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The influence of fibre chemical constitutents in oil-tempering of hardboard. Paszner, Laszlo 1963

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THE INFLUENCE OF FIBRE CHEMICAL CONSTITUENTS IN OIL-TEMPERING OF HARDBOARD by IASZLO PASZNER B.S.F. (Sopron Division) University of British Columbia 1958 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF * MASTER OF FORESTRY in the Department of Forestry We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA Ap r i l , I 9 6 3 In presenting this thesis in p a r t i a l fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It i s understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Wood Technology. Faculty of Var aat.r? The University of British Columbia, Vancouver 8, Canada. Date A p r i l 30, 1963  ABSTRACT This study was designed to examine effects of alcohol-benzene solubles, hemicellulose, modified cellulose, l i g n i n and modified l i g n i n residuals i n refined Douglas f i r Asplund fibre on the heat-activated poly-merization of tempering o i l applied to wet-batch process hardboards. Thin (0.05. cm.thickness) experimental boards were prepared with good formation properties and reproducibility for the study. Results of oil-tempering, heat-treatment and humidification treatments were compared with and with-out modifying the raw stock. Oil-tempering was most effective on boards made from unmodified or alcohol-benzene extracted f i b r e . An ultimate tensile strength increase of 105$ approximates gains had i n commercial practice. Heat-treatment alone was ineffective in developing extra strength, possibly because of extended hot-pressing of the boards. Among the wood constituents investi-gated l i g n i n was involved.in approximately 80$ of the extra strength devel-opment on,oil-tempering. It was found that oil-tempering effects could be severely de-pressed by mild oxidation of the fibre with acidified sodium chlorite (NaClOg). solution at 70° C. Accompanying weight loss was below 5$. Alter-natively, pa r t i a l deactivation was obtained by inhibition of the fibre sur-face or precondensing the lig n i n i n the raw stock with hot-water-soluble hemlock bark tannins. The tannins were introduced into the fibre struc-ture by a new method including hot-soaking and cold-precipitation at 3% slurry consistency. Strength development on oil-tempering was thus reduced by the oxidation treatment to approximately 20$ which was unaffected by i i . further chemical treatment. This residual strength increase may be due to some other effect than l i g n i n . Evidence for a chemical mechanism is suggested by observations that only a limited portion of the o i l takes part in strength development, pointing toward limited sites available for polycondensation. Possibly, these sites are inactivated.by even mild oxidizing treatments of the fi b r e . This suggests that l i g n i n quality i s more important than quantity of lignin, alcohol-benzene solubles, hemicellulose or cellulose in the oil-tempering mechanism. These findings are contradictory to the literature. To date, li g n i n has not been considered an important wood constituent i n strength development of different wood products by impregnation, and condensation-polymerization systems with unsaturated compounds. Further removal of li g n i n from the fibre (10 to 25$ weight loss) improved formation and bonding of fibres and the subsequent strength proper-ties of boards. This conforms to well described mechanisms accompanying fibre delignification. Additional l i g n i n removal (25 to 35$ weight loss with 5$ or less residual lignin) lowered fibre viscosity and board strength. Experimental strength and e l a s t i c i t y data across the 0 to 5$ and 10 to 15$ weight loss range were f i t t e d according to a mathematical model. The site and bonding mechanism between l i g n i n and tempering o i l have not been described. Some suggestion is made as to how this might occur. i x . ACKWOWLEDGEMEHT The w r i t e r ' s g r a t i t u d e i s e x p r e s s e d t o a l l t h o s e who a s s i s t e d i n o v e r c o m i n g t h e many d i f f i c u l t i e s e n c o u n t e r e d i n t h i s s t u d y . D e e p e s t g r a t i -t u d e , i s e x t e n d e d t o D r . J . W . W i l s o n , , A s s o c i a t e P r o f e s s o r , F a c u l t y o f F o r e s t r y , f o r M s p r o f e s s i o n a l a n d u n d e r s t a n d i n g g u i d a n c e i n p l a n n i n g a n d e x p e r i m e n t a t i o n p h a s e s , a s w e l l a s p r e p a r i n g t h e t h e s i s . O t h e r members o f t h e F a c u l t y o f F o r e s t r y who a s s i s t e d i n t h e s t u d y were D r . R . W . W e l l w o o d , D r . J . H . G . S m i t h , a n d D r . J . A . F . G a r d n e r . V a l u a b l e h e l p , b o t h i n a d v i s o r y a n d t e c h n i c a l c a p a c i t y was o b -t a i n e d f r o m M r . A . P a n t e l e j e v s , H e a d o f R e s e a r c h D e p a r t m e n t , , a n d o t h e r s t a f f a t C a n a d i a n F o r e s t P r o d u c t s L t d . , P a c i f i c V e n e e r a n d P l y w o o d D i v i s i o n , New W e s t m i n s t e r , B r i t i s h C o l u m b i a . The C o m p a n y ' s f i n a n c i a l c o n t r i b u t i o n t o typing a n d p r i n t i n g c o s t s o f t h i s t h e s i s i s a l s o much a p p r e c i a t e d . T h a n k s a r e e x p r e s s e d t o M e s s r s . G. I f j u a n d A . K o z a k , g r a d u a t e s t u d e n t s , F a c u l t y o f F o r e s t r y , f o r t h e i r a s s i s t a n c e p r o v i d e d i n c o m p u t e r p r o g r a m m i n g , a n d d a t a p r o c e s s i n g . The w r i t e r a l s o g r a t e f u l l y a c k n o w l e d g e s t h e f i n a n c i a l a s s i s t a n c e o b t a i n e d d u r i n g t h e p a s t t w o y e a r s f r o m t h e l a t i o n a l R e s e a r c h C o u n c i l o f C a n a d a . i i i . TABLE OF CONTENTS Page TITLE PAGE ABSTRACT . . • i TABLE OF CONTENTS . i i i ACKNOWLEDGEMENT.,... i x INTRODUCTION . . . . . . 1 LITERATURE REVIEW f 1 . Alcohol-benzene solubles. 8 2 . Lignin. . . . . . . . . . . . . . . . . 9 3 • Hemicellulose 15 if-. Cellulose 20 5- Tannins and other polyphenolic wood extractives . . . 2k. 6.. Heat-treatment of pressed hardboards., : .26 7 . Oil-tempering of pressed hardboards 2 8 • 8 . Humidif i c a t i o n of pressed .hardboards 30 MATERIALS AND METHODS . . . . . . . . . . 31 A. .Selection and Preparation of Materials. 31 1 . Collecting the fibrous material .. . . ' „. . . 31 2 . Temper ing o i l 32 B. Extraction and Modification of Fibre Constituents. . . . . 33 1 . Extraction of alcohol-benzene solubles 3^  • 2 . Removal of l i g n i n . . . . . . . 35 i v . Page 3» A l k a l i extraction of hemicelluloses. . . . . . . . . . k2 k. Cellulose modification by Cobalt 60 irradiation •.... . . h$ 5. i i g n i n deactivation following impregnation with hot-water-soluble hemlock bark extractives . . . . . . . . ^5 C. A n a l y t i c a l Methods • • kf 1. Alcohol-benzene extractives (TAPPI Standard; T 6m-5^) 7^ 2. Klason l i g n i n (TAPPI Standard? T l'3m-5^).« **7 3. U l t r a v i o l e t spectrophotonetrie l i g n i n determination i . HQ h. Micro-Kappa number . « » » . » . . . . • . . kQ 5. One per cent cupriethylenediamiae (CED) v i s c o s i t y . • . U9 D. Thin Board Preparation . . . . . . . . . . . . . . ^9 Step 1. Additives . . . . . . . . . . . . . . . . . . . . 52 Step 2. Mat formation . . 52 Step 3* Board pressing. » . . . . . . . . . . . . • . < . . 55 Step h» Post-pressing board treatments. . . . . . . . . . 57 a. Oil-tempering . . . . . . . . . . 57 b. Heat-treatment. • » » • « • • . . . . . . . . . . 58 c. Humidification. . » . • • . . . . . . . . • . . * 59 E. Testing Procedures 60 1* Specimen preparation . . . . . . . . . ...<><><>.. 6 l 2. Tensile strength t e s t , c a l c u l a t i o a of ultimate elonga-t i o n and modulus of e l a s t i c i t y . . . . . . . . . . . . 62 3. Adjustment of strength properties* . . . . . . . . . . . . 6k V . Page RESULTS. . 65 A. Investigation of Wood Constituents- . . . . . . 65 B. Effect of Lignin Removal ' 65 DISCUSSION- ' .67 A. Investigation of Wood Constituents . . 67 1,. Untreated Asplund Pulp 68 2. Alcohol^Benzene Extracted Fibre. 69 3'.. Modified Cellulose Fibre 69 k.'. Modified Hemicellulose Fibre . . . . . . . . . . . . 70 • 5.' . Delignif ied Fibre . 71 6. Deactivated Lignin' Fibre - f l ' B.' Effect' of D e l i g n i f i c a t i o n - . . . . . . . . . . . . . . . . 72 CONCLUSIONS• • • 78 LITERATURE CITED 81 TABLES AND FIGURES . . Table 1. Composition of l / 8 - i n c h Asplund f i b r e as determined by Bauer-McNett-fibre c l a s s i f i c a t i o n • . . * • ? • 91 Table ' 2> Specifications and some properties of GTLA.Polymer 91 Table .'3- Low temperature ehlorination of As-plund pulp fol - r lowed by 30 min.extraction with 3$ monoethanolamine 91 Table k. Low temperature ehlorination of Asplund pulp f o l -lowed by 30 min. extraction with hot water. . . . . 92 Table 5- Chlorination of Asplund pulp with t - b u t y l hypochlo-r i t e . 92 Page T a b l e 6. A n t i c i p a t e d a n d r e s i d u a l l i g n i n c o n t e n t o f s o d i u m c h l o r i t e t r e a t e d f i b r e as c a l c u l a t e d a n d d e t e r m i n e d by. m i c r o - K a p p a number a n d UV a b s o r p t i o n s p e c t r a , based on 31.0k%> K L a s o n l i g n i n yd T a b l e 7- One p e r c e n t c u p r i e t h y l e n e d i a m i n e v i s c o s i t y a n d c o r r e s p o n d i n g d e g r e e o f p o l y m e r i z a t i o n v a l u e s o f s o d i u m c h l o r i t e d p u l p 93 T a b l e , .8 . O i l a b s o r p t i o n v a l u e s o f b o a r d s o f d i f f e r e n t f i b r e c o m p o s i t i o n . 93 T a b l e 9* E f f e c t o f t e m p e r a t u r e on t e n s i l e s t r e n g t h o f o i l -t e m p e r e d h a r d b o a r d s 9k T a b l e 10. I n f l u e n c e o f s p e c i m e n w i d t h on t e n s i l e s t r e n g t h a n d c o e f f i c i e n t o f V a r i a t i o n (CV) o f t h i n u n t e m p e r e d b o a r d s 9k T a b l e 1 1 . I n t e r a c t i o n b e t w e e n wood c o n s t i t u e n t s a n d t e m p e r i n g o i l m e a s u r e d b y u l t i m a t e t e n s i l e s t r e n g t h , m o d u l u s o f e l a s t i c i t y ( M O E ) , a n d u l t i m a t e e l o n g a t i o n . .. • • 95 T a b l e 1 2 . S i g n i f i c a n t t e n s i l e s t r e n g t h d i f f e r e n c e s b e t w e e n u n t e m p e r e d b o a r d s o f d i f f e r e n t c h e m i c a l c o m p o s i t i o n 96 T a b l e ..13- I n t e r a c t i o n b e t w e e n b o a r d s o f v a r y i n g l i g n i n c o n t e n t a n d t e m p e r i n g o i l m e a s u r e d b y u l t i m a t e t e n s i l e . s t r e n g t h , u l t i m a t e , e l o n g a t i o n , a n d m o d u l u s of. e l a s t i c i t y . (MOE). . . . . . : 9 7 T a b l e Ik. S i g n i f i c a n t t e n s i l e s t r e n g t h d i f f e r e n c e s b e t w e e n u n t e m p e r e d b o a r d s p r e p a r e d f r o m d e l i g n i f i e d f i b r e . 98 •• V l l o .. Page o « o Figure 1/A Relationship between time, number of treatments and per cent weight loss obtained with 70° C. cooking temperature i n sodium chlorite solution « •> » » . « Figure l/b Relationship between time and per cent weight loss obtained with 70° C. cooking temperature i n sodium chlorite solution i . . . . . . . . . Figure 2. Laboratory forming box and hydraulic hot-press. . . Figure 3° Converted arbor press used for specimen preparation Figure 4. Adjustable-width cutting die used.for cutting speci-mens of uniform width. . . . . . . . Figure 5° CEJ d i a l microcator . . . . . . . . Figure 6 . Instron table model testing machine Figure 7» Tensile strength vs. specific gravity relationship. Example of graphical solution of specific gravity correction for ultimate tensile strength values . . Figure 8 . Interaction between wood constituents and tempering o i l as measured by ultimate tensile strength. . . . Figure 9 • Relationship of ultimate tensile' strength plus strength increase following oil-tempering to per cent weight loss and residual l i g n i n with chlorited Asplund fibre Figure 1 0 . Relationship of ultimate elongation plus elongation decrease following oil-tempering to per cent weight loss and residual l i g n i n with chlorited Asplund fibre © • o 99 100 101 102 103 10h 105 106 107 108 109 v i i i . . Page Figure 11. Relationship of modulus of e l a s t i c i t y (MOE) plus stiffness increase following oil-tempering to per cent weight loss and residual l i g n i n with chlorited Asplund fibre . . . . . . . . . . . . . . . . . . . . .110 Figure 12. Sample board of different fibre chemical constitu-" f c X O H • o * » o o o o e O o * e o « o » f t o o o * * » 111 -1-INTRODUCTION The hardboard industry i s one of the recently developed tranches of the wood-using industries. It is an outgrowth of pressure to u t i l i z e low cost residues and economics of production of other forest products, i.e., lumber, plywood, and furniture. The technical history of hardboard reaches far back into the years of industrial development. Effective commercial pro-duction of hardboard began however, with Mason's invention in 192^. By exploding wood chips into a f l u f f y mass of fibre, at high pressure and tem-perature i n the presence of water, he found a new and unique method for fibre preparation. Experiments in the investigation of fibre separation mechanism in the "Mason,gun" led to the invention of a second defiberizing method, named after i t s inventor, "Asplund process". During the more than ten years which elapsed between the invention of the two processes, hardboard production did riot increase at an expected rate. With the introduction of the Asplund pro-cess, production volume increased rapidly. The slow growth preceding 1938 was due to the effect of s t r i c t l y held product patents on the Masonite pro-cess. ^Between 1938 arid I9U8, however, an increase of 100$ was noted. Reports of United States hardboard production show a further sub-stantial increase i n production during the 10-year period of 19^7 to 1957 (138). In 19^ -8 approximately 52$ of tot a l fibreboard production was made up of hardboard (33)-. In 1957 Sweden produced U30,000 metric..tons of hardboard (83)- Currently Canada is producing approximately 321,000 metric tons of fibreboard annually, of which 25$ i s hardboard (119) . Total Canadian hard-- 2 -board production during the twelve-month period ending in December I 9 6 I was 288,157,088 sq.ft. (l/8-Inch basis) of which 10$ or approximately 1,000 metric tons was tempered hardboard (2k). The United States' economy absorbs two and one-quarter b i l l i o n square feet (l / 8-inch basis) of hardboard annually; of which only two. MITion square feet are produced i n the United States (142). Several advantages of hardboard made i t s phenomenal growth possible. Among these are relatively low capital requirements, wide variety of suitable raw materials, and ve r s a t i l i t y of resulting products. Capital requirements for erection and operation of hardboard plants are moderate when compared to certain other wood-using industries, i.e.,the pulp and paper industry. There are no specific requirements as to form of raw material; i t may be forest and factory residue, as well as from primary harvest. Versatility of properties makes hardboard suitable for numerous uses such as exterior and interior sheathing i n home building, concrete form lining, table and desk tops, cabinet backs and automobile applications, partitions and heavy-duty storage walls, cores for plastic laminate's, and floor underlayment. Good working properties, smooth cutting-, f l e x i b i l i t y , dimensional s t a b i l i t y and strength a l l contribute toward high c onsumer~ a c cepta nee and large market potential for the product..' Typical fibreboard processing starts with wood chips which are sep-arated Into individual fibres and fibre bundles i n the "Asplund defibrator" , at steam pressures of from 100 to 175 psi,and chip temperature of 3^0 to 375°F., in the presence of water. From the pulp thus obtained, a water suspension of approximately 3$ consistency i s made. Final board strength and hygroscopic properties can be improved by adding small amounts of synthetic resin and wax at this stage. These reagents are precipitated onto the fibres by small amounts of precipitating agents such as aluminum sulphate and sulphuric acid ( 3 0 , kj, 132, Ikj). The fibre i s then formed as a mat of controlled thick-ness either on a Fourdrinier, cylinder mold or a deckle, box. The drained mat i s cold-pressed to approximately 35$ solids content. This i s followed by trimming to approximate size and hot-pressing i n a multiple-opening press where elevated temperature and high pressure compress the mat and free It froms-'mblsture. The escape of moisture under pressure is f a c i l i t a t e d by a screen^placed under the mat which leaves a rough surface of wire impressions on the board. Subsequently, the boards are subjected to post-pressing treat-ments such as o i l dipping and/or heat-treatment, and humidification. . These treatments are applied for improvement of hardboard physical characteristic^. Through manipulation of manufacturing variables the whole, process of hard-board manufacture can be made f a i r l y flexible and suitable for producing: a greatly diversified product line (59* 137)* Hardboard may be defined as a type, of fibreboard above 0 .^0 speci-fic'gravity, manufactured from wood or other lignocellulosic fibres with primary bonding derived from the arrangement of fibres and their inherent ' adhesive properties (33) • Ohrthe basis of specific gravity, hardboards may be further classified as semi-hardboards ( 0.40 - 0 . 8 0 ) , hardboards ( 0 . 8 0 - 1 . 2 0 ) , and special or extra-hard hardboards (1.20-1.45)• • Oil-tempered hardboards occupy a unique place among fibreboards'. Kumar (73) estimates the amount of to t a l oil-tempered hardboard as 25 to 30$ of a l l hardboard produced. Oil-tempered hardboard. is used where extra strength and water resistance are required. This includes use i n home building as floor covering and exposed sheathing, stadium seat tops, form press l i n i n g , d r i l l stencils, hammers and moulded arti c l e s such as stool seats and backs, reflectors, and containers. O i l saturating and subsequent heat-treatment of -k-hardboard increases strength by 1 0 0 $ and improves dimensional s t a b i l i t y by 5 0 $ (63-, 6 5 , 9 5 ) • In general, tempered hardboards possess greater bending and tensile strength (tensile strength being approximately twice as high as modulus of rupture), and higher modulus of e l a s t i c i t y ( 7 3 ) - Consequent ly they are s t i f f e r . A further advantage of tempered boards compared to normal hardboards i s that they are less inclined to delaminate, making them especially suitable for uses where special shock resistance i s required. Economics of oil-tempered hardboard do not warrant wide product manufacture by present treatment methods. For one thing, the rate at which tempering o i l costs have risen has'/, not been followed by board prices. Current selling prices of two Canadian plants are given for econ-omic comparison of tempered and untempered hardboard manufacture. Plant A. l / 8-inch Standard Hardboard $69 .50/M. Sq.Ft l / 8-inch Tempered Hardboard $85.00/M.Sq.Ft Plant B. l / 8-inch Super Sealed Hardboard $65.00/M.Sq.Ft l/ 8-Inch Super Sealed Tempered Hardbd. $85.00/M.Sq.Ft Cost of"tempering o i l alone was $15.03/M.Sq.Ft. i n I 9 6 I . This suggests a marginal economic operation with tempered hardboards. Despite its great technological importance the action of temper-ing o i l s on extra strength development of hardboards has never been compre hehsively investigated. In the present study, i t Was f e l t that an investi gation of wood constituents, with regard to their interaction with temper-ing o i l s , could lead! to disclosure of an acceptable mechanism for o i l -tempering of hardboards. On the other hand, the discovery of a mechanism could eventually lead to the control of extra strength development for -5-which no method has been found as yet. Thereby, a tempering process of highly empirical nature could be replaced by methods giving predictable results. Explanations for strength differences between identical batches of tempered hardboards cannot be satisfactorily resolved u n t i l tempering process variables, with main emphasis on oil-tempering mechanism, are thoroughly investigated. . Since the action of heat-activated tempering o i l on extra strength development i s believed to be chemical i n nature (73), an inves-tigation of the interaction between certain wood constituents and temper-ing o i l seemed to be in order. Because of technical considerations i t was believed that some non-complex mechanical test would give most r e l i -able results. Tensile strength test and other derived data from this test were selected as a direct measure of the interaction between a particular wood constituent and tempering o i l . It was also hoped that fundamental information could be obtained regarding the tempering mechanism. At the same time, data obtained from tests had to be sufficiently reliable for understanding the significance of the influence of various wood- consti-tuents on one hand, and the manner by which their removal or modification affects tempered board properties on the other. Based on preliminary examination of wood component effects, the one most important1 from the standpoint of extra strength development, had to be singled out for closer investigation of mechanisms in hardboard tempering. In summary the objectives of this study were: 1. Comprehensive investigation of basic wood constituents vrith. regard to t h e i r interaction with tempering o i l as activated by heat. Selection of the most important wood constitutent(s) and further examination of these in regard to possible mechanisms. - 7 -LITERATURE REVIEW In the following a review is given of the effect of wood constit-uents and post-pressing treatments on strength and dimensional s t a b i l i t y of fibre-base products. Considerable literature has accumulated on chemical and physical properties of woods,and fibre products produced from them. For a long.per-iod wood was assumed to be a uniform chemical substance ( 5 * 0 . I n i t i a l analysis showed that wood is mostly composed df two substances, i.e., poly-saccharides and an inctf-usting material, later called lignin (115") • Progress i n wood chemistry has been greatly retarded by the chemi-cal complexity of wood constituents, as indicated by their relative composi-tion in situ (48). For example, the chemical structure of the li g n i n mole-cule i s s t i l l unknown. Chemical degradation of li g n i n provides a number of different building units, depending on the method of isolation ond reagents used. Furthermore, the question as to nature and extent of chemical and physical bonding between.wood constituents has yet to be settled ( 1 7 ) -This makes more d i f f i c u l t the examination of hypothesis relating product properties to wood constituents. Wood chemistry has been mainly concerned with products of the pulp and paper industry. The end products of pulping represent wood fibres in a more or less modified state dependent on chemicals and pulping conditions used. .Chemical and physical structure of wood pulp largely depends' on the pulping purification method used. No pulping method has been found as yet that facilitates removal of one or several of the wood constituents in a -8-single operation without causing serious degradation of remaining constit-uents (8). It i s for this reason that chemistry of wood constituents, Individually and as a complex, continues to be of great importance to the pulp, paper and fibre-processing industry. Hardboard is a wood-base product, made from pulps which may be obtained by Asplund or other mechanical or semi-chemical defiberizing pro-cesses. As such i t bears close relation to newsprint and other'coarse fibre products both i n physical and chemical characteristics (139)- Major d i f -ferences between paper and hardboard manufacture l i e in the nature (degree of f i b r i l l a t i o n , and fibre separation) and fineness of the fibrous material. Physical properties of hardboards have been f a i r l y well defined and found fundamentally similar to those of heavy papers. On the other hand, d i f f e r -ences seem to occur i n chemical composition of hardboards due to changes acquired by fibres during high temperature defiberizing and pressing stages (99/112)- Therefore, i t Is conceivable that major wood constituents such as alcohol-benzene solubles, l i g n i n , hemicellulose and cellulose could influence hardboard properties i n a somewhat different manner than those of papers. Modifications effected by the different hardboard treating methods should be reflected by measurable flexural and dimensional changes. Four wood constituents were examined i n the f i r s t phase of this study. 