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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 B r i t i s h Columbia  1958  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  *  MASTER OF FORESTRY  i n the Department of Forestry  We accept t h i s thesis as conforming t o the required standard  THE UNIVERSITY OF BRITISH COLUMBIA April,  I963  In presenting  t h i s thesis i n p a r t i a l f u l f i l m e n t of  the requirements f o r an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available f o r reference and study.  I further agree that permission  f o r extensive copying of t h i s thesis f o r scholarly purposes may granted by the Head of my Department or by his  be  representatives.  It i s understood that copying or publication of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department of Wood Technology. Faculty of Var aat.r? The University of B r i t i s h Columbia, Vancouver 8, Canada. Date  A p r i l 30,  1963  ABSTRACT  This study was designed t o examine e f f e c t s of alcohol-benzene solubles, hemicellulose, modified c e l l u l o s e , l i g n i n and modified l i g n i n residuals i n r e f i n e d Douglas f i r Asplund f i b r e on the heat-activated polymerization of tempering o i l applied t o wet-batch process hardboards.  Thin  (0.05. cm.thickness) experimental boards were prepared with good formation properties and r e p r o d u c i b i l i t y f o r the study.  Results of oil-tempering,  heat-treatment and humidification treatments were compared with and without modifying the raw stock. Oil-tempering was most e f f e c t i v e on boards made from unmodified or alcohol-benzene  extracted f i b r e .  An ultimate t e n s i l e strength increase  of 105$ approximates gains had i n commercial p r a c t i c e . Heat-treatment alone was i n e f f e c t i v e i n developing extra strength, possibly because of extended hot-pressing of the boards.  Among the wood constituents i n v e s t i -  gated l i g n i n was involved.in approximately opment  80$ of the extra strength devel-  on,oil-tempering. It was found that oil-tempering e f f e c t s could be severely de-  pressed by mild oxidation of the f i b r e with a c i d i f i e d sodium c h l o r i t e (NaClOg). s o l u t i o n at 70° C. Accompanying weight loss was below 5$. A l t e r natively, p a r t i a l deactivation was obtained by i n h i b i t i o n of the f i b r e surface or precondensing the l i g n i n i n the raw stock with hemlock bark tannins.  hot-water-soluble  The tannins were introduced into the f i b r e s t r u c -  ture by a new method including hot-soaking and c o l d - p r e c i p i t a t i o n at 3% s l u r r y consistency.  Strength development on oil-tempering was thus reduced  by the oxidation treatment to approximately  20$ which was unaffected by  ii.  further chemical treatment.  This r e s i d u a l strength increase may be due to  some other e f f e c t than l i g n i n . Evidence f o r a chemical mechanism i s suggested by observations that only a l i m i t e d portion of the o i l takes part i n strength development, pointing toward l i m i t e d s i t e s available f o r polycondensation.  Possibly,  these s i t e s are inactivated.by even mild oxidizing treatments of the f i b r e . This suggests that l i g n i n q u a l i t y i s more important than quantity of l i g n i n , alcohol-benzene solubles, hemicellulose or cellulose i n the oil-tempering mechanism.  These findings are contradictory to the l i t e r a t u r e .  To date,  l i g n i n has not been considered an important wood constituent i n strength development of d i f f e r e n t wood products by impregnation, and condensationpolymerization systems with unsaturated compounds. Further removal of l i g n i n from the f i b r e (10 t o 25$ weight loss) improved formation and bonding of f i b r e s and the subsequent t i e s of boards.  strength proper-  This conforms t o w e l l described mechanisms accompanying  fibre delignification.  Additional l i g n i n removal (25 t o 35$ weight loss  with 5$ or l e s s r e s i d u a l l i g n i n ) lowered f i b r e v i s c o s i t y 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 t o a mathematical model. The s i t e and bonding mechanism between l i g n i n and tempering o i l have not been described. Some suggestion i s made as to how t h i s might occur.  ix. ACKWOWLEDGEMEHT  The w r i t e r ' s  gratitude  i s expressed  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 tude, i s e x t e n d e d Forestry,  encountered  in this  t o D r . J . W . Wilson,, A s s o c i a t e  for M s  study.  Professor,  as w e l l as p r e p a r i n g the t h e s i s .  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 S m i t h , and D r . J . A . F .  i n the  at  Canadian Forest  Westminster,  typing and p r i n t i n g c o s t s Thanks a r e students,  expressed  programming, and data  i n p l a n n i n g and O t h e r members  of  c a p a c i t y was  Head o f R e s e a r c h Department,,  ob-  and other  The C o m p a n y ' s thesis  staff New  financial contribution to  i s a l s o much  appreciated.  t o M e s s r s . G. I f j u a n d A . K o z a k ,  graduate  for their assistance  computer  provided i n  processing.  The w r i t e r a l s o  Canada.  of  Gardner.  of t h i s  Faculty of Forestry,  obtained during the  grati-  Products L t d . , P a c i f i c Veneer and Plywood D i v i s i o n ,  B r i t i s h Columbia.  in  s t u d y were D r . R . W . W e l l w o o d ,  V a l u a b l e h e l p , both i n a d v i s o r y and t e c h n i c a l t a i n e d from M r . A . Pantelejevs,  Deepest Faculty  p r o f e s s i o n a l and understanding guidance  experimentation phases,  Dr. J.H.G.  t o a l l t h o s e who a s s i s t e d  gratefully  acknowledges  the  financial  p a s t two y e a r s f r o m the l a t i o n a l R e s e a r c h  assistance  Council of  i i i .  TABLE OF CONTENTS Page TITLE PAGE ABSTRACT  . .•  TABLE OF CONTENTS  . i i i  ACKNOWLEDGEMENT.,...  ix  INTRODUCTION . . . . .  1  .  f  LITERATURE REVIEW 1.  Alcohol-benzene s o l u b l e s .  2.  Lignin. . . . . . . . . .  8 .......  9  3 • Hemicellulose  15  if-.  Cellulose  20  5-  Tannins and other polyphenolic wood e x t r a c t i v e s . . .  2k.  6.. Heat-treatment of pressed hardboards.,  : .26  7.  Oil-tempering of pressed hardboards  28•  8.  Humidif i c a t i o n of pressed .hardboards  30  MATERIALS AND METHODS  . . . . . . . . . .  1 . C o l l e c t i n g the f i b r o u s m a t e r i a l .. . . '  „. . .  2 . Temper ing o i l E x t r a c t i o n and M o d i f i c a t i o n of Fibre Constituents.  31 31  A. .Selection and Preparation of M a t e r i a l s .  B.  i  31 32  ....  33  1.  E x t r a c t i o n of alcohol-benzene solubles  3^ •  2.  Removal of l i g n i n . . . . . . .  35  iv. Page 3»  A l k a l i extraction of hemicelluloses. . . . . . . . . .  k. C e l l u l o s e m o d i f i c a t i o n by Cobalt 60 i r r a d i a t i o n •.... . . 5.  h$  i i g n i n d e a c t i v a t i o n f o l l o w i n g impregnation w i t h h o t water-soluble hemlock bark e x t r a c t i v e s . . . . . . . .  C. A n a l y t i c a l Methods  • •  ^5 kf  1.  Alcohol-benzene e x t r a c t i v e s (TAPPI Standard;  T 6m-5^)  2.  Klason l i g n i n (TAPPI Standard?  3.  U l t r a v i o l e t spectrophotonetrie l i g n i n d e t e r m i n a t i o n i .  T l'3m-5^).«  ^7 **7 HQ  h. Micro-Kappa number . « » » . » . . . . • . .  kQ  5.  U9  One per cent cupriethylenediamiae  (CED) v i s c o s i t y . • .  D. Thin Board Preparation . . . . . . . . . . . . . . Step 1.  Additives . . . . . . . . . . . . . . . . . . . .  Step 2. Mat formation . . Step 3* Board p r e s s i n g . » . . . . . .  ......•.<..  52  55  . . . . . . . . .  57  a.  Oil-tempering  . . . . . . . . . .  57  b.  Heat-treatment. • » » • « • • . . . . . . . . . .  58  c.  Humidification. . » . • • . . . . . . . . • . . *  59 60  T e s t i n g Procedures 1*  Specimen preparation . . . . . . . . .  2.  T e n s i l e strength t e s t , c a l c u l a t i o a o f u l t i m a t e elonga-  ...<><><>..  t i o n and modulus of e l a s t i c i t y . . . . . . . . . . . . 3.  ^9  52  Step h» Post-pressing board treatments.  E.  k2  Adjustment o f strength p r o p e r t i e s * . . . . . . . . . . . .  6l  62 6k  V.  Page  RESULTS. . A.  65  I n v e s t i g a t i o n of Wood Constituents-  ......  B. E f f e c t of L i g n i n Removal  65  '  65  DISCUSSIONA.  '  I n v e s t i g a t i o n of Wood Constituents  . .  .67 67  1,. Untreated Asplund Pulp  68  2.  69  Alcohol^Benzene Extracted F i b r e .  3'.. Modified C e l l u l o s e Fibre  69  k.'. Modified Hemicellulose Fibre . . . . . . . . . . . .  70  • 5.' . D e l i g n i f i e d Fibre . 6.  71  Deactivated L i g n i n ' Fibre  -fl  ' 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 o f 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 • . . * • Table Table  ' 2>  •  S p e c i f i c a t i o n s and some properties of GTLA.Polymer  k.  with 3$ monoethanolamine  91  5-  91  Low temperature e h l o r i n a t i o n of Asplund pulp f o l lowed by 30 min. e x t r a c t i o n with hot water. . . . .  Table  91  .'3- Low temperature e h l o r i n a t i o n of As-plund pulp f o l - r lowed by 30 min.extraction  Table  ?  92  C h l o r i n a t i o n of Asplund pulp with t - b u t y l hypochlorite  .  92  Page Table  6.  A n t i c i p a t e d and r e s i d u a l l i g n i n chlorite treated fibre  as  content  of  sodium  c a l c u l a t e d and determined  by. m i c r o - K a p p a n u m b e r a n d UV a b s o r p t i o n  spectra,  b a s e d on 31.0k%> K L a s o n l i g n i n Table  7-  yd  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  and  c o r r e s p o n d i n g degree o f p o l y m e r i z a t i o n v a l u e s  of  sodium c h l o r i t e d p u l p Table  ,.8.  93  O i l a b s o r p t i o n values of boards  of different  fibre  composition. Table  9*  Effect  93  of temperature  on t e n s i l e  strength of o i l -  tempered hardboards Table  10.  Influence  of  9k  s p e c i m e n w i d t h on t e n s i l e  and c o e f f i c i e n t  strength  o f V a r i a t i o n (CV) o f t h i n  untempered  boards Table  11.  9k  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 oil  measured by u l t i m a t e t e n s i l e  of e l a s t i c i t y Table  12.  ..13-  strength,  modulus  (MOE), a n d u l t i m a t e e l o n g a t i o n .  Significant tensile untempered boards  Table  and tempering  • •  95  chemical composition  96  strength differences  of different  I n t e r a c t i o n between boards  ..  between  of varying l i g n i n  content  and tempering o i l measured by u l t i m a t e t e n s i l e . strength, ultimate, elongation, elasticity. Table  Ik.  (MOE).  . . . . .  Significant tensile  and modulus  of. 97  :  strength differences  between  untempered boards prepared from d e l i g n i f i e d f i b r e  .  98 ••  V l l  o  Page Figure 1/A  Relationship between time, number of treatments and per cent weight l o s s obtained with 7 0 ° C. cooking temperature i n sodium c h l o r i t e s o l u t i o n « • > » » .«  99  Figure l / b Relationship between time and per cent weight l o s s obtained with 7 0 ° C. cooking temperature i n sodium chlorite solution  i  .  .  .  .  .  .  .  .  .  100  Figure 2.  Laboratory forming box and hydraulic hot-press. . .  101  Figure 3°  Converted arbor press used f o r specimen preparation  102  Figure 4.  Adjustable-width  c u t t i n g d i e used.for cutting speci-  mens of uniform width. . . . . . . .  103  o «o  10h  Figure 5 °  CEJ d i a l microcator  Figure 6 .  Instron table model t e s t i n g machine  Figure 7»  Tensile strength v s . s p e c i f i c g r a v i t y r e l a t i o n s h i p .  . . . . . . . . ©  •  o  105  Example of graphical s o l u t i o n of s p e c i f i c g r a v i t y c o r r e c t i o n f o r ultimate t e n s i l e strength values Figure 8 .  . .  I n t e r a c t i o n between wood constituents and tempering o i l as measured by ultimate t e n s i l e strength. . . .  Figure 9 •  106  107  Relationship of ultimate t e n s i l e ' strength plus strength increase following oil-tempering t o per cent weight l o s s and r e s i d u a l l i g n i n with c h l o r i t e d Asplund f i b r e  Figure 1 0 .  108  Relationship of ultimate elongation plus elongation decrease  following oil-tempering t o per cent weight  l o s s and r e s i d u a l l i g n i n with c h l o r i t e d Asplund f i b r e  109  ..  viii.. Page Figure 11.  Relationship of modulus of e l a s t i c i t y (MOE) plus s t i f f n e s s increase following oil-tempering to per cent weight loss and r e s i d u a l l i g n i n with c h l o r i t e d Asplund f i b r e . . . . . . . . . . . . . . . . . . . .  Figure 12.  Sample board of d i f f e r e n t f i b r e chemical "  f  c  X  O  H  •  o  *  »  o  o  o  o  e  O  o  *  e  o  «  o  »  f  .110  constitut  o  o  o  *  *  »  111  -1-  INTRODUCTION  The hardboard industry i s one of the recently developed tranches of the wood-using i n d u s t r i e s .  I t i s an outgrowth of pressure t o u t i l i z e low  cost residues and economics of production of other forest products, i . e . , lumber, plywood, and f u r n i t u r e .  The technical history of hardboard  far back into the years of i n d u s t r i a l development.  reaches  E f f e c t i v e commercial  pro-  duction of hardboard began however, with Mason's invention i n 192^. By exploding wood chips into a f l u f f y mass of f i b r e , at high pressure and temperature i n the presence of water, he found a new and unique method f o r f i b r e preparation. Experiments  i n the investigation of f i b r e separation mechanism i n  the "Mason,gun" l e d t o the invention of a second d e f i b e r i z i n g method, named a f t e r i t s inventor, "Asplund process".  During the more than ten years which  elapsed between the invention of the two processes, hardboard production d i d riot increase at an expected r a t e .  With the introduction of the Asplund pro-  cess, production volume increased r a p i d l y .  The slow growth preceding 1938  was due t o the e f f e c t of s t r i c t l y held product patents on the Masonite process. ^Between 1938 arid I9U8, however, an increase of 100$ was noted. Reports of United States hardboard production show a further subs t a n t i a l increase i n production during the 10-year period of 19^7 to 1957 (138).  In 19^-8 approximately 52$ of t o t a l fibreboard production was made up  of hardboard (33)-. (83)-  In 1957 Sweden produced U30,000 metric..tons of hardboard  Currently Canada i s 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 i n December I 9 6 I  was  288,157,088 s q . f t . (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 - i n c h basis) of hardboard annually; of which o n l y two. M I T i o n square feet are produced i n the United States (142). Several advantages of hardboard made i t s phenomenal growth possible. Among these are r e l a t i v e l y low c a p i t a l requirements, wide v a r i e t y of suitable raw materials, and v e r s a t i l i t y of r e s u l t i n g products.  Capital requirements  for erection and operation of hardboard plants are moderate when compared t o certain other wood-using industries, i.e.,the pulp and paper industry. are  There  no s p e c i f i c requirements as t o form of raw material; i t may be forest and  factory residue, as w e l l as from primary harvest. V e r s a t i l i t y of properties makes hardboard suitable f o r numerous uses such as exterior and i n t e r i o r sheathing i n home building, concrete form l i n i n g , table and desk tops, cabinet backs and automobile applications, p a r t i t i o n s and heavy-duty storage walls, cores f o r p l a s t i c laminate's, and f l o o r 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 p o t e n t i a l f o r the product..' T y p i c a l fibreboard processing s t a r t s with wood chips which are separated Into i n d i v i d u a l f i b r e s and f i b r e bundles i n the "Asplund d e f i b r a t o r " , at steam pressures of from 100 to 175 psi,and chip temperature of 3^0 to 375°F., i n the presence of water.  From the pulp thus obtained, a water suspension of  approximately 3$ consistency i s made.  F i n a l board strength and hygroscopic  properties can be improved by adding small amounts of synthetic r e s i n and wax at t h i s stage.  These reagents are p r e c i p i t a t e d onto the f i b r e s by small  amounts of p r e c i p i t a t i n g agents such as aluminum sulphate and sulphuric a c i d  ( 3 0 , kj,  132,  Ikj).  The f i b r e i s then formed as a mat of controlled t h i c k -  ness either on a Fourdrinier, cylinder mold or a deckle, box.  The drained  mat i s cold-pressed to approximately 35$ s o l i d s content. This i s followed by trimming t o approximate size and hot-pressing i n a multiple-opening press where elevated temperature and high pressure compress the mat and free I t froms-'mblsture.  The escape of moisture under pressure i s 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 t o post-pressing t r e a t -  ments such as o i l dipping and/or heat-treatment, and humidification. . These treatments are applied f o r improvement of hardboard physical c h a r a c t e r i s t i c ^ . Through manipulation of manufacturing variables the whole, process of hardboard manufacture can be made f a i r l y f l e x i b l e and suitable f o r producing: a greatly d i v e r s i f i e d product l i n e (59*  137)*  Hardboard may be defined as a type, of fibreboard above 0 . ^ 0 specif i c ' g r a v i t y , manufactured from wood or other l i g n o c e l l u l o s i c f i b r e s with primary bonding derived from the arrangement of f i b r e s and t h e i r inherent adhesive properties (33) • Oh the basis of s p e c i f i c gravity, hardboards r  be further c l a s s i f i e d as semi-hardboards ( 0 . 4 0 - 0 . 8 0 ) , hardboards  '  may  (0.80-1.20),  and s p e c i a l or extra-hard hardboards ( 1 . 2 0 - 1 . 4 5 ) • • Oil-tempered hardboards occupy a unique place among fibreboards'. Kumar (73)  estimates the amount of t o t a l oil-tempered hardboard as 25 to 30$  of a l l hardboard produced.  Oil-tempered hardboard. i s used where extra  strength and water resistance are required.  This includes use i n home  b u i l d i n g as f l o o r covering and exposed sheathing, stadium seat tops, form press l i n i n g , d r i l l s t e n c i l s , hammers and moulded a r t i c l e s such as s t o o l seats and backs, r e f l e c t o r s , and containers. heat-treatment of  O i l saturating and subsequent  -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 t e n s i l e strength ( t e n s i l e 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 ) l y they are s t i f f e r .  Consequent  A further advantage of tempered boards compared to  normal hardboards i s that they are l e s s i n c l i n e d to delaminate, making them e s p e c i a l l y suitable f o r uses where s p e c i a l 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 r i s e n has'/, not been followed by board prices.  Current s e l l i n g prices of two Canadian plants are given f o r econ-  omic comparison of tempered and untempered hardboard manufacture.  Plant A.  Plant B.  l / 8 - i n c h Standard Hardboard  $ 6 9 .50/M. Sq.Ft  l / 8 - i n c h Tempered Hardboard  $85.00/M.Sq.Ft  l / 8 - i n c h Super Sealed Hardboard  $65.00/M.Sq.Ft  l / 8 - I n c h 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 . marginal economic operation with tempered  This suggests a  hardboards.  Despite i t s great technological importance the a c t i o n of tempering o i l s on extra strength development hehsively investigated.  of hardboards has never been compre  In the present study, i t Was f e l t that an i n v e s t i  gation of wood constituents, with regard to t h e i r i n t e r a c t i o n with tempering o i l s , could lead! t o disclosure of an acceptable mechanism f o r 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 f o r  -5which no method has been found as y e t .  Thereby, a tempering process  of  highly empirical nature could be replaced by methods giving predictable results.  Explanations  f o r strength differences between i d e n t i c a l batches  of tempered hardboards cannot be s a t i s f a c t o r i l y 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 t o be chemical i n nature (73), an invest i g a t i o n of the i n t e r a c t i o n between c e r t a i n wood constituents and tempering o i l seemed to be i n order.  Because of t e c h n i c a l considerations i t  was believed that some non-complex mechanical t e s t would give most r e l i able r e s u l t s .  Tensile strength t e s t and other derived data from t h i s test  were selected as a d i r e c t measure of the i n t e r a c t i o n between a p a r t i c u l a r wood constituent and tempering o i l .  I t was  also hoped that fundamental  information could be obtained regarding the tempering mechanism. At the same time, data obtained from t e s t s had to be s u f f i c i e n t l y r e l i a b l e for understanding the significance of the influence of various wood c o n s t i -  tuents on one hand, and the manner by which t h e i r removal or modification a f f e c t s tempered board properties on the other.  