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The influence of native fatty acids on the formation of glue bonds with heat-treated wood Hancock, William Vollor 1964

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T H E I N F L U E N C E O F N A T I V E F A T T Y A C I D S O N T H E F O R M A T I O N O F G L U E B O N D S W I T H H E A T - T R E A T E D W O O D by W I L L I A M V O L L O R H A N C O C K B . S . F . , T h e U n i v e r s i t y of B r i t i s h C o l u m b i a , 1949 M . F . , T h e U n i v e r s i t y of B r i t i s h C o l u m b i a , 1956 A T H E S I S S U B M I T T E D IN P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F D O C T O R O F P H I L O S O P H Y i n the D e p a r t m e n t of F o r e s t r y We a c c e p t t h i s t h e s i s as c o n f o r m i n g to the r e q u i r e d s t a n d a r d T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A A p r i l , 19 64 I n presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree a t the U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f a r t h e r agree t h a t p ermission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that copying o r p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed -without my w r i t t e n p e r m i s s i o n . Department of The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8, Canada. the U n i v e r s i t y of B r i t i s h Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY of WILLIAM VOLLOR HANCOCK B.S.F., The University of B r i t i s h Columbia, 1949 M.F., The Univ e r s i t y of B r i t i s h Columbia, 1956 FRIDAY, MAY 1, 1964, at 9:30 A.M. IN ROOM 237, FORESTRY AND GEOLOGY BUILDING COMMITTEE IN CHARGE Chairman: F.H. Soward P.G. Haddock R.W. Wellwood L.D. Hayward J.W. Wilson J.H.G. Smith D.J. Wort External Examiner: J.E. Marian Forest Products Laboratory Un i v e r s i t y of C a l i f o r n i a THE INFLUENCE OF NATIVE FATTY ACIDS ON THE FORMATION OF GLUE BONDS WITH HEAT-TREATED WOOD ABSTRACT The underlying cause was sought f o r " i n a c t i v a t i o n " , a heat-induced change i n the surface of veneer that i n -h i b i t s d i f f u s i o n of moisture i n t o the wood. I t was demonstrated, by the use of Douglas f i r wood, that the formation of an i n a c t i v a t e d surface could be prevented by e x t r a c t i o n w i t h c e r t a i n organic s o l v e n t s , but not w i t h water, e i t h e r before or a f t e r the wood was d r i e d , When the e x t r a c t a b l e m a t e r i a l s were removed, or were o r i g i n a l l y absent, no specimen examined showed degrada-t i o n , through the e f f e c t of heat, of the p o t e n t i a l f o r forming strong glue bonds. The f r e q u e n t l y p o s t u l a t e d statement r e l a t e d to formation of ether linkages from hydroxyl groups, i n heated wood, was found to be not c o r r e c t . Although o x i d a t i o n had been suggested as a c o n t r i b u -t i n g f a c t o r , i n a c t i v a t e d surfaces were prepared i n the absence of oxygen i n anything but minute amounts. Veneer was c o l l e c t e d from C o a s t a l and I n t e r i o r type Douglas f i r trees that e x h i b i t e d severe, moderate or no s u s c e p t i b i l i t y to the development of i n a c t i v a t i o n . Rep-r e s e n t a t i v e samples were e x t r a c t e d w i t h simple alkanes and a complete separation of the v a r i o u s components c a r r i e d out, using the techniques of g a s / l i q u i d , paper and t h i n - l a y e r chromatography. Q u a l i t a t i v e v a r i a b i l i t y was found, between and w i t h i n t r e e s . Strong c o r r e l a t i o n was found between the formation of an i n a c t i v a t e d surface and the presence of saturated f a t t y acids w i t h carbon-chain lengths i n excess of eighteen atoms. The r o l e of long-carbon-chain, saturated f a t t y acids as the causal agent of i n a c t i v a t i o n was s u b s t a n t i a t e d by the a p p l i c a t i o n of commercially-prepared a c i d s , of various chain lengths, to veneer that had proven i n -s u s c e p t i b l e . When heated, t h i s veneer developed an i n a c t i v a t e d s u r face. A theory was proposed, based on the work described i n t h i s t h e s i s , and the informat i o n a v a i l a b l e i n the l i t e r a t u r e , to e x p l a i n the mechanism of surface modi-f i c a t i o n . I t s t a t e s that removal of some or a l l of the l a s t molecular l a y e r of water from the wood surface, and the a p p l i c a t i o n of heat, permits the saturated long-chain f a t t y acids to hydrogen-bond w i t h the hydroxyl groups contained i n the wood c e l l u l o s e . The surface of the wood i s then s h i e l d e d by a hydrocarbon l a y e r w i t h very low f r e e surface energy that i s not- r e a d i l y wet-tab l e by the water contained i n a p p l i e d glue. GRADUATE STUDIES F i e l d of Study: F o r e s t r y Methods i n Wood Technology Research i n Wood Anatomy Commercial Timbers of the World Research i n the P r o p e r t i e s of J.W. Wilson R.W- Kennedy R.W. Wellwood Wood General F o r e s t r y Seminar R.W. Wellwood The S t a f f Related F i e l d s : Problems i n Forest Mensuration Forest Research Methods Organic Chemistry J.H.G, Smith J.H.G. Smith G.G.S. Dutton L.D. Hayward PUBLICATIONS Smith, J.H.G., P.G. Haddock and W.V. Hancock, 1956. Topo-physis and other influences on growth of cuttings from black cottonwood and Carolina poplar. Jour.For. 54(7): 471-472. Hancock, W.V. 1957. The d i s t r i b u t i o n of dihydroquercetin and a leucoanthocyanidin i n a Douglas-fir tree. For.Prod, Jour, .7(10):335-338, Northcott, P.L., H.G.M. Colbeck, W.V. Hancock and K.C. Shen, 1959.Undercure-casehardening i n plywood, For.Prod.Jour, 9(12):442-451. Hancock, W.V. and P.L. Northcott, 1961. Microscopic i d e n t i -f i c a t i o n of undercured glue bonds i n plywood, For.Prod, Jour. 11(7):316-319. Also Wood 27.(7 ,8) : 286-287 , 332-334. Northcott, P.L., W.V. Hancock and H.G.M. Colbeck. 1962. Water r e l a t i o n s i n phenolic (plywood) bonds, For.Prod,Jour. 12(10):478-486, Hancock, W.V, 1963, E f f e c t of heat treatment on the surface of Douglas-fir veneer. For. Prod. Jour, 13(2):81-88. Northcott, P.L., W.V. Hancock and H.G.M. Colbeck. 1963, Evidence i n d i c a t i n g the need for an ASTM standard of wood f a i l u r e . In press, Am,Soc, Testing materials, Proc, A B S T R A C T The u n d e r l y i n g cause was sought f o r " i n a c t i v a t i o n " , a heat-i n d u c e d change i n the s u r f a c e of v e n e e r that i n h i b i t s d i f f u s i o n of m o i s t u r e i n t o the wood. It was d e m o n s t r a t e d , by the use of Douglas f i r wood, that the f o r m a t i o n of an i n a c t i v a t e d s u r f a c e c o u l d be p r e v e n t e d by e x t r a c t i o n w i t h c e r t a i n o r g a n i c s o l v e n t s , but not w i t h w a t e r , e i t h e r b e f o r e o r a f t e r the wood was d r i e d . When the e x t r a c t a b l e m a t e r i a l s w e r e r e m o v e d , o r w e r e o r i g i n a l l y a b s e n t , no s p e c i m e n e x a m i n e d showed d e g r a d a t i o n , t h r o u g h the e f f e c t of h e a t , of the p o t e n t i a l f o r f o r m i n g s t r o n g glue bonds. The f r e q u e n t l y p o s t u l a t e d s t atement r e l a t e d to f o r m a t i o n , of ether l i n k a g e s f r o m h y d r o x y l g r o u p s , i n heated wood, was found to be not c o r r e c t . A l t h o u g h o x i d a t i o n had been s u g g e s t e d as a c o n t r i b u t i n g f a c t o r , i n a c t i v a t e d s u r f a c e s were p r e p a r e d i n the a b s ence of oxygen i n a n y t h i n g but m i n u t e amounts. V e n e e r was c o l l e c t e d f r o m C o a s t a l and I n t e r i o r type D o uglas f i r t r e e s that e x h i b i t e d s e v e r e , m o d e r a t e o r no s u s c e p t i b i l i t y to the d e v e l o p m e n t of i n a c t i v a t i o n . R e p r e s e n t a t i v e s a m p l e s w e r e i i i e x t r a c t e d w i t h s i m p l e a l k a n e s and a c o m p l e t e s e p a r a t i o n of the v a r i o u s components c a r r i e d out, u s i n g the techniques of g a s / l i q u i d , p aper and t h i n - l a y e r chromatography» Q u a l i t a t i v e v a r i a b i l i t y was found, between and w i t h i n t r e e s . S t r o n g c o r r e l a t i o n was found between the f o r m a t i o n of an i n a c t i v a t e d s u r f a c e and the p r e s e n c e of s a t u r a t e d fatty a c i d s w i t h c a r b o n -c h a i n l e n g t h s i n e x c e s s of eighteen a t o m s . The r o l e of l o n g - c a r b o n - c h a i n , s a t u r a t e d fat t y a c i d s as the c a u s a l agent of i n a c t i v a t i o n was s u b s t a n t i a t e d by the a p p l i c a t i o n of c o m m e r c i a l l y - p r e p a r e d a c i d s , of v a r i o u s c h a i n l e n g t h s , to v e n e e r that had p r o v e n i n s u s c e p t i b l e . When h e a t e d , t h i s v e n e e r d e v e l o p e d an i n a c t i v a t e d s u r f a c e . A t h e o r y was p r o p o s e d , b a s e d on the w o r k d e s c r i b e d i n th i s t h e s i s , and the i n f o r m a t i o n a v a i l a b l e i n the l i t e r a t u r e , to e x p l a i n the m e c h a n i s m of s u r f a c e m o d i f i c a t i o n . It states that r e m o v a l of some or a l l of the l a s t m o l e c u l a r l a y e r of w a t e r f r o m the wood s u r f a c e , and the a p p l i c a t i o n of h e a t , p e r m i t s the s a t u r a t e d l o n g - c h a i n f a t t y a c i d s to h y d r o g e n bond w i t h the h y d r o x y l groups c o n t a i n e d i n the wood c e l l u l o s e . The s u r f a c e of the wood i s then s h i e l d e d by a h y d r o c a r b o n l a y e r w i t h v e r y l o w f r e e s u r f a c e e n e r g y that i s not r e a d i l y wettable by the w a t e r c o n t a i n e d i n a p p l i e d glue. i A C K N O W L E D G E M E N T The author wishes to thank his committee for their constructive criticism and numerous helpful suggestions. Grateful acknowledgement is made to the Superintendent and Staff of the Vancouver Laboratory, Forest Products Research Branch of the Department of Forestry, for the extensive use of facilities and equipment. Particular thanks are due to Dr. E . P. Swan for operation of the gas chromatograph used in characterisation. Appreciation is also due to the members of the forest products industry who assisted in this study. Logs and veneer were supplied or peeled by Crown Zellerbach Building Materials Limited, Pacific Veneer and Plywood Division of Canadian Forest Products Limited and Western Plywood Company Limited. Adhesives were supplied by Monsanto Canada Limited and Reichhold Chemicals (Canada) Limited. This study was supported financially by the Forest Products Research Branch of the Department of Forestry. T A B L E O F C O N T E N T S Page I INTRODUCTION 1 II L I T E R A T U R E REVIEW 7 WOOD PROPERTIES R E L A T E D TO EXTRACTIVES 9 ADDITION OF "EXTRACTIVES" TO MODIFY PROPERTIES 12 E F F E C T O F CHEMICAL T R E A T M E N T 14 PITCH PROBLEMS IN PULPING 17 EXTRACTIVES FOUND IN SPECIES REPORTED TO B E SUSCEPTIBLE TO INACTIVATION 22 Douglas fir 22 Spruces 24 Pines 25 Hardwoods 28 PROBLEMS ENCOUNTERED WHEN DRYING V E N E E R A T HIGH T E M P E R A T U R E S 29 SUCCESSFUL DRYING A T HIGH T E M P E R A T U R E S 34 SPECIES E F F E C T S ON DRYING, A S S E M B L Y , PRESSING AND GLUABILITY 34 Effect of veneer surface and prepress treatment 37 The water relations theory 38 SUMMARY 40 Page III DRYING AND TESTING PROCEDURES 41 DRYING TECHNIQUES 41 TESTING PROCEDURE USED 42 IV E X P E R I M E N T A L PRELIMINARY EXPERIMENTS - DETERMINATION OF THE N A T U R E O F THE CAUSAL A G E N T 47 E X P E R I M E N T 1 47 Collection and preparation of material 47 Pressing and testing 48 E X P E R I M E N T 2 49 Collection and preparation of material 49 Pressing and testing 51 E X P E R I M E N T 3 52 Collection and preparation of material 52 Separation of extracts 53 Application of extracts 53 Pressing and testing 54 E X P E R I M E N T 4 55 Collection and preparation of material 55 Pressing and testing 56 E X P E R I M E N T 5 57 Collection and preparation of material 57 Pressing and testing 57 v i i Page E X P E R I M E N T 6 58 Collection and preparation of material 58 Pressing and testing 59 E X P E R I M E N T 7 59 Collection and preparation of material 59 Pressing and testing 6 l E X P E R I M E N T 8 61 Collection and preparation of material 61 Pressing and testing 62 COMPARISON OF THE EXTRACTIVES OF TREES WITH VARYING SUSCEPTIBILITY TO INACTIVATION 63 E X P E R I M E N T 9 63 Inactivation in Coastal Douglas fir 63 Low moisture content 63 (a) Collection and preparation of material 63 (b) Pressing and testing 64 High moisture content 65 (a) Collection and preparation of material 65 (b) Pressing and testing 65 Inactivation in Interior Douglas fir 66 Collection and preparation of material 66 Pressing and testing 69 v i i i P a g e E X P E R I M E N T 10 69 E x t r a c t i o n and c h a r a c t e r i z a t i o n of e x t r a c t s 69 E x t r a c t i o n and r e c o v e r y 70 S e p a r a t i o n of m a j o r f r a c t i o n s 71 (a) S t e a m v o l a t i l e s 71 (b) Waxes 71 (c) S e p a r a t i o n of f r e e a c i d s 72 (d) S e p a r a t i o n of fatty and r e s i n a c i d s 72 (e) S a p o n i f i c a t i o n and s e p a r a t i o n of c o m b i n e d a c i d s f r o m a l c o h o l s , u n s a p o n i f i a b l e s and other n b n a c i d i c components 73 (f) L y o p h i l i z a t i o n 74 P r e p a r a t i o n f o r c h a r a c t e r i z a t i o n 74 C h a r a c t e r i z a t i o n of e x t r a c t i v e f r a c t i o n s 75 (a) G a s - l i q u i d c h r o m a t o g r a p h y 75 (i) S t e ams-volatiles 75 ( i i ) F r e e fatty a c i d s 76 ( i i i ) C o m b i n e d a c i d s 76 (iv) R e s i n a c i d s 76 (b) C o n f i r m a t i o n by T h e r m o t r a c 77 (c) P a p e r c h r o m a t o g r a p h y 77 (i) R e s i n a c i d s 77 ( i i ) U n s a p o n i f i a b l e s 77 ix Page (d) Thin-layer chromatography 78 (i) Fatty acids 78 (ii) Unsaponifiables 78 E X P E R I M E N T 11 78 The efficiency of extraction with n-hexane and petroleum ether 78 Collection and preparation of material 78 Pressing and testing 79 EXPERIMENT 12 79 Correlation of presence of fatty acids and susceptibility to inactivation 79 Collection and preparation of material 79 Pressing and testing 80 V DISCUSSION OF RESULTS 8 1 PRELIMINARY EXPERIMENTS 81 THE N A T U R E OF THE CAUSAL AGENT 85 Re-impregnation with fractionated extract 86 Experiment 3 86 Experiment 4 86 The repeated development of an inactivated surface 90 Experiment 5 90 Drying of veneer in an inert atmosphere 92 Experiment 6 92 The effect of extraction with various solvents 93 Experiment 7 93 x Page Occurrence of inactivation within and between species 98 Experiment 8 98 IDENTIFICATION O F THE CAUSAL AGENT 100 Inactivation in Douglas fir 100 Experiment 9 100 Extraction and characterization of extracts 107 Experiment 10 107 Observations 109 Volatile fraction 109 Resin acids 115 Combined acids 115 Unsaponifiables 1 16 Fatty acids 116 Yields 117 THE EFFICIENCY OF EXTRACTION WITH n - H E X A N E AND P E T R O L E U M ETHER 119 Experiment 11 119 CORRELATION OF PRESENCE OF F A T T Y ACIDS AND SUSCEPTIBILITY TO INACTIVATION 119 Experiment 12 119 D E V E L O P M E N T OF THE THEORY OF INACTIVATION 125 Theories of adhesion 127 The gluing of wood 132 xi Page The role of fatty acids 134 Proposed theory of inactivation 139 VI SUMMARY AND SUGGESTIONS FOR ADDITIONAL R E S E A R C H 141 SUGGESTIONS FOR ADDITIONAL R E S E A R C H 144 Vn APPENDIX 146 VIII L I T E R A T U R E CITED 168 LIST O F ILLUSTRATIONS Table 1 Bond-quality evaluations of panels made from 82 veneer from a single source subjected to different drying schedules, with or without pre-extraction Table 2 Bond-quality evaluations of veneer which was 84 susceptible to inactivation and had been extracted with acetone and methanol/benzene prior to drying Table 3 Bond-quality evaluations of panels made from 87 veneers re-impregnated with various fractions of acetone or methanol/benzene extracts or from veneer dried in an inert atmosphere. Table 4 Bond-quality evaluations of panels made from 89 veneers re-impregnated with acetone or methanol/ benzene extracts with or without carbohydrate material. Table 5 Bond-quality evaluations of panels made from 91 veneer subjected repeatedly to an "inactivating" schedule with, surface removal between dryings. Table 6 Bond-quality evaluations of panels made from 96 Douglas fir veneers extracted with water or organic solvents before or after drying. Table 7 Bond-quality evaluations of panels made from veneers of various species or from various locations in a Douglas fir tree. 99 x i i P a ge S u m m a r y T a b l e 8 B o n d - q u a l i t y e v a l u a t i o n s of panels made 102 f r o m u n t r e a t e d v e n e e r f r o m a C o a s t a l D o uglas f i r . S u m m a r y T a b l e 9 B o n d - q u a l i t y e v a l u a t i o n s of panels made 103 f r o m u n t r e a t e d v e n e e r f r o m a C o a s t a l D o u g l a s f i r . V e n e e r was d r i e d and r e c o n d i t i o n e d to the m o i s t u r e contents shown and p r e s s e d i n t o p a n e l s . S u m m a r y T a b l e 10 B o n d - q u a l i t y e v a l u a t i o n s of panels made 104 f r o m u n t r e a t e d v e n e e r f r o m an I n t e r i o r D o uglas f i r ( Q u esnel f i r ) . S u m m a r y Ta b l e 11 B o n d - q u a l i t y e v a l u a t i o n s of pane l s made 105 f r o m u n t r e a t e d v e n e e r f r o m an I n t e r i o r D o uglas f i r ( T r e e 3). Ta b l e 12 Components of the v o l a t i l e f r a c t i o n of the e x t r a c t s 110 f r o m the v a r i o u s p o s i t i o n s i n C o a s t a l a n d I n t e r i o r D o u g l a s f i r s . T a b l e 13 F a t t y a c i d s found i n the f r e e a c i d components of 111 the e x t r a c t s f r o m the v a r i o u s p o s i t i o n s i n C o a s t a l and I n t e r i o r D o u g l a s f i r s . T a b l e 14 F a t t y a c i d s found i n the c o m b i n e d a c i d s components 112 of the e x t r a c t s f r o m the v a r i o u s p o s i t i o n s i n C o a s t a l and I n t e r i o r D o u g l a s f i r s . T a b l e 15 R e s i n a c i d s found i n the f r e e a c i d components of 113 the e x t r a c t s f r o m the v a r i o u s p o s i t i o n s i n C o a s t a l and I n t e r i o r D o uglas f i r s . T a b l e 16 U n s a p o n i f i a b l e components of the e x t r a c t s f r o m the 114 v a r i o u s p o s i t i o n s i n C o a s t a l and I n t e r i o r D o u g l a s f i r s . T a b l e 17 Y i e l d s of the V a r i o u s components f r o m the v a r i o u s 118 p o s i t i o n s i n C o a s t a l and I n t e r i o r D o u g l a s f i r s . S u m m a r y T a b l e 18 B o n d - q u a l i t y e v a l u a t i o n s of p a n e l s made 120 f r o m v e n e e r f r o m C o a s t a l o r I n t e r i o r D o u g l a s f i r , u n e x t r a c t e d o r e x t r a c t e d w i t h n-hexane o r p e t r o l e u m e t h e r , and d r i e d as shown. x i i i S u m m a r y T a b l e 19 B o n d - q u a l i t y e v a l u a t i o n s of p a n e l s made f r o m v e n e e r f r o m a C o a s t a l D o u g l a s f i r , not s u s c e p t i b l e to i n a c t i v a t i o n , w h i c h was co a t e d w i t h v a r i o u s fatty a c i d s and d r i e d f o r v a r i o u s t i m e s . F i g u r e I Gas c h r o m a t o g r a p h i c c h a r t f o r the s t e a m v o l a t i l e s r e c o v e r e d f r o m the H e a r t 3 p o r t i o n of the C o a s t a l D o u g l a s f i r . F i g u r e II Gas c h r o m a t o g r a p h i c c h a r t of the s t e a m v o l a t i l e s r e c o v e r e d f r o m the sapwood of the C o a s t a l D o u g l a s f i r . F i g u r e III Gas c h r o m a t o g r a p h i c c h a r t of the m e t h y l e s t e r s of the f r e e fat t y a c i d s r e c o v e r e d f r o m the H e a r t 4 p o r t i o n of T r e e 3, a f t e r d r y i n g . F i g u r e I V Gas c h r o m a t o g r a p h i c c h a r t of the r e s i n a c i d m e t h y l e s t e r s p r e p a r e d f r o m the e x t r a c t f r o m the H e a r t 1 p o r t i o n of the C o a s t a l D o u g l a s f i r . F i g u r e V P a p e r c h r o m a t o g r a m of the m e t h y l e s t e r s of the r e s i n a c i d s r e c o v e r e d f r o m the v a r i o u s e x t r a c t i v e f r a c t i o n s . F i g u r e V I T h i n - l a y e r c h r o m a t o g r a p h of the m e t h y l e s t e r s of the f r e e fat t y a c i d s r e c o v e r e d f r o m the v a r i o u s e x t r a c t i v e f r a c t i o n s . F i g u r e VII T h i n - l a y e r c h r o m a t o g r a p h of the u n s a p o n i f i a b l e p o r t i o n of the v a r i o u s e x t r a c t i v e f r a c t i o n s . S u p p l e m e n t a r y T a b l e 8 - 1 B o n d - q u a l i t y e v a l u a t i o n s of p a n e l s made f r o m u n t r e a t e d v e n e e r f r o m a C o a s t a l D o u g l a s f i r . T hese a r e d e t a i l e d m e a s u r e m e n t s t a k e n a f t e r the cold*-soak c y c l e of C S A 0-121, S u p p l e m e n t a r y T a b l e 8 - 2 B o n d - q u a l i t y e v a l u a t i o n s of pane l s made f r o m u n t r e a t e d v e n e e r f r o m a C o a s t a l D o u g l a s f i r . T h e se a r e d e t a i l e d m e a s u r e m e n t s taken a f t e r the b o i l / d r y / b o i l c y c l e of C S A 0-121. xiv Page S u p p l e m e n t a r y T a b l e 9 - 1 B o n d - q u a l i t y e v a l u a t i o n s of 157 pa n e l s made f r o m u n t r e a t e d v e n e e r f r o m a C o a s t a l D o u g l a s f i r . V e n e e r was d r i e d and r e c o n d i t i o n e d to the m o i s t u r e contents shown i n S u m m a r y Table 9. These a r e d e t a i l e d m e a s u r e m e n t s taken a f t e r the c o l d - s o a k c y c l e of C S A 0-121 Su p p l e m e n t a r y Table 9 - 2 B o n d - q u a l i t y e v a l u a t i o n s of 158 pane l s made f r o m u n t r e a t e d v e n e e r f r o m a C o a s t a l D o u g l a s f i r . V e n e e r was d r i e d and r e c o n d i t i o n e d to the m o i s t u r e contents shown i n S u m m a r y Tab l e 9. These a r e d e t a i l e d m e a s u r e m e n t s t a k e n a f t e r the b o i l / d r y / b o i l c y c l e of C S A 0-121. S u p p l e m e n t a r y T a b l e 10 B o n d - q u a l i t y e v a l u a t i o n s of 159 pa n e l s made f r o m u n t r e a t e d v e n e e r f r o m an I n t e r i o r D o u g l a s f i r ( Q u e s n e l f i r ) . These a r e d e t a i l e d m e a s u r e m e n t s . S u p p l e m e n t a r y T a b l e 1 1 - 1 B o n d - q u a l i t y e v a l u a t i o n s of 160 pa n e l s made f r o m u n t r e a t e d v e n e e r f r o m an I n t e r i o r D o u g l a s f i r ( T r e e 3). These a r e d e t a i l e d m e a s u r e m e n t s taken a f t e r the c o l d - s o a k c y c l e of C S A 0-121. S u p p l e m e n t a r y Table 1 1 - 2 B o n d - q u a l i t y e v a l u a t i o n s of l 6 l pa n e l s made f r o m u n t r e a t e d v e n e e r f r o m an I n t e r i o r D o u g l a s f i r ( T r e e 3). These a r e d e t a i l e d m e a s u r e m e n t s taken a f t e r the b o i l / d r y / b o i l c y c l e of C S A 0-121. S u p p l e m e n t a r y T a b l e 1 8 - 1 B o n d - q u a l i t y e v a l u a t i o n s of 162 pa n e l s made f r o m v e n e e r f r o m C o a s t a l o r I n t e r i o r D o uglas f i r , u n e x t r a c t e d o r e x t r a c t e d w i t h n-hexane or p e t r o l e u m e t h e r , and d r i e d as shown. These a r e d e t a i l e d m e a s u r e m e n t s t a k e n a f t e r the C S A 0-121 c o l d - s o a k c y c l e . S u p p l e m e n t a r y T a b l e 1 8 - 2 B o n d - q u a l i t y e v a l u a t i o n s of 164 pa n e l s made f r o m v e n e e r f r o m C o a s t a l o r I n t e r i o r D o u g l a s f i r , u n e x t r a c t e d o r e x t r a c t e d w i t h n-hexane o r p e t r o l e u m e t h e r , and d r i e d as shown. These a r e d e t a i l e d m e a s u r e m e n t s taken a f t e r the C S A 0-121 b o i l / d r y / b o i l c y c l e . X V S u p p l e m e n t a r y T a b l e 1 9 - 1 B o n d - q u a l i t y e v a l u a t i o n s of p a n e l s m a d e - f r o m veneer f r o m a C o a s t a l D ouglas f i r , not s u s c e p t i b l e to i n a c t i v a t i o n that was coate d w i t h v a r i o u s fatty a c i d s and d r i e d at v a r i o u s t e m p e r a t u r e s . These a r e d e t a i l e d m e a s u r e m e n t s taken a f t e r the c o l d - s o a k c y c l e of C S A 0-121. S u p p l e m e n t a r y T a b l e 1 9 - 2 B o n d - q u a l i t y e v a l u a t i o n s of pa n e l s made f r o m v e n e e r f r o m a C o a s t a l D ouglas f i r , not s u s c e p t i b l e to i n a c t i v a t i o n that was coate d w i t h v a r i o u s fat t y a c i d s and d r i e d at v a r i o u s t e m p e r a t u r e s . . These a r e d e t a i l e d m e a s u r e m e n t s tak e n a f t e r the b o i l / d r y / b o i l c y c l e of C S A 0-121. I I N T R O D U C T I O N The r a p i d i n c r e a s e , i n r e c e n t y e a r s , i n the c o n s u m p t i o n of " c o m p o s i t e wood"^is one of the m o s t i m p o r t a n t phenomena a f f e c t i n g the wo o d - u s i n g i n d u s t r i e s . Wood u t i l i z a t i o n has g r a d u a l l y become m o r e dependent upon the use of glue. The r e a s o n s f o r t h i s a r e s e v e r a l , one b e i n g the m a n n e r i n w h i c h f o r e s t r e s o u r c e s have been e x p l o i t e d . U s u a l l y , when a new f o r e s t a r e a has been opened up, the tendency has been to f e l l the b e s t stands f i r s t . The f i n e s t and l a r g e s t t r e e s a r e u s e d f o r a l l the p r o d u c t s r e q u i r e d . The f i n a l r e s u l t i s that p o o r e r q u a l i t y stands r e m a i n so that e f f i c i e n t r a w m a t e r i a l u t i l i z a t i o n then r e q u i r e s some means of f a s t e n i n g s m a l l p i e c e s together to p r o d u c e m e m b e r s of the s i z e s and q u a l i t i e s needed. W h e r e a s some types of c o m p o s i t e wood w e r e de v e l o p e d as an e c o n o m i c means to a c h i e v e m o r e c o m p l e t e u t i l i z a t i o n of w a s t e , o t h e r s a r e i n demand b e c a u s e they p o s s e s s c e r t a i n a t t r i b u t e s s u p e r i o r to those of s o l i d wood. Wood has e x c e l l e n t s t r e n g t h p r o p e r t i e s w i t h r e s p e c t to t e n s i o n , c o m p r e s s i o n and s t i f f n e s s but these a r e s t r o n g l y d i r e c t i o n a l . Footnote 1: the t e r m " c o m p o s i t e wood" i s us e d h e r e to i n c l u d e a l l manu-f a c t u r e d i t e m s c o m p o s e d of p i e c e s of wood, r a n g i n g i n s i z e f r o m v e r y s m a l l to v e r y l a r g e , that a r e h e l d together by a d h e s i v e . 2 R e q u i r e m e n t s i m p o s e d by many uses make i t n e c e s s a r y f o r the wood to be made m o r e n e a r l y i s o t r o p i c w i t h r e s p e c t to t h e s e , as w e l l as other p r o p e r t i e s s u c h as s h r i n k a g e . Wood c o n t a i n s knots- and ot h e r a b n o r m a l i t i e s w h i c h r e d u c e the s t r e n g t h and a d v e r s e l y a f f e c t i n a c h i n a b i l i t y and w h i c h c a n n o r m a l l y be r e m o v e d only by c u t t i n g one p i e c e of wood i n t o two o r m o r e p i e c e s . The v a r i a b l e s t r u c t u r e of wood w i t h i n a t r e e r e n d e r s l a r g e , s o l i d wooden m e m b e r s s u s c e p t i b l e to s p l i t t i n g and w a r p i n g due to i n h e r e n t d i f f e r -ences i n d i r e c t i o n a l s h r i n k a g e p r o p e r t i e s . The e f f e c t of these d e f e c t s can be r e d u c e d , o r e l i m i n a t e d , by bonding t o g e t h e r s m a l l e r p i e c e s of c l e a r wood of s i m i l a r s t r u c t u r e . W aste m e t a l s and many p l a s t i c s can be r e - u t i l i z e d at a h i g h r a t e of e f f i c i e n c y s i m p l y by r e m e l t i n g and r e c a s t i n g . T h i s i s not t r u e of wood. Waste wood i s m o s t r e a d i l y u s e d by f u r t h e r c o m m i n u t i o n f o r f u e l o r pulp p r o d u c t i o n , o r by b i n d i n g s m a l l p i e c e s t o g e t h e r w i t h glue to make p a r t i c l e b o a r d , o r other p r o d u c t s . E c o n o m i c c o n s i d e r a t i o n s d i c t a t e the m o s t c o m p l e t e p o s s i b l e usage of what i s an i n c r e a s i n g l y e x p e n s i v e r a w m a t e r i a l . T h i s g i v e s g r e a t i m p e t u s to the c o m p o s i t e wood . i n d u s t r i e s . P e r h a p s the m o s t i m p o r t a n t s i n g l e f a c t o r l i n k i n g the u t i l i z a t i o n of wood and glue has been the r e l a t i v e l y r a p i d d e v e l o p m e n t , i n the l a s t f o u r d e c a d e s , of b e t t e r types of g l u e , the m o s t i m p o r t a n t of these b e i n g the s y n t h e t i c r e s i n s . No t r u l y w a t e r p r o o f glue f o r wood was a v a i l a b l e u n t i l c o m p a r a t i v e l y r e c e n t l y so that the g l u i n g of wood was l i m i t e d to end p r o -ducts that w o u l d be u s e d only i n c o n d i t i o n s of s t a b l e , l o w m o i s t u r e content. T r a d i t i o n a l glues of a n i m a l o r v e g e t a b l e o r i g i n give bonds w i t h wood h a v i n g 3 e x c e l l e n t strength, p r o p e r t i e s when d r y . They a r e , u n f o r t u n a t e l y , r a p i d l y d e g r a d e d under c o n d i t i o n s that i n v o l v e e x p o s u r e to l i q u i d w a t e r o r h i g h h u m i d i t y and a r e l i a b l e to a t t a c k by i n s e c t s o r decay o r g a n i s m s . The development of the f i r s t t h e r m o s e t t i n g , phenol-formaldehyde r e s i n a d h e s i v e s , i n the e a r l y 1930*s, made i t p o s s i b l e to use wood under a m u c h w i d e r range of c o n d i t i o n s . The need f o r v a s t q u a n t i t i e s of s t r u c t u r a l m a t e r i a l s d u r i n g W o r l d W a r II s t i m u l a t e d the deve l o p m e n t of m o d i f i e d p h e n o l i c r e s i n s s u i t a b l e f o r the m a n u f a c t u r e of t h e r m o s e t t i n g , c o m p l e t e l y w a t e r p r o o f glues that w o u l d p r o v i d e bonds m o r e d u r a b l e than the wood i t s e l f . It then b e came p o s s i b l e to use c o m p o s i t e wood i n a l l l o c a l i t i e s w h e r e s o l i d wood of s i m i l a r s p e c i e s c o u l d be u s e d , without the l i m i t a t i o n s i m p o s e d by the a v a i l a b l e g r a d e s o r s i z e s . O t h e r s y n t h e t i c a d h e s i v e s have been d e v e l o p e d w i t h p r o p e r t i e s e q u i v a l e n t to those of the p h e n o l - f o r m a l d e h y d e t y p e , some p o s s e s s i n g c e r t a i n advantages f o r s p e c i f i c a p p l i c a t i o n s . G l u e s b a s e d on. r e s o r c i n o l -f o r m a l d e h y d e r e s i n s , w h i c h p r o d u c e w a t e r p r o o f bonds w i t h wood, can be c u r e d a t , o r s l i g h t l y a b o v e , r o o m t e m p e r a t u r e r a t h e r than r e q u i r i n g the h i g h t e m p e r a t u r e s needed to set m o s t p h e n o l i c s . M o d i f i e d p o l y v i n y l a c e t a t e r e s i n a d h e s i v e s w i l l p r o d u c e w a t e r p r o o f bonds o v e r a w i d e r range of wood m o i s t u r e contents than that p e r m i s s i b l e w i t h p h e n o l i c r e s i n s , at a l o w e r c o s t than the r e s o r c i n o l s . A t the p r e s e n t stage of d e v e l o p m e n t , h o w e v e r , they a r e s t i l l l i m i t e d i n a p p l i c a t i o n by s h o r t a l l o w a b l e - c l o s e d -a s s e m b l y t i m e s . The t h e r m o s e t t i n g , a l k a l i - c a t a l y s e d p h e n o l - f o r m a l d e h y d e r e s i n s s t i l l p r o v i d e the l o w e s t " i n - p l a c e " c o s t f o r a w a t e r p r o o f glue bond 4 w i t h wood. A s s u c h , they r e m a i n the m a j o r a d h e s i v e s f o r t h i s a p p l i c a t i o n . The l a r g e s t u s e r s of s y n t h e t i c r e s i n a d h e s i v e s a r e the m a n u f a c t u r e r s of p l y w o o d , p a r t i c l e b o a r d s a nd wood l a m i n a t e s . C o n s i d -e r a b l e amounts of n o n - w a t e r p r o o f , o r i n t e r i o r t y p e , a d h e s i v e s continue to be u s e d f o r m a t e r i a l d e s t i n e d f o r a p p l i c a t i o n s vJiere c o n d i t i o n s of use a r e not too s e v e r e . H o w e v e r , the w a t e r p r o o f , o r e x t e r i o r , type of s y n t h e t i c r e s i n s a r e c o m i n g i n t o w i d e r use as the v a l u e of t h e i r s p e c i a l p r o p e r t i e s i s m o r e w i d e l y a p p r e c i a t e d . The c o m b i n a t i o n of w e l l - p r e p a r e d wood s u r f a c e s w i t h a glue s u i t a b l e f o r the c o n d i t i o n s of s e r v i c e i n t e n d e d w i l l , i n m o s t c a s e s , p r o v i d e a f i n i s h e d a r t i c l e of h i g h q u a l i t y . M any a s s o c i a t e d p r o b l e m s r e s u l t f r o m l a c k of p r o p e r c o n t r o l i n the t r e a t m e n t p r i o r to p r e s s i n g . T h e r e a r e many r e p o r t s i n the l i t e r a t u r e of d i f f i c u l t i e s i n g l u i n g w h i c h a r e a p p a r e n t l y t r a c e a b l e to the s p e c i e s , o r n a t u r e of the wood b e i n g g l u e d , o r f o r w h i c h t h e r e i s no Eeady e x p l a n a t i o n . V a r i a t i o n s i n s t r e n g t h of d i f f e r e n t s p e c i e s of t i m b e r a r e depen-dent, i n l a r g e p a r t , upon the anatomy of the p a r t i c u l a r p i e c e of wood under t e s t . V a r i a b i l i t y i n a t t r i b u t e s w h i c h a r e n o n - a n a t o m i c a l , s u c h as c o l o u r , o d o u r , d e c a y - r e s i s t a n c e , r e a c t i o n w i t h c o a t i n g s , and t o x i c i t y , i s due to the n o n - l i g n o c e l l u l b s i c m a t e r i a l s found i n the wood. These m a y a l s o have some ef f e c t upon c e r t a i n p h y s i c a l p r o p e r t i e s , p a r t i c u l a r l y s h r i n k a g e and s w e l l i n g . A few r e f e r e n c e s a r e a v a i l a b l e w h i c h i n d i c a t e that t h e r e i s a v e r y d e f i n i t e s p e c i e s e f f e c t upon g l u i n g p r o p e r t i e s , a p p a r e n t l y t r a c e a b l e , at l e a s t p a r t i a l l y , to these " e x t r a c t a b l e " m a t e r i a l s . 