1. Alcohol-benzene-solubles Although the preserce of fats, waxes and resins i n wood"is known to complicate hardboard manufacture, information as to their precise i n f l u -ence on f i n a l hardboard properties is scarce. Experiments of Ogland (100) give some lead as to the effect of resin in hardboard. By removing acetone-- 9 -soluble resins, a greater reactivity of the fibre surface was clalmedjto-gether with higher resultant strength of boards prepared from such extracted pulp. At the same time, water absorption increased considerably, creating a less diraensionally stable product. Ogland (100) also removed resins by weak a l k a l i extraction and thereby increased hardboard strength considerably. However, this result should be accepted with certain reservations. His experimental results show that as sodium hydroxide concentration'was i n -creased from 0 to 25$ with Asplund pulp slurry at 2$ consistency, i n an extraction (temperature not stated) for 30 minutes, the resin content dropped from I .65 to 0.32$. This gave a strength increase of 50$ to boards prepared from such f i b r e . It i s well known (67) that such a l k a l i treatments remove other- wood and fibre constituents besides resin, making the pulp proportion-a l l y richer i n cellulose' content, poorer i n hemicelluloses, and'res'ult in increased fibre f l e x i b i l i t y . Certain of these factors could also account for the higher strength observed. Similar sodium hydroxide extractions by 'Runkel (111) gave the same effect, although his data indicate; hemicellulose removal. No reference has been found on the specific effect of alcohol-benzehe solubles in hardboards. On the basis of limited information and certainly questionable results, the effect of extractives on the f i n a l physical properties of hard-boards must be declared inconclusive. It i s possible, however, that natural resins may influence dimensional s t a b i l i t y of hardboards by forming natural sizing compounds. 2. Lignin Lignin has been credited as being responsible for most of the inter--f >-ibre strength of hardboards manufactured without resin additives - 1 0 - • . (11., 9 9 , 112, 139) • The pro'spect of "lignin activation", although allowed i n patent novelty, is s t i l l contraversial in the literature. Lignin is indefinitely defined as an amourphous mixture of high molecular weight components ( 3 , 12, 28, 34, 36, 4-2, 48, 55,"80, 82, '114, 115, 117, 128, l 4 l ) chemically bound together as a three dimensional structure, interpenetrating the hemicellulose and cellulose of the c e l l wall (15, 46, 8 l , 98, 105, 115, 126). Coniferous li g n i n as an incrusting. substance occurs in different parts of the plant c e l l and i s composed mainly, i f not entirely of phenyl-propane building units (12, 29, 36, 42, 48, 7 2 ) . Bonding of these units i s believed to-be accomplished by covalent linkages (>72, 8 l?),i.e., by aryl ether linkages between the fourth carbon (C^) on the benzene ring and the beta or gamma carbon of the side chain. Bonding between the Ci). and alpha carbon is lefts-'., l i k e l y ( 8 l ) . The possibility of a carbon to carbon bond can-not be eliminated. This could occur between C5 of the benzene ring and the beta or-gamma carbon of the side chain. A product i n which the,benzene nucleus i s linked both to side-chain ether and carbon to carbon bond is also possible ( 8 l ) . " ' Evidence on li g n i n composition has been provided by many investi-gators through mild oxidative treatments. Thus Lindgren ( 8 l ) obtained 50$ ' v a n i l l i n and 5*5$ veratric acid with free hydroxyl groups at Clj.. Isohemi-pinic acid was' obtained in the amount of 0 .9$ where the benzene nucleus carries two side-chains, and a free phenolic hydroxyl group. Goldschmid (42) treated wood at high temperature in the presence of water' and obtained' large amounts of coniferylaldehyde, p-co imaraldehyde, v a n i l l i n , vanillbyl methyl ketone, guaiacyl acttone.and several other unidentified compounds, as well as sugars and furfural evidently from the hydrolysis of carbohydrates. -11-Repeated" hydrolysis yielded more of the same products. In addition to simple products,some macromolecular l i g n i n i s also cleaved, thereby providing more intense color reaction i n the phyloroglucinol-hydrochloric acid test (des-cribed by De Baun and Nord (7))/than native lignin,indicating a more developed side-chain conjugation. The phloroglucinol-hydrochloric acid color reaction was also given by dloxane solution of the'extracted wood as an indication of coniferylalde-hyde. This was interpreted, though, as insufficient evidence for indication of any appreciable number of double bonds existing in situ i n lig n i n (12). The possibility that new double bonds are formed only during the isolation of l i g n i n was examined by ultraviolet absorption spectra by Goldschmid (42), and Cabott and Purves (15). Lignin, as determined by Aulin Erdtman (29) and Adler (3)> contains on the average k to 6 monomers. The exact position of the side-chain i s s t i l l unknown (72). This i s mainly due to the masking effect that i s exerted by the free phenoloic hyroxyl group on the side-chain constitution during oxidative delignification (28, 126, ikl) . The phenolic hydroxyl group, in para position to the propane side-chain (l4J), occurs i n lign i n partly on one end, and partly on, monomers joined by carbon-carbon bonds. Therefore, every lignin molecule must have at least one free phenolic hydroxyl group (3). "" In an isolated state, i t was found that l i g n i n contains alcoholic and the above-mentioned phenolic hydroxyl groups, as well as aldehyde groups (72). i t i s well known that alcoholic hydroxyls on side-chains are more re-active than phenolic hydroxyls. However, the reactivity of different hydroxyl groups may be. influenced by proper selection of reaction conditions (72) . Alcoholic hydroxyls are found to be easily replaced by sulfate and -12-sullphite groups ( 8 l ) . Sites of reaction are the same as those for the forma-tion of alcohol l i g n i n . Finally, oxygen-containing rings, such as lignans, may he opened by sulphite solutions which could render l i g n i n soluble (27 , 8 1 , 82) ••" Lignin i s not hydrolyzed by acids, but is : easily oxidized by d i f -ferent mildly acidic oxidizing agents ( 1 2 ) . It i s soluble i n a l k a l i solu-tions to different extents, depending on the swelling capacity of the solu-tion. A l k a l i l i g n i n i s recovered as a lignin-hemicellulose mixture ' ( 107)• This i s believed to give evidence for a lignin-carbohydrate complex in wood ( 1 0 6 ) . Further evidence for a lignin-carbohydrate complex was supplied by "Cabott and Purves ( 1 5 ) , Lindgren (81,) Nord and Schubert(98), Pew and Weyna ( IO5) , ' Sohn ( 1 2 6 ) , and Stewart and co-workers (130) . They showed, through different extraction methods,that a certain portion of the lig n i n is chemi-cally bound to carbohydrates, making complete l i g n i n removal from woody tissues practically impossible without changing the carbohydrate"composition. In a technical fibre separation process, wood is subjected to high temperatures in the presence of aqueous solutions. The li g n i n i s changed physically and chemically (42, 11, 9 9 , 112, 128,. 139)• On the other hand, on prolonged heating under these conditions large amounts of non-resistant-carbohydrates are dissolved with only small amounts of l i g n i n . Thermal decomposition of lig n i n i s of considerable importance from the Itandpoint of hardboard manufacture. In high-temperature heating of wood i n aqueous solutions, besides carbohydrate dissolution, a self-condensation within the lignin molecule has also been observed (46, 71 , 9 5 , 112, 1 3 9 ) . This self- . condensation and carbohydrate loss was found to be responsible for the slight-l y higher l i g n i n content of Asplund and Masonite pulps ( 7 2 , 84, 88, 9 9 , 113, 126), than that found for normal wood. The phenomenon of lig n i n self-con-densation on thermal treatment of li g n i n preparations was also observed by Levitifi, Thompson, and Purves (80), and Erby and Schuerch (28). According to Boehm (11), Kollmann (65), Nowak (99), Runkel (112) and Voss (139), protolignin is depolymerized i n the fibre on thermal treat-ment; on thermal after-treatment, as in the hot-pressing and heat-treating operations, i t i s recondensed. Thermoplastic characteristics of li g n i n (11, 46, 95, 99^ 112, 139) are believed to be f u l l y u t i l i z e d in producing wood fibres from solid wood,without causing extensive damage to the fibres,in the mechanical grinding operation. Furthermore, i n i t i a l strength of fibre-base products i s claimed to be due to "activated l i g n i n " , produced by the depolymerization and re-condensation processes. This claim was disproven by Klauditz (67, 68), Klauditz and Stegman (71) and Ogland (100), who pro-duced boards of substantially higher strength after removing large amounts of l i g h i n from the fi b r e . Increased strength and dimensional s t a b i l i t y could be also obtained on drying the boards made of delignified f i b r e . This was interpreted as being due to more effective bonding capacity of other wood constituents than lignin, resulting i n a better u t i l i z a t i o n of int r i n s i c fibre strength through improved papermaking properties of the • fibres. The importance of l i g n i n i n wood has been recognized as the compo-nent which, by i t s biological, physical and mechanical influence, acts on the wet-strength of wood i n a water-saturated condition (7l) • Klauditz and Stegmahh(7l) offer proof that lignin, through i t s deposition in the basic carbohydrate structure of the c e l l wall, reduces only hydration and swelling of these building materials. Polyuronides are thought to be particularly -14-Iriterpenetrated by l i g n i n , apparently bound both chemically and physically. This suggests a lignin-carbohydrate complex i n regions of the middle lamel-lae and the primary wall, providing wet strength of wood. Wacek arid Meralla (l4o) see the importanceof li g n i n i n hardboards in i t s fixing effect due to thermoplastic characteristics. 0*gland ( 1 0 0 ) concludes that lignin" i s a hydrophobic wood constituent that prevents swelling, decreases""water' absorp-tion but does not cause development of fibre to fibre bonding i n hardboard. Lignin <: activation, through heating in the def iberizing, process,"could give a plausible explanation for the necessity of synthetic resin additives to Asplund pulps ( 6 5 )• This' implies that temperatures used i n the Asplund •defiberlzing process are not high enough to activate l i g n i n . '.Although the chemical and physical action of ionizing radiation on cellulose has been studied extensively, information regarding effects on lign i n i s vague. According to references cited by Brauns and Brauns ( 1 2 ) , l i g n i n shows hardly any chemical change when irradiated with a beam of high energy electrons. Irradiated l i g n i n was found to have the same degree of solubility and ultraviolet and infrared absorption spectra as the original . li g n i n . Irradiated l i g n i n also reacts strongly with phloroglucinol-hydro-chloric acid,, giving an intense color reaction. Thus,the conclusion was drawn that.native l i g n i n in solid state i s rather resistant to high energy radiation. After an extensive literature search i t can be safely stated that there has been no suggestion of a relationship between l i g n i n and'the hard-board tempering process. - -3 . Hemicellulose The amount of hemicellulose i n woods and pulps has been the subject of numerous investigations. "This follows early observations that hemicellu-lose relates to the wide range of mechanical properties observed with wood pulps and regenerated cellulose. Few natural products are as complex and poorly defined in chemical nature as those included by the term "hemicellu-lose" (Ikk). Hemicelluloses are found universally i n nature and are"widely associated with cellulose ( 1 , 1 0 7 , 1 3 6 ) . The most usual hemicelluloses are those in which the main 'building unit i s D-xylose i n association with uronic acids, known as xy lain-polyuronides ( 6 7 > 107> 1 3 6 , Ikk) .• Hemi celluloses are " built up of. simple sugars; pentosans such as xylan and araban, hexosans such as manhan, galactan, glucan, and hexouronic acids such as glucuronic, and mannouronic acids ( 8 5 ) . The pentose L-arabinose is believed to •form'"'only on isolation of hemicelluloses giving rise to an araboglucuro-xylah of highly branched nature ( 2 5 ) . . In addition to the xylan-polyuronides assbelated with wood cellulose, a group of polysaccharides occurs known,as cellulbsans ( 3 9 ) . In the case of softwoods, these polysaccharides, constitute a large portion of the non-cellulosic carbohydrates^;.. Wethern (lMO estimated their amount in the order of 7 5 $ of hemicelluloses isolatable from softwoods. It has been shown that hydrolysis of softwood hemicellulose gives xylose, ara-binose, mannose, glucose, galactose, and ^-O-methyl-d-glucuronic' acid ( 8 5 , 1 3 3 ; 9 7 ) . McKenzie and Higgins ( 8 5 ) , and Prey and co-workers ( 1 0 7 ) , have found that there are no major differences in hemicellulose constitution between plants, however, these do respond differently to extraction. -16-Decomposition of hemicelluloses goes through' the same steps as found with sugars (107, 13*0. Goring and Timell ( k k ) found that hemicel-luloses have, on average, kO times lower molecular weight than celluloses with which they are associated. Opinions on this matter are not unanimous. Molecular weight variation between 19,000 and 67,000 ha6 been reported, depending on type of hemicellulose investigated (97). ilh Doaglas f i r a uronic-acid-free, water-soluble polysaccharide was found with a molecular weight of 67,000 (136) . Treiber and co-workers (I36) report chain-length ; measurements on coniferous wood hemicellulose i n the range of, 150-l60 unite,. On the other hand, Glaudemans^ and Timell ( k l ) reported a range of 80 to 330 units There i s l i t t l e known about the location of hemicellulose' within the c e l l wall., It is believed that hemicelluloses, mainly pentosans, are located on the outer portion bf the micellar.strands of cellulose in the secondary wall, partly i n close association with.cellulose and lig n i n (5^, 68, 9k, 130, 136). Hemicellulose of different composition can.be obtained by extrac-tion with different concentrations of a l k a l i solution at different "tempera-tures. The higher concentrations of 18$ and above remove mannan and reduced amounts of pentosans (136). Beta-cellulose i s formed as a secondary product of high concentration caustic extraction (146). In a l k a l i extraction, hemi-cellulose i s degraded to aldoses-and ketoses containing enol arid carbonyl groups. This decomposition of hemicelluloses i n a l k a l i solutions may be followed by ipbservation with ultraviolet absorption spectra (136). Decom-position products of a l k a l i hemicellulose have been found susceptible to condensation with l i g n i n (107, 113)> and to thermoplastic, furfural-resin -re-conversions (11-3). In acid hydrolysis of hemicellulose?monomer!c sugars are produced as decomposition products. Condensation of these sugars with li g n i n i s not considered possible ( 1 0 6 ) . The pentosan-lignin complex has been demonstrated by isolation of a l k a l i l i g n i n (lignin-xylan complex) (k2, 9k, 9 7 , 1 0 6 , 1 0 9 , 1 3 0 , I 3 6 ) and by mildly acidic methanol extraction of wood at high temperatures ( 1 2 9 ) . Calculations of Jayme ( 5 4 ) show 3«5# l i g n i n bound chemically to hemicellu-loses\ The removal of'either component results i n the removal of some of the other. ' Hemicelluloses play an. important, role i n production of fibre-base products.. Their influence on the quality and properties of cellulosic materials has been emphasized more in recent years than earlier ( I 3 6 ) .. These wood polysaccharides may lend valuable characteristics to cellulose fibres but, on the other hand, have some undesired effects. Thus i t is known from numerous investigations ( 8 5 , 1 3 6 , 140, 1^3) that hemicellulose --especially the polyuronides — through their physical and chemical proper-t i e s , and obviously by their special position i n the c e l l wall, exert a special bonding effect between individual fibres in paper sheet formation. Fineman ( 3 l ) > and Triber and co-workers ( 1 3 6 ) , distinguish two cellulosic phases in pulp: the highly crystalline phase -- the bulk of the f i b r e — and the amorphous, water-sensitive hemicellulose. Generally, hemicellulose i s believed'to be responsible for the strength of papers.,Swanson ( 1 3 1 ) determined an optimum hemicellulose con-tent --at which maximum bonding strength is obtained. McKenzie and Higgins ( 8 6 ) found hemicellulose important to fibre physical properties, such as swelling capacity and c r y s t a l l i n i t y . The strength of paper, according to -18-Cottrall" (18), depends not only on the extent of the fibre bonded area developed by fibre crossings, but also on the i n t r i n s i c strength of the bonds. Increasing amounts of short-chain hemicellulose. lower the i n t r i n -sic strength of the bond (60) . C'ottrall (18) also believes that the plas-t i c i t y of fibres must be related to their swelling capacity i n water. He found that greater amounts of hemicellulose, as shown by pentosan content, produced greater swelling capacities of fibres as reflected by their water 'retention. This was verified by Watson and co-workers (lV3).~ McKenzie and Higgins (85) liken hemicellulose with i t s i n a b i l i t y to crystallize'. The internal pressure developed upon swelling aids " f i b r i l l a t i o n of the fibres in beating. Swollen hemicellulose renders the fibre surface "tacky" and reconstitutes into a solid bond on drying. This suggests that non-cellu-lo s i c polysaccharides function as adhesiyes during sheet formation of papers (1^3) • The importance of hemicelluloses i n board strength development was also recognized by Klauditz (67, 68, 69,) Klauditz and Stegman (71), C)gland (100), Runkel (112), Runkel and Wilke (113) and Wacek and Meralla ( l4o) . The role of hemicelluloses is mainly viewed from the standpoint of strength development on reconstituting the wood fibre from water into board by hot-pressing, and by further heat-treatments. These investigators are opposed to the theory of "lignin activation", but considered hemicelluloses either by direct bonding effect on the fibre (69, JI, 100), or by changed state into furfural-base resins (112), as being responsible for the strength of hardboard. Admittedly,' i n a l l phases of thermal treatments occurring during hardboard manufacture, drastic changes take place in constitution of both -19-l i g n i n and hemicelluloses. The hydrolyzing effect on hemicelluloses at high temperature, in prescence of water, cannot be overlooked (5*0 . Under these conditions acetic acid and small quantities of formic acid are formed, main-l y from xylans (112). The possibility of furfural formation from hemicellu-lose and polycondensation with lignin has already been mentioned. Similarly, Prey, Waldmann and Stiglbrunner (106) and Klauditz (66) found that acetyl groups are. s p l i t off from wood on a l k a l i treatment. This results•in pro-ducts with lower strength and greater water sensitivity, although the l i g n i n is l e f t intact. They attributed this effect to losses in pentosan content and to the formation of. weakly hydrophylic hydroxyl groups. The role of hemicellulose i n hardboards was demonstrated by Klauditz (69), Klauditz and Stegmahn(7l)> and Ogland (100), Lignin was extracted from poplar wood and Asplund pulp by the sodium chlorite method described by Jayme (55)- After drying and board formation of the deligni-f i e d materials they obtained greater strengths than with samples in the original state. Furthermore, similar improved strength and dimensional s t a b i l i t y have been observed on delignified samples given pcst-pressing heat-treatments. This phenomenon was interpreted as being due to the increased-proportions of carbohydrates, increased intrinsic' fibre strength i n the delignified materials, and to the fact that technological properties of paper-making fibres were greatly improved by l i g n i n removal. The" analysis of volatile condensates resulting from heat-treatment, gave i .21$ water, acetic acid and carbon dioxide from the extracted material as' compared to 0.8l$ obtained from unextracted boards (7l)« Regarding these results,.the conclusions were drawn that heat-treatment does not. act on' lignin, but causes chemical and physical changes to hemicelluloses. -20-K u m a r (73) r e p o r t e d o n s o m e a s p e c t s o f a p o s s i b l e o i l - t e m p e r i n g m e c h a n i s m w i t h h a r d b o a r d s . H e b e l i e v e d t h a t h e m i c e l l u l o s e s a r e r e s p o n s i b l e f o r t h e h i g h s t r e n g t h . a n d d i m e n s i o n a l s t a b i l i t y o b t a i n e d i n t h e o i l - t e m p e r -i n g p r o c e s s . T h e s t a t e m e n t i s m a d e w i t h o u t e x p e r i m e n t a l e v i d e n c e , t h a t t h e a c i d p a r t o f t h e o i l a t t a c k s t h e w o o d f i b r e h e m i c e l l u l o s e , p r o d u c i n g r e d u c e - , a b l e g r o u p s o r w a t e r - r e p e l l i n g e t h e r b r i d g e s . H e f u r t h e r g i v e s c r e d i t t o f o r m a t i o n o f f o r m a l d e h y d e w h i c h , i n h i s o p i n i o n , p r o v i d e s h y d r o p h o b i c m e t h y l b r i d g e s . k. C e l l u l o s e C e l l u l o s e i s a n a t u r a l l y o c c u r r i n g h i g h p o l y m e r . B e c a u s e o f i t s r e l a t i v e l y u n i f o r m s t r u c t u r e i t f o r m s a g o o d e x a m p l e o f a m a c r o m o l e c u l e . T h i s i s o n e r e a s o n b e h i n d t h e l a r g e a m o u n t o f i n f o r m a t i o n a v a i l a b l e o n t h e m o l e c u l a r c o n f i g u r a t i o n a n d f i n e s t r u c t u r e o f c e l l u l o s e (23)-C e l l u l o s e i s c o n s i d e r e d a s b e i n g t h e d i f f i c u l t l y h y d r o l y z a b l e p o l y -s a c c h a r i d e f r a c t i o n o f h o l o c e l l u l o s e . I t i s c o m p r i s e d o f a n h y d r o g l u c o s e u n i t s e a c h u n i t c o n t a i n i n g , o n t h e a v e r a g e , t w o h y d r o x y l g r o u p s ( 6 l ) . H y d r o x y l g r o u p s i n f a v o u r a b l e l o c a t i o n o n t h e a n h y d r o g l u c o s e u n i t s m a y f o r m h y d r o g e n b o n d s w i t h n e i g h b o u r i n g h y d r o x y l g r o u p s (13> 6 l , 87, 90, 110) . C e l l u l o s e i s f o r m e d o f i n t e r s p e r s e d c r y s t a l l i n e a n d a m o r p h o u s r e g i o n s ( 6 l , 79> 110). I t i s g e n e r a l l y a c c e p t e d t h a t t h e s e r e g i o n s d o n o t r e p r e s e n t t w o d i f f e r e n t p h a s e s . C e l l u l o s e c h a i n s s t r e t c h f r o m c r y s t a l l i t e t o c r y s t a l l i t e t h r o u g h a m o r p h o u s r e g i o n s ( 6 l ) . T h e c r y s t a l l i t e s a r e c h a r a c t e r i z e d b y s h a r p x - r a y d i f f r a c t i o n p a t -t e r n i n d i c a t i n g a h i g h d e g r e e o f o r d e r (79) ' L e e (79) a n d R o l l i n s (110) r e p o r t e d a - d e g r e e o f p o l y m e r i z a t i o n f r o m 600 t o 6,000 m o n o m e r i c a n h y d r o --21-glucose units. More recent investigation by Goring and Timell (1+3) gives an average degree of polymerization for wood cellulose between 7,000 and 10,300, depending on the .