Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Influence of cellulose chain length on the mechanical behavior of Douglas fir wood in tension parallel… Ifju, Geza 1963

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

Item Metadata

Download

Media
831-UBC_1963_A1 I3 I5.pdf [ 11.08MB ]
Metadata
JSON: 831-1.0105581.json
JSON-LD: 831-1.0105581-ld.json
RDF/XML (Pretty): 831-1.0105581-rdf.xml
RDF/JSON: 831-1.0105581-rdf.json
Turtle: 831-1.0105581-turtle.txt
N-Triples: 831-1.0105581-rdf-ntriples.txt
Original Record: 831-1.0105581-source.json
Full Text
831-1.0105581-fulltext.txt
Citation
831-1.0105581.ris

Full Text

INFLUENCE OF CELLULOSE CHAIN LENGTH ON THE MECHANICAL BEHAVIOR OF DOUGLAS FIR WOOD IN TENSION PARALLEL TO GRAIN  by GEZA IFJU B.S.F.(Sopron D i v i s i o n ) U n i v e r s i t y of B r i t i s h Columbia 1959 M.P. Yale U n i v e r s i t y 1960  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  i n the Department of Forestry  We accept t h i s t h e s i s as conforming t o the r e q u i r e d standard  THE UNIVERSITY OF BRITISH COLUMBIA September, 1963  In the  presenting  r e q u i r e m e n t s f o r an advanced  British  Columbia, I agree  available mission  f o r reference  f o r extensive  representatives.  cation  Department o f  fulfilment of  s h a l l make i t f r e e l y  I further  copying of t h i s thesis  agree  that  f o r f i n a n c i a l gain  permission.  Forestry  ' Columbia,  September 27, 1963  that  per-  for.scholarly  by t h e Head o f my Department  The U n i v e r s i t y . o f B r i t i s h V a n c o u v e r 8, Canada.  Date  the L i b r a r y  I t i s understood  of this thesis  w i t h o u t my w r i t t e n  that  i n partial  d e g r e e a t the U n i v e r s i t y o f  and s t u d y .  p u r p o s e s may be g r a n t e d his  this thesis  o r by  copying or p u b l i -  shall  n o t be a l l o w e d  The U n i v e r s i t y o f B r i t i s h FACULTY OF GRADUATE  Columbia  STUDIES  PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY PUBLICATIONS Ifju,  G, and R.W. Kennedy* affecting microtensile F o r . Prod. J . .12(5):  1962. Some v a r i a b l e s s t r e n g t h o f Douglas f i r 213-217.  Kennedy, R.W. and G. I f j u . 1962. A p p l i c a t i o n o f m i c r o t e n s i l e t e s t i n g to t h i n wood s e c t i o n s T a p p i 45(9) : 725-733.  of  GEZA  B.SoF., The U n i v e r s i t y o f B r i t i s h  Ifju,  Ifju,  G. 1962. S t a t i s t i c s on p u l p and paper. In J.A. Crosse: Proceedings o f the seminar on f o r e s t r e s e r v a t i o n s i n the U.S.S.R. and t h e i r utilization. F a c u l t y o f F o r e s t r y , The U n i v e r s i t y o f B r i t i s h Columbia. pp. 52-59. G., R.W. Wellwood, and J.W. W i l s o n . 1963. Intra-increment r e l a t i o n s h i p of s p e c i f i c g r a v i t y , m i c r o t e n s i l e s t r e n g t h and e l a s t i c i t y i n Douglas f i r . Paper p r e s e n t e d t o the ann u a l S p r i n g Conference, P a c i f i c Coast Branch, Canadian Pulp & Paper A s s o c i a t i o n , May 9 - 1 1 , 1963, H a r r i s o n Hot Springs B. C.  Columbia  (Sopron D i v i s i o n ) 1959 M.F., Y a l e  K e l l o g g , R.M. and G. I f j u . 1962. I n f l u e n c e o f s p e c i f i c g r a v i t y and c e r t a i n o t h e r f a c t o r s on the t e n s i l e p r o p e r t i e s o f wood. F o r . Prod. J . 12(10): 463-407.  IFJU  U n i v e r s i t y , 1960  IN ROOM 237,. FORESTRY AND GEOLOGY BUILDING WEDNESDAY, SEPTEMBER 25, 1963 AT 2:30 P.M.  COMMITTEE IN CHARGE Chairman: F.H. Soward G.G.S. Dutton J.A.F. Gardner P.G. Haddock  J.H.G. Smith R.W. Wellwood J.W. W i l s o n  E x t e r n a l Examiner: University  R.W.  Kennedy  of Toronto  INFLUENCE OF CELLULOSE CHAIN LENGTH ON THE MECHANICAL BEHAVIOR OF DOUGLAS FIR WOOD IN TENSION PARALLEL TO GRAIN  i n c e l l u l o s e DP i f the c r y s t a l l i n e - a m o r p h o u s r a t i o o f cel= l u l o s e i n wood i s not a l t e r e d s i g n i f i c a n t l y by the t r e a t " ment a p p l i e d , such as accompanies gamma i r r a d i a t i o n .  ABSTRACT The c e l l u l o s e f r a c t i o n i n 100~micron t h i c k microtome s e c t i o n s from t h r e e growth increments o f a Douglas f i r t r e e was s y s t e m a t i c a l l y degraded through random s c i s s i o n of c h a i n s by means o f 0,1, 1.0, 10.0, and 15.0 megarad doses o f gamma i r r a d i a t i o n . Degree o f c e l l u l o s e poly= m e r i z a t i o n (DP) was e s t i m a t e d from r e s u l t s o f i n t r i n s i c v i s c o s i t y measurements on d i l u t e s o l u t i o n s o f c e l l u l o s e n i t r a t e i n acetone. C o n t r o l and i r r a d i a t e d samples were t e s t e d i n t e n s i o n p a r a l l e l to g r a i n by employing a micro s c a l e t e s t method. T e s t s were done at 25, 50, and 70°C temperatures i n combination w i t h m o i s t u r e - f r e e , a i r - d r y , and w a t e r ~ s a t u r a t e d c o n d i t i o n s o f t e s t specimens. U l t i m a t e t e n s i l e s t r e n g t h , an e l a s t i c i t y constant, u l t i m a t e t e n s i l e s t r a i n , and work to maximum t e n s i l e load have been c a l c u l a t e d from e x p e r i m e n t a l d a t a . R e s u l t were a n a l y z e d s t a t i s t i c a l l y i n r e l a t i o n t o c e l l u l o s e c h a i n l e n g t h , temperature, and moisture content. Regres s i o n e q u a t i o n s based on experimental r e s u l t s have been c o n s t r u c t e d . These e x p l a i n a l a r g e p a r t o f the v a r i a t i o n s i n t e n s i l e s t r e n g t h p r o p e r t i e s and a r e r e p o r t e d as t h r e e - d i m e n s i o n a l diagrams. I t i s shown that t e n s i l e s t r e n g t h b e h a v i o r o f Douglas f i r earlywood and latewood are d i s t i n c t l y d i f f e r e n t . S t r e n g t h p r o p e r t i e s o f latewood a r e not o n l y h i g h e r by a f a c t o r o f a p p r o x i m a t e l y 2 to 8 than those o f earlywood but a l s o t h e response o f the two growth zones to changes i n c e l l u l o s e c h a i n l e n g t h , temperature, and moisture i s different. The above c h a r a c t e r i s t i c s a r e due to d i f f e r e n t d e f o r m a t i o n mechanisms i n t e n s i o n p a r a l l e l to g r a i n o f the two growth zones. I t i s suggested that def o r m a t i o n i n earlywood i s i n t r a c e l l u l a r , whereas i n latewood i t i s an i n t e r - t r a c h e i d , phenomenon. Decrease o f c e l l u l o s e DP reduced t e n s i l e s t r e n g t h , u l t i m a t e s t r a i n , and work to maximum Load more i n the low than i n the h i g h DP r e g i o n s . T h i s i s e x p l a i n e d by the i n c r e a s i n g importance of i n t e r - c h a i n and/or i n t e r f i b r i l l a r slippage with decreasing chain length. E l a s t i c p r o p e r t i e s a r e but l i t t l e a f f e c t e d by changes  A change i n wood m o i s t u r e content a t time o f t e s t from the m o i s t u r e ~ f r e e t o the w a t e r = s a t u r a t e d c o n d i t i o n r e duces s t r e n g t h p r o p e r t i e s o f Douglas f i r by a p p r o x i m a t e l y 20 t o 50 p e r c e n t . The r e d u c t i o n s i n latewood s t r e n g t h are s i g n i f i c a n t l y h i g h e r than i n earlywood, A convex upward curve c o n f i g u r a t i o n r e l a t i n g s t r e n g t h and e l a s t i c i t y to m o i s t u r e content i s suggested from the e x p e r i m e n t a l data. E f f e c t o f temperature on s t r e n g t h p r o p e r t i e s o f Douglas f i r w i t h i n the range o f 25 t o 70°C i s minor i n comparison w i t h m o i s t u r e c o n t e n t . The r e l a t i o n s h i p i s probably l i n e a r . T e n s i l e s t r e n g t h c h a r a c t e r i s t i c s o f Douglas f i r wood w i t h degraded c e l l u l o s e a r e more s e n s i t i v e t o changes i n moisture content than a r e those o f wood h a v i n g c e l l u l o s e of l o n g - c h a i n s t r u c t u r e . T h i s b e h a v i o r o f wood i n t e n s i o n i s a l s o e x p l a i n e d by t h e s l i p p a g e mechanism o f deformation.  GRADUATE STUDIES F i e l d o f Study;  Forestry  Research i n Wood Anatomy Problems i n F o r e s t P r o d u c t s S t a t i s t i c a l Methods i n F o r e s t Research General F o r e s t r y Seminar Research i n the P r o p e r t i e s o f Wood Products  R.W. Wellwood R.W. Wellwood J.H.G. Smith The S t a f f R.W. Wellwood J.W. W i l s o n  Related F i e l d s : D i g i t a l Computer Programming Biometry Elements of M a t e r i a l S c i e n c e O r g a n i c Chemistry  C h a r l o t t e Froese D.P. Ormrod W.M. Armstrong J.P. Kutney  i.  ABSTRACT  The c e l l u l o s e f r a c t i o n i n 100-micron t h i c k microtome s e c t i o n s from three growth increments f i r t r e e was  of a Douglas  s y t e m a t i c a l l y degraded through random s c i s s i o n  of chains by means of 0.1, doses of gamma i r r a d i a t i o n . m e r i z a t i o n (DP) was  1.0,  10.0,  and  15.0 megarad  Degree of c e l l u l o s e p o l y -  estimated from r e s u l t s of i n t r i n s i c  v i s c o s i t y measurements on d i l u t e s o l u t i o n s of c e l l u l o s e n i t r a t e i n acetcne.  C o n t r o l and i r r a d i a t e d samples were  t e s t e d i n t e n s i o n p a r a l l e l to g r a i n by employing s c a l e t e s t method. temperatures  a micro-  Tests were done at 25, 50, and 70°C  i n combination w i t h m o i s t u r e - f r e e , a i r - d r y ,  and water-saturated c o n d i t i o n s of t e s t specimens. U l t i m a t e t e n s i l e s t r e n g t h , an e l a s t i c  constant,  u l t i m a t e t e n s i l e s t r a i n , and work to maximum t e n s i l e l o a d have been c a l c u l a t e d from experimental data. statistically temperature  R e s u l t s were  analyzed i n r e l a t i o n to c e l l u l o s e c h a i n l e n g t h ,  and moisture content.  Regression  equations  based on experimental r e s u l t s have been c o n s t r u c t e d .  These  explained a l a r g e p a r t of the v a r i a t i o n s i n t e n s i l e s t r e n g t h p r o p e r t i e s and are r e p o r t e d as three-dimensional diagrams. I t i s shown t h a t t e n s i l e s t r e n g t h behavior of Douglas f i r earlywood ent.  and latewood  are d i s t i n c t l y  Strength p r o p e r t i e s of latewood  differ-  are not only h i g h e r  ii.  by a f a c t o r of approximately 2 to 8 than those of e a r l y wood, but a l s o the response of the two growth zones to changes i n c e l l u l o s e c h a i n l e n g t h , temperature, and moist u r e content at t e s t i s d i f f e r e n t .  The above c h a r a c t e r -  i s t i c s are due to d i f f e r e n t deformation mechanisms i n t e n s i o n p a r a l l e l to g r a i n of the two growth zones.  It i s  suggested that deformation i n earlywood i s i n t r a - c e l l u l a r , whereas i n latewood i t i s p r i m a r i l y an i n t e r - t r a c h e i d , phenomenon. Decrease i n c e l l u l o s e DP reduced s t r e n g t h , u l t i m a t e s t r a i n , and work to maximum l o a d more i n the low than i n the h i g h DP r e g i o n s . importance  This i s e x p l a i n e d by the i n c r e a s i n g  of i n t e r - c h a i n and/or i n t e r - f i b r i l l a r s l i p p a g e  with decreasing chain length.  E l a s t i c p r o p e r t i e s are  but l i t t l e affecte.d by changes i n c e l l u l o s e DP i f the crystalline-amorphous r a t i o of c e l l u l o s e i n wood i s not a l t e r e d s i g n i f i c a n t l y by the treatment a p p l i e d , such as accompanies gamma i r r a d i a t i o n . A change i n wood moisture content at time of t e s t from the m o i s t u r e - f r e e t o the water-saturated cond i t i o n reduced s t r e n g t h p r o p e r t i e s of Douglas f i r by approximately 20 to 50 per cent.  The r e d u c t i o n s i n l a t e -  wood s t r e n g t h were s i g n i f i c a n t l y h i g h e r than i n earlywood. A convex upward curve c o n f i g u r a t i o n r e l a t i n g s t r e n g t h and e l a s t i c i t y to moisture content i s suggested from the experimental data.  iii.  E f f e c t of temperature  on s t r e n g t h p r o p e r t i e s o f  Douglas f i r w i t h i n the range of 25 t o 70°C i s minor i n comparison  w i t h that of moisture content.  The r e l a t i o n -  s h i p i s probably l i n e a r . T e n s i l e s t r e n g t h c h a r a c t e r i s t i c s o f Douglas f i r wood with degraded  c e l l u l o s e are more s e n s i t i v e to changes  i n moisture content than are those o f wood having c e l l u l o s e of l o n g - c h a i n s t r u c t u r e .  T h i s behavior o f wood i n  t e n s i o n i s a l s o e x p l a i n e d by the s l i p p a g e mechanism o f deformation.  \  xii.  ACKNOWLEDGEMENT  The w r i t e r g r a t e f u l l y acknowledges h i s indebtedness to Dr. R. W. Wellwood, P r o f e s s o r , F a c u l t y o f F o r e s t r y , for h i s c o n s c i e n t i o u s and s k i l f u l guidance during the whole o f a three-year  academic program; t o Dr. J . W. Wilson, Asso-  ciate Professor, Faculty of Forestry, f o r h i s valuable p r o f e s s i o n a l a s s i s t a n c e both a t the experimental  stage and  i n the a n a l y s i s o f the r e s u l t s ; t o Dr. J . H. G. Smith, and Dr. G. G. S. Dutton members o f the F a c u l t y o f F o r e s t r y , and the F a c u l t y o f A r t s and Science, Department of Chemistry, r e s p e c t i v e l y , f o r t h e i r a d v i s o r y help; t o Dr. R. W. Kennedy, A s s i s t a n t P r o f e s s o r , F a c u l t y o f F o r e s t r y , U n i v e r s i t y of Toronto, f o r the c r i t i c a l r e a d i n g of the t h e s i s ; t o Mr. A. G. Davies o f Atomic Energy o f Canada L i m i t e d , f o r the gamma i r r a d i a t i o n of the experimental  m a t e r i a l ; t o Mr. A.  Kozak, Graduate Student, F a c u l t y o f F o r e s t r y , f o r a s s i s t a n c e i n the s t a t i s t i c a l analyses;  t o Mr. L. Paszner, Graduate  Student, F a c u l t y of F o r e s t r y , f o r some of the i l l u s t r a t i o n s ; to the N a t i o n a l Research C o u n c i l of Canada, f o r p r o v i d i n g the f i n a n c i a l means t o c a r r y out the p r o j e c t ; a n d , l a s t , but not l e a s t , t o Mrs. G. I f j u f o r h e r encouragement, understanding, and u n f a i l i n g  patience.  iv.  TABLE OF CONTENTS Page TITLE PAGE ABSTRACT  i  TABLE OP CONTENTS  iv  ACKNOWLEDGEMENT  x i i  INTRODUCTION  1  MATERIAL AND METHODS  6  I MATERIAL  7  I I METHODS  11  1. Degradation o f C e l l u l o s e by Means o f Gamma Radiation  11  A. Previous work  11  i ) R a d i a t i o n chemistry o f h i g h polymers..  12  i i ) I n f l u e n c e o f gamma r a d i a t i o n on the chemical p r o p e r t i e s  o f wood and c e l -  lulose  -  14  i i i ) E f f e c t s o f gamma r a d i a t i o n on the physi c a l and mechanical p r o p e r t i e s and  o f wood  related materials  18  i v ) E f f e c t o f moisture content on degradat i o n by gamma rays v) The a f t e r - e f f e c t o f gamma r a d i a t i o n . . .  19 19  B. I r r a d i a t i o n o f Experimental M a t e r i a l by Gamma Rays  20  V.  Page 2. Tension Test Methods  22  A. P r e p a r a t i o n o f Test Specimen  22  B. Test V a r i a b l e s  23  i ) T e s t i n g machine v a r i a b l e s  23  i i ) Moisture content and temperature  24  3. Determination of C e l l u l o s e Degree o f Polymerization  28  A. N i t r a t i o n o f Wood Samples  29  B. Determination o f N i t r o g e n Content o f Cellulose Nitrates  34  C. V i s c o s i t y Measurements  36  D. Conversion o f I n t r i n s i c V i s c o s i t y t o DP Values  42  EXPERIMENTAL RESULTS  47  DISCUSSION  55  I INFLUENCE OF GAMMA RADIATION ON CELLULOSE CHAIN , LENGTH  55  I I EFFECTS OF CELLULOSE CHAIN LENGTH ON STRENGTH PROPERTIES PARALLEL TO GRAIN  61  I I I MOISTURE CONTENT SENSITIVITY OF TENSILE STRENGTH PROPERTIES  . "  80  IV INFLUENCE OF TEMPERATURE ON THE MECHANICAL BEHAVIOR OF WOOD IN TENSION PARALLEL TO GRAIN...  93  V EFFECTS OF INTERACTIONS AMONG CELLULOSE CHAIN LENGTH, TEMPERATURE AND MOISTURE CONTENT ON TENSILE STRENGTH PROPERTIES OF WOOD  98  Page VI RELATIVE AMOUNTS OP VARIATION IN TENSILE STRENGTH PROPERTIES ACCOUNTED FOR BY VARIOUS FACTORS 1. V a r i a t i o n  104  i n Strength P r o p e r t i e s Due t o  Treatments  104  2. F a c t o r s I n f l u e n c i n g T e n s i l e  Strength Prop-  e r t i e s Inherent i n Wood 3. V a r i a t i o n  i n Tensile  107  Strength P r o p e r t i e s Due  to Experimental E r r o r  111  CONCLUSIONS  114  REFERENCES  117  TABLES AND FIGURES  125  Table 1. Comparison o f c e l l u l o s e DP v a l u e s  calculated  f o r a sample with 35.0 d l / g i n t r i n s i c  vis-  cosity, using various relationships  126  Table 2. Mean u l t i m a t e t e n s i l e s t r e n g t h v a l u e s and t h e i r c o e f f i c i e n t s of v a r i a t i o n  127  Table 3. Mean e l a s t i c i t y v a l u e s „and t h e i r c o e f f i c i e n t s of v a r i a t i o n  1 28  Table 4. Mean v a l u e s o f u l t i m a t e t e n s i l e s t r a i n and t h e i r c o e f f i c i e n t s of v a r i a t i o n  1 29  Table 5. Mean v a l u e s of work t o maximum t e n s i o n l o a d and t h e i r c o e f f i c i e n t s o f v a r i a t i o n  130  Table 6. Moisture content o f a i r - d r y specimens a t test Table 7. I n t r i n s i c v i s c o s i t y of c e l l u l o s e i n Douglas f i r as measured a f t e r exposure o f wood t o  131  vii  v a r i o u s dosage l e v e l s o f gamma r a d i a t i o n . . . Table  132  8. C e l l u l o s e degree o f p o l y m e r i z a t i o n i n Douglas f i r wood measured a f t e r  exposure  to v a r i o u s i n t e g r a l doses o f gamma r a d i a t i o n 133 Table  9. A n a l y s i s o f v a r i a n c e o f earlywood  tensile  strength Table  134  10. A n a l y s i s o f v a r i a n c e o f latewood t e n s i l e • strength  Table  134  11. A n a l y s i s o f v a r i a n c e o f earlywood  elasticity  i n tension Table  135  12. A n a l y s i s o f v a r i a n c e o f latewood  elasticity  i n tension Table  135  13. A n a l y s i s o f v a r i a n c e o f earlywood u l t i m a t e tensile strain  Table  136  14. A n a l y s i s o f v a r i a n c e o f latewood u l t i m a t e tensile strain  Table  -. 136  15. A n a l y s i s o f v a r i a n c e o f work t o maximum t e n s i o n l o a d i n earlywood  Table  137  16. A n a l y s i s o f v a r i a n c e o f work t o maximum t e n s i o n l o a d i n latewood  Table  137  17. A n a l y s i s o f v a r i a n c e o f u l t i m a t e  tensile  strain including test f o r cellulose length tent Table  (DP), temperature  chain  ( T ) , moisture con-  (MC), wood zone ( Z ) , and increment ( I ) . 138  18. Regression  o f s t r e n g t h p r o p e r t i e s on c e l -  lulose intrinsic viscosity (T), and moisture content  (V), temperature (M)  139  viii  Page Table 19. Regression of s t r e n g t h p r o p e r t i e s on  cellu-  l o s e degree of p o l y m e r i z a t i o n (D), temperature ( T ) , and moisture  content  (M)  139  Table 20. Per cent v a r i a t i o n s i n s t r e n g t h p r o p e r t i e s accounted Table 21. Simple  f o r by v a r i a b l e s t e s t e d  140  c o r r e l a t i o n c o e f f i c i e n t s between  t e n s i l e s t r e n g t h p r o p e r t i e s and variables  experimental  .*.....~  140  Table 22. Comparison between c e l l u l o s e DP values obtained by u s i n g two  e m p i r i c a l methods of  conversion from i n t r i n s i c v i s c o s i t y  141  F i g u r e 1. Experimental m a t e r i a l s e l e c t e d at random from three growth increments  of a Douglas  f i r t r e e . Random assignment of  treatments  i s shown  142  F i g u r e 2. Intra-increment v a r i a t i o n i n u l t i m a t e t e n s i l e s t r e n g t h i n three growth of a Douglas f i r t r e e  increments .*  -  143  of a Douglas f i r t r e e . . . .  144  F i g u r e 3. Intra-increment v a r i a t i o n i n t e n s i o n p a r a l l e l - t o - g r a i n e l a s t i c modulus i n three growth increments  F i g u r e 4. Intra-increment v a r i a t i o n i n s p e c i f i c g r a v i t y i n three growth increments  of a  Douglas f i r t r e e  145  F i g u r e 5. D i s t r i b u t i o n of h o l o c e l l u l o s e i n three growth increments  of a Douglas f i r t r e e . . . .  146  ix  Figure  6. Intra-increment  v a r i a t i o n i n carbohydrates  i n three growth increments o f a Douglas f i r t r e e , expressed  as percentages o f  total holocellulose Figure  147  7. Converted arbor press with  adjustable  c u t t i n g d i e used f o r t e n s i o n t e s t specimen preparation Figure  148  8. Tension t e s t specimens enplosed  i n poly-  ethylene t e s t bags Figure  149  9. Tension t e s t specimen enclosed i n p l a c t i c t e s t bag i n p l a c e between g r i p s o f machine  F i g u r e 10. Table model I n s t r o n t e s t i n g equipped with constant  150  instrument  temperature cabinet  151  F i g u r e 11. M i c r o c a t o r d i a l i n d i c a t o r used f o r t h i c k ness measurements...  152  F i g u r e 12. Equipment used f o r v i s c o s i t y measurements of c e l l u l o s e F i g u r e 13. C e l l u l o s e  nitrate solutions  c h a i n depolymerization  153 i n the  n i t r a t i n g a c i d as r e l a t e d t o l e n g t h o f n i t r a t i o n time F i g u r e 14. Conversion  154  f a c t o r between degree o f p o l y -  m e r i z a t i o n and i n t r i n s i c v i s c o s i t y i n relation to i n t r i n s i c viscosity  155  F i g u r e 15. E f f e c t o f gamma r a d i a t i o n o f wood on c e l lulose intrinsic viscosity F i g u r e 16. E f f e c t o f gamma r a d i a t i o n o f wood on e e l -  1 56  X.  Page l u l o s e degree o f p o l y m e r i z a t i o n  1 56  F i g u r e 17. U l t i m a t e t e n s i l e s t r e n g t h as a f u n c t i o n of c e l l u l o s e c h a i n l e n g t h , temperature, and moisture content  ".'....*  1 57  F i g u r e 18. E l a s t i c i t y o f Douglas f i r i n t e n s i o n para l l e l t o g r a i n as a f u n c t i o n o f temperature, moisture content, and c e l l u l o s e  chain  length  1 58  F i g u r e 19. U l t i m a t e s t r a i n o f Douglas f i r i i i t e n s i o n p a r a l l e l t o g r a i n as  a f u n c t i o n o f tem-  p e r a t u r e , moisture content,  and c e l l u -  l o s e chain l e n g t h  1 59  F i g u r e 20. Work t o maximum l o a d o f Douglas f i r i n t e n s i o n p a r a l l e l to g r a i n as  a function  of temperature, moisture content,  and c e l -  l u l o s e chain length  160  F i g u r e 21. Diagram showing r e l a t i o n s h i p between u l t i m a t e t e n s i l e s t r e n g t h and 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 a t 50°C temperature and a i r - d r y moisture content and  condition.  Means  s c a t t e r around means are a l s o shown...  F i g u r e 22. Intra-increment  161  v a r i a t i o n o f t e n s i l e strength  p a r a l l e l t o g r a i n i n Douglas f i r determined a f t e r exposure of wood to v a r i o u s doses of gamma r a d i a t i o n  162  xi.  F i g u r e 23. I n f l u e n c e o f c e l l u l o s e c h a i n l e n g t h on moisture s e n s i t i v i t y of t e n s i l e  strength  of Douglas f i r wood APPENDIX  163 164  F o r t r a n Program Used f o r C a l c u l a t i o n o f I n t r i n s i c V i s c o s i t y of C e l l u l o s e  165  1  INTRODUCTION  Wood i s by no means an i d e a l engineering  material  the s t r e n g t h p r o p e r t i e s of which can be p r e d i c t e d by simple mathematical means. angles  This i s so mainly because, at v a r i o u s  t o the g r a i n , wood i s inhomogeneous and p a r t l y  because i t s r e a c t i o n s t o s t r e s s are extremely Even simple  complicated.  e x t e r n a l s t r e s s e s , such as l o n g i t u d i n a l t e n s i o n ,  have t o be t r a n s m i t t e d through an i r r e g u l a r network of c e l l w a l l s and spaces, and cannot, t h e r e f o r e , a c t i n any simple way on the w a l l m a t e r i a l i t s e l f .  I t i s true that  other  f i b r o u s m a t e r i a l s , such as t e x t i l e s and paper, are s i m i l a r i n these r e s p e c t s , but' inhomogeneous c o n s t i t u e n t s of the l a t t e r are f a b r i c a t e d to give a m a c r o s c o p i c a l l y  uniform  system. I t i s w e l l known that there are wide d i f f e r e n c e s between s t r e n g t h p r o p e r t i e s o f d i f f e r e n t species of wood. Pine and spruce woods, f o r example, are strong and r e l a t i v e l y l i g h t i n comparison with beech and oak woods which are r i g i d and hard, while ash and h i c k o r y are tough and r e s i l i e n t . V a r i a t i o n s i n the mechanical p r o p e r t i e s w i t h i n a s i n g l e species are a l s o known;  moreover, d i f f e r e n c e s i n s t r e n g t h  c h a r a c t e r i s t i c s w i t h i n a s i n g l e stem have been noted. Recently  i t has been shown (42) t h a t v a r i a t i o n s  2 i n mechanical and p h y s i c a l p r o p e r t i e s even w i t h i n a s i n g l e growth increment may be as wide, i f not wider, than  those  between two s p e c i e s o f wood. Although the reasons f o r these v a r i a t i o n s i n s t r e n g t h c h a r a c t e r i s t i c s have been s t u d i e d , i t cannot be claimed they a r e y e t f u l l y ' u n d e r s t o o d .  that  I t i s c o n c e i v a b l e , however,  t h a t s t r e n g t h d i f f e r e n c e s l i e p a r t l y i n the anatomical, p a r t l y i n the submicroscopic, p a r t l y i n the molecular  p a r t l y i n the chemical, and  c o n s t i t u t i o n o f wood.  Most o f the work done i n s t u d y i n g f a c t o r s i n f l u e n c ing  mechanical behavior  o f wood have been concerned with  the e f f e c t s o f i t s anatomical Information  and p h y s i c a l c h a r a c t e r i s t i c s .  i s l i m i t e d on how the chemical  wood i n f l u e n c e s t r e n g t h .  constituents of  Some r e p o r t s i n the l i t e r a t u r e  (24,25,47,48,49,81) i n d i c a t e t h a t t e n s i l e s t r e n g t h o f wood depends mostly on c e l l u l o s e content and c r u s h i n g s t r e n g t h on l i g n i n content.  L i g n i n serves a l s o as a water r e p e l l e n t  substance i n the c e l l w a l l , p r o t e c t i n g the h i g h l y hydrop h i l i c c e l l u l o s e and other carbohydrates e f f e c t s (47).  from h y d r a t i o n  The removal o f l i g n i n from the c e l l w a l l  r e s u l t s i n a complete l o s s o f wet s t r e n g t h o f wood, dry s t r e n g t h i s i n c r e a s e d 6 t o 10 f o l d  (49).  although  I t i s believed  that h e m i c e l l u l o s e s a r e r e s p o n s i b l e f o r the i n c r e a s e d . s t r e n g t h o f dry, d e l i g n i f i e d wood samples.  A subsequent  removal o f h e m i c e l l u l o s e s from the l i g n i n - f r e e c e l l r e s u l t s i n the l o s s o f d r y t e n s i l e s t r e n g t h (48,49).  walls If  3 the a c e t y l groups a r e s p l i t  o f f the h e m i c e l l u l o s e s by  treatment o f wood with c a u s t i c soda s o l u t i o n s , approximately 40 t o 50 p e r cent o f wet t e n s i l e s t r e n g t h i s l o s t phenomenon i s i n t e r p r e t e d as meaning that  (48).  This  polyuronides  i n f l u e n c e s t r e n g t h p r o p e r t i e s ; that i s , by the removal o f t h e i r a c e t y l content, the h y d r a t i o n c a p a c i t y o f wood i s increased. A number o f authors have l i k e n e d the c e l l w a l l o f wood f i b r e s to r e i n f o r c e d concrete  (25,79).  According t o  them, the s t e e l r o d framework i s analogous t o the c e l l u l o s e chains, and the concrete  t o the i n t e r m i c e l l a r l i g n i n .  While  t h i s analogy i s an o v e r s i m p l i f i c a t i o n o f the mechanical r o l e of the two major chemical c o n s t i t u e n t s , i t does emphasize the f a c t that c e l l u l o s e , by i t s c h a i n s t r u c t u r e , i s the most e f f e c t i v e c o n s t i t u e n t i n wood i n r e s i s t i n g t e n s i l e s t r e s s e s . I f t h i s i s the case, then q u a l i t a t i v e d i f f e r e n c e s i n the c e l l u l o s e chains should be r e f l e c t e d by d i f f e r e n c e s i n the t e n s i l e strength  behavior o f wood.  The purpose o f t h i s study was t o i n v e s t i g a t e how mechanical behavior o f wood i n t e n s i o n p a r a l l e l t o g r a i n i s i n f l u e n c e d by q u a l i t a t i v e v a r i a t i o n s i n c e l l u l o s e .  The  q u a l i t y o f c e l l u l o s e i n wood was measured by i t s mean degree of p o l y m e r i z a t i o n  [DP],  q u a l i t a t i v e property.  o r c h a i n l e n g t h , as i t s most apparent The assumption was made t h a t , i f  c e l l u l o s e i s r e s p o n s i b l e f o r the h i g h t e n s i l e  strength  p r o p e r t i e s o f wood, v a r i a t i o n i n i t s degree of polymeriza-  4 t i o n s h o u l d have some e f f e c t on those p r o p e r t i e s .  In  p h y s i c s o f w e l l o r i e n t e d h i g h polymers and f a b r i c s , i t has been shown t h a t degree o f p o l y m e r i z a t i o n i s an important f a c t o r i n f l u e n c i n g t e n a c i t y o f m a t e r i a l s o n l y below a c e r t a i n c r i t i c a l DP v a l u e .  This value i s considered the  one a t which a s l i p p a g e between n e i g h b o r i n g c h a i n s can occur due t o t h e reduced c o h e s i o n between those c h a i n s .  At high  DP v a l u e s , s t r e n g t h i s r e l a t i v e l y independent o f c h a i n l e n g t h , s i n c e t h e t o t a l energy b i n d i n g t o g e t h e r t h e n e i g h b o r i n g polymer c h a i n s i s much g r e a t e r t h a n t h a t o f any s i n g l e p r i m a r y v a l e n c e f o r c e between two monomer u n i t s o f t h e same chain. M o i s t u r e dependence o f wood s t r e n g t h p r o p e r t i e s i s a w e l l known and  w e l l s t u d i e d phenomenon.  Although  moisture  s e n s i t i v i t y o f s t r e n g t h has been c o n s i d e r e d due t o t h e h i g h l y h y g r o s c o p i c n a t u r e o f t h e carbohydrate  components, i t i s n o t  known how a q u a l i t a t i v e change i n c e l l u l o s e , t h e major carboh y d r a t e component o f wood, c o u l d i n f l u e n c e t h i s b a s i c behavior.  A second purpose o f t h i s experiment was t o study  whether wood w i t h c e l l u l o s e o f l o w DP would be more s e n s i t i v e 0  to moisture  content v a r i a t i o n s t h a n wood h a v i n g  cellulose  of long-chain s t r u c t u r e . Another o b j e c t i v e o f t h i s study was t o examine t h e i n f l u e n c e o f c e l l u l o s e c h a i n l e n g t h on t h e t e m p e r a t u r e dependence o f wood t e n s i l e s t r e n g t h p r o p e r t i e s .  Although  5  t h i s behavior o f wood i s g e n e r a l l y considered t o be mainly due t o l i g n i n and h e m i c e l l u l o s e s , which are thermo-sensitive components, i t i s not known how much c o n t r i b u t i o n i s made by c e l l u l o s e .  I t i s q u i t e conceivable t h a t t e n s i l e s t r e n g t h  of wood with low-DP c e l l u l o s e molecules  would be more  s e n s i t i v e t o temperature v a r i a t i o n s than that o f wood with long-chain  cellulose.  6  MATERIAL AND METHODS  The e x p e r i m e n t a l m a t e r i a l was c a r e f u l l y c h o s e n a n d a s a m p l i n g t e c h n i q u e was p r o p e r l y d e s i g n e d f o r t h e requirements  of t h i s experiment.  minimize the i n f l u e n c e of f a c t o r s , length,  on t e n s i l e  special  These w e r e n e c e s s a r y  to  other than c e l l u l o s e  strength properties.  Special  a t i o n s w e r e made t o k e e p v a r i a t i o n s i n s p e c i f i c  chain  considergravity  as  l o w a s p o s s i b l e s i n c e t h i s f a c t o r h a s r e p e a t e d l y b e e n shown to account  for a relatively large  strength characteristics  o f wood.  amount o f v a r i a t i o n i n The m a t e r i a l a n d t h e  s a m p l i n g t e c h n i q u e had t o be s u c h t h a t a n a t o m i c a l and p h y s i c a l f e a t u r e s , cent  cellulose  even l e s s  s u c h as f i b r i l  angle,  c o n t e n t and t r a c h e i d l e n g t h , were k e p t  f o r a l l the specimens  tested  f o r t h i s study to minimize v a r i a t i o n s i n strength due t o d i f f e r e n c e s  i n temperature  c o n d i t i o n s of the t e s t specimens.  and m o i s t u r e  uniform  developed properties  content  The r e l a t i v e l y  small  o f t h e t e n s i o n t e s t specimen gave an u n u s u a l p r o b l e m  i n m a i n t a i n i n g a constant moisture content test.  per  i n tension.  E x p e r i m e n t a l methods were a l s o s p e c i a l l y  size  important  throughout  the  7  I  The  MATERIAL  t e s t m a t e r i a l was  obtained  from a s i n g l e , f r e s h -  l y cut, Douglas f i r (Pseudotsuga m e n z i e s i i . ( M i r b . )  Franco)  t r e e , s e l e c t e d from a 150-year-old, even-aged stand, grown a on good s i t e at the U n i v e r s i t y of B r i t i s h Columbia Research A  F o r e s t , Haney, B.C.  The most important c h a r a c t e r i s t i c s  taken i n t o c o n s i d e r a t i o n i n the s e l e c t i o n were s t r a i g h t n e s s of stem, l a c k of l e a n i n g of the t r e e i n any a l a r g e diameter at b r e a s t height rate.  (dbh)  direction,  and  i n d i c a t i n g f a s t growth  In a d d i t i o n , such f e a t u r e s as r e l a t i v e p o s i t i o n of crown  i n the stand, l e n g t h of c l e a r b o l e , and were a l s o taken i n t o account.  symmetry of crown  Dimensions of the t r e e se-  l e c t e d i n regard to above c h a r a c t e r i s t i c s were as f o l l o w s : height  228ft, dbh  o u t s i d e bark 58 i n . , dbh  i n . , number of r i n g s at stump 149,  i n s i d e bark  54  d i s t a n c e from ground to  f i r s t l i v i n g branch 102 f t . Immediately a f t e r f e l l i n g , the b o l e was a t e s t b l o c k approximately 1 f t i n l e n g t h was above ground.  At t h i s l e v e l the g r a i n was  bucked  and  cut at 50 f t  t e s t e d and  found  to be s t r a i g h t , an important c h a r a c t e r i s t i c i n t e s t i n g m i c r o - s i z e specimens i n t e n s i o n p a r a l l e l to g r a i n .  The  growth r a t e was  a l s o s u f f i c i e n t l y f a s t f o r the requirements  of t h i s study.  The number of growth increments at t h i s  l e v e l was 131.  