5 S i n c e the g l u i n g of wood i s e s s e n t i a l l y a p h y s i c o c h e m i c a l pheno-menon, the c h e m i c a l c o n s t i t u e n t s of the wood w i l l e x e r c i s e a m o d i f y i n g i n f l u e n c e . C e r t a i n s p e c i e s have been found to be m o r e d i f f i c u l t t o glue than o t h e r s . The a c t u a l p r o p e r t y i n v o l v e d h a s , i n no c a s e , been d e t e r m i n e d but t r e a t m e n t s have been e v o l v e d , by t r i a l and e r r o r , that can s o m e t i m e s i m p r o v e the bonding q u a l i t i e s . O ther p r o b l e m s a r e e n c o u n t e r e d i n wood g l u i n g , some of w h i c h a p p e a r to be a s s i g n a b l e to p r o d u c t i o n v a r i a b l e s , but as y e t no e x p l a n a t i o n has been found f o r the defec t known as " c a s e - h a r d e n i n g " . Its e f f e c t on the p e r f o r m a n c e of glue-bonds i s w e l l d o cumented, but the u n d e r l y i n g cause i s o b s c u r e and i t s o c c u r r e n c e u n p r e d i c t a b l e . The t e r m " c a s e - h a r d e n i n g " has a s e c o n d m e a n i n g that d e s c r i b e s l u m b e r i m p r o p e r l y d r i e d , w i t h s e r i o u s d i f f e r e n t i a l s t r e s s e s between the s u r f a c e and i n t e r i o r . To a v o i d c o n f u s i o n * m e m b e r s of the s t a f f of the D i v i s i o n of F o r e s t P r o d u c t s of the C o m m o n w e a l t h S c i e n t i f i c and I n d u s t r i a l R e s e a r c h O r g a n i z a t i o n i n A u s t r a l i a have suggested " i n a c t i v a t i o n " as an a l t e r n a t i v e name f o r the defect a f f e c t i n g g l u i n g p r o p e r t i e s . T h i s s y n o n y m w i l l be uSed henceforward.. The concept q o v e r e d by the t e r m i n a c t i v a t i o n i s c o n t a i n e d i n the d e f i n i t i o n p r e s e n t e d by N o r t h c o t t and h i s c o w o r k e r s (81): I n a c t i v a t i o n , f o r the p u r p o s e s of t h i s p a p e r , w i l l be d e f i n e d as a change i n the s u r f a c e c o n d i t i o n of the wood, other than a s u r f a c e c o a t i n g f r o m e x t e r n a l s o u r c e s , s u c h as o i l o r gum, that i s i n d u c e d , o r i n t e n s i f i e d , by the m a n u f a c t u r i n g p r o c e s s e s and that m akes the s u r f a c e d i f f i c u l t to glue. A c h a r a c t e r i s t i c of i n a c t i v a t i o n i s that i t c a n be c o r r e c t e d by l i g h t l y s a n d i n g the s u r f a c e of the wood. 6 These w o r k e r s have shown that one of the r e s u l t s of s e v e r e o v e r - d r y i n g of v e n e e r i s the d e v e l o p m e n t , f o r r e a s o n s as y e t unknown, of a s u r f a c e that i n h i b i t s d i f f u s i o n i n t o the wood of m o i s t u r e c o n t a i n e d i n a p p l i e d glue. It i s p o s s i b l e that t h i s type of s u r f a c e i s the m a j o r , i f not the o n l y , u n d e r l y i n g cause of t r u e i n a c t i v a t i o n . W h i l e o t h e r f a c t o r s „ alone o r i n c o m b i n a t i o n , c a n p r o d u c e the type of bond u s u a l l y c l a s s e d as i n a c t i v a t e d , they do so through, m e c h a n i s m s that c a n be e x p l a i n e d . G e n e r a l l y , the n e c e s s a r y i m p r o v e m e n t i n bond q u a l i t y c a n be brought about by t i g h t e r c o n t r o l of p r e t r e a t m e n t and g l u i n g c o n d i t i o n s . The o c c u r r e n c e , due to p r o d u c t i o n v a r i a b l e s , of a s u r f a c e that i n h i b i t s m o i s t u r e d i f f u s i o n , to w h i c h the t e r m " i n a c t i v a t e d s u r f a c e " i s now r e s t r i c t e d , has been shown to be e r r a t i c and u n p r e d i c t a b l e . A n u n d e r -s t a n d i n g of the m e c h a n i s m i n v o l v e d i n the f o r m a t i o n of s u c h a s u r f a c e s h o u l d l e a d to a b e t t e r u n d e r s t a n d i n g of the e f f e c t of heat on the c h e m i c a l and p h y s i c a l b e h a v i o u r of wood. The o b j e c t i v e of t h i s t h e s i s can thus be st a t e d as f o l l o w s : to d e t e r m i n e the u n d e r l y i n g c a u s e of the .development of an i n a c t i v a t e d s u r f a c e w h i c h s o m e t i m e s o c c u r s when wood i s heated. II L I T E R A T U R E R E V I E W A puzzling aspect of inactivation is the manner of its occurrence. It can arise suddenly in the production of a plywood mill that continued to operate on raw material from the same source with no change in manufac-turing procedures. Of course, the defect can be due to lack of control of production variables but this can usually be detected and corrected. The recognition of inactivation as a surface phenomenon goes back many years. Knight discussed it in his major work Adhesives for Wood (53), his comments being reproduced, in condensed form, below: With some manufactured wooden materials, notably veneers and plywood, a change in surface conditions occurs that makes them difficult to glue. Dr . N.S. deBruyne, in 1937, first recognized this as a defect, and not an accident, and called it case-hardening. Rayner found that sanding cured it and this remedy has not yet been improved upon. Case-hardening is characterised by easy separation of the joint, under a peeling action, which exposes a layer of glue that looks somewhat dull and dusty, with few or no adherent wood fibres. It can be present in any degree, from a joint slightly below standard to very poor. DeBruyne postulated chemical changes in the nature of the wood surface. Adhesion depends on the mutual attraction of polar groups in wood and glue, but under the intense heating and drying inseparable from the manufacture of plywood with phenolic film glue, the polar groups on the surface lose this power of attraction by uniting with each other. As the bonds so formed cannot easily be broken, or their polar nature be restored to them, the surface remains perman-ently deficient in glue-taking powers. Glazing through metal caul contact was thought to be a cause but this has been shown to be not so. No way of detecting the presence of case-hardening by inspection has yet been found. Dr . M . G . M . Pryor investigated case-hardening and maintains the 8 o r i g i n i s i n the v e n e e r s . If these a r e i n i t i a l l y sound i n the g l u e -t a k i n g s e n s e , then the subsequent a p p l i c a t i o n of p r e s s u r e and h e a t , and the c o n t i g u i t y of m e t a l s u r f a c e s w i l l be without p e r m a n e n t eff e c t . H e a t i n g v e n e e r to 160°C c a u s e s only a t e m p o r a r y r e d u c t i o n i n a d h e s i v e p o w e r s and i s a-s^ribed to m o i s t u r e l o s s . The same r e s u l t can be o b t a i n e d by d e s i c c a t i o n at r o o m t e m p e r a t u r e , P r y o r showed that none of the types of v e n e e r d r y e r i n use c o u l d cause c a s e - h a r d e n i n g . D i p p i n g i n w a t e r w i l l not n o r m a l i s e t r u l y c a s e - h a r d e n e d v e n e e r . W e t t i n g agents i n the glue have no e f f e c t . M i c r o s c o p i c s e c t i o n s show a l o o s e and f u z z y s u r f a c e w i t h b l o c k e d c a v i t i e s . R e m o v a l of the d e b r i s by s t r i p p i n g the s u r f a c e w i t h c o l l o d i o n f i l m r e s t o r e s i t s g l u a b i l i t y . G l u e w e l l r u b b e d i n w i l l c u r e c a s e - h a r d e n i n g . It has been found i n b i r c h , b e e c h , g u a r e a , gaboon and s p r u c e plywood. It i s m o s t c o m m o n i n t h i n n e r sheets. It i s m o r e c o m m o n w i t h h i g h - t e m p e r a t u r e p h e n o l i c l i q u i d o r f i l m glues than w i t h h o t - p r e s s u r e a s - t h i s i s not e x p l a i n a b l e by any of the f o r e g o i n g . In a s s e m b l y w o r k i t o c c u r r e d e q u a l l y w i t h c a s e i n and s y n t h e t i c r e s i n glues. The B r i t i s h F o r e s t P r o d u c t s L a b o r -a t o r y a t t e m p t e d to r e p r o d u c e c a s e - h a r d e n i n g i n 1/8-inch b e e c h v e n e e r s by e x c e s s i v e p e e l i n g p r e s s u r e but w e r e unable to do so. D u r i n g the s e c o n d W o r l d W a r , a g r e a t many a i r c r a f t w e r e made of wood, a use w h e r e any f a i l u r e c a n be of c r i t i c a l i m p o r t a n c e . Many d i f f i c u l t i e s w e r e e n c o u n t e r e d , p a r t i c u l a r l y i n a s s e m b l y g l u i n g , so a t h o r -ough i n v e s t i g a t i o n i n t o t h e i r c ause was c a r r i e d out by K a u f e r t at the U. S. F o r e s t P r o d u c t s L a b o r a t o r y (49). H i s r e p o r t , i n a b r i d g e d f o r m , f o l l o w s . In c o n t r a s t to w e l l - p l a n e d , n o r m a l wood surfaces,.. p l y w o o d s o m e t i m e s p r e s e n t s m o r e d i f f i c u l t g l u i n g p r o b l e m s a l t h o u g h , n o r m a l l y , i t can be glued s a t i s f a c t o r i l y . S u r f a c e c o n d i t i o n s that may develop d u r i n g v e n e e r and p l y w o o d m a n u f a c t u r e , and may be a c c e n t u a t e d by the t e c h n i q u e s u s e d i n a i r c r a f t a s s e m b l y g l u i n g , a r e b e l i e v e d r e s p o n s i b l e f o r these o c c a s i o n a l d i f f i c u l t i e s . Some of the s u r f a c e changes that o c c u r i n p l y w o o d m a n u f a c t u r e , and may i n t e r f e r e w i t h the a d h e s i o n of glue i n s e c o n d a r y g l u i n g , a r e r e a d i l y r e c o g n i z e d . S e r i o u s g l a z i n g of the s u r f a c e s d u r i n g h o t - p r e s s i n g i s u s u a l l y r e c o g n i z e d as u n d e s i r a b l e . H e a v y b l e e d - t h r o u g h of g l u e s , and s i m i l a r d e p o s i t s , on the f a c e s of p l y w o o d may a l s o i n t e r f e r e w i t h glue a d h e s i o n to some extent. In a d d i t i o n to these r e c o g n i z a b l e s u r f a c e c o n d i t i o n s that i n t e r f e r e w i t h a d h e s i o n of g l u e s , h o w e v e r , t h e r e appear to be o t h e r s that a r e not so e a s i l y d e t e c t e d , and of w h i c h the cause i s not y e t known. A n u m b e r of e x a m p l e s of p l y w o o d of t h i s type have been r e c e i v e d f r o m a i r c r a f t f a b r i c a t o r s who had e x p e r i e n c e d d i f f i c u l t y i n bonding t h e m s t r o n g l y together w i t h c o l d - s e t t i n g glues i n a s s e m b l y g l u i n g o p e r a t i o n s . 9 N u m e r o u s g l u i n g t e s t s have been made on t h i s m a t e r i a l at the F o r e s t P r o d u c t s L a b o r a t o r y a n d , i n many c a s e s , the e x p e r i e n c e of a i r c r a f t f a b r i c a t o r s w i t h the p l y w o o d i n q u e s t i o n has been v e r i f i e d . P l y w o o d so t e s t e d had been p r o d u c e d by s e v e r a l m a n u f a c t u r e r s , w i t h v e n e e r f r o m d i f f e r e n t s o u r c e s . T h i s d i f f i c u l t y has been e n c o u n t e r e d i n y e l l o w b i r c h , sweetgum, D o u g l a s - f i r and y e l l o w p o p l a r and m o s t o f t e n , though not e x c l u s i v e l y , i n the h e a r t w o o d of these s p e c i e s . The p l y w o o d was g e n e r a l l y of good q u a l i t y and i t s a p p e a r a n c e gave no i n d i c a t i o n that t r o u b l e w o u l d be e x p e r i e n c e d i n m a k i n g s a t i s f a c t o r y s e c o n d a r y glue j o i n t s to i t s s u r f a c e . The n a t u r e of these u n f a v o u r a b l e s u r f a c e c o n d i t i o n s , w h i c h p r o b a b l y d e v e l o p e d d u r i n g p l y w o o d m a n u f a c t u r e , has not been s a t i s f a c t o r i l y d e t e r m i n e d . L i g h t s a n d i n g of the p l y w o o d s u r f a c e s to be glued i s the m o s t e f f e c -t i v e and p r a c t i c a l means thus f a r found f o r c o r r e c t i n g such u n f a v o u r -a b l e s u r f a c e c o n d i t i o n s . V a r i o u s other m e t h o d s , s u c h as m o i s t e n i n g w i t h w a t e r , the use of w e t t i n g a g e n t s , and t r e a t m e n t w i t h c h e m i c a l s have been t r i e d . None of t h e m has been found as r e l i a b l e , o r as g e n e r a l l y e f f e c t i v e , as l i g h t sanding. In g e n e r a l , l i g h t s a n d i n g was as e f f e c t i v e as heavy s a n d i n g and s h o u l d , i f p o s s i b l e , be l i m i t e d to • 00 1 i n c h . WOOD P R O P E R T I E S R E L A T E D TO E X T R A C T I V E S A s e a r c h of the l i t e r a t u r e r e l a t e d to the e x t r a c t a b l e m a t e r i a l s i n wood made i t a p p a r e n t that t h e r e i s a v e r y wide v a r i e t y of s u b s t a n c e s p r e s e n t i n d i f f e r e n t s p e c i e s ( 1 , 29 , 30, 45, 56). Many of these c o n t a i n f u n c t i o n a l groups w h i c h can take p a r t i n c h e m i c a l r e a c t i o n s . T h e r e were j many e x a m p l e s of the e f f e c t s of e x t r a n e o u s components on wood p r o p e r t i e s . I s e n b e r g , B u c h a n a n and W i s e , i n t h e i r c o m p r e h e n s i v e s u r v e y of the e x t r a n e o u s components of A m e r i c a n pulpwoods , c a r e f u l l y s e p a r a t e d the t o t a l s u b s t a n c e of the t r e e i n t o f o u r p a r t s (44): i . the c e l l w a l l s , c o n s i s t i n g of c e l l u l o s e , h e m i c e l l u l o s e s and l i g n i n and s o m e t i m e s s m a l l amounts of p e c t i c s u b s t a n c e s and m i n e r a l m a t t e r ; i i . the e x t r a c t i v e s w h i c h a r e r e m o v a b l e by c o l d w a t e r a n d / o r one o r m o r e of s u c h n e u t r a l s o l v e n t s as e t h e r , a l c o h o l s , b e n z e n e , p e t r o l e u m e t h e r , c h l o r o f o r m o r m e t h y l e n e c h l o r i d e ; 10 i i i . s u b s t a n c e s w h i c h a r e not p a r t of the c e l l w a l l but a r e not readily-r e m o v a b l e by s o l v e n t s , s u c h as s t a r c h g r a i n s and c r y s t a l s of c a l c i u m o x a l a t e o r s i l i c a ; i v . s e c r e t i o n s of the l i v i n g t r e e , s u c h as the o l e o r e s i n s of some c o n i f e r s . F o r the p u r p o s e s of t h i s t h e s i s , the t e r m e x t r a c t i v e s o r e x t r a c -t a b l e m a t e r i a l i n c l u d e s c l a s s e s i i and i v above, that i s , e x t r a n e o u s m a t e r -i a l o r s e c r e t i o n s of the l i v i n g t r e e . B o t h a r e r e m o v a b l e by s o l v e n t e x t r a c t i o n . These w o r k e r s s t a t e d s u c c i n c t l y the g e n e r a l i n f l u e n c e of these e x t r a c t a b l e m a t e r i a l s on the p r o p e r t i e s and uses of wood: The e x t r a n e o u s components c h a r a c t e r i z e a s p e c i f i c wood, often f a r m o r e s h a r p l y than do the c e l l w a l l components. The f o r m e r , r a t h e r than the l a t t e r j l e n d i n d i v i d u a l i t y to the wood. The c o l o u r of a wood, i t s odour and i t s t a s t e a r e due to the ex t r a n e o u s components. Some ex t r a n e o u s components i n c r e a s e (and c e r t a i n of t h e m d e c r e a s e ) the r e s i s t a n c e of the wood to i n s e c t o r fungal a t t a c k . C e r t a i n of t h e m i n h i b i t the d e p r e d a t i o n s of m a r i n e b o r e r s . Some a l s o p r e v e n t the wood f r o m b e i n g s u i t a b l y p u l p e d by the s u l f i t e p r o c e s s . O t h e r s give r i s e to d i g e s t e r c o r r o s i o n i n the k r a f t p r o c e s s . Some ex t r a n e o u s components a r e quite t o x i c to man, and give r i s e to ann o y i n g i n d u s t r i a l h a z a r d s . Such p r o p e r -t i e s as u l t r a v i o l e t f l u o r e s c e n c e , o r even d e n s i t y , o f t e n depend on ex t r a n e o u s components. C e r t a i n of t h e m a r e quite f l a m m a b l e and i n c r e a s e the r i s k of f i r e ; t hese same components may a l s o s e r v e to i n c r e a s e the f u e l v a l u e of the wood. In other w o r d s , we c a n say that the ex t r a n e o u s components " f i n g e r p r i n t " a wood and give i t c e r t a i n c h e m i c a l s p e c i f i c i t y . A l t h o u g h t h e r e a r e often m a r k e d d i f f e r e n c e s among c l o s e l y r e l a t e d s p e c i e s , t h e r e a r e often s t r i k i n g s i m i l a r i t i e s among m e m b e r s of c e r t a i n p l a n t groups. A n d e r s o n (2), i n what i s p r o b a b l y the d e f i n i t i v e study to date on p o n d e r o s a pine ( P i n u s ^ p o n d e r o s a D o u g l . ), p o i n t e d out how the " i n d i v i d -u a l c h a r a c t e r i s t i c s , p r o p e r t i e s , and uses of p o n d e r o s a pine can be a t t r i b -uted l a r g e l y to the quantity and c h e m i c a l nature of i t s e x t r a c t i v e compon-11 e n t s " . P o n d e r o s a pine c o n t a i n s p i n o s y l v i n and i t s m o n o m e t h y l e t h e r , w h i c h a r e r e s p o n s i b l e f o r the r e f r a c t o r y n a t u r e of many of the pi n e s i n s u l p h i t e p u l p i n g . P i t c h - b l e e d i n g i n s e r v i c e , due to the exudation of o l e o -r e s i n , i s a f r e q u e n t c a u s e of s e r i o u s d e g r a d a t i o n i n the p a i n t i n g q u a l i t i e s of t h i s s p e c i e s . N a r a y a n a m u r t i (75) c o n c l u d e d that the e x t r a c t i v e s c a n a f f e c t the h y g r o s c o p i c i t y , s w e l l i n g and s h r i n k a g e of wood, and, at h i g h t e m p e r a t u r e s , m a y have p l a s t i c i s i n g e f f e c t s . He has r e c o r d e d t h e i r i n f l u e n c e on the modulus of e l a s t i c i t y and s t u d i e d t h e i r e f f e c t on p l a s t i c f l o w i n wood d u r i n g l o a d i n g . The e f f e c t on the g l u i n g of wood i s of s p e c i a l i m p o r t a n c e . E x a m -p l e s a r e a l s o g i v e n of the r o l e p l a y e d by e x t r a c t i v e s i n i d e n t i f i c a t i o n , d u r a b i l i t y , c o l o u r , c o r r o s i o n of m e t a l s o r of the d i f f u s i o n of gases and io n s t h r o u g h wood. W e s t e r n l a r c h ( L a r i x o c c i d e n t a l i s Nutt. ) f r e q u e n t l y e x h i b i t s , on the s u r f a c e of m a c h i n e d wood, a s u g a r y exudate w h i c h has been c h a r a c t e r -i z e d as a g a l a c t a n (27). The q u a l i t y of glue bonds ob t a i n a b l e w i t h t h i s s p e c i e s , u s i n g an e x t e r i o r - t y p e p h e n o l i c r e s i n a d h e s i v e , i s i n f l u e n c e d to a m a r k e d degree by the amount of t h i s exudate. P l y w o o d pa n e l s made f r o m v e n e e r s w i t h h e avy d e p o s i t s c o n t a i n e d glue bonds i n c a p a b l e of m e e t i n g the i n d u s t r y s t a n d a r d f o r e x t e r i o r g l u e l i n e q u a l i t y . The bond q u a l i t y i n c r e a s e d as the amount of s u r f a c e d e p o s i t d e c r e a s e d . The g l u a b i l i t y w i t h u r e a - f o r m a l d e h y d e r e s i n glues of quipo ( G a v a n i l l e s i a p l a t a n i f o l i a H.B.K.) was a f f e c t e d a d v e r s e l y by the h i g h a l k a l i content of t h i s s p e c i e s (75). In t e s t s w i t h ebony ( D i o s p y r o s ebenum Koen. ), 12 the sapwood, w h i c h has a v e r y m u c h l o w e r e x t r a c t i v e s content than the h e a r t w o o d , glued b e t t e r than the l a t t e r under some c o n d i t i o n s and w i t h c e r t a i n a d h e s i v e s . T r o o p and W a n g a a r d (100) glued twenty-nine t r o p i c a l A m e r i c a n woods, white oak ( Q u e r c u s a l b a L. ) and B u r m a teak ( T e c t o n a g r a n d i s L . f . ) w i t h r e s o r c i n o l and p h e n o l / r e s o r c i n o l - f o r m a l d e h y d e g l u e s . The glues w e r e not e q u a l l y s a t i s f a c t o r y f o r g l u i n g oak and mahogany (Swietenia spp. ). A l t h o u g h shear s t r e n g t h s and wood f a i l u r e v a l u e s w e r e , i n g e n e r a l , s t r o n g l y c o r r e l a t e d w i t h s p e c i f i c g r a v i t y , some anomalous r e s u l t s w e r e obtained. These i n d i c a t e d that components of c e r t a i n s p e c i e s i n t e r f e r e d w i t h the a d h e s i v e s . They p o s t u l a t e d that t h i s i n t e r f e r e n c e c o u l d be due to d e f e c t i v e s u r f a c i n g o r to the c h a r a c t e r of the c h e m i c a l c o n s t i t u e n t s , s u c h as gums, o i l s , r e s i n s and w a x e s , w h i c h a r e found i n the e x t r a c t i v e s of many woods. M i l l e r (72) c o l l e c t e d D o u g l a s f i r ( P s e u d o t s u g a m e n z i e s i i ( M i r b . ) F r a n c o ) f r o m v a r i o u s l o c a l i t i e s i n O r e g o n and t e s t e d i t s p e r m e a b i l i t y , using r a t e of a i r flow and r a t e of l i q u i d p e n e t r a t i o n along the g r a i n . The r e s u l t s c l e a r l y i n d i c a t e d r e g i o n a l d i f f e r e n c e s , w i t h h e a r t w o o d of t r e e s f r o m e a s t e r n O r e g o n b e i n g g e n e r a l l y m u c h l e s s p e r m e a b l e t h a n that f r o m s t o c k grown n e a r e r the c o a s t . He suggested that p e r m e a b i l i t y may be a s s o c i a t e d w i t h both the m i c r o s t r u c t u r e and the c h e m i c a l c o m p o s i t i o n of the wood. A D D I T I O N O F " E X T R A C T I V E S " TO M O D I F Y P R O P E R T I E S It i s f r e q u e n t l y d e s i r a b l e to add a m e a s u r e of w a t e r - r e p e l l e n c y to wooden, o r c o m p o s i t e wood, products„ T h i s may be done by the a d d i t i o n of s u i t a b l e m a t e r i a l s , s u c h as e m u l s i f i e d p a r a f f i n , to c o m m i n u t e d wood 13 b e f o r e the f i n a l bonding p r o c e s s . A l t e r n a t i v e l y , a s u r f a c e t r e a t m e n t may be g i v e n to the f i n i s h e d p r o d u c t , whether c o m p o s i t e o r s o l i d . U n f o r t u n -a t e l y , the s i z i n g of f i b r o u s p r o d u c t s d u r i n g m a n u f a c t u r e n o r m a l l y l e a d s to s t r e n g t h l o s s i n the f i n i s h e d p r o d u c t . S i n c l a i r , E v a n s and S a l l a n s (91) investigated, the p o s s i b i l i t y of s i z i n g the f i n i s h e d p r o d u c t , when p r o d u c i n g b o a r d and p a p e r . They w e r e ab l e to s a t i s f a c t o r i l y v a p o u r s i z e these m a t e r -i a l s by e x p o s i n g t h e m to the v a p o u r s of m e d i u m - c h a i n - l e n g t h fatty a c i d s (10 to 16 c a r b o n s ) , at t e m p e r a t u r e s c o m m o n l y u s e d f o r d r y i n g these p r o d u c t s . The h i g h e r the t e m p e r a t u r e u s e d , the m o r e r a p i d was the v a p o u r s o r p t i o n . The fatty acid, m o l e c u l e s a p p e a r e d to f o r m e s t e r s w i t h the c e l l u l o s e . The amount of fatty a c i d n e c e s s a r y f o r s i z i n g was v e r y s m a l l - 0-35 to 0-60 p e r c e n t , b a s e d on d r y weight of f i b r e . The m a t e r i a l s they u s e d a r e , of c o u r s e , c o n s t i t u e n t s of the e x t r a c t i v e s of v a r i o u s s p e c i e s of wood. It w o u l d be p o s s i b l e f o r the same p r o c e s s to take p l a c e i n the n a t i v e wood, d u r i n g h e a t i n g . In f a c t , they d i d note that above 140°C a s i z i n g e f f e c t took p l a c e w i t h no a d d i t i o n of fatty a c i d . S i m i l a r l y , the s i z i n g e f f e c t on p a p e r of the a d d i t i o n of s t e a r i c , and o t h e r fatty a c i d s c o m m o n l y found i n wood, has been s t u d i e d t h o r o u g h l y by Swanson and C o r d i n g l y (97). S e l f - s i z i n g i s of c o n c e r n to p a p e r m a k e r s s i n c e i t r e d u c e s the a b s o r b e n c y of paper p r o d u c t s . T h i s o c c u r s d u r i n g s t o r -age under n o r m a l c o n d i t i o n s , w i t h i n the t i m e p e r i o d s expected i n o r d i n a r y w a r e h o u s e p r a c t i c e . T h i s w o r k d e a l s w i t h pulp b u t , s i n c e the s u r f a c e of wood, f o r the p u r p o s e of f o r m i n g an a d h e s i v e bond, i s c l o s e l y analagous to the s u r f a c e of p u l p , t h e i r r e s u l t s a r e of c o n s i d e r a b l e i n t e r e s t . 14 They p o i n t e d out, by m a t h e m a t i c a l a n a l y s i s , that n e i t h e r r o u g h -n e s s n o r p o r o s i t y i s l i a b l e to change s u f f i c i e n t l y to a f f e c t a b s o r b e n c y . W h a t e v e r changes take p l a c e , the r e s u l t m u s t be a change i n f r e e s u r f a c e e n e r g y of the pul p s u r f a c e to a v a l u e l e s s than that of the f r e e s u r f a c e e n e r g y of w a t e r , at w h i c h po i n t r e s i s t a n c e to the p e n e t r a t i o n of w a t e r w o u l d o c c u r . P o l a r s o l i d s , s u c h as wood or p u l p , have h i g h f r e e s u r f a c e e n e r -g i e s . A d e c r e a s e i n the a t t r a c t i v e f o r c e s a s s o c i a t e d w i t h the s u r f a c e w o u l d o c c u r i f the s u r f a c e b e came mare h y d r o c a r b o n - l i k e through c h e m i c a l a l t e r -a t i o n of the f i b r e c o n s t i t u e n t s o r i f the s u r f a c e w e r e c o v e r e d w i t h one o r m o r e of c e r t a i n of the c o n s t i t u e n t s p r e s e n t i n wood, They w e r e abl e to show that s e l f - s i z i n g c o u l d be dev e l o p e d i n pulp t h r o u g h v a p o u r - s i z i n g w i t h s t e a r i c a c i d , the r a t e of s i z i n g d e v e l o p -m ent b e i n g S t r o n g l y i n f l u e n c e d by t e m p e r a t u r e . The i n i t i a l r a t e of s o r p t i o n at 105°C was 75 t i m e s as f a s t as the r a t e a t 70°C and 225 t i m e s as f a s t as the r a t e at 25°C. T h e i r e x p e r i m e n t s showed c o n c l u s i v e l y that i t was p o s s i b l e to t r a n s f e r s t e a r i c a c i d o v e r a c o n s i d e r a b l e d i s t a n c e at r e l a t i v e l y l o w t e m p e r a t u r e s . S i m i l a r r e s u l t s w e r e found f o r o l e i c a c i d , the r a t e b e i n g m u c h s l o w e r . E s t e r s of the fatty a c i d s ( u n s p e c i f i e d ) d i d not p r o d u c e s i z i n g a f t e r many h o u r s at 105°C. T h i s was ev i d e n c e of the n a t u r e of the a t t a c h -ment w h i c h w o u l d a p p e a r to be t h r o u g h the c a r b o x y l group. E F F E C T O F . C H E M I C A L T R E A T M E N T It has been found that c h e m i c a l t r e a t m e n t w i l l i m p r o v e the g l u -a b i l i t y o r , i n one c a s e , the p e n e t r a b i l i t y , of r e f r a c t o r y s p e c i e s of wood. 15 E x t e n s i v e w o r k on c h e m i c a l p r e t r e a t m e n t of s u c h woods i s r e p o r t e d f r o m the U. S. F o r e s t P r o d u c t s L a b o r a t o r y at M a d i s o n (103). A s o l u t i o n of 2 s o d i u m h y d r o x i d e p r o v e d e f f e c t i v e i n r e d u c i n g the tendency to " s t a r v e d " j o i n t s i n woods w h i c h f r e q u e n t l y show t h i s defect. S o d i u m h y d r o x i d e , or l i m e w a t e r , t r e a t m e n t s a l s o i n c r e a s e d the glue-bond q u a l i t y i n c a s e i n - g l u e j o i n t s w i t h woods that n o r m a l l y do not glue w e l l w i t h t h i s a d h e s i v e . The r e s u l t s w i t h o s a g e - o r a n g e ( M a c l u r a p o m i f e r a (Raf.) Schn. ) we r e p a r t i c u l -a r l y good, the bond s t r e n g t h b e i n g r a i s e d (in s h e a r ) f r o m 294 to 3,000 p s i and the wood f a i l u r e p e r c e n t a g e f r o m e s s e n t i a l l y n o thing to 35 p e r cent. A m m o n i a , benz e n e , h y d r o c h l o r i c a c i d and c h l o r i d e of l i m e w e r e a l s o t r i e d on v a r i o u s s p e c i e s . H y d r a t e d l i m e gave s l i g h t l y b e t t e r r e s u l t s than s o d i u m h y d r o x i d e w i t h h i c k o r y ( C a r y a sp. u n s p e c i f i e d ) , r e d gum ( L i q u i d a m b a r  s t y r a c i f l u a L.) and b l a c k c h e r r y ( P r u n u s s e r o t i n a E h r h . ). Some of the other t r e a t m e n t s i m p r o v e d the bonding w i t h one o r two s p e c i e s but the r e s u l t s w e r e not c o n s i s t e n t . Rapp, r e p o r t e d by T r o o p and W a n g a a r d (100), t r e a t e d l i g n u m v i t a e ( G u a i a c u m o f f i c i n a l e L. ) by w a s h i n g m a c h i n e - p l a n e d s u r f a c e s w i t h c a r b o n t e t r a c h l o r i d e , b e n z e n e , acetone or a l c o h o l . None of these treatments was as e f f e c t i v e as an a p p l i c a t i o n of 10 p e r cent s o d i u m h y d r o x i d e , w h i c h was w i p e d off a f t e r t e n m i n u t e s and f o l l o w e d by w a t e r w a s h i n g . Sanding p r i o r to c a u s t i c w a s h i n g was found to i m p r o v e r e s u l t s . It was suggested t h i s m i g h t be due to i t s p e r m i t t i n g a m o r e th o r o u g h c l e a n i n g of the s u r f a c e . T r o o p and W a n g a a r d (100), i n v e s t i g a t i n g the g l u a b i l i t y of teak Footnote 2: d e f i c i e n t i n glue due to o v e r - p e n e t r a t i o n i n t o the wood. 16 found one l o t w h i c h d i d not need p r i o r t r e a t m e n t to f o r m a good bond. How-e v e r , u s i n g d i f f e r e n t m a t e r i a l , they w e r e ab l e to i n c r e a s e s h e a r s t r e n g t h f r o m 1025 to 1262 p s i , and wood f a i l u r e f r o m 63 to 83 p e r c e n t , by w a s h i n g the s u r f a c e s of r e f r a c t o r y g l u i n g s t o c k w i t h acetone, N a r a y a n a m u r t i (75) r e p o r t e d i m p r o v e d g l u a b i l i t y w i t h the h e a r t -wood of ebony a f t e r e x t r a c t i o n w i t h e t h e r , a l c o h o l o r benzene. He was a l s o a b l e to l o w e r glue-bond q u a l i t y i n o t h e r s p e c i e s by a p p l y i n g the e x t r a c -t i v e s f r o m the ebony heartwood. K n i g h t ^ (53) m e n t i o n s that i t was at one t i m e c o m m o n p r a c t i c e to sponge the s u r f a c e s of many hardwoods w i t h a s o l u t i o n of 10 p e r cent s o d i u m h y d r o x i d e , when u s i n g a n i m a l g l u e , i n o r d e r to i m p r o v e bond s t r e n g t h . A n a l t e r n a t i v e m e t h o d , u s e d f o r B u r m a t e a k , was to sand the s u r f a c e , the e f f e c t b e i n g a t t r i b u t e d to the b r e a k i n g up of a c o a t i n g of o i l on the wood s u r f a c e . W a r d r o p and D a v i e s (108) s t u d i e d sapwood s p e c i m e n s of r a d i a t a pine ( P i n u s r a d i a t a D. Don) and B i s h o p pine ( P i n u s m u r i c a t a D. Don) w h i c h w e r e known to r e s i s t p e n e t r a t i o n by aqueous p r e s e r v a t i v e s , y e t w e r e a m e n a b l e to p e n e t r a t i o n by c r e o s o t e o i l . O n l y a few p i t s w e r e a s p i r a t e d , so t h i s f e a t u r e was not r e s p o n s i b l e f o r the i m p e n e t r a b l e c o n d i t i o n . The s i n k a g e t i m e i n w a t e r , a f t e r v a c u u m p u m p i n g , was u s e d as an a r b i t r a r y m e a s u r e of p e r m e a b i l i t y . It was shown that p r e - e x t r a c t i o n w i t h a l c o h o l and e t h e r g r e a t l y r e d u c e d the s i n k a g e t i m e . Jn r a d i a t a pine and a s p r u c e , the s i n k a g e t i m e was g r e a t l y i n c r e a s e d by p r e v i o u s d r y i n g . H o w e v e r , the i n c r e a s e d i d not o c c u r i f the s p e c i m e n s w e r e p r e - e x t r a c t e d w i t h a l c o h o l 17 and ether. E x t r a c t i o n a f t e r d r y i n g a t 102°C d i d not r e d u c e the sinkage t i m e . M i c r o s c o p i c e x a m i n a t i o n d i s c l o s e d the p r e s e n c e of o i l d r o p l e t s i n the r a y p a r e n c h y m a w h i c h , on d r y i n g of the wood, tended to c o a l e s c e , s p r e a d i n g o v e r the i n n e r s u r f a c e of the r a y p a r e n c h y m a . P I T C H P R O B L E M S I N P U L P I N G One of the m o s t t h o r o u g h l y s t u d i e d phenomena, that i s r e l a t e d to wood e x t r a c t i v e s , i s the o c c u r r e n c e i n the pulp s l u r r y of the r e s i n o u s m a t e r -i a l f r e e d d u r i n g the p a p e r m a k i n g p r o c e s s . The m o s t i m p o r t a n t m a n i f e s -t a t i o n i s the a g g l o m e r a t i o n of m a s s e s of " p i t c h " at v a r i o u s l o c a t i o n s i n the m a c h i n e r y o r on the p a p e r sheet. These i n t e r f e r e w i t h p r o p e r d r a i n a g e on s c r e e n s , w i t h the m a i n t e n a n c e of the p r o p e r type of s u r f a c e on f e l t s , and may cause d e f e c t s i n the f i n i s h e d sheet. When p r e s e n t as a d i f f u s e c o a t i n g on the p u l p , p i t c h i s thought to be r e s p o n s i b l e f o r the d e v e l o p m e n t of s e l f - s i z i n g (97). A g r e a t many f a c t o r s a p p a r e n t l y i n f l u e n c e the s e v e r i t y and o c c u r -r e n c e of p i t c h i n g and some of the e v i d e n c e i n the l i t e r a t u r e i s c o n t r a d i c t o r y . S t a r o s t e n k o and h i s f e l l o w w o r k e r s (93) a t t r i b u t e d the d egree of p i t c h i n g t r o u b l e to the c o m p o s i t i o n of the r e s i n , b a s e d on the f o l l o w i n g f i n d i n g s . When the r e s i n a c i d s content was v e r y l o w ( l e s s than 25 p e r c e n t ) , o r v e r y h i g h ( o v e r 75 p e r c e n t ) , the s t i c k i n e s s of the r e s i n was m i n i m a l . The m i x i n g of r e s i n a c i d s w i t h n e u t r a l s u b s t a n c e s o r fat t y a c i d s made the m i x t u r e m o r e s t i c k y . In the p r e s e n c e of the m o r e l i q u i d f a t t y a c i d s o r n e u t r a l s u b s t a n c e s , the r e s i n a c i d s a l s o l i q u i f i e d , c h a nging the r e s i n to a state that c o u l d cause c o n s i d e r a b l e t r o u b l e . Gymene, f o r m e d d u r i n g c o o k i n g , a c t e d as a s o l v e n t , 18 p e r m i t t i n g the r e s i n components to m i x . The cymene f l a s h e d off d u r i n g b l o w i n g , l e a v i n g the n o w - s t i c k y p i t c h behind. M a h d a l i k (65) p l a c e d the b l a m e f o r p i t c h t r o u b l e , that o c c u r s d u r i n g sulphate p u l p i n g of f r e s h s p r u c e wood, on the p l a s t i c state of the p i t c h , t h i s i n t u r n b e i n g due to the p r e s e n c e of t e r p e n e s . S t o r a g e of the wood a l l o w e d these t e r p e n e s to e v a p o r a t e , changing the p h y s i c o c h e m i c a l p r o p e r t i e s , thus r e n d e r i n g the p i t c h b r i t t l e and h a r m l e s s . U n f o r t u n a t e l y he d i d not p r o v i d e s u b s t a n t i a t i n g e x p e r i m e n t a l work. P u l p w o o d i s s o m e t i m e s s t o r e d b e f o r e use i n the b e l i e f that t h i s r e d u c e s the p i t c h i n g p r o b l e m . Many hypotheses have been put f o r t h as to the e f f e c t of t i m e and type of s t o r a g e upon the r e s i n . L e v i t i n (62) found thatoin r e d and whi t e pine ( P i n u s s t r o b u s L. and P. r e s i n o s a A i t o n ) , w a t e r -s t o r e d m a t e r i a l c o n t a i n e d m o r e fatty a c i d s , and l e s s fatty a c i d e s t e r s , i n the sapwood, than the n o n - w a t e r e d , m a t c h e d m a t e r i a l . T h i s d i f f e r e n c e he a t t r i b u t e d to, h y d r o l y s i s due to w a t e r s t o r a g e , s i n c e i t o c c u r r e d at a s l o w e r r a t e d u r i n g d r y s t o r a g e . H y d r o l y s i s o c c u r r e d i n the h e a r t w o o d r e s i n s to a m u c h s m a l l e r extent. He a l s o suggested (61) thatOC-pinene, the m a i n t e r p e n e f r a c t i o n , i s s l i g h t l y w a t e r s o l u b l e so m i g h t be r e d