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Foliage and bark as modifiers for plywood urea-formaldehyde resins Rosales Urbano, Danilo Adolfo 1980

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FOLIAGE AND BARK AS MODIFIERS FOR PLYWOOD UREA-FORMALDEHYDE RESINS by DANILO ADOLFO^ROSALES URBANO B . S c . F o r e s t r y , U n i v e r s i d a d N a c i o n a l d e l C e n t r o d e l P e r u , 1 9 7 3 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE-i n t h e D e p a r t m e n t o f F o r e s t r y We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA O c t o b e r , 1980 c D a n i l o A d o l f o R o s a l e s Urbano In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the 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 , I ag ree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d that c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f Forestry , The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 wesbrook P l a c e Vancouver, Canada V6T 1W5 OctoDer 14, 1980. ABSTRACT T h i s work f o l l o w s s u c c e s s f u l r e s e a r c h by s t a f f members a t F o r i n t e k Canada C o r p . i n m o d i f y i n g and e x t e n d i n g p h e n o l -f o r m a l d e h y d e (PF) plywood r e s i n s w i t h powdered t r e e f o l i a g e s and b a r k s . I n the p r e s e n t s t u d y , two u r e a - f o r m a l d e h y d e (UF) r e s i n s , one c o m m e r c i a l and one l a b o r a t o r y s y n t h e s i z e d , were m o d i f i e d a t 15» 30 and k$fo a d d i t i o n l e v e l s w i t h f i n e l y ground w h i t e s p r u c e [ P i c e a g l a u c a (Moench.) V o s s ] f o l i a g e or w e s t e r n hemlock [ T s u g a h e t e r o p h y l l a ( R a f . ) S a r g . ] b a r k . Two f i v e - p l y D o u g l a s - f i r [ P s e u d o t s u g a m e n s i e z i i ( M i r b . ) F r a n c o ] t e s t plywood p a n e l s (38 x 38 cm) were made a t 32kg/l00 m d o u b l e g l u e l i n e s p r e a d l e v e l , s i x and t e n m i n p r e s s i n g t i m e a t 1^9°C. The c o m m e r c i a l and l a b o r a t o r y s y n t h e s i z e d wheat f l o u r e x t e n d e d UF r e s i n s were u s e d as c o n t r o l s . S h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s were r e c o r d e d f o r s e t s o f t e s t specimens a f t e r c o n d i t i o n i n g a t -22°C and EMC o f about G% (Dry t e s t ) , one vacuum p r e s s u r e c y c l e , f i v e vacuum p r e s s u r e c y c l e s and b o i l i n g c y c l e . ' Most f o r m u l a t i o n s w i t h the c o m m e r c i a l UF r e s i n c o n t a i n i n g f o l i a g e o r b a r k y i e l d e d good bond q u a l i t y (wood f a i l u r e and s h e a r s t r e n g t h ) s i m i l a r to t h e c o n t r o l when t e s t e d d r y and a f t e r one vacuum p r e s s u r e c y c l e . F o l l o w i n g i i i m ulti-cycle t e s t i n g , one formulation containing f o l i a g e ~ gave s i m i l a r wood f a i l u r e percentage to the control. Two formulations containing "bark improved glue bond d u r a b i l i t y y i e l d i n g 3 to 1 2 % higher wood f a i l u r e than the control. Results with the laboratory r e s i n were not as good, showing bond qua l i t y lower than with the commercial UF formulation. No formulation survived b o i l i n g treatment implying that no modification among those used improved UF r e s i n d u r a b i l i t y under conditions of high moisture and-temperature. Both UF resins were successfully extended by various fo l i a g e and bark additions. I t was found that both materials can be used as p a r t i a l substitutes f o r the con-ventional extender wheat f l o u r up to the kOfo l e v e l . This information may be of use to some developing countries that import wheat to flour-extended UF resins used to bond i n t e r i o r grade plywoods. Such countries could benefit by making use of l o c a l tree foliages or barks. iv TABLE OF CONTENTS Page T I T L E PAGE l ABSTRACT i i TABLE OF CONTENTS i v L I S T OF TABLES v i i L I S T OF FIGURES - i x ' ACKNOWLEDGEMENT x i . 