The mean diameter o f the t e s t b l o c k was 36  i n . i n s i d e bark. The t e s t b l o c k was shipped to the l a b o r a t o r y on the day o f f e l l i n g , a f t e r wrapping i n a p o l y e t h y l e n e sheet to prevent d r y i n g below the f i b r e s a t u r a t i o n p o i n t .  This  was done i n order t o e l i m i n a t e p o s s i b l e development of s t r e s s e s i n the b l o c k due t o shrinkage, which might have caused u n d e s i r a b l e v a r i a t i o n i n s t r e n g t h and r e l a t e d properties.  During the e n t i r e m a t e r i a l h a n d l i n g procedure,  s p e c i a l care was e x e r c i s e d t o maintain the t e s t m a t e r i a l i n a water s a t u r a t e d c o n d i t i o n . A sample was l a t e r e x t r a c t e d from the 44- t o 51year increments, g i v i n g a s m a l l b l o c k 5 i n . i n l e n g t h and approximately 14 i n . i n t a n g e n t i a l width.  The r a d i a l width  of the b l o c k was determined by dimension o f the e i g h t i n clude?! increments.  Twenty 2/3-in. wide specimen b l o c k s were  s p l i t r a d i a l l y from the t e s t b l o c k .  A special  splitting  t o o l w i t h r e l a t i v e l y s m a l l b e v e l angle c u t t i n g edge was used i n t h i s o p e r a t i o n .  The compression  component o f wedg-  i n g f o r c e o f such a t o o l was r e l a t i v e l y low, so t h a t by i t s use, f i b r e damage due t o t r a n s v e r s e compressive was not l i k e l y t o occur.  stresses  The b l o c k s were then submerged  i n water a t room temperature  i n a vacuum d e s i c c a t o r .  Vacuum was a p p l i e d i n t e r m i t t e n t l y u n t i l the b l o c k s had become s o f t enough f o r microtome s e c t i o n i n g .  On the average,  9  2 to 3 days were r e q u i r e d to a t t a i n s u f f i c i e n t s o f t e n i n g . The water-logged b l o c k , with increment 44 f a c i n g upward, was  p l a c e d i n the jaws of a s m a l l r i g i d v i s e spe-  c i a l l y designed This v i s e was stem.  f o r s e c t i o n i n g 5 to 6 i n . l o n g wood samples.  gripped i n t o the microtome press by a short  The l o n g jaws of the v i s e provided support f o r the  b l o c k s u f f i c i e n t to overcome pressure o r i g i n a t i n g from the microtome blade at the time of s e c t i o n i n g .  The  adjustable  microtome grip'-was f i r s t turned i n the h o r i z o n t a l plane u n t i l the g r a i n of wood had become approximately with the d i r e c t i o n of c u t t i n g .  The g r i p was  parallel  then t i l t e d i n  the d e s i r e d d i r e c t i o n to produce t r u e t a n g e n t i a l s e c t i o n s as judged on the two  t r a n v e r s e f a c e s of the b l o c k .  44 p r o v i d e d m a t e r i a l f o r proper alignment  and  Increment  adjustments.  S e c t i o n s obtained from t h a t increment were d i s c a r d e d ; cut from increments  those  45, 46 and 47 were kept f o r the exper-  iment. Prom the beginning to the end of each of the three growth increments  i n each b l o c k , a s e r i e s of 100-micron-  t h i c k , t a n g e n t i a l microtome s e c t i o n s was  cut.  The  blocks  were kept i n a s a t u r a t e d c o n d i t i o n d u r i n g microtoming by w e t t i n g the s u r f a c e w i t h water u s i n g a camel-hair Approximately increment.  40 to 60 s e c t i o n s were obtained from  brush. one  Microtome s e c t i o n s were packed i n s e r i e s  and  s t o r e d i n separate h e a t - s e a l e d p o l y e t h y l e n e bags, a c c o r d i n g to o r i g i n a l b l o c k and growth increment number.  Each s e r i e s  10  was of  c a r e f u l l y examined as to s t r a i g h t n e s s of g r a i n and l a c k c u r l i n g ; , only those marked i n F i g u r e 1 were f i n a l l y i n -  cluded.  Approximately 5 ml of 1 per cent thymol  solution  i n d i s t i l l e d water was added to each bag t o prevent microb i o l o g i c a l attack.  S t o r i n g of the s e c t i o n s was  to  to minimize h y d r o l y t i c degradation of  5°C temperature,  done a t 1  the carbohydrate components of wood. The mechanical, p h y s i c a l and chemical c h a r a c t e r i z a t i o n of increments 45, 46 and 47 have been r e p o r t e d elsewhere /  \  (42;.  i  n  Here'Asome of the r e s u l t s of those analyses are shown  graphically.  In F i g u r e s 2 and 3 v a r i a t i o n i n t e n s i l e s t r e n g t h  and modulus of e l a s t i c i t y are shown, while F i g u r e 4 and 5 represent i n t r a - i n c r e m e n t v a r i a t i o n s i n s p e c i f i c g r a v i t y , h o l o c e l l u l o s e content unadjusted f o r r e s i d u a l l i g n i n .  and  In  F i g u r e 6 the h y d r o l y s i s products of h o l o c e l l u l o s e are g i v e n d i a g r a m a t i c a l l y as percentages of f i v e types of sugars based on the weight of h o l o c e l l u l o s e .  V a r i a t i o n i n the amount of  c e l l w a l l m a t e r i a l i n the three growth increments has been s t u d i e d by ¥orrall(l05), u s i n g the micro-scanning technique of  Green and W o r r a l l ( 3 3 ) .  His r e s u l t s c o i n c i d e d w i t h those  of  specific gravity variations.  Per cent latewood i s a l s o  g i v e n f o r each increment i n F i g u r e s 2, 3 and 4; i t was d e t e r mined by u s i n g a semi-microscopic technique on t r a n s v e r s e s u r f a c e s of b l o c k s s t a i n e d w i t h a m a l a c h i t e b l u e double  stain.  green-methylene  11  II  METHODS  1.  Degradation o f C e l l u l o s e by Means o f Gamma R a d i a t i o n  A.  Previous Work Gamma rays are produced  e i t h e r by s h o o t i n g r a p i d  e l e c t r o n s on m e t a l l i c t a r g e t s o r by r a d i a t i o n from c e r t a i n by-products o f n u c l e a r f i s s i o n . . In the f i r s t case, the f a s t e l e c t r o n s are produced by resonant transformers, Van der G r a f f machines, o r l i n e a r a c c e l e r a t o r s . case, one u s u a l l y employs ray source.  I n the second  fin  Co as a v e r y e f f i c i e n t gamma  I f the elemental c o b a l t , which e x i s t s as s e v e r a l  i s o t o p e s , i s exposed  t o the neutron f l u x o f an atomic r e -  60 a c t o r , the  Co i s o t o p e i s converted i n t o a gamma i r r a -  d i a t o r w i t h a h a l f - l i f e time o f 5.3 years (68).  Many such  sources o f v a r y i n g s t r e n g t h are now a v a i l a b l e on t h i s  con-  t i n e n t and p r o v i d e a simple, permanent and constant source f o r gamma r a y s . The measurement o f i r r a d i a t i o n i s based on the l o n g - e s t a b l i s h e d dosimetry of X-rays.  There, the "roentgen  u n i t " has been d e f i n e d and i n t r o d u c e d as the r a d i a t i o n i n t e n s i t y which produces u n i t i o n i z a t i o n i n 1 ml o f d r y a i r a t 0°C and atmospheric p r e s s u r e .  F o r r a d i a t i o n s other  than X-ray, the "rep" i s used, an a b b r e v i a t i o n o f "roentgen e q u i v a l e n t p h y s i c a l " , i n d i c a t i n g that the rep i s that u n i t  12  of dosage producing the same i o n i z a t i o n e f f e c t as roentgen of X-rays.  one  Recently, "rad" and " f e r m i s " have been  i n t r o d u c e d which are s l i g h t l y l a r g e r u n i t s than rep.  All  these u n i t s , however, are v e r y s m a l l q u a n t i t i e s and  one  f r e q u e n t l y uses k i l o r e p , k i l o r a d or" k i l o f e r m i s f o r  1000,  and megarep, megarad or megafermis f o r 10  i)  units.  R a d i a t i o n chemistry of h i g h polymers In order to understand  the f i n a l r e s u l t s of i r r a d -  i a t i o n on the chemical p r o p e r t i e s of wood, i t seems t o be a p p r o p r i a t e to summarize and b r i e f l y d i s c u s s the  elementary  processes which are the immediate consequences of i r r a d i a t i o n . These primary e f f e c t s are those which g i v e r i s e t o  secondary  and t e r t i a r y steps which, i n t u r n , l e a d to a s e r i e s of molecular events.  F i n a l l y , these molecular processes cause  the changes i n the p r o p e r t i e s of i r r a d i a t e d m a t e r i a l s . The impact  of photon, a s s o c i a t e d w i t h gamma r a d i a t i o n ,  on organic molecules, i n i t i a t e s e s s e n t i a l l y two  primary  processes a c c o r d i n g to Bovey (10); 1. e l e c t r o n s are r e moved from atomic n u c l e i and p o s i t i v e l y charged  molecule  ions are formed; 2. e l e c t r o n s are l i f t e d t o h i g h e r o r b i t a l s and n e u t r a l but " e x c i t e d " molecules are formed. processes happen i n the same molecule, an e x c i t e d  I f both molecule  i o n i s generated. These forms  of molecules are v e r y u n s t a b l e and  13  undergo r a p i d l y one o f s e v e r a l p o s s i b l e changes.  I n the  case o f i o n i z a t i o n , there may be an immediate recombination of two charged p a r t i c l e s w i t h the disappearance o f the active center.  However, i n the case o f h i g h energy  radiation,  such as gamma r a d i a t i o n , the e l e c t r o n u s u a l l y l e a v e s the molecule w i t h enough energy t o prevent an immediate recombination. A frequent secondary e f f e c t o f i o n i z a t i o n i s the l i b e r a t i o n o f hydrogen atoms which immediately r e a c t w i t h one another t o produce a hydrogen molecule and a p o s i t i v e l y charged f r e e r a d i c a l i o n .  I f the two hydrogen atoms, u n i t e d  i n t o a molecule, were adjacent on the same organic molecule, a double bond may be formed.  I f , however, the hydrogen  atom r e a c t s w i t h the hydrogen atom o f an adjacent molecule, H  2  i s a l s o evolved and a p o s i t i v e l y charged  transition  s t a t e i s generated which, i n t u r n , forms a c r o s s - l i n k between the two c h a i n s . Another secondary e f f e c t o f r a d i a t i o n i s the f a c t t h a t e x c i t e d molecules can undergo spontaneous and produce a p a i r o f f r e e r a d i c a l s .  dissociations  These can e i t h e r com-  b i n e w i t h f r e e hydrogen atoms, thereby producing a d i s p r o p o r t i o n a t i o n o f the c h a i n , o r may u n i t e with other r a d i c a l s of the same type. As may be assumed from the mechanisms mentioned, there are two p a r t i c u l a r l y s i g n i f i c a n t consequences o f  14  r a d i a t i o n , i . e . , degradation  and c r o s s - l i n k i n g .  r e s u l t o f the treatment depends on the r e l a t i v e of these two processes.  I f degradation  The net proportion  i s dominant, the  i r r a d i a t e d sample i s e m b r i t t e l e d , i t s o r i g i n a l degree o f polymerization  i s reduced as are i t s s t r e n g t h p r o p e r t i e s .  I f , however, c r o s s - l i n k i n g p r e v a i l s , the polymeric  material  gains s u b s t a n t i a l l y i n toughness, r i g i d i t y and r e s i s t a n c e against  solvents. Polymeric  substances, t h e r e f o r e , can a r b i t r a r i l y be  c l a s s i f i e d i n t o two groups: 1. m a t e r i a l s which, at c e r t a i n r a d i a t i o n dosage l e v e l s , form a d d i t i o n a l chemical  bonds  r e s u l t i n g i n improved p r o p e r t i e s ; 2. m a t e r i a l s which suffer-:f r a c t u r e o f polymeric  ii)  chains or s p l i t t i n g o f f o f s i d e groups.  Influence o f gamma r a d i a t i o n on the .chemicalr.properties of wood and c e l l u l o s e Wood and c e l l u l o s e belong to the second group.  Rel-  a t i v e l y s m a l l i n t e g r a l doses of r a d i a t i o n destroy c e l l u l o s e and  other p o l y s a c c h a r i d e s ,  although wood as a l i g n i n - c a r b b -  hydrate complex r e a c t s somewhat d i f f e r e n t l y from c e l l u l o s e towards r a d i a t i o n .  Relatively..few extensive i n v e s t i g a t i o n s  have been c a r r i e d out i n t h i s f i e l d . have progressed  Even fewer o f them  to such a p o i n t as t o produce ground f o r  g e n e r a l i z a t i o n s on the importance of f a c t o r s such as' the r a t e o f i r r a d i a t i o n and the p h y s i c a l s t a t e o f the i r r a d i a t e d  15  material. L i g n i n appears • t o be r e l a t i v e l y u n a f f e c t e d by i r r a d i a t i o n (11).  I t i s b e l i e v e d t h a t the r e s i s t a n c e of t h i s  c o n s t i t u e n t of wood t o i r r a d i a t i o n i s due t o i t s aromatic nature, the benzene nucleus being very s t a b l e i n t h i s  regard.  R e s u l t s from s e v e r a l i n v e s t i g a t i o n s i n t h i s f i e l d , as c i t e d by Brauns (11), however, cannot be i n t e r p r e t e d as meaning that l i g n i n i s e n t i r e l y u n a l t e r e d , merely t h a t i t i s not g r e a t l y changed i n a manner that i s d e t e c t a b l e by the chemical tests applied.  According  t o Smith and Mixer (86), l i g n i n i n  wood serves as a p r o t e c t i v e m a t e r i a l f o r the carbohydrate components a g a i n s t i r r a d i a t i o n .  They found that d i r e c t  i r r a d i a t i o n of wood h o l o c e l l u l o s e produced g r e a t e r degradat i o n than i r r a d i a t i o n o f wood f o l l o w e d by p r e p a r a t i o n o f holocellulose.  A s i m i l a r e f f e c t was noted w i t h  when a styrene-isobuthylene  copolymer was i r r a d i a t e d ; i . e . ,  the benzene nucleus o f styrene p r o t e c t e d from excessive  styrene  the i s o b u t y l e n e  degradation ( 1 ) .  One of the most comprehensive s t u d i e s on the e f f e c t s of gamma r a d i a t i o n on c e l l u l o s e has been c a r r i e d out by B l o u i n and Arthur  (9).  They i r r a d i a t e d p u r i f i e d  5 c e l l u l o s e from 10  cotton  8 t o 10  r a d dosages.  The major changes  induced by i r r a d i a t i o n were cleavage o f the c e l l u l o s e chains, and  formation  of carbonyl and c a r b o x y l groups.  I t i s of  i n t e r e s t t o note i n that study that the c e l l u l o s e molecule was not s i g n i f i c a n t l y a f f e c t e d u n t i l i t r e c e i v e d a dosage  16  g r e a t e r than 10 izations  rads, a f t e r which the number o f depolymer-  , the number o f c a r b o n y l groups, and the  number of  c a r b o x y l groups formed i n c r e a s e d w i t h f u r t h e r i n c r e a s e i n dosage.  I t has a l s o been found that the formation o f carbon-  y l groups i s by f a r the most important occurs.  chemical change which  The number o f carboxyls formed i s of the same order  of magnitude as the number o f c h a i n cleavages,  suggesting  that each c h a i n cleavage produces one c a r b o x y l group, while the number o f carbonyls produced i s approximately  twenty  times the number o f carboxyls formed. R a d i a t i o n causes random depolymerization and decomp o s i t i o n o f c e l l u l o s e both i n the e a s i l y hydrolyzed o r amorphous areas and the r e s i s t a n t o r c r y s t a l l i n e regions (84).  This i s q u i t e u n l i k e any chemical treatment  on wood  or c e l l u l o s e which p r e f e r e n t i a l l y a f f e c t s amorphous c e l l u l o s e . There i s a d e f i n i t e i n c r e a s e i n the r a t e o f h y d r o l y s i s o f c e l l u l o s e a f t e r i r r a d i a t i o n and w i t h i t there i s an i n c r e a s e d r a t i o between r a t e o f sugar p r o d u c t i o n and d e s t r u c t i o n , hence, an i n c r e a s e i n sugar y i e l d (62).  An important  increase i n  the r a t e o f h y d r o l y s i s , i n t u r n , r e q u i r e s t h a t the average c h a i n l e n g t h be reduced  t o 200 glucose u n i t s or l e s s (60).  The maximum o v e r a l l y i e l d o f sugar o b t a i n a b l e by d i l u t e a c i d h y d r o l y s i s o f i r r a d i a t e d c o t t o n l i n t e r s i s approximately 65 p e r cent, almost  three times the y i e l d o b t a i n b l e from  u n t r e a t e d samples (84).  The corresponding y i e l d from  p u r i f i e d wood pulp i s even h i g h e r , about 70 t o 75 p e r cent (70).  17  I r r a d i a t e d samples show no i n c r e a s e d water s o l u b i l i t y u n t i l t r e a t e d w i t h a dosage o f 5x10 rads (9). Q 10  At  roentgens, c o t t o n c e l l u l o s e becomes approximately 10  per cent water-soluble and a t 3*3x10  i t i s completely  s o l u b l e (9). The d i l u t e a l k a l i s o l u b i l i t y o f i r r a d i a t e d Q  c e l l u l o s e i n c r e a s e s w i t h i n c r e a s e i n dosage, .and a t 10  rads  i t becomes 70 t o 75 p e r cent s o l u b l e . There i s some evidence i n d i c a t i n g t h a t  another  chemical e f f e c t o f gamma r a d i a t i o n on wood i s the d i s r u p t i o n or a l t e r a t i o n o f a p o s s i b l e bond between l i g n i n and carbohydrates.  I t has been found that i r r a d i a t e d wood samples  could be s u l f o n a t e d e a s i e r than u n t r e a t e d samples, which suggests a s p l i t t i n g o f the l i g n i n - c a r b o h y d r a t e complex by gamma r a y s , s i n c e there i s no evidence that any b a s i c chemi c a l change had taken p l a c e i n the l i g n i n i t s e l f (11). Another i n d i c a t i o n o f the a l t e r a t i o n o f the chemical bond between l i g n i n and c e l l u l o s i c m a t e r i a l s i s that while u n t r e a t e d wood appears t o be r e l a t i v e l y u n a f f e c t e d by the enzymatic  a c t i o n o f rumen b a c t e r i a , f e r m e n t a b i l i t y i n c r e a s e s 6 8  r a p i d l y between 6.5x10 however, not c l e a r l y  and 10  rads dosages (60,62). I t i s ,  established, whether o r not t h i s  i n c r e a s e d d i g e s t i b i l i t y o f wood i s due only t o the severe d e p o l y m e r i z a t i o n o f the c e l l u l o s e molecules alone.  18  iii)  E f f e c t s o f gamma r a d i a t i o n on the p h y s i c a l and mechanical p r o p e r t i e s o f wood and r e l a t e d m a t e r i a l s  As a r e s u l t o f chemical degradation o f c e l l u l o s e , gamma r a d i a t i o n induces changes i n the p h y s i c a l and mecha n i c a l p r o p e r t i e s o f wood.  Among the p h y s i c a l p r o p e r t i e s ,  wood-moisture r e l a t i o n s h i p i s a f f e c t e d most n o t i c e a b l y . has been reported water, adsorbs" periods  that i r r a d i a t e d wood, when submerged i n  significantly  than do untreated  have been obtained  more water i n r e l a t i v e l y  samples (23).  when i r r a d i a t e d samples were exposed t o These changes i n  nature o f wood, however, come i n t o e f f e c t  only a t r e l a t i v e l y heavy doses o f r a d i a t i o n . 7 than 10  short  Similar effects  c o n d i t i o n s o f h i g h r e l a t i v e humidity (23). the hygroscopic  It  At l e s s  rads, the e f f e c t may even be n e g l i g i b l e .  On the  b a s i s o f these f i n d i n g s .Seaman e t a l . (84) suggested t h a t , besides  chemical degradation,  an i n c r e a s e i n the r e l a t i v e  amount o f amorphous c e l l u l o s e by i r r a d i a t i o n might occur as a s t r u c t u r a l change. i c i t y values  However, the small changes i n hyroscop-  suggest that there i s no marked a l t e r a t i o n i n  the submicroscopic s t r u c t u r e o f the c e l l u l o s e network. The apparent decrease i n c r y s t a l l i n i t y , as a l s o i n d i c a t e d by the i n c r e a s e d h y d r o l y s W b i l i t y  of. c e l l u l o s e , could conceiv- <•-  a b l y be due t o the c h e m i c a l l y a l t e r e d s t r u c t u r e o f c e l l u l o s e , r a t h e r than t o an a l t e r a t i o n o f the c r y s t a l l i n e s t r u c t u r e . Strength p r o p e r t i e s o f c e l l u l o s i c m a t e r i a l s a r e  19  a l s o a f f e c t e d "by i r r a d i a t i o n through degradation.  Ultimate  t e n s i l e s t r e n g t h , as w e l l as u l t i m a t e e l o n g a t i o n , have been r e p o r t e d t o be reduced by exposure t o gamma rays (9,28,29, 65).  As another support f o r the assumption  t h a t there i s  no s h i f t i n g o f the crystalline-amorphous r a t i o . . i n i r r a d i a t i o n , G i l f i l l a n and Linden (28,29) found no observable i n the s t r e s s - s t r a i n c h a r a c t e r i s t i c s  differences  o f gamma r a d i a t e d c o t t o n  and those o f the c o n t r o l m a t e r i a l .  i v ) E f f e c t o f moisture content on degradation by gamma rays Glegg and K e r t e s z (30) i r r a d i a t e d c o t t o n c e l l u l o s e 4  6  and p u r i f i e d wood pulp t o doses from 6x10 t o 2.3x10 rads a t d i f f e r e n t moisture contents o f the samples.  They  found t h a t wood c e l l u l o s e i r r a d i a t e d a t 5.6,4.6 and 3.3 per cent moisture content showed e s s e n t i a l l y the same r e d u c t i o n i n i n t r i n s i c v i s c o s i t y a t comparable i r r a d i a t i o n dosages.  I r r a d i a t i o n a t three low moisture content  (0.32, 0.30 and 0.26 p e r cent) a l s o gave s i m i l a r  levels  results  at comparable dosage l e v e l s , which suggests t h a t a t low moisture content l e v e l s c e l l u l o s e i s a t l e a s t as s u s c e p t i b l e to degradation by gamma rays as samples with h i g h moisture contents. v)  The a f t e r - e f f e c t o f gamma r a d i a t i o n An i n t e r e s t i n g phenomenon, the a f t e r - e f f e c t o f  r a d i a t i o n , has been observed by Glegg and K e r t e s z (30).  20  U n l i k e samples .at h i g h e r moisture content, they found that v i s c o s i t y o f i r r a d i a t e d c e l l u l o s e a t lower than 1 p e r cent moisture content p r o g r e s s i v e l y decreased beyond that measured, s h o r t l y a f t e r the end o f i r r a d i a t i o n .  This a f t e r -  e f f e c t was g r e a t e r than the primary e f f e c t , which suggests that some type o f a c t i v a t e d molecule .irradiation.  Paramagnetic resonance  i s formed d u r i n g a b s o r p t i o n measure-  ments r e v e a l e d that the a c t i v e molecules a f t e r were o f the f r e e r a d i c a l type.  irradiation  I t was shown t h a t 5.5x10  rad i r r a d i a t i o n o f samples o f low moisture content gave moderate a b s o r p t i o n , and a t h i g h e r moisture content, v e r y s l i g h t a b s o r p t i o n a f t e r f i v e days.  T h i r t y days l a t e r , only  a weak s i g n a l was obtained from the samples a t 0.32 p e r cent moisture content, and a b a r e l y d i s c e r n i b l e s i g n a l from t h a t i r r a d i a t e d a t 4.6 p e r cent moisture content.  I t appears  that i r r a d i a t i o n o f d r y c e l l u l o s e i n a i r l e a d s t o formation of f r e e . r a d i c a l s which are capable o f s u r v i v i n g l o n g a f t e r the end o f i r r a d i a t i o n and g i v e r i s e t o f u r t h e r depolymerization.  B.  I r r a d i a t i o n o f Experimental M a t e r i a l w i t h Gramma Rays The microtomed wood s e c t i o n s wrapped i n h e a t - s e a l e d  p o l y e t h y l e n e bags were sent t o Atomic Energy o f Canada L t d . , Commercial Products D i v i s i o n , Ottawa, Canada, f o r gamma radiation.  The p o l y e t h y l e n e i n s u r e d the maintenance o f  21  moisture s a t u r a t e d c o n d i t i o n o f the sections d u r i n g and after irradiation.  Pour doses o f i r r a d i a t i o n were a p p l i e d  to the wood samples i n order t o produce v a r i o u s degradations of the c e l l u l o s e .  These were 0.1, 1.0, 10.0, and 15.0 mega-  rads. A l l samples, except those r e c e i v i n g 10.0 megarad dosage, were i r r a d i a t e d i n a G-ammacell 220 a t approximately 1 megarad per hour dose r a t e .  The specimens i r r a d i a t e d t o  10.0 megarads r e c e i v e d the doses i n a G-ammacell 200,which was capable o f d e l i v e r i n g only 0.1 megarad dosage p e r hour. These d i f f e r e n t dose r a t e s were used because the work l o a d on the G-ammacell 220 was too h i g h a t  the time t o put a l l  the samples through i r r a d i a t i o n s i n a reasonable time. This was due t o l i m i t e d s i z e o f the gamma c e l l . The source o f gamma r a d i a t i o n i n the c e l l s was CogQ, the nominal s t r e n g t h o f which f o r a maximum dose r a t e was approximately 1500 c u r i e s .  The dose u n i f o r m i t y 4-  within  the chambers o f the c e l l s was nominally -5 p e r  cent, a v a l u e which was considered s u f f i c i e n t f o r t h i s experiment. the samples.  R a d i a t i o n dosages were randomly assigned t o The p o s i t i o n o f the groups r e l a t i v e t o each  other i n the o r i g i n a l b l o c k i s shown i n F i g u r e 1.  22  2. TensionTest  Methods  A. P r e p a r a t i o n of Test Specimens In order to minimize the inherent v a r i a t i o n of woody m a t e r i a l , t e n s i o n t e s t samples were taken from the same r e l a t i v e p o s i t i o n i n the three growth Based on the r e s u l t s of i n t r a - i n c r e m e n t  increments.  s t u d i e s (42),  30  and 80 per cent p o s i t i o n s r e l a t i v e to the beginningig-f the growth increments,  provided m a t e r i a l with  approximately  average s t r e n g t h p r o p e r t i e s f o r e a r l y - and latewood, tively.  Two  respec-  microtome s e c t i o n s were taken from c l o s e to  each of these two p o s i t i o n s , which provided  enough m a t e r i a l  f o r t e n s i o n p a r a l l e l to g r a i n s t u d i e s . The t e n s i o n t e s t specimens were 2.5 mm r e c t a n g u l a r s t r i p s prepared  x 100  mm  by punching the s e l e c t e d m i c r o -  tome s e c t i o n blanks, u s i n g a s p e c i a l l y machined c u t t i n g d i e f i x e d on a 1/2-ton converted  arbor p r e s s .  assembly i s shown i n F i g u r e 7.  The c u t t i n g  T h i s form of specimen has  been shown to g i v e the h i g h e s t s t r e n g t h v a l u e s , as w e l l as the best r e p l i c a t i o n , i n t e n s i l e s t r e n g t h p r o p e r t i e s (42). S p e c i a l care was  e x e r c i s e d i n punching as to wood g r a i n  d i r e c t i o n of specimen. wide was was  A p a r t approximately  t o r n o f f the edge of a wet  then p l a c e d on an IBM  1 to 2  section.  mm  The s e c t i o n  card, so t h a t the t o r n edge  o r i e n t e d p a r a l l e l with rows of number.  I t was  was  pressed  l i g h t l y a g a i n s t the paper so t h a t i t adhered to the card  23  due  to surface tension.  modified  The card was then p l a c e d onto the  stage o f the arbor p r e s s .  I t s edge,  perpendicular  to the t o r n s i d e o f the s e c t i o n , was h e l d against a guide s t i c k clamped t o the s i d e o f the stage.  Side-matched  specimens were punched by moving the card along the guide s t i c k , w i t h approximately 3 t o 3.5 mm a f t e r each c u t . to seven specimens could be obtained  Five  from each s e c t i o n u s i n g  t h i s technique; i . e . , 10 t o 14 from the two s e c t i o n s a t the same r e l a t i v e p o s i t i o n w i t h i n increments. Each group o f 10 t o 14 specimens was kept i n a 250 mm by 25 mm Pyrex t e s t tube.  Approximately 2 t o 3 ml  of 1 p e r cent aqueous s o l u t i o n o f thymol was added as a p r e s e r v a t i v e and f o r the purpose o f m a i n t a i n i n g s a t u r a t e d a i r c o n d i t i o n i n s i d e the tube.  a moisture  The tube was  subsequently c l o s e d w i t h a neoprene stopper.  Specimens  were then s t o r e d a t 1 to 5°C temperature u n t i l f i n a l conditioning.  B.  Test  Variables  i ) T e s t i n g machine v a r i a b l e s The  t e n s i o n t e s t s were conducted on a t a b l e model  Instron Tensile Tester.  In a l l t e s t s the l o a d was a p p l i e d  w i t h continuous motion o f the moving cross-head, producing a constant  r a t e o f e l o n g a t i o n a t 0.005 in./min.  Each  24  specimen was  t e s t e d over a 1.5  i n . span which r e s u l t e d i n  0.00333 in./min r a t e of s t r a i n .  The l o a d was  recorded  a u t o m a t i c a l l y throughout the t e s t on a chart moving with a constant  speed of 1 in./min.  the c h a r t was  10 grams.  S e n s i t i v i t y of r e a d i n g  Ultimate  t e n s i l e l o a d , l o a d to  u n i t s t r a i n w i t h i n the p r o p o r t i o n a l l i m i t , and  ultimate  t e n s i l e s t r a i n were read d i r e c t l y from the c h a r t , and a p p r o p r i a t e s t r e n g t h values were c a l c u l a t e d . area under the l o a d - e l o n g a t i o n curve was a planimeter, was  on  The  the  total  measured u s i n g  from which the work to maximum t e n s i o n l o a d  calculated.  A t o t a l of 540 t e n s i o n  -.:  specimens were  tested. i  i i ) Moisture  content  and  temperature  In order to study the i n f l u e n c e of the degree of polymerization  of c e l l u l o s e on the moisture dependence of  wood s t r e n g t h p r o p e r t i e s , the specimens were t e s t e d at three d i f f e r e n t c o n d i t i o n s of moisture content. f r e e , a i r - d r y , and  Moisture-  s a t u r a t e d c o n d i t i o n s were chosen to cover  the p o s s i b l e widest range of s t r e n g t h v a r i a t i o n i n r e l a t i o n to moisture content.:  The  e f f e c t s of temperature on  the  t e n s i l e s t r e n g t h p r o p e r t i e s were examined over a r e l a t i v e l y narrow range from 25 to 70°C.  Although i t appeared d e s i r a b l e  to i n c r e a s e the temperature range f o r a more thorough examination of the temperature e f f e c t , the  facilities  25  a v a i l a b l e r e s t r i c t e d t h i s p a r t of the experiment.  Three  temperature c o n d i t i o n s were used i n the experiment, namely 25, 50 and 70°C. The r e l a t i v e l y s m a l l s i z e o f the t e s t  specimens  r e q u i r e d c a r e f u l c o n t r o l of moisture content d u r i n g t e s t s . On the average, the t e s t of one specimen was completed i n approximately 3 to 8 minutes, d u r i n g which p e r i o d the t h i n wood s e c t i o n s would have changed t h e i r moisture content r e g a r d l e s s of how c a r e f u l l y they had been p r e c o n d i t i o n e d . Therefore., each t e s t specimen was p l a c e d i n a p l a s t i c bag s p e c i a l l y made f o r t h i s purpose from 1.0 m i l p o l y e t h y l e n e , u s i n g an e l e c t r i c s o l d e r i n g i r o n .  In the m i d - p o r t i o n of  the bag an ' o v e r - f o l d i n g ' was made, so that when the spec1  imen was t e s t e d between the jaws of the t e s t i n g machine the l o o s e f o l d e l i m i n a t e d t e s t i n g the p o l y e t h y l e n e w i t h the wood section.  Two t e s t specimens i n p l a s t i c bags are shown i n  F i g u r e 8.  F i g u r e 9 shows how  such a specimen i s gripped  i n the t e s t i n g machine. Those specimens t e s t e d i n the m o i s t u r e - f r e e cond i t i o n were d r i e d over phosphorus pentoxide i n vacuo at 60°C f o r at l e a s t 72 hours. air-dried.  The t e s t p i e c e s were f i r s t  Each of them was then p l a c e d i n a p l a s t i c bag,  one end of which was kept open; and the bags were then p l a c e d i n a vacuum d e s i c c a t o r . an i n d i c a t o r i n the d e s i c c a t o r .  Copper s u l f a t e was used as When the blue c o l o r of the  26  copper s u l f a t e disappeared the d r y i n g was considered complete.  On average, t h i s c o n d i t i o n was a t t a i n e d a f t e r 48  hours d r y i n g i n the c o n d i t i o n s p e c i f i e d above. a l l y the ' s k i n  1  Occasion-  formed on the s u r f a c e o f the phosphorus:  pentoxide was removed t o r e a c t i v a t e the d r y i n g agent.  After  the d i s c o l o r a t i o n o f the copper s u l f a t e i n d i c a t o r , the specimens were kept i n the d e s i c c a t o r f o r an a d d i t i o n a l 24 " hours i n order t o ensure complete  removal o f moisture.  A few s e c t i o n s d r i e d i n t h i s manner showed moisture  con-  t e n t s r a n g i n g from 0.008 t o 0.17 p e r cent, w i t h an average o f 0.09 ;per cent, upon subsequent  oven-drying.  was considered zero i n the a n a l y s i s .  T h i s low v a l u e  A f t e r the d r y i n g was  done, the specimen bags were q u i c k l y c l o s e d and h e a t - s e a l e d to prevent moisture p i c k up by the specimen.  A f t e r the  c l o s u r e o f the p l a s t i c bags, they were r e p l a c e d i n the desiccator u n t i l tested. Specimens t e s t e d i n the water-saturated c o n d i t i o n were t r a n s f e r r e d from the t e s t tubes t o the t e s t bags, approximately 1 ml o f water was added, then the bags/\heatsealed.  No moisture content determinations were made f o r  these specimens s i n c e i t was the i n t e n t i o n only t o keep them a t a moisture content .above f i b r e - s a t u r a t i o n p o i n t . The specimens t e s t e d i n a i r - d r y c o n d i t i o n were p r e c o n d i t i o n e d i n an Aminco A i r e constant temperature and humidity c a b i n e t .  Dry-bulb temperature^in the c a b i n e t  27  were 25°C, 5C°C and 70°C, the temperaturesat which the specimens were t e s t e d f o l l o w i n g c o n d i t i o n i n g .  The r e l a t i v e  humidity c o n d i t i o n s were chosen i n such a way t h a t the r e s u l t i n g e q u i l i b r i u m moisture contents (EMC) were t o be approximately 12 p e r cent.  The procedure i n p r e c o n d i t i o n -  i n g was s i m i l a r t o that d e s c r i b e d f o r the m o i s t u r e - f r e e samples except that here the completion o f c o n d i t i o n i n g was  determined by u s i n g dummy microtome s e c t i o n s , prepared  i n the same way as the t e s t specimens and from the same m a t e r i a l , and kept i n open p l a s t i c bags s i m i l a r t o that employed i n c o n d i t i o n i n g the t e s t m a t e r i a l .  Each  test  specimen was kept i n the c o n d i t i o n i n g cabinet f o r a t l e a s t 48 hours, although the dummy p i e c e s a t t a i n e d constant weight a f t e r the f i r s t  24 hours .  The temperature was kept under c l o s e c o n t r o l during the e n t i r e p e r i o d o f t e s t i n g . A s m a l l wooden cabinet was b u i l t around the g r i p s o f the t e s t i n g machine i n which the temperature was kept a t the r e q u i r e d l e v e l .  A large  c a p a c i t y f o r c e d a i r c i r c u l a t i o n oven and the t e s t  cabinet  were connected through a f l e x i b l e p l a s t i c tube 2 i n . i n diameter, which s u p p l i e d enough heat t o the 3/4 cu f t cabinet to h o l d a constant temperature w i t h i n - 0.5°C.  