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Some gluing characteristics of ocotea usambarensis (engl.) Mungúre, Waweru 1988

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SOME GLUING CHARACTERISTICS OF OCOTEA USAMBARENSIS (ENGL.) by W A W E R U M U N G ' U R E B . S c . F o r . , U n i v e r s i t y o f N a i r o b i , K e n y a , 1984 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L 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 M A S T E R O F S C I E N C E in T H E F A C U L T Y O F G R A D U A T E S T U D I E S D E P A R T M E N T O F F O R E S T R Y W e accept this thesis as c o n f o r m i n g to the requi red standard 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 October 1988 ©Waweru M u n g ' u r e , 1988 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. 1 further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of t-p ±£c, 7 ft.V The University of British Columbia Vancouver, Canada Date ? / //  DE-6 (2788) A B S T R A C T The g l u a b i l i t y of a Kenyan t r o p i c a l hardwood, camphor wood (Ocotea usambarensis) was i n v e s t i g a t e d . Four room-temperature c u r i n g r e s i n adhesives, p h e n o l - r e s o r c i n o l formaldehyde (PRF), urea-formaldehyde (UF), p o l y v i n y l - a c e t a t e (PVA) and c a s e i n were used. Machine-planed wood samples were e x t r a c t e d with e i t h e r hot water, 10% s o l u t i o n of sodium hydroxide, alcohol-benzene, s u r f a c e t r e a t e d with 3% n i t r i c a c i d , or l e f t u n t r e a t e d ( c o n t r o l ) b e f o r e g l u i n g . Using a double glue spread of 410.6 g/m2 (85 l b per 1000 f t 2 ) and the manufacturers recommended assembly times of each of the 4 g l u e s , wood b l o c k s approximately 25.4 x 101.6 x 304 mm (1 x 4 x 12 in) were bonded t o g e t h e r . G l u i n g and p r e s s i n g were c a r r i e d out at room temperature (21-24°C) . A p r e s s i n g p r e s s u r e of 1,379 kPa (200 p s i ) was a p p l i e d over a p e r i o d of 24 h. A f t e r c o n d i t i o n i n g , the j o i n t s t r e n g t h and wood f a i l u r e of both the u n t r e a t e d and t r e a t e d b l o c k s were determined by the ASTM standar d glue b l o c k shear t e s t . The b l o c k s bonded wit h PVA and c a s e i n were t e s t e d dry. Block shear specimens f o r PRF were t e s t e d dry, a f t e r c o l d soaking, and b o i l i n g i n water. Blocks bonded with UF were t e s t e d dry and a f t e r c o l d soaking i n water. S t a t i s t i c a l a n a l y s i s showed t h a t s t r e n g t h of adhesion j o i n t s bonded with PVA adhesive was s i g n i f i c a n t l y improved by i i i s u r f a c e t r e a t i n g with weak n i t r i c a c i d , p r i o r t o g l u i n g . However, none of the f o u r wood pre-treatments s i g n i f i c a n t l y improved g l u a b i l i t y of camphor wood with PVA as f a r as wood f a i l u r e i s concerned. Surface treatment of camphor wood with sodium hydroxide s o l u t i o n , and e x t r a c t i o n with alcohol-benzene, p r i o r t o g l u i n g , enhanced i t s g l u a b i l i t y with c a s e i n adhesive. Removal of the a l c o h o l - b e n z e n e - s o l u b l e and sodium h y d r o x i d e - s o l u b l e e x t r a c t i v e s s i g n i f i c a n t l y i n c r e a s e d dry bond s t r e n g t h of the b l o c k s bonded w i t h PRF adhesive. However, on l y the alcohol-benzene e x t r a c t i o n i n c r e a s e d wood f a i l u r e . The c o l d soak treatment g e n e r a l l y reduced the bond s t r e n g t h of b l o c k s bonded with PRF adhesive. Wood f a i l u r e percentage was i n c r e a s e d by the c o l d soak treatment except i n b l o c k s made with sodium h y d r o x i d e - t r e a t e d wood. The b o i l treatment was observed t o reduce bond s t r e n g t h i n a l l the treatments except i n the c o n t r o l . Other than i n the sodium hydroxide treatment,the amount of wood f a i l u r e i n c r e a s e d as a r e s u l t of the b o i l treatment. U n t r e a t e d camphor wood bonded w e l l with UF adhesive. Bond s t r e n g t h was s i g n i f i c a n t l y reduced by c o l d soak treatment. i v TABLE OF CONTENTS ABSTRACT i i TABLE OF CONTENTS i v LIST OF TABLES v i i LIST OF FIGURES i x LIST OF APPENDICES X ACKNOWLEDGEMENT x i 1.0 INTRODUCTION 1 1.1 Wood Products Industry i n Kenya 1 1.2 Scope and O b j e c t i v e of Study 3 2.0 LITERATURE REVIEW 6 2.1 E f f e c t of E x t r a c t i v e s on G l u i n g 6 2.2 E f f e c t s of Chemical Treatment of Wood Surfaces P r i o r t o G l u i n g 14 3.0 MATERIALS AND METHODS 21 3.1 Wood Samples 21 3.2 Wood Adhesives 21 3.2.1 C a s e i n 21 3.2.2 P h e n o l - r e s o r c i n o l - f ormaldehyde 22 3.2.3 Urea-formaldehyde 22 3.2.4 P o l y v i n y l - a c e t a t e 22 3.3 Experimental Design 23 3.4 Experimental Procedure 24 3.4.1 S p e c i f i c g r a v i t y d e t e r m i n a t i o n 24 3.4.2 Wood pH d e t e r m i n a t i o n 25 3.4.3 T o t a l e x t r a c t i v e s content determination..25 3.5 P r e l i m i n a r y Experiments 25 V 3.6 T r e a t i n g of Wood Samples P r i o r t o G l u i n g 26 3.6.1 E x t r a c t i o n with alcohol-benzene 26 3.6.2 E x t r a c t i o n w i t h hot water 27 3.6.3 Surface treatment with n i t r i c a c i d 28 3.6.4 Surface treatment w i t h sodium hydroxide s o l u t i o n 29 3.7 Main Experiment 29 3.7.1 Adhesive a p p l i c a t i o n , p r e s s i n g and c o n d i t i o n i n g of t e s t j o i n t s 30 3.7.2 P r e p a r a t i o n of b l o c k shear specimens 31 3.7.3 T e s t i n g procedure 32 3.7.3.1 Dry t e s t 32 3.7.3.2 C o l d soak t e s t 32 3.7.3.3 B o i l t e s t 33 3.8 S t a t i s t i c a l A n a l y s i s 33 4.0 RESULTS AND DISCUSSION 34 4.1 Wood C h a r a c t e r i z a t i o n 34 4.2 G l u i n g w i t h P o l y v i n y l - a c e t a t e (PVA) Adhesive.... 35 4.2.1 Dry t e s t : Bond shear s t r e n g t h and wood f a i l u r e p ercent 35 4.3 G l u i n g w i t h C a s e i n Adhesive 38 4.3.1 Dry t e s t : Bond shear s t r e n g t h and wood f a i l u r e p ercent 38 4.4 G l u i n g with P h e n o l - R e s o r c i n o l Formaldehyde Adhesive 42 4.4.1 Dry t e s t : Bond shear s t r e n g t h and wood f a i l u r e percent 42 4.4.2 C o l d soak t e s t : Bond shear s t r e n g t h and wood f a i l u r e p ercent 44 4.4.3 B o i l t e s t : Bond shear s t r e n g t h and wood f a i l u r e percent 45 v i 4.6 Comparison of Bond Strength T e s t s f o r Wood Blocks Bonded with P h e n o l - r e s o r c i n o l Formaldehyde Adhesive 47. 4.6.1 General d i s c u s s i o n on g l u i n g camphor wood with p h e n o l - r e s o r c i n o l formaldehyde adhesive 4 9 4.7 G l u i n g w i t h Urea Formaldehyde 51 4.7.1 Dry t e s t : Shear s t r e n g t h and wood f a i l u r e percent 52 4.7.2 C o l d soak t e s t : Shear s t r e n g t h and wood f a i l u r e percent 52 5.0 SUMMARY AND CONCLUSION 54 REFERENCES 57 v i i L I S T OF T A B L E S Table Page 1 Type of t e s t s 61 2 Formulation of glues and g l u i n g c o n d i t i o n s 62 3 T o t a l e x t r a c t i v e s content i n camphor wood 63 4a Average bond s t r e n g t h of b l o c k s bonded wi t h PVA (dry t e s t ) 64 4b Average wood f a i l u r e of b l o c k s bonded with PVA (dry t e s t ) 65 5a A n a l y s i s of v a r i a n c e f o r bond s t r e n g t h o f b l o c k s bonded with PVA (dry t e s t ) 66 5b A n a l y s i s of v a r i a n c e f o r wood f a i l u r e o f b l o c k s bonded with PVA (dry t e s t ) 66 6 S t a t i s t i c a l r a n k i n g by Duncan's m u l t i p l e range t e s t f o r bond s t r e n g t h and wood f a i l u r e of b l o c k s bonded with PVA 67 7a Average bond s t r e n g t h of b l o c k s bonded wi t h c a s e i n (dry t e s t ) 68 7b Average bond s t r e n g t h o f b l o c k s bonded with c a s e i n (dry t e s t ) 69 8a A n a l y s i s o f v a r i a n c e f o r bond s t r e n g t h o f b l o c k s bonded with c a s e i n (dry t e s t ) 70 8b A n a l y s i s o f v a r i a n c e f o r wood f a i l u r e o f b l o c k s bonded with c a s e i n (dry t e s t ) 70 9 S t a t i s t i c a l r a n k i n g by Duncan's M u l t i p l e Range t e s t f o r bond s t r e n g t h and wood f a i l u r e of b l o c k s bonded with c a s e i n 71 10a Average bond s t r e n g t h of b l o c k s bonded wi t h PRF (dry t e s t ) 72 10b Average wood f a i l u r e of b l o c k s bonded wi t h PRF (dry t e s t ) 73 11a /Analysis of v a r i a n c e f o r bond s t r e n g t h of b l o c k s bonded wi t h PRF (dry t e s t ) 74 l i b A n a l y s i s o f v a r i a n c e f o r wood f a i l u r e o f b l o c k s bonded with PRF (dry t e s t ) 74 v i i i 12a Average bond s t r e n g t h of b l o c k s bonded with PRF ( c o l d soak t e s t ) 75 12b Average wood f a i l u r e of b l o c k s bonded with PRF ( c o l d soak t e s t ) 76 13a A n a l y s i s of v a r i a n c e f o r bond s t r e n g t h of b l o c k s bonded with PRF ( c o l d soak t e s t ) 77 13b /Analysis of v a r i a n c e f o r wood f a i l u r e of b l o c k s bonded with PRF ( c o l d soak t e s t ) 77 14a Average bond s t r e n g t h of b l o c k s bonded with PRF ( b o i l t e s t ) 78 14b Average wood f a i l u r e of b l o c k s bonded with PRF ( b o i l t e s t ) 79 15a A n a l y s i s of v a r i a n c e f o r bond s t r e n g t h of b l o c k s bonded with PRF ( b o i l t e s t ) 80 15b A n a l y s i s of v a r i a n c e f o r wood f a i l u r e of b l o c k s bonded with PRF ( b o i l t e s t ) 80 16 S t a t i s t i c a l r a n k i n g by Duncan's M u l t i p l e Range t e s t f o r bond s t r e n g t h and wood f a i l u r e of b l o c k s bonded wi t h PRF 81 17 Comparison of bond s t r e n g t h t e s t r e s u l t s o f b l o c k s bonded with PRF 82 18a Average bond s t r e n g t h o f b l o c k s bonded wi t h UF (dry t e s t ) 83 18b Average wood f a i l u r e of b l o c k s bonded wi t h UF (dry t e s t ) 83 19a Average bond s t r e n g t h o f b l o c k s bonded with UF ( c o l d soak t e s t ) 84 19b Average wood f a i l u r e o f b l o c k s bonded with UF ( c o l d soak t e s t ) 84 20 Summary of bond s t r e n g t h and wood f a i l u r e r e s u l t s 85 i x L I S T OF F I G U R E S F i g u r e Page 1 Average bond s t r e n g t h and wood f a i l u r e of wood f a i l u r e of b l o c k s bonded with PVA (dry t e s t ) 86 2 Average bond s t r e n g t h and wood f a i l u r e of b l o c k s bonded with c a s e i n (dry t e s t ) 87 3 Average bond s t r e n g t h and wood f a i l u r e of b l o c k s bonded with PRF (dry t e s t ) 88 4 Average bond s t r e n g t h and wood f a i l u r e o f b l o c k s bonded with PRF ( c o l d soak t e s t ) 89 5 Average bond s t r e n g t h and wood f a i l u r e of b l o c k s bonded with PRF ( b o i l t e s t ) 90 6 Bond s t r e n g t h and wood f a i l u r e of u n e x t r a c t e d b l o c k s bonded with PVA/ c a s e i n , PRF and UF adhesives (dry t e s t ) 91 7 Bond s t r e n g t h and wood f a i l u r e o f hot water e x t r a c t e d b l o c k s bonded with PVA, c a s e i n , and PRF adhesives (dry t e s t ) 92 8 Bond s t r e n g t h and wood f a i l u r e of n i t r i c a c i d t r e a t e d b l o c k s bonded with PVA, c a s e i n and PRF adhesives (dry t e s t ) 93 9 Bond s t r e n g t h and wood f a i l u r e o f NaOH t r e a t e d b l o c k s bonded wi t h PVA, c a s e i n and PRF adhesives (dry t e s t ) 94 10 Bond s t r e n g t h and wood f a i l u r e o f a l c o h o l -benzene e x t r a c t e d b l o c k s bonded wi t h PVA, c a s e i n and PRF adhesives (dry t e s t ) 95 11 Form and dimensions of b l o c k shear t e s t specimen 96 12 Shearing t o o l 97 X L I S T OF A P P E N D I C E S APPENDIX I. Species description 98 APPENDIX I I . ASTM standard, D 905-81 99 APPENDIX I I I . ASTM standard, 104 x i ACKNOWLEDGEMENTS I wish t o express my s i n c e r e g r a t i t u d e t o Dr. L. Paszner who was my t h e s i s s u p e r v i s o r . His p r o f e s s i o n a l and under-s t a n d i n g guidance d u r i n g my graduate t r a i n i n g and t h e s i s p r e p a r a t i o n i s g r a t e f u l l y acknowledged. S p e c i a l thanks are due to Dr. J.D. B a r r e t t f o r h i s constant a s s i s t a n c e and numerous h e l p f u l suggestions through-out the course of my study. The v a l u a b l e a d v i c e o f f e r e d by Dr. S. Avramidis d u r i n g the p r e p a r a t i o n of t h i s t h e s i s i s t h a n k f u l l y noted. Thanks are expressed t o Dr. A. Kozak and Dr. P. M a r s h a l l f o r t h e i r a d v i c e on the s t a t i s t i c a l a n a l y s i s . A p p r e c i a t i o n s are a l s o due t o my f e l l o w students e s p e c i a l l y , Agusto Quide, Ben Dawson-Andoh and Simon E l l i s f o r the l i v e l y d i s c u s s i o n s we had i n the course of p r e p a r i n g t h i s t h e s i s . The f i n a n c i a l b a c k i n g of Canadian I n t e r n a t i o n a l Development Agency and Kenyan Government, a l s o made the study p o s s i b l e . S p e c i a l thanks are due t o my wife, Serah Wangui, who has p a t i e n t l y endured my absence from Kenya f o r two y e a r s . F i n a l l y , t o those who I d i d not mention but who, o t h e r -wise, deserve t o be remembered, I a l s o send my s i n c e r e g r a t i t u d e . 1 1.0 I N T R O D U C T I O N 1.1 Wood Products Industry i n Kenya The demand f o r wood products i n Kenya has been r i s i n g r a p i d l y and w i l l continue t o r i s e i n the f u t u r e . A c c o r d i n g t o FAO (10) estimates of the consumption of i n d u s t r i a l roundwood, i n Kenya, i s expected t o r i s e from 740,000 m^ to 1.067 m i l l i o n m^ by the year 2,000. These f i g u r e s i n d i c a t e a c o n t i n u i n g r a p i d i n c r e a s e i n the volume of domestic consump-t i o n of wood pr o d u c t s . The growth of wood products consumption i n Kenya i s a t t r i b u t a b l e t o a r a p i d p o p u l a t i o n growth, estimated at an annual r a t e of 4%, and the i n c r e a s i n g per c a p i t a consumption of wood and wood products, as a r e s u l t of a g e n e r a l improve-ment i n the standard of l i v i n g . To meet t h i s r i s i n g demand f o r wood products, w i t h i n the c o n s t r a i n t of a f i x e d f o r e s t l a n d base, two op t i o n s open t o the Kenyan government are: a more i n t e n s i v e f o r e s t management to maximize y i e l d from the a v a i l a b l e f o r e s t l a n d and more r a t i o n a l and e f f i c i e n t u t i l i z a t i o n of the a v a i l a b l e wood. Over the past two decades, c o n s i d e r a b l e measures of s i l v i c u l t u r a l manipulations of the growing t r e e s stock has been implemented i n the country. However, the improvement of the e f f i c i e n c y of timber c o n v e r s i o n and the u t i l i z a t i o n of wood p r o c e s s i n g r e s i d u e s has not been adequately addressed. Due to the h i g h demand f o r wood products, the l a r g e o l d -growth f o r e s t i n Kenya i s being r a p i d l y d e p l e t e d . T h i s has 2 r e s u l t e d i n a decrease i n the a v a i l a b i l i t y of s o l i d s t r u c t u r a l timber, e s p e c i a l l y f o r hardwoods. Thus the f u t u r e of the wood i n d u s t r y , i n Kenya, almost c e r t a i n l y l i e s with the g r e a t e r use of r e c o n s t i t u t e d wood pr o d u c t s . As the i n d u s t r y s h i f t s more towards r e c o n s t i t u t e d products t h e r e w i l l be an i n c r e a s i n g l y g r e a t e r use of adhesives t o convert second-growth timber i n t o s e r v i c e a b l e p r o d u c t s . G l u i n g i s one means by which the wood-products i n d u s t r i e s f i l l the gap between market needs and wood supply. I f the t r e e s are not long enough, s h o r t e r p i e c e s are end-j o i n t e d i n t o longer p i e c e s ; i f the wood i s not wide enough, narrow p i e c e s are edge-glued i n t o wider m a t e r i a l ; i f the wood i s of low q u a l i t y , the knots and other n a t u r a l d e f e c t s are cut out and the remaining p i e c e s are glued t o g e t h e r (34). The q u a l i t y of wood products such as plywood, laminated timber, and p a r t i c l e b o a r d , and the performance of glu e d j o i n t s i n such manufactured items as wood f u r n i t u r e depend upon the success of glue bond formation (15) . Bonding of wood with glue i s a complex process, because the q u a l i t y of a g l u i n g o p e r a t i o n i s dependent on a l a r g e number of f a c t o r s . The f a i l u r e t o p r o p e r l y c o n t r o l any one of these f a c t o r s can r e s u l t i n a d e f e c t i v e or weakened glue j o i n t . The cause of f a u l t y j o i n t s may be c a t e g o r i z e d as r e l a t e d t o : (i) the k i n d of wood and i t s p r e p a r a t i o n p r i o r t o g l u i n g ; ( i i ) the type, q u a n t i t y and q u a l i t y of the adhesive; 3 ( i i i ) the c o m p a t i b i l i t y of the g l u i n g process with the wood and adhesive used; (iv) j o i n t design, assembly time and clamping p r e s s u r e ; and (v) post-treatment or exposure c o n d i t i o n s of the f i n i s h e d glue j o i n t . A number of these f a c t o r s are i n t e r r e l a t e d such t h a t a change i n one may r e q u i r e a change i n another. The e f f e c t of these f a c t o r s on a glu e d j o i n t v a r i e s from adhesive t o adhesive (10). In bonding wood with adhesives one must be aware t h a t wood i s not a uniform substance, but a complex m a t e r i a l t h a t v a r i e s s i g n i f i c a n t l y i n many of i t s p r o p e r t i e s and i t would be a mere chance i f the same bonding m a t e r i a l and procedure would be s u i t a b l e f o r the e n t i r e range of wood s p e c i e s . Wood f a c t o r s r e l e v a n t t o good adhesion i n c l u d e ; w e t t a b i l i t y , s u r f a c e t e x t u r e , aging p r i o r t o g l u i n g and s p e c i e s (density, e x t r a c t i v e s , moisture content, and pH). Each of these f a c t o r s p l a y s an important r o l e i n the formation of s t r o n g and durable glue j o i n t s . U s u a l l y , i t i s t h e r e f o r e , d i f f i c u l t t o p i n p o i n t which p l a y s a g r e a t e r r o l e than the ot h e r . Furthermore, some of these f a c t o r s are c l o s e l y r e l a t e d (41, 19) 1.2 Scope and O b j e c t i v e of Study Ocotea usambarensis, commonly known as camphor wood, i s abundant i n the montane r a i n f o r e s t s of Tanzania and Kenya. 4 Camphor wood i s yellow-brown, darkening on exposure t o a i r and has a medium t e x t u r e with marked s t r i p e or r i b b o n f i g u r e on r a d i a l l y sawn f a c e s . The timber works e a s i l y with both power and hand t o o l s . However, i t has a moderate g l u a b i l i t y c h a r a c t e r i s t i c (6). Over the years, g l u i n g d i f f i c u l t i e s have been observed i n Kenya's wood i n d u s t r y when c e r t a i n hardwood s p e c i e s , l i k e camphor wood were used f o r composite products and i n f u r n i t u r e making. There are r e p o r t s of g l u e - j o i n t delamina-t i o n s even f o r j o i n t s made u s i n g k i l n d r i e d lumber. Thus, wood moisture content i s not the s o l e determining f a c t o r of a s t r o n g durable glue bond. Adhesion, and hence s t r e n g t h of the glue bonds, i s a f f e c t e d by the s u r f a c e p r o p e r t i e s of the s u b s t r a t e . In the case of wood the s u r f a c e c h a r a c t e r i s t i c s t h a t may a f f e c t glue bond formation are q u i t e complex. One of the f a c t o r s t h a t appears t o a f f e c t adhesion i s the amount and type of extraneous components present i n the wood (15). No formal study has been c a r r i e d out to i n v e s t i g a t e the s p e c i f i c nature of the e x t r a c t i v e s present i n Kenyan hardwoods and t h e i r probable e f f e c t s on adhesion. The main o b j e c t i v e of t h i s study i s t o determine i f any of the e x t r a c t i v e s removed by v a r i o u s s o l v e n t s c o n t r i b u t e s t o the adhesion problems i n camphor wood.