1 . 0 INTRODUCTION 1 2 . 0 REVIEW OF LITERATURE 2 . 1 U r e a - F o r m a l d e h y d e R e s i n C h a r a c t e r i s t i c s 4 2 . 2 M o d i f i e r s and E x t e n d e r s f o r UF r e s i n s 5 2 . 3 F a c t o r s A f f e c t i n g G l u e E x t e n d e r P e r f o r m a n c e 1 1 2 . 4 F a c t o r s A f f e c t i n g P l y w o o d Bond Q u a l i t y 2 . 4 . 1 V e n e e r q u a l i t y 1 3 2 . 4 . 2 G l u e v i s c o s i t y 1 5 2 . 4 . 3 Glue- a p p l i c a t i o n , a s s e m b l y t i m e and p r e s s i n g 1 6 2 . 5 G l u e Cure I n d i c a t o r s 2 0 2 . 6 Some A s p e c t s o f Wood A d h e s i o n 2 1 2 . 7 A s s e s s i n g Plywood Bond Q u a l i t y 2 4 3 . 0 MATERIALS AND METHODS 3 . 1 E x p e r i m e n t a l P l a n 2 7 3 . 2 V e n e e r 2 9 V Page 3.3 UF R e s i n s 30 3.4 F o l i a g e and B a r k 31 3.5 G l u e M i x P r o p e r t i e s 33 3.6 D i f f e r e n t i a l S c a n n i n g C a l o r i m e t r y 34 3.7 Plywood M a n u f a c t u r e 35 3.8 B o n d - Q u a l i t y T e s t i n g 36 3.9 S t a t i s t i c a l A n a l y s e s 37 4.o RESULTS 4.1 M o d i f i e d C o m m e r c i a l UF G l u e 38 4.2 M o d i f i e d L a b o r a t o r y UF G l u e ( U F i ) 38 4.3 S t a t i s t i c a l A n a l y s e s 39 5.0 DISCUSSION 5-1 F o l i a g e and B a r k P r o p e r t i e s 41 5.2 M o d i f i e d C o m m e r c i a l UF G l u e P r o p e r t i e s 42 5-3 D i f f e r e n t i a l S c a n n i n g C a l o r i m e t r y 46 5-4 Bond Q u a l i t y o f M o d i f i e d Commercial UF G l u e 5.4.1 D r y t e s t 47 5.4.2 Vacuum p r e s s u r e - o n e c y c l e 50 5.4.3 Vacuum p r e s s u r e - f i v e c y c l e s 53 5.4.4 B o i l - d r y - b o i l t e s t 57 5.5 M o d i f i e d L a b o r a t o r y UF G l u e ( U F i ) P r o p e r t i e s 58 5.6 Bond Q u a l i t y o f M o d i f i e d L a b o r a t o r y UF G l u e ( U F i ) 59 v i Page 5.6.1 Dry t e s t 59 5.6.2 Vacuum pressure-one c y c l e 61 5.6.3 Vacuum p r e s s u r e - f i v e c y c l e s 62 5.7 Use of F o l i a g e and Bark with UF Resins 64 6.0 CONCLUSIONS 67 LITERATURE CITED 70 APPENDICES 109 v i i L I S T OF TABLES T a b l e Page 1 V e n e e r q u a l i t y a n a l y s e s 80 2 V e n e e r r o u g h n e s s measurements 81 3 F o l i a g e and b a r k powder p r o p e r t i e s 82 4 G l u e mix p h y s i c a l p r o p e r t i e s 83 5 Average (n=20) s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s o f UF g l u e t r e a t m e n t c o m b i n a t i o n s 84 6 Average (n=20) s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s o f U F i g l u e t r e a t m e n t c o m b i n a t i o n s 85 7 A n a l y s i s o f v a r i a n c e f o r d r y - s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s f o r t e s t i n g the e f f e c t o f g l u e , m i x and p r e s s i n g t ime on t h e UF g l u e bond q u a l i t y 86 8 A n a l y s i s o f v a r i a n c e f o r vacuum p r e s s u r e -'shear "strengths and wood f a i l u r e p e r c e n t a g e s f o r t e s t i n g t h e e f f e c t o f - g l u e mix and p r e s s i n g t ime on the UF g l u e bond q u a l i t y 87 9 A n a l y s i s , o f v a r i a n c e f o r vacuum p r e s s u r e f i v e c y c l e - s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s f o r t e s t i n g t h e e f f e c t o f g l u e mix and p r e s s i n g t ime on the UF g l u e bond q u a l i t y 88 10 A n a