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 Division) University of B r i t i s h Columbia 1959 M.P. Yale University 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 thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1963 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that per-m i s s i o n f o r extensive copying of t h i s t h e s i s f o r . s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that copying or p u b l i -c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n p e r mission. Department of Forestry ' The U n i v e r s i t y . o f B r i t i s h Columbia, Vancouver 8, Canada. Date September 27, 1963 PUBLICATIONS I f j u , G, and R.W. Kennedy* 1962. Some variables a f f e c t i n g microtensile strength of Douglas f i r For. Prod. J . .12(5): 213-217. Kennedy, R.W. and G. I f j u . 1962. Application of microtensile t e s t i n g to thin wood sections Tappi 45(9) : 725-733. Kellogg, R.M. and G. I f j u . 1962. Influence of s p e c i f i c gravity and certain other factors on the t e n s i l e properties of wood. For. Prod. J . 1 2(10): 463-407. I f j u , G. 1962. S t a t i s t i c s on pulp and paper. In J.A. Crosse: Proceedings of the seminar on forest reservations in the U.S.S.R. and th e i r u t i l i z a t i o n . Faculty of Forestry, The Uni-v e r s i t y of B r i t i s h Columbia. pp. 52-59. I f j u , G., R.W. Wellwood, and J.W. Wilson. 1963. Intra-increment relationship of s p e c i f i c g r a v i ty, microtensile strength and e l a s t i c i t y i n Douglas f i r . Paper presented to the an-nual Spring Conference, P a c i f i c Coast Branch, Canadian Pulp & Paper Association, May 9 - 1 1 , 1963, Harrison Hot Springs B. C. The U n i v e r s i t y of B r i t i s h Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY of GEZA IFJU B.SoF., The Uni v e r s i t y of B r i t i s h Columbia (Sopron Div i s i o n ) 1959 M.F., Yale University, 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.H.G. Smith J.A.F. Gardner R.W. Wellwood P.G. Haddock J.W. Wilson External Examiner: R.W. Kennedy U n i v e r s i t y of Toronto INFLUENCE OF CELLULOSE CHAIN LENGTH ON THE MECHANICAL BEHAVIOR OF DOUGLAS FIR WOOD IN TENSION PARALLEL TO GRAIN ABSTRACT The c e l l u l o s e f r a c t i o n in 100~micron thick microtome sections from three growth increments of a Douglas f i r tree was systematically degraded through random sc i s s i o n of chains by means of 0,1, 1.0, 10.0, and 15.0 megarad doses of gamma i r r a d i a t i o n . Degree of c e l l u l o s e poly= merization (DP) was estimated from results 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 solutions of ce l l u l o s e n i t r a t e i n acetone. Control and i r r a d i a t e d samples were tested i n tension p a r a l l e l to grain by employing a micro scale test method. Tests were done at 25, 50, and 70°C temperatures i n combination with moisture-free, air-dry, and water~saturated conditions of test specimens. Ultimate t e n s i l e strength, an e l a s t i c i t y constant, ultimate t e n s i l e s t r a i n , and work to maximum te n s i l e load have been calculated from experimental data. Result were analyzed s t a t i s t i c a l l y in r e l a t i o n to ce l l u l o s e chain length, temperature, and moisture content. Regres sion equations based on experimental r e s u l t s have been constructed. These explain a large part of the v a r i a -tions i n t e n s i l e strength properties and are reported as three-dimensional diagrams. It i s shown that t e n s i l e strength behavior of 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 . Strength properties of latewood are not only higher by a fa c t o r of approximately 2 to 8 than those of earlywood but also the response of the two growth zones to changes i n c e l l u l o s e chain length, temperature, and moisture 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 -ferent deformation mechanisms i n tension p a r a l l e l to grain of the two growth zones. I t i s suggested that de-formation 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 int e r - t r a c h e i d , phenomenon. Decrease of c e l l u l o s e DP reduced t e n s i l e strength, ultimate s t r a i n , and work to maximum Load more i n the low than i n the high DP regions. This i s explained by the increasing importance of inter-chain 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 properties are but l i t t l e affected 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 cel= lulose 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 applied, 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 test from the moisture~free to the water=saturated condition re-duces strength properties of Douglas f i r by approximately 20 to 50 per cent. The reductions in latewood strength are s i g n i f i c a n t l y higher than i n earlywood, A convex up-ward curve configuration r e l a t i n g strength and e l a s t i c i t y to moisture content i s suggested from the experimental data. E f f e c t of temperature on strength properties of Douglas f i r within the range of 25 to 70°C i s minor i n comparison with 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 strength c h a r a c t e r i s t i c s of 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 of wood having c e l l u l o s e of long-chain structure. This behavior of wood i n ten-sion i s also explained by the slippage mechanism of deformation. GRADUATE STUDIES F i e l d of Study; Forestry Research i n Wood Anatomy Problems i n Forest Products S t a t i s t i c a l Methods i n Forest Research General Forestry Seminar Research i n the Properties of Wood Products R.W. Wellwood R.W. Wellwood J.H.G. Smith The S t a f f R.W. Wellwood J.W. Wilson Related F i e l d s : D i g i t a l Computer Programming Biometry Elements of Material Science Organic Chemistry Charlotte Froese D.P. Ormrod W.M. Armstrong J.P. Kutney i . ABSTRACT The cellulo s e f r a c t i o n i n 100-micron thick micro-tome sections from three growth increments of a Douglas f i r tree was sytematically degraded through random s c i s s i o n of chains by means of 0.1, 1.0, 10.0, and 15.0 megarad doses of gamma i r r a d i a t i o n . Degree of cellulo s e poly-merization (DP) was estimated from results 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 solutions of cellulose n i t r a t e i n acetcne. Control and i r r a d i a t e d samples were tested i n tension p a r a l l e l to grain by employing a micro-scale test method. Tests were done at 25, 50, and 70°C temperatures i n combination with moisture-free, air-dry, and water-saturated conditions of test specimens. Ultimate t e n s i l e strength, an e l a s t i c constant, ultimate t e n s i l e s t r a i n , and work to maximum te n s i l e load have been calculated from experimental data. Results were s t a t i s t i c a l l y analyzed i n r e l a t i o n to cellulose chain length, temperature and moisture content. Regression equations based on experimental results have been constructed. These explained a large part of the variations i n t e n s i l e strength properties and are reported as three-dimensional diagrams. It i s shown that t e n s i l e strength behavior of Douglas f i r earlywood and latewood are d i s t i n c t l y d i f f e r -ent. Strength properties of latewood are not only higher i i . by a factor of approximately 2 to 8 than those of early-wood, but also the response of the two growth zones to changes i n cellulose chain length, temperature, and mois-ture content at test i s d i f f e r e n t . The above character-i s t i c s are due to di f f e r e n t deformation mechanisms i n tension p a r a l l e l to grain 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 primarily an inter-tracheid, phenomenon. Decrease i n cellulose DP reduced strength, ultimate s t r a i n , and work to maximum load more i n the low than i n the high DP regions. This i s explained by the increasing importance of inter-chain 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 properties are but l i t t l e affecte.d by changes i n cellulo s e DP i f the crystalline-amorphous r a t i o of cellulose i n wood i s not altered s i g n i f i c a n t l y by the treatment applied, 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 test from the moisture-free to the water-saturated con-d i t i o n reduced strength properties of Douglas f i r by approximately 20 to 50 per cent. The reductions i n l a t e -wood strength were s i g n i f i c a n t l y higher than i n earlywood. A convex upward curve configuration r e l a t i n g strength and e l a s t i c i t y to moisture content i s suggested from the experimental data. i i i . E f f e c t of temperature on strength properties of Douglas f i r within the range of 25 to 70°C i s minor i n comparison with that of moisture content. The r e l a t i o n -ship i s probably l i n e a r . Tensile strength characteristics of Douglas f i r wood with degraded cellulose are more sensitive to changes i n moisture content than are those of wood having c e l l u -lose of long-chain structure. This behavior of wood i n tension i s also explained by the slippage mechanism of deformation. \ x i i . ACKNOWLEDGEMENT The writer g r a t e f u l l y acknowledges his indebtedness to Dr. R. W. Wellwood, Professor, Faculty of Forestry, for his conscientious and s k i l f u l guidance during the whole of a three-year academic program; to Dr. J . W. Wilson, Asso-ciate Professor, Faculty of Forestry, f o r his valuable professional assistance both at the experimental stage and i n the analysis of the res u l t s ; to Dr. J . H. G. Smith, and Dr. G. G. S. Dutton members of the Faculty of Forestry, and the Faculty of Arts and Science, Department of Chemistry, respectively, f o r t h e i r advisory help; to Dr. R. W. Kennedy, Assistant Professor, Faculty of Forestry, University of Toronto, f o r the c r i t i c a l reading of the thesis; to Mr. A. G. Davies of Atomic Energy of Canada Limited, f o r the gamma i r r a d i a t i o n of the experimental material; to Mr. A. Kozak, Graduate Student, Faculty of Forestry, f o r assistance i n the s t a t i s t i c a l analyses; to Mr. L. Paszner, Graduate Student, Faculty of Forestry, f o r some of the i l l u s t r a t i o n s ; to the National Research Council of Canada, fo r providing the f i n a n c i a l means to carry out the project; and,last, but not lea s t , to Mrs. G. I f j u f o r her encouragement, understanding, and u n f a i l i n g patience. i v . TABLE OF CONTENTS Page TITLE PAGE ABSTRACT i TABLE OP CONTENTS i v ACKNOWLEDGEMENT x i i INTRODUCTION 1 MATERIAL AND METHODS 6 I MATERIAL 7 II METHODS 11 1. Degradation of Cellulose by Means of Gamma Radiation 11 A. Previous work 11 i ) Radiation chemistry of high polymers.. 12 i i ) Influence of gamma radiation on the chemical properties of wood and c e l -lulose - 14 i i i ) E f f ects of gamma radiation on the phys-i c a l and mechanical properties of wood and related materials 18 iv) E f f e c t of moisture content on degrada-t i o n by gamma rays 19 v) The af t e r - e f f e c t of gamma radiation... 19 B. Irr a d i a t i o n of Experimental Material by Gamma Rays 20 V . Page 2. Tension Test Methods 22 A. Preparation of Test Specimen 22 B. Test Variables 23 i ) Testing machine variables 23 i i ) Moisture content and temperature 24 3. Determination of Cellulose Degree of Polymer-i z a t i o n 28 A. Nit r a t i o n of Wood Samples 29 B. Determination of Nitrogen Content of Cellulose Nitrates 34 C. Vi s c o s i t y Measurements 36 D. Conversion of I n t r i n s i c V i s c o s i t y to DP Values 42 EXPERIMENTAL RESULTS 47 DISCUSSION 55 I INFLUENCE OF GAMMA RADIATION ON CELLULOSE CHAIN , LENGTH 55 II EFFECTS OF CELLULOSE CHAIN LENGTH ON STRENGTH PROPERTIES PARALLEL TO GRAIN 61 III 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 104 1. Variation i n Strength Properties Due to Treatments 104 2. Factors Influencing Tensile Strength Prop-ert i e s Inherent i n Wood 107 3. Variation i n Tensile Strength Properties Due to Experimental Error 111 CONCLUSIONS 114 REFERENCES 117 TABLES AND FIGURES 125 Table 1. Comparison of cellulos e DP values calculated f o r a sample with 35.0 dl/g i n t r i n s i c v i s -cosity, using various relationships 126 Table 2. Mean ultimate t e n s i l e strength values 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 values „and t h e i r coefficients of v a r i a t i o n 1 28 Table 4. Mean values of ultimate 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 values of work to maximum tension 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 130 Table 6. Moisture content of air-dry specimens at test 131 Table 7. I n t r i n s i c v i s c o s i t y of cellulos e i n Douglas f i r as measured a f t e r exposure of wood to v i i various dosage leve l s of gamma radiation... 132 Table 8. Cellulose degree of polymerization i n Douglas f i r wood measured a f t e r exposure to various i n t e g r a l doses of gamma radiation 133 Table 9. Analysis of variance of earlywood t e n s i l e strength 134 Table 10. Analysis of variance of latewood t e n s i l e • strength 134 Table 11. Analysis of variance of earlywood e l a s t i c i t y i n tension 135 Table 12. Analysis of variance of latewood e l a s t i c i t y i n tension 135 Table 13. Analysis of variance of earlywood ultimate t e n s i l e s t r a i n 136 Table 14. Analysis of variance of latewood ultimate t e n s i l e s t r a i n -. 136 Table 15. Analysis of variance of work to maximum tension load i n earlywood 137 Table 16. Analysis of variance of work to maximum tension load i n latewood 137 Table 17. Analysis of variance of ultimate t e n s i l e s t r a i n including test f o r cellulose chain length (DP), temperature (T), moisture con-tent (MC), wood zone (Z), and increment (I). 138 Table 18. Regression of strength properties on c e l -lulose 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) 139 v i i i Page Table 19. Regression of strength properties on c e l l u -lose degree of polymerization (D), temper-ature (T), and moisture content (M) 139 Table 20. Per cent variations i n strength properties accounted f o r by variables tested 140 Table 21. Simple correlation c o e f f i c i e n t s between te n s i l e strength properties and experimental variables .*.....~ 140 Table 22. Comparison between cellulos e DP values obtained by using two empirical methods of conversion from i n t r i n s i c v i s c o s i t y 141 Figure 1. Experimental material selected at random from three growth increments of a Douglas f i r tree. Random assignment of treatments i s shown 142 Figure 2. Intra-increment v a r i a t i o n i n ultimate ten-s i l e strength i n three growth increments of a Douglas f i r tree .* - 143 Figure 3. Intra-increment v a r i a t i o n i n tension-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 of a Douglas f i r tree.... 144 Figure 4. Intra-increment v a r i a t i o n i n s p e c i f i c gravity i n three growth increments of a Douglas f i r tree 145 Figure 5. D i s t r i b u t i o n of holocellulose i n three growth increments of a Douglas f i r tree.... 146 i x Figure 6. Intra-increment v a r i a t i o n i n carbohydrates i n three growth increments of a Douglas f i r tree, expressed as percentages of t o t a l holocellulose 147 Figure 7. Converted arbor press with adjustable cutting die used f o r tension test specimen preparation 148 Figure 8. Tension test specimens enplosed i n poly-ethylene test bags 149 Figure 9. Tension test specimen enclosed i n p l a c t i c test bag i n place between grips of machine 150 Figure 10. Table model Instron testing instrument equipped with constant temperature cabinet 151 Figure 11. Microcator d i a l indicator used f o r thick-ness measurements... 152 Figure 12. Equipment used f o r v i s c o s i t y measurements of cellul o s e n i t r a t e solutions 153 Figure 13. Cellulose chain depolymerization i n the n i t r a t i n g acid as related to length of n i t r a t i o n time 154 Figure 14. Conversion factor between degree of poly-merization and i n t r i n s i c v i s c o s i t y i n re l a t i o n to i n t r i n s i c v i s c o s i t y 155 Figure 15. Effe c t of gamma radiation of wood on c e l -lulose i n t r i n s i c v i s c o s i t y 1 56 Figure 16. Effe c t of gamma radiation of wood on e e l -X. Page lulose degree of polymerization 1 56 Figure 17. Ultimate t e n s i l e strength as a function of cellulose chain length, temperature, and moisture content ".'....* 1 57 Figure 18. E l a s t i c i t y of Douglas f i r i n tension par-a l l e l to grain as a function of temperature, moisture content, and cellulose chain length 1 58 Figure 19. Ultimate s t r a i n of Douglas f i r i i i tension p a r a l l e l to grain as a function of tem-perature, moisture content, and c e l l u -lose chain length 1 59 Figure 20. Work to maximum load of Douglas f i r i n tension p a r a l l e l to grain as a function of temperature, moisture content, and c e l -lulose chain length 160 Figure 21. Diagram showing relationship between ultimate t e n s i l e strength and cellulos e i n t r i n s i c v i s c o s i t y at 50°C temperature and air-dry moisture content condition. Means and scatter around means are also shown... 161 Figure 22. Intra-increment v a r i a t i o n of t e n s i l e strength p a r a l l e l to grain i n Douglas f i r determined af t e r exposure of wood to various doses of gamma radiation 162 x i . Figure 23. Influence of cellulos e chain length 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 163 APPENDIX 164 Fortran Program Used f o r Calculation of I n t r i n s i c V i s c o s i t y of Cellulose 165 1 INTRODUCTION Wood i s by no means an i d e a l engineering material the strength properties of which can be predicted by simple mathematical means. This i s so mainly because, at various angles to the grain, wood i s inhomogeneous and par t l y because i t s reactions to stress are extremely complicated. Even simple external stresses, such as longitudinal tension, have to be transmitted through an ir r e g u l a r network of c e l l walls and spaces, and cannot, therefore, act i n any simple way on the wall material i t s e l f . I t i s true that other fibrous materials, such as t e x t i l e s and paper, are similar i n these respects, but' inhomogeneous constituents of the l a t t e r are fabricated to give a macroscopically uniform system. It i s well known that there are wide differences between strength properties of diff 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 hickory are tough and r e s i l i e n t . Variations i n the mechanical properties within a single species are also known; moreover, differences i n strength characteristics within a single stem have been noted. Recently i t has been shown (42) that variations 2 i n mechanical and physical properties even within a single growth increment may be as wide, i f not wider, than those between two species of wood. Although the reasons f o r these variations i n strength ch a r a c t e r i s t i c s have been studied, i t cannot be claimed that they are yet fully'understood. I t i s conceivable, however, that strength differences 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 chemical, and pa r t l y i n the molecular constitution of wood. Most of the work done i n studying factors influenc-ing mechanical behavior of wood have been concerned with the effects of i t s anatomical and physical c h a r a c t e r i s t i c s . Information i s lim i t e d on how the chemical constituents of wood influence strength. Some reports i n the l i t e r a t u r e (24,25,47,48,49,81) indicate that t e n s i l e strength of wood depends mostly on cel l u l o s e content and crushing strength on l i g n i n content. Lignin serves also as a water repellent substance i n the c e l l wall, protecting the highly hydro-p h i l i c c e l l u l o s e and other carbohydrates from hydration effects (47). The removal of l i g n i n from the c e l l wall results i n a complete loss of wet strength of wood, although dry strength i s increased 6 to 10 f o l d (49). I t i s believed that hemicelluloses are responsible f o r the increased . strength of dry, d e l i g n i f i e d wood samples. A subsequent removal of hemicelluloses from the l i g n i n - f r e e c e l l walls results i n the loss of dry t e n s i l e strength (48,49). I f 3 the acetyl groups are s p l i t o ff the hemicelluloses by treatment of wood with caustic soda solutions, approximately 40 to 50 per cent of wet t e n s i l e strength i s l o s t (48). This phenomenon i s interpreted as meaning that polyuronides influence strength properties; that i s , by the removal of t h e i r acetyl content, the hydration capacity of wood i s increased. A number of authors have likened the c e l l wall of wood f i b r e s to reinforced concrete (25,79). According to them, the s t e e l rod framework i s analogous to the cel l u l o s e chains, and the concrete to the inter m i c e l l a r l i g n i n . While t h i s analogy i s an oversimplification of the mechanical role of the two major chemical constituents, i t does emphasize the fact that c e l l u l o s e , by i t s chain structure, i s the most eff e c t i v e constituent i n wood i n r e s i s t i n g t e n s i l e stresses. I f t h i s i s the case, then qual i t a t i v e differences i n the cell u l o s e chains should be ref l e c t e d by differences i n the te n s i l e strength behavior of wood. The purpose of t h i s study was to investigate how mechanical behavior of wood i n tension p a r a l l e l to grain i s influenced by qu a l i t a t i v e variations i n c e l l u l o s e . The quality of cellulo s e i n wood was measured by i t s mean degree of polymerization [DP], or chain length, as i t s most apparent qua l i t a t i v e property. The assumption was made that, i f cel l u l o s e i s responsible f o r the high t e n s i l e strength properties of wood, v a r i a t i o n i n i t s degree of polymeriza-4 t i o n should have some e f f e c t on those p r o p e r t i e s . I n physics of w e l l o r i e n t e d high polymers and f a b r i c s , i t has been shown that degree of po 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 of m a t e r i a l s only below a c e r t a i n c r i t i c a l DP value. This value i s considered the one at which a slippage between neighboring chains can occur due to the reduced cohesion between those chains. At high DP values, s t r e n g t h i s r e l a t i v e l y independent of chain l e n g t h , since the t o t a l energy b i n d i n g together the neighbor-i n g polymer chains i s much greater than that of any s i n g l e primary valence f o r c e between two monomer u n i t s of the same chain. Moisture dependence of wood streng 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 of streng t h has been considered due to the h i g h l y hygroscopic nature of the carbohydrate components, i t i s not 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 , the major carbo-hydrate component of wood, could i n f l u e n c e t h i s b a s i c behav-i o r . A second purpose of t h i s experiment was to study whether wood wi t h c e l l u l o s e of low 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 than wood having c e l l u l o s e of long-chain s t r u c t u r e . Another o b j e c t i v e of t h i s study was to examine the i n f l u e n c e of c e l l u l o s e chain l e n g t h on the temperature-dependence of wood t e n s i l e strength p r o p e r t i e s . Although 5 this behavior of wood i s generally considered to be mainly due to l i g n i n and hemicelluloses, which are thermo-sensitive components, i t i s not known how much contribution i s made by c e l l u l o s e . It i s quite conceivable that t e n s i l e strength of wood with low-DP cellulose molecules would be more sensitive to temperature variations than that of wood with long-chain c e l l u l o s e . 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 and 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 s p e c i a l r e q u i r e m e n t s o f t h i s e x p e r i m e n t . These were n e c e s s a r y t o m i n i m i z e t h e i n f l u e n c e o f f a c t o r s , o t h e r t h a n c e l l u l o s e c h a i n l e n g t h , 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 . S p e c i a l c o n s i d e r -a t i o n s were made t o keep 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 as l o w as p o s s i b l e s i n c e t h i s f a c t o r has r e p e a t e d l y b e e n shown t o a c c o u n t f o r a r e l a t i v e l y l a r g e amount o f v a r i a t i o n 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 o f wood. The m a t e r i a l and t h e s a m p l i n g t e c h n i q u e h a d t o be s u c h t h a t even l e s s i m p o r t a n 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 , s u c h as f i b r i l a n g l e , p e r c e n t c e l l u l o s e 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 u n i f o r m f o r a l l t h e s p e c i m e n s t e s t e d i n t e n s i o n . 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 d e v e l o p e d f o r t h i s s t u d y t o m i n i m i z 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 t e m p e r a t u r e and m o i s t u r e c o n t e n t c o n d i t i o n s o f t h e t e s t s p e c i m e n s . The r e l a t i v e l y s m a l l s i z e o f t h e t e n s i o n t e s t s p e c i m e n gave a n 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 c o n s t a n t m o i s t u r e c o n t e n t t h r o u g h o u t t h e t e s t . 7 I MATERIAL The test material was obtained from a single, fresh-l y cut, Douglas f i r (Pseudotsuga menziesii.