^ 1 The q u a l i t a t i v e a n a l y s i s of the v a r i o u s e x t r a c t i v e s present i n camphor wood i s beyond the scope of t h i s study. 5 The study proposes a h y p o t h e s i s t h a t chemical treatment of camphor wood s u r f a c e s with 1 0 % sodium hydroxide s o l u t i o n , 3 % n i t r i c a c i d , or e x t r a c t i o n with alcohol-benzene, and hot water, p r i o r to g l u i n g , improves glue bond and d u r a b i l i t y . The f o l l o w i n g s h a l l be i n v e s t i g a t e d : (i) the g l u i n g c h a r a c t e r i s t i c s of s o l i d camphor wood (unextracted) samples u s i n g f o u r room temperature c u r i n g adhesives, v i z ; p h e n o l - r e s o r c i n o l formaldehyde (PRF), urea-formaldehyde (UF), p o l y v i n y l - a c e t a t e (PVA), and c a s e i n ; ( i i ) the amount of alcohol-benzene, hot water, c o l d water, and c a u s t i c soda (NaOH) s o l u b l e e x t r a c t i v e s i n camphor wood and the e f f e c t of t h e i r removal on the g l u i n g c h a r a c t e r i s t i c s ; ( i i i ) the e f f e c t of s u r f a c e treatment (oxidation) of camphor wood with weak n i t r i c a c i d s o l u t i o n , on the g l u i n g c h a r a c t e r i s t i c s ; and (iv) the e f f e c t of c o l d water soak and b o i l treatments, b e f o r e t e s t i n g , on the s t r e n g t h of the wood-glue bond. 6 2 . 0 L I T E R A T U R E REVIEW T h i s s e c t i o n covers a s e l e c t e d review of e x i s t i n g l i t e r a t u r e on: (i) e f f e c t s of e x t r a c t i v e s on g l u i n g , and ( i i ) e f f e c t s of chemical treatment of wood s u r f a c e s p r i o r t o g l u i n g . 2.1 E f f e c t of E x t r a c t i v e s on G l u i n g Woods of d i f f e r e n t s p e c i e s vary widely i n the nature and amount of t h e i r e x t r a c t i v e s . E x t r a c t i v e q u a n t i t i e s vary w i t h i n t r e e (24). Heartwood normally has s u b s t a n t i a l l y h i g h e r q u a n t i t i e s of e x t r a c t i v e s than sapwood (13, 39). Many of the t r o p i c a l hardwoods are c h a r a c t e r i z e d by h i g h e x t r a c t i v e content (39). Isenberg et al. (25) i n t h e i r study of the extraneous components of American pulpwoods, s u b d i v i d e d the t o t a l substance of the t r e e i n t o f o u r groups: (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 , l i g n i n and sometimes s m a l l amounts of p e c t i c substances and m i n e r a l matter; ( i i ) the e x t r a c t i v e s which are removable by c o l d water and/or one or more of n e u t r a l s o l v e n t s such as acetone, ether, a l c o h o l s , benzene, petroleum ether, c h l o r o f o r m or methylene c h l o r i d e ; 7 ( i i i ) substances which though not p a r t of the c e l l w a l l , but are not r e a d i l y removable by s o l v e n t s , such 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 or s i l i c a ; and (iv) s e c r e t i o n s of the l i v i n g t r e e such as r e s i n s . In t h i s t h e s i s , the term e x t r a c t i v e ( s ) r e f e r s t o substances i d e n t i f i e d under ( i i ) and (iv) above, t h a t i s , extraneous m a t e r i a l or s e c r e t i o n s of the l i v i n g t r e e . G l u i n g d i f f i c u l t i e s have been n o t i c e d i n wood i n d u s t r i e s when c e r t a i n s p e c i e s of wood, with h i g h e x t r a c t i v e content, e.g. t r o p i c a l hardwoods, are used f o r r e c o n s t i t u t e d wood pro d u c t s . R e s u l t s from s e v e r a l e m p i r i c a l s t u d i e s p o i n t out t h a t the r o l e of e x t r a c t i v e s may some times be very important i n the g l u i n g of wood (15, 17, 28, 39). Troop and Wangaard (45) i n v e s t i g a t e d the g l u i n g p r o p e r t i e s of twenty-nine t r o p i c a l American woods i n a d d i t i o n t o Burma teak and domestic white oak. R e s o r c i n o l and phenol-r e s o r c i n o l adhesives were employed i n the study. These two types of adhesives were 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 white oak and Burma teak. The g e n e r a l t r e n d was t h a t of i n c r e a s i n g j o i n t s t r e n g t h and d e c r e a s i n g wood f a i l u r e with i n c r e a s e i n s p e c i f i c g r a v i t y . However, some anomalous r e s u l t s were a l s o o btained. These suggested some i n t e r f e r e n c e of wood c o n s t i t u e n t s with the adhesive i n c e r t a i n s p e c i e s . They p o s t u l a t e d t h a t such i n t e r f e r e n c e c o u l d be the r e s u l t of d e f e c t i v e s u r f a c i n g or due to the 8 c h a r a c t e r of chemical components, such as gums, r e s i n s , o i l s , and waxes which occur i n v a r y i n g amounts as e x t r a c t i v e s i n many woods. Narayanamurti (35) concluded t h a t the d i s t r i b u t i o n of e x t r a c t i v e s v a r i e s both v e r t i c a l l y and h o r i z o n t a l l y i n a t r e e . He p o i n t s out t h a t e x t r a c t i v e s 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 shrinkage of wood, and, at h i g h temperatures may have other e f f e c t s . T h e i r 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 importance. Western l a r c h (Larix occidentalis) u s u a l l y e x h i b i t s , on the s u r f a c e of machined wood, a sugary exudate. The q u a l i t y of glue bonds ob t a i n e d with 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 type p h e n o l i c r e s i n adhesive, i s i n f l u e n c e d t o a markable extent by the amount of t h i s exudate. Plywood panels made from veneers e x h i b i t i n g heavy d e p o s i t s develop glue bonds which do not meet the i n d u s t r y standard 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 decreased (5). Narayanamurti et al. (36) r e p o r t on the i n f l u e n c e of e x t r a c t i v e s on the s e t t i n g of adhesives. The e f f e c t of v a r i o u s e x t r a c t i v e s from Acacia catechu and Tectona grandis (teak) on the g e l a t i o n time and r i g i d i t y modulus of animal glue and A e r o l i t e , an urea-formaldehyde r e s i n , were i n v e s t i -gated. They concluded t h a t e x t r a c t i v e s a f f e c t the v i s c o s i t y and r i g i d i t y of g l u e . The e f f e c t may vary from glue to glue and from s p e c i e s to s p e c i e s . The e f f e c t s of teak e x t r a c t i v e s were more pronounced than those of the Acacia s p e c i e s . 9 Hancock (21) s t u d i e d the i n f l u e n c e of n a t i v e f a t t y a c i d s on the formation of glue bonds with heat t r e a t e d D o u g l a s - f i r veneers. He noted t h a t heat i n a c t i v a t e d the veneer, thus forming a weak glue bond. He p o s t u l a t e d t h a t , the removal of water from wood, and the a p p l i c a t i o n of heat, permits the m i g r a t i o n of f a t t y a c i d s onto the wood s u r f a c e . The f a t t y a c i d s reduce the w e t t a b i l i t y of veneer and a l s o a f f e c t r a t e and depth of p e n e t r a t i o n of glu e . Chugg and Gray (17) i n a study, u s i n g Afrormosia elata wood, r e p o r t t h a t e x t r a c t i v e s i n h i b i t the s e t t i n g of most adhesives, p a r t i c u l a r l y animal glue, c a t a l y s e d phenol-formaldehyde, and p o l y v i n y l a c e t a t e . E x t r a c t i v e s a l s o lower the s u r f a c e t e n s i o n of the wood and reduce w e t t a b i l i t y , which i s e s s e n t i a l f o r a s t r o n g glue bond. Goto et al. (20) i n v e s t i g a t e d the g l u i n g of t r o p i c a l woods. They concluded t h a t the r e l a t i o n s h i p between the glue j o i n t s t r e n g t h and percentage of e i t h e r c o l d or hot water-s o l u b l e e x t r a c t i v e s was not s i g n i f i c a n t . However, glue j o i n t s t r e n g t h i n c r e a s e d with the decrease of percentage of ether s o l u b l e e x t r a c t i v e s , i f the e f f e c t of s p e c i f i c g r a v i t y i s excluded. They a l s o noted the value of pH and percentage e x t r a c t had l e s s important e f f e c t s on the glue j o i n t s t r e n g t h than w e t t a b i l i t y and s p e c i f i c g r a v i t y . Kawamura (30) r e p o r t s on the i n f l u e n c e of e x t r a c t s from kapur wood (Dryobalonops lanceolata) i n the c u r i n g of uns a t u r a t e d p o l y e s t e r r e s i n v a r n i s h . C e r t a i n p o r t i o n s of the e x t r a c t i v e s were shown t o impede the p o l y m e r i z a t i o n of the 10 p o l y e s t e r r e s i n v a r n i s h . On the other hand, other p o r t i o n s of the kapur wood e x t r a c t i v e s had no i n h i b i t o r y e f f e c t . Sakuno and Goto (40) i n t h e i r study of t h i r t y s i x s p e c i e s r e p o r t t h a t s p e c i f i c glue j o i n t s t r e n g t h was s i g n i f i -c a n t l y c o r r e l a t e d with percent ether e x t r a c t , f o r u r e a -formaldehyde, f o r woods of s p e c i f i c g r a v i t y 0.8 and l e s s . There was no s i g n i f i c a n t c o r r e l a t i o n (at 5 percent l e v e l of s i g n i f i c a n c e ) between glue j o i n t s t r e n g t h and e t h e r e x t r a c t s percent f o r wood s p e c i e s with s p e c i f i c g r a v i t y h i g h e r than 0.8. Imamura et al. (26) s t u d i e d the e f f e c t of wood e x t r a c -t i v e s on g l u i n g and c o a t i n g of kapur wood {Dryobalanops spp.). They a l s o noted t h a t , n-hexane and e t h e r - s o l u b l e e x t r a c t i v e s i n h i b i t e d the g l u i n g a b i l i t y of p h e n o l i c r e s i n . F u r t h e r , the e x t r a c t i v e s i n h i b i t e d the c u r i n g of u n s a t u r a t e d p o l y e s t e r r e s i n v a r n i s h , as w e l l . As a l r e a d y noted by Kawamura (30), the i n h i b i t i n g e f f e c t was shown by only c e r t a i n p o r t i o n s of the e x t r a c t i v e s . O n i s h i and Goto (37) i n v e s t i g a t e d the i n f l u e n c e of water (hot and cold) and alcohol-benzene s o l u b l e wood e x t r a c t i v e s on the g e l a t i o n time of urea-formaldehyde and the compressive s t r e n g t h of s e t t i n g m a t e r i a l . The g e l a t i o n time of urea-formaldehyde, t o which wood e x t r a c t i v e s were added, i n c r e a s e d with the i n c r e a s e d amount of hot and c o l d w a t e r - s o l u b l e e x t r a c t i v e s . For c o l d water e x t r a c t i v e s the g e l a t i o n time decreases with decrease i n pH. Alcohol-benzene s o l u b l e 11 e x t r a c t i v e s a l s o a f f e c t e d the g e l a t i o n time of urea-formaldehyde, though t o a l e s s e r extent than water e x t r a c t . Wellons and Krahmer (47) analyzed a random assortment of delaminated e x t e r i o r hardwood plywoods with the aim of d e t e r -mining the causes f o r d e l a m i n a t i o n . They s t a t e t h a t t h e r e are s e v e r a l f a c t o r s t h a t c o u l d cause such d e l a m i n a t i o n . I f the adhesive f a i l e d t o wet and pe n e t r a t e the wood, a weak and l e s s durable glue bond would be formed. A l s o , the adhesive may have bonded t o a t h i n l a y e r of e x t r a c t i v e s t h a t l a t e r c o u l d be leached from the g l u e l i n e , hence the d e l a m i n a t i o n . Weak g l u e l i n e s might a l s o occur i f the e x t r a c t i v e s at the wood s u r f a c e d i s s o l v e i n t o the adhesive and e i t h e r a c c e l e r a t e i t s cure or make i t too v i s c o u s t o p e n e t r a t e the wood s t r u c t u r e . Anaike et al. (3) r e p o r t on the i n h i b i t o r y e f f e c t of kapur wood e x t r a c t s on the g e l a t i o n of the urea r e s i n adhesives. Water e x t r a c t s were more e f f i c i e n t i n r e t a r d i n g the g e l a t i o n of urea and urea-melamine r e s i n s f o l l o w e d by methanol e x t r a c t s . They delayed the g e l a t i o n of the urea r e s i n more e f f e c t i v e l y than t h a t of the urea-melamine r e s i n . E t h e r and n-hexane e x t r a c t s had l i t t l e or no i n h i b i t o r y e f f e c t . J a i n et al. (28) observed t h a t e x t r a c t i v e s p l a y a very important r o l e i n g l u i n g of Shorea robusta (sal) with u r e a -formaldehyde and phenol-formaldehyde r e s i n s . The i n h i b i t o r y e f f e c t of Taxus mairei heartwood e x t r a c t i v e s on the c u r i n g of the unsatu r a t e d p o l y e s t e r r e s i n 12 has been r e p o r t e d by Lee et al. (27). The methanol e x t r a c t i t s e l f and the e t h e r - s o l u b l e , the w a t e r - s o l u b l e and the w a t e r - i n s o l u b l e f r a c t i o n s d e r i v e d from the methanol e x t r a c t showed an i n h i b i t o r y e f f e c t on the c u r i n g of un s a t u r a t e d p o l y e s t e r r e s i n s , but the n-hexane s o l u b l e f r a c t i o n d i d not. Lee et al. (33) s t u d i e d the i n h i b i t o r y e f f e c t of Diospyros sp heartwood e x t r a c t i v e s on the c u r i n g of the uns a t u r a t e d p o l y e s t e r r e s i n . The methanol e x t r a c t showed an i n h i b i t o r y e f f e c t on the c u r i n g of un s a t u r a t e d p o l y e s t e r r e s i n s . The methanol e x t r a c t was f r a c t i o n a t e d i n t o s e v e r a l f r a c t i o n s . Among these f r a c t i o n s , n-hexane s o l u b l e a c i d , e t h e r - s o l u b l e a c i d and e t h e r - s o l u b l e p h e n o l i c f r a c t i o n s showed an i n h i b i t o r y e f f e c t but n-hexane-soluble n e u t r a l , e t h e r - s o l u b l e n e u t r a l , w a t e r - s o l u b l e and w a t e r - i n s o l u b l e f r a c t i o n s d i d not. Abe and Akimoto (1) i n v e s t i g a t e d the i n s u f f i c i e n t g l u a b i l i t y of kapur wood by s t u d y i n g the e f f e c t of the c u r i n g r e a c t i o n of wood e x t r a c t i v e s on the r e s o l type p h e n o l i c r e s i n . The s t r o n g a c i d and weak a c i d f r a c t i o n s of the et h e r s o l u b l e p a r t and the e t h e r - i n s o l u b l e p a r t of the e t h a n o l -benzene e x t r a c t i v e s showed s t r o n g i n h i b i t o r y e f f e c t s on c u r i n g of the r e s o l r e s i n . However, the e t h e r - s o l u b l e n e u t r a l f r a c t i o n showed no or l e s s e r e f f e c t . R a i s i n g the temperature d u r i n g c u r i n g tended t o reduce the i n h i b i t i o n . Kanazawa et al. (29) r e p o r t e d on the poor g l u a b i l i t y of teak wood with urea r e s i n adhesives. They i n v e s t i g a t e d the e f f e c t s of hot-water e x t r a c t i v e s on the c u r i n g r e a c t i o n of 13 the adhesive. The hot water e x t r a c t , e s p e c i a l l y i t s methanol i n s o l u b l e p a r t , was found to r e t a r d the g e l a t i o n of the urea r e s i n adhesive. Chow and Chunsi (16) examined adhesion s t r e n g t h and wood f a i l u r e r e l a t i o n s h i p s i n wood-glue bonds of s i x Burmeses hardwoods. P h e n o l - r e s o r c i n o l formaldehyde, urea formaldehyde and c a s e i n adhesives were used. They concluded t h a t g l u e -j o i n t shear s t r e n g t h had no s i g n i f i c a n t r e l a t i o n s h i p with the e x t r a c t i v e content of s u b s t r a t e woods. T h i s f i n d i n g i s e s s e n t i a l l y the same as t h a t of Goto et al. (20). Abe and Ono (2) r e p o r t e d on the e f f e c t of a c i d i t y of some t r o p i c a l wood e x t r a c t i v e s on the c u r i n g of r e s o l . E x t r a c t i v e s from kapur and a p i t o n g wood were used i n the study. The r e s u l t s demonstrated t h a t the a c i d i t y of the e x t r a c t i v e s i n t e r f e r e s with the c u r i n g r a t e of r e s o l r e s i n s . Yatagai and Takahashi (48) examined the e f f e c t of wood e x t r a c t i v e s , from 70 t r o p i c a l wood s p e c i e s , on c u r i n g time of u n s a t u r a t e d p o l y e s t e r r e s i n v a r n i s h . E t h y l ether, n-hexane, acetone and methanol were used as s o l v e n t s f o r removal of the e x t r a c t i v e s . The acetone e x t r a c t i v e s had no i n f l u e n c e on the v a r n i s h c u r i n g time. The c u r i n g time of the v a r n i s h was p rolonged by n-hexane e x t r a c t i v e s . Slay et al. (45) i n v e s t i g a t e d the c a t a l y t i c e f f e c t s of e x t r a c t i v e s from p r e s s u r e - r e f i n e d f i b e r s on the g e l time of urea-formaldehyde r e s i n . Six s p e c i e s of wood, b l a c k Tupelo, h i c k o r y , white oak, red oak, sweet-gum and l o b l o l l y pine were used i n the study. T h e i r f i n d i n g s i n d i c a t e t h a t the g e l time 14 of the UF resin was affected by addition of small amounts of extractives. The gel time of the resin-extractive mixture increased exponentially as i t s pH increased. 2.2 Effects of Chemical Treatment of Wood Surfaces Prior to Rapp (45)^ investigated the p o s s i b i l i t y of using various surface treatments to improve the g l u a b i l i t y of lignum v i t a t e (Guaiacum o f f i c i n a l e ) by removal of at least part of the resinous extractives contained i n lignum vitae wood. Among the treatments applied to normal machine-planed lumber were solvents such as carbon tetrachloride, benzene, acetone and alcohol. The most successful treatment was an application of 10% caustic soda solution, wiped on the surface, allowed to remain for 10 minutes, and removed by washing with water. A resorcinol resin was employed. The average re s u l t s are shown below: Gluing Shear strength (psi) Wood f a i l u r e (%) Control (untreated) 1185 ( 8,170 kPa) 22 Washed with NaOH 1770 (12,204 kPa) 30 Sanded; washed with NaOH 2000 (13,790 kPa) 37 Original not seen. Cited from Troop and Wangaard (45). 