u c e d by prolonged, w a t e r s t o r a g e . The w o r k of H a r r i s (37) suggested that the d e p o s i t i o n of p i t c h on m e t a l p a r t s of m a c h i n e r y m a y be due to the r e a c t i o n of f r e e fatty a c i d s w i t h the m e t a l to f o r m l o w - m e l t i n g , t a c k y s a l t s . These cause f u r t h e r " a g g l o m e r a t i o n , s i n c e they a r e l e s s s t r o n g l y a d s o r b e d on the f i b e r s than the s o d i u m s a l t s of fatty and r e s i n a c i d s . The a d d i t i o n of e t h e r - s o l u b l e e x t r a c -19 tives from the pulp caused pitching trouble while the addition of alcohol-soluble material did not. Fatty acid esters and unsaponifiables are less soluble in alcohol than in ether while resin acids are very soluble in both. The addition of extra rosin to the beater stock did not increase pitch diffic-ulties. Pitching would appear to have been due to the fatty acids and/or unsaponifiables. Seasoning of pulp by heating to 100°C for several hours had been reported, by other workers, to have altered resin composition so pitching was minimized. This was tried by Harris and produced very slight changes, with the maximum change in the water soluble fraction, which increased, and the ester fraction, which decreased. Bethge and Lindgren (9) reported that hydrolysis occurred in the fats during storage of European spruce and that the resin acids were oxidized. The hydrolysis facilitated the dissolution of the extractives, during the preparation of viscose pulp, but the influence of oxidation could not be judged. These findings are in accord with the work of others, which they report, that also contained evidence for the atmospheric oxidation of unsat-urated fatty acids, of fats containing such acids, and of resin acids. The unsaponifiable portion of birch wood became oxidized to acids which, like resin acids, esterify more slowly than fatty acids. No similar oxidation of extractives has been reported for spruce wood, its content of unsaponi-fiable material remaining unchanged during storage. KahJtla (47) divided the pitch contained in sulphite cooks into dispersible pitch and emulsifiable pitch, the problem of pitching being entirely dependent upon the former. He developed a linear equation relating 20 the amount of dispersible pitch and the amount of deposited pitch. Contrary to the results reported above, the amount of ether-soluble or petroleum-ether-soluble material present did not affect the amount of dispersible pitch nor the severity of pitching on the steel vessels used in experiments. On the other hand, Thommen (99) claimed that chemical analysis of natural resins and pitch, comparing the amount of single components, did not yield any clue as to the causes of the sticky deposits. In a second article (98) he presented evidence that, during storage, the resinous substances in spruce wood undergo physical and chemical changes, losing stickiness. This has been attributed to oxidation. His results indicated that the same amount of oxygen was in the extract whether the wood was stored in the presence or absence of air. He concluded that the hardening of natural resins during storage of the wood is governed by a maturing process, proceeding independently of the presence of oxygen. Conversely, Lawrence (59) attributed the difference between the resin acids extracted from pine wood chips and those contained in the oleo-resin, to oxidation due to the large surface area of the chips. The oxida-tion of the resin acid3 in the chips was quite rapid, La a few hours the levopimaric acid content was one-half that of the oleoresin. When the surface area was decreased by extracting small blocks, instead of chips, the oxidized acids were greatly decreased. A study of the oxidation of some of the pure resin acids was carried out. Pure levopimaric acid was usually resistant to oxidation, however, in the presence of light and a sensitizer, it was rapidly oxidized. Several products were isolated and characterized from the oxidation of the pure acids. The conditions favouring the forma-tion of some of these products were determined. About 20 per cent of the acids extracted from wood chips had been oxidized to some extent. Approx-imately the same amount of oxidized resin acids were present in black liquor soap. Spruce logs that were never water-stored caused less pitch trouble when pulped than water-stored logs, even if the latter were dry-stored for a period prior to use (28). The logs that were partially dry-stored were, in turn, less troublesome than those completely water-stored. A correlation was not established between total resin content and pitch deposits, the average amount of pitch present (but not necessarily troublesome) in the cooked pulp being about the same for water or land-stored wood. The resin content of the wood seemed to decrease during storage, regardless of which type of environment was used. Pertinent to the suggestion made elsewhere that the fatty acids may be physiologically active, is the observation made during this' work that logs cut in December or March yielded higher resin contents than did logs cut in October. Vincent (105) found that the conditions used during preparation of. ethanolic solutions of pitch, for use in preparing artificial pitch suspen-sions, had a large effect on the amount of pitching that occurred in experi-ments. Heating the solvent during extraction increased the pitching. Since prolonged heating with access to air produced very low deposits, it was considered that the role of oxidation in this phenomenon was estab-lished. The presence of pulp increased the sensitivity to the conditions, of 22 the experiments. In a further series of tests (106), various surface-active agents, a chelating agent, and high-boiling hydrocarbons, introduced into the system, were effective in lowering the amount of pitch deposition. EXTRACTIVES FOUND IN SPECIES REPORTED TO B E SUSCEPTIBLE (  TO INACTIVATION The literature on extractives content of various species is not yet voluminous. It is being added to at a rapid rate, due to the increase, in recent years, of interest in these materials. Because the extractives, and particularly the natural secretions, of the pines form the basis of the naval stores industry, most of what has been done deals with them. The author's own experience has been confined to the development of inactiva-tion in Douglas fir and in Engelmann and western white spruce. There is little in the literature on the extractives of these species. Inactivation, or what appears to be inactivation, has recently been reported to occur in veneer of jack pine (Pinus banksiana Lamb.) (40). It is also of frequent occurrence in factories producing hot-press plywood using yellow birch veneer (Betula alleghaniensis Britt.). A search of the literature was made, concentrated on these and related species, to determine what extractives they contained and what variability was to be expected between and within species and trees, Douglas fir Graham and Kurth (34) characterized the various extracts obtained with ether j acetone and cold water frdmthree different samples of Douglas fir. They were able to identify abietic, oleic, linoleic and 23 lignoceric acid ? phytosterol, a crystalline flavanone, a catechol tannin, a phlobaphene and a galactan. The fatty acids were found in both the free and combined states while the resin acids were present only in the free state. There was a marked difference in the amount of ether extract from sample I, which had. been aged one year, and sample II, which was freshly cut. Sample III, from rapidly grown wood from a younger tree, contained a higher percentage of the flavanone than either of the other samples. Dihydroquercetin, first isolated by Pew (84), and probably the flavanone found by Graham and Kurth, was present in varying concentrations at various heights in a Douglas fir tree (36). The highest concentration was found just inside the heartwood/sapwood boundary, falling off rapidly toward the pith and more rapidly toward the bark. An unidentified leucoanthocyan-idin showed a similar distribution, although present in much smaller amounts. Gardner and Barton (32) found the same pattern existed in other Douglas fir of much greater age, also in western larch. Kennedy and Wilson (52) corroborated these findings, demonstrating as well that, in trees containing "target pattern", or concentric, alternating zones of heartwood and apparent sapwood (judged on colour), the light-coloured material contained much lower concentrations of dihydroquercetin than adjacent, apparently normal heartwood. By extracting with solvents the lignin residue of the dilute-acid hydrolysis of Douglas fir wood waste, Clark, Hicks and Harris (21) were able to isolate a high melting point wax, eicosanoic, docosanoic, tetracos-anoic and oleic acids, eicosanol-1, docosanol-1, docosane, tetracosane and hexacosane. These were presumed to have come from the original wood# 24 rather than the lignin molecule. The extractives also included a heptane-insoluble acidic resin and residual sugars. Lewis (63) determined the ether, alcohol, acetone and water-soluble portions of Douglas fir to be 1* 05, 3-81, 0» 02 and 1* 04 per cent respectively (sequential extraction) but did not break down the individual extracts into their components. Spruces Cherches, Bardyshev and Kokhanskaya (19) fractionated the rosin acid fraction of European spruce (Picea excelsa Link), recovering the following acids: abietic, dextropimaric, palustric, neoabietic, dehydro-abietic and probably dihydr ©abietic. Small quantities of four other acids were detected, though not identified, by chromatography and spectroscopy. "Working with purified rosin from resin obtained by tapping, Cherches, Bardyshev and Tkachenko (20) characterized abietic j neoabietic, palustric, levopimaric, dextropimaric, dehydroabietic and dihydroabietic acids in Picea ajanensis Fisch. Gas~liquid chromatography was used by Bethge and Lindgren (9) to isolate the fatty acids from European spruce. They found linoleic, oleic, an isomer of linoleic or linolenic acid, small amounts of palmitic, 14-methyl palmitic and arachidic acids and traces of 15 others. The cleavage products of the esters contained mainly glycerol. The relative amounts of the various acids from different specimens were quite variable. Barton and Gardner (5) compared the phenolic and carbohydrate extractives of white spruce (Picea glauca (Moench) Voss) with those of Engelmann spruce (Picea engelmanni Parry). At least five phenolic com-ponents were detected in the acetone extractives of each, the relative con-centration varying between the two species, and with the solvent used. Similar variations were evident between different samples of the same species. Their results suggested that the heartwood extractives of these two species are so similar as to discourage further search for a simple method of separating them through chemical test. Since the two species overlap in range, are frequently milled together, but are subject to different export regulations, their separation is a matter of some interest. The extractives of Sitka spruce (Picea sitchensis (Bong. ) Carr . ) are apparently very different from those of the other spruces (55). Ether extraction removed an amount of extractives equal to 2 per cent of the dry weight of the wood. This was separated into an ether-insoluble precipitate of a lignin-like fraction and neutral, acidic and phenolic fractions. The neutral material contained a conjugated monoterpene diene, possible cara-di'ene, an unsaturated alcohol, ^-sitosterol and 1-2-octyl-(3-sitosterol phthalate. The phenolic fraction yielded acetovanillone, vanillin and vanillyl alcohol. No tropolones or volatile or fatty acids were found but a lignin-like acid was present. Recovery from the cyclohexylamine salts gave an oil or solid from which a low-melting acid fraction (ca. 50°C) could be regenerated. Pines Laidlaw and Smith (57) found large intra- and interspecific diff-erences in the arabinogalactans of closely related pines. Whereas lodge-pole pine (Pinus contorta var. la ti folia S. Wats. ) extract yielded arabinose and galactose units, on hydrolysis, in the ratio of 1 to 7, a second log of approximately the same age contained the same two components but in vastly different proportions. Yield ratios for radiata pine, Jeffrey pine (Pinus jeffreyi Grev. & Balf. ) and jack pine were 1 to 8, 4 to 5 and 1 to 13 respectively. The rosin acid fraction of oleoresin from "Siberian cedar" (Pinus sibirica Mayr. ) contained abietic, dextropimaric and isodextro-pimaric acids (48), Benzene extraction of green sawdust of seven species of the southern pines showed the fatty acid fraction to contain mainly oleic and linoleic acids with smaller amounts of linolenic , palmitic , stearic and ligno-ceric acids. Arachidic and behenic acids were detected in five species (18). The combined acids, when saponified, gave only higher fatty acids, with little or no contamination, except one pond pine (Pinus rigida var. serotina (Michx. ) Loud. ) which contained pinosylvin monomethyl ether. A l l sapon-ifications contained glycerol. Reference was made to the work of Bergstrom who found oleic, linoleic, linolenic, lauric, myristic, palmitic, stearic, arachidic, behenic and lignoceric acids in Scots pine (Pinus sylvestris L . ) and to that of Kahila who apparently found the same acids in European spruce. Anderson (2) studied the distribution of acetone-soluble extrac-tives in ponderosa pine from separate stands ranging in age from 82 to 366 27 years. Cross sections were taken at 1, 32 and 64 feet and sampled at the pith, outer heartwood, inner and outer sapwood. The extractives content of heartwood varied with height in ithe tree, some, but not a l l , trees having less in the higher sections. The percentage content in the heartwood was • •''•1.1 always higher than for the sapwood. In most trees the outer sap contained less than the inner sapwood. The major differences were found between the outer heartwood and the adjacent inner sapwood. Age of the tree was not a factor in any of these findings. There were more resin acids in the heartwood than in the sapwood and more in the heartwood at the butt than at the top. The sapwood content was more variable. Sapwood contained more fatty acids than did the heartwood but there was little difference in the sapwood with position in the tree. Butt heartwood contained much less than did the top heartwood. The distribution of volatiles was less predic-table, the butt heartwood generally containing the largest amount. The resin distribution in young ponderosa pine was examined by Paul (83) in two each of dominant, codominant and intermediate trees from each of three levels of stocking. Sections were collected at 1, 16, 36 and 80 feet, the distribution from pith to bark being determined. Great variability was found in the resin content^ even in outer sapwood that showed no external indications of unusually high resin content. The average resin content decreased progressively from the base upward. Trees from the sparsely stocked stand generally had a much higher resin content than trees from moderately or well stocked stands. Levitin (60) compared the. diethyl ether extracts of white pine 2 8 and red pine. Quantitatively the red pine heartwood contained much more resin than did the white pine, but the sapwoods contained about the same quantity. In general, the qualitative composition varied but little, both containing essentially the same resin acids, fatty acids, fatty acid esters and non-saponifiables. However, the heartwoods of both species contained more resin acids, less fatty acids and less combined fatty acids than the sapwood. The combined acids of the sapwood were present as glycerol and sterol esters even though no glycerol was present in the esters of most of the heartwood extractives. The heartwoods also contained more non-saponifiables than the sapwoods. In a further study (61), knots and resinous areas of red and white pine were found to contain more resin and a higher proportion of terpenes than did clear wood. Hardwoods Clermont (22) delineated the fatty acids of yellow birch, paper birch (Betula papyrifera Marsh. ) , trembling aspen (Populus tremuloides Michx. ) and basswood (Tilia americana L . ), separating the wood into sapwood and heartwood whenever possible. Diethyl ether was used for extractions. The extract was separated into three fractions - free fatty acids, combined fatty acids and unsaponifiable material. The methyl esters were prepared and gas-liquid chromatography used for character-ization. Essentially the same acids were found in both the free and combined portions of all species. The major portion of all fractions consisted of the unsaturated acids with linoleic acid the main constituent. Palmitic acid predominated in the saturated fraction of some species, 29 stearic in others. Only aspen and yellow birch showed true heartwood. In aspen, the saturated/unsaturated ratio of acids was similar in both types of tissue. Yellow birch contained much more saturated acid and less unsat-urated acid in the heartwood than in the sapwood. Saturated acids with chain lengths ranging from 6 to 24 carbon atoms were found. Unsaturated acids with from 12 to 18 carbon chains were identified and a few acids were observed which could not be positively identified, PROBLEMS ENCOUNTERED WHEN DRYING V E N E E R A T HIGH  T E M P E R A T U R E S One of the major consumers of wood and glue, in the manufacture of composite wood, is the plywood industry. This has reached its maximum development in British Columbia and the northwestern United States<, because of the availability of large quantities of old-growth Douglas fir peeler stock, an excellent source of raw material, available in economic large sizes. As the industry has expanded, the supply of this material has become relatively less abundant. Attention has turned to other species and to less accessible stands of Douglas f ir , which include the Interior type. At the same time, in common with most other industries, the more efficient use of machinery and manpower has become a necessity for economic survival. It has been possible to increase production with the same equipment by raising dryer temperatures in steam-heated dryers. The development of direct-fired oil and gas dryers has made available 30 still higher temperatures. Concurrent with these developments, there have appeared a number of gluing problems, particularly with the phenolic-resin types of glues. Some of these have been blamed on the increased dryer temperatures or the use of direct-firing, others on the various species used. Stensrud (94) found that Interior Douglas fir was more difficult to process than the Coastal type, and that dryer temperature had a serious effect on gluing, since quality of the glue-bond decreased with increased dryer temperature. Currier (23) showed that plywood made from veneer dried ; above 204°C had lower breaking strength, after subjection to a 2-cycle boil test, than controls dried at lower temperatures. Even well-bonded exterior plywood, from high-temperature-dried veneers, was frequently of substandard strength. The general situation to be expected with direct-fired dryers is thoroughly covered in the Adhesive Manufacturers' Status Report on Direct-fired Dryers , published in 1956 by the Technical Committee of the West Coast Adhesive Manufacturers (109). The major advantages to be gained are : lower initial cost for the same capacity, compared to steam dryers, elimination of the steam-generating unit, and attractive fuel oil costs for oil-firing, compared to operation of an oil-fired steam boiler. No serious problems have been encountered with cold-press, or conventional hot-press, protein-based glues. However, from the first installation designed to produce plywood for exterior u s e » severe bond degrade has been experienced. While direct gas-fired dryers can be used for drying veneer that is to be used for the manufacture of exterior-grade plywood, this is only possible if drying conditions approximate those generally used in steam dryers. Temperatures must be kept below 204°C since veneer dried above this temperature in steam dryers possesses inferior bonding qualities. Veneer can be dried satisfactorily in direct-oil-fired dryers if they are operated at temperatures below those customarily used in steam-heated dryers. This, of course, greatly reduces capacity. Veneer dried in direct-fired dryers was frequently of a type that did not glue well and appeared to come within the classification defined as inactivated. Various attempts were made to improve its surface condition. A series of surface-active agents were tried, including alkyl aryl sulfonates, polyethylene glycol, ethers, soaps and lignosulfonates, all without effect on bond quality. Increasing the solids content of an exterior-type adhesive provided a much wider range of acceptable bonding conditions with steam-dried veneers. A similar attempt, with veneer from both oil and gas direct-fired dryers, was unsuccessful. Resins with a higher than normal viscosity did improve bond quality but consistently satisfactory results were not obtained. The use of various types and grades of extenders gave inconclusive results. The only really successful treatment was light wire-brushing, to remove the surface layer. A comprehensive study of the effect of dryer temperature, glues and peeling tightness on the quality of bond with Interior-type Douglas fir veneer was carried out by Bryant and Stensrud (17). Air dried veneer 32 gave the best bonds, veneer dried at the higher dryer temperature used producing the poorer quality bonds, as recorded by shear strength and a cyclic boil test. The various glues also reacted differently to changes in peeling and in drying conditions. The better plywood was produced from the veneer which was more tightly peeled. Stensrud (94), working on another phase of this study, found that removing some of the rolls from one deck of a dryer gave veneer with better gluing characteristics than that produced in a lower deck with all rolls in place. The degradation was attributed to the "ironing" effect of the rolls. It is possible, of course, that the effect was due to temperature differentials that frequently exist at various levels in the same dryer. While evaluating a direct-fired, oil-fed dryer that was producing veneer with inferior gluing properties, Sisterhenm (92) found very large temperature differences (to 47°C) within the same cross section. Modifications to equalize the temperature distribution, lower the tempera-ture over-all , and improve the efficiency of combustion, greatly improved the bonding qualities. It has been suggested that calendering is more severe in an oi l -fired dryer than im a steam-heated one. To test this premise, Raymond (85) used Douglas fir heartwood and sapwood and western hemlock (Tsuga  heterophylla (Raf.) Sarg.) veneer. Part of the veneer was passed through an oil-fired dryer and part through a steam-heated dryer, with half of the veneer stripped to prevent roll contact. There were no consistent effects of calendering on bond quality, using exterior-type glue. Exterior-type 33 bonds, using veneer from a steam-heated dryer, were superior to those with similar veneer from an oil-fired, dryer. Exterior bonding character-istics of hemlock were adversely affected to a lesser extent, in oil-fired drying, than were those of Douglas f ir , especially heartwood. . The postulate of deBruyne (see Knight above) that intense heating causes the polar groups on the surface of wood to lose their power of attraction for adhesives, by uniting with each other, has received considerable support from other sources. Stensrud (94) claimed that his results verified the loss of polarity at veneer surfaces through excessive heating, Iyer (46) quoted the work of deBruyne and Rayner in his Doctoral dissertation: The only instance cited so far where wood fails to behave as a polar substance is when it is overheated. DeBruyne points out the conclusion arrived at by C . A . A . Rayner of Aero Research Ltd. according to whom overheated wood does not adhere to polar glues and also water is no longer absorbed to the same extent as by normal cellulose. Various other instances of a similar type., all pointing towards the change of nature of cellulose on heating can be cited. The one that pertains to us at .this moment is the behaviour of such overheated wood towards glues which are proved to be polar. DeBruyne, referring to the practical impor-tance of this factor., viz. the change in the nature of cellulose on heating, writes: The trouble arises in thin plywood sheets, probably because the thicker sheets have a sufficient reserve of internal moisture to prevent the change, and it is confined to the outermost layers of the outer veneers, probably because they are the parts that get most thoroughly dried in the press. The manufacturers of adhesives are often blamed when it is found that apparently good, sound quality plywood that has passed all the tests required by BSS 4V3 cannot be stuck to other wood components, but the trouble lies in the plywood and not in the adhesive subsequently used. Iyer reached the general conclusion that the loss of polarity is due to the change in constitution and the conversion of the hydroxyl groups 34 to ether linkages. SUCCESSFUL DRYING A T HIGH T E M P E R A T U R E S In contrast to other reported work* Milligan and Davies (73) were able to dry Douglas f ir , hemlock, balsam (Abies sp. unspecified) and Sitka spruce veneers, without degrade, in a direct-gas-fired dryer, at o temperatures as high as 287 C and air velocities to 9000 fpm. Drying was extremely rapid. One-eighth-inch Douglas fir heartwood, that would have required 13 minutes in a normal steam-heated dryer at 1 8 2 ° C , was dried in slightly under one minute. The major difference in their drying technique was close control of veneer temperature. By the use of radia-tion pyrometers, the dryer was calibrated so that veneer emerged just as " it reached the desired moisture content. The surface temperature of the veneer never exceeded 138°C. It would appear from their work that the bonding quality of the veneer was excellent. Consistently good exterior-grade bonds were obtained with phenolic-resin type glues. Apparently the rate of water removal is not a factor in producing degrade. What does seem to be involved is the increase in temperature of the veneer, due to its being subjected to high drying temperatures after the removal of most of the water it contained. SPECIES E F F E C T S ON DRYING, ASSEMBLY, PRESSING AND GLUABILITY The veneer cutting and drying properties of Engelmann spruce (Picea engelmanni Parry) were investigated at the U. S. Forest Products Laboratory (104). Although a low recovery of face grade veneers was found, and. the knotty nature of the logs led to poor over-all veneer recov-ery, no pretreatment was necessary, nor were there any peeling problems. Heating in water produced, a fuzzy peel with sapwood, cold-peeled material being processed satisfactorily. It is reported that commercial users of the green veneer have experienced no drying or gluing difficulties, using dryer temperatures of 122 ° C to 163°C. Although no mention was made of the adhesive types used, in view of the preponderance of the interior-type adhesives in American plywood production, they were probably of this class. Nevertheless, Northcott, Hancock and their co-workers at the Vancouver Laboratory of the Forest Products Laboratories of Canada, have received numerous complaints from Canadian users of this species, or the similar western white spruce (Picea glauca (Moench)Voss var. albertiana (S. Brown) Sarg, ), that it was difficult to obtain consistently good bonds with exterior-type phenolic glues (80). Within the geographical range of Douglas f ir , two types are widely recognized, being classed as separate species by some botanists. The so-called Coastal type is generally considered to contain softer, more easily peeled wood, eminently suitable for plywood manufacture. The Interior type is more refractory during peeling and is reported by some mill personnel (40) to be more difficult to glue. Northcott (78), working with Interior and Coastal Douglas f ir , had demonstrated the degrading effect of high drying temperatures upon subsequent bonding with phenolic-resin glues. He had also shown that 36 apparent differences exist between trees from the same locality, or from different localities. A series of extensive experiments was carried out to investigate the effect of drying schedules, and of several other factors, on the glue-bond quality of Douglas f i r and of other species, including Engelmann •2 spruce . The first of these (80) tested the effect of drying temperature, drying time, storage time before gluing and tissue type (sapwood or heart-wood) on the subsequent glue-bond quality of Engelmann spruce veneer. This work was gradually expanded to include veneer moisture content at time of gluing, length of closed assembly time, length of press time, the effect of sanding and the effect of species. Coastal and Interior Douglas f ir , cottonwood (Populus trichocarpa Torr . & Gray), an Abies (probably A. amabilis (Dougl. ) Forb.) and Engelmann spruce were used. A definite species effect was found, including substantial differences in the two types of Douglas fir. ' Douglas fir and Engelmann spruce w e r e adversely affected by increasingly severe drying schedules but cottonwood and Abies were not. • The bond quality of all species decreased with increasing moisture content at the time of gluing. Sanding improved the bond quality of all species, Coastal Douglas fir being improved Footnote 3:. The ranges of Engelmann spruce and of western white spruce overlap and separation of the species is impossible without the foliage. No distinction is made between them during milling. Because of the preponder-ance of Engelmann spruce on the timber limits from which experimental material was obtained, it was assumed to be this species. 37 the least. Longer assembly time, or longer press time, improved the bond quality in all species except Coastal Douglas fir. Effect of veneer surface and prepress treatment Various other pieces of evidence, from prior experiments, were introduced. These indicated that a frequent cause of poor bond quality was a type of undercured bond which continued to cure in service. As a result of this work, an hypothesis was formulated to explain the development of low-wood-failure plywood bonds. Various conditions of pretreatment, particularly severe drying schedules, tend to reduce the hygroscopicity of the surface of veneer. This condition, and other factors that tend to increase the moisture at the glue line at the time of pressing, are the cause of a type of bond which shows low wood-failure when tested in shear and has the appearance of being undercured. Northcott, Hancock and Colbeck (81) extended this work in an effort to further clarify the inter-relationships between the various factors and to find means of improving the bond quality, particularly of veneers with reduced hygroscopicity. The gluing of glass, which has a similar type of gluing surface to wood (88, 110), to other glass, or to well-dried wood, showed that, with the particular phenolic-resin glue used, the escape of moisture was essential for the production of a high-quality bond. Glass-to-glass bonds, where moisture escape was strongly inhibited, were very poor. Glass-to-absorptive-=wood bonds were moderately good but would not withstand severe accelerated-weathering treatments. Absorptive wood bonded exceedingly well to itself. 38 Severely over-dried wood, which gave poor bonds under normal bonding conditions, was restored to a condition which permitted it to glue well by lengthening the closed assembly time. The effect was further enhanced by spreading all bonding surfaces with adhesive. Further experiments were carried out to study the effects of closed assembly time* of drying time and temperature, of spread, both qualitative and quanti-tative, of sanding, of veneer moisture content when adjusted by recondit-ioning, and of treatment of the surface with chemicals. The spreading variables included double-spreading, or applying one-half the desired amount of glue to each of the contact faces in each bond. The apparent success of spraying with sodium hydroxide indicated that the glue being used, a caustic-catalysed phenolic-resin type, might have a similar effect if given a chance to act on both bonding surfaces. The results from the panels that were double-spread showed that this was the case. The water-relations theory, in its final form, was developed from this work. The water relations theory This theory was postulated by Northcott, Hancock and Colbeck (81). Because of their applicability, two of the conclusions which form part of the over-all theory are pertinent here, and are stated as follows: i . The range of moisture conditions, at the instant of pressing, that will produce a satisfactory glue-bond with phenolic-resin glues, is considerably narrower than is generally thought. It is suggested that the acceptable upper limit of moisture content is dictated by the consideration that an excess of water may upset the condensation reaction. The resulting glue polymers have poorer cohesion and/or adhesion than those whi ch are obtained under optimum conditions of moisture. The lower acceptable limit of moisture is considered to be governed by the explanation that a dried-out glue will not flow 39 enough to produce a good bond. i i . The moisture condition, at the instant of pressing, which seems to be so important, is the result of a rather complicated interaction of several manufacturing variables, including the following: the veneer-drying process, in which excessively severe drying conditions change unpredictably the wettability characteristics of the wood (inactivation) and hence the rate at which water from the glue dissipates into the wood; the veneer-peeling process, through the roughness of peel and/or severity of the lathe checks - the rougher the peel, the poorer the bond in the case of high-moisture conditions; the moisture content of the veneer at lay-up, which adds a variable amount of water to the assembly; the glue spread, which adds a variable amount of water to the assembly; the assembly time, which controls the amount of water which dissipates from the glue, either into the wood or by evaporation; the caustic of the glue, which improves the hygroscopicity of the surface of inactivated veneers, thereby restoring, to a consid-erable degree, the ability of the wood to absorb water from the glue. It is apparent that all of the above factors, excepting one, are susceptible to some measure of control in the plywood-making process. The susceptibility to loss of hygroscopicity is the single variable that cannot be predicted. Adjustment in the normal veneer drying schedule, by using lower temperatures and more closely controlled drying times, will apparently mitigate the effect of this defect. Since it is not possible, at this stage, to know when it will appear, control is feasibly only by reducing dryer productivity. Since this will increase drying costs, it is economically undesirable. 