(Mirb.) Franco) tree, selected from a 150-year-old, even-aged stand, grown a on Agood s i t e at the University of B r i t i s h Columbia Research Forest, Haney, B.C. The most important cha r a c t e r i s t i c s taken into consideration i n the selection were straightness of stem, lack of leaning of the tree i n any direction, and a large diameter at breast height (dbh) i n d i c a t i n g fast growth rate. In addition, such features as r e l a t i v e p o s i t i o n of crown i n the stand, length of clear bole, and symmetry of crown were also taken into account. Dimensions of the tree se-lected i n regard to above characteristics were as follows: height 228ft, dbh outside bark 58 i n . , dbh inside bark 54 i n . , number of rings at stump 149, distance 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 bole was bucked and a test block approximately 1 f t i n length was cut at 50 f t above ground. At t h i s l e v e l the grain was tested and found to be straight, 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 micro-size specimens i n tension p a r a l l e l to grain. The growth rate was also 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 of the test block was 36 i n . inside bark. The test block was shipped to the laboratory on the day of f e l l i n g , a f t e r wrapping i n a polyethylene sheet to prevent drying below the f i b r e saturation point. This was done i n order to eliminate possible development of stresses i n the block due to shrinkage, which might have caused undesirable v a r i a t i o n i n strength and related prop-e r t i e s . During the entire material handling procedure, spe c i a l care was exercised to maintain the test material i n a water saturated condition. A sample was l a t e r extracted from the 44- to 51-year increments, giving a small block 5 i n . i n length and approximately 14 i n . i n tangential width. The r a d i a l width of the block was determined by dimension of the eight i n -clude?! increments. Twenty 2/3-in. wide specimen blocks were s p l i t r a d i a l l y from the test block. A special s p l i t t i n g t o o l with r e l a t i v e l y small bevel angle cutting edge was used i n t h i s operation. The compression component of wedg-ing force of such a t o o l was r e l a t i v e l y low, so that by i t s use, f i b r e damage due to transverse compressive stresses was not l i k e l y to occur. The blocks were then submerged i n water at room temperature i n a vacuum desiccator. Vacuum was applied intermittently u n t i l the blocks had be-come soft enough f o r microtome sectioning. On the average, 9 2 to 3 days were required to a t t a i n s u f f i c i e n t softening. The water-logged block, with increment 44 facing upward, was placed i n the jaws of a small r i g i d v i s e spe-c i a l l y designed f o r sectioning 5 to 6 i n . long wood samples. This vise was gripped into the microtome press by a short stem. The long jaws of the v i s e provided support f o r the block s u f f i c i e n t to overcome pressure originating from the microtome blade at the time of sectioning. The adjustable microtome grip'-was f i r s t turned i n the horizontal plane u n t i l the grain of wood had become approximately p a r a l l e l with the d i r e c t i o n of cutting. The grip was then t i l t e d i n the desired d i r e c t i o n to produce true tangential sections as judged on the two tranverse faces of the block. Increment 44 provided material f o r proper alignment and adjustments. Sections obtained from that increment were discarded; those cut from increments 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 block, a series of 100-micron-thick, tangential microtome sections was cut. The blocks were kept i n a saturated condition during microtoming by wetting the surface with water using a camel-hair brush. Approximately 40 to 60 sections were obtained from one increment. Microtome sections were packed i n series and stored i n separate heat-sealed polyethylene bags, according to o r i g i n a l block and growth increment number. Each series 10 was c a r e f u l l y examined as to straightness of grain and lack of curling;, only those marked i n Figure 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 to prevent micro-b i o l o g i c a l attack. Storing of the sections was done at 1 to 5°C temperature, to minimize hydrolytic degradation of the carbohydrate components of wood. The mechanical, physical and chemical characteriza-t i o n of increments 45, 46 and 47 have been reported elsewhere / \ i n (42;. Here'Asome of the results of those analyses are shown graphically. In Figures 2 and 3 v a r i a t i o n i n t e n s i l e strength and modulus of e l a s t i c i t y are shown, while Figure 4 and 5 represent intra-increment variations i n s p e c i f i c gravity, and holocellulose content unadjusted f o r residual l i g n i n . In Figure 6 the hydrolysis products of holocellulose are given diagramatically as percentages of f i v e types of sugars based on the weight of holocellulose. Variation i n the amount of c e l l wall material i n the three growth increments has been studied by ¥orrall(l05), using the micro-scanning technique of Green and Worrall(33). His results coincided with those of s p e c i f i c gravity variations. Per cent latewood i s also given f o r each increment i n Figures 2, 3 and 4; i t was deter-mined by using a semi-microscopic technique on transverse surfaces of blocks stained with a malachite green-methylene blue double s t a i n . 11 II METHODS 1. Degradation of Cellulose by Means of Gamma Radiation A. Previous Work Gamma rays are produced either by shooting rapid electrons on metallic targets or by radiation from certain by-products of nuclear f i s s i o n . . In the f i r s t case, the fast electrons are produced by resonant transformers, Van der Graff machines, or l i n e a r accelerators. In the second fin case, one usually employs Co as a very e f f i c i e n t gamma ray source. I f the elemental cobalt, which exists as several isotopes, i s exposed to the neutron f l u x of an atomic re-60 actor, the Co isotope i s converted into a gamma i r r a -diator with a h a l f - l i f e time of 5.3 years (68). Many such sources of varying strength are now available on thi s con-tinent and provide a simple, permanent and constant source f o r gamma rays. The measurement of i r r a d i a t i o n i s based on the long-established dosimetry of X-rays. There, the "roentgen uni t " has been defined and introduced as the radiation i n t e n s i t y which produces unit ionization i n 1 ml of dry a i r at 0°C and atmospheric pressure. For radiations other than X-ray, the "rep" i s used, an abbreviation of "roentgen equivalent physical", indicating that the rep i s that unit 12 of dosage producing the same ion i z a t i o n effect as one roentgen of X-rays. Recently, "rad" and "fermis" have been introduced which are s l i g h t l y larger units than rep. A l l these units, however, are very small quantities and one frequently uses kilorep, k i l o r a d or" kilofermis f o r 1000, and megarep, megarad or megafermis f o r 10 units. i ) Radiation chemistry of high polymers In order to understand the f i n a l results of i r r a d -i a t i o n on the chemical properties of wood, i t seems to be appropriate to summarize and b r i e f l y discuss the elementary processes which are the immediate consequences of i r r a d i a t i o n . These primary effects are those which give r i s e to secondary and t e r t i a r y steps which, i n turn, lead to a series of molecular events. F i n a l l y , these molecular processes cause the changes i n the properties of i r r a d i a t e d materials. The impact of photon, associated with gamma radiation, 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 according to Bovey (10); 1. electrons are re-moved from atomic nuclei and p o s i t i v e l y charged molecule ions are formed; 2. electrons are l i f t e d to higher o r b i t a l s and neutral but "excited" molecules are formed. I f both processes happen i n the same molecule, an excited molecule ion i s generated. These forms of molecules are very unstable and 13 undergo rapid l y one of several possible changes. In the case of ionization, there may be an immediate recombination of two charged p a r t i c l e s with the disappearance of the active center. However, i n the case of high energy radiation, such as gamma radiation, the electron usually leaves the molecule with enough energy to prevent an immediate recom-bination. A frequent secondary effect of io n i z a t i o n i s the l i b e r a t i o n of hydrogen atoms which immediately react with one another to produce a hydrogen molecule and a p o s i t i v e l y charged free r a d i c a l ion. I f the two hydrogen atoms, united into a molecule, were adjacent on the same organic molecule, a double bond may be formed. I f , however, the hydrogen atom reacts with the hydrogen atom of an adjacent molecule, H 2 i s also evolved and a p o s i t i v e l y charged t r a n s i t i o n state i s generated which, i n turn, forms a cross-link between the two chains. Another secondary effect of radiation i s the fact that excited molecules can undergo spontaneous dissociations and produce a pa i r of free r a d i c a l s . These can either com-bine with free hydrogen atoms, thereby producing a dispro-portionation of the chain, or may unite with other rad 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 of 14 radiation, i . e . , degradation and cross-linking. The net result of the treatment depends on the r e l a t i v e proportion of these two processes. I f degradation i s dominant, the irr a d i a t e d sample i s embritteled, i t s o r i g i n a l degree of polymerization i s reduced as are i t s strength properties. I f , however, cross-linking p r e v a i l s , the polymeric material gains substantially i n toughness, r i g i d i t y and resistance against solvents. Polymeric substances, therefore, can a r b i t r a r i l y be c l a s s i f i e d into two groups: 1. materials which, at certain radiation dosage l e v e l s , form additional chemical bonds re s u l t i n g i n improved properties; 2. materials which suffer-:-fracture of polymeric chains or s p l i t t i n g o ff of side groups. i i ) Influence of gamma radiation on the .chemicalr.properties of wood and cellulos e Wood and cellulose belong to the second group. Rel-a t i v e l y small i n t e g r a l doses of radiation destroy cellulose and other polysaccharides, although wood as a lignin-carbb-hydrate complex reacts somewhat d i f f e r e n t l y from cellulose towards radiation. Relatively..few extensive investigations have been carried out i n this f i e l d . Even fewer of them have progressed to such a point as to produce ground f o r generalizations on the importance of factors such as' the rate of i r r a d i a t i o n and the physical state of the ir r a d i a t e d 15 material. Lignin appears • to be r e l a t i v e l y unaffected by i r r a d -i a t i o n (11). It i s believed that the resistance of th i s constituent of wood to i r r a d i a t i o n i s due to i t s aromatic nature, the benzene nucleus being very stable i n t h i s regard. Results from several investigations i n t h i s f i e l d , as ci t e d by Brauns (11), however, cannot be interpreted as meaning that l i g n i n i s e n t i r e l y unaltered, merely that i t i s not greatly changed i n a manner that i s detectable by the chemical tests applied. According to Smith and Mixer (86), l i g n i n i n wood serves as a protective material f o r the carbohydrate components against i r r a d i a t i o n . They found that direct i r r a d i a t i o n of wood holocellulose produced greater degrada-t i o n than i r r a d i a t i o n of wood followed by preparation of holocellulose. A s i m i l a r effect was noted with styrene when a styrene-isobuthylene copolymer was irr a d i a t e d ; i . e . , the benzene nucleus of styrene protected the isobutylene from excessive degradation (1). One of the most comprehensive studies on the effects of gamma radiation on ce l l u l o s e has been carried out by Blouin and Arthur (9). They i r r a d i a t e d p u r i f i e d cotton 5 8 cell u l o s e from 10 to 10 rad dosages. The major changes induced by i r r a d i a t i o n were cleavage of the cellulos e chains, and formation of carbonyl and carboxyl groups. It i s of interest to note i n that study that the cellulos e molecule was not s i g n i f i c a n t l y affected u n t i l i t received a dosage 16 greater than 10 rads, a f t e r which the number of depolymer-izations , the number of carbonyl groups, and the number of carboxyl groups formed increased with further increase i n dosage. It has also been found that the formation of carbon-y l groups i s by f a r the most important chemical change which occurs. The number of carboxyls formed i s of the same order of magnitude as the number of chain cleavages, suggesting that each chain cleavage produces one carboxyl group, while the number of carbonyls produced i s approximately twenty times the number of carboxyls formed. Radiation causes random depolymerization and decom-position of cellulos e both i n the e a s i l y hydrolyzed or amorphous areas and the resistant or c r y s t a l l i n e regions (84). This i s quite unlike any chemical treatment on wood or cellulo s e which p r e f e r e n t i a l l y affects amorphous c e l l u l o s e . There i s a d e f i n i t e increase i n the rate of hydrolysis of cellulose a f t e r i r r a d i a t i o n and with i t there i s an increased r a t i o between rate of sugar production and destruction, hence, an increase i n sugar y i e l d (62). An important increase i n the rate of hydrolysis, i n turn, requires that the average chain length be reduced to 200 glucose units or les s (60). The maximum ove r a l l y i e l d of sugar obtainable by d i l u t e acid hydrolysis of irr a d i a t e d cotton l i n t e r s i s approximately 65 per cent, almost three times the y i e l d obtainble from untreated samples (84). The corresponding y i e l d from p u r i f i e d wood pulp i s even higher, about 70 to 75 per cent (70). 17 Irradiated samples show no increased water solu-b i l i t y u n t i l treated with a dosage of 5x10 rads (9). At Q 10 roentgens, cotton cellulo s e becomes approximately 10 per cent water-soluble and at 3*3x10 i t i s completely soluble (9). The di l u t e a l k a l i s o l u b i l i t y of irra d i a t e d Q c e l l u l o s e increases with increase i n dosage, .and at 10 rads i t becomes 70 to 75 per cent soluble. There i s some evidence in d i c a t i n g that another chemical effect of gamma radiation on wood i s the disruption or a l t e r a t i o n of a possible bond between l i g n i n and carbo-hydrates. It has been found that i r r a d i a t e d wood samples could be sulfonated easier than untreated samples, which suggests a s p l i t t i n g of the lignin-carbohydrate complex by gamma rays, since there i s no evidence that any basic chem-i c a l change had taken place i n the l i g n i n i t s e l f (11). Another indica t i o n of the a l t e r a t i o n of the chemical bond between l i g n i n and c e l l u l o s i c materials i s that while untreated wood appears to be r e l a t i v e l y unaffected by the enzymatic action of rumen bacteria, fermentability increases 6 8 rapidly between 6.5x10 and 10 rads dosages (60,62). I t i s , however, not c l e a r l y established, whether or not t h i s increased d i g e s t i b i l i t y of wood i s due only to the severe depolymerization of the cel l u l o s e molecules alone. 18 i i i ) E f f ects of gamma radiation on the physical and mechanical properties of wood and related materials As a result of chemical degradation of ce l l u l o s e , gamma radiation induces changes i n the physical and mech-ani c a l properties of wood. Among the physical properties, wood-moisture relationship i s affected most noticeably. It has been reported that i r r a d i a t e d wood, when submerged i n water, adsorbs" s i g n i f i c a n t l y more water i n r e l a t i v e l y short periods than do untreated samples (23). Similar effects have been obtained when irr a d i a t e d samples were exposed to conditions of high r e l a t i v e humidity (23). These changes i n the hygroscopic nature of wood, however, come into effect only at r e l a t i v e l y heavy doses of radiation. At less 7 than 10 rads, the effect may even be ne g l i g i b l e . On the basis of these findings .Seaman et a l . (84) suggested that, besides chemical degradation, an increase i n the r e l a t i v e amount of amorphous cellulo 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. However, the small changes i n hyroscop-i c i t y values suggest that there i s no marked a l t e r a t i o n i n the submicroscopic structure of the cellulos e network. The apparent decrease i n c r y s t a l l i n i t y , as also indicated by the increased hydrolysWbility of. c e l l u l o s e , could conceiv- <•-ably be due to the chemically altered structure of ce l l u l o s e , rather than to an a l t e r a t i o n of the c r y s t a l l i n e structure. Strength properties of c e l l u l o s i c materials are 19 also affected "by i r r a d i a t i o n through degradation. Ultimate t e n s i l e strength, as well as ultimate elongation, have been reported to be reduced by exposure to gamma rays (9,28,29, 65). As another support f o r the assumption that there i s no s h i f t i n g of the crystalline-amorphous ratio.. 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 differences 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 of gamma radiated cotton and those of the control material. iv) E f f e c t of moisture content on degradation by gamma rays Glegg and Kertesz (30) irr a d i a t e d cotton cellul o s e 4 6 and p u r i f i e d wood pulp to doses from 6x10 to 2.3x10 rads at diff e r e n t moisture contents of the samples. They found that wood cellulos e i r r a d i a t e d at 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 reduction i n i n t r i n s i c v i s c o s i t y at comparable i r r a d i a t i o n dosages. I r r a d i a t i o n at three low moisture content lev e l s (0.32, 0.30 and 0.26 per cent) also gave s i m i l a r results at comparable dosage l e v e l s , which suggests that at low moisture content l e v e l s c e l l u l o s e i s at least as susceptible to degradation by gamma rays as samples with high moisture contents. v) The af t e r - e f f e c t of gamma radiation An inte r e s t i n g phenomenon, the af t e r - e f f e c t of radiation, has been observed by Glegg and Kertesz (30). 20 Unlike samples .at higher moisture content, they found that v i s c o s i t y of ir r a d i a t e d cellulose at lower than 1 per cent moisture content progressively decreased beyond that mea-sured, shortly a f t e r the end of i r r a d i a t i o n . This a f t e r -effect was greater than the primary e f f e c t , which suggests that some type of activated molecule i s formed during .i r r a d i a t i o n . Paramagnetic resonance absorption measure-ments revealed that the active molecules a f t e r i r r a d i a t i o n were of the free r a d i c a l type. It was shown that 5.5x10 rad i r r a d i a t i o n of samples of low moisture content gave moderate absorption, and at higher moisture content, very s l i g h t absorption a f t e r f i v e days. Thirty days l a t e r , only a weak signal was obtained from the samples at 0.32 per cent moisture content, and a barely discernible signal from that ir r a d i a t e d at 4.6 per cent moisture content. It appears that i r r a d i a t i o n of dry cellulos e i n a i r leads to formation of free.radicals which are capable of surviving long a f t e r the end of i r r a d i a t i o n and give r i s e to further depolymer-i z a t i o n . B. I r r a d i a t i o n of Experimental Material with Gramma Rays The microtomed wood sections wrapped i n heat-sealed polyethylene bags were sent to Atomic Energy of Canada Ltd., Commercial Products Division, Ottawa, Canada, f o r gamma radiation. The polyethylene insured the maintenance of 21 moisture saturated condition of the sections during and aft e r i r r a d i a t i o n . Pour doses of i r r a d i a t i o n were applied to the wood samples i n order to produce various degradations of the ce 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 receiving 10.0 megarad dosage, were ir r a d i a t e d i n a G-ammacell 220 at approximately 1 megarad per hour dose rate. The specimens i r r a d i a t e d to 10.0 megarads received the doses i n a G-ammacell 200,which was capable of deli v e r i n g only 0.1 megarad dosage per hour. These dif f e r e n t dose rates were used because the work load on the G-ammacell 220 was too high at the time to 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 to li m i t e d size of the gamma c e l l . The source of gamma radiation i n the c e l l s was CogQ, the nominal strength of which f o r a maximum dose rate was approximately 1500 curies. The dose uniformity 4 -within the chambers of the c e l l s was nominally -5 per cent, a value which was considered s u f f i c i e n t f o r t h i s experiment. Radiation dosages were randomly assigned to the samples. The pos i t i o n of the groups r e l a t i v e to each other i n the o r i g i n a l block i s shown i n Figure 1. 22 2. TensionTest Methods A. Preparation of Test Specimens In order to minimize the inherent v a r i a t i o n of woody material, tension test samples were taken from the same r e l a t i v e p o sition i n the three growth increments. Based on the results of intra-increment studies (42), 30 and 80 per cent positions r e l a t i v e to the beginningig-f the growth increments, provided material with approximately average strength properties f o r early- and latewood, respec-t i v e l y . Two microtome sections were taken from close to each of these two positions, which provided enough material f o r tension p a r a l l e l to grain studies. The tension test specimens were 2.5 mm x 100 mm rectangular s t r i p s prepared by punching the selected micro-tome section blanks, using a s p e c i a l l y machined cutting die fi x e d on a 1/2-ton converted arbor press. The cutting assembly i s shown i n Figure 7. This form of specimen has been shown to give the highest strength values, as well as the best r e p l i c a t i o n , i n t e n s i l e strength properties (42). Special care was exercised i n punching as to wood grain d i r e c t i o n of specimen. A part approximately 1 to 2 mm wide was torn o f f the edge of a wet section. The section was then placed on an IBM card, so that the torn edge was oriented p a r a l l e l with rows of number. It was pressed l i g h t l y against the paper so that i t adhered to the card 23 due to surface tension. The card was then placed onto the modified stage of the arbor press. Its edge, perpendicular to the torn side of the section, was held against a guide s t i c k clamped to the side of the stage. Side-matched specimens were punched by moving the card along the guide s t i c k , with approximately 3 to 3.5 mm af t e r each cut. Five to seven specimens could be obtained from each section using t h i s technique; i . e . , 10 to 14 from the two sections at the same r e l a t i v e p o sition within increments. Each group of 10 to 14 specimens was kept i n a 250 mm by 25 mm Pyrex test tube. Approximately 2 to 3 ml of 1 per cent aqueous solution of thymol was added as a preservative and f o r the purpose of maintaining a moisture saturated a i r condition inside the tube. The tube was subsequently closed with a neoprene stopper. Specimens were then stored at 1 to 5°C temperature u n t i l f i n a l con-dit i o n i n g . B. Test Variables i ) Testing machine variables The tension tests were conducted on a table model Instron Tensile Tester. In a l l tests the load was applied with continuous motion of the moving cross-head, producing a constant rate of elongation at 0.005 in./min. Each 24 specimen was tested over a 1.5 i n . span which resulted i n 0.00333 in./min rate of s t r a i n . The load was recorded automatically throughout the test on a chart moving with a constant speed of 1 in./min. S e n s i t i v i t y of reading on the chart was 10 grams. Ultimate t e n s i l e load, load to unit s t r a i n within the proportional 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 chart, and the appropriate strength values were calculated. The t o t a l area under the load-elongation curve was measured using a planimeter, from which the work to maximum tension load was calculated. A t o t a l of 540 tension -.: specimens were tested. i i i ) Moisture content and temperature In order to study the influence of the degree of polymerization of c e l l u l o s e on the moisture dependence of wood strength properties, the specimens were tested at three d i f f e r e n t conditions of moisture content. Moisture-free, air-dry, and saturated conditions were chosen to cover the possible widest range of strength v a r i a t i o n i n r e l a t i o n to moisture content.: The effects of temperature on the t e n s i l e strength properties 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 desirable to increase the temperature range f o r a more thorough examination of the temperature effect, the f a c i l i t i e s 25 available r e s t r i c t e d t h i s part of the experiment. Three temperature conditions were used i n the experiment, namely 25, 50 and 70°C. The r e l a t i v e l y small size of the test specimens required careful control of moisture content during tests. On the average, the test of one specimen was completed i n approximately 3 to 8 minutes, during which period the thin wood sections would have changed t h e i r moisture content regardless of how c a r e f u l l y they had been preconditioned. Therefore., each test specimen was placed i n a p l a s t i c bag s p e c i a l l y made fo r th i s purpose from 1.0 mil polyethylene, using an e l e c t r i c soldering i r o n . In the mid-portion of the bag an 'over-folding 1' was made, so that when the spec-imen was tested between the jaws of the tes t i n g machine the loose f o l d eliminated testing the polyethylene with the wood section. Two test specimens i n p l a s t i c bags are shown i n Figure 8. Figure 9 shows how such a specimen i s gripped i n the testing machine. Those specimens tested i n the moisture-free con-d i t i o n were dried over phosphorus pentoxide i n vacuo at 60°C f o r at le a s t 72 hours. The test pieces were f i r s t a i r - d r i e d . Each of them was then placed i n a p l a s t i c bag, one end of which was kept open; and the bags were then placed i n a vacuum desiccator. Copper sulfate was used as an indicator i n the desiccator. When the blue color of the 26 copper sulfate disappeared the drying was considered com-plete. On average, t h i s condition was attained a f t e r 48 hours drying i n the condition specified above. Occasion-a l l y the 'skin 1 formed on the surface of the phosphorus: pentoxide was removed to reactivate the drying agent. After the discoloration of the copper sulfate indicator, the specimens were kept i n the desiccator f o r an additional 24 " hours i n order to ensure complete removal of moisture. A few sections dried i n t h i s manner showed moisture con-tents ranging from 0.008 to 0.17 per cent, with an average of 0.09 ;per cent, upon subsequent oven-drying. This low value was considered zero i n the analysis. After the drying was done, the specimen bags were quickly closed and heat-sealed to prevent moisture pick up by the specimen. After the closure of the p l a s t i c bags, they were replaced i n the desiccator u n t i l tested. Specimens tested i n the water-saturated condition were transferred from the test tubes to the test bags, approximately 1 ml of water was added, then the bags/\heat-sealed. No moisture content determinations were made f o r these specimens since i t was the intention only to keep them at a moisture content .above fibre-saturation point. The specimens tested i n air-dry condition were preconditioned i n an Aminco Aire constant temperature and humidity cabinet. Dry-bulb temperature^in the cabinet 27 were 25°C, 5C°C and 70°C, the temperaturesat which the specimens were tested following conditioning. The r e l a t i v e humidity conditions were chosen i n such a way that the res u l t i n g equilibrium moisture contents (EMC) were to be approximately 12 per cent. The procedure i n precondition-ing was si m i l a r to that described f o r the moisture-free samples except that here the completion of conditioning was determined by using dummy microtome sections, prepared i n the same way as the test specimens and from the same material, and kept i n open p l a s t i c bags sim i l a r to that employed i n conditioning the test material. Each test specimen was kept i n the conditioning cabinet f o r at least 48 hours, although the dummy pieces attained constant weight a f t e r the f i r s t 24 hours . The temperature was kept under close control during the entire period of testing. A small wooden cabinet was b u i l t around the grips of the test i n g machine i n which the temperature was kept at the required l e v e l . A large capacity forced a i r c i r c u l a t i o n oven and the test 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 supplied enough heat to the 3/4 cu f t cabinet to hold a constant temperature within - 0.5°C. The thermostat of the oven was set approximately 2°C higher than the test temperature since i t was found that the cabinet attained a temperature 2°C lower than the oven. This was probably 28 due to the heat loss i n the cabinet and i n the tube i n spite of the c a r e f u l l y applied insulation. In Figure 10 the test set-up i s shown. Thickness of specimen was measured using a precision d i a l indicator shown i n Figure 11 and described i n d e t a i l by Bystedt and Anderson (13). Measurements were made including the two sheets of polyethylene'enclosing the specimen. The thickness of the p l a s t i c as subsequently measured was subtracted from the t o t a l thickness. The average of three measurements was used to calculate cross-sectional dimensions. Specimen width could be conveniently measured through the transparent polyethylene with the aid of a microscope. Cross-sectional area of each tension test specimen was calculated by simple m u l t i p l i c a t i o n . 