15 In one s e r i e s of t e s t s the r e s u l t s o b t a i n e d from the combina-t i o n of sanding and c a u s t i c soda treatment averaged 2760 p s i (19,030 kPa) with 56% wood f a i l u r e . In a study c a r r i e d out by Gamble Bros., Inc. (45)3 i t was shown t h a t washing of teak (Tectona grandis) s u r f a c e (contains an o i l y e x t r a c t i v e ) with acetone p r i o r t o g l u i n g with a r e s o r c i n o l adhesive, improved the j o i n t shear s t r e n g t h and i n c r e a s e d wood f a i l u r e . By means of t h i s technique j o i n t s t r e n g t h was i n c r e a s e d from 1025 to 1262 p s i (7,067-8,701 kPa) and wood f a i l u r e from 63 t o 83% i n comparison with u n t r e a t e d c o n t r o l specimens. Troop and Wangaard (45) concluded t h a t Burma teak does not n e c e s s a r i l y r e q u i r e p r e l i m i n a r y treatment b e f o r e g l u i n g with r e s o r c i n o l adhesive. The j o i n t s had an average shear-s t r e n g t h of 2040 p s i (14,065 kPa) and 92% wood f a i l u r e . In a study done at the F o r e s t Products Laboratory (Madison (4)) i t was found t h a t s u r f a c e treatment with 10% c a u s t i c soda improved the g l u a b i l i t y of c e r t a i n American hardwoods. The e n t i r e group of t r e a t e d j o i n t s (13 species) when glu e d with animal glue showed 51% g r e a t e r average s t r e n g t h and 97% more wood f a i l u r e than the u n t r e a t e d j o i n t s of the same s p e c i e s g l u e d under s t a r v e d - j o i n t c o n d i t i o n s . A s i m i l a r t r e n d was observed with c a s e i n g l u e . However, one s p e c i e s (osage-orange) gave s t r i k i n g r e s u l t s . Osage-orange c o n t a i n s a l a r g e amount of e x t r a c t i v e s and i s very d i f f i c u l t O r i g i n a l not seen. C i t e d from Troop and Wangaard (45). t o j o i n with c a s e i n g l u e . Untreated osage-orange wood showed p r a c t i c a l l y no adhesion; the j o i n t s showed an average shear s t r e n g t h of only 294 p s i (2027 kPa) and no wood f a i l u r e . A f t e r treatment with c a u s t i c soda, the average j o i n t s t r e n g t h was over 3000 p s i (20,684 kPa) and the wood f a i l u r e was 35%. Knight, r e p o r t e d by Hancock (22), i n d i c a t e s t h a t i t was at one time common p r a c t i c e t o wipe the s u r f a c e s of many hardwoods with a s o l u t i o n of 10% sodium hydroxide, when u s i n g animal glue, i n order t o improve bond s t r e n g t h . Narayanamurti (35) noted t h a t the e f f e c t of e x t r a c t i v e s on wood g l u i n g i s of s p e c i a l importance. He f u r t h e r noted t h a t improvement of g l u a b i l i t y of heartwood a f t e r e x t r a c t i o n was e v i d e n t . Thomas (44) has shown t h a t removal of a l a r g e p a r t of the e t h e r and benzene-soluble p o r t i o n of the wax present i n the t r o p i c a l wood of determa (Ocotea rubra Mez), caused a c o n s i d e r a b l e i n c r e a s e i n the gluebond q u a l i t y o b t a i n e d with a p h e n o l i c r e s i n . The removal of the e x t r a c t i v e s caused i n change i n the bond q u a l i t y with melamine-formaldehyde as the adhesive. He concluded t h a t a chemical i n c o m p a t i b i l i t y e x i s t s between phenol-formaldehyde and the wax-like substance i n determa and t h a t with the wax removed, a s a t i s f a c t o r y . j o i n t can be o b t a i n e d with phenol-formaldehyde. Hancock (22) showed t h a t the reduced adhesion of oven-d r i e d D o u g l a s - f i r veneer i s p r i m a r i l y the r e s u l t of e x t r a c -t i v e m i g r a t i o n t o the s u r f a c e . He a l s o determined t h a t the 17 acetone or a combination of acetone and methanol/benzene e x t r a c t a b l e f r a c t i o n s were r e s p o n s i b l e f o r the i n h i b i t i o n . Wangaard and Granados (46) i n v e s t i g a t e d the e f f e c t of e x t r a c t i v e s on water-vapor s o r p t i o n by wood. Nine t r o p i c a l hardwoods ranging from 3 to 17% i n e x t r a c t i v e content were used. They found out t h a t t h e r e was no s i g n i f i c a n t r e l a t i o n -s h i p between t o t a l s o r p t i o n and a c c e s s i b i l i t y of bonding s i t e s f o r e i t h e r h i g h or low e x t r a c t i v e content m a t e r i a l . Bryant (14) s t u d i e d the e f f e c t of v a r i o u s chromium complexes (pH 1.95 - 4.05). D o u g l a s - f i r veneer s u r f a c e s were m o d i f i e d f o r the purpose of improving the bond q u a l i t y of the plywood. The treatment of veneers with chromium complex s o l u t i o n s impaired the glue-bond q u a l i t y r a t h e r than improving i t . Few of the plywood panels made with t r e a t e d veneers compared f a v o r a b l y with the c o n t r o l s . He p o s t u l a t e d t h a t the h i g h pH of the t y p i c a l p h e n o l i c adhesive mix used may have rendered the chromium complexes i n e f f e c t i v e as bonding agents, and may have had a d e l e t e r i o u s e f f e c t on the adhesive i t s e l f as judged by the i n c r e a s e i n v i s c o s i t y . When a urea r e s i n was used the r e s u l t s were more encouraging due t o b e t t e r pH c o m p a t i b i l i t y . Chen (15) s t u d i e d the e f f e c t of e x t r a c t i v e removal on adhesion and w e t t a b i l i t y of some t r o p i c a l hardwoods. Machined wood s u r f a c e s of e i g h t t r o p i c a l s p e c i e s were t r e a t e d with a 10% s o l u t i o n of sodium hydroxide, acetone, and alcohol-benzene. A f t e r r e c o n d i t i o n i n g , wood b l o c k s were glue d with urea-formaldehyde and r e s o r c i n o l - f o r m a l d e h y d e 18 r e s i n adhesives. Untreated wood b l o c k s were used as c o n t r o l s . The r e s u l t s i n d i c a t e d t h a t the adhesive j o i n t s t r e n g t h was improved by a l l the treatments i n a l l the sp e c i e s , except one. E x t r a c t i v e removal treatment improved w e t t a b i l i t y and i n c r e a s e d pH of wood i n a l l the s p e c i e s t e s t e d . J a i n et al. (27) s t u d i e d the e f f e c t of e x t r a c t i v e s on g l u i n g of Pinus roxburghii (Chir) from I n d i a . Veneers were s u b j e c t e d t o e x t r a c t i o n with hot water, ether, a l c o h o l -benzene, 1% NaOH s o l u t i o n i n d i v i d u a l l y and a l s o s u c c e s s i v e l y . Plywood panels were made u s i n g the e x t r a c t e d and un e x t r a c t e d ( c o n t r o l ) veneers. Urea-formaldehyde ( c o l d - s e t and hot-set) and phenol-formaldehyde (water-soluble and a l c o h o l - s o l u b l e ) adhesives were used. The r e s u l t s showed t h a t , i n case of c o l d - s e t UF glue, an improvement i n d r y - s t r e n g t h o c c u r r e d i n case of ether, 1% NaOH and e x t r a c t i v e f r e e samples. However, i t i s only i n the case of e t h e r - e x t r a c t e d samples t h a t an improvement i n b o i l t e s t s t r e n g t h was n o t i c e d . With h o t - s e t UF, d e f i n i t e improvements i n case of hot water and eth e r e x t r a c t e d samples were observed i n dry and b o i l - t e s t v a l u e s but the r e s u l t s were b e t t e r with hot water e x t r a c t e d samples. R e s u l t s of g l u i n g with PF (water-soluble) i n d i c a t e d t h a t alcohol-benzene e x t r a c t e d samples and ether e x t r a c t e d samples g l u e d b e t t e r than the c o n t r o l s . In the case of PF ( a l c o h o l -s o l u b l e ) the removal of e x t r a c t i v e s seemed t o abate g l u a b i l i t y . 19 R o f f a e l and Rauch (38) i n v e s t i g a t e d the i n f l u e n c e of e x t r a c t i v e s on the g l u i n g of oak p a r t i c l e s with a l k a l i n e phenol-formaldehyde r e s i n . The r e s u l t s showed t h a t e x t r a c -t i v e s from o l d oak t r e e s are more a c i d i c and e x h i b i t a h i g h e r b u f f e r i n g c a p a c i t y than those from younger t r e e s . In ge n e r a l , e x t r a c t i o n of oak p a r t i c l e s with b o i l i n g water f a v o u r a b l y a f f e c t e d the g l u a b i l i t y of the p a r t i c l e s . E x t r a c -t i o n with 1-n sodium carbonate s o l u t i o n i n s t e a d of water brought about a f u r t h e r improvement i n the g l u a b i l i t y of oak u s i n g a l k a l i n e PF r e s i n . A d d i t i o n of sodium hydroxide (3% r e l a t e d t o dry wood) c o n s i d e r a b l y improved the g l u a b i l i t y of oak p a r t i c l e s . Dougal et al. (18) examined the g l u e l i n e c h a r a c t e r i s t i c s and bond d u r a b i l i t y of southeast A s i a n s p e c i e s a f t e r s o l v e n t e x t r a c t i o n and p l a n i n g of veneers. Veneers of f i v e wood sp e c i e s were e i t h e r planed, e x t r a c t e d with a one percent c a u s t i c s o l u t i o n , or l e f t u n t r e a t e d b e f o r e g l u i n g . Two types of p h e n o l i c adhesives were used. One of t h e i r c o n c l u s i o n s was t h a t , one percent c a u s t i c e x t r a c t i o n f o r 60 seconds, f o l l o w e d by a 60-second r i n s e b e f o r e g l u i n g , darkened the veneer s u r f a c e s and d i d not c o n s i s t e n t l y i n c r e a s e the percentage of wood f a i l u r e . In 1983, K e l l y et al. (31) i n v e s t i g a t e d the e f f e c t s of f i v e s u r f a c e a c t i v a t i n g reagents on the shear s t r e n g t h of bonded s o l i d wood p a n e l s : n i t r i c a c i d , s u l f u r i c a c i d , hydrogen peroxide, potassium p e r s u l f a t e and potassium p e r i o d a t e . F i v e d i f f e r e n t wood s p e c i e s were used i n t h i s 20 study: t h r e e hardwoods and two softwoods. No wood adhesive was used, the reagents a c t e d as c a t a l y s t s f o r a c t i v a t i n g b r i d g i n g m a t e r i a l s such as l i g n i n and h e m i c e l l u l o s e s . The r e s u l t s demonstrated t h a t s o l i d wood panels can be bonded by such a c t i v a t i o n of the wood s u r f a c e . However, the shear s t r e n g t h of the products was h i g h l y dependent on the s u r f a c e a c t i v a t i n g reagent and wood s p e c i e s used. Prolonged n i t r i c a c i d a c t i v a t i o n was shown t o degrade the wood s u b s t r a t e . In summary, wood e x t r a c t i v e s , and p a r t i c u l a r l y the a c i d i c e x t r a c t i v e s , were shown i n the past t o s e r i o u s l y i n t e r f e r e with the s e t t i n g of adhesives. The i n h i b i t o r y e f f e c t was most pronounced on c a s e i n , phenol ( r e s o r c i n o l ) -formaldehyde and l e a s t on urea-formaldehyde. N e u t r a l i z a t i o n with a l k a l i s o l u t i o n s (1-3%) or removal with s u i t a b l e s o l v e n t s was necessary t o o b t a i n a c c e p t a b l y s t r o n g glue bonds. The extent of the i n h i b i t o r y e f f e c t was shown t o be p r o p o r t i o n a l t o the c o n c e n t r a t i o n of a c i d i c e x t r a c t i v e s with even r e l a t i v e l y low c o n c e n t r a t i o n s b e i n g a l s o e f f e c t i v e . 21 3 . 0 M A T E R I A L S AND METHODS 3.1 Wood Samples A i r - d r y samples of camphor wood, Ocotea usambarensis, i n form of sawn lumber with dimensions of 25.4 mm x 101.6 mm x 609.6 mm (1 i n x 4 i n x 24 in) were ob t a i n e d from t h r e e separate timber yards i n N a i r o b i , Kenya. Thus, the samples should r e p r e s e n t the camphor wood p o p u l a t i o n used i n the f u r n i t u r e and j o i n e r y i n d u s t r y i n Kenya. Some of the boards were q u a r t e r sawn while others were f l a t sawn. The samples, on a r r i v a l i n Vancouver, were stacked with 12.7 mm (0.5 in) spacers between, i n a 50 ± 2% r e l a t i v e humidity room [dry bulb 23 ± 1°C (73.4 ± 2°F) having an a i r speed approximately 70 m/min (200 f t / m i n ) ] t o permit c o n t r o l l e d c o n d i t i o n i n g . 3.2 Wood Adhesives Four room-temperature c u r i n g glues were used i n t h i s study. The c a s e i n , 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 (PRF) and ur e a - formaldehyde (UF) r e s i n s were s u p p l i e d by Borden Chemical Company (Canada) L i m i t e d . The p o l y v i n y l - a c e t a t e (PVA) was s u p p l i e d by Crown P a i n t s and B u i l d i n g Products (Kenya) L i m i t e d . 3.2.1 Casein Casco-casein 42-28G i s a premium grade glue t h a t i s r e a d i l y mixed with water. I t i s room c u r i n g and i s 22 recommended f o r i n t e r i o r use. I t complies with the type I I I glue bond requirements of Canadian Standard A s s o c i a t i o n (CSA) 0132.2 M 1977 (8). 3.2.2 Ph 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 Cascophen LT-75 i s a l i q u i d r e s i n which when mixed with a dry powdered hardener, c a t a l y s t FM-282C, produces a phenol-r e s o r c i n o l - f ormaldehyde adhesive t h a t i s room temperature s e t t i n g . Tests i n Borden l a b o r a t o r i e s i n d i c a t e t h a t r e p r e s e n t a t i v e l o t s of t h i s adhesive meet CSA standard 0112.7-1960 (Type 1) s p e c i f i c a t i o n f o r wet use s e r v i c e . I t produces a waterproof and weatherproof bond with wood (8). 3.2.3 Urea-formaldehyde Casco UF 109 with 221 hardener i s a c o l d - s e t t i n g u r e a -formaldehyde glue t h a t cures t o a h i g h l y w a t e r - r e s i s t a n t bond. I t meets the requirements of CSA 0112.5-M1977 f o r type 1 urea r e s i n adhesives (7) . 3.2.4 P o l y v i n y l - a c e t a t e P o l y v i n y l r e s i n emulsions are marketed as milky-white f l u i d s t o be used at room temperature i n the form s u p p l i e d by the manufacturer, normally without a d d i t i o n of separate hardeners. The adhesive s e t s when the water of the emulsion p a r t i a l l y d i f f u s e s i n t o the wood and the e m u l s i f i e d r e s i n c o a g u l a t e s . There i s no apparent chemical c u r i n g r e a c t i o n a s s o c i a t e d with the hardening of t h i s adhesive (41). 2 3 T h e r e s i n e m u l s i o n s t e n d t o c r e e p w h e n j o i n t s a r e s u b j e c t e d t o l o a d s a t t e m p e r a t u r e s a b o v e 4 9 ° C ( 1 2 0 ° F ) f o r s u s t a i n e d p e r i o d s , a n d p o s s e s s o n l y f a i r w a t e r a n d m o i s t u r e r e s i s t a n c e ( 1 9 ) . 3 . 3 E x p e r i m e n t a l D e s i g n T h e e x p e r i m e n t w a s c a r r i e d o u t u s i n g a c o m p l e t e l y r a n d o m i z e d d e s i g n . T h e d e s i g n o f t h e e x p e r i m e n t i n c l u d e d t w o v a r i a b l e s , g l u e t y p e s a n d w o o d . T h e d e s i g n u s e d w a s a s i n d i c a t e d b e l o w : V a r i a b l e s L e v e l s G l u e s F o u r - P V A - C a s e i n - U F - P R F W o o d F i v e - u n e x t r a c t e d w o o d ( c o n t r o l ) - e x t r a c t e d w i t h h o t w a t e r - s u r f a c e t r e a t e d w i t h d i l u t e n i t r i c a c i d - s u r f a c e t r e a t e d w i t h 10% s o d i u m h y d r o x i d e s o l u t i o n - e x t r a c t e d w i t h a l c o h o l -b e n z e n e . R e p l i c a t e s ( a s s e m b l i e s ) T h r e e - ( f o r P V A ) T h r e e - ( f o r c a s e i n ) S i x - ( f o r U F ) N i n e - ( f o r P R F ) . D u p l i c a t e s ( s h e a r b l o c k s / a s s e m b l y ) F i v e T o t a l c o m b i n a t i o n s ( s h e a r b l o c k s ) 4 0 5 ^ T h e t e s t s w e r e c a r r i e d o u t a s i n d i c a t e d i n T a b l e 1 . q O n l y o n e w o o d l e v e l ( u n e x t r a c t e d w o o d ) w a s u s e d w i t h U F g l u e . 3.4 Experimental Procedure 3.4.1 S p e c i f i c gravity determination S p e c i f i c gravity was determined by obtaining green and oven-dry volume of four specimens, each 25 mm x 25 mm x 77 mm (1 i n x 1 i n x 3 in) i n siz e . The specimens were soaked i n a st e e l cylinder f i l l e d with water for 4 days, at 827 kPa (120 psi) to make sure they were water saturated. The length, width and thickness dimensions, of the water saturated specimens, were taken at 3 di f f e r e n t points, the ends and the center of the specimen. Green weight and volume of each specimen was determined. The specimens were then oven-dried at 103 ± 2°C to constant weight. The basic (green) s p e c i f i c gravity of each of the specimen was calculated as follows: Green s p e c i f i c gravity = (cJe'eV^volume* 1 D e n s i t y o f water Where: O.D weight = weight of oven-dry specimen. Green volume = volume of water saturated specimen. The average value of the four specimens was adopted as the s p e c i f i c gravity of camphor wood. 3.4.2 Wood pH determination The sawdust generated during the i n i t i a l cutting of the boards, before gluing, was used for pH determination. 25 Five grams of sawdust was mixed with 50 cm-* of d i s t i l l e d water. The mixture was allowed to stand for 2 h with occasional s t i r r i n g . Then the mixture was f i l t e r e d and the f i l t r a t e used for pH determination using a standard pH meter. Average pH value of f i v e samples (wood sawdust and d i s t i l l e d water) was taken as the pH of camphor wood at room temperature. 3.4.3 Total extractives content determination Again, sawdust generated during the cutti n g of the boards before gluing provided the wood powder that was used i n t h i s part of the study. Three solvents: alcohol-benzene, water, and 1% sodium hydroxide were used. The procedure adopted by ASTM (see Appendix III) was followed when conducting t h i s t e s t . 3.5 Preliminary Experiments To determine the best conditions f o r gluing camphor wood, some preliminary experiments were conducted. Camphor wood blocks approximately 25.4 mm x 101.6 mm x 304.8 mm (1 i n x 4 i n x 12 in) were used i n t h i s part of the study. The blocks were planed down to a thickness of 19 mm (3/4 in) just p r i o r to gluing. Using a double glue spread of 410.6 g/m2 (85 l b per 1000 f t 2 ) and the recommended assembly times of each of the 4 glues, the following gluing conditions were tested: 26 (i) G l u i n g and p r e s s i n g at room temperature, 21-23°C, f o r 24 h u s i n g a p r e s s u r e of 1,379 kPa (200 p s i ) . ( i i ) G l u i n g and p r e s s i n g at room temperature, 21-23°C, f o r 24 h u s i n g under 1,724 kPa (250 p s i ) . For each glue, t h r e e glued stocks were made. F i v e m o d i f i e d (see F i g u r e 11) t e s t specimens were cut from each of the g l u e d b l o c k s . The specimens were t e s t e d i n accordance with S e c t i o n s 8 and 9 of the ASTM standard, D905-81 (Appendix I D • The f i r s t s et of c o n d i t i o n s gave s a t i s f a c t o r y r e s u l t s and was adopted f o r the main experiment. 3.6 T r e a t i n g of Wood Samples P r i o r t o G l u i n g F i v e d i f f e r e n t groups of camphor wood samples were used i n t h i s study. Each group of samples was randomly a s s i g n e d one of the f o l l o w i n g treatments: (i) e x t r a c t i o n with alcohol-benzene; ( i i ) e x t r a c t i o n with hot water; ( i i i ) s u r f a c e treatment with 3% n i t r i c a c i d ; (iv) s u r f a c e treatment with 10% sodium hydroxide s o l u t i o n ; (v) no treatment ( c o n t r o l ) . 3.6.1 E x t r a c t i o n with alcohol-benzene For t h i s treatment a s o l v e n t c o n s i s t i n g of one volume of benzene and two volumes of 95% e t h a n o l was used. The wood samples c o n s i s t e d of machine-planed p i e c e s of 25.4 mm x 101.6 27 mm x 304.8 mm (1 i n x 4 i n x 12 in) i n s i z e . The samples were p l a c e d i n a g l a s s tank a f t e r which the tank was f i l l e d w i th alcohol-benzene s o l u t i o n . The tank was covered with a g l a s s pane and s i l i c o n grease was a p p l i e d a l l around t o ensure t h a t the set up was a i r t i g h t . The samples were allowed t o stand f o r 6 days, at room temperature (21-24°C) , with two renewals of the alcohol-benzene s o l v e n t . A f t e r s i x days the alcohol-benzene s o l u t i o n was r e p l a c e d with methanol and the samples were allowed t o stand f o r 24 h. The methanol was used t o e x t r a c t the alcohol-benzene s o l v e n t from the wood samples. Then the samples were c o n d i t i o n e d u n t i l most or a l l of the two s o l v e n t s mentioned above, had evaporated. One face of each sample was l i g h t l y p l a n ed [1.6 mm ( l / 1 6 t h in) removed] to remove any extraneous m a t e r i a l s t h a t might have migrated from the core t o the s u r f a c e of the sample d u r i n g the c o n d i t i o n i n g p e r i o d . A f t e r t h i s , the samples were planed down t o a t h i c k n e s s of 19 mm (3/4 i n ) . The g l u i n g , c u t t i n g of t e s t specimens and t e s t i n g was c a r r i e d out i n accordance with the method o u t l i n e d e a r l i e r . 