The thermostat  of the oven was set approximately 2°C h i g h e r than the t e s t temperature  s i n c e i t was found that the cabinet  a temperature  2°C lower than the oven.  attained  This was probably  28  due to the heat l o s s i n the cabinet and  i n the tube i n  s p i t e of the c a r e f u l l y a p p l i e d i n s u l a t i o n . the t e s t set-up  In F i g u r e  10  i s shown.  Thickness  of specimen  was  measured u s i n g a p r e c i s i o n  d i a l i n d i c a t o r shown i n F i g u r e 11 and d e s c r i b e d i n d e t a i l by Bystedt  and Anderson (13).  i n c l u d i n g the two specimen.  The  measured was  Measurements were made  sheets of p o l y e t h y l e n e ' e n c l o s i n g  t h i c k n e s s of the p l a s t i c as  subsequently  s u b t r a c t e d from the t o t a l t h i c k n e s s .  average of three measurements was s e c t i o n a l dimensions.  the  The  used to c a l c u l a t e c r o s s -  Specimen width could be  conveniently  measured through the transparent polyethylene with the a i d of a microscope.  C r o s s - s e c t i o n a l area of each t e n s i o n  t e s t specimen was  c a l c u l a t e d by simple  3.  of C e l l u l o s e Degree of P o l y m e r i z a t i o n  Determination  multiplication.  There are s e v e r a l methods a v a i l a b l e f o r the  de-  t e r m i n a t i o n of c h a i n l e n g t h of both s y n t h e t i c an n a t u r a l h i g h polymers.  One  of the e a r l i e s t techniques  i s the  pre-  d i c t i o n of DP from v i s c o s i t y measurements on d i l u t e s o l u t i o n s of polymers.  This method i s based on the o b s e r v a t i o n that  the i n c r e a s e i n v i s c o s i t y of the polymer s o l u t i o n , over that of the s o l v e n t , i s r e l a t e d to the c h a i n l e n g t h , v i d e d that the t e s t - c o n d i t i o n s are constant.  pro-  In s p i t e of the  29  r e l a t i v e l y l o n g h i s t o r y of t h i s method, there has  been no  unique r e l a t i o n s h i p developed, mainly because the  influence  of c e r t a i n c o n t r i b u t i n g f a c t o r s , other than mere average chain length,  i s not  known.  Two  of these f a c t o r s are  o r i e n t a t i o n of the l o n g - c h a i n molecules d u r i n g the of l i q u i d i n the viscometer, and  the  efflux  the r e l a t i v e f l e x i b i l i t y  of the polymer molecules i n the f l o w i n g  solution.  Empirical  equations, however, are a v a i l a b l e i n the l i t e r a t u r e r e l a t i n g intrinsic l o s e and  v i s c o s i t y to degree of p o l y m e r i z a t i o n of  cellu-  cellulose derivatives. In t h i s experiment the c e l l u l o s e c h a i n l e n g t h  determined by  one  was  of the e m p i r i c a l methods i n v o l v i n g meas-  urement of i n t r i n s i c v i s c o s i t y .  The  converted i n t o h i g h l y s u b s t i t u t e d  c e l l u l o s e i n wood  cellulose nitrate,  was  and  the i n t r i n s i c v i s c o s i t y of the n i t r a t e determined i n acetone s o l u t i o n , u s i n g a c a p i l l a r y type of viscometer.  The  intrin-  s i c v i s c o s i t y values c a l c u l a t e d from the e f f l u x times were properly  adjusted, and  the degree of p o l y m e r i z a t i o n of  l o s e computed with the a i d of an e m p i r i c a l  A.  relationship.  N i t r a t i o n of Wood Samples The  microtome s e c t i o n s  growth increment were d i v i d e d  cellu-  i n each s e r i e s of each  i n t o e a r l y - and  latewood  zones, a c c o r d i n g to the r e l a t i v e amounts of these zones  30  i n the p a r t i c u l a r increment.  This was  done by simply counting  the t o t a l number of s e c t i o n s i n each s e r i e s , then determini n g the s e c t i o n number by c a l c u l a t i n g where the d i v i s i o n was  to be made, u s i n g per cent latewood p r e v i o u s l y measured  f o r each of the three growth increments.  Earlywood and  late-  wood thus obtained from each s e r i e s were handled s e p a r a t e l y in nitration.  T h i s r e s u l t e d i n a t o t a l number of 6 0 . n i t r a t i o n s ,  30 of which were earlywood and 30 were latewood samples.  Prom  each of the three increments, two r e p l i c a t e n i t r a t i o n s were made a t each of the f i v e degradation l e v e l s , f o r earlywood and latewood s e p a r a t e l y . Each sample was  then p l a c e d i n a separate saran  screen c o n t a i n e r of approximately 10 mesh.  These c o n t a i n e r s  were c o n v e n i e n t l y made i n the l a b o r a t o r y from o r d i n a r y mosq u i t o screen, u s i n g an e l e c t r i c s o l d e r i n g i r o n to s e a l the samples i n t o them.  The saran c o n t a i n e r s were p l a c e d i n t o  a l a r g e , approximately 1 - l i t e r , Soxhlet e x t r a c t i o n apparatus and e x h a u s t i v e l y e x t r a c t e d i n a mixture of benzene and per cent e t h y l a l c o h o l i n 2:1  95  ratio.  The e x t r a c t i v e - f r e e m a t e r i a l was  air-dried  and  ground i n a Wiley m i l l to pass a 40-mesh and be r e t a i n e d on an 80-mesh s i e v e .  Approximately 20 to 30 per cent of  the wood meal passed the 80-mesh s i e v e when u n i r r a d i a t e d or s l i g h t l y t r e a t e d wood meal samples were prepared.  About  40 per cent of the wood meal was l o s t through s i e v i n g from the 10 and 15 megarad i r r a d i a t e d m a t e r i a l .  E s p e c i a l l y low  31  y i e l d s o f wood meal were obtained when 15 megarad i r r a d i a t e d earlywood  samples were screened.  The wood meal was n i t r a t e d i n a non-degrading mixture as d e s c r i b e d by Alexander and M i t c h e l l ( 2 ) .  acid This  was prepared by adding c a u t i o u s l y and v e r y s l o w l y , w i t h a s p a t u l a 202 g o f phosphorus pentoxide t o 500 g of 90 p e r cent fuming n i t r i c a c i d a t -5°C and contained i n a 1 - l i t r e Erlenmeyer f l a s k .  The a c i d was kept i c e - c o l d by  immersion  i n an i c e water bath and was s w i r l e d c o n t i n u o s l y d u r i n g a d d i t i o n o f phosphorus pentoxide.  T h i s produced a mixture  w i t h composition of 64 p e r cent n i t r i c a c i d , 26 p e r cent phosphoric a c i d and 10 p e r cent phosphorus pentoxide ( 2 ) . With o c c a s i o n a l shaking, the s o l u t i o n was complete  ina  few hours, and the mixture was then t r a n s f e r r e d i n t o a g l a s s - s t o p p e r e d b o t t l e and r e f r i g e r a t e d u n t i l used f o r nitration.  The mixture was used i n v a r i a b l y w i t h i n 12 hours  from p r e p a r a t i o n . A 20 g portbn of the prepared n i t r i c a c i d mixture was weighed out i n t o a weighing b o t t l e o f about  50 ml  c a p a c i t y and p l a c e d i n a constant temperature bath a t 17 +0.5 C.  One-half gram o f wood meal was i n t r o d u c e d q u i c k l y  i n t o the n i t r a t i n g a c i d mixture.  N i t r a t i o n was then allowed  to proceed f o r 40 hours, the sample b e i n g s w i r l e d o c c a s i o n a l l y during t h i s period.  The n i t r a t e d wood meal was then  q u a n t i t a t i v e l y t r a n s f e r r e d i n t o a f r i t t e d g l a s s Buchner type o f f u n n e l which was approximately 200 ml i n c a p a c i t y .  32  Cold tap water (about 14°C) sample.  The  n i t r a t e was  was  used i n t r a n s f e r r i n g  the  thoroughly washed w i t h 1000  of c o l d water, u s i n g m i l d  ml  s u c t i o n , then soaked i n 50 ml  1 per cent sodium carbonate s o l u t i o n f o r 5 minutes. was  f i n i s h e d with 500 ml  and  The  sample was  ml Erlenmeyer f l a s k u s i n g 200  extracted  Washing  of c o l d tap water f o l l o w e d by  ml of c o l d d i s t i l l e d water. i n t o a 250  of  ml  500  transferred of methyl a l c o h o l ,  i n methyl a l c o h o l f o r 12 hours with  occasional  swirling. Next, the c e l l u l o s e n i t r a t e was transferred  into a f r i t t e d  an a d d i t i o n a l 100 ml  g l a s s c r u c i b l e and  of methyl a l c o h o l .  p l a c e d i n an oven maintained at 60°C. drying,  quantitatively  the sample was  dry and  crucible quantitatively.  The  washed with  The  crucible  A f t e r 10 minutes  could be removed from dry c e l l u l o s e n i t r a t e  transferred  i n t o a 250-ml Erlenmeyer f l a s k and  acetone was  added.  Erlenmeyer f l a s k was dissolved  was  200  the was  ml  of  A f t e r 48 hours, w i t h i n which timeVthe o f t e n s w i r l e d , most of the n i t r a t e  i n the acetone.  A few u n d i s s o l v e d p a r t i c l e s ,  however, always remained on the bottom of the f l a s k except for  the  15 megarad i r r a d i a t e d samples which  completely d u r i n g the 48 hours. centrifuged The  s o l u t i o n was  then  to remove the u n d i s s o l v e d n i t r a t e p a r t i c l e s . clear, yellowish  the tube of the c e n t r i f u g e water.  The  dissolved  s o l u t i o n was  i n t o 2.5  decanted from  1 of c o l d  distilled  In the water, the c e l l u l o s e n i t r a t e immediately  33  p r e c i p i t a t e d and c o u l d c o n v e n i e n t l y be c o l l e c t e d around a glass rod.  The p u r i f i e d c e l l u l o s e n i t r a t e was f i r s t a i r -  d r i e d and then p l a c e d i n a vacuum d e s i c c a t o r c o n t a i n i n g phosphorus;: pentoxide as d r y i n g agent.  Vacuum was  applied  and the d e s i c c a t o r was p l a c e d i n t o an oven maintained at 60°C temperature.  Drying was  continued f o r 48 to 72 hours,  w i t h i n which p e r i o d the s k i n formed on the s u r f a c e o f the d r y i n g agent was  o c c a s i o n a l l y removed; the vacuum was  p e r i o d i c a l l y checked and r e s t o r e d by a p p l y i n g additionals u c t i o n to the d e s i c c a t o r .  A f t e r t h i s d r y i n g p e r i o d the  c e l l u l o s e n i t r a t e was ready f o r n i t r o g e n a n a l y s i s and v i s c o s i t y measurement. Optimum r e a c t i o n time of 40 hours n i t r a t i o n determined e x p e r i m e n t a l l y .  M a t e r i a l obtained from the same  increments as those used i n the main experiment was i n t o e a r l y - and latewood.  was  divided  I t was n i t r a t e d f o r v a r i o u s  l e n g t h s of time from 22 to 80 hours, and the i n t r i n s i c v i s c o s i t y v a l u e s determined.  R e s u l t s of t h i s p r e l i m i n a r y  experiment are shown i n F i g u r e 12•  Both e a r l y - and latewood  samples a t t a i n e d the h i g h e s t i n t r i n s i c v i s c o s i t y v a l u e s at approximately 35 to 45 hours n i t r a t i o n time.  Nitrogen  content of the samples appeared to be independent of l e n g t h of n i t r a t i o n time w i t h i n the experimental range.  The r e s u l t s  were i n agreement w i t h the n i t r a t i o n times used by T i m e l l (93,94,95), who  applied s i m i l a r l y long n i t r a t i o n periods  w i t h wood of s e v e r a l c o n i f e r o u s s p e c i e s .  I t seems reasonable  34  to assume t h a t optimum n i t r a t i o n p e r i o d i s r e l a t e d to l i g n i n content of wood s i n c e hardwood s p e c i e s having lower  lignin  content, such as aspen, r e q u i r e only 1 hour n i t r a t i o n to a t t a i n the necessary degree of s u b s t i t u t i o n and optimum v i s c o s i t y values  B.  (94).  Determination  of Nitrogen Content  of C e l l u l o s e N i t r a t e s  N i t r o g e n content of c e l l u l o s e n i t r a t e s was  determined  by a m i c r o - K j e l d a h l method, e s s e n t i a l l y as developed  by  Ma  and Zuazaga (66) and m o d i f i e d by T i m e l l and Purves (97). D u p l i c a t e determinations were done on each c e l l u l o s e n i t r a t e sample except f o r a few cases where the d i f f e r e n c e between the two r e p l i c a t e s was  g r e a t e r than 0.25  per cent.  For  these l a t t e r samples a t h i r d determination was made, and the average of the two  c l o s e s t values  used.  The c e l l u l o s e n i t r a t e to be analyzed was phosphorous pentoxide 15-25 - 0.05 flask. was  mg  sample was  dried  i n vacuo as s p e c i f i e d e a r l i e r .  over A  weighed on an a n a l y t i c a l balance w i t h i n  mg and t r a n s f e r r e d d i r e c t l y to a 30 ml m i c r o - K j e l d a h l Approximately  addedC"followed  The sample was  0.1  g of reagent grade s a l y c i l i c  acid  by 2.5 ml of concentrated s u l f u r i c a c i d .  allowed to d i s s o l v e completely i n the a c i d .  In g e n e r a l , the n i t r a t e s were q u i t e hard to d i s s o l v e , t h e r e fore<] i t was  iJ  /  a d v i s a b l e to a l l o w the n i t r a t e - a c i d mixture  stand over/night.  This p r e c a u t i o n was  taken to avoid  to  35  incomplete s o l u t i o n which could have l e d to low a c c o r d i n g to T i m e l l and  Purves  Approximately 0.3 t h i o s u l f a t e and  0.6  results  (97).  g of a n a l y t i c a l grade sodium •  g anhydrous potassium s u l f a t e were  added to the brown s o l u t i o n .  The  mixture was  then g e n t l y  heated f o r h a l f an hour on a m i c r o - K j e l d a h l heater, heat b e i n g g r a d u a l l y f u r i c a c i d began.  i n c r e a s e d u n t i l r e f l u x i n g of the  The  s o l u t i o n was  c y s t a l c l e a r , p l u s an a d d i t i o n a l ensure complete d i g e s t i o n .  10 minutes i n order to  In g e n e r a l , the d i g e s t i o n  l u l o s e n i t r a t e weighed i n t o the  water and  transferred  g l a s s d i s t i l l i n g apparatus.  Twenty ml  then added.  the b a s i c  steam-distilled  cent b o r i c a c i d that had  previously  a g a i n s t a mixed i n d i c a t o r .  of methyl red i n the  same s o l v e n t .  ml  The  cent sodium  ammonia formed i n i n t o 25 ml  of 0.8  been made s l i g h t l y  of 0.1  per  cent  per acid  of a of  solution  A f t e r 5 to 10 minutes  the ammonium hydroxyde formed i n the  Erlenmeyer f l a s k was  had  of 35 per  cent ethanol s o l u t i o n  one  hydrochloric  part  per  bromcresol green and  distillation,  d i l u t e d with 15  This i n d i c a t o r c o n s i s t e d  mixture of f i v e p a r t s of 0.1  cel-  q u a n t i t a t i v e l y to an a l l -  hydroxide s o l u t i o n was s o l u t i o n was  was  flask.  a c i d i c , c o l o r l e s s l i q u i d was  of d i s t i l l e d  sul-  heated u n t i l i t became  complete i n 2 to 4 hours depending on the amount of  The  the  receiving  d i r e c t l y t i t r a t e d with standard 0.03  a c i d u n t i l the red c o l o r of the  d e f i n i t e l y reappeared, 5 to 9 ml  indicator  of a c i d b e i n g  usually  N  36  required. Blank determinations gave an average of 0.05  ml of 0.03N a c i d .  consumption  The analyses were a c c o r d i n g l y  c o r r e c t e d and the n i t r o g e n content c a l c u l a t e d i n the Sallowi n g manner:  where N = n i t r o g e n content i n per cent, K = amount of 0.03N h y d r o c h l o r i c a c i d i n ml, W = *weight of the dry c e l l u l o s e n i t r a t e sample i n g. In order to t e s t the method, a n a l y t i c a l grade potassium n i t r a t e was 13.76  and 13.75  b e i n g 13.85  analyzed.  Three samples gave 13.79,  per cent n i t r o g e n , the c a l c u l a t e d  per cent.  content  The d e v i a t i o n from the t h e o r e t i c a l  n i t r o g e n content of potassium n i t r a t e was probably due to the moisture content of the sample s i n c e i t was dried before a n a l y s i s . was  + - 0.1  The average  not oven-  accuracy of the method  'tper cent, although i n some cases o n l y about - 0.25  per cent.  C.  V i s c o s i t y Measurements Two  to s i x mg  w i t h i n - 0.001  mg  of c e l l u l o s e n i t r a t e were weighed  on a m i c r o - a n a l y t i c a l balance, and trans^  f e r r e d to a 15 ml p o l y e t h y l e n e t e s t tube f i t t e d w i t h a p e r f e c t l y - c l o s i n g p o l y e t h y l e n e cap.  Ten ml of a n a l y t i c a l  grade acetone were added and the tube c o n t i n u o u s l y r o t a t e d  37  f o r 24 hours. n i t r a t e was  A f t e r t h i s time, s o l u t i o n o f the c e l l u l o s e  complete.  A 5 ml a l i q u o t of the above s o l u t i o n  was t r a n s f e r r e d by p i p e t t e (ASTM No.  t o a c l e a n Cannon-Fenske  (14)  50) viscometer suspended i n a v i s i b i l i t y J a r +  o  Bath at 25.-r , 0.1 :  C.  A f t e r w a i t i n g 5 min f o r the adjustment  of temperature, the c a p i l l a r y tube of the viscometer was f i l l e d by g e n t l e p r e s s u r e on the s u r f a c e of the s o l u t i o n i n the open arm of the instrument.  This p r e s s u r e , c o n v e n i e n t l y  a p p l i e d from a rubber b u l b , minimized e r r o r due to evapora t i o n when the s o l u t i o n i s drawn up the c a p i l l a r y by d i r e c t suction.  The equipment  i s shown i n F i g u r e 13.  used i n the v i s c o s i t y measurements E f f l u x times, 163.5  to 350.0 sec,  were measured w i t h a stop-watch r e a d i n g to 0.1  sec. A l l  +  v a l u e s were checked to a constancy of - 0.2 sec. The s p e c i f i c v i s c o s i t y ,  , was  the e x p r e s s i o n t / t - 1, where t was Q  s o l u t i o n and t  that, of  c a l c u l a t e d from  the e f f l u x time of the  the pure acetone, assuming the  d e n s i t i e s of the s o l v e n t and the s o l u t i o n to be equal.  The  s p e c i f i c v i s c o s i t y v a l u e s so c a l c u l a t e d were c o r r e c t e d f o r k i n e t i c energy l o s s e s , a c c o r d i n g to T i m e l l (91), i n the f o l l o w i n g manner: 7 Here "7  1  sp  7 sp  1-F  1  Q  t  +  1 J  i s the c o r r e c t e d s p e c i f i c v i s c o s i t y , * ? "  observed v a l u e , and F  Q  g  the  a f a c t o r c a l c u l a t e d f o r the v i s -  cometer from the e x p r e s s i o n :  38  o  8 ~ >n  /o  t  o  L  U  J  In t h i s e x p r e s s i o n m, the k i n e t i c energy c o e f f i c i e n t , was taken as u n i t y , i . e . , end e f f e c t s f o r the c a p i l l a r y were n e g l e c t e d ; d , d e n s i t y o f acetone, was 0.785; V, the volume Q  i n ml o f the viscometer "bulb, 3.65;  , the v i s c o s i t y o f  pure acetone, 0.003095 p o i s e ; t , the e f f l u x time o f pure acetone, 7.75 F  q  163.5 sec; and 1 , the l e n g t h o f the c a p i l l a r y ,  cm.  S u b s t i t u t i n g the above v a l u e s i n t o the expression,  f o r the viscometer used i n t h i s experiment  was  calculated  as 0.0296359.  The mean shear r a t e o r v e l o c i t y g r a d i e n t was c a l c u l a t e d from the formula: 8 g  =  3  Tr 3 r  V t  CO  Here, r equals the r a d i u s o f the c a p i l l a r y (0.02125 cm), and t i s the e f f l u x  time.  A f t e r having the s p e c i f i c v i s c o s i t y v a l u e s c o r r e c t e d f o r k i n e t i c energy l o s s , the i n t r i n s i c v i s c o s i t i e s were calculated Davison  by means o f the Schult'z-Blanschke,  ( 2 0 ) , and Huggins fYl]  =  1  as g i v e by  (39,40) equation:  ^ Sp / C  / - A  where D?]g. i s the i n t r i n s i c v i s c o s i t y corresponding t o the shear, G, a t which the measurement was made; K i s a f a c t o r taken as 0.30, a c c o r d i n g t o Davison  ( 2 0 ) ; and C i s the con-  39  centration. The i n t r i n s i c v i s c o s i t y , [^Jg., c a l c u l a t e d by u s i n g the above formula, v a r i e d i n a r e g u l a r manner  corresponding  to the shear dependence of the v i s c o s i t y as'found (90,91,92).  by T i m e l l  On the other hand, the r a t e of shear  was  dependent upon the e f f l u x time which, i n t u r n , was  influenced  by both the c o n c e n t r a t i o n and the degree of p o l y m e r i z a t i o n of the c e l l u l o s e n i t r a t e .  In order to o b t a i n comparable  v a l u e s f o r the v a r i o u s c o n c e n t r a t i o n s of d i f f e r e n t n i t r a t e s , a l l r e s u l t s were adjusted to 500 sec gradient.  This was  DP  velocity  done by u s i n g the f o l l o w i n g r e l a t i o n -  s h i p r e p o r t e d by Davison  log [^] oO 5  (20):  =  P  l o  ^5§0  +  l  0  t6)  S ^ G  where Gf can be c a l c u l a t e d from equation  CO,  and P i s the  slope of the s t r a i g h t l i n e r e l a t i n g the l o g of i n t r i n s i c v i s c o s i t y to the l o g of r a t e of shear. P as a slope may  be determined by the f o l l o w i n g e x p r e s s i o n : p  Davison  In other words,  _  C7)  d loggia d log- Gr  (20) determined P e x p e r i m e n t a l l y and c a l c u l a t e d an  equation to f i t the curve r e l a t i n g P to i n t r i n s i c  viscosity.  T h i s equation has the f o l l o w i n g form: P = 0.0039 [ 7 J  5 0 0  - 0.8  x IO"  8  i^  00  Since P i s r e l a t e d to i n t r i n s i c v i s c o s i t y at 500 sec  in  40  equation ( 8 3 , the v a l u e obtained by s u b s t i t u t i n g V^]Q i n the equation was used to c a l c u l a t e the f i r s t approximation the slope P.  T h i s v a l u e then i n s e r t e d i n equation (6) gave  the f i r s t approximation to E^^oo equation  of  w  k i c h , resubstituted into  , gave a b e t t e r estimate of P.  technique was  This b r a c k e t i n g  continued u n t i l the r e s u l t i n g C ^ J ^ Q Q  changed w i t h i n 0.001  intrinsic  N  A  D  N  0  ^  viscosity.  Since complete n i t r a t i o n c o u l d not be a t t a i n e d , the e f f e c t of the degree of s u b s t i t u t i o n had to be  taken  i n t o c o n s i d e r a t i o n i n order to a r r i v e at comparable v i s cosity values.  An e m p i r i c a l equation, developed  L i n d s l e y and Prank (64), was used to convert the v i s c o s i t y as determined corresponding  f  intrinsic  i n t o i n t r i n s i c v i s c o s i t y of the  trinitrate.  log[1] where E*!]^  by  T  = log f  x  + (14.15 - X)B + logl*}]  = i n t r i n s i c v i s c o s i t y of the  (3)  trinitrate,  = a f a c t o r which takes i n t o account  the  departure of the u n i t molecular weight from that of c e l l u l o s e t r i n i t r a t e because of the lower degree of s u b s t i t u t i o n , x  = the n i t r o g e n content of the sample, and  B  = an e m p i r i c a l constant having a v a l u e of 0.114.  Prom the above f  = 1.833  - 0.0589 x  Here x i s a l s o the percentage  of n i t r o g e n i n the sample.  41  Since a l l the v i s c o s i t y measurements were c a r r i e d out at 25°C temperature, another adjustment o f the i n t r i n s i c v i s c o s i t y v a l u e s became necessary.  A l l r e s u l t s were con-  v e r t e d i n t o v a l u e s corresponding to those taken at 20°C temperature.  T h i s was done by simply m u l t i p l y i n g the i n t r i n -  s i c v i s c o s i t i e s determined by 1,04716.  This f a c t o r  was  obtained from the r e l a t i o n s h i p r e p o r t e d by T r e i b e r and Abrahamson (98). I t should be noted that the above, r a t h e r i n v o l v e d , mathematical approach needed approximately the same amount of time as would have been spent on determining experimenta l l y the s t r a i g h t l i n e r e l a t i o n s h i p between reduced v i s c o s i t y and c o n c e n t r a t i o n , and reduced v i s c o s i t y and shear sp r a t e f o r each sample to be analyzed, and e x t r a p o l a t i n g to zero c o n c e n t r a t i o n and 500 sec~^ shear r a t e . was  the case only when a desk c a l c u l a t o r was used f o r the  calculations. 1620  However, t h i s  A computer program was w r i t t e n f o r the IBM  e l e c t r o n i c computer of the U n i v e r s i t y o f B r i t i s h  Columbia which c a l c u l a t e d the i n d i v i d u a l i n t r i n s i c v i s c o s i t y v a l u e s i n approximately 8 seconds.  U s i n g t h i s technique  approximately 9 hours were saved on each average  intrinsic  v i s c o s i t y v a l u e based on 4 r e p l i c a t e measurements.  For  t h i s program only a s i x d i g i t i d e n t i f i c a t i o n number, the e f f l u x time i n seconds, the c o n c e n t r a t i o n i n g/100  ml,  and the corresponding n i t r o g e n content i n p e r cent had t o be punched on IBM c a r d s .  A copy of the program i s attached  to the appendix o f t h i s t h e s i s .  42  D.  Conversion  of I n t r i n s i c V i s c o s i t y to DP  I t has been  Values  the o b j e c t i v e f o r q u i t e some time to  e s t a b l i s h a r e l a t i o n s h i p between i n t r i n s i c v i s c o s i t y degree of p o l y m e r i z a t i o n of c e l l u l o s e .  Unfortunately,  unique f a c t o r or formula has been developed may  no  as yet which  be a p p l i c a b l e to a wide range of DP v a l u e s .  Each  expression r e p o r t e d i n the l i t e r a t u r e i s the r e s u l t e m p i r i c a l determinations  and  of  and a p p l i c a b l e only w i t h i n r e l -  a t i v e l y narrow, s p e c i f i c circumstances. a somewhat a r b i t r a r y procedure was  In t h i s experiment  f o l l o w e d i n determining  the conversion f a c t o r f o r each c e l l u l o s e n i t r a t e sample tested. T i m e l l ' s data provided the b a s i s f o r the tions (93).  calcula-  He r e p o r t e d i n t r i n s i c v i s c o s i t y v a l u e s , as w e l l  as degree of p o l y m e r i z a t i o n data, f o r 24 n a t i v e c e l l u l o s e s of v a r i o u s sources, i n c l u d i n g 6 hardwood and 6 c o n i f e r o u s species.  DP values were determined by a l i g h t s c a t t e r i n g  technique, while the i n t r i n s i c v i s c o s i t i e s were obtained u s i n g a m o d i f i e d Ubbelohde c a p i l l a r y viscometer acetate as the s o l v e n t .  and  n-butyl  A c c e p t i n g the r e s u l t s of the  l i g h t s c a t t e r i n g measurements as the t r u e DP v a l u e s , i t i s p o s s i b l e to c a l c u l a t e a conversion f a c t o r f o r each c e l l u l o s e sample t e s t e d .  This f a c t o r (K), however, i s not  a constant number f o r a l l the c e l l u l o s e samples i n c l u d e d i n T i m e l l ' s study, but an almost p e r f e c t l i n e a r r e l a t i o n s h i p e x i s t s between i t and i n t r i n s i c v i s c o s i t y .  In F i g u r e  14  43  K,  c a l c u l a t e d from data o f T i m e l l (93), i s p l o t t e d a g a i n s t i n -  trinsic viscosity.  Elsewhere (96) i t has been r e p o r t e d  t h a t when acetone i s used as a s o l v e n t , a conversion f a c t o r h i g h e r approximately  by 20 should be used, i n order t o o b t a i n  DP v a l u e s o f comparable magnitude.  The dotted l i n e i n F i g u r e  14 may t h e r e f o r e represent the K - i n t r i n s i c v i s c o s i t y  rel-  a t i o n s h i p when acetone i s used as a s o l v e n t , as was the case i n t h i s study.  F o r each c e l l u l o s e n i t r a t e sample the ap-  p r o p r i a t e c o n v e r s i o n f a c t o r was c a l c u l a t e d from the equation shown i n F i g u r e 14, and the i n t r i n s i c v i s c o s i t y m u l t i p l i e d by the number so obtained t o c a l c u l a t e the corresponding degree o f p o l y m e r i z a t i o n . I t i s r e a l i z e d t h a t the above procedure t o c a l c u l a t e DP v a l u e s i s r a t h e r a r b i t r a r y as a r e a l l such methods.  There-  f o r e , the c e l l u l o s e DP v a l u e s r e p o r t e d here cannot be cons i d e r e d as the t r u e v a l u e s but only as approximations what might e x i s t i n wood.  of  I n the enormous l i t e r a t u r e on  t h i s s u b j e c t , e m p i r i c a l r e l a t i o n s h i p s range from the use of simple c o n v e r s i o n f a c t o r s between v i s c o s i t y and DP, t o complicated l o g a r i t h m i c or e x p o n e n t i a l f u n c t i o n s .  This  r e s u l t s i n a wide range o f p o s s i b l e DP v a l u e s c a l c u l a t e d from the same i n t r i n s i c v i s c o s i t y depending on the p a r t i c u l a r e m p i r i c a l formula used.  Staudinger's  o r i g i n a l p r o p o s a l was  t h a t a t low c o n c e n t r a t i o n s :  ^1 1  = K  sp  Qo3  M C  m  gm  44  w h e r e i s  the s p e c i f i c v i s c o s i t y , K  m  i s a factor deter-  mined experimentally, M i s the molecular weight of the c e l l u l o s e d e r i v a t i v e , and C „ i s the c o n c e n t r a t i o n i n moles mg of monomer per l i t e r .  This r e l a t i o n s h i p i s now  often  used i n the form: [*]] = K One value f o r K  m  OO  DP  of the d i f f i c u l t i e s of a t t a i n i n g an accurate m  i s the f a c t t h a t most of the  between [*]] and DP depend on osmotic number-average molecular weights.  correlations  r e s u l t s , " which g i v e  A valid correlation  should depend on the use of e i t h e r v e r y narrow f r a c t i o n s , f o r which the number-average DP equals weight-average v a l u e s , or a molecular weight method which g i v e s the weight-average DP.  The l i g h t s c a t t e r i n g technique i s considered to be  such a method. Recently, more p r e c i s e measurements tend to show a more complicated r e l a t i o n s h i p .  T h i s i s probably due to the  f a c t t h a t there i s no simple c o r r e l a t i o n of the numberaverage molecular weights and i n t r i n s i c v i s c o s i t i e s u n l e s s the molecular weight d i s t r i b u t i o n i n each sample i s the the same.  Here, the shape of the d i s t r i b u t i o n curve comes  into effect.  I t i s q u i t e p o s s i b l e t h a t the h i g h e r DP  have broader d i s t r i b u t i o n curves than the lower In t h i s case an e x p o n e n t i a l type of r e l a t i o n s h i p  fractions  fractions. prevails;  45  " [*7] = K  m  DP  .  a  •  C120  I n t h i s equation the g r e a t e r the discrepancy among the d i s t r i b u t i o n curves w i t h i n a sample, the lower the exponent a . I t has been shown (40,67,77) that the simple c o r r e l a t i o n of Staudinger g i v e s a good approximation I f the DP/E^j r a t i o i s p l o t t e d a g a i n s t DP,  of low  DP.  a minimum i s  obtained i n the v i c i n i t y of DP 100 a f t e r which there appears to be a r e g i o n of c o n t i n u a l l y i n c r e a s i n g v a l u e s . DP i s w e l l approximated by a s i n g l e K 200.  Harland  relationship to 1800  (34),  m  Thus the  f a c t o r say below DP  on the, other hand, claims t h a t the  p?]=0.0108 DP  i s v a l i d over a DP range of  100  f o r c e l l u l o s e n i t r a t e of 14 per cent n i t r o g e n i n  ethyl butyrate.  Kraemer's K  m  value of 3.7x10  , as c i t e d  by Ott et a l . (#7), i s much lower than the one mentioned earlier.  L i n d s l e y and Prank (64)  of degree of s u b s t i t u t i o n of DP,  calculated a K  0  12x10  -3  samples.  i n t h e i r study of dependence  f o r t r i n i t r a t e i n acetone  m  f a c t o r of  o at 20 C f o r f r a c t i o n a t e d  They a l s o r e p o r t that f o r u n f r a c t i o n a t e d n i t r a t e s  the constant should be l a r g e r .  H o l t z e r , Benoit and Doty  (38) found t h a t Staudinger's law was  obeyed over a range  of 150 to 4500 DP  The v a l u e of K  (number-average).  was  ffi  found to be 5.0x10 ' when the weight-average DP was  considered.  An e x t e n s i v e osmotic pressure and c e l l u l o s e n i t r a t e v i s c o s i t y study by Immergut, Ranby and Mark (43) l e d to a v a l u e of 10x10  when DP was  a number-average v a l u e .  These two  latter  46  values  are c o n s i s t e n t i f one c o n s i d e r s that the  average  DP i s approximately twice as l a r g e as the number-  average DP  (77).  weight-  T r e i b e r and Abrahamson (98) r e p o r t e d a  v a l u e of 13.6x10"^ f o r K . T i m e l l ' s study (93), which i n v o l v e d v i s c o s i t y measurements of c e l l u l o s e n i t r a t e s i n b u t y l a c e t a t e , and DP determinations of the same m a t e r i a l u s i n g a l i g h t  scatter-  i n g technique, r e s u l t e d i n an e x p o n e n t i a l equation, the K  m  f a c t o r b e i n g equal to 0.278 and  the exponent 0.572.  In  t h i s study the DP v a l u e s measured were o b v i o u s l y weightaverage  figures. I t i s beyond the scope of t h i s study to present a  comprehensive l i t e r a t u r e survey on the s u b j e c t of v i s c o s i t y DP r e l a t i o n s h i p .  The above f i g u r e s , however, show the  rather large discrepancies i n this f i e l d .  The DP v a l u e s  c a l c u l a t e d f o r an imaginary c e l l u l o s e n i t r a t e with i n t r i n s i c v i s c o s i t y of 35.0  d l / g i n acetone, u s i n g the d i f f e r e n t  r e l a t i o n s h i p s mentioned above, are shown i n Table 1. of the same sample was  DP  a l s o c a l c u l a t e d on the b a s i s of the  technique used i n t h i s study f o r the experimental data.  47  EXPERIMENTAL RESULTS  Pour t e n s i l e s t r e n g t h parameters were c a l c u l a t e d from the raw experimental  data.  Ultimate t e n s i l e  strength  was obtained by d i v i d i n g the i n d i v i d u a l maximum." l o a d values i n kg by corresponding  p  c r o s s - s e c t i o n a l areas i n cm . by  Elas-  t i c i t y v a l u e s were c a l c u l a t e d j y m u l t i p l y i n g by 100 the l o a d i n kg a t 0.01 i n . / i n . s t r a i n w i t h i n the p r o p o r t i o n a l l i m i t 2 and d i v i d i n g t h a t number by the c r o s s - s e c t i o n a l area i n cm . Both u l t i m a t e t e n s i l e s t r e n g t h and e l a s t i c i t y values were converted  i n t o p s i u n i t s , u s i n g a conversion f a c t o r of 14.22.  U l t i m a t e s t r a i n values were c a l c u l a t e d from e l o n g a t i o n data, read from the t e s t i n g machine chart and t a k i n g i n t o account the t e s t speed and the span over which the specimens were tested.  Work t o maximum t e n s i o n l o a d was c a l c u l a t e d from  the area under the l o a d - e l o n g a t i o n diagram from the machine c h a r t , c o n v e r t i n g t h a t number i n t o u n i t value of i n . l b / i n . S i x t e s t r e s u l t s obtained from the three growth increments i n each of the experimental  test conditions  were considered as r e p l i c a t e s and t h e i r mean value c a l c u l a t e d . These average s t r e n g t h p r o p e r t i e s are given i n Tables 2, 3, 4, and 5.  A l s o i n c l u d e d are c o e f f i c i e n t s of v a r i a t i o n i n -  d i c a t i n g the p e r cent d i s p e r s i o n of the data around each mean value  reported.  In Tables 2, 3, 4 and 5, s t r e n g t h p r o p e r t i e s o f e a r l y - and latewood are t a b u l a t e d s e p a r a t e l y because i n a l l  48  cases  they were so d i s t i n c t l y d i f f e r e n t .  was f o l l o w e d throughout  This arrangement  f o r a l l values r e p o r t e d .  