40 SUMMARY There is considerable evidence in the literature for the influence of extractives on the nature and reactions of wood. Many species effects were also reported, some of which were related to the extraneous mater-ials. Chemicals present in some woods have been used successfully to produce a water-repellent surface on paper and particle-board and the 'effect was shown to be temperature dependent. There is insufficient ( evidence to judge which of the reported components, found in species susceptible to inactivation, could be involved in the process. Nevertheless, conclusions which may be drawn relating specific chemical constituents to a species effect in gluing must be in agreement with the published findings. Severe drying schedules have been blamed for some gluing diff-iculties although other workers have been able to dry successfully using very high air temperatures with careful control of veneer temperature. A theory has been postulated that inactivation is the result of the presence of an excess of water at the glue-line at the time of pressing. Further, the one factor contributing to such an excels, which cannot be explained by lack of control of production variables, is the change in surface hygroscopicity in some, and only some, veneer, when it is subjected to severe drying schedules. Ill DRYING AND TESTING PROCEDURES DRYING TECHNIQUES The temperature of a veneer being dried will not exceed 100°C until most of the water is driven from it, after which the temperature will rise rapidly. Veneers with different initial moisture contents, dried at the same ambient temperature for the same time, will become heated above 100°C at different times. Some will therefore be maintained at elevated temperatures for longer periods than the others. The technique was therefore adopted of drying all veneer with the material in a blower oven, suspended from a strongly-damped balance. Measurements were taken with the blower fan switched off for a few seconds. A l l measure-ments were related to an "oven-dry" condition. This was empirically set at the end of the first five-minute period of drying during which less than one gram of water was lost from a 12 x 12-inch veneer. It was calculated from the records of the veneer dried for the longest time. Since there were usually three veneers, or sets of veneers , dried for 40, 20 or 10 minutes beyond the oven-dry point, the assumption of an oven-dry point for the fourth veneer, or set, could be made with reasonable accuracy. In practice, this was found to correspond to a moisture content of about 2 per cent. This last amount was removed over a long period and probably 42 did not prevent the veneer temperature from rising to the temperature of the ambient air. Wood dried from a swelling agent, such as water, has different physical properties than wood dried from a non-swelling agent. Al l veneer (except one specified lot) extracted with organic solvents was sub-sequently immersed in several changes of distilled water over a period of several days before drying took place. Thus the wood was dried from a water-soaked condition. This technique is covered by the term "water-soaked" in the following descriptions of procedure. TESTING PROCEDURE USED A most urgent need in the technology of gluing wood is a rapid, accurate method of assessing the quality of the bond obtained. A great deal of research has been carried out and many papers have been published in this field but there is little agreement on which of the available tests is the best. The various tests fall into several fairly well-defined categories, depending on the variable measured. The Forest Products Laboratory of the Department of Scientific and Industrial Research in England has developed a knife test whereby a levering action is applied to the surface ply, tending to separate it from the adjacent cross-band. The quality of the bond is determined by compar-ison of the appearance of the break with a photographic standard. This test (54) has been found to give fairly consistent results between operators, regardless of experience, and, it is claimed, very good results with experienced operators. While this test has been found useful for a rapid 43 assessment of bond quality immediately after pressing, it has not, in practice, proven to have the reproducibility between operators of the ;. wood-failure method discussed below. Wakefield (107) Criticised knife-testing generally since it tends to cause misinterpretation of the bond quality. The resistance to splitting between the plies varies greatly and the percentage of fibre adhesion depends not only on the quality of the bond, but also upon the surface of the veneers bonded. The tightness of the veneer affects the amount of loose fibre attached to the surface after breaking. Hopkins (43) examined the relationship between the apparent behaviour of wood adhesives in tests of their permanence and the construc-tion of the test specimens. Quantitative tests showed that wood species, nature of the wood construction and size of the specimen have an important bearing on the apparent permanence of an adhesive. Small test specimens were found to exhibit greater mechanical stressing on glue-lines than relatively larger specimens. He concluded that greater emphasis should be attached to the construction of test specimens in any effort to interpret and develop test methods for wood adhesives. Baur (6) pointed out that the commonly used tensile-shear specimen is incorrectly classed as a true shear test since failure occurs through a splitting process. This objection does not, however, mean that the test is not efficient in separating bond qualities. Percentage wood failure alone may not be a reliable means of assessing the quality of a glued joint (8). However, when considered in 44 conjunction with the load at failure, it provides a valuable means for assessing the quality of a glue and of a glue bond. A high percentage of wood failure indicates that the glue used is as strong as, or stronger than, the wood, provided the load at failure is not so low as to cast doubt on the quality of the wood used. A low percentage of wood failure does not necessarily indicate a poor grade of glue. If the load at failure is high and the percentage of wood failure is low, the glue is satisfactory. Northcott and his associates at the Vancouver Laboratory of the Forest Products Laboratories of Canada have carried out extensive tests Over a period of more than 12 years in an effort to determine the most suitable test for bond quality evaluation. The effect of species on wood failure was included in an early paper (79). A new type of test was devel-oped for use in testing the gluability of a species with a certain glue (77) which proved impractical for use in production testing of plywood. In a recent, large-scale experiment (82) the "selection efficiency" of each of ten potential methods of bond quality evaluation was determined. These methods included breaking loads and wood failures measured after subjection of the plywood to a variety of treatment combin-ations prior to testing. The results of work spread over several years, totalling 591 panels, were analysed by an IBM 1620 digital computer. It was determined that,the single factor of per cent wood failure was the most efficient, of the systems used, in properly assessing the durability in service of the exterior-grade plywood bonds tested. 45 Since panels used in the above study were the panels produced in the study of inactivation, the results were considered sufficient justifi-cation for the use of wood failure as the major criterion of bond quality. There i s , however, one situation in which the percentage wood failure reading alone will not give an accurate bond quality estimate. Should the material under test contain a large amount of latewood in each annual ring, many bonds will be made between two latewood faces. The glue may actually be broken by the wood, the broken specimen showing very little evidence of wood failure. Still , the high breaking load found will indicate that the bond was a good one. The quality of the bond can then only be judged by considering both breaking load and per cent wood failure. Western softwood plywood, manufactured in Canada, is nor-mally tested under Canadian Standards Association specifications CSA 0-121-1961, for Douglas fir plywood and CSA 0-151-1961 for western softwood construction plywood. Two of the tests contained therein, which have proven applicable to the detection of bonds made with inactivated veneers, are the cold soak test and the boiling test. The former consists of immersion in cold water at room temperature for 48 hours, followed by drying for 8 hours at a temperature of 63°C ^ 3°C and two cycles of soaking for 16 hours and drying for 8 hours under the same conditions. Shear specimens are then soaked for a further 16 hours and tested wet. The boiling test comprises boiling in water for 4 hours, drying for 20 hours at 63°C * 3 ° C , boiling for an additional 4 hours and testing while wet. 46 Both tests were applied to all but a few of the panels manufac-tured for this study. Breaking loads and. per cent wood failure were recor-ded in all cases. Complete results are included in the Appendix tables. Because per cent wood failure had been shown to be suitable, in most cases, for an accurate estimate of bond quality, a summary set of tables is provided with the text. These contain, in all but a few instances, only an average wood failure reading for the specimens tested by the two CSA 0-121 methods. IV E X P E R I M E N T A L PRELIMINARY EXPERIMENTS - DETERMINATION OF THE NATURE OF THE CAUSAL A G E N T Al l chemicals used throughout these experiments are of reagent grade, unless otherwise stated, EXPERIMENT 1 Collection and preparation of material A single 48-inch by 96-inch sheet of 0- 133-inch nominal green thickness veneer was collected from the commercial production of Western Plywood Co, Ltd, , Vancouver. The origin was the central interior of the province but the exact source was not known. Thirty-two one-foot-square veneers were prepared and, from these, twelve were selected randomly, using a table of random numbers. One veneer was dried for 10, 20, 30 or 60 minutes at each of 107°C , 171°C or 2 3 2 ° C . These temperatures were chosen to represent a mild schedule, the schedule provided by a commercial veneer dryer used in previous work, and the practical limit of the available oven. Four pieces, 6- by 6-inches, were cut from each dried veneer, one being used for contact angle measure-48 ments and three for the pressing of a panel. Many of the extractives found in conifers are hydrophobic substances. The presence of such materials in a piece of wood could affect the free surface energy, hence the contact angle formed with liquids. Therefore, in addition to the material prepared for dryings as described above, three additional 12- by 12-inch, undried veneers were clipped to provide sets of three 6- by 6-inch veneers and extracted for 16 hours with each of: i . a saturated aqueous solution of ethylene diamine tetra-acetic acid (a chelating agent), i i . acetone, i i i . methanol/benzene in the ratio of 1:2. The extracted veneers were water-soaked for 72 hours in distilled water, placed in fresh distilled water for an additional 48 hours and dried in a blower oven at 171°C for 10, 30 or 60 minutes beyond the 4 oven-dry condition. Pressing and testing Each of the fifteen sets of veneers, extracted and unextracted, was pressed into a plywood panel using a commercially-prepared phenol-formaldehyde glue. One minute closed assembly time was used with 141°C platen temperature, 200 psi pressure and 5 minutes press time. Glue spread was set at 50 pounds per thousand square feet of double glue-Footnote 4: Because of the need for brevity, these are recorded in the tables as OD + 10, OD *-30 and OD|60 respectively. 49 line {MDGL). Al l panels were hot-staeked for at least 16 hours at 116°C then cooled to room temperature for testing. The knife test specified in British-Standard BSS 1415:1956 was used. Test results are contained in Table 1. (See page 82). E X P E R I M E N T 2 Collection and preparation of material Material collected from manufacturing plants usually has an incomplete history. Only an estimate of storage conditions can be obtained, the source of the material being often uncertain within wide limits. In order to eliminate as many variables as possible, including the effect of water storage, or of prolonged storage of any type, fresh material was collected in the fieid. Interior Douglas fir is considered by members of the industry to be more susceptible to "inactivation" than the Coastal type (4)p so a tree was selected near Merritt , B. C. This was a codominant tree;, with dbh of 20;.7 inches, a total height of 117 feet and considered to be repres-entative of the stand. It grew on a good site on a well-drained sidehill. Henceforward this is referred to as Tree No. 1. A 52-inch log was removed immediately above an 18-inch stump. A second 52-inch log was removed from the 40 to 45 foot level. The logs were covered on the ends with polyethylene then trucked to Vancouver, arriving within 14 hours of the tree being felled. The logs were completely wrapped in polyethylene before placement in covered outside storage. Five days later they were peeled into 0* 109-inch veneer, 50 on a commercial lathe producing a smooth, tight peel. Veneer from the butt log was separated into sapwood and inner and outer heartwood, that from the top log into sapwood and heartwood. It was clipped into 12- by 12-inch pieces, wrapped in aluminum foil and polyethylene and placed in a freezer at - 3 6 ° C . Because of references in the literature to the possible effects on gluability of wood that had been in contact with metal, the earlier extraction included an aqueous extraction with a solution of a chelating agent. However, certain references were found which stated that metallic contact was not a factor. In order to introduce as few variables as possible, this step was omitted from this experiment. If the results indicated the necessity, it could be included in a replicated experiment. The fact that it was not necessary eould be important information. Twelve pieces of the inner heartwood from the butt log were placed in extractors, especially constructed for the purpose, and hot extracted under reflux with the following: acetone - 12 hours fresh acetone - 4 hours methanol/benzene 1:2 - 12 hours fresh methanol/benzene 1:2 - 4 hour s This was followed by 72 hours soaking in distilled water and 240 hours soaking in fresh distilled water. Solvents were recovered at a maximum temperature of 74°C using a flash evaporator. The extract and residual solvent were lyophil-ized to remove water and then stored in a refrigerator at 1°C. 51 Three pieces of the untreated veneer from the same source were dried in a blower oven, at 1 8 5 ° C , to the oven-dry condition followed by an additional 40 minutes drying. The technique of suspension previously described served to establish the time required to reach the oven-dry condition. This was found to be 10 minutes. Similarly, nine veneers were dried to the oven-dry condition then three dried for each of an additional 10, 20 or 60 minutes. The extracted veneers were stickered and dried at 107°C in a blower oven to reduce the moisture content. They were not dried below the fibre saturation point. They were then dried individually to give sets of three, dried for 10, 20, 40 or 60 minutes beyond the oven-dry condition. Pressing and testing Dried veneers, not in process, were stored in a freezer, wrapped in aluminum foil and polyethylene to minimize chemical change or moisture adsorption. Moisture pickup was determined at lay-up tims and found to have been less than 1 per cent, so veneers were allowed to thaw and reach: room temperature while exposed to the atmosphere. During this process, they picked up 2 to 3 per cent moisture, reaching the ideal moisture range for gluing with phenolic resin glues. Each set of three veneers was formed into a plywood panel, using commercial phenol-formaldehyde resin glue, collected from a freshly-made batch at a local plywood plant. The same gluing practice was followed as was used in the mill - pressing for 5 minutes at 200 psi with maximum 10 minutes closed assembly time and 141°C platen temper-52 ature. Panels were hot-stacked at least 16 hours at 118°C. Panels were trimmed and sawn into three pieces. Two pieces were cut into standard plywood shear specimens for CSA 0-121 testing and one piece was put into dry storage. Each panel provided ten shear specimens, 5 of which were tested after each of the cold-soak and boil/dry/boil cycles. The breaking loads for these specimens in shear, and estimated percentage wood failures are contained in Table 2. (See page 84)^  E X P E R I M E N T 3 Collection and preparation of material Twenty-four pieces of veneer, 6- by 6-inches, were selected randomly from the inner butt heartwood of Tree 1 and numbered Lot 1. These were hot extracted for 12 hours in each of four lots of solvent, the first two being acetone the second two being a mixture of methanol/ benzene in the ratio of 1:2. Twelve sheets were extracted in each of two extractors, all lots of solvent and extract being kept separate. Each lot of solvent was recovered on a flash evaporator, at a maximum temperature of 6 3 ° C , under vacuum. The residual was lyophilized to remove the water that had been extracted from the veneer. The first extraction, judging by the colour, had removed almost all of the extractable material. The extracts used in the re-impreg-nation were the first acetone or methanol/benzene extract from one extrac-tor, i . e. from 12 sheets of veneer. 53 Separation of extracts The acetone extract was scraped from the lyophilization flask and placed in an extraction thimble in a soxhlet apparatus. It was extrac-ted for 3-1/2 hours with diethyl ether, washed with ether, then extracted for 3-1/2 hours with acetone. A white precipitate was left in the thimble. This was acetone-washed, the washings being added to the original acetone. Similarly the methanol/benzene extract was fractionated into ether soluble, methanol/benzene soluble and insoluble portions. The ether extracts were taken to dryness on a flash evaporator. They were re-impregnated in the original solvents. The balance of the acetone extract was washed from the lyophilization flask with acetone. A flaky, white material did not dissolve so was removed by suction filtration and washed, the washings being added to the acetone solution. This residual acetone solution was not taken to dryness. The white precipitates from the solvent-extracted material -2 were dried at room temperature (21°C) and less than 10 Torr . for 20 hours. Infrared spectra were determined which indicated that the material consists of carbohydrates with many hydroxyl groups which are probably hemicelluloses. Application of extracts Fifteen pieces of the extracted veneer, which had been water stored, were dried at 107°C to constant weight. Each piece was lightly sanded on both faces. The various solutions were applied, by solvent-54 cleaned paint brush, to all faces of randomly selected sets of three veneers, as follows: Set E A the ether-soluble portion of the acetone extract; Set A the ether-insoluble, acetone-soluble portion of the acetone extract; Set E M B the ether-soluble fraction of the methanol/benzene extract; Set MB the ether-insoluble, methanol/benzene-soluble portion of the methanol/benzene extract; Set RA the residual acetone extract, unfractionated, with the precipitate filtered out. The five sets spread with extract were dried individually at 185°C for 40 minutes beyond the oven-dry condition. In addition, the following material was prepared: Set E X T 1 veneer removed from an extractor at the end of the first acetone extraction and dried, after water soaking, at 185°C for 60 minutes beyond the oven-dry conditions Set Check 1 untreated veneer from the inner butt heartwood, Tree 1, dried , to constant weight at 107°C and lightly sanded on both faces; Set Check 2 a replicate of Check 1. Pressing and testing Each set was pressed into a similarly numbered plywood panel using 5 minutes closed assembly time, 141°C platen temperature, 200 psi pressure and 5-1/2 minutes press time, pressing.one panel per opening. The complete panels were hot-stacked at 118°C for a minimum of 16 hours to complete the curing cycle. The glue was Reichhold EPH-142-C-1 , a commercial phenol-formaldehyde mix, prepared by the manufacturer and spread at the rate of 50 pounds MDGL, The gluing and pressing schedule given above will hereafter be called the standard schedule. 55 Each panel was cut to provide 3 shear specimens which were tested after subjection to the cold-soak cycle of CSA 0-121. The breaking loads and per cent wood failures for these specimens are contained in Table 3. (See page 87)l E X P E R I M E N T 4 Collection and preparation of material Twenty-four pieces of inner butt heartwood veneer, 6- by 6-inches, numbered Lot 2, were fully extracted as before. The material was soaked in distilled water for 15 days, dried to constant weight at 1 0 0 ° C , then lightly sanded on all faces. Each lot of extract was taken to dryness on a flash-evaporator at maximum 6 3 ° C , lyophilized and extrac-ted with acetone in a soxhlet apparatus, thus separating out the carbo-hydrate material. A set of three veneers was used for each of the following treatments. The material from the first of each pair of extractions was used for the impregnation with methanol/benzene extract and the impregnation with the acetone extract from Lot 1. Since it is possible that the second extraction of each pair could contain the causal agent, the combined acetone extract from the current extraction (Lot 2) was used. The acetone solutions were applied by paint brush but only to the contact surfaces that would be used in forming the glue bonds. 56 Set 2-A a 25-ml aliquot of the combined acetone extracts from Lot 2. It contained 1.68 g of extractives; Set 2-AC a 50-ml aliquot as for 2 -A, plus 20 ml of water was used to dissolve the carbohydrate fraction from the acetone extract of Lot 2 in a soxhlet thimble. A 25-ml aliquot of the recovery (56 ml) was applied to the contact surfaces; Set 2-AC-5 as for set 2-AC but a 5-ml aliquot was used; Set 1-A a 25-ml aliquot of the first acetone extract of Lot 1. It contained 5: 85 g of extractives. Set 1-AC a 25-ml aliquot as for Set 1-A, plus 10 ml of water in which was dissolved one-half of the carbohydrates from the first acetone extract of Lot 1; Set 2-MB a 25-ml aliquot of the methanol/benzene extract of Lot 2. It contained 0* 55 g of extractives; Set 2 -MBC a 25-ml aliquot as for set 2-MB plus 10 ml of water in which was dissolved the carbohydrate fraction from the first methanol/benzene extraction of Lot 2; Set Check 3 extracted veneer, water-soaked and dried at 100°C to constant weight A l l the above sets, except Check 3, were dried at 185°C for 40 minutes beyond the oven-dry condition. In additori, two sets of untreated, inner heartwood veneer from Tree 1 were dried for 10 o r 20 minutes beyond the oven-dry condition (Check 4 and Check 5 respectively), to serve as controls, demonstrating the development of inactivation in unextracted veneer. Pressing and testing The panels were pressed on the standard schedule, except that five minutes press time was used. The glue was Monsanto P F 514 phenol-formaldehyde resin glue, spread at the rate of 50 pounds MDGL. 57 Each panel was cut into three cold-soak specimens which were processed through the test cycles and broken as before. Bond qualities are given in Table 4. (See page 89). E X P E R I M E N T 5 Collection and preparation of material Thirty pieces of outer butt heartwood veneer from Tree 1, 6- by 6-inches, were placed in a blower oven, suspended on glass rods to minimize interference with the air-flow pattern. They were dried for 42 minutes at 1 8 5 ° C , producing, it was assumed, an inactivated surface on each veneer. Three veneers were selected randomly as sample U - l (dried once, unsanded), foil wrapped, polyethylene wrapped and placed in a freezer at - 3 6 ° C . The balance of the veneers were lightly machine' sanded to remove the discoloured face. Three were randomly selected as -sample S-1 (dried once, sanded) and stored as above. This procedure was repeated four more times to produce five sets of veneers that had been exposed to an inactivating drying schedule one to five times, with surface removal after all, or a l l but one, of the cycles. These appear in Table 5 as panels U - l to U-5 for the five that were not sanded after the last drying, and S-l to S-5 for those that were sanded after the last drying. Pressing and testing After nine days storage, the veneers were glued into panels on the standard schedule, using Monsanto P F 514 phenolic-resin glue from ^ 58 a commercial mix. Three shear specimens were cut from each panel, after removing 1/2-inch of trim to reduce edge effect. These were subjected to the cold soak cycle of CSA 0-121 before testing. Test results are given in Table 5. (See page 91). E X P E R I M E N T 6 Collection and preparation of material Two sets of three veneers, 6- by 6-inches, from the inner base heartwood of Tree 1 were dried, one set at a time, in a vacuum oven that had been swept three times with nitrogen, with high-vacuum pumping between sweepings. The nitrogen was passed through a solution of pyrogallol in 50 per cent aqueous sodium hydroxide (15 g per 100 ml) to remove oxygen. The purified nitrogen was then diffused into concen-trated sulfuric acid to remove water before being admitted to the oven. In previous work it had been found that the drying rate of veneer dropped quickly with a drop in the volume of air passing over the specimens. Douglas fir heartwood would dry in about 10 minutes at 185°C when a single 12- by 12-inch specimen was suspended in a blower oven, of 24- by 24-inch cross section, with an air speed of 250 fpm. As the number of introduced veneers was increased, the rate of air-flow dropped and the drying rate also fell. These findings have been corrob-orated by the work of Milligan and Davies (73) and of others. The drying time used in the vacuum oven was therefore empirically set at twice the normal time required to dry for 40 minutes beyond the oven-dry 59 condition. A 45-minute period was also required for the oven to come up to temperature. Drying was carried out for 145 minutes at tempera-tures up to 1 8 1 ° C , the limit of the oven. The veneer, on removal from the oven, appeared to approx-imate the desired conditions of over-drying, or to be dried somewhat beyond the desired level. Pressing and testing Panels were processed with the panels of Experiment 3 above, the results being included in Table 3. (See page 87). E X P E R I M E N T 7 Collection and preparation of material Insufficient material remained from Tree 1 for the complete experiment. A butt log from a second Interior Douglas fir was collected in the field and designated Tree 2. Two sets of panels were included to test the susceptibility of veneer from this tree to inactivation. On the assumption that the veneer from Tree 2 would prove to be susceptible to the development of an inactivated surface, (which proved to be correct), the combined veneer from Trees 1 and 2 was considered to be one source of material. The following panels were prepared: Set Tree 2 12 pieces of 12- by 12-inch, 0* 133-inch, nominal green thickness veneer from the inner heartwood of Tree 2 were dried at 185°C for 0, 10, 20 or 40 minutes beyond the oven-dry condition. Each set was marked with the time of drying; 60 Set Tree 2B a replicate of the above! Set A / M / B 12 pieces of butt heartwood from Tree 2 were extracted with acetone and methanol/benzene and dried at 185°C for 0, 10, 20 or 40 minutes beyond the oven-dry condition; Set A 9 pieces of heartwood (exact position uncertain) from the butt log of Tree 1 were extracted with acetone only and dried in sets of three at 185°C for 10, 20 or 40 minutes beyond the oven-dry condition; Set M / B 12 pieces of butt heartwood from Tree 2 were extracted with methanol/benzene only and dried in sets of three at 185°C for 0, 10, 20 or 40 minutes beyond the oven-dry condition; Set M E K 12 pieces of butt heartwood from Tree 2 were extracted with methyl ethyl ketone and dried in sets of three at 185°C for 0, 10, 20 or 40 minutes beyond the oven-dry condition; Set P E 12 pieces of inner heartwood from Tree 2 were extracted with petroleum ether (boiling range 6 5 - 1 1 0 ° C ) and dried in sets of three at 185°C for 0, 10, 20 or 40 minutes beyond the oven-dry condition; Set Dry Ext 9 pieces of inner butt heartwood from Tree 1 were dried to constant weight at 107°C and lightly sanded. They were then extracted with acetone distilled from anhydrous calcium sulphate and with methanol/benzene 1:2 from freshly-opened drums of anhydrous material. The extracted veneer was dried in sets of three at 185°C for 10, 20 or 40 minutes beyond the oven-dry condition. Panel Dry Ext 10 was water-soaked before the final drying, the other two were notj Set WB 12 pieces of outer butt heartwood from Tree 1 were soaked overnight in distilled water, then boiled for 24 hours and stored in fresh distilled water for 9 days prior to redrying. The veneer was dried in sets of three at 185°C for 0, 10, 20 or 40 minutes beyond the oven-dry condition; Set WS 9 pieces of inner butt heartwood from Tree 1 were soaked in distilled water for 7 weeks then dried at 185°C for 20 (sic), 20 or 40 minutes beyond the oven-dry condition; 61 Set In A / M / B 1 12 pieces of veneer from the outer butt heartwood of Tree 1 were dried, in sets of three at 185°C for 40 minutes beyond the oven-dry condition, extracted with acetone and methanol/benzene, water-soaked and dried to constant weight at 105°C; Set In A / M / B 2 12 pieces of veneer from the butt heartwood of Tree 2 were dried in sets of three at 185°C for 0, 10, 20 or 40 minutes beyond the oven-dry condition, extracted with acetone and methanol/benzene, water-soaked and dried to constant weight at 105°C. Set In A 12 pieces of butt heartwood from Tree 2 were dried in sets of three at 185°C for 0, 10, 20 or 40 minutes beyond the oven-dry condition then extracted with acetone, water-soaked and dried to constant weight at 105°C. A l l of the material that was extracted before drying was also water-soaked between extraction and drying. This information was not included in the detailed statements of pretreatment to keep them as simple as possible. Pressing and testing Pressing was carried out on the standard schedule. Each panel provided five shear specimens which were tested after the cold-soak cycle of CSA 0-121. Test results are given in Table 6. (See page 96). E X P E R I M E N T S Collection and preparation of material The following material was prepared: Set F l OB outer heartwood from the butt log of Tree 1. Three panels were prepared by random selection of material and drying at 185°C for 10, 20 or 40 minutes beyond the oven-dry condition. These panels were marked F l OB 10, F l OB 20 and F l OB 40 to indicate drying time within the set; 62 Set F l T heartwood from the top log of Tree 1. Four panels were pre-pared and dried for 0, 10, 20 or 40 minutes beyond the oven-dry condition and marked accordingly; Set Abies 1 a single 0* 177-inch, nominal green thickness, roughly-peeled veneer, identifiable only as Abies species, was cut into 12-by 12-inch pieces and used for four panels. These were randomly selected and dried for 0, 10, 20 or 40 minutes beyond the oven-dry condition and marked accordingly; Set Abies 2 a replicate of the above, except that smoothly-cut veneer was used; Set Sitka 1 a single 0« 177-inch, nominal green thickness, Sitka spruce veneer was cut into 12- by 12-inch pieces. These were randomly assigned to form four panels which were dried for 0, 10, 20 or 40 minutes beyond the oven-dry condition and marked accordingly. Pressing and testing The glue used in previous work was acquired from commer-cial production as needed. This means there was little control over the age of the mix, although it was never more than two days. The varia-tions in preparation, known to exist between various mil ls , had been accepted as part of the unavoidable experimental error. At this time, a suitable premixed type of resin became available so that it was now possible to mix glue as needed. Several batches could be made, under controlled conditions, from the same lot of resin. This basic resin does change, but only slowly if properly stored, therefore it was felt that a more reproducible glue was obtainable by this method. This glue, Reichhold CW 339, was used for all subsequent experimental work and, except as noted, all glues were mixed from the same resin lot. Panels were pressed on the standard schedule except that 63 the press time was adjusted to ten minutes where the thicker Abies and Sitka spruce veneers were used. This exceeds by one minute the recommended press time for these constructions and glue. Five shear specimens were prepared and tested after the cold-soak cycle of CSA 0-121. Results are presented ih Table 7. (See page 99). COMPARISON OF THE EXTRACTIVES OF TREES WITH VARYING SUS-CEPTIBILITY TO INACTIVATION E X P E R I M E N T 9 ______-_-___——_____—______ t Inactivation in Coastal Douglas fir  Low moisture content (a) Collection and preparation of material A sequential sample was collected from a log of Coastal Douglas f ir , peeled at Crown Zellerbach Building Materials, Ltd. , Fraser Mil ls . The log was a 26-inch diameter No. 3 peeler from Vancouver Island, probably from Roys ton. Peeling was moderately tight, to produce veneer of 0' 133-inch nominal green thickness. Veneer was collected from the following locations in the log: Sap 1 - outer portion adjacent to the cambial zone; Sap 2 - inner portion of sapwood band, 1 to 2 inches from the cambial zone; Heart 1 - outermost heartwood (see below); 64 Heart 2 - heartwood 1 inch from the sapwood/heartwood boundary; Heart 3 - heartwood 3 inches from the sapwood/heartwood boundary; Heart 4 - heartwood 5 inches from the sapwood/heartwood boundary; Heart 5 - heartwood 7 inches from the sapwood/heartwood boundary; Heart 6 - heartwood 8 inches from the sapwood/heartwood boundary, 3 inches from the geometric centre of the log. Veneer from the sapwood/heartwood boundary contained some mixed veneer, which was sorted into sapwood and heartwood. The sapwood was included in Sap 2 and the heartwood was classified as Heart 1. From each position, sufficient material was collected to produce at least 60 veneers, 12- by 12-inches, except for Heart 1 where only 30 veneers were available. From each group, 15 veneers were selected randomly and dried in sets of three, at 1 8 5 ° C , for 0, 10, 20, 40 or 60 minutes beyond the oven-dry condition. An arbitrary scale of roughness had been established for other work. Because of the possible effect of roughness on inactivation, through the provision of local pockets of high glue concentration, it was considered worthwhile to grade the veneers used in this experiment. Those panels which contained one or more veneers worse than 5 on the roughness scale (the arbitrary separation point between "rough" and "smooth") are indicated in Table 8. Detailed records were made of the roughness of all veneers. (b) Pressing and testing Panels were glufed and pressed on the standard schedule, adjusted for veneer thickness. Ten shear specimens were prepared from each panel of which five were subjected to the cold-soak and five to the 65 boil/dry/boil cycle of CSA 0-121 before testing. Results are presented in Table 8. This is divided into two portions, the Supplementary Table, included in the Appendix, which contains the test results in detail, and the Summary Table which contains the figures needed for rapid compar-isons. This is included in the text, Section V. (See page 102). High moisture content (a) Collection and preparation of material From each position in the Coastal Douglas f ir , a further twelve veneers were collected. These were used for the manufacture of four panels, two each of rough and smooth veneer, one of each pair being oven-dried and the other dried for 60 minutes beyond the oven-dry condition. After drying, all veneer was reconditioned to approximately 6 per cent moisture content. This was achieved by spraying each panel with an amount of water equivalent to six per cent of the dry weight of wood, wrapping all veneers in one waterproof package and allowing the veneer moisture content to come to equilibrium over a period of several days. The accuracy of the technique can be judged from the moisture contents recorded for heartwood in Table 9. Due to an error in presetting an automatic balance, the sapwood was sprayed to a higher moisture content than was intended. (b) Pressing and testing The recommended pressing time, fof^  the glue and construction being used, was 3-1/2 minutes. In all previous pressing, 5-1/2 minutes had been used to give a safety factor against the production of apparently 66 inactivated bonds through under-pressing. Since, in this case, marginal bonding conditions were sought, the recommended press time was used. A l l other conditions of pressing and testing were as before. Re suits are tabulated in Table 9 with the detailed test figures in the Supplementary-Table in the Appendix and the figures needed for rapid comparison in the Summary Table, included in text Section V. (See page 103). Inactivation in Interior Douglas fir Collection and preparation of material Material for this experiment was obtained from Western Plywood (Cariboo) Limited, located at Quesnel, B; C. Within the timber limits from which this mill draws its logs, Company foresters recognize three ecological types of Douglas fir. The western part of the area contains Coastal Douglas fir. The inland portion is divided into "Dry" and "Very dry" and the logs kept separate. It is claimed by mill personnel that the three types have distinctive peeling and gluing characteristics but there was no opportunity to check this. The "Dry" type is the more common of the two Interior forms so a log of this material was obtained from the mill pond.and labelled Quesnel fir. Mil l practice is to presteam the logs but, to avoid introduction of a further set of variables, the log was peeled unsteamed for this study. The log was 21 inches in diameter with the characteristic narrow sapwood band of Interior fir. It has been water-floated for an unknown time, probably not exceeding a few days, and had not been frozen. It was peeled to a nominal green thickness of 0* 133-inches, 67 producing veneer that was somewhat looser than that obtained from the Coastal fir. Veneer was collected from each of the following positions in the log: Sapwood - all apparent sapwood; Heart 1 - heartwood adjacent to the sapwood/heartwood boundary; Heart 2 - heartwood 2 inches from the sapwood/heartwood boundary; Heart 3 - heartwood 4 inches fromthe sapwood/heartwood boundary; Heart 4 - heartwood 6 inches from the sapwood/heartwood boundary; Heart 5 - heartwood 8 inches from the sapwood/heartwood boundary and about 2 inches from the geometric centre of the log. The veneer was wrapped in polyethylene and shipped to Vancouver, being four days in transit at ambient temperatures. It was then stored at 1 ° C , except when in process. A second log, numbered Tree 3, was collected in the field from a freshly-felled tree, also from the Dry portion of the timber limits. The butt appeared sound after felling, except for one small pitch shake, and no rot was visible. A 52-inch log was collected above a 12-inch stump. This was trucked immediately to the mill-site where it was dumped into the mill-pond. It was towed across the mill-pond and moved to dry storage until loaded for shipment the same day. The total water-flotation period did not exceed one hour. The log was trucked to Vancouver, being in transit for three days, and was placed in covered outside storage until peeled. Five days after felling, the log was peeled on a commercial lathe, producing very tightly-peeled 0-109-inch, nominal green thickness, veneer. Before peeling, the log was marked in one-inch increments from the sapwood/heartwood boundary (which was regular but not confined to 68 one growth ring) at each end. After peeling, the veneer was clipped according to the colour coding remaining on the veneer ends. Veneer which ended in different colour zones on the two ends of the log was not used. Peeled veneer was stored at - 1 ° C until dried, except when in process. The following material was recovered: Sapwood - all recovered sapwood; Heart 1 - heartwood adjacent to the sapwood/heartwood boundary; Heart 2 - heartwood 1-1/2 to 2-1/2 inches from the sapwood/ heartwood boundary; Heart 3 - heartwood 2-1/2 to 3-1/2 inches from the sapwood/ heartwood boundary; Heart 4 - heartwood 3-1/2 to 4-1/2 inches from the sapwood/ heartwood boundary; Heart 5 - heartwood 4-1/2 to 5-1/2 inches from the sapwood/ heartwood boundary; Heart 6 - heartwood 5-1/2 to 6-1/2 inches from the sapwood/ heartwood boundary, 6 inches from the geometric centre of the log. In error, the lathe operator "rounded up" the log and much of the outer sapwood was lost, so only one lot of sapwood was collected. The log shattered through a pitch-shake when a 12-inch diameter core remained. The veneer was clipped to 12- by 12-inch sheets, wrapped in polyethylene and stored at - 3 6 ° C . From each position in the log from Tree 3, 12 pieces of veneer were selected on a statistically random basis and dried in sets o of three, at 185 C , for 0, 10, 20 or 40 minutes beyond the oven-dry condition. In a similar manner, veneer was selected and prepared from positions Sap, Heart 1 and Heart 3 of the tree marked Quesnel fir. 69 Pressing and testing Panels were pressed on the standard schedule and cut into shear specimens. Five specimens were subjected to each of the cold-soak and boil/dry/boil cycles of CSA 0-121 before testing. Detailed test results are contained in Supplementary Tables 10 and 11 in the Appendix. Summary Tables 10 and 11 consist of those figures needed for a rapid comparison of test results. (See pages 104 and 105). EXPERIMENT 10 Extraction and characterization of extracts The results of Experiments 8 and 9 (see Section V) indicated that the Coastal fir was not susceptible to the development of inactivation, the Quesnel fir demonstrated variable susceptibility with distance from the cambium and Tree 3 was very susceptible, except for the anomalous section Heart 5» at any position from cambium to the limit of sampling. Twelve sheets of veneer, 12- by 12-inches, were collected from each of eight positions in the three trees, as follows: Coastal fir - Sapwood Heart 1 Heart 3 Quesnel fir - Sapwood Heart 1 Heart 3 Tree 3 - Heart 4 Heart 5 Two additional lots of twelve sheets were collected from the 70 Heart 4 portion of Tree 3. One of these was dried for 40 minutes after reaching the oven-dry condition at 185°C. The other was dried similarly and sanded, the cycle being repeated, three times. Extraction and recovery It had been shown in experiment 7 that petroleum ether with a boiling range of 6 5 - 1 1 0 ° C was an efficient solvent for the causal agent. Since this solvent extracts a fairly narrow range of materials from those presumed to occur in Douglas f ir , it was considered the most suitable available solvent. Because of the large quantities of material that must be handled and the relatively high-boiling level of the proposed solvent, the extract would be exposed to temperatures higher than desirable, in view of the known lability of some components. It was suggested by Dr, L . D. Hayward of the Department of Chemistry, University of British Columbia (39), that low-boiling-range petroleum ether would reduce the problem due to thermolability and would probably do as effic-ient an extraction as the higher-boiling-range material. Some extractions had been carried out with the higher-boiling-range material (Quesnel f ir , all components) but the balance of the extractions were done with purified normal hexane (Eastman Kodak PI 135). Due to misrepresenta-tion by a supplier, one lot of solvent used for extraction of the dried and dried/sanded material actually consisted of n-hexane containing a propor-tion of n-pentane. The lower boiling point of this material, sold and labelled as n-hexane, indicated contamination. The presence of the lower homologue was verified through gas-liquid chromatography. However, 71 the results of subsequent gluing tests indicated complete removal of the causal agent so the extractions were not repeated. Each lot of 12 sheets was extracted for 12 hours in each of two lots of solvent, maintained just below the boiling point. The solvent lots were combined and recovered on a flash, evaporator under vacuum at maximum 6 3 ° C . The veneer was washed with fresh solvent and the washings added to the main body. The small amount of water removed from the veneer was eliminated from the solvent in a separatory funnel. The viscous, brown extract was lyophilized to remove residual water and placed in a freezer at - 3 6 ° C where it remained except when in process. Separation of major fractions (see flow sheet on page 71a) (a) Steam volatiles The extract from Quesnel fir sapwood (or other sample) was placed in a steam distillation apparatus with a little water and processed until no further material came over in the steam. The residual non-volatile material and water were washed with ether (diethyl) into a separatory funnel, chilled for one hour at 1°C and the two phases separated. The water phase was chilled and washed with ether twice more. The ether washings were combined, dried over anhydrous sodium sulphate and taken to dryness on a flash evaporator at 21°C in a tared flask. Net weight of the dry extract was recorded. (b) Waxes The dried extract was dissolved in cold acetone and placed in a 71a petroleum ether extract non steam volatile fatty acids combined acids resin acids sterols alcohols waxes unsaponifiables steam volatile^ terpenes (gas /liquid chromato-graphy) waxes insoluble cold acetone centrifugation, decantation soluble water soluble water soluble non-esterified evaporation ether K2CO3 solution ether soluble (1 )• acidify (2) ether extract (3) methanol/sulphuric acid sodium chloride (4) partition between ether/hexane and potassium carbonate solution combined acids sterols alcohols unsaponifiables ether soluble esterified water soluble acidify ether extract V combined acids fatty acid  methyl esters (gas /liquid chromatography thin-layer chromatography) boron trifluoride / methanol reagent: free resin acids (1) methanol, potassium hydroxide dried (2) ether extrac-ted ether soluble — ; alcohols  sterols unsapo"nifiables (paper chromato-graphy thin-layer chrom-atography) combined acids methyl esters diazo- (gas/liquid chromatography) methane 1 resin acid methyl esters (paper chromatography thin-layer chromatography gas/liquid chromatography) 72 freezer at - 1 2 ° C for four hours. The resulting precipitate of wax was recovered by centrifugation and decantation, dried under vacuum at 2 l ° C and the dry weight determined. The wax was then put into storage in a freezer. The acetone was removed from the residual extract on a flash-evaporator at maximum 2 2 ° C . (c) Separation of free acids The residual extract was dissolved in 25 ml of ether and extracted three times with 20 ml portions of cold potassium carbonate. The free acids were recovered from the aqueous layer by acidification to pH 3 with 6N sulphuric acid and extraction with three portions of ether. This solution was dried over sodium sulphate, the ether removed on a flash-evaporator and the net dry weight recorded. The material from the original solution that did not react with potassium carbonate, consisting of fats , combined acids , sterols, alcohols and other non-acidic materials , was recovered by drying the ether solution over sodium sulphate and evaporation of the ether. A net weight was recorded. (d) Separation of fatty and resin acids The free acids were separated, into classes using the method of Wolff and Scholze (111) with slight modifications. To the dry free acids, 4 ml per g of methanol and 2 ml per g of sulphuric acid/methanol 1:4 were added and the mixture refluxed for 2 minutes. Five volumes of 7 per cent sodium chloride solution were added so that separate aqueous and organic phases formed. The solution was extracted with one portion of ether/n-hexane 73 1:1 and 3 portions of ether. The combined organic solutions were washed with 7 per cent sodium chloride solution until neutral and extracted with cold 5 per cent potassium carbonate solution. The more reactive fatty acids were methylated by this process, so remained in the organic solution, while the less reactive resin acids passed into the aqueous solution as potassium salts. The fatty acid methyl esters were recovered by drying the organic solution over sodium sulphate and removing the solvent on a flash evaporator. The aqueous solution was acidified to pH 3 with 6 N sulphuric acid and extracted three times with ether. The freed resin acids were recovered by drying the ether solution over sodium sulphate and flash evaporation of the solvent. Net weights of all recoveries were recorded. This method of separation was used in preference to the more generally used amine salt method because it provided a shorter route to the desired methyl esters of the fatty acids. (e) Saponification and separation of combined acids from alco-hols, unsaponifiables and other nonacidic components The dry nonacidic material from the first potassium carbonate separation was dissolved in 100 ml of 5 per cent potassium hydroxide in ethanol and the mixture refluxed for one hour, cooled and the ethanol evaporated. One hundred ml of water were added to the saponification mixture. After standing, the solution was extracted with three portions of ether. The ether solution was dried over sodium sulphate and the ether 74 removed by flash evaporation to yield the unsaponifiable materials and the ether soluble products of hydrolysis. From the aqueous layer the acids freed by saponification were recovered by acidification to pH 3 with 6 N sulphuric acid and extraction with three portions of ether. The ether solution was dried over sodium sulphate and the acidic material recovered by flash evaporation. (f) Lyophilization The total yield of all fractions, in some cases, exceeded the initial amount, indicating the presence of water in at least some of the extracts. This was rectified, by lyophilization. The original extract was now separated into the five major components - volatile s, free fatty acids, free resin acids, free acids from the originally combined acids, and the unsaponifiable material combined with the cleavage products from the saponification. (A sixth, minor, wax fraction was also recovered but because of its general distribution and the minuteness of the quantities recovered, it was not considered further. ) Preparation for characterization It was proposed to use gas-liquid chromatography for part of the characterization procedure. Therefore it was necessary to prepare methyl esters of the various acid fractions, since it is for this class of derivatives that the most reliable techniques have been developed. The free fatty acids were methylated in the process of recovery of the various extractive fractions. The combined acid fractions were methylated using 75 boron trifluoride/methanol reagent and the method of Met calfe and Schmitz (71). Diazomethane was used to methylate the free re^sin acids. Dilute solutions of each component were prepared in n-hexane for injection into the chromatograph. Solutions in acetone, at a concen-tration of 2 micrograms per microliter were prepared for thin-layer and paper chromatography. Characterization of extractive fractions (a) Gas-liquid chromatography A Beckman GC2A gas-liquid chromatograph with a thermal conductivity.detector was used. Helium was used as the carrier gas. The operating conditions are given in the pertinent sections below, (i) Steam-volatiles Since these were expected to be mainly volatile terpenes , they were run at a column temperature of 130°C and a flow rate of 100 ml per minute of helium on two columns , one with tritolyl phosphate as the stationary phase and the other with di-n-decyl phthalate, as used by Haslam and Jeffs (38). The retention times for known terpenes were the same as those given by these authors, so that the terpenes present in the steam volatiles were identified from their retention times in the two columns. Figure l i s one such chromatogram. (See page 146). A higher-boiling fraction did not readily elute at the temperature used. A 12-foot, 1/4-inch o. d. stainless steel column was prepared, packed with silicone gum QF-1 ( 14 per cent) on Gas Chrom C L (80-100 mesh). A temperature of 160°C was used with a flow rate 76 of 60 ml per minute of helium. "Various unknowns, identified as compounds A to N , were found. A complete list of terpenes and unknowns for each position in each log examined, is given as Table 12. A representative chromatogram is presented as Figure II. (See pages 110 and 147). (ii) Free fatty acids These were examined using a 10-foot, 1/4-inch o. d. stainless steel column (Gas Chrom C L A (80-100 mesh) coated, with Reso-flex LAC2R446 30 per cent) at a temperature of 230°C and 144 ml per minute of helium. This was an adaptation from Beckman application data sheet GC-89-B (7). The methyl esters of known fatty acids were used for compar-ison. These included the various odd-numbered acids that were found in the extracts. The results are given as Table 13 and a representative chromato-gram is presented as Figure III. (See pages 111 and 148). (iii) Combined acids These were, in fact, all fatty acids and were completely resolvable by the above technique. Results of this separation are presented as Table 14. (Seepage 112). (iv) Resin acids The methyl esters were examined using a 6-foot, 1/4-inch o„ d. stainless steel column, using as the stationary phase neopentyl glycol adipate on Gas Chrom C L A (15-9 per cent). Operating temperature was 2 2 0 ° C and the flow rate of helium was 140 ml per minute. It was not possible to determine the identity of all components. Those which eluted at the same time as reference materials are named in 77 Table 15 and Figure IV, the rest being identified by elution times only, (b) Confirmation by Thermotrac A Thermotrac attachment for the chromatograph was used for confirmation of the results found with the various columns at fixed temperatures and for the results with paper or thin-layer chromatography of the unsaponifiable fraction. A linear temperature programme was used, rising from 150°C to 300°C in 15 minutes. The elution times agreed with those found in the literature and were in agreement with the results of the previous chromatographic work. It was possible by cross reference to the two systems to separate the fatty acids of similar chain length accor-ding to degree of unsaturation. Table 16 contains the results obtained with the unsaponifiable fractions when run on the thermotrac. (Page 114), (c) Paper chromatography (i) Resin acids The technique of Daniels and Enzell (24) was used to characterize the methyl esters except that Whatman fine glass paper GFB was used as substrate. The chromatogram was run in solution A. Because of the sensitivity of the developed chromatogram to light, it was recorded photographically and appears as Figure V. (See page 150). (ii) Unsaponifiables A descending chromatogram was prepared by spotting 200 micrograms of each fraction on Whatman No. 1 filter paper. This was developed overnight in a solution of n-butanol/acetic acid/water in the ratios of 4:1:5, dried and sprayed with periodate/permanganate reagent. 78 (d) Thin-layer chromatography (i) Fatty acids The methyl esters were run as an ascending chromato-gram in a solution of diethyl ether/n-hexane/acetic acid in the ratios of 50/50/1. The substrate was Kieselgel D F - 5 , available from Chemie Erzeugnisse und Adsorptionstechnik AG , Muttenz, Switzerland. Antimony pentachloride was used for development. A photograph of the plate is presented as Figure VI. (See page 151). The various reference standards were not freshly prepared but do serve to locate the C^g acids which run as a group on this type of plate. (ii) Unsaponifiables A Kieselgel plate was prepared, spotted with the various fractions and run as an ascending chromatogram in diethyl ether/n-hexane/ acetic acid in the ratios of 50/50/1. This was developed in 50/50 vol/vol sulphuric acid/acetic anhydride. Because of the effects of the high temperature used in the gas chromatograph, the results could not be directly compared with the results of this plate (See Figure VII). (Page 152). E X P E R I M E N T 11 The efficiency of extraction with n-hexane and petroleum ether  Collection and preparation of material Those veneers which had been dried before extraction were water-soaked and dried to constant weight at 107°C. The balance were 79 water-soaked and dried at 1 8 5 ° C , in sets of three, for 0, 10, 20 or 40 minutes beyond the oven-dry point. In addition, randomly selected veneers from untreated material from the Coast and Quesnel fir were dried to constant weight at 107°C to provide controls on the gluing process. Pressing and testing Each set of veneers was glued into a panel on the standard schedule. The test results are given in detail in Supplementary Table 18 in the Appendix. Summary Table 18 contains average figures for the breaking loads and per cent wood failures. Because of the effect of the high content of latewood on the test figures for Tree 3, resulting in high breaking loads and erratic wood failures, the breaking loads were retained for comparative purposes. (See page 120). E X P E R I M E N T 12 Correlation of presence of fatty acids and susceptibility to inactivation  Collection and preparation of material Veneer collected from the Coastal Douglas fir had proven insusceptible to the development of an inactivated surface. Eighty-seven pieces of veneer, 12- by 12-inches, were selected from the remaining Heart 4 and Heart 5 material and dried to constant weight at 107°C. These were randomly distributed into twenty-nine sets of three veneers and a net weight taken for each set. Four sets of veneers were chosen at random and were coated 80 on the faces to be used for bonding, with one of the five available fatty acids. An amount of acid equal to one per cent of the dry weight of the veneer set being treated was dissolved in n-hexane. The solution was spread on the veneer faces with a solvent-cleaned paint brush. One set of veneers was spread out and left to dry at room temperature, the other three being dried for 40 minutes in a blower oven at 107°C , 149°C and o 185 C , respectively. Similarly, enough veneer to make four panels was spread with an amount of commercial abietic acid equal to one per cent of the dry weight of the panel treated, and dried as above. A single panel was painted with n-hexane and allowed to dry at room temperature. The three panels for each acid were dried consecutively in a I blower oven with the lower-temperature drying done first. When each group for one acid was completed, the oven was held at 232°C for 20 minutes to scour out residual acid. Pressing and testing A 3-ply plywood panel was pressed from each set of three veneers, using the standard schedule. From each panel, ten shear spec-imens were sawn. Of these, five were subjected to each of the cold-soak and boil/dry/boil cycles of CSA 0-121 and tested. Test results are given in Supplementary Table 19 and in concise form in Summary Table 19. (See page 123). V D I S C U S S I O N O F R E S U L T S PRELIMINARY EXPERIMENTS A series of preliminary experiments was carried out in an attempt to learn something of the nature of the causal agent of inactivation. The only certain test for the presence of an inactivated surface was to measure the bond quality of veneer glued under standard conditions. Subsequent study of the bonding surfaces was difficult or impossible, so a non-destructive test for the presence of inactivation was sought. Measurement of the angle formed by a drop of water in contact with the surface under study had been used to measure the wettability of various samples of wood (31, 94). Since the technique appeared applicable to the study of an inactivated surface , material was collected from an Interior Douglas f ir , the type reported to be susceptible to inactivation* as explained in the Experimental Section under Experiment 1. It is apparent from the results of Table 1 (page 82) that there is a reduction in bond quality, as measured by the knife test, with increas-ing time or temperature of drying, except for the material that was extracted. Here there is no apparent correlation between drying time and bond quality. This evidence indicates that inactivation increases in intensity with increased drying time or temperature, except in extracted 82 Table 1 Bond-quality evaluations of panels made from veneer from a single source subjected to different drying schedules, with or without pre-extraction. Treatment Per cent wood failure Time Temp C° 10 min 107 80 2 20 min 1 1 30 30 min " 30 60 min " 70 10 min 171 70 20 min " 65 30 min " 65 60 min " 5 10 min 232 40 20 min " 10 30 min " 0 60 min " 20 Panels made from extracted veneer OD+10 min 171 85 OD*30 min " 85 OD*60 min " 70 1 A visual estimate, made in comparison with a photographic standard, of the percentage of the area of the glue-line where failure took place within the wood. 2 Each figure is the average of the readings from two tests , one on each of the outermost glue-lines, as specified in British Standard 1455:1956, British-made plywood for general purposes. 83 veneers. An attempt was made to correlate the contact angle formed with pure water, on the surface of this veneer, with the gluability of the veneer. In some cases, a weak correlation existed between contact angle and surface pretreatment. However, technical difficulties appeared to preclude the obtaining of acceptable results. Further work was discon-tinued in favour of the more promising approach through extraction. A comparison was therefore made between the gluing proper-ties of veneer that had been pre-extracted with organic solvents and material from the same source that was not treated prior to gluing. The breaking loads and per cent wood failures of the panels made from uhextracted veneer, shown in Table 2, (page 84) substantiate the suscep-tibility of this material to the development of inactivation. There is an effect at the shortest time and a rapid decline in quality beyond that point. Conversely, the extracted material produced high-quality bonds at all levels of treatment. It is apparent that development of an inactivated surface has been prevented by the extraction of susceptible material, prior to drying, with the organic solvents used. Although the effects of inactivation can be mitigated by sanding, this is the first successful attempt at control  of this phenomenon through prevention. It therefore represents an  original contribution to the search for the underlying causal agent. 84 Table 2 Bond-quality evaluations of veneer which was susceptible to inactivation and had been extracted with acetone and methanol/ benzene prior to drying. a. Measured as breaking load and percentage wood failure after the cold-soak cycle of CSA 0-121  Drying Breaking load psi Per cent wood failure time Extracted Unextracted Extracted Unextracted OD+10 273 300 129 113 85 95 15 5 190 230Avg. 132 130 Avg. 90 80 Avg.. 30 5 Avg. 2 05 239 161 133 95 89 25 16 OD+20 2 03 200 31 0 75 85 5 0 2 08 200 Avg. 45 12 Avg. 90 70 Avg. 10 0 Avg. 2 00 202 19 22 85 81 0 3 OD+40 192 136 0 32 90 40 5 0 1 09 182 Avg. 0 8 Avg. 70 90 Avg. 0 0 Avg. 205 165 40 16 95 77 5 2_ OD+60 142 177 0 11 90 90 0 10 196 196 Avg. 85 0 Avg. 80 75 Avg. 5 5 Avg. 209 184 37 27 75 82 10 6 b. Measured as breaking load and percentage wood failure after the boil/ dry/boil cycle of CSA 0-121  Drying Breaking load psi Per cent wood failure time Extracted Unextracted Extracted Unextracted OD+10 236 216 90 69 95 100 10 0 199 201 Avg. 161 140 Avg. 100 70 Avg. 10 10 Avg. 215 213 142 120 85 90 5 7 OD+20 190 194 20 0 90 75 0 0 201 222 Avg. 57 31 Avg. 75 90 Avg. 0 0 Avg. 1 83 198 34 28 50 76 0 0 OD+40 181 220 0 56 90 80 0 5 230 165 Avg. 42 0 Avg. 85 85 Avg. 0 0 Avg. 220 203 0 20 80 84 0 1 OD+60 1 66 205 36 37 90 90 5 5 110 184 Avg. 90 0 Avg. 35 95 Avg. 10 0 Avg. ' 2 09 176 96 52 50 72 5 5 85 THE N A T U R E O F T H E CAUSAL A G E N T Beyond the fact that the extractives were involved, little was yet known of the principle by which they were effective. Nor was it known which of the many possible constituents was responsible. A series of i experiments was therefore carried out to test various approaches that appeared promising. Re-impregnation with fractionated extract would indicate which fraction was responsible, provided the inactivated condition could be re-established by this technique. It was realised that failure of re-impregnated veneer to develop inactivation would not mean that the active ingredient was not present in the extract. Extraction might have changed its charac-ter or it might not be replaced in its original position. The drying of veneer in an inert atmosphere, with subsequent testing for inactivation, would provide evidence for the role of oxidation, which is supposed to occur readily in extractives of some species (see Section II). The induction of inactivation more than once, in a single spec-imen, could be a useful technique. If it were possible to do this an unlim-ited number of times ± a physical or chemical change in the surface, such as the cross-linking of hydroxyl groups, as postulated by deBruyne and others j, would appear to be involved. A limited reproducibility would appear to indicate the consumption of a causal agent, giving evidence for the role of extractives. 86 The extraction of veneer with various solvents, with a subse-quent check for inactivation, could provide useful information about the solubility of the causal agent. It was suggested (51) that the soaking in water after extraction, used in the previous experiment, might have had an effect. The solvents studied should therefore include water. An investigation of the occurrence of inactivation in various species, and within species and trees, should provide evidence about the role of extractives, since some information is available about the distri-bution of various extractives in different species. This would be partic-ularly useful if the extraction with various solvents indicated the classes of compounds involved. Re-impregnation with fractionated extract  Experiment 3 Table 3 (page 87) contains the results of the initial attempt to re-establish an inactivated surface through impregnation with extract. It is apparent that the ability of the extracted veneer to provide excellent bonds after severe drying was not impaired by the presence of the various extractive fractions used nor by the total acetone extract^, The control panels indicated that the gluing conditions used were conducive to the formation of good bonds. The specimen that was dried and glued after extraction with acetone only indicated that this is enough to prevent the formation of an inactivated surface. Experiment 4 It was thought that it would be possible to produce inactivation 87 Table 3 Bond-quality evaluations of panels made from veneer re-impregnated with various fractions of acetone or methanol/benzene extracts or from veneer dried in an inert atmosphere. Panel number Breaking load psi 1 Per cent wood failure 1 A v j . Avg. E A 208 207 219 211 100 ioo„ 100 100 A 108 110 169 129 90 75 2 90 85 RA 235 179 187 200 70 95 90 85 E M B 94 162 126 127 95 100 100 98 MB 258 226 227 237 100 100 100 100 E X T 1 187 205 243 212 100 95 100 98 ID 1 0 0 0 0 0 0 0 0 ID 2 0 0 0 0 0 0 0 0 Check 1 177 166 183 175 100 100 100 100 Check 2 173 179 183 178 100 100 90 97 Panel coding: See Section IV, experiments 3 and 6 Veneer coated with fractions of acetone extract: E A coated with the ether-soluble portion A coated with the ether-insoluble, acetone soluble portion RA coated with the acetone-soluble portion of the complete extract Veneer coated with fractions of methanol/benzene extract E M B coated with the ether-soluble portion MB coated with the ether-insoluble, acetone soluble portion E X T 1 veneer extracted with one lot of acetone and dried at 185°C for 60 minutes beyond the oven-dry condition ID 1 veneer dried in an inert atmosphere ID 2 replicate Check 1 untreated veneer' dried to constant weight at 107°C and lightly sanded on both faces Check 2 replicate 1 Measurements were taken after the cold-soak cycle of CSA 0-121 2 Possible edge effect. 88 in re-impregnated wood, after which the isolation of the causal agent could begin. On the basis of the evidence provided by experiment 3, it appeared that the extraction or re-impregnation had changed the causal agent or its relationship to the substrate. It was also possible, of course, that the causal agent was the carbohydrate material which was removed from the extractive fractions. Since the search for the causal agent was to be guided by the results from this work, it was imperative to replicate the experiment, including the effect of the carbohydrate material in the variables. The only known reference to the occurrence of interference with bonding, brought about by carbohydrates, is the trouble experienced in gluing western larch when the surfaces show heavy deposits of a galactan. Graham and Kurth (34) reported that 70 per cent of the cold-water extract of Douglas fir wood was a galactan. Experiment 3 was therefore repeated with the added factor q,f inclusion, in some panels, of the carbohydrate material. The purpose was to test the susceptibility to inactivation of treated veneer re-impregnated with very small or very large amounts of extract, of two different origins, with and without the addition of carbohydrate material. In no case was the quality of the glue-bond lowered by the presence of the extractives (Table 4 page 89). The check panels gave the desired results. The fully extrac-ted panel gave an excellent bond while the bond quality of the unextracted, but more severely dried panel, Check 5, was lower than the quality of the 89 Table 4 Bond-quality evaluations of panels made from veneers re-impregnated with, acetone or methanol/benzene extracts with or without carbohydrate material. 