-.starting material and efficiency of the nitration procedure. For native cellulose, a weight-average degree of polymerization of 15,000 and higher may be obtained, which would correspond to a molecular weight of 2.5 million. Because of close hydrogen bonding, the Crystallites are very resistant to swelling effects that can be produced by water and other polar solvents (90, 6l). Viscosity of cellulose solutions is considered as one of the most important test methods for characterizing cellulose. It i s related to Strength properties-of papers. Viscosity change during processing, and strength of the finished product, have been found to be direct functions of cellulose chain length (DP) (91). The amorphous regions arelbuilt up of short-chain polymeric units with an average degree of polymerization of 200, and a.molecular weight of 30,000. Collectively, these polymers are called hemicelluloses and Include the previously discussed pentoses, hexoses, and polyuronic acids (18, 6l). In wood fibres the major part of the cellulosic material i s situa ted i n the secondary wall (110). F i b r i l s making up the c e l l wall have a crystalline orientation parallel to the long axis of the f i b r i l s , although the f i b r i l s are wound around the long axis of the fibres i n a spiral-like manner (23, 110, kk). Klauditz (67) draws a similarity between reinforced concrete and the wood structure; where cellulose would represent the rein-forcing steel bars; hemicelluloses would be the tiny wires holding the bars together within the structure and the li g n i n would represent the con-crete, giving body and r i g i d i t y to the structure as whole. -22-The mechanism of paper strength has been found to depend on the state and bonding capacity of the cellulose fibres. To obtain a firm bond on dewatering of papers, the fibres must be brought in close enough con-tact for the formation of. hydrogen bonds between the active cellulose sur-faces. At the same time, the environment on the cellulose surface must be favourable for such bond formation. On evaporating the water from a sheet of paper the hydroxyl groups on adjacent f i b r i l s are brought close enough to each other for hydrogen bonding rather than bonding with the water mole-cules . This occurs with higher frequency as more and more water is removed. For hydrogen bonding to occur, the hydroxyl groups of the cellulose f i b r i l s must be oriented outward. The strength of paper i s thus determined by the number of hydrogen bonds that are formed during the drying process ( 1 3 ) • However, since-the occurrence of such bonds in paper i s relatively low, the strength of paper must be dependent mainly on inter-fibre bonding, afforded by the hemicelluloses, and fibre arrangement in sheets of papers, and only to a limited extent on hydrogen bonding. Elastic properties of fibres are improved by removal of li g n i n and hemicellulose ( 6 9 ) • By increasing the cellulose, content i n the wood fibre — through the removal.of other wood constituents — a strength i n -crease is obtained as. evidenced by the increased breaking length"of a paper sheet". Unfortunately, the wet-strength of such papers is practically zero-On drying the sheet, good strength i s obtained. The breaking length reaches a minimum as more and more hemicellulose is removed. This was explained as being due to the unsatisfactory.b.onding existing between cellulose molecules in situ ( 6 7 ) . Alpha cellulose — the residue remaining after extraction of holocellulose with 1 7 * 5 $ caustic solution — contains extraneous hexoses and -23-pentoses i n small amounts detectable only by chromatographic methods (1, 110 ) . Investigations of i n t r i n s i c fibre strength showed that the cellulose i s the chief chemical portion of the fibre influencing the i n t r i n s i c fibre strength ( 6 0 . In hardboard strength development, major consideration must be given to the wood "gluing" constituents i n which li g n i n and cellulose hardly par t i -cipate ( 6 5 ) . Finally, experiments of Fisher 1 ( 3 2 ) showing that the swelling and water retention of cellulose can be regulated by resin and plasticizing additives, respectively, thus reducing water pick up and shrinkage under certain sets of atmospheric conditions. Investigations of Arthur ( 5 ) , Blouin and Arthur (9) > Charlesby ( 1 6 ) , Glaudemans and co-workers (Uo)j Lawton and co-workers ( 7 7 ) , Mater ( 9 2 ) j Seaman and co-workers (122), Smith and Mixer (124) and Winogradoff (148) ' on the effect of high-energy irradiation pf wood,' show marked degradation of the polysaccharide portion. Irradiation of sugar solutions gives strange results such as inversion and increase of solution acidity. Hexoses were changed to uronic acids in good yields. The irradiation of polysaccharides resulted i n decreased viscosity, an increase i n reducing power and increased acidity of solutions. Winogradoff (148) found a decrease i n tensile strength of cellulose materials which he interpreted, based on x-ray diffraction studies, as being due to decrease of c r y s t a l l i n i t y . Lawton and co-workers ( 7 7 , 7 8 ) obtained a completely water-soluble f i l t e r paper when irradiated • • 6 at 3 . 3 x 10 megarads. At small dosages of 10 equivalent roentgens, Seaman and co-workers (122) found very l i t t l e change i n wood, but by further increas-ing irradiation dosages a decrease i n the degree of polymerization was Q observed. They obtained a water-soluble cellulose at 10 rads. Degradation of cellulose by gamma irradiation may follow two mechanisms*, direct chain -24-scission at the aeetal linkage, or an oxidative process following i n i t i a -tion caused by the energy of irradiation ( 1 6 ) . Depolymerization is not affected by degree of c r y s t a l l i n i t y . Blouin and co-workers ( 9 ) irradiated purified cotton and found an increase in carbonyl and carboxyl groups and chain-length cleavage i n the ratio of 20:1:1. (Twenty times more aldehyde groups were formed than carboxy groups). The DP decreased from 4,400 to 5 6 as radiation dosage was increased from 0 to 1 0 8 rads. Irradiation to 107 rads resulted i n DP values of 1 8 0 in oxygen and 210 i n nitrogen atmosphere. Water solubility of cellulose increased from 0.1 to 10.4$. A water solubility of 0 . 5 $ was obtained at 10? rads. No difference was found in infrared absorption spectra of irradiated cellulose. Smith and Mixer (124) showed that natural aromatic compounds, such as lig n i n and extractives, exerted a slight protec tive effect (approximately 3^$) on the radiolysis. of redwood cellulose. No effect has been found on gross analytical composition of wood. Moisture pick-up'was found to be lowest at 5 x 1 0 ? rads. In summary, while Cobalt 6 0 irradiation does not -affect the analy t i c a l composition of wood, i t may influence the degree of polymerization to such an extent that water-insoluble cellulose is made completely soluble, thus reducing the in t r i n s i c fibre strength as degree of polymerization is randomly decreased. . No reference has been found dealing with any aspect of cellulose and tempering o i l interaction of hardboards. 5 « Tannins and other polyphenolic wood extractives' The bark of different'; wood species, as well as other parts of plants and trees, contain naturally occurring tannins in different amounts. -25-Tannins find wide u t i l i z a t i o n i n the leather industry, and In the drug i n ~ dustry as antioxidants. Dihydroquercetin (ta x i f o l i n ) , a 3"by<iroxy flavanone, has been found i n Douglas f i r heartwood. It has been identified by Pew (103, 10k) and later described by Gardner and Barton (35), and Kurth and Chan (76). Dihydro-quercetin i n Douglas f i r heartwood was found i n the amount, of 1.5$ by Gardner and Barton (35) and shown to be responsible for the d i f f i c u l t i e s encountered i n calcium-base sulphite pulping of this species by Pew (103)° Adler (2), and Adler and Stockman (k)s found similar effects of catechin tannins on unpeeled, floated spruce logs used for pulp production" purposes. It-was observed that unpeeled spruce logs, floated over the sum-mer months, gave higher amounts of screenings after sulphite pulping than logs peeled before water storage. After a thorough investigation of pos-sible causes of this phenomenon.it was found that tannins of the catechin type penetrated the sapwood portion of the logs, resulting i n an insoluble lignin-phenol condensation product when such wood is exposed to higher tem-peratures such as encountered, i n pulping processes. The Isolated tannis were found to belong to the d-catechin family, giving an intense violet color reaction when treated with a solution of sulfuric acid and methanol in the' volumetric ratio of Itk (2) . The lignin-tannln complex has been'shown to exist through methanol extracts of such "damaged wood". Color reactions both of the sulfuric acid-methanol and phloroglucinol-hydrochloric acid' type were obtained, proving the presence of d-catechin tannin, and coniferyl-aldehyde resulting from lignin, respectively. This color reaction i s not given by^  hydrolysable tannins, such as g a l l i c acid (2). - 2 6 -Reaction between lig n i n and d-catechin i s believed to take place between the benzyl alcohol groups of li g n i n and the reactive positions of the polyphenyl nucleus of the d-catechin giving an unreactive lignin-poly-phenol complex i n wood. The. usual mechanism of lig n i n sulphonation did not occur, thereby giving rise to an unusually high amount of screenings. The removal of this lignin Tpolyphenol complex from wood by 1 N sodium hydroxide-formaldehyde solution was without, success (4). 6 . Heat-treatment of pressed hardboards Heat-treatment has today become common practice in.most' hardboard mills. The function of heat-treatment is to improve flexural and "dimensional properties of the boards. The chemical composition of hardboard-composing wood fibres i s changed by removing constitutional water, resulting i n higher strength and dimensional s t a b i l i t y ( 5 9 , 4 7 ) . In addition, the cure of resin additives i s carried to completion. The mechanism of heat-treatment i s s t i l l somewhat obscure, possibly the result of complications arising from the lignin-carbohydrate complex. The theory of lig n i n recondensation' as opposed to complete dehydration of hemicellulose i s s t i l l not completely settled. According to Klauditz ( 7 1 ) the firm bond between fibres resulting from thermal treatment of wood and fibreboards i s due to re-gluing the cellulose residues of the c e l l walls within their middle lamellae and primary walls by hemicelluloses, in parti-cular by polyuronides. The. strength increase can hardly be due to increase of i n trinsic fibre strength, but must be a result of the dehydration of hemicellulose, thereby increasing the fibre to fibre bond area ( 7 1 , 1 0 2 ) . The increased fibre bond strength gives rise to a better u t i l i z a t i o n of -27-i n t r i n s i c fibre strength (71) • Parallel to this, heat-treatment causes reduced moisture re-absorption of the fibres. Heat-treated boards do not reach the moisture content of untreated boards when subjected to "similar atmospheric conditions, i.e.»their equilibrium moisture content i s reduced (it-7, 71, 112). The effect of heat-treatment on the fibre to fibre bond cannot be f u l l y realized since the strength of individual fibres is already u t i l i z e d up to 70 to 80$. Additional information on effects of heat-treatment of hardboards i s given by Morath (95), Ogland (101), Ogland and Emilsson (102), Runkel (112) and Voss (139) • Voss (139) points out a few process variables that influence physical properties of heat-treated hardboards. By heat-treatment at 170 to 180° C. the strength properties are i n i t i a l l y increased (bending and tensile strength, and modulus of elasticity) to a maximum of 50$ (kj, 112). Pro-longed heating results i n decrease of flexural properties. Factors working together i n this process are level of temperature and duration of heat-treat-ment. Decrease in flexural properties i s due to the r i g i d i t y of fibres that i s acquired by overdrying them (127)• Along with increase of modulus of ela s t i c i t y , the limit of proportionality i s raised practically to the point of rupture. However, these properties are much dependent upon moisture con-tent at the time of testing. Kumar (7*0 found that an increase in moisture content from 3 to 12$ decreased modulus of rupture by 40$ and' modulus of el a s t i c i t y by i+5 to 50$. On the other hand, the hygroscopic properties did not change after a certain period of heat-treatment. Unfortunately, one must be satisfied with less than the maximum improvement bf dimensional s t a b i l i t y . An improvement of only 25$ is obtained with commercial heat-treatment (kf, 112). -28-The leveling off of hygroscopic improvement and point of maximum strength do not coincide, maximum strength being far below the point of maximum dimensional s t a b i l i t y . Voss (.139) regards both flexural and dimen-sional improvements'as being due to recondensation of lig n i n on one hand, and to shrinkage and losses of water of constitution from the cellulosic regions on the other. The loss of hydroxyls i s believed to result in more hydrophobic ether bridges, or hydrogen bonding as observed with paper by Mark (90). McKnight and Mason (88) credit the improved hygroscopic proper-ties of wood to the lowered water sorption of the heat-treated l i g n i n . The possibility of reorganization i n the cellulose chain system i s mentioned with certain reservations. Heat-treatment also results i n darkening of boards, probably because of their mild oxidation in the presence of a i r (139) • 7. Oil-tempering of pressed hardboards-Information about oil-tempering of hardboard i s scarce- Most re-ports on hardboards recognize only the importance of oil-tempered hardboards but do not go into extensive discussion of other than some aspects of pro-cess variables and resulting products. A summary of findings by Koilmann (65), Kumar (73), and Mbrath (95), and a short description presented by P^AuO. (33), follows. Selected high-quality hardboards are dipped i n a hot bath of tempering o i l . The most frequently used o i l s are tung, linseed, p e r i l l a , soyabean, and t a l l o i l ; f i s h o i l i s rarely used because boards treated with i t acquire an unpleasant and lasting odor. Just recently, June I96I, U.S. patent No. 2,988,462 was issued to the Masonite Corporation for the use of hydro-carbon drying o i l s for the impregnation of lignocellulose hardboard (51)-Heating of the o i l facilitates easier and better board penetration. The discovery that limited o i l absorption gives rise to maximum strength and dimensional improvement upon tempering (73, 95) has lead to thinning of oils with different organic solvents. Morath (95) found that o i l i n excess of 15 to 20$ is wasted since i t only raises specific gravity of the boards without giving the benefits of further strength improvement.' Thin-ning of o i l s promotes penetration and gives means for controlling the amounts of solids retained i n the boards. In general, o i l absorption increases with increasing board density. Young and Majka (151) patented a different method for incorporat-ing o i l i n hardboard. They incorporated drying-oil in hardboard by dispers-ing a finely-divided,fat-sorbing material i n the slurry, carrying an appre-.. ciable-amount of the drying-oil. From the resulting slurry a mat is formed and oil-tempered hardboard produced by one of the conventional hardboard manufacturing processes. The method would result i n a more uniformly treated tempered board and savings i n time and equipment. Board dipping i s followed by heat-treatment, the tempering process being essentially_the same as discussed i n the foregoing section. It should be pointed out that results of oil-tempering are not the same as those of heat-treatment alone i The 25 to 50$ strength increase by heat-treatment is raised to 80 to 110$ in the oil-tempering process. Similarly,, dimensional s t a b i l i t y i s increased to 35 to 50$ as compared to 25$ obtained by heat-treatment. According to Kumar (73), the level of temperature i s set only by the danger of self-ignition. , However, too high temperature may result in"loss of strength and extensive darkening of the board surface due to ^ heavy oxidation; Temperatures in the range of 165 to 175° C safely meet -30-a l l requirements for oil-tempering of hardboards. The chemical mechanism of the process is completely unexplored* Kumar (73) has speculated that hemicellulose is the causal factor, as has been discussed. 8 . Humidification of pressed :hardboards Tempered as well as untempered hardboards are humidifed after thermal treatment. Boards come from the hot-press or heat-treating chamber practically oven-dry. Although boards are at their highest strength values in this state (7^) they are extremely unstable dimensionally u n t i l they reach equilibrium with the surrounding atmosphere. Humidification i s designed to hasten and control the process of reaching equilibrium through use of controlled temperature and relative humidity (20> 135)- The desired equilibrium moisture content of 8 to 10$ depending on regional atmospheric conditions, i s heat stabilized i n the boards over a certain period bf time by keeping the boards in the humidifying chamber. According to Klauditz and Stegmann(7l) humidification further lowers the swelling and water absorption of polyuronides and other c e l l wall materials exposed to different atmospheric conditions. - 3 1 -MATERIALS AND METHODS . A. Selection and Preparation of Materials 1 . Collecting the fibrous material Douglas f i r Asplund fibre served as starting material for this study. This was obtained from the production line of Canadian Forest Products Limited, Pacific Veneer and Plywood Division, New Westminster, British Columbia. The point for collection was chosen as the outlet open-ing of the Sprout Waldron refiner (Model No. 3 6 - 2 ) .prior to size addition and consistency regulation. At present, two types of fibre are produced in this hardboard plant, one, a coarser fibre used for the manufacture of their regular hardboard, while the other, called "l / 8-inch fibre", i s used as furnish for special purpose boards such as printed hardboard. This l a t -ter type of fibre was selected because of i t s more uniform refining! It was anticipated that this fibre would react more uniformly i n chemical treatments, provide better board formation and give good texture to" thin fibreboards produced from i t . The fibre was refined at a plate setting of 0.030-inch and gave a Bauer-McNett fibre classification as shown In Table 1 Enough material was collected at one. time to satisfy the needs of the whole-experiment. It'was gatherd.at approximately 30$ consistency by hand squeezing, weighed to estimate amount, re-slurried i n a large vessel and washed with tap-water to neutral pH. The procedure aimed' at thorough mixing of the.sample, as well as adjustment of pH for control of acid hydro ly s i s during prolonged storage i n wet condition. It has been shown by Klauditz ( 6 8 ) , Runkel ( i l l ) , Stewart and co-workers ( 1 2 9 ) , and Voss (139) that acetic.acid and formic acid are responsible for hydrolytic degradation i n the l i v i n g tree on one hand. These same acids are formed during.the high-temperature defiberizing process, resulting i n losses of hydrolyzable l i g n i n and pentosans on the other. Fines were retained during f i n a l pulp thickening by re-circulating the drainage water. After f i n a l dewatering the mat was slightly cold-pressed to remove excess water, placed i n a polyethylene bag, and stored at 1 5 ° C. Chemical properties of the raw fibre are described in later sections. ' t 2 . Tempering o i l Fresh, commercial tempering o i l was obtained from the o i l dipping machine at the above hardboard m i l l . An amount, sufficient for the whole experiment, was collected and stored i n a sealed can u n t i l further"use. The raw o i l i s manufactured by Imperial O i l Ltd. and mixed with other necessary ingredients (linseed o i l , possibly maleic anhydride) at Reichhold Chemical (Canada) Ltd., Port Moody, British Columbia. A l l jinformation regarding the nature and specifications of the o i l was obtained from Chemical Products Department, Imperial O i l Ltd., Toronto, Canada ( 2 1 , 2 6 ) . "CTLA Polymer" (the commercial name of this tempering o i l ) i s a pre-polymer of cracked naphtha gas o i l fraction which contains straight, branched and cyclic mono- and di-olefines, naphthenes, as well as normal and iso-paraffins. It i s heat-reactive and i s prepared by partial polymer-ization of olefins over hot clay.' The polymer, being highly unsaturated, dries by both oxidation and polymerization. A characteristic property of the o i l is i t s tendency for depolymerization or rearrangement on extensive heating. This has been observed as an inherent characteristic of dicylco-pentadienes with an endo-methylene bridge In the molecule. To reduce heat -33-required for polymerizing the o i l , one per cent maleic anhydride addition is made. This provides a new polymer of the "CTLA Polymer", which i s claimed to give greater strength and better flexibility"than can be ob-tained by heat soaking with "CTLA Polymer" alone. The reduced heat require-ment also lessens the danger of self-ignition in the hardboard tempering process. The tendency for depolymerization on prolonged heating i s further reduced by addition of certain amounts of linseed o i l . "CTLA Polymer" is soluble in aromatic, paraffinic and chlorinated hydrocarbons, acetates, ketones, and alcohols above butyl alcohol ..' .It i s compatible with various drying-oils, both raw and bodied, such as linseed, tung, soyabean, castor, and f i s h o i l s . Furthermore, i t i s also compatible with rosin, rosin esters, coumars, modified alkyds, modified phenolics, natural and synthetic rubbers, and nitrocellulose. "CTLA Polymer",is used extensively i n other industries,, such as core o i l testing, where i t replaced natural drying-oils such as linseed o i l . Specifications and some typical properties of "CTLA Polymer" are given in Table 2. B. Extraction and Modification of Fibre Constituents Investigation of the proposed hypothesis called for two major types of treatments, those done on the Asplund fibre arid those applied to prepared fibreboards. The latter are described i n another section. Both are non-destructive i n that only part of the fibre i s removed, modified or altered when a particular variable is under investigation. Fibre treatments were believed to be most adequate for removal or partia l deactiviation of the particular, wood constituents most commonly con-* -34-sidered as influencing physical properties of wood. Particle size of the raw material (Asplund fibre) made i t possible to carry out fibre treatments, similar to those used i n analytical investigations, with f a i r degrees of uniformity and reproducibility. As anticpated, t r i a l treatments on small samples were reproduced on larger scale without change of procedures. In every case an analytical method with known action on the wood has been f o l -lowed for a certain treatment. Suitability of the method to this purpose was f i r s t verified using a closely controlled range of variables. By this method, treatment conditions were worked out that gave best results. Thus, individual treatments were shown as being efficient in removal or alteration of a particular wood constituent, with the least possible change in other wood constituents and the fibre structure i t s e l f . Wood constituents most often discussed in the literature as i n f l u -encing paper and hardboard physical properties were examined in preliminary experiments. .These included quantitative (alcohol-benzene solubles, lignin, and hemicellulose) and qualitative (cellulose, and deactivated lignin) mani-pulations of the fibre material. 