. Vev.  Single Measur.  Mean Value  Std. 3>ev.  Holocellulose Preparations 9-1  9-2  9-3  9-4  .669 .695 .642 .670 .641 .703 .725 .730 .706 .712 .652 .658 .596 .647 .663 .695 .686 .702 .672 .709  .643  .715  .643  .693  .022  .823 .793 .810 .311 .829  .813  .012  .872 .858 .869 .821 .872  .858 • .022  .027  .820 .771 .773 .783 .808  .792  .021  .014  .817 .820 .826 .820 .814  .819  .005  .014  .865 .874 .870 .855 .875  .868  .008  .020  .845 .845 ,847 .868 .867  .855  .012  .014  Groundwood Pulps '  10-1  10-2  .661 .671 .633 .651 .653 .643 .673 ' .685 .639 .657  .654  .659  -  140 -  T a b l e 4/f. •1 - £(35 min) <£(o)  Product Code No.  •HO, d i s t i l l e d Single Measur.  Mean Value  18.6% NaOH Std. J>ev.  Single Measur.  Mean Value  Std. 3»ev.  Groundwood Pulp&  10-3  10-4  .672 .662 .664 ,653 .663 .648 .644 .649 .685 .677  .663  .661  .007  .888 .890 .890 .893 .891  .890  .002  -.019  .903 .900 .899 .902 .874  .896  .012  Table 5. P r o p e r t i e s o f v i s c o s e p u l p s t r e a t e d w i t h v a r i o u s doses o f gamma-radiation.  Product Code  3-2  No.  Treatment, Mrd  cellulose,  Intrinsic Viscosity,  10%  NaOH  Solubility,  %  [?3  %  90.3 90.0  12.8  9.5  6.0  8S.4  82.4 63.2  4.5 3.0 2.1  9.9 12.6  47.5  1.3  43.1  0.0  97.5  13.2  1.6  0.5 1.0  97.5 96.0  6.2  1.8 3.3  2.0  91.1  4.7 3.1  4.0  75.9  2.1  5.1 14.1  6.0  66.5  1.3  32.9  0.0 0.5 1.0 2.0 4.0 6.0  3-4  Alpha-  15.5 25.2  - 142 -  T a b l e 6.  M u l t i p l e c u r v i l i n e a r c o v a r i a n c e a n a l y s i s f o r the " r e l a t i o n s h i p between 10% NaOH s o l u b i l i t y and 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 o f i r r a d i a t e d and untreated viscose pulps.  DP  Groups Set  1  (untreated  pulps)  Set  2  ( i r r a d i a t e d pulp No. 3--2)  3  Set  3  ( i r r a d i a t e d p u l p No. 3--4)  3,  11  Total Difference f o r testing  slopes  17 4  Sums Difference f o r testing  P  levels  1.343 N.S.  21 2  Combined r e g r e s s i o n 23  3.074 N.S.  FIGURES  -144 -  CA)  Warty l a y e r Fibrillar  layer  }  Tertiary layer  Secondary w a l l Transition layer Primary w a l l Middle lamella Angiospermous wood (birch)  (B)  Coniferous wood (spruce)  Outer surface (PJ Inner surface lP l Primary wall \ Innsr layer of secondary wall Outer layerof secondary wall IS,) (0-B.Lamellae) Middle layer of secondary (1-S Lamellae) nil (S?) ld  (Ca. 30 - ISO [Several lamellae lamellae) intermedial! between of the S a layers) s  (C)  t  Warty l a y e r (W) mm /fiJjK  Figure 1.  (Several lamellae of orientation intermediate between that of the 5 and layers)  Inner (S.)] •—-Main (SX)?- Secondary wall Outer (SJ)J Primary w a l l (P) Middle lamella (M)  Schematic representation of the c e l l w a l l o r g a n i s a t i o n i n a coniferous tracheid and/or angiospermous wood f i b r e , with respective m i c r o f i b r i l o r i e n t a t i o n : (A) a f t e r Meier (187); (B) a f t e r Wardrop and Harada as i n Wardrop (316). a f t e r Tsoumis (301). *  F i g u r e 2.  The u n i t c e l l as p r o p o s e d by Meyer and M i s c h (197).  - 146 -  Stress <£(t)  \  °  G  o  s  /£6l) s t r a i n /applied at / f i n i t e rate  1  ***'-t  ,i  Time  F i g u r e 3.  S t r e s s r e l a x a t i o n under constant ( a f t e r Leaderman ( 1 6 1 ) ) .  strain  -  147 -  F i g u r e 5.  Gas chromatogram o f the a c e t y l a t e d h y d r o l y s a t e s hemlock groundwood p u l p No. 10-2 ( b r i g h t e n e d ) .  of western  Components: 1.  