3.6.2 E x t r a c t i o n with hot water Machine-planed camphor wood samples, 25.4 mm x 101.6 mm x 609.6 mm (1 i n x 4 i n x 24 in) were used. The samples were p l a c e d i n a water bath c o n t a i n i n g c o l d water and allowed t o soak f o r 24 h. E x t r a c t i o n was c a r r i e d out at 97 ± 2°C f o r 4 8 h, with two changes of water. At the end of t h i s 28 treatment the samples were c o n d i t i o n e d f o r one week i n a c o n d i t i o n i n g chamber set at 80% r e l a t i v e humidity [dry bulb 49 ± 1°C (120 ± 2°F) ] . T h i s step was aimed at e l i m i n a t i n g / r e d u c i n g any m i g r a t i o n of e x t r a c t i v e s from the core t o the wood s u r f a c e , which u s u a l l y occurs due to f a s t d r y i n g of green lumber. The wood samples were c o n d i t i o n e d at 50% [dry bulb 23 ± 1°C (73.4 ± 2°F) ] r e l a t i v e humidity u n t i l the d e s i r a b l e e q u i l i b r i u m moisture content was a t t a i n e d . C o n d i t i o n i n g was f o l l o w e d by p l a n i n g the samples t o a t h i c k n e s s of 19 mm (3/4 in) and c r o s s - c u t t i n g i n t o 304.8 mm (12 in) p i e c e s . The g l u i n g , c u t t i n g of t e s t specimens and t e s t i n g was done f o l l o w i n g the procedure o u t l i n e d i n the p r e c e d i n g s e c t i o n ( s ) . 3.6.3 Surface treatment with n i t r i c a c i d Camphor wood samples were machine-planed and cut i n t o s u i t a b l e s i z e , approximately 19 mm x 101.6 mm x 304.8 mm (3/4 i n x 4 i n x 12 i n ) . A th r e e percent n i t r i c a c i d s o l u t i o n was brushed onto the s u r f a c e s t h a t were to be j o i n e d . These s u r f a c e s were then h e a t - t r e a t e d under an i n f r a - r e d source f o r 30 min. A f t e r the treatment the board s u r f a c e s were n e u t r a l i z e d by we t t i n g with d i s t i l l e d water f o l l o w e d by exposing the wet s u r f a c e t o ammonia vapour f o r f i v e minutes. The samples were then c o n d i t i o n e d again t o the d e s i r a b l e e q u i l i b r i u m moisture content i n a c o n t r o l l e d temperature and humidity (C.T.H.) room. Glui n g , c u t t i n g of t e s t specimens, 2 9 and t e s t i n g was c a r r i e d out i n accordance with the method o u t l i n e d e a r l i e r on. 3.6.4 Surface treatment with sodium hydroxide s o l u t i o n The wood samples were machine-planed and cut to s i z e , approximately 19 mm x 101.6 mm x 304.8 mm (3/4 i n x 4 i n x 12 i n ) . The wood s u r f a c e s , t o be j o i n e d , were wiped with a p i e c e of c l o t h s a t u r a t e d with sodium hydroxide s o l u t i o n c o n s i s t i n g of 10 p a r t s by weight of sodium hydroxide ( c a u s t i c soda) and 90 p a r t s of water. A f t e r 10 minutes the s u r f a c e s were r i n s e d with d i s t i l l e d water and then wiped dry with a c l e a n white c l o t h u n t i l they showed no d i s c o l o r a t i o n . F o l l o w i n g t h i s step, the t r e a t e d samples were c o n d i t i o n e d t o the d e s i r e d moisture content. G l u i n g , c u t t i n g of t e s t specimens, and t e s t i n g was c a r r i e d out i n accordance with the method d e s c r i b e d above. 3.7 Main Experiment From the r e s u l t s o b t a i n e d i n the p r e l i m i n a r y experiment the f o l l o w i n g c o n d i t i o n s were used f o r a l l the f o u r g l u e s : (i) A glue spread of 410.6 g/m2 (85 l b s per 1000 f t 2 ) . ( i i ) G l u i n g and p r e s s i n g at room temperature (21-24°C) . ( i i i ) Press p r e s s u r e of 1,379 kPa (200 p s i ) . (iv) P r e s s i n g time of 24 h. Camphor wood samples which were of s t r a i g h t g r a i n and f r e e from d e f e c t s such as knots, b i r d s eyes, sho r t g r a i n , decay and unusual d i s c o l o r a t i o n s w i t h i n the s h e a r i n g area 30 were used. The g r a i n d i r e c t i o n was p a r a l l e l t o the lo n g e s t dimension of the b l o c k . The b l o c k s were planed j u s t p r i o r t o g l u i n g and assembled i n p a i r s i n such a way t h a t b l o c k s of approximately the same s p e c i f i c g r a v i t y ( a i r dry) were gl u e d t o g e t h e r . The s u r f a c e s of the b l o c k s remained unsanded and f r e e from d i r t . The moisture content of the wood at the time of g l u i n g was 9-12% based on oven-dry weight as determined by use of r e p r e s e n t a t i v e samples. 3.7.1 Adhesive a p p l i c a t i o n , p r e s s i n g and c o n d i t i o n i n g of t e s t j o i n t s Each glue was mixed a c c o r d i n g t o the manufacturer's i n s t r u c t i o n s and used w i t h i n the recommended time (pot l i f e ) . A glue spread of 410.6 g/m2 (85 pounds per 1,000 sq. f t . ) of j o i n t area double spread was used. The weighed amount of adhesive was spread manually with a rubber r o l l e r . The f o r m u l a t i o n of the glues and g l u i n g c o n d i t i o n s used are shown i n Table 2. The g l u e - c o a t e d b l o c k s were then assembled and p r e s s e d at room temperature (21-23°C) with a p r e s s u r e of 1,379 kPa (200 p s i ) f o r 24 h. The b l o c k s , upon removal from the p r e s s , were c o n d i t i o n e d at a r e l a t i v e humidity 50 ± 2% and at a temperature of 23 ± 1°C (73.4 ± 2°F) f o r a p e r i o d of 7 days, a f t e r which they were cut i n t o t e s t specimens. 31 3.7.2 P r e p a r a t i o n of b l o c k shear specimens Due t o the l i m i t e d amount and width of camphor wood m a t e r i a l which was a v a i l a b l e t o conduct t h i s study, a s l i g h t m o d i f i c a t i o n of the t e s t specimen s i z e was r e q u i r e d . The camphor lumber had a nominal width of 101.6 mm ( 4 i n ) . Instead of the ASTM standard b l o c k of 44.4 mm x 50.8 mm x 12 mm (1 3/4 i n x 2 i n x 3/4 in) a m o d i f i e d specimen, 44.4 mm x 44.4 mm x 12 mm (1 3/4 i n x 1 3/4 i n x 3/4 in) was adopted f o r t h i s study. The 6.4 mm (1/4 in) r e d u c t i o n i n width was checked t o be of l i t t l e s i g n i f i c a n c e t o the v a l i d i t y of the t e s t r e s u l t s . S t i c k l e r (43), i n a study on b l o c k shear specimen geometry, concluded t h a t specimen width has no s i g n i f i c a n t e f f e c t on u n i t shear s t r e n g t h . On the other hand, specimen l e n g t h had a s i g n i f i c a n t e f f e c t on u n i t shear s t r e n g t h . A l e n g t h of shear plane p a r a l l e l t o g r a i n of 1 i n c h , he observed, i s due to optimum dimension of the b l o c k shear specimen. The b l o c k shear specimens were cut i n such a way t h a t the g r a i n d i r e c t i o n was p a r a l l e l t o the d i r e c t i o n of l o a d i n g d u r i n g t e s t . Surfaces were smooth, p a r a l l e l t o each other and p e r p e n d i c u l a r to the h e i g h t . The width and l e n g t h of each specimen at the g l u e l i n e was measured t o the nearest 0.25 mm (0.01 in) and the shear area c a l c u l a t e d . The specimens were l e f t i n the c o n d i t i o n i n g atmosphere d e s c r i b e d i n S e c t i o n 3.7.1 u n t i l t e s t e d , except d u r i n g the 32 c u t t i n g o p e r a t i o n s . The c o l d s o a k a n d b o i l t e s t s p e c i m e n s w e re t r e a t e d b e f o r e t h e y were t e s t e d . 3.7.3 T e s t i n g p r o c e d u r e The b l o c k s h e a r s p e c i m e n s u s e d i n t h i s s t u d y h a d s h e a r a r e a v a r y i n g b e t w e e n 1677.4 a n d 1806.4 mm2 (2.6 a n d 2.8 s q . i n . ) i n s t e a d o f t h e 1935.5 mm2 (3 s q . i n . ) o f t h e ASTM (D905-81) s t a n d a r d b l o c k s h e a r ' s p e c i m e n . A T i n u s O l s e n h y d r a u l i c t e s t i n g m a c h i n e / f i t t e d w i t h a s h e a r i n g t o o l c o n t a i n i n g a s e l f - a l i g n i n g s e a t t o e n s u r e u n i f o r m d i s t r i b u t i o n o f l o a d , was u s e d ( F i g . 1 2 ) . The l o a d was a p p l i e d a t a u n i f o r m r a t e , w i t h a c o n t i n u o u s m o t i o n o f t h e m o v a b l e h e a d a t a r a t e o f 6.35 x 1 0 " ^ mm/s (0.015 i n / m i n ) t o f a i l u r e . 3.7.3.1 D r y t e s t The d r y b l o c k s were t e s t e d f o l l o w i n g t h e p r o c e d u r e o u t l i n e d a b o v e . S h e a r s t r e s s a t f a i l u r e f o r e a c h t e s t b l o c k was r e c o r d e d a n d t h e s h e a r s t r e n g t h c a l c u l a t e d . The s h e a r s t r e n g t h a t f a i l u r e i n k i l o p a s c a l s (kPa) was b a s e d on t h e g l u e l i n e a r e a b e t w e e n t h e two l a m i n a t i o n s m e a s u r e d t o t h e n e a r e s t 0.25 mm2 (0.01 i n 2 ) , a n d r o u n d e d . E s t i m a t e d p e r c e n t a g e o f wood f a i l u r e was r e c o r d e d f o r e a c h b l o c k . 3.7.3.2 C o l d s o a k t e s t A p o r t i o n ( s e e T a b l e 2) o f t h e t e s t s p e c i m e n s g l u e d w i t h 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 a n d u r e a - f o r m a l d e h y d e w e re 33 soaked i n c o l d water, at 21°C (70°F) t o 24°C (75°F) f o r 48 h. While s t i l l wet, they were t e s t e d t o f a i l u r e i n a s i m i l a r method to t h a t used f o r the dry specimens. Shear s t r e n g t h and percent wood f a i l u r e of each specimen was recorded. 3.7.3.3 B o i l t e s t The b o i l t e s t was used only f o r the t e s t specimens gl u e d with 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 . The t e s t specimens were b o i l e d i n water f o r 4 h and then d r i e d at a temperature of 60 + 3°C (140 + 5°F) f o r 20 h. Then the t e s t specimens were b o i l e d again i n water f o r another 4 h, c o o l e d i n water at 21 ± 3°C (70 ± 5°F) and t e s t e d by l o a d i n g t o f a i l u r e while they were s t i l l wet. E v e n t u a l l y , the percentage wood f a i l u r e was estimated and the shear s t r e n g t h c a l c u l a t e d . 3.8 S t a t i s t i c a l A n a l y s i s The average v a l u e s of both the shear s t r e n g t h and wood f a i l u r e were c a l c u l a t e d . Shear s t r e n g t h and wood f a i l u r e were analysed s e p a r a t e l y . One way a n a l y s i s of v a r i a n c e was performed f o r both the shear s t r e n g t h and wood f a i l u r e a c c o r d i n g t o type of t e s t . Where s i g n i f i c a n t d i f f e r e n c e s were n o t i c e d , Duncan's new m u l t i p l e range t e s t was used t o separate the set of means i n t o subsets of homogeneous means. 34 4 . 0 R E S U L T S AND D I S C U S S I O N 4.1 Wood C h a r a c t e r i z a t i o n The s p e c i f i c g r a v i t y (G) (at 12% m.c.) va l u e s , based on oven-dry weight and green volume, are i n the range of 0.52 to 0.53, with a sample mean of 0.52 and a standard d e v i a t i o n of 0.005. T h i s mean G of 0.52 ± 0.005 o b t a i n e d f o r camphor wood samples used i n t h i s study, compares w e l l t o a value of 0.59 r e p o r t e d by Bengough (11) (Appendix I ) . pH va l u e s , of f i v e samples, are i n the range of 2.89 to 2.96. The average pH value i s 2.93 and with a standard d e v i a t i o n of 0.026. T h i s i n d i c a t e s t h a t camphor wood i s s t r o n g l y a c i d i c . The r e s u l t s of t o t a l e x t r a c t i v e content d e t e r m i n a t i o n are summarized i n the Table 3. Weight percentage of camphor wood matter, s o l u b l e i n hot one percent c a u s t i c soda s o l u t i o n (NaOH) i s 24.1, on the m o i s t u r e - f r e e b a s i s . T h i s value i s an average of thr e e d e t e r m i n a t i o n s . These r e s u l t s i n d i c a t e t h a t a high p r o p o r t i o n of camphor wood e x t r a c t i v e s are s o l u b l e i n alcohol-benzene, hot water and c o l d water. I t should be p o i n t e d out t h a t these v a l u e s are not from s u c c e s s i v e e x t r a c t i o n s . A l s o these r e s u l t s were ob t a i n e d from a small set of samples and do not t h e r e f o r e r e p r e s e n t the q u a n t i t y of e x t r a c t i v e s i n every sample of camphor wood s p e c i e s , s i n c e the d i s t r i b u t i o n of e x t r a c t i v e s 35 i s expected t o vary c o n s i d e r a b l y w i t h i n a s i n g l e t r e e and among t r e e s . 4.2 G l u i n g with P o l y v i n y l - a c e t a t e (PVA) Adhesive 4.2.1 Dry Te s t : Bond shear s t r e n g t h and wood f a i l u r e p ercent The average shear s t r e n g t h and percentage wood f a i l u r e are shown i n Tables 4a and 4b. The standard d e v i a t i o n , minimum, maximum and range f o r both shear s t r e n g t h and percentage wood f a i l u r e are a l s o presented. These va l u e s are the average of 15 measurements per treatment. F i g u r e 1 r e p r e s e n t s a histogram of the average shear s t r e n g t h and percentage wood f a i l u r e . As i s ev i d e n t from Tables 4a,b and F i g u r e 1, the b l o c k s made with wood t h a t had been s u r f a c e t r e a t e d with d i l u t e n i t r i c a c i d , and n e u t r a l i z e d with ammonia gas produced the h i g h e s t average shear s t r e n g t h (14,692 kPa); while those made from wood, s u r f a c e t r e a t e d with 10% sodium hydroxide s o l u t i o n showed the h i g h e s t percentage wood f a i l u r e (70%). Alcohol-benzene e x t r a c t e d wood showed the lowest values f o r both the average shear s t r e n g t h (7,452 kPa) and percentage wood f a i l u r e ( 6%). One way a n a l y s i s of v a r i a n c e f o r shear s t r e n g t h and wood f a i l u r e are shown i n Table 5. The s t a t i s t i c a l r a n k i n g of the means, by Duncan's m u l t i p l e range t e s t , f o r both the shear s t r e n g t h and wood f a i l u r e are presented i n Table 6. 36 T h e a n a l y s i s o f v a r i a n c e r e s u l t s f o r s h e a r s t r e n g t h ( T a b l e 5 a ) i n d i c a t e t h a t t h e t r e a t m e n t m e a n s a r e s i g n i f i -c a n t l y d i f f e r e n t ( i . e . , a t 0 . 0 1 l e v e l o f s i g n i f i c a n c e ) . D u n c a n ' s m u l t i p l e r a n g e t e s t ( T a b l e 6) r a n k s u n e x t r a c t e d , h o t w a t e r e x t r a c t e d , a n d s o d i u m h y d r o x i d e t r e a t e d w o o d a s h a v i n g s i m i l a r a v e r a g e b o n d s h e a r s t r e n g t h . S a m p l e s s u r f a c e t r e a t e d w i t h n i t r i c a c i d h a d t h e h i g h e s t b o n d s h e a r s t r e n g t h w h i l e a l c o h o l - b e n z e n e e x t r a c t e d h a d t h e l o w e s t . T h e a v e r a g e b o n d s h e a r s t r e n g t h o f n i t r i c a c i d t r e a t e d w o o d i s s i g n i f i c a n t l y h i g h e r t h a n t h a t o f t h e u n e x t r a c t e d w o o d ( c o n t r o l ) . O n t h e b a s i s o f a v e r a g e b o n d s h e a r s t r e n g t h i t i s e v i d e n t t h a t s u r f a c e t r e a t i n g t h e w o o d w i t h n i t r i c a c i d , p r i o r t o g l u i n g , i m p r o v e d i t s g l u a b i l i t y w i t h P V A T r e a t i n g t h e w o o d w i t h s o d i u m h y d r o x i d e o r e x t r a c t i n g i t w i t h h o t w a t e r , p r i o r t o g l u i n g , d o e s n o t i m p r o v e i t s g l u a b i l i t y w i t h P V A . E x t r a c t i n g t h e w o o d w i t h a l c o h o l - b e n z e n e , p r i o r t o g l u i n g , r e s u l t e d i n a n i n f e r i o r j o i n t w h e n c o m p a r e d t o t h e u n e x t r a c t e d w o o d ( c o n t r o l ) . T h e a n a l y s i s o f v a r i a n c e r e s u l t s ( w o o d f a i l u r e ) s h o w n i n T a b l e 5 b i n d i c a t e t h a t t h e t r e a t m e n t m e a n s a r e n o t a l l e q u a l . T h e w o o d f a i l u r e r a n k i n g i n T a b l e 6 s h o w s t h a t t h e h i g h e s t p e r c e n t a g e w o o d f a i l u r e (70%) o b t a i n e d w i t h s o d i u m h y d r o x i d e t r e a t e d w o o d i s n o t s i g n i f i c a n t l y d i f f e r e n t a t 0 . 0 5 l e v e l f r o m t h e 56% v a l u e o f t h e c o n t r o l . T h e p e r c e n t a g e w o o d f a i l u r e g i v e n b y t h e n i t r i c a c i d t r e a t m e n t (49%) i s n o t s i g n i f i c a n t l y , a t 0 . 0 5 l e v e l , d i f f e r e n t f r o m t h e 56% e x h i b i t e d b y t h e u n t r e a t e d w o o d . H o w e v e r , i t ( n i t r i c a c i d 37 treatment) i s s i g n i f i c a n t l y d i f f e r e n t from the 70% of the sodium hydroxide t r e a t e d wood. The percentage wood f a i l u r e showed by the hot water e x t r a c t e d wood (18%) and a l c o h o l -benzene e x t r a c t e d wood (6%) are not s i g n i f i c a n t l y d i f f e r e n t (at 0.05 l e v e l ) but both of them are s i g n i f i c a n t l y lower than those of the other t h r e e treatments. On the b a s i s of average percentage wood f a i l u r e none of the f o u r wood pre-treatments s i g n i f i c a n t l y improved the g l u a b i l i t y of camphor wood when glue d with PVA adhesive. These r e s u l t s are not very much d i f f e r e n t from those o b t a i n e d by Goto et a l . (20). They observed t h a t the r e l a t i o n s h i p between g l u e - j o i n t s t r e n g t h and percentage of e i t h e r c o l d or hot water s o l u b l e e x t r a c t i v e s i s not s i g n i f i -cant. The r e s u l t s o b t a i n e d i n t h i s study suggest t h a t e x t r a c t i v e s removal, u s i n g hot water, sodium hydroxide s o l u t i o n or alcohol-benzene does not improve g l u e - j o i n t s t r e n g t h . At the same time the r e s u l t s of t h i s study are i n c o n t r a d i c t i o n with those r e p o r t e d by Chugg et al. (17), Wellons et al. (47), Abe et al. (1). G e n e r a l l y r e s u l t s from t h e i r s t u d i e s suggest t h a t e x t r a c t i v e s a f f e c t the formation of a glue bond e i t h e r p h y s i c a l l y , c h e m i c a l l y or both p h y s i c a l l y and c h e m i c a l l y . 