1. Extration of alcohol-benzene solubles The extraction procedure was essentially that prescribed by TAPPI Standards T 6m-54. The purpose of this treatment was to remove natural resins, fats, oils and waxes found in Douglas f i r in the amount of 9-6$ (based on the oven-dry weight of original wood) (75)> as well as prepara-tion of the raw material (Asplund fibre) for different chemical treatments. Although Ogland (100) has reported that acetone-extracted fibre produces fibreboards of higher strength, this solvent was avoided because of i t s -35-swelling effect on wood. Alcohol-benzene extraction i s also a customary pre-treatment for wood and fibre before extraction of other chemical com-ponents. A large Soxhlet apparatus was used for fibre extraction with an f alcohol-benzene/mixture i n the volumetric ratio of 1:2. Methanol was used as the alcoholic component. Each fibre<batch,approximately 200 g. oven-dry, was extracted for 8 hours with number of siphonings regulated to 7 to- 8 per hour. After completion of extration the fibre was washed through with methanol and then with hot water. The wet fibre/.was spread out and"air-dried for one week. 2. Removal of lig n i n A choice of methods is available for removing li g n i n from wood. Preference was given to methods that would selectively attack l i g n i n and would require only mild treatment conditions (temperature, pH, solution concentration, and time) to avoid degradation of the other wood constit-uents . An optimum method should afford an undisturbed examination of the changes i n the interaction-induced strength in partial or complete absence of l i g n i n from the fibreboard, made of such treated fib r e . Furthermore, close control on the amount of lig n i n removed is desirable. The-method should also be adaptable to preparation of larger amounts of fibre with acceptable reproducibility. Delignification may be defined as the process of removing lignin present i n wood, or woody plants (12, 1^9). In a technical sense the pro-cess is synonymous with chemical pulping, and subsequent bleaching (8, 37)• Delignification aims at isolation of a more of less pure cellulose, or at -36-the intermediate product holocellulose. An analytical delignification involves removal of lig n i n with a minimum amount of hydrolytic and' oxida-tive action on cellulose and associated polysaccharides. These constitute holocellulose or the entire polysaccharide fraction of the wood. (6, 50, 55, 150) . The three mechanisms believed to be involved i n delignification are hydrolysis (a) t combination of reactant chemicals with l i g n i n which enhance i t s solubility (b), and degradative breakdown of li g n i n into smaller frag-ments causing ready sol u b i l i t y ( c ) . a. That some part of the li g n i n goes into solution;on boiling wood with hot water has been demonstrated by Goldschmid (42), Klauditz (66), Runkel (111), Sohn (126) and Stanek (128) . The preparation of "native l i g n i n " by ethyl alcohol (or methyl alcohol) extraction of wood has been used i n analytical experimentation (12). Extensive reviews on lig n i n isolation by alkaline hydrolysis of wood and u t i l i z a t i o n of the a l k a l i lignins i s given by Brauns and Brauns (12) and Merewether (93, 94). b. Combination of reactant chemicals with l i g n i n , which enhance i t s s o l u b i l i t y i n water or other solvent used, i s the basis for major pulp-ing processes. For example, l i g n i n can be rendered soluble by cooking with acid sulphites. The solute, In the form of lignosulphonic acid, has pro-vided material for many investigations on li g n i n structure (27, 34, 36, 80, 8 l , 82). Commercial pulping processes do not remove a l l l i g n i n from the wood during cooking because"of solvent diffusion and complete solubilization d i f f i c u l t i e s i n superficial regions i n the c e l l wall. Attempts to further reduce l i g n i n by these procedures result i n severe hydrolysis of. the., poly-- 3 7 -saccharlde portion as evidenced by losses i n yield, pulp viscosity, and paper strength ( 8 , V 3 , 8 l ) . cjv Degradative breakdown of lignin into smaller fragments causing ready solubility is by far the most effective method of removing l i g n i n . This is accomplished by oxidative treatments which have the great advantage of selectivity, i.e.,low degrading action on the cellulosic portion of wood ( 8 , 6k). This characteristic of controlled oxidation is f u l l y u t i l i z e d in pulp bleaching ( 8 ) . In oxidations with more or less strong oxidizing agents such as hydrogen peroxide, hypochlorite, chlorine dioxide, chlorine, acidified sodium chlorite solution, nitrobenzene, t-butyl hypochlorite and numerous solutions containing active chlorine, the amount of lignin removed is depen-dent on reaction conditions —: time, solution concentration, pH, and temper-ature -- and the relative amount of li g n i n present i n wood ( 1 0 8 ). The degree of l i g n i n oxidation i s , therefore, dependent on the experimenter through his control of reaction conditions. Careful control gives similar results with different oxidizing agents ( 5 0 ) . A number of oxidizing agents were tried under different reaction conditions i n preparation for this study. This was necessary to determine procedures for removal of controlled amounts of lignin, and for quantita-tive oxidation of l i g n i n without solubilization. It soon became evident that the sodium chlorite method offers great advantages over a l l other oxidation procedures for the removal of controlled amounts of li g n i n from Asplund pulp; The set-up is relatively simple, the amount of l i g n i n removed is a time-or treatment-dependent vari-able when other factors are kept constant. The preparation of cooking chemicals i s not too elaborate as compared to some of the other procedures.' The method was essentially that described by Jayme (55), further refined by Wise and co-workers (150), and cited by Koeppen and Cohen (6k). Investigations of the method by Barton (6), Brauns and Brauns (12), Giertz (38), Huang (50), Koeppen and Cohen (6k) and Rapson (108) show that sodium chlorite i n slightly acidic medium has only very mild action on cellulose, but specifically attacks l i g n i n in wood.. Chlorine dioxide — formed i n the reaction mixture i n the presence of aldehydes — is unreactive toward alco-hols and carbohydrates. Under specific conditions, chlorite solutions have* the same action as chlorine, but do not have equivalent oxidizing power (6k). Giertz (37) showed that chlorite solutions do not react with phenols, cresols or saturated aliphatic compounds and react only slowly with quinone-forming phenols, with ligniivcontaining materials such as sawdust, and lignosulphonic acid. The temperature and pH have been found c r i t i c a l to the chlorite \ delignifying process (6k, 108) . With increasing temperature there is a stead decrease in yield of holocellulose and i t s apparent l i g n i n content, and an increase i n the amount of l i g n i n removed. This phenomenon i s ex-plained by the assumption that a portion of the l i g n i n i s chemically bound to the cellulosic or hemicellulosic constituents of wood and removal of this i s accompanied by removal of a portion of the latter constituent (8, 56, 66, 6k,. 91) 105)« It is advisable, therefore, to keep reaction temperatures below 70° C. (6k, ikk). Rapson (108) found that maximum brightness was ob-tained with sodium chlorite bleaching of chemical pulps by buffering pH at about k. Brightness f e l l off only slightly as the pH dropped to one, but decreased sharply as a l k a l i n i t y was reached. The effect of pH between k and 1 was found 'to be negligible on pulp viscosity. Only a slight drop was found in i n t r i n s i c viscosity when pH f e l l below 2. This was probably due to hydrolytic degradation of the pulp at such high acidity. Maximum lig n i n solubility, maximum brightness and minimum cellulose degradation f a l l within pH values of 3 to 5 (108). Experimental runs were made on 5-g- portions of alcohol-benzene extracted Asplund fibre with the delignification process described by Wise and Jahn (IU9) • Only slight modifications were used to adapt the method to extraction of larger amounts of pulp needed for board preparation. In experimental runs, the 5-g.samples were suspended in,l60 ml. solution containing 1.5 g.sodium chlorite (NaC102) and 0.5 ml. of glacial acetic acid. The pH of the slurry of s'uch chemical composition is about 5-No further pH adjustments were made since with progress of cooking the liquor became slightly more acidic. The reaction vessels (stoppered 500 ml. Erlenmeyer flasks) were placed i n a constant-temperature bath, controlled at 70° + 1° C After each consecutive hour the same amount of chemicals were again added as a.concentrated li q u i d (10 ml.of aqueous solution' con-taining the above amounts of sodium chlorite and acetic acid). One fibre sample, was removed after each hour and washed with 700 ml- of 1$ acetic acid on a Buchner funnel- The mother liquor was recirculated three times to retain fines. The mat was pressed by hand between recirculations to secure a good f i l t e r i n g pad. The 1$ acetic acid'wash was followed by 300 ml-of cold d i s t i l l e d water. Washing with water was continued i f the pulp s t i l l smelled of free chlorine. Each sample was then oven dried to constant weight, and the weight loss was expressed as the percentage of the calculated oven-dry weight of the original sample. -40-After several t r i a l cooks i t was found that 10 h r i .e .,.9 repeated treatments were necessary to obtain no further weight loss on additional treatment. This related to 36.2$ weight loss. The relationship between num-ber of treatments and per cent weight loss is plotted in Figure 1 A. • Each point on the graph represents the average of three cooks. From this graphic representation the weight loss could be extrapolated and defined by number of treatments, as well as by cooking time. With these results, large batches of fibre (60 g.oven-dry plus anticipated weight loss on treatment) were extracted to make up a series of samples with weight losses at 5, 10, 15, 20, 25, 30 and 35$ corresponding to anticipated lignin losses of 16, 32, 48, 64, 8l, 97 and 113$, respectively. (Anticipated lignin loss calculations are based on 31«04$ Klasoh li g n i n content determined by the 72$ sulfuric acid method.) Weight loss below 5$ was found to be time dependent, so that a series of similar cooks was set up as above. Samples were removed at 10 minute intervals up to 60 minutes without further chemical addition. Thus, the relationship of per cent weight loss to time of cooks could he esta-blished. Results are plotted in Figure 1 B. For this figure times have been extrapolated from 1, 2, 3, and 4$ weight losses corresponding to anticipated lignin losses of 3, 6, 10 and 13$ respectively. It should be mentioned that d i f f i c u l t i e s were encountered i n reaching the point of maximum weight loss producible by repeated"chlorite treatments. The unusually high weight loss (36.2$) is believed to be the result of changed chemical composition of the Asplund fib r e . The experiments of Ifju (53) show that in extraction of 1Douglas f i r micro.-sections a maximum weight loss of 28$ could be obtained with 7 treatments. Subsequent treatments . l a -fas many as k) did not cause additional weight loss in his sections. A number of lignin-oxidizing procedures were tr i e d for quantita-tive oxidation of.lignin without solubilization. The purpose of such •treatment was to elucidate the chemistry involved in the interaction be-tween l i g n i n and tempering o i l as activated by heat. Although, a l l efforts to achieve this were without success, they did afford a good survey of avail-able lignin oxidation methods. These experiments gave further proof that choice of the sodium chlorite method for controlled degree of li g n i n oxida-i • ' tion was the best procedure available. Chlorinations at low temperature (0° C.) were carried out using, buffer solutions to reduce the hydrolytic action of the. hydrogen chloride formed. This allowed close control of pH through.i the experiment. The procedures of investigations by Giertz (37)* Grangard (4-5), Hatch (8) and Rapson (168) were considered, and followed. However, the resulting chloro-li g n i n was hot-water-soluble which was objectionable for purposes of this study because of losses encountered in'the hot-pressing of boards pre-pared from such chlorinated fi b r e . Results of these experiments are given in Table 3* and results of hot-water extraction under similar conditions as with 3$ monoethanolamine are summarized i n Table 4. Hydrogen peroxide of 30$ volume was tried as a means for oxidizing lignin in s i t u . The 5 g-pulp samples were suspended i n 300 ml.hydrogen per-oxide for a period of two hours at room temperature. No apparent change took place after this extraction. The weight loss obtained was 1.21$. Hot hydrogen peroxide extraction for the same length of time only doubled the weight loss, consequently, this treatment was abandoned. The method of chlorine substitution into the aromatic nucleus of the lignin molecule, described by Schuerch and co-workers (28, 96, Ilk), was used for one experimental run but gave very poor results with Asplund pulp. T-butyl hypochlorite solution was prepared according to the procedure des-cribed, by Schuerch (116) . Besides the strong oxidizing action of t-butyl hypochlorite solution^the resulting chloro-lignin was hot-water-soluble and was easily removed i n the hot-pressing operation,giving a board with badly charred surface. Results of these experiments are summarized in Table 5. Finally, a method described by Purves and co-workers (80) was tri e d . They prepared chlorinated lignin without solubilizing i t by bub-bling nitrogen gas through the chlorite solution containing the wood meal. Chlorine dioxide, which has been found responsible for l i g n i n oxidation and solubilization (6, 8, 38, 50, 6k, 80), was removed as i t was formed. Five grams of air-dry Asplund fibre were suspended in l60, ml.of solution contain- . ing 1.5 g-of sodium chlorite and 0.5 ml. of glacial acetic acid, as used in the treatment prescribed by Wise and Jahn (1^9) • Using carbon dioxide i n -stead of nitrogen gas gave 5*5$ weight loss after one hour extraction at room temperature. " In summary, none of the four treatments tried on this Asplund fibre provided a means of oxidizing l i g n i n without i t s simultaneous solu-b i l i z a t i o n . 3. Alkali extraction of hemicelluloses Mild caustic treatments have been found most useful in removal of 1 hemicelluloses. Thereby, alkaline hydrolysis of lignin and cellulose i s avoided (12). The extraction aimed at a quantitative removal of the hemi-A3-celluloses from the Asplund pulp. Amount of hemicelluloses removed by the treatment was expressed i n terms of weight loss produced by the caustic treatment. The extraction of hemicelluloses is dependent on a number of fac-tors of which solution concentration, temperature, time and type of raw mat-e r i a l are most important. Maximum solu b i l i t y i s reached with 10$ sodium hydroxide solution which removes mainly beta cellulose. (Beta cellulose/ a fraction of the hemicelluloses", i s defined as that part of the carbohydrate portion which goes into solution with 17°5$ sodium hydroxide solution and precipitates upon neutralization of the extraction liquor (lk6)) . Studies on the a l k a l i extraction of hemicelluloses by Booker (10), Prey and co-, ' workers (106), Nelson (97), Reyes (109) and Wilson and co-workers (146.) revealed that ^hemicelluloses are easily hydrolyzed by acids, but solubilized only by a l k a l i solutions. .Analytical investigations of Asplund pulps by Klauditz and Stegmann (7l)>'M$rath (95) and Voss (139) have .shown approxi-mately 8$ pentosans, based on oven-dry weight of the pulp. They extracted the hemicelluloses with 10$ aqueous sodium hydroxide solution at 100° C. for 2 hours. " -Comprehensive reviews by Booker (10), Nelson (97) and Prey and co-workers (106) on removal of hemicelluloses from wood, show that there exists a limited amount of pentosans not extractible under any set of conditions. In the extraction of pentosans, the reaction i s rapid at f i r s t , followed by a negligible,amount of diffusion of pentosans from the rather inacces-sible regions of the c e l l structure. The rate at which pentosans can be removed from wood i s largely dependent on the equilibrium swelling of the polysaccarides, and on particle size. Furthermore, rate i s dependent on -kk-temperature, concentration of extraction solution, wood morphological struc-ture, and amount of lignin present.. 'I in the wood. On this basis, i t is poin-ted out that hemicelluloses can be prepared with greater success from holo-cellulose. (Holocellulose i s defined as the lignin-free carbohydrate frac-tion, i.e., the to t a l polysaccharide fraction of wood (150).) Although i t is possible to extract hemicelluloses directly from wood by a l k a l i treat-ment, but the most suitable conditions must be worked'out for each species, type of wood, or f i b r e . For determining the best extraction conditions a series of a l k a l i treatments was carried out with different reaction conditions. Sodium hydroxide solutions of different concentrations from 0.1 to 10$, reaction temperatures of 30 and 6 0 ° C. and reaction times of 3 0 , 60 and 9 0 minutes were used. In the' experiment 5g.samples of alcohol-benzene extracted Asplund fibre were treated with caustic according to a schedule, and washed free of a l k a l i with water u n t i l the f i l t r a t e gave no red color reaction on treatment with 1 $ phenolphthaleln-ethanol solution. The objective was to devise a pro-cedure which would produce a weight loss of 8 to 9$* . based on the oven-dry weight of the alcohol-benzene extracted f i b r e . An 8 . 