Based on preliminary  examination of wood component e f f e c t s , the one most important from the 1  standpoint  of extra strength development, had to be singled out for  closer i n v e s t i g a t i o n of mechanisms i n hardboard tempering.  In summary  the objectives of t h i s study were: 1.  Comprehensive i n v e s t i g a t i o n of basic wood constituents vrith. regard to t h e i r i n t e r a c t i o n with tempering o i l as activated by heat.  Selection of the most important wood constitutent(s) and further examination of these i n regard to possible mechanisms.  -7-  LITERATURE REVIEW  In the following a review i s given of the e f f e c t of wood c o n s t i t uents and post-pressing treatments on strength and dimensional s t a b i l i t y of fibre-base products. Considerable l i t e r a t u r e has accumulated  on chemical and physical  properties of woods,and f i b r e products produced from them.  For a long.per-  iod wood was assumed to be a uniform chemical substance ( 5 * 0 .  Initial  analysis showed that wood i s mostly composed df two substances, i.e., polysaccharides and an inctf-usting material, l a t e r c a l l e d l i g n i n (115") • Progress i n wood chemistry has been greatly retarded by the chemic a l complexity of wood constituents, as indicated by t h e i r r e l a t i v e composit i o n i n s i t u (48).  For example, the chemical structure of the l i g n i n mole-  cule i s s t i l l unknown.  Chemical degradation of l i g n i n provides a number of  d i f f e r e n t b u i l d i n g units, depending on the method of i s o l a t i o n ond reagents used.  Furthermore, the question as t o nature and extent of chemical and  physical bonding between.wood constituents has yet to be s e t t l e d  (17)-  This makes more d i f f i c u l t the examination of hypothesis r e l a t i n g 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 f i b r e s i n a more or l e s s modified state dependent on chemicals and pulping conditions used.  .Chemical and physical structure of wood pulp l a r g e l y depends' on the  pulping p u r i f i c a t i o n method used.  No pulping method has been found as yet  that facilitates removal of one or several of the wood constituents i n a  -8single operation without causing serious degradation of remaining c o n s t i t uents (8).  I t i s f o r t h i s reason that chemistry of wood constituents,  I n d i v i d u a l l y and as a complex, continues t o be of great importance to the pulp, paper and fibre-processing industry. Hardboard  i s a wood-base product, made from pulps which may  be  obtained by Asplund or other mechanical or semi-chemical d e f i b e r i z i n g processes. As such i t bears close r e l a t i o n to newsprint and other'coarse f i b r e products both i n physical and chemical c h a r a c t e r i s t i c s (139)-  Major d i f -  ferences between paper and hardboard manufacture l i e i n the nature (degree of f i b r i l l a t i o n , and f i b r e separation) and fineness of the fibrous material. Physical properties of hardboards have been f a i r l y w e l l 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 f i b r e s during high temperature stages (99/112)-  d e f i b e r i z i n g and pressing  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 d i f f e r e n t manner than those of papers.  Modifications effected by the d i f f e r e n t hardboard t r e a t i n g methods  should be r e f l e c t e d by measurable f l e x u r a l and dimensional changes. Four wood constituents were examined i n the f i r s t phase of t h i s study. 1.  Alcohol-benzene-solubles  Although the preserce of f a t s , waxes and resins i n wood"is known to complicate hardboard manufacture,  information as t o t h e i r precise i n f l u -  ence on f i n a l hardboard properties i s scarce. Experiments of Ogland give some lead as t o the e f f e c t of r e s i n i n hardboard.  (100)  By removing acetone-  -9-  soluble r e s i n s , a greater r e a c t i v i t y of the f i b r e surface was clalmedjtogether 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, t h i s r e s u l t should be accepted with c e r t a i n reservations. His experimental r e s u l t s show that as sodium hydroxide  concentration'was i n -  creased from 0 to 25$ with Asplund pulp s l u r r y at 2$ consistency, i n an extraction (temperature not stated) f o r 30 minutes, the r e s i n content dropped from I . 6 5 to 0.32$. from such f i b r e .  This gave a strength increase of 50$ t o boards prepared  I t i s w e l l known (67) that such a l k a l i treatments remove  other- wood and f i b r e constituents besides r e s i n , making the pulp proportiona l l y r i c h e r i n cellulose' content, poorer i n hemicelluloses, and'res'ult i n increased f i b r e f l e x i b i l i t y .  Certain of these factors could a l s o account  for the higher strength observed.  Similar sodium hydroxide  extractions by  'Runkel (111) gave the same e f f e c t , although h i s data indicate; hemicellulose removal.  No reference has been found on the s p e c i f i c e f f e c t of a l c o h o l -  benzehe solubles i n hardboards. On the basis of l i m i t e d information and c e r t a i n l y questionable r e s u l t s , the e f f e c t of extractives on the f i n a l physical properties of hardboards must be declared inconclusive. resins may influence dimensional  I t i s possible, however, that natural  s t a b i l i t y of hardboards by forming natural  s i z i n g compounds. 2.  Lignin  L i g n i n has been credited as being responsible f o r most of the inter--f -ibre strength of hardboards manufactured without r e s i n additives >  -10-  (11., 9 9 , 112,  •  .  139) • The pro'spect of " l i g n i n a c t i v a t i o n " , although allowed i n  patent novelty, i s s t i l l contraversial i n the l i t e r a t u r e . L i g n i n i s i n d e f i n i t e l y defined as an amourphous mixture of high molecular weight components ( 3 , 12, 28, 34, 117,  36, 4-2, 48,  5 5 , " 8 0 , 82,'114,  115,  128, l 4 l ) chemically bound together as a three dimensional structure,  interpenetrating the hemicellulose and c e l l u l o s e of the c e l l wall (15, 8 l , 9 8 , 105, 115,  126).  46,  Coniferous l i g n i n as an incrusting. substance occurs  i n d i f f e r e n t parts of the plant c e l l and i s composed mainly, i f not e n t i r e l y of phenyl-propane  b u i l d i n g units (12,  2 9 , 36, 42,  48,  72).  Bonding of these  units i s believed to-be accomplished by covalent linkages (>72, 8 l ? ) , i . e . , by a r y l ether linkages between the fourth carbon (C^) the beta or gamma carbon of the side chain.  on the benzene r i n g and  Bonding between the Ci). and alpha  carbon i s lefts-'., l i k e l y ( 8 l ) . The p o s s i b i l i t y of a carbon to carbon bond cannot be eliminated. This could occur between C5 of the benzene r i n g 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 i s also possible ( 8 l ) .  "  '  Evidence on l i g n i n composition has been provided by many i n v e s t i gators through mild oxidative treatments.  Thus Lindgren ( 8 l ) obtained 50$ '  v a n i l l i n and 5*5$ v e r a t r i c a c i d with free hydroxyl groups at Clj..  Isohemi-  p i n i c a c i d was' obtained i n the amount of 0 . 9 $ where the benzene nucleus carries two side-chains, and a free phenolic hydroxyl group. treated wood at high temperature amounts of coniferylaldehyde,  Goldschmid  (42)  i n the presence of water' and obtained' large  p-co imaraldehyde, v a n i l l i n , v a n i l l b y l methyl  ketone, guaiacyl acttone.and several other u n i d e n t i f i e d compounds, as w e l l as sugars and f u r f u r a l evidently from the hydrolysis of carbohydrates.  -11Repeated" hydrolysis yielded more of the same products.  In addition t o 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 a c i d test (described by De Baun and Nord (7))/than native l i g n i n , i n d i c a t i n g a more developed side-chain conjugation. The phloroglucinol-hydrochloric a c i d color r e a c t i o n was also given by dloxane s o l u t i o n of the'extracted wood as an i n d i c a t i o n of coniferylaldehyde.  This was interpreted, though, as i n s u f f i c i e n t evidence f o r i n d i c a t i o n  of any appreciable number of double bonds e x i s t i n g i n s i t u i n l i g n i n  (12).  The p o s s i b i l i t y that new double bonds are formed only during the i s o l a t i o n of l i g n i n was examined by u l t r a v i o l e t absorption spectra by Goldschmid (42), and Cabott and Purves (15). Adler (3)>  Lignin, as determined by A u l i n Erdtman (29) and  contains on the average k t o 6 monomers.  the side-chain i s s t i l l unknown (72).  The exact p o s i t i o n of  This i s mainly due t o the masking  e f f e c t that i s exerted by the free phenoloic hyroxyl group on the side-chain constitution during oxidative d e l i g n i f i c a t i o n (28,  126,  ikl) .  The phenolic  hydroxyl group, i n para p o s i t i o n t o the propane side-chain (l4J), occurs i n l i g n i n p a r t l y on one end, and p a r t l y on, monomers joined by carbon-carbon bonds.  Therefore, every l i g n i n molecule must have at least one free phenolic  hydroxyl group (3).  ""  In an i s o l a t e d state, i t was found that l i g n i n contains a l c o h o l i c and the above-mentioned phenolic hydroxyl groups, as well as aldehyde groups (72).  i t i s well known that a l c o h o l i c hydroxyls on side-chains are more r e -  active than phenolic hydroxyls.  However, the r e a c t i v i t y of d i f f e r e n t  hydroxyl groups may be. influenced by proper s e l e c t i o n of reaction conditions (72) . A l c o h o l i c hydroxyls are found t o be e a s i l y replaced by sulfate and  -12sullphite groups ( 8 l ) . Sites of reaction are the same as those f o r the format i o n of alcohol l i g n i n .  F i n a l l y , oxygen-containing r i n g s , such as lignans,  may he opened by sulphite solutions which could render l i g n i n soluble ( 2 7 , 8 1 , 82) ••" L i g n i n i s not hydrolyzed by acids, but i s e a s i l y oxidized by d i f :  ferent m i l d l y a c i d i c oxidizing agents ( 1 2 ) . tions to different tion.  I t i s soluble i n a l k a l i solu-  extents, depending on the swelling capacity of the solu-  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 t o give evidence f o r a lignin-carbohydrate complex i n wood (106).  Further evidence f o r a lignin-carbohydrate complex was supplied by  "Cabott and Purves ( 1 5 ) , Lindgren (81,) Nord and Schubert(98), Pew and Weyna ( I O 5 ) , ' Sohn ( 1 2 6 ) , and Stewart and co-workers (130) . different  They showed, through  extraction methods,that a certain portion of the l i g n i n i s chemi-  c a l l y bound t o carbohydrates, making complete l i g n i n removal from woody tissues p r a c t i c a l l y  impossible without changing the carbohydrate"composition.  In a t e c h n i c a l f i b r e separation process, wood i s subjected t o high temperatures  i n the presence of aqueous solutions.  p h y s i c a l l y and chemically (42, 11,  The l i g n i n i s changed  9 9 , 112, 128,. 139)• On the other hand,  on prolonged heating under these conditions large amounts of non-resistantcarbohydrates are dissolved with only small amounts of l i g n i n .  Thermal  decomposition of l i g 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 d i s s o l u t i o n , a self-condensation within the l i g n i n molecule has also been observed (46, 7 1 , 9 5 , 112, 1 3 9 ) .  This s e l f - .  condensation and carbohydrate loss was found t o be responsible f o r the s l i g h t 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 l i g n i n self-con-  densation on thermal treatment of l i g n i n preparations was also observed by L e v i t i f i , Thompson, and Purves (80), and Erby and Schuerch (28). According t o Boehm (11), Kollmann (65), Nowak (99), Runkel (112) and Voss (139), p r o t o l i g n i n i s depolymerized i n the f i b r e on thermal t r e a t ment; on thermal after-treatment, operations, i t i s recondensed.  as i n the hot-pressing and heat-treating  Thermoplastic c h a r a c t e r i s t i c s of l i g n i n (11,  46, 95, 99^ 112, 139) are believed t o be f u l l y u t i l i z e d i n producing wood f i b r e s from s o l i d wood,without causing extensive damage t o the f i b r e s , i n the mechanical grinding operation.  Furthermore, i n i t i a l strength of f i b r e -  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 produced boards of s u b s t a n t i a l l y higher strength a f t e r removing large amounts of l i g h i n from the f i 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 d e l i g n i f i e d f i b r e . This was interpreted as being due t o more e f f e c t i v e bonding capacity of other wood constituents than l i g n i n , r e s u l t i n g i n a better u t i l i z a t i o n of i n t r i n s i c f i b r e 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 component which, by i t s b i o l o g i c a l , 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 l i g n i n , through i t s deposition i n the basic carbohydrate structure of the c e l l w a l l , reduces only hydration and swelling of these b u i l d i n g materials.  Polyuronides  are thought t o be p a r t i c u l a r l y  -14Iriterpenetrated by l i g n i n , apparently bound both chemically and p h y s i c a l l y . This suggests a lignin-carbohydrate complex i n regions of the middle lamellae and the primary w a l l , providing wet strength of wood. Wacek arid Meralla (l4o)  see the importanceof l i g n i n i n hardboards i n i t s f i x i n g e f f e c t due t o  thermoplastic c h a r a c t e r i s t i c s .  0*gland ( 1 0 0 )  concludes that l i g n i n " i s a  hydrophobic wood constituent that prevents swelling, decreases""water' absorpt i o n but does not cause development of f i b r e t o f i b r e bonding i n hardboard. L i g n i n <: a c t i v a t i o n , through heating i n the def i b e r i z i n g , process,"could  give  a plausible explanation f o r the necessity of synthetic r e s i n additives to Asplund pulps ( 6 5 ) •  This' implies that temperatures used i n the Asplund  •defiberlzing process are not high enough t o activate l i g n i n . '.Although the chemical and physical a c t i o n of i o n i z i n g r a d i a t i o n on c e l l u l o s e has been studied extensively, information regarding e f f e c t s on l i g n i n i s vague.  According t o references c i t e d by Brauns and Brauns ( 1 2 ) ,  l i g n i n shows hardly any chemical energy e l e c t r o n s .  change when i r r a d i a t e d with a beam of high  Irradiated l i g n i n was found t o have the same degree of  s o l u b i l i t y and u l t r a v i o l e t and i n f r a r e d absorption spectra as the o r i g i n a l . lignin.  Irradiated l i g n i n also reacts strongly with  c h l o r i c acid,, giving an intense color r e a c t i o n .  phloroglucinol-hydro-  Thus,the conclusion was  drawn that.native l i g n i n i n s o l i d state i s rather r e s i s t a n t t o high energy radiation. A f t e r an extensive l i t e r a t u r e search i t can be s a f e l y stated that there has been no suggestion of a r e l a t i o n s h i p between l i g n i n and'the hardboard tempering process.  -  -  3.  Hemicellulose  The amount of hemicellulose i n woods and pulps has been the subject of numerous i n v e s t i g a t i o n s . "This follows e a r l y observations that hemicellulose r e l a t e s to the wide range of mechanical properties observed with wood pulps and regenerated c e l l u l o s e .  Few  natural products are as complex and  poorly defined i n chemical nature as those included by the term "hemicellulose"  (Ikk). Hemicelluloses are found u n i v e r s a l l y i n nature and  associated with cellulose ( 1 , 1 0 7 , 1 3 6 ) .  are"widely  The most usual hemicelluloses are  those i n which the main 'building unit i s D-xylose i n association with uronic acids, known as xylain-polyuronides ( 6 7 > 107> 1 3 6 ,  Ikk) .• Hemi celluloses are "  b u i l t up of. simple sugars; pentosans such as xylan and araban, hexosans such as manhan, galactan, glucan, and hexouronic mannouronic acids ( 8 5 ) .  acids such as glucuronic, and  The pentose L-arabinose i s believed t o •form'"'only  on  i s o l a t i o n of hemicelluloses g i v i n g r i s e to an araboglucuro-xylah of highly branched nature ( 2 5 ) . . In a d d i t i o n to the xylan-polyuronides assbelated with wood c e l l u l o s e , a group of polysaccharides occurs known,as cellulbsans ( 3 9 ) . In the case of softwoods, these polysaccharides, constitute a large portion of the n o n - c e l l u l o s i c carbohydrates^;..  Wethern (lMO  estimated t h e i r  amount i n the order of 7 5 $ of hemicelluloses i s o l a t a b l e from softwoods.  It  has been shown that hydrolysis of softwood hemicellulose gives xylose, arabinose, mannose, glucose, galactose, and ^-O-methyl-d-glucuronic' a c i d ( 8 5 , 133; 9 7 ) .  McKenzie and Higgins ( 8 5 ) , and Prey and co-workers ( 1 0 7 ) , have  found that there are no major differences i n hemicellulose constitution between plants, however, these do respond d i f f e r e n t l y to e x t r a c t i o n .  -16Decomposition of hemicelluloses goes through' the same steps as found with sugars (107, 13*0.  Goring and T i m e l l ( k k )  found that hemicel-  luloses have, on average, kO times lower molecular weight than c e l l u l o s e s with which they are associated.  Opinions on t h i s matter are not unanimous.  Molecular weight v a r i a t i o n between 19,000 and 67,000 ha6 been reported, depending on type of hemicellulose investigated (97). uronic-acid-free, water-soluble  ilh Doaglas f i r a  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 T i m e l l ( k l )  reported a range of 80 t o  330 units There i s l i t t l e known about the l o c a t i o n of hemicellulose' within the c e l l wall., I t i s believed that hemicelluloses, mainly pentosans, are located on the outer portion bf the micellar.strands of cellulose i n the secondary w a l l , p a r t l y i n close association with.cellulose and l i g n i n (5^,  68, 9k, 130, 136). Hemicellulose of d i f f e r e n t composition  can.be obtained by extrac-  t i o n with d i f f e r e n t concentrations of a l k a l i solution at d i f f e r e n t "temperatures.  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 t o 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 u l t r a v i o l e t absorption spectra (136).  Decom-  p o s i t i o n products of a l k a l i hemicellulose have been found susceptible t o condensation with l i g n i n (107, 113)> and t o thermoplastic, f u r f u r a l - r e s i n  -reconversions  (11-3).  In a c i d hydrolysis of hemicellulose monomer!c sugars ?  are produced as decomposition products.  Condensation of these sugars with  l i g n i n i s not considered possible ( 1 0 6 ) . The pentosan-lignin complex has been demonstrated by i s o l a t i o n of a l k a l i l i g n i n ( l i g n i n - x y l a n complex) (k2,  9k,  9 7 , 1 0 6 , 1 0 9 , 1 3 0 , I 3 6 ) and  by mildly a c i d i c methanol extraction of wood at high temperatures  (129).  Calculations of Jayme ( 5 4 ) show 3 « 5 # l i g n i n bound chemically to hemicelluloses\  The removal of'either component r e s u l t s 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 q u a l i t y and properties of c e l l u l o s i c  materials has been emphasized more i n recent years than e a r l i e r ( I 3 6 ) .. These wood polysaccharides may  lend valuable c h a r a c t e r i s t i c s to cellulose  f i b r e s but, on the other hand, have some undesired e f f e c t s . known from numerous investigations ( 8 5 , 1 3 6 , e s p e c i a l l y the polyuronides  —  140,  1^3)  Thus i t i s  that hemicellulose --  through t h e i r physical and chemical  proper-  t i e s , and obviously by t h e i r s p e c i a l p o s i t i o n i n the c e l l w a l l , exert a s p e c i a l bonding e f f e c t between i n d i v i d u a l f i b r e s i n paper sheet Fineman ( 3 l ) > and Triber and co-workers ( 1 3 6 ) , phases i n pulp:  d i s t i n g u i s h two  formation. cellulosic  the highly c r y s t a l l i n e phase -- the bulk of the  fibre—  and the amorphous, water-sensitive hemicellulose. Generally, hemicellulose i s believed'to be responsible f o r the strength of papers.,Swanson ( 1 3 1 )  determined an optimum hemicellulose con-  tent --at which maximum bonding strength i s obtained. ( 8 6 ) found hemicellulose important  McKenzie and Higgins  to f i b r e p h y s i c a l 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  -18Cottrall" ( 1 8 ) , depends not only on the extent of the f i b r e bonded area developed by f i b r e 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 -  s i c strength of the bond ( 6 0 ) .  C'ottrall (18) also believes that the plas-  t i c i t y of f i b r e s must be r e l a t e d t o t h e i r swelling capacity i n water.  He  found that greater amounts of hemicellulose, as shown by pentosan content, produced greater swelling capacities of f i b r e s as r e f l e c t e d by t h e i r water This was v e r i f i e d by Watson and co-workers (lV3).~  'retention.  McKenzie and  Higgins (85) l i k e n hemicellulose with i t s i n a b i l i t y to crystallize'. The i n t e r n a l pressure developed upon swelling aids " f i b r i l l a t i o n of the f i b r e s i n beating.  Swollen hemicellulose renders the f i b r e surface "tacky" and  reconstitutes i n t o a s o l i d bond on drying.  