38 4.3 G l u i n g with Casein Adhesive 4.3.1 Dry Te s t : Bond shear s t r e n g t h and wood f a i l u r e percent Tables 7a and 7b summarize the average shear s t r e n g t h and percentage wood f a i l u r e f o r the wood b l o c k s bonded with c a s e i n adhesive. The standard d e v i a t i o n , minimum, maximum and range val u e s are a l s o p r e s e n t e d i n the t a b l e s . F i g u r e 2 a l s o d e p i c t s average bond shear s t r e n g t h and percentage wood f a i l u r e f o r the f i v e treatment combinations of wood and c a s e i n adhesive. Blocks made from wood t h a t had been t r e a t e d with sodium hydroxide s o l u t i o n , produced the h i g h e s t average bond shear s t r e n g t h of 14,297 kPa; while those made from n i t r i c a c i d t r e a t e d wood gave the lowest, 5,911 kPa. The b l o c k s made from u n t r e a t e d wood (co n t r o l ) had the second lowest average bond shear s t r e n g t h . As shown i n Table 7b, b l o c k s made from hot water e x t r a c t e d wood gave the h i g h e s t percentage wood f a i l u r e (78%). No wood f a i l u r e was n o t i c e d i n the b l o c k s made from wood t h a t had been s u r f a c e t r e a t e d with n i t r i c a c i d p r i o r t o g l u i n g . The b l o c k s made from alcohol-benzene e x t r a c t e d wood and sodium hydroxide t r e a t e d wood e x h i b i t e d percentage wood f a i l u r e s of 51% and 45%, r e s p e c t i v e l y ; these v a l u e s are highe r than t h a t of the c o n t r o l (15%). The a n a l y s i s of v a r i a n c e t a b l e s f o r average shear s t r e n g t h and wood f a i l u r e developed are presented i n Tables 8a and b. From the a n a l y s i s of v a r i a n c e r e s u l t s i t i s 39 e v i d e n t t h a t the shear s t r e n g t h treatment means are s i g n i f i -c a n t l y d i f f e r e n t at 0.01 l e v e l . Duncan's M u l t i p l e Range t e s t (Table 9) ranks the sodium hydroxide, and alcohol-benzene treatment means f o r shear s t r e n g t h development i n the same group. T h i s means t h a t although the treatment mean of sodium hydroxide t r e a t e d wood (14,297 kPa) i s h i g h e r than t h a t of alcohol-benzene t r e a t e d wood (12,955 kPa) the two means are not s i g n i f i c a n t l y d i f f e r e n t , at 0.05 l e v e l . The range t e s t f u r t h e r i n d i c a t e s t h a t the average shear s t r e n g t h s f o r b l o c k s made with alcohol-benzene e x t r a c t e d wood, and hot water e x t r a c t e d wood are not s i g n i f i c a n t l y d i f f e r e n t , at 0.05 l e v e l . However, the hot water treatment mean i s s i g n i f i c a n t l y d i f f e r e n t (at 0.05 l e v e l ) from t h a t of sodium hydroxide treatment. The c o n t r o l and hot water treatment means are not s i g n i f i c a n t l y d i f f e r e n t , at 0.05 l e v e l . The n i t r i c a c i d treatment mean (5,911 kPa) i s the lowest and i s a l s o s i g n i f i c a n t l y d i f f e r e n t from the other f o u r treatment means. From the shear s t r e n g t h r e s u l t s i t i s ev i d e n t t h a t s u r f a c e t r e a t i n g of camphor wood with sodium hydroxide, and e x t r a c t i n g with alcohol-benzene p r i o r t o g l u i n g improves i t s g l u a b i l i t y with c a s e i n adhesive. Adhesion i n camphor wood i s not s i g n i f i c a n t l y improved by e x t r a c t i n g the wood with hot water i . e . , p r i o r t o the g l u i n g o p e r a t i o n . I t seems t h a t s u r f a c e t r e a t i n g of camphor wood with n i t r i c a c i d , p r i o r t o g l u i n g , lowers i t s g l u a b i l i t y with c a s e i n adhesive. 40 As i n d i c a t e d by a n a l y s i s of v a r i a n c e r e s u l t s (Table 8a), f o r percentage wood f a i l u r e , the treatment means are not s i g n i f i c a n t l y e q u a l . As shown i n Table 8, hot water treatment mean (78%) i s the h i g h e s t and a l s o s i g n i f i c a n t l y h i g h e r than the o t h e r s . Percentage wood f a i l u r e s of 51% and 45% produced by sodium hydroxide, and alcohol-benzene t r e a t -ments, r e s p e c t i v e l y , are not s i g n i f i c a n t l y d i f f e r e n t at the 0.05 l e v e l . The 15% wood f a i l u r e e x h i b i t e d by the c o n t r o l i s not s i g n i f i c a n t l y d i f f e r e n t from the lowest percentage wood f a i l u r e (0%) produced by the n i t r i c a c i d treatment. In view of the percentage wood f a i l u r e r e s u l t s , i t can be s t a t e d t h a t g l u a b i l i t y of camphor wood with c a s e i n adhesive was improved by s u r f a c e t r e a t i n g i t with sodium hydroxide, e x t r a c t i n g i t with hot water and alcohol-benzene p r i o r t o g l u i n g . On the other hand, s u r f a c e t r e a t i n g with n i t r i c a c i d had a ne g a t i v e e f f e c t on adhesion. These r e s u l t s are q u i t e s i m i l a r t o those o b t a i n e d by other workers. In t e s t s done at F o r e s t Products Laboratory, Madison (4), i t was shown t h a t when wood s u r f a c e s were t r e a t e d with chemical s o l u t i o n s b e f o r e g l u i n g , the q u a l i t y of the j o i n t s was improved on s e v e r a l s p e c i e s with animal and c a s e i n g l u e s . Treatment with a s o l u t i o n of c a u s t i c soda (sodium hydroxide) strengthened c a s e i n glue j o i n t s i n woods t h a t o r d i n a r i l y are j o i n e d with t h i s glue with some d i f f i -c u l t y . T h i s type of treatment i n c r e a s e d the j o i n t s t r e n g t h as w e l l as the wood f a i l u r e . A s i m i l a r t r e n d was observed i n t h i s study. A c c o r d i n g t o Knight (22) i t was at one time common p r a c t i c e t o wipe the s u r f a c e s of many hardwoods with 10% sodium hydroxide, b e f o r e g l u i n g with animal glue, i n order t o improve bond s t r e n g t h . Narayanamurti et a l . (36) found t h a t hot water e x t r a c t i v e s of Tectona grandis, i n low c o n c e n t r a t i o n s (2%), s l i g h t l y i n c r e a s e the modulus of r i g i d i t y and reduce the g e l a t i o n time of animal glue n e a r l y t o h a l f . They a l s o noted t h a t h i g h e r c o n c e n t r a t i o n s reduce the r i g i d i t y modulus by about 11% but i n c r e a s e . t h e g e l a t i o n time by over 200%; these two aspects g i v e r i s e t o a s t a r v e d j o i n t which e x h i b i t s low s t r e n g t h and low percentage of wood f a i l u r e . T h i s probably e x p l a i n s the r e s u l t s , of the hot water treatment, o b t a i n e d i n t h i s study i . e . , an i n c r e a s e i n both bond s t r e n g t h and wood f a i l u r e with removal of hot water e x t r a c t i v e s . Chugg and Gray (17) have i n d i c a t e d t h a t e x t r a c t i v e s from Afrormosia elata i n h i b i t the s e t t i n g of animal g l u e . The same authors r e p o r t t h a t e x t r a c t i v e s lower the s u r f a c e t e n s i o n of the wood s u r f a c e and reduce w e t t a b i l i t y , which i s e s s e n t i a l f o r a good glue bond. On the other hand, some of the r e s u l t s o b t a i n e d i n t h i s study are i n c o n t r a d i c t i o n with some r e s u l t s o b t a i n e d by other r e s e a r c h e r s while, i n v e s t i g a t i n g g l u i n g of t r o p i c a l hardwoods. Goto et al. (20) p o i n t out t h a t the r e l a t i o n s h i p between g l u e - j o i n t s t r e n g t h and percentage of e i t h e r c o l d or O r i g i n a l not seen. C i t e d from Hancock (22). 42 hot water s o l u b l e e x t r a c t i v e s i s not s i g n i f i c a n t . Chow and Chunsi (16), i n t h e i r study of adhesion s t r e n g t h of s i x Burmese hardwoods, concluded t h a t g l u e - j o i n t shear s t r e n g t h had no s i g n i f i c a n t r e l a t i o n s h i p with the e x t r a c t i v e content. 4.4 G l u i n g with Phenol-Resorcinol-Formaldehyde Adhesive 4.4.1 Dry t e s t : Bond shear s t r e n g t h and wood f a i l u r e percent The r e s u l t s of bond s t r e n g t h and percentage wood f a i l u r e are shown i n Tables 10a and 10b. The r e l a t i o n s h i p between bond s t r e n g t h and percentage wood f a i l u r e i s shown i n F i g u r e 3. Both, i n the case of alcohol-benzene e x t r a c t e d (14,543 kPa) as w e l l as t h a t of sodium hydroxide t r e a t e d wood (14,629 kPa), the bond s t r e n g t h i s h i g h e r than t h a t of the c o n t r o l . On the other hand, t h a t of hot water e x t r a c t e d (10,411 kPa), and n i t r i c a c i d t r e a t e d wood (9,709 kPa) i s lower than t h a t of the c o n t r o l (12,924 kPa). Again, n i t r i c a c i d treatment produced the lowest average bond s t r e n g t h . As can be seen i n Table 10b, the percentage wood f a i l u r e f o r alcohol-benzene e x t r a c t e d wood i s the h i g h e s t (98%). No wood f a i l u r e was observed i n the b l o c k s made with n i t r i c a c i d t r e a t e d wood. Blocks made with sodium hydroxide t r e a t e d wood, and hot water e x t r a c t e d wood showed percentage wood f a i l u r e s of 75% and 60%, r e s p e c t i v e l y . These two values, as w e l l as t h a t f o r alcohol-benzene e x t r a c t e d wood are h i g h e r than t h a t shown by the c o n t r o l (30%). 43 In Table 16, the s t a t i s t i c a l r a n k i n g of the shear s t r e n g t h , treatment means, by Duncan's M u l t i p l e Range t e s t puts alcohol-benzene e x t r a c t e d wood, and sodium hydroxide t r e a t e d wood i n the same group. These two treatment means are s i g n i f i c a n t l y h i g h e r than t h a t of the c o n t r o l . The average shear s t r e n g t h s of b l o c k s made with hot water e x t r a c t e d wood, and n i t r i c a c i d t r e a t e d wood are not s i g n i f i -c a n t l y d i f f e r e n t , at 0.05 l e v e l . However, both of them are s i g n i f i c a n t l y lower than t h a t of the c o n t r o l . On average bond shear s t r e n g t h b a s i s , i t can be s t a t e d t h a t , e x t r a c t i n g camphor wood u s i n g alcohol-benzene or s u r f a c e t r e a t i n g i t with sodium hydroxide, p r i o r t o g l u i n g , improves i t s g l u a b i l i t y with p h e n o l - r e s o r c i n o l formaldehyde adhesive. Surface t r e a t i n g the wood with n i t r i c a c i d or e x t r a c t i n g i t with hot water, p r i o r t o g l u i n g , does not improve i t s g l u a b i l i t y with p h e n o l - r e s o r c i n o l formaldehyde adhesive. As i n d i c a t e d by a n a l y s i s of v a r i a n c e r e s u l t s (Table 11a) the percentage wood f a i l u r e means are s i g n i f i c a n t l y d i f f e r e n t , at 0.05 l e v e l . Only the sodium hydroxide, and hot water treatment means are not s i g n i f i c a n t l y d i f f e r e n t , at 0.05 l e v e l (Table 11a). A l s o from the r a n k i n g of the means shown i n Table 16, i t i s ev i d e n t t h a t the treatment means f o r alcohol-benzene e x t r a c t i o n , hot water e x t r a c t i o n , and sodium hydroxide treatment are s i g n i f i c a n t l y h i g h e r than t h a t of the c o n t r o l . On the other hand, the n i t r i c a c i d treatment mean i s s i g n i f i c a n t l y lower than t h a t of the c o n t r o l . Thus, on 44 wood f a i l u r e b a s i s , i t can be s t a t e d t h a t benzene, hot water, and sodium hydroxide treatments enhanced adhesion i n camphor wood. On the c o n t r a r y , t r e a t i n g the wood with n i t r i c a c i d , p r i o r t o g l u i n g , lowers i t s g l u a b i l i t y with p h e n o l - r e s o r c i n o l formaldehyde adhesive. I t i s a l s o important t o note t h a t the h i g h e s t shear s t r e n g t h and wood f a i l u r e were ob t a i n e d f o r the a l c o h o l -benzene e x t r a c t e d wood. 4.4.2 C o l d soak t e s t : Bond shear s t r e n g t h and wood f a i l u r e percent R e s u l t s of the c o l d soak t e s t , average shear s t r e n g t h and percentage wood f a i l u r e , are shown i n Tables 12a and 12b, r e s p e c t i v e l y . The average shear s t r e n g t h , f o r the d i f f e r e n t treatments, i n order of i n c r e a s i n g magnitude i s as f o l l o w s : N i t r i c a c i d - t r e a t e d wood (1321 kPa), hot water e x t r a c t e d wood (10,421 kPa), c o n t r o l (11,509 kPa), sodium hydroxide t r e a t e d wood (12,708 kPa), and a l c o h o l benzene e x t r a c t e d wood (14,609 kPa). Percentage wood f a i l u r e f o r the c o l d soak t e s t i n the same order i s n i t r i c a c i d t r e a t e d wood (0%), sodium hydroxide t r e a t e d wood (42%), c o n t r o l (60%), hot water e x t r a c t e d wood (91%), and alcohol-benzene e x t r a c t e d wood (100%). A n a l y s i s of v a r i a n c e r e s u l t s shown i n Table 13a i n d i c a t e t h a t the bond shear s t r e n g t h means are not s i g n i f i c a n t l y equal at 0.05 l e v e l . S i m i l a r l y t h i s o b s e r v a t i o n i s a l s o t r u e f o r the wood f a i l u r e percent (Table 13b). S t a t i s t i c a l r a n k i n g by average shear s t r e n g t h v a l u e s (Table 16) i n d i c a t e s t h a t none of the means i s s t a t i s t i c a l l y 45 s i m i l a r t o any other. Alcohol-benzene and sodium hydroxide treatment means are s i g n i f i c a n t l y h i g h e r than the mean of the c o n t r o l . T h i s i s an i n d i c a t i o n t h a t these two types of treatments improved g l u a b i l i t y of camphor wood with phenol-r e s o r c i n o l formaldehyde, as f a r as c o l d soak t e s t i s concerned. The hot water treatment appears t o have lowered adhesion, although not t o a very great e x t e n t . Blocks made with n i t r i c a c i d t r e a t e d wood developed an extremely low bond s t r e n g t h , about 9 times lower than t h a t of the c o n t r o l . Duncan's M u l t i p l e Range t e s t (Table 16) ranks a l c o h o l -benzene, and hot water treatments as having s i m i l a r wood f a i l u r e percent, the c o n t r o l i s ranked t h i r d , sodium hydroxide treatment f o u r t h and n i t r i c a c i d treatment l a s t . These r e s u l t s c l e a r l y i n d i c a t e t h a t on the b a s i s of wood f a i l u r e percent, alcohol-benzene, and hot water treatments improved adhesion; while sodium hydroxide and n i t r i c a c i d treatments had a ne g a t i v e e f f e c t on adhesion. 4.4.3 B o i l t e s t : Bond shear s t r e n g t h and wood f a i l u r e percent The g l u e l i n e shear s t r e n g t h f o r the s i x treatments i n a d e c r e a s i n g order i s alcohol-benzene (13,759 kPa), c o n t r o l (12,926 kPa), sodium hydroxide (10,103 kPa), hot water (9,920 kPa), and n i t r i c a c i d (9,523 kPa) (Table 14a). Hot water, sodium hydroxide, and n i t r i c a c i d treatments have shear s t r e n g t h v a l u e s lower than t h a t f o r the c o n t r o l . The alcohol-benzene treatment mean i s h i g h e r (see F i g u r e 5 ) . 46 Table 14b pr e s e n t s the percentage wood f a i l u r e r e s u l t s f o r the b o i l t e s t . As can be seen from the r e s u l t s , b l o c k s made with alcohol-benzene t r e a t e d wood showed the g r e a t e s t (100%) amount of wood f a i l u r e , f o l l o w e d by those made from hot water e x t r a c t e d wood (87%). The c o n t r o l (56%) i s p l a c e d t h i r d , sodium hydroxide t r e a t e d wood f o u r t h (45%), and n i t r i c a c i d t r e a t e d wood l a s t with a 13 percent wood f a i l u r e . A n a l y s i s of v a r i a n c e r e s u l t s f o r both bond shear s t r e n g t h and percentage wood f a i l u r e are shown i n Tables 15a and b. These r e s u l t s i n d i c a t e t h a t the bond shear s t r e n g t h treatment means are s i g n i f i c a n t l y d i f f e r e n t at 0.05 l e v e l of s i g n i f i c a n c e ; t h i s i s a l s o the case f o r percentage wood f a i l u r e treatment means. The r e s u l t s f o r Duncan's M u l t i p l e Range t e s t , average shear s t r e n g t h , and wood f a i l u r e percent are shown i n Table 16. The alcohol-benzene treatment and the c o n t r o l are ranked as having average shear s t r e n g t h v a l u e s which are not s i g n i f i c a n t l y d i f f e r e n t . Sodium hydroxide, hot water, and n i t r i c a c i d treatments are a l s o ranked as being s i m i l a r i n average bond shear s t r e n g t h . These r e s u l t s seem t o i n d i c a t e t h a t none of the f o u r d i f f e r e n t treatments improved adhesion, as f a r as the b o i l t e s t i s concerned. For wood f a i l u r e percent, the range t e s t puts a l c o h o l -benzene and hot water treatments i n the same group i . e . , they are not s i g n i f i c a n t l y d i f f e r e n t at 0.05 l e v e l . Both of these treatments showed an average wood f a i l u r e percent, which a c c o r d i n g t o the range t e s t , are s i g n i f i c a n t l y h i g h e r than 47 t h a t f o r the c o n t r o l . The c o n t r o l and the sodium hydroxide treatment means are c l a s s i f i e d as not s i g n i f i c a n t l y d i f f e r e n t . The n i t r i c a c i d treatment mean i s s i g n i f i c a n t l y lower than the other f o u r means. For t h i s p a r t i c u l a r t e s t , the r e s u l t s suggest t h a t alcohol-benzene, and hot water treatments improved bond q u a l i t y ( i n terms of percentage wood f a i l u r e ) . 4.6 Comparison of Bond Strength Tests f o r Wood Blocks Bonded with Phenol-Resorcinol-Formaldehyde Adhesive As i s ev i d e n t from Table 17, the bond shear s t r e n g t h va l u e s of the dry t e s t are, g e n e r a l l y h i g h e r than those of the c o l d soak or b o i l t e s t . Blocks made from u n e x t r a c t e d wood l o s t 11% of t h e i r shear s t r e n g t h due t o soaking i n c o l d water. When s u b j e c t e d t o the b o i l t e s t , b l o c k s made from u n e x t r a c t e d wood gained about 0.01% shear s t r e n g t h i . e . , t a k i n g the dry shear s t r e n g t h as the standard. The r e d u c t i o n i n s t r e n g t h observed i n the c o l d t e s t can be assumed t o be a r e s u l t of the decrease i n s t r e n g t h of the wood, due t o h i g h moisture content at the time of t e s t i n g . Most of the s t r e n g t h p r o p e r t i e s and e l a s t i c c h a r a c t e r i s t i c s of wood vary i n v e r s e l y with the moisture content of the wood (13, 23). The wood f a i l u r e r e s u l t s support the above-mentioned assumptions; i t i n c r e a s e d from 30% (dry t e s t ) t o 60% f o r the c o l d soak t e s t . Thus, a r e d u c t i o n i n shear s t r e n g t h of the wood i t s e l f r a t h e r than a s t r o n g e r glue j o i n t . However, the b o i l t e s t gave some unexpected r e s u l t s i n t h a t i n s t e a d of the bond s t r e n g t h d e c r e a s i n g i t a c t u a l l y 48 increased. Probably the increase i n bond strength i s due to a post-cure phenomenon of the adhesive as a result of r a i s i n g the temperature (b o i l i n g ) . Although, the wood f a i l u r e percent for the b o i l test i s lower than that of the dry test, i t i s s l i g h t l y higher than that for the cold soak t e s t . Again t h i s i s contrary to what one would have expected. Due to thermal p l a s t i c i z a t i o n of wood by the hot water, the shear strength would be expected to decrease. For the b o i l test the loss i n shear strength i s 5% for blocks made from hot water extracted wood. However, blocks made from hot water extracted wood showed s l i g h t l y higher strength i n the cold soak test than i n the dry t e s t . The wood f a i l u r e values for the cold and b o i l tests are higher than that of the dry t e s t . Blocks made from wood that had been treated with n i t r i c acid p r i o r to gluing showed a major loss (86%) i n strength when subjected to the cold soak t e s t . For the b o i l test, blocks made with n i t r i c acid treated wood showed a very s l i g h t loss (2%) i n shear strength. The wood f a i l u r e values were 0%, 0% and 13%, for the dry, cold soak test and b o i l test, respectively. Considering the shear strength and wood f a i l u r e r e s u l t s , i t can be stated that soaking of the test specimens i n cold water p r i o r to t e s t i n g resulted i n a degrade of the glue i t s e l f rather than the wood. B o i l i n g the test specimens seems to have resulted i n some weakening of the wood i t s e l f ; hence the increase i n the amount of wood f a i l u r e . 