3. Determination of Cellulose Degree of Polymerization There are several methods available f o r the de-termination of chain length of both synthetic an natural high 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 solutions of polymers. This method i s based on the observation that the increase i n v i s c o s i t y of the polymer solution, over that of the solvent, i s related to the chain length, pro-vided that the test-conditions are constant. In spite of the 29 r e l a t i v e l y long history of t h i s method, there has been no unique relationship developed, mainly because the influence of certain contributing factors, other than mere average chain length, i s not known. Two of these factors are the orientation of the long-chain molecules during the e f f l u x of l i q u i d i n the viscometer, and 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 flowing solution. Empirical equations, however, are available i n the l i t e r a t u r e r e l a t i n g i n t r i n s i c v i s c o s i t y to degree of polymerization of c e l l u -lose and c e l l u l o s e derivatives. In t h i s experiment the cellulose chain length was determined by one of the empirical methods involving meas-urement of i n t r i n s i c v i s c o s i t y . The cellulose i n wood was converted into highly substituted cellulose n i t r a t e , 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 solution, using a c a p i l l a r y type of viscometer. The i n t r i n -s i c v i s c o s i t y values calculated from the efflux times were properly adjusted, and the degree of polymerization of c e l l u -lose computed with the aid of an empirical relationship. A. N i t r a t i o n of Wood Samples The microtome sections i n each series of each growth increment were divided into early- and latewood zones, according 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 sections i n each series, then determin-ing the section number by ca l c u l a t i n g where the d i v i s i o n was to be made, using per cent latewood previously measured for each of the three growth increments. Earlywood and l a t e -wood thus obtained from each series were handled separately i n n i t r a t i o n . This resulted i n a t o t a l number of 60.nitrations, 30 of which were earlywood and 30 were latewood samples. Prom each of the three increments, two re p l i c a t e n i t r a t i o n s were made at each of the f i v e degradation l e v e l s , for earlywood and latewood separately. Each sample was then placed i n a separate saran screen container of approximately 10 mesh. These containers were conveniently made i n the laboratory from ordinary mos-quito screen, using an e l e c t r i c soldering i r o n to seal the samples into them. The saran containers were placed into a large, approximately 1 - l i t e r , Soxhlet extraction apparatus and exhaustively extracted i n a mixture of benzene and 95 per cent ethyl alcohol i n 2:1 r a t i o . The extractive-free material was a i r - d r i e d and ground i n a Wiley m i l l to pass a 40-mesh and be retained on an 80-mesh sieve. Approximately 20 to 30 per cent of the wood meal passed the 80-mesh sieve when unirradiated or s l i g h t l y treated wood meal samples were prepared. About 40 per cent of the wood meal was l o s t through sieving from the 10 and 15 megarad ir r a d i a t e d material. Es p e c i a l l y low 31 yields of wood meal were obtained when 15 megarad irradiated earlywood samples were screened. The wood meal was nitrated i n a non-degrading acid mixture as described by Alexander and M i t c h e l l (2). This was prepared by adding cautiously and very slowly, with a spatula 202 g of phosphorus pentoxide to 500 g of 90 per cent fuming n i t r i c acid at -5°C and contained i n a 1 - l i t r e Erlenmeyer f l a s k . The acid was kept ice-cold by immersion i n an ice water bath and was swirled continuosly during addition of phosphorus pentoxide. This produced a mixture with composition of 64 per cent n i t r i c acid, 26 per cent phosphoric acid and 10 per cent phosphorus pentoxide (2). With occasional shaking, the solution was complete i n a few hours, and the mixture was then transferred into a glass-stoppered bottle and refrigerated u n t i l used f o r n i t r a t i o n . The mixture was used invariably within 12 hours from preparation. A 20 g portbn of the prepared n i t r i c acid mixture was weighed out into a weighing bottle of about 50 ml capacity and placed i n a constant temperature bath at 17 +0.5 C. One-half gram of wood meal was introduced quickly into the n i t r a t i n g acid mixture. N i t r a t i o n was then allowed to proceed f o r 40 hours, the sample being swirled occasion-a l l y during t h i s period. The nitrated wood meal was then quantitatively transferred into a f r i t t e d glass Buchner type of funnel which was approximately 200 ml i n capacity. 32 Cold tap water (about 14°C) was used i n transferring the sample. The n i t r a t e was thoroughly washed with 1000 ml of cold water, using mild suction, then soaked i n 50 ml of 1 per cent sodium carbonate solution f o r 5 minutes. Washing was finished with 500 ml of cold tap water followed by 500 ml of cold d i s t i l l e d water. The sample was transferred into a 250 ml Erlenmeyer f l a s k using 200 ml of methyl alcohol, and extracted i n methyl alcohol 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 quantitatively transferred into a f r i t t e d glass crucible and washed with an additional 100 ml of methyl alcohol. The crucible was placed i n an oven maintained at 60°C. After 10 minutes drying, the sample was dry and could be removed from the crucible quantitatively. The dry c e l l u l o s e n i t r a t e was transferred into a 250-ml Erlenmeyer f l a s k and 200 ml of acetone was added. After 48 hours, within which timeVthe Erlenmeyer f l a s k was often swirled, most of the n i t r a t e dissolved i n the acetone. A few undissolved 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 ir r a d i a t e d samples which dissolved completely during the 48 hours. The solution was then centrifuged to remove the undissolved n i t r a t e p a r t i c l e s . The clear, yellowish solution was decanted from the tube of the centrifuge into 2.5 1 of cold d i s t i l l e d water. In the water, the cel l u l o s e n i t r a t e immediately 33 precipitated and could conveniently be collected 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 -dried and then placed i n a vacuum desiccator containing phosphorus;: pentoxide as drying agent. Vacuum was applied and the desiccator was placed into an oven maintained at 60°C temperature. Drying was continued f o r 48 to 72 hours, within which period the skin formed on the surface of the drying agent was occasionally removed; the vacuum was p e r i o d i c a l l y checked and restored by applying additional-suction to the desiccator. After t h i s drying period the cellulos e n i t r a t e was ready f o r nitrogen analysis and v i s -cosity measurement. Optimum reaction time of 40 hours n i t r a t i o n was determined experimentally. Material obtained from the same increments as those used i n the main experiment was divided into early- and latewood. It was ni t r a t e d f o r various lengths 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 values determined. Results of t h i s preliminary experiment are shown i n Figure 12• Both early- and latewood samples attained the highest i n t r i n s i c v i s c o s i t y values 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 length of n i t r a t i o n time within the experimental range. The results were i n agreement with the n i t r a t i o n times used by Timell (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 with wood of several coniferous species. I t seems reasonable 34 to assume that optimum n i t r a t i o n period i s related to l i g n i n content of wood since hardwood species having lower l i g n i n content, such as aspen, require only 1 hour n i t r a t i o n to a t t a i n the necessary degree of substitution and optimum v i s c o s i t y values (94). B. Determination of Nitrogen Content of Cellulose Nitrates Nitrogen content of cellul o s e n i t r a t e s was determined by a micro-Kjeldahl method, e s s e n t i a l l y as developed by Ma and Zuazaga (66) and modified by Timell and Purves (97). Duplicate determinations were done on each cellulo s e n i t r a t e sample except f o r a few cases where the difference between the two replicates was greater 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 closest values used. The cellul o s e n i t r a t e to be analyzed was dried over phosphorous pentoxide i n vacuo as sp e c i f i e d e a r l i e r . A 15-25 mg sample was weighed on an a n a l y t i c a l balance within - 0.05 mg and transferred d i r e c t l y to a 30 ml micro-Kjeldahl f l a s k . Approximately 0.1 g of reagent grade s a l y c i l i c acid was addedC"followed by 2.5 ml of concentrated s u l f u r i c acid. The sample was allowed to dissolve completely i n the acid. In general, the n i t r a t e s were quite hard to dissolve, there-fore<] i t was advisable to allow the n i t r a t e - a c i d mixture to iJ / stand over/night. This precaution was taken to avoid 35 incomplete solution which could have led to low results according to Timell and Purves (97). Approximately 0.3 g of a n a l y t i c a l grade sodium • thiosulfate and 0.6 g anhydrous potassium sulfate were added to the brown solution. The mixture was then gently heated fo r h a l f an hour on a micro-Kjeldahl heater, the heat being gradually increased u n t i l refluxing of the s u l -f u r i c acid began. The solution was heated u n t i l i t became cys t a l clear, plus an additional 10 minutes i n order to ensure complete digestion. In general, the digestion was complete i n 2 to 4 hours depending on the amount of c e l -lulose n i t r a t e weighed into the f l a s k . The a c i d i c , colorless l i q u i d was diluted with 15 ml of d i s t i l l e d water and transferred quantitatively to an a l l -glass d i s t i l l i n g apparatus. Twenty ml of 35 per cent sodium hydroxide solution was then added. The ammonia formed i n the basic solution was steam-distilled into 25 ml of 0.8 per cent boric acid that had previously been made s l i g h t l y acid against a mixed indicator. This indicator consisted of a mixture of f i v e parts of 0.1 per cent ethanol solution of bromcresol green and one part of 0.1 per cent solution of methyl red i n the same solvent. After 5 to 10 minutes d i s t i l l a t i o n , the ammonium hydroxyde formed i n the receiving Erlenmeyer f l a s k was d i r e c t l y t i t r a t e d with standard 0.03 N hydrochloric acid u n t i l the red color of the indicator had d e f i n i t e l y reappeared, 5 to 9 ml of acid being usually 36 required. Blank determinations gave an average consumption of 0.05 ml of 0.03N acid. The analyses were accordingly corrected and the nitrogen content calculated i n the Sallow-ing manner: where N = nitrogen content i n per cent, K = amount of 0.03N hydrochloric acid i n ml, W = *weight of the dry cellul o s e n i t r a t e sample i n g. In order to test the method, a n a l y t i c a l grade potassium n i t r a t e was analyzed. Three samples gave 13.79, 13.76 and 13.75 per cent nitrogen, the calculated content being 13.85 per cent. The deviation from the t h e o r e t i c a l nitrogen content of potassium n i t r a t e was probably due to the moisture content of the sample since i t was not oven-dried before analysis. The average accuracy of the method + 't-was - 0.1 per cent, although i n some cases only about - 0.25 per cent. C. V i s c o s i t y Measurements Two to s i x mg of c e l l u l o s e n i t r a t e were weighed within - 0.001 mg on a micro-analytical balance, and trans^ ferred to a 15 ml polyethylene test tube f i t t e d with a p e r f e c t l y - c l o s i n g polyethylene cap. Ten ml of a n a l y t i c a l grade acetone were added and the tube continuously rotated 37 f o r 24 hours. After t h i s time, solution of the cellulo s e n i t r a t e was complete. A 5 ml aliquot of the above solution was transferred by pipette to a clean Cannon-Fenske (14) (ASTM No. 50) viscometer suspended i n a v i s i b i l i t y Jar + o Bath at 25.-r:, 0.1 C. After waiting 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 gentle pressure on the surface of the solution i n the open arm of the instrument. This pressure, conveniently applied from a rubber bulb, minimized error due to evapor-ation when the solution i s drawn up the c a p i l l a r y by direct suction. The equipment used i n the v i s c o s i t y measurements i s shown i n Figure 13. E f f l u x times, 163.5 to 350.0 sec, were measured with a stop-watch reading to 0.1 sec. A l l + values 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 calculated from the expression t / t Q - 1, where t was the ef f l u x time of the solution and t that, of the pure acetone, assuming the densities of the solvent and the solution to be equal. The s p e c i f i c v i s c o s i t y values so calculated were corrected f o r k i n e t i c energy losses, according to Timell (91), i n the following manner: 7 sp 7 sp 1 1-F Q t + 1 J Here "71 i s the corrected s p e c i f i c viscosity,*? " g the observed value, and F Q a factor calculated f o r the v i s -cometer from the expression: 38 o 8~ >n t L U J / o o In t h i s expression m, the ki n e t i c energy c o e f f i c i e n t , was taken as unity, i . e . , end effects f o r the c a p i l l a r y were neglected; d Q, density of acetone, was 0.785; V, the volume i n ml of the viscometer "bulb, 3.65; , the v i s c o s i t y of pure acetone, 0.003095 poise; t , the e f f l u x time of pure acetone, 163.5 sec; and 1, the length of the c a p i l l a r y , 7.75 cm. Substituting the above values into the expression, F q f o r the viscometer used i n this experiment was calculated as 0.0296359. The mean shear rate or v e l o c i t y gradient was c a l -culated from the formula: 8 V g = 3 T r r 3 t CO Here, r equals the radius of the c a p i l l a r y (0.02125 cm), and t i s the ef f l u x time. After having the s p e c i f i c v i s c o s i t y values corrected 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 by means of the Schult'z-Blanschke, as give by Davison (20), and Huggins 1 (39,40) equation: f Y l ] = ^ 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 to the shear, G, at which the measurement was made; K i s a factor taken as 0.30, according to Davison (20); 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., calculated by using the above formula, varied i n a regular manner corresponding to the shear dependence of the v i s c o s i t y as'found by Timell (90,91,92). On the other hand, the rate of shear was dependent upon the e f f l u x time which, i n turn, was influenced by both the concentration and the degree of polymerization of the cellul o s e n i t r a t e . In order to obtain comparable values f o r the various concentrations of di f f e r e n t DP n i t r a t e s , a l l results were adjusted to 500 sec v e l o c i t y gradient. This was done by using the following r e l a t i o n -ship reported by Davison (20): l o g [ ^ ] 5 o O = P l o^5§0 + l 0 S ^ G t6) where Gf can be calculated from equation CO, and P i s the slope of the straight 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 rate of shear. In other words, P as a slope may be determined by the following expression: p _ d l o g g i a C7) d log- Gr Davison (20) determined P experimentally and calculated 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 v i s c o s i t y . This equation has the following form: P = 0.0039 [ 7 J 5 0 0 - 0.8 x I O " 8 i^00 Since P i s related to i n t r i n s i c v i s c o s i t y at 500 sec i n 40 equation ( 8 3 , the value obtained by substituting V^]Q i n the equation was used to calculate the f i r s t approximation of the slope P. This value then inserted i n equation (6) gave the f i r s t approximation to E^^oo w k i c h , resubstituted into equation , gave a better estimate of P. This bracketing technique was continued u n t i l the r e s u l t i n g C^J^ Q Q N A D N 0 ^ changed within 0.001 i n t r i n s i c v i s c o s i t y . Since complete n i t r a t i o n could not be attained, the effect of the degree of substitution had to be taken into consideration i n order to arrive at comparable v i s -cosity values. An empirical equation, developed by Lindsley and Prank (64), was used to convert the i n t r i n s i c v i s c o s i t y as determined into i n t r i n s i c v i s c o s i t y of the corresponding t r i n i t r a t e . l o g [ 1 ] T = l o g f x + (14.15 - X)B + logl*}] (3) where E*!]^  = i n t r i n s i c v i s c o s i t y of the t r i n i t r a t e , f = a factor which takes into account the departure of the unit 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 substitution, x = the nitrogen content of the sample, and B = an empirical constant having a value of 0.114. Prom the above f = 1.833 - 0.0589 x Here x i s also the percentage of nitrogen i n the sample. 41 Since a l l the v i s c o s i t y measurements were carried out at 25°C temperature, another adjustment of the i n t r i n s i c v i s c o s i t y values became necessary. A l l results were con-verted into values corresponding to those taken at 20°C temperature. This was done by simply multiplying 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 factor was obtained from the relationship reported by Treiber and Abrahamson (98). It should be noted that the above, rather involved, mathematical approach needed approximately the same amount of time as would have been spent on determining experiment-a l l y the straight l i n e relationship between reduced v i s c o s i t y and concentration, and reduced v i s c o s i t y and shear sp rate f o r each sample to be analyzed, and extrapolating to zero concentration and 500 sec~^ shear rate. However, t h i s was the case only when a desk calculator was used f o r the calculations. A computer program was written f o r the IBM 1620 electronic computer of the University of B r i t i s h Columbia which calculated the in 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 values i n approximately 8 seconds. Using t h i s technique approximately 9 hours were saved on each average i n t r i n s i c v i s c o s i t y value based on 4 re 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 eff l u x time i n seconds, the concentration i n g/100 ml, and the corresponding nitrogen content i n per cent had to be punched on IBM cards. A copy of the program i s attached to the appendix of th i s thesis. 42 D. Conversion of I n t r i n s i c V i s c o s i t y to DP Values It has been the objective f o r quite some time to establish a relationship between i n t r i n s i c v i s c o s i t y and degree of polymerization of c e l l u l o s e . Unfortunately, no unique factor or formula has been developed as yet which may be applicable to a wide range of DP values. Each expression reported i n the l i t e r a t u r e i s the re s u l t of empirical determinations and applicable only within r e l -a t i v e l y narrow, s p e c i f i c circumstances. In t h i s experiment a somewhat arbit r a r y procedure was followed i n determining the conversion factor f o r each cellulose n i t r a t e sample tested. Timell's data provided the basis f o r the ca l c u l a -tions (93). He reported i n t r i n s i c v i s c o s i t y values, as well as degree of polymerization data, f o r 24 native celluloses of various sources, including 6 hardwood and 6 coniferous species. DP values were determined by a l i g h t scattering 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 using a modified Ubbelohde c a p i l l a r y viscometer and n-butyl acetate as the solvent. Accepting the results of the l i g h t scattering measurements as the true DP values, i t i s possible to calculate a conversion factor f o r each c e l -lulose sample tested. This factor (K), however, i s not a constant number f o r a l l the cellulose samples included i n Timell's study, but an almost perfect l i n e a r relationship exists between i t and i n t r i n s i c v i s c o s i t y . In Figure 14 43 K , calculated from data of Timell (93), i s plotted against i n -t r i n s i c v i s c o s i t y . Elsewhere (96) i t has been reported that when acetone i s used as a solvent, a conversion factor higher approximately by 20 should be used, i n order to obtain DP values of comparable magnitude. The dotted l i n e i n Figure 14 may therefore represent the K - i n t r i n s i c v i s c o s i t y r e l -ationship when acetone i s used as a solvent, as was the case i n t h i s study. For each ce l l u l o s e n i t r a t e sample the ap-propriate conversion factor was calculated from the equation shown i n Figure 14, and the i n t r i n s i c v i s c o s i t y multiplied by the number so obtained to calculate the corresponding degree of polymerization. It i s rea l i z e d that the above procedure to calculate DP values i s rather a r b i t r a r y as are a l l such methods. There-fore, the cellulos e DP values reported here cannot be con-sidered as the true values but only as approximations of what might exist i n wood. In the enormous l i t e r a t u r e on th i s subject, empirical relationships range from the use of simple conversion factors between v i s c o s i t y and DP, to complicated logarithmic or exponential functions. This results i n a wide range of possible DP values calculated 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 empirical formula used. Staudinger's o r i g i n a l proposal was that at low concentrations: 1^ = K M C Qo3 1 sp 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 cellulo s e derivative, and C „ i s the concentration i n moles mg of monomer per l i t e r . This relationship i s now often used i n the form: [*]] = K m DP O O One of the d i f f i c u l t i e s of attaining an accurate value f o r K i s the fact that most of the correlations m between [*]] and DP depend on osmotic results," which give number-average molecular weights. A v a l i d correlation should depend on the use of either very narrow fractions, f o r which the number-average DP equals weight-average values, or a molecular weight method which gives the weight-average DP. The l i g h t scattering technique i s considered to be such a method. Recently, more precise measurements tend to show a more complicated relationship. This i s probably due to the fact that there i s no simple co r r e l a t i o n of the number-average molecular weights and i n t r i n s i c v i s c o s i t i e s unless 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 e f f e c t . I t i s quite possible that the higher DP fractions have broader d i s t r i b u t i o n curves than the lower f r a c t i o n s . In t h i s case an exponential type of relationship p r e v a i l s ; 45 " [*7] = K m DP a . • C120 In t h i s equation the greater the discrepancy among the d i s t r i b u t i o n curves within a sample, the lower the exponent a . It has been shown (40,67,77) that the simple cor-r e l a t i o n of Staudinger gives a good approximation of low DP. I f the DP/E^j r a t i o i s plotted against 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 region of continually increasing values. Thus the DP i s well approximated by a single K m factor say below DP 200. Harland ( 3 4 ) , on the, other hand, claims that the relationship p?]=0.0108 DP i s v a l i d over a DP range of 100 to 1800 f o r cellul o s e n i t r a t e of 14 per cent nitrogen i n ethyl butyrate. Kraemer's K m value of 3.7x10 , as cited by Ott et a l . (#7), i s much lower than the one mentioned e a r l i e r . Lindsley and Prank (64) i n t h e i r study of dependence of degree of substitution of DP, calculated a K factor of 0 m -3 o 12x10 f o r t r i n i t r a t e i n acetone at 20 C f o r fractionated samples. They also report that f o r unfractionated nitrates the constant should be larger. Holtzer, Benoit and Doty (38) found that Staudinger's law was obeyed over a range of 150 to 4500 DP (number-average). The value of Kffi was found to be 5.0x10 ' when the weight-average DP was considered. An extensive osmotic pressure and cellul 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) led to a value of 10x10 when DP was a number-average value. These two l a t t e r 46 values are consistent i f one considers that the weight-average DP i s approximately twice as large as the number-average DP (77). Treiber and Abrahamson (98) reported a value of 13.6x10"^ f o r K . Timell's study (93), which involved v i s c o s i t y measurements of cellulo s e n i t r a t e s i n butyl acetate, and DP determinations of the same material using a l i g h t scatter-ing technique, resulted i n an exponential equation, the K m factor being equal to 0.278 and the exponent 0.572. In t h i s study the DP values measured were obviously weight-average 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 subject of v i s c o s i t y -DP relationship. The above figures, however, show the rather large discrepancies i n t h i s f i e l d . The DP values calculated f o r an imaginary cellul 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 dl/g i n acetone, using the different relationships mentioned above, are shown i n Table 1. DP of the same sample was also calculated on the basis 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 strength parameters were calculated from the raw experimental data. Ultimate t e n s i l e strength was obtained by div i d i n g the ind i v i d u a l maximum." load values p i n kg by corresponding cross-sectional areas i n cm . Elas-by t i c i t y values were calculatedjymultiplying by 100 the load i n kg at 0.01 i n . / i n . s t r a i n within the proportional l i m i t 2 and dividing that number by the cross-sectional area i n cm . Both ultimate t e n s i l e strength and e l a s t i c i t y values were converted into p s i units, using a conversion factor of 14.22. Ultimate s t r a i n values were calculated from elongation data, read from the testing machine chart and taking into account the test speed and the span over which the specimens were tested. Work to maximum tension load was calculated from the area under the load-elongation diagram from the machine chart, converting that number into unit value of i n . l b / i n . Six test results obtained from the three growth increments i n each of the experimental test conditions were considered as replicates and th e i r mean value calculated. These average strength properties are given i n Tables 2, 3, 4, and 5. Also included are co e f f i c i e n t s of v a r i a t i o n i n -dicating the per cent dispersion of the data around each mean value reported. In Tables 2, 3, 4 and 5, strength properties of early- and latewood are tabulated separately 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 . This arrangement was followed throughout f o r a l l values reported. Strength values i n the above tables are further divided into three groups according to the three temperature l e v e l s at which specimens were tested. Within each temperature l e v e l , the means of strength properties i n Tables 2, 3, 4 and 5 are grouped •  under three moisture content conditions as indicated by 0 (zero), air-dry and saturated. The zero moisture content corresponds to a moisture-free state of the specimens at test, while the saturated condition refers to a moisture content higher than the fibre-saturation point of the wood. The actual moisture contents attained by the air-dry specimens during pre-conditioning were determined as described e a r l i e r . These values are given i n Table 6. The temperature and r e l -ative humidity conditions at which the specimens were dried are also reported i n Table 6. In Tables 2, 3, 4 and 5, as well as i n Table 6, the experimental results are tabulated i n r e l a t i o n to in t e g r a l i r r a d i a t i o n dose to which the test samples had been exposed p r i o r to testing. In Table 7, experimental results of cellulose i n t r i n s i c v i s c o s i t y measurements are given with t h e i r c o e f f i c i e n t s of var i a t i o n , based on four replicates of each mean. Also included i n thi s table are the averages of duplicate determinatioir?of nitrogen content. Values are tabulated according to nominal i n t e g r a l i r r a d i a t i o n dosages to which the wood samples had been exposed. 