1 1 Panel number Breaking load psi Per cent wood failure Avg. Avg. 1 - A 126 145 152 141 95 100 95 97 1 - A C 127 148 131 135 95 100 95 97 2 - A 108 146 132 129 80 100 100 93 2 - A C 127 139 111 126 90 95 75 86 2 - A C - 5 134 118 138 130 95 80 95 90 2 - MB 100 148 133 127 90 95 100 95 2 - MBC 174 179 165 172 80 100 90 90 Check 3 163 133 150 149 80 100 90 90 Check 4 123 177 183 161 70 60 90 73 Check 5 62 84 63 70 10 5 5 7 Panel coding: See Section IV, experiment 4 Veneer coated with fractions of acetone extract: 1 - A coated with the acetone-soluble portion 1 - A C as 1 - A plus carbohydrate material 2 - A replicate of 1 - A using a different acetone extract 2 - A C replicate of 1 - A C using a different acetone extract 2 - A C - 5 as 2 - A C but only one-fifth as much material was applied Veneer coated with fractions of methanol/benzene extract: 2 - MB coated with the methanol/benzene soluble portion 2 - MBC as 2 - MB plus carbohydrate material Check 3 veneer extracted with acetone and methanol/benzene and dried to constant weight at 100°C. Check 4 untreated veneer dried at 185°C for 10 minutes beyond the oven-dry condition Check 5 untreated veneer dried at 185°C for 20 minutes beyond the oven-dry condition 1 Measurements were taken after the cold-soak cycle of CSA 0-121, 90 less severely dried panel, Check 4. The extractives removed by the solvents used included a large number of classes of material which were located in various positions in the original tree (41). The action of removal and re-impregnation completely changed the physical relationship between the wood and the extractives. It is also quite probable that chemical changes took place during the operation. The repeated development of an inactivated surface Experiment 5 The attempt to produce an inactivated surface repeatedly on the same piece of veneer, with surface removal between treatment, was not successful. The results given in Table 5 (page 91) show that the unsanded material exhibited a rapid falling off in bond quality after the first cycle, slight improvement in the second and third cycles, and rapid improvement in the fourth and fifth cycles. The material that was sanded after each cycle showed a gradual falling off in breaking load and, to a lesser extent, in wood failure, but the bonds in all cases exceeded the requirements of the industry standard for bond quality. This material had been subjected to a very severe overall drying cycle. It is probable that the lowering of bond quality with time, in the sanded material, was due to degrading of the wood by pyrolysis. The unsanded specimens showed the expected low wood failure in the first three cycles. The somewhat higher values shown by one specimen, in each of the second and third cycles, occurred in the specimen that was outermost in the panel, where an edge effect might play a part. The major defect in 91 Table 5 Bond-quality evaluations of panels made from veneer subjected repeatedly to an "inactivating" drying schedule with surface removal between dryings 1 1 Panel number Breaking load psi Per cent wood failure Avg. Avg. S 1 185 165 199 183 95 95 90 93 S 2 148 170 179 166 80 90 100 90 S 3 150 176 157 161 100 90 95 95 S 4 111 142 137 130 80 90 80 83 S 5 98 126 119 114 80 80 90 83 U 1 109 127 90 109 15 15 5 12 U 2 52 107 62 74 40 10 20 23 U 3 135 53 114 101 60 15 25 33 U 4 132 146 144 141 100 100 100 100 U 5 121 118 130 123 80 80 60 73 Panel coding: see Section IV, experiment 5. S 1 to S 5 indicate panels removed after one to five cycles of drying, each veneer being sanded after each drying cycle. U 1 to U 5 indicate panels removed after one to five cycles of drying, each veneer being sanded after all but the last cycle to which it was subjected. The first drying cycle consisted of drying for 40 minutes beyond the oven-dry condition at 185°C. The balance of the cycles consisted of drying for 40 minutes at 185°C. 1 Measurements were taken after the cold-soak cycle of CSA 0-121. 92 an inactivated bond is improper polymerisation of the glue, due to the presence of excess moisture. Proximity to the edge of the panel during pressing would have the effect of lowering the moisture content through evaporation loss. The high values found after the fourth and fifth cycles indicated that the process of inactivation had been arrested. The lower values of the fifth cycle may have been due to the offsetting effect of pyro-lysis , since the values were comparable to the values for sanded specimens. This experiment suggested that inactivation is not continually reproducible in a single veneer so that chemical or physical changes in the newly exposed wood surface cannot be held to be responsible. It is not likely that the wood would be "fixed" in a reactive state by heat, any such fixation probably tending to the form of non-reactivity. The gluability of a surface after several exposures to high temperature followed by sanding is therefore attributed to the absence of an interfering factor. One hypothesis that does fit the observed data is the migration to the surface of some substances contained in a reservoir in the wood. Heat can bring about movement of these postulated materials in several ways - vaporisation, physical flow or pressure differential in the ray cells due to the production of gases by volatilisation or decarboxylation. Drying of veneer in an inert atmosphere Experiment 6 From the results contained in the literature, it is possible to make certain assumptions about the extractable materials to be found in Douglas fir. Resin and fatty acids are present, as are terpenes, steroids, tannins, flavanones and other materials, some of them being much more chemically reactive than others. Some of these materials are supposed to undergo auto-oxidation or to volatilize at room temperature over a period of time. The composition of an extract may vary with the conditions of extraction and certainly varies with position in the tree. There may also be a difference within the "species" of Douglas f ir , with two broad types of material existing. The reaction to varying conditions of drying or extraction should yield information of value in studying these possibilities. Included in Table 3 (page 87) are the bond quality evaluations for the two panels dried on a schedule calculated to produce an inactivated surface, but in an inert atmosphere. Both panels gave strong evidence of an inactivated surface. They absorbed a normal amount of glue during spreading so did not appear to be over-dried to the point of pyrolysis. In all tests, the bond failure was completely within the glue-line, with good transfer of the glue. Within the limits of oxygen-removal achieved by the techniques used, oxygen does not appear to be essential for the development of inactivation. The effect of extraction with various solvents  Experiment 7 The extraction of veneer, followed by check gluing, is a less complex and time-consuming procedure than the characterization of the entire range of compounds found in a sample of wood. Extraction with a number of solvents was therefore tried in an attempt to learn more about the nature of the causal agent. ' 94 In all previous extractions, green (i.e. water-containing) veneer was extracted with hot solvents so that hot water was actually one of the solvents. In addition, all veneer was water soaked after extraction, to re-establish aqueous saturation of the wood. Because of the possibility of involvement of water in the process, the presence of water was included as a variable. . It has been suggested above that the mechanism of inactivation involves the movement to the veneer surface of materials contained in the ray parenchyma. The material lining the ray cells is different from the material found in the tracheid walls. It is possible that, if material is extruded from the rays, it will react with the tracheid walls. Chemical bonding may take place or the action may be purely physical. In view of the apparent insolubility of the causal agent, as reported earlier, it is improbable that the last suggestion is correct. However, the assumption of insolubility was based on very little evidence. An attempt was therefore made to extract the causal agent after inactivation, using various solvents. Acetone appeared to be an effective solvent for the causal agent, based on one small panel. Acetone was therefore included as a solvent for panels prepared over the full range of drying. Methyl ethyl ketone, a higher homologue of acetone, was included for comparison and to estimate the effect of the carbonyl group on extraction. The work done on self-sizing, in the pulp industry, supplied the information that the fatty acids are involved in the phenomenon. A solvent with a restricted affinity for the extractives of wood, but which ; 95 will extract fatty material, is petroleum ether. It was included in the list of solvents to be used. Full extraction with acetone and methanol/benzene was retained, for the time being, until the efficacy of the acetone or one of the other solvents was firmly established. It is evident from the figures contained in Table 6 (page 96) that boiling or soaking veneer in water prior to drying had no apparent effect on the causal agent. The quality of the glue-line was lowered rapidly by pretreatment with high temperature. The causal agent was removable, in the absence of water, by acetone followed by methanol/benzene. The physical appearance of the extract was quite different from that obtained from the extractions carried out on green veneer. The extract was much less opaque and closer in appearance to oleoresin. Veneer from Tree 2 clearly showed the effects of inactivation after drying at elevated temperatures. The variability in this character-istic is illustrated by the substantial difference in rate of development between the two lots. Acetone, petroleum ether or methyl ethyl ketone will each do an efficient extraction of the causal agent, when the per cent wood failure and breaking loads are both considered. The complete extraction with acetone and methanol/benzene gives * on the average, slightly higher per cent wood failure, whereas the breaking strengths are slightly lower. It is apparent that the conclusion reached in earlier work, that the causal agent could not be extracted after drying, was in error. Acetone 96 Table 6 Bond-quality evaluations of panels made from Douglas fir veneers extracted with water or organic solvents before or after drying Panel banker Breaking load psi Per cent wood failure 2 Avg. Avg WB OD 130 131 107 127 125 124 100 100 95 100 100 99 WB OD*10 145 131 134 143 127 136 10 90 40 • 80 70 58 WB OD+20 124 150 151 156 151 146 70 80 85 50 80 73 WB OD+40 99 52 66 92 20 66 20 0 5 40 0 .13 WS OD+20 124 160 142 81 133 128 5 15 5 10 5 8 WS OD+20 128 144 164 153 149 148 25 60 50 45 25 41 WS OD+40 73 71 106 0 50 60 5 20 5 0 5 7 Tree 2 OD 222 234 236 231 55 65 70 63 Tree 2 OD+10 194 187 170 184 55 40 35 43 Tree 2 OD+20 139 138 142 139 30 50 45 42 Tree 2 OD+40 0 0 0 0 0 0 0 0 Tree 2B OD 154 142 130 142 20 15 0 12 Tree 2B OD+10 76 131 8 72 0 20 5 8 Tree 2B OD+20 15 0 0 5 0 0 0 0 Tree 2B OD+40 0 0 0 0 0 0 0 0 A / M / B OD 177 162 168 169 100 100 100 100 A / M / B OD+10 200 174 177 184 100 100 100 100 A / M / B OD+20 189 185 167 180 95 100 100 98 A / M / B OD+40 171 155 163 163 100 95 100 98 M / B OD 285 260 271 272 95 95 100 97 M / B OD+10 208 226 211 215 100 90 95 95 M / B OD+20 218 213 168 200 90 95 95 93 M / B OD+40 168 169 171 169 85 90 90 88 P E OD 173 200 193 189 100 90 80 90 P E OD+10 196 144 160 167 95 100 95 97 P E OD+20 207 198 165 190 80 75 65 73 P E OD+40 200 205 163 189 100 95 95 97 A OD+10 152 170 155 170 193 168 90 95 100 95 100 96 A OD+20 130 137 153 159 135 142 100 100 100 100 100 100 A OD+40 185 160 122 122 122 142 95 95 100 100 95 97 97 Table 6 - Continued 1 1 Panel number Breaking load psi Avg. Per cent wood failure Avg. M E K OD 215 237 194 215 95 90 85 90 M E K OD+10 203 194 213 203 90 95 85 90 M E K OD+20 155 161 165 160 85 90 85 87 M E K OD+40 200 207 191 200 90 75 75 80 Dry Ext. OD*10 171 160 149 166 154 160 100 100 100 100 100 100 Dry Ext. QD+20 147 166 174 148 151 157 95 100 100 100 100 99 Dry Ext. OD+40 173 170 175 182 203 181 100 100 100 95 90 97 In A / M / B 1 OD+40 161 177 151 163 95 95 100 97 In A / M / B 1 OD+40 191 163 147 167 95 100 95 97 In A / M / B 1 OD-40 165 182 157 168 70 80 85 78 In A / M / B 1 OD+40 148 157 187 164 100 90 90 93 In A / M / B 2 OD 207 224 230 220 100 100 100 100 In A / M / B 2 OD+10 167 177 168 171 100 85 100 95 In A / M / B 2 OD+20 184 215 230 210 95 90 100 95 In A / M / B 2 OD+40 169 167 149 162 90 95 95 93 In A OD 172 203 203 193 90 90 95 92 In A OD+10 177 213 160 183 90 90 85 88 In A OD+20 154 152 151 152 80 75 80 78 In A OD+40 137 137 135 136 90 85 90 88 Panel codingisee Section IV, experiment 7. The various panel codes indicate the solvent used for extraction and the time of extraction with respect to drying, as follows: Extracted before drying WB with boiling water WS with cold water A / M / B with acetone and methanol/benzene M / B with methanol/benzene P E with petroleum ether A with acetone M E K with methyl ethyl ketone Dry Ext. with anhydrous acetone and methanol/benzene Extracted after drying In A / M / B 1) with acetone and In A / M / B 2) methanol/benzene In A with acetone Not extracted Tree 2 Tree 2B 1 Measurements were taken after the cold-soak cycle of CSA 0-121. 98 and methanol/benzene extraction, or extraction with acetone alone, will effectively restore the gluing qualities of over-dried, inactivated veneer. Occurrence of inactivation within and between species  Experiment 8 The effects of species and of position within a tree are readily demonstrable from the bond quality evaluations contained in Table 7 (page 99). The gluability of Sitka spruce was completely unaffec-ted by the over-drying, regardless of severity. The smoothly-cut Abies veneer was used to produce panels with bonds that were unaffected by the severe treatment. The roughly-cut panel did show varying bond quality, but in an erratic manner. Excessive roughness can cause the accumulation of glue in pockets, with a consequent excess of liquid at the glue-line, leading to development of an inactivated bond. It is probable that this is the case here. Both samples of Douglas fir show susceptibility to inactivation but it developed more slowly than it did in the veneer from the inner heartwood from the butt log of the same tree, which was included in an earlier experiment. The taxifolin distribution in a Douglas fir tree (36) showed, this same pattern of correlation between heartwood of the same chronological age from different heights in the tree. The inner butt heartwood, which was chronologically older, was different, in that case lower quantitatively in taxifolin content. Sitka spruce, which does not develop an inactivated surface, contains a completely different complex of extractives from Douglas f ir , 99 Table 7 Bond-quality evaluations of panels made from veneers of various species of from various locations in a Douglas fir tree Panel number Breaking load psi Per cent wood failure Avg. Avg. F l OB OD+10 140 177 171 115 165 154 60 10 70 65 5 42 F l OB OD+20 136 163 157 150 123 146 100 50 50 80 70 70 F l OB OD+40 105 115 97 125 155 119 5 15 0 5 10 7 F l T OD 150 159 132 159 144 149 95 100 95 95 100 97 F l T OD+10 135 115 113 111 118 118 100 100 100 100 100 100 F l T OD+20 133 135 137 126 128 132 100 100 100 85 100 97 F l T OD+40 104 91 108 72 124 100 40 20 30 5 60 31 Abies 1 OD 44 46 66 63 63 56 25 60 40 40 60 45 Abies 1 OD+10 91 86 77 71 84 82 95 90 95 95 100 95 Abies 1 OD+20 73 46 85 87 80 74 60 30 70 80 30 54 Abies 1 OD+40 83 81 87 93 80 85 90 85 95 95 90 91 Abies 2 OD 80 83 90 83 81 83 100 95 100 95 95 97 Abies 2 OD+10 72 82 78 85 114 86 100 100 100 90 100 98 Abies 2 OD+20 90 92 74 78 81 83 100 100 100 100 100 100 Abies 2 OD+40 53 93 80 74 89 78 100 100 90 95 100 97 Sitka 1 OD 89 87 91 86 93 89 100 100 100 100 100 100 Sitka 1 OD+10 94 110 75 102 89 94 100 100 80 100 100 96 Sitka 1 OD+20 59 84 73 81 80 75 95 95 95 100 100 97 Sitka 1 OD+40 85 96 74 77 74 81 100 100 100 100 100 100 Panel coding: see section IV, experiment 8. The panel coding represents the species of veneer used and the position within the tree from which it was obtained. F l OB outer heartwood from the butt log of Douglas fir Tree 1. F I T heartwood from the top log of Douglas fir Tree 1 Abies 1 veneer collected from commercial production, roughly peeled, identifiable only as Abies species. Abies 2 a replicate of Abies 1, smoothly peeled. Sitka 1 veneer collected from commercial production, identifiable only as Sitka spruce. 1 Measurements were taken after the cold-soak cycle of CSA 0-121, 100 based on the one available reference (55). Engelmann spruce and white spruce, which are susceptible to inactivation, probably contain extractives much more similar to those of Douglas fir and to those of the closely related European spruce (9, 19). IDENTIFICATION OF THE CAUSAL A G E N T It has been shown conclusively, for the first time, that the  severity of inactivation of a surface can vary between species and within a  single tree. Some control can therefore be exercised over this phenomenon through selection of material. Within the limits of oxygen-removal that were achieved, oxygen has been shown to be not essential to the process of inactivation. Further, evidence has been presented that the causal agent is a mobile, chemical entity and not a surface condition of the vood. These two attributes of a  causal agent of inactivation are the first to be determined. The causal agent had been removed from veneer either before or after it was inactivated, by each of several solvents, among them petroleum ether (a solvent that extracts a narrower range of extractives from wood than the others used). Sole use of this solvent reduced the complexity of extraction and characterization of the materials from surfaces that were inactivated to varying degrees. A series of experiments was therefore executed to find veneer demonstrating a range of susceptibilities to the development of an inactivated surface and to determine the underlying chemical differences responsible for the variations. 101 Inactivation in Douglas fir  Experiment 9 Two types of Douglas fir are recognized by users of wood products - Coastal and Interior. It is traditional that more trouble is expected from inactivation when logs from the Interior are used but, as with all "mill" information in this field, it is not possible to get unequi-vocal statements as to frequency and conditions of occurrence. A difference that characterizes the two types of wood is differential permeability to creosote. It is possible that the extractives in the two types of Douglas fir are dissimilar, such variability as exists being related to suscepti-bility to inactivation. Some information is available from the work of others as to the extractives expected in Douglas fir. There are some similarities between the extractives of Douglas fir and of other species which are susceptible to inactivation. Variation has also been shown by the author to exist within a tree of Interior Douglas fir with respect to ease of inactivation. The bond-quality evaluations for the material collected from the two types of Douglas fir are given in Tables 8,9,10 and 11 (pages 102 to 105). It is apparent that the Coastal Douglas fir was not susceptible to the develop-ment of an inactivated surface. Neither was there any effect due to the varying degrees of roughness evident in the panels. Although there were a few anomalous values , a continual 102 Summary Table 8 Bond-quality evaluations of panels made from untreated veneer from a Coastal Douglas fir Panel number Rough Per cent wood Panel no^ Rough Per cent vv failure failure 3 Sap 1 OD 2 yes 671 Heart 3 OD 100 OD*10 64 OD+10 96 OD+20 95 OD+20 99 OD+40 yes 97 OD+40 90 OD+60 89 OD+60 97 Sap 2 OD 94 Heart 4 OD 100 OD+10 99 OD+10 100 OD+20 88 OD+20 yes 100 OD+40 49 OD+40 yes 100 OD*60 90 OD+60 74 Heart 1 OD 98 Heart 5 OD yes 99 OD+10 95 OD+10 yes 95 OD+20 100 OD+20 yes 96 OD+40 yes 99 OD*40 yes 91 OD*60 yes 98 OD+60 yes 85 Heart 2 OD 100 Heart 6 OD yes 97 OD+10 85 OD +10 yes 90 OD-20 yes 100 OD+20 yes 95 OD+40 100 OD+40 yes 91 OD+60 95 OD+60 yes 95 1 Each figure is the average of ten plywood shear specimens of which five were tested after each of the cold-soak and boil/dry/boil cycles of CSA 0-121. Detailed figures are contained in Supplementary Table 8 in the Appendix. 2 This indicates the panel contained veneer with a surface roughness exceeding the minimum rating for "rough" on an arbitrary scale of .roughness. 3 For explanation of panel coding see Section IV, experiment 9. 103 Summary Table 9 Bond-quality evaluations of panels made from untreated veneer from a Coastal Douglas fir. Veneer was dried and reconditioned to the moisture contents shown and pressed into panels Panel number Rough Moisture Per cent content wood failure Sap 1 S O D 3 9-2 121 R O D yes 2 9«8 10 S OD+60 9. 1 58 R OD+60 yes 2 1 Sap 2 S OD 8.6 17 R OD yes — - 65 S OD+60 8-7 20 R OD*60 yes 8« 6 23 Heart 1 S OD 6*7 77 R O D yes 6^ 5 89 S OD+60 6« 4 15 R OD+60 yes 6«2 21 Heart 2 S OD 7-3 54 R OD yes 61 S OD+60 6-0 57 R OD+60 yes 6-3 7 Heart 3 S OD 5-7 90 R OD yes 5- 6 38 S OD+60 6.5 8 R OD+60 yes 20 Heart 4 S OD 6-4 89 R O D yes 6-0 46 S OD+60 6-0 46 R OD+60 yes 5-9 52 Heart 5 S OD 7-4 85 R OD yes 6- 8 97 S OD+60 7- 0 47 R OD+60 yes 7-3 35 Heart 6 S OD missing R OD yes 85 S OD+60 — 3 R OD+60 yes 6«5 75 1 Each figure is the average of ten plywood shear specimens of which five were tested after each of the cold-soak and boil/dry/boil cycles of CSA 0-121. Detailed figures are in Supplementary Table 9 in the Appendix. 2 This panel contained veneer with a surface roughness exceeding the mini-mum rating for "rough" on an arbitrary scale of roughness. 3 For explanation of panel coding see Section IV, experiment 9. 104 Summary Table 10 Bond-quality evaluations of panels made from untreated veneer from an Interior Douglas fir (Quesnel fir). Per cent wood Panel number Breaking load failur 2 1 1 Sap OD 100 91 OD + 10 130 58 OD +20 58 83 OD +40 115 68 Heart 1 OD 170 92 OD + 10 113 90 OD +20 107 56 OD + 40 64 85 Heart 3 OD 119 95 OD + 10 117 72 OD+20 141 93 OD + 40 105 57 1 Each figure is the average of ten plywood shear specimens of which five were tested after each of the cold-soak and boil/dry/ boil cycles of CSA 0-121. Detailed figures are contained in Supplementary Table 10 in the Appendix. 2 For explanation of panel coding see Section IV, experiment 9. 105 Summary Table 11 Bond-quality evaluations of panels made from untreated veneer from an Interior Douglas fir (Tree 3) Panel number Breaking load Per cent wood failure 2 J 1 „ 1 Sap OD 148 92 1 OD+10 205 57 OD+20 156 22 OD +40 123 4 Heart 1 OD 284 45 OD + 10 232 36 OD + 20 215 8 OD +40 154 11 Heart 2 OD 232 26 OD + 10 221 16 OD + 20 240 56 OD +40 152 19 Heart 3 OD 267 73 OD +10 244 60 OD +20 180 14 OD+40 134 7 Heart 4 OD 289 66 OD -+10 233 69 OD +20 155 37 OD+40 132 22 Heart 5 OD 202 55 OD+10 205 70 OD +20 264 48 OD +40 197 89 Heart 6 OD 255 87 OD +10 212 45 OD + 20 193 55 OD+40 134 23 .1 Each figure is the average of ten plywood, shear specimens of vhich five were tested after each of the cold-soak and boil/dry/boil cycles of CSA 0-121. Detailed figures are in Supplementary Table 11 in the Appendix. 2 For explanation of panel coding see Section IV, experiment 9. 106 problem when dealing with wood, in general the bond quality was good. There was no apparent evidence of inactivation. Although the sapwood was, on the average, lower in bond quality than the heartwood, it contained no pattern of decreasing bond quality with increasing drying time. The low bond quality of panels Sap 1 OD, Sap 1 OD-10 and Sap 2 OD+40 (see Table 8) must be ascribed to unknown factors. Although the moisture contents of the test panels exceeded, in all cases, the allowable maximum for the phenolic glue used, a number of good bonds were produced. There was a slight indication of decreasing bond quality with increased drying, in some casesi but the pattern was not consistent. Also , there was no apparent pattern of changing bond quality within the heartwood with changing distance from.the pith. The somewhat lower bond qualities obtained with the sapwood are undoubtedly due to the excessive moisture content that was used. Again there is no consistent effect due to the amount of roughness present. Tree 3 was obviously quite susceptible to the development of an inactivated surface at any position in the stem, with the exception of the one designated Heart 5. Because of the relatively high percentage of latewood contained in this log, it frequently happened that a large propor-tion of the wood forming a particular glue-line was latewood. This material can form exceedingly strong bonds and appears capable of developing greater strength than the glue. It is necessary, during examin-ation of this material, to carefully consider both the per cent wood failure and the breaking loads when assessing bond quality. 107 The Quesnel fir also demonstrated a tendency to inactivation but it was not nearly as susceptible as Tree 3. Further, the sapwood and Heart 1 appeared less susceptible than the Heart 3 position. Again the tendency for bond quality to decrease with increased severity of treatment prior to gluing is more apparent if breaking load and per cent wood failure are both considered. Extraction and characterization of extracts  Experiment 10 As stated above, the general plan in this experimental work was to locate trees demonstrating varying susceptibilities to inactivation. The extractives, from these trees would then be characterized so that correlations between extractive content and susceptibility could be examined. The first three trees collected definitely varied in their capa-city to produce inactivated bonds and, in addition, two of them displayed varying degrees of susceptibility between different positions within the tree. Material was therefore collected fromithe positions noted below in the various trees. Since the Coastal Douglas fir had shown no influence of the effect of high temperature, it provided the nonsusceptible material. Veneer was collected from the Sapwood, Heart 1 and Heart 3 positions to provide replicates of this type of wood. Since the Sapwood, Heart 1 and Heart 3 positions of the Quesnel fir had shown varying susceptibility during the testing, veneer was collected from these positions. A sample was also taken from the very susceptible Heart 4 position of Tree 3 and 108 and from the anomalous Heart 5 position. Since it had been found possible to extract the causal agent of inactivation after drying the veneer, a further 12-sheet sample was collec-ted from Heart 4 position of Tree 3 and dried for 40 minutes beyond the oven-dry condition. If chemical changes taking place in the extractives are the causal agent, they should appear as differences in the extractives removed before and after drying from matched specimens. Evidence has been collected which indicates that a movement to the surface is involved since inactivation cannot be accomplished an indefinite number of times. If such a movement occurs, the surface of a dried panel should have a higher concentration of extractives than the body of the panel. Twelve sheets of veneer from Tree 3, Heart 4 were dried for 40 minutes beyond the oven-dry condition, sanded sufficiently to remove the discoloured surface, and the sanding dust recovered. This procedure was repeated twice more, 40 minutes drying being used. Material used to prepare extractives therefore included the following: Coastal Douglas fir - 12 sheets of sapwood - 12 sheets of the Heart 1 portion - 12 sheets of the Heart 3 portion Quesnel Douglas fir - 12 sheets of sapwood (Interior type with - 12 sheets of the Heart 1 portion varying suscepti- - 12 sheets of the Heart 3 portion bility) Tree 3 - 12 sheets of the Heart 4 portion (Interior type with - 12 sheets of the Heart 5 portion high susceptibility) - 12 sheets of the Heart 4 portion that were dried for 40 minutes beyond the oven-dry condition 109 Tree 3 Continued - 12 sheets from the Heart 4 portion that were dried for 40 minutes beyond the oven-dry condition and sanded. The •7^  cycle was repeated three times. Details of the components found in the various samples are given in Tables 12 through 16 (pages 110 throughll4). A waxy fraction was recovered from all samples but the amounts were very small , so were not examined in detail. Each of the other fractions recovered was examined using gas-liquid, paper and thin-layer chromatography for characterization and confirmation by cross-reference. Many compounds could be definitely identified by comparison with known standards. Others could not be named with certainty but their presence or absence in the various fractions could be established. The sanding dust yielded extractives at about the same rate as the solid,, sanded material. However, there was evidence of loss of mater-ial through adhesion to the sandpaper, so no conclusions could be drawn as to the relative yields from the surfaces removed by sanding and the main body of the veneer. Observations Volatile fraction The volatile fraction does not give the same results with gas-liquid chromatography and with thin-layer chromatography. The much wider range present in the fraction heated in the chromatograph probably contains products of rearrangement or polymerisation due to the high temperatures employed. Evidence for this is provided by the fact that the material from Tree 3, Heart 4 that was heated for a total of 120 110 Table 12 Components of the volatile fraction of the extracts from the various posi-tions in Coastal and Interior Douglas fir T3 O r-. r o O +J +J rrj O r-n r o £ U U £ O 4J +J Q . B ) « J ^ « , « - r H + J ' * r H a, rt S E E + ' - + ' + » « » " M , ) »"H A\ rt\ s« MH rM - ,, » , I, <0 0) M J H r i f H - : - , £ K W ffi 0 K « r-4 ' ti ti <0 (V) CVj (ti CO Component U +> ti CQ CO Q) 8 2 2 y a H £ £ cX-pinene P P P P P P camphene P P P P P P P P 0-pinene P P P t P P P P A4-carene P A3-carene P P P P P tX-phellandrene P P P P P tt-terpinene P t P P P O-phellandrene P P P P P P 3, 8-menthediene P P P p-cymene P P P P ? terpinolene P P Unknown A P P P Unknown B P P P P P P Unknown C P P P P P P P Unknown D P bornyl alcohol P P P P P P P P P Unknown F P P P P P P P Unknown G P P P Unknown H P P P P P P P P bornyl acetate P P P P Unknown J P P Unknown K P Unknown L P Unknown M P . ? Unknown N P P P P P indicates a definite peak on the chromatographic chart ? indicates probable occurrence, t a trace I l l Table 13 Fatty acids found in the free acid components of the extracts from the various positions in Coastal and Interior Douglas fir u a nJ A o i ro U S P P o C Q • H u CJ • H CO o cc) I—I r—1 3 rt o i I—1 O P S P P P P o •f-l o a tH <D CO r - l o o o .a <0 r-l o ro CJ r - i oo 00 00 i — i —-1 i — 1 O U u t P s t P P P p P u n) co +-00 o I 00 • H r - l u nJ rH o I o o • H ti CO r-i « o I 0J OJ u •w U 9) O 0 OJ U O U U P t P s P t s s Sample Coast fir Sapwood Heart 1 Heart 3 Quesnel fir Sapwood Heart 1 Heart 3 Tree 3 Heart 4 Heart 5 Heart 4 dried and extracted Heart 4 dried and sanded 1 Indicates length of carbon chain and number of double bonds present and trivial name of the acid. 2 Indicates present in the sample under test P indicates a large peak on the chromatographic chart S indicates a smaller peak showing a smaller amount is present t indicates a trace amount is present Traces only - no clear evidence of any one acid t p p P P t t P P 112 Table 14 Fatty acids found in the combined acids components of the extracts from the various positions in Coastal and Interior Douglas firs V 4) o o .5 .3 l O <u •H O ro (\J ,-, ^ 1 1 1 o - ^ i n v o r ^ o o o o o o o o o o • - l i - l r H i - l r - l r - l i - i r H - r - l i - l r v ] U U U U U U U U O U U Sample  Coast fir Sapwood P P P P P P P P P Heart 1 P P P P P P P P P Heart 3 P P P P P P P P P Quesnel fir Sapwood P P P P P P P P P Heart 1 P P P P P P P P P Heart 3 P P P P P P P P P Tree 3 Heart 4 P P P P P P P P P Heart 5 P 2 Heart 4 dried P P P P P P P P P ? and extracted Heart 4 dried P P P P P P P P P ? and sanded 1 Indicates number of carbon atoms present and the number of double bonds where this is known. 2 Indicates probable occurrence P indicates present in the sample under test. 113 Table 15 Resin acids found in the free acid components of the extracts from the various positions in Coastal and Interior Douglas firs. CQ CQ [fl CQ CD CD cu CQ +» + J +> ti ti ti ti ti •-4 • i H •r-t a a a a oo * • Coast fir -'HV;•, • Sapwood t t t t P Sample M * ^ m ^ oo , a 3 £ •- 2 -2 s o U _ -2 * * co * 3 .5 _ CD M 5 T -3 a o 45 CD o -H ^ nj 3 ^ ™ vO . O o (3 rt O " - S I S " 0 ^ a JT >^ o ^ C N O O o< T 3 m T _ rt P Heart 1 t t ' P P P • . t t Heart 3 t t P P P P t t Quesnel fir Sapwood t P P P Heart 1 t t t P P P Heart 3 t t t t P P P Tree 3 Heart 4 t t t t P P P Heart 5 t p p Heart 4 dried t t P P P and extracted Heart 4 dried No resin acids present and sanded ! 1 Indicates the elution times under the conditions used where the acid was not identified. P Indicates present in the sample under test. t Indicates present in trace amounts in the sample under test. 114 Table 16 Unsaponifiable components of the extracts from the various positions in Coastal and Interior Douglas firs Sample Coast fir Sapwood Heart 1 Heart 3 o u <D O >> i—I o CO <D +-> A • i - i B oo co fl CO -u fl • H a CO fl • i - l s CO <D 4-> fl a 00 00 CO 0) -u rt • H a 00 00 CO <D +J fl ••-I a CO <D -M fl • r - l a ro oo CO fl • I - l a CO <D fl • I - l a o CQ +J fl 4 Quesnel fir Sapwood Heart 1 Heart 3 P P P P P P P P P P Tree 3 Heart 4 p P p P P Heart 5 • P P P P Heart 4 dried P ? and extracted Heart 4 dried ? P P P P P and sanded 1 Indicates the elution times under the conditions used where the com-ponents were not identified. P Indicates a definite peak on the chromatographic chart. ? Indicates probable occurrence. 