49 C o l d soaking and b o i l i n g of b l o c k s made with wood t h a t had been t r e a t e d with sodium hydroxide s o l u t i o n r e s u l t e d i n a 13% and 31% drop i n shear s t r e n g t h , r e s p e c t i v e l y . S u r p r i s i n g l y , the wood f a i l u r e v a l u e s of the c o l d soak t e s t and b o i l t e s t were lower than t h a t of the dry t e s t . I t seems t h a t the drop i n bond s t r e n g t h i s probably the r e s u l t of degradation t h a t might have taken p l a c e i n the glue i t s e l f r a t h e r than i n the wood. Blocks made with alcohol-benzene e x t r a c t e d wood had s l i g h t l y h i g h e r (0.4%) s t r e n g t h i n the c o l d soak t e s t than found f o r the dry t e s t specimen. The s t r e n g t h v a l u e s f o r the b o i l t e s t were lower than t h a t o b t a i n e d i n the dry t e s t . Alcohol-benzene treatment showed the h i g h e s t amount of wood f a i l u r e (dry t e s t 98%, c o l d soak 100% and b o i l t e s t 100%), when compared t o the hot water, n i t r i c a c i d , sodium hydroxide and the c o n t r o l treatments. The h i g h amount of wood f a i l u r e suggests t h a t the wood-glue j o i n t , i n alcohol-benzene e x t r a c t e d wood, f a i l e d mainly as a r e s u l t of the wood s t r e s s and t h a t the adhesion i n h i b i t o r y f a c t o r s e v i d e n t with other treatments and adhesive were removed by t h i s s o l v e n t system most e f f e c t i v e l y . 4.6.1 General d i s c u s s i o n on g l u i n g camphor wood with 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 adhesive Over the years, attempts have been made by many r e s e a r c h e r s t o determine the i n f l u e n c e of e x t r a c t i v e s on g l u a b i l i t y of wood with p h e n o l i c r e s i n s (15, 18, 22, 47). Some of the r e s u l t s from t h i s study compare f a v o u r a b l y with 50 t h e i r f i n d i n g s r e p o r t e d i n the e x i s t i n g l i t e r a t u r e on adhesion i n wood. Rapp (45)^ showed t h a t v a r i o u s s u r f a c e treatments can be employed to improve adhesion i n a t r o p i c a l hardwood. Among the s u r f a c e treatments used was wiping the wood s u r f a c e , p r i o r t o g l u i n g , with 10% c a u s t i c soda s o l u t i o n . The r e s u l t s i n d i c a t e d t h a t both the shear s t r e n g t h and wood f a i l u r e v a l u e s were h i g h e r than those of the u n t r e a t e d wood. Gamble et al. (45) ^ have shown t h a t removal of a c e t o n e - s o l u b l e p o r t i o n of the wax present i n a t r o p i c a l wood (Tectona grandis), r e s u l t e d i n a c o n s i d e r a b l e i n c r e a s e i n the glue-bond q u a l i t y o b t a i n e d with a r e s o r c i n o l adhesive. S i m i l a r r e s u l t s are r e p o r t e d by Thomas (44), u s i n g e t h e r and benzene as e x t r a c t i n g s o l v e n t s . Hancock (22) has shown t h a t a r e d u c t i o n i n adhesion of oven-dried veneer i s p r i m a r i l y because of e x t r a c t i v e s m i g r a t i o n to the s u r f a c e . He a l s o determined t h a t the i n h i b i t i o n was caused by acetone or a combination of acetone and methanol/benzene e x t r a c t a b l e f r a c t i o n s . E x t r a c t i v e s may have an u n f a v o r a b l e e f f e c t on the p o l a r i t y and w e t t a b i l i t y of wood (24). Chen (15) found t h a t the removal of e x t r a c t i v e s from wood s u r f a c e s with v a r i o u s s o l v e n t s improved the w e t t a b i l i t y of wood. However, he a l s o observed t h a t t h e r e was no d i r e c t r e l a t i o n s h i p between w e t t a b i l i t y and g l u a b i l i t y u s i n g r e s o r c i n o l - f o r m a l d e h y d e 6 C i t e d from Troop and Wangaard (45). ^ C i t e d from Troop and Wangaard (45). r e s i n . J a i n et al. (27) i n d i c a t e t h a t alcohol-benzene e x t r a c t e d samples of Pinus roxburghii g l u e d b e t t e r than the u n e x t r a c t e d samples. They f u r t h e r noted t h a t hot water e x t r a c t e d samples d i d not show a remarkable improvement i n bond q u a l i t y , i n comparison with the u n e x t r a c t e d samples. The r e s u l t s of the present study show a s i m i l a r t r e n d . R o f f a e l et a l . (38) observed t h a t e x t r a c t i o n of oak p a r t i c l e s with b o i l i n g water f a v o u r a b l y a f f e c t e d the g l u a b i l i t y of the p a r t i c l e s . T h i s c o n t r a d i c t s the f i n d i n g s of the present study. However, they a l s o r e p o r t an improve-ment i n g l u a b i l i t y with a d d i t i o n of sodium hydroxide s o l u t i o n ; t h i s b i t of t h e i r f i n d i n g s i s i n c l o s e agreement with the present r e s u l t s . I t i s e v i d e n t from the present r e s u l t s t h a t s u r f a c e treatment with sodium hydroxide s o l u t i o n s i g n i f i c a n t l y i n c r e a s e d the w o o d - f a i l u r e values of camphor wood b l o c k s , glued with 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 adhesive. However, these r e s u l t s , i n d i c a t i n g t h a t the sodium hydroxide treatment was e f f e c t i v e , c o n t r a d i c t the f i n d i n g s of Dougal et a l . (18). They r e p o r t e d t h a t e x t r a c t i o n of some S.E. A s i a n hardwoods, with sodium hydroxide s o l u t i o n , d i d not c o n s i s t e n t l y i n c r e a s e the wood f a i l u r e v a l u e s . 4.7 G l u i n g with Urea Formaldehyde For t h i s p a r t of the study, only one wood l e v e l was used i . e . , u n e x t r a c t e d wood. The r e s u l t s obtained, e s p e c i a l l y the wood f a i l u r e , l e n d to the c o n c l u s i o n t h a t camphor wood glues 52 w e l l with urea formaldehyde. Hence, the author d i d not f i n d i t e s s e n t i a l t o i n v e s t i g a t e the adhesion with UF r e s i n i . e u s i n g p r e - t r e a t e d camphor wood. 4.7.1 Dry t e s t : Shear s t r e n g t h and wood f a i l u r e p ercent Bond shear s t r e n g t h and percentage wood f a i l u r e r e s u l t s are shown i n the Tables 18a and 18b. The u n t r e a t e d camphor wood showed a reasonably h i g h average shear s t r e n g t h when bonded with urea-formaldehyde adhesive. I t a l s o showed a very h i g h percentage of wood f a i l u r e which suggests t h a t i t s the wood i t s e l f t h a t f a i l e d , d u r i n g t e s t i n g , r a t h e r than the adhesive. From t h i s o b s e r v a t i o n , i t can be s t a t e d t h a t camphor wood glues w e l l with urea formaldehyde adhesive. 4.7.2 C o l d soak t e s t : Shear s t r e n g t h and wood f a i l u r e p ercent Tables 19a and 19b present the shear s t r e n g t h and wood f a i l u r e r e s u l t s f o r the c o l d soak t e s t . The r e s u l t s show a r e d u c t i o n i n shear s t r e n g t h from 13,654 kPa f o r the dry t e s t t o 6,898 kPa f o r the c o l d soak t e s t . There i s a l s o a r e d u c t i o n i n wood f a i l u r e percentage from 97% t o 66%. Most assemblies bonded with urea-formaldehyde are intended f o r i n t e r i o r use because the g l u e l i n e s are not f u l l y waterproof, only h i g h l y w a t e r - r e s i s t a n t (19). A combination of h i g h r e l a t i v e humidity and h i g h temperature d e t e r i o r a t e s 5 3 urea re s i n glue bonds i n a r e l a t i v e l y short time. Resistance to c y c l i c soaking and drying exposures i s reasonably good i f the test pieces are plywood or t h i n members, but only moderate i f the pieces are thick (like the one used i n t h i s study) (41). 54 5 . 0 SUMMARY AND C O N C L U S I O N A summary of the r e s u l t s o b t a i n e d i n t h i s study i s given i n Table 20. F i g u r e s 6, 1, 8, 9, 10 f u r t h e r i l l u s t r a t e these r e s u l t s . Under the l i g h t of t h i s study i s concluded t h a t : (1) On bond s t r e n g t h b a s i s , s u r f a c e treatment of camphor wood with n i t r i c a c i d , p r i o r t o g l u i n g , improved i t s g l u a b i l i t y with PVA. However, on percentage wood f a i l u r e b a s i s , none of the f o u r wood pre-treatments s i g n i f i c a n t l y improved adhesion between PVA adhesive and camphor wood. (2) From the standpoint of bond shear s t r e n g t h , s u r f a c e treatment of camphor wood with sodium hydroxide, and e x t r a c t i o n with alcohol-benzene, p r i o r t o g l u i n g , enhanced i t s g l u a b i l i t y with c a s e i n adhesive. Adhesion was not improved by e i t h e r e x t r a c t i n g the wood with hot water or by s u r f a c e t r e a t i n g with n i t r i c a c i d p r i o r t o g l u i n g i t with c a s e i n adhesive. In view of percentage wood f a i l u r e , g l u a b i l i t y of camphor wood with c a s e i n was improved by s u r f a c e t r e a t i n g i t with sodium hydroxide s o l u t i o n , and e x t r a c t i n g with a l c o h o l -benzene or hot water p r i o r t o g l u i n g o p e r a t i o n . Surface t r e a t i n g with n i t r i c a c i d had a ne g a t i v e e f f e c t on adhesion. ( 3 ) E x t r a c t i n g camphor wood u s i n g alcohol-benzene or s u r f a c e t r e a t i n g i t with sodium hydroxide, p r i o r t o g l u i n g with PRF, improved adhesion. On the 55 c o n t r a r y , t r e a t i n g i t with n i t r i c a c i d or e x t r a c t i n g i t with hot water lowered adhesion. Alcohol-benzene, and hot water e x t r a c t i o n improved adhesion; while sodium hydroxide and n i t r i c a c i d treatments had a ne g a t i v e e f f e c t . (4) C o l d water soaking of specimens bonded with PRF specimens, p r i o r t o t e s t i n g , r e s u l t e d i n a r e d u c t i o n i n bond s t r e n g t h of b l o c k s made from u n e x t r a c t e d wood, n i t r i c a c i d t r e a t e d and sodium hydroxide t r e a t e d wood. Blocks made with n i t r i c a c i d t r e a t e d wood showed a remarkable drop i n bond s t r e n g t h . But a s l i g h t i n c r e a s e i n bond s t r e n g t h was observed with alcohol-benzene and hot water treatments. There was an i n c r e a s e i n percent wood f a i l u r e f o r the hot water, and alcohol-benzene treatments. (5) A drop i n bond s t r e n g t h was observed when t e s t specimens made from n i t r i c a c i d t r e a t e d , a l c o h o l benzene e x t r a c t e d , and sodium hydroxide t r e a t e d wood were b o i l e d i n water b e f o r e t e s t i n g . However, the b l o c k s made from u n e x t r a c t e d wood gained i n bond s t r e n g t h a f t e r b o i l i n g . Probably, a po s t - c u r e of the adhesive took p l a c e as a r e s u l t of temperature i n c r e a s e . The b o i l treatment was observed t o i n c r e a s e amount of wood f a i l u r e i n a l l the treatments except the sodium hydroxide treatment. 56 (6) Using dry bond s t r e n g t h and percent wood f a i l u r e as a c r i t e r i a , i t was found t h a t camphor wood bonds w e l l with urea-formaldehyde adhesive without any s u r f a c e treatment as suggested h e r e i n . 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The i n h i b i t o r y e f f e c t of Diospyros sp. Heartwood e x t r a c t i v e s on the c u r i n g of the un s a t u r a t e d p o l y e s t e r r e s i n . J . Japan Wood Res. Soc. 21 (2):107-112. 34. M u l l i n s , E . J . and T.S. McKnight. 1981. Canadian Woods, t h e i r P r o p e r t i e s and Uses. U n i v e r s i t y of Toronto Press, B u f f a l o , London. 389 pp. 35. Narayanamurti, D. 1957. The r o l e of e x t r a c t i v e s i n wood. Holz Roh-Werkstoff. 15 (9) :370-380. 36. Narayanamurti, D., R.C. Gupta and G.M. Verma. 1962. In f l u e n c e of e x t r a c t i v e s on the s e t t i n g of adhesives. Holzforschung und Holzverwertung 14:85-88. 37. O n i s h i , H. and T. Goto. 1971. Studie s on wood g l u i n g . V I I I . The e f f e c t s of wood e x t r a c t i v e s on the g e l a t i o n time of urea-formaldehyde r e s i n adhesive. Shimane A g r i . C o l l . Matsue, Japan. B u l l . No. 5:61-65. 38. R o f f a e l , V.E. and W. Rauch. 1974. 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Adhesive d u r a b i l i t y : specimen designs f o r a c c e l e r a t e d t e s t s . F o r e s t Prod. J . 18 (9) :84-90. 44. Thomas, R.J. 1959. G l u i n g c h a r a c t e r i s t i c s on determa. F o r e s t Prod. J . 9(8):266-271. 45. Troop, B.S. and F.F. Wangaard. 1950. The g l u i n g p r o p e r t i e s of c e r t a i n t r o p i c a l Americans woods. O f f i c e of Naval Research, Yale Univ. School of F o r e s t r y , New Haven, Con. Techn. Rep. No. 4. 10 pp. 46. Wangaard, F.F. and L.A. Granados. 1967. The e f f e c t s of e x t r a c t i v e s on water-vapor s o r p t i o n by wood. Wood S c i . Tech. 1 (1967) :253-277. 47. Wellons, J.D. and R.L. Krahmer. 1973. C h a r a c t e r i s t i c s of delaminated e x t e r i o r hardwood plywood. Dept. F or. Prod. P r o j e c t F-918, Oregon State Univ. 8 pp. 48. Ya t a g a i , M. and T. Takahashi. 1980. T r o p i c a l wood e x t r a c t i v e s ' e f f e c t s on d u r a b i l i t y , p a i n t c u r i n g time, and pulp sheet s p o t t i n g . Wood S c i . 12 (3):176-181. Table 1. Type of t e s t s A dhesive/Test Wood PRF Casein UF PVA Unextracted wood E x t r a c t e d wood: (i) with alcohol-benzene ( i i ) with hot water Surface t r e a t e d : (i) with 10% NaOH ( i i ) with d i l u t e n i t r i c a c i d Dry Cold soak B o i l Dry Cold soak B o i l Dry Cold soak B o i l Dry Cold soak B o i l Dry Cold soak B o i l Dry Dry Cold soak Dry Dry Dry Dry Dry _* Dry Dry Dry Dry *No jo i n t s were made using treated camphor wood and UF adhesive. Table 2 : Formulation of glues and g l u i n g c o n d i t i o n s Item Glue Phenol r e s o r c i n o l -formaldehyde Urea-formaldehyde P o l y v i n y l -acetate Casein Mixing r a t i o of glues Resin Water 100 100 100 100 200 Hardner 15 10 - -Gluing conditions Glue spread (g/m2) 410.6 410.6 410.6 410.6 Open assembly time (min) 10 5 3 5 Closed assembly 30 20 10 20 Temperature (°C) 21 21 21 21 Pressure (kg/cm2) 14 14 14 14 Time (h) 24 24 24 24 to Table 3: Total Extractives Content in Camphor Wood S p e c i e s Hot Water E x t r a c t i v e s (%) A l coho l —Benzene E x t r a c t i v e s (%) Co ld Water E x t r a c t i v e s (%) C a m p h o r wood 9.0 10.2 8.8 * * E a c h value is an ave rage of 3 de te rm ina t i ons and is on a mo is tu re - f ree b a s i s . Table 4a: Average Bond Strengtn of Blocks Bonded with PVA (DRY TEST) . Trea tmen ts (Wood) Mean Bond S t reng th (kPa) S tandard Dev ia t ion Minimum Bond S t reng th (kPa) Max imum Bond S t reng th (kPa) - Range (kPa) S tanda rd E r r o r of Mean C o e f f . of Va r i a t i on (%) U n e x t r a c t e d (Cont ro l ) 13209 1992 9735 16251 6516 514 15 Hot Water E x t r a c t e d 12164 1315 9839 14789 4950 3 4 0 11 N i t r i c ac id Treated 14692 1889 11514 16968 5 4 5 4 4 8 8 13 10% NaOH Treated 12745 2247 9742 16072 6 3 3 0 5 8 0 18 A .—Benzene E x t r a c t e d 7452 1690 3 8 8 9 9818 5929 436 23 Table 4 b : Average Wood Failure of Blocks Bonded with PVA (DRY TEST) Trea tmen ts (Wood) Mean Wood Failure (%) S tandard Dev ia t ion Minimum Wood Failure (%). Max imum Wood Failure (%) Ranqe (%) S t a n d a r d E r ro r of Mean C o e f f . of Va r ia t i on (%) U n e x t r a c t e d (Cont ro l ) 56 30 20 100 8 0 8 54 Hot Water E x t r a c t e d 18 24 5 80 75 6 129 N i t r i c ac id Treated 49 28 0 100 100 7 58 10% NaOH Treated 70 25 20 100 8 0 6 35 A - B e n z e n e E x t r a c t e d 6 9 0 25 25 2 156 Table 5a: Analysis of Variance for Bond Srength of Blocks Bonded with PVA (DRY TEST) . Source of Var i a t i o n Degrees of Freedom Sum of Squares Mean Square Computed f Wood Erro r Total 4 70 74 . 449392385.253 240426625.067 689819010.320 112348096.313 3434666.072 32.71 Table 5b: Analysis of Variance for Wood Failure of Blocks Bonded with PVA (DRY TEST) . Source of Vari a t i o n Degrees of Freedom Sum of Squares Mean Square I Computed f Wood Erro r Total 4 70 74 42721.333 41316.666 84038.000 10680.333 590.238 18.09 Table 6: Statistical Ranking by Duncan's Multiple Range Test for Bond Strength and Wood Failure of Blocks Bonded with PVA . STRENGTH fkPa) RANKING OF TREATMENT MEANS Dry Test NIT. UNX. NAO. WAT. 14692 13209 12745 12164 BEN. 7452 WOOD FAILURE (%) RANKING OF TREATMENT MEANS Dry Test NAO. UNX. NIT. WAT. 70 5 6 49 18 BEN. 6 N.B. 1. Means underscored by the same line are not signif icantly different at the 5% level of signif icance. 2. BEN.=A. -Benzene extracted ; NIT.=Nitric acid t reated ; NAO.=NaOH t reated; WAT.=Hot water extracted ; UNX.=Unextracted(Control) . Table 7a: Average Bond Strength of Blocks Bonded with Casein (DRY TEST). Treatments (Wood) Mean Bond Strength (kPa) Standard Deviation Minimum Bond Strength (kPa) Maximum Bond Strength (kPa) Range (kPa) Standard E r r o r of Mean Coeff. of Var i a t i o n I (%) Un e x t r a c t e d (Control) 9933 4207 2723 - 16175 13452 1086 42 Hot Water E x t r a c t e d 11520 1398 9522 14493 4971 361 12 Ni t r i c acid Treated 5911 1727 2744 8336 5592 446 29 10% NaOH Treated 14297 2523 9632 17961 8329 651 18 A - B e n z e n e E x t r a c t e d 12955 2168 8963 17078 8115 560 17 Table 7b: Average Wood Failure of Biccks Bonded with Casein (DRY TEST) . Trea tmen ts (Wood) Mean Wood F a i l y e m Standard Dev ia t ion Minimi) r Wood fa i lure M Max imum Wood Failure i%) Ranqe (%) S tanda rd E r r o r of Mean j Coe f f , ->.? Var lot ";>•"• (%) < 1 Unex t r a c t e d (Cont ro l ) Hot Water E x t r a c t e d N i t r i c ac id Treated 10% NaOH Treated A .—Benzene E x t r a c t e d 15 78 0 51 45 19 30 34 23 25 0 1 0 10 60 100 0 100 90 60 75 90 80 50 129 39 67 Table 8 a : Ana l ys i s of Va r iance for Bond Sreng th of B locks B o n d e d with C a s e i n (DRY TEST) S o u r c e of Va r ia t i on Degrees of F reedom Sum of Squares Mean Squa re C o m p u t e d f Wood 4 629570759 .013 1 5 7 3 9 2 6 8 9 . 7 5 3 2 3 . 3 5 E r r o r 70 . 4 7 1 8 4 6 9 0 2 . 5 3 3 6 7 4 0 6 7 0 . 0 3 6 Total 74 1101417661.547 -Table 8b: Ana lys i s of Va r iance for Wood Failure of B locks Bonded with C a s e i n (DRY TEST) S o u r c e of Va r ia t i on Degrees of F reedom Sum of Squa res Mean Square C o m p u t e d f Wood 4 57137.520 14284 .380 24.13 Er ro r 70 41437.600 591.966 Total 74 98575 .120 Table 9: Statistical Ranking by Duncan's Multiple Range Test for Bond Strength and Wood Failure of Blocks Bonded with Casein. STRENGTH (kPa) RANKING OF TREATMENT MEANS Dry Test NAO. BEN. WAT. UNX. 14297 12955 11520 9933 NIT. 5911 WOOD FAILURE (%) RANKING OF TREATMENT MEANS • Dry Test WAT. NAO. BEN. UNX. 78 51 45 15 NIT. 0 N.B. 1. Means underscored by the same line are not signif icantly different at the 5% level of signif icance. 2. BEN.=A. -Benzene extracted ; NIT.=Nitric acid t reated ; NAO.=NaOH t reated; WAT.=Hot water extracted ; UNX.