49 Cellulose degree of polymerization values calculated from i n t r i n s i c v i s c o s i t i e s are given 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 dispersion are reported i n th i s table since DP values were calculated only.from mean v i s c o s i t y data. Results of v i s c o s i t y measurements and DP calculations are also shown graphically i n Figures 15 and 16 respective-l y . Curves f i t t e d by using the least squares method to a l l experimental data, as well as the averages of those data, are shown i n these figures. Here, too, data obtained from early-and latewood are shown separately, the s o l i d l i n e and f u l l c i r c l e s corresponding to latewood, and the dotted l i n e and empty c i r c l e s to earlywood r e s u l t s . S t a t i s t i c a l techniques were used to evaluate the significance of variations induced by the three treatments. Analysis of variance was calculated f o r each strength prop-erty tested. Here, again, early- and latewood values were handled separately. In Tables 9 through 16 results of eight analyses of variance are given, one f o r each of the four strength properties tested, f o r early- and latewood sep-arately. In these tables the f i r s t factor i s degree of polymerization (DP), the second i s temperature (T), and the t h i r d i s moisture content (MC). The interactions of the three treatments were also tested and they also are included i n the tables. Only i n one case was i t doubtful that the property 50 of early- and latewood was of two different populations and thi s was f o r ultimate t e n s i l e s t r a i n . In order to test t h i s , an analysis of variance was calculated f o r ultimate s t r a i n values of both early- and latewood included. The resu l t of t h i s analysis i s given i n Table 17 i n which the ultimate s t r a i n values of the three growth increments were also tested. The analysis revealed that s t r a i n behavior of the two wood zones was highly s i g n i f i c a n t l y d i f f e r e n t , as well as that the three growth increments were not different from each other i n respect to ultimate s t r a i n i n tension. Most of the s i g n i f i c a n t interactions i n Table 17 are those involving wood zone, ind i c a t i n g that the s t r a i n behavior of earlywood and that of latewood are not only of a dif f e r e n t order of magnitude, but also that the two zones reacted i n a different manner to the treatments used. On the basis of these findings, ultimate s t r a i n results obtained from early- and latewood were handled separately i n subsequent analyses. No sim i l a r tests of wood zones were carried out with regard to strength, e l a s t i c i t y and work to maximum load because of obvious differences between these properties i n early- and latewood. In Tables 9 and 10 the analyses of variance show that ultimate t e n s i l e strength of both early- and latewood were s i g n i f i c a n t l y influenced by the treatments at the 0.1 per cent l e v e l of pro b a b i l i t y . No interactions occurred s i g n i f -icant among the three treatment^ that i s , at a l l temperatures and moisture contents wood reacted i n the same manner to variations i n cellulose DP. Conversely, at a l l DP and tern-51 perature l e v e l s , changes i n moisture content induced the same type of va r i a t i o n i n te n s i l e 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 property i s apparent f o r both early- and latewood. An exception to thi s general statement i s latewood elas-t i c i t y which appears to be unchanged by variations i n c e l -lulose DP. In earlywood, e l a s t i c i t y of the most severely degraded samples i s s i g n i f i c a n t l y lower than that of wood having cellulose of higher molecular weight. The analysis of ultimate s t r a i n values i s given i n Tables 13 and 14. It should be noted i n these tables that the r e l a t i v e l y narrow temperature range alone did not induce any s i g n i f i c a n t effect on the s t r a i n behavior of either early- or latewood. 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 s i g n i f i c a n t manner at the 0.1 per cent pro b a b i l i t y l e v e l . For both early- and latewood ultimate s t r a i n values, temperature and' moisture content interaction i s highly s i g n i f i c a n t . From Table 4 i t may be seen that the above effect i s due to an interes t i n g trend i n s t r a i n values. It i s noticeable that, at the highest moisture content l e v e l latewood s t r a i n i n -creased with increasing temperature, at the two lower moisture l e v e l s i t decreased with increasing temperature. In the case of earlywood ultimate s t r a i n values, a sim i l a r 52 highly s i g n i f i c a n t interaction was obtained between temper-ature and moisture content. In addition, here, a highly s i g n i f i c a n t interaction between cellulos e DP and moisture content was( calculated. The analyses of variance of work to maximum load values f o r early- and latewood are given i n Tables 15 and 16 respectively. In these, some of the interactions between treatment effects 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 addition to the main ef f e c t s . For earlywood samples, a l l the f i r s t order interactions show s t a t i s t i c a l significance, although they are seemingly of less importance than the main treatment eff e c t s . Nevertheless, the results of analyses indicate that at various temperature and moisture content l e v e l s , variations i n cellul o s e DP induced di f f e r e n t changes i n work values. The analysis of work to maximum tension load for latewood specimens, as shown i n Table 16, indicates that the only f i r s t order interaction inducing s i g n i f i c a n t v a r i a t i o n i n work values of t h i s wood zone was that between cellulos e DP and moisture content. On the other hand, a l l f i r s t order interaction i n earlywood work values turned out 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 . The analyses of variance of strength properties also gave a basis f o r subsequent regression analyses of the data. F i r s t l y , a l l means reported i n Tables 2 through 5 were plotted against temperature, moisture content and ce 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 . From these plots the general 53 trend of points with regard to each variable was examined and various preliminary curves were f i t t e d to f i n d the mathematical expression best describing the relationships. In these operations the least squares method was used, and the model giving s i g n i f i c a n t l y highest R value was selected. Secondly, the possible interactions were included i n the f i n a l regression equations. Only those interactions were included i n these relationships which had been proved s i g n i f i c a n t i n the previous analyses of variance calculations. Accordingly, for ultimate strength values, no interactions were included i n the regression equations, whereas f o r work to ultimate tension load i n earlywood, the basic equation describing variations due to i n t r i n s i c v i s c o s i t y , temperature, and moisture content included a l l the possible f i r s t order interaction terms. The equations calculated i n the above manner are reported i n Table 18. Similar relationships were calculated f o r strength properties with DP values included instead of i n t r i n s i c v i s c o s i t i e s as measures of cellulose chain length. These l a t t e r equations are given i n Table 19. The response surfaces based on the best f i t t i n g mathematical models are shown i n Figures 17 through 20. In each figure, early- and latewood results are given separately, since the equations describing variations i n strength properties of the two wood zones were also found to be d i f f e r e n t . The r e l a t i v e importance of factors influencing t e n s i l e 54 strength properties was examined by p a r t i t i o n i n g the R p values of each regression equation. I f 100xR i s the per cent v a r i a t i o n explainable by the factors examined,then p a r t i t i o n i n g t h i s according to those factors gives the per cent v a r i a t i o n accounted f o r by each factor. Results of these calculations are given i n Table 20. The variations due to the interactions between cellulos e i n t r i n s i c v i s c o s i t y , temperature, and moisture content are not l i s t e d i n d i v i d u a l l y i n t h i s table because t h e i r t o t a l contribution to changes i n strength properties was generally smaller than that of any one of the main effects 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 interactions includes the t o t a l amount of v a r i a t i o n induced by such interactions. In Table 21 simple correlation c o e f f i c i e n t s are reported. These numbers were calculated on the basis of each variable alone, considering that a l l the residual 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 error i n ultimate t e n s i l e strength values i s also i l l u s t r a t e d graphically i n Figure 21. In t h i s figure, the range of t e n s i l e strength values obtained f o r air-dry earlywood specimens at 50°C i s plotted over the mathematically f i t t e d regression l i n e . The s o l i d l i n e curve represents the values f i t t e d by using the least 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 of Douglas f i r wood induced a r e l a t i v e l y large reduction i n both cellul o s e chain length and strength properties p a r a l l e l to grain. The effect was such that wood samples radiated to 10 and 15 megarad doses became f r a g i l e , especially i n the water-saturated condition. No v i s i b l e changes i n color appeared as a result of radia-t i o n even at as high as 15 megarad treatment, i n contrast to findings of investigators i n e a r l i e r studies (45,60,78). I f the darkening effect were due to oxidation associated with degradation, the fact that the wood samples i n t h i s experiment were radiated i n well-sealed bags i n the saturated condition, could have prevented such a chemical reaction through the r e s t r i c t i o n of the amount of available oxygen. The only noticeable difference between radiated and untreated wood sections was that the former had a s l i g h t l y unpleasant, a c i d i c smell upon opening the bags. This smell 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 severely treated ones. Figure 15 i s a diagram representing the effect of gamma radiation of wood on cellulose i n t r i n s i c v i s c o s i t y . 56 The general configuration of the curves i s sim i l a r to what would be expected on the basis of theoreti c a l calculations of Charlesby (17), Bovey (10), and Chapiro (16). Charlesby (17), working with i r r a d i a t e d cotton 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 plotted against i r r a d i a t i o n dose on a log-log scale, a convex-upward curve was obtained. However, when the v i s c o s i t y was related to the sum- of the actual and the'virtual' radiation dose on the same scale, an almost perfect straight l i n e prevailed. Here, the v i r t u a l radiation dose was defined as the dose which would be re-quired to degrade a cellulos e molecule of i n f i n i t e length to a polymer having the same degree of polymerization 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 radiation dose was estimated to be one megarad. Through several t r i a l s i t was found that, when th i s dose was used as v i r t u a l dose, the points plotted on a log-log scale were well positioned on a straight l i n e . Using the value obtained t h i s way, a simple l i n e a r regression was calculated with the aid of the least squares method between log[ v?] and log(R+R Q), where R was the actual dose to which the samples were ex-posed, and R Q was the v i r t u a l radiation dose taken as 1 megarad. The equation calculated from combining a l l early-and latewood data has the following form: logH] = -0.8589 log(R+R Q) + 1.5714 According to Charlesby (17) and Chapiro (16), the regression 57 c o e f f i c i e n t of the log(R+R Q) term, i . e . , the slope of the l i n e i s the same number as the exponent i n equation 0 0 quot-ed e a r l i e r . By t h i s mathematical approach i t was hoped to obtain a more r e a l i s t i c conversion method from i n t r i n s i c v i s c o s i t y to DP. However, the K m factor f o r such a r e l a -tionship could not be calculated i n a si m i l a r manner, so that a unique formula f o r DP calculations a f t e r various doses of gamma radiation could not be developed. The gain here i s s t i l l considerable, i n that the exponent f o r a possible exponential relationship i s probably more accurate than the ones developed i n dif f e r e n t experiments and under dif f e r e n t conditions. For example, the exponent of 0.8589 i s consider-ably larger than the one developed by Timell (93), which was 0.572. Nevertheless, the exponent so calculated f o r a possible exponential relationship between i n t r i n s i c v i s c o s i t y and DP, i s well i n the range of such values determined by various workers, as the range i s generally given as 0.70 to 1.00 (77). From the above calculations a method f o r converting v i s c o s i t i e s into DP values may be developed. I f the o r i g -i n a l DP of cellulose i n wood, as determined using the con-version factor derived from data of Timell (93), i s accepted as true value, the factor K i n an exponential expression m may be calculated. I f the K m factor i s calculated by sub-s t i t u t i n g the o r i g i n a l DP of cellulose 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, the number obtained i s 0X219. The same number f o r summerwood 58 cellulose becomes 0.0215. I f the above K m factors and the exponent 0.8589 are used i n an expression of the exponential type, a new set of DP values may be obtained which may be somewhat more accurate than the "empirical values calculated i n t h i s experiment. In Table 22, cellul o s e i n t r i n s i c v i s -c o s i t i e s are given with the corresponding two DP values, one calculated by the empirical method described i n Methods Section, the other by using the aforementioned exponential relationship. This l a t t e r technique may be regarded as more accurate because, i n the former procedure, a rather long extrapolation had to be made from the l i n e a r relationship based on data of Timell (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 radiation dose estimated i n th i s study f o r wood was i n good agreement with Charlesby's (17) figure, which was found to be the same value i n that study on cotton l i n t e r s . This can only exist i f the i n i t i a l DP values of the two types of cellulose are equal, and i f the rate of degradation by gamma rays of the two types i s the same. The f i r s t part of the above assumption i s supported by the recent findings of Goring and Timell (31) that a l l native celluloses have approximately the same degree of polymerization i n t h e i r natural state, independent of source. The second part of the assumption i s i n contrast with the theory of Smith and Mixer (86) that l i g n i n serves as a protective medium against i r r a d i a t i o n . 59 The curves r e l a t i n g cellulose DP to v a r i a t i o n i n radiation dose are shown i n Figure 16. They conform to the general expectation that there i s a r e l a t i v e l y large reduction i n cellulos e DP at low in t e g r a l doses, followed by gradually decreasing degradation. Bovey (10) has given a simple mathematical expression describing the relationship: DP DP = 1 +,S where DP i s the degree of polymerization a f t e r radiation; DPQ, the i n i t i a l degree of polymerization of the polymer; and S, the number of scissions per o r i g i n a l chain.. The above mathematical expression represents a hyperbolic curve asymptotic to the S axis horizontally, and to the l i n e intercepting the S axis at the value of -1 v e r t i c a l l y . The above function can be written as: i - = 4- d + s) DP ~ DP o which means that the reciprocal of DP af t e r degradation w i l l be a l i n e a r function of the number of scissions, with an intercept on the jjp— axis at jp-". o On the basis of the above considerations an attempt was made to calculate a regression of the reci p r o c a l of DP on radiation dose. The equations f o r early- and' latewood samples, respectively, are: -|jp-.= -0.000005745 + 0.00005512 R 60 - g j r = -0.00001082 + 0.00003654 R where R i s the actual radiation dose to which the samples had been exposed p r i o r to DP determinations. Although the correlations f o r the above regressions were found to be very high (0.91 and 0.87), they gave values too low to 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 of the constant term i n both equations indicates that degrees of polymerization," obtainable for i n i t i a l c e l l u l o s e are negative numbers, which i s obvi-ously meaningless. Bovey (10) questioned the v a l i d i t y of such a calcu l a t i o n because of the low, often negative, results for . i n i t i a l DP values. Neal and Kraessig (73) have developed an expression to calculate the f r a c t i o n of bonds broken by gamma rays. They found that, i f the i n i t i a l and the re s u l t i n g cellulose DP's are known, the f r a c t i o n of bonds broken can be calculated by the following simple formula : Fraction of bonds broken = o By d e f i n i t i o n , i n t h i s expression DP and DP Q should be number-average values. These authors claim that sat i s f a c t o r y results can be obtained i f i n t r i n s i c v i s c o s i t y values are substituted f o r DP numbers. Although i n t r i n s i c v i s c o s i t y data are correlated to an average closer to the weight-average, rather than to the number-average DP values, the f r a c t i o n of 61 bonds broken should be a l i n e a r function of i n t e g r a l radiation dose <-l73). Data of Meal and Kraessig (73) conformed well to t h i s l i n e a r i t y . In this experiment, the f r a c t i o n of bonds broken, calculated from either v i s c o s i t y or DP values, did not show a l i n e a r relationship with i n t e g r a l radiation dose. The configuration of the curve suggests that at high dosage le v e l s the' f r a c t i o n of bonds broken increases more rapidly with increasing doses than at low l e v e l s . However, the small number of dosage l e v e l s used i n t h i s study does not allow any manipulation leading to the reasons f o r t h i s non-linearity. II EFFECTS OF CELLULOSE CHAIN LENGTH ON STRENGTH PROPERTIES OF WOOD PARALLEL TO GRAIN To develop better understanding of the factors responsible f o r the relationship of strength properties and cell u l o s e chain length of wood, i t seems appropriate to f i r s t review the mechanism of deformation under t e n s i l e stresses. When a s o l i d i s i n a stress-free state, i t s molecules or other submicroscopic elements are i n a stable, equilibrium position. The a t t r a c t i n g and r e p e l l i n g molecular forces cancel each other. In stressed state, however, the molecular spaces, and also the molecular forces, are of d i f f e r e n t magnitude (74, 75). I f , f o r instance, the body i s subjected to t e n s i l e stress 62 which causes an expansion, the molecular spaces grow larger i n the d i r e c t i o n of tension. In that d i r e c t i o n the r e p e l l i n g forces become smaller, and the a t t r a c t i n g forces increase, provided that the applied stress i s within the e l a s t i c range of the material. There prevails a new equilibrium between the t e n s i l e force plus the r e p e l l i n g forces on the one hand, and the molecular a t t r a c t i n g forces on the other. The f i r s t two forces together tend to increase the molecular spaces, an while the l a t t e r force tends to decrease them innattempt to restore 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 o r i g i n a l p o sition with respect to one another, but i n the course of time, or with increase i n the applied force, more and more bonds get into the force range of new s i t e s . By t h i s a new equilibrium position i s established i n which the a t t r a c t i n g and r e p e l l i n g forces are equal and where no external t e n s i l e stress i s necessary to achieve the body length. The material i s then stress-free again, but p l a s t i c -a l l y deformed. B r i e f l y then, t h i s i s the molecular mecha-nism of stress 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 to s t r u c t u r a l and chemical complexities of the material. Tracheid walls of conifers can be looked upon as a network of bond chains, some of which consist of segments of c e l l u l o s e chains, others of secondary valence forces between molecules 63 and t h e i r segments. The weakest primary valence forces exi s t i n g i n .a single c e l l u l o s e chain are the -C-O-C- bridges connecting the glucose units to each other. According to Mark, i n Ott (76), the strength of these bridges i s approx-imately 1 ,144,000 p s i . I f a more accurate calculation i s used thi s value can reach 2,133,000psi (77) for an idealized c e l l u l o s e sample of the highest possible orientation. The l a t e r a l forces between the chain molecules are 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 investigation of IR spectra of c e l l u l o s e . The force necessary to break a secondary valence bond of the above type i s only approximately 43,000 p s i , as was estimated from breaking sucrose crystals (76). Due to t h i s great difference between the two forces, i t seems to be evident that, when an external force i s applied, de-formation takes place i n the inter-molecular bonds. The strength of the -C-O-C- bonds i s so high that extension of the molecular chain i t s e l f cannot be rea l i z e d . Bond deformation, therefore, i s a property of the weaker type, the inter-chain bonds. For an i d e a l polymeric material i n which chains are oriented p a r a l l e l , deformation due to external stress can occur as slippage. In thi s process the hydrogen bonds which hold the chains together l a t e r a l l y must be overcome. S l i d i n g of the molecules upon each other can star t when the energy necessary f o r t h i s purpose i s less than that required f o r 64 breaking the primary valence forces along the chains. In order to p u l l out a chain molecule embedded among;; others i n t h i s i d e a l arrangement, the force to be applied would depend on the t o t a l l a t e r a l cohesive force 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 (72) made an attempt to calculate the minimum number of glucose residues i n a chain which would be necessary to produce an o v e r a l l energy of the l a t e r a l bonds higher than that repre-sented by a single primary valence bond. He estimated that i f 70 glucose units of one chain are associated with 70 units of a neighboring chain, through a l l possible hydrogen bonds, the l a t e r a l energy would be high enough to effect breaking of a chain at a -C-O-G- linkage. Prom the above, i t i s evident that i f the number of cross-links i s less than that produced by approximately 200 to 250 hydrogen bonds, s l i p p i n g w i l l take place. Then i t follows that slippage w i l l occur the more readily, the smaller the number of l a t e r a l l i n k s . Tensile strength, therefore, should depend on chain length of c e l l u l o s e . On the other hand, cellulose beyond a certain c r i t i c a l chain length should show t e n s i l e strength independent of DP. Systematic investigations of Skoone and Harris (85) with cellul o s e acetate have c l e a r l y shown t h i s relationship between chain length and strength. They foundthat, when / t e n s i l e strength and ultimate elongation were plotted 65 against number-average DP of the acetate, the slope of the curve describing the relationship was more or less constant up to approximately 200 to 250 DP. Above th i s c r i t i c a l value the increase i n strength with chain length became less pro-nounced, as i f the chains had obtained a s u f f i c i e n t length to be e f f e c t i v e l y bonded together by secondary forces and thus to u t i l i z e the longitudinal strength of the chains. Although this i s i n general agreement with the slippage theory of deformation, there occurs a r e l a t i v e l y large difference between the actual and the theore t i c a l value of the l i m i t i n g degree of polymerization. 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 fact that the molar cohesion of -COOCH^ groups, substituted f o r the hydroxyls i n cellulose acetate, i s only 5600 kg c a l per mole, while that f o r OH groups i s 7250 (67,76). In addition, the orientation of molecules i n synthetic high polymers i s f a r from being perfect as was assumed i n the Meyer's (72) 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 Harris (85) that, whereas ultimate elongation values almost completely l e v e l l e d off at a DP of approximately 250, t e n s i l e strength did not reach a constant value even at a DP of 500. Indeed, there have been reports i n the l i t e r a t u r e of a high correlation between strength and DP f o r different v a r i e t i e s of cotton f i b r e s at DP l e v e l s as high as 8,000 .to 10,000 (37). 66 In natural f i b r e s , the condition of i d e a l orientation i s never realized, therefore the relationship i s often obscured. In well oriented ramie, hemp and f l a x f i b r e s , Meyer and Lotmar, as ci t e d i n Ott (76) and by Hermans (36), found modulus of e l a s t i c i t y i n the same order of magnitude as the values computed f o r an i d e a l f i b r e . This merely suggests that rupture of primary valence bonds i s involved i n breaking cellul o s e i n materials of high orientation. In less well oriented c e l l u l o s i c materials, the ultimate strength values are much lower than the calculated figures, the difference being primarily due to the p i t c h of the s p i r a l structure. Berkley and Woodyard (8) found a very high correlation (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 of the s p i r a l structure of c e l l u l o s e . The orientation effect i s d e f i n i t e l y present i n woody f i b r e s as well, so that the c r i t i c a l DP of cellulose should be higher than the theo-r e t i c a l l y calculated one-. Before a bond can contribute to the strength of the material, i t has to be oriented i n the di r e c t i o n of stresses. This orientation i s f i r s t produced i n the bonds or bond series of the shortest length which event results i n the stressing and, consequently, breaking of bonds successively introduced. The breakdown of one bond allows the stress to pass to another i n p a r a l l e l with i t . In wood f i b r e s a relationship between strength 67 properties and cellulose chain length i s further modified by the fact that approximately 30 to 35 per cent of the cellulo s e i s i n an amorphous state (80). In the amorphous regions of the c e l l u l o s e , only a proportion of the available OH groups i s hydrogen bonded. According to Lauer (59), an average of two OH groups per glucose residue are available fo r reaction with hydrophilc reagents which can penetrate f r e e l y into these regions. 