6 8 $ weight loss was obtained under the following conditions: 9 0 minute reaction time, 60° C-temperature with7$ sodium hydroxide at 3 $ consistency. Seven per cent weight 'loss was obtained with the same reaction time and temperature by using only 5 $ caustic solutiono A l l other attempts at lower temperatures, shorter reac-tion times and lower solution concentrations gave lower weight loss results. The set of conditions thus determined was considered satisfactory for the removal of a major portion of hemicelluloses from large fibre batches needed for board formation. Thus alcohol-benzene extracted Asplund fibre was extrac ted under the above set of conditions using enough material to give 60 g. of -45-oven-dry,, heraicellulose-free pulp for board preparation purposes. v 4. Cellulose modification by Cobalt 60 irradiation.' Approximately 200 g.air-dry alcevhol-benzene extracted Asplund fibre were sent, i n a sealed polyethylene bag, to Atomic Energy of Canada Ltd., Commercial Products Division, Ottawa, Canada, for Cobalt 60 i r r a d i -ation. Following i n i t i a l correspondence i t was decided that 10^ rads gamma irradiation should result in sufficient random degradation of cellulose chain-length to be detected in standard strength test. The organization provides assistance to those i n t e r e s t e d iri'effects of gamma radiation on different materials. It operates two gamma c e l l s , "Gammacell 100" and "Gamacell 200", capable of delivering- 3 x 110^ roentgens/ hr. each, representing a nominal Cobalt 60 source strength for a maximum dose rate of 680 curies and 1,500 curies, respectively. A dose uniformity of - 5 per cent is feasible with normal sample sizes. The irradiation chambers .are of limited size, being 1.5 i n . i n diameter by 4.5 i n . i n height in case of "Gammacell 100" and 3*5 i n . in diameter by 5*5 i n . in height i n case of 'Gammacell 200". Irradiation time can be automatically set with a timing device incorporated with the c e l l s . The gammacells can be operated safely and e f f i c i e n t l y without extensive training of personnel. The Cobait source is well shielded,- which eliminates the need of elaborate precautions. Load-ing of the irradiation chamber is f a c i l i t a t e d through a drawer which is automatically moved in and out of the radiation f i e l d . ^ 5• Lignin deactivation following impregnation with hot-water-soluble hemlock bark extractives. Earlier observations by Adler (2), Adler and Stockman (k) and Pew (103, 10k) gave one. possible means of li g n i n deactivation i n s i t u . The phenomenon of li g n i n condensation with water-soluble bark extractives i s believed to take place on heat-treatment of. the impregnated material. This same chemical reaction was intentionally initiated on one batch of Asplund fibre i n the hot-pressing operation after impregnating the fibre with hot-water-soluble hemlock bark extractives. Thereby, a reduced;ia^e-r^tioii 1. between l i g n i n and o i l was suspected. The treatment was devised to. give some evidence for the chemical nature of hardboards to o i l interaction re-suiting i n extra strength development obtained on oil-tempering of hard-' boards. A solution of hot-water-soluble hemlock bark extractives of the catechin type was prepared according to Scoi^t (320), and Scott and Gardner (121), from freshly peeled hemlock bark. The bark was reduced to small par-t i c l e s and initially;extracted with cold water at room temperature for 2k hours to remove the cold-water-soluble fraction. After draining the cold water extracts., a hot water extraction was carried out on the same bark at 100° C. for 3 hours. The extract was drained and f i l t e r e d while hot. Thus a dark brown solution was obtained which turned lighter on cooling, giving a good crop of precipitates on cooling.. It was found that the 1,500 ml.' solution contained 2.6$ solids, of which approximately 57$ was tannin (120). An i n i t i a l impregnation of 5g» of Asplund pulp gave 18.51$ weight gain,"show Ing that hot-water-soluble bark extractives can be successfully precipitated onto the fibre on cooling. Similarly, 60 g. oven-dry fibre was impregnated with 1,500 ml. of the bark extract solution at 80° C. for 2 hours. After cooling the slurry i t was washed twice with cold water, formed into a mat -kl-and hot-pressed into a board as described i n later sections. The retained f i l t r a t e gave a 7 * 0 8 6 g.loss of solids corresponding to 1 1 . 8 1 $ weight gain on the fibre of which approximately 6 . 7 $ was due to tannins. C. Analytical Methods 1 . Alcohol-benzene extractives (TAPPI Standard: T 6 m-5k) Replicate 5 g.samples of fibre were extracted under conditions described by TAPPI Standard T 6 m-5k for determining the approximate amount of alcohol-benzene extractives removed. After proper washing and oven dry-ing overnight to constant weight at 1 0 5 ° C the amount of alcohol-benzene solubles was found to be 7«^5$ of the weight of the moisture-free fibre. > 2 . Klason li g n i n (TAPPI Standard: T 13 m-54) For characterization of the raw material (alcohol-benzene extrac-ted Asplund fibre) regarding i t s l i g n i n content, two sets of 7 2 $ sulfuric acid-insoluble Klason lignin determinations were conducted, giving a total of four replicates. The method described i n TAPPI Standards T 13m-5^ has been followed. ,An average of 31 •04$ was calculated from the replicates with a l l replicates deviating not more than t l/lOO of the mean value. This aver-age served as basic l i g n i n content for the calculation of anticipated lignin contents of sodium chlorite'treated pulps, and for reference li g n i n content value for ultraviolet spectrophotometric lignin determinations. It should be mentioned that d i f f i c u l t i e s were encountered i n securing replicates of good agreement. Similar d i f f i c u l t i e s have been reported earlier i n the literature by Klauditz and co-workers ( 7 0 ) , McKnight and Mason ( 8 8 ) , Nowak ( 9 9 ) , Runkel and Wilke ( 1 1 3 ) , and Sohn ( 1 2 6 ) . In some t r i a l s strangely high -HQ-values were obtained. The higher l i g n i n content i s believed to be due to changed chemical constituion of the wood fibre acquired in the defiberizing process. The anticipated lignin contents of sodium chlorite treated fibres are based on 31*04$ Klason lignin and presented i n Table 6 . 3« Ultraviolet spectrophometric li g n i n determination This lignin determination involved a l l sodium cnlorite treated pulps using the alcohol-benzene extracted Asplund pulp with i t s known 31*04$ Klason l i g n i n as standard lignin sample. The method as described by Johnson, Moore and Zank (58) was carefully followed. Samples with approximately 6 mg. li g n i n content (sample sizes were based on anticipated lignin contents) were dissolved in 10 ml. of 25$ acetyl bromide and diluted to 200 ml. volume with reagent grade acetic acid. Absorp-tion was measure at 280 mjj.wave length with a Beckman DU spectrophotometer. Duplicate determinations gave poor reproducibility, possibly due to the same factor(s) influencing sodium chlorite treatments and Klason lignin determina tion. Therefore, values presented in Table 6 should be accepted only as approximate residual l i g n i n contents of chlorited pulps. h.. Micro-Kappa number Micro-Kappa number (Kappa number is the number of m i l l i l i t e r s of 0.1 N.potassiumpermanganate solution consumed per gram of moisture-free pulp under conditions specified in TAPPI Standard. T 236111-60) converted to r e s i -dual l i g n i n per cent was determined on chlorited pulps with less than 15$ anticipated l i g n i n content. Result of the determinations are given i n Table -49-5. One per cent cupriethylenediamine (CED) viscosity Viscosity measurements using 1$ CED solution and the f a l l i n g b a l l method, described in TAPPI Standard:. T 230 sm-50 and discussed by McLean and Walker (89)7 were performed on chlorited pulps of more than 25$ weight loss i n the laboratories of Columbia Cellulose Co. Ltd., Prince Rupert, British Columbia. The viscosity values obtained were converted to. degree of poly-merization (DP) values using the nomographs developed by Dobo and Kobe (22) and are presented in Table 7« D. Thin Board Preparation Boards of 0.5 mm.(500 microns) nominal thickness have been prepared from differently treated fibre to provide material for physical test proce-dures. Hardboards of this thickness have not been reported previously. They include a l l usual commercial hardboard characteristics of. wet-batch process boards. Justification of thin boards in this study, compared "to commercial thicknesses,is outlined as follows: i . By reducing board thickness the problem of obtaining uniform o i l penetration was eliminated. I i i . Thin boards require proportionally smaller amounts of fi b r e . This reduced the amount of fibre that had to be prepared by each of the foregoing treatments, the amounts of chemicals used in the fibre preparations and reduced the size of necessary .containers and . equipment for maintaining uniform fibre treatment conditions. In other words, the problems of material batch handling and treatment uniformity was greatly simplified. i i i . Large size testing machines with, wide range of loading capacity-are necessary for testing macrospecimens. Such equipment is not available within the Faculty of Forestry. To use available test-ing f a c i l i t i e s designed- for testing micro specimens one is restricted to a maximum loading capacity of 50 kg. This required that specimens of relatively small dimensions be prepared. In i -t i a l calculations showed that tempered and untempered boards of 0.5 mm.nominal thickness would provide test specimens 1 of reason-able width,that failed i n tension,without exceeding the 50 kg.load range. Specimens of such dimensions could not be prepared from hardboards of commercial thickness. i v . Specimens for testing could be prepared with a cutting die, giving highly reproducible specimens with uniform width and length, thus reducing the number of necessary measurements on the specimens previous to testing. Thereby, variation and error within test results were greatly reduced. The preparation of machined test specimens having similar dimensional accuracy from board of com-mercial thicknesses i s time consuming and impractical. A board with 0.?0 (g/cm.) nominal specific gravity was desired to represent medium density hardboard. Since late r a l dimension of the forming box were pre-determined (l6-in. x l6-in.) the necessary amount of fibrous material could be calculated. Decision had to be made on uniform density versus changing thick-ness caused by different types of fibres. In this respect specific gravity has been shown to c r i t i c a l l y influence hardboard strength in commercial pro--51-duction of hardboard (M-S, 59, 63, 65, 7^ , 118, I37). Fibre treatments were expected to modify fibre dimensions and composition of boards made of such fibres. Boards made of coarser fibre retain a large amount of resiliency during the pressing operation while fine fibres compact to a high specific gravity (137)' Therefore, after consideration of these factors, i t was decided to produce boards with the same basic weight per unit volume. In other words, the boards were pressed to the same nominal thickness contain-ing equal amounts of fibrous material'. This f a c i l i t a t e d a comparison of the strength values obtained on the basis of specific gravity, and reduced inter-nal variation due to differences i n specific gravity. On the basis of the above dimensions and specific gravity target, the necessary amount of oven-dry f i b r e — unextracted control and extracted when prepared from chemically-modifed fibres — was calculated as follows.: Board area 16 in.x 16 in. = 256 sq<>in.= 1652 cm2. Thickness 0.05cm. Volume: = 82.60 cm3 Specific gravity 6.70 (g/cm3) = 57.82 g. Five per- cent loss i n forming a 2.89 g. Total oven-dry fibre: 60.71 g. Plus 5 g-for analytical tests: • 65.71 g. Fibre moisture content: 7-76$ = 70.80'g. In calculating the amount of raw fibre necessary for a particular fibre treatment (described i n previous paragraphs) additional amounts of fibre were necessary to make up the losses encountered during treatments. -52-Step 1. Additives The prepared batches of fibres' were moistened the day previous to board formation. Since small amounts of rosin soap and phenolic resin were added to the fibre-water slurry at 2.5$ consistency, the fibre required agi-tation i n a plastic container to secure uniform distribution of the additives. One per cent phenolic resin (at 42$ solids content) and 1.5$ "Paracol" rosin soap (at 75$ solids content) were added (based on the oven-dry weight of the fibre) and mixed for 15 minutes. Mixing was followed by addition.of 0.35$ f commercial alum and 0.35$ sulfuric acid, to precipitate the;'resin and Paracol onto the fi b r e s . The slurry was mixed again for 5 minutes and the pH was checked with Beckman HydronPaper "A". A pH value between k and 5 was accepted. Step 2. Mat formation As mentioned above, the boards were processed to replicate wet-batch hardboard manufacture on laboratory scale. The success of the whole experiment was dependent on uniformity of board formation. The forming box, a plant fabricated steel box with manually opera-ted drainage value on the bottom (See Figure 2), had inside measurements of l 6 i n . by 16 i n . and was 30 i n . high. The false bottom-plate was raised' approximately 2 inches above the tap opening. A fine screen (60-mesh) was clipped t i g h t l y onto the false bottom-plate. The box was then-filled to about one-half (marked on one of the inside walls) i t s depth with water. The sized and resin-treated fibre was then poured into the box, and agitated for several minutes. At the end of the swirling a few straight strokes were made between opposite walls with a wooden s t i r r e r , to minimize currents -53-that tended to make the boards heavier i n the centre. The slurry was allowed to settle for the predetermined time and subsequently drained free of water. - An i n i t i a l problem in obtaining good board formation characteris-tics was found to be mainly due to uneven settling and subsequent draining of the stock. Boards were heavier towards the edges and at the outlet side. Also, more than 5$ loss was encountered in the beginning due to improper f i t -ting of the false bottom-plate into the forming box. Drainage time seemed to have a marked effect on board uniformity and on the amount of fibre re-tained after drainage. It was found that the fibre had to be slurried well to disintegrate fibre "clumps" and,thereby eliminate "density spots". Re-circulation of fines was not possible since any distrubance above the mat resulted i n uneven board texture. The slurry, once settled, could not be disturbed without destruction of the mat structure. These problems-were remedied i n the following ways: i . Settling times, were varied according to type of f i b r e . Longest settling times, 20 minutes, were allowed for sodium chlorite treated fibre which had 20$ and higher weight losses after treat-ment. Fibres prepared the same way, but. to lower level of weight losses (15$ and under) behaved differently regarding settling speed and drainage. These included untreated Asplund fibre, sodium hydroxide extracted fibre, and fibres qualitatively modi-fied i n cellulose and lignin constitution. The latter group behaved similarly i n a l l stages of board formation and w i l l be referred to henceforth as "coarse fibre" in contrast to slow set-t l i n g "fine fi b r e " . Settling time for a l l types of coarse fibre -54-was set at 10 minutes. i i . Drainage time (speed of water drainage from the forming box with-out fibre losses i n excess of 5$) w&s increased for fibres prepared by chlorite delignification from 20$ weight loss and up. The time for draining a certain amount of water from the forming box was regulated by a manually operated valve. Drainage time for the finer type of fibre was regulated to 25 min. and for the coarser type of fibre to 15 minutes. i i i . Large weight losses during draining were reduced by f i t t i n g a tight seal around the edges below the false bottom-plate. In addition, -with finer fibre a f i l t e r paper was inserted between the false bottom-plate and the screen, to provide more uniform drainage. . i v . Fewer "density spots" and more uniform drainage were' obtained with the tightly f i t t e d false bottom-plate. v. Distribution of fibre within the forming box was secured by further reducing the slurry consistency to about one-thirtieth of the o r i -ginal consistency i n the plastic container. This provided a better distribution of the fibre within the forming box. It also solved the problem of retaining the fines since the coarser fibres settled out faster than the fines,providing a natural f i l t e r i n g pad for the fines. The mat was removed with the aid of two heavy wire handles welded to the bottom-plate. After removal of the clips from the bottom-plate edges the mat was placed, together with the screen, between two highly polished steel cauls, ready for the pressing operation.. -55-Step 3« Board pressing In the wet and semi-dry hardboard pressing operation a screen is needed, usually underneath the mat, to f a c i l i t a t e the escape of moisture from the inside of the mat. Such boards w i l l have one smooth side and one rough side bearing impressions of the screen, frequently distinguished as top and bottom of SIS boards. Partial dewatering is possible previous to hot-pressing. In cases where high cold-pressing pressures are used l i t t l e water squeeze-out w i l l occur during the hot-pressing operation. Thus, the amount of resin and other solids washed away by the departing hot water and steam w i l l be minimized, resulting i n improved strength. As would be expec-ted, i n the case of a particular fibre type, press-platen temperature, pres-sing time and pressures used are c r i t i c a l i n regard to physical characteris-t i c s of the board, produced under a certain set of these conditions. High temperature, high pressure and the presence, of.moisture is the key to greater compressibility of the mat. Higher densities and more even binder distribution i s obtained under such conditions 'due to resin flow and the plasticizing action of the high-pressure steam (118). Turner and co-workers (137) found that increasing molding tempera-ture substantially increased flexural properties of boards, but that tough-ness values were markedly reduced. Since drying of the boards is dependent upon the amount of heat supplied, time and temperature may be used with great f l e x i b i l i t y . With longer molding times the level of press-platen temperature can be decreased. By using different pressures or mechanical stoppers (spacers) the thickness and density can be controlled. Usually a short breathing cycle i s introduced after a brief high i n i t i a l pressure, to provide for release of trapped steam from inside the board. Optimum condi-tions for obtaining,maximum strength and dimensional s t a b i l i t y must be adjusted to the kind of fibre, type of equipment available, and production rate. ' . Through a considerable number of t r i a l s i t was learned that "coarse fibre" requires shorter settling and drainage times for uniform mat formation, also required somewhat higher pressures i n the hot-pressing operation. The "fine fibre" required lower ^ pressures for attaining a predetermined speci-f i c gravity. For the coarser type of fibre the following pressing cycle was worked put: The wet mat, placed between two cauls with the' screen under-neath the mat,- was positaone^d'in the centre of the'press plates of a '2k-in. by 24-in. hydraulic laboratory hot-press (See Figure 2 ). , A constant plate tem-perature of 175° G. was set by adjusting the steam pressure to^OQ psi. i n the system. After closing the press an i n i t i a l pressure of 225 psi.was applied for 30 seconds and a breathing period of one minute was allowed without pressure. The pressure was then increased to 200 psi.for an addi-tional 1.5 minutes. Finally, the screen was removed and the board was re-T pressed at 400 psi.for 2 minutes. This re-pressing was designed to smooth the rough side and complete the curing to such an extent that practically no strength increase should result on subsequent heat-treatment of the boards. For pressing mats of the finer type fibres, the times i n the press-ing cycle were kept the same as above, but pressure was altered. The i n i t i a l pressure was set at 150 p s i . One minute breathing time was allowed as before . The f i n a l pressure was set at 100 psi., with re-pressing at 400 psi.without screen for 2 minutes. { -57-A l l boards were trimmed to l 4 - i n . by l 4 - i n . with a paper cutter, soon after removal from the hot-press, then weighed on a balance to check for possible large weight losses originating during board formation. Trimmed boards were accepted i f their weight was above kk grams. A weight variation between 42 and 48 g. occurred. Step 4. Post-pressing board treatments The three post-pressing treatments selected were those used most frequently to improve the physical properties of commercial hardboards. The effect of these treatments, as described i n earlier sections, are of known value to the industry, although mechanisms by which these occur are not f u l l y understood. A code number was assigned to every board immediately after c l i p -ping to size, for identification purposes. Subsequently, each board was cut into 7-in. by 7-in. quarters. Post-pressing treatments *ere randomly assigned to these quarters. a. Oilrtempering The objective-was to give a controlled excess of o i l solids to the experimental boards to secure maximum interaction between o i l and wood constituents under investigation. One board segment representing each fibre treatment was placed on a wire rack. The loaded rack was then sub-merged into the tempering o i l for a certain period of time. After dipping the boards were individually blotted on paper towels to remove excess o i l from the surface. In commercial oil-tempering, approximately 6 to 8$ o i l solids are absorbed by the boards. Preliminary investigations on the amount of o i l absorbed by the experimental thin boards showed that the o i l had to be diluted to a 1:7 ratio with benzene, to obtain complete saturation slightly higher than that produced in commercial oil-tempering. The amount of o i l absorbed i s further influenced by type of fibre, specific gravity of boards, and viscosity of the o i l (73) • Temperature was not found c i r i t i c a l with o i l of such dilution. O i l absorption values obtained in the above described manner after a 5-second dip at room temperature, are given i n Table 8 for boards made of Asplund fibre (control), alcohol-benzene extracted, sodium hydroxide extrac-ted, modified cellulose-, l i g n i n deactivated and sodium chlorite delignified fibre boards • -The weight gain or per cent o i l solids absorption is calculated from the oven-dry weights of the untreated boards and from the weight, after o i l soaking and evaporation of the diluent i n a vacuum oven at k0° C. and 25 in.Hg*. vacuum, as per cent of the untreated board weight. b. Heat-treatment .-Heat-treatment was given to a l l of the oil-treated boards and to one set of untreated boards i n forced circulation laboratory oven, manufac-tured by Precision Scientific Co. with a temperature range of 35° to l 8 0 ° C. The.boards were loaded on the same rack used for o i l dipping and placed •inside the oven which was set at 1 5 5 ° C.with the fan on, and kept there for h hours. Since "over drying" has been shown to result i n strength losses (102, 139) a short experiment was set up to investigate the effect of d i f -ferent temperatures on the tensile strength of oil-tempered specimens pre-pared from thin experimental boards. Three levels of temperatures were selected: 130°, 155°, and 170° C. Duration of treatment was k hours. Ten replicates were used for each temperature l e v e l . Results are given i n Table 9. Strength loss due to specimen surface charring occurred at the highest temperature l e v e l . c. Humidification Since humidification i s usually the last post-pressing step i t was included In this experiment. However, since the tensile strength tests were performed on oven-dry specimens, the humidification treatment was not expec-ted to influence the strength of the boards to any appreciable extent. Ogland and Emilsson (102) and Kumar (Jk), found that the strength of hard-boards has been appreciably reduced as moisture content of specimens was increased from 5 to 30$. After the heat-treatment of the two sets of 7-in. by 7-in. boards, (one set oil-tempered),< a third set of boards was selected and placed into the chamber of an Aminco Aire, Model .Wo. 4-5^ 75, humidifying cabinet pre-viously adjusted to give 9*0$ relative humidity at 2k° C. dry-bulb tempera-ture. These conditions were kept for 2k hours. The boards were then re-moved and stored i n polyethylene bags. No moisture content measurements were made on boards prepared by different treatments. - 6 0 -E. Testing Procedures " The influence of certain wood constituents on the level of inter-action- initiated hy heat-treatment of boards dipped i n tempering o i l was examined by measurement of the mechanical property, ultimate tensile strength. Since tensile strength i s a pure mechanical test i t was expected to give direct comparisons of the level of the above" interaction. With com-mercial' hardboards a good relationship .has been found between modulus of rupture (MOR) and tensile strength.' From personal data of Currier ( 1 9 ) , and Wilson (14-5), i t Is evident that there exists a f a i r l y constant relation ship between tensile strength (parallel to the plane of the board) and MOR for a certain set of boards manufactured under similar conditions. Currier ( 1 9 ) found a ratio df 0 . 