This suggests that non-cellu-  l o s i c polysaccharides function as adhesiyes during sheet formation  of  papers (1^3) • The importance of hemicelluloses i n board strength development was a l s o recognized by Klauditz (67, 68, 6 9 , ) Klauditz and Stegman (71), C)gland (100), Runkel (112), Runkel and Wilke (113) and Wacek and Meralla ( l 4 o ) . The r o l e of hemicelluloses i s mainly viewed from the standpoint of strength development on r e c o n s t i t u t i n g the wood f i b r e from water i n t o board by hotpressing, and by further heat-treatments.  These investigators are opposed  to the theory of " l i g n i n a c t i v a t i o n " , but considered hemicelluloses e i t h e r by d i r e c t bonding e f f e c t on the f i b r e (69, JI,  100), or by changed state  into furfural-base resins (112), as being responsible f o r the strength of hardboard. Admittedly,' i n a l l phases of thermal treatments occurring during hardboard manufacture, d r a s t i c changes take place i n c o n s t i t u t i o n of both  -19l i g n i n and hemicelluloses.  The hydrolyzing e f f e c t on hemicelluloses at high  temperature, i n prescence of water, cannot be overlooked (5*0 . Under these conditions a c e t i c a c i d and small quantities of formic a c i d are formed, mainl y from xylans (112).  The p o s s i b i l i t y of f u r f u r a l formation from hemicellu-  lose and polycondensation with l i g n i n has already been mentioned. Prey, Waldmann and Stiglbrunner (106)  and Klauditz (66)  groups are. s p l i t o f f from wood on a l k a l i treatment.  Similarly,  found that a c e t y l  This r e s u l t s • i n pro-  ducts with lower strength and greater water s e n s i t i v i t y , although the l i g n i n is l e f t intact.  They a t t r i b u t e d t h i s e f f e c t to losses i n 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 c h l o r i t e method described by Jayme (55)-  A f t e r drying and board formation of the d e l i g n i -  f i e d materials they obtained greater strengths than with samples i n the original state.  Furthermore, similar improved strength and  dimensional  s t a b i l i t y have been observed on d e l i g n i f i e d samples given pcst-pressing heattreatments.  This phenomenon was  proportions of carbohydrates,  interpreted as being due to the increased-  increased i n t r i n s i c ' f i b r e strength i n the  d e l i g n i f i e d materials, and to the f a c t that technological properties of paper-making f i b r e s were greatly improved by l i g n i n removal.  The" analysis  of v o l a t i l e condensates r e s u l t i n g from heat-treatment, gave i.21$  water,  a c e t i c a c i d 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' l i g n i n , but causes chemical and physical changes to hemicelluloses.  -20Kumar mechanism  with  for  the  high  ing  process.  acid  part  able  groups  reported  hardboards.  strength.and The  of  formation  (73)  the or  is  made  the  water-repelling  formaldehyde  k.  Cellulose  aspects  dimensional  attacks  of  some  He b e l i e v e d  statement o i l  on  without  ether in  possible  obtained  oil-tempering  i n  experimental  fibre  He  opinion,  are  responsible  the  oil-temper-  evidence,  hemicellulose,  bridges. his  a  hemicelluloses  stability  wood  which,  that  of  further  producing gives  provides  that  the  reduce-,  credit  to  hydrophobic  methyl  bridges.  Cellulose relatively This  is  uniform  one  molecular  is  a  naturally  structure  reason  behind  configuration  it  the  and  occurring  forms  large  fine  of  cellulose  (23)-  of  holocellulose.  units  unit  bonds  favourable  with  is  formed  It  is  neighbouring of  amorphous  tern  chains  regions  (6l).  a  a -degree  high of  being It  that  the  are  degree  is  comprised two  (13>  and  amorphous  regions  from  do  order  polymerization  not  crystallite  (79)'  from  600  by  groups may 110)  regions  to  (79)  6,000  (6l). form  . (6l,  represent  sharp  Lee to  90,  on  the  poly-  anhydroglucose  units  87,  its  hydrolyzable  of  hydroxyl  6l,  characterized of  difficultly  anhydroglucose  groups  these  stretch  the  average,  crystalline  crystallites  indicating  reported  accepted  Cellulose  The  on  hydroxyl  interspersed  generally  phases.  location  as  of  macromolecule.  structure  fraction  i n  a  available  saccharide  groups  of  information  considered  on the  example  Because  of  is  containing,  good  polymer.  amount  Cellulose  each  a  high  and  hydrogen  Cellulose 79>  two  110).  different  crystallite  x-ray  Hydroxyl  through  diffraction Rollins  monomeric  (110)  anhydro-  pat-  -21glucose u n i t s . More recent i n v e s t i g a t i o n by Goring and Timell (1+3) gives an average degree of polymerization f o r wood cellulose between 7,000 and 10,300, depending on the .-.starting material and e f f i c i e n c y of the n i t r a t i o n procedure.  For native c e l l u l o s e , a weight-average degree of polymerization  of 15,000 and higher may be obtained, which would correspond to a molecular weight of 2.5 m i l l i o n .  Because of close hydrogen bonding, the C r y s t a l l i t e s  are very r e s i s t a n t to swelling e f f e c t s that can be produced by water and other polar solvents (90, 6 l ) . V i s c o s i t y of cellulose solutions i s considered as one of the most important  t e s t methods for characterizing c e l l u l o s e .  Strength properties-of papers.  I t i s related to  V i s c o s i t y change during processing, and  strength of the f i n i s h e d product, have been found t o be d i r e c t functions of cellulose chain length (DP) (91). The amorphous regions a r e l b u i l t up of short-chain polymeric units with an average degree of polymerization of 200, and a.molecular weight of 30,000.  C o l l e c t i v e l y , these polymers are c a l l e d hemicelluloses and Include  the previously discussed pentoses, hexoses, and polyuronic acids (18, 6 l ) . In wood f i b r e s the major part of the c e l l u l o s i c 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  c r y s t a l l i n e o r i e n t a t i o n p a r a l l e l 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 f i b r e s i n a s p i r a l - l i k e manner (23, 110, kk).  K l a u d i t z (67) draws a s i m i l a r i t y between reinforced  concrete and the wood structure; where cellulose would represent the r e i n forcing s t e e l bars;  hemicelluloses would be the t i n y wires holding the  bars together within the structure and the l i g n i n would represent the concrete, 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 f i b r e s .  To obtain a firm bond  on dewatering of papers, the f i b r e s must be brought i n close enough contact for the formation of. hydrogen bonds between the active cellulose surfaces.  At the same time, the environment on the c e l l u l o s e surface must be  favourable f o r 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 f o r hydrogen bonding rather than bonding with the water molecules .  This occurs with higher frequency as more and more water i s removed.  For hydrogen bonding to occur, the hydroxyl groups of the cellulose must be oriented outward.  fibrils  The strength of paper i s thus determined by the  number of hydrogen bonds that are formed during the drying process  (13)•  However, since-the occurrence of such bonds i n paper i s r e l a t i v e l y low,  the  strength of paper must be dependent mainly on i n t e r - f i b r e bonding, afforded by the hemicelluloses, and f i b r e arrangement i n sheets of papers, and only to a l i m i t e d extent on hydrogen bonding. E l a s t i c properties of f i b r e s are improved by removal of l i g n i n and hemicellulose ( 6 9 ) • fibre —  By increasing the cellulose, content i n the wood  through the removal.of other wood constituents —  a strength i n -  crease i s obtained as. evidenced by the increased breaking length"of a paper sheet".  Unfortunately, the wet-strength  of such papers i s p r a c t i c a l l y zero-  On drying the sheet, good strength i s obtained.  The breaking length reaches  a minimum as more and more hemicellulose i s removed.  This was explained as  being due to the unsatisfactory.b.onding e x i s t i n g between c e l l u l o s e molecules in situ ( 6 7 ) .  Alpha c e l l u l o s e —  the residue remaining a f t e r extraction of  holocellulose with 1 7 * 5 $ caustic solution —  contains extraneous hexoses and  -23pentoses i n small amounts detectable only by chromatographic methods (1, 110 ) . Investigations of i n t r i n s i c f i b r e strength showed that the cellulose i s the chief chemical portion of the f i b r e influencing the i n t r i n s i c f i b r e strength (60.  In hardboard strength development, major consideration must be given  to the wood "gluing" constituents i n which l i g n i n and c e l l u l o s e hardly p a r t i cipate ( 6 5 ) . F i n a l l y , experiments of Fisher ( 3 2 ) 1  showing that the swelling  and water r e t e n t i o n of cellulose can be regulated by r e s i n and p l a s t i c i z i n g additives, r e s p e c t i v e l y , thus reducing water pick up and shrinkage under c e r t a i n 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 e f f e c t of high-energy i r r a d i a t i o n pf wood,' show marked degradation of the polysaccharide p o r t i o n .  I r r a d i a t i o n of sugar solutions gives strange  r e s u l t s such as inversion and increase of s o l u t i o n a c i d i t y . changed to uronic acids i n good y i e l d s .  Hexoses were  The i r r a d i a t i o n of polysaccharides  resulted i n decreased v i s c o s i t y , an increase i n reducing power and increased a c i d i t y of s o l u t i o n s . Winogradoff (148) found a decrease i n t e n s i l e strength of cellulose materials which he interpreted, based on x-ray d i f f r a c t i o n studies, as being due to decrease of c r y s t a l l i n i t y . (77,  Lawton and co-workers  7 8 ) obtained a completely water-soluble f i l t e r paper when i r r a d i a t e d  at 3 . 3 x 10  • •  megarads.  At small dosages of 10  6  equivalent roentgens, Seaman  and co-workers (122) found very l i t t l e change i n wood, but by further increasing i r r a d i a t i o n dosages a decrease i n the degree of polymerization  was  Q  observed.  They obtained a water-soluble  cellulose at 10  rads.  Degradation  of c e l l u l o s e by gamma i r r a d i a t i o n may follow two mechanisms*, d i r e c t chain  -24-  s c i s s i o n at the aeetal linkage, or an oxidative process following i n i t i a t i o n caused by the energy of i r r a d i a t i o n ( 1 6 ) . Depolymerization i s not affected by degree of c r y s t a l l i n i t y . Blouin and co-workers ( 9 ) i r r a d i a t e d p u r i f i e d cotton and found an increase i n carbonyl and carboxyl groups and chain-length cleavage i n the r a t i o of 20:1:1. carboxy groups).  (Twenty times more aldehyde groups were formed than  The DP decreased from 4,400 to 5 6 as r a d i a t i o n dosage  was increased from 0 t o 1 0 8 rads.  I r r a d i a t i o n to 107 rads r e s u l t e d i n DP  values of 1 8 0 i n oxygen and 210 i n nitrogen atmosphere.  Water s o l u b i l i t y  of cellulose increased from 0.1 t o 10.4$. A water s o l u b i l i t y of 0 . 5 $ was obtained at 10? rads.  No difference was found i n infrared absorption  spectra of i r r a d i a t e d c e l l u l o s e .  Smith and Mixer (124) showed that natural  aromatic compounds, such as l i g n i n and extractives, exerted a s l i g h t protec t i v e e f f e c t (approximately 3^$) on the radiolysis. of redwood c e l l u l o s e . e f f e c t has been found on gross a n a l y t i c a l composition of wood.  No  Moisture  pick-up'was found to be lowest at 5 x 1 0 ? rads. In summary, while Cobalt 6 0 i r r a d i a t i o n does not -affect the analy t i c a l composition of wood, i t may influence the degree of polymerization t o such an extent that water-insoluble c e l l u l o s e i s made completely soluble, thus reducing the i n t r i n s i c f i b r e strength as degree of polymerization i s randomly decreased. . No reference has been found dealing with any aspect of cellulose and tempering o i l i n t e r a c t i o n of hardboards. 5«  Tannins and other polyphenolic wood extractives'  The bark of different'; wood species, as w e l l as other parts of plants and trees, contain naturally occurring tannins i n d i f f e r e n t amounts.  -25Tannins f i n d wide u t i l i z a t i o n i n the leather industry, and In the drug i n ~ dustry as antioxidants. Dihydroquercetin ( t a x i f o l i n ) , a 3"by<iroxy flavanone, has been found i n Douglas f i r heartwood.  I t has been i d e n t i f i e d by Pew  (103, 10k)  l a t e r described by Gardner and Barton (35), and Kurth and Chan (76).  and  Dihydro-  quercetin i n Douglas f i r heartwood was found i n the amount, of 1.5$ by Gardner and Barton (35) and shown to be responsible f o r the d i f f i c u l t i e s encountered i n calcium-base sulphite pulping of t h i s species by Pew Adler (2), and Adler and Stockman (k)  s  (103)°  found similar e f f e c t s of  catechin tannins on unpeeled, f l o a t e d spruce logs used f o r pulp production" purposes.  It-was observed that unpeeled spruce logs, f l o a t e d over the sum-  mer months, gave higher amounts of screenings a f t e r sulphite pulping than logs peeled before water storage. A f t e r a thorough i n v e s t i g a t i o n of poss i b l e causes of t h i s phenomenon.it was found that tannins of the catechin type penetrated the sapwood portion of the logs, r e s u l t i n g i n an insoluble lignin-phenol condensation product when such wood i s exposed to higher temperatures such as encountered, i n pulping processes.  The Isolated tannis  were found to belong t o the d-catechin family, giving an intense v i o l e t color r e a c t i o n when treated with a solution of s u l f u r i c a c i d and methanol i n the' volumetric r a t i o of Itk  (2).  The l i g n i n - t a n n l n complex has been'shown  to e x i s t through methanol extracts of such "damaged wood".  Color reactions  both of the s u l f u r i c acid-methanol and phloroglucinol-hydrochloric acid' type were obtained, proving the presence of d-catechin tannin, and coniferylaldehyde r e s u l t i n g from l i g n i n , r e s p e c t i v e l y .  This color reaction i s not  given by^ hydrolysable tannins, such as g a l l i c a c i d  (2).  -26-  Reaction between l i g n i n and d-catechin i s believed t o take place between the benzyl alcohol groups of l i g n i n and the reactive positions of the polyphenyl nucleus of the d-catechin giving an unreactive l i g n i n - p o l y phenol complex i n wood.  The. usual mechanism of l i g n i n sulphonation d i d not  occur, thereby giving r i s e t o an unusually high amount of screenings.  The  removal of t h i s l i g n i n p o l y p h e n o l complex from wood by 1 N sodium hydroxideT  formaldehyde solution was without, success (4). 6.  Heat-treatment  Heat-treatment mills.  of pressed hardboards  has today become common practice in.most' hardboard  The function of heat-treatment  p r o p e r t i e s of the boards.  i s t o improve f l e x u r a l and "dimensional  The chemical composition of hardboard-composing  wood f i b r e s i s changed by removing c o n s t i t u t i o n a l water, r e s u l t i n g i n higher strength and dimensional s t a b i l i t y ( 5 9 , 4 7 ) . In addition, the cure of r e s i n additives i s carried t o completion. The mechanism of heat-treatment  i s s t i l l somewhat obscure, possibly  the r e s u l t of complications a r i s i n g from the lignin-carbohydrate complex. The theory of l i g n i n recondensation' as opposed to complete dehydration of hemicellulose i s s t i l l not completely s e t t l e d .  According t o Klauditz ( 7 1 )  the firm bond between f i b r e s r e s u l t i n g from thermal treatment of wood and fibreboards i s due t o re-gluing the c e l l u l o s e residues of the c e l l walls within t h e i r middle lamellae and primary walls by hemicelluloses, i n p a r t i cular by polyuronides. of  The. strength increase can hardly be due t o increase  i n t r i n s i c f i b r e strength, but must be a r e s u l t of the dehydration of  hemicellulose, thereby increasing the f i b r e t o f i b r e bond area ( 7 1 , 1 0 2 ) . The increased f i b r e bond strength gives r i s e t o a better u t i l i z a t i o n of  -27i n t r i n s i c f i b r e strength (71) • P a r a l l e l t o t h i s , heat-treatment causes reduced moisture re-absorption of the f i b r e s .  Heat-treated boards do not  reach the moisture content of untreated boards when subjected t o "similar atmospheric conditions, i.e.»their equilibrium moisture content i s reduced (it-7, 71, 112). The e f f e c t of heat-treatment on the f i b r e t o f i b r e bond cannot be f u l l y r e a l i z e d since the strength of i n d i v i d u a l f i b r e s i s already u t i l i z e d up t o 70 to 80$. Additional information on e f f e c t s of heat-treatment of hardboards i s given by Morath (95), Ogland (101), Ogland and Emilsson (102), Runkel (112) and Voss (139) • Voss (139) points out a few process variables that influence physical properties of heat-treated hardboards.  By heat-treatment at 170 to  180° C. the strength properties are i n i t i a l l y increased (bending and t e n s i l e strength, and modulus of e l a s t i c i t y ) t o a maximum of 50$ (kj, 112). Prolonged heating r e s u l t s i n decrease of f l e x u r a l properties.  Factors working  together i n t h i s process are l e v e l of temperature and duration of heat-treatment.  Decrease i n f l e x u r a l properties i s due to the r i g i d i t y of f i b r e s that  i s acquired by overdrying them (127)•  Along with increase of modulus of  e l a s t i c i t y , the l i m i t of proportionality i s raised p r a c t i c a l l y to the point of rupture. However, these properties are much dependent upon moisture content at the time of t e s t i n g .  Kumar (7*0 found that an increase i n moisture  content from 3 t o 12$ decreased modulus of rupture by 40$ and' modulus of e l a s t i c i t y by i+5 t o 50$. On the other hand, the hygroscopic properties did not change a f t e r a certain period of heat-treatment. Unfortunately, one must be s a t i s f i e d with l e s s than the maximum improvement bf dimensional stability.  An improvement of only 25$ i s obtained with commercial heat-  treatment (kf,  112).  -28-  The l e v e l i n g o f f of hygroscopic improvement and point of maximum strength do not coincide, maximum strength being f a r below the point of maximum dimensional s t a b i l i t y .  Voss (.139) regards both f l e x u r a l and dimen-  sional improvements'as being due t o recondensation of l i g n i n on one hand, and t o shrinkage and losses of water of constitution from the c e l l u l o s i c regions on the other.  The loss of hydroxyls i s believed to r e s u l t i n more  hydrophobic ether bridges, or hydrogen bonding as observed with paper by Mark (90).  McKnight and Mason (88) credit the improved hygroscopic proper-  t i e s of wood t o the lowered water sorption of the heat-treated l i g n i n .  The  p o s s i b i l i t y of reorganization i n the cellulose chain system i s mentioned with certain reservations.  Heat-treatment  also r e s u l t s i n darkening of boards,  probably because of t h e i r mild oxidation i n the presence of a i r (139) •  7.  Oil-tempering of pressed  hardboards-  Information about oil-tempering of hardboard i s scarceports on hardboards  recognize only the importance  of oil-tempered  Most r e hardboards  but do not go i n t o extensive discussion of other than some aspects of process variables and r e s u l t i n g 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 r a r e l y used because boards treated with i t acquire an unpleasant and l a s t i n g odor.  Just recently, June I 9 6 I , U.S. patent No.  2,988,462 was issued to the Masonite Corporation f o r the use of hydrocarbon drying o i l s f o r the impregnation of l i g n o c e l l u l o s e hardboard (51)-  Heating of the o i l f a c i l i t a t e s easier and better board penetration.  The  discovery that l i m i t e d o i l absorption gives r i s e to maximum strength and dimensional  improvement upon tempering (73, 95) has lead t o thinning of  o i l s with d i f f e r e n t organic solvents.  Morath (95) found that o i l i n  excess of 15 t o 20$ i s wasted since i t only r a i s e s s p e c i f i c gravity of the boards without  giving the benefits of further strength improvement.' Thin-  ning of o i l s promotes penetration and gives means f o r c o n t r o l l i n g 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 d i f f e r e n t method f o r incorporating o i l i n hardboard.  They incorporated d r y i n g - o i l i n hardboard by dispers-  ing a f i n e l y - d i v i d e d , f a t - s o r b i n g material i n the s l u r r y , carrying an appre-.. ciable-amount of the d r y i n g - o i l .  From the r e s u l t i n g s l u r r y a mat i s formed  and oil-tempered hardboard produced by one of the conventional hardboard manufacturing processes.  The method would r e s u l t 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 e s s e n t i a l l y _ t h e same as discussed i n the foregoing s e c t i o n .  