Rhamnose  5. Galactose  Time, min  F i g u r e 6",  Gas chromatogram o f the a c e t y l a t e d h y d r o l y s a t e s cottonwood groundwood No. 10-4 ( b r i g h t e n e d ) .  o f western  Components:  Figure  7.  Gas chromatogram o f the a c e t y l a t e d h y d r o l y s a t e s o f w e s t e r n cottonwood p e r a c e t i c a c i d h o l o c e l l u l o s e No. 9-4.  5  Recorder Response  T,  1  I  2G  30  1 AO Time, min  F i g u r e 8.  Gas chromatogram o f the a c e t y l a t e d h y d r o l y s a t e s c o n i f e r o u s s u l p h a t e pulp No. 7-1.  o f unbleached '  F i g u r e 9.  Gas chromatogram o f the a c e t y l a t e d h y d r o l y s a t e s c o n i f e r o u s s u l p h a t e pulp No. 7-2.  of  bleached  Components:  F i g u r e 10. Gas chromatogram o f the a c e t y l a t e d h y d r o l y s a t e s o f b l e a c h e d p r e d o m i n a n t l y angiospermous s u l p h a t e pulp No. 8-2.  F i g u r e 11.  Gas chromatogram o f the a c e t y l a t e d h y d r o l y s a t e s v i s c o s e pulp No. 1-2.  of coniferous  F i g u r e 12. Gas chromatogram o f the a c e t y l a t e d h y d r o l y s a t e s o f a l p h a c e l l u l o s e p u l p No. 0-3.  as  Time, wir.  F i g u r e 13»  Gas chromatogram o f the a c e t y l a t e d h y d r o l y s a t e s c o n i f e r o u s s u l p h i t e p u l p No. 6-1.  of  bleached  1.00  0.00  0.00125  0.0.1  0.10  1.00  10.00 Relaxation  14. —  ' 35.00  time (min)  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 curves f o r groundwood p u l p s f o l l o w i n g water o r c a u s t i c s t e e p i n g ( n = 5 ) .  3.-Q0-1  Residual;' v Stress Key:  :<5(t) .0.80  1.  Coniferous h o l o c e l l u l o s e  2.  Angiospermous h o l o c e l l u l o s e Ho0  p u l p No. 9-3. p u l p No. 9 - 4 .  Steeped  i n distilled  (1 rain, 2 2 ° C ) .  Steeped  i n 18.6$ NaOH (25 s e c , 2 2 ° C ) . ' <  0.60  0.402.  1 2'  0.20 -  0.00 J^y  1  0.00 0.00125.  0.01  0.10-  10.00  1.00  R e l a x a t i o n time Figure  15.  T y p i c a l 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 curves f o r h o l o c e l l u l o s e pulps f o l l o w i n g water o r c a u s t i c steeping (n = 5 ) .  ; 1 35.0Q. (rain)  VO  COO  0.00]25  0.01  0.10  1.00  10.00 Relaxation time (min)  F i g u r e 16.  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 c u r v e s f o r paper pulps, f o l l o w i n g water o r c a u s t i c s t e e p i n g ( n = 5 ) .  35.00  Key: 1.  1.00 -,  2. Residual Stress (£<t)/€#o>)  0.30  •  Coniferous s u l p h i t e acetate pulp No. 5-1. ©<-cellulose p u l p No. 0-3 prepared from c o n i f e r o u s s u l n h i t e a c e t a t e p u l p No. 5-1. steeped  in distilled  steeped  i n l 8 . 6 ? o NaOH  H 0 (1 m m , (25 o  22°C).  0.60*  0.40 •  0.20  —I  0.00 0.00125  0.01  — I —  0.10  1.00  10.00"  35.00  R e l a x a t i o n time (min) F i g u r e 17.  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 curves f o r a c e t a t e and a l p h a - c e l l u l o s e p u l p s f o l l o w i n g water o r c a u s t i c s t e e p i n g (n = 5 ) .  Key:  1. 2. 3.  C o n i f e r o u s s u l p h i t e p u l p No. 2-2 C o n i f e r o u s s u l p h a t e p u l p No. 3-4 Angiospermous s u l p h a t e p u l p No. 2-3  1.00 steeped i n d i s t i l l e d water (1 m i n , 2 2 ° C )  Residual stress (£(t>/£(o))  steeped i n 18.6% NaOH (25. s e c , 2 2 ° C )  0.80  0.60 «  0.40  0.20 0.00 0.00125"  0.01  — i — 0.10  1.00  10.00  35.00  Relaxation time ( n i n ) ' Figure  18.  T y p i c a l 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 curves f o r t h r e e v i s c o s e p u l p s f o l l o w i n g water o r c a u s t i c s t e e p i n g (n = 5). .  -162 -  y = 0.4782  0.30  tfhere y =  0.75  + 0,3011  1'- €1* (35 r u n )  lo-x o f NaOH steeped snecir.ens  x = pulp h e n i c e l l u l o r . e content r = > 0.71**; s E E = 0.037; DF = 12  °o o  0.70 .  0.65 .  0.60 ">eeped i n 18.6% N,;.0H (25 s e c , 22°C) Dissipated Stress 1 -  ^  0.55  Stepped i n d i s t i l l e d (1 min, 22°C)  (35 rr.in)  <5 (o) 0.50  0.45 y = 0.6147 where y 0.40  .  x  r  - 0.2083  log  = 1 -  (35 r.in) o f water steeped <S ( n ) - pulp h e m i c e l l u l o s e c o n t e n t = 0 . 8 7 * * ; Ser » 0 . 0 1 4 ; DF = 12  T  speci-ens  TT  T 5  Hemicellulose content, %  Figure 19.  C o r r e l a t i o n between f r a c t i o n a l stress r e l a x a t i o n of 14 viscose pulps read a f t e r 35 min r e l a x a t i o n time f o l l o w i n g steeping i n water or c a u s t i c and pulp hemicellulose content.  vatei  0.80  .9-2 0,70.  10-4  Dissipated Stress 1 -  • 9-4  9-3 ®9-l  10-3  10-2 10-1  (35 min) (o) O.60 ON  7-1?  u>  0.50 19 pulps  0.40  (0-1—5-1)  —T—  10  Figure  20.  20  30 L i g n i n content, %  R e l a t i o n s h i p between 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 (n = 5) and l i g n i n c o n t e n t s as o b s e r v e d on water s t e e p e d samples o f v a r i o u s p u l p t y p e s a f t e r 35 min r e l a x a t i o n t i m e . Code numbers r e f e r to p u l p s l i s t e d i n T a b l e 2.  0.90%  10-4 10-310-1-« 10-2-«  •-9-2 ^9-4 0.30.  - 8-1 -9-1  \>6-l  •>9-3 .ipnted Stress g£(35  N  7-2  0 8-2  min)  7-1  •19 p u l p s  •  (0-1 —  5-1)  0.60  0.50 10  20  30 Lignin content, %  Figure  21,  R e l a t i o n s h i p between 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 (n = 5) and l i g n i n c o n t e n t s as observed on c a u s t i c steeped (18.6% NaOH) samples o f v a r i o u s pulp t y p e s a f t e r 35 min r e l a x a t i o n time. Code numbers r e f e r to p u l p s l i s t e d i n Table 2.  10-4 0.90 Dissipated Stress 1  - (2(35  y = 0.595 + 0.005x + 0.076 log where y =  E  oT  £  6-1  0.B0 C a u s t i c steeped  \  9-4 n^°°-V  min)  x = h e m i c e l l u l o s e content r = 0.92**; S = 0.039: DP => 29  min)  ~STol  1 - d(35  10-3  x  CO  specimens  0.70  0.60 ' . V a t e r steeped specimens  '8-1  0.50 •  y » 0.549 + 0.013 x - 0.189 l o g x where y = 1 - £ ( 3 5 min) <£(o) x = h e m i c e l l u l o s e content r = 0.94 **; = 0.026; DP = 29 0.40  i 10  •  1 .  •  20 Hemicellulose  F i g u r e 22.  30 content,%  R e l a t i o n s h i p between 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 (n=5) and h e m i c e l l u l o s e c o n t e n t s as observed on water and c a u s t i c (18.6% NaOH) s t e e p e d samples o f v a r i o u s p u l p t y p e s a f t e r 35 min r e l a x a t i o n t i m e .  0.80.  ••  Dissipatcd Stress 1 -d<3*> mU: <&<•-•) 0. 70.  • 9-2 10-2 10-1  —  10-3 10-4  •  —  9-3 . . 9 - 1  O.60.  • >  7-1 • 7-2 1  0.50j  y - -0.7004 - 0.0106x + 1.1155 log x r = 0.842*"* c - 0.043; DF » 29 "£E  S" ,  I  •  9  6^V.  8 - 2  e 0-1*0,5-1  0.40  • • • •  X .  9  9  9  ^  1 40  50  60  70  80  90  100  Cellulose content, Z. F i g u r e 23*  R e l a t i o n s h i p between 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 ( n = 5) a n d c e l l u l o s e c o n t e n t s a s o b s e r v e d o n w a t e r s t e e p e d s a m p l e s o f v a r i o u s p u l p t y p e s a f t e r 35 m i n r e l a x a t i o n time. Code n u m b e r s r e f e r t o p u l p s l i s t e d i n T a b l e 2.  10-4  0.90 ©•  10-3  10-1 10-2  Dissipated Stress  0.80  run) <S(c)  (35  0.70  y  r  0.60  1.5841 - 0.0168x - 1.9435 l o g x 0.905** 0.041; DF = 29  0-1-U5-1  0.50 40  50  60  70  80  90 Cellulose  F i g u r e 24.  