=Unextracted(Control) . Table 10a: Average Bond Strength of Blocks bonded with PRF (DRY TEST) . Trea tmen ts (Wood) Mean Bond S t reng th (kPa) S tandard Dev ia t ion Minimum Bond S t reng th (kPa) Max imum Bond S t reng th (kPa) Range (kPa) S tanda rd E r ro r of Mean C o e f f . of Va r i a t i on (%) U n e x t r a c t e d (Contro l ) 12924 1597 9687 15258 5571 412 12 Hot Water E x t r a c t e d 10411 1866 7 7 5 0 15113 7 3 6 3 4 8 2 18 Ni t r ic ac id Treated 9709 2150 6 3 8 5 14300 7915 5 5 5 22 10% NaOH Treated 14629 2752 10977 18719 7 742 711 19 A . - B e n z e n e E x t r a c t e d 14543 1534 12038 17037 4999 396 11 Table 10b: Average Wood Failure of Blocks Bonded with PRF (DRY TEST) Trea tmen ts (Wood) Mean Wood Failure (%) Standard Dev ia t ion Minimum Wood Failure Max imum Wood Fai lure (%) Ranqe (%) S tanda rd E r r o r of Mean C o e f f . of V a r i a t i o n (%) U n e x t r a c t e d (Cont ro l ) 30 24 0 70 70 6 79 Hot Water E x t r a c t e d 60 35 0 100 100 9 58 N i t r i c ac id Treated 0 0 0 0 0 - -10% NaOH Treated 75 21 20 100 8 0 5 "28 A . - B e n z e n e E x t r a c t e d 98 4 90 100 10 1 4 Table 11a: Analysis of Variance for Bond Srength of Blocks Bonded with PRF (DRY TEST) Source of Var i a t i o n Degrees of Freedom Sum of Squares Mean Square Computed f Wood 4 315354452.618 78838613.153 19.15 Er r o r 70 288109729.733 4115853.282 Total 74 603464182.347 Table 11b: Analysis of Variance for Wood Failure of Blocks Bonded with PRF (DRY TEST) . Source of Vari a t i o n Degrees of Freedom Sum of Squares Mean Square Computed f Wood 4 88655.333 22163.833 49.66 Erro r 70 31243.333 446.333 Total 74 119898.667 Table 12a: Average Bond Strength of Blocks Bonded with PRF (COLD SOAK TEST) . Trea tmen ts (Wood) Mean Bond S t reng th (kPa) S tandard Dev ia t ion Minimum Bond S t reng th (kPa) Max imum Bond S t reng th (kPa) Range (kPa) S tanda rd E r r o r of Mean C o e f f . of Va r i a t i on (%) U n e x t r a c t e d (C o.ntrol) 11509 1164 9556 13638 4 0 8 2 301 10 Hot Water E x t r a c t e d 10421 856 8 8 3 2 12245 3413 221 8 N i t r i c ac id Tr e a t e d 1321 469 772 2144 1372 121 36 10% NaOH Treated 12708 2158 7398 15893 8 4 9 5 557 17 A .—Benzene E x t r a c t e d 14609 1570 10666 16217 5551 4 0 5 11 Table 12b: Average Wood Failure of Blocks Bonded with PRF (COLD SOAK TEST) Trea tmen ts (Wood) Mean Wood Failure (%) Standard Dev ia t ion Minimum Wood Failure (%) Max imum Wood Fa i I u r e (%) Range (%) Standa rd E r ro r of Mean C o e f f . of Va r i a t i on (%) U n e x t r a c t e d (Cont ro l ) 60 33 10 100 90 9 56 Hot Water E x t r a c t e d 91 15 60 100 40 4 16 N i t r i c ac id Treated 0 0 0 0 0 - -10% NaOH Treated 42 24 10 70 60 6 5 8 A . — B e n z e n e E x t r a c t e d 100 0 100 100 0 0 0 Table 13a: Ana l ys i s of Var iance for Bond S reng th of B locks Bonded with P R F (COLD SOAK TEST) S o u r c e of Va r ia t i on Degrees of F reedom Sum of S q u a r e s Mean Square C o m p u t e d f Wood 4 1565248081 .556 391312020 .389 26 .05 Er ro r 70 131038117.957 1899103.159 Total 74 1696286199.514 Table 13b: Ana l ys i s of Var iance for Wood Failure of B l o c k s Bonded with P R F (COLD SOAK TEST) . S o u r c e of Va r ia t i on Degrees of Freedom Sum of S q u a r e s Mean Squa re C o m p u t e d f Wood 4 9 7 2 8 2 . 0 0 0 2 4 3 2 0 . 5 0 0 6 3 . 6 0 Er ro r 70 26766 .666 3 8 2 . 3 8 1 Total 74 124048 .667 Table 14a: Average Bond Strength of Blocks Bonded with PRF (BOIL TEST) . Trea tmen ts (Wood) Mean Bond S t reng th (kPa) S tandard Dev ia t ion Minimum Bond S t reng th • (kPa) Max imum Bond S t r e n g t h (kPa) Range (kPa) S t a n d a r d E r r o r of Mean C o e f f . of Va r i a t i on (%) U n e x t r a c t e d (Cont ro l ) 12926 1840 10590 15210 4 6 2 0 5 5 5 14 Hot Water E x t r a c t e d 9920 1212 8157 12707 4 5 5 0 366 12 N i t r i c ac id Treated 9523 2478 5130 12411 7281 747 26 10% NaOH Treated 10103 1271 8143 12997 4 8 5 4 3 8 3 13 A . - B e n z e n e E x t r a c t e d 13759 1344 11342 15961 4619 4 0 3 10 Table 14b: Average Wood Failure of Blocks Bonded with PRF (BOIL TEST) . Trea tmen ts (Wood) Mean Wood Fa i I u r e (%) Standard Dev ia t ion Minimum Wood Failure (%) : Max imum : Wood Failure ; (%) Ranqe (%) S t a n d a r d ' E r ro r of Mean C o e f f . of V a r i a t i o n (%) U n e x t r a c t e d (Cont ro l ) 56 31 10 95 8 5 9 55 Hot Water E x t r a c t e d 87 15 60 100 4 0 4 17 N i t r i c ac id Treated 13 18 0 : 50 50 5 136 10% NaOH Treated 45. 37 5 95 90 11 82 A . - B e n z e n e E x t r a c t e d 100 0 100 ; 100 0 0 0 Table 15a: Analysis of Variance for Bond Srength of Blocks Bonded with PRF (BOIL TEST) Source of Var i a t i o n Degrees of Freedom Sum of Squares • Mean Square Computed f Wood 4 149574795.732 : 37373698.933 13.20 Err o r 70 138824944.581 : 2833162.134 Total 74 288399740.315 : Table 15b: Analysis of Variance for Wood Failure of Blocks Bonded with PRF (BOIL TEST) . Source of Var i a t i o n Degrees of Freedom Sum of Squares Mean Square Computed f Wood 4 52548.182 13137.045 23.19 Err o r 7 0 ; 28322.727 566.455 Total 74 : 80870.909 81 Table 16: Statistical Ranking by Duncan's Multiple Range Test for Bond Strength and Wood Failure of Blocks Bonded with PRF. STRENGTH (kPa) RANKING OF TREATMENT MEANS Dry Test NAO. BEN. UNX. WAT. NIT. 14629 14543 12924 10411 9709 Cold Soak Test BEN. NAO. UNX. WAT. NIT. 14609 12708 11509 " 10421 1321 Boil Test BEN. UNX. NAO. WAT. NIT. 13759 12926 10103 9920 9523 WOOD FAILURE (%) RANKING OF TREATMENT MEANS-Dry Test BEN. NAO. WAT. UNX. NIT. 98 75 60 30 0 Cold Soak Test BEN. WAT. UNX. NAO. NIT. 100 91 60 42 0 Boil Test BEN. WAT. UNX. NAO. NIT. 100 87 56 45 13 N.B. 1. Means underscored by the same line are not signif icant ly different at the 5% level of s igni f icance. 2. B E N . = A . - B e n z e n e ex t rac ted ; NIT. = Nitr ic acid t reated; NAO. = NaOH t reated; WAT. = Hot 'water ex t rac ted ; UNX. = Unextracted(Control ) . Table 17: Comparison of Bond Strength Test Results of blocks bonded with PRF . DRY TEST COLD SOAK TEST BOIL TEST Treatments (Wood) Mean Bond Strength (kPa) Mean Wood Failure (%) Mean Bond Strength (kPa) Mean Wood Failure (%) Mean Bond Stren g t h (kPa) Mean Wood Failure U n e x t r a c t e d (Control) 12924 30 11509 60 12926 56 Hot Water E x t r a c t e d 10411 60 10421 91 9920 87 N i t r i c acid Treated 9709 0 1321 0 9523 13 10% NaOH Treated 14629 75 12708 42 10103 45 A.-Benzene E x t r a c t e d 14543 98 14609 100 13759 100 Table 18a: Average Bond Strength of Blocks bonded with UF (DRY TEST) Trea tmen ts (Wood) Mean Bond S t reng th (kPa) S tandard Dev ia t ion Minimum Bond S t reng th (kPa) Max imum Bond S t reng th (kPa) Range (kPa) S t a n d a r d E r ro r of Mean C o e f f . of Va r i a t i on (%) U n e x t r a c t e d (Cont ro l ) 13654 2409 1008 20181 10101 622 18 Table 18b: Average Wood Failure of Blocks bonded with UF (DRY TEST) . Trea tmen ts (Wood) Mean Bond S t reng th (kPa) S tandard Dev ia t ion Minimum Bond S t reng th (kPa) Max imum Bond S t reng th (kPa) Range (kPa) S tanda rd E r r o r of Mean C o e f f . of Va r i a t i on (%) U n e x t r a c t e d (Cont ro l ) 97 6 80 100 20 2 6 Table 19a: Average Bond Strength of Blocks bonded with .UF (COLD SOAK TEST) Trea tmen ts (Wood) Mean Bond S t reng th (kPa) S tandard Dev ia t ion Minimum Bond S t reng th (kPa) Max imum Bond S t reng th (kPa) Range (kPa) S tanda rd E r ro r of Mean C o e f f . of Va r i a t i on (%) U n e x t r a c t e d (Cont ro l ) 6898 2 8 2 5 1579 11569 9 9 9 0 729 41 Table 19b: Average Wood Failure of Blocks bonded with UF (COLD SOAK TEST) . Trea tmen ts (Wood) Mean Bond S t reng th (kPa) S tandard Dev ia t ion Minimum Bond S t reng th (kPa) Max imum Bond S t reng th (kPa) Range (kPa) S tanda rd E r r o r of Mean C o e f f . of Va r i a t i on (%) U n e x t r a c t e d (Cont ro l ) 66 31 15 100 8 5 8 47 Table 2 0 : Summary of Bond Strength and Wood Failure Results. Trea tmen ts (Wood) PVA Mean Mean Bond Wood S t reng th : Failure (kPa) . (%) Case in Mean Mean. Bond S t reng th (kPa) Wooa Failure (%) P R F Mean Bond S t reng th Ok Pa) Mean Wood Fai lure (%) UF Mean Bond S t reng th (kPa) Mean Wood Failure (%) Unex t r a c t e d (Cont ro l ) Hot Water-E x t r a c t e d N i t r i c ac id Treated 10% NaOH Treated A . - B e n z e n e E x t r a c t e d D 13209 D 56 D 9 9 3 3 D 15 D 12924 D 30 •' C 11509 C 60 : B 12926 B 56 : D 12164 D 18 D 11520 D 78 D 10411 D 60 '. C 10421 C 91 : B 9920 B 87 ; D 14692 D 49 D 5911 D 0 D 9709 D 0 C 1321 C 0 B 9523 B 13 D 12745 D 70 D 14297 D 51 D 14629 D 75 C 12708 C 42 • B 10103 B 45 D 7452 D 6 D 12955 D 45 D 14543 D 98 r 14609 C 100 B 13759 B 100 D 13654 C 6 8 9 8 D 97 C 66 N.B: B = Boi l test ; C = Cold soak tes t ; D = Dry tes t Figure 1. Average Bond Strength and Wood Failure of Blocks bonded with PVA (DRY TEST) 1 6 0 0 0 1 4 0 0 0 -1 2 0 0 0 CL 1 0 0 0 0 cn c 8 0 0 0 -CO XI O 6 0 0 0 CO 4 0 0 0 -2 0 0 0 •100 Legend Bond Strength LZ2 Wood Failure UNX. WAT. NIT. WOOD CONDITION NAO. BEN. N.B BEN.=Alcohol -Benzene extracted ; NA0. = Na0H treated ; NIT. = Nitric acid t reated ; WAT. = Hot water extracted ; UNX.=Unextracted(Control). - 8 0 - 6 0 - 4 0 _^ £ XI o o 20 Figure 2. Average Bond Strength and Wood Failure of Blocks bonded with Casein (DRY TEST) 16000-14000-12000-CL 10000 cn c 8000-cu _^ -«—> ( / ) O 6000-CO 4 0 0 0 2 0 0 0 0 J Legend Bond Strength [Z2 Wood Failure NAO. BEN. WOOD CONDITION N.B BEN.=Alcohol -Benzene extracted ; NA0.=Na0H treated ; NIT.=Nitric acid t reated ; WAT.=Hot water extracted ; UNX.=Unextracted(Control). -80 100 60 & cu 3 "O o 40 O -20 00 Figure 3. Average Bond Strength and Wood Failure of Blocks bonded with PRF (DRY TEST) N.B BEN =Alcoho l -Benzene extracted ; NAO.=NaOH treated ; NIT.=Nitric acid t reated ; WAT.=Hot water extracted ; UNX.=Unextracted(Control). Figure 4. Average Bond Strength and Wood Failure of Blocks bonded with PRF (COLD SOAK TEST) . UNX. WAT. NIT. NAO. BEN. WOOD CONDITION N.B BEN.=Alcohol -Benzene extracted ; NAO.=NaOH treated ; NIT.=Nitric acid t reated ; WAT.=Hot water extracted ; UNX.=Unextracted(Control). Figure 5. Average Bond Strength and Wood Failure of Blocks bonded with PRF (BOIL TEST) . UNX. WAT. NIT. NAO. BEN. WOOD CONDITION N.B BEN.=Alcohol -Benzene extracted ; NAO.=NaOH treated ; NIT.=Nitric acid t reated ; WAT.=Hot water ext racted ; UNX.=Unextracted(Control). ure 6. Bond Strength and Wood Failure of Unextracted Blocks Bonded with PVA, Casein, PRF and UF Adhesives (DRY TEST) . Figure 7. Bond Strength and Wood Failure of Hot Water Extracted Blocks Bonded with PVA, Casein and PRF Adhesives (DRY TEST) . CO "U c o CD 1 6 0 0 0 1 4 0 0 0 -1 2 0 0 0 CL 1 0 0 0 0 cn c 8 0 0 0 0 6 0 0 0 -100 4 0 0 0 2 0 0 0 -P V A C A S . A D H E S I V E P R F 6 0 K "D O O Legend Bond Strength LZ2I Wood Failure Figure 8. Bond Strength and Wood Failure of Nitric Acid .Treated Blocks Bonded with PVA, Casein end PRF Adhesives (DRY TEST) . Figure 9. Bond Strength and Wood Failure of NaOH Treated Blocks Bonded with PVA, Casein and PRF Adhesives (DRY TEST) Figure 10. Bond Strength and Wood Failure of Alcohol-Benzene Extracted Blocks Bonded with PVA.Casein and PRF Adhesives(DRY TEST). 96 Figure 11 Form and d i m e n s i o n of b l o c k s h e a r t e s t s p e c i m e n 97 A ( Secna* M-A i Figu. 12. Shearing tool APPENDIX I 98 Species D e s c r i p t i o n * Ocotea usambarensis M u t h i t i Camphor wood Lauraceae D e n s i t y (at 12% MC): 592.7 kg/m 3 (37 l b s / f t 3 ) S p e c i f i c g r a v i t y (at 12% MC): 0.59 Shrinkage (green t o a i r d r y ) : R a d i a l 2.5%; T a n g e n t i a l 4.0 B o t a n i c a l name: L o c a l name: Trade name: Family: W o r k a b i l i t y : G l u a b i l i t y : T r e a t a b i l i t y : Seasoning r a t e : Uses: Moderately easy Average Extremely r e s i s t a n t Moderate F u r n i t u r e , j o i n e r y , l o r r y bodies, boats p a n e l l i n g and o v e r l a y veneer *From Timber L e a f l e t No. 1 "Commercial Timbers of Kenya", Bengough, C.C. (12). APPENDIX I I . 99 Designation: D 905 - 49 (Reapproved 1981)" Standard Test Method for S T R E N G T H P R O P E R T I E S O F ADHESIVE BONDS IN S H E A R BY C O M P R E S S I O N L O A D I N G 1 This standard is issued under the fixed designation D 905; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last rcapproval. A superscript epsilon (<) indicates an editorial change since the last revision or reapproval. This method has been approved for use by agencies of the Department of Defense to replace method 1031 of Federal Test Method Standard No. 175a and for listing in the DoD Index of Specifications and Standards. " N OTE—S e c t i o n 2 was added editorially and subsequent sections renumbered in March 1985. INTRODUCTION The accuracy of the results of strength tests of adhesive bonds will depend on the conditions under which the bonding process is carried out. Unless otherwise agreed upon by the manufacturer and the purchaser, the bonding conditions shall be prescribed by the manufacturer of the adhesive. In order to ensure that complete information is available to the individual conducting the tests, the manufacturer of the adhesive shall furnish numerical values and other specific information for each of the following variables: (/) The moisture content of the wood at the time of gluing. (2) Complete mixing directions for the adhesive. (3) Conditions for applications of the adhesive including the rate of spread or thickness of film, number of coats to be applied, whether to be applied to one or both surfaces, and the conditions of drying where more than one coat is required. (4) Assembly conditions before application of pressure, including the room temperature, length of time, and whether open or closed assembly is to be used. (5) Curing conditions, including the amount of pressure to be applied, the length of time under pressure and the temperature of assembly when under pressure. It should be stated whether this temperature is that of the glue line, or of the atmosphere at which the assembly is to be maintained. (6) Conditioning procedure before testing, unless a standard procedure is specified, including the length of time, temperature, and relative humidity. A range may be prescribed for any variable by the manufacturer of the adhesive if it can be assumed by the test operator that any arbitrarily chosen value within such a range or any combination of such values for several variables will be acceptable to both the manufacturer and the purchaser of the adhesive. 1. Scope 1.1 This test method covers the determination of the comparative shear strengths of adhesive bonds used for bonding wood and other similar materials, when tested on a standard specimen under specified conditions of preparation, con-ditioning, and loading in compression. This test method is intended primarily as an evaluation of adhesives for wood. 1 This test method is under the jurisdiction of A S T M C o m -mittee D-14 on Adhesives and is the direct responsibility of Subcommittee DI4.30 on W o o d Adhesives. Current edition approved Sept. 30. 1949. Published N o v e m -ber 1949. Originally published as D 9 0 5 - 4 7 T . Last previous edition D 9 0 5 - 4 7 T . 100 2. Applicable Document 2.1 ASTM Standard: D 143 Methods of Testing Small Clear Speci-mens of Timber2 3. Apparatus 3.1 The testing machine shall have a capacity of not less than 6810 kg (15 000 lb) in compres-sion and shall be fitted with a shearing tool containing a self-aligning seat to ensure uniform lateral distribution of the load. The machine shall be capable of maintaining a uniform rate of loading such that the load may be applied with a continuous motion of the movable head to max-imum load at a rate of 6.35 x 10-3 mm/s (0.015 in./min) with a permissible variation of ±25 %. The shearing tool shown in Fig. 1 has been found satisfactory. The testing machine shall be located in an atmosphere such that the moisture content of the specimens developed under the conditions prescribed in Section 6 is not noticeably altered during testing. 4. Test Specimens 4.1 Test specimens shall conform to the form and dimensions shown in Fig. 2. The specimens shall be cut from test joints prepared as described in Sections 5 and 6. 4.2 At least 20 specimens shall be tested, rep-resenting at least four different joints. 5. Preparation of Test Joints 5.1 Hard maple blocks (Acer saccharum or Acer nigrum), having a minimum sp gr of 0.65 based on oven-dry weight and volume shall be selected (Note). These blocks shall be of straight grain and free from defects including knots, bird-seye, short grain, decay, and any unusual discol-orations within the shearing area. The blocks shall be of suitable size preferably so that five test specimens may be cut from one test joint as shown in Fig. 3. Blocks approximately 19 by 63.5 by 304 mm (Vi by 2'/2 by 12 in.) have been found to be satisfactory for this purpose. The grain direction shall be parallel to the longest dimen-sion of the block. The blocks shall be at the equilibrium moisture content recommended by the manufacturer of the adhesive. In the absence of such recommendation, the moisture content shall be from 10 to 12% based on oven-dry weight as determined on representative samples in accordance with Sections 122 to 125 of Mcth-D905 ods D 143. The blocks shall be surfaced, just prior to gluing, preferably with a hand-feed join-ter, and the blocks weighed and assembled in pairs so that blocks of approximately the same specific gravity are glued together. The surfaces shall remain unsanded and shall be free from dirt. NOTE—A method for selecting maple blocks of sat-isfactory specific gravity is described in the Appendix to this method. For referee tests, the specific gravity of blocks may be determined in accordance with Section 115 of Methods D 143. 5.2 The adhesive shall be prepared and ap-plied to the blocks in accordance with the pro-cedure recommended by the manufacturer of the adhesive. The glue-coated blocks shall then be assembled and pressed, likewise in accordance with the recommendations of the manufacturer of the adhesive. 6. Conditioning of Test Joints 6.1 The joints, upon removal from pressure shall be conditioned at a relative humidity of 50 ± 2 % and at a temperature of 23 ± 1°C (73.4 ± 2°F) either for a period of 7 days or until speci-mens reach equilibrium as indicated by no pro-gressive changes in weight, whichever is the shorter period. The length of this period of con-ditioning may be extended beyond this limit by written agreement between the purchaser and the manufacturer of the adhesive. 7. Preparation of Specimens 7.1 Cut the specimens as shown in Fig. 3 so that the grain direction is parallel to the direction of loading during test. Take care in preparing the test specimens to make the loaded surfaces smooth and parallel to each other and perpen-dicular to the height. Take care also in reducing the lengths of the laminations to 44.4 mm (l3/4 in.) to ensure that the saw cuts extend to, but not beyond, the glue line. Measure the width and length of the specimen at the glue line to the nearest 0.25 mm (0.010 in.) to determine the shear area. 7.2 Retain specimens in the conditioning at-mosphere described in Section 6 until tested, except during the cutting operations. 8. Procedure 8.1 Place the test specimen in the shearing 1 Annual Honk of ASTM Stumlurds. V o l 04.09. 101 # D 905 A i I Metric Equivalents in. 'A % IV. 2 m m 6 J 19 44.4 50.8 F I G . 2 Form and Dimensions of Test Specimen APPENDIX (Nonmandatory Information) XI. M E T H O D FOK SELECTING M A P L E BLOCKS OF SATISFACTORY SPECIFIC GRAVITY X1.1 Cut the hard maple blocks into some standard size such as 19 by 63.5 by 304 m m (Vi by 2'/J by 12 in.) after conditioning. Measure the linear dimensions of the blocks in inches, using a suitable caliper or other measuring device. Determine the percentage moisture content of the blocks in accordance with Sections 122 to 125 of Methods D 143. D o not use these samples in further tests. 1 0 2 tool so that the load may be applied as described in Section 3. The position of the specimen in one type of shearing tool is shown in Fig. 1. Apply the loading with a continuous motion of the movable head at a rate of 0.37 mm (0.015 in.)