I t should  be pointed out that r e s u l t s of oil-tempering are not the same as those of heat-treatment a l o n e i  The 25 to 50$ strength increase by heat-treatment i s  r a i s e d t o 80 t o 110$ i n the oil-tempering process.  Similarly,, dimensional  s t a b i l i t y i s increased to 35 t o 50$ as compared t o 25$ obtained by heattreatment.  According to Kumar (73), the l e v e l of temperature i s set only  by the danger of s e l f - i g n i t i o n . , However, too high temperature may r e s u l t i n " l o s s of strength and extensive darkening of the board surface due t o heavy oxidation;  Temperatures i n the range of 165 t o 175° C  safely meet  ^  -30a l l requirements f o r oil-tempering of hardboards. The chemical mechanism of the process i s completely unexplored* Kumar (73)  has speculated that hemicellulose i s the causal f a c t o r , as has  been discussed. 8.  Humidification of pressed :hardboards  Tempered as well as untempered hardboards are humidifed a f t e r thermal treatment.  Boards come from the hot-press or heat-treating chamber  p r a c t i c a l l y oven-dry. i n t h i s state (7^)  Although boards are at t h e i r highest strength values  they are extremely unstable dimensionally u n t i l they  reach equilibrium with the surrounding atmosphere.  Humidification i s  designed t o hasten and control the process of reaching equilibrium through use of controlled temperature and r e l a t i v e humidity (20>  135)-  The desired  equilibrium moisture content of 8 t o 10$ depending on regional atmospheric conditions, i s heat s t a b i l i z e d i n the boards over a certain period bf time by keeping the boards i n 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 d i f f e r e n t atmospheric conditions.  -31-  MATERIALS AND METHODS . A.  Selection and Preparation of Materials 1.  C o l l e c t i n g the fibrous material  Douglas f i r Asplund f i b r e served as s t a r t i n g material f o r t h i s study.  This was obtained from the production l i n e of Canadian Forest  Products Limited, P a c i f i c Veneer and Plywood D i v i s i o n , New Westminster, B r i t i s h Columbia.  The point f o r c o l l e c t i o n was chosen as the outlet open-  ing of the Sprout Waldron r e f i n e r (Model No. 3 6 - 2 ) . p r i o r to size addition and consistency r e g u l a t i o n .  At present, two types of f i b r e are produced  i n t h i s hardboard plant, one, a coarser f i b r e used f o r the manufacture of t h e i r regular hardboard, while the other, c a l l e d " l / 8 - i n c h f i b r e " , i s used as f u r n i s h f o r special purpose boards such as printed hardboard.  This l a t -  ter type of f i b r e was selected because of i t s more uniform r e f i n i n g ! I t was anticipated that t h i s f i b r e would react more uniformly i n chemical treatments, provide better board formation and give good texture to" t h i n fibreboards produced from i t .  The f i b r e was refined at a plate s e t t i n g of  0.030-inch and gave a Bauer-McNett f i b r e c l a s s i f i c a t i o n as shown In Table 1 Enough material was collected at one. time t o s a t i s f y the needs of the whole-experiment.  It'was gatherd.at approximately 30$ consistency by  hand squeezing, weighed t o estimate amount, r e - s l u r r i e d i n a large vessel and washed with tap-water t o neutral pH.  The procedure aimed' at thorough  mixing of the.sample, as w e l l as adjustment of pH f o r control of acid hydro l y s i s during prolonged storage i n wet condition.  I t has been shown by  Klauditz ( 6 8 ) , Runkel ( i l l ) , Stewart and co-workers ( 1 2 9 ) , and Voss (139) that a c e t i c . a c i d and formic a c i d are responsible f o r hydrolytic degradation  i n the l i v i n g tree on one hand.  These same acids are formed during.the  high-temperature d e f i b e r i z i n g process, r e s u l t i n g 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 r e - c i r c u l a t i n g the drainage water. the mat was  After f i n a l  dewatering  s l i g h t l y cold-pressed to remove excess water, placed i n a  polyethylene bag, and stored at 1 5 °  C.  Chemical properties of the raw f i b r e are described i n l a t e r sections.  ' 2.  t  Tempering o i l  Fresh, commercial tempering o i l was machine at the above hardboard m i l l . experiment, was  obtained from the o i l dipping  An amount, s u f f i c i e n t f o r the whole  collected and stored i n a sealed can u n t i l further"use.  raw o i l i s manufactured by Imperial O i l L t d . and mixed with other  The  necessary  ingredients (linseed o i l , possibly maleic anhydride) at Reichhold Chemical (Canada) L t d . , Port Moody, B r i t i s h Columbia. nature and s p e c i f i c a t i o n s of the o i l was  A l l jinformation regarding the  obtained from Chemical Products  Department, Imperial O i l Ltd., Toronto, Canada ( 2 1 ,  26).  "CTLA Polymer" (the commercial name of t h i s tempering o i l ) i s a pre-polymer of cracked naphtha gas o i l f r a c t i o n which contains straight, branched and c y c l i c mono- and d i - o l e f i n e s , naphthenes, as w e l l as normal and i s o - p a r a f f i n s .  I t i s heat-reactive and i s prepared by p a r t i a l polymer-  i z a t i o n of o l e f i n s over hot clay.' The polymer, being highly unsaturated, dries by both oxidation and polymerization.  A c h a r a c t e r i s t i c property of  the o i l i s i t s tendency for depolymerization or rearrangement on extensive heating.  This has been observed as an inherent c h a r a c t e r i s t i c of d i c y l c o -  pentadienes with an endo-methylene bridge In the molecule.  To reduce heat  -33required f o r polymerizing i s made.  the o i l , one per cent maleic anhydride addition  This provides a new polymer of the "CTLA Polymer", which i s  claimed t o give greater strength and better f l e x i b i l i t y " t h a n can be obtained by heat soaking with "CTLA Polymer" alone.  The reduced heat require-  ment also lessens the danger of s e l f - i g n i t i o n i n the hardboard tempering process.  The tendency f o r depolymerization on prolonged heating i s further  reduced by addition of certain amounts of linseed o i l . "CTLA Polymer" i s soluble i n aromatic, p a r a f f i n i c and chlorinated hydrocarbons, acetates, ketones, and alcohols above butyl alcohol ..' .It i s compatible with various d r y i n g - o i l s , 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 r o s i n , r o s i n esters, coumars, modified alkyds, modified  phenolics,  natural and synthetic rubbers, and n i t r o c e l l u l o s e . "CTLA Polymer",is used extensively i n other industries,, such as core o i l t e s t i n g , where i t replaced natural d r y i n g - o i l s such as linseed o i l . Specifications and some t y p i c a l properties of "CTLA Polymer" are given i n Table 2.  B.  Extraction and Modification of Fibre  Constituents  Investigation of the proposed hypothesis c a l l e d f o r two major types of treatments, those done on the Asplund f i b r e arid those applied t o prepared fibreboards. are non-destructive  The l a t t e r are described i n another section.  Both  i n that only part of the f i b r e i s removed, modified or  altered when a p a r t i c u l a r variable i s under i n v e s t i g a t i o n . Fibre treatments were believed t o be most adequate f o r removal or p a r t i a l d e a c t i v i a t i o n of the particular, wood constituents most commonly con-*  -34sidered as influencing physical properties of wood.  P a r t i c l e size of the  raw material (Asplund f i b r e ) made i t possible to carry out f i b r e treatments, similar to those used i n a n a l y t i c a l investigations, with f a i r degrees of uniformity and r e p r o d u c i b i l i t y .  As anticpated, t r i a l treatments on small  samples were reproduced on larger scale without change of procedures.  In  every case an a n a l y t i c a l method with known action on the wood has been f o l lowed for a c e r t a i n treatment. was  S u i t a b i l i t y of the method to t h i s purpose  f i r s t v e r i f i e d using a c l o s e l y controlled range of v a r i a b l e s .  By t h i s  method, treatment conditions were worked out that gave best r e s u l t s . Thus, i n d i v i d u a l treatments were shown as being e f f i c i e n t i n removal or a l t e r a t i o n of a p a r t i c u l a r wood constituent, with the l e a s t possible change i n other wood constituents and the f i b r e structure i t s e l f . Wood constituents most often discussed i n the l i t e r a t u r e as i n f l u encing paper and hardboard physical properties were examined i n preliminary experiments. .These included quantitative (alcohol-benzene solubles, l i g n i n , and hemicellulose) and q u a l i t a t i v e ( c e l l u l o s e , and deactivated l i g n i n ) manipulations of the f i b r e material.  1.  Extration of alcohol-benzene solubles  The extraction procedure was Standards T  e s s e n t i a l l y that prescribed by TAPPI  6m-54. The purpose of t h i s treatment was to remove natural  resins, f a t s , o i l s and waxes found i n Douglas f i r i n the amount of (based on the oven-dry weight of o r i g i n a l wood) (75)>  9-6$  as w e l l as prepara-  t i o n of the raw material (Asplund f i b r e ) for d i f f e r e n t chemical treatments. Although Ogland (100) has reported that acetone-extracted fibreboards of higher strength, t h i s solvent was  f i b r e produces  avoided because of i t s  -35swelling e f f e c t on wood. Alcohol-benzene  extraction i s also a customary  pre-treatment f o r wood and f i b r e before extraction of other chemical components. A large Soxhlet  apparatus was used f o r f i b r e extraction with an  f  alcohol-benzene/mixture  i n the volumetric r a t i o of 1:2.  as the a l c o h o l i c component.  Methanol was used  Each fibre<batch,approximately 200 g. oven-dry,  was extracted f o r 8 hours with number of siphonings regulated t o 7 to- 8 per hour.  A f t e r completion of extration the f i b r e was washed through with  methanol and then with hot water.  The wet fibre .was spread out and"air/  dried f o r one week. 2.  Removal of l i g n i n  A choice of methods i s available f o r removing l i g n i n from wood. Preference was given t o methods that would s e l e c t i v e l y 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 c o n s t i t uents . An optimum method should a f f o r d an undisturbed examination of the changes i n the interaction-induced strength i n p a r t i a l or complete absence of l i g n i n from the fibreboard, made of such treated f i b r e .  Furthermore,  close control on the amount of l i g n i n removed i s d e s i r a b l e .  The-method  should also be adaptable t o preparation of larger amounts of f i b r e with acceptable r e p r o d u c i b i l i t y . D e l i g n i f i c a t i o n may be defined as the process of removing l i g n i n present i n wood, or woody plants (12, 1^9). In a technical sense the process i s synonymous with chemical pulping, and subsequent bleaching (8, 37)• D e l i g n i f i c a t i o n aims at i s o l a t i o n of a more of less pure c e l l u l o s e , or at  -36the intermediate product h o l o c e l l u l o s e .  An a n a l y t i c a l d e l i g n i f i c a t i o n  involves removal of l i g n i n with a minimum amount of h y d r o l y t i c and' oxidat i v e a c t i o n on c e l l u l o s e and associated polysaccharides.  These constitute  holocellulose or the entire polysaccharide f r a c t i o n of the wood. (6, 50, 55, 150) . The three mechanisms believed t o be involved i n d e l i g n i f i c a t i o n are hydrolysis ( a ) combination t  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 (b), and degradative breakdown of l i g n i n i n t o smaller f r a g ments causing ready s o l u b i l i t y ( c ) .  a.  That some part of the l i g n i n goes into solution;on b o i l i n g  wood with hot water has been demonstrated by Goldschmid (42), K l a u d i t z (66), Runkel  (111), Sohn (126) and Stanek (128) . The preparation of "native  l i g n i n " by e t h y l alcohol (or methyl alcohol) extraction of wood has been used i n a n a l y t i c a l experimentation  (12).  Extensive reviews on l i g n i n  i s o l a t i o n by a l k a l i n e hydrolysis of wood and u t i l i z a t i o n of the a l k a l i l i g n i n s i s given by Brauns and Brauns (12)  b.  and Merewether (93, 9 4 ) .  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 f o r major pulping processes.  For example, l i g n i n can be rendered soluble by cooking with  a c i d s u l p h i t e s . The solute, In the form of lignosulphonic a c i d , has provided material f o r many investigations on l i g n i n structure (27, 34, 36, 80, 8l,  82).  Commercial pulping processes do not remove a l l l i g n i n from the  wood during cooking because"of solvent d i f f u s i o n and complete s o l u b i l i z a t i o n d i f f i c u l t i e s i n s u p e r f i c i a l regions i n the c e l l w a l l .  Attempts t o further  reduce l i g n i n by these procedures r e s u l t i n severe hydrolysis of. the., poly-  -37saccharlde portion as evidenced by losses i n y i e l d , pulp v i s c o s i t y ,  and  paper strength ( 8 , V 3 , 8 l ) . cjv  Degradative breakdown of l i g n i n into smaller fragments  causing  ready s o l u b i l i t y i s by f a r the most e f f e c t i v e method of removing l i g n i n . This i s accomplished by oxidative treatments which have the great advantage of s e l e c t i v i t y , i.e.,low degrading a c t i o n on the c e l l u l o s i c portion of wood ( 8 , 6k).  This c h a r a c t e r i s t i c of controlled oxidation i s f u l l y u t i l i z e d i n  pulp bleaching  (8).  In oxidations with more or l e s s strong o x i d i z i n g agents such as hydrogen peroxide, hypochlorite, chlorine dioxide, chlorine, a c i d i f i e d sodium c h l o r i t e solution, nitrobenzene, t - b u t y l hypochlorite and numerous solutions containing active chlorine, the amount of l i g n i n removed i s dependent on reaction conditions —: time, s o l u t i o n concentration, pH, and temperature -- and the r e l a t i v e amount of l i 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 h i s control of r e a c t i o n conditions.  Careful control gives s i m i l a r  r e s u l t s with d i f f e r e n t o x i d i z i n g agents ( 5 0 ) . A number of o x i d i z i n g agents were t r i e d under d i f f e r e n t reaction conditions i n preparation for t h i s study.  This was  necessary to determine  procedures for removal of controlled amounts of l i g n i n , and for quantitat i v e oxidation of l i g n i n without s o l u b i l i z a t i o n . I t soon became evident that the sodium c h l o r i t e method o f f e r s great advantages over a l l other oxidation procedures for the removal of controlled amounts of l i g n i n from Asplund pulp;  The  set-up i s r e l a t i v e l y  simple, the amount of l i g n i n removed i s a time-or treatment-dependent v a r i able when other factors are kept constant.  The preparation of cooking  chemicals i s not too elaborate as compared t o some of the other procedures.' The method was  e s s e n t i a l l y that described by Jayme ( 5 5 ) , further  r e f i n e d by Wise and co-workers  Investigations of the method by Barton (6), Brauns and Brauns (12), (38),  Huang (50),  (6k).  (150), and c i t e d by Koeppen and Cohen  Koeppen and Cohen (6k)  and Rapson (108)  Giertz  show that sodium  c h l o r i t e i n s l i g h t l y a c i d i c medium has only very mild a c t i o n on c e l l u l o s e , but s p e c i f i c a l l y attacks l i g n i n i n wood.. Chlorine dioxide — reaction mixture i n the presence of aldehydes — hols and carbohydrates.  formed i n the  i s unreactive toward a l c o -  Under s p e c i f i c conditions, c h l o r i t e solutions have* (6k).  the same a c t i o n as chlorine, but do not have equivalent o x i d i z i n g power Giertz (37)  showed that c h l o r i t e solutions do not react with phenols, cresols  or saturated a l i p h a t i c 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 c h l o r i t e d e l i g n i f y i n g process (6k,  \  108) . With increasing temperature there i s a  stead decrease i n y i e l d of h o l o c e l l u l o s e 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 c e l l u l o s i c or hemicellulosic constituents of wood and removal of t h i s i s accompanied by removal of a portion of the l a t t e r constituent (8, 66,  6k,. 91)  105)«  below 70° C. (6k,  56,  I t i s advisable, therefore, to keep r e a c t i o n temperatures ikk).  Rapson (108)  found that maximum brightness was  ob-  tained with sodium c h l o r i t e bleaching of chemical pulps by b u f f e r i n g pH at about k.  Brightness  f e l l o f f only s l i g h t l y as the pH dropped to one,  decreased sharply as a l k a l i n i t y was  reached.  but  The e f f e c t of pH between k and  1 was found 'to be negligible on pulp v i s c o s i t y . in intrinsic viscosity  when pH f e l l below 2.  Only a s l i g h t drop was  found  This was probably due to  hydrolytic degradation of the pulp at such high a c i d i t y .  Maximum l i g n i n  s o l u b i l i t y , 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 f i b r e with the d e l i g n i f i c a t i o n process described by Wise and Jahn (IU9) •  Only s l i g h t 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 c h l o r i t e (NaC102) and 0.5 ml. of g l a c i a l acetic acid.  The pH of the s l u r r y of s'uch chemical composition i s about  5-  No further pH adjustments were made since with progress of cooking the liquor became s l i g h t l y more a c i d i c .  The reaction vessels (stoppered  500 ml.  Erlenmeyer f l a s k s ) 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 l i q u i d (10 ml.of aqueous solution' cont a i n i n g the above amounts of sodium c h l o r i t e and acetic a c i d ) .  One f i b r e  sample, was removed after each hour and washed with 700 ml- of 1$ acetic acid on a Buchner funnelretain fines.  The mother l i q u o r was r e c i r c u l a t e d three times to  The mat was pressed by hand between r e c i r c u l a t i o n s 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 ovendry weight of the o r i g i n a l sample.  -40A f t e r 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 r e l a t e d t o 36.2$ weight l o s s .  The r e l a t i o n s h i p between num-  ber of treatments and per cent weight loss i s plotted i n Figure 1 A. • Each point on the graph represents the average of three cooks. representation  the weight loss could be extrapolated  of treatments, as well as by cooking time.  From t h i s graphic  and defined by number  With these r e s u l t s , large batches  of f i b r e (60 g.oven-dry plus anticipated weight loss on treatment) were extracted t o make up a series of samples with weight losses at 5, 10, 15, 20, 25,  30 and 35$ corresponding to anticipated l i g n i n losses of 16, 32, 48, 64,  8 l , 97 and 113$, r e s p e c t i v e l y .  (Anticipated l i g n i n loss calculations are  based on 31«04$ Klasoh l i g n i n content determined by the 72$ s u l f u r i c a c i d method.) Weight loss below 5$ was found to be time dependent, so that a series of s i m i l a r cooks was set up as above.  Samples were removed at 10  minute i n t e r v a l s up t o 60 minutes without further chemical a d d i t i o n .  Thus,  the r e l a t i o n s h i p of per cent weight loss to time of cooks could he established.  Results are plotted i n Figure 1 B.  been extrapolated  For t h i s figure times have  from 1, 2, 3, and 4$ weight losses corresponding t o  anticipated l i g n i n losses of 3, 6, 10 and 13$ r e s p e c t i v e l y . 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$) i s believed to be the  r e s u l t of changed chemical composition of the Asplund f i b r e .  The experiments  of I f j u (53) show that i n extraction of 1Douglas f i r micro.-sections a maximum weight loss of 28$ could be obtained with 7 treatments.  Subsequent treatments  . l a -  fas many as k) d i d not cause a d d i t i o n a l weight loss i n h i s sections. A number of l i g n i n - o x i d i z i n g procedures were t r i e d f o r quantitat i v e oxidation o f . l i g n i n without s o l u b i l i z a t i o n .  The purpose of such  •treatment was to elucidate the chemistry involved i n the i n t e r a c t i o n between l i g n i n and tempering o i l as activated by heat.  Although, a l l e f f o r t s  to achieve t h i s were without success, they d i d afford a good survey of a v a i l able l i g n i n oxidation methods.  These experiments gave further proof that  choice of the sodium c h l o r i t e method f o r controlled degree of l i g n i n oxidai  •  '  t i o n was the best procedure a v a i l a b l e . 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 r e s u l t i n g chloro-  l i g n i n was hot-water-soluble which was objectionable for purposes of t h i s study because of losses encountered in'the hot-pressing of boards prepared from such chlorinated f i b r e .  Results of these experiments are given  i n Table 3* and r e s u l t s of hot-water extraction under similar conditions as with 3$ monoethanolamine are summarized  i n Table 4.  Hydrogen peroxide of 30$ volume was t r i e d as a means f o r oxidizing lignin in situ.  