115 minutes at 185°C contains only these higher-boiling materials, most of them unknowns. There is no pattern within the volatile fraction that is consis-tent with the susceptibility of the various wood samples to inactivation. A l l of the components found in Tree 3, Heart 4 and Quesnel fir Heart 3 are present in one or more of the samples from the Coast fir except terpinolene and this is absent from Tree 3., Heart 4 after heating. Resin acids The major components of the resin acids, as distinguished by gas-liquid chromatography, are common to all types of material. The traces of the acids with lower elution times are less systematic in distri-bution but all are either present in susceptible and nonsusceptible material or are present only in Tree 3, Heart 4 and absent in Quesnel fir Heart 3. On the paper chromatogram three major components appear in all samples. By comparison with the data of the reference paper and the commercial standard, these are the dehydroabietate, the abietate and the pimarate/isopimarate methyl esters. There is complete agreement between the presence of those fractions which were mobile and the results from the same material on the gas-liquid chromatograph. Combined acids The combined acids, all of which are fatty acids , are remar-kably uniform in their distribution. A l l materials have exactly the same composition except the anomalous Tree 3, Heart 5, and the possible traces 116 of C20 saturated acid in the dried portions of Tree 3, Heart 4, although these are probably artifacts. Un saponif iabl e s The major components of the un sap onif iabl es are distributed through all types of material and there is no minor component restricted to the susceptible material except the fractions found in the seriously over-heated Tree 3, Heart 4, sanded. It is suggested that they are products of pyrolysis or degradation from other causes since they occur nowhere else. The paper chromatograph showed the presence of glycerol in all components, this being determined by comparison with a known standard. Fatty acids Only in the fatty acids is there a pattern that correlates with the degree of susceptibility to inactivation. The Coastal Douglas f ir , which is apparently insusceptible to inactivation, contains mainly short-chain, saturated acids, some C J Q unsaturated or saturated acids and only traces of saturated acids above Ci8» The Quesnel f ir , which shows some effect of over-drying, contains amounts of the C2Q» o r higher, saturated acids that are larger in the more susceptible material. Tree 3, Heart 4, which is very susceptible to the development of inactivation, contains a relatively large amount of cosanoic and docos-anoic acids, and the higher homologue is present in good yield in the heated 117 material. The anomalous section contains only traces of fatty acids with no measurable amount of any one acid. The thin-layer chromatogram gave results that agreed with those of the gas-liquid chromatograph. For example, the Coast Sapwood sample showed clear spots for Cj2» ^16* ^18 a n c * 2^0 acids with the last a very faint spot. Tree 3, Heart 4 showed spots for C 1 2 » C\4' ^ l 6 » ^18 a n c * clearly visible spots for C20 a n d C22-Each of the samples shows a bluish spot, with various inten-sities of colour., below the spot for C2  acid. This material was not iden-tified on the gas chromatograph. Yields The table of yields (Table 17, page 118) demonstrates graphic-ally the very great variation in extractives content to be found within a species and even at different points at the same level in a single stem. Also remarkable is the variation in percentage composition of the various major components between trees and with position within a tree. It will be noted that the sample from Tree 3, Heart 4, which showed the highest degree of susceptibility to inactivation, also had an inordinately large steam-volatile content, 19.87 g of volatiles compared with 7. 37 g of non-volatiles. Although there was no apparent correlation between the type of volatiles found, and inactivation, a second sample from this material was examined and found to contain 9. 19 g total extract, most of which was non-volatiles. It would appear, then, that the first sample 118 Table 17 Yields of the various components from the various positions in Coastal and Interior Douglas firs Yields Grams per kilo Per cent of total yield Sample source Coast fir Sapwood Heart 1 Heart 3 Quesnel fir Sapwood Heart 1 Heart 3 Tree 3 Heart 4 Heart 5 Heart 4 dried and extracted Heart 4 dried and sanded CQ +J rt r - i O > u O to CO O u a CO T l U rt rt CO T l • H O rt xi .fl 1 o U CO T l u rt Fl •r-l CQ <D PH CQ <0 r-H rO • H Fl O o< rt co Fl 31 3-60 3-91 38 6- 10 6-48 08 2-99 3-07 26 3-93 4-20 19'87 7*37 27*24 13«2 10-0 32-4 44"4 CO •n • H CJ rt rt o 18-2 16-8 36- 1 28-9 35-0 24-4 18*6 32-2 24-8 43-0 99 8-28 9*27 35*7 19' 9 5-7 38*7 55-6 11-4 28*5 45-2 14-9 39'9 21-0 16-1 34' 6 28-3 37-1 64 3*34 4'00 12*4 49*5 20' 1 18-0 6 l « 9 23-44 4»50 4.94 50.6 7*5 12-9 29- 0 58-1 22 2*59 2-81 12-2 35-3 29"4 23- 1 47-5 05 1«62 1-67 33-9 32- 3 0-0 33-8 66-2 119 contained a "pocket" of volatile material, THE EFFICIENCY OF EXTRACTION WITH n - H E X A N E AND P E T R O L E U M E T H E R Experiment 11 It was assumed that the extractives that were analysed contained the causal agent of inactivation, based on the previous successful attempts at removal. In view of the importance of this assumption, it was consid-ered necessary to confirm it experimentally. Breaking loads and per cent wood failures for the test speci-mens made from panels prepared from the extracted veneer, and suitable control panels, are contained in Table 18 (page 120). The control panels, dried at 107°C , gave excellent results throughout, with essentially 100 per cent wood failure, indicating that gluing conditions were good. The extracted material, including that extracted after drying, also gave high bond quality readings. The percentage wood failure is , in some specimens, low in Tree 3 Heart 4 but the breaking loads are abnormally high; inspection indicates the presence of large amounts of latewood. It is apparent that the causal agent has been removed in all cases. CORRELATION OF PRESENCE O F F A T T Y ACIDS AND SUSCEPTIBILITY  TO INACTIVATION  Experiment 12 An apparent correlation was found between the presence of 120 Summary Table 18 Bond-quality evaluations of panels made from veneer from Coastal or Interior Douglas f ir , unextracted or extracted with n-hexane or petroleum ether, and dried as shown Panel number Quesnel fir extracted with petroleum ether: dried at 185°C Per cent wood failure Panel number Coast fir extracted with n-hexane: dried at 185°C Per cent wood failure Sapwood OD OD + 10 OD+20 OD + 40 98-100 Sapwood OD OD+10 OD +20 OD + 40 100 98 98 86 Heart 1 OD OD+10 OD + 20 OD+40 83 94 91 91 Heart 1 OD OD+10 OD +20 OD +40 100 100 100 100 Heart 3 OD OD +10 OD+20 OD +40 100 95 94 63 Heart 3 OD OD +10 OD +20 OD +40 96 99 98 98 Quesnel fir unextracted: oven-dried at 107°C Coast fir unextracted: oven-dried at 107°C Sapwood Panel 1 Sapwood Panel 2 Heart 1 Panel 1 Heart 1 Panel 2 Heart 3 Panel 1 Heart 3 Panel 2 86 85 99 97 95 98 Sapwood Panel 1 Sapwood Panel 2 Heart 1 Panel 1 Heart 1 Panel 2 Heart 3 Panel 1 Heart 3 Panel 2 100 100 100 98 98 100 1 Each figure is the average of ten plywood shear specimens of vhich five were tested after each of the cold-soak and boil/dry/boil cycles of CSA 0-121. Detailed figures are in Supplementary Table 18 in the Appendix. 2 For explanation of panel coding see Section IV, experiment 11. C O N T I N U E D 121 Table 18 Continued Tree 3 extracted with n-hexane: Breaking Per cent dried, at 185°C load wood failure Heart 4 OD 258 28 OD + 10 250 35 OD+20 228 17 OD+40 212 48 Heart 4 OD 260 76 replicate OD+ 10 230 62 QD*20 206 76 OD+40 208 79 Heart 5 OD 221 71 OD+10 221 68 OD +20 194 69 OD+40 213 63 Tree 3 extracted with n-hexane after Breaking Per cent drying and sanding: load wood dried at 185°C failure Heart 4 OD+40 207 83 OD+40 170 85 OD +402 88 Tree 3 extracted with n-hexane after o drying: dried at 185 C Heart 4 OD+40 219 80 OD+40 259 79 OD+40 206 85 OD+40 236 59 1 Each figure is the average of ten plywood shear specimens of which five were tested after each of the cold-soak and boil/dry/boil cycles of CSA 0-121. Detailed figures are in Supplementary Table 18 in the Appendix. 2 Because of severe treatment, resulting in embrittlement of the veneer, sufficient only was recovered for two full size panels and one small one. This was knife tested so no breaking load is available. For explanation of panel coding see Section IV, experiment 11. 122 saturated, long-carbon-chain fatty acids and the development of an inacti-vated surface. Since some of these chemicals are available in reasonable grades of purity, without contamination from the other components present in wood, it was feasible to study the effect of introduction of these chemicals into nonsusceptible wood. A successful attempt to produce inactivation with such introduction would be strong evidence for their role in this phenomenon. Of the fatty acids found in Douglas fir in this work, the following were available in sufficient quantity for experimental work -lauric , myristic , palmitic, stearic and behenic. The original attempt to produce inactivation by re-impregnation with extract had failed. Since abietic acid was now known to be a component of the extractives in this material, and was present in the original extract as a contaminant of the fatty acids (from the present point of view), it was also included in this experiment to study its effect on the gluability of wood. It was noticed during gluing that the panels coated with stearic or behenic acid, and which had been dried at room temperature, did not absorb the glue well and the panel surface seemed strongly hydrophobic. The effect was less pronounced in , or visually absent from, the panels dried at higher temperatures. Detailed test results are given in Supplemen-tary Table 19 in the Appendix. Summary Table 19 (page 123) contains average figures for the per cent wood failures from all tests. From these a rapid assessment of comparative bond quality can be made. 123 Summary Table 19 Bond-quality evaluations of panels made from veneer from a Coastal Douglas f ir , not susceptible to inacti-vation, which was coated with various fatty acids and dried at room temperature or for 40 minutes at elevated temperatures. Acid used Physical constants Per cent wood failures Melting Boiling Drying temperature point C° point C° 2 1 ° C 107°C 150°C 185°C Laurie C H 3 ( C H 2 ) 1 0 C O 2 H 48(44)2 225 (100 mm) 97 1 98 100 24 Myristic C H 3 { C H 2 ) l 2 C 0 2 H 54 3 250-5(100 mm) 96 97 84 11 Palmitic C H 3 ( C H 2 ) l 4 C 0 2 H 63-642 271-5(100 mm) 5.7 91 97 12 Stearic C H 3 ( C H 2 ) l 6 C 0 2 H 69-703 291 (110 \ 2 mm) 64 61 94 14 Behenic C H 3 ( C H 2 ) 2 0 C D 2 H 80 2 306 ( 60 \ 2 mm) 41 38 56 3 Abietic C 2 0 H 3 0 ° 2 172-1753 decompos 2 es 100 100 92 89 None - control, untreated 100 100 100 83 None - control, hexane-treated 99 1 Each figure is the average of ten plywood shear specimens of which five were tested after each of the cold-soak and boil/dry/boil cycles of CSA 0-121. Detailed figures are contained in Supplementary Table 19 in the Appendix. Source of constants - 2 Lange's Handbook of Chemistry, 7th Edition, 1949. 3 The Merck Index, 7th Edition, I960. 124 The spread at the rate of 10 grams per kilo of dry wood was higher than the total quantity of non-volatile extract fouiid in any of the test material. Since the actual recovered amount of any specific fatty acid was not known for the extracted material, a standard spread was used which might assist in comparing the effects of the various acids on gluability. The pattern of results reveals two sub-patterne.. There was a falling off in bond quality of panels prepared from veneer dried at the highest temperatures § with the greatest effect shown by those coated with the higher-chain-length acids. In addition * there is an effect of bond quality improvement with increase in drying temperature above room temperature, except for the two lowest-chain-length acids. Also , the peak is reached at a higher temperature with longer-chain-length - \ palmitic at 1 0 7 ° C , stearic at 2 4 9 ° C , whereas behenic shows only a slight peaking at 149°C. It is suggested that this is due to interference with the physical penetration of the glue into the wood by the acid, regardless of the substrate^ i .e . the effect is not due to heat. The fatty acids of short-chain-length are soluble in water, with a decrease in solubility accompanying increasing chain length. It is quite possible that such an effect is operative here. Also the various acids melt at different temper-atures so that physical absorption into the wjod would be enhanced by increasing temperatures in proportion to the melting points. Absorption into the wood could reduce the physical blocking of moisture. In any case, an equivalent amount of higher homologue is more effective in inducing 125 inactivation at room temperature, or at higher temperature. The control, unspread panels and the panel sprayed with n-hexane show, in general, very good bonds with a slight falling off at 185°C although all panels would pass the industry standard. It is noted that severe inactivation occurs only at the very highest temperature used and, judging from the combined test results, more readily with the longer-chain-length acids. Panels sprayed with abietic acid showed no decrease in glue bond quality with increasing drying temperature. Although some of the per cent wood failures were slightly lower at higher temperatures, the breaking loads were sometimes increased. D E V E L O P M E N T O F THE THEORY OF INACTIVATION The consensus expressed in the literature is that the gluing of wood is a complex phenomenon, subject to many difficulties. The failure of wood/adhesive systems has been attributed to many causes, among them improper preparation or machining, modification of the wood by the glue used, or the effect of species. In most cases the underlying factors inherent in a species effect have not been sought, although some gluing difficulties have been attributed to the chemical composition of the wood, which is one of the main species differences. Inactivation is one of the most perplexing problems associated with the gluing of wood. Many possible causes have been suggested but a comprehensive explanation had not previously been found. The most widely accepted hypothesis had been that heating of the wood, during drying 126 of veneer, destroyed its polarity through formation of ether linkages. The adhesion theory of deBruyne (26) states that only materials of like polarity will form bonds. The loss of polarity of the wood was supposed to make it insusceptible of being glued with polar glues. It was shown experi-mentally that wood extracted with various solvents, before or after drying, no longer has decreased potential for forming strong bonds with glue so that the mechanism suggested above is not operative. The occurrence of an inactivated surface was also demonstrated to depend on the presence in wood of long-carbon-chain, saturated fatty acids. Inactivation can be prevented from developing in normally suscep-tible material by proper extraction, or brought about in normally insuscep-tible material through the addition of suitable fatty acids. Results obtained from the author's experimental work, and from that contained in the liter-ature, show the variability that can be expected in the distribution of each extractive found, both between and within trees of a species. A logical  explanation is immediately apparent for the unpredictable occurrence of  inactivation - it occurs when there are present within wood certain chem- ical substances which vary widely in their distribution. Although it has been established, with reasonable certainty, that the presence of specific fa£ty acids is essential for the production of an inactivated surface when veneer is heated to high temperature, the mechanism by which the surface is modified has not been fully explained. 127 Mevrertheless^ through a synthesis of the information provided by the work covered in this thesis, and the literature, a reasonable hypothesis can be put forward. Theories of adhesion Adhesion has traditionally been divided into two types, mechanical and specific, which are due to physical and chemical factors respectively. While mechanical adhesion undoubtedly plays a part in some adhesive bonds, it has been shown to be nonessential for the formation of strong adhesive joints and to play only a minor role in most of them. The practice of tooth-planing wooden joints prior to gluing has now been discredited by the U. S. Forest Products Laboratory (102). A series of elegant experiments, carried out by Marian and Stumbo (67), provide evidence for the predominance of specific adhesion in the gluing of wood. WoOci treated with a monomolecular silane layer, so that the glue could "key" into the wood structure, but could not wet the wood, produced joints with strength values of the order of 15 to 20 per cent of that obtained with untreated wood. The coating of the surface of a veneer by fatty acid, that spread under the influence of heat, would be expected to have a similar effect. This is the type of mechanism that is strongly suggested by the findings reported herein. One of the most widely accepted preconditions for the formation of an adhesive bond has been that postulated by deBruyne, whereby the adhesive and adherend must be of similar polarity. A great deal of recent 128 work casts doubt on its universal applicability. Meissner and Merri l l (70) reported the results of two other sets of investigators, as follows. Callner and Woodworth tried combinations of adhesives and adherends showing large and small differences in melting points, polarities, hardnesses or coefficients of expansion. In all cases they obtained a bond, including mercury with ice, glass and styrene. Bonds formed regardless of the magnitude of the contact angles involved. Loughborough and Haas were unable to find any surface to which water would not stick as ice, for pot-ential use in airplane de-icing. Meissner and Merri l l suggested that an adhesive bond will form if a low molecular weight material, at a tempera-ture above its melting point, is brought into contact with a solid surface and is then allowed to freeze into place. Thermoplastic high polymers react similarly above a temperature which appears to correspond to the second order transition temperature, probably due to a rapid increase in rota-tional and vibrational freedom of the molecular chain segments. Mobility is essential so that force fields can key into each other. Mobility can be increased below the normal point by. the addition of a solvent or can be destroyed by causing crosslinking. This suggests that a liquid will bond to a solid surface with which it is brought is ©thermally into contact if the combination is then cooled below the transition temperature (first or second order) of the liquid. A bond will also form if the liquid's transition temperature is increased above the system's temperature as by cros slinking or solvent evaporation. Meissner and Merr i l l also reported the work of Loughborough 129 and Haas, and of Woodruff, who obtained, good bonds between ice and polyethylene or glass; Wood's metal and stainless steel or bakelite; stainless steel and naphthalene or water. These bonds correlated no better with contact angle than with polarity. It was not their intention to show that the polarity rule was not correct, only that bond strength does not seem to depend on one factor. Bikerman, in a series of papers (104, 11, 12, 13, 14) proposed a theory that no chemical or physicochemical affinity need exist between an adhesive and an adherend. An adhesive joint is almost invariably broken by mechanical means, a separation along the interface between the two materials occurring so rarely that it does not need to be considered. He claimed that failure takes place across the adherend^,the adhesive, or a weak boundary layer between them. Considerable substantiating evidence was provided that materials normally considered difficult to glue, such as polyethylene j could, in a pure state, be glued readily. Sharpe and Schonhorn (90) stated that deBruyne's adhesion rule had been proven invalid by work done in their laboratory. They also made the very important point that spreading (hence wetting) is a non-reciprocal property. If pure A spreads on pure B , then pure B will not spread on pure A . For spreading to occur, the surface free energy of the solid must equal or exceed the sum of the surface free energies of the liquid (in contact with its saturated vapour) and of the solid/s_i_£_t interface. The various lots of veneer that have been extracted* then dried at high temperature, or extracted after such drying have all glued well. 130 Evidently the gluing properties of the wood itself were not directly affected but were modified by the fatty acid fraction. DeBruyne's postulate of the necessity of like polarities and the change in polarity of wood does not apply under these conditions. The spreading of a long-chain fatty acid on the surface of wood would change the nature of the surface to that of a hydrocarbon if the carboxyl groups reacted with the wood. The free surface energy would then be greatly reduced and the wood would not then wet with water. DeBruyne, in a recent publication (25), modified his views, stating that adhesion has now been shown by various experimenters to be due to electromagnetic interactions produced by continual fluctuations in the distribution of electrons within the molecules. Since these forces act over a very short range, it is imperative that surfaces to be glued be in close contact. Theoretically, truly plane surfaces would adhere spontan-eously. In practice, this condition of close contact is normally achieved by the insertion of a liquid between solid surfaces. While it would not be theoretically necessary for the liquid to wet the surfaces * it would not then come in close contact with the surfaces which are rough on the micro-scopic level. Wetting is therefore a practical necessity. Substantiating evidence for this postulate was provided by the work of Swanson (96) on the adhesion of pulp. The strength of paper is not due to mechanical entanglement but to the various attractive forces. Intimate contact of the elements is brought about by the Campbell effect -131 extreme capillarity due to fine fibrillation causes very great pressures to be exerted during drying. Beater adhesives or hemicelluloses help to bridge the remaining gaps. Nissan (76) presented a strong case for the assumption that the bonding of paper is due to hydrogen bonding and, to a lesser extent, to van der Waal's forces. Although his conclusions are restricted to paper, it is probable that they apply equally to wood since wood also reacts through hydroxyl groups. Mark (69) showed, through thermodynamic considerations, that the theoretical strengths of pure materials, and of bonds between dissimilar materials, greatly exceed those realised in practice. Further, while bonds can be formed by non-wetting adhesives, they will be greatly inferior to those formed by wetting adhesives. It would appear that there is agreement on two major points -adhesion is due to one or more of the molecular valence forces, so intimate contact is essential, because of the rapid falling off of their effect with distance; wetting of the surface is essential although there is no agree-ment as to whether this is due to practical or thermodynamic consider-ations. There is nothing in the literature at variance with the findings of this thesis except the original postulate of deBruyne with respect to polarity, and this has now been disclaimed. Some explanation for the effect of fatty acids on gluability can also be given on the basis of the findings of others. 132 The gluing of wood Due to their physicochemical properties, wood surfaces presented a more complex set of phenomena than other materials of simple surface texture. They varied in their reaction to wetting, depending oh preparation, machining, aging and mode of drying (66, 68). In addition, according to Gray (35), surface contamination occurred rapidly and modified existing conditions. His work indicated that:the obtaining of adequate wetting of the surface was usually more of a problem than obtaining adequate adhesion. The variability between species he attributed to various factors, among them low-molecular-weight fatty acids for oak, beech and damp Parana pine (Araucaria angustifolia (Bert.) O. Ktze.) , but gave no supporting evidence. Tyltins (101) measured quantitatively the moisture and liquid water absorption of Scots pine that had been dried at various temperatures in different media. Irrespective of drying agent, the hygroscopicity dropped by 8 per cent, compared to air dry wood, when the samples were dried at 80 to 1 1 0 ° C , The absorption of liquid water was not influenced by temperature of drying but was decreased by drying in petrolatum. Drying at 120-125°C in petrolatum decreased vapour-absorption by 25 per cent. While Tyltins did not expand his work to include gluing, the drop in absorbency would be expected to adversely affect wettability. Salamon (87) has also demonstrated a drop in the hygroscopicity of western hemlock (expressed as equilibrium moisture content) following high-temperature drying. 133 Keith (50) found that wood dried at high temperatures suffered more degrade in strength properties than did material dried gradually at room temperature. Woods with contrasting component tissues, for example dense latewood bands, showed greater structural deterioration through repeated drying than woods characterized by a more nearly uniform structure. While he did not carry out such tests, it would be expected that the more severely degraded material would give lower breaking strengths if glued and tested. Whereas some of the veneers tested in the present work did show apparent effects of hydrolysis, these did not seem to be a major factor in the loss of gluability. Loss of strength by the wood itself would be expected to result in high wood failure with low breaking load. Inactivated bonds demonstrat e low wood failure and low breaking load. The measurement of accessibility of cellulose from wood pulp, or other sources, showed diminution due to repeated drying and wetting o r to treatment with boiling water (3,58). Similar results are not available for wood and their applicability is questionable. In the current research severe drying adversely affected the gluability of some veneer only after a considerable time and of other veneer not at al l . Suchsland (95) determined that increased depth of penetration of glue did not provide high breaking loads with j oints of Scots pine. Neither penetration of the glue nor rate of spread could be related to the quality of the joint when the gluing surfaces were plane and undamaged, the 134 glue was uniformly distributed and suitable pressure was applied to ensure perfect contact between the surfaces. Because of the small size of the panels used in the research for this thesis, it was not possible to obtain exact readings of glue spread. The results generally agreed with those of Suchsland, with the variation in glue spread having little effect on bond quality. The role of fatty acids Mitchell, Seborg and Millett (74) heated extractive-free Douglas fir cross sections and sawdust at different temperatures for different times in an open, or a closed, pressure system. In some experiments, circulated air or an inert atmosphere was introduced. Variations in heating conditions affected the chemical composition of the volatile products and the residue, and the hygroscopic and dimensional changes of the residue. Appreciable changes occurred only at tempera-tures well in excess of those used in commercial drying and only at extended times. Treatments in the range of the temperatures used for drying veneers had little effect on any components. Unfortunately, the material was extracted prior to heating so the effect of very high tempera-tures on extractives was not included in the results. The role of extractives in the development of waterproofing in aged paper has been mentioned above. Gorskii and his co-workers (33) utilized the distillation residue from the manufacture of synthetic fatty acids as a waterproofing agent for porous and semihard insulation board. It proved to be an economical substitute for rosin and paraffin. This 135 material undoubtedly contained many fatty acids of high boiling point, although this could not be determined. Schonhorn (88) found, that a monomolecular layer of stearic acid (or other similar, but unspecified jnaterial) could serve as an adhes-ive between aluminum plates and polyethylene. When a layer of acid was floated on water, the acidic end of each molecule tended to go into solution while the hydrocarbon end tended to point upward when many molecules were pushed together. When aluminum sheets were raised through the floating layer from below the water surface, the carboxylic acid radicals attached themselves to the surface of the aluminum. The free hydro-carbon ends could then be embedded in molten polyethylene, serving as an efficient adhesive. If more than a monolayer of acid was used, it tended to act as a parting agent. Once coated with the monomolecular layer, the aluminum would no longer absorb atmospheric water or gases in appreciable amounts. There are major points of agreement and of disagreement between this system and the attachment of fatty acids to the surface of wood. The aluminum surfaces were probably coated with a film of aluminum hydroxide hence the bonding surface would have similarities to that of wood. A multimolecular layer could exist on the aluminum but, since molten fatty acids should be absorbable into the cell cavities of wood, it is probable that only a monomolecular layer, bonded probably by hydrogen bonds, would remain at the surface of wood. The evidence for this is the reduction in apparent interference with bonding when using 136 increasing temperature and increasing molecular weight of acid. The higher the molecular weight in these materials, the higher the melting temperature. Inactivation would not then be due to any parting action of the fatty acids. Borgin (16) showed that water can displace a hydrocarbon from the surface of cellulose-containing materials, including wood. The interfacial affinity between cellulose and water is much higher than between cellulose and hydrocarbon. The hydrophilic behaviour of cellu-lose could be greatly reduced by coating or impregnating it with various hydrophobic organic materials, oils, waxes and different high polymers (15). The contact angle was increased, depending upon the material used, but the effect, in no case, was found to be a permanent one. Any hydrophobic material was displacable from the surface of the cellulose by water. The affinity bf cellulose for water can therefore not be perman-ently reduced by sorption of hydrophobic materials, but the time required for water to wet cellulose can be considerably increased. Borgin's work provides a ready explanation for the observation that long closed assembly times will dry out a normal bond but will give good results with an inactivated bond. Given time, the water in the glue will replace the fatty acids on the surface of the wood. The saponifying effect of the alkali in the glue would, of course, increase the effect. In a study of the effect of increasing carboxyl concentration on adhesion to cellulose of an iso-viscous series of vinyl chloride-vinyl acetate-maleic acid copolymers, it was found that a plot of the log of 137 adhesion, over the log of the carboxyl concentration gave a straight line (42). Analysis showed that these data conformed to an equation of the type Adhesion = K(COOH) n , similar to the Freundlich adsorption isotherm which was derived from measurements involving the adsorption of pure compounds, such as acetic and benzoic acid, by charcoal (89). Within the range 20 to 5,0°C> the exponent is reasonably close to the theoretical value of 0* 67 which was predicted by Gyani for surface sorption. These measure-ments have been interpreted to mean that adhesion is the resultant of the relative magnitudes of the energy of cohesion within the adhesive and the energy of sorption. The former is greater than the latter which results in an increase in adhesion with increasing temperature. Recent work has shown that the same type of curve is obtained when aluminum (probably partially covered with an oxide coating) is substituted for cellulose as the adherend. It has been found in the current work that interference with adhesion varies with the presence of saturated fatty acids but not with the presence of unsaturated acids. Although the unsaturated acids were of shorter chain length, so that a direct comparison could not be made, it would be expected that the more flexible chains would lead to less density of packing hence to a lessened result per unit area for the unsaturated acids. The energy of cohesion within saturated fatty acids should vary with chain length. Longer-chain acids would require higher temperatures to react with the surface of wood. Long and his colleagues at the Paint Research Institute (64) 138 provided a possible explanation for the varying effect with fatty acid, chain length and type which agrees with the above. Using a Langmuir balance, they calculated the force required to pull one molecule of each of many saturated, or unsaturated, fatty acids from the surface of water. Paist of this force is due to cohesion as the molecule is pulled from among its fellows, part to adhesion to the water surface. They were able to separate the total force into its components and demonstrated that the force of adhesion is of the order of magnitude of van der "Waal's forces or hydro-gen bonding. In a further series of experiments it was demonstrated that it is virtually impossible to remove all of the last layer of water molecules from a hydrophilic surface by high vacuum and temperature. Since water is therefore present under normal conditions on a hydrophilic surface, they postulatedthat adhesion is due to hydrogen bonding. Further, the force per molecule required to remove a saturated fatty acid from the surface of water increases linearly to about 14-carbon chain length * then exponentially to 22 carbons, the limit of their experiment. Unsaturated acids, with equal chain lengths, demonstrated greatly inferior adhesive properties, which was attributed to the ability of the saturated acid molecules to pack more closely per unit area of surface. In the current research it was found that the interfering effect was due to saturated fatty acids with greater chain length than 18 carbon atoms. It was previously shown (81) that, given time, water would displace such acids from the surface of wood. It is possible, then, that the shorter-chain acids also react with the wood but are more readily displaced by the 139 by the water of the glue. Although Long found thatit is difficult to remove the last layer of water from the surface of other hydrophilic substances, this is apparently not the case with wood. Marian (68) has postulated that a mono-molecular layer of water covers all the available wood surface at about 10 per cent moisture content and that this is essential for bonding. It is relatively easy to remove some of this monolayer since wood is readily reduced below 10 per cent moisture content and there is no inherent gradient in the distribution of moisture in wood. Proposed theory of inactivation A synthesis of the findings from the research done for this thesis and those from the literature discussed above yields a theory to explain the nature of the underlying mechanism that is involved when an inactivated surface is formed. Inactivation occurs when veneer containing saturated, long-carbon-chain fatty acids is subjected to high drying temperatures. High temperatures and long drying times remove much of the last monolayer of water molecules from the wood. Water normally has greater affinity for the wood than do the fatty acids. The short-chain acids may be largely volatilized or may react with the wood. The long-chain acids are rendered more mobile but are not driven off. When water has been removed from the bonding sites (wood hydroxyl groups) through the application of heat, the acids will react with these hydroxyl groups through hydrogen 140 bonding. When water is re-introduced, it will quickly displace the short-chain or unsaturated acids but cannot quickly displace the long-chain acids, although it will do so in time. If an attempt is made to glue the wood • while the fatty acids are still bonded to the surface, the hydrocarbon end of the acid will repel the water of the glue and proper penetration will not occur. When a monolayer of water has re-established itself on the surface of the wood, the gluability will be restored. This theory is in agreement with all the known facts and does give an explanation for the development of a water-repellent surface which sometimes occurs when Douglas fir veneer (or veneer of other species) is heated. SUMMARY AND SUGGESTIONS FOR ADDITIONAL R E S E A R C H 142 The findings from this experimental work, which are listed below, are claimed as original contributions to fundamental knowledge of the interaction of wood with its environment: (1) Severe heating of veneer does not always result in inactivation, that i s , a loss in potential for forming good bonds with glue. (2) Inactivation can be controlled by extraction of susceptible wood material with certain organic solvents, either before or after drying. (3) The presence of oxygen is not a prerequisite to the formation of an inactivated surface on veneer. (4) A demonstrable variability exists, between and within species and trees, in susceptibility to the development of an inactivated surface on heated veneer. (5) Considerable qualitative variability is exhibited in the extractives found in samples of Douglas fir wood. Yields of major fractions of extractives, for which quantitative measurements were taken, varied widely between and within trees. (6) Two components of the resin acid fraction of the veneer extracts, those eluting on the gas/liquid chromatograph after 2»8 and 4.2 minutes, appeared in all samples obtained from the Coastal Douglas f ir , and were absent from the Interior Douglas fir 143 material that was examined. No other correlation was found between the distribution of extractives and the botanical classification of Douglas fir into two varieties or species, (7) Of all the components separated from the various extractive fractions, only the saturated, long-carbon-chain fatty acids occurred in a pattern that could be correlated with the occurrence of inactivation. (8) A l l of the veneer demonstrating susceptibility to inactivation contained more than a trace of arachidic, behenic or lignoceric acid (the carbon skeletons of which consist of 20, 22 and 24 atoms respectively). The severity of inactivation found also correlated well with the relative amounts of these acids present, as determined by gas/liquid chromatography. (9) Inactivation can be brought about, in veneer that does not naturally contain a causal agent, by the surface application of saturated fatty acids of suitable chain length. (10) It is therefore established, with reasonable certainty, that the underlying causal agent for the phenomenon of inactivation of veneer is the presence in the veneer of saturated fatty acids with a carbon-chain length in excess of eighteen atoms. (11) A theory of the mechanism for the inactivation of a veneer surface has been postulated: Removal of some or all of the last molecular layer of water 144 from the wood, and the application of heat, permits the saturated, long-chain fatty acids to move onto the wood surface and to hydrogen bond with the hydroxyl groups of the wood cellulose. The surface of the wood is thus covered with a hydrocarbon layer with very low free surface energy that is not readily wettable by the applied glue. SUGGESTIONS FOR ADDITIONAL R E S E A R C H Conclusive evidence has been presented for the role of extractives in the development of an inactivated surface on Douglas fir veneer. Other species are known to be susceptible to inactivation and to contain a wide range of extractives. A series of experiments, using the techniques described herein, would readily determine the presence of similar materials to those found in the Douglas fir that was susceptible to the development of an inactivated surface. If it could be shown that inactivation is due to the presence of one class of components in all cases, when remedial measures were found they would be generally applicable. The theory postulated is in agreement with the findings of the present work and the published results of others, except where shown to be not applicable. However, further work is necessary to strengthen, or modify, the theory. It is suggested that this could take the form of surface examination, using X-ray or 145 solid-state spectrophotometric techniques. Comparisons would be made between surfaces demonstrating varying degrees of inactivation. V I I A P P E N D I X C o l u m n t y p e : 9' - i" o . d . s t e i n l e s p s t e e l F e e t e i n g : G a s C h r o n C L A (80-100 mash) • U a t l o r . o r y p h a s e : t r i t o l y l p h o s p h a t e F l o w r a t e : 100 r a l / m l n . He C u r r e n t : 250 m i l l l a j n p e r e g C h a r t < j p e e d : 0.2 i n . / m i n . T e m p e r a t u r e : 1J0°C Sample: 1 m i c r o l i t e r ! 