Strength  values i n the above t a b l e s are f u r t h e r d i v i d e d i n t o three groups a c c o r d i n g t o the three temperature were t e s t e d .  l e v e l s a t which specimens  Within each temperature  l e v e l , the means of  s t r e n g t h p r o p e r t i e s i n Tables 2, 3, 4 and 5 are grouped •• under three moisture content c o n d i t i o n s as i n d i c a t e d by 0 ( z e r o ) , a i r - d r y and s a t u r a t e d . corresponds  The zero moisture  content  t o a m o i s t u r e - f r e e s t a t e of the specimens a t t e s t ,  while the s a t u r a t e d c o n d i t i o n r e f e r s to a moisture h i g h e r than the f i b r e - s a t u r a t i o n p o i n t o f the wood.  content The  a c t u a l moisture contents a t t a i n e d by the a i r - d r y specimens d u r i n g p r e - c o n d i t i o n i n g were determined These v a l u e s are g i v e n i n Table 6.  as d e s c r i b e d e a r l i e r .  The temperature  and r e l -  a t i v e humidity c o n d i t i o n s a t which the specimens were d r i e d are a l s o r e p o r t e d i n Table 6. In Tables 2, 3, 4 and 5, as w e l l as i n Table 6, the experimental r e s u l t s are t a b u l a t e d i n r e l a t i o n t o i n t e g r a l i r r a d i a t i o n dose t o which the t e s t samples had been exposed prior to testing.  I n Table 7, experimental r e s u l t s o f  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 measurements are g i v e n with t h e i r c o e f f i c i e n t s o f v a r i a t i o n , based on f o u r r e p l i c a t e s of each mean.  A l s o i n c l u d e d i n t h i s t a b l e are the averages  of d u p l i c a t e determinatioir?of n i t r o g e n content. are t a b u l a t e d a c c o r d i n g t o nominal  integral  Values  irradiation  dosages t o which the wood samples had been exposed.  49  C e l l u l o s e degree of p o l y m e r i z a t i o n v a l u e s c a l c u l a t e d from i n t r i n s i c v i s c o s i t i e s are g i v e n i n Table 8 i n r e l a t i o n to  i n t e g r a l i r r a d i a t i o n dosages, growth increments and wood  zones.  No measures of d i s p e r s i o n are r e p o r t e d i n t h i s t a b l e  s i n c e DP v a l u e s were c a l c u l a t e d only.from mean v i s c o s i t y data. R e s u l t s of v i s c o s i t y measurements and DP c a l c u l a t i o n s are a l s o shown g r a p h i c a l l y i n F i g u r e s 15 and 16 r e s p e c t i v e ly.  Curves f i t t e d by u s i n g the l e a s t squares method to a l l  experimental data, as w e l l as the averages shown i n these f i g u r e s . and latewood  of those data, are  Here, too, data obtained from  early-  are shown s e p a r a t e l y , the s o l i d l i n e and f u l l  c i r c l e s corresponding t o latewood, and the dotted l i n e and empty c i r c l e s to earlywood  results.  S t a t i s t i c a l techniques were used t o evaluate the s i g n i f i c a n c e of v a r i a t i o n s induced by the three treatments. A n a l y s i s of v a r i a n c e was c a l c u l a t e d f o r each s t r e n g t h property tested.  Here, again, e a r l y - and latewood v a l u e s were  handled s e p a r a t e l y .  In Tables 9 through 16 r e s u l t s of e i g h t  analyses of v a r i a n c e are g i v e n , one f o r each of the f o u r s t r e n g t h p r o p e r t i e s t e s t e d , f o r e a r l y - and latewood arately.  I n these t a b l e s the f i r s t  p o l y m e r i z a t i o n (DP), the second t h i r d i s moisture content  (MC).  sep-  f a c t o r i s degree of  i s temperature  ( T ) , and  the  The i n t e r a c t i o n s of the  three treatments were a l s o t e s t e d and they a l s o are i n c l u d e d i n the t a b l e s . Only i n one case was i t d o u b t f u l t h a t the p r o p e r t y  50  of e a r l y - and latewood was of two d i f f e r e n t p o p u l a t i o n s and t h i s was f o r u l t i m a t e t e n s i l e s t r a i n .  In order t o t e s t  this,  an a n a l y s i s of v a r i a n c e was c a l c u l a t e d f o r u l t i m a t e s t r a i n values of both e a r l y - and latewood i n c l u d e d .  The r e s u l t  of t h i s a n a l y s i s i s g i v e n i n Table 17 i n which the u l t i m a t e s t r a i n values of the three growth increments  were a l s o t e s t e d .  The a n a l y s i s r e v e a l e d t h a t s t r a i n behavior of the two wood zones was h i g h l y s i g n i f i c a n t l y d i f f e r e n t , as w e l l as t h a t the three growth increments  were not d i f f e r e n t from each  other i n r e s p e c t t o u l t i m a t e s t r a i n i n t e n s i o n .  Most of  the s i g n i f i c a n t i n t e r a c t i o n s i n Table 17 are those  involving  wood zone, i n d i c a t i n g that the s t r a i n behavior of earlywood and t h a t of latewood are not only of a d i f f e r e n t order of magnitude, but a l s o that the two zones r e a c t e d i n a d i f f e r e n t manner t o the treatments used.  On the b a s i s of these f i n d i n g s ,  u l t i m a t e s t r a i n r e s u l t s obtained from e a r l y - and latewood were handled  s e p a r a t e l y i n subsequent a n a l y s e s .  No s i m i l a r  t e s t s of wood zones were c a r r i e d out w i t h regard t o s t r e n g t h , e l a s t i c i t y and work t o maximum l o a d because of obvious d i f f e r e n c e s between these p r o p e r t i e s i n e a r l y - and latewood. In Tables 9 and 10 the analyses of v a r i a n c e show that u l t i m a t e t e n s i l e s t r e n g t h o f both e a r l y - and latewood were s i g n i f i c a n t l y i n f l u e n c e d by the treatments cent l e v e l of p r o b a b i l i t y .  No i n t e r a c t i o n s occurred  i c a n t among the three treatment^ and moisture  a t the 0.1 p e r signif-  that i s , a t a l l temperatures  contents wood r e a c t e d i n the same manner to  v a r i a t i o n s i n c e l l u l o s e DP.  Conversely, a t a l l DP and tern-  51  perature l e v e l s , changes i n moisture content induced the same type o f v a r i a t i o n  i n tensile strength.  E l a s t i c i t y values are analyzed i n Tables 11 and 12. Here, again, The s i g n i f i c a n t  effect  of treatments on t h i s  mechanical p r o p e r t y i s apparent f o r both e a r l y -  and latewood.  An e x c e p t i o n t o t h i s g e n e r a l statement i s latewood  elas-  t i c i t y which appears t o be unchanged by v a r i a t i o n s  i n cel-  l u l o s e DP. degraded  I n earlywood,  e l a s t i c i t y o f the most s e v e r e l y  samples i s s i g n i f i c a n t l y lower than that o f wood  having c e l l u l o s e  o f h i g h e r molecular weight.  The a n a l y s i s of u l t i m a t e s t r a i n values i s given i n Tables 13 and 14.  I t should be noted i n these t a b l e s that  the r e l a t i v e l y narrow temperature any s i g n i f i c a n t early-  effect  or latewood.  range alone d i d not induce  on the s t r a i n behavior o f e i t h e r  However, the other two treatments i n -  fluenced ultimate s t r a i n i n a s t a t i s t i c a l l y manner a t the 0.1 p e r cent p r o b a b i l i t y early-  significant  level.  F o r both  and latewood u l t i m a t e s t r a i n v a l u e s , temperature and'  moisture content i n t e r a c t i o n  i s highly significant.  Table 4 i t may be seen that the above e f f e c t interesting  trend i n s t r a i n values.  From  i s due t o an  I t i s noticeable that,  a t the h i g h e s t moisture content l e v e l latewood s t r a i n i n creased w i t h i n c r e a s i n g temperature, at the two lower moisture l e v e l s  i t decreased w i t h i n c r e a s i n g  temperature.  In the case of earlywood u l t i m a t e s t r a i n v a l u e s , a s i m i l a r  52  h i g h l y s i g n i f i c a n t i n t e r a c t i o n was ature and moisture content.  obtained between temper-  In a d d i t i o n , here, a h i g h l y  s i g n i f i c a n t i n t e r a c t i o n between c e l l u l o s e DP and content was  (  moisture  calculated.  The analyses of v a r i a n c e of work to maximum l o a d v a l u e s f o r e a r l y - and latewood respectively. treatment  e f f e c t s appear to be s t a t i s t i c a l l y s i g n i f i c a n t , i n For earlywood  samples, a l l  order i n t e r a c t i o n s show s t a t i s t i c a l  although they are seemingly treatment  16  In these, some of the i n t e r a c t i o n s between  a d d i t i o n t o the main e f f e c t s . the f i r s t  are g i v e n i n Tables 15 and  effects.  of l e s s importance  significance, than the main  N e v e r t h e l e s s , the r e s u l t s of analyses  i n d i c a t e t h a t at v a r i o u s temperature  and moisture  content  l e v e l s , v a r i a t i o n s i n c e l l u l o s e DP induced d i f f e r e n t changes i n work v a l u e s . l o a d f o r latewood  The a n a l y s i s of work to maximum t e n s i o n specimens, as shown i n Table 16,  t h a t the only f i r s t  order i n t e r a c t i o n i n d u c i n g s i g n i f i c a n t  v a r i a t i o n i n work v a l u e s of t h i s wood zone was c e l l u l o s e DP and moisture content. first  order i n t e r a c t i o n i n earlywood  to be s t a t i s t i c a l l y  indicates  that between  On the other hand, a l l work values turned out  significant.  The analyses of v a r i a n c e of s t r e n g t h p r o p e r t i e s a l s o gave a b a s i s f o r subsequent r e g r e s s i o n analyses of the data.  F i r s t l y , a l l means r e p o r t e d i n Tables 2 through  5 were p l o t t e d a g a i n s t temperature, cellulose intrinsic viscosity.  moisture content  and  From these p l o t s the g e n e r a l  53  trend of p o i n t s with regard to each v a r i a b l e was examined and v a r i o u s p r e l i m i n a r y curves were f i t t e d t o f i n d the mathematical expression best d e s c r i b i n g the r e l a t i o n s h i p s . I n these operations  the l e a s t squares method was used, and  the model g i v i n g s i g n i f i c a n t l y h i g h e s t R value was s e l e c t e d . Secondly, the p o s s i b l e i n t e r a c t i o n s were i n c l u d e d i n the f i n a l r e g r e s s i o n equations.  Only those i n t e r a c t i o n s were  i n c l u d e d i n these r e l a t i o n s h i p s which had been proved s i g n i f i c a n t i n the previous  analyses  of v a r i a n c e c a l c u l a t i o n s .  A c c o r d i n g l y , f o r u l t i m a t e s t r e n g t h v a l u e s , no i n t e r a c t i o n s were i n c l u d e d i n the r e g r e s s i o n equations,  whereas f o r work  to u l t i m a t e t e n s i o n l o a d i n earlywood, the b a s i c d e s c r i b i n g v a r i a t i o n s due t o i n t r i n s i c v i s c o s i t y , and moisture content  equation temperature,  i n c l u d e d a l l the p o s s i b l e f i r s t  order  i n t e r a c t i o n terms. The  equations c a l c u l a t e d i n the above manner are  r e p o r t e d i n Table  18.  S i m i l a r r e l a t i o n s h i p s were c a l c u l a t e d  f o r s t r e n g t h p r o p e r t i e s with DP values i n c l u d e d i n s t e a d of i n t r i n s i c v i s c o s i t i e s as measures of c e l l u l o s e c h a i n l e n g t h . These l a t t e r equations are g i v e n i n Table  19.  The response  s u r f a c e s based on the best f i t t i n g mathematical models are shown i n F i g u r e s  17 through 20.  In each f i g u r e , e a r l y - and  latewood r e s u l t s are given s e p a r a t e l y , s i n c e the equations d e s c r i b i n g v a r i a t i o n s i n s t r e n g t h p r o p e r t i e s of the two wood zones were a l s o found t o be d i f f e r e n t . The  r e l a t i v e importance of f a c t o r s i n f l u e n c i n g t e n s i l e  54  s t r e n g t h p r o p e r t i e s was  examined by p a r t i t i o n i n g the R p  values of each r e g r e s s i o n equation.  I f 100xR  i s the per  cent v a r i a t i o n e x p l a i n a b l e by the f a c t o r s examined,then p a r t i t i o n i n g t h i s a c c o r d i n g to per cent v a r i a t i o n accounted  those f a c t o r s g i v e s the  f o r by each f a c t o r . R e s u l t s o f  these c a l c u l a t i o n s are g i v e n i n Table 20.  The  variations  due to the i n t e r a c t i o n s between c e l l u l o s e i n t r i n s i c temperature,  and moisture  content are not l i s t e d  viscosity,  individually  i n t h i s t a b l e because t h e i r t o t a l c o n t r i b u t i o n to changes i n s t r e n g t h p r o p e r t i e s was  g e n e r a l l y s m a l l e r than t h a t of  any one of the main e f f e c t s alone.  In Table 20, per cent  v a r i a t i o n i n a p a r t i c u l a r strength property explainable by i n t e r a c t i o n s i n c l u d e s the t o t a l amount of v a r i a t i o n induced by such i n t e r a c t i o n s . c o e f f i c i e n t s are r e p o r t e d .  In Table 21 simple  correlation  These numbers were c a l c u l a t e d  on the b a s i s of each v a r i a b l e alone, c o n s i d e r i n g t h a t a l l the r e s i d u a l v a r i a t i o n was  due to experimental  error.  Besides the c o e f f i c i e n t s of v a r i a t i o n i n Table  2,  the experimental e r r o r i n u l t i m a t e t e n s i l e s t r e n g t h values i s a l s o i l l u s t r a t e d g r a p h i c a l l y i n F i g u r e 21.  In t h i s  f i g u r e , the range of t e n s i l e s t r e n g t h values obtained f o r a i r - d r y earlywood specimens at 50°C i s p l o t t e d over the mathematically  f i t t e d r e g r e s s i o n l i n e . The s o l i d  line  curve represents the values f i t t e d by u s i n g the l e a s t squares method, and the dotted l i n e s represent the range of experimental  data.  55  DISCUSSION  I  INFLUENCE OP GAMMA RADIATION ON CELLULOSE CHAIN LENGTH Gamma i r r a d i a t i o n o f Douglas f i r wood induced a  r e l a t i v e l y l a r g e r e d u c t i o n i n both c e l l u l o s e c h a i n and  strength properties p a r a l l e l to grain.  length  The e f f e c t was  such that wood samples r a d i a t e d t o 10 and 15 megarad doses became f r a g i l e , e s p e c i a l l y i n the water-saturated c o n d i t i o n . No v i s i b l e changes i n c o l o r appeared as a r e s u l t o f r a d i a t i o n even a t as h i g h as 15 megarad treatment, i n c o n t r a s t to f i n d i n g s o f i n v e s t i g a t o r s i n e a r l i e r s t u d i e s I f the darkening e f f e c t were due t o o x i d a t i o n w i t h degradation,  (45,60,78).  associated  the f a c t that the wood samples i n t h i s  experiment were r a d i a t e d i n w e l l - s e a l e d bags i n the  saturated  c o n d i t i o n , could have prevented such a chemical r e a c t i o n through the r e s t r i c t i o n o f the amount o f a v a i l a b l e oxygen. The  only n o t i c e a b l e d i f f e r e n c e between r a d i a t e d and untreated  wood s e c t i o n s was that the former had a s l i g h t l y unpleasant, a c i d i c s m e l l upon opening the bags.  This s m e l l was somewhat  stronger f o r the 10 and 15 megarad i r r a d i a t e d samples than f o r the l e s s s e v e r e l y t r e a t e d ones. F i g u r e 15 i s a diagram r e p r e s e n t i n g  the e f f e c t  of gamma r a d i a t i o n o f wood on 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 .  56  The  g e n e r a l c o n f i g u r a t i o n o f the curves i s s i m i l a r to what  would be expected on the b a s i s of t h e o r e t i c a l c a l c u l a t i o n s of Charlesby (17), Bovey (10), and Chapiro (16).  Charlesby  (17), working with i r r a d i a t e d c o t t o n l i t e r s , found that when i n t r i n s i c v i s c o s i t y was p l o t t e d against  i r r a d i a t i o n dose  on a l o g - l o g s c a l e , a convex-upward curve was obtained. However, when the v i s c o s i t y was r e l a t e d t o the sum- o f the a c t u a l and t h e ' v i r t u a l ' r a d i a t i o n dose on the same s c a l e , an almost p e r f e c t s t r a i g h t l i n e p r e v a i l e d . r a d i a t i o n dose was defined quired  Here, the v i r t u a l  as the dose which would be r e -  t o degrade a c e l l u l o s e molecule o f i n f i n i t e  length  to a polymer having the same degree o f p o l y m e r i z a t i o n  as  the i n i t i a l c e l l u l o s e . In t h i s experiment the v i r t u a l r a d i a t i o n dose was estimated t o be one megarad.  Through s e v e r a l t r i a l s i t was  found t h a t , when t h i s dose was used as v i r t u a l dose, the p o i n t s p l o t t e d on a l o g - l o g s c a l e were w e l l p o s i t i o n e d on a straight l i n e .  U s i n g the value obtained t h i s way, a  simple l i n e a r r e g r e s s i o n was c a l c u l a t e d w i t h the a i d of the l e a s t squares method between log[ ?] and log(R+R ), v  Q  where R was the a c t u a l dose to which the samples were exposed, and R megarad.  Q  was the v i r t u a l r a d i a t i o n dose taken as 1  The equation c a l c u l a t e d from combining a l l e a r l y -  and latewood data has the f o l l o w i n g form:  logH]  = -0.8589 log(R+R ) + 1.5714 Q  According t o Charlesby (17) and Chapiro (16), the r e g r e s s i o n  57  c o e f f i c i e n t of the log(R+R ) term, i . e . , the slope of the Q  l i n e i s the same number as the exponent i n equation 0 0 ed e a r l i e r .  quot-  By t h i s mathematical approach i t was hoped to  o b t a i n a more r e a l i s t i c c o n v e r s i o n method from i n t r i n s i c v i s c o s i t y t o DP.  However, the K  m  f a c t o r f o r such a r e l a -  t i o n s h i p could not be c a l c u l a t e d i n a s i m i l a r manner, so that a unique formula f o r DP c a l c u l a t i o n s a f t e r v a r i o u s doses of gamma r a d i a t i o n could not be developed.  The g a i n here i s  s t i l l c o n s i d e r a b l e , i n that the exponent f o r a p o s s i b l e e x p o n e n t i a l r e l a t i o n s h i p i s probably more accurate than the ones developed i n d i f f e r e n t experiments and under d i f f e r e n t c o n d i t i o n s . F o r example,  the exponent of 0.8589 i s c o n s i d e r -  a b l y l a r g e r than the one developed by T i m e l l (93), which was 0.572.  N e v e r t h e l e s s , the exponent so c a l c u l a t e d f o r a  p o s s i b l e e x p o n e n t i a l r e l a t i o n s h i p between i n t r i n s i c  viscosity  and DP, i s w e l l i n the range o f such v a l u e s determined by v a r i o u s workers, as the range i s g e n e r a l l y g i v e n as 0.70 t o 1.00 (77). From the above c a l c u l a t i o n s a method f o r c o n v e r t i n g v i s c o s i t i e s i n t o DP v a l u e s may be developed. inal  If  the o r i g -  DP of c e l l u l o s e i n wood, as determined u s i n g the con-  v e r s i o n f a c t o r d e r i v e d from data o f T i m e l l (93), i s accepted as t r u e v a l u e , the f a c t o r K  i n an e x p o n e n t i a l expression m  may be c a l c u l a t e d .  I f the K  m  f a c t o r i s c a l c u l a t e d by sub-  s t i t u t i n g the o r i g i n a l DP o f c e l l u l o s e i n earlywood, and the corresponding i n t r i n s i c v i s c o s i t y i n equation 0 O, number obtained i s 0X219.  the  The same number f o r summerwood  58  c e l l u l o s e becomes 0.0215.  I f the above K  m  f a c t o r s and  the  exponent 0.8589 are used i n an e x p r e s s i o n of the exponential type, a new  set of DP values may  be obtained which may  be  somewhat more accurate than the "empirical v a l u e s c a l c u l a t e d i n t h i s experiment.  In Table 22, c e l l u l o s e i n t r i n s i c  vis-  c o s i t i e s are g i v e n w i t h the corresponding two DP v a l u e s , one c a l c u l a t e d by the e m p i r i c a l method d e s c r i b e d i n Methods S e c t i o n , the other by u s i n g the aforementioned relationship.  This l a t t e r technique may  exponential  be regarded as more  accurate because, i n the former procedure,  a rather long  e x t r a p o l a t i o n had to be made from the l i n e a r r e l a t i o n s h i p based on data of T i m e l l (93).  This was  necessary to cover  the wide range of v i s c o s i t y values had i n t h i s experiment. The  1 megarad v i r t u a l r a d i a t i o n dose estimated i n  t h i s study f o r wood was (17) f i g u r e , which was  i n good agreement with  found to be the same value i n that  study on c o t t o n l i n t e r s . DP values of the two  Charlesby's  This can only e x i s t i f the  types of c e l l u l o s e are equal, and i f  the r a t e of degradation by gamma rays of the two i s the same.  initial  types  The f i r s t p a r t of the above assumption i s  supported by the recent f i n d i n g s of Goring and T i m e l l (31) that a l l n a t i v e c e l l u l o s e s have approximately  the same  degree of p o l y m e r i z a t i o n i n t h e i r n a t u r a l s t a t e , independent of  source.  The second p a r t of the assumption i s i n c o n t r a s t  w i t h the theory of Smith and Mixer  (86) that l i g n i n serves  as a p r o t e c t i v e medium a g a i n s t i r r a d i a t i o n .  59  The curves r e l a t i n g c e l l u l o s e DP to v a r i a t i o n i n r a d i a t i o n dose are shown i n F i g u r e 16.  They conform t o  the g e n e r a l e x p e c t a t i o n t h a t there i s a r e l a t i v e l y  large  r e d u c t i o n i n c e l l u l o s e DP a t low i n t e g r a l doses, f o l l o w e d by g r a d u a l l y d e c r e a s i n g degradation.  Bovey (10) has given a  simple mathematical expression d e s c r i b i n g the r e l a t i o n s h i p : DP =  DP 1 +,S  where DP i s the degree o f p o l y m e r i z a t i o n a f t e r r a d i a t i o n ; DP , the i n i t i a l degree o f p o l y m e r i z a t i o n of the polymer; Q  and S, the number of s c i s s i o n s p e r o r i g i n a l chain..  The  above mathematical expression represents a h y p e r b o l i c curve asymptotic  to the S a x i s h o r i z o n t a l l y , and t o the l i n e  i n t e r c e p t i n g the S a x i s a t  the v a l u e o f -1 v e r t i c a l l y .  The above f u n c t i o n can be w r i t t e n a s :  i - ~=DP4- d  DP  o  + s)  which means t h a t the r e c i p r o c a l o f DP a f t e r degradation  will  be a l i n e a r f u n c t i o n of the number o f s c i s s i o n s , with an i n t e r c e p t on the jjp—  a x i s a t jp-". o  On the b a s i s o f the above c o n s i d e r a t i o n s an attempt was made to c a l c u l a t e a r e g r e s s i o n o f the r e c i p r o c a l o f DP on r a d i a t i o n dose.  The equations  f o r e a r l y - and' latewood  samples, r e s p e c t i v e l y , a r e : -|jp-.= -0.000005745 + 0.00005512 R  60  -gjr  = -0.00001082 + 0.00003654 R  where R i s the a c t u a l r a d i a t i o n dose t o which the samples had been exposed p r i o r t o DP determinations.  Although the  c o r r e l a t i o n s f o r the above r e g r e s s i o n s were found t o be v e r y h i g h (0.91  and 0.87), they gave values too low t o be  considered f o r c a l c u l a t i n g DP values r e s u l t i n g from gamma radiation.  The negative value o f the constant term i n both  equations i n d i c a t e s that degrees of polymerization," o b t a i n a b l e for  i n i t i a l cellulose  ously meaningless.  are negative numbers, which i s o b v i -  Bovey (10) questioned the v a l i d i t y o f  such a c a l c u l a t i o n because o f the low,  o f t e n negative, r e s u l t s  f o r . i n i t i a l DP v a l u e s . Neal and K r a e s s i g (73) have developed to  an expression  c a l c u l a t e the f r a c t i o n o f bonds broken by gamma r a y s .  They found t h a t , i f the i n i t i a l and the r e s u l t i n g c e l l u l o s e DP's  are known, the f r a c t i o n o f bonds broken can be c a l c u l a t e d  by the f o l l o w i n g simple formula : F r a c t i o n o f bonds broken = o By d e f i n i t i o n , i n t h i s expression DP and DP number-average v a l u e s .  Q  should be  These authors c l a i m that s a t i s f a c t o r y  r e s u l t s can be obtained i f i n t r i n s i c v i s c o s i t y values a r e s u b s t i t u t e d f o r DP numbers.  Although i n t r i n s i c  viscosity  data are c o r r e l a t e d t o an average c l o s e r t o the weight-average, r a t h e r than t o the number-average DP v a l u e s , the f r a c t i o n o f  61  bonds broken should be a l i n e a r f u n c t i o n of i n t e g r a l r a d i a t i o n dose <-l73). this  Data of Meal and  Kraessig  (73)  conformed w e l l  to  linearity. In t h i s experiment, the f r a c t i o n of bonds broken,  c a l c u l a t e d from e i t h e r v i s c o s i t y or DP v a l u e s , d i d not a l i n e a r r e l a t i o n s h i p w i t h i n t e g r a l r a d i a t i o n dose. configuration  show The  of the curve suggests that at h i g h dosage  l e v e l s the' f r a c t i o n of bonds broken i n c r e a s e s with i n c r e a s i n g doses than at low  levels.  more r a p i d l y  However, the  number of dosage l e v e l s used i n t h i s study does not  small  allow  any m a n i p u l a t i o n l e a d i n g to the reasons f o r t h i s n o n - l i n e a r i t y .  II  EFFECTS OF CELLULOSE CHAIN LENGTH ON OF WOOD PARALLEL TO  STRENGTH PROPERTIES  GRAIN  To develop b e t t e r understanding of the responsible  f o r the r e l a t i o n s h i p of s t r e n g t h  c e l l u l o s e chain length  factors  properties  of wood, i t seems a p p r o p r i a t e to  and first  review the mechanism of deformation under t e n s i l e s t r e s s e s . When a s o l i d i s i n a s t r e s s - f r e e s t a t e , i t s molecules or other submicroscopic elements are i n a s t a b l e , e q u i l i b r i u m  position.  The  each other.  a t t r a c t i n g and  In s t r e s s e d  r e p e l l i n g molecular f o r c e s  cancel  s t a t e , however, the molecular spaces, and  molecular f o r c e s , are of d i f f e r e n t magnitude (74, f o r instance,  75).  the body i s subjected to t e n s i l e s t r e s s  also If,  the  62  which causes an expansion, the molecular spaces grow l a r g e r i n the d i r e c t i o n of t e n s i o n . f o r c e s become s m a l l e r , and provided  In that d i r e c t i o n the r e p e l l i n g  the a t t r a c t i n g f o r c e s  increase,  t h a t the a p p l i e d s t r e s s i s w i t h i n the e l a s t i c range  of the m a t e r i a l .  There p r e v a i l s a new  e q u i l i b r i u m between  the t e n s i l e f o r c e p l u s the r e p e l l i n g f o r c e s on the one hand, and  the molecular a t t r a c t i n g f o r c e s on the other.  two  f o r c e s together  The  first  tend to i n c r e a s e the molecular spaces, an  while the l a t t e r f o r c e tends to decrease them innattempt to r e s t o r e the o r i g i n a l shape of the body. At f i r s t , the molecules r e t a i n t h e i r p o s i t i o n w i t h r e s p e c t to one  another, but  original  i n the course of  time, or with i n c r e a s e i n the a p p l i e d f o r c e , more and more bonds get i n t o the f o r c e range of new new  sites.  By t h i s a  e q u i l i b r i u m p o s i t i o n i s e s t a b l i s h e d i n which the  a t t r a c t i n g and r e p e l l i n g f o r c e s are equal and where no e x t e r n a l t e n s i l e s t r e s s i s necessary to achieve the body length.  The m a t e r i a l i s then s t r e s s - f r e e again, but  a l l y deformed.  plastic-  B r i e f l y then, t h i s i s the molecular mecha-  nism of s t r e s s and  deformation.  With wood, however, rheology at the molecular l e v e l cannot be as simple as the c l a s s i c examination due s t r u c t u r a l and  chemical complexities  to  of the m a t e r i a l .  Tracheid w a l l s of c o n i f e r s can be looked upon as a network of bond chains, some of which c o n s i s t of segments of c e l l u l o s e chains, others  of secondary valence f o r c e s between molecules  63  and t h e i r segments. The  weakest primary valence f o r c e s  e x i s t i n g i n .a s i n g l e c e l l u l o s e c h a i n a r e the -C-O-C- b r i d g e s connecting the glucose u n i t s t o each other. Mark, i n O t t (76), the s t r e n g t h o f i m a t e l y 1 ,144,000 p s i .  According t o  these b r i d g e s i s approx-  I f a more accurate c a l c u l a t i o n i s used  t h i s value can reach 2,133,000psi (77) f o r an i d e a l i z e d c e l l u l o s e sample of the h i g h e s t p o s s i b l e o r i e n t a t i o n . l a t e r a l f o r c e s between the c h a i n molecules  The  a r e the hydrogen  bonds and the common van der Waals' bonds, as was demonstrated by E l l i s and Bath (21) i n an i n v e s t i g a t i o n o f IR s p e c t r a of  cellulose.  The f o r c e necessary t o break a secondary  valence bond o f the above type i s only approximately psi, Due  43,000  as was estimated from b r e a k i n g sucrose c r y s t a l s ( 7 6 ) . t o t h i s great d i f f e r e n c e between the two f o r c e s , i t seems  to be evident t h a t , when an e x t e r n a l f o r c e i s a p p l i e d , deformation takes p l a c e i n the i n t e r - m o l e c u l a r bonds.  The  s t r e n g t h o f the -C-O-C- bonds i s so h i g h t h a t extension of the molecular c h a i n i t s e l f  cannot be r e a l i z e d .  Bond  deformation,  t h e r e f o r e , i s a p r o p e r t y o f the weaker type, the i n t e r - c h a i n bonds. For an i d e a l polymeric m a t e r i a l i n which chains are o r i e n t e d p a r a l l e l , deformation due to e x t e r n a l s t r e s s can occur as s l i p p a g e .  I n t h i s process the hydrogen bonds which  h o l d the chains together l a t e r a l l y must be overcome. of  Sliding  the molecules upon each other can s t a r t when the energy  necessary f o r t h i s purpose i s l e s s than t h a t r e q u i r e d f o r  64  b r e a k i n g the primary valence f o r c e s along the c h a i n s .  In  order to p u l l out a c h a i n molecule embedded among;; others i n t h i s i d e a l arrangement, the f o r c e to be a p p l i e d would depend on the t o t a l l a t e r a l cohesive f o r c e between those  chains,  which, on the other hand, i s dependent upon the number of monomers p a r t i c i p a t i n g i n such a l a t e r a l bond.  Meyer  made an attempt to c a l c u l a t e the minimum number of r e s i d u e s i n a c h a i n which would be necessary  (72)  glucose  to produce an  o v e r a l l energy of the l a t e r a l bonds h i g h e r than that r e p r e sented by a s i n g l e primary valence bond. i f 70 glucose u n i t s of one u n i t s of a neighboring  He estimated  c h a i n are a s s o c i a t e d with  that  70  c h a i n , through a l l p o s s i b l e hydrogen  bonds, the l a t e r a l energy would be h i g h enough to e f f e c t breaking of a c h a i n at a -C-O-G- l i n k a g e . Prom the above, i t i s evident t h a t i f the number of c r o s s - l i n k s i s l e s s than t h a t produced by 200  approximately  to 250 hydrogen bonds, s l i p p i n g w i l l take p l a c e .  f o l l o w s t h a t s l i p p a g e w i l l occur the more r e a d i l y , s m a l l e r the number of l a t e r a l l i n k s .  Then i t  the  Tensile strength,  t h e r e f o r e , should depend on c h a i n l e n g t h of c e l l u l o s e . the other hand, c e l l u l o s e beyond a c e r t a i n c r i t i c a l l e n g t h should show t e n s i l e s t r e n g t h independent of Systematic  On  chain DP.  i n v e s t i g a t i o n s of Skoone and H a r r i s  (85)  with c e l l u l o s e a c e t a t e have c l e a r l y shown t h i s r e l a t i o n s h i p between c h a i n l e n g t h and s t r e n g t h . /  They foundthat,  when  t e n s i l e s t r e n g t h and u l t i m a t e e l o n g a t i o n were p l o t t e d  65  a g a i n s t number-average DP of the a c e t a t e , the slope of the curve d e s c r i b i n g the r e l a t i o n s h i p was more or l e s s up to approximately  200 to 250 DP.  constant  Above t h i s c r i t i c a l value  the i n c r e a s e i n s t r e n g t h with c h a i n l e n g t h became l e s s pronounced, as i f the chains had obtained a s u f f i c i e n t l e n g t h to be e f f e c t i v e l y bonded together by secondary  f o r c e s and  thus to u t i l i z e the l o n g i t u d i n a l s t r e n g t h of the chains. Although  t h i s i s i n g e n e r a l agreement w i t h the s l i p p a g e  theory of deformation,  there occurs a r e l a t i v e l y l a r g e  d i f f e r e n c e between the a c t u a l and the t h e o r e t i c a l value of the l i m i t i n g degree of p o l y m e r i z a t i o n .  However, the l e v e l  of l i m i t i n g DP at 200 to 250 can be p a r t l y explained by  the  f a c t t h a t the molar cohesion of -COOCH^ groups, s u b s t i t u t e d f o r the hydroxyls i n c e l l u l o s e a c e t a t e , i s only 5600 kg c a l per mole, while that f o r OH groups i s 7250 (67,76). a d d i t i o n , the o r i e n t a t i o n of molecules  i n synthetic high  polymers i s f a r from b e i n g p e r f e c t as was Meyer's (72)  In  assumed i n the  calculation.  I t i s i n t e r e s t i n g to note i n the work of Skoone and H a r r i s (85) t h a t , whereas u l t i m a t e e l o n g a t i o n values almost  completely l e v e l l e d o f f a t a DP of approximately  250,  t e n s i l e s t r e n g t h d i d not reach a constant v a l u e even a t a DP of 500.  Indeed, there have been r e p o r t s i n the l i t e r a t u r e  of a h i g h c o r r e l a t i o n between s t r e n g t h and DP f o r d i f f e r e n t v a r i e t i e s of c o t t o n f i b r e s at DP l e v e l s as h i g h as 8,000 .to 10,000 (37).  66  In n a t u r a l f i b r e s , the c o n d i t i o n i s never r e a l i z e d , t h e r e f o r e obscured.  In w e l l o r i e n t e d  of i d e a l orientation  the r e l a t i o n s h i p i s o f t e n ramie, hemp and f l a x f i b r e s ,  Meyer and Lotmar, as c i t e d i n Ott (76) and by Hermans ( 3 6 ) , found modulus o f e l a s t i c i t y i n the same order o f magnitude as the v a l u e s computed f o r an i d e a l f i b r e .  This merely  suggests that rupture o f primary valence bonds i s i n v o l v e d i n breaking c e l l u l o s e i n materials In l e s s w e l l oriented strength  of high orientation.  c e l l u l o s i c materials,  the u l t i m a t e  v a l u e s a r e much lower than the c a l c u l a t e d  figures,  the d i f f e r e n c e b e i n g p r i m a r i l y due t o the p i t c h o f the s p i r a l structure.  B e r k l e y and Woodyard (8) found a v e r y h i g h  c o r r e l a t i o n (0.954) between the d i r e c t l y measure t e n s i l e strength, and that computed from the average angle o f the s p i r a l structure  of c e l l u l o s e .  The o r i e n t a t i o n e f f e c t i s  d e f i n i t e l y present i n woody f i b r e s as w e l l , so that the c r i t i c a l DP o f c e l l u l o s e should be h i g h e r than the theor e t i c a l l y c a l c u l a t e d one-. Before a bond can c o n t r i b u t e the m a t e r i a l , stresses.  