The 5 g-pulp samples were suspended i n 300 ml.hydrogen per-  oxide f o r a period of two hours at room temperature. took place a f t e r t h i s e x t r a c t i o n .  No apparent change  The weight loss obtained was 1.21$.  Hot  hydrogen peroxide extraction f o r the same length of time only doubled the weight l o s s , consequently, t h i s treatment was abandoned.  The method of chlorine s u b s t i t u t i o n into the aromatic nucleus of the l i g n i n molecule, described by Schuerch and co-workers (28, 96, Ilk), used for one experimental  was  run but gave very poor r e s u l t s with Asplund pulp.  T-butyl hypochlorite solution was prepared according to the procedure described, by Schuerch (116) . Besides the strong o x i d i z i n g action of t-butyl hypochlorite solution^the r e s u l t i n g c h l o r o - l i g n i n was hot-water-soluble and was e a s i l y removed i n the hot-pressing operation,giving a board with badly charred surface.  Results of these experiments are summarized i n Table 5.  F i n a l l y , a method described by Purves and co-workers (80) was tried.  They prepared chlorinated l i g n i n without s o l u b i l i z i n g i t by bub-  b l i n g nitrogen gas through the c h l o r i t e solution containing the wood meal. Chlorine dioxide, which has been found responsible f o r l i g n i n oxidation and s o l u b i l i z a t i o n (6, 8, 38, 50, 6k, 80), was removed as i t was formed.  Five  grams of a i r - d r y Asplund f i b r e were suspended i n l60, ml.of solution contain- . ing 1.5 g-of sodium c h l o r i t e and 0.5 ml. of g l a c i a l a c e t i c acid, as used i n the treatment prescribed by Wise and Jahn (1^9) • Using carbon dioxide i n stead of nitrogen gas gave 5*5$ weight loss a f t e r one hour extraction at room temperature.  "  In summary, none of the four treatments t r i e d on t h i s Asplund f i b r e provided a means of o x i d i z i n g l i g n i n without i t s simultaneous solubilization.  3.  A l k a l i extraction of hemicelluloses  Mild caustic treatments have been found most u s e f u l i n removal of 1  hemicelluloses. avoided  (12).  Thereby, a l k a l i n e hydrolysis of l i g n i n and c e l l u l o s e i s The extraction aimed at a quantitative removal of the hemi-  A3celluloses 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 i s dependent on a number of f a c tors of which solution concentration, temperature, time and type of raw mate r i a l are most important.  Maximum s o l u b i l i t y i s reached with 10$ sodium  hydroxide solution which removes mainly beta c e l l u l o s e .  (Beta c e l l u l o s e / a  f r a c t i o n of the hemicelluloses", i s defined as that part of the carbohydrate portion which goes into solution with 17°5$ sodium hydroxide solution and p r e c i p i t a t e s upon n e u t r a l i z a t i o n of the extraction l i q u o r (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 e a s i l y hydrolyzed by acids, but s o l u b i l i z e d only by a l k a l i solutions. . A n a l y t i c a l investigations of Asplund pulps by Klauditz and Stegmann (7l)>'M$rath (95) and Voss (139) have .shown approximately 8$ pentosans, based on oven-dry weight of the pulp.  They extracted  the hemicelluloses with 10$ aqueous sodium hydroxide solution at 100° for 2 hours. "  C.  -  Comprehensive reviews by Booker (10), Nelson (97) and Prey and coworkers (106) on removal of hemicelluloses from wood, show that there exists a l i m i t e d amount of pentosans not e x t r a c t i b l e 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 d i f f u s i o n of pentosans from the rather inaccess i b l e regions of the c e l l structure.  The rate at which pentosans can be  removed from wood i s l a r g e l y dependent  on the equilibrium swelling of the  polysaccarides, and on p a r t i c l e s i z e .  Furthermore, rate i s dependent  on  -kktemperature, concentration of e x t r a c t i o n solution, wood morphological structure, and amount of l i g n i n present.. 'I i n the wood.  On t h i s b a s i s , i t i s poin-  ted out that hemicelluloses can be prepared with greater success from holocellulose.  (Holocellulose i s defined as the l i g n i n - f r e e carbohydrate f r a c -  t i o n , i . e . , the t o t a l polysaccharide f r a c t i o n of wood (150).)  Although i t  i s possible to extract hemicelluloses d i r e c t l y from wood by a l k a l i t r e a t 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 c a r r i e d out with d i f f e r e n t r e a c t i o n conditions.  Sodium  hydroxide solutions of d i f f e r e n t concentrations from 0.1 to 10$, reaction temperatures of 3 0 and 6 0 ° C. and r e a c t i o n times of 3 0 , 6 0 and 9 0 minutes were used.  In the' experiment 5g.samples  of alcohol-benzene extracted Asplund  f i b r e 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 s o l u t i o n .  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 . obtained under the following conditions:  An 8 . 6 8 $ weight loss was  9 0 minute reaction time, 6 0 ° 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-  t i o n times and lower solution concentrations gave lower weight l o s s r e s u l t s . The set of conditions thus determined was considered s a t i s f a c t o r y f o r the removal of a major portion of hemicelluloses from large f i b r e batches needed f o r board formation. Thus alcohol-benzene extracted Asplund f i b r e was extrac ted under the above set of conditions using enough material to give 60 g. of  -45oven-dry,, heraicellulose-free pulp f o r board preparation purposes. v  4.  Cellulose modification by Cobalt 60 irradiation.'  Approximately 200 g.air-dry alcevhol-benzene  extracted Asplund  f i b r e were sent, i n a sealed polyethylene bag, t o Atomic Energy of Canada Ltd., Commercial Products D i v i s i o n , 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  i r r a d i a t i o n should r e s u l t i n s u f f i c i e n t random degradation of cellulose chain-length t o be detected i n standard strength t e s t . The organization provides assistance t o those i n t e r e s t e d iri'effects of gamma r a d i a t i o n on d i f f e r e n t materials.  I t 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 f o r a maximum dose rate of 680 curies and 1,500 curies, r e s p e c t i v e l y . A dose uniformity of - 5 per cent i s f e a s i b l e with normal sample s i z e s .  The i r r a d i a t i o n chambers .are  of l i m i t e d s i z e , being 1.5 i n . i n diameter by 4.5 i n . i n height i n case of "Gammacell 100" and 3*5 i n . i n diameter by 5*5 i n . i n height i n case of 'Gammacell 200".  I r r a d i a t i o n 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 t r a i n i n g of personnel.  The Cobait  i s well shielded,- which eliminates the need of elaborate precautions. ing of the i r r a d i a t i o n chamber i s f a c i l i t a t e d through a drawer automatically moved i n and out of the r a d i a t i o n f i e l d . 5•  L i g n i n deactivation following impregnation hot-water-soluble  hemlock bark e x t r a c t i v e s .  Load-  which i s ^  with  source  E a r l i e r observations by Adler (2), Adler and Stockman (k) and Pew (103, 10k) gave one. possible means of l i g n i n deactivation i n s i t u .  The  phenomenon of l i g n i n condensation with water-soluble bark extractives i s believed t o take place on heat-treatment of. the impregnated  m a t e r i a l . This  same chemical reaction was i n t e n t i o n a l l y i n i t i a t e d on one batch of Asplund f i b r e i n the hot-pressing operation a f t e r impregnating the f i b r e with hotwater-soluble hemlock bark e x t r a c t i v e s . between l i g n i n and o i l was suspected.  Thereby, a reduced;ia^e-r^tioii . 1  The treatment was devised to. give  some evidence f o r the chemical nature of hardboards  to o i l interaction r e -  s u i t i n g 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 t o Scoi^t (320), and Scott and Gardner (121), from f r e s h l y peeled hemlock bark.  The bark was reduced t o small parf o r 2k  t i c l e s and initially;extracted with cold water a t room temperature hours t o remove the cold-water-soluble f r a c t i o n .  A f t e r draining the cold  water extracts., a hot water extraction was carried out on the same bark at 100° C. f o r 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 l i g h t e r on cooling, giving a good crop of p r e c i p i t a t e s on cooling.. I t was found that the 1,500 ml.' solution contained 2.6$ s o l i d s , 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 p r e c i p i t a t e d onto the f i b r e on cooling.  S i m i l a r l y , 60 g. oven-dry f i b r e was  impregnated  with 1,500 ml. of the bark extract s o l u t i o n at 80° C. f o r 2 hours.  After  cooling the s l u r r y i t was washed twice with cold water, formed i n t o 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 t o 1 1 . 8 1 $ weight gain on the f i b r e of which approximately 6 . 7 $ was due to tannins.  C.  A n a l y t i c a l Methods 1.  Alcohol-benzene  extractives (TAPPI Standard:  T 6 m-5k)  Replicate 5 g.samples of f i b r e were extracted under conditions described by TAPPI Standard T 6 m-5k f o r determining the approximate amount of alcohol-benzene extractives removed. A f t e r proper washing and oven drying 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 f i b r e . > 2.  Klason l i g n i n (TAPPI Standard: T 13  m-54)  For characterization of the raw material (alcohol-benzene extracted Asplund f i b r e ) regarding i t s l i g n i n content, two sets of 7 2 $ s u l f u r i c acid-insoluble Klason l i g n i n determinations were conducted, giving a t o t a l of four r e p l i c a t e s .  The method described i n TAPPI Standards T 13m-5^ has  been followed. ,An average of 31 •04$ was  calculated from the r e p l i c a t e s with  a l l r e p l i c a t e s deviating not more than t l/lOO of the mean value.  This aver-  age served as basic l i g n i n content f o r the c a l c u l a t i o n of anticipated l i g n i n contents of sodium c h l o r i t e ' t r e a t e d pulps, and f o r reference l i g n i n content value f o r u l t r a v i o l e t spectrophotometric l i g n i n determinations.  It should  be mentioned that d i f f i c u l t i e s were encountered i n securing r e p l i c a t e s of good agreement.  Similar d i f f i c u l t i e s have been reported e a r l i e r i n the  l i t e r a t u r e by Klauditz and co-workers ( 7 0 ) , McKnight and Mason ( 8 8 ) , Nowak (99),  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 f i b r e acquired i n the d e f i b e r i z i n g process.  The anticipated l i g n i n contents of sodium c h l o r i t e treated f i b r e s  are based on 31*04$ Klason l i g n i n and presented i n Table 6 . 3«  U l t r a v i o l e t spectrophometric l i g n i n determination  This l i g n i n determination involved a l l sodium c n l o r i t e 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 l i g n i n sample. Moore and Zank (58) was  The method as described by Johnson,  c a r e f u l l y followed.  Samples with approximately 6 mg. l i g n i n content (sample sizes were based on anticipated l i g n i n contents) were dissolved i n 10 ml. of 25$ a c e t y l bromide and d i l u t e d to 200 ml. volume with reagent grade a c e t i c a c i d . t i o n was measure at 280 mjj.wave length with a Beckman DU  Absorp-  spectrophotometer.  Duplicate determinations gave poor r e p r o d u c i b i l i t y , possibly due to the same factor(s) influencing sodium c h l o r i t e treatments and tion.  Klason l i g n i n determina  Therefore, values presented i n Table 6 should be accepted only as  approximate r e s i d u a l l i g n i n contents of c h l o r i t e d pulps.  h.. Micro-Kappa number Micro-Kappa number (Kappa number i s 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 s p e c i f i e d i n TAPPI Standard. T 236111-60) converted to r e s i dual l i g n i n per cent was determined on c h l o r i t e d pulps with l e s s than 15$ anticipated l i g n i n content.  Result of the determinations are given i n Table  -495.  One per cent cupriethylenediamine  (CED) v i s c o s i t y  V i s c o s i t y measurements using 1$ CED solution and the f a l l i n g b a l l method, described i n TAPPI Standard:. T 230 sm-50 and discussed by McLean and Walker (89)7 were performed on c h l o r i t e d pulps of more than 25$ weight loss i n the laboratories of Columbia Cellulose Co. Ltd., Prince Rupert, B r i t i s h Columbia.  The v i s c o s i t y values obtained were converted to. degree of poly-  merization (DP) values using the nomographs developed by Dobo and Kobe (22) and are presented i n Table 7« D.  Thin Board Preparation Boards of 0.5 mm.(500 microns) nominal thickness have been prepared  from d i f f e r e n t l y treated f i b r e to provide material for physical test procedures.  Hardboards of t h i s thickness have not been reported previously.  They  include a l l usual commercial hardboard c h a r a c t e r i s t i c s of. wet-batch process boards.  J u s t i f i c a t i o n of t h i n boards i n t h i s 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 f i b r e .  This  reduced the amount of f i b r e that had t o be prepared by each of the foregoing treatments,  the amounts of chemicals used i n the f i b r e  preparations and reduced the size of necessary .containers and . equipment for maintaining uniform f i b r e treatment conditions. In other words, the problems of material batch handling and treatment uniformity was greatly s i m p l i f i e d .  i i i . Large size t e s t i n g machines with, wide range of loading capacityare necessary f o r t e s t i n g macrospecimens.  Such equipment i s not  available within the Faculty of Forestry. To use available t e s t ing f a c i l i t i e s designed- f o r t e s t i n g micro specimens r e s t r i c t e d to a maximum loading capacity of 50 kg.  one i s This required  that specimens of r e l a t i v e l y small dimensions be prepared.  Ini-  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 f a i l e d 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 f o r t e s t i n g 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 t o t e s t i n g .  Thereby, v a r i a t i o n and error within test  r e s u l t s were greatly reduced.  The preparation of machined t e s t  specimens having similar dimensional accuracy from board of commercial thicknesses i s time consuming and impractical. A board with 0.?0  (g/cm.) nominal s p e c i f i c gravity was desired to  represent medium density hardboard.  Since l a t e 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 t h i c k ness caused by d i f f e r e n t types of f i b r e s .  In t h i s respect s p e c i f i c gravity  has been shown to c r i t i c a l l y influence hardboard strength i n commercial pro-  -51duction of hardboard (M-S, 59, 63, 65, 7^, 118, I37). Fibre treatments were expected t o modify f i b r e dimensions and composition of boards made of such fibres.  Boards made of coarser f i b r e r e t a i n a large amount of r e s i l i e n c y  during the pressing operation while fine f i b r e s compact to a high s p e c i f i c gravity (137)' Therefore, after consideration of these factors, i t was decided t o produce boards with the same basic weight per unit volume. In other words, the boards were pressed t o the same nominal thickness containing 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 s p e c i f i c gravity, and reduced internal v a r i a t i o n due t o differences i n s p e c i f i c gravity. On the basis of the above dimensions and s p e c i f i c gravity target, the necessary amount of oven-dry f i b r e — unextracted control and extracted when prepared from chemically-modifed f i b r e s — was calculated as follows.: Board area  16 in.x 16 i n . = 256 sq<>in.= 1652  Thickness  0.05cm.  S p e c i f i c gravity  6.70 (g/cm3)  Volume:  Five per- cent loss i n forming  82.60 cm3  =  57.82 g.  a  2.89 g. 60.71 g.  Plus 5 g-for a n a l y t i c a l t e s t s : 7-76$  2  =  Total oven-dry f i b r e :  Fibre moisture content:  cm.  • 65.71 g. =  70.80'g.  In c a l c u l a t i n g the amount of raw f i b r e necessary f o r a p a r t i c u l a r f i b r e treatment (described i n previous paragraphs) additional amounts of f i b r e were necessary to make up the losses encountered during treatments.  -52-  Step 1.  Additives  The prepared batches of fibres' were moistened the day previous t o board formation.  Since small amounts of r o s i n soap and phenolic r e s i n were  added t o the fibre-water s l u r r y at 2.5$ consistency, the f i b r e required a g i t a t i o n i n a p l a s t i c container t o secure uniform d i s t r i b u t i o n of the a d d i t i v e s . One per cent phenolic r e s i n (at 42$ s o l i d s content) and 1.5$  "Paracol" r o s i n  soap (at 75$ s o l i d s content) were added (based on the oven-dry weight of the f i b r e ) and mixed f o r 15 minutes.  Mixing was followed by addition.of 0.35$ f  commercial alum and 0.35$ s u l f u r i c a c i d , t o p r e c i p i t a t e the;'resin and Paracol onto the f i b r e s .  The s l u r r y was mixed again f o r 5 minutes and the pH  checked with Beckman HydronPaper "A". Step 2.  Mat  A pH value between k and 5 was  was accepted.  formation  As mentioned above, the boards were processed t o r e p l i c a t e batch hardboard manufacture on laboratory s c a l e .  wet-  The success of the whole  experiment was dependent on uniformity of board formation. The forming box, a plant fabricated s t e e l 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 . h i g h .  The f a l s e bottom-plate was  approximately 2 inches above the tap opening. clipped t i g h t l y onto the f a l s e bottom-plate.  raised'  A f i n e screen (60-mesh) was The box was t h e n - f i l l e d t o  about one-half (marked on one of the inside walls) i t s depth with water. The sized and r e s i n - t r e a t e d f i b r e was then poured i n t o the box, and agitated f o r several minutes.  At the end of the s w i r l i n g a few straight strokes were  made between opposite walls with a wooden s t i r r e r , t o minimize currents  -53that tended t o make the boards heavier i n the centre.  The s l u r r y was  allowed to s e t t l e for the predetermined time and subsequently drained free of water. - An i n i t i a l problem i n obtaining good board formation characterist i c s was found t o be mainly due t o uneven s e t t l i n g and subsequent draining of the stock. Boards were heavier towards the edges and at the outlet side. Also, more than 5$ loss was encountered i n the beginning due to improper t i n g of the f a l s e bottom-plate into the forming box.  fit-  Drainage time seemed  to have a marked e f f e c t on board uniformity and on the amount of f i b r e r e tained a f t e r drainage.  I t was found that the f i b r e had to be s l u r r i e d w e l l  to disintegrate f i b r e "clumps" and,thereby eliminate "density spots".  Re-  c i r c u l a t i o n of fines was not possible since any distrubance above the mat resulted i n uneven board texture.  The s l u r r y , once s e t t l e d , could not be  disturbed without destruction of the mat  structure.  These problems-were remedied i n the following ways: i.  S e t t l i n g times, were varied according to type of f i b r e .  Longest  s e t t l i n g times, 20 minutes, were allowed f o r sodium c h l o r i t e treated f i b r e which had 20$ and higher weight losses a f t e r t r e a t ment.  Fibres prepared the same way, but. t o lower l e v e l of weight  losses (15$  and under) behaved d i f f e r e n t l y regarding s e t t l i n g  speed and drainage. sodium hydroxide  These included untreated Asplund f i b r e ,  extracted f i b r e , and f i b r e s q u a l i t a t i v e l y modi-  f i e d i n cellulose and l i g n i n c o n s t i t u t i o n .  The l a t t e r group  behaved s i m i l a r l y i n a l l stages of board formation and w i l l be r e f e r r e d to henceforth as "coarse f i b r e " i n contrast to slow sett l i n g "fine f i b r e " .  S e t t l i n g time f o r a l l types of coarse f i b r e  -54was set at 10 minutes. ii.  Drainage time (speed of water drainage from the forming box without f i b r e losses i n excess of 5$) &s w  increased f o r f i b r e s prepared  by c h l o r i t e d e l i g n i f i c a t i o n from 20$ 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 f o r the f i n e r type of f i b r e was regulated to 25 min. and f o r the coarser type of f i b r e to 15 minutes. iii.  Large weight losses during draining were reduced by f i t t i n g a t i g h t seal around the edges below the f a l s e bottom-plate.  In addition, -  with f i n e r f i b r e a f i l t e r paper was inserted between the f a l s e bottom-plate and the screen, t o provide more uniform drainage. .iv.  Fewer "density spots" and more uniform drainage were' obtained with the t i g h t l y f i t t e d f a l s e bottom-plate.  v.  D i s t r i b u t i o n of f i b r e within the forming box was secured by further reducing the s l u r r y consistency to about o n e - t h i r t i e t h of the o r i g i n a l consistency i n the p l a s t i c container. This provided a better d i s t r i b u t i o n of the f i b r e within the forming box.  