l y s i s o f v a r i a n c e f o r d r y - s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s f o r t e s t i n g the e f f e c t o f g l u e mix and p r e s s i n g t i m e on t h e U F i bond q u a l i t y 89 11 A n a l y s i s o f v a r i a n c e f o r vacuum p r e s s u r e -s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s f o r t e s t i n g the e f f e c t o f g l u e mix and p r e s s i n g t ime on t h e U F i g l u e bond q u a l i t y 90 12 A n a l y s i s o f v a r i a n c e f o r vacuum p r e s s u r e f i v e c y c l e - s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s f o r t e s t i n g t h e e f f e c t o f g l u e mix and p r e s s i n g t i m e on the U F i g l u e bond q u a l i t y 91 v i i i Table Page 13 Duncan's multiple range tests for shear strengths of treatments bonded with UP glue 92 14 Duncan's multiple range tests for wood f a i l u r e percentages of treatments bonded with UF glue 93 15 Duncan's multiple range tests for shear-strengths of treatments bonded with UFi glue 94 16 Duncan's multiple range tests for wood f a i l u r e percentages of treatments bonded with UFi glue 95 i x LIST OF FIGURES Figure Page 1 DSC thermograms of UF r e s i n with wheat f l o u r , 30% f o l i a g e and 30$ bark 96 2 Dry-shear strengths and wood f a i l u r e percentages f o r treatments bonded with the commercial UF glue 97 3 Vacuum pressure-shear strengths and wood f a i l u r e percentages for treatments bonded with the commercial UF glue- 98 4 Vacuum pressure f i v e cycle-shear strengths and wood f a i l u r e percentages for treatments bonded with the commercial UF glue 99 5 Dry shear strengths and wood f a i l u r e percentages for treatments bonded with the laboratory UF glue (UFi) 100 6 Vacuum pressure-shear strengths and wood f a i l u r e percentages for treatments bonded with the laboratory UF glue (UFi) 101 7 Vacuum pressure f i v e cycle-shear strengths and wood percentages for treatments bonded with the laboratory UF glue (UFi) 102 8 Dependence of plywood bond qua l i t y on the UF glue mix and pressing time i n t e r a c t i o n according to dry-shear strengths and wood -f a i l u r e percentages 103 9 Dependence of plywood bond qua l i t y on the UF glue mix and pressing time i n t e r a c t i o n according to vacuum pressure-shear strengths and wood f a i l u r e percentages 104 10 Dependence of plywood bond quality on the UF glue mix and pressing time i n t e r a c t i o n according to vacuum pressure f i v e cycle-shear strengths and wood f a i l u r e percen-tages 105 X F i g u r e Page 11 Dependence o f plywood bond q u a l i t y on t h e U F i g l u e mix and p r e s s i n g t i m e i n t e r a c t i o n a c c o r d i n g to d r y - s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s 106 12 Dependence o f plywood bond q u a l i t y on t h e U F i g l u e mix and p r e s s i n g - t i m e i n t e r a c t i o n a c c o r d i n g to vacuum p r e s s u r e - s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s 107 13 Dependence o f plywood bond q u a l i t y on the U F i g l u e mix and p r e s s i n g t i m e i n t e r a c t i o n a c c o r d i n g to vacuum p r e s s u r e f i v e c y c l e -s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n -t a g e s 108 x i ACKNOWLEDGEMENT The deepest g r a t i t u d e i s expressed to Dr. J.W. Wilson, F a c u l t y o f F o r e s t r y , The U n i v e r s i t y o f B r i t i s h Columbia, and Dr. P.R. S t e i n e r , F o r i n t e k Canada C o r p o r a t i o n , under whose s u p e r v i s i o n t h i s study was accomplished. A p p r e c i a t i o n i s a l s o due Mr. L. V a l g and Dr. N.C. Franz, F a c u l t y o f F o r e s t r y , The U