100 content, %  R e l a t i o n s h i p between 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 (n = 5) and c e l l u l o s e c o n t e n t s as observed a f t e r 35 min r e l a x a t i o n time on c a u s t i c s t e e p e d (18.6% NaOH) samples o f v a r i o u s p u l p t y p e s . Code numbers r e f e r t o p u l p s l i s t e d i n T a b l e 2.  -  168  -  Dissipated Stress 1 ^(t)  0.90 •  0.80 •  0.70 •  0.60  .+  3-2  ( 6 sec)  0.50 •  •+  3-4  ( 6 sec)  + -+- + • 0.40 O  i  l  T"  T"  2  3  T-  4  5  6  Mr ad  Figure 25.  Short and long time response i n 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 (n = 5) of two viscose pulps exoosed ( a i r - d r y ) to d i f f e r e n t gamma-radiation l e v e l s and then steeped i n 18.6% NaOH (30 sec, 22°C).  '  0  '  '  I  I  1  I  10  20  30  40 10% NaOH s o l u b i l i t y , %  Figure 26. Correlation between fractional stress relaxation (n = 5) of irradiated and untreated viscose pulps read after 35 min relaxation time following steeping i n 18.6% NaOH and pulp caustic s o l u b i l i t y .  - I /u -  Figure 27. Relationship between c a u s t i c s o l u b i l i t y and r e l a t i v e amount of hemicelluloses of 14 viscose pulps.  0.80 Steeped (25  i n 1 8 . 6 % NaOH  s e c , 22°C)  2-1'  o 0.70 Dissipated Stress  1  *~  I I I I I  2-2'  o II  3-2'  o I I I I I  <^ (35 m i n ) S'(o)  o  2-3'  0.60  I I I 3-3'  o  2-4'  I  3-4'  o  zzzzzzzzzzzz o  i i  0.50  I  o  i !  i !  I  o  I  2-3  o  2-2  '  2-4  !  I  o  i n 1 8 . 6 °NaOH  (48 h r ,  22°C)  o  I  I  3-4  I I  o  3-2'  o  2-2'  o I  I  T  2-3  Z Z Z Zo2 ?  3-3  ?3  o  I  '  3-2  2-1  a AO  6  Steeped 2-1'  Steeped (I min,  indistilled 22°C)  I  I  water 2-1  O  a  2-2  Steeped  3-3'  O i  / / / / / / . I I I  o in distilled  (43 h r , 22°C)  3-4  3-3  *i.t;er  Figure 28". F r a c t i o n a l stress r e l a x a t i o n r e s u l t s (n = 5) on seven viscose pulps as read a f t e r 35 min r e l a x a t i o n time following short and long time steeping i n water or caustic.  o  3-4  l . O O l  Residual  Stres  8. 80  ( t )  G"(  o)  <X60.  ( £ ( t ) / G £ ( o ) as read a f t e r 6 sec r e l a x a t i o n time  O-  •  °  O.A0.  > < s ( t ) / ^ ( o ) as read aftea* 100 min r e l a x a t i o n time 0.25 0.1  10  100  I 1000  10000  100000  S t e e p i n g time, min  Figure 29.  E f f e c t o f s t e e p i n g time i n 18.6% NaOH ( 2 2 ° C ) on r e s i d u a l s t r e s s r e l a x a t i o n (n = 5) o f v i s c o s e p u l p No. 3-2.  -  DVGOT  1 / J  y = 0.58*911 + where y = 1 -  -  0.0105S5x  g£ (35 - i n )  of  steeped  0.75  XaOH specimens x = s o l u b i l i t y i n 10% I^aOI! r - 0.S3**; DF = 12  S  F E  = 0.030;  .  0°  0.70  0.65.  Dissipated  1  -  0.60 Stress  S t e e p e d i n 1 8 . 6 % NaOH (25 s e c , 22o c)  (35 n t n ) (o)  0.55 Steeped i n d i s t i l l e d (1 n»in, 2 2 ° C )  water  0.50  0.45 v  = 0.5181.39 - 0.004345 x w h e r e y = 1 - c& (35 r-irQ  er (c)  0.4o.  x r  of water steeped specimens s o l u b i l i t y i n 10% :;aOH. 0.60*; S = 0.023; DF = 12 E E  10  —T"  —r  12  .14  10% NaOH s o l u b i l i t y .  Figure  30.  C o r r e l a t i o n between 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 (n=5) o f 14 v i s c o s e p u l p s r e a d a f t e r 35 min r e l a x a t i o n time f o l l o w i n g s t e e p i n g i n water o r c a u s t i c (18.6% NaOH) and c a u s t i c s o l u b i l i t y .  %  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0101003/manifest

Comment

Related Items