I t also solved  the problem of r e t a i n i n g the fines since the coarser f i b r e s settled out f a s t e r than the fines,providing a natural f i l t e r i n g pad for the f i n e s . The mat was removed with the a i d of two heavy wire handles welded to the bottom-plate.  After removal of the c l i p s from the bottom-plate edges  the mat was placed, together with the screen, between two highly polished s t e e l cauls, ready f o r the pressing operation..  -55Step 3«  Board pressing  In the wet and semi-dry hardboard pressing operation a screen i s needed, usually underneath the mat, t o 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.  hot-pressing.  P a r t i a l dewatering i s possible previous to  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. amount of r e s i n and other s o l i d s washed away by the departing steam w i l l be minimized, r e s u l t i n g i n improved strength. ted,  Thus, the  hot water and  As would be expec-  i n the case of a p a r t i c u l a r f i b r e type, press-platen temperature, pres-  sing time and pressures used are c r i t i c a l i n regard to physical characterist i c s of the board, produced under a c e r t a i n set of these conditions.  High  temperature, high pressure and the presence, of.moisture i s the key to greater compressibility of the mat.  Higher densities and more even binder  d i s t r i b u t i o n i s obtained under such conditions 'due to r e s i n flow and the p l a s t i c i z i n g action of the high-pressure steam (118). Turner and co-workers (137)  found that increasing molding tempera-  ture s u b s t a n t i a l l y increased f l e x u r a l properties of boards, but that toughness values were markedly reduced.  Since drying of the boards i s 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 l e v e l of press-platen  temperature can be decreased.  By using d i f f e r e n t  pressures or mechanical  stoppers (spacers) the thickness and density can be c o n t r o l l e d .  Usually a  short breathing cycle i s introduced a f t e r a b r i e f high i n i t i a l pressure, to provide f o r 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 a v a i l a b l e , and production rate.  '  .  Through a considerable number of t r i a l s i t was learned that "coarse f i b r e " requires shorter s e t t l i n g and drainage times for uniform mat  formation,  also required somewhat higher pressures i n the hot-pressing operation. "fine f i b r e " required lower ^pressures f o r attaining a predetermined  The  speci-  f i c gravity. For the coarser type of f i b r e 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 temperature of 175° G. was the system.  set by adjusting the steam pressure to^OQ psi. i n  A f t e r closing the press an i n i t i a l pressure of 225 psi.was  applied f o r 30 seconds and a breathing period of one minute was without pressure.  allowed  The pressure was then increased to 200 p s i . f o r an addi-  t i o n a l 1.5 minutes.  F i n a l l y , the screen was removed and the board was r e T  pressed at 400 p s i . f o r 2 minutes.  This re-pressing was designed to smooth  the rough side and complete the curing to such an extent that p r a c t i c a l l y no strength increase should r e s u l t on subsequent heat-treatment  of the boards.  For pressing mats of the f i n e r type f i b r e s , the times i n the pressing  cycle were kept the same as above, but pressure was a l t e r e d . The  pressure was  initial  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. {  -57A l l boards were trimmed t o 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 o r i g i n a t i n g during board formation. Trimmed boards were accepted i f t h e i r weight was above kk grams. A weight v a r i a t i o n 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  e f f e c t of these treatments, as described i n e a r l i e r 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 t o every board immediately after ping to s i z e , f o r i d e n t i f i c a t i o n purposes. cut  clip-  Subsequently, each board was  into 7 - i n . by 7-in. quarters. Post-pressing treatments *ere randomly  assigned to these quarters. a. Oilrtempering The objective-was t o give a controlled excess of o i l solids to the  experimental boards to secure maximum i n t e r a c t i o n between o i l and wood  constituents under i n v e s t i g a t i o n .  One board segment representing each  f i b r e treatment was placed on a wire rack.  The loaded rack was then sub-  merged into the tempering o i l f o r a certain period of time. the  After dipping  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 t h i n boards showed that the o i l had to be d i l u t e d t o a 1:7  r a t i o with benzene, to obtain complete saturation s l i g h t l y  higher than that produced i n commercial oil-tempering.  The amount of o i l  absorbed i s further influenced by type of f i b r e , s p e c i f i c gravity of boards, and v i s c o s i t y 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 d i l u t i o n . O i l absorption values obtained i n the above described manner after a 5-second dip at room temperature, are given i n Table 8 f o r boards made of Asplund f i b r e ( c o n t r o l ) , alcohol-benzene extracted, sodium hydroxide extracted, modified cellulose-, l i g n i n deactivated and sodium c h l o r i t e d e l i g n i f i e d f i b r e boards  •  -  The weight gain or per cent o i l s o l i d s absorption i s calculated from the oven-dry weights of the untreated boards and from the weight, a f t e r 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 o i l - t r e a t e d boards and to one set of untreated boards i n forced c i r c u l a t i o n laboratory oven, manufactured by Precision S c i e n t i f i c Co. with a temperature range of 35° to l 8 0 ° C. The.boards were loaded on the same rack used f o r o i l dipping and placed •inside the oven which was set at 1 5 5 ° C . w i t h the fan on, and kept there for h hours.  Since "over drying" has been shown t o r e s u l t i n strength losses (102, 139) a short experiment was set up t o investigate the e f f e c t of d i f ferent temperatures on the t e n s i l e strength of oil-tempered specimens prepared from t h i n experimental boards.  Three l e v e l s of temperatures were  130°, 155°, and 170° C. Duration of treatment was k hours. Ten  selected:  r e p l i c a t e s were used f o r each temperature l e v e l . 9.  Results are given i n Table  Strength loss due to specimen surface charring occurred at the highest  temperature  c.  level.  Humidification  Since humidification i s usually the l a s t post-pressing step i t was included In t h i s experiment.  However, since the t e n s i l e strength t e s t s were  performed on oven-dry specimens, the humidification treatment was not expected t o influence the strength of the boards t o any appreciable extent. Ogland and Emilsson (102) and Kumar (Jk), found that the strength of hardboards has been appreciably reduced as moisture content of specimens was increased from 5 t o 30$. A f t e r the heat-treatment of the two sets of 7-in. by 7-in. boards, (one set oil-tempered),< a t h i r d set of boards was selected and placed into the chamber of an Aminco A i r e , Model .Wo. 4-5^75, humidifying cabinet previously adjusted to give 9*0$ r e l a t i v e humidity at 2k° C. dry-bulb temperature.  These conditions were kept f o r 2k hours.  moved and stored i n polyethylene bags.  The boards were then r e -  No moisture content measurements  were made on boards prepared by d i f f e r e n t treatments.  -60-  E.  Testing Procedures " The influence of c e r t a i n wood constituents on the l e v e l of i n t e r -  action- i n i t i a t e d hy heat-treatment of boards dipped i n tempering o i l  was  examined by measurement of the mechanical property, ultimate t e n s i l e strength. to  Since t e n s i l e strength i s a pure mechanical t e s t i t was expected  give d i r e c t comparisons of the l e v e l of the above" i n t e r a c t i o n .  With com-  mercial' hardboards a good r e l a t i o n s h i p .has been found between modulus of rupture (MOR)  and t e n s i l e strength.' From personal data of Currier ( 1 9 ) ,  and Wilson (14-5), i t Is evident that there e x i s t s a f a i r l y constant r e l a t i o n ship between t e n s i l e strength ( p a r a l l e l to the plane of the board) and for  a certain set of boards manufactured under s i m i l a r conditions.  (19)  found a r a t i o df 0 . 5 2  f o r l / 8 - i n . Standard hardboard when MOR  'divided,by t e n s i l e strength. (ll+5)  MOR  Currier was  The same' r a t i o was found to be 0 . 5 7 by Wilson  on l / 8 - i n . oven-dry.samples  at  0.35$  somewhat higher f o r tempered hardboard.  resin solids.  The r a t i o was  The data of Currier ( 1 9 ) gave ah  average r a t i o of GU58 f o r l / 8 - i n . tempered boards made by the wet-batch process.  :  Mechanical t e s t i n g f o r the main body of the work was preceded by i n v e s t i g a t i o n of factors such as influence of specimen width on t e n s i l e strength and the necessary number of specimens needed f o r estimating a tens i l e strength difference of 1 0 0 . kg/cm? at 0 . 0 1 $ p r o b a b i l i t y l e v e l . Straight, rectangular specimens of 3 , 5 , 7 , 9 and 1 1 mm.width were included i n t e s t s to examine optimum specimen width.. Ten  specimens  of each width' were randomly cut from a t h i n board made of Asplund f i b r e , and tfested,as w i l l be described i n l a t e r Sections.  Results of group aver-  ages were, compared on the basis of average s p e c i f i c - g r a v i t y - c o r r e c t e d ,  u l t i m a t e t e n s i l e strength and c o e f f i c i e n t s of v a r i a t i o n ' ( C V $ ) .  Highest  t e n s i l e strength and lowest c o e f f i c i e n t of v a r i a t i o n were obtained, f o r specimens of.9 mm.width. Results of t h i s t e s t are summarized i n Table 10. Test data obtained on 9 mm.specimens were used f o r c a l c u l a t i n g , • the necessary number of specimens. described by Snedecor (125).  Computations were based on a procedure  I t was found that e s t i m a t i o n of a t e n s i l e  strength d i f f e r e n c e of 100 kg/cm , at 0.01$ p r o b a b i l i t y , r e q u i r e d 22 r e p l i 2  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 c o n s t i t u t i o n and subjected t o c e r t a i n post-pressing treatments formed m a t e r i a l f o r s p e c i men p r e p a r a t i o n .  A l l 7 - i h . by 7-in. board segments were f i r s t cut i n halves,  g i v i n g 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 a n d - p a r a l l e l smooth cuts were produced on both edges w i t h a c i r c u l a r planer saw.  Finished  width of such sections was i n the order of 3-35 i n . v  From each of the 7 - i n . by 3«35-in. boards, 12 rectangular s p e c i mens of 9 mm. nominal width were punched w i t h a -g--ton Wilson arbor press equipped w i t h an adjustable width c u t t i n g d i 2 as shown i n F i g u r e 3«  The  c u t t i n g d i e head i s depicted i n Figure k. By a d j u s t i n g spacer width t o 3 t o 11 mm.the p r e v i o u s l y described specimens could be prepared w i t h t h i s same die.  Thus, from each 7 - i n . by 7 - i n . board, 2k specimens of 9-mm.bj 85-mm.  nominal s i z e were prepared. i d e n t i f i c a t i o n purposes.  Specimens were numbered from 1 t o 2k f o r  -62-  • 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 oven-dry  overnight.  Each  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  matic balance. measurements  Average  thickness  done on t h e  a.dial  gage m i c r o c a t o r  sented  i n Figure  5«  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  specimens,  (ih,  57)*  At the  auto-  at  t h e ' t w o ends a n d ' i n the  three  centre,  A photograph of the microcator i s  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  by  prethe  specimens were  determined w i t h c a l i p e r s r e a d i n g t o an accuracy  o f 0.001  F r o m these d a t a  (oven-dry weight,  length),  specific  gravity values  (based  specimen i n the u s u a l way. specimens-were  2.  A f t e r t h e measurements polyethylene  strength test,  F o l l o w i n g t h e above  tensile  strength tests.  Testing procedures  completed  preparations  Instron tester  A photograph of t h e machine i s The s p e c i m e n s w e r e  ultimate  the  specimens were  subjected  given i n Figure  a p p l i e d by an adjustable constant  i n . apart, at  cross-arm descent  o f 0.01 i n . / m i n .  c a l system and s m a l l motor, the  selected  t o give  with a.  4-5 i n . - l b .  s p e e d b y t w o worm g e a r s .  ;  (62).  6.  torque-wrench set  I n t h i s c a s e a g e a r r a t i o was  by  and Kennedy and I f j u  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 changes.'  to  tester.  have been d e s c r i b e d e a r l i e r  g r i p p e d b e t w e e n t w o j a w s 1.5  The l o w e r c r o s s - a r m i s moved a t  ratio  the  These were done on a n I n s t r o n t a b l e - m o d e l  on t h e  each  elasticity,  ?  pressure  computed f o r  bags.  B r o u g h t o n . a n d M a t l i n ( I 3 ) . , l f j u and Kennedy (52),  constant  were  calculation of  e l o n g a t i o n and modulus o f (a)  w i d t h , and  on o v e n - d r y volume) were  stored i n sealed  Tensile  average t h i c k n e s s ,  cm.'  -  The gear  a speed  of  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 -  load-cell is  connected w i t h an  automatically  -63recording t r a v e l l i n g chart on which load deformation curves are r e g i s t e r e d . The  chart speed i s adjustable by interchangeable  or multiples of possible cross-arm speeds. 1 in./min. was  gears to speeds s i m i l a r to  In t h i s study a chart speed of  selected.  ->.,. By these arrangements simple load-elongation r e l a t i o n s h i p s were' established f o r each specimen.  From the r e l a t i o n s h i p s ultimate t e n s i l e  strength (kg/aa. ), ultimate elongation * ( i n . / i n . ) and modulus of e l a s t i c i t y 2  (kg../em.2) were c a l c u l a t e d . Ultimate load readings were taken from the chart at the points.of rupture.  Ultimate t e n s i l e 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 f o r any sample t o be strained from a relaxed  state to the point of rupture depends upon the inherent s t r a i n behaviour of the p a r t i c u l a r material, but i s also dependent upon the length of specimen under t e s t , and speed of load a p p l i c a t i o n . Ultimate elongation, therefore, can be calculated as the quotient of time to f a i l u r e and gage length over cross-arm speed. of specimens. (c)  I t was  possible to do t h i s because of rectangular shape  •  Modulus of e l a s t i c i t y or s t i f f n e s s i s determined as the  quotient"  of load t o u n i t s t r a i n (the load of the extended s t r a i g h t portion of the load-elongation gage length, 1.5  curve w i t h i n the l i m i t of p r o p o r t i o n a l i t y at the point of in.) and cross-sectional area at point of f a i l u r e .  Since  the rate of elongation i s dependent on the rate of load a p p l i c a t i o n , crossarm  speed must a l s o be taken i n t o consideration when c a l c u l a t i n g modulus of  elasticity. *  Notes  On the following pages the term ultimate elongation i s used interchangeable f o r ultimate s t r a i n .  -61+-  3«  Adjustment of strength  properties  Both s p e c i f i c gravity (33, 1+7, 4-9, 63, 65, 73* 118, 137) and moisture content (74, 102) influence commercial hardboard strength.  With i n -  creasing s p e c i f i c gravity boards of higher strength and s t i f f n e s s are obtained.  For comparable r e s u l t s , therefore, the e f f e c t of s p e c i f i c gravity  must be removed, i . e . , a l l strength values must be adjusted t o one common specific gravity. S p e c i f i c gravity values,  calculated from values taken previous t o  t e n s i l e strength t e s t , were f i r s t correlated with ultimate t e n s i l e strength to e s t a b l i s h a regression study.  c o e f f i c i e n t f o r each board -type encountered i n the  A l l boards, including the controls, were grouped according t o p o s t -  :  pressing treatments and the average s p e c i f i c gravity was calculated f o r each group.  This average s p e c i f i c gravity served as "basic s p e c i f i c gravity" to  which a l l t e n s i l e strength values were adjusted f o r each chemical treatment, with the following formula: Y' = Y i * B ( ^ - X ) ±  Where:  Y' = adjusted t e n s i l e strength value X i o group mean s p e c i f i c gravity (basic s p e c i f i c gravity) X i = p a r t i c u l a r sample s p e c i f i c gravity B  • p a r t i c u l a r board type regression c o e f f i c i e n t  Y i = P a r t i c u l a r sample t e n s i l e strength Graphical  (unadjusted)  solution of the s p e c i f i c gravity adjustment i s given i n Figure 7«  A l l regression and s p e c i f i c gravity correction calculations were performed . by the IBM 1620 computer. There were no adjustments made f o r moisture content since a l l samples were at oven-dry condition at time of t e s t i n g .  -65-  RT5SIILTS  A.  Investigation of Wood Constituents  O i l absorption, average s p e c i f i c gravity, ultimate t e n s i l e strength, average ultimate elongation and'average modulus of e l a s t i c i t y (MOE) values are given i n Table 1 1 for boards at three treatment l e v e l s f o r each wood constituent investigated.  S p e c i f i c gravity, (based on averages  obtained from each board treatment) corrected t e n s i l e strength, and per cent r e l a t i v e strength increase values due t o oil-tempering, are also included i n Table 1 1 .  These are also presented as a bar diagram (Figure 8 ) . These r e -  s u l t s served as basis f o r s e l e c t i n g important wood constituent(s) f o r f u r ther i n v e s t i g a t i o n of oil-tempering e f f e c t s .  Relative strength increase was  taken as an i n d i c a t i o n of degree of i n t e r a c t i o n between a c e r t a i n wood constituent and tempering o i l .  S i g n i f i c a n t differences of untempered board  strengths from d i f f e r e n t designations (A t o F) have been calculated by Tukey's method as described by Snedecor ( 1 2 5 ) .  Results of calculations are  summarzied i n Table 1 2 . B.  E f f e c t of L i g n i n Removal The influence of weight loss on untempered and tempered board  properties i s summarized i n Table 1 3 , and presented diagrammatically i n Figures 9, 1 0 , and 1 1 .  In Figure 7 an example i s given of the s p e c i f i c  gravity and t e n s i l e strength r e l a t i o n s h i p f o r one tempered and untempered board, together with the graphical method used for s p e c i f i c gravity corrections on t e n s i l e strength values.  S i g n i f i c a n t difference f o r untem-  -66pered board strength values were calculated by the above method and are presented i n Table  lk.  Curves i n Figure 9 were f i t t e d t o the experimental s p e c i f i c grav i t y adjusted t e n s i l e strength data across the 0 to 5 and 1 0 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 f o r each s e c t i o n .  How-  ever, t h i s 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 s i m i l a r equations were com-  puted and r e s u l t s plotted i n Figure-1:1 over the whole weight loss scale. In Figure 1 2 sample boards of d i f f e r e n t f i b r e chemical constitut i o n are presented.  -  -67-  DISCUSSION A.  Investigation of Wood Constituents The i n v e s t i g a t i o n was designed t o discover any f i b r e chemical con-  stituent's) involved i n the large improvements i n physical properties and dimensional s t a b i l i t y , accompanying tempering of.hardboards.  F i r s t , i t must  be pointed out that heat-treatment alone gave no improvement t o any type of untempered board under i n v e s t i g a t i o n .  This suggested that a l l p h y s i c a l  improvements obtained on heat-treatment of oil-soaked boards were due t o 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 t o oil-tempering e f f e c t s .  Heat-treatment applied t o activate o i l -  tempering may be described as a variable i n development of board strength. This i s shown by the s i g n i f i c a n t l y higher t e n s i l e strength values shown i n Table 11. For t h i s reason comparative heat-treatment controls were eliminated i n l a t e r experiments. Strength of boards made from untreated Asplund f i b r e served as control f o r the f i r s t experiment.  On t h i s basis, a f t e r adjustment of  strength values on average s p e c i f i c gravity, of board treatments, one may" d i s t i n g u i s h absolute strength increase due t o f i b r e treatment alone. Strength values of tempered boards, on the other hand, are compared d i r e c t l y t o corresponding untempered board strength a f t e r adjusting both t o the corresponding average board treatment s p e c i f i c g r a v i t y .  Strength increase  r e s u l t i n g from tempering has been expressed as a percentage of the value for a corresponding untempered board, and i s c a l l e d r e l a t i v e strength  -68increase herein. t h i s way,  Since the e f f e c t of absolute strength increase i s removed  the method of comparing a l l strength values to the control has  been used.  