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 cellul o s e are not believed to be discrete e n t i t i e s , i t i s reasonable to assume that deformation due to external stresses takes place p r e f e r e n t i a l l y i n the less r i g i d l y bonded amorphous zones. As a r e s u l t , the slippage phenomenon i n wood fi b r e s should take place between micelles or whole f i b r i l s which are held together r e l a t i v e l y 'loosely' by amorphous ce l l u l o s e , rather than between ind i v i d u a l molecules. It follows from the above considerations that degradation of cellul o s e by chemical means should have a greater effect on the e l a s t i c properties of wood than a ran-dom s c i s s i o n of chains. Wakeham, as c i t e d by Ott et al.(77). and Hermans (36) report that i t i s possible through chemical degradation to a t t a i n reductions i n strength properties while the X-ray structure and the average cellulo s e chain length of the material remain unchanged. Due to greater f l e x i b i l i t y of the amorphous regions, a more even d i s t r i b u t i o n of stresses may be achieved. This 68 may p a r t l y eliminate the successive breaking of the c e l l u l o s e chains due to stress concentrations mentioned e a r l i e r . On the other hand, various constituents such as l i g n i n , hemi-celluloses and extraneous materials deposited i n the amorphous regions may increase the chance of non-uniform stressing of the cellul o s e chains. These deposits may be looked upon as minute blocks among the cord-like cellul o s e molecules. When stress i s applied to t h i s system, a free orientation of the cords i n the d i r e c t i o n of stresses would be prevented by the blocks. This should re s u l t i n stress concentrations and hence a greater p r o b a b i l i t y of successive rupture of the chains. The relationship between ultimate t e n s i l e strength and cellul o s e chain length of Douglas f i r wood obtained i n th i s experiment i s shown i n Figure 17., Because of the uncertainty i n the conversion of i n t r i n s i c v i s c o s i t y to DP, strength was plotted against v i s c o s i t y . However, considering the apparent relationship between the two, i n t r i n s i c v i s -cosity may be taken as a direct measure of chain length. The relationship between strength and cellul o s e DP i s such that the curves have a large slope i n the region of small chain length, followed by a gradually decreasing slope as increasingly higher c e l l u l o s e DP values are maintained. The configuration of the curves suggests an asymptotic approach to a constant value at very high DP regions. This f i n d i n g i s i n good agreement with the results 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 (85), f o r c e l l u l o s e acetate, r e v e a l s that the general response of t e n s i l e strength of wood to changes i n c e l l u l o s e chain l e n g t h i s s i m i l a r to that of the acetate samples. At low DP regions, u l t i m a t e t e n s i l e strength i s more s e n s i t i v e to d i f f e r e n c e s i n c e l l u l o s e chain l e n g t h than at high DP l e v e l s . On the b a s i s of the-o r e t i c a l deformation considerations as discussed e a r l i e r , i t seems reasonable to assume that the slippage mechanism i s an important c o n t r i b u t o r to strength behavior of wood. The f a c t that slippage occurs more r e a d i l y i n wood wit h s h o r t -chain c e l l u l o s e suggests that i n t r i n s i c f o r c e s responsible f o r such slippage are r e l a t e d to chain l e n g t h . In s p i t e of the. complex chemical 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 appreciated 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-a n i c a l p r o p e r t i e s . In c e l l u l o s e , such as that of ramie or hemp, the c o n t r i b u t i o n of the hydrogen bonds to p h y s i c a l and mechanical 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 chains i s obscured by f a c t o r s of s t r u c t u r a l and/or chemical nature. As a r e s u l t , a degradation of c e l l u l o s e chains does not b r i n g about as great a r e d u c t i o n i n strength as would be expected were a l l the a v a i l a b l e hydroxyls engaged i n i n t e r -7G chain cohesion, and were a l l the chains perfectly oriented i n the longitudinal d i r e c t i o n . One effect of t h i s i s that no sharply distinguished c r i t i c a l DP can be established from the curves i n Figure 17. These curves, f i t t e d to the ex-perimental data obtained at various temperature and moisture content l e v e l s , f l a t t e n out rather gradually with increasing DP values. This i s quite unlike what would be expected f o r the relationship i n an i d e a l , homogeneous high polymer. In wood, slippage i s probably a factor of deformation i n quite high DP regions and gradually increases with decreasing chain length. This seems to be a reasonable assumption i f one consideres that - deformation takes place i n the amor-phous regions, but not i n the r i g i d c r y s t a l l i t e s . It has been mentioned e a r l i e r that the physical structure of the cellul o s e i n the c e l l wall varies from 'badly' disorganized amorphous state, through r e l a t i v e l y well organized mesomorphous and paracrystalline zones, to perfect c r y s t a l s . 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; properties dependent upon those phases. Even at high average DP lev e l s there may be s i t e s of loosely linked cellul o s e chains with r e l -a t i v e l y low cohesive forces among them. In these regions, a slippage may occur upon application of external stresses regardless of high DP, f o r i t i s the number of hydrogen bonds, rather than the chain length d i r e c t l y , that i s the l i m i t i n g factor to strength. As cellul o s e becomes degraded, more 71 and more s i t e s of various disorganization reach a condition i n which the number of l a t e r a l bonds i s no longer enough to r e s i s t stresses. Therefore, slippage w i l l occur and, as a r e s u l t , decrease t e n s i l e strength. Differences between the strength-DP relationship of early- and latewood may be noted i n Figure 17. The response of strength of latewood to changes i n cellulos e chain length i s les s pronounced than that of earlywood. The decrease i n slope with increasing DP i s more gradual f o r the former. Also, while i n earlywood, strength at 2.5 dl/g i n t r i n s i c v i s c o s i t y i s only 40 per cent of that at 35.0 dl/g, i n latewood t h i s figure i s 55 per cent over the same v i s -cosity range. In other words, the r e l a t i v e strength loss due to cellulos e degradation i s greater f o r the early- than fo r the latewood samples. Both of the above differences suggest that there may be a basic difference between the properties of cellulos e i n the two wood zones. The orientation of cellulos e i n latewood i s reported-l y steeper than i n earlywood (41,101,102). The possible effect of orientation on the strength-DP relationship l i e s i n the fact that separation of cellulos e chains or micelles i s easier at an angle to t h e i r axis than when stress i s applied a x i a l l y . As a re s u l t , t e n s i l e stress applied to wood with higher f i b r i l angle should produce a slippage between cellulo s e chains or micelles at a higher DP l e v e l than i n wood with small f i b r i l angle. 72 Another factor that could influence configuration of strength-DP curve i s the s i g n i f i c a n t l y higher degree of c r y s t a l l i n i t y of latewood than that of earlywood, as ob-served by lee (63). Since strength behavior i s mainly dependent on the amorphous cel l u l o s e , a s h i f t i n the crys-talline-amorphous r a t i o towrd higher values should result in- a s h i f t i n DP dependence of strength properties. The higher the r e l a t i v e amount of amorphous ce l l u l o s e , the greater the influence of DP variations on strength characteristics of wood. On the basis of e a r l i e r development of a model equation (42), i t was possible i n t h i s study to mathemat-i c a l l y estimate the intra-ihcrement strength v a r i a t i o n f o r the three increments tested. In Figure 22 the curves represent changes i n ultimate wet t e n s i l e strength i n r e l -ation to r e l a t i v e position i n the increment. The appropriate regression c o e f f i c i e n t s of the corresponding equations were calculated by substituting average strength values obtained a f t e r various dosage l e v e l s of gamma radiation, i n saturated conditions, at 25°C, into the basic mathematical model. This model equation i s also shown i n Figure 22. The above substitution could be done because early and l a t e -wood specimens were taken from approximately 30 and 80 per cent p o s i t i o n r e l a t i v e to the beginning of the incre-ments respectively. Average latewood 73 percentage of the three growth increments wasj used f o r S i n the calculations. Wo attempt was made to estimate intra-increment changes i n strength of air-dry specimens because the o r i g i n a l model was based on strength values taken at moisture contents above the fibre-saturation point. However, the assumption was made that a f t e r various radiation treatments the basic arctangent function would accurately describe the strength-va r i a t i o n s . Since the independent variables i n the mathemat-i c a l model are only per cent position i n the increment, and latewood per cent, the above assumption could be made safely. There i s no reason to believe that either of these two growth-ri n g c h a r a c t e r i s t i c s would suffer any change due to gamma radiation. Among the strength properties studied, e l a s t i c i t y was the least affected by changes i n cellulos e chain length. The basic reason f o r t h i s behavior of wood may l i e i n the mode of cellulos e degradation by gamma rays. As discussed e a r l i e r , extension due to external stresses takes place i n the amorphous regions of the cellulose and not to 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 that de-formation i s the property of the secondary valence bonds because the observed t o t a l elongation of wood i n tension i s much greater 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 either the r e l a t i v e amount of amorphous 74 cellul o s e was increased, or i f the t o t a l number of hydrogen bonds was decreased. F i r s t l y , with i r r a d i a t i o n the crystalline-amorphous r a t i o i s believed to remain constant (84). Since the r e l -ative amount of the amorphous phase of cellulose 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 since a main chain s c i s s i o n process does not involve a reduction i n the number of l a t e r a l bonds. From these considerations i t seems to be reasonable that the immediate response of wood to applied stresses remains un-changed aft e r random s c i s s i o n of cellulose chains, since neither the r e l a t i v e number of the l a t e r a l bonds nor t h e i r strength i s changed. Modulus of e l a s t i c i t y i s calculated as the slope of the i n i t i a l part 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 material to applied stresses. Since slippage 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 high stress l e v e l s , e f f e c t -ing a break i n the specimen, i t does not have an influence on the slope at the early part 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 affected by variations i n c e l l u l o s e chain length i n a way s i m i l a r to that i n ultimate t e n s i l e strength. The general configuration 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 v i s -cosity i s such that t h e i r i n i t i a l slopes gradually 75 decrease toward higher DP regions. There appears to be considerable deviation i n the reaction of wood s t r a i n to cellulo s e DP from the curves reported by Skoone and Harris (85) f o r cellul o s e acetate. For wood, there exists a continuous increase i n s t r a i n with increasing 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 region. The difference may be explained on the same grounds as were mentioned i n connection with t e n s i l e strength, i . e , by chemical complexity and s t r u c t u r a l imperfections of wood. The s i m i l a r i t y between the response of ultimate s t r a i n and that of strength to variations i n c e l l u l o s e DP may be that the same mechanism governs both of these properties. Indeed, the two are i n such close r e l a t i o n that t h e o r e t i c a l l y either may be considered a condition of ultimate f a i l u r e . Failure i n a specimen due to external forces can either be looked upon as a phenomenon due to c r i t i c a l stress con-d i t i o n or as one due to c r i t i c a l state of material deforma-ti o n . Reduction i n ultimate t e n s i l e s t r a i n as a result of random depolymerization of cellul 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 150 f o r both early- and latewood. This i s a r e l a t i v e figure very si m i l a r to that found i n t e n s i l e strength over the same DP range, confirming the close correlation between ultimate 76 stress and ultimate s t r a i n . The fact that ultimate s t r a i n values of latewood were generally higher than those of earlywood cannot he adequately explained on the basis of c e l l u l o s e structure. In f a c t , the higher degree of c r y s t a l ] i n i t y of the former would indicate 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 fact that latewood specimens f a i l e d i n longitudinal shear, especially at high DP l e v e l s , i n d i c a t i n g that a substantial part of the deformation i n t h i s type of wood took place i n the heavily l i g n i f i e d middle lamella. This assumption i s i n contrast with e a r l i e r observations made by Garland (26), Gerry (27), and Koehler (51) who reported that c e l l s either broke right across the double wall or separated between the outer and middle layers of the secondary wall. More recently, the occurrence of t h i s l a t t e r type of f a i l u r e i n tension has been confirmed by Lagergren,Rydholm and Stockman (55), and Carlsson and lagergren (15). Evidences of middle lamella f a i l u r e also appear i n the l i t e r a t u r e . Kollmann (52) c i t e s Clarke who showed that f a i l u r e i n s t a t i c bending of ash wood occurred i n the middle lamella, leaving the c e l l wall un-damaged. Recently, I f j u and Kennedy (41) as well as Wellwood (102) have suggested that such f a i l u r e might res u l t i n longitudinal micro-tension tests of wet Douglas f i r latewood specimens. It i s quite conceivable that c e l l s with thick secondary wall, consisting of highly oriented and highly c r y s t a l l i n e c e l l u l o s e , may be stronger i n tension p a r a l l e l 77 to grain than the cementing material i n i t s longitudinal shear resistance, latewood tracheids of Douglas f i r f u l f i l l these requirements to effect a separation i n the middle lamella upon application of t e n s i l e stresses. The middle lamella of conifer tracheids has been reported to contain some 70 to 72 per cent l i g n i n (7,57,58). Recent studies conducted by Asunmaa and lange (5) have revealed that concentration of hemicelluloses i s also high i n the outer region of the c e l l wall. Both l i g n i n ; arid hemicelluloses are known to exist i n an amorphous phase i n the c e l l wall, which condition should be accompanied by p l a s t i c mechanical behavior. In latewood where a part of the deformation takes place i n t h i s amorphous cementing layer, at least 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 -dicate middle lamella deformation i n t h e i r s i t e s of tension f a i l u r e . Work to maximum load may be regarded as the t o t a l energy required to break a piece of 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 influence of ultimate t e n s i l e strength and e l a s t i c i t y , as well as ultimate elongation of the specimen, are apparent on t h i s property. Work to maximum load, therefore, may be considered as a good single measure of the mechanical behavior of wood, combining the effects of a number of properties which operate simultaneously during stressing of 78 the specimen. Since a l l the simple strength properties were inversely affected "by degradation of cell u l o s e , work to maximum load showed a similar, but more pronounced response to DP. Early-wood suffered a reduction i n work of 80 to 85 per cent, while latewood from 75 to 80 per cent. The curve r e l a t i n g maximum work to cellulos e chain length, shown i n Figure 20, i s s i m i l a r to those obtained f o r strength and s t r a i n , however, the curvalinearity here i s more pronounced. This i s due to the greater drop i n th i s property over the DP range from 5500 to 150 than was obtained f o r the simple strength prop-perties. A calculation based on the o r e t i c a l energy values may be of interest, to 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 tested i n tension p a r a l l e l to grain. In order to do t h i s , a number of assumptions have to be made. F i r s t l y , i t i s assumed that a l l t e n s i l e strength of wood i s due to cellulos e and that the other constituents do not take part i n the mechanism of response to t e n s i l e stresses. Secondly, deformation, and consequently work, takes place only i n the amorphous regions of the ce l l u l o s e . Thirdly, deformation i s the property of the secondary valence bonds and therefore the primary bonds do not contribute to the work values. With these assumptions the theoreti c a l and the actual energy values may be compared. A 40 i n . l b / cu i n . maximum work with oven-dry Douglas f i r earlywood corresponds 79 to 4.5x10 erg / cu i n . The energy per secondary bond as calculated by Mark, i n Ott (76), i s approximately 3x10"*^ ergs. From these, i t follows that i f a l l the deformation took 20 place among the hydrogen bonds, approximately 1.5x10 bonds would have to be broken i n 1 cu i n . of earlywood. I f the weight of that cube i s calculated, using a s p e c i f i c gravity (weight oven-dry/volume green), and an average volumetric shrinkage of 12 per cent, the resu l t i s 2.9 g of wood substance. It i s further assumed that about 40 to 45 per cent of t h i s wood substance i s cellulos e of long-chain structure 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 per cent of t h i s i s i n the amorphous phase.If the above corrections are made, the remaining amorphous cellulos e i n 1 cu i n . of Douglas f i r earlywood i s 0.40 g. With the aid of Avogadro's number (6.023x102^ per mole) and the molecular weight of glucose anhydride of 162, as well as considering that each glucose unit has 3 available OH groups f o r hydrogen bonding, a t o t a l number of possible 21 bonds i n 1 cu i n . of earlywood i s calculated to be 4.0x10 . 20 Comparing t h i s number with the 1.5x10 calculated from the experimental work values, i t i s estimated that only about 1/26 of the t o t a l bond energy i n wood with pe r f e c t l y oriented ce l l u l o s e 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 fact that i n the amorphous regions much less than 3 bonds per glucose residue form actual cross-links (59). Also, the st r u c t u r a l complexity i n wood 80 does not allow a uniform stressing of a l l cellulose chains when load i s applied. When a calculation, s i m i l a r to that described above i n d e t a i l , i s carried out f o r latewood, an e f f i c i e n c y number of approximately 1/18 i s obtained. This difference -may be explained on the basis of better organization and more perfect orientation on the part of latewood (42,63,101). Another explanation may be the recent b e l i e f that the c e l l wall of earlywood i s less closely packed than that of l a t e -wood (105), which should result i n a smaller number of available OH groups that could actually participate i n hydrogen bonding. I l l MOISTURE CONTENT SENSITIVITY OF TENSILE STRENGTH PROPERTIES It i s of importance to consider the means by which water i s retained i n wood, to understand the behavior of wood under stress conditions. Any c a p i l l a r y space which i s large i n comparison with the dimensions of a water mole-cule can be penetrated by vapor through simple d i f f u s i o n mechanism. Water of thi s type i s commonly ca l l e d free water since 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 place, therefore, the penetration of t h i s vapor does not involve true sorption. Consequently, variations i n the amount of free water are not accompanied by differences i n physical and mechanical properties of wood. Surface bound water i s the f i r s t type held by wood through true sorption. This water i s held 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 the water molecules, and 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 distance between some water molecules and the c e l l wall material becomes small enough, and the force of a t t r a c t i o n large enough to bind the two together and to draw the water into the micellar spaces and amorphous regions. The a t t r a c t i v e forces may become so great that they cause distortions i n the f i b r i l l a r network, and swelling takes place. It i s the OH groups of the glucose units i n c e l l u l o s e , and those of the other sugar units of the hemicelluloses, that o f f e r the s i t e s for attachment to the molecularly-sorbed water. I f the water molecule approaches these s i t e s i n close proximity, the energy of binding between i t and the carbohydrate chain i s the same as the energy of the l a t e r a l hydrogen bond between two OH groups i n neighboring chains. When close approach i s prevented, the energy of binding i s smaller. The above type of molecular sorption 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 surfaces of the cellulo s e 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 possible points along t h e i r lengths, 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 regions, the maximum binding energy between cellulose and water cannot be r e l i z e d . Even i n these regions, cellulose chains are so closely packed that they can off e r s u f f i c i e n t b a r r i e r to the closest approach of the water molecule. Therefore, the binding energy be-comes only the average of many degrees of binding. Yet, th i s energy may be s u f f i c i e n t l y large to set up stresses i n the f i b r i l l a r network as a result of swelling, and break a few of the i n i t i a l l y stable ce l l u l o s e - t o - c e l l u l o s e hydrogen bonds i n the paracrystalline or mesomorphous regions. There-by, some new s i t e s are made available f o r water entry, at a l a t e r stage of sorption. The water so adsorbed by wood, forms bridges between OH groups of neighboring chains i n the amorphous regions. The binding force between the OH groups at the ends of the bridges i s much smaller, and i s more readi l y broken by ex-ternal stresses, than the hydrogen bonds between OH groups i n intimate contact. When te n s i l e stress i s applied to the swollen material, the water molecules i n the bridges can 83 move from one OH group i n the cellul o s e chain to another. This 'jump' process results i n o v e r a l l slippage i n the material. In t h i s sense, the water molecules \.sorbed onto the surface of the cellul o s e micelles may be considered as a 'lubricant'. The above i n e l a s t i c exchange of hydrogen bonds be-tween the neighboring 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 stress condition. The structure of wood and the c e l l wall i t s e l f i s f a r too i r r e g u l a r f o r direct correlation between the molecular and bulk properties to be established quantitatively. Consequent-l y , the simple l u b r i c a t i o n role of water bridges i n wet wood i s an oversimplification of the problem. But i t does give some idea of what could happen i n the wet c e l l wall when i t i s subjected to stresses. Frey-Wyssling (24) has postulated that increased p l a s t i c i t y i n the wet state i s a f i b r i l l a r rather than a molecular phenomenon. According to him, there must be con-siderable 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 forces which hold the m i c r o f i b r i l s together i n the c e l l wall, since they cannot elongate i n d i v i d u a l l y unless 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 describe what takes place i n wet wood when stressed, the degree of c r y s t a l l i n i t y should be i n close r e l a t i o n with the e l a s t i c properties of wood. 84 The f i b r i l l a r interpretation of the strength-moisture relationship assignes an important role to the incrusting materials between the m i c r o f i b r i l s (24). These substances may determine to a large extent the e l a s t i c i t y and extens-i b i l i t y of wood. Wall constituents such as l i g n i n , hemicel-luloses and small amounts of pectins are now believed to be p a r t l y distributed among the cellulo s e m i c r o f i b r i l s . Some evidence has recently been gathered according 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 associated with the paracrystalline phase around the cellulose c r y s t a l l i t e s (19). Hemicelluloses are also believed to be concentrated between the m i c r o f i b r i l s , a l -though i t i s quite conceivable that s l i g h t distortions i n the paracrystalline regions are due to chains of non-cellulosic polysaccharides which, by virtue of t h e i r chemical structure, cannot f i t pe r f e c t l y into the r i g i d form of c r y s t a l l i t e s (19, 79). A l l of these constituents, with the exception of l i g n i n , are very sensitive to swelling with water. Therefore, t h e i r influence on strength properties 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 ind i v i d u a l constituents (18). It has been shown that up to 50 per cent of the adsorbed water i s held by the amorphous cel l u l o s e , about 37.5 per cent by the hemicelluloses, and the remaining 12.5 per cent by l i g n i n . This 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 o f c e l l u l o s e i n a t t r a c t i n g w a t e r . I t i s o n l y r e a s o n a b l e t o assume t h a t t h e i r i n f l u e n c e on t h e m o i s t u r e dependence 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 o n e . 