n i v e r s i t y o f B r i t i s h Columbia, f o r t h e i r a d v i c e and review o f the t h e s i s . The a s s i s t a n c e g i v e n by Mr. Axe l Andersen, F o r i n t e k Canada C o r p o r a t i o n , d u r i n g experimental phases o f the study and Mr. H a r j i t Grewal, graduate student, F a c u l t y o f F o r e s t r y , d u r i n g a n a l y s i s o f r e s u l t s i s t h a n k f u l l y noted. The author i s a l s o g r a t e f u l f o r b e i n g allowed to use F o r i n t e k Canada C o r p o r a t i o n L a b o r a t o r y f a c i l i t i e s and f o r m a t e r i a l s used. S p e c i a l thanks i s due to Dr. V. Nordin, Dean, F a c u l t y of F o r e s t r y , U n i v e r s i t y o f Toronto and CIDA Co o r d i n a t o r , f o r a s s i s t i n g the author's study i n Canada. F i n a l l y , the author i s a p p r e c i a t i v e of the f i n a n c i a l support from Canadian I n t e r n a t i o n a l Development Agency (CIDA). 1 1.0 INTRODUCTION Urea-formaldehyde (UF) i s the t y p i c a l r e s i n used i n hardwood plywood manufacture. The cured glue produces good, water r e s i s t a n t bonds but i s r e s t r i c t e d to i n t e r i o r use because of s u s c e p t i b i l i t y to hydrolysis at higher temperatures (about 60°C) i n the presence of moisture (Troughton, 1968). Recent concern on price and a v a i l a b i l i t y of petroleum, the raw material f o r exterior grade phenolic resins, provides incentive for developing new non-petroleum based resins or for improving d u r a b i l i t y of ex i s t i n g i n t e r i o r q u a l i t y adhesives. Many studies (Blomquist and Olson, 1964; G i l l e p s i e et a l . , 1964; Steiner, 1973; Steiner and Chow, 1974) --have indicated that UF modification with synthetic or natural materials improves d u r a b i l i t y . For example, UF modifications with melamine, p o l y v i n y l acetate, f u r f u r y l alcohol, addi-t i o n a l urea and other materials have improved UF bond d u r a b i l i t y . In the l a s t few years i n t e r e s t has focussed on using fo l i a g e and bark as extenders or substitutes f o r r e s i n i t s e l f , e s pecially with phenol-formaldehyde (PF). Research conducted at Forintek Canada Corp. has indicated that both materials have good adhesive properties (Steiner and Chow, 1975; Chow, 1977; Chow, Steiner and Rozon, 1979). 2 Wheat f l o u r i s the t y p i c a l extender i n UF and PF mixes. I n UF f o r m u l a t i o n s , the extender comprises about kOfo of the mix t o t a l s o l i d s content. The amount o f wheat f l o u r used f o r plywood manufacture i s enormous. I n North America the t o t a l amount employed f o r t h i s purpose i s more than 45 thousand m e t r i c tons per year, i n F a r E a s t coun-t r i e s more than 200 thousand m e t r i c tons per year are used (Barton et a l . , 1978). I n Peru, the plywood i n d u s t r y uses on l y UF r e s i n and the consumption of wheat f l o u r i s more than one thousand m e t r i c tons per year (Rosales, 1980). The p r i c e o f wheat f l o u r has t r i p l e d i n r e c e n t years to about 20 to 25 Cdn. cents per kg and supply f o r t h i s purpose i s i n c o m p e t i t i o n with food needs. T h i s i s aggra-va t e d i n d e v e l o p i n g c o u n t r i e s where the import cost o f wheat f l o u r i s a gr e a t burden. The importance of r e p l a c i n g wheat f l o u r by l o c a l products i s e v i d e n t . In view o f the above, the f i r s t o b j e c t i v e o f t h i s study was to evaluate B.C. white spruce [ P i c e a g l a u c a (Moench.) Voss.] f o l i a g e and western hemlock [Tsuga h e t e r o -p h y l l a (Raf.) Sarg.] bark powders as m o d i f i e r s f o r plywood UF r e s i n s with purpose of improving glue bond d u r a b i l i t y ( m o d i f i e r a c t i o n ) . A second o b j e c t i v e was to examine the i n f l u e n c e o f these m a t e r i a l s on UF glue p r o p e r t i e s with p o s s i b i l i t y of r e p l a c i n g wheat f l o u r by f o l i a g e or. bark (extender a c t i o n ) . 