i t has t o be o r i e n t e d  t o the s t r e n g t h o f i n the d i r e c t i o n o f  This o r i e n t a t i o n i s f i r s t produced i n the bonds  or bond s e r i e s o f the s h o r t e s t  l e n g t h which event r e s u l t s  i n the s t r e s s i n g and, consequently, b r e a k i n g o f bonds successively  introduced.  The breakdown o f one bond allows the  s t r e s s t o pass t o another i n p a r a l l e l with i t . In wood f i b r e s a r e l a t i o n s h i p between  strength  67  p r o p e r t i e s and c e l l u l o s e c h a i n l e n g t h i s f u r t h e r modified by the f a c t t h a t approximately  30 to 35 per cent of the  c e l l u l o s e i s i n an amorphous s t a t e (80).  In the amorphous  regions of the c e l l u l o s e , only a p r o p o r t i o n of the a v a i l a b l e OH groups i s hydrogen bonded. average of two for  According to Lauer (59),  an  OH groups per glucose r e s i d u e are a v a i l a b l e  r e a c t i o n with h y d r o p h i l c reagents  f r e e l y i n t o these r e g i o n s .  which can  penetrate  On the other hand, the  hydroxyl  groups are a l l s a t i s f i e d i n the c r y s t a l l i n e zones.  Although  these regions of c e l l u l o s e are not b e l i e v e d to be d i s c r e t e e n t i t i e s , i t i s reasonable  to assume t h a t deformation  due  to  e x t e r n a l s t r e s s e s takes p l a c e p r e f e r e n t i a l l y i n the l e s s r i g i d l y bonded amorphous zones.  As a r e s u l t , the  slippage  phenomenon i n wood f i b r e s should take p l a c e between m i c e l l e s or whole f i b r i l s which are h e l d together r e l a t i v e l y ' l o o s e l y ' by amorphous c e l l u l o s e , r a t h e r than between i n d i v i d u a l molecules.  I t f o l l o w s from the above c o n s i d e r a t i o n s that  degradation  of c e l l u l o s e by chemical means should have a  g r e a t e r e f f e c t on the e l a s t i c p r o p e r t i e s of wood than a r a n dom  s c i s s i o n of c h a i n s .  Wakeham, as c i t e d by Ott et a l . ( 7 7 ) .  and Hermans (36) r e p o r t t h a t i t i s p o s s i b l e through degradation  chemical  to a t t a i n r e d u c t i o n s i n s t r e n g t h p r o p e r t i e s  while the X-ray s t r u c t u r e and the average c e l l u l o s e  chain  l e n g t h of the m a t e r i a l remain unchanged. Due  to g r e a t e r f l e x i b i l i t y  of the amorphous r e g i o n s ,  a more even d i s t r i b u t i o n of s t r e s s e s may  be achieved.  This  68  may  p a r t l y e l i m i n a t e the s u c c e s s i v e breaking of the  chains due  cellulose  to s t r e s s c o n c e n t r a t i o n s mentioned e a r l i e r .  On  the other hand, v a r i o u s c o n s t i t u e n t s such as l i g n i n , hemic e l l u l o s e s and extraneous m a t e r i a l s deposited i n the amorphous regions may  i n c r e a s e the chance of non-uniform s t r e s s i n g of  the c e l l u l o s e c h a i n s .  These d e p o s i t s may  be looked upon as  minute b l o c k s among the c o r d - l i k e c e l l u l o s e molecules.  When  s t r e s s i s a p p l i e d to t h i s system, a f r e e o r i e n t a t i o n of the cords i n the d i r e c t i o n of s t r e s s e s the b l o c k s .  would be prevented  by  This should r e s u l t i n s t r e s s concentrations  and  hence a g r e a t e r p r o b a b i l i t y of s u c c e s s i v e rupture of the chains. The r e l a t i o n s h i p between u l t i m a t e t e n s i l e and  strength  c e l l u l o s e c h a i n l e n g t h of Douglas f i r wood obtained i n  t h i s experiment i s shown i n F i g u r e 17.,  Because of the  u n c e r t a i n t y i n the conversion of i n t r i n s i c v i s c o s i t y to s t r e n g t h was  p l o t t e d against v i s c o s i t y .  However, c o n s i d e r i n g  the apparent r e l a t i o n s h i p between the two, c o s i t y may  DP,  intrinsic  vis-  be taken as a d i r e c t measure of c h a i n l e n g t h .  The r e l a t i o n s h i p between s t r e n g t h and c e l l u l o s e  DP  i s such t h a t the curves have a l a r g e slope i n the r e g i o n of s m a l l c h a i n l e n g t h , f o l l o w e d by a g r a d u a l l y decreasing  slope  as i n c r e a s i n g l y h i g h e r c e l l u l o s e DP values are maintained. The  c o n f i g u r a t i o n of the curves suggests an  asymptotic  approach to a constant value at v e r y h i g h DP r e g i o n s .  This  f i n d i n g i s i n good agreement with the r e s u l t s of s i m i l a r  69  experiment scon regenerated  c e l l u l o s e and other high, polymers.  A comparison of the r e s u l t s of t h i s experiment w i t h the curves shown "by Skoone and H a r r i s ( 8 5 ) , f o r c e l l u l o s e a c e t a t e , r e v e a l s t h a t the g e n e r a l response o f t e n s i l e  strength  o f wood t o changes i n c e l l u l o s e c h a i n l e n g t h i s s i m i l a r t o t h a t of the a c e t a t e samples.  At low DP r e g i o n s , u l t i m a t e  t e n s i l e s t r e n g t h i s more s e n s i t i v e t o d i f f e r e n c e s i n c e l l u l o s e c h a i n l e n g t h t h a n a t h i g h DP l e v e l s . o r e t i c a l deformation seems r e a s o n a b l e an important The  On the b a s i s of t h e -  c o n s i d e r a t i o n s as d i s c u s s e d e a r l i e r , i t  t o assume t h a t the s l i p p a g e mechanism i s  c o n t r i b u t o r to strength behavior  of wood.  f a c t t h a t s l i p p a g e occurs more r e a d i l y i n wood w i t h s h o r t -  c h a i n c e l l u l o s e suggests t h a t i n t r i n s i c f o r c e s r e s p o n s i b l e f o r such s l i p p a g e are r e l a t e d t o c h a i n l e n g t h .  In s p i t e of  the. complex c h e m i c a l and s t r u c t u r a l make-up of wood f i b r e s , the hydrogen bonds, so w e l l a p p r e c i a t e d i n c e l l u l o s e f i b r e research, are a l s o d e c i s i v e i n determination  of wood mech-  anical properties. I n c e l l u l o s e , such as t h a t of ramie or hemp, the c o n t r i b u t i o n of the hydrogen bonds t o p h y s i c a l and m e c h a n i c a l p r o p e r t i e s i s apparent and almost q u a n t i t a t i v e .  However, i n  wood, the e f f e c t of l a t e r a l l i n k a g e s between c e l l u l o s e c h a i n s i s obscured by f a c t o r s of s t r u c t u r a l and/or nature.  As a r e s u l t , a d e g r a d a t i o n  chemical  of c e l l u l o s e c h a i n s does  not b r i n g about as g r e a t a r e d u c t i o n i n s t r e n g t h as would be expected were a l l the a v a i l a b l e h y d r o x y l s engaged i n i n t e r -  7G c h a i n cohesion,  and were a l l the chains p e r f e c t l y o r i e n t e d  i n the l o n g i t u d i n a l d i r e c t i o n .  One  e f f e c t of t h i s i s that  no s h a r p l y d i s t i n g u i s h e d c r i t i c a l DP can be e s t a b l i s h e d from the curves i n Figure 17.  These curves, f i t t e d to the  ex-  perimental data obtained at v a r i o u s temperature and moisture content  l e v e l s , f l a t t e n out r a t h e r g r a d u a l l y with i n c r e a s i n g  DP v a l u e s .  This i s q u i t e u n l i k e what would be expected f o r  the r e l a t i o n s h i p i n an i d e a l , homogeneous h i g h polymer. wood, s l i p p a g e i s probably  a f a c t o r of deformation  In  i n quite  h i g h DP regions and g r a d u a l l y i n c r e a s e s with  decreasing  chain l e n g t h .  assumption i f  one  This seems to be a reasonable  consideres that - deformation  takes p l a c e i n the amor-  phous r e g i o n s , but not i n the r i g i d  crystallites.  I t has been mentioned e a r l i e r that the p h y s i c a l s t r u c t u r e of the c e l l u l o s e i n the c e l l w a l l v a r i e s from 'badly' d i s o r g a n i z e d amorphous s t a t e , through r e l a t i v e l y w e l l organized mesomorphous and p a r a c r y s t a l l i n e zones, to perfect crystals.  The gradual t r a n s i t i o n from one phase to  the other would assume a s i m i l a r l y gradual change in; p r o p e r t i e s dependent upon those phases. there may  Even at h i g h average DP  levels  be s i t e s of l o o s e l y l i n k e d c e l l u l o s e chains with  a t i v e l y low cohesive f o r c e s among them. s l i p p a g e may  rel-  In these r e g i o n s , a  occur upon a p p l i c a t i o n of e x t e r n a l s t r e s s e s  r e g a r d l e s s of h i g h DP,  f o r i t i s the number of hydrogen bonds,  r a t h e r than the c h a i n l e n g t h d i r e c t l y , that i s the f a c t o r to s t r e n g t h .  limiting  As c e l l u l o s e becomes degraded, more  71  and more s i t e s o f v a r i o u s d i s o r g a n i z a t i o n reach a c o n d i t i o n i n which the number o f l a t e r a l bonds i s no l o n g e r enough t o r e s i s t stresses.  Therefore, s l i p p a g e w i l l occur and, as  a r e s u l t , decrease t e n s i l e s t r e n g t h . D i f f e r e n c e s between the strength-DP of  relationship  e a r l y - and latewood may be noted i n F i g u r e 17.  response  o f s t r e n g t h of latewood  The  t o changes i n c e l l u l o s e  c h a i n l e n g t h i s l e s s pronounced than t h a t o f earlywood.  The  decrease i n slope w i t h i n c r e a s i n g DP i s more gradual f o r the former.  A l s o , while i n earlywood,  s t r e n g t h a t 2.5 d l / g  i n t r i n s i c v i s c o s i t y i s o n l y 40 p e r cent o f t h a t a t 35.0 d l / g , i n latewood  t h i s f i g u r e i s 55 p e r cent over the same v i s -  c o s i t y range.  In other words, the r e l a t i v e s t r e n g t h l o s s  due t o c e l l u l o s e degradation i s g r e a t e r f o r the e a r l y - than for  the latewood  samples.  Both o f the above d i f f e r e n c e s  suggest t h a t there may be a b a s i c d i f f e r e n c e between the p r o p e r t i e s o f c e l l u l o s e i n the two wood zones. The o r i e n t a t i o n o f c e l l u l o s e i n latewood ly  s t e e p e r than i n earlywood  (41,101,102).  e f f e c t o f o r i e n t a t i o n on the strength-DP  i s reported-  The p o s s i b l e  relationship  lies  in  the f a c t t h a t s e p a r a t i o n o f c e l l u l o s e chains o r m i c e l l e s  is  e a s i e r a t an angle t o t h e i r a x i s than when s t r e s s i s  applied a x i a l l y .  As a r e s u l t , t e n s i l e s t r e s s a p p l i e d t o  wood with h i g h e r f i b r i l angle  should produce a s l i p p a g e  between c e l l u l o s e chains o r m i c e l l e s a t a h i g h e r DP l e v e l than i n wood w i t h s m a l l f i b r i l  angle.  72  Another f a c t o r that could i n f l u e n c e c o n f i g u r a t i o n of strength-DP curve i s the s i g n i f i c a n t l y h i g h e r degree of c r y s t a l l i n i t y of latewood than that of earlywood, as served by l e e ( 6 3 ) .  Since s t r e n g t h behavior  ob-  i s mainly  dependent on the amorphous c e l l u l o s e , a s h i f t i n the c r y s talline-amorphous  r a t i o towrd h i g h e r values should  result  in- a s h i f t i n DP dependence of s t r e n g t h p r o p e r t i e s .  The  h i g h e r the r e l a t i v e amount of amorphous c e l l u l o s e , the g r e a t e r the i n f l u e n c e of DP v a r i a t i o n s on s t r e n g t h c h a r a c t e r i s t i c s of wood. On the b a s i s of e a r l i e r development of a model equation  (42), i t was  i c a l l y estimate  p o s s i b l e i n t h i s study to mathemat-  the i n t r a - i h c r e m e n t  strength v a r i a t i o n  f o r the three increments t e s t e d .  In F i g u r e 22 the  curves  represent changes i n u l t i m a t e wet  t e n s i l e strength i n r e l -  a t i o n to r e l a t i v e p o s i t i o n i n the increment.  The  appropriate  r e g r e s s i o n c o e f f i c i e n t s of the corresponding  equations  were c a l c u l a t e d by s u b s t i t u t i n g average s t r e n g t h values obtained a f t e r v a r i o u s dosage l e v e l s of gamma r a d i a t i o n , i n s a t u r a t e d c o n d i t i o n s , at 25°C, i n t o the b a s i c mathematical model.  This model equation i s a l s o shown i n F i g u r e 22.  above s u b s t i t u t i o n could be done because e a r l y and wood specimens were taken from approximately per cent p o s i t i o n r e l a t i v e to the beginning ments r e s p e c t i v e l y .  Average  latewood  30 and  The  late80  of the i n c r e -  73  percentage o f the three growth increments wasj used f o r S i n the c a l c u l a t i o n s . Wo attempt was made t o estimate  intra-increment  changes i n s t r e n g t h o f a i r - d r y specimens because the o r i g i n a l model was based on s t r e n g t h v a l u e s taken a t moisture above the f i b r e - s a t u r a t i o n p o i n t . was  contents  However, the assumption  made t h a t a f t e r v a r i o u s r a d i a t i o n treatments the b a s i c  arctangent  f u n c t i o n would a c c u r a t e l y d e s c r i b e the strength-  variations.  Since the independent v a r i a b l e s i n the mathemat-  i c a l model a r e only per cent p o s i t i o n i n the increment, and latewood per cent, the above assumption c o u l d be made s a f e l y . There i s no reason t o b e l i e v e t h a t e i t h e r o f these two growthr i n g c h a r a c t e r i s t i c s would s u f f e r any change due t o gamma radiation. Among the s t r e n g t h p r o p e r t i e s s t u d i e d , was  elasticity  the l e a s t a f f e c t e d by changes i n c e l l u l o s e c h a i n l e n g t h .  The b a s i c reason f o r t h i s behavior  o f wood may l i e i n the  mode o f c e l l u l o s e degradation by gamma r a y s . earlier,  extension due t o e x t e r n a l s t r e s s e s  As d i s c u s s e d takes p l a c e i n  the amorphous regions o f the c e l l u l o s e and not t o any known extent i n the r i g i d c r y s t a l l i t e s .  I t i s assumed t h a t de-  formation i s the p r o p e r t y o f the secondary valence bonds because the observed t o t a l e l o n g a t i o n o f wood i n t e n s i o n i s much g r e a t e r than could be expected from primary valence deformation.  Consequently, a change i n e l a s t i c i t y would  only be expected i f e i t h e r the r e l a t i v e amount o f amorphous  74  c e l l u l o s e was bonds was  increased,  or i f the t o t a l number of hydrogen  decreased.  F i r s t l y , with i r r a d i a t i o n the r a t i o i s b e l i e v e d to remain constant  crystalline-amorphous (84).  Since the  rel-  a t i v e amount of the amorphous phase of c e l l u l o s e i s not changed, no adjustment i n o v e r a l l amount of deformation i s expected.  Secondly, the number of hydrogen bonds remains  r e l a t i v e l y constant  s i n c e a main c h a i n s c i s s i o n process does  not i n v o l v e a r e d u c t i o n i n the number of l a t e r a l bonds. these c o n s i d e r a t i o n s  i t seems to be reasonable that  the  immediate response of wood to a p p l i e d s t r e s s e s remains changed a f t e r random s c i s s i o n of c e l l u l o s e chains, neither  un-  since  the r e l a t i v e number of the l a t e r a l bonds nor  s t r e n g t h i s changed.  From  their  Modulus of e l a s t i c i t y i s c a l c u l a t e d  as the slope of the i n i t i a l p a r t of the s t r e s s - s t r a i n curve, i.e.,  i t i s measured by the i n i t i a l response of the  to a p p l i e d s t r e s s e s .  material  Since s l i p p a g e between m i c r o f i b r i l s  or c r y s t a l l i t e s w i l l occur only at h i g h s t r e s s l e v e l s , ing  a break i n the specimen, i t does not have an  effect-  influence  on the slope at the e a r l y p a r t of the s t r e s s - s t r a i n curve. Ultimate  t e n s i l e s t r a i n values were a f f e c t e d by  v a r i a t i o n s i n c e l l u l o s e c h a i n l e n g t h i n a way that i n u l t i m a t e t e n s i l e s t r e n g t h .  The  s i m i l a r to  general  of curves r e l a t i n g s t r a i n to c e l l u l o s e i n t r i n s i c c o s i t y i s such that t h e i r i n i t i a l slopes  configuration vis-  gradually  75  decrease toward h i g h e r DP r e g i o n s .  There appears to be  c o n s i d e r a b l e d e v i a t i o n i n the r e a c t i o n of wood s t r a i n to c e l l u l o s e DP from the curves r e p o r t e d by Skoone and H a r r i s (85) f o r c e l l u l o s e a c e t a t e . continuous  For wood, there e x i s t s a  i n c r e a s e i n s t r a i n with i n c r e a s i n g DP values at  even 5000 DP.  However, the curves  of acetate samples have  a d e f i n i t e tendency to l e v e l o f f to a constant value at the around^200 to 300  DP r e g i o n .  The d i f f e r e n c e may  be  on the same grounds as were mentioned i n connection t e n s i l e strength, i . e ,  by chemical  complexity  and  explained with structural  i m p e r f e c t i o n s of wood. The  s i m i l a r i t y between the response of u l t i m a t e  and t h a t of s t r e n g t h to v a r i a t i o n s i n c e l l u l o s e DP may  strain be  that the same mechanism governs both of these p r o p e r t i e s . Indeed, the two e i t h e r may  are i n such c l o s e r e l a t i o n t h a t t h e o r e t i c a l l y  be considered a c o n d i t i o n of u l t i m a t e  F a i l u r e i n a specimen due  to e x t e r n a l f o r c e s can e i t h e r  be looked upon as a phenomenon due d i t i o n or as one due  failure.  to c r i t i c a l s t r e s s con-  to c r i t i c a l s t a t e of m a t e r i a l deforma-  tion. Reduction  i n u l t i m a t e t e n s i l e s t r a i n as a r e s u l t  of random depolymerization  of c e l l u l o s e was  i n the order of  40 to 45 per cent between DP l e v e l s of 5500 and both e a r l y - and latewood.  150 f o r  This i s a r e l a t i v e f i g u r e very  s i m i l a r to t h a t found i n t e n s i l e s t r e n g t h over the same DP range, c o n f i r m i n g the c l o s e c o r r e l a t i o n between u l t i m a t e  76  s t r e s s and u l t i m a t e The  strain.  f a c t that u l t i m a t e s t r a i n values  of latewood were  g e n e r a l l y h i g h e r than those of earlywood cannot he explained  on the b a s i s of c e l l u l o s e s t r u c t u r e .  adequately  In f a c t ,  the  h i g h e r degree of c r y s t a l ] i n i t y of the former would i n d i c a t e a lower e x t e n s i b i l i t y .  The answer may  l i e , however, i n the  f a c t that latewood specimens f a i l e d i n l o n g i t u d i n a l shear, e s p e c i a l l y at h i g h DP l e v e l s , i n d i c a t i n g t h a t a s u b s t a n t i a l p a r t of the deformation i n t h i s type of wood took p l a c e i n the h e a v i l y l i g n i f i e d middle l a m e l l a . i n c o n t r a s t with e a r l i e r observations Gerry (27), and Koehler (51) who  This assumption i s made by Garland  reported  (26),  that c e l l s e i t h e r  broke r i g h t across the double w a l l or separated  between the  outer and middle l a y e r s of the secondary w a l l .  More r e c e n t l y ,  the occurrence of t h i s l a t t e r type of f a i l u r e i n t e n s i o n been confirmed by Lagergren,Rydholm and C a r l s s o n and l a g e r g r e n  (15).  occurred  (102)  Kollmann (52)  cites  showed that f a i l u r e i n s t a t i c bending of ash wood  i n the middle l a m e l l a , l e a v i n g the c e l l w a l l  damaged.  and  Evidences of middle l a m e l l a  f a i l u r e a l s o appear i n the l i t e r a t u r e . Clarke who  Stockman (55),  has  Recently,  un-  I f j u and Kennedy (41) as w e l l as Wellwood  have suggested that such f a i l u r e might r e s u l t i n  l o n g i t u d i n a l micro-tension specimens.  t e s t s of wet  I t i s q u i t e conceivable  Douglas f i r latewood  that c e l l s with t h i c k  secondary w a l l , c o n s i s t i n g of h i g h l y o r i e n t e d and c r y s t a l l i n e c e l l u l o s e , may  be s t r o n g e r  highly  i n tension p a r a l l e l  77  to  g r a i n than the cementing m a t e r i a l i n i t s l o n g i t u d i n a l shear  resistance,  latewood t r a c h e i d s o f Douglas f i r f u l f i l l  these  requirements t o e f f e c t a s e p a r a t i o n i n the middle l a m e l l a upon application of tensile stresses. The middle l a m e l l a o f c o n i f e r t r a c h e i d s has been r e p o r t e d t o c o n t a i n some 70 t o 72 p e r cent l i g n i n Recent s t u d i e s conducted by Asunmaa and lange  (7,57,58).  (5) have  r e v e a l e d that c o n c e n t r a t i o n o f h e m i c e l l u l o s e s i s a l s o h i g h i n the outer r e g i o n of the c e l l w a l l .  Both l i g n i n ; arid  h e m i c e l l u l o s e s a r e known t o e x i s t i n an amorphous phase i n the c e l l w a l l , which c o n d i t i o n should be accompanied by p l a s t i c mechanical behavior. of the deformation  I n latewood where a p a r t  takes p l a c e i n t h i s amorphous cementing  layer, at l e a s t at high stress l e v e l s , a greater elongation i s expected than i n earlywood specimens which do not i n d i c a t e middle l a m e l l a deformation  i n t h e i r s i t e s of tension  failure. Work t o maximum l o a d may be regarded  as the t o t a l  energy r e q u i r e d t o break a p i e c e o f wood 1 cu i n . i n volume. Since i t i s measured by the area under the s t r e s s - s t r a i n curve, the i n f l u e n c e of u l t i m a t e t e n s i l e s t r e n g t h and e l a s t i c i t y , as w e l l as u l t i m a t e e l o n g a t i o n o f the specimen, are apparent on t h i s p r o p e r t y .  Work t o maximum l o a d , t h e r e f o r e ,  may be considered as a good s i n g l e measure o f the mechanical behavior  o f wood, combining the e f f e c t s o f a number o f  p r o p e r t i e s which operate  simultaneously  during s t r e s s i n g of  78  the specimen. Since a l l the simple s t r e n g t h p r o p e r t i e s were i n v e r s e l y a f f e c t e d "by degradation of c e l l u l o s e , work t o maximum l o a d showed a s i m i l a r , but more pronounced response t o DP.  Early-  wood s u f f e r e d a r e d u c t i o n i n work o f 80 t o 85 p e r cent, while latewood from 75 to 80 p e r cent.  The curve r e l a t i n g  maximum work t o c e l l u l o s e c h a i n l e n g t h , shown i n F i g u r e 20, i s s i m i l a r to those obtained f o r s t r e n g t h and s t r a i n , however, the c u r v a l i n e a r i t y here i s more pronounced.  This i s due t o  the g r e a t e r drop i n t h i s p r o p e r t y over the DP range  from  5500 to 150 than was obtained f o r the simple s t r e n g t h propperties. A c a l c u l a t i o n based on t h e o r e t i c a l energy v a l u e s may be o f i n t e r e s t , t o estimate the e f f i c i e n c y i n u t i l i z a t i o n of bond energy when wood i s t e s t e d i n t e n s i o n p a r a l l e l to grain.  In order t o do t h i s , a number o f assumptions  to be made.  have  F i r s t l y , i t i s assumed that a l l t e n s i l e s t r e n g t h  of wood i s due t o c e l l u l o s e and that the other c o n s t i t u e n t s do not take p a r t i n the mechanism o f response t o t e n s i l e stresses.  Secondly, deformation, and consequently work,  takes p l a c e only i n the amorphous r e g i o n s o f the c e l l u l o s e . T h i r d l y , deformation i s the p r o p e r t y o f the secondary valence bonds and t h e r e f o r e the primary bonds do not c o n t r i b u t e t o the work v a l u e s .  With these assumptions  the t h e o r e t i c a l and  the a c t u a l energy v a l u e s may be compared.  A 40 i n . l b / cu i n .  maximum work w i t h oven-dry Douglas f i r earlywood  corresponds  79  to 4.5x10  e r g / cu i n .  The energy p e r secondary bond as  c a l c u l a t e d by Mark, i n Ott (76), i s approximately 3x10"*^ ergs. From these, i t f o l l o w s t h a t i f a l l the deformation  took 20  p l a c e among the hydrogen bonds, approximately  1.5x10  would have t o be broken i n 1 cu i n . o f earlywood. weight o f t h a t cube i s c a l c u l a t e d , u s i n g a s p e c i f i c  bonds  I f the gravity  (weight oven-dry/volume green), and an average v o l u m e t r i c shrinkage o f 12 p e r cent, the r e s u l t i s 2.9 g o f wood substance.  I t i s f u r t h e r assumed t h a t about 40 t o 45 p e r  cent o f t h i s wood substance  i s c e l l u l o s e of long-chain  s t r u c t u r e which can e f f e c t i v e l y r e s i s t t e n s i l e  stresses,  and only about 30 p e r cent o f t h i s i s i n the amorphous phase.If the above c o r r e c t i o n s are made, the remaining amorphous c e l l u l o s e i n 1 cu i n . o f Douglas f i r earlywood i s 0.40 g.  With the a i d o f Avogadro's number (6.023x10 ^ p e r 2  mole) and the molecular weight o f glucose anhydride o f 162, as w e l l as c o n s i d e r i n g t h a t each glucose u n i t has 3 a v a i l a b l e OH groups f o r hydrogen bonding, bonds i n 1 cu i n . o f earlywood  a t o t a l number o f p o s s i b l e 21 i s c a l c u l a t e d t o be 4.0x10 . 20  Comparing t h i s number w i t h the 1.5x10  c a l c u l a t e d from the  experimental work v a l u e s , i t i s estimated that only about 1/26 o f the t o t a l bond energy i n wood with p e r f e c t l y o r i e n t e d cellulose i s u t i l i z e d i n tension p a r a l l e l to grain.  The i n -  e f f i c i e n c y may l i e i n the f a c t t h a t i n the amorphous regions much l e s s than 3 bonds p e r glucose r e s i d u e form cross-links  (59).  actual  A l s o , the s t r u c t u r a l complexity i n wood  80  does not allow a uniform s t r e s s i n g o f a l l c e l l u l o s e chains when l o a d i s a p p l i e d . When a c a l c u l a t i o n , s i m i l a r t o that described  above  i n d e t a i l , i s c a r r i e d out f o r latewood, an e f f i c i e n c y number o f approximately 1/18 i s obtained. may be explained  This d i f f e r e n c e -  on the b a s i s o f b e t t e r o r g a n i z a t i o n and more  p e r f e c t o r i e n t a t i o n on the p a r t o f latewood (42,63,101). Another e x p l a n a t i o n may be the recent b e l i e f that the c e l l w a l l o f earlywood i s l e s s c l o s e l y packed than that o f l a t e wood (105), which should  r e s u l t i n a s m a l l e r number o f  a v a i l a b l e OH groups that could a c t u a l l y p a r t i c i p a t e i n hydrogen bonding.  I l l MOISTURE CONTENT SENSITIVITY OF TENSILE STRENGTH PROPERTIES  I t i s o f importance to consider the means by which water i s r e t a i n e d i n wood, t o understand the behavior o f wood under s t r e s s c o n d i t i o n s .  Any c a p i l l a r y space which i s  l a r g e i n comparison with the dimensions o f a water molecule can be penetrated mechanism.  by vapor through simple d i f f u s i o n  Water o f t h i s type i s commonly c a l l e d f r e e water  s i n c e i t s presence i n wood i n no way depends on any s p e c i f i c a t t r a c t i o n between the wood substance and the vapor.  81  No  esergy exchange between wood and water vapor takes p l a c e ,  t h e r e f o r e , the p e n e t r a t i o n of t h i s vapor does not true sorption.  involve  Consequently, v a r i a t i o n s i n the amount of  f r e e water are not accompanied by d i f f e r e n c e s i n p h y s i c a l and mechanical p r o p e r t i e s of wood. Surface bound water i s the f i r s t type h e l d by wood through t r u e s o r p t i o n .  This water i s h e l d by a t t r a c t i o n  between s p e c i f i c s i t e s of the wood substance and molecules, and  the water  i s independent of c a p i l l a r y spaces.  As,.a  r e s u l t of d i f f u s i o n , the d i s t a n c e between some water molecules and  the c e l l w a l l m a t e r i a l becomes small enough, and  f o r c e of a t t r a c t i o n l a r g e enough to b i n d the two and  together  to draw the water i n t o the m i c e l l a r spaces and  regions.  The  a t t r a c t i v e f o r c e s may  the  amorphous  become so great  that  they cause d i s t o r t i o n s i n the f i b r i l l a r network, and  swelling  takes p l a c e . It and  i s the OH groups of the glucose u n i t s i n c e l l u l o s e ,  those of the other sugar u n i t s of the h e m i c e l l u l o s e s ,  o f f e r the s i t e s f o r attachment to the water.  that  molecularly-sorbed  I f the water molecule approaches these s i t e s i n  close proximity,  the energy of b i n d i n g between i t and  carbohydrate c h a i n i s the same as the energy of the hydrogen bond between two  OH groups i n neighboring  the  lateral chains.  When c l o s e approach i s prevented, the energy of b i n d i n g i s smaller. The above type of molecular s o r p t i o n of water can  82  only occur on htose OH groups which are exposed i n the amorphous regions and on the c r y s t a l l i n e s u r f a c e s of the cellulose micro-structure.  Since, i n the c r y s t a l l i n e  regions,  the chains are "bonded together l a t e r a l l y at a l l p o s s i b l e p o i n t s along t h e i r l e n g t h s , i t i s impossible that water molecules would be able to break these hydrogen bonds and be adsorbed by the OH groups thus exposed. When water enters the amorphous r e g i o n s , the maximum b i n d i n g energy between c e l l u l o s e and water cannot be  relized.  Even i n these r e g i o n s , c e l l u l o s e chains are so c l o s e l y packed that they can o f f e r s u f f i c i e n t b a r r i e r to the c l o s e s t approach of the water molecule.  Therefore,  the b i n d i n g energy be-  comes only the average of many degrees of b i n d i n g . t h i s energy may  Yet,  be s u f f i c i e n t l y l a r g e to set up s t r e s s e s  i n the f i b r i l l a r network as a r e s u l t of s w e l l i n g , and break a few  of the i n i t i a l l y  s t a b l e c e l l u l o s e - t o - c e l l u l o s e hydrogen  bonds i n the p a r a c r y s t a l l i n e or mesomorphous r e g i o n s . by, some new  There-  s i t e s are made a v a i l a b l e f o r water entry, at a  l a t e r stage of s o r p t i o n . The water so adsorbed by wood, forms b r i d g e s between OH groups of neighboring  chains i n the amorphous r e g i o n s .  The b i n d i n g f o r c e between the OH groups at the ends of the b r i d g e s i s much s m a l l e r , and  i s more r e a d i l y broken by  ex-  t e r n a l s t r e s s e s , than the hydrogen bonds between OH groups i n intimate contact.  When t e n s i l e s t r e s s i s a p p l i e d to the  swollen m a t e r i a l , the water molecules i n the b r i d g e s  can  83  move from one OH group i n the c e l l u l o s e c h a i n to another. T h i s 'jump' process r e s u l t s i n o v e r a l l s l i p p a g e i n the m a t e r i a l . In  t h i s sense, the water molecules  of  the c e l l u l o s e m i c e l l e s may  \.sorbed onto the s u r f a c e  be considered as a  'lubricant'.  The above i n e l a s t i c exchange of hydrogen bonds between the n e i g h b o r i n g c e l l u l o s e chains cannot  adequately  represent the s t r a i n behavior of wood i n s t r e s s c o n d i t i o n . The s t r u c t u r e of wood and the c e l l w a l l i t s e l f i s f a r too i r r e g u l a r f o r d i r e c t c o r r e l a t i o n between the molecular b u l k p r o p e r t i e s to be e s t a b l i s h e d q u a n t i t a t i v e l y . ly,  and  Consequent-  the simple l u b r i c a t i o n r o l e of water b r i d g e s i n wet wood  i s an o v e r s i m p l i f i c a t i o n of the problem.  But i t does g i v e  some i d e a of what could happen i n the wet  c e l l w a l l when  it  i s s u b j e c t e d to s t r e s s e s . Frey-Wyssling  (24) has p o s t u l a t e d t h a t i n c r e a s e d  p l a s t i c i t y i n the wet  s t a t e i s a f i b r i l l a r r a t h e r than a  molecular phenomenon.  A c c o r d i n g to him,  there must be  con-  s i d e r a b l e creep of i n d i v i d u a l m i c r o f i b r i l s upon each other due to r e l a t i v e l y poor cohesion between them.  Therefore,  both e x t e n s i b i l i t y and e l a s t i c i t y must depend f i r s t l y on the f o r c e s which h o l d the m i c r o f i b r i l s together i n the w a l l , s i n c e they cannot  cell  elongate i n d i v i d u a l l y u n l e s s t h e i r  r e c i p r o c a l cohesion i s broken.  I f t h i s theory can r e a l l y  d e s c r i b e what takes p l a c e i n wet wood when s t r e s s e d , the degree of c r y s t a l l i n i t y should be i n c l o s e r e l a t i o n with the e l a s t i c p r o p e r t i e s of wood.  84  The f i b r i l l a r i n t e r p r e t a t i o n of the strength-moisture r e l a t i o n s h i p assignes an important r o l e to the i n c r u s t i n g m a t e r i a l s between the m i c r o f i b r i l s may  determine  (24).  These  substances  to a l a r g e extent the e l a s t i c i t y and  i b i l i t y of wood.  extens-  Wall c o n s t i t u e n t s such as l i g n i n , h e m i c e l -  l u l o s e s and s m a l l amounts of p e c t i n s are now  b e l i e v e d to  be p a r t l y d i s t r i b u t e d among the c e l l u l o s e m i c r o f i b r i l s . Some evidence has r e c e n t l y been gathered a c c o r d i n g to which l i g n i n may  penetrate even the m i c r o f i b r i l s themselves  and  be found a s s o c i a t e d with the p a r a c r y s t a l l i n e phase around the c e l l u l o s e c r y s t a l l i t e s  (19).  H e m i c e l l u l o s e s are a l s o  b e l i e v e d t o be concentrated between the m i c r o f i b r i l s , a l though i t i s q u i t e c o n c e i v a b l e that s l i g h t d i s t o r t i o n s i n the p a r a c r y s t a l l i n e regions are due to chains of n o n - c e l l u l o s i c p o l y s a c c h a r i d e s which, by v i r t u e of t h e i r chemical s t r u c t u r e , cannot f i t p e r f e c t l y i n t o the r i g i d form of c r y s t a l l i t e s 79).  (19,  A l l of these c o n s t i t u e n t s , with the exception of l i g n i n ,  are very s e n s i t i v e to s w e l l i n g with water.  Therefore, t h e i r  i n f l u e n c e on s t r e n g t h p r o p e r t i e s i n r e l a t i o n to moisture content must be  decisive.  Experimental evidence has been obtained that water adsorbed  i n wood i s equal to the t o t a l water sorbed by the  i n d i v i d u a l c o n s t i t u e n t s (18).  I t has been shown t h a t up  to 50 per cent of the adsorbed water i s h e l d by the amorphous c e l l u l o s e , about 37.5  per cent by the h e m i c e l l u l o s e s , and  the remaining 12.5 per cent by l i g n i n .  