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 a d s o r p t i o n i n t h e r e g i o n s between t h e m i c r o f i b r i l s . T h i s s u g g e s t s 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 m o i s t u r e - d e p e n d e n t s t r e n g t h b e h a v i o r o f wood i s a complex p r o b l e m . Not o n l y does t h e s t r u c t u r a l a r r a n g e m e n t o f t h e c e l l u l o s e f ramework have t o be t a k e n i n t o a c c o u n t , as i s 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 , b u t a l s o t h e 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 t h e n o n - c e l l u l o s i c s u b s t a n c e s have t o be g i v e n a t t e n t i o n . The r e s u l t s o f t h i s e x p e r i m e n t show t h a t a l l s t r e n g t h p r o p e r t i e s 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 c o n t e n t i n t h e r a n g e f r o m o v e n - d r y t o w a t e r - s a t u r a t e d c o n -d i t i o n s . B e c a u s e o n l y t h r e e m o i s t u r e c o n t e n t l e v e l s were i n c l u d e d i n t h i s s t u d y , t h e g e n e r a l p a t t e r n o f 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 t o m o i s t u r e c o n t e n t c a n n o t be p r e d i c t e d w i t h any c e r t a i n t y . However , a n i n t e r e s t i n g r e s u l t i s t h e f a c t t h a t , r e g a r d l e s s o f c e l l u l o s e DP o f t h e sample o r t e s t t e m p e r a t u r e , 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 c o u l d be 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 d e t e r m i n e d a t m o i s t u r e - f r e e and a i r - d r y c o n d i t i o n s . On t h e o t h e r h a n d , s a m p l e s w i t h m o i s t u r e c o n t e n t s h i g h e r t h a n t h e f i b r e - s a t u r a t i o n 86 point were invariably found to be of lower strength than those i n the moisture-free or air-dry state. These suggest an unusual configuration of the curve describing strength-moisture content relationship i n that i t i s probably convex, rather than concave, as i s the case i n a number of other strength properties. It has long been established that below the f i b r e -saturation point v a r i a t i o n i n strength i s not d i r e c t l y proportional to 1 the change i n moisture content, but follows di f f e r e n t laws. Most frequently the relationship i s such that when the logarithm of strength value i s plotted against moisture content, the resultant points l i e very close to a straight l i n e (103). This relationship indicates 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 larger variations i n strength than the same magnitude of moisture changes at a higher moisture content l e v e l . Crushing strength i n compression p a r a l l e l to the grain shows the most consistent logarithmic relationship with moisture content, so that t h i s property has become the one often used f o r determination of fibre-saturation point (99). Other properties, however, exhibit considerable discrepancy i n t h e i r r e l a t i o n to moisture (22,32,52,83,106). Deviations from the logarithmic relationship as proposed by Wilson (103) are such that f o r a given property either l i n e a r , convex or concave curvalinear equations may represent behavior. 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 strength of wood p a r a l l e l to grain, and even le s s i s known about the effect of moisture content on th i s property. The reason f o r sc a r c i t y of information i s due to the fact that t e n s i l e strength p a r a l l e l to grain rep-resents the highest strength property of wood, even ex-ceeding i n value the modulus of rupture as derived from bending tests, so that i t i s not generally a r e s t r i c t i n g feature i n engineering design. It has long been observed that s t r u c t u r a l members i n wooden construction seldom f a i l i n tension under stress conditions, but that other strength properties c r i t i c a l l y affect the loading of such members. P a r t i c u l a r l y involved are the r e l a t i v e l y low values of shear p a r a l l e l , and compression perpendicular, to the grain that often cause f a i l u r e at the joints long before tension stresses approach c r i t i c a l l i m i t s . The same low strength properties make i t extremely d i f f i c u l t to develop an e f f i c i e n t test method f o r tension p a r a l l e l to grain. I t i s only reasonable that more attention has been paid to the l i m i t i n g properties than to t e n s i l e strength of wood along the grain. The few experimental results available from par-a l l e l to grain tension tests i n r e l a t i o n to moisture content of wood are those quoted by Kollmann (52). These are from data of Kuch, Kttch and Teschov, Schlyter and Winberg, Graf, and Winter. Results of tension tests 88 obtained by Kuch f o r beech, as well as by Graf f o r spruce, indicate the fact that t e n s i l e strength p a r a l l e l to grain i s probably another property of wood with r e l a t i o n to moisture content changes that i s inadequately represented by the logarithmic equation proposed by Wilson (103). The p e c u l i a r i t y of t e s i l e strength p a r a l l e l to grain-moisture content diagrams i s that the highest value i s not reached at the lowest moisture content, but that i t f a l l s somewhere between 5 and 10 per cent moisture content, from which i t drops by approximately 25 to 30 per cent at the f i b r e -saturation point. Strength of oven-dry wood i s also lower than the maximum discussed above, and the rate of decrease i n strength between 10 and 0 per cent moisture content i s roughly equal to that between 10 per cent and the f i b r e -saturation point. Values of Schlyter and Winberg as recorded by Kollmann (52) show a l i n e a r increase i n t e n s i l e strength p a r a l l e l to grain from the fibre-saturation point to about 6 per cent moisture content, but values below 6 per cent are not available i n t h e i r study. Kuch, as ci t e d by Kollmann (52), also investigated the te n s i l e strength behavior of European ash which showed no r e l a t i o n whatso-ever to changes i n moisture content. Reasons f o r maximum te n s i l e strength at moisture contents above oven-dry have been given by Kollmann (52). He believes that increased mobility of str u c t u r a l elements 89 due to a minimum moisture content, i s necessary to reli e v e l o c a l i z e d stresses during testing. Thereby, a more even d i s t r i b u t i o n of stresses i s produced throughout the entire cross-section of the test specimen, which could result i n increased t e n s i l e strength. Hermans (36) likened the amorphous regions of c e l -lulose to cords clamped i n a rending apparatus. I f stress i s applied to the system made up of cords of unequal length, f a i l u r e w i l l occur at a r e l a t i v e l y low load l e v e l due to non-uniform stressing of the cords. However, i f the cords have been previously knotted to each other , tension i s more evenly divided and a higher ultimate strength w i l l be attained. The knots i n th i s l a t t e r system represent co-hesive forces between cellulos e chains produced by the increasing number of hydrogen bonds with decreasing moisture content, while the former arrangement i s analogous to swollen cellul o s e i n which the chain molecules are not linked f i r m l y due to the presence of water. A reduction.in moisture content, should, therefore, result i n apparent improvement i n the mechanical properties of wood. The above analogy could be reversed i f the cords i n the rending apparatus are substituted by ones of equal length. A knotting of these cords should res u l t i n a less uniform d i s t r i b u t i o n of the t e n s i l e force, consequently a lower t e n s i l e strength should be attained. This l a t t e r analogy suggests that with decreasing moisture content, 90 strength, i s decreased due to increased l a t e r a l cohesion which, i n turn, produces l o c a l i z e d stresses. It seems that both mechanisms play a part i n the determination of moisture dependence of wood strength properties. Above a certain moisture content l e v e l , c e l l u l o s e existing i n the f i r s t arrangement preva i l s , whereas at low moisture l e v e l s mech-anism of the second type of cellul o s e arrangement wins out. In moisture content regions where maximum te n s i l e strength i s attained, the two types of mechanism could be at equi-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 ultimate t e n s i l e strength. The convex upward configuration i s also suggested here. Variation i n e l a s t i c i t y caused by differences i n moisture content was by f a r the most important factor i n t h i s study and exceeded the influence of cellul o s e DP. In contrast to cellul o s e chain length, moisture content i s expected to play a s i g n i f i c a n t role i n determining e l a s t i c properties of wood. At least one of the two conditions i s required to effect 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 either produce a change i n the crys-talline-amorphous r a t i o of c e l l u l o s e , or i t should affect the binding energy of the hydrogen bonds between chains. An increase 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 that i t substantially 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. Hermans' (36) analogy of the cord system may also be applicable here i n explaining the convex shape of the elasticity-moisture content curve. An increase i n moisture content i n the wood induced an increase i n ultimate t e n s i l e s t r a i n i n earlywood and a decrease i n latewood. The difference i n the response i n the two wood zones may be attributed to the difference i n t h e i r deformation mechanisms i n tension p a r a l l e l to 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 least at r e l a t i v e l y high stress 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 stresses are high enough, deformation and f a i l u r e w i l l occur i n the heavily l i g n i f i e d middle lamella. In summerwood, where the above requirement i s f u l f i l l e d due to the high strength of the thick middle layer of secondary wall, ultimate elongation i s a sum of the deformation suffered by the c e l l u l o s i c secondary wall, and that of the p l a s t i c but high-strength middle lamella. As moisture content increases, strength of the secondary wall decreases accordingly, z and the middle lamella component of the s t r a i n decreases. This i s because extension i n the middle lamella i s possible only at extremely high load l e v e l s . The res u l t i s that the o v e r a l l ultimate t e n s i l e s t r a i n of the specimen i s reduced as moisture content increases. In earlywood, the middle lamella cannot contribute to deformation due to i t s extremely high strength properties and to the low 92 strength of the r e l a t i v e l y t h i n secondary wall. Here, an increase i n moisture content results 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 part of the c e l l wall which eventually increases t o t a l deformation i n stress conditions. The influence of moisture on deformation properties of earlywood cellulo s e may be more pronounced than that i n latewood due to the greater r e l a t i v e amount of amorphous regions i n the former. In latewood, the influence of moisture content on work' to maximum load was greater than i n earlywood. The reason f o r t h i s i s the difference i n s t r a i n behavior of these two wood types i n r e l a t i o n to moisture content. Where as i n latewood both strength and s t r a i n were substantially reduced by increases i n moisture content, i n earlywood, ultimate t e n s i l e strength decreased, but ultimate s t r a i n became greater , at high moisture l e v e l s . Since work to maximum load i s a measure of mechanical behavior of wood, including stress and deformation ch a r a c t e r i s t i c s of the material, the combined effect of the simultaneous events occurring i n tension tests had to be diff e r e n t i n the two wood zones. Nevertheless, the results of t h i s experiment indicate that the energy required to break a piece of wood i n tension p a r a l l e l to grain i s lower f o r wet wood than f o r dry wood. 93 IV INFLUENCE OF TEMPERATURE ON THE MECHANICAL BEHAVIOR OF WOOD IN TENSION PARALLEL TO GRAIN Mechanical behavior of wood i s influencedby tem-perature changes i n such a way that the higher the temper-ature the lower the strength. The effect has been con-sidered large enough by certain authorities (89) to jus-t i f y corrections of "test results to standard temperature, the c o e f f i c i e n t being approximately 1 per cent per degree centigrade .below certain 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 properties with increasing temperature, i s due to increased Brownian motions of atoms through greater excitation. The higher energy thus acquired by the atoms results i n diminishing cohesion between molecules with increasing temperature. At the submicroscopic l e v e l , the amorphous system, as well 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 intermolecular forces within and between those regions decrease. I f sorbed water molecules are present i n the amorphous regions, they further increase the distance between the c r y s t a l l i t e s through excitation. It i s generally considered that the influence of temperature on strength properties of wood i s an i n t e r -c e l l u l a r rather than an i n t e r - f i b r i l l a r phenomenon. I t i s the middle lamella which has the greatest .'.,:r: 94 temperature s e n s i t i v i t y . Since the middle lamella con-s i s t s mostly of l i g n i n and hemicelluloses, i t s temperature s e n s i t i v i t y i s greater than that of the secondary wall due to the p l a s t i c properties of these constituents. The middle lamella can be p l a s t i c i z e d i n two 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 i s believed to take place i n the hemi-cell u l o s e part of the middle lamella. In practice, t h i s low softening temperature i s u t i l i z e d i n the semichemical pulping process where def i b e r i z a t i o n i s done i n t h i s tem-perature range. Another way of p l a c t i c i z i n g the middle lamella i s to increase the temperature to a l e v e l higher than 160°C. In t h i s case i t i s the l i g n i n that softens. This higher softening point i s u t i l i z e d i n the Asplund and Masonite defibrating processes. The mechanical properties of wood at various temperature and moisture content conditions have been studied by Sulzberger (89). He found that both crushing strength and modulus of e l a s t i c i t y i n compression along the grain, decreased most nearly i n a l i n e a r manner be-tween -20 and +80°C, fo r several conifers and'porous woods. In some species, such as s i t k a spruce, hoop pine and mountain ash, a convex upward curve gave a better f i t when wood was tested at high moisture content l e v e l s , due to an i n -creased rate of strength reduction between 70 and 80°C. E l a s t i c i t y values obtained from s t a t i c bending tests showed 95 the same general trend, but without curvalinearity at high moisture contents. Sano and his coworkers (82) obtained a l i n e a r relationship between t e n s i l e strength along the grain and temperature within the same temper-ature range as that used by Sulzberger (89), indicating that t h i s strength property of wood exhibits a sim i l a r general response to variations i n temperature as compres-sion p a r a l l e l to grain. It should be mentioned that, while strength i n compression was reduced by 40 to 50 per cent over the temperature range from -20 to 60°C, t e n s i l e strength decreased by only 10 per cent over the same range. This indicates that i f the p l a s t i c components of the c e l l wall, such as l i g n i n and the hemicelluloses, are respons-i b l e f o r the temperature dependence of strength, they are also responsible f o r the compressive strength of wood. This i s i n accordance with the assumption made e a r l i e r that the major role of cellulos e i s to give wood a high t e n s i l e strength, whereas l i g n i n serves the primary me-chanical role of r e s i s t i n g compressive stresses. A l l strength properties of Douglas f i r i n tension p a r a l l e l to grain as studied i n t h i s experiment were but s l i g h t l y affected by temperature variations within the experimental l i m i t s . Nevertheless, the effect was such that an increase i n temperature decreased strength proper-t i e s , with the possible exception of ultimate t e n s i l e s t r a i n which occasionally showed an increase with increasing 96 temperature. Ultimate t e n s i l e strength of earlywood was reduced by approximately 15 per cent over the temperature range from 25 to 70°C, while latewood showed about 30 per cent reduction i n thi s property over the same temperature range. This difference i n temperature s e n s i t i v i t y of strength of the two wood zones can be attributed to the greater contribution of the middle lamella to strength properties i n latewood. The thermo-sensitivity -of l i g n i n , approximately 70 per cent of which i s deposited i n the middle lamella, could influence the t e n s i l e strength-tem-perature relationship of latewood to a greater 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 t h i s zone. The influence of temperature on apparent e l a s t i c i t y was sim i l a r to that of the ultimate strength properties. Both strength and e l a s t i c i t y varied l i n e a r l y with temper-ature, although the three l e v e l s of temperature used i n th i s study do not allow description of an exact configura-t i o n describing t h i s relationship. In Figures. 17 and 18 the various planes i n the three-dimensional diagrams represent strength and e l a s t i c i t y respectively at various temperature l e v e l s . The spacing of the planes i s proportion-a l to the corresponding temperature differences which indicate the l i n e a r relationship. A discussion on the influence of temperature 97 on ultimate 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 appropriate since the effect was shown to be non-s i g n i f i c a n t . Nevertheless, the small effect of temperature i s graphically shown i n Figure 19. In latewood, the peculiar appearance of the planes may be recognized i n that they intercept each other, i n d i c a t i n g a s i g n i f i c a n t i n t e r -action between temperature and moisture content. This int e r a c t i o n w i l l be discussed l a t e r . The energy required to break the specimen i n tension p a r a l l e l to grain was lowered by increasing temperature. The r e l a t i v e amount of energy saved.by increasing the temper-ature from 25 to 70°C was less than 10 per cent f o r early-wood, but amounted to approximately 30 per cent f o r l a t e -wood. This i s attributed to the differences i n the de-formation mechanism of the two wood zones i n tension par-a l l e l to grain, as discussed e a r l i e r i n connection with t e n s i l e strength. Since ultimate t e n s i l e s t r a i n was not affected s i g n i f i c a n t l y by variations i n temperature, the rate of reduction i n work to maximum load was s i m i l a r to that i n ultimate t e n s i l e strength and/or e l a s t i c i t y . 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 of mechanical behavior of Douglas f i r wood i n tension p a r a l l e l to grain, r e l a t i v e variations i n strength properties due to differences i n moisture content .were greatly influenced by cellulose chain length. Early-wood samples, not treated by gamma radiation, suffered approximately 20 per cent reduction i n ultimate t e n s i l e strength over the range of oven-dry to water-saturated conditions. Samples from the same wood zone, with low DP values, showed about 40 per cent strength loss over the same moisture content range. Strength of latewood with severely degraded ce l l u l o s e also showed a greater s e n s i t i v -i t y to moisture content changes than that of the same growth zone but with undegraded c e l l u l o s e . Here, the range of re l a t i v e strength loss between the lowest and the highest DP values was found to be only about 5 per cent. The curves representing moisture s e n s i t i v i t y of te n s i l e strength are shown i n Figure 23, where per cent reduction i n strength due to differences i n moisture content between oven-dry and water-saturated conditions was plotted against i n t r i n s i c v i s c o s i t y . The continuous increase i n moisture s e n s i t i v i t y with decreasing chain length may be noted i n thi s figure. The above behavior of wood may be explained by the 99 slippage mechanism of f a i l u r e . Strength of wood with c e l -lulose of long-chain structure should not he affected by variations i n moisture content to the same extent as wood with short, degraded cellulo s e molecules. Swelling agents, such as water, diminish the cohesion between m i c r o f i b r i l s or molecular bundles i n wood. In fi b r e s of long cellulose chain structure the energy of 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 high to effect f a i l u r e i n primary valence bonds, rather than between molecules through s l i p -page. In short-chain structures, a relatively small increase i n moisture content may lower the in t e g r a l l a t e r a l bond to such a l e v e l that slippage between elements could occur upon application of external stresses. This behavior i s sim i l a r to the dependence of strength on cellulos e DP, ex-cept that here the strength of the bonds i s affected through swelling rather than the number of those bonds through decrease i n cellulos e chain length. Another item of significance to be noted i n Figure 23 i s the appreciably greater r e l a t i v e losses i n strength of latewood, upon increases i n moisture content, than those of earlywood. While reduction i n strength of early-wood ranges from approximately 20 to 40 per cent, that of latewood i s as high as 49 to 54 per cent, depending on cell u l o s e chain length. The reason f o r t h i s difference may be explained by the fact that s p e c i f i c gravity of latewood i n Douglas f i r i s approximately 3.0 to 3.5 times 100 that of earlywood (42). I t has long been recognized that swelling and shrinking of wood are affected by s p e c i f i c gravity variations i n that the higher the s p e c i f i c gravity the greater the dimensional changes due to variations i n moisture content. There have even been equations constructed to represent average relations between density and shrinkage and swelling (12,99). A greater swelling, on the other hand, results i n a proportionally larger area increase of speci-men. Ultimate load per unit area, therefore, decreases. Consistent with these considerations i s the fact that average loss i n modulus of rupture of coast-type Douglas f i r , as calculated from data reported by Wangaard (99), i s 35 per cent between air-dry and green condition, whereas that f o r i n t e r i o r type Douglas f i r over the same moisture content range i s only 33*3 per cent. Average s p e c i f i c gravity of the former i s reported to be 0.45 and f o r the l a t t e r i t i s 0.41. Moisture s e n s i t i v i t y of latewood strength, due to variations i n cellulose chain length, seems to be lower than that of earlywood. This i s indicated by the consider-ably smaller slope of the l i n e representing latewood strength loss i n r e l a t i o n to v i s c o s i t y i n Figure 23. This may be explained by the difference i n the c r y s t a l l i n i t y of the two wood zones (63). Since moisture adsorption as well as deformation take place i n the amorphous regions, s i g -n i f i c a n t l y lower percentage of amorphous cellulos e should 101 be accompanied by s i g n i f i c a n t l y lover s e n s i t i v i t y of strength values to moisture. On the other hand, degradation of cellulo s e of a greater r e l a t i v e amount of the amorphous zone should result i n a greater chance of slippage, con-sequently a higher 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 interaction between temperature and cellulose DP, and between temperature and moisture content, i n terms of ultimate t e n s i l e strength was n e g l i g i b l e as well as s t a t i s t i c a l l y non-significant. This was probably due to the narrow range i n temperature used i n t h i s study. In terms of e l a s t i c i t y , no f i r s t order interaction was found to be either 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 large enough fo r serious consideration. In t h i s l a t t e r property, the only factor inducing substantial changes was moisture content. Ultimate t e n s i l e s t r a i n i n earlywood was 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 interaction between cellulos e chain length and moisture content. This interaction i n s t r a i n was such that i n high DP regions there appeared to be a large increase i n e x t e n s i b i l i t y with increasing moisture content, while at low DP l e v e l s the effect of moisture content was minor, and occasionally even a decrease i n s t r a i n was observed with increasing moisture content. This peculiar s t r a i n behavior of wood, especially i n the earlywood zone, was unexpected. The only explanation of i t would be a hypothesis that, even i n earlywood, at high DP l e v e l s 102 there must occur a considerable extension of the c e l l wall before slippage between chains or m i c r o f i b r i l s develops. In these regions, moisture content p l a s t i c i z e s the c e l l wall material i n such a way that the higher the moisture content the greater the extension before ultimate f a i l u r e . In addition, the c e l l wall may offe r s u f f i c i e n t resistance to applied stresses to cause some deformation i n the middle lamella as well. On the other hand, when cellulose chain length i s low, the stresses developed during t e n s i l e testing can never reach a l e v e l at which stretching of the middle lamella can substantially contribute to ov e r a l l deformation. Also, slippage between m i c r o f i b r i l s i n the low DP region can occur at low load l e v e l s at which stretching of the c e l l wall i t s e l f i s not influenced by the addition of water. This happens because slippage can develop even i n the dry material e f f e c t i n g early f a i l u r e , without the weak-ening of l a t e r a l cohesive forces by the addition of water. An interaction between cellulose chain length and moisture content should exist i n terms of latewood s t r a i n values as well, i f the mechanism of deformation were sim i l a r i n the two growth zones. This was not found i n thi s study, so that i t i s assumed that different mechanisms govern s t r a i n behavior of early- and latewood. It i s conceivable that regardless of variations i n DP, the c e l l wall of latewood has such high strength that a great part of the deformation takes place i n then middle lamella. 103 Both early- 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 interaction with regard to both moisture content and temperature. In earlywood the effect was rather minor. Nevertheless, i t was such that s t r a i n decreased with increasing temperature i n the moisture-free wood, and i t increased or remained constant regardless of variations i n test temperature above the fibre-saturation point. Late-wood ultimate t e n s i l e s t r a i n showed a rather highly s i g n i f -icant interaction between moisture content and temperature. Here the general effect was such that while s t r a i n of dry samples decreased with increasing temperature, i n wet specimens i t increased substantially upon increase i n tem-perature. In dry latewood, however, the relationship i s not quite straight forward. The above interaction effect i s f a i r l y conclusive proof of the hypothesis that part of the deformation i n latewood takes place i n the middle lamella. As was stressed e a r l i e r , one of the possible ways of weak-ening the middle lamella between c e l l s i s to heat wood to approximately 50 to 100°C i n the presence of moisture. Work to maximum load showed highly s i g n i f i c a n t f i r s t order interactions among the three variables tested. As, this property i s considered the one combining a l l strength, s t r a i n and e l a s t i c i t y , these interactions were closely correlated to those found i n connection with the above simple strength properties. 104 VI RELATIVE AMOUNTS OP VARIATION IN TENSILE STRENGTH PROPERTIES ACCOUNTED FOR BY VARIOUS FACTORS j The effectiveness of the experiment may be estimated on the basis of what proportion of the t o t a l v a r i a t i o n i n strength properties tested has been accounted for by the experimentally controlled variables. The squares of cor-r e l a t i o n c o e f f i c i e n t s calculated f o r the multiple regression equations provide a direct numerical measure here (82). These numbers can be looked upon as percentages of v a r i a -t i o n explainable by the independent variables included i n the corresponding equations. The per cent residual 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 of the material and to experimental error. 