5 2 for l / 8 - i n . Standard hardboard when MOR was 'divided,by tensile strength. The same' ratio was found to be 0 . 5 7 by Wilson (ll+ 5 ) on l / 8 - i n . oven-dry.samples at 0 . 3 5 $ resin solids. The ratio was somewhat higher for tempered hardboard. The data of Currier ( 1 9 ) gave ah average ratio of GU58 for l / 8 - i n . tempered boards made by the wet-batch process. : Mechanical testing for the main body of the work was preceded by investigation of factors such as influence of specimen width on tensile strength and the necessary number of specimens needed for estimating a ten-s i l e strength difference of 1 0 0 . kg/cm? at 0 . 0 1 $ probability l e v e l . Straight, rectangular specimens of 3 , 5 , 7 , 9 and 1 1 mm.width were included in tests to examine optimum specimen width.. Ten specimens of each width' were randomly cut from a thin board made of Asplund fibre, and tfested,as w i l l be described in later Sections. Results of group aver-ages were, compared on the basis of average specific-gravity-corrected, ultimate t e n s i l e strength and coefficients of variation'(CV$). Highest t e n s i l e strength and lowest co e f f i c i e n t of v a r i a t i o n were obtained, for specimens of.9 mm.width. Results of t h i s test are summarized i n Table 10. Test data obtained on 9 mm.specimens were used for calculating , • the necessary number of specimens. Computations were based on a procedure described by Snedecor (125). I t was found that estimation of a t e n s i l e strength difference of 100 kg/cm2, at 0.01$ p r o b a b i l i t y , required 22 r e p l i -cate samples from each board type. Twenty-four were used since t h i s number was conveniently prepared from a p a r t i c u l a r 7-in. by 7-in. board segment. 1. Specimen preparation Boards prepared from f i b r e s of d i f f e r e n t chemical constitution and subjected to certain post-pressing treatments formed material for speci-men preparation. A l l 7-ih. by 7-in. board segments were f i r s t cut i n halves, giving two sections of 7-in by 3«5-in. nominal s i z e . To secure uniform width of a l l sections they were-held together as a s o l i d block and-parallel smooth cuts were produced on both edges with a c i r c u l a r planer saw. Finished width of such sections vwas i n the order of 3-35 i n . From each of the 7-in. by 3«35-in. boards, 12 rectangular speci-mens of 9 mm. nominal width were punched with a -g--ton Wilson arbor press equipped with an adjustable width cutting d i 2 as shown i n Figure 3« The cutting die head i s depicted i n Figure k. By adjusting spacer width to 3 to 11 mm.the previously described specimens could be prepared with t h i s same di e . Thus, from each 7-in. by 7-in. board, 2k specimens of 9-mm.bj 85-mm. nominal size were prepared. Specimens were numbered from 1 to 2k for i d e n t i f i c a t i o n purposes. - 6 2 -• T e s t i n g was p r e c e d e d b y o v e n d r y i n g s p e c i m e n s o v e r n i g h t . E a c h o v e n - d r y s p e c i m e n was a c c u r a t e l y w e i g h e d t o 0.0005 g - o n a S p o e r h a s e a u t o -m a t i c b a l a n c e . A v e r a g e t h i c k n e s s o f e a c h s p e c i m e n was o b t a i n e d f r o m t h r e e m e a s u r e m e n t s done o n t h e s p e c i m e n s , a t t h e ' t w o e n d s a n d ' i n t h e c e n t r e , b y a . d i a l gage m i c r o c a t o r (ih, 57)* A p h o t o g r a p h o f t h e m i c r o c a t o r i s p r e -s e n t e d i n F i g u r e 5« A t t h e same t i m e , a v e r a g e l e n g t h a n d w i d t h o f t h e s p e c i m e n s w e r e d e t e r m i n e d w i t h c a l i p e r s r e a d i n g t o a n a c c u r a c y o f 0.001 c m . ' F r o m these d a t a ( o v e n - d r y w e i g h t , a v e r a g e t h i c k n e s s , w i d t h , a n d l e n g t h ) , s p e c i f i c g r a v i t y v a l u e s ( b a s e d o n o v e n - d r y v o l u m e ) were c o m p u t e d f o r e a c h s p e c i m e n i n t h e u s u a l w a y . A f t e r t h e m e a s u r e m e n t s were c o m p l e t e d t h e s p e c i m e n s - w e r e s t o r e d i n s e a l e d p o l y e t h y l e n e b a g s . 2. T e n s i l e s t r e n g t h t e s t , c a l c u l a t i o n o f u l t i m a t e e l o n g a t i o n a n d m o d u l u s o f e l a s t i c i t y , ( a ) F o l l o w i n g t h e a b o v e p r e p a r a t i o n s t h e s p e c i m e n s w e r e s u b j e c t e d t o t e n s i l e s t r e n g t h t e s t s . T h e s e w e r e done o n a n I n s t r o n t a b l e - m o d e l t e s t e r . T e s t i n g p r o c e d u r e s on t h e I n s t r o n t e s t e r h a v e b e e n d e s c r i b e d e a r l i e r b y B r o u g h t o n . a n d M a t l i n ( I 3 ) . ? , l f j u a n d K e n n e d y ( 5 2 ) , a n d K e n n e d y a n d I f j u ( 6 2 ) . A p h o t o g r a p h o f t h e m a c h i n e i s g i v e n i n F i g u r e 6 . The s p e c i m e n s w e r e g r i p p e d b e t w e e n t w o j a w s 1.5 i n . a p a r t , w i t h a . c o n s t a n t p r e s s u r e a p p l i e d b y a n a d j u s t a b l e t o r q u e - w r e n c h s e t a t 4-5 i n . - l b . -The l o w e r c r o s s - a r m i s moved a t c o n s t a n t s p e e d b y two worm g e a r s . The worm g e a r s a r e l i n k e d t o a d r i v e m o t o r w i t h h e a d s p e e d a d j u s t e d b y g e a r r a t i o c h a n g e s . ' I n t h i s ; c a s e a g e a r r a t i o was s e l e c t e d t o g i v e a s p e e d o f c r o s s - a r m d e s c e n t o f 0.01 i n . / m i n . The u p p e r j a w i s - c o n n e c t e d t o a n e l e c t r i -c a l s y s t e m a n d s m a l l m o t o r , t h e l o a d - c e l l i s c o n n e c t e d w i t h a n a u t o m a t i c a l l y -63-recording travelling chart on which load deformation curves are registered. The chart speed i s adjustable by interchangeable gears to speeds similar to or multiples of possible cross-arm speeds. In this study a chart speed of 1 in./min. was selected. ->.,. By these arrangements simple load-elongation relationships were' established for each specimen. From the relationships ultimate tensile strength (kg/aa. 2), ultimate elongation *(in./in.) and modulus of e l a s t i c i t y (kg../em.2) were calculated. Ultimate load readings were taken from the chart at the points.of rupture. Ultimate tensile strength was computed as the quotient of ultimate load over the cross-sectional area at point of f a i l u r e . (b) The time necessary for any sample to be strained from a relaxed state to the point of rupture depends upon the inherent strain behaviour of the particular material, but i s also dependent upon the length of specimen under test, and speed of load application. Ultimate elongation, therefore, can be calculated as the quotient of time to failure and gage length over cross-arm speed. It was possible to do this because of rectangular shape of specimens. • (c) Modulus of e l a s t i c i t y or stiffness i s determined as the quotient" of load to unit strain (the load of the extended straight portion of the load-elongation curve within the limit of proportionality at the point of gage length, 1.5 in.) and cross-sectional area at point of f a i l u r e . Since the rate of elongation is dependent on the rate of load application, cross-arm speed must also be taken into consideration when calculating modulus of e l a s t i c i t y . * Notes On the following pages the term ultimate elongation i s used interchangeable for ultimate strain. -61+-3« Adjustment of strength properties Both specific gravity (33, 1+7, 4-9, 63, 65, 73* 118, 137) and mois-ture content (74, 102) influence commercial hardboard strength. With i n -creasing specific gravity boards of higher strength and stiffness are obtained. For comparable results, therefore, the effect of specific gravity must be removed, i . e . , a l l strength values must be adjusted to one common specific gravity. Specific gravity values, calculated from values taken previous to tensile strength test, were f i r s t correlated with ultimate tensile strength to establish a regression coefficient for each board -type encountered i n the study. A l l boards, including the controls, were grouped according to post- : pressing treatments and the average specific gravity was calculated for each group. This average specific gravity served as "basic specific gravity" to which a l l tensile strength values were adjusted for each chemical treatment, with the following formula: Y' = Yi * B (^ - X ±) Where: Y' = adjusted tensile strength value Xi o group mean specific gravity (basic specific gravity) Xi = particular sample specific gravity B • particular board type regression coefficient Yi = Particular sample tensile strength (unadjusted) Graphical solution of the specific gravity adjustment i s given i n Figure 7« A l l regression and specific gravity correction calculations were performed . by the IBM 1620 computer. There were no adjustments made for moisture content since a l l samples were at oven-dry condition at time of testing. -65-RT5SIILTS A. Investigation of Wood Constituents O i l absorption, average specific gravity, ultimate tensile strength, average ultimate elongation and'average modulus of e l a s t i c i t y (MOE) values are given in Table 11 for boards at three treatment levels for each wood con-stituent investigated. Specific gravity, (based on averages obtained from each board treatment) corrected tensile strength, and per cent relative strength increase values due to oil-tempering, are also included in Table 1 1 . These are also presented as a bar diagram (Figure 8 ) . These re-sults served as basis for selecting important wood constituent(s) for fur-ther investigation of oil-tempering effects. Relative strength increase was taken as an indication of degree of interaction between a certain wood con-stituent and tempering o i l . Significant differences of untempered board strengths from different designations (A to F) have been calculated by Tukey's method as described by Snedecor ( 1 2 5 ) . Results of calculations are summarzied in Table 1 2 . B. Effect of Lignin Removal The influence of weight loss on untempered and tempered board properties i s summarized in Table 1 3 , and presented diagrammatically in Figures 9, 1 0 , and 1 1 . In Figure 7 an example i s given of the specific gravity and tensile strength relationship for one tempered and untempered board, together with the graphical method used for specific gravity cor-rections on tensile strength values. Significant difference for untem--66-pered board strength values were calculated by the above method and are presented in Table lk. Curves i n Figure 9 were f i t t e d to the experimental specific gra-vity adjusted tensile strength data across the 0 to 5 and 10 to 3 5 $ weight loss range by a multiple regression polynomial. For best f i t the curve has been divided i n two parts using a separate equation for each section. How-ever, this would by no means suggest that the curves are not continuous functions. For the modulus of e l a s t i c i t y data similar equations were com-puted and results plotted i n Figure-1:1 over the whole weight loss scale. In Figure 12 sample boards of different fibre chemical constitu-tion are presented. --67-DISCUSSION A. Investigation of Wood Constituents The investigation was designed to discover any fibre chemical con-stituent's) involved i n the large improvements i n physical properties and dimensional stability, accompanying tempering of.hardboards. F i r s t , i t must be pointed out that heat-treatment alone gave no improvement to any type of untempered board under investigation. This suggested that a l l physical improvements obtained on heat-treatment of oil-soaked boards were due to oil-tempering alone. The usual improvements accompanying post-pressing heat-treatment were supplanted by the prolonged hot-pressing operation-in these t r i a l s . Thereby, non-confounded observations were made possible with regard to oil-tempering effects. Heat-treatment applied to activate o i l -tempering may be described as a variable i n development of board strength. This i s shown by the significantly higher tensile strength values shown in Table 11. For this reason comparative heat-treatment controls were elimina-ted i n later experiments. Strength of boards made from untreated Asplund fibre served as control for the f i r s t experiment. On this basis, after adjustment of strength values on average specific gravity, of board treatments, one may" distinguish absolute strength increase due to fibre treatment alone. Strength values of tempered boards, on the other hand, are compared direct-l y to corresponding untempered board strength after adjusting both to the corresponding average board treatment specific gravity. Strength increase resulting from tempering has been expressed as a percentage of the value for a corresponding untempered board, and i s called relative strength -68-increase herein. Since the effect of absolute strength increase is removed this way, the method of comparing a l l strength values to the control has not been used. Direct comparison by relative strength increase gives an unbiased estimate of wood constituent influences on development of tempered board strength. An interesting phenomenon was observed on plotting specific gravi-ty-tensile strength curves. The relationship between these factors was significant in a l l cases of untempered boards. However, when corresponding tempered values were plotted, the relationship became non-significant, possi-bly due to reduced range of s p e c i f i c gravity and increased variation of ten-si l e strength. This has been interpreted as being one evidence for limited effects of oil-tempering, and i s a verification of Kumar's (73) findings. The limit i s believed to be related to number of sites available for poly-condensation between wood constituent(s) and the absorbed o i l . Any excess of o i l solids beyond this limit necessarily increases specific gravity with-out further improving strength. The tensile strength and specific gravity relationship for one board type, both tempered and untempered i s shown in Figure 7 . 1 . Untreated Asplund Pulp (Control) The untempered thin boards, prepared from non-extracted Asplund fibre, developed an oven-dry tensile strength of 1299 kg./cm?, which i s higher than values given i n the literature for boards of normal thickness ( 7 1 , 1 0 0 ) . Tempering gave a relative strength increase of 114$, a 90$ i n -crease i n modulus of e l a s t i c i t y , and a slight drop in ultimate elongation. The relative strength increase is of the magnitude obtained i n the commer-c i a l tempering process ( 7 3 , 9 5 ) . O i l solids were calculated at 10 .7$ i n -6 9-this t r i a l . 2. Alcohol-Benzene Extracted Fibre By removing 7 * 5 $ of the raw fibre as alcohol-benzene solubles a slight, but non-significant, absolute strength increase was found. On the other hand, oil-tempering resulted i n 1 1 7 $ relative strength increase. This suggested that alcohol-benzene solubles are not directly involved i n the heat-activated interaction between hardboard and tempering o i l . Their re-moval resulted i n a slight absolute strength increase, possibly due to im-proved fibre bonding. Since most treatments required alcohol-benzene extraction previous to chemical modification, this result suggested that ' observation on other wood constituents were non-confounded. Results of oil-tempering on a l l boards, prepared from differently treated fibre, pre-viously extracted with alcohol-benzene, could be attributed to the parti-cular fibre treatment alone. No real differences were found for ultimate elongation and modulus of e l a s t i c i t y values of boards made of Asplund fibre and alcohol-benzene extracted pulp. Boards of the latter type of pulp, how-ever, tended to absorb slightly more o i l than the control boards when exposed to the same o i l bath. 3. Modified Cellulose Fibre Boards made from gamma-irradiated fibre gave non-significant d i f -ferences for absolute board strength'. The slight Increase of absolute board strength may be attributed to the removal of alcohol-benzene solubles before irradiation. Tempered boards, however, gave only 4 8 $ relative strength i n -crease when compared to untempered board strength following the same fibre treatment. This phenomenon is not due to reduced interaction between wood -70-and tempering o i l , but probably to reduced int r i n s i c fibre strength. The fact that untempered boards did not show any absolute strength loss can be explained by low inter-fibre bonding as the limiting factor, and thereby incomplete u t i l i z a t i o n of in t r i n s i c fibre strength with this treatment. Inter-fibre failures occur during-mechanical testing. Conversely, with tempered boards, individual fibres are broken showing better inter-fibre bonding and improved elastic properties of boards. This also suggests that tempering increases in t r i n s i c fibre bonding rather than strengthening of individual fibres. The decreased i n t r i n s i c fibre strength due to irradia-tion i s reflected by drop in ultimate elongation, although the modulus of , el a s t i c i t y value was i n the same range as found for tempered boards made from Asplund f i b r e . Almost the same o i l absorption.has been observed with boards.made from gamma irradiated fibre as with boards made from alcohol-benzene extracted f i b r e . k. Modified Hemicellulose Fibre Partial removal of hemicelluloses resulted i n l i t t l e absolute increase i n board strength. Relative strength increase, however, has been reduced to 70$, suggesting that hemicelluloses do play some part i n the tempering mechanism. They may be involved i n proportion to their occurance . in wood fi b r e . It i s suspected that the differential relative strength loss of k0$ is not a l l due to removal of hemicelluloses. Qualitative analysis of. treatment liquor showed traces of lig n i n after ac i d i f i c a t i o n . This may have originated from a lignin-xylan complex (107)• As w i l l be discussed later even a small loss of lig n i n can result i n considerable reduction of relative strength increase. Ultimate elongation and modulus of el a s t i c i t y values are -71-in general the same as those obtained for control boards. It is interesting to note that o i l absorption was slightly higher than with control boards. 5 . Delignified Fibre As expected, untempered boards made from delignified fibre gave highly significant absolute strength increase at the 5$ probability l e v e l . This phenomenon has been reported earlier by Klauditz and Stegman (71) and by Ogland (100). The absolute strength of delignified fibre-boards was ll+6$ higher than the control boards. As discussed (page 12), this absolute strength increase is due -to increased bonding capacity of hemicelluloses and to improved paper-making characteristics of delignified fibres. Relative strength increase on oil-tempering was found to be lowest of the whole series On the average, 37$ relative strength increase was obtained on boards made from fibre on which an anticipated weight loss of 32$ (corresponding to 1$ residual lignin) was produced by 7 successive sodium chlorite treatments. This i s not surprising when viewed i n terms of relative amount of aromatic compound available for polycondensation in. the delignified f i b r e . A fur-ther hypothesis of the experiment is based on this factor, while not exclud-ing the possibility of o i l polycondensation with other non-aromatic wood constituents, or self polymerization. Lower relative strength increase following delignification is one fact pointing; toward a chemical nature of tempering mechanism. 