T h i s suggests that  85  t h e r e l a t i v e l y s m a l l amount o f h e m i c e l l u l o s e s p l a y s a p a r t a l m o s t as i m p o r t a n t as t h a t It  is  only reasonable  m o i s t u r e dependence  of c e l l u l o s e  t o assume t h a t  in attracting  their influence  water.  on t h e  o f s t r e n g t h w o u l d a l s o be a n i m p o r t a n t  one. The h y d r o p h o b i c l i g n i n may p r e v e n t w a t e r i n the r e g i o n s between the m i c r o f i b r i l s .  This  adsorption  suggests  t h a t a s i m p l e m o l e c u l a r a p p r o a c h to. t h e e x p l a n a t i o n o f moisture-dependent problem.  s t r e n g t h b e h a v i o r o f wood i s a  complex  Not o n l y does t h e s t r u c t u r a l arrangement  of  the  c e l l u l o s e f r a m e w o r k h a v e t o be t a k e n i n t o a c c o u n t ,  as  is  c o n v e n i e n t l y done i n p u r e c e l l u l o s e r e s e a r c h ,  but also  the  c h e m i c a l and p h y s i c a l p r o p e r t i e s o f the n o n - c e l l u l o s i c substances  h a v e t o be g i v e n  The r e s u l t s properties content  attention.  o f t h i s e x p e r i m e n t show t h a t a l l  t e s t e d v a r i e d s i g n i f i c a n t l y w i t h changes i n m o i s t u r e  i n the range from oven-dry to w a t e r - s a t u r a t e d  ditions.  Because  only three moisture content l e v e l s  included i n t h i s study,  the general p a t t e r n of  v a r i a t i o n i n r e l a t i o n to moisture content w i t h any c e r t a i n t y . fact  strength  that,  regardless  temperature,  were  strength  c a n n o t be  However, an i n t e r e s t i n g r e s u l t  predicted is  o f c e l l u l o s e DP o f t h e s a m p l e o r  no s f e t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s  e s t a b l i s h e d between any o f t h e s t r e n g t h p r o p e r t i e s at moisture-free  con-  and a i r - d r y c o n d i t i o n s .  the test  c o u l d be determined  On t h e o t h e r h a n d ,  samples w i t h m o i s t u r e contents h i g h e r t h a n the  fibre-saturation  86  p o i n t were i n v a r i a b l y found to be of lower s t r e n g t h those i n the m o i s t u r e - f r e e  or a i r - d r y s t a t e .  an unusual c o n f i g u r a t i o n of  than  These suggest  the curve d e s c r i b i n g  strength-  moisture content r e l a t i o n s h i p i n that i t i s probably convex, r a t h e r than concave, as i s the case i n a number of  other  strength properties. I t has l o n g been e s t a b l i s h e d that below the s a t u r a t i o n p o i n t v a r i a t i o n i n s t r e n g t h i s not  directly  p r o p o r t i o n a l to the change i n moisture content, but  follows  1  d i f f e r e n t laws.  fibre-  Most f r e q u e n t l y the r e l a t i o n s h i p i s such  that when the l o g a r i t h m  of  s t r e n g t h value  i s plotted  against moisture content, the r e s u l t a n t p o i n t s l i e very to a s t r a i g h t l i n e  (103).  close  This r e l a t i o n s h i p i n d i c a t e s that  changes i n moisture content at low moisture l e v e l s induce r e l a t i v e l y l a r g e r v a r i a t i o n s i n s t r e n g t h than the same magnitude of moisture changes at a h i g h e r moisture content level. Crushing s t r e n g t h i n compression p a r a l l e l to  the  g r a i n shows the most c o n s i s t e n t l o g a r i t h m i c r e l a t i o n s h i p with moisture content, so that t h i s property has become the  one  o f t e n used f o r determination  (99).  of f i b r e - s a t u r a t i o n p o i n t  Other p r o p e r t i e s , however, e x h i b i t c o n s i d e r a b l e i n t h e i r r e l a t i o n to moisture (22,32,52,83,106).  discrepancy Deviations  from the l o g a r i t h m i c r e l a t i o n s h i p as proposed by Wilson are such t h a t f o r a given p r o p e r t y or concave curvalinear equations may  e i t h e r l i n e a r , convex represent  behavior.  (103)  87  There i s r e l a t i v e l y l i t t l e  information  concerning  t e n s i l e s t r e n g t h o f wood p a r a l l e l t o g r a i n , and even l e s s i s known about the e f f e c t o f moisture content property. to  on t h i s  The reason f o r s c a r c i t y o f i n f o r m a t i o n i s due  the f a c t that t e n s i l e s t r e n g t h p a r a l l e l t o g r a i n r e p -  r e s e n t s the h i g h e s t s t r e n g t h p r o p e r t y o f wood, even exceeding i n value the modulus o f rupture as d e r i v e d from bending t e s t s , so t h a t i t i s not g e n e r a l l y a r e s t r i c t i n g feature  i n engineering design.  I t has l o n g been observed  t h a t s t r u c t u r a l members i n wooden c o n s t r u c t i o n seldom f a i l i n t e n s i o n under s t r e s s c o n d i t i o n s , but that  other  s t r e n g t h p r o p e r t i e s c r i t i c a l l y a f f e c t the l o a d i n g o f such members.  P a r t i c u l a r l y i n v o l v e d are the r e l a t i v e l y low  v a l u e s o f shear p a r a l l e l , and compression p e r p e n d i c u l a r , to  the g r a i n that o f t e n cause f a i l u r e a t the j o i n t s l o n g  before t e n s i o n s t r e s s e s approach c r i t i c a l l i m i t s .  The  same low s t r e n g t h p r o p e r t i e s make i t extremely d i f f i c u l t t o develop an e f f i c i e n t t e s t method f o r t e n s i o n p a r a l l e l t o grain.  I t i s only reasonable  t h a t more a t t e n t i o n has  been p a i d t o the l i m i t i n g p r o p e r t i e s than t o t e n s i l e s t r e n g t h o f wood along the g r a i n . The few experimental  r e s u l t s a v a i l a b l e from par-  a l l e l to g r a i n t e n s i o n t e s t s i n r e l a t i o n t o moisture content  o f wood are those quoted by Kollmann (52).  These  are from data o f Kuch, Kttch and Teschov, S c h l y t e r and Winberg, Graf, and Winter.  Results of tension t e s t s  88  obtained by Kuch f o r beech, as w e l l as by Graf f o r spruce, i n d i c a t e the f a c t t h a t t e n s i l e s t r e n g t h p a r a l l e l t o g r a i n i s probably another p r o p e r t y o f wood with r e l a t i o n t o moisture content changes that i s inadequately represented by the l o g a r i t h m i c equation proposed by Wilson (103). The p e c u l i a r i t y o f t e s i l e s t r e n g t h p a r a l l e l t o grain-moisture content diagrams i s t h a t the h i g h e s t value i s not reached at the lowest moisture content, but that i t f a l l s somewhere between 5 and 10 p e r cent moisture content, from which i t drops by approximately 25 t o 30 p e r cent a t the f i b r e saturation point.  Strength of oven-dry wood i s a l s o  lower  than the maximum d i s c u s s e d above, and the r a t e o f decrease i n s t r e n g t h between 10 and 0 p e r cent moisture content i s roughly equal to t h a t between 10 p e r cent and the f i b r e saturation point. Values o f S c h l y t e r and Winberg as recorded by Kollmann (52) show a l i n e a r i n c r e a s e i n t e n s i l e s t r e n g t h p a r a l l e l t o g r a i n from the f i b r e - s a t u r a t i o n p o i n t t o about 6 p e r cent moisture content, but v a l u e s below 6 p e r cent are not a v a i l a b l e i n t h e i r study.  Kuch, as c i t e d by  Kollmann (52), a l s o i n v e s t i g a t e d the t e n s i l e s t r e n g t h b e h a v i o r o f European ash which showed no r e l a t i o n whatsoever t o changes i n moisture  content.  Reasons f o r maximum t e n s i l e s t r e n g t h a t moisture contents above oven-dry have been g i v e n by Kollmann (52). He b e l i e v e s that i n c r e a s e d m o b i l i t y o f s t r u c t u r a l elements  89  due t o a minimum moisture content, i s necessary t o r e l i e v e l o c a l i z e d stresses during t e s t i n g .  Thereby, a more even  d i s t r i b u t i o n of s t r e s s e s i s produced  throughout  the e n t i r e  c r o s s - s e c t i o n o f the t e s t specimen, which could r e s u l t i n increased t e n s i l e strength. Hermans (36) l i k e n e d the amorphous regions o f c e l l u l o s e to cords clamped i n a rending apparatus.  I f stress  i s a p p l i e d t o the system made up o f cords o f unequal l e n g t h , f a i l u r e w i l l occur a t a r e l a t i v e l y low l o a d l e v e l due t o non-uniform  s t r e s s i n g o f the cords.  However, i f the cords  have been p r e v i o u s l y knotted t o each other , t e n s i o n i s more evenly d i v i d e d and a h i g h e r u l t i m a t e s t r e n g t h w i l l be attained.  The knots i n t h i s l a t t e r system represent co-  h e s i v e f o r c e s between c e l l u l o s e chains produced  by the  i n c r e a s i n g number o f hydrogen bonds w i t h d e c r e a s i n g moisture content, while the former arrangement i s analogous t o swollen c e l l u l o s e i n which the c h a i n molecules are not l i n k e d f i r m l y due to the presence  o f water. A r e d u c t i o n . i n  moisture content, should, t h e r e f o r e , r e s u l t i n apparent improvement i n the mechanical p r o p e r t i e s o f wood. The above analogy c o u l d be reversed i f the cords i n the rending apparatus are s u b s t i t u t e d by ones o f equal length.  A k n o t t i n g of these cords should r e s u l t i n a l e s s  uniform d i s t r i b u t i o n o f the t e n s i l e f o r c e ,  consequently  a lower t e n s i l e s t r e n g t h should be a t t a i n e d . analogy suggests t h a t with d e c r e a s i n g moisture  This l a t t e r content,  90  strength, i s decreased due to i n c r e a s e d l a t e r a l  cohesion  which, i n t u r n , produces l o c a l i z e d s t r e s s e s . I t seems t h a t both mechanisms p l a y a p a r t i n the determination of moisture dependence of wood s t r e n g t h p r o p e r t i e s . Above a c e r t a i n moisture content l e v e l , c e l l u l o s e e x i s t i n g i n the  first  arrangement p r e v a i l s , whereas at low moisture l e v e l s mechanism of the second type of c e l l u l o s e arrangement wins out. In moisture content r e g i o n s where maximum t e n s i l e s t r e n g t h i s a t t a i n e d , the two types of mechanism c o u l d be a t e q u i librium. Moisture content changes i n t h i s study induced a v a r i a t i o n i n e l a s t i c i t y s i m i l a r to that i n u l t i m a t e t e n s i l e strength. here.  The convex upward c o n f i g u r a t i o n i s a l s o  suggested  V a r i a t i o n i n e l a s t i c i t y caused by d i f f e r e n c e s i n  moisture content was by f a r the most important f a c t o r i n t h i s study and exceeded the i n f l u e n c e of c e l l u l o s e  DP.  In c o n t r a s t to c e l l u l o s e c h a i n l e n g t h , moisture content i s expected to p l a y a s i g n i f i c a n t r o l e i n determining p r o p e r t i e s of wood.  elastic  At l e a s t one of the two c o n d i t i o n s  i s r e q u i r e d to e f f e c t s i g n i f i c a n t changes i n e l a s t i c i t y . The treatment  should e i t h e r produce a change i n the c r y s -  talline-amorphous r a t i o of c e l l u l o s e , or i t should a f f e c t the b i n d i n g energy of the hydrogen bonds between c h a i n s . An i n c r e a s e i n moisture content f u l f i l l s the l a t t e r  con-  d i t i o n i n t h a t i t s u b s t a n t i a l l y diminishes the l a t e r a l cohesion between m i c r o f i b r i l s and/or other submicroscopic  91  elements i n wood. may  Hermans' (36) analogy of the cord system  a l s o be a p p l i c a b l e here i n e x p l a i n i n g the convex shape  of the e l a s t i c i t y - m o i s t u r e content curve. An i n c r e a s e i n moisture content i n the wood induced an i n c r e a s e i n u l t i m a t e t e n s i l e s t r a i n i n earlywood a decrease i n latewood.  and  The d i f f e r e n c e i n the response  i n the two wood zones may be a t t r i b u t e d to the d i f f e r e n c e i n t h e i r deformation mechanisms i n t e n s i o n p a r a l l e l t o grain.  While i n earlywood, extension i s an i n t r a - c e l l u l a r  event, that i n latewood, at l e a s t at r e l a t i v e l y h i g h s t r e s s l e v e l s , i s p a r t l y an i n t e r - f i b r e phenomenon.  When s t r e s s e s  are h i g h enough, deformation and f a i l u r e w i l l occur i n the h e a v i l y l i g n i f i e d middle l a m e l l a .  In summerwood, where  the above requirement i s f u l f i l l e d due to the h i g h s t r e n g t h of the t h i c k middle l a y e r of secondary w a l l , u l t i m a t e e l o n g a t i o n i s a sum of the deformation s u f f e r e d by the c e l l u l o s i c secondary w a l l , and that of the p l a s t i c but h i g h - s t r e n g t h middle l a m e l l a .  As moisture content i n c r e a s e s ,  s t r e n g t h of the secondary w a l l decreases a c c o r d i n g l y , z and the middle l a m e l l a component  of the s t r a i n decreases.  This i s because e x t e n s i o n i n the middle l a m e l l a i s p o s s i b l e only at extremely h i g h l o a d l e v e l s .  The r e s u l t i s that  the o v e r a l l u l t i m a t e t e n s i l e s t r a i n of the specimen i s reduced as moisture content i n c r e a s e s .  In earlywood, the  middle l a m e l l a cannot c o n t r i b u t e to deformation due to i t s extremely h i g h s t r e n g t h p r o p e r t i e s and to the low  92  s t r e n g t h o f the r e l a t i v e l y t h i n secondary w a l l .  Here, an  i n c r e a s e i n moisture content r e s u l t s i n weakening and p l a s t i c i z a t i o n of the c e l l u l o s i c p a r t of the c e l l w a l l which e v e n t u a l l y i n c r e a s e s t o t a l deformation i n s t r e s s conditions.  The i n f l u e n c e o f moisture on deformation  p r o p e r t i e s o f earlywood c e l l u l o s e may be more  pronounced  than that i n latewood due t o the g r e a t e r r e l a t i v e amount of amorphous r e g i o n s i n the former. In latewood, the i n f l u e n c e of moisture content on work' t o maximum l o a d was g r e a t e r than i n earlywood.  The  reason f o r t h i s i s the d i f f e r e n c e i n s t r a i n behavior o f these two wood types i n r e l a t i o n t o moisture content. Where as i n latewood both s t r e n g t h and s t r a i n were s u b s t a n t i a l l y reduced by i n c r e a s e s i n moisture content, i n earlywood, u l t i m a t e t e n s i l e s t r e n g t h decreased, but u l t i m a t e s t r a i n became g r e a t e r , a t h i g h moisture l e v e l s .  Since work t o  maximum l o a d i s a measure o f mechanical b e h a v i o r o f wood, i n c l u d i n g s t r e s s and deformation c h a r a c t e r i s t i c s o f the m a t e r i a l , the combined e f f e c t o f the simultaneous  events  o c c u r r i n g i n t e n s i o n t e s t s had t o be d i f f e r e n t i n the two wood zones.  Nevertheless, the r e s u l t s o f t h i s  experiment  i n d i c a t e that the energy r e q u i r e d t o break a p i e c e o f wood i n t e n s i o n p a r a l l e l t o g r a i n i s lower f o r wet wood than f o r d r y wood.  93  IV  INFLUENCE OF TEMPERATURE ON THE MECHANICAL BEHAVIOR OF WOOD IN TENSION PARALLEL TO GRAIN  Mechanical behavior perature  of wood i s influencedby  changes i n such a way  ature the lower the s t r e n g t h .  tem-  that the h i g h e r the temperThe  e f f e c t has been con-  s i d e r e d l a r g e enough by c e r t a i n a u t h o r i t i e s (89) to j u s t i f y c o r r e c t i o n s of "test r e s u l t s to standard  temperature,  the c o e f f i c i e n t being approximately 1 per cent per degree centigrade .below c e r t a i n c r i t i c a l temperature l e v e l s . At the molecular  l e v e l , reduction i n strength  p r o p e r t i e s with i n c r e a s i n g temperature, i s due  to  increased  Brownian motions of atoms through g r e a t e r e x c i t a t i o n . The higher energy thus acquired by the atoms r e s u l t s i n d i m i n i s h i n g cohesion between molecules with i n c r e a s i n g temperature. system,  At the submicroscopic  l e v e l , the amorphous  as w e l l as the c r y s t a l l i n e l a t t i c e , i s expanded  and thereby the i n t e r m o l e c u l a r f o r c e s w i t h i n and between those regions decrease. present  I f sorbed water molecules are  i n the amorphous r e g i o n s , they f u r t h e r i n c r e a s e  d i s t a n c e between the c r y s t a l l i t e s through e x c i t a t i o n . I t i s g e n e r a l l y considered  that the i n f l u e n c e of  temperature on s t r e n g t h p r o p e r t i e s of wood i s an  inter-  c e l l u l a r r a t h e r than an i n t e r - f i b r i l l a r phenomenon. i s the middle l a m e l l a which has the g r e a t e s t  It .'. :r: ,  the  94  temperature s e n s i t i v i t y .  Since  the middle l a m e l l a con-  s i s t s mostly of l i g n i n and h e m i c e l l u l o s e s ,  i t s temperature  s e n s i t i v i t y i s g r e a t e r than that of the secondary w a l l to the p l a s t i c p r o p e r t i e s of these c o n s t i t u e n t s . middle l a m e l l a can be p l a s t i c i z e d  i n two  due  The  ways. One  i s to  heat the wood to 50 to 100°C i n the presence of water. This p l a s t i c i z a t i o n cellulose low  i s b e l i e v e d to take p l a c e i n the hemi-  p a r t of the middle l a m e l l a .  In p r a c t i c e , t h i s  s o f t e n i n g temperature i s u t i l i z e d i n the  p u l p i n g process where d e f i b e r i z a t i o n perature  range.  Another way  semichemical  i s done i n t h i s tem-  of p l a c t i c i z i n g  the middle  l a m e l l a i s to i n c r e a s e the temperature to a l e v e l than 160°C.  In t h i s case i t i s the l i g n i n that  higher  softens.  T h i s h i g h e r s o f t e n i n g p o i n t i s u t i l i z e d i n the Asplund  and  Masonite d e f i b r a t i n g processes. The mechanical p r o p e r t i e s of wood at  various  temperature and moisture content c o n d i t i o n s have been s t u d i e d by Sulzberger  (89).  He found that both  crushing  s t r e n g t h and modulus of e l a s t i c i t y i n compression  along  the g r a i n , decreased most n e a r l y i n a l i n e a r manner between -20  and  +80°C, f o r s e v e r a l c o n i f e r s and'porous woods.  In some s p e c i e s , such as s i t k a spruce, hoop pine and  mountain  ash, a convex upward curve gave a b e t t e r f i t when wood was  t e s t e d at h i g h moisture content l e v e l s ,  creased  due  to an i n -  r a t e of s t r e n g t h r e d u c t i o n between 70 and  E l a s t i c i t y values  obtained  80°C.  from s t a t i c bending t e s t s showed  95  the same g e n e r a l t r e n d , but without c u r v a l i n e a r i t y a t h i g h moisture contents.  Sano and h i s coworkers (82)  obtained a l i n e a r r e l a t i o n s h i p between t e n s i l e s t r e n g t h along the g r a i n and temperature w i t h i n the same temperature range as that used by S u l z b e r g e r (89), i n d i c a t i n g that t h i s s t r e n g t h p r o p e r t y o f wood e x h i b i t s a s i m i l a r g e n e r a l response t o v a r i a t i o n s i n temperature as compression p a r a l l e l to grain.  I t should be mentioned  that,  while s t r e n g t h i n compression was reduced by 40 t o 50 p e r cent over the temperature range from -20 t o 60°C, t e n s i l e s t r e n g t h decreased by only 10 p e r cent over the same range. This i n d i c a t e s that i f the p l a s t i c components o f the c e l l w a l l , such as l i g n i n and the h e m i c e l l u l o s e s , a r e responsi b l e f o r the temperature dependence o f s t r e n g t h , they are a l s o r e s p o n s i b l e f o r the compressive s t r e n g t h o f wood. This i s i n accordance w i t h the assumption made e a r l i e r t h a t the major r o l e o f c e l l u l o s e i s t o g i v e wood a h i g h t e n s i l e s t r e n g t h , whereas l i g n i n serves the primary mec h a n i c a l r o l e of r e s i s t i n g compressive s t r e s s e s . A l l s t r e n g t h p r o p e r t i e s o f Douglas f i r i n t e n s i o n p a r a l l e l t o g r a i n as s t u d i e d i n t h i s experiment were but s l i g h t l y a f f e c t e d by temperature v a r i a t i o n s w i t h i n the experimental l i m i t s .  N e v e r t h e l e s s , the e f f e c t was such  that an i n c r e a s e i n temperature decreased s t r e n g t h p r o p e r t i e s , w i t h the p o s s i b l e e x c e p t i o n o f u l t i m a t e t e n s i l e s t r a i n which o c c a s i o n a l l y showed an i n c r e a s e w i t h i n c r e a s i n g  96  temperature. U l t i m a t e t e n s i l e s t r e n g t h of earlywood was reduced by approximately 15 p e r cent over the temperature range from 25 t o 70°C, while latewood showed about 30 p e r cent r e d u c t i o n i n t h i s p r o p e r t y over the same temperature range.  T h i s d i f f e r e n c e i n temperature s e n s i t i v i t y o f  s t r e n g t h o f the two wood zones can be a t t r i b u t e d t o the g r e a t e r c o n t r i b u t i o n o f the middle l a m e l l a t o s t r e n g t h p r o p e r t i e s i n latewood.  The t h e r m o - s e n s i t i v i t y -of l i g n i n ,  approximately 70 p e r cent o f which i s d e p o s i t e d i n the middle l a m e l l a , could i n f l u e n c e the t e n s i l e strength-temp e r a t u r e r e l a t i o n s h i p of latewood to a g r e a t e r extent than i n earlywood.  This i s supported by the apparent i n t e r -  tracheid f a i l u r e i n this  zone.  The i n f l u e n c e o f temperature on apparent e l a s t i c i t y was s i m i l a r t o that o f the u l t i m a t e s t r e n g t h p r o p e r t i e s . Both s t r e n g t h and e l a s t i c i t y v a r i e d l i n e a r l y w i t h temperature, although the three l e v e l s o f temperature used i n t h i s study do not a l l o w d e s c r i p t i o n o f an exact c o n f i g u r a tion describing this relationship.  In Figures.  17 and 18  the v a r i o u s planes i n the t h r e e - d i m e n s i o n a l diagrams represent s t r e n g t h and e l a s t i c i t y r e s p e c t i v e l y a t v a r i o u s temperature l e v e l s .  The s p a c i n g o f the planes i s p r o p o r t i o n -  a l t o the corresponding temperature d i f f e r e n c e s which i n d i c a t e the l i n e a r r e l a t i o n s h i p . A d i s c u s s i o n on the i n f l u e n c e o f temperature  97  on u l t i m a t e t e n s i l e s t r a i n as found i n t h i s study would not be a p p r o p r i a t e s i n c e the e f f e c t was significant.  Nevertheless,  shown to be non-  the s m a l l e f f e c t of temperature  i s g r a p h i c a l l y shown i n F i g u r e 19.  In latewood, the  p e c u l i a r appearance of the planes may  be recognized  i n that  they i n t e r c e p t each other, i n d i c a t i n g a s i g n i f i c a n t a c t i o n between temperature and moisture content. i n t e r a c t i o n w i l l be d i s c u s s e d The  inter-  This  later.  energy r e q u i r e d to break the specimen i n t e n s i o n  p a r a l l e l to g r a i n was  lowered by i n c r e a s i n g temperature.  r e l a t i v e amount of energy saved.by i n c r e a s i n g the temperature from 25 to 70°C was  l e s s than 10 per cent f o r e a r l y -  wood, but amounted to approximately wood.  30 per cent f o r l a t e -  This i s a t t r i b u t e d to the d i f f e r e n c e s i n the  de-  formation mechanism of the two wood zones i n t e n s i o n para l l e l to g r a i n , as d i s c u s s e d e a r l i e r i n connection t e n s i l e strength.  with  Since u l t i m a t e t e n s i l e s t r a i n was  not  a f f e c t e d s i g n i f i c a n t l y by v a r i a t i o n s i n temperature,  the  r a t e of r e d u c t i o n i n work to maximum l o a d was  s i m i l a r to  that i n u l t i m a t e t e n s i l e s t r e n g t h and/or e l a s t i c i t y .  The  98  V  EFFECTS OF INTERACTIONS AMONG CELLULOSE CHAIN LENGTH, TEMPERATURE AND MOISTURE CONTENT ON TENSILE STRENGTH PROPERTIES OF WOOD  In t h i s study o f mechanical behavior o f Douglas f i r wood i n t e n s i o n p a r a l l e l t o g r a i n , r e l a t i v e v a r i a t i o n s i n s t r e n g t h p r o p e r t i e s due t o d i f f e r e n c e s i n moisture  content  .were g r e a t l y i n f l u e n c e d by c e l l u l o s e c h a i n l e n g t h .  Early-  wood samples, not t r e a t e d by gamma r a d i a t i o n ,  suffered  approximately 20 p e r cent r e d u c t i o n i n u l t i m a t e t e n s i l e s t r e n g t h over the range o f oven-dry t o water-saturated conditions.  Samples from the same wood zone, with low DP  v a l u e s , showed about 40 p e r cent s t r e n g t h l o s s over the same moisture content range.  Strength o f latewood  with  s e v e r e l y degraded c e l l u l o s e a l s o showed a g r e a t e r s e n s i t i v i t y t o moisture content changes than t h a t o f the same growth zone but w i t h undegraded c e l l u l o s e .  Here, the range o f  r e l a t i v e s t r e n g t h l o s s between the lowest and the h i g h e s t DP v a l u e s was found t o be only about 5 per cent.  The curves  r e p r e s e n t i n g moisture s e n s i t i v i t y o f t e n s i l e s t r e n g t h are shown i n F i g u r e 23, where p e r cent r e d u c t i o n i n s t r e n g t h due t o d i f f e r e n c e s i n moisture content between oven-dry and water-saturated c o n d i t i o n s was p l o t t e d a g a i n s t i n t r i n s i c viscosity.  The continuous i n c r e a s e i n moisture  sensitivity  w i t h d e c r e a s i n g c h a i n l e n g t h may be noted i n t h i s f i g u r e . The above behavior o f wood may be e x p l a i n e d by the  99  s l i p p a g e mechanism of f a i l u r e .  Strength o f wood with  cel-  lulose o f l o n g - c h a i n s t r u c t u r e should not he a f f e c t e d by v a r i a t i o n s i n moisture content  t o the same extent as wood  with s h o r t , degraded c e l l u l o s e molecules.  S w e l l i n g agents,  such as water, d i m i n i s h the cohesion between m i c r o f i b r i l s or molecular bundles i n wood.  In f i b r e s of long c e l l u l o s e  c h a i n s t r u c t u r e the energy o f l a t e r a l cohesion so reduced can s t i l l be s u f f i c i e n t l y h i g h t o e f f e c t f a i l u r e i n primary valence bonds, r a t h e r than between molecules through s l i p page.  In s h o r t - c h a i n s t r u c t u r e s , a relatively small i n c r e a s e  i n moisture content may lower the i n t e g r a l l a t e r a l bond to such a l e v e l t h a t s l i p p a g e between elements could upon a p p l i c a t i o n o f e x t e r n a l s t r e s s e s .  occur  This behavior i s  s i m i l a r t o the dependence o f s t r e n g t h on c e l l u l o s e DP, except t h a t here the s t r e n g t h o f the bonds i s a f f e c t e d through s w e l l i n g r a t h e r than the number o f those bonds through decrease i n c e l l u l o s e c h a i n l e n g t h . Another item o f s i g n i f i c a n c e t o be noted i n F i g u r e 23 i s the a p p r e c i a b l y g r e a t e r r e l a t i v e l o s s e s i n s t r e n g t h of latewood, upon i n c r e a s e s i n moisture content, those o f earlywood.  than  While r e d u c t i o n i n s t r e n g t h o f e a r l y -  wood ranges from approximately  20 to 40 p e r cent, that o f  latewood i s as h i g h as 49 t o 54 p e r cent, depending on c e l l u l o s e chain length.  The reason f o r t h i s d i f f e r e n c e  may be explained by the f a c t t h a t s p e c i f i c g r a v i t y o f latewood i n Douglas f i r i s approximately  3.0 t o 3.5 times  100  that of earlywood (42).  I t has l o n g been recognized  s w e l l i n g and s h r i n k i n g of wood are a f f e c t e d by  that  specific  g r a v i t y v a r i a t i o n s i n that the h i g h e r the s p e c i f i c g r a v i t y the g r e a t e r the dimensional moisture content.  changes due  to v a r i a t i o n s i n  There have even been equations c o n s t r u c t e d  to represent average r e l a t i o n s between d e n s i t y and and s w e l l i n g (12,99).  shrinkage  A g r e a t e r s w e l l i n g , on the other hand,  r e s u l t s i n a p r o p o r t i o n a l l y l a r g e r area i n c r e a s e of s p e c i men.  U l t i m a t e l o a d per u n i t area, t h e r e f o r e ,  decreases.  C o n s i s t e n t with these c o n s i d e r a t i o n s i s the f a c t that average l o s s i n modulus of rupture of coast-type Douglas f i r ,  as  c a l c u l a t e d from data reported by Wangaard (99),  per  i s 35  cent between a i r - d r y and green c o n d i t i o n , whereas t h a t f o r i n t e r i o r type Douglas f i r over the same moisture range i s only 33*3 per cent.  Average s p e c i f i c g r a v i t y of  the former i s r e p o r t e d to be 0.45 is  content  and f o r the l a t t e r i t  0.41. Moisture  s e n s i t i v i t y of latewood s t r e n g t h , due  to  v a r i a t i o n s i n c e l l u l o s e c h a i n l e n g t h , seems to be lower than that of earlywood.  This i s i n d i c a t e d by the  consider-  a b l y s m a l l e r slope of the l i n e r e p r e s e n t i n g latewood s t r e n g t h l o s s i n r e l a t i o n to v i s c o s i t y i n F i g u r e 23.  This may  be  explained by the d i f f e r e n c e i n the c r y s t a l l i n i t y of the two  wood zones (63).  as deformation  Since moisture a d s o r p t i o n as w e l l  take p l a c e i n the amorphous r e g i o n s ,  n i f i c a n t l y lower percentage of amorphous c e l l u l o s e  sigshould  101  be accompanied by s i g n i f i c a n t l y l o v e r s e n s i t i v i t y of s t r e n g t h v a l u e s to moisture.  On the other hand, degradation of  c e l l u l o s e of a g r e a t e r r e l a t i v e amount o f the amorphous zone should r e s u l t i n a g r e a t e r chance of s l i p p a g e , consequently a h i g h e r moisture s e n s i t i v i t y i n r e l a t i o n to c e l lulose  DP. The i n t e r a c t i o n between temperature  DP,  and between temperature  and  cellulose  and moisture content, i n terms  of u l t i m a t e t e n s i l e s t r e n g t h was n e g l i g i b l e as w e l l as s t a t i s t i c a l l y non-significant. narrow range i n temperature  T h i s was  probably due to the  used i n t h i s study.  of e l a s t i c i t y , no f i r s t order i n t e r a c t i o n was  In terms  found to  be e i t h e r s t a t i s t i c a l l y s i g n i f i c a n t , or l a r g e enough f o r serious consideration.  In t h i s l a t t e r p r o p e r t y , the only  f a c t o r i n d u c i n g s u b s t a n t i a l changes was moisture U l t i m a t e t e n s i l e s t r a i n i n earlywood  was  content. found to  have s t a t i s t i c a l l y s i g n i f i c a n t i n t e r a c t i o n between c e l l u l o s e c h a i n l e n g t h and moisture content. s t r a i n was  This i n t e r a c t i o n i n  such t h a t i n h i g h DP r e g i o n s there appeared  to  be a l a r g e i n c r e a s e i n e x t e n s i b i l i t y with i n c r e a s i n g moisture content, while at low DP l e v e l s the e f f e c t of moisture was minor, and o c c a s i o n a l l y even a decrease i n s t r a i n observed with i n c r e a s i n g moisture content.  was  This p e c u l i a r  s t r a i n behavior of wood, e s p e c i a l l y i n the earlywood was unexpected.  zone,  The only e x p l a n a t i o n of i t would be a  hypothesis t h a t , even i n earlywood,  content  at h i g h DP  levels  102  there must occur a c o n s i d e r a b l e before  s l i p p a g e between chains  extension  of the c e l l  wall  o r m i c r o f i b r i l s develops.  In these r e g i o n s , moisture content p l a s t i c i z e s the c e l l w a l l m a t e r i a l i n such a way that the h i g h e r the moisture content the g r e a t e r the extension before u l t i m a t e In a d d i t i o n , the c e l l w a l l may o f f e r s u f f i c i e n t  failure.  resistance  to a p p l i e d s t r e s s e s t o cause some deformation i n the middle l a m e l l a as w e l l .  On the other hand, when c e l l u l o s e c h a i n  l e n g t h i s low, the s t r e s s e s developed during t e n s i l e t e s t i n g can never reach a l e v e l at which s t r e t c h i n g o f the middle l a m e l l a can s u b s t a n t i a l l y c o n t r i b u t e t o o v e r a l l deformation. A l s o , s l i p p a g e between m i c r o f i b r i l s i n the low DP r e g i o n can occur a t low l o a d l e v e l s a t which s t r e t c h i n g o f the c e l l w a l l i t s e l f i s not i n f l u e n c e d by the a d d i t i o n o f water.  This happens because s l i p p a g e can develop even i n  the dry m a t e r i a l e f f e c t i n g e a r l y f a i l u r e , without the weakening o f l a t e r a l cohesive  f o r c e s by the a d d i t i o n o f water.  An i n t e r a c t i o n between c e l l u l o s e c h a i n l e n g t h and moisture content should values  e x i s t i n terms o f latewood s t r a i n  as w e l l , i f the mechanism o f deformation were s i m i l a r  i n the two growth zones.  This was not found i n t h i s study,  so that i t i s assumed that d i f f e r e n t mechanisms govern s t r a i n behavior o f e a r l y - and latewood.  I t i s conceivable  that  r e g a r d l e s s o f v a r i a t i o n s i n DP, the c e l l w a l l o f latewood has  such h i g h s t r e n g t h that a great p a r t o f the deformation  takes p l a c e i n then middle l a m e l l a .  103  Both e a r l y - and latewood t e n s i l e s t r a i n values showed s i g n i f i c a n t i n t e r a c t i o n with regard t o both moisture content and temperature. minor.  I n earlywood  the e f f e c t was r a t h e r  Nevertheless, i t was such that s t r a i n decreased  with i n c r e a s i n g temperature and i t i n c r e a s e d o r remained i n t e s t temperature  i n the m o i s t u r e - f r e e wood, constant r e g a r d l e s s of v a r i a t i o n s  above the f i b r e - s a t u r a t i o n p o i n t .  wood u l t i m a t e t e n s i l e s t r a i n showed a r a t h e r h i g h l y  Late-  signif-  i c a n t i n t e r a c t i o n between moisture content and temperature. Here the g e n e r a l e f f e c t was such that while s t r a i n o f dry samples decreased with i n c r e a s i n g temperature,  i n wet  specimens i t i n c r e a s e d s u b s t a n t i a l l y upon i n c r e a s e i n temperature.  In d r y latewood, however, the r e l a t i o n s h i p i s  not q u i t e s t r a i g h t forward.  The above i n t e r a c t i o n e f f e c t  i s f a i r l y c o n c l u s i v e proof of the hypothesis that p a r t o f the deformation i n latewood  takes p l a c e i n the middle  lamella.  