1• Variation i n Strength Properties Due to Treatments In Table 20 the correlation c o e f f i c i e n t s are given as percentages of change i n strength properties due to controlled experimental treatments as based on the t o t a l amount of v a r i a t i o n i n those properties. These figures indicate that differences i n cellulose chain length, tem-perature, and moisture content together induced 57 to 71 per cent change i n the various mechanical properties tested, except f o r latewood e l a s t i c i t y , which could be explained to only 36 per cent by the above factors. These values 105 may be considered acceptable when dealing with a b i o l o g i c a l product such as wood. In spite of the c a r e f u l l y followed procedures i n the selection and preparation of material, and tension testing, some inherent wood chara c t e r i s t i c s could not be controlled. In general, strength properties of earlywood could be explained by the effects of experimental variables to a greater degree than those of latewood. The reason f o r t h i s probably l i e s i n the fact 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 of earlywood seem to be 5 to 10 per cent lower than those fo r latewood, as can be seen i n Tables 2 to 5. In a l l except e l a s t i c properties, cellulose chain length, measured either as i n t r i n s i c v i s c o s i t y or calculated as DP, was the most important single factor influencing t e n s i l e strength properties of both early- and latewood of Douglas f i r . The effect i s especially pronounced i n earlywood where the v a r i a t i o n due to differences i n c e l -lulose i n t r i n s i c v i s c o s i t y amounts from 42 to 63 per cent, as shown i n Table 20. This was expected because of the very wide range of v i s c o s i t y values used. The degree of polymerization i n control specimens was some 35 times that of the most severely degraded ones, and i n t r i n s i c v i s c o s i t y values ranged between 2.3 to 35.0 dl/g, a factor of more than 15 times. In Table 21, the simple correlation c o e f f i c i e n t s 106 are given. The squares of these values can also he looked upon as percentages representing that portion of the t o t a l v a r i a t i o n which can he accounted f o r by the single variable i n question. Here again, cellul o s e chain length, either as i n t r i n s i c v i s c o s i t y i n dl/g or as actual DP value, i s the most important single factor 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 strength properties alone. Por e l a s t i c i t y of both early- and latewood, as well as f o r ultimate t e n s i l e strength of latewood, moisture content i s shown to be the most important single factor. In a l l other properties tested, moisture content ranks second to cellul o s e DP. In general, moisture content v a r i a -t i o n affected strength, s t r a i n and' maximum work values to a greater extent i n l a t e - than i n earlywood. In Table 20 i t i s shown that, whereas i n latewood moisture content differences cotributed 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 strength cha r a c t e r i s t i c s mentioned above, i n earlywood t h i s range extended only from-approx-imately 3 to 10 per cent depending again on property. The simple correlation c o e f f i c i e n t s recorded i n Table 21 indicate s i m i l a r importance of moisture content on strength properties along the grain. Variation i n temperature was the least important of the factors studied i n t h i s experiment. It i s apparent, as indicated e a r l i e r , that the experimental range f o r tern-107 perature was the most lim i t e d of a l l the factors tested. In earlywood, the r e l a t i v e amount of v a r i a t i o n i n strength and e l a s t i c i t y induced by differences i n test temperature was approximately 6 per cent, while i n latewood th i s value ranged between 3 and 8 percent. This indicates that early-wood was somewhat more sensitive to temperature variations than was latewood. In maximum work and ultimate t e n s i l e s t r a i n values the effect of t h i s variable was small 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. Factors Influencing Tensile Strength Properties Inherent i n Wood The influence of wood v a r i a b i l i t y on t e n s i l e strength properties was minimized through sampling technique. Never-theless, certain variables of anatomical and submicroscop-i c nature remained uncontrolled. One anatomical factor that might have caused differences i n strength properties could be the v a r i a t i o n i n tracheid length. The fact that specimens were taken from the same r e l a t i v e p o sition 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 tracheids produced were of different length.' I t i s reasonable to assume that, 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 orientation of c e l l u l o s e i n the secondary c e l l wall could have 108 occurred among the increments tested. Wardrop (101) has reported that i n tracheids of radiata pine and Douglas f i r the smaller f i b r i l angles were found i n the longer elements within a single tree. These two factors could have account-ed for some v a r i a t i o n i n strength properties as i t i s well recognized that the greater strength of wood l i e s i n the dir e c t i o n of the cellulos e chains, that i s , i n the di r e c t i o n of the m i c r o f i b r i l s . The influence of tracheid length and f i b r i l angle on te n s i l e strength of wood has been reported by Wardrop (101), I f j u and Kennedy (41), Kellogg and I f j u (44), and Wellwood (102). From these studies i t i s evident that tracheid length and f i b r i l angle can exert t h e i r i n -fluence on strength properties only i f the s p e c i f i c gravity range of the material i s narrow. In thi s study r e l a t i v e density of wood was kept constant f o r the specimens, through the sampling design, so that the influence of anatomical factors could not be overshadowed by that of s p e c i f i c gravity. E a r l i e r , i n an investigation of intra-increment variations of strength properties p a r a l l e l to grain (42), i t was found that differences tangentially 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 within a growth increment. They were s t i l l between 5 and 25 per cent, a somewhat lower value than the coefficients of va r i a t i o n i n the four strength properties obtained i n t h i s 109 experiment. The difference may l i e i n the fact that, while i n the intra-increment study specimens were obtained from a block only 3 i n . i n tangential width, here the tangential range from which the test material was extracted was approximately f i v e times as wide. It i s also possible that variations i n anatomical cha r a c t e r i s t i c s do not occur only between increments. They may be present within a certain tangential width of the same increment, causing a v a r i a t i o n i n strength properties through tracheid length and /or f i b r i l angle differences. One possible error l i e s i n the fact that the dir e c t i o n of a l l tracheary elements i n a test block was considered uniform. Of course, t h i s assumption i s only generally true, since even a very small piece of wood, having a few tracheids i n thickness, can exhibit deviation from the p a r a l l e l arrangement of i t s tracheids. In fa c t , i t i s true that l o c a l l y , at s i t e s of tracheid endings, a deviation from the p a r a l l e l arrangement i s necessary to f i l l space. This microscopic misalignment of the tracheids would be of minor importance only i f the tracheid length i were constant i n the experimental material, as the number of tracheid endings i s i n direct r e l a t i o n to tracheid length. A tracheid misalignment due to growth conditions should be of greater importance. I r r e g u l a r i t i e s i n the arrangement of tracheids i s a f a i r l y frequent occurrence i n wood. The causes may be of several origins, f o r example 110 the v i c i n i t y of an inter-gram knot, natural bending i n the tree developed i n the competition f o r l i g h t , or a leaning due either to a constant d i r e c t i o n of wind during growing period or to slope of the ground on which the tree was grown. Although i n the selection of material the straightness of grain was c a r e f u l l y inspected by macros-copic means, occasional deviation from pe r f e c t l y straight alignment of the tracheids was noticed at time of microtome sectioning. Thus, some tension test specimens contained f i b r e s which lay at some angle to the d i r e c t i o n of load application. However small that angle might have been, i t s influence on t e n s i l e strength properties could contribute substantially to the v a r i a t i o n i n strength properties. This assumption i s supported by Hearmon, as c i t e d i n Meredith (71), who published a vector 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 longitudinal-transverse plane, with changing grain d i r e c t i o n . I t can be seen i n that diagram that r e l a t i v e l y small deviations from the longitudinal d i r e c t i o n result i n great reductions i n e l a s t i c i t y . Strength properties, other than e l a s t i c modulus, tested i n t h i s study may conceivably follow a s i m i l a r relationship to grain d i r e c t i o n . 11-1 3• Variation i n Tensile Strength Properties Due to Experimental Error Another part of v a r i a t i o n i n t e n s i l e strength properties unaccounted fo r by changes i n cellulos e DP, tem-perature and moisture content, were those due apparently to experimental error. One such possible error could have been introduced by the fact that rectangular specimens were used i n the tests. It i s known from various experi-mental stress analyses that, where there are abrupt changes i n either cross-sectional dimensions or i n the e l a s t i c properties of a piece of material under stress, stresses con-centrate at those s i t e s causing early f a i l u r e at r e l a t i v e l y low load l e v e l s (69). When a specimen i s clamped i n grips, such stress concentrations develop near the gripped area due to an abrupt change i n e l a s t i c behavior of the material at the grips. This often results i n f a i l u r e at grips. In t h i s experiment stress concentrations at grips were minimized. The gripping surfaces of the jaws were l i n e d with thin, hard-rubber sheets which provided a suf-f i c i e n t l y uniform hold on the specimen, and also 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 wood and the gripping assembly. Tightening of the jaws was accomplish-ed through a constant-torque-wrench which eliminated crush-ing of f i b r e s due to excessive pressure. In spite of these 112 precautions, about 5 to 10 per cent of the specimens f a i l e d at grips. A preliminary analysis showed that specimens that f a i l e d at or.near the jaws did not produce s i g n i f i c a n t l y lower strength values than those breaking between grips. On th i s basis, test results from specimens which broke at grips were retained. In an e a r l i e r study (42), various tension test specimen designs were investigated, with special emphasis on the r e p l i c a b i l i t y of test r e s u l t s , .as well as on the incidence of f a i l u r e at or near the grips. In that ex-periment i t was found that, when specimens are prepared from microtome sections of wood, the best results are obtained when testing rectangular pieces. Both higher ultimate t e n s i l e strength values and better r e p l i c a b i l i t y , as evidenced by co e f f i c i e n t s of var i a t i o n , were obtained by using a rectangular specimen design, while the incidence of grip f a i l u r e was of the same order of magnitude as that with necked-down test pieces. The use of a s t r i p of wood section with uniform cross-section along i t s length does not eliminate the presence of stress concentrations at grips. It i s only an improved form of specimen over various other types used by di f f e r e n t workers (41,46,50,101,102). Therefore, ultimate s t r a i n values, e l a s t i c i t y constants, and work to maximum, load data calculated on the basis of specimen 113 elongation observed as cross-head t r a v e l on the testing machine, cannot be accepted as true properties of the material. But they may be considered as apparent values. Nevertheless, they can be safely used within the study f o r comparative purposes. Stress concentrations i n the material under stress conditions may be due to incorrect gripping. I f a specimen i s clamped between the jaws of the testing machine i n such a way that one part of i t i s stressed before the other would carry any load, a non-uniform stress d i s t r i b u t i o n occurs. In a study of intra-increment strength variations i n Douglas f i r wood (42), the effects of various specimen misalignments have been investigated. In that experiment i t has been found that severe strength reductions can only be obtained when a rectangular specimen i s misaligned as much as 5° or more from the correct v e r t i c a l position, l e s s than 5° deviation from v e r t i c a l alignment of the speci-men did not produce a s i g n i f i c a n t l y lower strength or e l a s t i c i t y value, but variations with misgripped pieces were higher and occurrence of f a i l u r e at grips- was more frequent. In t h i s experiment, each tension test specimen was care-f u l l y positioned between the jaws although small, experi-mentally uncontrolable deviations from the correct position could have occurred, inducing additional v a r i a t i o n i n strength properties. 114 CONCLUSIONS From th i s study of the effects of cellulose chain length on the mechanical behavior of Douglas f i r wood i n tension p a r a l l e l to grain the following conclusions are drawn: 1. Cellulose i s degraded by exposure of wood to gamma rays. The random chain s c i s s i o n produces a large reduction i n cellulose DP at low in t e g r a l doses followed by a gradual-l y decreasing degradation. 2. Tensile strength properties of 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 quantitative but also q u a l i t a t i v e , i . e . , the response by mechanical char a c t e r i s t i c s of the two wood zones to changes i n temperature, moisture content, and cellul o s e chain length does not follow the same general trend. 3. It i s suggested that deformation i n Douglas f i r earlywood due to longitudinal t e n s i l e stresses 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 inter-tracheid one. 4. Variation i n cellulose chain length influences strength properties of wood to a greater extent i n the low than i n the high DP regions. The configuration of curves r e l a t i n g ultimate t e n s i l e strength , ultimate s t r a i n , and work to maximum tension load values to cellulose 115 chain length i s such that i t suggests asymptotic approach to a constant value at very high DP l e v e l s . This behavior i s explained by the slippage mechanism of deformation. are 5. E l a s t i c properties are not, orAvery s l i g h t l y influenced by changes i n cellulos e DP. This i s attributed to the fact that random s c i s s i o n of cellulos 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. Variations i n moisture content induce highly s i g n i f i c a n t changes i n t e n s i l e strength properties of Douglas f i r . The effect i s greater on l a t e - than on earlywood. The experimental results suggest a convex upward configuration of curves r e l a t i n g ultimate t e n s i l e strength and e l a s t i -c i t y to moisture content. 7. Influence of temperature within the range of 25 to 70°G i s minor i n comparison with that induced by cellulose DP and moisture content. On the basis of experimental results there i s no reason to suggest deviation from a l i n e a r relationship between strength properties and temperature. 8. Moisture s e n s i t i v i t y of wood with low-DP cellulos e i s higher than that of wood with cellul o s e of long-chain structure. This behavior of wood i n tension p a r a l l e l to grain i s also explainable by the slippage mechanism of deformation. , 9. I t i s suggested that the best single measure of the 116 mechanical behavior of wood i n tension p a r a l l e l to grain i s the value of work to maximum load. This t e n s i l e strength parameter includes a l l stress and deformation char a c t e r i s t i c s of the material that occur simultaneous-l y i n testing. It can also be looked upon as an energy necessary to break a specimen, therefore, i t can be of direct value i n p r a c t i c a l applications such as de-f i b e r i z a t i o n . 117 REFERENCES 1. Alexander, P., and A. Charlesby. 1955. Radiation protection of isobutyl and styrene. Proc. Royal Soc. A230: 136-145. 2. Alexander, W. 1., and R. 1. M i t c h e l l . 1949. Rapid measure-ment of cel 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. Anal. Chem. 21:1497-1500. 3. Alfrey, T. 1948. Mechanical behavior of high polymers. Interscience Publishers, Inc., New York. 581pp. 4. Arthur, J . C. 1958. The effects of gamma radiation on cotton. - I I I . Proposed mechanism of the effects of high energy gamma radiation on some of the molecular properties of p u r i f i e d cotton. Textile 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 of cellulose and hemicellulose i n the c e l l wall of spruce, b i r c h and cotton. Svensk Papperstid. 57: 501-516. 6. Badger, R. M., and R. H. Blaker. 1949. The investigation of the properties of n i t r o c e l l u l o s e molecules i n solution by l i g h t - s c a t t e r i n g methods. J . Phys. Chem. 53M056-1069. 7. Bailey, A. J . 1936. Lignin i n Douglas f i r . Composition of the middle lamella. Ind. Eng. Chem. 8:52-55. 8. Berkley, E. E., and 0. C. Woodyard. 1938. A new micro-photometer f o r analyzing X-ray d i f f r a c t i o n patterns of raw cotton f i b r e . Ind. Eng. Chem. 10:451-455. 9. Blouin, F. A., J . C. Arthur. 1958. The effects of gamma radiation on cotton. - I. Some of the properties of p u r i f i e d cotton i r r a d i a t e d i n oxygen and nitrogen atmospheres. Textile Res. J. 38:198-204. 10. Bovey, F. A. 1958. The effect of i o n i z i n g radiation on natural and synthetic high polymers. Polymer Re-views Vol. I. Interscience Publishers, Inc., New York. 287pp. 11. Brauns, F. E., and D. A. Brauns. 1960. The chemistry of l i g n i n . Supplement volume f o r 1949-1958. Academic Press, New York. 861 pp. 118 12. Brown, H. P., A. J . Panshin, and C. C. Porsaith. 1952. Textbook of wood technology. McGraw-Hill Book Co. Inc., New York. 783pp. 13. Bystedt, J., and A-M. Anderson. 1957. Measuring thickness of sheet materials by a precision d i a l indicator. Svensk Papperstid. 60:492-496. 14. Cannon, P. M., and M. R. Penske. 1938. Viscosi t y measure-ment. Ind. Eng. Chem. 10:297-301. 15. Carlsson, C. A., and S. Lagergren. 1957. Studies on the i n t e r f i b e r bonds of wood. Part 2. Microscopic examination of the zone of f a i l u r e . Svensk Pappers-t i d . 60:664-670. 16. Chapiro, A. 1962. Radiation chemistry of polymeric systems. High polymers, Volume XV. Interscience Publishers, Inc., New York. 712pp. 17. Charlesby, A. 1955. The degradation of cellulo s e by ion-i z i n g radiation. J . Polymer S c i . 15:263-267. 18. Commonwealth S c i e n t i f i c and Industrial Research Organization. 1954-1959. Sorption studies. 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 research on c e l l wall structure. Proceedings of the P i f t h World Forestry Congress. Vol. I I . pp. 1279-1288. 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 cellulo 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 bridging i n cel l u l o s e as shown by infrared absorption spectra. J . Am. Chem. Soc. 62:2859-2861. 22. Ellwood, E. 1. 1954. Properties of American beech i n tension and i n compression perpendicular to the grain and t h e i r r e l a t i o n to drying. Yale University, School of Forestry B u l l e t i n 61. 23. F r e i d i n , A. S. 1958. Diestvie radioaktivnogo na f i z i k o -mekhanicheskie svoistva drevesiny. Derev. Prom. 7(9):13-15. ( E f f e c t of radioactive radiation on the physical and mechanical properties of wood. C.S.I.R.O. Austr a l i a , Translation No. 4417.) 24. Frey-Wyssling, A. 1952. Deformation and flow i n biolog-i c a l systems. North Holland Publ. Co., Amsterdam. 552pp. . 119 25. Frey-Wyssling, A. 1953. Die pfla n z l i c h e Zellwand. Sprin-ger, B e r l i n . 367pp. 26. Garland, H. 1939. A microscopic study of coniferous wood i n r e l a t i o n to i t s strength properties. An. Mo. Bot. Garden 26:1-93. 27. Gerry, E. 1915. Fibre measurement studies: length v a r i a -tions, where they occur and t h e i r r e l a t i o n to the strength and uses of wood. Science 41-179 205. - 28. G i l f i l l a n , E. S., and 1. linden. 1957. Some effects of nuclear i r r a d i a t i o n on cotton yarn. Textile Res. J . 27:87-92. 29. , ] , 1955. Effects of nuclear i r r a d i a t i o n on the strength of yarns. Textile Res. J. 25:773-777. 30. Glegg, R. E., and Z. I. Kertesz. 1957. Ef f e c t of gamma radiation 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. Timell. 1962. Molecular weight of native c e l l u l o s e s . Tappi 45:454-460. 32. Goulet, M. 1960. Die Abhangigkeit der Querzugfestigkeit von Eichen-, Buchen-, und Pichtenholz von Peuchtig-k e i t und Temperatur i n Bereich von 0° bis 100°C. Holz Roh- Werkstoff 18:325-331. 33. Green, H. V., and J. Worrall. 1963. Wood quality studies. Part I.: A scanning microphotometer f o r automatically measuring and recording cer t a i n wood ch a r a c t e r i s t i c s . Pulp and Paper Research Institute of Canada. Technical Rept. No. 331. 37pp. 34. Harland,.¥. G. 1952. Relation between i n t r i n s i c v i s c o s i t y and degree of polymerization. Nature 170:667. 35. Harmon, D. J . 1957. Effects of Cobalt 60 radiation on the physical properties of t e x t i l e cords. Textile Res. J. 27:318-324. 36. Hermans, P. H. Physics and chemistry of c e l l u l o s e f i b r e s . E l s e v i e r Publishing Co., Inc., New York. 534pp. 37. Hessler, L. E., M. E. Simpson, and E. E. Berkley. 1948. Degree of polymerization, s p i r a l structure, and strength of cotton f i b e r . Textile Res. J . 18:679-683. 38. Holtzer, A. -M., H. P. Benoit, and P. Doty. 1954. The molecular configuration and hydrodynamic behavior of cellul o s e t r i n i t r a t e . J. Phys. Chem. 58:624-634. 120 39. Huggins, M. L. 1942. The v i s c o s i t y of d i l u t e solutions of long-chain molecules. - IV. Dependence on concentra-t i o n . J. Am. Chem. Soc. 64:2716-2718. 40. . 1958. Physical chemistry of high polymers. John Wiley & Sons, Inc., New York. 175pp. 41. I f j u , G., and R. W. Kennedy. 1962. Some variables a f f e c t -ing microtensile strength of Douglas f i r . Forest Prod. J . 12:213-217. 42. , R. W. Wellwood, and J . W. Wilson. 1963. Intra-increment. relationship of s p e c i f i c gravity, microten-s i l e strength and e l a s t i c i t y i n Douglas f i r . Paper presented to the annual Spring Conference, P a c i f i c Coast Branch, Canadian Pulp & Paper Association, May 9-11, 1963, Harrison Hot Springs, B.C. 43. Immergut, E. H., B. G. Ranby, and H. F. Mark. 1953. Recent work on molecular weight of c e l l u l o s e . Ind. Eng. Chem. 45:2483-2490. 44. Kellogg, R. M., and G. I f j u . 1962. Influence of s p e c i f i c gravity and certain other factors on the t e n s i l e properties of wood. Forest Prod. J. 12:463-470. 45. Kenaga, D. 1., and E. B. Cowling. 1959. Ef f e c t of gamma radiation on ponderosa pine: hygroscopicity, swelling and decay s u s c e p t i b i l i t y . Forest Prod. J . 9:112-116. 46. Kennedy, R. W., and G. I f j u . 1962. Application of micro-t e n s i l e t e s t i n g to thi n wood sections. Tappi 45: 725-733. 47. Klauditz, W. 1952. Zur biologisch-mechanischen Wirkung des Lignins im Stammholz der Nadel- und .flaubholzer. Holzforsch. 6:70-82. 48. . 1957. Zur biologisch-mechanischen Wirkung der Acetylgruppen i n Festigungsgewebe der laubhttlzer. Holzforsch. 11:47-55. 49. . 1957. Zur biologisch-mechanischen Wirkung der Cellulose und Hemicellulose im Festigungsgewebe der laubholzer. Holzforsch. 11:110-116. 50. Kloot, N. H. 1952. A micro-testing technique f o r wood. Austral. J. Appl. S c i . 3:125-143. 51. Koehler, A. 1933. Causes of brashness i n wood. U.S. Dept. Agriculture Technical B u l l e t i n No. 342. 121 52. Kollmann, P. 1951. Technologie des Holzes und der Holz-werkstoffe. Band I. Springer, B e r l i n . 1050pp. 53. . 1952. Die Bedeutung der Temperatur ftlr die E l a s t i z i t a t und Pestigkeit des Holzes. Holz Roh-Werkstoff 10:269-279. 54 . 1960. Die Abhangigkeit der elastischen Eigenschaften von Holz der Temperature. Holz Roh-Werkstoff 18:308-314. 55. lagergren, S., S. Rydholm, and L. Stockman. 1957. Studies on the i n t e r f i b e r bonds of wood. Part 1. Tensile strength of wood af t e r heating, swelling, and delign-i f i c a t i o n . Svensk Papperstid. 60:632-644. 56. Lang, W. 1957. Beitrag zur Bestimmung des DP-Grades von Ni-tro-Cellulosen mit h i l f e viscosimetrischer Messung-en. Svensk Papperstid. 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 wall of normal and reaction wood of spruce and a few hardwoods. Svensk Papperstid. 57:525-532. 58. . 1954. • The d i s t r i b u t i o n of the components i n the plant c e l l wall. Svensk Papperstid. 57:563-567. 59. lauer, K. 1951. Zur Kenntnis der Zellulosefasern. VI. Mitteilung: Zur Kenntnis der Struktur der Baumwall-Paser. Kolloid-Z. 121:36-39. 60. Lawton, E. J., ¥. D. Bellamy, R. E. Hungate, M. P. Bryant, and E. H a l l . 1951. Some effects of high v e l o c i t y electrons on wood. Science 113:380-382. 61. , , , , 1951. Studies on the changes produced i n wood exposed to high v e l o c i t y electrons. Tappi 34:113A-116A. 62. , A. Bueche, and J . Balwit. 1953. Irr a d i a t i o n of polymers by high energy electrons. Nature 172:76-77. 63. Lee, C. L. 1961. C r y s t a l l i n i t y of wood cel l u l o s e f i b r e s . Porest Prod. J. 11:108-112. 64. Lindsley, 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 related to degree of n i t r a t i o n . Ind. Eng. Chem. 45:2491-2497. 65. Loos, W. E. 1962. Effe c t of gamma radiation on the toughness of wood. Porest Prod. J . 12:261-264. 66. Ma, T. S., and G. Zuazaga. 1942. Micro-Kjeldahl determina-t i o n of nitrogen. Ind. Eng. Chem. 14:280-282. 122 67. Mark, H. 1950. Physical chemistry of high polymeric systems. Interscience Publishers, Inc., New York. 506pp. 68. . 1957. Radiation chemistry and wood. Composite Wood 4:1-8. 69. Markwardt, L. J., and W. G. Youngquist. 1956. Tension test methods f o r wood, wood-base materials, and sandwich constructions. U.S. Dep. Agr., Forest Ser., Forest Prods. Lab., Rept. No. 2055. 70. Mater, J . 1957. Chemical effects of high-energy i r r a d i a -t i o n of wood. Forest Prod. J . 7:208-209. 71. Meredith, R. 1953. Mechanical properties of wood and paper. North Holland Publ., Amsterdam. 298pp. 72. Meyer, E. H. 1950. Natural and synthetic high polymers. High polymers, Vol. IV. Interscience Publishers, Inc., New York. 891pp. 73. Neal, J . L.,.and H. A. Kraessig. 1963. Degradation of cellulose with megavolt electrons. Tappi 46:70-72. 74. Nissan, A. H., and H. G. Higgins. 1959. Molecular approach to the problem of v i s c o e l a s t i c i t y . Nature 184:1477-1478. 75. , and S. S. Sternstein. 1962. Cellulose as a v i s c o e l a s t i c material. Pure Appl. Chem. 5:131-146. 76. Ott, E. 1946. Cellulose and cellulos e derivatives. Interscience Publishers, Inc., New York. 1076pp. 77. , H. M. Spurlin, and M. W. Graff i n . 1955. Cellulose and cellu l o s e derivatives. 2nd. ed., High polymers Vol. V., Part I I I . , Interscience Publishers, Inc., New York. pp.1057-1601. 