Direct comparison by r e l a t i v e strength increase gives an  not  unbiased  estimate of wood constituent influences on development of tempered board strength. An i n t e r e s t i n g phenomenon was t y - t e n s i l e strength curves.  observed on p l o t t i n g s p e c i f i c g r a v i -  The r e l a t i o n s h i p between these factors was  s i g n i f i c a n t i n a l l cases of untempered boards.  However, when corresponding  tempered values were plotted, the r e l a t i o n s h i p became non-significant, p o s s i bly  due to reduced range of s p e c i f i c gravity and increased v a r i a t i o n of ten-  s i l e strength.  This has been interpreted as being one evidence for l i m i t e d  e f f e c t s of oil-tempering, and i s a v e r i f i c a t i o n of Kumar's (73) f i n d i n g s . The l i m i t i s believed t o be r e l a t e d to number of s i t e s available f o r polycondensation between wood constituent(s) and the absorbed o i l .  Any excess  of o i l solids beyond t h i s l i m i t necessarily increases s p e c i f i c gravity without further improving  strength.  The t e n s i l e strength and s p e c i f i c gravity  r e l a t i o n s h i p f o r one board type, both tempered and untempered i s shown i n Figure  7. 1.  Untreated Asplund Pulp (Control)  The untempered t h i n boards, prepared from non-extracted Asplund f i b r e , developed an oven-dry t e n s i l e strength of 1299 kg./cm?, which i s higher than values given i n the l i t e r a t u r e f o r boards of normal thickness (71,  100).  Tempering gave a r e l a t i v e 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 s l i g h t drop i n ultimate elongation. The r e l a t i v e strength increase i s of the magnitude obtained i n the commerc i a l tempering process ( 7 3 ,  95).  O i l solids were calculated at 1 0 . 7 $  in  -6 9  this  trial.  2. Alcohol-Benzene Extracted Fibre By removing 7 * 5 $ of the raw f i b r e as alcohol-benzene solubles a s l i g h t , but non-significant, absolute strength increase was found.  On the  other hand, oil-tempering resulted i n 1 1 7 $ r e l a t i v e strength increase.  This  suggested that alcohol-benzene solubles are not d i r e c t l y involved i n the heat-activated i n t e r a c t i o n between hardboard and tempering o i l . Their r e moval resulted i n a s l i g h t absolute strength increase, possibly due t o improved f i b r e bonding.  Since most treatments required alcohol-benzene  extraction previous to chemical modification, t h i s r e s u l t suggested that ' observation on other wood constituents were non-confounded.  Results of  oil-tempering on a l l boards, prepared from d i f f e r e n t l y treated f i b r e , previously extracted with alcohol-benzene, could be a t t r i b u t e d to the p a r t i cular f i b r e treatment alone.  No r e a l 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 f i b r e and alcohol-benzene extracted pulp.  Boards of the l a t t e r type of pulp, how-  ever, tended to absorb s l i g h t l y more o i l than the control boards when exposed t o the same o i l bath.  3.  Modified Cellulose Fibre  Boards made from gamma-irradiated f i b r e gave non-significant d i f ferences f o r absolute board strength'.  The s l i g h t Increase of absolute board  strength may be a t t r i b u t e d t o the removal of alcohol-benzene solubles before irradiation.  Tempered boards, however, gave only 4 8 $ r e l a t i v e strength i n -  crease when compared t o untempered board strength following the same f i b r e treatment.  This phenomenon i s not due t o reduced i n t e r a c t i o n between wood  -70and tempering o i l , but probably t o reduced i n t r i n s i c f i b r e strength.  The  fact that untempered boards d i d not show any absolute strength loss can be explained by low i n t e r - f i b r e bonding as the l i m i t i n g f a c t o r , and thereby incomplete  u t i l i z a t i o n of i n t r i n s i c f i b r e strength with t h i s treatment.  I n t e r - f i b r e f a i l u r e s occur during-mechanical  testing.  Conversely,  with  tempered boards, i n d i v i d u a l f i b r e s are broken showing better i n t e r - f i b r e bonding and improved e l a s t i c properties of boards.  This a l s o suggests that  tempering increases i n t r i n s i c f i b r e bonding rather than strengthening of individual fibres.  The decreased  i n t r i n s i c f i b r e strength due t o i r r a d i a -  t i o n i s r e f l e c t e d by drop i n ultimate elongation, although the modulus of , e l a s t i c i t y value was i n the same range as found f o r 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 i r r a d i a t e d f i b r e as with boards made  from a l c o h o l -  benzene extracted f i b r e .  k.  Modified Hemicellulose Fibre  P a r t i a l removal of hemicelluloses resulted i n l i t t l e increase i n board strength.  absolute  Relative strength increase, however, has been  reduced to 70$, suggesting that hemicelluloses do play some part i n the tempering mechanism. i n wood f i b r e .  They may be involved i n proportion t o t h e i r occurance .  I t i s suspected that the d i f f e r e n t i a l r e l a t i v e strength loss  of k0$ i s not a l l due to removal of hemicelluloses.  Qualitative analysis of.  treatment l i q u o r showed traces of l i g n i n a f t e r a c i d i f i c a t i o n . originated from a l i g n i n - x y l a n complex (107)•  This may have  As w i l l be discussed l a t e r  even a small l o s s of l i g n i n can r e s u l t i n considerable reduction of r e l a t i v e strength increase.  Ultimate elongation and modulus of e l a s t i c i t y values are  -71-  i n general the same as those obtained f o r control boards. to note that o i l absorption was  5.  It i s interesting  s l i g h t l y higher than with control boards.  D e l i g n i f i e d Fibre  As expected, untempered boards made from d e l i g n i f i e d f i b r e gave highly s i g n i f i c a n t absolute strength increase at the 5$ p r o b a b i l i t y l e v e l . This phenomenon has been reported e a r l i e r by Klauditz and Stegman (71) by Ogland (100).  and  The absolute strength of d e l i g n i f i e d fibre-boards was ll+6$  higher than the control boards.  As discussed (page 1 2 ) , t h i s absolute  strength increase i s due -to increased bonding capacity of hemicelluloses and to improved paper-making c h a r a c t e r i s t i c s of d e l i g n i f i e d f i b r e s .  Relative  strength increase on oil-tempering was found to be lowest of the whole series On the average, 37$ r e l a t i v e strength increase was obtained on boards made from f i b r e on which an anticipated weight loss of 32$ (corresponding to 1$ r e s i d u a l l i g n i n ) was produced by 7 successive sodium c h l o r i t e  treatments.  This i s not surprising when viewed i n terms of r e l a t i v e amount of aromatic compound available f o r polycondensation in. the d e l i g n i f i e d f i b r e .  A fur-  ther hypothesis of the experiment i s based on t h i s factor, while not excluding the p o s s i b i l i t y of o i l polycondensation with other non-aromatic wood constituents, or s e l f polymerization. Lower r e l a t i v e strength increase following d e l i g n i f i c a t i o n i s one f a c t pointing; toward a chemical nature of tempering mechanism.  6.  Deactivated L i g n i n Fibre  Considerable time was  spent i n devising a method by which l i g n i n  deactivation i n - s i t u 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 b u i l d i n g unit seemed t o offer a good way t o accomplish t h i s .  Unfor- -  tunately, a l l l i g n i n o x i d i z i n g methods t r i e d rendered the oxidized l i g n i n hot-water-soluble, thereby confounding observations on deactivated l i g n i n . Another f e a s i b l e way c f l i g n i n deactivation was attempted through ' precondensing l i 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 t o condense-with l i g n i n on high temperature treatment, such as hot-pressing of the mat.  The f i b r e thus'  treated showed no change.in absolute board strength, but the effect- of o i l tempering was reduced t o about one-half of control values.  This may be  counted as a d d i t i o n a l -evidence f o r the chemical nature of the i n t e r a c t i o n and also points toward l i g n i n as the most important wood, constituent i n -  .  volved i n the" heat-activated i n t e r a c t i o n with the tempering o i l . .  B.  E f f e c t of D e l i g n i f i c a t i o n Further investigation of hardboard-oil-tempering was centered on  l i 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 i n f l u e n t i a l wood component  involved i n the i n t e r a c t i o n and that the mechanism may be due t o con- •  densation of l i g n i n and tempering o i l . Only one per cent weight loss accompanying l i g n i n oxidation r e s u l t s i n more than 50$ drop of r e l a t i v e board strength; This one per cent weight loss was found t o correspond t o 28.72$ r e s i d u a l l i g n i n as estimated by the ultraviolet  spectrophotometry method (58).  Successive losses of 3 to 5$  l i g n i n gave.lowest r e l a t i v e strength increase on oil-tempering,i .e ., 20 to 25$«  I t i s ''..thoughtthat t h i s r e s i d u a l 20 to 25$ r e l a t i v e strength increase  -73may r e s u l t from some other factor than l i g n i n .  This portion of r e l a t i v e  strength development may be a t t r i b u t e d to a second mechanism occuring during the oil-tempering process.  The tremendous drop of r e l a t i v e strength  with r e l a t i v e l y small amount of l i g n i n loss i s best evidence for the •chemical nature of the mechanism, and suggests a l i m i t e d number of react i v e s i t e s a v a i l a b l e for the tempering process.  The. mild l i g n i n ' o x i d i z i n g  treatment seems to destroy p r e f e r e n t i a l l y the sites, most important standpoint of a d d i t i o n a l strength development on oil-tempering.  from the  It i s  therefore possible that reactive a l c o h o l i c hydroxyl groups are oxidized to non-reactive aldehyde, or even carboxylic a c i d groups. An investigation" undertaken i n further study consisted of making a series of boards from f i b r e containing, controlled amounts of l i g n i n .  Non-  s i g n i f i c a n t differences we're obtained f o r absolute strength values of boards made of- d e l i g n i f i e d f i b r e of weight losses 10$ and under (corresponding to 1 7 . 1 6 $ r e s i d u a l l i g n i n ) when compared to t e n s i l e strength of control board. A l l strength values from 15$ weight loss and above gave s i g n i f i c a n t d i f f e r ences at the 5$ p r o b a b i l i t y l e v e l .  (See Table  lh).  On inspection of Figure 9 i t becomes evident that possibly two mechanisms occur i n oil-tempering of hardboards.  I t i s a l s o evident that  the maj-or mechanism relates to l i g n i n q u a l i t y rather than quantity, at l e a s t within 1 to 5$ l i g n i n removal. nated by  This portion of the curve i s desig-  "A". Abrupt loss i n r e l a t i v e strength accompanying oil-tempering i s a  most valuable piece of evidence for the correctness of the hypothesis.  It  not only shows that l i g n i n is^the most important wood constituent involved' i n the i n t e r a c t i o n , but i t a l s o points c l e a r l y toward a chemical mechanism.  The mechanism proved to.be most e f f e c t i v e on boards prepared from either untreated or alcohol-benezene extracted Asplund f i b r e .  Although i t . must be  accepted that some chemical change had taken place during the d e f i b e r i z i n g process, these changes must have q u a n t i t a t i v e l y involved other wood c o n s t i tuents than l i g n i n , since commercial pressing of Asplund pulp gives approximately 85 to 90$ y i e l d .  This y i e l d loss could be r e a l i z e d i n proportionally  higher l i g n i n content of the r e s u l t i n g f i b r e . value of 31*04$ was each.  An average Kias.on l i g n i n  obtained oh two i n d i v i d u a l attempts with two r e p l i c a t e s  This corresponds to a 9*8$ y i e l d loss or 90.2$ y i e l d , calculated on  the basis of 28$ average l i g n i n content reported for Douglas f i r (1^9). higher l i g n i n content i s possibly due to hot-water-solubles, carbohydrates.  The  and loss of  The p o s s i b i l i t y of hemicellulose degradation and condensa-  t i o n to acid-insoluble l i g n i n - l i k e furfural-base resins cannot be and has been reported i n the l i t e r a t u r e (107,  excluded  112).  Relating ultimate elongation to percent weight loss showed similar relationships, giving generally lower ultimate elongation values for tempered boards than corresponding untempered boards.  The curve for r e l a t i v e  elongation decrease i n Figure 10 shows s i m i l a r i t y 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 t e n s i l e strength, although the minimum i s not reached at 5$ weight l o s s .  Here, too, the i n t e r a c t i o n of tempering-induced  r e l a t i v e 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 c u r v i l i n e a r pattern.  -75-  Attempts t o investigate l i g n i n deactivation along the zero weight l o s s scale were not s u c c e s s f u l .  I t was. belieyed> .-t^€' ~'Dy 'Hnding a suitable i  method f o r c o n t r o l l e d l i g n i n oxidation without  :  s o l u b i l i z a t i o n of oxidation pro-  ducts, one could obtain valuable information leading to more complete understanding of the l i g n i n - o i l i n t e r a c t i o n / 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 l i g n i n i s removed, up to the point where most of the l i g n i n has been removed.  During t h i s period normal paper bonding  e f f e c t s occur and bejsome of more importance as l i g n i n i s progressively removed. U l t r a v i o l e t spectrophotometric  l i g n i n determinations  on samples  with an a n t i c i p a t e d weight l o s s of 2 5 $ gave 6 . 2 8 $ r e s i d u a l l i g n i n . S i m i l a r i t y of mechanisms for absolute and r e l a t i v e strength i n creases i s quite s t r i k i n g as the l i g n i n content i s successively reduced. Strength increase of boards of d e l i g n i f i e d f i b r e has been reported e a r l i e r by Klauditz and Stegmann(7l), and Ojland (100).  Generally  stronger.boards  are produced on removing l i g n i n from the f i b r e because of better bonding capacity of hemicelluloses, and improved paper-making c h a r a c t e r i s t i c s of the f i b r e s .  This l a t t e r property of d e l i g n i f i e d f i b r e s has been experienced  i n t h i n board formation.  .It may  be seen from Table 9 that s p e c i f i c gravity  values r i s e with decreasing amounts of r e s i d u a l l i g n i n i n the f i b r e .  Through  better f i b r e to f i b r e bonding, the i n t r i n s i c f i b r e strength can be more economically u t i l i z e d i n board strength development, r e s u l t i n g i n increased tens 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 $ r e l a t i v e strength increase.  This small portion of  -76r e l a t i v e strength increase, as compared to the major e f f e c t of tempering although not investigated i n any d e t a i l , may he due to the i n t e r a c t i o n of other wood constituents, possibly to hemicelluloses, or to physical f i b r e to f i b r e bonding, similar to that produced on addition of small amounts of synthetic r e s i n s , or to an i n t e r a c t i o n of o i l with incompletely  polymerized  phenol-formaldehyde r e s i n incorporated i n the f u r n i s h i n the amount of This l a t t e r p o s s i b i l i t y must a l s o be considered since S e i f e r t (123) that approximately  1$.  found  10$ of the phenolic r e s i n incorporated i n hardboards i s  present i n an incompletely polymerized  state.  This portion of the r e s i n  may be extracted under c e r t a i n 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 s l i g h t  de-  crease towards the end of the scale i s s t i l l evidenced with both r e l a t i v e s t i f f n e s s and r e l a t i v e elongation.  This suggested that other rate deter-  mining factors are involved to a greater extent than observed with ultimate t e n s i l e strength.  One  of the factors may be moisture pick up during t e s t -  :  ing since a l l samples were tested i n an oven-dry condition, but not protected from atmospheric reconditioning during the one or two minutes required for t e s t s .  Higher hygroscopicity of hemicelluloses,present i n r e l a t i v e l y  greater proportions toward the higher weight loss portion of the curve, may increase moisture regain of these samples to an extent that the e f f e c t could be observed i n 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 t e n s i l e strength. The t h i r d portion of the weight l o s s - t e n s i l e strength curve, designated as "C" i n Figure 9, i s possibly not distinguished because of d i f f e r e n t  -77behaviour 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 p u r i f i c a t i o n process as evidenced from the increasing amounts -of negative differences between calculated and estimated contents, together with serious degradations the f i b r e .  weight l o s s .  of the cellulose portion of  The l a t t e r i s evidenced by 1$ cupriethylenediamine  measurements.  lignin  viscosity  Serious v i s c o s i t y drop was found on samples from 25 t o 35$ ( V i s c o s i t y measurements on lower weight loss samples could  not be obtained by t h i s 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 f o r the 25$ weight loss sample.  Such a drop of  v i s c o s i t y would be expected to result i n lowered i n t r i n s i c f i b r e strength (70) as-evidenced  by f l a t t e n i n g of both untempered and tempered board  strength curves. Ultimate elongation, modulus of e l a s t i c i t y , and weight loss r e l a 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 f i n d i n g explanations f o r these phenomenons.  -78-  CONCLUSIOHS  From t h i s study of wood constituents involved i n the heat-activated oil-tempering of hardboards which r e s u l t s 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 e f f e c t i v e (105$ ultimate t e n s i l e strength increase  on boards prepared from Asplund f i b r e not modified by chemical treatment 2.  Removal of alcohol-benzene solubles has no influence on oil-tempering.  3 • Gama i r r a d i a t i o n at 10T rads gave no e f f e c t on untempered board strength but reduced r e l a t i v e t e n s i l e strength gain on oil-tempering compared, t o 114$ obtained with boards from Asplund f i b r e .  to 48$ as This drop Of  r e l a t i v e strength i s believed t o be due t o reduced i n t r i n s i c f i b r e strength rather than to reduced l e v e l of the o i l t o wood i n t e r a c t i o n . k.  Quantitative removal of hemicelluloses resulted i n a 7 0 $ r e l a t i v e strength increase, i n d i c a t i n g that hemicelluloses are also involved t o •some extent i n the i n t e r a c t i o n .  D i f f i c u l t i e s i n s p e c i f i c and complete  removal of hemicelluloses from the wood f i b r e make a non-confounded investigation .5.  of t h i s e f f e c t  impossible.  I t was found that l i g n i n i s a major wood constituent responsible f o r the strength increase '; r e s u l t i n g from oil tempering of hardboards.. r  The mechanism i s 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 i n and between f i b r e s .  Evidence f o r chemical bonding i s as follows:  -79i.  Only a l i m i t e d amount of o i l i s involved i n the i n t e r a c t i o n as evidenced by non-significant s p e c i f i c g r a v i t y - t e n s i l e strength relationships for all;oil-tempered hardboards containing an excess (more than 1 0 $ ) of o i l s o l i d s .  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 $ . ii.  ;  Removal of only 1 $ l i g n i n by an oxidation method resulted i n a 5 0 $ drop i n t h e . r e l a t i v e strength increase obtained by tempering, suggesting that l i g n i n q u a l i t y . i s more important than quantity,  iii.  Removal of 3 to 5$ l i g n i n provides a low.point increase. sites  iv.  i n relative  strength  The data suggest, .that at t h i s point 8 0 $ of r e a c t i v e "  are i n h i b i t e d .  Impregnation of f i b r e with hot-water-soluble  hemlock bark tannins  before pressing provide a 5 0 $ drop i n relative' strength increase on oil-tempering. , v.  Thereby, i t i s thought that a second method has  been used to inactivate bonding s i t e s . The  "  '  '  "CTIA Polymer" i s known to be unstable and susceptible to r e -  arrangement on prolonged heating when used as foundry core binder, but i s stable when combined with .unsaturated seed o i l , or maleic anhydride. oil 6.  compounds such as l i n -  Possibly l i g n i n also acts as an  stabilizer.  Evidence i s given f o r a second, minor f a c t o r , i n oil-tempering of hardboards.  This has not been'investigated  in detail.  L i g n i n i s not  thought to be responsible f o r t h i s e f f e c t since progressive removal of l i g n i n does not influence t h i s second mechanism. :  • •  .  7.  Past the 5$ weight l o s s point on the curve, the strength of untempered boards increases proportionally to the amount of l i g n i n removed by o x i dation technique.  