As was s t r e s s e d e a r l i e r , one o f the p o s s i b l e ways of weakening the middle l a m e l l a between c e l l s i s t o heat wood t o approximately 50 t o 100°C i n the presence of moisture. Work to maximum l o a d showed h i g h l y s i g n i f i c a n t order i n t e r a c t i o n s among the three v a r i a b l e s t e s t e d . t h i s p r o p e r t y i s considered the one combining  As,  a l l strength,  s t r a i n and e l a s t i c i t y , these i n t e r a c t i o n s were c l o s e l y c o r r e l a t e d t o those found i n connection with the above simple s t r e n g t h p r o p e r t i e s .  first  104  VI  RELATIVE AMOUNTS OP VARIATION IN TENSILE STRENGTH PROPERTIES ACCOUNTED FOR BY VARIOUS FACTORS j  The  e f f e c t i v e n e s s o f the experiment may be estimated  on the b a s i s o f what p r o p o r t i o n o f the t o t a l v a r i a t i o n i n s t r e n g t h p r o p e r t i e s t e s t e d has been accounted f o r by the experimentally  controlled variables.  The squares o f c o r -  r e l a t i o n c o e f f i c i e n t s c a l c u l a t e d f o r the m u l t i p l e r e g r e s s i o n equations provide a d i r e c t numerical  measure here (82).  These numbers can be looked upon as percentages o f v a r i a t i o n e x p l a i n a b l e by the independent v a r i a b l e s i n c l u d e d i n the corresponding  equations.  The p e r cent r e s i d u a l v a r i a -  t i o n i s then due to inherent v a r i a b i l i t y o f and  1•  t o experimental  the m a t e r i a l  error.  V a r i a t i o n i n Strength P r o p e r t i e s Due to Treatments In Table 20 the c o r r e l a t i o n c o e f f i c i e n t s are given  as percentages of change i n s t r e n g t h p r o p e r t i e s due t o c o n t r o l l e d experimental  treatments as based on the t o t a l  amount o f v a r i a t i o n i n those p r o p e r t i e s .  These f i g u r e s  i n d i c a t e t h a t d i f f e r e n c e s i n c e l l u l o s e c h a i n l e n g t h , temperature,  and moisture content  together  induced  57 t o 71  per cent change i n the v a r i o u s mechanical p r o p e r t i e s t e s t e d , except f o r latewood e l a s t i c i t y , which could be explained to only 36 p e r cent by the above f a c t o r s . These values  105  may  be  considered acceptable when d e a l i n g with a b i o l o g i c a l  product such as wood. procedures i n the  In s p i t e of the  s e l e c t i o n and  c a r e f u l l y followed  p r e p a r a t i o n of m a t e r i a l ,  and  t e n s i o n t e s t i n g , some inherent wood c h a r a c t e r i s t i c s could not be  controlled. In g e n e r a l , s t r e n g t h p r o p e r t i e s  be  of earlywood could  explained by the e f f e c t s of experimental v a r i a b l e s  g r e a t e r degree than those of latewood.  The  to  a  reason f o r t h i s  probably l i e s i n the f a c t that the average c o e f f i c i e n t s of v a r i a t i o n i n a l l properties 10 per  of earlywood seem to be  cent lower than those f o r latewood, as can be  Tables 2 to  c e l l u l o s e chain  l e n g t h , measured e i t h e r as i n t r i n s i c v i s c o s i t y or was  the most important s i n g l e f a c t o r  t e n s i l e strength properties of Douglas f i r . The  calculated  influencing  of both e a r l y - and  latewood  e f f e c t i s e s p e c i a l l y pronounced i n  earlywood where the v a r i a t i o n due  to d i f f e r e n c e s  in cel-  l u l o s e i n t r i n s i c v i s c o s i t y amounts from 42 to 63 per as shown i n Table 20.  This was  expected because of  v e r y wide range of v i s c o s i t y v a l u e s used. polymerization  i n c o n t r o l specimens was  of the most s e v e r e l y  degraded ones, and  v a l u e s ranged between 2.3 than 15  seen i n  5.  In a l l except e l a s t i c p r o p e r t i e s ,  as DP,  5 to  to 35.0  The  cent, the  degree of  some 35 times that intrinsic viscosity  d l / g , a f a c t o r of more  times. In Table 21,  the  simple c o r r e l a t i o n c o e f f i c i e n t s  106  are g i v e n .  The squares of these v a l u e s can a l s o he  looked upon as percentages  r e p r e s e n t i n g t h a t p o r t i o n of  the t o t a l v a r i a t i o n which can he accounted v a r i a b l e i n question.  f o r by the s i n g l e  Here again, c e l l u l o s e c h a i n l e n g t h ,  e i t h e r as i n t r i n s i c v i s c o s i t y i n d l / g or as a c t u a l DP v a l u e , i s the most important s i n g l e f a c t o r i n t h i s  study  accounting f o r up;; to .-about ! y 50 per cent of the t o t a l v a r i a t i o n i n s t r e n g t h p r o p e r t i e s alone. Por e l a s t i c i t y of both e a r l y - and latewood, as f o r u l t i m a t e t e n s i l e s t r e n g t h of latewood,  as w e l l  moisture  content i s shown to be the most important s i n g l e f a c t o r . In a l l other p r o p e r t i e s t e s t e d , moisture content second to c e l l u l o s e DP. tion affected  ranks  In g e n e r a l , moisture content v a r i a -  s t r e n g t h , s t r a i n and' maximum work v a l u e s  to a g r e a t e r extent i n l a t e - than i n earlywood.  In Table  20 i t i s shown t h a t , whereas i n latewood moisture  content  d i f f e r e n c e s c o t r i b u t e d from 1 *3 to 34 per cent of the t o t a l v a r i a t i o n i n the three s t r e n g t h c h a r a c t e r i s t i c s mentioned above, i n earlywood i m a t e l y 3 t o 10 per  t h i s range extended  only from-approx-  cent depending again on p r o p e r t y .  The  simple c o r r e l a t i o n c o e f f i c i e n t s recorded i n Table 21 i n d i c a t e s i m i l a r importance  of moisture content on s t r e n g t h  p r o p e r t i e s along the g r a i n . V a r i a t i o n i n temperature  was  the l e a s t  of the f a c t o r s s t u d i e d i n t h i s experiment.  important  I t i s apparent,  as i n d i c a t e d e a r l i e r , that the experimental range f o r tern-  107  perature  was  the most l i m i t e d of a l l the f a c t o r s t e s t e d .  In earlywood, the r e l a t i v e amount of v a r i a t i o n i n s t r e n g t h and  e l a s t i c i t y induced by d i f f e r e n c e s i n t e s t temperature  was  approximately 6 per cent, while i n latewood t h i s  ranged between 3 and 8 percent.  value  This i n d i c a t e s that e a r l y -  wood was  somewhat more s e n s i t i v e to temperature v a r i a t i o n s  than was  latewood.  s t r a i n values  In maximum work and u l t i m a t e  the e f f e c t of t h i s v a r i a b l e was  tensile  s m a l l to  n e g l i g i b l e , although s t a t i s t i c a l l y s i g n i f i c a n t at the  0.1  per cent l e v e l of p r o b a b i l i t y .  2.  F a c t o r s I n f l u e n c i n g T e n s i l e Strength P r o p e r t i e s  Inherent  i n Wood The  i n f l u e n c e of wood v a r i a b i l i t y on t e n s i l e  p r o p e r t i e s was theless,  minimized through sampling technique.  c e r t a i n v a r i a b l e s of anatomical and  i c nature remained u n c o n t r o l l e d . might have caused  One  Never-  submicroscop-  anatomical f a c t o r that  differences i n strength properties  be the v a r i a t i o n i n t r a c h e i d l e n g t h .  strength  The  could  f a c t that specimens  were taken from the same r e l a t i v e p o s i t i o n of three growth increments does not  exclude the p o s s i b i l i t y that i n the  three growing seasons the t r a c h e i d s produced were of d i f f e r e n t length.' I t i s reasonable to assume t h a t , along with v a r i a t i o n i n tracheid length, differences i n f i b r i l l a r o r i e n t a t i o n of c e l l u l o s e i n the secondary c e l l w a l l could have  108  occurred among the increments t e s t e d .  Wardrop (101) has  r e p o r t e d t h a t i n t r a c h e i d s o f r a d i a t a pine and Douglas f i r the s m a l l e r f i b r i l angles were found i n the l o n g e r elements within a single tree.  These two f a c t o r s could have account-  ed f o r some v a r i a t i o n i n s t r e n g t h p r o p e r t i e s as i t i s w e l l recognized  t h a t the g r e a t e r s t r e n g t h o f wood l i e s i n the  d i r e c t i o n o f the c e l l u l o s e chains, t h a t i s , i n the d i r e c t i o n of the m i c r o f i b r i l s .  The i n f l u e n c e o f t r a c h e i d l e n g t h and  f i b r i l angle on t e n s i l e s t r e n g t h of wood has been r e p o r t e d by Wardrop (101), I f j u and Kennedy (41), K e l l o g g and I f j u (44), and Wellwood (102).  From these s t u d i e s i t i s evident  that t r a c h e i d l e n g t h and f i b r i l angle can exert t h e i r i n f l u e n c e on s t r e n g t h p r o p e r t i e s only i f the s p e c i f i c g r a v i t y range o f the m a t e r i a l i s narrow.  In t h i s study r e l a t i v e  d e n s i t y o f wood was kept constant  f o r the specimens, through  the sampling design,  so t h a t the i n f l u e n c e o f anatomical  f a c t o r s c o u l d not be overshadowed by that o f s p e c i f i c gravity. E a r l i e r , i n an i n v e s t i g a t i o n o f intra-increment v a r i a t i o n s o f s t r e n g t h p r o p e r t i e s p a r a l l e l t o g r a i n (42), i t was found that d i f f e r e n c e s t a n g e n t i a l l y were minor i n comparison with those i n the r a d i a l d i r e c t i o n w i t h i n a growth increment.  They were s t i l l between 5 and 25 p e r  cent, a somewhat lower value than the coefficients of v a r i a t i o n i n the f o u r s t r e n g t h p r o p e r t i e s obtained  i n this  109  experiment.  The d i f f e r e n c e may l i e i n the f a c t  while i n the intra-increment  that,  study specimens were  obtained  from a b l o c k only 3 i n . i n t a n g e n t i a l width, here the t a n g e n t i a l range from which the t e s t m a t e r i a l was e x t r a c t e d was approximately f i v e times as wide.  I t i s also possible  that v a r i a t i o n s i n anatomical c h a r a c t e r i s t i c s do not occur only between increments.  They may be present  within a  c e r t a i n t a n g e n t i a l width of the same increment,  causing  a v a r i a t i o n i n s t r e n g t h p r o p e r t i e s through t r a c h e i d l e n g t h and  / o r f i b r i l angle d i f f e r e n c e s . One p o s s i b l e e r r o r l i e s i n the f a c t that the  d i r e c t i o n of a l l tracheary considered  uniform.  elements i n a t e s t b l o c k was  Of course, t h i s assumption i s only  g e n e r a l l y t r u e , s i n c e even a very small p i e c e o f wood, having a few t r a c h e i d s i n t h i c k n e s s , can e x h i b i t d e v i a t i o n from the p a r a l l e l arrangement o f i t s t r a c h e i d s . it  i s true  In f a c t ,  that l o c a l l y , a t s i t e s of t r a c h e i d endings,  a d e v i a t i o n from the p a r a l l e l arrangement i s necessary to fill  space.  This microscopic  misalignment o f the t r a c h e i d s  would be o f minor importance only i f the t r a c h e i d l e n g t h i were constant  i n the experimental m a t e r i a l , as the number  of t r a c h e i d endings i s i n d i r e c t r e l a t i o n t o t r a c h e i d l e n g t h . A t r a c h e i d misalignment due to growth c o n d i t i o n s should be o f g r e a t e r importance.  I r r e g u l a r i t i e s i n the  arrangement o f t r a c h e i d s i s a f a i r l y frequent i n wood.  occurrence  The causes may be o f s e v e r a l o r i g i n s , f o r example  110  the v i c i n i t y of an inter-gram  knot, n a t u r a l bending i n  the t r e e developed i n the competition l e a n i n g due  e i t h e r to a constant  f o r l i g h t , or a  d i r e c t i o n of wind  during  growing p e r i o d or to slope of the ground on which the was  grown.  Although i n the s e l e c t i o n of m a t e r i a l  s t r a i g h t n e s s of g r a i n was  tree  the  c a r e f u l l y i n s p e c t e d by macros-  c o p i c means, o c c a s i o n a l d e v i a t i o n from p e r f e c t l y s t r a i g h t alignment of sectioning.  the t r a c h e i d s was  n o t i c e d at time of microtome  Thus, some t e n s i o n t e s t specimens  contained  f i b r e s which l a y at some angle to the d i r e c t i o n of l o a d application.  However s m a l l that angle might have been, i t s  i n f l u e n c e on t e n s i l e s t r e n g t h p r o p e r t i e s could  contribute  s u b s t a n t i a l l y to the v a r i a t i o n i n s t r e n g t h p r o p e r t i e s . This assumption i s supported by Hearmon, as c i t e d i n Meredith (71), who  published  a v e c t o r diagram showing  the v a r i a t i o n i n modulus of e l a s t i c i t y of spruce wood i n the l o n g i t u d i n a l - t r a n s v e r s e plane, direction.  with changing g r a i n  I t can be seen i n that diagram that  relatively  small d e v i a t i o n s from the l o n g i t u d i n a l d i r e c t i o n r e s u l t i n great r e d u c t i o n s  i n e l a s t i c i t y . Strength p r o p e r t i e s ,  than e l a s t i c modulus, t e s t e d i n t h i s study may  other  conceivably  f o l l o w a s i m i l a r r e l a t i o n s h i p to g r a i n d i r e c t i o n .  11-1  3•  V a r i a t i o n i n T e n s i l e Strength  P r o p e r t i e s Due t o  Experimental E r r o r  Another p a r t o f v a r i a t i o n i n t e n s i l e  strength  p r o p e r t i e s unaccounted f o r by changes i n c e l l u l o s e DP, temperature  and  moisture content, were those due apparently  to experimental e r r o r .  One such p o s s i b l e e r r o r could have  been introduced by the f a c t that r e c t a n g u l a r were used i n the t e s t s . mental s t r e s s analyses  specimens  I t i s known from v a r i o u s  experi-  t h a t , where there a r e abrupt changes  i n e i t h e r c r o s s - s e c t i o n a l dimensions or i n the e l a s t i c p r o p e r t i e s o f a p i e c e o f m a t e r i a l under s t r e s s , s t r e s s e s conc e n t r a t e a t those s i t e s causing e a r l y f a i l u r e a t r e l a t i v e l y low l o a d l e v e l s (69).  When a specimen i s clamped i n g r i p s ,  such s t r e s s concentrations due  develop near the gripped  to an abrupt change i n e l a s t i c behavior of the m a t e r i a l  at the g r i p s .  This o f t e n r e s u l t s i n f a i l u r e at g r i p s .  In t h i s experiment s t r e s s concentrations were  area  minimized.  at grips  The g r i p p i n g s u r f a c e s o f the jaws were  l i n e d w i t h t h i n , hard-rubber sheets which provided  a suf-  f i c i e n t l y uniform h o l d on the specimen, and a l s o produced a gradual  t r a n s i t i o n i n e l a s t i c i t y between  the g r i p p i n g assembly.  Tightening  the wood and  of the jaws was accomplish-  ed through a constant-torque-wrench which e l i m i n a t e d i n g of f i b r e s due t o excessive pressure.  crush-  In s p i t e o f these  112  p r e c a u t i o n s , about 5 t o 10 p e r cent of the specimens f a i l e d at g r i p s .  A p r e l i m i n a r y a n a l y s i s showed that specimens  that f a i l e d a t or.near  the jaws d i d not produce s i g n i f i c a n t l y  lower s t r e n g t h values than those breaking between g r i p s .  On  t h i s b a s i s , t e s t r e s u l t s from specimens which broke a t g r i p s were r e t a i n e d . In an e a r l i e r study  (42), v a r i o u s t e n s i o n t e s t  specimen designs were i n v e s t i g a t e d , with s p e c i a l emphasis on the r e p l i c a b i l i t y o f t e s t r e s u l t s , .as w e l l as on the i n c i d e n c e o f f a i l u r e at o r near the g r i p s .  I n that ex-  periment i t was found t h a t , when specimens are prepared from microtome s e c t i o n s of wood, the best r e s u l t s are obtained when t e s t i n g r e c t a n g u l a r p i e c e s .  Both h i g h e r  u l t i m a t e t e n s i l e s t r e n g t h values and b e t t e r r e p l i c a b i l i t y , as evidenced  by c o e f f i c i e n t s o f v a r i a t i o n , were obtained  by u s i n g a r e c t a n g u l a r specimen design, while the i n c i d e n c e of g r i p f a i l u r e was of the same order o f magnitude as t h a t with necked-down t e s t p i e c e s . The use o f a s t r i p of wood s e c t i o n with  uniform  c r o s s - s e c t i o n along i t s l e n g t h does not e l i m i n a t e the presence o f s t r e s s c o n c e n t r a t i o n s at g r i p s .  I t i s only an  improved form o f specimen over v a r i o u s other types used by d i f f e r e n t workers (41,46,50,101,102).  Therefore,  u l t i m a t e s t r a i n v a l u e s , e l a s t i c i t y constants, and work to maximum, l o a d data c a l c u l a t e d on the b a s i s o f specimen  113  e l o n g a t i o n observed as cross-head machine, cannot be accepted material.  t r a v e l on the t e s t i n g  as t r u e p r o p e r t i e s o f the  But they may be considered  Nevertheless,  as apparent v a l u e s .  they can be s a f e l y used w i t h i n the study  f o r comparative purposes. S t r e s s concentrations  i n the m a t e r i a l under s t r e s s  c o n d i t i o n s may be due t o i n c o r r e c t g r i p p i n g .  If  a specimen  i s clamped between the jaws of the t e s t i n g machine i n such a way t h a t one p a r t o f i t i s s t r e s s e d before the other would c a r r y any l o a d , a non-uniform s t r e s s d i s t r i b u t i o n occurs.  I n a study o f intra-increment  strength v a r i a t i o n s  i n Douglas f i r wood (42), the e f f e c t s of v a r i o u s specimen misalignments have been i n v e s t i g a t e d .  I n that experiment  i t has been found t h a t severe s t r e n g t h r e d u c t i o n s  can only  be obtained when a r e c t a n g u l a r specimen i s m i s a l i g n e d as much as 5° or more from the c o r r e c t v e r t i c a l p o s i t i o n , l e s s than 5° d e v i a t i o n from v e r t i c a l alignment of the specimen d i d not produce a s i g n i f i c a n t l y lower s t r e n g t h o r e l a s t i c i t y value, but v a r i a t i o n s with misgripped  p i e c e s were  h i g h e r and occurrence of f a i l u r e at grips- was more frequent. In  t h i s experiment, each t e n s i o n t e s t specimen was c a r e -  f u l l y p o s i t i o n e d between the jaws although s m a l l , e x p e r i mentally u n c o n t r o l a b l e could have occurred, strength properties.  d e v i a t i o n s from the c o r r e c t p o s i t i o n  inducing a d d i t i o n a l v a r i a t i o n i n  114  CONCLUSIONS  From t h i s study o f the e f f e c t s o f c e l l u l o s e l e n g t h on the mechanical behavior  chain  of Douglas f i r wood i n  t e n s i o n p a r a l l e l t o g r a i n the f o l l o w i n g c o n c l u s i o n s are drawn: 1. C e l l u l o s e i s degraded by exposure o f wood t o gamma r a y s . The random c h a i n s c i s s i o n produces a l a r g e r e d u c t i o n i n c e l l u l o s e DP a t low i n t e g r a l doses f o l l o w e d by a g r a d u a l l y decreasing  degradation.  2. T e n s i l e s t r e n g t h p r o p e r t i e s o f Douglas f i r earlywood are d i s t i n c t l y d i f f e r e n t from those  of latewood.  The d i f f e r e n -  ces, are not only q u a n t i t a t i v e but a l s o q u a l i t a t i v e , i . e . , the response by mechanical c h a r a c t e r i s t i c s of the two wood zones to changes i n temperature, moisture  content,  and c e l l u l o s e c h a i n l e n g t h does not f o l l o w the same general trend. 3. I t i s suggested that deformation due  i n Douglas f i r earlywood  t o l o n g i t u d i n a l t e n s i l e s t r e s s e s i s an i n t r a - c e l l u l a r  phenomenon, whereas i n latewood i t i s an i n t e r - t r a c h e i d one. 4. V a r i a t i o n i n c e l l u l o s e chain l e n g t h i n f l u e n c e s s t r e n g t h p r o p e r t i e s of wood t o a g r e a t e r extent i n the low than i n the h i g h DP r e g i o n s .  The c o n f i g u r a t i o n of curves  r e l a t i n g ultimate t e n s i l e strength , ultimate  strain,  and work t o maximum t e n s i o n l o a d values to c e l l u l o s e  115  c h a i n l e n g t h i s such t h a t i t suggests asymptotic to  a constant value at v e r y h i g h DP l e v e l s .  approach  This behavior  i s e x p l a i n e d by the s l i p p a g e mechanism o f deformation. are 5. E l a s t i c p r o p e r t i e s are not, orAvery s l i g h t l y i n f l u e n c e d by changes i n c e l l u l o s e DP.  T h i s i s a t t r i b u t e d t o the  f a c t t h a t random s c i s s i o n of c e l l u l o s e chains i n wood by gamma rays does not a l t e r the crystalline-amorphous r a t i o of c e l l u l o s e . 6. V a r i a t i o n s i n moisture content induce h i g h l y s i g n i f i c a n t changes i n t e n s i l e s t r e n g t h p r o p e r t i e s o f Douglas f i r . The e f f e c t i s g r e a t e r on l a t e - than on earlywood.  The  experimental r e s u l t s suggest a convex upward c o n f i g u r a t i o n of curves r e l a t i n g u l t i m a t e t e n s i l e s t r e n g t h and e l a s t i c i t y to moisture  content.  7. I n f l u e n c e o f temperature  w i t h i n the range of 25 to 70°G  i s minor i n comparison with that induced by c e l l u l o s e DP and moisture content. On the b a s i s o f experimental r e s u l t s there i s no reason t o suggest d e v i a t i o n from a l i n e a r r e l a t i o n s h i p between s t r e n g t h p r o p e r t i e s and temperature. 8. Moisture s e n s i t i v i t y o f wood with low-DP c e l l u l o s e i s h i g h e r than t h a t of wood w i t h c e l l u l o s e o f l o n g - c h a i n structure.  T h i s behavior o f wood i n t e n s i o n p a r a l l e l t o  g r a i n i s a l s o e x p l a i n a b l e by deformation. 9. I t i s suggested  the s l i p p a g e mechanism o f  , that the best s i n g l e measure o f the  116  mechanical behavior of wood i n t e n s i o n p a r a l l e l t o g r a i n i s the value of work t o maximum l o a d .  This t e n s i l e  s t r e n g t h parameter i n c l u d e s a l l s t r e s s and deformation c h a r a c t e r i s t i c s of l y i n testing.  the m a t e r i a l t h a t occur  simultaneous-  I t can a l s o be looked upon as an energy  necessary to break a specimen, t h e r e f o r e , i t can be of d i r e c t value i n p r a c t i c a l a p p l i c a t i o n s such as defiberization.  117  REFERENCES 1. Alexander, P., and A. Charlesby. of i s o b u t y l and s t y r e n e . 136-145.  1955. R a d i a t i o n p r o t e c t i o n Proc. Royal Soc. A230:  2. Alexander, W. 1., and R. 1. M i t c h e l l . 1949. Rapid measurement o f c e l l u l o s e v i s c o s i t y by the n i t r a t i o n method. A n a l . Chem. 21:1497-1500. 3. A l f r e y , T. 1948. Mechanical behavior o f h i g h polymers. I n t e r s c i e n c e P u b l i s h e r s , Inc., New York. 581pp. 4. Arthur, J . C. 1958. The e f f e c t s o f gamma r a d i a t i o n on c o t t o n . - I I I . Proposed mechanism o f the e f f e c t s o f h i g h energy gamma r a d i a t i o n on some o f the molecular properties of p u r i f i e d cotton. T e x t i l e Res. J . 38: 204-206. 5. Asunmaa, S., and P. V. lange. 1954. The d i s t r i b u t i o n o f c e l l u l o s e and h e m i c e l l u l o s e i n the c e l l w a l l of spruce, b i r c h and c o t t o n . Svensk P a p p e r s t i d . 57: 501-516. 6. Badger, R. M., and R. H. B l a k e r . 1949. The i n v e s t i g a t i o n of the p r o p e r t i e s o f n i t r o c e l l u l o s e molecules i n s o l u t i o n by l i g h t - s c a t t e r i n g methods. J . Phys. Chem. 53M056-1069. 7. B a i l e y , A. J . 1936. L i g n i n i n Douglas f i r . Composition of the middle l a m e l l a . Ind. Eng. Chem. 8:52-55. 8. Berkley, E . E., and 0. C. Woodyard. 1938. A new microphotometer f o r a n a l y z i n g X-ray d i f f r a c t i o n p a t t e r n s of raw c o t t o n f i b r e . Ind. Eng. Chem. 10:451-455. 9. B l o u i n , F. A., J . C. A r t h u r . 1958. The e f f e c t s o f gamma r a d i a t i o n on c o t t o n . - I . Some o f the p r o p e r t i e s o f p u r i f i e d c o t t o n i r r a d i a t e d i n oxygen and n i t r o g e n atmospheres. T e x t i l e Res. J . 38:198-204. 10. Bovey, F. A. 1958. The e f f e c t o f i o n i z i n g r a d i a t i o n on n a t u r a l and s y n t h e t i c h i g h polymers. Polymer Reviews V o l . I . I n t e r s c i e n c e P u b l i s h e r s , Inc., New York. 287pp. 11. Brauns, F. E., and D. A. Brauns. 1960. The chemistry o f lignin. Supplement volume f o r 1949-1958. Academic Press, New York. 861 pp.  118 12. Brown, H. P., A. J . Panshin, and C. C. P o r s a i t h . 1952. Textbook of wood technology. McGraw-Hill Book Co. Inc., New York. 783pp. 13. Bystedt, J . , and A-M. Anderson. 1957. Measuring t h i c k n e s s of sheet m a t e r i a l s by a p r e c i s i o n d i a l i n d i c a t o r . Svensk P a p p e r s t i d . 60:492-496. 14. Cannon, P. M., and M. R. Penske. 1938. V i s c o s i t y measurement. Ind. Eng. Chem. 10:297-301. 15. C a r l s s o n , C. A., and S. Lagergren. 1957. Studies on the i n t e r f i b e r bonds o f wood. P a r t 2. M i c r o s c o p i c examination of the zone o f f a i l u r e . Svensk Papperst i d . 60:664-670. 16. Chapiro, A. 1962. R a d i a t i o n chemistry of polymeric systems. High polymers, Volume XV. I n t e r s c i e n c e P u b l i s h e r s , Inc., New York. 712pp. 17. Charlesby, A. 1955. The degradation o f c e l l u l o s e by i o n i z i n g r a d i a t i o n . J . Polymer S c i . 15:263-267. 18. Commonwealth S c i e n t i f i c and I n d u s t r i a l Research O r g a n i z a t i o n . 1954-1959. S o r p t i o n s t u d i e s . Annual Repts. 54/55, 55/56, 56/57, 57/58, 58/59. 19. Dadswell, H. E., and A. B. Wardrop. 1960. Recent progress i n r e s e a r c h on c e l l w a l l s t r u c t u r e . Proceedings of the P i f t h World F o r e s t r y Congress. V o l . I I . pp. 12791288. 20. Davison, P. P. 1957. Rapid determination of i n t r i n s i c v i s c o s i t y of c e l l u l o s e n i t r a t e . Tappi 40:975-977. 21. E l l i s , J . W., and J . Bath. 1940. Hydrogen b r i d g i n g i n c e l l u l o s e as shown by i n f r a r e d a b s o r p t i o n s p e c t r a . J . Am. Chem. Soc. 62:2859-2861. 22. Ellwood, E. 1. 1954. P r o p e r t i e s of American beech i n t e n s i o n and i n compression p e r p e n d i c u l a r to the g r a i n and t h e i r r e l a t i o n to d r y i n g . Yale U n i v e r s i t y , School of F o r e s t r y B u l l e t i n 61. 23. F r e i d i n , A. S. 1958. D i e s t v i e r a d i o a k t i v n o g o na f i z i k o mekhanicheskie s v o i s t v a d r e v e s i n y . Derev. Prom. 7(9):13-15. ( E f f e c t o f r a d i o a c t i v e r a d i a t i o n on the p h y s i c a l and mechanical p r o p e r t i e s o f wood. C.S.I.R.O. A u s t r a l i a , T r a n s l a t i o n No. 4417.) 24. Frey-Wyssling, A. 1952. Deformation and f l o w i n b i o l o g i c a l systems. North Holland P u b l . Co., Amsterdam. 552pp. .  119 25. Frey-Wyssling, A. 1953. Die p f l a n z l i c h e Zellwand. ger, B e r l i n . 367pp.  Sprin-  26. Garland, H. 1939. A m i c r o s c o p i c study of c o n i f e r o u s wood i n r e l a t i o n t o i t s s t r e n g t h p r o p e r t i e s . An. Mo. Bot. Garden 26:1-93. 27. Gerry, E. 1915. F i b r e measurement s t u d i e s : l e n g t h v a r i a t i o n s , where they occur and t h e i r r e l a t i o n t o the s t r e n g t h and uses o f wood. Science 41-179 205. - 28. G i l f i l l a n , E. S., and 1. l i n d e n . 1957. Some e f f e c t s o f n u c l e a r i r r a d i a t i o n on c o t t o n y a r n . T e x t i l e Res. J . 27:87-92. 29.  , ] , 1955. E f f e c t s o f n u c l e a r i r r a d i a t i o n on the s t r e n g t h o f yarns. T e x t i l e Res. J. 25:773-777.  30. Glegg, R. E., and Z. I . K e r t e s z . 1957. E f f e c t of gamma r a d i a t i o n on c e l l u l o s e . J . Polymer S c i . 26:289-297. 31. Goring, D. A. I . , and T. E . T i m e l l . 1962. Molecular weight of n a t i v e c e l l u l o s e s . Tappi 45:454-460. 32. Goulet, M. 1960. Die Abhangigkeit der Q u e r z u g f e s t i g k e i t von E i c h e n - , Buchen-, und P i c h t e n h o l z von P e u c h t i g k e i t und Temperatur i n B e r e i c h von 0° b i s 100°C. Holz Roh- Werkstoff 18:325-331. 33. Green, H. V., and J . W o r r a l l . 1963. Wood q u a l i t y s t u d i e s . P a r t I . : A scanning microphotometer f o r a u t o m a t i c a l l y measuring and r e c o r d i n g c e r t a i n wood c h a r a c t e r i s t i c s . Pulp and Paper Research I n s t i t u t e o f Canada. T e c h n i c a l Rept. No. 331. 37pp. 34. Harland,.¥. G. 1952. R e l a t i o n between i n t r i n s i c v i s c o s i t y and degree of p o l y m e r i z a t i o n . Nature 170:667. 35. Harmon, D. J . 1957. E f f e c t s of Cobalt 60 r a d i a t i o n on the p h y s i c a l p r o p e r t i e s of t e x t i l e cords. T e x t i l e Res. J . 27:318-324. 36. Hermans, P. H. P h y s i c s and chemistry o f c e l l u l o s e f i b r e s . E l s e v i e r P u b l i s h i n g Co., Inc., New York. 534pp. 37. H e s s l e r , L. E., M. E. Simpson, and E . E. B e r k l e y . 1948. Degree of p o l y m e r i z a t i o n , s p i r a l s t r u c t u r e , and strength of cotton f i b e r . T e x t i l e Res. J . 18:679683. 38. H o l t z e r , A. -M., H. P. B e n o i t , and P. Doty. 1954. The molecular c o n f i g u r a t i o n and hydrodynamic behavior of c e l l u l o s e t r i n i t r a t e . J . Phys. Chem. 58:624-634.  120 39.  40.  Huggins, M. L. 1942. The v i s c o s i t y of d i l u t e s o l u t i o n s of l o n g - c h a i n molecules. - IV. Dependence on concentrat i o n . J . Am. Chem. Soc. 64:2716-2718. . 1958. P h y s i c a l chemistry John Wiley & Sons, Inc., New York.  of h i g h polymers. 175pp.  41. I f j u , G., and R. W. Kennedy. 1962. Some v a r i a b l e s a f f e c t i n g m i c r o t e n s i l e s t r e n g t h of Douglas f i r . Forest Prod. J . 12:213-217. 42.  , R. W. Wellwood, and J . W. Wilson. 1963. I n t r a increment. r e l a t i o n s h i p o f s p e c i f i c g r a v i t y , microtens i l e s t r e n g t h and e l a s t i c i t y i n Douglas f i r . Paper presented t o the annual S p r i n g Conference, P a c i f i c Coast Branch, Canadian Pulp & Paper A s s o c i a t i o n , May 9-11, 1963, H a r r i s o n Hot Springs, B.C.  43. Immergut, E. H., B. G. Ranby, and H. F. Mark. 1953. Recent work on molecular weight o f c e l l u l o s e . Ind. Eng. Chem. 45:2483-2490. 44. K e l l o g g , R. M., and G. I f j u . 1962. Influence o f s p e c i f i c g r a v i t y and c e r t a i n other f a c t o r s on the t e n s i l e p r o p e r t i e s of wood. F o r e s t Prod. J . 12:463-470. 45. Kenaga, D. 1., and E . B. Cowling. 1959. E f f e c t of gamma r a d i a t i o n on ponderosa p i n e : h y g r o s c o p i c i t y , s w e l l i n g and decay s u s c e p t i b i l i t y . F o r e s t Prod. J . 9:112-116. 46. Kennedy, R. W., and G. I f j u . 1962. A p p l i c a t i o n o f microt e n s i l e t e s t i n g t o t h i n wood s e c t i o n s . Tappi 45: 725-733. 47. K l a u d i t z , W. 1952. Zur biologisch-mechanischen Wirkung des L i g n i n s im Stammholz der Nadel- und .flaubholzer. H o l z f o r s c h . 6:70-82. 48.  . 1957. Zur biologisch-mechanischen Wirkung der Acetylgruppen i n Festigungsgewebe der laubhttlzer. H o l z f o r s c h . 11:47-55.  49.  . 1957. Zur biologisch-mechanischen Wirkung der C e l l u l o s e und H e m i c e l l u l o s e im Festigungsgewebe der l a u b h o l z e r . H o l z f o r s c h . 11:110-116.  50. K l o o t , N. H. 1952. A m i c r o - t e s t i n g technique f o r wood. A u s t r a l . J . Appl. S c i . 3:125-143. 51. Koehler, A. 1933. Causes o f brashness i n wood. U.S. Dept. A g r i c u l t u r e T e c h n i c a l B u l l e t i n No. 342.  52.  121 Kollmann, P. 1951. Technologie des Holzes und der H o l z w e r k s t o f f e . Band I . Springer, B e r l i n . 1050pp.  53.  . 1952. Die Bedeutung der Temperatur ftlr d i e E l a s t i z i t a t und P e s t i g k e i t des Holzes. Holz RohWerkstoff 10:269-279.  54  . 1960. Die Abhangigkeit der e l a s t i s c h e n E i g e n s c h a f t e n von Holz der Temperature. Holz RohWerkstoff 18:308-314.  55. l a g e r g r e n , S., S. Rydholm, and L. Stockman. 1957. Studies on the i n t e r f i b e r bonds o f wood. P a r t 1. T e n s i l e s t r e n g t h o f wood a f t e r h e a t i n g , s w e l l i n g , and d e l i g n ification. Svensk P a p p e r s t i d . 60:632-644. 56. Lang, W. 1957. B e i t r a g z u r Bestimmung des DP-Grades von Ni-tro-Cellulosen m i t h i l f e v i s c o s i m e t r i s c h e r Messungen. Svensk P a p p e r s t i d . 60:233-242. 57. Lange, P. W. 1954. The d i s t r i b u t i o n of l i g n i n i n the c e l l w a l l o f normal and r e a c t i o n wood o f spruce and a few hardwoods. Svensk P a p p e r s t i d . 57:525-532. 58.  . 1954. • The d i s t r i b u t i o n o f the components i n the p l a n t c e l l w a l l . Svensk P a p p e r s t i d . 57:563-567.  59. l a u e r , K. 1951. Zur Kenntnis der Z e l l u l o s e f a s e r n . VI. M i t t e i l u n g : Zur Kenntnis der S t r u k t u r der BaumwallPaser. K o l l o i d - Z . 121:36-39. 60. Lawton, E . J . , ¥. D. Bellamy, R. E . Hungate, M. P. Bryant, and E. H a l l . 1951. Some e f f e c t s o f h i g h v e l o c i t y e l e c t r o n s on wood. Science 113:380-382. 61.  ,  , , , 1951. Studies on the changes produced i n wood exposed t o h i g h v e l o c i t y e l e c t r o n s . Tappi 34:113A-116A.  62.  , A. Bueche, and J . B a l w i t . 1953. I r r a d i a t i o n of polymers by h i g h energy e l e c t r o n s . Nature 172:76-77.  63. Lee, C. L. 1961. C r y s t a l l i n i t y o f wood c e l l u l o s e Porest Prod. J . 11:108-112.  fibres.  64. L i n d s l e y , C. H., M. B. Prank, 1953. I n t r i n s i c v i s c o s i t y of n i t r o c e l l u l o s e r e l a t e d t o degree o f n i t r a t i o n . Ind. Eng. Chem. 45:2491-2497. 65. Loos, W. E. 1962. E f f e c t o f gamma r a d i a t i o n on the toughness o f wood. Porest Prod. J . 12:261-264. 66. Ma, T. S., and G. Zuazaga. 1942. M i c r o - K j e l d a h l determinat i o n o f n i t r o g e n . Ind. Eng. Chem. 14:280-282.  122 67. Mark, H. 1950. P h y s i c a l chemistry of h i g h polymeric systems. I n t e r s c i e n c e P u b l i s h e r s , Inc., New York. 506pp. 68.  . 1957. R a d i a t i o n chemistry and wood. Wood 4:1-8.  Composite  69. Markwardt, L. J . , and W. G. Youngquist. 1956. Tension t e s t methods f o r wood, wood-base m a t e r i a l s , and sandwich c o n s t r u c t i o n s . U.S. Dep. Agr., F o r e s t Ser., F o r e s t Prods. Lab., Rept. No. 2055. 70. Mater, J . 1957. Chemical e f f e c t s o f high-energy i r r a d i a t i o n o f wood. Forest Prod. J . 7:208-209. 71. Meredith, R. paper.  1953. Mechanical p r o p e r t i e s of wood and North Holland Publ., Amsterdam. 