78. Paton, J . M., and R. F. S. Hearman. 1957. Eff e c t of exposure to gamma rays on hygroscopicity of s i t k a spruce. Nature 180:651-653. 79. Preston, R. D. 1960. Anisotropy i n the microscopic and submicroscopic structure of wood. Proceedings of the F i f t h World Forestry Congress, Vol. I I . pp.1298-1307. 80. Ranby, B. G. 1958. The fin e structure of cellulos e f i b r i l s . C o l l e c t i o n of Papers, Symposium of the B r i t i s h Paper and Board Makers' Association. Kenley, England. 487pp. 123 81. Hunger, H.G., and W. Klauditz. 1953. ITber Beziehungen zwischen der chemischen Zusammensetzung und den Festigkeitseigenschaften des Stammholzes von Pappeln. Holzforsch. 7:43-58. 82. Sano, E. 1961. Effects of temperature on the mechanical properties of wood. I I . Tension p a r a l l e l to grain. J. Japan. Wood Res. Soc. 7:189-191. 83. Schniewind, A. P. 1962. Tensile strength perpendicular to grain as a function of moisture content i n C a l i -f o r n i a black oak. Forest Prod. J . 12:249-252. 84. Seaman, J . F., M. A. M i l l e t t , and E. J . Lawton. 1952. Effe c t of high 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. Harris. 1945. Polymolecularity and mechanical properties of cellulo s e acetate. Ind. Eng. Chem. 35J478-482. 86. Smith, D. M., and R. Y. M i x e r / 1959. The effect of l i g n i n on the degradation of wood by gamma i r r a d i a t i o n . Radiation Res. 11:776-780. 87. Snedecor, G. W. 1957. S t a t i s t i c a l methods. The Iowa State College Press, Ames, Iowa. 534pp. 88. Stone, J . E. 1955. The rheology of cooked wood. I I . Eff e c t of temperature. Tappi 38:552-559. 89. Sulzberger, P. H. 1953. The effect of temperature on the strength of wood, plywood and glued j o i n t s . Dep. Supply, Aeronautical Res. Consultative Committee, Au s t r a l i a . Rept. ACA-46. 44pp. 90. Timell, T. E. 1954. The effect of rate of shear on the v i s c o s i t y of d i l u t e solutions of ce l l u l o s e n i t r a t e . Svensk Papperstid. 57:777^788. 91. . . 1954. The influence of rate of shear on viscosity-concentration relationship f o r di l u t e solutions of cellulo s e n i t r a t e . Svensk Papperstid. 57:844-849. 92. . 1954. The effect of solvent-solute i n t e r -action on the v i s c o s i t y of d i l u t e solutions of cell u l o s e n i t r a t e . Svensk Papperstid. 57:913-920. 93. . 1957. Molecular weight of native c e l l u l o s e . Svensk Papperstid. 60:836-842. 94. . 1957. Molecular properties of seven native ce l l u l o s e s . Tappi 40:25-29. 124 95. Timell, 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 alpha-cellulose of wood. Tappi. 40:30-33. • 96. , and E. C. Jahn. 1951. A study of the i s o l a t i o n and polymolecularity of paper b i r c h . Svensk Papperstid. 54:831-846. 97. , and C. B. Purves. 1951. A study of the i n i t i a l stages of the methylation of c e l l u l o s e . Svensk Papperstid. 54:303-332. 98. Treiber, E., and B. Abrahamson. 1959. Gfesichtpunkte zur viscosimetrischen DP-Bestimmung. Holzforsch. 13: 161-177. 99. Wangaard, P. P. 1950. The mechanical properties of wood. John Wiley & Sons, Inc., New York. 377pp. 100. . 1957. A new approach to the determination of f i b e r saturation point from mechanical tests. Porest Prod. J. 7:410-416. 101. Wardrop, A. B. 1951. C e l l wall organization and the properties of xylem. - I. C e l l wall organization and the v a r i a t i o n i n breaking load i n tension of the xylem i n conifer stems. Austral. J. S c i . Research Series B. 4:391-414. 102. Wellwood, R. W. 1962. Tensile t e s t i n g of small 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., Technical Bui. No. 282. 88pp. 104. Wise, I . E., and E. C. Jahn. 1952. Wood chemistry. Vol. I. Reinhold Publishing Co., New York. 105. Worrall, J . G-. 1963. The relationship between f r a c t i o n a l void volume and wood quality i n western Canadian conifers. B.S.P. Thesis, Faculty of Forestry, The University of B r i t i s h Columbia. 44pp. 106. Youngs, R. L. 1957. The perpendicular-to-grain mechanical properties of red oak as related to temperature, moisture content and time. U. S. Dep. Agr., Forest Ser., Forest Prods. Lab. Rept. No. 2079. TABIES AND FIGURES LO Table 1. Comparison of cellulose DP values calculated f o r a sample with 35.0 dl/g i n t r i n s i c v i s c o s i t y , using various relationships. Relationship Resulting DP Authority [7] = 0.0108 DP 3241 Harland (34) [7] = 5x10" 3 DP 7000 Holtzer,Benoit and Doty (38) [V] =10x10"3 DP ' 3500 Immergut, Ranby and Mark (43) [V] =3.7x10""5DP 9459 Kraemer (77) IV] =12x10~5 DP 2917 Lindsley and Prank (64) [?] =13.6x10"5DP 2574 Treiber and Abrahamson (98) [V] =0.278 D P 0 , 5 7 2 3541 Timell (93) Described i n text 5425 Used i n th i s experiment Table 2. Mean u l t i m a t e t e n s i l e strength values 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 emp. Moist. I n t e g r a l I r r a d i a t i o n Dose (megarad) 0) Pi Cond. 0.0 1.0 10.0 15.0 otS) OC S. p s i B s. p s i B S. p s i B S. p s i B S. p s i B 6 . 5899 20 6530 18 5113 40 4736 23 2346 15 O R A i r - d r y 6154 23 6173 13 5983 27 4788 10 2299 15 Sat. 4680 10 4929 16 4060 16 3385 10 1403 16 0 5814 24 5037 18 5163 31 . 4137 17 2159 11 c 50 A i r - d r y 5378 17 5523 16 5047 22 3785 23 2003 20 c f Sat. 4691 20 4485 9 3444 19 2783 17 1228 16 f- 0 5189 13 4478 14 3542 29 3616 15 1935 13 70 A i r - d r y 4954 16 4667 12 4447 19 3903 24 1770 12 Sat. 3930 10 3740 4 2862 19 2496 9 1212 22 0 36021 22 31595 36 31912 23 22977 30 17337 27 25 A i r - d r y 32475 30 31142 26 29639 23 22873 20 17229 15 Sat. 19198 23 17278 25 17899 19 12959 18 8540 20 0 28351 27 26970 28 26838 27 20197 28 13625 33 50 A i r - d r y 30244 22 24560 28 26132 28 24548 23 14676 17 c c Sat. 15300 21 15247 28 14575 27 12622 27 7436 27 & a 0 26907 32 25156 29 27611 28 24738 26 14494 25 70 A i r - d r y 29228 35 24108 34 24247 31 21387 19 14353 21 Sat. 14297 25 12812 27 12395 24 9496 24 6498 19 Table 3. Mean e l a s t i c i t y values and t h e i r c o e f f i c i e n t s of variation. Temp. Moist. Integral I: rradiation Dose (megarad) CD -Cond. 0.0 0.1 1.0 10.0 15.0 c o oc E CV E • CV E CV E CV E CV ISJ 10*psi ±7° 103psi ±% 103psi ±% lO^psi & 1O^psi +<fo 0 544.0 12 533.7 10 483.4 26 492.8 14 425.2 8 25 Air-dry 527.3 16 506.3 8 467.3 26 532.9 14 421,7 12 . Sat. 401.4 14 405.5 13 332.7 25 390.0 13 295.8 15 xi o 0 544.1 16 503.0 8 500.6 29 512.0 11 393.2 12 o £ 50 Air-dry 478.0 15 478.8 12 440.8 24 464.2 14 364.3 12 >> H Sat. 370.2 23 374.3 10 318.0 22 318.6 25 240.6 11 cd r v i 0 465.3 12 473.5 9 430.9 17 425.3 14 406.1 11 FH 70 Air-dry 465.7 16 473.3 7 441.0 15 454.0 18 363.8 17 Sat. 298.2 13 292.2 9 248.6 22 299.2 16 205.2 25 0 2194.8 15 1939.4 27 1978.6 15 2042.8 23 2044.5 12 25 Air-dry 2034.6 23 1888.8 20 2037.4 22 2030.8 15 2115.2 20 Sat. 1674.0 23 1576.3 15 1593.3 16 1543.1 21 1607.4 12 o 0 1925.4 19 1823.3 17 1877.3 20 1759.8 30 1962.9 22 o ;s 50 Air-dry 1746.2 23 1645.0 19 1775.0 20 1946.8 11 1890.0 8 CD +> Sat. 1600.1 20 1421.5 27 1405.8 14 1429.6 22 1389.8 21 0 1713.4 24 1726.8 18 1846.9 17 1827.1 11 1852.1 19 . 70 Air-dry 1727.8 28 1805.2 22 1773.1 14 1895.6 14 1907.4 16 Sat. 1322.1 20 1192.41 17 1200.3 19 1242.0 19 1000.5 23 Table 4. Mean values of ultimate t e n s i l e s t r a i n and t h e i r coefficients of v a r i a t i o n . Temp. Moist. Integral Irradiation Dose (megarad) 0 Cond. 0.0 0.1 1.0 10.0 15.0 d o °C e CV e CV e CV e CV e CV I S ] i n . / i n . ±?° i n . / i n . +<fo i n . / i n . ±% i n . / i n . & i n . / i n . ±fi 0 .01159 10 .01316 "10 .01135 17 .01096 17 .00630 1 25 Air-dry .01298 16 .01342 4 .01458 8 .00976 16 • .00574 11 Sat. .01421 20 .01552 16 .01584 23 .00937 18 .00480 13 o o 0 .01156 19 .01105 16 .01111 9 .00865 9 .00626 11 50 Air-dry .01249 9 .01266 7 .01302 7 .00901 17 .00587 13 H Sat. .01706 20 .01586 12 .01586 31 .01053 9 .00589 10 W 0 .01193 16 .01007 17 .00878 25 .00901 11 .00560 10 70 Air-dry .01164 13 .01076 8 .01141 15 .00928 10 .00538 20 Sat. .01780 22 .01669 9 .01740 35 .01130 23 .00644 5 0 .01869 12 .01798 14 .01799 17 .01301 18 .00893 15 25 Air-dry .02024 18 .02018 10 .01744 18 .01297 11 .00901 12 Sat. .01517 15 .01335 8 .01366 8 .01001 14 .00608 17 -ci o 0 .01736 10 .01612 16 .01589 17 .01242 15 .00719 27 o [2 50 Air-dry .02076 17 .01870 18 .01787 10 .01441 17 .00804 12 OJ •p Sat. .01397 17 .01747 22 .01430 13 .01162 19 .00652 13 Hi 0 .01750 17 .01622 14 .01649 15 .01553 18 .00830 12 70 Air-dry .01943 8 .01634 23 .01524 23 .01257 21 .00852 11 Sat. .01934 32 .01955 22 .01786 21 .01175 40 .00830 27 Table 5. Mean values of work to maximum tension load and t h e i r coefficients of v a r i a t i o n . Temp. Moist. Integral I r radiation Dc >se (megarad) CD Cond. 0.0 0.1 1.0 .10.0 15.0 o °C w Ln.lb/in^ ° I W/ •> Ln; l b / i n -9 Ln.llf/in? & in.lD7in3 in.lS/in^ 25 0 Air-dry Sat. 37.16 42.07 36-. 34 28 38 27 43.85 43.09 -38.60 28 18 21 30.04 44.86 35.05 54 31 30 24.87 22.60 16.91 47 20 18 - 6.96 6.84 3.52 29 21 28 O O 50 0 Air-dry Sat. 33.47 33.12 43.86 41 24 9 28.06 34.04 36.71 40 ' 22 18 28.01 30.31 29.62 35 15 31 17.14 33.70 14.68 26 39 19 6.96 5.71 3.70 22 24 34 Earl; 7© 0 Air-dry Sat. 30.74 28.32 36.79 24 22 6 22.10 24.45 34.67 30 20 9 17.20 25.48 26.72 48 28 32 17.22 17.36 12.92 20 37 35 5.55 4.78 4.20 19 25 20 25 0 Air-dry Sat. 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 latewoo< 50 0 Air-dry Sat. 250.88 318.23 120.56 34 18 6 220.99 234.29 145.20 46 35 12 218.53 237.33 ' 117.88 44 35 30-129.21 181.73 78.61 37 38 26 •52.42 53.16 26.66 51 33 24 latewoo< 70 0 Air-dry Sat. 264.93 284.46 155.59 37 41 19 213.56 211.01 152.76 43 51 19 231.94 195.34 133.27 41 48 32 199.37 157.83 64.53 43 14 45 -59.87 59.61 28.85 35 25 14 Table 6. Moisture content of air-dry specimens-at test. Drying Conditions Integral ir] "adiation dose (megarad) Zone Temp. °C Rel. Hum. * 0.0 0.1 1.0 10.0 15.0 Zone EMC % EMC % EMC % EMC % EMC % o o R H o3 25 50 70 68 73 78 10.46 13.15 15.44 11.12 12.54 15.53 11.26 12.95 14.22 11.54 12.31 14.62 11.75 12.51 13.21 Latewood 25 50 70 68 73 78 10.61 12.70 14.12 11.34 12.60 13.92 ; 11.58 12.58 13.05 12.16 12.34 -13.18 12.53 12.42 12.96 132 Table 7. I n t r i n s i c v i s c o s i t y of cellulos e i n Douglas f i r as measured a f t e r exposure of wood to various dosage l e v e l s of gamma radiation. Dose negarad Incr. No. Sample. No. Vise. dl/g Earlywood Latewood CV N cont, fo Vise. dl/g CV M cont. 0.0 45 45 46 46 47 47 Average 1 2 1 2 1 2 34.208 34.189 33.470 35.944 34.100 33.632 34.257 6.17 6.28 6.11 2.52 0.59 4.82 4.42 13.51 13.43 13.83 13.40 13.57 13.49 13.54 36.707 35.735 35.800 37.621 34.620 35.108 35.932 5.53 6.65 7.84 1.63 5.90 4.39 5.32 3.45 3.43 3.53 3.41 3.50 3.65 3.50 0.1 45 45 46 46 47 47 Average 1 2 1 2 1 2 32.451 31.017 32.375 32.499 35.383 33.078 32.801 2.71 0.32 4.02 9.26 2.19 1.18 4.95 13.42 13.56 13.43 13.40 13.11 13.19 13.35 34.923 35.048 36:T34 34.775 32.841 33.412 34.522 3.34 1.29 0.46 3.42 0.72 0.28 1.59 3.52 3.48 3.43 3.68 3.43 3.50 3.51 1.0 45 45 46 46 47 47 Average 1 2 1 2 1 2 19.739 21.798 20.627 21.182 21.206 21.274 20.971 2.35 3-58 2.68 1.63 1.88 0.72 2.14 13.64 13.38 13.67 13.50 13.61 13.67 13.58 21.809 20.639 21.646 21.416 20.967 20.374 21.142 1.90 0.92 1.90 1.33 2.65 4.15 2.14 3.79 3.80 3.64 3.84 3.72 3.89 3.78 10.0 45 45 46 46 47 47 1 2 1 2 1 2 Average : 6.758 6.757 7.288 7.448 7.449 7.532 7.205 3.95 2.14 0.20 5.44 1.05 2.30 2.51 13.88 14.11 13.92 13.88 13.69 13.76 13.87 8.107 7.455 8.477 8.476 7.866 7.529 7.985 0.85 1.20 1.28 2.01 3.19 2.45 1.83 3.48 4.00 3.57 3.65 3.81 3.86 3.73 15.0 45 45 46 46 47 47 1 2 1 2 1 2 Aver* ige 2.442 2.444 2.620 2.141 2.004 2.367 2.336 8.18 5.02 2.16 12.64 tt.00 8.37 8.40 13.36 13.41 12.67 13.39 13.71 13.37 13.32 2.712 3.066 1.906 2.010 2.441 1.675 2.302 3.16 8.43 9.44 5.36 6.48 7.31 6.70 2.99 3.08 3.56 3.62 3.20 3.29 13.29 Table 8. Cellulose degree of polymerization i n Douglas f i r wood measured a f t e r exposure to various integral doses of gamma radiation. Increment Sample Integral Irradiation Dose . (megarad) 1MO . 0.0 0.1 1.0 10.0 15.0 45 1 5233 4812 2259 539 167 TJ 45 2 5228 4481 2614 539 167 o 46 1 5054 4794 2409 592 180 46 2 5664 4823 2505 608 144 H 47 1 5206 5523 2510 608 134 U <a 47 2 5093 • 4960 2522 617 161 Average • • 5246 4899 2470 584 159 45 1 5859 5408 2616 676 187 45 2 5611 5439 2411 609 214 46 1 5628 5712 2587 716 127 o 46 2 6096 5372 2546 716 135 CD 47 1 5334 4904 2468 651 167 -P a m 47 2 5454 5040 2366 617 111 Average : 5660 5313 2499 664 157 Table 9. Analysis of variance of earlywood ultimate tensile strength. Source DP v SS MS F DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL 4 2 2' 8 8 4 16 225 269 406,716,000 49,594,500 76,967,300 10,008,300 •"5,608,930 1,892,120 4,877,790 163,709,260 719,374,000 101,679,000 24,797,200 38,483,500 1,251,040 701,116 473,032 304,862 727,597 139.74 ** 34.32 ** 52.89 ** 1.72 NS 0.96 NS 0.65 NS 0.42 NS Table 10. Analysis of variance of latewood ultimate t e n s i l e strength. Source DP SS MS P DP 4 5, 716 ,280, 000 1,429 ,070, OOC 39.82 ** T 2 838 ,995, 000 419 ,497, OOC 11.69 ** MC 2 8, 202 ,570, 000 4,101 ,280, OOC 114.29 ** DPxT 8 194 ,205, 000 24 ,275, 70C 0.68 NS DPxMC 8 337 ,021, 000 42 ,127, 60C 1.17 NS TxMC 4 66 ,689, 000 16 ,672, 20C 0.46 NS DPxTxMC 16 181 ,628, 000 11 ,351, 70C 0.32 NS ERROR 225 8, 074 ,212, 000 35 ,885, 40C TOTAL 269 23, 511 ,600, 000 ** s i g n i f i c a n t at the 0.1 per cent l e v e l of probability * s i g n i f i c a n t at the 0.5 per cent l e v e l of probability NS non s i g n i f i c a n t Table 11. Analysis of variance of earlywood e l a s t i c i t y i n tension. Source DE SS MS F -DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL 4 2 2 8 8 4 16 225 269 414,354 208,035 1,313,200 15,538 10,485 37,503 24,159 1,040,816 3,064,090 103,588 104,017 656,601 1,942 1,311 9,376 1,510 4,627 22.39 ** 22.48 ** 141.91 ** 0.42 NS 0.28 NS 2.03 NS 0.33 NS Table 12. Analysis of variance of latewood e l a s t i c i t y i n tension. Source DF SS, MS F DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL 4 2 2 8 8 4 16 225 269 338,448 3,720,300 13,702,000 202,785 701,660 458,988 661,025 -26,032,494 45,817,700 84,612 1,860,150 6,851,040 25,348 87,708 165,256 28,687 115,700 0.73 NS 16.09 ** 59.21 ** 0.22 NS 0.76 NS 1.43 NS 0.25 NS Table 13. Analysis of variance of earlywood ultimate t e n s i l e s t r a i n . Source DP SS MS P , DP 4 .002426850 .000606713 152.75 ** T 2 .000009724 .000004862 1.22 NS MC 2 .000447140 .000223570 56.29 ** DPxT 8 .000045416 .000005677 1.43 NS DPxMC 8 .000308967 .000038621 9.72 ** TxMC 4 .000108169 .000027042 6.81 ** DPxTxMC 16 .000037198 .000002325 0.59 NS ERROR 225 .000893636 .000003972 TOTAL 269 .004277100 Table 14. Analysis of variance of latewood ultimate ten s i l e s t r a i n . Source DP SS MS P DP 4 .003855360 .000963841 139.22 ** T 2 .000024439 .000012220 1.77 NS MC 2 .000218715 .000109357 .15.80 #* DPxT 8 .000022977 .000002872 0.41 NS DPxMC 8 .000075749 .000009469 1.37 NS TxMC 4 .000272998 .000068250 . 9.86 ** DPxTxMC 16 .000144660 .000009041 , 1.31 NS ERROR 225 .001557769?*' .000006923 TOTAL 269 .006172259 Table 15. Analysis of variance of work to maximum tension load i n earlywood. Source DP SS MS . P DP 4 34,022.2 8,505.6 138.30 ** T 2 3,193.7 1,596.8 25.96 ** MC 2 481.5 240.7 3.91 * DPxT 8 1,414.8 176.9 2.-88 ** DPxMC 8 1,736.4 217.1 3.53 ** TxMC 4 715.3 178.8 2.91 •* DPxTxMC 16 1,518.1 94.9 1.54 NS ERROR 225 13,843.2 61.5 TOTAL 269 56,925.2 Table 16. Analysis of variance of work to maximum tension load i n latewood. Source DP SS MS P DP T MC DPxT DPxMC TxMC DPxTxMC ERROR TOTAL 4 2 2 8 8 4 16 225 269 1,350,060 58,564 612,501 35,931 100,215 40,733 37,513 1,046,313 3,281,830 337,516 29,282 306,250 4,491 12,527 10,183 2,345 4,650 72.58 ** 6.30 ** 65.86 ** 0.97 NS 2.69 ** 2.19 NS 0.50 NS Table 17. Analysis of variance of ultimate t e n s i l e s t r a i n including test f o r cel l u l o s e chain length (DP),temperature (T),moisture content (MC), wood zone (Z), and increment ( I ) . Source DP SS MS P DP " 4 .00619136 .00154784 329.95 *# T 2 .00000312 .00000156 0.33 NS MC 2 .00007827 .00003914 8.34 ** I 2 .00000648 .00000324 0.69 NS Z 1 .00153345 .00153345 326.89 ** DPxT 8 .00003191 .00000399 0.85 NS DPxMC 8 .00019744. .00002468 5.26 #* DPxI 8 .00001411 .00000176 0.37 NS DPxZ 4 .00010590 .00002648 5.64 ** TxMC 4 .00034621 .00008655 18.45 ** Txl 4 .00001036 .00000259 0.55 NS TxZ 2 .00003372 .00001686 3.59 * MCxI 4 .00002450 .00000613 1.30 NS MCxZ 2 .00059411 .00029705 63.32 ** IxZ • 2 .00007228 .00003614 7.70 ** DPxTxMC ' 16 .00011639 .00000727 1.55 NS DPxTxI 16 .00004077 .00000255 0.54 NS DPxTxZ 8 .00003242 .00000405 0.86 NS DPxMCxI 16 .00024057 .00001504 3.20 ** DPxMCxZ 8 .00019286 .00002411 5.13 ** DPxIxZ 8 .00010315 .00001289 2.74 *•# TxMCxI 8 .00005785 .00000723 1.54 NS TxMCxZ 4 .00003382 .00000845 1.80 NS TxIxZ 4 .00002835 .00000709 1.51 NS MCxIxZ 4 .00011033 .00002758 5.87 ERROR 390 .00182949 .00000469 TOTAL 539 .01202920 Table 18. Regressions of strength properties on cellulose 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). ri to Strength Property Regression Equation R2 i •a cd Strength E l a s t . Strain Max.Work S=2598+2692 logV -21.991 -1.92M2 E=465.4+75.44 logV -1.33T -0.26M^ _ 6 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 • CD •P cd Hi Strength E l a s t . S t r a i n Max.Work S=19133+9815 logV -85.64T -20.32M2 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-2.32M2-0.43M logV .6007 .3638 .6796 .5690 Table 19. Regressions of strength properties on cellulose degree of polymerization (Dj,temperature (T), and moisture content (M). • ri Strength Property Regression Equation R2 Earlyw. Strength E l a s t . Strain Max.Work S= -831.0+2042.9 logD -22.0 T -1 .9 M2 E=37.0+56.9 logD -133T -0.26M^ e=-3.77x103+4.56x103logD-2.51x10?T-7.01x10'ffir+3.42x10PM logD+8.25x10'T M W=-44.4+25.01 logD+0.26T-0.022M2-0.l6T logD+0.13M logD-K).0042T M .7029 .5727 .6583 .6787 • ! 3 CD -P cd H) Strength El a s t . S t r a i n Max.Work S=6571+7460 logD -85.6T -20.3M2 E=2251-3909 D -6.08T -0.82 W~ ~ r 0 r e=-3.54x103+6.23x103logD-3.34x10pT-9.40x15¥+3.69x10°T M W=-105.1+109.1 logD-0.65T-0.22M^+0.46M logD .5984 .3635 .6751 .5702 Table 20. Per cent variations i n strength properties accounted for by variables tested. • tsi Strength Property P a r t i a l Corr elation Coef f i c i e n t x J00 Intr.Visc. E emperature Moist.Cont. Interact. Total i H 03 Tensile strength E l a s t i c i t y Ultimate St 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 22.81 1 .89 71.02 57.53 68.47 70.75 latew. T ensile Strength E l a s t i c i t y Ultimate St 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 -2.68 0.45 60.07 36.38 67.96 56.90 Table 21. Simple c o r r e l a t i o n coefficients between ten s i l e strength properties and experimental variables. • CSJ Strength Property Intr.Visc. DP Temperature Moist.Cont. i 03 Tensile Strength E l a s t i c i t y Ultimate St r a i n Maximum Work 0.7382 0.3132 0.7408 0.7703 0.7332 0.3091 0.7350 0.7676 -0.2620 -0.2584 -0.0519 -0^2342 -0.3168 -0.6492 . 0.3190 -00.0151 latew. T ensile Strength E l a s t i c i t y Ultimate St r a i n Maximum Work 0.4826 0.0281 0.7872 0.6230 0.4802 0.0219 0.7843 0.6227 -0.1822 -0.2838 -0.1560 -0.1167 -0.5827 -0.5379 0.0462 -0.4113 141 Table 22. Comparison between cellulo s e DP values obtained by using two empirical methods of conversion from i n t r i n s i c v i s c o s i t y . Wood zone Radiation dose megarad I n t r i n s i c V i s c o s i t y dl/g DP by iV ] dependent K factor DP by emp. exponential relationship 0.0 34.257 5246 5246 ft o 0.1 32.801 4899 4979 o 1 .0 20.971 2470 2958 10.0 7.205 584 853 15.0 2.336 159 230 0.0 35.932 5660 5660 ft o 0.1 34.522 5313 5400 1.0 21.142 2499 3050 EH 10.0 7.985 664 982 15.0 2.302 157 231 CM 0 1 2 3 4 NO MARK 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 Figure 1. Experimental material selected at random from three growth increments of a Douglas f i r tree. Random assignment of tceatments by gamma radi a t i o n i s also shown. 143 o< 1 1 1 i i i— •10 -20 -30 -40 50 Radial distance from the beginning of the 45 th- increment (in-) Figure 2. Intra-increment v a r i a t i o n i n ultimate t e n s i l e strength i n three growth increments of a Douglas f i r tree. 144 I000 -IOOO-IOOO -IOOO -•IO -20 -30 -40 -50 Radial distance from the beginning of the 45 th- increment (in) Figure 3. Intra-increment v a r i a t i o n i n ten s i o n - p a r a l l e l -to-grain e l a s t i i c modulus i n three growth rings of a Douglas f i r tree. 1 45 0 IO 0 20 0-30 0-40 0 5 0 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 gravity i n three growth rings of a Douglas f i r tree. 82i i 1 1 1 1 1 1 1 r 0 growth ring 45 A + growth ring 46 81 - A growth ring 47 7 5 -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 holocellulose i n three groxrth increments of a Douglas f i r "tree. 147 o o 5 EH fe! p q EH o o 80 75 70 \: I , 5 - 4 5 6 POSITION IN RING 10 'A M H H ^ POSITION IN SING 1 .0 pq EH §0.5 o 20 EH p q o 1 5 o 1 2 3 4 5 6 POSITION IN RING pq EH o o Ssi < i EH O 1 2 3 4 5 6 POSITION IN RING INCREMENT .'45 o o INCREMENT ' 46 + — + INCREMENT "'47 A A T \ 2 1 4 i 6' 1 POSITION IN RING Figure 6. Intra-increment v a r i a t i o n i n carbohydrates i n three growth increments of a Douglas f i r tree, expressed as percentages of t o t a l holocellulose. Figure 7. Converted arbor press with adjustable cutting die used f o r tension test specimen preparation. Figure 8. Tension test specimens enclosed i n polyethylene t e s t b a g s . 1 50 Pigure 10. Table model Instron t e s t i n g instrument equipped with constant temperature cabinet. Figure 11. Microcator d i a l indicator used f o r thickness measurements. Figure 15. Equipment used i n v i s c o s i t y measurements of cellulose n i t r a t e solutions. 155 0 10 20 30 40 50 60 CELLULOSE INTRINSIC VISCOSITY (dl/g) Figure 14. Conversion factor between degree of polymerization 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 v i s c o s i t y . 156 o I — ' 1 1 — 1 0 1 „ 10 15 N INTEGRAL DOSE OF GAMMA RADIATION (megarad) Figure 15. Effe c t of gamma radiation of wood on 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 . H INTEGRAL IRRADIATION DOSE (megarad) Figure 16. Effe c t of gamma radiatio n of wood on cellulos e degree of polymerization. 25°C 157 TO 13 TO S TO-INTRINSIC VISCOSITY 1000 (dl/g) 2000 3000 %000 5000, CELLULOSE DEGREE OF POLYMERIZATION Figure 17. Ultimate t e n s i l e strength as a function of cellulose chain length, moisture content,and temperature. 30 35 (dl/g) 0 5 10 15 20 25 CELLULOSE INTRINSIC VISCOSITY b i'50- i6oov: sdoo '5600 4 6 0 0 bboo* CELLULOSE DEGREE OF POLYMERIZATION )-3 o 00 Figure 3 8. E l a s t i c i t y of Douglas f i r i n tension p a r a l l e l to grain as a function of temperature,moisture content,and cellulose 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 H-3 Figure 19. Ultimate s t r a i n of Douglas f i r i n tension p a r a l l e l to grain as a function of temperature, moisture content., ..and c e l l u l o s e chain length. CELLULOSE DEGREE OP POLYMERIZATION > Figure 20. Work to maximum load of Douglas f i r i n tensidn* p a r a l l e l to grain as a function of temperature, moisture content, and cellulos e chain length. *=> 2000 o § 1000 Hi o 10 15 20 25 CELLULOSE INTRINSIC VISCOSITY Cdl/g) 30 35 Figure 21. Diagram showing r e l a t i o n s h i p between ultimate t e n s i l e strength and cellulo s e i n t r i n s i c v i s c o s i t y at 50°C temperature and a i r -dry moisture content.condition. Means and scatter about means are also shown. 162 10 20 30 40 50 60 70 80 90 RELATIVE POSITION IN GROWTH INCREMENT (%) 100 Figure 22. Intra-increment v a r i a t i o n of t e n s i l e strength p a r a l l e l to grain i n Douglas f i r determined a f t e r exposure of wood to various doses of gamma radiation. 163 pq co M o S O o pq 5 o ^40 EH O O P"H § 3 0 co CQ O a EH EH CQ pq § 2 0 al EH pq EH o o 10 .LATEWOOD \ \ 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 Figure 23. Influence of cellulos e chain length 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. 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) (V)T (V)T20) 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 0 1 2 3 4 NO MARK -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 Figure 1. Experimental material selected at random from three growth increments of a, Douglas f i r tree. Random assignment of treatments by gamma radiation i s also shown. / ' Ol 1 1 1 • 1—L_ U •10 "20 -30 -40 -50 Radial distance from the beginning of the 45 th- increment (in) Figure 2. Intra-increment v a r i a t i o n i n ultimate t e n s i l e strength i n three growth increments of a Douglas f i r tree. •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 tension-p?.r?Jlel~ to-grain e l a s t i i c modulus i n three growth rings of a Douglas f i r tree. 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 gravity i n three growth rings of a Douglas f i r tree. 82 81 75 ° growth ring 45 + growth ring 46 * growth ring 47 0 R2=-6239 R=-7899 SEE= -8431 0 10 20 30 40 50 60 70 80 90 100 Relative position in growth ring (%) Figure: 5. Di s t r i b u t i o n -of holocellulose i n three growth increments of a Douglas f i r tree. EH pq EH o o o s 20 80 75 70 4 EH pq g o o t 10* 1 2 3 4 5 b" POSITION IN RING T i 2 j 4 5' ^' POSITION IN 1ING 1 .0 pq EH o u < o pq f i ^ 'j 4 5 6* POSITION IN RING EH pq o 1 5 o Is! pq EH & O O !25 «; EH O < Hi 1 2 3 4 5 6 POSITION IN RING ~ 1 2 3 4 5 6 POSITION IN RING 'INCREMENT 45 o o INCREMENT 46 + + INCREMENT 47 A -A Figure 6. Intra-increment v a r i a t i o n i n carbohydrates i n three growth increments of a Douglas f i r tree, expressed as percentages of t o t a l holocellulose. 10 20 30 40 50 60 ' 70 LENGTH OF NITRATION TIME (hrs) Figure 13. Cellulose chain depolymerization in-the n i t r a t i n g acid as related to length of n i t r a t i o n time. Figure 14. Conversion factor between degree of polymerizati 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 v i s c o s i t y . O I i I I 0 1 10 15 INTEGRAL DOSE OF GAMMA RADIATION (megarad). Figure 15. Effect of gamma radiation of wood on cellulose i n t r i n s i c v i s c o s i t y . is; o M E H < U CS] , , M 0 1 ; 10 15 INTEGRAL IRRADIATION DOSE (megarad) Figure 16. Effect- of gamma radiation of wood on cellulose degree of polymerization. 25°C 0 150 T o — T 5 — m INTRINSIC VISCOSITY 1000 2000 30 000 5000.-CELLULOSE DEGREE OP POLYMERIZATION Figure 17. Ultimate ten s i l e strength as a function of cellulose chain, length, 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 tension p a r a l l e l to grain as a function of temperature,moisture content,and cellulose chain length. figure 19. 10 15 20 25 30 35 CELLULOSE INTRINSIC, VISCO.SITY .(dl/g). 0 150 1000 2000 3000 4000 5000 CELLULOSE DEGREE OF POLYMERIZATION Ultimate s t r a i n of Douglas f i r i n tension p a r a l l e l to grain as a function of temperature, moisture content, ..and..cellulose, .chain.length. 0 150 1000 2000 3000 4000 5000 5 CELLULOSE DEGREE OP POLYMERIZATION • ^ a i'igure 20. Work to maximum load of Douglas f i r i n tension p a r a l l e l to grain as a function of temperature, moisture content, and cellulose chain length. •H CO CELLULOSE INTRINSIC VISCOSITY (dl/g) Figure 21. Diagram showing rela t i o n s h i p between ultimate t e n s i l e strength and cellulo s e i n t r i n s i c v i s c o s i t y at 50°C temperature and a i r -dry moisture content,condition. Means and scatter about means are also 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 strength p a r a l l e l to grain i n Douglas f i r determined after exposure of wood to various doses of gamma radiation. o pq o EH P q M PH O CS S o EH O « s o Pq co pq ca 55 20 EH EH cti is; is; w pq EH « 12! EH O CQ O 10 LATEWOOD 0 5 10 15 20 25 30 35 CELLULOSE INTRINSIC VISCOSITY (dl/g) 0 1000 2000 3000 4000 5000 CELLULOSE DEGREE OP POLYMERIZATION figure 23. Influence of cellulose chain length on moisture s e n s i t i v i t y of tens i l e strength of 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