Above the 25$ weight loss point, where probably i n -  creasing amounts of hemicelluloses are removed with l i g n i n and  consider-  able reduction of cellulose chain-length i s evident from v i s c o s i t y measurements, the strength increase i s possibly governed by these f a c tors.  However, t h i s does not seem to influence the second mechanism of  oil-tempering i n t h i s region to any greater, or measurable, extent. 8.  The exact s i t e of chemical bonding has not been described.  The fact that  i n t e r a c t i o n between the board and tempering o i l has been s i g n i f i c a n t l y v.  reduced by l i g n i n oxidation and tannin, condensation treatments,  points.  toward a l i m i t e d number of very reactive groups involved i n a mechanism. Since a l c o h o l i c 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  l i g n i n and tempering o i l takes place at an unsaturated double bond; or at some a l c o h o l i c hydroxyl- group on the straight chain portion of the phenylpropane l i g n i n b u i l d i n g u n i t .  Interaction with phenolic hydroxyls  i s 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 t e n s i l e strength.  I t should be noted that u l t i -  mate elongation values were lower f o r 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 r e s i d u a l l i g n i n content of samples was  reduced.  -81LITERATURE  1.  Adams,  G.A.  and  alpha 2.  Adler,  E .  1951  peeled, 3»  ___  •  S.  _ _ _ _ _ _  a n t  wood  Sulphite  ^"  Stockman.  from unpeeled,  Arthur,  6.  J . C .  fied  cotton.  Barton,  De  i n  Baun,  acid  E .  State Sc.  and  1953  •  The  J . C . Arthur Part  1958.  properties  of  641-647. of  spruce  54  the  (l4);  effects  properties  or  of  p u r i -  204-206. l i g n i n  and  sodium  chlor-  496-502.  qualitative  evaluation  bleaching  1,  J r .  1958.  Textile  Extraction  University  R.M.  of  phloroglucinol-  l i g n i n  preparations;  f  of  pulp.  TAPPI  effect  of  Monograph  of  New  of  Res.  The J .  28  College  of  radiation  198-204.  (3)2  hemicelluloses  York,  gamma  f r o m woody  Forestry,  '  G  tissues.  Syracuse,  M.  1940.  Plastics  and  chemicals  from wood.  Paper  Trade  J .  T 249-251.  F . E . and  Supplement 13.  A  the  phenolic  Thesis.  110; Brauns,  1951» i n  un-  10.  cotton.  Booker,  Boehm,  e t . a l .  F.A.  33 (10):  of  6 l (l8B);  mechanism  molecular  of  from  445-450.  Papperstid.  28 (3);  J .  with  -'71-73.'  (2)s  No.  some  products  Tappi  Nord.  on  12.  solution^  pulping  Svensk  Proposed on  reaction  test  Blouin,  11.  The  acid  L . A .  II.  Research  F . F .  Series  10.  Textil  R . M . and  _4  Sulphite  wood  Estimation  Papperstid,  logs.  radiation  hydrochloric  Beeman,  9.  Part  gamma  .1950.  J . S .  Tappi 8.  1958.  energy  ite 7.  J r .  high  spruce  5k (13)2  1958.  Svensk  1951«  of  Papperstid.  Wallden.  floated  477-482.  5.  I.  l i g n i n .  associated  672-676  properties  Svensk  and  i n  Polysaccharides  ( l l ) ;  pulping  logs.  groups  38  Tappi.  Hernestam  ^  1955•  Bishop.  floated  hydroxyl ^°  C T .  cellulose.  CITED  Broughton,  G.  paper.  D.A. Volume  for  and N . A . Part  I.  I960. 1949-1958.  Brauns.  Matlin. Tappi  1951°  _4  The  chemistry  Academic The  of  Press,  mechanical  l i g n i n . New  York.  behavious  of  493-498...  ( l l ) ;  1  14.  Bystedt,  J .  and A . M . Anderson.  materials  60 (13): 15  •  Cabott,  I.M.  acidity process.  by  and i n  a  precision  492-496. C.B.  Purves.  pulping Pulp  of  Paper  1957» d i a l  Mag.  indicator.  1956.  spruce  Measuring  The  Can.  Svensk  effect  periodate  57 (4):  thickness  of  l i g n i n  of  Papperstid.  temperature by  151-158.  sheet  the  and  sulphite  -8216.  Charlesby, A. 1955• The degradation of cellulose by i o n i z i n g r a d i a t i o n . J . of Polymer S c i . 15: 263-270.  17.  Clermont, L.P. and F. Bender. I96I. E f f e c t 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 .  18.  C o t t r a l l , L.G. 1 9 5 2 . The influence of hemicelluloses i n wood pulp: f i b r e s on t h e i r papermaking properties. Tappi 35 ( 9 ) ' '4-71-480.  19.  Currier, R.A. I 9 6 2 . 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Determination of comp o s i t i o n and i d e n t i f i c a t i o n of 2 - 0 - (4-0Methyl-D-glucopyranosyduronic acid)-D-xylose. J . Am. Chem. Soc. 7 § (June): 2 5 0 5 - 2 5 0 7 .  26.  ENJAY. 1 9 6 2 . "CTLA Polymer". B u l l . No. l 8 . pp. l 6 .  27.  Enkvist, T. and E. Hagglund. 1 9 5 0 . Studien "Tiber den Zusammenhang . zwischen Sulfidierung, Methlylierung und S u l f i t i e r u n g von L i g n i n . Svensk Paperstid. 53 ( 4 ) : 8 5 - 9 3 .  28.  Erby, W.A. and C. Schuerch. I 9 6 2 . Some observations on l i g n i n access i b i l i t y i n wood made during a two-stage degradation. Tappi 45 ( 5 ) : ' 409-413.  29.  Erdtman, G.A. 1 9 5 4 . Spectrographic contributions t o 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.  Cellulose v i s c o s i t y conversions.;  ENJAY Company Inc., New York, Technical  -8330.  F i c k l e r , H.H. platten.  61  (k)t  1958. 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On s t r u c t u r a l e l e ments i n l i g n i n . Svensk Papperstid. 57 (17): 633-637.  37.  G i e r t z , H.W.  1951«  Development i n bleaching process.  Tappi 34  (5):  209-215. 38.  • 715):  1951» Chlorine dioxide bleaching. 469-V760  Svensk Papperstid.  5^  39.  Gillham, J.K. and T.E. T i m e l l . 1958. The polysaccharides of white b i r c h (Betula p a p i r i f e r a ) Part 7» Carbohydrates associates with the alpha cellulose component. Svensk, Paperstid. 6 l (lj)t ^kO-^hk.  40.  Glaudemans, C.P.J., E. Pas'sagila and E.A. W i e l i c k i . 1962. Stabilization of cellulose subject to high energy r a d i a t i o n . Tappi 45 (7): 5>+2-  547.  ~  •  ______ * T i m e l l . 1958. The polysaccharides of white b i r c h ~° (Betula papyrifera) Part. 6. Molecular properties of hemicellulose. Svensk Papperstid. 6 l ( l ) s 1-9. a n d  42.  T , E  Goldschmid, 0 . 1955« Aqueous hydrolysis of l i g n i n . I . Paper chromatographic separation of monomeric l i g n i n degradation products. Tappi  38 (12):  728-732.  43.  Goring , D.A.I. and.'T.E. T i m e l l . . I 9 6 2 . Molecular weight of native c e l l u l o s e . Tappi 45 ( 6 ) : 454-459. -  44.  Goring, D.A.I, and T.E. T i m e l l . i 9 6 0 . Molecular properties of a native wood c e l l u l o s e . Svensk Papperstid. 63 (l6)s 524-527. 1  -84-  45.  Grangard, D.H.  39(5): 46.  195^*  Bleaching I .  The chlorination of pulp.  Tappi  270-276.  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.  H a r r i s , E.E.  1955•  Highlights In the chemistry of l i g n i n .  Prod. J . 5 ( l ) t 49.  Forest  26-31.  Hofstrand, A.D. 1958. 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Hydrolytic degration within trees and i t s e f f e c t s on the mechanical pulping and other propert i e s of wood. Tappi 44 ( l l ) : 798-813.  130.  Fifth edition.  1946.  The Iowa  Heat, s t a b i l i z e d wood.  and J.A. McPherson. 1955• The non-resistant components of the wood of Eucalyptus regnans (F. M e r e l l ) . Part IV. Holzforsch.  2 (5)s  140-W^  ~  131.  Swanson. J.W. 1956. Beater adhesives and f i b r e bonding. further research. Tappi 39 (5): 257-267.  132.  Thode, E.F., and Shwe Htoo. 1955* Surface properties of r o s i n size p r e c i p i t a t e . Tappi 38 (12): 705-709.  133.  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 r e l a t e d physical e f f e c t s . Tappi 45 ( 6 ) : 433-442.  134.  T i m e l l , T.E. i960. I s o l a t i o n of hardwood glucomannans. s t i d . 6 3 (.15): 472- 476.  135.  Toth, J . , T. Asztalos and G . Balogh. 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.  I96I.  The need f o r  Svenk Papper-  Farostlemez K i l m a t i z a l a s a .  -90137-  Turner, H.D., J;B. Hoh'f and S.L. Schwartz. 1948. E f f e c t of some manufacturing variables on the properties of fibreboard prepared from m i l l e d Douglas f i r . Forest Prod. Res .Soc. Proceedings 2: 110-112.  138.  U.S.  139.  Voss, K. 1952. Die Warmebehandlung von Holzfaser-Hartplatten. Roh- Werkstoff 10 (8); 299-305.  140.  Wacek. A. and S. Meralla. 1952. Holzforsch. 6 (3)2 65-70.  'Ikl.  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.  Faserverfilzung und  Holz  Faserverklebung.  and K. K r a t z l . 1948. Constitution of the side-chain of l i g n i n . J . Polymer S c i . 3 (4): 539-548.  14-2.  Walling, W.C. I 9 6 I . Hardboard ....State of the industry and i t s pract 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 a l k a l i - s o l u b l e 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 t e n s i l e strength vs. modulus of rupture r a t i o f o r hardboard. University of B r i t i s h Columbia, Faculty of Forestry.  146.  Wilson, K., E. Ringstrom and I . Hedlund. 1952. The a l k a l i s o l u b i l i t y of pulp. Svensk Papperstid. 55 (2)s 31-37.  147.  Wilson, W.S. 1951. 561-566.  148.  Winogradoff, N.N. Nature 172s  149.  Wise, L.E. and E . C Jahn. 1952. Wood chemistry. Second E d i t i o n , Reinheld Publishing Corp. New  15C)•  151.  The mechanism of f i b r e bonding. 1950. 72-75.  Tappi _  (12):  X-ray i r r a d i a t i o n of cellulose acetate. V o l . I and I I . York.  , M. Murphy and A.A. d'Addieco. 1946. Chlorite holocellulose, ' i t s f r a c t i o a t i o n and bearing on summative wood analysis and on studies on the hemicelluloses. Paper Trade J . 122 (2)j 35-43« 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 f i b r e as.determined by Bauer-McNett f i b r e c l a s s i f i c a t i o n . Screen Mesh Size  Fraction  s  20  25.3  35  35.1  65  27-5  150  12.1  Total :  Table 2 .  lOO.0 %  S p e c i f i c a t i o n s and some properties of CTLA Polymer ( 2 6 ) . Test  Gravity, API  Value I k •  6 -  -  V i s c o s i t y , SSU at 2 1 0 ° F.  100  Nonvolatile matter, Wt. $ Min.  .  Iodine No., cg./g., Min.  -  Test Method  250  80  240  Water V o l . $ Max.  0.8  J F l a s h , COC °F., Min.  210  ASTM D 2 7 8 - 5 5 ASTM D  8 8 - 5 3  ASTM D 1 5 4 - 5 3 " ASTM D 5 5 5 - 5 4 ASTM D  9 5 - 46  ASTM D  9 2- 52  Table 3 • Low temperature c h l o r i n a t i o n of Asplund pulp followed by 3 0 min. e x t r a c t i o n with 3 $ monoethanolamine. Sample No. 1  '  4  1  5 6  20 20  2  3  Chlorination Time^ min.  •  40 40 80 80  '  Weight l o s s or g a i n $ f  *  Weight l o s s following 3 0 min. e x t r a c t i o n with 3 $ monoethanolamine, %  -  5 . 2 8  -  *  -  - 3 . 2 6  -  0.90  -  8.77  * 0 . 7 0 _ 8 . 8 6  -92-  Table .4.  Low temperature c h l o r i n a t i o n of Asplund pulp followed by.30 min. extraction with hot - water < >  , Sample No.  Weight l o s s or. gain, $  Treatment  7  40 min. c h l o r i n a t i o n  *  8  kO min. c h l o r i n a t i o n plus hot water extraction  -1.6k.  Hot water extraction only  - 0.50  9  Table 5.  Chlorination of Asplund pulp with t - b u t y l  Sample 10 11 12  Table 6 .  Sample No..  Chlorination with t-BuOCl  - 4.30 T-BuOCI wash only  Weight l o s 6 ^  I  2  9 10 11  12  - 0.26  Anticipated and r e s i d u a l l i g n i n content of sodium c h l o r i t e treated f i b r e as calculated and determined, by micro-Kappa number and UV absorption spectra, based on 31.04$ Klason l i g n i n .  2 3 4  7 8  * 1.01  Chlorination with t-BuOCl  i-  . 5 6  hypochlorite.  Weight l o s s or «»in. -•'  Treatment  Nr>.  ^ 8  1  Anticipated  '•  Micro-Kappa Lianin. _  UV L i g n i n ,  $  31.04 30.34 29.63 28.91 28ol6  3 4 '5 10 15 20 25 30  lignin,  27.41' .  23-38 18.87 13.80 8.05  --  28.72  •-  16.20  13.72  5.64 3.46  1.21  26.95 25.96 23.33 20.23 17.16 10.36 6.28  -93-  Table 7 .  Sample No.  One per cent cupriethylenediamine v i s c o s i t y and corresponding degree of polymerization values of sodium c h l o r i t e d pulp.  Weight loss,  i  1 $ CED v i s c o s i t y , cp.  D.P. (22)  10  25  136  2390  11  30  105  2210  12  35  56  1885  Table 8 .  Sample No.  O i l absorption values of boards of d i f f e r e n t f i b r e composition.  Treatment  Weight loss' Ave. by Treatmnti Sp. Gr. >  Oil Absorption,  %  1  Asplund f i b r e  -  • 71  10.70  A  Alcohol-benzene extracted f i b r e  -  •79  13.10  B  Sodium hydroxide extracted f i b r e  -  •78  14.20  C  Modified cellulose f i b r e  -  .79  13.70  D  Lignin deactivated f i b r e  -  •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  .  -94Table 9 .  E f f e c t of temperature on t e n s i l e strength of oil-tempered - hardboards. . •  Sample 'No.  Average Sp.Gr. Corr. Tensile S t r ; , kg/cm?  Temperature. °C.  Comparative Untempered Str.» kg/cm?  1-10  130  1435  859  11-20  155  1750  885  21-30  175  1214  946  Table 10.  Specimen Width., mm.  Influence of specimen width on t e n s i l e strength and coe f f i c i e n t of v a r i a t i o n (CV) of t h i n untempered boards.  -  Average Sp.Gr. Corrected Tensile Strv» • kg/cm?  Coefficient of Variation, £ N =  3  588  16.97  5  726  , 18.54  7  858  11.08  9  945  5-95  11  874  10.60  20  Table 1 1 .  Interaction between Wood Constituents and Tempering O i l Measured by Ultimate Tensile Strength, Modulus of E l a s t i c i t y (MOE), and Ultimate Elongation.  Ave. Ave. Oil Absorp Spec. Ult.Tens. t i o n Jravity, Strength, g-/em? kg./cmr i •724 1291 Humldificat. 1236 .712 Heat-Treatm. -B18 Oil-Temprd . 1 0 . 7 . 2801 .696 1288 H. .687 1332 H-T. .788 0-T. 3040 13.1 1566 H. • 730 1482 H-T. •737 2284 . 7 8 6 0-T. 13-7 .682 1558 H. 1627 H-T.716 2718 0-T. Ik.2 •777 3184 H. •799 .784 H-T. 3011 0-T. 13.0 4513 .895 .686 H. I687 H-T. 11.2 .786 2826 0-T.  Wood Constituent Board under Investigation Treatment Asplund Fibre  A]_ A2 A3 AlcohoBi Benzene B Extractives B^ Modified C Cellulose C Co Di Hemi cellulose D 2  1  2  2  El E E3 Modified F Lignin F (Tannin Impreg) F3 Lignin  2  1 2  Note:  ?  Ave. Spec.Gravity Relative Ave. Ultimate Strength Corrected MOE Slongation, Tensile Str.. Increase. Remarks kg/cm? kg/ cm'r i n . / i n . 1 12,831 0 . 0 1 8 4 9 1299 1271 1 2 , 0 2 9 O..OI679 114 2779 . 24.263 0 . 0 1 5 1 0 . Ave. Sp.Gr. 13>072 0 . 0 1 7 7 2 1403 1466 12,024 0 . 0 1 8 9 9 f o r Correc22,947 0 . 0 1 7 9 4 3037 . .117 .. .. t i o n s : 1548 1 6 , 9 8 8 0.01426 H.: .726 1451 H-T.: .727 1 7 , 4 9 1 0.01184 0.01149 0-T.: .813 2 2 9 8 48 24,659 15,928 0.01602 16 51 16,928 0.01506 1642 70 24,335 0.01404 2803 36,406 0 . 0 1 3 4 7 3079 2830 40,273 0 . 0 1 0 6 1 0 . 0 1 1 6 5 4213 46,073 37 1867 1 5 , 7 9 7 0.01473 f  23,191  0.1477  Each value represents an average of 24 measurements.  2948  58  Table 12,  S i g n i f i c a n t tensile strength differences between untempered boards of d i f f e r e n t chemical composition.  Y  Y  Board \^  S = 292.4;  3079 - Y E  1867 - Y  1654 - Y  F.  D  A  1299  1780 *  562 *  B  1403  I676 *  459 NS  G  - 1548  1531 *  314 NS .  D  1654  1425' *  208 NS  F  1867  1212 *  E •  3079  Sy - 119.9;  D = Q.Sy;  NS  _  _  D = 526 kg/cm?  A difference of 526 kg./cm?. i s needed to declare a difference between any two strength values as s i g n i f i c a n t 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 T e n s i l e  between  S t r e n g t h ,  O i l Weight L o s s  $ C  L i g n i n  Absorp-  Content,  Board  $  Treatment tlumidifiec  31-04  Tempered  0-T.  $ 13.1  13.8  H .  2  27.81  13.6  0-T H .  3  26.53  0-T  4  24.09  0-T.  5  20.89  0-T.  •  13.2  H .  13.9  H .  13.7  H .  10  17.72  0-T.  12.9  H .  15  16.24  0-T  12.5  H .  20  10.42  0-T.  13.6  H .  25  6.41  0-T.  13.0  H .  30  3.85  0-T.  15.2  H .  35 Note:  1.8  0-T.  A v e .  14.9  o f  V a r y i n g  E l o n g a t i o n ,  Corrected  S p e c . H i t .  t i o n , jravi+y,  H .  1 . 29.64  Boards  U l t i m a t e  ft/cm3 .749 .811 •705  .817 .703  .762 .715 •770 .713 •777 .704 •774 •738  •790 •747 .817 .786 .825 .780 .845 •799  .867 .785 .891  T e n s .  S t r e n g t h ,  kg/cm?  1781  3651  L i g n i n  C o n t e n t  a n d Modulus  i486  2050  163b 2147 1514 1975 1702 2093  2096 2600  2187 2575 2841 3011 3850 4679 3767 4771 3959 4803  T e m p e r i n g  E l a s t i c i t y  R e l a t i v e  A v e .  R e l a t i v e  S t r e n g t h  U l t .  E l o n g .  Increase^ E l o n g a t i o n Decrease,  i  104.9  i n . / i n .  0.02059 0.01686  *.  .22.4  0.00631  1342 I962  a n d  o f  46.2 .  38.0 31.2 30.5  0.00657 0.0092'+ 0.00735  0.01039 0.00727  0.01286 0.00733  0.01125  * 4.1  20.5 30.5 .'43,0  23.0 .... 0,06742 .34.1 0.01645 24.1 0.00930 43.4 0.01261 26.7 0.00926 17-7 0.01467 , 6.0 O.OO913 37.7 0.01994 0.01366 21.5 31.5 0.01995 26.6 0.01421 28.7 0.01761 21.3 0.01393 20.9  O i l  M e a s u r e d  b y  U l t i m a t e  ( M O E ) .  R e l a t i v e A v e .  S t i f f n e s s  MOE,  I n c r e a s e .  kg/cm?  $  Remarks  14,924  26,315 -.76.3. _  23,577 31,798 .34.9. 18,118 25,992 43-3 15,523  29,229  57.8  Average 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 . :  .0-T.:  .756  .819  14,379 28,917 101.0.  19,930  29.945 .. _69..7 22,547 I30 474 35.2 24,346 ;  32,237 32.5  28,864 34,713 34,485  20.2  42,899 24.4 35,406 44,346 37,708 44,429  25.2 17.8  Values f o r 1, 2, 3, 4$ weight losses represent an average of 24 measurements while those f o r C , 5, 10, 15, 20, 25, 30, 35$ weight loss are averages of 48 measurements.  Table 14.  S i g n i f i c a n t t e n s i l e strength differences between untempered beards prepared from delignified fibre.  Y Wt.Los^\ *.  Y \  3953 - Y  •-  3850 - Y  35  25  2841 - Y  2187 - Y  30  20  15  3767 - Y  2096 - Y  1781  - Y 0  10  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  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  25 .  3850  103 NS  _  35  3957  -  . S = 299.78;  Sy = 86.57;  *  D = Q. Sy;  _  *  -  79 NS _  -  . _  -  -  _ _  1  • _  -  _  -  _  D =.444 kg/cm?  A .difference of 4;44 kg/cm? i s required to declare a difference between any two strength values as s i g n i f i c a n t at the 5$ probability l e v e l .  Figure lA. Relationship between time, number of treatments and weight loss obtained with 70°C. cooking temperature in sodium chlorite solution.  4 _6!_3iV.ie  id.20—itiw  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 f o r specimen preparation.  -103-  Figure k.  Adjustfble-width cutting die used f o r cutting specimens of uniform width.  Figure 5.  CEJ d i a l microcator  -105-  Figure 6 .  Instron table model t e s t i n g 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_  "  Example-. I. Unadjusted strength: 1600 kg.jcm Adjusted strength : 1665 kg,/cm  2  2.Unadjusted strength: 1474 kg./cm Adjusted strength: 1280 kg./cm  2  UNTEMPERED  2  B a sic specif ic gravity: .726  65  .66  .67  .68  .69  .70  . 71  .72  .73  .74  .75  .75  .77  .78 .79 BO Specific gravity  .81  CM.  xT 6  «5000f c  Figure 8. Interaction between wood constituents and tempering oil as measured by ultimate (H: Humidified; T-. Tempered ) tensile strength. 114  11,7  48  _>  5J_  Relative Strength increase %  B E  54000  o  i  3000  2000  1000 H  Asplund pulp (Control)  Alcohol-benzene extractive (7.45% removed)  Modified cellulose (i0 rads. gamma irradiation) 7  H  Hemicellulose (8.68% removed)  Lignin  (30 %removed)  H  Modified lignin (6.7%tannin impregn)  Figure 9. Relationship of ultimate tensile strength plus strength increase following oil-tempering to » 100per oent weight loss, and residual lignin oontent with chlohted Asplund fibre. c  'A'  j  'B  CO  2  4  /  LEGEND: • Untempered o Tempered - Strength increase Calculated curve. @  60  40"  y= I755.66 -584.47X+303.73X -5_.27X +2.8IX R*0.943 2  3  4  |nY=6.48-0.43 InX  20-  R-0.754  "202T  to o  80  |Y=3^98.45-_3f34X+^6l.36X -l7895X^930X *J^ R = 0.978 o".c.**1>^  3104  3*  10  15  20  25  17.16  16.20  10.36  6.28  30 35 Weight loss % 3.16 1.8 Residual lignin,%  Figure 10.  Relationship of ultimate elongation plus elongation decrease following oil-tempering to percent weight loss and residual lignin with chlorited Asplund fibre.  .030-  80-  o co o O  _ 9  o  60-  e c o  UJ  .010-  40-  20  LEGEND• • Untempered o Tempered A Elongation decrease 25 31.04  20.23  17.16  16.20  1036  6.28  30 3*5 Weight loss % 3.16  IJB  Residual lignin,%  Figure II. Relationship of modulus of elasticity (MOE) plus  O 31.04  5 , 20.23  10  15  i  (  17.16  1620  20 , 10.36  25 6.28  30 35 Weight loss % , 3.16 1.8 Residual lignin % t  -IllFigure 12.  Sample "boards of d i f f e r e n t f i b r e chemical c o n s t i t u t i o n .  Asplund f i b r e (Untempered)  Asplund f i b r e (Tempered)  Sodium-hydroxide extracted f i b r e extracted f i b r e ( 7 - 5 $ removed) (8.7$ removed)  Modified l i g n i n fibre ( 6 . 7 $ tannin solids)  Modified c e l l u l o s e fibre ( 1 0 rads gamma irradiation)  Oxidized l i g n i n fibre (1$ weight l o s s )  Oxidized l i g n i n fibre (2$ weight l o s s )  Oxidized l i g n i n fibre ( 3 $ weight l o s s )  Oxidized l i g n i n fibre (4$ weight l o s s )  Oxidized l i g n i n fibre (5$ weight l o s s )  Oxidized l i g n i n Oxidized l i g n i n fibre fibre (10$ weight l o s s ) (15$ weight l o s s )  Oxidized l i g n i n fibre (20$ weight l o s s )  Oxidized l i g n i n fibre  Oxidized l i g n i n fibre  Oxidized l i g n i n fibre  A l c o h o l -be nz e ne  Oxidized l i g n i n fibre  (25$ weight l o s s ) ( 3 0 $ weight l o s s ) ( 3 5 $ weight l o s s )  7  ( 3 5 $ weight l o s s ) (Tempered)  

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