/ min to failure as prescribed in Section 3. 9. Calculation 9.1 Calculate the shear stress at failure in pounds-force per square inch (or kilopascals) based on the glue line area between the two laminations measured to the nearest 0.06 cm2 (0.01 in.2), and report for each specimen together with the estimated percentage of wood failure. 10. Report 10.1 The report shall include the following: 10.1.1 Complete identification of the adhesive 0 905 tested, including type, source, manufacturer's code numbers, form, etc. 10.1.2 Application and bonding conditions used in preparing the specimens. 10.1.3 Conditioning procedure used for the specimens. 10.1.4 Temperature and relative humidity in the test room. 10.1.5 Number of specimens tested. 10.1.6 Number of joints represented. 10.1.7 Maximum and minimum shear stresscsat failure and percentages of wood failure. The standard deviation or all individual test val-ues, or both, for the failing load values and wood failure values may be included in the report al the option of either the purchaser or the manu-facturer of the adhesive. 10.1.8 The average shear stress at failure and the average percentage of wood failure. T A B L E I Faclors for Corrected Weight in Crams Moisture Content. - . . „. Factor 1 4 10.83 5 10.88 6 10.92 7 10.96 8 11.00 9 11.03 10 11.08 II 11.12 12 11.15 13 11.20 14 11.23 15 11.27 A These values arc the weights of ! i n . ' in sugar maple in grams, at the moisture content values indicated, which would have a sp gr of 0.65 on the oven-dry weigh! and volume basis. Weigh all blocks to be used in the test at this moisture content: do not use those blocks having a weight less than the above calculated value. 103 # D 9 0 5 X1.2 Calculate the volume of the blocks to the nearest I c m 1 (0.1 in.') and express the average per-centage moisture content to the nearest whole number. Determine the numerical value of the factor for this moisture content by reference to Table 1. which is based on hard maple blocks that have a specific gravity of 0.65 on the oven-dry weight and volume basis and which were conditioned to various moisture content values. X U Multiply the factor iii 1 able I by lite volume of the block in cubic inches to obtain the weight of the block in grams which would have a specific gravity of 0.65 on the oven-dry weight and volume basis. The American Society for Tesline and Materials takes no position resinning the validity of any paten! riehl* abseiled in connection with any item mentioned in this standard. Users oflhts slandatd arc expressly advised that determination ol the volubly ol unv such patent rights, and the risk of infringement of such rights, are finitely their own responsibility. This slumlord Is subject to revision at any lime tiy Itie responsible teclltiiciilcommittee mid must tie icvii'ncd ever\' live \cuis anil if not revised, either reapproved or wittidrawn. Your comments are invited either for revision ol this standard or tor tnlduionul standards and should be addressed to ASTM Headquarters. Your comments will receive careful considcraiion al a mcciiny ol the responsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should make your views known to the ASTM Committee on Standards. 1916 Race St.. Philadelphia. I'A 19103. 104 A P P E N D I X III. Designation: D 1107 — 84 Technical Association ol Pulp and Paper Industry Standard Method T 204 os-76 Standard Test Method for A L C O H O L - B E N Z E N E SOLUBILITY O F W O O D 1 This standard is issued under the fixed designation D 1107; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (<) indicates an editorial change since the last revision or reapproval. 1. Scope 1.1 This test method covers the determination of the alcohol-benzene soluble content of wood, which is a measure of the waxes, fats, resins, and oils, plus tannins and certain other ether-insolu-ble components. 1.2 This standard may involve hazardous ma-terials, operations, and equipment. This standard does not purport to address all of the safely prob-lems associated with its use. It is the responsibil-ity of whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limi-tations prior to use. Specific precautionary' state-ments are given in Section 4.1.1. 2. Significance and Use 2.1 The alcohol-benzene extract of wood con-sists of the soluble materials not generally consid-ered part of the wood substance. They are pri-marily the waxes, fats, resins, and some gums, as well as some water-soluble substances. The amounts are influenced by seasoning and drying. 3. Apparatus 3.1 Filtering Crucibles—Alundum or fritted-glass filtering crucibles of coarse porosity. 3.2 Extraction Apparatus—A compact form of Soxhlet extraction apparatus, with ground-glass joints, is preferable. The apparatus shall consist of the following items: 3.2.1 Soxhlet Extraction Flask having a ca-pacity of 250 mL. 3.2.2 Soxhlet Extraction Tube, 45 to 50 mm in inside diameter, having a capacity to the top of the siphon of approximately 100 mL and a siphon tube approximately 55 mm in height. Extraction tubes of these dimensions siphon more rapidly than extractors with higher siphon tubes. 3.2.3 Condenser of the Hopkins inner-cooled type. 4. Reagent 4.1 Alcohol-Benzene Solution—Mix 1 volume of ethyl alcohol (95 %) and 2 volumes of chemi-cally pure benzene. 4.1.1 Caution—This method requires the use of benzene, lt has been established that exposure to benzene may present a serious health hazard to humans. U. S. Government regulations ad-ministered by the Occupational Safety and Health Administration are in effect which pre-scribe rules and regulations on the use of ben-zene. These regulations must be consulted before experimental programs employing benzene are undertaken. 1 5. Test Specimen 5.1 The test specimen shall consist of 2 g of air-dried sawdust that has been ground to pass a 425-|im sieve and be retained on a 250-u.m sieve. 6. Procedure 6.1 Weigh two 2-g test specimens in tared Alundum or fritted-glass crucibles. Dry one spec-imen in an oven for 2 h at 100 to 105°C, then place in a loosely stoppered weighing bottle, cool in a desiccator, and weigh. Continue the drying for 1-h periods until the weight is constant. Cal-' This test method is under the jurisdiction of A S T M C o m -mittee D-7 on W o o d and is the direct responsibility of Subcom-mittee D07.I4 on Chemical Tests. Current edition approved A p r i l 27, 1984. Published June 1984. Originally published as D 1 1 0 7 - 50. Last previous edition D 1107 - 56 (1979). 105 <# D1107 culatc the proportions of moisture-free sawdust in the air-dry specimen. 6.2 Place the other specimen in a Soxhlet extraction apparatus having a tared Soxhlet ex-traction flask. Set a small cone of fine-mesh screen wire in the top of the crucible to prevent loss of specimen. Extract with 150 mL of alcohol-benzene solution for 6 to 8 h, keeping the liquid boiling briskly. This-should provide four to six siphonings per hour. 6.3 After evaporating the solvent from the extraction flask, dry the flask and contents in an oven for l h at 100 to 105°C, cool in a dessicator, and weigh. Continue the drying until there is no further loss in weight. 7. Calculation and Report 7.1 Report the results as weight percentage of alcohol-benzene soluble matter in the moisture-free wood, calculated as follows: Alcohol - benzene soluble matter, % = <,Wi/WsP) x 100 where: W2 = weight of dried extract, 6.3, IV, = weight of test specimen used in 6.2, and P = proportion of moisture-free wood in the air-dry specimen (7.1). 7.2 The results shall be based on the average of at least two determinations. 8. Precision and Bias2 8.1 Data obtained in a round robin test in-volving five laboratories indicate a repeatability of 11 % and a reproducibility of 20 %. 8.2 Bias is unknown. 1 Data for this section obtained by the Techncial Association o f the Pulp and Paper Industry, P . O . Box 105113, Atlanta, G A 30348. The A merican Society for Test inn and Materials lakes no position respecting the validity ofany patent rights asserted in connect ion villi any item mentioned in this standard. Users of this standard arc expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, are entirely their own responsibility. This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and if not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standards and should be addressed to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should make your views known to the ASTM Committee on Standards. 1916 Race St.. Philadelphia, Pa. 19103. 106 Designation: D1110 - 84 Technical Association o( Pulp and Paper Industry Standard Method T 207 om-81 Standard Test Methods for WATER SOLUBILITY OF WOOD1 This standard is issued under the fixed designation D 1110; the number immediately following the designation indicates the year of original adaption or, in the ca>e of revision, the year of Inst revision, A number In parentheses indicates the year of last reapproval. A superscript cpsilon (<) indicates an editorial change since the last revision or reapproval. 1. Scope 1.1 These test methods2 cover the determina-tion of the water solubility of wood. Two meth-ods are given, as follows: 1.1.1 Method A—Cold-Water Solubility— This method provides a measure of the tannins, gums, sugars, and coloring matter in the wood. 1.1.2 Method B—Hot- Water Solubility—Th is method provides a measure of the tannins, gums, sugars, coloring matter, and starches in the wood. 1.2 This standard may involve hazardous ma-terials, operations, and equipment. This standard does not purport to address all of the safety prob-lems associated with its use. It is the responsibil-ity of whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limi-tations prior to use. 2. Significance and Use 2.1 Cold water removes a part of such extra-neous materials as tannins, gums, sugars, and coloring matters. Hot water removes these plus the starches. M E T H O D A — C O L D - W A T E R SOLUBILITY 3. Apparatus 3.1 Filtering Crucibles—Alundum or fritted-glass crucibles of coarse porosity will be required. 3.2 Filtering Flask—A suction filtering flask, equipped with a rubber flange for the crucible and funnel, shall be provided. 4. Test Specimen 4.1 The test specimen shall consist of 2 g of air-dried sawdust that has been ground to pass a 425-u.m sieve and be retained on a 250-um sieve. 5. Procedure 5.1 Place a 2-g test specimen, the moisture content of which has been previously deter-mined, in a 400-mL beaker, and cover with 300 mL of distilled water. Let this mixture digest at a temperature of 23 ± 2°C, with frequent stirring, for 48 h. 5.2 Filter the material on an Alundum or fritted-glass crucible, using suction, wash with cold distilled water, and dry to constant weight at 100 to 105°C. Drying usually requires approx-imately 4 h. Place the crucible in a loosely stop-pered weighing bottle, cool in a desiccator, and weigh. 6. Report 6.1 Report the results as percentage of matter soluble in cold water, on the moisture-free basis, calculated as follows: C o l d water s o l u b i l i t y . % = [( H ' , - M ' : ) / M - ' , ] x 100 where: W\ — weight of moisture-free specimen used in ' 5.1, and H 2 = weight of dried specimen after extraction with cold water (5.2). 1 These lest methods arc under the jurisdiction of A S T M Committee D-7 on W o o d and are the direct responsibility of Subcommitte D07.I4 on Chemical Tests. Current edition approved Apri l 27, 1984. Published June 1984. Originally published as D 1110- S O T . Last previous edi-tion D 1110-56(1977) . 1 For further information on these test methods, the following references may be consulted: Schorger. A . W . . "Chemistry of Cellulose and Woods , " 1926, p 506. M c G r a w - H i l l . N . Y . Hawlcy and Wise. "Chemistry of W o o d . " 1926. p. 134, Chemical Catalog C o . , N . Y . 107 # D1110 M E T H O D B—HOT-WATER SOLUBILITY 7. Apparatus 7.1 Digestion Apparatus—A 200-mL Erlen-meyer flask provided with a reflux condenser shall be used. 7.2 Water Bath, so constructed that the water can be maintained at boiling temperature and at a conslant-level just above the solution in the flask. 7.3 Filtering Crucible and Filtering Flask— See Section 3. 8. Test Specimen 8.1 See Section 4. 9. Procedure 9.1 Place a 2-g test specimen, the moisture content of which has been previously deter-mined, and 100 mL of distilled water in the Erlenmeyer flask and attach the reflux condenser. Place the flask in the boiling water bath, with the solution in the flask just below the level of the water in the bath, and heat gently for 3 h. 9.2 Filter the contents of the flask on a tared Alundum or fritted-glass crucible, using suction, wash with hot water, and dry to constant weight at 100 to 105°C. Place the crucible in a loosely stoppered weighing bottle, cool in a desiccator, and weigh. 10. Report 10.1 Report the results as percentage of matter soluble in hot water, on the moisture-free basis, calculated as follows: Hot water solubility, % = \{W, - W2)/W,] x 100 where: H', = weight of moisture-free specimen used in 9.1, and Wi = weight of dried specimen after extraction with hot water (9.2). 11. Precision and Bias* 11.1 All data obtained in one laboratory by testing 20 woods. Repeatability, Repeatability, as Solubility, % % of Solubility C o l d (1.1 to 6.3%) 0.14 5.7 Hot (1.6 to 9.0%) 0.15 3.8 11.2 Reproducibility and bias are unknown. 1 Data in this section obtained from the Technical Associa-tion of the Pulp and Paper Industry, P . O . Box 105113, Atlanta, G A 30348. The American Society for Testing and Materials takes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, are entirely their own responsibility. This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and if not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standards and should be addressed to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should make your views known to the ASTM Committee on Standards. 1916 Race St.. Philadelphia. Pa. 19103. 108 Designation: D1109 - 84 Technical Association of Pulp and Paper Industry Standard Method T 212 os-76 Standard Test Method for 1 % SODIUM HYDROXIDE SOLUBILITY OF WOOD1 This standard is issued under the fixed designation D 1109; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript cpsilon (i) indicates an editorial change since the last revision or reapproval. 1. Scope 1.1 This test method covers the determination of the solubility of wood in a hot dilute alkali solution. A 1 % solution of Sodium hydroxide (NaOH) is used. One application is in determin-ing the degree of fungus decay that has taken place in a given wood sample. As the wood decays, the percentage of alkali-soluble material increases in proportion to the decrease in pulp yield caused by the decay. 1.2 This standard may involve hazardous ma-terials, operations, and equipment. This standard does not purport to address all of the safety prob-lems associated with its use. It is the responsibil-ity of whoever uses this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limi-tations prior to use. 2. Significance and Use 2.1 Hot alkali extracts low molecular weight carbohydrates consisting mainly of hemicellulose and degraded cellulose in wood. This solubility of wood is an indication of the degree of fungal decay, or degradation by heat, light, oxidation, etc. The more decay or degradation, the higher the solubility. 3. Apparatus 3.1 Water Bath—The water bath shall be de-signed so that the temperature of the material during treatment is uniformly maintained at 97 to lOCC. When a new bath is used the temper-ature shall be checked to ensure the use of proper conditions. The type of bath recommended is one that is covered and that has holes in the top of such size that beakers may be set down in the bath until they are supported by the flared rim of the beakers. The top of the beaker shall be nearly level with the cover of the bath. By using this type of bath the sides of the beakers arc entirely surrounded by boiling water or steam. The water level in the bath shall be maintained above the level of the liquid in the beakers. 3.2 Beakers—The beakers shall be tall-form, 200-mL, alkali-resistant glass2 beakers. 3.3 Filtering Crucibles—Alundum or fritted-glass crucibles of medium porosity are recom-mended for filtering the treated sawdust. 4. Reagents 4.1 Sodium Hydroxide Solution (7.0 % ) — A l -low a chemically pure NaOH solution (50 %) to stand about 1 week in a stoppered vessel to permit settling of Na2C03 and other insoluble impurities. Dilute the supernatant clear solution with distilled water free of C0 2 and adjust to between 0.9 and 1.1 % NaOH. 4.2 Acetic Acid (70 % ) . 5. Test Specimen 5.1 The test specimen shall consist of air-dried sawdust that has been ground to pass a 425-um sieve and be retained on a 250-|im sieve. The weight of the test specimen shall be such that it will be equivalent to 2 ± 0.1 g of moisture-free wood. 6. Procedure 6.1 Place two test specimens in 200-mL, tall-form beakers and add to each 100 mL of NaOH ' This test method is under the jurisdiction of A S T M C o m -mittee D-7 on W o o d and is the direct responsibility of Subcom-mittee D07.14 on Chemical Tests. Current edition approved A p r i l 27, 1984. Published June 1984. Originally published as D 1 1 0 9 - SOT. Last previous edi-tion D 1109-56(1978) . 1 Borosilicate glass has been found satisfactory for this pur-pose. 109 # D1109 solution (1 %) measured carefully with a gradu-ate. After stirring well, place the covered beakers in the water bath, which shall be boiling steadily. Leave the beakers in the bath for exactly 1 h, stirring the contents three times, at periods of 10, 15, and 25 min after the beakers are placed in the bath. 6.2 At the end of 1 h, filter the contents of each beaker by suction on a tared crucible. Wash the sawdust with 100 mL of hot water, then with 50 mL of acetic acid (10 %), and then thoroughly with hot water. Dry the crucible and contents to constant weight at 100 to 105°C, cool in a desic-cator, and weigh in a stoppered weighing bottle. 7. Calculation and Report 7.1 Report the results as weight percentage of matter soluble in 1 % sodium hydroxide solution, on the moisture-free basis, calculated as follows: Matter soluble in caustic soda, % = [W - Hy/H ' i ) x 100 where: H-'i = weight of moisture-free wood in specimen prior to test (Section 5), and \V2 = weight of dried specimen after treatment with the NaOH solution (6.2). 7.2 Base the results on the average of at least two determinations. 8. Precision and Bias1 8.1 Results obtained from an interlaboratory study by nine laboratories on four woods indicate a repeatability of 0.45 and reproducibility of 1.96. The solubility of the wood samples ranged from 11.2 to 17.0%. 8.2 Bias is unknown. 3 Data in this section obtained by the Technical Association of the Pulp and Paper Industry, P . O . Box 105113. Atlanta. G A 30348. The American.Society for Testing and Materials lakes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, are entirely their own responsibility. This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and if not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standards and should be addressed to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should make your views known to the ASTM Committee on Standards. 1916 Race St.. Philadelphia. Pa. 19103. 

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