6. Deactivated Lignin Fibre Considerable time was spent i n devising a method by which lignin deactivation i n - situ could be achieved without removal of the oxidation products from the f i b r e . . Oxidation of side-chain on the phenyl-propane - - -72- ' l i g n i n building unit seemed to offer a good way to accomplish th i s . Unfor- -tunately, a l l l i g n i n oxidizing methods tried rendered the oxidized lignin hot-water-soluble, thereby confounding observations on deactivated l i g n i n . Another feasible way cf lig n i n deactivation was attempted through ' precondensing li g n i n with some other aromatic compound. An absorbed amount of 12$ hot-water-soluble hemlock bark extracts, representing approximately 7$ tannins by weight (120), i s supposed to condense-with li g n i n on high temperature treatment, such as hot-pressing of the mat. The fibre thus' treated showed no change.in absolute board strength, but the effect- of o i l -tempering was reduced to about one-half of control values. This may be counted as additional -evidence for the chemical nature of the interaction and also points toward lignin as the most important wood, constituent i n - . volved in the" heat-activated interaction with the tempering o i l . . B. Effect of Delignification Further investigation of hardboard-oil-tempering was centered on li g n i n as the most important wood constituent. Results of preliminary i n -vestigation had indicated that l i g n i n i s the most influential wood compon-ent involved i n the interaction and that the mechanism may be due to con- • densation of l i g n i n and tempering o i l . Only one per cent weight loss accompanying li g n i n oxidation results in more than 50$ drop of relative board strength; This one per cent weight loss was found to correspond to 28.72$ residual lignin as estimated by the ultraviolet spectrophotometry method (58). Successive losses of 3 to 5$ l i g n i n gave.lowest relative strength increase on oil-tempering,i .e ., 20 to 25$« It is ''..thoughtthat this residual 20 to 25$ relative strength increase - 7 3 -may result from some other factor than l i g n i n . This portion of relative strength development may be attributed to a second mechanism occuring dur-ing the oil-tempering process. The tremendous drop of relative strength with r e l a t i v e l y small amount of li g n i n loss is best evidence for the •chemical nature of the mechanism, and suggests a limited number of reac-tive sites available for the tempering process. The. mild lignin'oxidizing treatment seems to destroy preferentially the sites, most important from the standpoint of additional strength development on oil-tempering. It i s therefore possible that reactive alcoholic hydroxyl groups are oxidized to non-reactive aldehyde, or even carboxylic acid groups. An investigation" undertaken in further study consisted of making a series of boards from fibre containing, controlled amounts of l i g n i n . Non-significant differences we're obtained for absolute strength values of boards made of- delignified fibre of weight losses 10$ and under (corresponding to 17.16$ residual lignin) when compared to tensile strength of control board. A l l strength values from 15$ weight loss and above gave significant d i f f e r -ences at the 5$ probability l e v e l . (See Table l h ) . On inspection of Figure 9 i t becomes evident that possibly two mechanisms occur i n oil-tempering of hardboards. It is also evident that the maj-or mechanism relates to lignin quality rather than quantity, at least within 1 to 5$ l i g n i n removal. This portion of the curve is desig-nated by "A". Abrupt loss i n relative strength accompanying oil-tempering is a most valuable piece of evidence for the correctness of the hypothesis. It not only shows that li g n i n is^the most important wood constituent involved' i n the interaction, but i t also points clearly toward a chemical mechanism. The mechanism proved to.be most effective on boards prepared from either untreated or alcohol-benezene extracted Asplund fib r e . Although it. must be accepted that some chemical change had taken place during the defiberizing process, these changes must have quantitatively involved other wood consti-tuents than lignin, since commercial pressing of Asplund pulp gives approxi-mately 85 to 90$ y i e l d . This yield loss could be realized in proportionally higher l i g n i n content of the resulting f i b r e . An average Kias.on l i g n i n value of 31*04$ was obtained oh two individual attempts with two replicates each. This corresponds to a 9*8$ yield loss or 90.2$ yield, calculated on the basis of 28$ average lignin content reported for Douglas f i r (1^9). The higher l i g n i n content is possibly due to hot-water-solubles, and loss of carbohydrates. The poss i b i l i t y of hemicellulose degradation and condensa-tion to acid-insoluble lignin-like furfural-base resins cannot be excluded and has been reported i n the literature (107, 112). Relating ultimate elongation to percent weight loss showed similar relationships, giving generally lower ultimate elongation values for tem-pered boards than corresponding untempered boards. The curve for relative elongation decrease in Figure 10 shows similarity to those obtained for other strength properties. Modulus of e l a s t i c i t y , as shown i n Figure 11, follows the same general pattern as found for tensile strength, although the minimum is not reached at 5$ weight loss. Here, too, the interaction of tempering-induced relative increase of modulus of e l a s t i c i t y , was highest for the boards made from untreated pulp. Relative modulus of e l a s t i c i t y increase followed the same curvilinear pattern. - 7 5 -Attempts to investigate l i g n i n deactivation along the zero weight loss scale were not successful. It was. belieyed> i.-t^€' :~'Dy 'Hnding a suitable method for controlled li g n i n oxidation without solubilization of oxidation pro-ducts, one could obtain valuable information leading to more complete under-standing of the l i g n i n - o i l interaction/ From the second part of the curve i n Figure 9> designated as "B" i t i s evident that no major changes take place regarding the mechanism of oil-tempering as more and more lignin i s removed, up to the point where most of the l i g n i n has been removed. During this period normal paper bonding effects occur and bejsome of more importance as li g n i n i s progressively re-moved. Ultraviolet spectrophotometric li g n i n determinations on samples with an anticipated weight loss of 2 5 $ gave 6 . 2 8 $ residual l i g n i n . Similarity of mechanisms for absolute and relative strength i n -creases i s quite striking as the lignin content is successively reduced. Strength increase of boards of delignified fibre has been reported earlier by Klauditz and Stegmann(7l), and Ojland (100). Generally stronger.boards are produced on removing l i g n i n from the fibre because of better bonding capacity of hemicelluloses, and improved paper-making characteristics of the fibres. This latter property of delignified fibres has been experienced in thin board formation. .It may be seen from Table 9 that specific gravity values rise with decreasing amounts of residual li g n i n i n the f i b r e . Through better fibre to fibre bonding, the i n t r i n s i c fibre strength can be more econ-omically u t i l i z e d in board strength development, resulting i n increased ten-s i l e strength, ultimate elongation and modulus of e l a s t i c i t y . Oil-tempering of corresponding boards follows a similar pattern, giving on the average 2 0 $ relative strength increase. This small portion of -76-relative strength increase, as compared to the major effect of tempering although not investigated i n any detail, may he due to the interaction of other wood constituents, possibly to hemicelluloses, or to physical fibre to fibre bonding, similar to that produced on addition of small amounts of synthetic resins, or to an interaction of o i l with incompletely polymerized phenol-formaldehyde resin incorporated i n the furnish in the amount of 1$. This latter possibility must also be considered since Seifert (123) found that approximately 10$ of the phenolic resin incorporated i n hardboards is present i n an incompletely polymerized state. This portion of the resin may be extracted under certain conditions. Ultimate elongation and modulus of e l a s t i c i t y values show trends • similar to those had with ultimate 'tensile strength. . However, a slight de-crease towards the end of the scale is s t i l l evidenced with both relative stiffness and relative elongation. This suggested that other rate deter-mining factors are involved to a greater extent than observed with ultimate tensile strength. One of the factors may be moisture pick up during test- : ing since a l l samples were tested i n an oven-dry condition, but not protec-ted from atmospheric reconditioning during the one or two minutes required for tests. Higher hygroscopicity of hemicelluloses,present i n relatively greater proportions toward the higher weight loss portion of the curve, may increase moisture regain of these samples to an extent that the effect could be observed in strength data. Thereby, modulus of e l a s t i c i t y and ultimate elongation could be more sensitive, toward moisture changes than ultimate tensile strength. The third portion of the weight loss-tensile strength curve, desig-nated as "C" i n Figure 9, is possibly not distinguished because of different -77-behaviour on oil-tempering, but because of some other competing mechanism-. This may be the range within which increased portions of hemicelluloses are also removed i n the purification process as evidenced from the increasing amounts -of negative differences between calculated and estimated l i g n i n contents, together with serious degradations of the cellulose portion of the f i b r e . The latter i s evidenced by 1$ cupriethylenediamine viscosity measurements. Serious viscosity drop was found on samples from 25 to 35$ weight loss. (Viscosity measurements on lower weight loss samples could not be obtained by this method because of high l i g n i n content). At 35$ weight loss the extrapolated degree of polymerization (DP) was found to be only 79$ of that measured for the 25$ weight loss sample. Such a drop of viscosity would be expected to result i n lowered intrinsic fibre strength (70) as-evidenced by flattening of both untempered and tempered board strength curves. Ultimate elongation, modulus of el a s t i c i t y , and weight loss rela-tionships follow, the same pattern. Besides the above discussed moisture i n fluences, loss of hemicelluloses and drop of degree of polymerization must also be considered for finding explanations for these phenomenons. -78-CONCLUSIOHS From this study of wood constituents involved i n the heat-activa-ted oil-tempering of hardboards which results i n extra strength.and dimen-sional s t a b i l i t y , the following conclusions can be drawn: 1. Oil-tempering i s most effective (105$ ultimate tensile strength increase on boards prepared from Asplund fibre not modified by chemical treatment 2. Removal of alcohol-benzene solubles has no influence on oil-tempering. 3 • Gama irradiation at 10T rads gave no effect on untempered board strength but reduced relative tensile strength gain on oil-tempering to 48$ as compared, to 114$ obtained with boards from Asplund f i b r e . This drop Of relative strength i s believed to be due to reduced intrinsic fibre strength rather than to reduced level of the o i l to wood interaction. k. Quantitative removal of hemicelluloses resulted i n a 7 0 $ relative strength increase, indicating that hemicelluloses are also involved to •some extent i n the interaction. D i f f i c u l t i e s i n specific and complete removal of hemicelluloses from the wood fibre make a non-confounded investigation of this effect impossible. .5. It was found that l i g n i n i s a major wood constituent responsible for the strength increase '; resulting from oil rtempering of hardboards.. The mechanism is proposed as involving heat^activated chemical bonding between l i g n i n and tempering o i l , forming a stable chemical complex with in and between fibres. Evidence for chemical bonding i s as follows: -79-i . Only a limited amount of o i l is involved in the interaction as evidenced by non-significant specific gravity-tensile strength relationships for all;oil-tempered hardboards containing an excess (more than 1 0 $ ) of o i l solids. The minimum amount of o i l required has not been investigated, but by commercial practice i t i s thought to be i n the order of 6 to 8 $ . ; i i . Removal of only 1 $ l i g n i n by an oxidation method resulted in a 5 0 $ drop in the.relative strength increase obtained by tempering, suggesting that l i g n i n quality.is more important than quantity, i i i . Removal of 3 to 5$ l i g n i n provides a low.point i n relative strength increase. The data suggest, .that at this point 8 0 $ of reactive" sites are inhibited. i v . Impregnation of fibre with hot-water-soluble hemlock bark tannins before pressing provide a 5 0 $ drop in relative' strength increase on oil-tempering. Thereby, i t is thought that a second method has , been used to inactivate bonding sites . " ' ' v. The "CTIA Polymer" is known to be unstable and susceptible to re-arrangement on prolonged heating when used as foundry core binder, but is stable when combined with .unsaturated compounds such as l i n -seed o i l , or maleic anhydride. Possibly l i g n i n also acts as an o i l s t a bilizer. 6 . Evidence i s given for a second, minor factor, in oil-tempering of hard-boards. This has not been'investigated i n d e t a i l . Lignin is not thought to be responsible for this effect since progressive removal of li g n i n does not influence this second mechanism. : • • . 7 . Past the 5$ weight loss point on the curve, the strength of untempered boards increases proportionally to the amount of li g n i n removed by oxi-dation technique. Above the 25$ weight loss point, where probably i n -creasing amounts of hemicelluloses are removed with li g n i n and consider-able reduction of cellulose chain-length i s evident from viscosity measurements, the strength increase is possibly governed by these fac-tors. However, this does not seem to influence the second mechanism of oil-tempering i n this region to any greater, or measurable, extent. 8 . The exact site of chemical bonding has not been described. The fact that interaction between the board and tempering o i l has been significantly v. reduced by li g n i n oxidation and tannin, condensation treatments, points. toward a limited number of very reactive groups involved i n a mechanism. Since alcoholic hydroxyl groups on the side-chain are far-more reactive than phenolic hydroxyls ( 7 2 , 8 l ) i t i s l i k e l y that polycondensation of li g n i n and tempering o i l takes place at an unsaturated double bond; or at some alcoholic hydroxyl- group on the straight chain portion of the phenylpropane l i g n i n building unit. Interaction with phenolic hydroxyls is less l i k e l y . 9 - Ultimate elongation and modulus of e l a s t i c i t y follow the same general pattern as found for tensile strength. It should be noted that u l t i -mate elongation values were lower for a l l oil-tempered boards, but i n -creased together with modulus of e l a s t i c i t y as residual l i g n i n content of samples was reduced. -81-L I T E R A T U R E C I T E D 1. A d a m s , G . A . a n d C T . B i s h o p . 1955• P o l y s a c c h a r i d e s a s s o c i a t e d w i t h a l p h a c e l l u l o s e . T a p p i . 38 ( l l ) ; 672-676 2. A d l e r , E . 1951 • S u l p h i t e p u l p i n g p r o p e r t i e s o f s p r u c e w o o d f r o m u n -p e e l e d , f l o a t e d l o g s . S v e n s k P a p p e r s t i d . 5k (13)2 445-450. 3» _ _ _ S . H e r n e s t a m a n d I . W a l l d e n . 1958. E s t i m a t i o n o f p h e n o l i c h y d r o x y l g r o u p s i n l i g n i n . S v e n s k P a p p e r s t i d , 6 l (l8B); 641-647. ^ ° _ _ _ _ _ _ a n t ^ ^ " S t o c k m a n . 1951« S u l p h i t e p u l p i n g p r o p e r t i e s o f s p r u c e w o o d f r o m u n p e e l e d , f l o a t e d l o g s . S v e n s k P a p p e r s t i d . 54 ( l 4 ) ; 477-482. 5. A r t h u r , J . C . J r . 1958. P a r t I I . P r o p o s e d m e c h a n i s m o f t h e e f f e c t s o f h i g h e n e r g y gamma r a d i a t i o n o n s o m e m o l e c u l a r p r o p e r t i e s o r p u r i -f i e d c o t t o n . T e x t i l R e s e a r c h J . 28 (3); 204-206. 6. B a r t o n , J . S . .1950. T h e r e a c t i o n p r o d u c t s o f l i g n i n a n d s o d i u m c h l o r -i t e i n a c i d s o l u t i o n ^ T a p p i 33 (10): 496-502. 7. D e B a u n , R . M . a n d F . F . N o r d . 1951» A q u a l i t a t i v e p h l o r o g l u c i n o l -h y d r o c h l o r i c a c i d t e s t i n t h e e v a l u a t i o n o f l i g n i n p r e p a r a t i o n s ; f T a p p i _4 (2)s -'71-73.' 8. B e e m a n , L . A . e t . a l . 1953 • T h e b l e a c h i n g o f p u l p . T A P P I M o n o g r a p h S e r i e s N o . 10. 9. B l o u i n , F . A . a n d J . C . A r t h u r J r . 1958. T h e e f f e c t o f gamma r a d i a t i o n o n c o t t o n . P a r t 1, T e x t i l e R e s . J . 28 (3)2 198-204. ' G 10. B o o k e r , E . 1958. E x t r a c t i o n o f h e m i c e l l u l o s e s f r o m w o o d y t i s s u e s . S t a t e U n i v e r s i t y o f New Y o r k , C o l l e g e o f F o r e s t r y , S y r a c u s e , M . S c . T h e s i s . 11. B o e h m , R . M . 1940. P l a s t i c s a n d c h e m i c a l s f r o m w o o d . P a p e r T r a d e J . 110; T 249-251. 12. B r a u n s , F . E . a n d D . A . B r a u n s . I960. T h e c h e m i s t r y o f l i g n i n . S u p p l e m e n t V o l u m e f o r 1949-1958. Academic P r e s s , New Y o r k . 13. B r o u g h t o n , G . a n d N . A . M a t l i n . 1951° T h e m e c h a n i c a l b e h a v i o u s o f p a p e r . P a r t I . T a p p i _4 ( l l ) ; 493-498... 1 14. B y s t e d t , J . a n d A . M . A n d e r s o n . 1957» M e a s u r i n g t h i c k n e s s o f s h e e t m a t e r i a l s b y a p r e c i s i o n d i a l i n d i c a t o r . S v e n s k P a p p e r s t i d . 60 (13): 492-496. 15 • C a b o t t , I . M . a n d C . B . P u r v e s . 1956. T h e e f f e c t o f t e m p e r a t u r e a n d a c i d i t y i n p u l p i n g o f s p r u c e p e r i o d a t e l i g n i n b y t h e s u l p h i t e p r o c e s s . P u l p P a p e r M a g . C a n . 57 (4): 151-158. - 8 2 -1 6 . Charlesby, A. 1955• The degradation of cellulose by ionizing radia-tion. J . of Polymer S c i . 15: 263-270. 17 . Clermont, L.P. and F. Bender. I96I. Effect of solutions of nitrogen dioxide, sulphur dioxide, hydrogen sulphide, and chlorine i n d i -methylformamide and dimethylsulphoxide on wood. Rept. from Pulp and Paper Mag. of Canada, January, pp. 8 . 1 8 . Cottrall, L.G. 1952. The influence of hemicelluloses i n wood pulp: fibres on their papermaking properties. Tappi 35 ( 9 ) ' '4-71-480. 1 9 . Currier, R.A. I962. Personal communication about tensile strength, modulus of rupture relationship for commercial hardboard. ' Oregon State University, Corvallis, Oregon, U.S.A. 2 0 . 1957« Effect of cyclic humidification on dimensional sta-b i l i t y of commercial hardboards. Fores Prod. J . 7 (3)t 9 5 - 1 0 0 . 21. Demisch, R.R. 1962. Personal communication about properties of "CTLA Polymer". Imperial O i l Ltd., Toronto, Canada. 2 2 . Dobo, E.J. and K.A. Kobe. 1957 • Cellulose viscosity conversions.; Tappi 40 ( 7 ) : 584-587-2 3 . Dolmetsch, H. 1954. Uber den Aufbau der Cellulose i n den Zellwanden den pflanzliche'n Fasercellen. Holz Roh- Werkstoff 12. ( l l ) : 419-426. 24. Dominion Bureau of Statistics.. I 9 6 I . Production and shipments of hardboard. Table 1 . Dominion Bureau of Statistics 9 ( 1 2 ) : 112. 25« Dutton, G.G.S. and F. Smith. 1956. The constituion of hemicellulose of western hemlock (Tsuga heterophylla) I. Determination of com-position and identification of 2 - 0 - (4-0Methyl-D-glucopyranosyduronic acid)-D-xylose. J . Am. Chem. Soc. 7§ (June): 2505-2507. 2 6 . ENJAY. 1962. "CTLA Polymer". ENJAY Company Inc., New York, Technical B u l l . No. l 8 . pp. l 6 . 2 7 . Enkvist, T. and E. Hagglund. 1950. Studien "Tiber den Zusammenhang . zwischen Sulfidierung, Methlylierung und Sulfitierung von Lignin. Svensk Paperstid. 53 ( 4 ) : 8 5 - 9 3 . 2 8 . Erby, W.A. and C. Schuerch. I 9 6 2 . Some observations on li g n i n acces-s i b i l i t y i n wood made during a two-stage degradation. Tappi 45 ( 5 ) : ' 409-413 . 2 9 . Erdtman, G.A. 1954. Spectrographic contributions to l i g n i n chemistry V. Phenolic groups i n spruce l i g n i n . Svensk Papperstid. 57 ( 2 0 ) : 745-760. -83-30. Fickler, H.H. 1958. Beitrag zur Quellungsvergutung von Holzfaser-platten. Industrieversuche mit Tallwachs. Svensk Papperstid. 61 (k)t 99-102. 31. Fineman, M.N. 1952. The role of the hemicelluloses i n the mechanism of wet-strength. Tappi 35 (7) : 320-327. 32. Fisher, H.D. 1951 •.- Effect of urea and related compounds on the mechani-.. cal properties of paper. Tappi 34 (6): 376-288. 33» Food and Agricultural Organization of the United Nations. 1957. Fibre-board and particle board. F.A.O., and Economic Commission for Europe, Geneva. 34. Freudenberg, K., W. Siebert, W. Heimberger and R. Kraft. 1950. Ultra-violet • spectrums of li g n i n and l i g n i n like materials. Berliner Deutsche Chemical Gesellschaft §3; 533-538. 35. Gardner, J.A.F. and G.M. Barton, i 9 6 0 . The distribution of dihydrdquer-cetin i n Douglas f i r and western larch. Forest Prod.J. 10 ( 3 ) : 171-173. 36. Gierer. J., B.O. Lindgren, and H . Mikawa. 1954. On structural ele-ments i n l i g n i n . Svensk Papperstid. 57 (17): 633-637. 37. Giertz, H.W. 1951« Development in bleaching process. Tappi 34 (5) : 209-215. 38. • 1951» Chlorine dioxide bleaching. Svensk Papperstid. 5^ 715): 469-V760 39. Gillham, J.K. and T.E. Timell. 1958. The polysaccharides of white birch (Betula papirifera) Part 7» Carbohydrates associates with the alpha cellulose component. Svensk, Paperstid. 6 l (lj)t ^kO-^hk. 4 0 . Glaudemans, C.P.J., E. Pas'sagila and E.A. Wielicki. 1962. Stabilization of cellulose subject to high energy radiation. Tappi 45 (7) : 5>+2-547. ~ • ______ a n d T , E * Timell. 1958. The polysaccharides of white birch ~ ° (Betula papyrifera) Part. 6 . Molecular properties of hemicellulose. Svensk Papperstid. 6 l (l)s 1-9. 4 2 . Goldschmid, 0 . 1955« Aqueous hydrolysis of l i g n i n . I. Paper chromato-graphic separation of monomeric lig n i n degradation products. Tappi 38 (12): 728-732. 43. Goring , D.A.I. and.'T.E. Timell. . I962. Molecular weight of native cellulose. Tappi 45 ( 6 ) : 454-459. -44. Goring, D.A.I, and T.E. Timell. i 9 6 0 . Molecular properties of a native wood cellulose. Svensk Papperstid. 63 ( l6)s 1 524-527. -84-45. Grangard, D.H. 195^* Bleaching I. The chlorination of pulp. Tappi 39(5): 270-276. 46. Gupta, P,R., A. Rezanovich and D.A.I. Goring. 1962. The adhesive properties of l i g n i n . Pulp Paper Mag. Can. 65 ( l ) : T21-T30. 47. Hamar, K. i960. A kemeny farostlemez mino'se'get befolyasold egyes technologiai tenyezokrb*l. Faipar 10 (8): 253-255. 48. Harris, E.E. 1955• Highlights In the chemistry of l i g n i n . Forest Prod. J . 5 ( l ) t 26-31. 49. Hofstrand, A.D. 1958. Relationship of specific gravity to moduli of rupture and e l a s t i c i t y i n commercial hardboard. Forest Prod. J . 8.(6): 177-180. 50. Huang, R.Y.-M. 1958. Oxidative delignification of wood and some organic reactions of chlorine dioxide. M.A. Sc. Thesis, Toronto. 51. Hunt, H.R. (Assignor to Masonite Corporation). I 9 6 1 . Impregnating l i g -nocellulose hardboard with hydrocarbon drying o i l s . U.S. Patent No. 2,988,462. 52. I f j u , G. and R.W. Kennedy. .1962. Some variables affecting microten-s i l e strength of Douglas F i r . Fores Prod. J . 12 (4): 213-217. 53« • 1963* Personal communication. 54. Jayme, G. 1945. 1st Holz ein einheitlicher Rohstoff? Holzforsch. 3 (2): 8O-89. 55. • 1942. Uber die Herstellung von Holocellulose und Cellstoffe mittels Natriumchlorlte.. Cellulose Chem. 20: 43-49. 56. , H. Knolle and G. Rapp. 1958. Entwicklung und endguTtige Fassung der Ligninbestimmungsmethode nach Jayme and Knolle. Papier12 ( l 7 / l 8 ) : 464-467. 57. Johansson, C E . 1958. CEJ Mikrokators No. 509 (E), and 510 (E) . Aktebolaget C E . Johansson, Eskilstuna, Sweden, pp. 7101-7117* 58. Johnson, D.B., W.E. Moore and L.C. Zank. 1961. The spectrophotometric determination of l i g n i n i n small wood samples. Tappi 44 ( l l ) : 793-798. 59* Kearton, CM. 1954. The effect of operating variables on hardboard values. Forest Prod. J . 4 (3): 146-147. 60. Keeney, F.C 1952. Physical properties of slash pine semichemical kraft pulp and i t s f u l l y chlorinated component. Tappi 3_5 (12): 555-563. -85-61 . Kennedy, R.J. 1962. Some observations on the mechanism of resin-cellu-lose interactions. Tappi _5 ( 9 ) : 738-741. 62. Kennedy, R.W. and G. I f j u . I 9 6 2 . Applications of microtensile testing to thin wood sections. Tappi _ ( 9 ) : 725-733. 63. Kloot, N.H. 1954. A. Survey of mechanical properties of some fibre building boards. Asutral. J . Appl. S c i . j> ( l ) : 18-35. 64. Koeppen, A.V. and W.E. Cohen. 1955. A study of "chlorite" and "chlorine" holocelluloses prepared from Eucalyptus regnans. Holzforsch. 7 (4): 120-110. 65. Kollmann, F. 1950. Qualitatsbestimmende Factoren bei der Herstellung von Holzfaser und Holzspanplatten. Svensk Papperstid. 53 (19)J 591-604. 66. Klauditz, W. 1957* Zur biologisch-mechanischen Wirkung der Acetylgroup-pen im Festigungsgewebe der Laubholzer. Holzforsch. 11 (2); 47-44. ^7* . 1957« Zur biologish-mechanischen Wirkung der Cellulose und Hemicellulose im Festigungsgewebe der Laubholzer. Holzforsch. 11 (4): 110-116. 68. . 1951. Beitrage zur chemischen und physicalischen Technolo-gie des Holzes und Holzfaserstoffe. Holzforsch. 5 ( 3 ) : 58-67. 69. 1948. Vergleischende Papiertechnische . Untersuchungen an Nadelholz und Laubholz-Zellstoffen. Holz Roh- Werkstoff 6 (4): 127-135. 