298pp.  72. Meyer, E . H. 1950. N a t u r a l and s y n t h e t i c h i g h polymers. High polymers, V o l . IV. I n t e r s c i e n c e P u b l i s h e r s , Inc., New York. 891pp. 73. Neal, J . L.,.and H. A. K r a e s s i g . 1963. Degradation of c e l l u l o s e with megavolt e l e c t r o n s . Tappi 46:70-72. 74. Nissan, A. H., and H. G. H i g g i n s . 1959. Molecular approach to the problem o f v i s c o e l a s t i c i t y . Nature 184:14771478. 75. 76. 77.  , and S. S. S t e r n s t e i n . 1962. C e l l u l o s e as a v i s c o e l a s t i c m a t e r i a l . Pure Appl. Chem. 5:131-146. O t t , E. 1946. C e l l u l o s e and c e l l u l o s e d e r i v a t i v e s . I n t e r s c i e n c e P u b l i s h e r s , I n c . , New York. 1076pp. , H. M. S p u r l i n , and M. W. G r a f f i n . 1955. C e l l u l o s e and c e l l u l o s e d e r i v a t i v e s . 2nd. ed., High polymers V o l . V., Part I I I . , I n t e r s c i e n c e P u b l i s h e r s , Inc., New York. pp.1057-1601.  78. Paton, J . M., and R. F. S. Hearman. 1957. E f f e c t of exposure t o gamma rays on h y g r o s c o p i c i t y of s i t k a spruce. Nature 180:651-653. 79. Preston, R. D. 1960. Anisotropy i n the microscopic and submicroscopic s t r u c t u r e of wood. Proceedings of the F i f t h World F o r e s t r y Congress, V o l . I I . pp.12981307. 80. Ranby, B. G. 1958. The f i n e s t r u c t u r e o f c e l l u l o s e fibrils. C o l l e c t i o n of Papers, Symposium o f the B r i t i s h Paper and Board Makers' A s s o c i a t i o n . Kenley, England. 487pp.  123 81. Hunger, H.G., and W. K l a u d i t z . 1953. ITber Beziehungen zwischen der chemischen Zusammensetzung und den F e s t i g k e i t s e i g e n s c h a f t e n des Stammholzes von Pappeln. H o l z f o r s c h . 7:43-58. 82. Sano, E. 1961. E f f e c t s o f temperature on the mechanical p r o p e r t i e s of wood. I I . Tension p a r a l l e l t o g r a i n . J . Japan. Wood Res. Soc. 7:189-191. 83. Schniewind, A. P. 1962. T e n s i l e s t r e n g t h p e r p e n d i c u l a r to g r a i n as a f u n c t i o n of moisture content i n C a l i f o r n i a b l a c k oak. F o r e s t Prod. J . 12:249-252. 84. Seaman, J . F., M. A. M i l l e t t , and E . J . Lawton. 1952. E f f e c t of h i g h energy cathode rays on c e l l u l o s e . Ind. Eng. Chem. 44:2848-2852. 85. Skoone, A. M., and M. H a r r i s . 1945. P o l y m o l e c u l a r i t y and mechanical p r o p e r t i e s of c e l l u l o s e a c e t a t e . Ind. Eng. Chem. 35J478-482. 86. Smith, D. M., and R. Y. M i x e r / 1959. The e f f e c t o f l i g n i n on the degradation of wood by gamma i r r a d i a t i o n . R a d i a t i o n Res. 11:776-780. 87. Snedecor, G. W. 1957. S t a t i s t i c a l methods. C o l l e g e Press, Ames, Iowa. 534pp.  The Iowa State  88. Stone, J . E . 1955. The rheology of cooked wood. I I . E f f e c t of temperature. Tappi 38:552-559. 89. Sulzberger, P. H. 1953. The e f f e c t of temperature on the s t r e n g t h of wood, plywood and glued j o i n t s . Dep. Supply, A e r o n a u t i c a l Res. C o n s u l t a t i v e Committee, A u s t r a l i a . Rept. ACA-46. 44pp. 90. T i m e l l , T. E. 1954. The e f f e c t o f r a t e of shear on the v i s c o s i t y of d i l u t e solutions of c e l l u l o s e n i t r a t e . Svensk P a p p e r s t i d . 57:777^788. 91.  . . 1954. The i n f l u e n c e of r a t e o f shear on viscosity-concentration relationship f o r dilute solutions of c e l l u l o s e n i t r a t e . Svensk P a p p e r s t i d . 57:844-849.  92.  . 1954. The e f f e c t of s o l v e n t - s o l u t e i n t e r a c t i o n on the v i s c o s i t y o f d i l u t e s o l u t i o n s o f c e l l u l o s e n i t r a t e . Svensk P a p p e r s t i d . 57:913-920.  93.  . 1957. Molecular weight o f n a t i v e Svensk P a p p e r s t i d . 60:836-842.  94.  . 1957. Molecular p r o p e r t i e s of seven n a t i v e c e l l u l o s e s . Tappi 40:25-29.  cellulose.  124 95. T i m e l l , T. E. 1957. N i t r a t i o n as a means of i s o l a t i o n of a l p h a - c e l l u l o s e of wood. Tappi. 40:30-33. • 96.  97.  , and E. C. Jahn. 1951. A study of the i s o l a t i o n and p o l y m o l e c u l a r i t y of paper b i r c h . Svensk P a p p e r s t i d . 54:831-846. , and C. B. Purves. 1951. i n i t i a l stages of the methylation Svensk P a p p e r s t i d . 54:303-332.  A study of the of c e l l u l o s e .  98. T r e i b e r , E., and B. Abrahamson. 1959. Gfesichtpunkte zur v i s c o s i m e t r i s c h e n DP-Bestimmung. H o l z f o r s c h . 13: 161-177. 99. Wangaard, P. P. 1950. The mechanical p r o p e r t i e s of wood. John Wiley & Sons, Inc., New York. 377pp. 100.  . 1957. A new approach to the determination of f i b e r s a t u r a t i o n p o i n t from mechanical t e s t s . Porest Prod. J . 7:410-416.  101.  Wardrop, A. B. 1951. C e l l w a l l o r g a n i z a t i o n and the p r o p e r t i e s of xylem. - I . C e l l w a l l o r g a n i z a t i o n and the v a r i a t i o n i n breaking l o a d i n t e n s i o n of the xylem i n c o n i f e r stems. A u s t r a l . J . S c i . Research  S e r i e s B. 4:391-414.  102.  Wellwood, R. W. 1962. T e n s i l e t e s t i n g of s m a l l wood samples. Pulp Paper Mag. Can. 63:T61-T67.  103.  Wilson, T. R. C. 1932. Strength-moisture r e l a t i o n f o r wood. U.S. Dep. Agr., Porest Ser., T e c h n i c a l B u i . No. 282. 88pp.  104.  Wise, I . E., and E. C. Jahn. 1952. Wood chemistry. V o l . I . Reinhold P u b l i s h i n g Co., New York.  105.  Worrall, J . G-. 1963. The r e l a t i o n s h i p between f r a c t i o n a l v o i d volume and wood q u a l i t y i n western Canadian c o n i f e r s . B.S.P. T h e s i s , F a c u l t y of F o r e s t r y , The U n i v e r s i t y of B r i t i s h Columbia. 44pp.  106.  Youngs, R. L. 1957. The p e r p e n d i c u l a r - t o - g r a i n mechanical p r o p e r t i e s of red oak as r e l a t e d to temperature, moisture content and time. U. S. Dep. Agr., F o r e s t Ser., F o r e s t Prods. Lab. Rept. No. 2079.  TABIES AND FIGURES  LO  Table 1.  Comparison o f c e l l u l o s e DP values c a l c u l a t e d f o r a sample with 35.0 d l / g i n t r i n s i c v i s c o s i t y , u s i n g v a r i o u s r e l a t i o n s h i p s .  R e s u l t i n g DP  Relationship  Authority  [7] = 0.0108 DP  3241  Harland (34)  [7] = 5x10"  DP  7000  Holtzer,Benoit  DP '  3500  Immergut, Ranby and Mark (43)  [V] =3.7x10"" DP  9459  Kraemer (77)  IV]  2917  L i n d s l e y and Prank (64)  [?] =13.6x10" DP  2574  T r e i b e r and Abrahamson (98)  [V] =0.278 D P  3541  T i m e l l (93)  5425  Used i n t h i s experiment  [V] =10x10"  3  3  5  =12x10~  5  DP 5  0 , 5 7 2  Described i n t e x t  and Doty (38)  Table 2. 1  0)  emp.  Pi o  tS)  OC  Mean u l t i m a t e t e n s i l e s t r e n g t h v a l u e s and t h e i r c o e f f i c i e n t s o f v a r i a t i o n . Moist. Cond.  0.0 S. psi  Integral  B  s. psi  B  I r r a d i a t i o n Dose 10.0 1.0 S. S. psi psi  B  B  (megarad) 15.0 S. psi  B  6 . 5899 A i r - d r y 6154 S a t . 4680  20 23 10  6530 6173 4929  18 13 16  5113 5983 4060  40 27 16  4736 4788 3385  23 10 10  2346 2299 1403  15 15 16  c 50 c  0 5814 A i r - d r y 5378 S a t . 4691  24 17 20  5037 5523 4485  18 16 9  5163 5047 3444  31 . 22 19  4137 3785 2783  17 23 17  2159 2003 1228  11 20 16  70  0 5189 A i r - d r y 4954 S a t . 3930  13 16 10  4478 4667 3740  14 12 4  3542 4447 2862  29 19 19  3616 3903 2496  15 24 9  1935 1770 1212  13 12 22  31595 31142 17278 26970 24560 15247 25156 24108 12812  36 26 25 28 28 28  31912 29639 17899 26838 26132 14575 27611 24247 12395  23 23 19  22977 22873 12959 20197 24548 12622  OR  ff-  25  c c  50  &  a 70  0 36021 22 A i r - d r y 32475 30 Sat. 19198 23 0 28351 27 A i r - d r y 30244 22 Sat. 15300 21 0 26907 32 A i r - d r y 29228 35 Sat. 14297 25  29 34 27  27 28 27 28 31 24  30 20 18 28 23 27 24738 26 21387 19 9496 24  17337 27 17229 15 8540 20 13625 33 14676 17 7436 27 14494 25 14353 21 6498 19  Table 3. Temp. CD  c  o  ISJ  >>  103psi  ±%  103psi  ±%  lO^psi  25  0 Air-dry . Sat.  544.0 527.3 401.4  12 16 14  533.7 506.3 405.5  10 8 13  483.4 467.3 332.7  26 26 25  50  0 Air-dry Sat.  544.1 478.0 370.2  16 15 23  503.0 478.8 374.3  8 12 10  500.6 440.8 318.0  70  0 Air-dry Sat.  465.3 465.7 298.2  12 16 13  473.5 473.3 292.2  9 7 9  25  0 Air-dry Sat.  2194.8 2034.6 1674.0  15 23 23  1939.4 1888.8 1576.3  50  0 Air-dry Sat.  1925.4 1746.2 1600.1  19 23 20  1823.3 1645.0 1421.5  70  0 Air-dry Sat.  1713.4 1727.8 1322.1  24 28 20  cd  o o ;s  I n t e g r a l I:r r a d i a t i o n Dose (megarad) 10.0 0.1 1.0  0.0  E CV 10*psi ±7°  H  rFH vi  Moist. -Cond.  oc  xi  o o £  Mean e l a s t i c i t y v a l u e s and t h e i r c o e f f i c i e n t s of v a r i a t i o n .  CD +>  &  E  CV  1O^psi  +<fo  492.8 532.9 390.0  14 14 13  425.2 421,7 295.8  8 12 15  29 24 22  512.0 464.2 318.6  11 14 25  393.2 364.3 240.6  12 12 11  430.9 441.0 248.6  17 15 22  425.3 454.0 299.2  14 18 16  406.1 363.8 205.2  11 17 25  27 20 15  1978.6 2037.4 1593.3  15 22 16  2042.8 2030.8 1543.1  23 15 21  2044.5 2115.2 1607.4  12 20 12  17 19 27  1877.3 1775.0 1405.8  20 20 14  1759.8 1946.8 1429.6  30 11 22  1962.9 1890.0 1389.8  22 8 21  1726.8 18 1805.2 22 1192.41 17  1846.9 1773.1 1200.3  17 14 19  1827.1 1895.6 1242.0  11 14 19  1852.1 1907.4 1000.5  19 . 16 23  E•  CV  E  CV  E  15.0  CV  Table 4.  0  d o  IS]  o o H W  -ci o o [2  Temp. M o i s t . Cond.  0.0 CV e i n . / i n . ±?°  °C  I n t e g r a l I r r a d i a t i o n Dose (megarad) 0.1 1.0 10.0 CV CV e e i n . / i n . +<fo i n . / i n . ±%  CV e in./in. &  15.0 CV e i n . / i n . ±fi  25  0 Air-dry Sat.  .01159 10 .01298 16 .01421 20  .01316 "10 .01342 4 .01552 16  .01135 17 .01458 8 .01584 23  .01096 17 .00630 1 16 • .00976 .00574 11 .00480 13 .00937 18  50  0 Air-dry Sat.  .01156 19 .01249 9 .01706 20  .01105 16 .01266 7 .01586 12  .01111 9 .01302 7 .01586 31  .00865 9 .00901 17 .01053 9  .00626 11 .00587 13 .00589 10  70  0 Air-dry Sat.  .01193 16 .01164 13 .01780 22  .01007 17 .01076 8 .01669 9  .00878 25 .01141 15 .01740 35  .00901 11 .00928 10 .01130 23  .00560 10 .00538 20 .00644 5  25  0 Air-dry Sat.  .01869 12 .02024 18 .01517 15  .01798 14 .02018 10 .01335 8  .01799 17 .01744 18 .01366 8  .01301 18 .01297 11 .01001 14  .00893 15 .00901 12 .00608 17  50  0 Air-dry Sat.  .01736 10 .02076 17 .01397 17  .01612 16 .01870 18 .01747 22  .01589 17 .01787 10 .01430 13  .01242 15 .01441 17 .01162 19  .00719 27 .00804 12 .00652 13  70  0 Air-dry Sat.  .01750 17 .01943 8 .01934 32  .01622 14 .01634 23 .01955 22  .01649 15 .01524 23 .01786 21  .01553 18 .01257 21 .01175 40  .00830 12 .00852 11 .00830 27  OJ  •p Hi  Mean values o f u l t i m a t e t e n s i l e s t r a i n and t h e i r c o e f f i c i e n t s o f v a r i a t i o n .  Table 5. Temp. CD  Moist. Cond.  °C  I n t e g r a l I r r a d i a t i o n Dc>se (megarad) 0.1 1.0 .10.0  0.0 w  °I  Ln.lb/in^ 37.16 28 42.07 38 36-. 34 27  28 18 21  Ln.llf/in?  & in.lD7in3  in.lS/in^  54 31 30  24.87 22.60 16.91  47 20 18  - 6.96 6.84 3.52  29 21 28  28.06 34.04 36.71  40 ' 28.01 22 30.31 18 29.62  17.14 33.70 14.68  22 24 34  22.10 24.45 34.67  30 20 9  17.20 25.48 26.72  17.22 17.36 12.92  26 39 19 20 37 35  6.96 5.71 3.70  24 22 6  35 15 31 48 28 32  5.55 4.78 4.20  19 25 20  348.59 357.06 163.29  34 31 8  292.86 307.57 126.82  48 23 29  289.41 296.54 134.02  29 38 17  156.11 157.58 72.59  50 32 14  74.43 80.76 26.32  31 10 23  0 Air-dry Sat.  250.88 318.23 120.56  34 18 6  220.99 234.29 145.20  46 35 12  218.53 44 237.33 ' 35 117.88 30-  129.21 181.73 78.61  37 38 26  •52.42 53.16 26.66  51 33 24  0 Air-dry Sat.  264.93 284.46 155.59  37 41 19  213.56  43 51 19  231.94 195.34 133.27  199.37 157.83 64.53  43 14 45  -59.87 59.61 28.85  35 25 14  O O  50  0 Air-dry Sat.  33.47 33.12 43.86  41 24 9  7©  0 Air-dry Sat.  30.74 28.32 36.79  25  0 Air-dry Sat.  50  70  latewoo<  W/ • > Ln; l b / i n - 9  15.0  30.04 44.86 35.05  25  0 Air-dry Sat.  Earl;  o  Mean v a l u e s o f work t o maximum t e n s i o n load and t h e i r c o e f f i c i e n t s of v a r i a t i o n .  43.85 43.09 -38.60  211.01  152.76  41 48 32  Table 6.  Moisture content o f a i r - d r y specimens-at  I n t e g r a l i r ]"adiation dose  (megarad)  Zone  Drying C o n d i t i o n s  test.  Temp. °C  *  EMC %  EMC %  EMC %  EMC %  EMC %  o o  25  68  10.46  11.12  11.26  11.54  11.75  50  73  13.15  12.54  12.95  12.31  12.51  70  78  15.44  15.53  14.22  14.62  13.21  25  68  10.61  11.34  11.58  12.16  12.53  50  73  12.70  12.60  12.58  12.34 -  12.42  70  78  14.12  13.92 ;  13.05  13.18  12.96  R  H  Latewood  o3  Rel.  Hum.  0.0  0.1  1.0  10.0  15.0  132  Table 7.  Dose  I n t r i n s i c v i s c o s i t y o f c e l l u l o s e i n Douglas f i r as measured a f t e r exposure o f wood t o v a r i o u s dosage l e v e l s o f gamma r a d i a t i o n . I n c r . Sample.  negarad  No.  No.  0.0  45 45 46 46 47 47  1 2 1 2 1 2  Average  0.1  45 45 46 46 47 47  1 2 1 2 1 2  Average  1.0  45 45 46 46 47 47  1 2 1 2 1 2  10.0  1 2 1 2 1 2  Average :  15.0  45 45 46 46 47 47 Aver* ige  34.208 34.189 33.470 35.944 34.100 33.632  Latewood Earlywood CV M cont. CV N cont, V i s e . dl/g fo 6.17 6.28 6.11 2.52 0.59 4.82  1 2 1 2 1 2  36.707 35.735 35.800 37.621 34.620 35.108  5.53 6.65 7.84 1.63 5.90 4.39  3.45 3.43 3.53 3.41 3.50 3.65  34.257 4.42 13.54  35.932 5.32  3.50  13.42 13.56 13.43 13.40 13.11 13.19  34.923 3.34 35.048 1.29 36:T34 0.46 34.775 3.42 32.841 0.72 33.412 0.28  3.52 3.48 3.43 3.68 3.43 3.50  32.801 4.95 13.35  34.522 1.59  3.51  1.90 0.92 1.90 1.33 2.65 4.15  3.79 3.80 3.64 3.84 3.72 3.89  21.142 2.14  3.78  0.85 1.20 1.28 2.01 3.19 2.45  3.48 4.00 3.57 3.65 3.81 3.86  7.985 1.83  3.73  3.16 8.43 9.44 5.36 6.48 7.31  2.99 3.08 3.56 3.62 3.20 3.29  32.451 31.017 32.375 32.499 35.383 33.078  19.739 21.798 20.627 21.182 21.206 21.274  2.71 0.32 4.02 9.26 2.19 1.18  2.35 3-58 2.68 1.63 1.88 0.72  13.51 13.43 13.83 13.40 13.57 13.49  13.64 13.38 13.67 13.50 13.61 13.67  20.971 2.14 13.58  Average 45 45 46 46 47 47  Vise. dl/g  6.758 6.757 7.288 7.448 7.449 7.532  3.95 2.14 0.20 5.44 1.05 2.30  13.88 14.11 13.92 13.88 13.69 13.76  7.205 2.51 13.87 2.442 2.444 2.620 2.141 2.004 2.367  8.18 5.02 2.16 12.64 tt.00 8.37  13.36 13.41 12.67 13.39 13.71 13.37  2.336 8.40 13.32  21.809 20.639 21.646 21.416 20.967 20.374  8.107 7.455 8.477 8.476 7.866 7.529  2.712 3.066 1.906 2.010 2.441 1.675  2.302 6.70 13.29  Table 8.  Cellulose  degree o f p o l y m e r i z a t i o n i n Douglas f i r wood measured  a f t e r exposure t o v a r i o u s i n t e g r a l doses o f gamma r a d i a t i o n . Increment 1MO .  TJ  o  H U  <a  o CD -P  a m  0.0 1 2 1 2 1 2  45 45 46 46 47 47 Average  I n t e g r a l I r r a d i a t i o n Dose . (megarad)  Sample  • •  45 45 46 46 47 47 Average :  1 2 1 2 1 2  0.1  1.0  10.0  15.0  5233 5228 5054 5664 5206 5093  4812 4481 4794 4823 5523 • 4960  2259 2614 2409 2505 2510 2522  539 539 592 608 608 617  167 167 180 144 134 161  5246  4899  2470  584  159  5859 5611 5628 6096 5334 5454  5408 5439 5712 5372 4904 5040  2616 2411 2587 2546 2468 2366  676 609 716 716 651 617  187 214 127 135 167 111  5660  5313  2499  664  157  Table 9. Source DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL  A n a l y s i s o f v a r i a n c e o f earlywood u l t i m a t e t e n s i l e DP 4 2 2' 8 8 4 16 225 269  v  SS  406,716,000 49,594,500 76,967,300 10,008,300 •"5,608,930  1,892,120  4,877,790 163,709,260 719,374,000  MS 101,679,000 24,797,200 38,483,500 1,251,040 701,116 473,032 304,862 727,597  strength.  F 139.74 34.32 52.89 1.72  0.96 0.65 0.42  ** ** ** NS NS NS NS  Table 10. A n a l y s i s o f v a r i a n c e o f latewood u l t i m a t e t e n s i l e Source DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL  DP  SS  4 2 2 8 8 4 16 225 269  5,716 ,280, 000 838 ,995, 000 8, 202 ,570, 000 194 ,205, 000 337 ,021, 000 66 ,689, 000 181 ,628, 000 8, 074 ,212, 000 23, 511 ,600, 000  MS 1,429 ,070, OOC 419 ,497, OOC 4,101 ,280, OOC 24 ,275, 70C 42 ,127, 60C 16 ,672, 20C 11 ,351, 70C 35 ,885, 40C  strength.  P 39.82 11.69 114.29 0.68 1.17 0.46 0.32  ** s i g n i f i c a n t a t the 0.1 p e r cent l e v e l of p r o b a b i l i t y * s i g n i f i c a n t a t the 0.5 p e r cent l e v e l of p r o b a b i l i t y NS non s i g n i f i c a n t  ** ** **  NS NS NS NS  Table  11. A n a l y s i s o f v a r i a n c e of earlywood e l a s t i c i t y i n t e n s i o n .  Source DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL  Table  DE 4 2 2 8 8 4 16 225 269  SS 414,354 208,035 1,313,200 15,538 10,485 37,503 24,159 1,040,816 3,064,090  MS 103,588 104,017 656,601 1,942 1,311 9,376 1,510 4,627  F 22.39 22.48 141.91 0.42 0.28 2.03 0.33  ** ** ** NS NS NS NS  12. A n a l y s i s o f v a r i a n c e o f latewood e l a s t i c i t y i n t e n s i o n .  Source DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL  DF 4 2 2 8 8 4 16 225 269  SS, 338,448 3,720,300 13,702,000 202,785 701,660 458,988 661,025 26,032,494 45,817,700  MS 84,612 1,860,150 6,851,040 25,348 87,708 165,256 28,687 115,700  F 0.73 16.09 59.21 0.22 0.76 1.43 0.25  NS ** ** NS NS NS NS  Table 13. A n a l y s i s o f v a r i a n c e of earlywood u l t i m a t e t e n s i l e Source ,  DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL  DP 4 2 2 8 8 4 16 225 269  SS .002426850 .000009724 .000447140 .000045416 .000308967 .000108169 .000037198 .000893636 .004277100  MS .000606713 .000004862 .000223570 .000005677 .000038621 .000027042 .000002325 .000003972  P 152.75 1.22 56.29 1.43 9.72 6.81 0.59  Table 14. A n a l y s i s o f v a r i a n c e o f latewood u l t i m a t e t e n s i l e Source DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL  DP  SS  4 2 2 8 8 4 16 225 269  .003855360 .000024439 .000218715 .000022977 .000075749 .000272998 .000144660 .001557769?*' .006172259  MS .000963841 .000012220 .000109357 .000002872 .000009469 .000068250 .000009041 .000006923  strain.  ** NS ** NS ** ** NS  strain. P  139.22 1.77 .15.80 0.41 1.37 . 9.86 , 1.31  **  NS  #*  NS NS  **  NS  Table  15. A n a l y s i s o f v a r i a n c e o f work t o maximum t e n s i o n l o a d i n earlywood.  Source DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL  Table  16.  Source DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL  DP  SS  4 2 2 8 8 4 16 225 269  34,022.2 3,193.7 481.5 1,414.8 1,736.4 715.3 1,518.1 13,843.2 56,925.2  MS . 8,505.6 1,596.8 240.7 176.9 217.1 178.8 94.9 61.5  P 138.30 25.96 3.91 2.-88 3.53 2.91 1.54  ** ** * ** ** •* NS  A n a l y s i s of v a r i a n c e o f work t o maximum t e n s i o n l o a d i n latewood. DP 4 2 2 8 8 4 16 225 269  SS 1,350,060 58,564 612,501 35,931 100,215 40,733 37,513 1,046,313 3,281,830  MS 337,516 29,282 306,250 4,491 12,527 10,183 2,345 4,650  P 72.58 6.30 65.86 0.97 2.69 2.19 0.50  ** ** ** NS ** NS NS  Table 17. A n a l y s i s o f v a r i a n c e o f u l t i m a t e t e n s i l e s t r a i n i n c l u d i n g cellulose  test f o r  c h a i n l e n g t h (DP),temperature (T),moisture content (MC),  wood zone ( Z ) , and increment ( I ) . Source DP T MC I Z DPxT DPxMC DPxI DPxZ TxMC Txl TxZ MCxI MCxZ IxZ • DPxTxMC ' DPxTxI DPxTxZ DPxMCxI DPxMCxZ DPxIxZ TxMCxI TxMCxZ TxIxZ MCxIxZ ERROR TOTAL  "  DP  SS  4 2 2 2 1 8 8 8 4 4 4 2 4 2 2 16 16 8 16 8 8 8 4 4 4 390 539  .00619136 .00000312 .00007827 .00000648 .00153345 .00003191 .00019744. .00001411 .00010590 .00034621 .00001036 .00003372 .00002450 .00059411 .00007228 .00011639 .00004077 .00003242 .00024057 .00019286 .00010315 .00005785 .00003382 .00002835 .00011033 .00182949 .01202920  MS .00154784 .00000156 .00003914 .00000324 .00153345 .00000399 .00002468 .00000176 .00002648 .00008655 .00000259 .00001686 .00000613 .00029705 .00003614 .00000727 .00000255 .00000405 .00001504 .00002411 .00001289 .00000723 .00000845 .00000709 .00002758 .00000469  P 329.95 0.33 8.34 0.69 326.89 0.85 5.26 0.37 5.64 18.45 0.55 3.59 1.30 63.32 7.70 1.55 0.54 0.86 3.20 5.13 2.74 1.54 1.80 1.51 5.87  *#  NS  **  NS  **  NS  #*  NS  ** **  NS  *  NS  ** **  NS NS NS  ** **  *•#  NS NS NS  Table 18. ri S t r e n g t h to  i  •a cd  • CD •P cd Hi  Regressions of s t r e n g t h p r o p e r t i e s on 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 (V), temperature ( T ) , and moisture content (M). Regression  Property  Equation  R  2  Strength Elast. Strain Max.Work  S=2598+2692 logV -21.991 -1.92M E=465.4+75.44 logV -1.33T -0.26M^ _ e=4.76x10'+5.09x103logV-2.29x1 O^T-1.30x10 MN-1.19x10% logV+6.33xlO'T M W=-0.46+31 .65 logV-0.0lT-0.019M^-0.213T logV+0.28lMc: logV+0.005T M  .7102 .5753 .'6847 .6865  Strength Elast. Strain Max.Work  S=19133+9815 logV -85.64T -20.32M E=2258-85.13V-6.08T-0.82M^ . , e=6.97x1 (5346.19x1 03logV-3.34x1 S^T-9.40x10°M^+3.70x10°T M W=70.03+155.73 logV-0.64T-2.32M -0.43M logV  .6007 .3638 .6796 .5690  2  6  2  2  Table 19.  Regression  R  Equation  2  Earlyw.  • Strength ri P r o p e r t y  Regressions o f s t r e n g t h p r o p e r t i e s on c e l l u l o s e degree of p o l y m e r i z a t i o n (Dj,temperature ( T ) , and moisture content (M).  Strength Elast. Strain Max.Work  S= -831.0+2042.9 logD -22.0 T -1.9 M E=37.0+56.9 logD -133T -0.26M^ e=-3.77x103+4.56x103logD-2.51x10 T-7.01x10'ffir+3.42x10 M logD+8.25x10'T M W=-44.4+25.01 logD+0.26T-0.022M -0.l6T logD+0.13M logD-K).0042T M  .7029 .5727 .6583 .6787  •  Strength Elast. Strain Max.Work  S=6571+7460 logD -85.6T -20.3M E=2251-3909 D - 6 . 0 8 T -0.82 W~ ~ r r e=-3.54x103+6.23x103logD-3.34x10 T-9.40x15¥+3.69x10°T W=-105.1+109.1 logD-0.65T-0.22M^+0.46M logD  .5984 .3635 .6751 .5702  !3  CD -P cd H)  2  ?  P  2  2  0  p  M  Table 20. •  P e r cent v a r i a t i o n s i n s t r e n g t h p r o p e r t i e s accounted f o r by v a r i a b l e s tested.  Strength Property  tsi  i  P a r t i a l Corr e l a t i o n Coeff i c i e n t x J00 Total I n t r . V i s c . E emperature Moist.Cont. I n t e r a c t .  Tensile strength Elasticity H Ultimate S t r a i n Maximum Work  54.96 9.96 42.36 63.38  5.93 5.94 0.55 0.30  10.13 41.63 2.75 '.5228  Tensile Strength Elasticity Ultimate S t r a i n Maximum Work  23.27 0.08 61.87 40.19  3.08 7.71 0.60 1.24  33.72 28.59 8.17 15.02  latew.  03  Table 21.  Property  i ET le na ss it li ec i tSyt r e n g t h latew.  03  -2.68 0.45  60.07 36.38 67.96 56.90  Simple c o r r e l a t i o n c o e f f i c i e n t s between t e n s i l e s t r e n g t h p r o p e r t i e s and experimental v a r i a b l e s .  • Strength  CSJ  22.81 1 .89  71.02 57.53 68.47 70.75  Intr.Visc.  DP  Temperature Moist.Cont.  0.7350 0.7676  -0.2620 -0.2584 -0.0519 -0^2342  -0.3168 -0.6492 . 0.3190 -00.0151  0.4802 0.0219 0.7843 0.6227  -0.1822 -0.2838 -0.1560 -0.1167  -0.5827 -0.5379 0.0462 -0.4113  Ultimate S t r a i n Maximum Work  0.7382 0.3132 0.7408 0.7703  0.7332 0.3091  Tensile Strength Elasticity Ultimate S t r a i n Maximum Work  0.4826 0.0281 0.7872 0.6230  141  Table 22.  Comparison between c e l l u l o s e DP v a l u e s  obtained  by u s i n g two e m p i r i c a l methods o f conversion from intrinsic viscosity.  Wood zone  ft o o  ft o EH  Radiation dose megarad  Intrinsic Viscosity dl/g  DP by iV ] DP by emp. dependent exponential K factor relationship  0.0  34.257  5246  5246  0.1  32.801  4899  4979  1 .0  20.971  2470  2958  10.0  7.205  584  853  15.0  2.336  159  230  0.0  35.932  5660  5660  0.1  34.522  5313  5400  1.0  21.142  2499  3050  10.0  7.985  664  982  15.0  2.302  157  231  CM  0 1 2  3  4 NO MARK  F i g u r e 1.  UNTREATED CONTROL RADIATED AT 0.1 megarad RADIATED AT 1.0 megarad RADIATED AT 10.0 megarad RADIATED AT 15.0 megarad NOT INCLUDED IN THE EXPERIMENT  Experimental m a t e r i a l s e l e c t e d a t random from three growth increments of a Douglas f i r t r e e . Random assignment o f tceatments by gamma r a d i a t i o n i s a l s o shown.  143  o<  1  1  1  •10  -20  -30  i i  -40  — i  50  Radial distance from the beginning of the 45 th- increment (in-)  F i g u r e 2.  Intra-increment v a r i a t i o n i n u l t i m a t e t e n s i l e s t r e n g t h i n three growth increments o f a Douglas f i r t r e e .  144  I000 -  IOOO-  IOOO -  IOOO -  •IO  -20  -30  -40  -50  Radial distance from the beginning of the 45 th- increment (in)  F i g u r e 3. Intra-increment v a r i a t i o n i n t e n s i o n - p a r a l l e l t o - g r a i n e l a s t i i c modulus i n three growth r i n g s of a Douglas f i r t r e e .  145  0 IO  0 20  0-30  0-40  050  Radial distance from the beginning of the 45th- increment (in)  Figure 4.  Intra-increment v a r i a t i o n i n s p e c i f i c g r a v i t y i n three growth r i n g s o f a Douglas f i r t r e e .  82i  i  1  1  1  1  growth ring 4 5 + growth ring 4 6 A growth ring 4 7 0  81 -  1  1  1  r  70  80  90  A  75-  0  10  20  30  40  50  60  100  Relative position in growth ring (%)  F i g u r e 5.  D i s t r i b u t i o n o f h o l o c e l l u l o s e i n three groxrth increments o f a Douglas f i r "tree.  147 20 80  EH pq  o o  o 15 o  75 70  5  6  \: I  ,5-4 5 POSITION IN RING  1 2 3 4 5 6 POSITION IN RING  10 EH  fe!  pq  pq  EH  EH  o o  o o  Ssi 'A  <i EH  O  M  H H ^ POSITION I N SING  1 2 3 4 5 6 POSITION IN RING  1 .0  pq EH  §0.5 o  T 1  INCREMENT  .'45  INCREMENT  '46  INCREMENT  "'47  o  o +—+  A  A  \ 2 1 4 i 6' POSITION IN RING  F i g u r e 6.  Intra-increment v a r i a t i o n i n carbohydrates i n three growth increments o f a Douglas f i r t r e e , expressed as percentages o f t o t a l h o l o c e l l u l o s e .  F i g u r e 7.  Converted arbor press with a d j u s t a b l e c u t t i n g d i e used f o r t e n s i o n t e s t specimen p r e p a r a t i o n .  F i g u r e 8.  Tension t e s t specimens enclosed i n polyethylene test  bags.  1 50  Pigure 10.  Table model I n s t r o n t e s t i n g instrument  equipped  with constant temperature c a b i n e t .  F i g u r e 11.  M i c r o c a t o r d i a l i n d i c a t o r used f o r t h i c k n e s s measurements.  F i g u r e 15.  Equipment used i n v i s c o s i t y measurements of cellulose nitrate  solutions.  155  0  10  20  30  CELLULOSE INTRINSIC VISCOSITY  F i g u r e 14.  40  50  (dl/g)  Conversion f a c t o r between degree of p o l y m e r i z a t i o n and i n t r i n s i c v i s c o s i t y i n r e l a t i o n t o i n t r i n s i c viscosity.  60  156  o  I—'  1  1  —  1  0 1 „ 10 15 INTEGRAL DOSE OF GAMMA RADIATION (megarad) N  F i g u r e 15. E f f e c t o f gamma r a d i a t i o n intrinsic viscosity.  o f wood on c e l l u l o s e  H  INTEGRAL IRRADIATION DOSE (megarad) F i g u r e 16. E f f e c t o f gamma r a d i a t i o n o f wood on c e l l u l o s e degree o f p o l y m e r i z a t i o n .  157 25°C  TO  13  TO  S  INTRINSIC VISCOSITY ISCOSITY ( d l / g )  TO-  2000 3000 %000 5000, 1000 CELLULOSE DEGREE OF POLYMERIZATION F i g u r e 17. U l t i m a t e t e n s i l e s t r e n g t h as a f u n c t i o n o f c e l l u l o s e c h a i n l e n g t h , moisture content,and temperature.  30 35 0 5 10 15 20 25 CELLULOSE INTRINSIC VISCOSITY (dl/g)  b i'50-  i6oov: sdoo  '5600 4 6 0 0  bboo*  CELLULOSE DEGREE OF POLYMERIZATION  )-3  o  00  F i g u r e 3 8. E l a s t i c i t y o f Douglas f i r i n t e n s i o n p a r a l l e l t o g r a i n as a f u n c t i o n o f temperature,moisture content,and c e l l u l o s e chain length.  .0150^  . 01255 .0100§ fe w .0075^ CQ  .0050^ .0025^ 3  •IO 15 20 25 30 35 QELLULQSE INTRINSIC, VISCOSITY .(dl/gL 0 150 1000 2000 3000 4000 5000 CELLULOSE DEGREE OF POLYMERIZATION F i g u r e 19.  H3  U l t i m a t e s t r a i n o f Douglas f i r i n t e n s i o n p a r a l l e l to g r a i n as a f u n c t i o n o f temperature, moisture content., ..and c e l l u l o s e c h a i n l e n g t h .  CELLULOSE DEGREE OP POLYMERIZATION Figure 20.  >  Work t o maximum l o a d o f Douglas f i r i n tensidn* p a r a l l e l t o g r a i n as a f u n c t i o n o f temperature, moisture content, and c e l l u l o s e c h a i n l e n g t h .  *=> 2000 o §  1000  Hi  30  o  10 15 20 25 CELLULOSE INTRINSIC VISCOSITY Cdl/g)  F i g u r e 21.  Diagram showing r e l a t i o n s h i p between u l t i m a t e t e n s i l e s t r e n g t h and 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 a t 50°C temperature and a i r dry moisture c o n t e n t . c o n d i t i o n . Means and s c a t t e r about means are a l s o shown.  35  162  10  20  30  40  50  60  70  80  RELATIVE POSITION IN GROWTH INCREMENT  Figure 22.  90  100  (%)  Intra-increment v a r i a t i o n o f t e n s i l e s t r e n g t h p a r a l l e l t o g r a i n i n Douglas f i r determined a f t e r exposure o f wood t o v a r i o u s doses o f gamma r a d i a t i o n .  163  pq  O  o  co pq  .LATEWOOD  M  o 5 S o EH ^O4 0  \  \  §30 O P"H  co pq CQ § 2 0 O  a  al  EH EH  pq  10  EH  o CQ o EH  0 5 10 i~5 20 25 30" ^5~ CELLULOSE INTRINSIC VISCOSITY (dl/g) 0 1 0 0 0 2 0 0 0 3000 4000 5000 CELLULOSE DEGREE OF POLYMERIZATION  F i g u r e 23.  I n f l u e n c e o f c e l l u l o s e c h a i n l e n g t h on moisture s e n s i t i v i t y o f t e n s i l e s t r e n g t h o f Douglas f i r wood.  164  APPENDIX  165 FORTRAN PROGRAM USED FOR CALCULATION OF INTRINSIC VISCOSITY VALUES OF CELLULOSE.  FF=.0299558 GN=334543.7 T0=163.5 PRINT 1 1 FORMAT(45H  NO.  VSP  VSPC  (V)  4 READ 5,N,T,C,PN 5  FORMAT(16,F6.1,F6.5,P6.2) VSP=(T/T0)-1. VSP2=VSP*(1.+(FF*(T+TO)/T)) G=GN/T VIG=(VSP2/C)/(1.+.3*VSP2) P1=.0039*VIG-.000000008*(VIG**4) X=Pl*L0GF(G/500.)+LOGF(VIG) VI51=2.71828**X P2=.0039*VI51-.000000008*(VI51**4) Y=P2*LOGF(G/500.)+L0GF(VIG) VI52=2.71828**Y P3=.0039*VI52-.000000008*(VI52**4) Z=P3*LOGF(G/500.)+LOGF(VIG) VI5=2.71828**Z A=1.833-.0589*PN B=Z+LOGF(A)+(14.15-PN)*.114*2.3026 VI5T=2.71828**B VI5T2=VI5T*1.04716 PRINT 20,N,VSP,VSP2,VI5,VI5T,VI5T2  20 F0RMAT(I6,F8.4,F8.4,P8.4,F8.4,F8.4) GO TO 4 END  (V)T  (V)T20)  0  1  2 3 4  NO MARK  Figure 1.  -UNTREATED CONTROL RADIATED AT 0.1 megarad RADIATED AT 1.0 megarad RADIATED AT 10.0 megarad RADIATED AT 15.0 megarad. NOT INCLUDED IN THE EXPERIMENT  Experimental m a t e r i a l s e l e c t e d a t random from three growth increments of a, Douglas f i r t r e e . Random assignment o f treatments by gamma r a d i a t i o n i s a l s o shown. / '  Ol  1  •10  1 "20  1  -30  •  1—L_ -40  U  -50  Radial distance from the beginning of the 45 th- increment (in)  F i g u r e 2.  Intra-increment v a r i a t i o n i n u l t i m a t e t e n s i l e s t r e n g t h i n three growth increments of a Douglas f i r t r e e .  •10  -20  -30  -40  -50  Radial distance from the beginning of the 45 th- increment (in) Fugere 3, Intra-increment v a r i a t i o n i n t e n s i o n - p ? . r ? J l e l ~ t o - g r a i n e l a s t i i c modulus i n three growth r i n g s of a Douglas f i r t r e e .  010  0-20  0 30  0-40  050  Radial distance from the beginning of the 45th- increment (in)  Figure 4.  Intra-increment v a r i a t i o n i n s p e c i f i c g r a v i t y i n three growth r i n g s of a Douglas f i r t r e e .  82  ° growth ring 45 + growth ring 46 * growth ring 47  81  0  R =-6239 R=-7899 SE = -8431 2  E  75  0  10  20  30  40  50  60  70  80  90  100  Relative position in growth ring (%)  Figure: 5.  D i s t r i b u t i o n -of h o l o c e l l u l o s e i n three growth increments o f a Douglas f i r t r e e .  20 EH  pq  80 EH  EH  pq  o o  75  o o  o  15  Is!  s  70  4 t  1 2 3 4 5 b" POSITION IN RING  1 2 3 4 5 6 POSITION IN RING ~  10* EH  pq  pq  g  EH & O O  o o  !25  «;  EH O  <  Hi  T i  2  j  4  5' ^'  POSITION IN 1ING  1  2  3  4  5 6  POSITION IN RING  1 .0  pq EH  o < o u  'INCREMENT  45  o  o  INCREMENT  46  +  +  INCREMENT  47  A  -A  pq  f  i ^ 'j 4 5 6* POSITION IN RING  Figure 6.  Intra-increment v a r i a t i o n i n carbohydrates i n three growth increments o f a Douglas f i r t r e e , expressed as percentages o f t o t a l h o l o c e l l u l o s e .  10  20  30  40  50  60  '  70  LENGTH OF NITRATION TIME (hrs)  Figure 13.  C e l l u l o s e chain depolymerization l e n g t h of n i t r a t i o n time.  in-the n i t r a t i n g a c i d as r e l a t e d to  Figure 14.  Conversion f a c t o r between degree of p o l y m e r i z a t i and i n t r i n s i c v i s c o s i t y i n r e l a t i o n to i n t r i n s i c viscosity.  O  I  I  i  0 1 10 INTEGRAL DOSE OF GAMMA RADIATION  F i g u r e 15. E f f e c t o f gamma r a d i a t i o n intrinsic viscosity.  I  15 (megarad).  o f wood on c e l l u l o s e  is;  o  M EH <U CS]  ,  ,  M  0  1 10 15 INTEGRAL IRRADIATION DOSE (megarad) ;  F i g u r e 16. Effect- o f gamma r a d i a t i o n o f wood on c e l l u l o s e degree o f p o l y m e r i z a t i o n .  25°C  To—T5—m 0 150  INTRINSIC VISCOSITY 1000 2000 30  CELLULOSE DEGREE OP  000 5000.-  POLYMERIZATION  Figure 17. U l t i m a t e t e n s i l e s t r e n g t h as a f u n c t i o n of c e l l u l o s e chain, l e n g t h , moisture content,and temperature.  0 5 10 ' 15 20 25 30 35 CELLULOSE INTRINSIC VISCOSITY (dl/g)  fr-f^o"  looo-i,  2doo 'jboo 4600 bborr  CELLULOSE DEGREE OP POLYMERIZATION  o CO  Figure 18. E l a s t i c i t y of Douglas f i r i n t e n s i o n p a r a l l e l to g r a i n as a f u n c t i o n of temperature,moisture content,and c e l l u l o s e chain l e n g t h .  10 15 20 25 30 35 CELLULOSE INTRINSIC, VISCO.SITY .(dl/g). 0 150 1000 2000 3000 4000 5000 CELLULOSE DEGREE OF POLYMERIZATION  figure 19.  U l t i m a t e s t r a i n of Douglas f i r i n t e n s i o n p a r a l l e l t o g r a i n as a f u n c t i o n of temperature, moisture content, ..and..cellulose, .chain.length.  0 150  1000  2000  3000 4000 5000  CELLULOSE DEGREE OP POLYMERIZATION  i'igure 20.  •  5  ^ a Work to maximum l o a d of Douglas f i r i n t e n s i o n p a r a l l e l to g r a i n as a f u n c t i o n of temperature, moisture content, and c e l l u l o s e c h a i n l e n g t h .  •H CO  CELLULOSE INTRINSIC  F i g u r e 21.  VISCOSITY ( d l / g )  Diagram showing r e l a t i o n s h i p between u l t i m a t e t e n s i l e s t r e n g t h and 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 a t 50°C temperature and a i r dry moisture c o n t e n t , c o n d i t i o n . Means and s c a t t e r about means are a l s o shown.  0  10  20  30  40  50  60  70  80  90  100  RELATIVE POSITION IN GROWTH INCREMENT (#)  Figure 22.  Intra-increment v a r i a t i o n of t e n s i l e s t r e n g t h p a r a l l e l t o g r a i n i n Douglas f i r determined a f t e r exposure of wood t o v a r i o u s doses of gamma r a d i a t i o n .  o pq o EH P q  LATEWOOD  M PH O CS S  o  EH  O  « s o Pq co pq ca 55  20  EH EH  cti is; is; w pq EH «  10  12!  EH O CQ O  0 5 10 15 20 25 30 35 CELLULOSE INTRINSIC VISCOSITY (dl/g) 0 1000 2000 3000 4000 5000 CELLULOSE DEGREE OP POLYMERIZATION  f i g u r e 23.  Influence of c e l l u l o s e chain l e n g t h on moisture s e n s i t i v i t y of t e n s i l e s t r e n g t h o f Douglas f i r wood.  

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.831.1-0105581/manifest

Comment

Related Items