1 1 1 < • 1 1 1 1 1 1 > 1 1 1 1 1 1 1 1 1 1 1 1— i 0 10 20 JO 40 50 Time ln minutes Figure I. Gas chromatographic chart for the steam volatiles recovered from the Heart 3 portion of the Coastal Douglas fir. 147 4 ? If o o us §=§ I u s <8 a C o l u m n t y p e : 12' - J" o ' . d . s t a i n l e s s s t e e l P a o k l n p : G a s C h r o m C L A (80-100 m e s h ) S t a t i o n a r y p h a s e : s i l i c o n e g u m - i F - l 13«7 p e r c e n t F l o w r a t e : 60 o i l / a i n . C u r r e n t : 2 5 0 m i l l i a m p e r e s C h a r t s p e e d : 0-2 i n . / m i n . T e m p e r a t u r e : 160 ° C S a m p l e : 2 m i c r o l i t e r s J O O £ J3 U/uA T i m e In m i n u t e s 12 1 6 Figure II. Gas chromatographic chart of the steam volatiles recovered from the sapwood of the Coastal Douglas fir. 148 s t e e l C o l u m n t y p e : 1 0 ' - i " o . d . = t t l n l e s s P a c k i n g : G a < = C h r o n C L A ( 8 0 - 1 0 0 m e s h ) S t e t l o n a r y o h a s e : L A C 2 R 4 4 6 ( R e s o f l e x ) 30 p e r o e n t F l o w r a t e : 1 4 4 m l / m l n . H e C u r r e n t : 250 m i l l i a m p e r e s C h a r t s p e e d : 0 * 2 l n . / m i n . T e m p e r a t u r e : 230°C S a m p l e : 10 m i c r o l i t e r s 1 0 T i m e i n m i n u t e s 2 0 3 0 Figure III. Gas chromatographic chart of the methyl esters bf the free fatty acids recovered from the Heart 4 portion of Tree 3, after drying 149 VJ C o l u r n t y p e : 6'- J" o . d . s t e i n l e s " s t e e l P a c k i n g : G a s C h r o m CLA (80-100 m e s h ) S t o t i o n c r y p h a s e : n e o p e n t y l g l y c o l a d l p e t e (15.9 p e r c e n t ) F l o w r a t e : 1 4 0 r a l / m l n . H e C u r r e n t : 250 m i l l i a m p e r e s C h a r t s p e e d : 0 ' 2 I n . / m i n . T e m p e r a t u r e : 2 2 0 ° C S a r i p l e : 5 m i c r o l i t e r s 1 0 2 0 T i m e i n m i n u t e s JO 40 Figure IV. Gas chromatographic chart of the resin acid methyl esters prepared from the extract from the Heart 1 portion of the Coas-tal Douglas fir. 150 Figure V. Paper chromatogram of the methyl esters of the resin acids recovered from the various extractive fractions. Reading from right to left, these are as follows: Quesnel fir - Sapwood - Heart 1 - Heart 3 Coast fir - Sapwood - Heart 1 - Heart 3 Tree 3 - Heart 4 Commercial reference standard Tree 3 - Heart 4, dried - Heart 5 Commercial reference standard. 151 Figure VI. Thin-layer chromatograph of the methyl esters of the free fatty acids recovered from the various extractive fractions. Reading from left to right, these are as follows: Quesnel fir - Sapwood - Heart 1 - Heart 3 Coast fir - Sapwood - Heart 1 - Heart 3 Tree 3 - Heart 4 Reference standard C^g acids Reference standard CJO~18 acids Reference standard C22-26 acids Tree 3 - Heart 4, dried and sanded - Heart 4, dried - Heart 5. 152 Figure VII. Thin-layer chromatograph of the unsaponifiable portion of the various extractive fractions. Reading from left to right, these a re as follows: Quesnel fir - Sapwood - Heart 1 - Heart 3 Coast fir - Sapwood - Heart 1 - Heart 3 Tree 3 - Heart 4 Glycerol Blank (^-sitosterol Ergosterol Phytosterol Ceryl alcohol Tree 3 - Heart 4, dried - Heart 4, dried and sanded - Heart 5. 153 Supplementary Table 8 - 1 Bond-quality evaluations of panels made from untreated veneer from a Coastal Douglas fir. These are detailed measurements taken after the cold-soak cycle of CSA 0-121. See Summary Table 8 for evaluation. Panel number Breaking load psi Per cent wood failure Avg. Avg. OD 65 100 60 95 95 85 80 15 85 40 85 63 OD i-10 60 150 120 130 100 112 85 80 50 85 75 75 OD+20 75 80 70 75 75 75 85 100 100 95 100 96 OD +40 130 115 140 85 65 107 100 100 100. 100 100 100 OD+60 85 85 70 65 50 71 95 90 85 100 100 94 OD 205 70 75 75 140 OD+10 90 90 150 165 50 OD +20 120 175 150 120 135 OD +40 60 110 100 105 75 OD +60 65 70 80 125 90 OD 120 90 110 105 120 OD+10 105 75 95 80 100 OD+20 90 125 210 100 180 OD + 40 105 95 120 100 100 OD +60 95 80 80 90 85 113 80 100 95 95 95 93 109 100 100 100 100 95 99 140 85 90 95 85 95 90 90 15 50 45 75 40 45 85 95 100 90 95 80 92 109 100 90 100 90 100 96 91 95 100 100 100 100 99 143 100 100 100 100 100 100 104 100 100 100 100 100 100 86 100 95 100 100 100 99 OD 110 225 130 110 110 136 100 100 100 100 100 100 OD+10 110 110 130 155 100 121 85 55 95 90 90 81 OD+20 85 110 110 90 95 98 100 100 100 100 100 100 OD +40 105 105 80 120 90 100 100 100 100 100 100 100 OD +60 160 90 160 90 95 119 100 90 95 95 100 96 OD 135 105 130 145 125 OD +10 125 125 110 195 120 OD +20 100 90 100 150 100 OD+40 90 85 85 80 110 OD +60 95 85 75 100 160 OD 115 120 100 115 105 OD+10 125 120 145 100 130 OD +20 130 190 180 115 175 OD +40 100 85 95 85 145 OD + 60 90 85 100 90 110 128 100 100 100 100 100 100 135 95 90 100 100 95 96 108 100 100 100 100 100 100 90 100 100 95 100 100 99 103 100 100 95 100 100 99 111 100 100 95 100 100 99 124 100 100 100 100 100 100 156 100 100 100 100 100 100 102 100 100 100 100 100 100 95 35 100 90 100 35 72 154 Supplementary Table 8 - 1 Continued Panel number Breaking load psi Avg. Per cent wood failure Avg. Heart 5 OD 105 120 140 100 110 115 100 100 100 100 10U 100 OD +10 60 140 90 95 120 101 95 95 100 100 100 98 OD +20 110 125 150 130 125 128 100 100 95 95 100 98 OD +40 95 130 105 80 100 104 90 90 90 80 100 90 OD +60 190 45 45 65 65 82 80 60 100 70 95 81 Heart 6 OD 70 125 95 115 105 102 95 85 100 90 100 94 OD +10 110 80 120 80 65 91 100 75 90 100 75 88 OD+20 75 70 90 90 100 85 90 100 95 80 100 93 OD+40 145 115 90 105 105 112 100 100 100 90 60 90 OD+60 70 125 90 110 65 92 100 95 80 90 100 93 155 Supplementary Table 8 - 2 Bond-quality evaluations of panels made from untreated veneer from a Coastal Douglas fir. These are detailed measurements taken after the boil/dry/boil cycle of CSA 0-121. See summary Table 8 for evaluation. Panel number Breaking load psi Per cent wood failure Sap 1 Sap 2 Heart 1 Heart 2 Heart 3 Avg. Avg. OD 85 100 85 75 100 89 95 80 55 85 35 70 OD+10 140 160 85 115 140 128 55 55 35 40 80 53 OD +20 55 70 115 90 105 87 90 90 90 100 95 93 OD +40 90 65 70 75 85 77 90 95 100 95 90 94 OD + 60 90 75 50 95 90 80 65 90 95 85 85 84 OD 95 105 75 210 245 144 95 95 100 100 85 95 OD +10 180 0 80 70 80 82 100 100 95 100 100 99 OD+20 70 155 125 90 70 102 90 95 80 95 75 87 OD +40 80 60 90 125 175 106 80 35 45 45 65 .54 OD + 60 65 145 65 70 150 99 75 100 95 75 90 87 OD 90 100 100 85 110 97 95 100 100 100 100 99 OD + 10 80 110 75 85 80 86 100 95 100 95 70 92 OD +20 190 190 170 160 180 178 100 100 95 100 100 99 OD +40 100 110 125 95 70 100 95 95 100 100 100 98 OD + 60 115 80 85 110 105 99 100 100 95 100 95 98 OD 95 95 90 95 240 123 100 100 100 100 100 100 OD + 10 115 130 110 120 130 121 75 80 90 90 100 89 OD +20 80 90 75 90 100 87 100 100 100 100 100 100 OD +40 120 90 115 90 85 100 100 100 100 100 100 100 OD+60 185 105 85 95 90 112 90 95 90 100 95 94 OD 105 145 145 110 105 122 100 100 100 100 100 100 OD +10 190 150 105 90 110 129 100 95 90 100 95 96 OD + 20 85 70 110 120 110 99 100 100 100 95 95 98 OD+40 75 95 95 95 100 92 95 100 100 100 50 89 OD+60 85 90 90 95 170 106 100 100 95 85 95 95 C O N T I N U E D 156 Supplementary Table 8 - 2 Continued Panel number Breaking load psi Per cent wood failure Avg. Avg, Heart 4 OD 95 100 95 90 95 95 100 100 100 100 100 100 OD +10 110 105 145 145 90 119 100 100 100 100 100 100 OD +20 110 120 165 175 80 130 100 100 100 100 100 100 OD +40 130 130 100 90 145 119 100 100 100 100 100 100 OD + 60 110 95 80 85 95 | I 93 85 20 95 85 95 76 Heart 5 OD 115 110 100 85 85 99 100 100 95 100 100 99 OD +10 115 130 90 130 130 119 95 95 85 95 85 91 OD + 20 90 110 95 90 100 95 95 100 95 100 80 94 OD +40 135 95 70 120 95 107 95 90 85 100 95 93 OD+60 90 55 100 70 25 68 85 95 100 85- 75 88 Heart 6 OD 135 80 110 105 95 105 100 100 100 100 95 99 OD +10 84 92 80 75 90 84 95 90 100 90 85 92 OD + 20 105 80 100 100 90 95 100 90 100 100 95 97 OD +40 100 40 105 105 95 89 95 95 80 90 100 92 OD -60 60 95 100 110 105 94 100 95 95 100 100 98 \ [ 157 Supplementary Table 9 - 1 Bond-quality evaluations of panels made from untreated veneer from a Coastal Douglas fir. Veneer was dried and reconditioned to the moisture contents shown in Summary Table 9. These are detailed measurements taken after the cold-soak cycle of CSA.0-121. See Summary Table 9 for evaluation. Panel number Sap 1 S OD R OD S OD +60 R OD+60 Breaking load psi Per cent wood failure 6 Avg. 'Avg. 75 90 45 50 65 15 20 10 10 15 14 15 20 25 25 30 23 20 15 5 15 10 13 60 70 55 45 45 55 80 75 65 60 40 64 5 0 20 5 5 7 10 25 20 5 15 15 2S OD 75 45 55 60 65 60 45 20 30 20 20 27 R OD 90 90 80 80 70 82 10 65 10 80 80 49 S OD + 60 30 35 35 35 35 34 25 10 20 20 25 20 R OD +60 20 15 15 10 5 13 15 15 20 10 20 16 Heart 1 S OD 100 100 100 120 115 107 90 95 50 95 90 84 R OD 100 115 95 110 95 103 70 95 85 85 85 84 S OD+60 60 50 60 50 55 55 15 25 20 40 15 21 R OD +-60 75 60 65 60 75 67 40 25 20 20 40 29 Heart 2 S OD 130 110 120 130 130 124 20 10 20 25 30 21 R OD 90 90 90 90 100 9 2 20 40 15 60 50 37 S OD +60 65 75 75 65 65 69 90 85 40 20 10 49 R OD+60 65 75 60 65 60 65 30 5 5 10 0 10 Heart 3 S OD 110 90 95 95 85 95 100 85 80 90 85 88 R OD 135 135 130 115 130 129 40 50 60 85 50 57 S OD +60 55 50 50 95 75 65 20 5 10 30 10 15 R OD +60 80 90 70 90 90 84 15 15 15 20 30 17 Heart 4 S OD 120 115 105 105 125 114 90 75 100 90 75 86 R OD 100 95 105 95 85 96 60 30 50 50 50 48 S OD +60 105 125 85 120 110 109 80 60 60 20 10 46 R OD+60 75 75 75 70 70 73 50 40 30 50 40 42 Heart 5 S OD 85 125 95 110 115 106 90 85 100 80 80 87 R OD 80 80 80 95 90 85 100 90 90 95 100 95 S OD+60 110 70 120 120 90 102 70 75 13 50 30 52 R OD +60 60 45 80 85 100 74 50 25 55 40 20 38 Heart 6 S OD missing R OD 85 85 85 85 95 90 S OD+60 5 5 35 30 5 16 5 0 5 5 0 3 R OD +60 75 65 90 55 60 69 75 80 50 60 knot 66 158 Supplementary Table 9 - 2 Bond-quality evaluations of panels made from untreated veneer from a Coastal Douglas fir. Veneer was dried and reconditioned to the moisture contents shown in Summary Table 9. These are detailed measurements taken after the boil/dry/boil cycle of CSA 0-121. See Summary Table 9 for evaluation. Panel number Breaking load psi Per cent wood failure Avg. Avg Sap 1 S OD 72 82 80 83 80 79 5 5 15 10 15 10 ROD 30 50 0 48 58 37 0 0 15 10 5 6 S OD + 60 50 65 80 55 60 62 60 65 20 80 30 51 ROD + 60 50 55 43 48 49 49 30 20 65 5 15 27 Sap 2 S OD 60 50 50 60 50 54 5 5 0 20 5 7 ROD 50 65 80 65 75 67 95 100 25 95 85 80 S OD + 60 55 55 25 45 65 49 60 10 0 0 25 19 ROD + 60 15 10 20 21 47 23 60 10 5 25 45 29 Heart 1 S OD 78 94 112 97 105 97 90 90 55 90 40 73 ROD 110 90 95 125 105 105 100 80 100 85 100 93 S OD + 60 115 70 60 75 80 80 0 0 25 0 15 8 ROD + 60 76 77 64 80 58 71 10 15 5 25 15 14 Heart 2 S OD 90 85 80 90 75 84 50 95 100 90 95 86 ROD 88 100 80 105 85 92 55 80 100 95 95 85 S OD + 60 68 64 62 60 63 63 75 85 55 60 45 64 ROD+60 47 58 65 60 68 60 0 5 0 5 5 3 Heart 3 S OD 95 95 95 80 100 93 100 95 80 95 85 91 ROD 157 146 145 151 183 156 25 40 30 5 0 20 S OD + 60 80 45 65 50 55 59 0 0 0 0 5 1 ROD + 60 80 100 70 85 115 90 20 35 5 35 15 22 Heart 4 S OD 88 79 95 96 95 91 90 95 95 90 90 92 ROD 120 105 80 110 100 103 90 30 10 40 50 44 S OD + 60 missing ROD+60 80 85 85 70 65 77 80 35 85 75 35 62 Heart 5 S OD 110 125 110 95 95 107 100 45 85 100 90 84 ROD 100 80 98 85 70 87 100 95 100 100 100 99 S OD + 60 75 50 65 80 55 65 80 10 20 90 15 43 ROD + 60 60 62 68 65 71 65 25 45 40 25 25 3.2 Heart 6 S OD missing ROD 71 74 73 75 85 80 S OD + 60 10 0 10 0 0 4 0 0 20 0 0 4 ROD + 60 55 35 25 50 90 51 50 80 95 95 100 84 159 Supplementary Table 10 Bond-quality evaluations of panels made from untreated veneer from an Interior Douglas fir (Quesnel fir). These are detailed measurements. See Summary Table 10 for evaluation. Panel number Tested after the CSA 0-121 cold-soak cycle Breaking load psi Per cent wood failure Avg. Avg, Sap OD 113 106 106 0 90 83 100 85 85 90 90 88 OD + 10 130 127 130 125 145 133 95 95 80 30 40 68 OD+20 70 64 73 66 30 61 90 95 95 95 40 83 OD +40 95 138 140 120 122 123 100 50 90 80 20 68 Heart 1 OD 180 175 157 148 170 .166 80 75 95 100 95 89 OD + 10 112 112 110 115 132 116 95 90 95 60 100 88 OD +20 85 115 125 112 100 107 5 80 50 50 85 54 OD+40 50 25 65 55 50 49 95 95 100 100 100 98 Heart 3 OD 146 140 140 112 cull 110 95 95 90' 95 cull 93 OD +10 93 105 135 145 103 116 95 80 100 60 80 83 OD+20 138 150 135 145 137 141 100 95 95 90 80 92 OD+40 120 150 100 116 145 126 50 80 25 50 95 60 Tested after the CSA 0-121 boil/dry/boil cycle  Breaking load psi Per cent wood failure Avg. Avg, Sap OD 135 125 125 84 115 117 95 100 100 75 100 94 OD +10 112 130 142 125 123 126 25 30 40 95 45 47 OD +20 57 47 68 67 40 56 90 95 70 75 85 83 OD +40 80 133 113 105 106 107 95 75 25 50 95 68 Heart 1 OD 190 175 185 170 152 174 100 90 90 95 100 95 OD +10 96 96 100 115 138 109 100 80 95 90 95 92 OD +20 110 105 92 110 112 106 50 75 35 50 80 58 OD +40 82 82 93 48 86 78 45 70 45 100 100 72 Heart 3 OD 138 135 112 120 132 127 100 100 95 95 95 97 OD +10 90 112 150 140 95 118 60 35 65 70 75 61 OD +20 130 160 148 140 128 141 95 100 90 95 90 94 OD+40 89 154 60 0 112 83 45 85 30 5 100 53 160 Supplementary Table 11-1 Bond-quality evaluations of panels made from untreated veneer from an Interior Douglas fir (Tree 3). These are detailed measurements taken after the cold-soak cycle of CSA 0-121. See Summary Table 11 for evaluation. Panel number Breaking load psi Per cent wood failure Sap OD 95 160 150 145 155 Avg. 141 90 95 100 95 95 Avg, 95 OD •  10 185 215 270 225 215 222 0 35 25 90 35 37 OD •20 170 130 210 140 160 162 40 50 0 15 0 21 OD -40 90 140 100 140 120 118 0 0 0 0 10 2 Heart 1 OD 300 340 330 250 350 314 85 90 25 15 80 59 OD -10 235 300 240 260 260 259 15 30 50 35 15 29 OD -20 250 245 190 245 240 234 5 0 0 25 0 6 OD -40 245 0 190 170 145 130 0 0 0 0 5 1 Heart 2 OD 245 230 285 250 225 247 15 15 25 30 10 19 OD •10 205 230 275 200 210 224 5 30 0 0 0 7 OD -20 300 310 240 260 285 279 80 75 60 75 15 61 OD '40 180 185 125 200 170 172 10 0 10 20 25 13 Heart 3 OD 265 265 315 265 325 287 90 75 55 90 80 74 OD •10 270 245 310 250 290 273 50 25 75 25 40 43 OD -20 210 210 215 235 190 212 25 5 5 0 5 8 OD -40 160 160 60 180 150 142 25 0 0 0 15 8 Heart 4 OD 350 290 380 290 315 325 40 75 65 80 50 62 OD • 10 225 275 275 250 250 255 80 80 75 65 80 74 OD -20 215 230 220 240 205 222 25 0 5 40 70 28 OD -40 140 175 135 140 150 148 0 15 0 30 25 14 Heart 5 OD 275 170 260 160 130 199 40 75 45 35 25 44 OD -10 235 235 220 210 265 233 80 85 95 30 70 72 OD -20 330 280 280 270 325 297 35 60 20 10 80 41 OD •40 190 230 235 195 230 216 80 95 95 95 95 92 Heart 6 OD 345 300 250 285 195 275 85 85 100 85 55 82 OD -10 230 235 235 160 260 224 35 70 85 45 45 56 OD '20 155 200 230 225 200 202 65 75 55 55 75 65 OD '40 100 175 180 149 140 149 0 25 30 60 25 28 161 Supplementary Table 1 1 - 2 Bond-quality evaluations of panels made from untreated veneer from an Interior Douglas fir (Tree 3). These are detailed measurements taken after the boil/dry/boil cycle of CSA 0-121. See Summary Table 11 for evaluation. Panel number Sap Breaking load psi Per cent wood failure Avg. Avg. OD 190 175 130 120 160 155 85 90 90 100 80 89 OD + 10 195 170 225 175 175 188 85 75 80 80 60 76 OD + 20 120 150 195 170 115 150 0 25 90 0 0 23 OD + 40 140 140 130 120 115 129 0 0 15 15 0 6 Heart 1 OD 265 260 250 240 240 251 10 5 50 5 80 30 OD *10 210 190 220 195 205 204 15 80 15 10 90 42 OD *20 195 210 210 200 170 197 5 10 25 0 5 9 OD +40 175 175 200 190 150 178 5 80 0 15 0 20 Heart 2 OD 225 250 235 200 175 217 20 30 25 45 45 33 OD + 10 210 220 205 215 245 219 30 15 5 60 10 24 OD +20 220 215 190 215 205 209 85 20 40 40 80 51 OD +40 135 170 130 100 140 133 10 15 75 10 15 25 Heart 3 OD 250 250 245 225 250 246 80 40 80 80 80 72 OD +10 225 190 220 225 210 214 75 80 80 60 90 77 OD+20 135 190 200 80 135 148 5 15 30 25 20 19 OD+40 140 80 115 145 150 126 5 0 10 0 15 6 Heart 4 OD 255 245 250 225 275 254 60 70 80 75 60 69 OD+10 225 245 175 185 230 212 40 60 75 70 80 65 OD *20 190 200 175 185 195 189 80 15 25 60 45 45 OD +40 165 185 125 180 120 115 55 40 0 45 10 30 Heart 5 OD 190 220 240 210 160 204 75 80 60 70 45 65 OD +10 170 190 185 180 160 177 90 35 85 55 80 69 OD +20 225 290 215 200 230 232 75 25 15 80 75 54 OD +40 145 200 165 165 215 178 85 95 75 80 90 85 Heart 6 OD 255 270 225 205 220 235 85 80 95 100 100 92 OD +10 215 200 185 180 215 199 40 30 35 25 40 34 OD +20 180 220 150 160 210 184 85 40 15 30 50 44 OD +40 140 150 65 105 135 119 25 15 5 5 35 17 162 Supplementary Table 1 8 - 1 Bond-quality evaluations of panels made from veneer from Coastal or Interior Douglas f ir , unextracted or extracted with n-hexane or petroleum ether, and dried as shown. These are detailed measurements taken after the CSA 0-121 cold-soak cycle. See Summary Table 18 for evaluation. Breaking load psi Per cent wood failure Avg. Avg. Quesnel fir extracted with petroleum ether Sapwood OD OD+10 153 138 131 174 168 153 100 100 95 100 100 99 Dried at OD+20 185°C OD+40 100 113 100 102 112 105 100 100 100 100 100 100 Heart 1 OD 155 115 140 115 95 124 75 80 40 75 100 74 OD+10 150 135 160 150 140 147 100 100 95 100 85 96 Dried at OD+20 105 115 90 120 125 111 90 95 95 100 100 96 185°C OD+40 100 105 95 175 120 119 95 95 90 95 85 92 Heart 3 OD 150 126 144 130 150 140 100 100 100 100 100 100 OD+10 138 95 240 95 92 132 100 90 95 80 90 91 Dried at OD+20 135 135 145 150 145 142 80 95 100 80 100 91 185°C OD+40 110 122 105 150 124 122 75 95 95 75 85 85 Quesnel fir unextracted oven-dried at 107°C Sapwood Panel 1 89 63 65 70 94 76 95 100 100 100 65 92 Panel 2 105 95 70 95 70 87 80 80 100 100 100 92 Heart 1 Panel 1 131 165 145 163 184 157 100 100 100 100 95 99 Panel 2 122 150 145 135 145 139 100 90 100 100 100 98 Heart 3 Panel 1 100 117 154 163 165 140 50 100 100 100 100 90 Panel 2 185 173 143 138 157 159 100 100 100 95 100 99 Coast fir extracted with n-hexane Sapwood OD 75 85 65 80 90 79 100 100 100 100 100 100 OD+10 80 70 80 80 90 78 100 100 100 100 90 98 Dried at OD+20 80 70 75 80 85 78 90 95 100 100 100 97 185°C OD+40 70 70 60 70 75 69 85 85 85 85 70 82 C O N T I N U E D 163 Supplementary Table 1 8 - 1 Continued Breaking load psi Per cent wood failure Avg. Avg. Heart 1 OD 170 160 175 150 160 163 100 100 100 100 100 100 OD<,10 170 140 125 165 180 156 100 100 100 100 100 100 Dried at OD+20 195 205 190 155 150 179 100 100 100 100 100 100 185°C OD+40 100 125 125 145 150 129 100 100 100 100 100 100 Heart 3 OD 230 185 130 120 110 155 100 95 95 95 100 97 OD+10 150 195 140 180 150 163 100 100 85 100 100 97 Dried at OD+20 160 155 155 155 165 158 95 100 100 85 100 96 185°C OD*40 145 145 145 160 140 147 100 100 100 100 90 98 Coast f ir , unextracted, -oven-dried at 107°C Sapwood Panel 1 247 257 248 305 230 257 100 100 100 100 100 100 Panel 2 80 55 58 75 85 71 100 100 100 100 100 100 Heart 1 Panel 1 157 165 166 150 150 158 100 100 95 100 100 99 Panel 2 146 146 148 138 146 145 100 100 100 100 100 100 Heart 3 Panel 1 150 147 163 160 150 154 95 100 100 100 100 99 Panel 2 113 173 162 198 160 161 100 100 100 100 100 100 Tree 3 extracted with n-hexane Heart 4 OD 250 290 265 300 305 282 40 35 15 15 5 22 OD+10 190 215 210 250 210 215 20 0 30 75 65 38 Dried at OD+20 245 250 280 230 335 268 20 0 30 25 45 24 185°C OD*40 210 150 220 265 210 211 95 20 75 25 20 47 Heart 4 OD 270 270 335 245 265 277 95 100 60 90 95 88 ReplicateOD+10 300 205 210 245 280 248 60 95 95 5 45 60 Dried at OD+20 190 210 265 195 195 211 50 95 90 80 95 82 185°C OD*40 200 245 225 220 245 227 80 95 95 85 100 91 Heart 5 OD 215 260 300 225 245 245 75 80 60 90 50 71 OD+10 210 290 205 200 260 233 70 15 85 95 85 70 Dried at OD+20 200 200 210 235 175 204 90 100 15 75 60 68 185°C OD+40 270 195 215 200 205 217 20 40 30 95 80 53 Tree 3 extracted with n-hexane after drying Heart 4 OD*40 250 240 225 225 180 224 100 70 90 75 55 78 Dried OD+40 280 250 290 270 320 282 90 100 45 95 85 83 at OD*40 185 215 210 240 205 211 100 100 70 80 55 81 185°C OD+40 215 240 225 295 230 241 80 5 75 100 45 61 Tree 3 extracted with n-hexane after sandin g Heart 4 OD+40 315 200 220 180 240 231 80 95 65 70 90 80 Dried at OD+40 195 150 210 175 190 184 95 100 100 90 80 93 185°C OD+40 80 80 80 164 Supplementary Table 1 8 - 2 Bond-quality evaluations of panels made from veneer from Coastal or Interior Douglas f ir , unextracted or extracted with n-hexane or petroleum ether, and dried as shown. These are detailed measurements taken after the CSA 0-121 boil/dry/boil cycle. See Summary Table 18 for evaluation. Breaking load psi Per cent wood failure Quesnel fir extracted Avg, —-with petroleum ether I Sapwood OD Dried OD+10 6.0 70 103 82 152 93 100 100 100 90 90 96 at OD+20 li85°C OD+40 130 122 114 165 105 127 100 100 100 100 100 100 Heart 1 OD 100 115 115 110 120 114 100 85 80 100 95 92 Dried OD+10 130 150 165 140 160 149 85 90 95 100 85 91 at OD+20 155 115 160 145 130 141 70 100 80 100 80 86 185°C OD+40 95 120 130 80 130 111 100 80 85 95 95 91 Heart 3 OD 150 170 142 152 133 149 100 100 100 100 100 100 Dried OD+40 142 96 102 150 128 124 100 95 100 100 100 99 at OD+20 147 145 130 160 165 149 85 100 100 100 100 97 185°C OD+40 145 128 116 110 95 119 25 80 30 35 35 41 Quesnel fir unextracted oven-dried at 107°C Sapwood Panel 1 45 67 95 86 83 75 100 75 80 45 100 80 Panel 2 80 100 102 73 88 89 55 75 80 90 90 78 Heart 1 Panel 1 120 145 122 142 185 143 100 100 100 95 100 99 Panel 2 145 128 144 143 140 140 95 100 95 95 95 96 Heart 3 Panel 1 180 122 222 274 172 194 100 95 100 100 100 99 Panel 2 165 165 i 145 137 163 155 90 100 100 100 100 98 Coast fir extracted ! with n-hexane Sapwood OD 75 70 65 80 75 73 100 100 100 100 100 100 Dried OD+10 85 75 65 75 85 77 100 100 100 90 100 98 at OD--20 65 75 70 75 60 69 100 95 100 100 100 99 185°C ODf40 65 75 65 60 60 65 85 95 100 75 90 89 Heart 1 OD 120 140 175 155 130 144 100 100 100 100 100 100 Dried OD+10 185 125 170 125 150 151 100 100 100 100 100 100 at OD+20 135 170 145 205 150 161 100 100 100 100 100 100 185°C OD+40 110 135 110 120 130 121 100 100 100 100 100 100 C O N T I N U E D 165 Supplementary Table 1 8 - 2 Continued Breaking load psi Per cent wood failure Avg. Avg. Heart 3 OD 180 175 115 180 225 175 100 95 100 90 95 96 Dried OD+10 155 160 110 115 150 138 100 100 100 100 100 100 at OD+20 140 165 140 170 135 150 100 100 100 100 100 100 185°C OD+40 165 140 140 150 125 144 100 100 100 95 100 99 Coast fir ', unextracted, oven-dried at 107°C Sapwood Panel 1 226 263 240 266 237 244 100 100 95 100 100 99 Panel 2 130 98 80 57 82 89 100 100 100 100 100 100 Heart 1 Panel 1 150 175 163 165 160 161 100 100 100 100 100 • 100 Panel 2 140 140 145 148 178 150 80 100 100 100 100 . 96 Heart 3 Panel 1 65 60 148 125 145 108 100 100 90 100 100 98 Panel 2 205 220 168 160 207 220 100 100 100 100 85 97 Tree 3 extracted with n-hexane Heart 4 OD 205 245 215 250 255 234 80 15 70 10 0 35 Dried OD+10 210 195 195 170 155 185 15 5 55 75 5 31 at OD+20 185 200 190 180 185 188 0 0 5 25 15 9 185°C OD+40 220 200 225 200 220 213 25 40 35 50 75 49 Heart 4 OD 285 205 200 235 285 242 30 80 100 95 15 64 Dried OD+10 200 195 220 220 230 213 90 75 5 60 90 64 at OD+20 210 200 160 210 225 201 80 95 30 95 70 74 185°C OD+40 160 175 165 210 230 188 80 85 80 65 30 68 Replicate Heart 5 OD 255 205 140 220 170 198 85 95 85 40 50 71 Dried OD+10 190 250 190 205 215 210 60 55 80 75 60 65 at OD+20 180 190 185 180 185 184 70 60 70 80 70 70 185°C OD+40 210 200 235 175 210 206 80 65 80 95 45 73 Tree 3 i extracted with n-hexane after drying Heart 4 OD+40 195 230 215 195 235 214 65 100 50 100 95 82 Dried OD+40 195 225 280 230 250 236 100 95 80 45 5 75 at OD+40 195 2 10 175 225 200 201 95 80 95 80 95 89 185°C OD+40 255 210 260 245 190 232 70 30 40 75 70 57 Tree 3 < extracted with nrhexane after sanding Heart 4 OD+40 185 205 205 170 170 183 80 95 75 95 80 85 Dried OD+40 175 175 140 170 120 156 70 80 55 80 100 77 at OD+40 95 95 95 185°C 166 S u p p l e m e n t a r y T a b l e 1 9 - 1 B o n d - q u a l i t y e v a l u a t i o n s of pan e l s made f r o m v e n e e r f r o m a C o a s t a l Douglas f i r , not s u s c e p t i b l e to i n a c t i v a t i o n , that was coated w i t h v a r i o u s fatty a c i d s and d r i e d at v a r i o u s t e m p e r a t u r e s . These a r e d e t a i l e d m e a s u r e m e n t s t a k e n a f t e r the c o l d - s o a k c y c l e of C S A 0-121. See S u m m a r y T a b l e 19 f o r e v a l u a t i o n . A c i d and d r y i n g t e m p e r a t u r e L a u r i e 21°C 107°C 150°C 185QC B r e a k i n g l o a d p s i 120 138 144 137 166 141 176 215 220 203 205 204 255 238 242 228 220 237 68 70 55 0 0 39 P e r cent wood f a i l u r e 100 100 95 95 100 98 90 100 100 100 100 98 100 100 100 100 100 100 20 5 0 0 0 5 M y r i s t i c 2l°C 146 196 130 120 155 149 100 100 95 100 100 99 107°C 165 210 157 150 152 167 100 100 95 100 100 99 150°C 175 160 145 185 185 170 100 75 40 85 100 80 185°C 45 110 42 25 90 62 0 15 10 0 10 7 P a l m i t i c 21°C 120 120 147 148 135 134 70 20 90 40 85 61 107°C 165 205 172 170 200 182 100 100 100 95 80 95 150°C 197 180 207 150 135 174 95 90 100 95 100 96 185°C 107 127 50 80 0 73 0 25 10 15 0 10 S t e a r i c 21°C 208 115 130 160 226 167 80 30 55 80 80 65 107OC 165 170 200 162 157 171 75 50 80 30 85 64 150°C 175 126 130 120 168 144 80 95 95 90 100 92 185°C 118 68 106 102 130 105 25 5 0 10 25 13 B e h e n i c 21°C 155 150 170 120 172 107°C 142 185 182 137 194 150°C 165 168 140 132 132 185°C 55 48 74 70 70 153 50 35 70 20 70 49 168 45 25 50 75 35 46 147 55 45 25 90 80 59 63 0 5 0 0 5 2 C o n t r o l 21°C 145 140 140 125 u n t r e a t e d 107°C 167 186 125 122 150°C 252 228 227 173 185°C 182 150 163 175 A b i e t i c 21°C 143 145 145 153 107°C 180 220 215 200 150°C 134 136 190 170 185°C 125 135 168 135 137 137 100 100 100 100 100 100 187 155 100 100 100 100 100 100 150 206 100 100 95 100 100 99 126 159 45 100 85 100 75 81 170 151 100 100 100 100 100 100 192 201 100 100 100 100 100 100 142 154 80 90 100 100 100 94 138 140 90 85 80 80 85 84 Hexane- 21°C 150 154 135 182 180 160 100 95 95 100 100 98 t r e a t e d 167 Supplementary Table 1 9 - 2 Bond-quality evaluations of panels made from veneer from a Coastal Douglas fir , not susceptible to inactivation, that was coated with various fatty acids and dried at various temperatures. These are detailed measurements taken after the boil/dry/boil cycle of CSA 0-121. See Summary Table 19 for evaluation. Acid and drying B r e a k i n g l o a d p s i  temperature s  Laurie 2 1 ° C 160 160 126 123 173 107°C 187 184 167 177 149 150°C 142 220 152 160 152 185°C 47 92 97 52 50 Myristic 2 1 ° C 195 160 95 159 165 107°C 166 166 156 190 165 150°C 87 9 122 115 157 185°C 110 168 163 100 42 Palmitic 21°C 130 122 107 123 138 107°C 165 124 230 182 240 150°C 144 132 135 142 130 185°C 149 87 110 106 106 Stearic 21°C 128 184 190 130 127 107°C 175 153 198 210 203 150°C 130 126 120 125 130 1850C 145 146 110 130 112 Behenic 21°C 147 132 145 145 147 107°C 168 145 147 116 175 150°C 132 138 135 150 152 185°C 65 70 37 93 25 Control 21°C 137 126 143 130 132 107°C 192 168 193 200 205 150°C 227 157 192 152 172 185°C 137 167 150 150 163 Abietic 2 1 ° C 130 174 132 125 125 107°C 177 215 175 107 200 150°C 175 130 187 130 135 185°C 147 127 157 152 130 Hexane- 2 1 ° C 141 162 134 183 202 treated Per cent wood failure Avg. Avg. 148 100 90 90 100 100 96 173 100 100 100 100 95 99 165 100 100 100 100 100 100 67 45 20 50 45 55 43 155 95 100 85 95 90 93 169 95 95 95 90 100 95 82 100 100 95 100 40 87 117 25 10 5 10 25 15 124 60 15 40 55 100 54 188 80 100 95 90 75 88 136 100 100 100 95 100 99 112 25 0 5 35 0 13 152 30 60 95 75 60 64 188 95 35 10 80 70 58 126 90 90 100 100 100 96 128 5 5 35 15 15 15 143 10 5 85 40 20 32 150 40 20 40 50 0 30 141 25 75 70 55 35 52 58 0 10 0 5 0 3 134 100 100 100 95 100 99 192 100 100 100 100 100 100 180 100 100 100 100 100 100 153 100 95 85 100 40 84 137 100 100 100 100 100 100 175 100 100 100 100 100 100 151 100 75 95 95 80 89 143 100 90 95 95 85 93 164 95 100 100 100 100 99 Vm L I T E R A T U R E C I T E D 1. Anderson, A . B. I960. Biochemistry of wood extractives. Proceedings, Fifth World For. Cong. , Seattle. 6 pp. 2. . 1962. The influence of extractives on tree properties. II Ponderosa pine (Pinus ponderosa Dougl. ). J . Inst. Wood Sci. No. 10:29-47. 3. 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Soc. meeting, Bremerton, Wash. 15 pp. 18. Buchanan, M . A. , R. V. Sinnett, and J . A. Jappe. 1959. The fatty acids of some American pulpwoods. Tappi 42(7):578-583. 19. Cherches, Kh. A. , I. I. Bardyshev, and Zh. F. Kokhanskaya. 1961. The resin acid composition of rosin obtained from common spruce (Picea excelsa Link. ). Zhur. Priklad. Khim. 34(4):938-94l. (In Russian..) 20. • f a n d o . T. Tkachenko. I960. The resin acids in spruce (Picea ajanensis Fisch. ) resin. Zhur. Priklad. Khim. 33( 10):2381-2383. (In Russian. ) 21. Clark, I. T. , J. R. Hicks, and E . E . Harris. 1948. Constituents of extractives from Douglas fir lignin residue. J . Am. Chem. Soc. 70(11):3729-3731. 22. Clermont, L . P. 1961. The fatty acids of aspen poplar, basswood, yellow birch and white birch. Pulp Pap. Mag. Can. 62(12):T511-T514. 23. Curr ier , R. A . 1958. High dryer temperatures - do they harm Douglas-fir veneer? For . Prod. J . 8(4): 128-136. 24. Daniels, P . , and C. Enzell. 1962. Paper chromatography of resin acids. Acta Chem. Scand. 16(6): 1530-1532. i 25. deBruyne, N. A . 1962, The action of adhesives. Scientific American 206(4): 114-126. 170 26. deBruyne, N. A . , and R. Houwink. 1951. Adhesion and adhesives. Elsevier Publishing Company, New York. 517 pp. 27. Douglas F ir Plywood Association. I960. Exterior gluing of western larch. Lab. rept. no. 83. 17 pp. 28. Ellefsen, 0. , and O. Langsetmo. I960. Varying timber transport and storage conditions and the influence upon the pitch deposits of the corresponding unbleached pulps. Norsk Skogind. 14( 11):474-478. 29. Erdtman, H. 1949. Heartwood extractives of conifers. Tappi 32_(7):305-310. 30. . 1958. Conifer chemistry and taxonomy of conifers. Fourth International Cong. Biochem. , Vienna. Proc. Vol. II. 285 pp. 31. Freeman, H. G. , and F . F . Wangaard. I960. Effect of wettability of wood on glue-line behaviour of two urea resins. For. Prod. J . Ij0(6):311-315. 32. Gardner, J . A . F . , and G. M . Barton. 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