70. , . 0. Marshall, and W. Ginzel. 194 7. Ermittlung der Zugfestig-keit von Zellstoff-Fasern. Holzforsch. 1 ( 3 ) : 99-103. 71. « and G. Stegmann, 1951* Uber grundlegenden chemischen und physicalischen Vorgange bei der Warmevergutung von Holzfaserplatten. Holsforsch. 5 ( l ) : 68-74. 1 : 72. Kratzl, K., K. Buchtela, J . Gratzl, J . Zauner and 0. Ettingshausen. I 9 6 2 . Lignin and plastics. The reactions of li g n i n with phenol and isocyanates. Tappi 45 (2): I I 3 - I I 9 . 73« Kumar, V.B. 1961. Neure Untersuchungen an tJlgeharteten Faserplatten. Holz Roh- Werkstoff 19 (1): 15-20. 74. I958. Non-destructive test for quality evaluation of fibre boards. Svensk Papperstid. 6l (15): 461-470. 75« Kurth, E.F. 1948. Chemical analysis of western woods. Paper Trade J . 127 (2): 82-84. -86-7 6 . Kurth, E.F. and F.L. Chan. 1 9 5 1 . .Dihydroquercetin as an antitoxidant. Am. O i l Chemists Soc. 28 (10): 4 3 3 - 4 3 6 . 77• Lawton, E.J., W.D. Bellamy, R.E. Hungate, M.P. Bryant and E. H a l l . 1 9 5 1 . Some effects of high volocity electrons on wood. Science 1 1 3 : 3 8 0 - 3 8 2 . 7 8 . - • , , , . 1 9 5 1 . Studies on the changes produced in wood exposed to high velocity electrons. Tappi _ (12): 113A-116A. 7 9 . Lee, C L . I 9 6 I . Crystallinity of wood cellulose fibres. Forest Prod. J. 11 (2): 108-112. • 8 0 . Levitin, N., K.S. Thompson and C.B. Purves. 1 9 5 5 . The oxidation of spruce periodate li g n i n with sodium chlorite and chlorine dioxide 1" Pulp Paper Mag. Can. 56 ( 5 ) : 1 1 7 - 1 3 0 . 81. Lindgren, B.O. 1952. The sulphonatable groups of l i g n i n . Svensk Papperstid. 55 ( 3 )s 7 8 - 7 9 . 8 2 . • and U. Saeden. 1 9 5 1 . Sulphonation and dissolution of the l i g -nins of monocotyledons and dicotyledons with sulphite solutions at pH 4 to 7 . Svensk Papperstid. _ (23): 7 9 5 - 7 9 8 . 8 3 - Lofgren, G. 1958. Avsattningsforhallandena for fibrebard. Svensk Papperstid. 6 l (10): 327-334. Qk. Lowgren, U. 1948. Holzfaserung i n Asplund Defibrator. Paper Trade J. 127 (12): i+lJ+3. 85. McKenzie, A.W. and H.G. Higgins. i960. Heterogeneous acid hydrolysis of cellulose i n the presence of pentosans. Svensk Papperstid. 63 (16): 53O-534. 86. , and . 1958. The structure and properties of paper. Part.II. Svensk Papperstid. 6l ( 2 0 ) : 893-901. 87. , and 1957. The reactivity of cellulose. Holzfor-sch. 10 (6): 179-184. 88. McKnight, T.S. and S.G. Mason. 1958. The sorption of vapors by l i g n i n : Svensk Papperstid. 6 l (12): 3 8 3 - 3 8 8 . 89. McLean, J.D. and'F. Waler. 1950. Viscosity i n cupriethylenediamine. Tappi 33 (2): 5 7 - 5 9 -9 0 . Mark, H.F. 1951. Why and how can two fibres adhere to each other?" Paper Trade J. 132 ( l ) : 3 1 = 3 9 . 9 1 . Martin, A.F. 1951. Towards a reference viscosity method for cellulose. Tappi 34 ( 8 ) : 3 6 3 - 3 6 6 . -87-92. Mater, J . 1957' Chemical effects of high-energy irradiation of wood. Forest Prod. J . 7 (6 ) : 208-209. 93. Merewether, J.W.T. I962. The precipitation of l i g n i n from Eucalyptus kraft black liquors. Tappi 45 (2); I59-I63. 9^ * . 1957« A lignin-carbohydrate complex in wood. Holzforsch. 11 (3): 65-80. 95• M8rath, E. 1949. Die Holzfaserplatte. Holzforsch. 4 ( l ) : 14-25. 96. Nakano, J . and C. Schuerch. i960. The reaction of spruce li g n i n with tert.-butyl hypochloritej a study of the accessibility of l i g n i n i n wood. J . American Chem. Soc. 82; 1677-1684. 97• Nelson, R. 1957 • Factors influencing the removal of pentosans from wood by a l k a l i : Evidence of the lignin-carbohydrate bond. PhD. Thesis. State University of New York. 98. Nord, F.F. and W.J. Schubert. 1951- Enzymatic studies on cellulose li g n i n and the mechanism of l i g n i f i c a t i o n . Holzforsch. 5 ( l ) : 1-9* 99* Nowak, A. 1954. Die Verwandung von Lignocellulose bei Warmebehandlung unter pH Kontrolle mit besonder Beriicksichtigung der Herstellung von Fraserplatten. Holz Roh- Werkstoff 12 ( l l ) : 427-434. 100. *0*gland, N.J. 1955* Hemicellulosans och ligninets r o l l vid framstall-ning av harda trafiberskivor. Svensk Paperstid. 58. (2): 50-51. 101. . 19.51. The sizing of hardboards and heat-treatment after pressing. Papper och Tra. 33: 8 - I 3 . 102. • and E.B. Emilsson. 1951* Einwirkung der Warmebehandlung auf die Biegefestigkeit und Elasticitate von harten Faserplatten. Svensk Papperstid. _4 (17): 597-602. 103. Pew, J.C. 1949. Douglas f i r heartwood flavanone. Its properties and influence on sulphite pulping. Tappi 32 ( l ) : 39-41. 104. . 1948. A falvanone from Douglas f i r heartwood. J . American Chem. Soc. 70: 3031-3034. 105. • and P. Weyna. 1962. Fine grinding enzyme digestion and the ligniivcellulose bond in wood. Tappi 45 (3); 247-256. 106. Prey, V., E. Waldmannand F. Stiglbrunner. 1955« Zur Kenntnis des Alka l i l i g n i n s . Holzforsch. £ (3): 76-84. 107 a , and H. Swoboda. 1955 • A l k a l i decomposition of hemi-celluloses. Holzforsch. 9 ( l ) : 10-14. =88-108. Rapson, W.H. 1956. The role of pH i n bleaching pulp. Tappi 39 (5): 284-295- ~~ 109. Reyes, A. 1957• Studies of wood hemicelluloses Isolation of hemi-cellulose as beater additive. M. Sc. Thesis, State University of New York, Syracuse. 110. Rollins, M.L. and V.W. Tripp. I96I. The architecture of cellulose: A microscopic review. Forest Prod. J . 11 ( l l ) : 4-93-504. 111. Runkel, R.O.H. 1954. Die Sorption der Holzfaser i n morphologisch-chemischer Betrachtung. Holz Roh- Werkstoff 12 (6): 226-232. 112. ' . 1951. ?'Ur kenntnis des thermoplastischen Verhaltens von Holz. Holz Roh- . Werkstoff 9 (2): 41-53. 113. and K.D. Wilke. 1951. Zur Kenntnis des thermoplastischen Verhaltens von Folz. I. und I I . Mitteilung. Holz Roh-Werkstoff £ (7):: 260-270. 114. Sarkanen, K. and C. Schuerch. 1957. Lignin structure XI. A quanti-tative study of the alcoholysis of l i g n i n . J . Am. Chem. Soc. 79: 4203-4209. 115. Schubert, W.J. 1954. Uber lig n i n und lignifizierung. 14 Mitteilung. Holz Roh- Werkstoff 12 (10): 373-377. 116. Schuerch, C. 1952« The solvent properties of liquids and their rela-tion to solubility, swelling,. isolation and fractionation of li g n i n . J . Am. Chem. Soc. 7_s 506I-5067. 117. Schulerud, C F . and J.B. -Doughty. I96I. Reactive lignin-derived pro-ducts i n phenolic, high-pressure laminates. Tappi 44 ( l l ) : 8230-830. 118. Schwartz, S.L. and P.K. Braid. 1951. Effect of molding temperature on the strength and dimensional s t a b i l i t y of hardboards from fiber-ized water-soaked f i r chips. Paper Trade J . 132 (27): 20-25. 119. Schwartz, H. and F.W. King. I96I. Use of wood and wood residues i n pro-duction of fiberboard and particle board. Forest Prod. Research Branch, Ottawa Lab. Techn. Note No. 31. pp.24. 120. Scott, D.S. 1956. Recovery of tannin from western hemlock bark, I. Extraction rates with water as a solvent. Pulp Paper Mag. Can. 57 (5h 139-141. 121. Scott, D.S. and J.A.F. Gardner. 1952. Economics of tannin production from sea-water floated western hemlock bark. British Columbia Lumberman 36 (4): 51, 116-124. - 8 9 -122. Seaman, J.F., M.A. M i l l e t t and E.J. Lawton. 1952. Effect of high-energy cathode rays on cellulose. Ind. Eng. Chem. 44 (12): 2842-2852. 1 2 3 . Seifert, K. 1958.. Die Bestimmung von Phenolharzen i n Holzfaserung Holz-spanplatten. Holz Roh- Werkstoff 1 6 ( 9 ) : 335-340. 124. Smith, D.M. and R.I. Mixer. 1 9 5 9 . The effects of l i g n i n on degradation of wood by gamma radiation. Radiation Research 11: 7 7 6 - 7 8 0 . 1 2 5 . Snedecor. G J W . 1959« S t a t i s t i c a l methods. F i f t h edition. The Iowa State College Press, Ames. Iowa. 1 2 6 . Sohn, A.N.V. 1953. Versuche zur Steigerung des phenolishen Characters von Lignin. Holzforsch. 7 ( l ) : 1-8. 1 2 7 . Stamm, A.J.> H.K. Burr, and A.A. Kline. 1946. Heat, stabilized wood. Ind. Eng. Chem.. 38 ( 6 ) : 63O-634. 1 2 8 . Stanek, D.A. 1958. Study of the low molecular weight phenols formed upon hydrolysis of aspenwood. Tappi 41 (10): 6 O I-609. 129. Stewart, CM., J.K. Kottek, H.E. Dadswell and A.J. Watson. I961. The process of fibre separation. I I I . Hydrolytic degration within trees and i t s effects on the mechanical pulping and other proper-ties of wood. Tappi 44 ( l l ) : 798-813. 130. and J.A. McPherson. 1955• The non-resistant components of the wood of Eucalyptus regnans (F. Merell). Part IV. Holzforsch. 2 (5 ) s 140-W^ ~ 1 3 1 . Swanson. J.W. 1956. Beater adhesives and fibre bonding. The need for further research. Tappi 39 (5): 257-267. 132. Thode, E.F., and Shwe Htoo. 1955* Surface properties of rosin size precipitate. Tappi 38 (12): 705-709. 1 3 3 . Thompson, N.S., J.R. Peckham and E.F. Thode. I962.. Studies i n f u l l chemical pulping. I I . Carbohydrate changes and related physical effects. Tappi 45 ( 6 ) : 433-442. 134. Timell, T.E. i960. Isolation of hardwood glucomannans. Svenk Papper-s t i d . 6 3 (.15): 472- 476. 135. Toth, J., T. Asztalos and G . Balogh. I 9 6 I . Farostlemez Kilmatizalasa. Faipar 11 (6): ,187-189. 136. Treiber, E., H. Toplak and M.H. Ruck. 1955. Physicalischechemische Untersuchungen an einigen Hemicellulosen. Holzforsch. 9 (2): 49-59. -90-137- Turner, H.D., J;B. Hoh'f and S.L. Schwartz. 1948. Effect of some manu-facturing variables on the properties of fibreboard prepared from milled Douglas f i r . Forest Prod. Res .Soc. Proceedings 2: 110-112. 138. U.S. Department of Commerce. 1959. Construction materials s t a t i s t i c s , 1947-1957. U.S. Department of Commerce, Business and Defence Administration, p. 6. 139. Voss, K. 1952. Die Warmebehandlung von Holzfaser-Hartplatten. Holz Roh- Werkstoff 10 (8); 299-305. 140. Wacek. A. and S. Meralla. 1952. Faserverfilzung und Faserverklebung. Holzforsch. 6 (3)2 65-70. 'Ikl. and K. Kratzl. 1948. Constitution of the side-chain of l i g n i n . J . Polymer Sci . 3 (4): 539-548. 14-2. Walling, W.C. I 9 6 I . Hardboard ....State of the industry and i t s prac-t i c e . Forest Prod. J . 11 (11); 519-522. 143. Watson, A.J., CM. Stewart, and H.E. Dadswell. 1956. The influence of the alkali-soluble polysaccharides on pulp and paper properties. Tappi 39 ('5'): 318-324. 144. Wethern, J.D. 1952. Some molecular properties of hemicelluloses of black spruce. Tappi 35 (6): 267-271. 145. Wilson, J.W. 1962. Personal communication about tensile strength vs. modulus of rupture ratio for hardboard. University of British Columbia, Faculty of Forestry. 146. Wilson, K., E. Ringstrom and I. Hedlund. 1952. The a l k a l i solubility of pulp. Svensk Papperstid. 55 (2)s 31-37. 147. Wilson, W.S. 1951. The mechanism of fibre bonding. Tappi _ (12): 561-566. 148. Winogradoff, N.N. 1950. X-ray irradiation of cellulose acetate. Nature 172s 72-75. 149. Wise, L.E. and E.C Jahn. 1952. Wood chemistry. Vol. I and I I . Second Edition, Reinheld Publishing Corp. New York. 15C)• , M. Murphy and A.A. d'Addieco. 1946. Chlorite holocellulose, 'it s fractioation and bearing on summative wood analysis and on studies on the hemicelluloses. Paper Trade J . 122 (2)j 35-43« 151. Young, H.H. and E.J. Majka (Assignors to Swift & Company). 1961. Incorporating o i l i n hardboard. U.S. Patent No. 2,978,382. TABLES AND FIGURES / \ Table 1 . Composition of l / 8 - i n c h Asplund fibre as.determined by Bauer-McNett fibre c l a s s i f i c a t i o n . Screen Mesh Fraction Size s 2 0 2 5 . 3 3 5 3 5 . 1 6 5 2 7 - 5 1 5 0 1 2 . 1 Total : lOO.0 % Table 2 . Specifications and some properties of CTLA Polymer ( 2 6 ) . Test Value Test Method Gravity, API - 6 - I k • ASTM D 2 7 8 - 5 5 Viscosity, SSU at 2 1 0 ° F. 1 0 0 - 2 5 0 ASTM D 8 8 - 5 3 Nonvolatile matter, Wt. $ Min. . 8 0 ASTM D 1 5 4 - 5 3 " Iodine No., cg./g., Min. 240 ASTM D 5 5 5 - 5 4 Water Vol. $ Max. 0 . 8 ASTM D 9 5 - 46 J Flash, COC °F., Min. 2 1 0 ASTM D 9 2 - 5 2 Table 3 • Low temperature chlorination of Asplund pulp followed by 3 0 min. extraction with 3 $ monoethanolamine. Sample No. Chlorination Time^ min. Weight loss or gain f $ Weight loss following 3 0 min. extraction with 3 $ monoethanolamine, % 1 ' 2 0 ' * 5 . 2 8 -2 2 0 - * 0.90 3 • 40 - 3 . 2 6 -4 40 - - 8 . 7 7 5 8 0 * 0 . 7 0 1 6 8 0 _ 8 . 8 6 - 9 2 -Table .4. Low temperature chlorination of Asplund pulp followed by.30 min. extraction with hot - water <> , Sample No. Treatment Weight loss or. gain, $ 7 40 min. chlorination * ^ 8 8 kO min. chlorination plus hot water extraction -1.6k. 9 Hot water extraction only - 0.50 Table 5. Chlorination of Asplund pulp with t-butyl hypochlorite. Sample N r > . Treatment Weight loss or «»in. -•' 10 Chlorination with t-BuOCl * 1.01 11 Chlorination with t-BuOCl - 4.30 12 T-BuOCI wash only - 0.26 Table 6 . Anticipated and residual l i g n i n content of sodium chlorite treated fibre as calculated and determined, by micro-Kappa num-ber and UV absorption spectra, based on 31.04$ Klason l i g n i n . Sample Weight l o s 6 ^ Anticipated l i g n i n , Micro-Kappa UV Lignin, No.. Lianin. _ $ i - I ' • 31.04 2 1 30.34 - 28.72 3 2 29.63 - 26.95 4 3 28.91 - 25.96 . 5 4 28ol6 - 23.33 6 ' 5 27.41' 20.23 7 10 23-38 17.16 8 15 . 18.87 • - 16.20 9 20 13.80 13.72 10.36 10 25 8.05 5.64 6.28 11 12 30 3.46 1.21 - 9 3 -Table 7 . One per cent cupriethylenediamine viscosity and corresponding degree of polymerization values of sodium chlorited pulp. Sample No. Weight loss, i 1$ CED viscosity, cp. D.P. (22) 10 25 136 2390 11 30 105 2210 12 35 56 1885 Table 8 . O i l absorption values of boards of different fibre composition. Sample No. Treatment Weight loss' by Treatmnti > Ave. Sp. Gr. O i l Absorption, % 1 Asplund fibre - • 71 10.70 A Alcohol-benzene extracted fibre - •79 13.10 B Sodium hydroxide extracted fibre - •78 14.20 C Modified cellulose fibre - .79 13.70 D Lignin deactivated fibre - •67 11.20 2 Delignified fibre 1 .71 13.80 • 3 Delignified fibre 2 •70 13.60 4 Delignified fibre . 3 .72 13.20 5 Delignified fibre ' 4 •71 13.90 6 Delignified fibre 5 .70 13 .70 7 Delignified fibre 10 • 74 12.90 8 Delignified fibre 15 •75 12.50 9 Delignified fibre 20 •79 13.60 10 Delignified fibre 25 •78 13.00 11 Delignified fibre 30 .80 15.20 12 Delignified fibre 35 •79 14.90 -94-Table 9 . Effect of temperature on tensile strength of oil-tempered - hardboards. . • Sample 'No. Temperature. °C. Average Sp.Gr. Corr. Tensile Str;, kg/cm? Comparative Untempered Str.» kg/cm? 1-10 130 1435 859 11-20 155 1750 885 21-30 175 1214 946 Table 10. Influence of specimen width on tensile strength and co-efficient of variation (CV) of thin untempered boards. Specimen Width., mm. Average Sp.Gr. - Corrected Tensile Strv» • kg/cm? Coefficient of Variation, £ N = 20 3 588 16.97 5 726 , 18.54 7 858 11.08 9 945 5-95 11 874 10.60 Table 1 1 . Interaction between Wood Constituents and Tempering O i l Measured by Ultimate Tensile Strength, Modulus of El a s t i c i t y (MOE), and Ultimate Elongation. Wood Constituent under Investigation Board Treatment O i l Absorp t i o n ? Ave. Spec. Jravity, Ave. Ult.Tens. Strength, Ave. MOE f Ave. Ultimate Slongation, Spec.Gravity Corrected Tensile Str.. Relative Strength Increase. Remarks i g-/em? kg./cmr kg/ cm'r i n . / i n . kg/cm? 1 Asplund Fibre A]_ Humldificat. A2 Heat-Treatm. A3 Oil-Temprd . 1 0 . 7 . •724 .712 -B18 1291 1236 2 8 0 1 12,831 1 2 , 0 2 9 24.263 0 . 0 1 8 4 9 O..OI679 0 . 0 1 5 1 0 . 1299 1271 2779 . 114 Ave. Sp.Gr. for Correc-tions: H.: . 7 2 6 H-T.: . 7 2 7 0-T.: .813 Alcoho-Benzene Extractives Bi H. B 2 H-T. B^ 0-T. 1 3 . 1 . 6 9 6 . 6 8 7 .788 1288 1332 3040 13>072 12,024 22 ,947 0 . 0 1 7 7 2 0 . 0 1 8 9 9 0 . 0 1 7 9 4 1403 1466 3037 . . 1 1 7 .. .. Modified Cellulose C1 H. C 2 H-T. Co 0-T. 13-7 • 730 •737 .786 1566 1482 2284 1 6 , 9 8 8 1 7 , 4 9 1 24 ,659 0.01426 0.01184 0.01149 1548 1 4 5 1 2 2 9 8 48 Hemi cellulose Di H. D 2 H-T-0-T. Ik.2 .682 .716 •777 1558 1627 2718 15,928 1 6 , 9 2 8 24 ,335 0.01602 0 . 0 1 5 0 6 0.01404 16 51 1642 2 8 0 3 70 Lignin El H. E 2 H-T. E 3 0-T. 1 3 . 0 •799 .784 . 8 9 5 3184 3011 4513 36,406 40 ,273 46,073 0 . 0 1 3 4 7 0 . 0 1 0 6 1 0 . 0 1 1 6 5 3079 2 8 3 0 4213 37 Modified Lignin (Tannin Impreg) F1 H. F 2 H-T. F3 0-T. 11.2 .686 . 7 8 6 I 6 8 7 2826 1 5 , 7 9 7 2 3 , 1 9 1 0.01473 0.1477 1867 2948 58 Note: Each value represents an average of 24 measurements. Table 12, Significant tensile strength differences between untempered boards of different chemical composition. Y Board \^ Y 3079 - Y 1867 - Y 1654 - Y E F. D A 1299 1780 * 562 * NS B 1403 I676 * 459 NS G - 1548 1531 * 314 NS . D 1654 1425' * 208 NS F 1867 1212 * _ E • 3079 _ S = 292.4; Sy - 119.9; D = Q.Sy; D = 526 kg/cm? A difference of 526 kg./cm?. is needed to declare a difference between any two strength values as significant at the 5$ probability l e v e l . T a b l e 13. I n t e r a c t i o n b e t w e e n B o a r d s o f V a r y i n g L i g n i n C o n t e n t a n d T e m p e r i n g O i l M e a s u r e d b y U l t i m a t e T e n s i l e S t r e n g t h , U l t i m a t e E l o n g a t i o n , a n d M o d u l u s o f E l a s t i c i t y ( M O E ) . W e i g h t L o s s $ L i g n i n C o n t e n t , B o a r d T r e a t m e n t O i l A b s o r p -t i o n , A v e . S p e c . j r a v i + y , C o r r e c t e d H i t . T e n s . S t r e n g t h , R e l a t i v e S t r e n g t h I n c r e a s e ^ A v e . U l t . E l o n g a t i o n R e l a t i v e E l o n g . D e c r e a s e , A v e . M O E , R e l a t i v e S t i f f n e s s I n c r e a s e . R e m a r k s $ $ ft/cm3 k g / c m ? i i n . / i n . *. k g / c m ? $ C 31-04 t l u m i d i f i e c T e m p e r e d 13.1 .749 .811 1781 3651 104.9 0.02059 0.01686 .22.4 14,924 26,315 -.76.3. _ A v e r a g e S p e c i f i c G r a v i t y f0] C o r r e c t i o n H . : .756 0 - T . : .819 1 . 29.64 H . 0 - T . 13.8 •705 .817 1342 I 9 6 2 46.2 . 0.00631 0.00657 * 4.1 23,577 31,798 .34.9. 2 27.81 H . 0 - T 13.6 .703 .762 i486 2050 38.0 0.0092'+ 0.00735 20.5 18,118 25,992 43-3 3 26.53 H . 0 - T • 13.2 .715 •770 163b 2147 31.2 0.01039 0.00727 30.5 15,523 29,229 57.8 . 4 24.09 H . 0 - T . 13.9 .713 •777 1514 1975 30.5 0.01286 0.00733 .'43,0 14,379 28,917 101.0. 5 20.89 H . 0 - T . 13.7 .704 •774 1702 2093 23.0 .... 0.01125 0,06742 .34.1 19,930 29.945 .. _69..7 10 17.72 H . 0 - T . 12.9 •738 •790 2096 2600 24.1 0.01645 0.00930 43.4 22,547 I30;474 35.2 15 16.24 H . 0 - T 12.5 •747 .817 2187 2575 17-7 0.01261 0.00926 26.7 24,346 32,237 32.5 20 10.42 H . 0 - T . 13.6 .786 .825 2841 3011 6.0 0.01467 , O.OO913 37.7 28,864 34,713 20.2 25 6.41 H . 0 - T . 13.0 .780 .845 3850 4679 21.5 0.01994 0.01366 31.5 34,485 42,899 24.4 30 3.85 H . 0 - T . 15.2 •799 .867 3767 4771 26.6 0.01995 0.01421 28.7 35,406 44,346 25.2 35 1.8 H . 0 - T . 14.9 .785 .891 3959 4803 21.3 0.01761 0.01393 20.9 37,708 44,429 17.8 Note: Values for 1, 2, 3, 4$ weight losses represent an average of 24 measurements while those for C , 5, 10, 15, 20, 25, 30, 35$ weight loss are averages of 48 measurements. Table 14. Significant tensile strength differences between untempered beards prepared from delignified f i b r e . Y Wt.Los^\ *. \ Y 3953 - Y 3850 - Y 3767 - Y 2841 - Y 2187 - Y 2096 - Y 1781 - Y • - 35 25 30 20 15 10 0 1 13^2 2611 * 2508 * •2425 * 1499 * 845 * 745 * 439 NS 2 1486 2467 * 2364 * 2281 * 1355 * 701 * 610 * 295 NS 4 1514 2439 * 2336 * 2253 * 1324 * 673 * . 582 * 267 NS 3 1636 2317 * 2214 * 2131 * 1205 * 551 * ' . 460 145 NS 5 1702 2251 * 2148. * 2065 * 1139 * 485 * 394 NS 79 NS 0 1781 2172 * 2069 * 1986 * . 1060 * 4o6 NS 315 NS _ 10 2096 1857 * 1764 * 1671.* 745 * 91 NS . - -15 • 2187 1766 * 1663 * 1580 * 654 * - _ 20 2841 1112 * 1009 * 926 * _ - _ 30 . 3767 186 NS 83 NS - _ 1 25 . 3850 103 NS _ • _ 35 3957 - - _ - _ . S = 299.78; Sy = 86.57; D = Q. Sy; D =.444 kg/cm? A .difference of 4;44 kg/cm? is required to declare a difference between any two strength values as significant at the 5$ probability le v e l . Figure lA. Relationship between time, number of treatments and weight loss obtained with 70°C. cooking temperature in sodium chlorite solution. _6!_3iV.ie id . 2 0—itiw 4 tie No. of treatments, Time, hr. 1.8 Residual lignin,% Figure IB. Relationship between time and per oent weight loss obtained with 70°C. cooking temperature in sodium chlorite solution. o Time, min. Figure 2. Laboratory forming box and hydraulic hot-press. -102-Pigure 3. Converted arbor press used for specimen preparation. - 1 0 3 -Figure k. Adjustfble-width cutting die used for cutting specimens of uniform width. Figure 5. CEJ d i a l microcator - 1 0 5 -Figure 6 . Instron table model testing machine Figure?. Tensile strength vs. specific gravity relationship. Example of graphical solution of specific gravity correction for ultimate tensile strength values. TEMPERED -Y» 177!__!64L_ —• " UNTEMPERED Example-. I. Unadjusted strength: 1600 kg.jcm Adjusted strength : 1665 kg,/cm2 2.Unadjusted strength: 1474 kg./cm2 Adjusted strength: 1280 kg./cm2 B a sic specif ic gravity: .726 65 .66 .67 .68 .69 .70 . 71 .72 .73 .74 .75 .75 .77 .78 .79 BO .81 Specific gravity CM. xT 6 «5000f c B E 54000 3000 2000 1000 Figure 8. Interaction between wood constituents and tempering oil as measured by ultimate 114 tensile strength. 11,7 48 (H: Humidified; T-. Tempered ) _> 5J_ H Relative Strength increase % H o i H Asplund pulp (Control) Alcohol-benzene Modified extractive cellulose (7.45% removed) (i07rads. gamma irradiation) Hemicellulose L i g n i n Modified lignin (8.68% removed) (30 %removed) (6.7%tannin impregn) Figure 9. Relationship of ultimate tensile strength plus strength increase following oil-tempering to c » per oent weight loss, and residual lignin oontent with chlohted Asplund fibre. 'A' j ' B |Y=3^98.45-_3f34X+^6l.36X2-l7895X^930X4*J^/ R = 0.978 o".c.**1>^ LEGEND: • Untempered o Tempered - Strength increase @Calculated curve. y= I755.66 -584.47X+303.73X2 -5_.27X3+2.8IX4 R*0.943 100-80 60 40" |nY=6.48-0.43 InX R-0.754 20-3* to o CO 10 15 20 25 30 35 Weight loss % "202T 3104 17.16 16.20 10.36 6.28 3.16 1.8 Residual lignin,% .030-Figure 10. Relationship of ultimate elongation plus elongation decrease following oil-tempering to percent weight loss and residual lignin with chlorited Asplund fibre. 80-o co o O _ o 9 .010-60-e c o UJ 40-LEGEND• • Untempered 20 o Tempered A Elongation decrease 25 30 3*5 Weight loss % 31.04 20.23 17.16 16.20 1036 6.28 3.16 I J B Residual lignin,% Figure II. Relationship of modulus of elasticity (MOE) plus O 5 10 15 20 25 30 35 , i ( , Weight loss % , 31.04 20.23 17.16 1620 10.36 6.28 3.16 1.8 Residual lignin t% - I l l -Figure 12. Sample "boards of different f i b r e chemical constitution. Asplund f i b r e (Untempered) Asplund f i b r e (Tempered) A l c ohol -be nz e ne extracted f i b r e ( 7 - 5 $ removed) Oxidized l i g n i n f i b r e (1$ weight loss) Sodium-hydroxide extracted f i b r e (8.7$ removed) Oxidized l i g n i n f i b r e (2$ weight loss) Modified l i g n i n f i b r e (6.7$ tannin solids) Oxidized l i g n i n f i b r e ( 3 $ weight loss) Modified cellulose f i b r e (10 7 rads gamma ir r a d i a t i o n ) Oxidized l i g n i n f i b r e (4$ weight loss) Oxidized l i g n i n Oxidized l i g n i n Oxidized l i g n i n Oxidized l i g n i n f i b r e f i b r e f i b r e f i b r e (5$ weight loss) (10$ weight loss) (15$ weight loss) (20$ weight loss) Oxidized l i g n i n Oxidized l i g n i n Oxidized l i g n i n Oxidized l i g n i n f i b r e f i b r e f i b r e f i b r e (25$ weight loss) ( 3 0 $ weight loss) ( 3 5 $ weight loss) ( 3 5 $ weight loss) (Tempered) 

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