3 The o r i g i n a l i n t e n t i o n o f t h i s work was to evaluate f o l i a g e and "bark from P e r u v i a n t r e e s p e c i e s . E f f o r t s to o b t a i n these m a t e r i a l s f a i l e d and t h e r e f o r e Canadian products were used. However, i t i s hoped t h a t r e s u l t s from t h i s study w i l l p r o v i d e a basis' f o r e v a l u a t i o n o f P e r u v i a n products i n the near f u t u r e . 4 2.0 REVIEW OF LITERATURE 2.1 Urea-formaldehyde Resin.Characteristics A UF r e s i n i s the condensation product of urea and formaldehyde. These can be polymerized to an e f f e c t i v e r e s i n under proper molar r a t i o s , concentration, tempera-ture, time and pH conditions.-(Rayner, 1965). By varying these factors a wide.variety of UF resins can be made. Consequently, a UF r e s i n i s not a single compound of fix e d chemical i d e n t i t y and i t s composition i s not well defined. Steiner (1973)» indicated that the formaldehyde-to-urea molar r a t i o governs to some extent the ultimate bond dura-b i l i t y . For s p e c i f i c purposes, such as i n plywood, veneering and assembly gluing, the molar r a t i o i s usually lUsl . 7 5~l.9F and r a r e l y above 1U:2F (Rayner, 1965). The UF mix also contains a substantial proportion of protein-starch exten-der, a minor proportion of l i g n o c e l l u l o s i c f i l l e r , water and an acid s a l t c a t a l y s t ( S e l l e r s , 1976). UF r e s i n reaction rate during the curing process i s increased considerably by acids or substances capable of l i b e r a t i n g acid when mixed with the r e s i n . Setting consists of chemical curing and migration of the water which i s pa r t l y contained i n the l i q u i d glue and p a r t l y chemically l i b e r a t e d from the r e s i n during the condensation process (Kollmann et a l . , 1975). 5 Cured UF resins regardless of type or extension are weakened "by continued exposure to temperatures from 4 9 ° to 7 0°C and the higher the temperature the greater the ef f e c t (Blomquist and Olson, 1 9 5 7 ) ' Good quality UF glues produce good plywood grades and highly cold water r e s i s t a n t "bonds. The main advantages of UF resins are t h e i r low cost, . compatibility with low cost extenders, nontoxicity and v e r s a t i l i t y . They can be formulated to cure at any tempe-rature between 2 0 and 1 5 0°C and they can be re a d i l y modified or copolymerized with many materials to f i t a variety of applications (Meyer, 1 9 7 9 ) . Other advantages of UF resins are t h e i r resistance to fungi, worms and termites, t h e i r lower s e n s i t i v i t y to wood moisture when -compared to pheno-l i c s and the fact that they produce gluelines v i r t u a l l y i n v i s i b l e (Meyer, 1 9 7 9 ) . Besides hydrolysis at high temperature, another d i s -advantage of UF i s the pungent odor of formaldehyde released during manufacture and use of products. 2 . 2 Modifiers and Extenders for UF Resins In t h i s study the term modifier w i l l be used to mean a material with inherent adhesiveness, that increases glue d u r a b i l i t y (resistance to moisture and heat). An extender i s a material having some adhesive action added to an adhesive to reduce the amount of primary binder required per unit 6 a r e a o f adherend s u r f a c e (CSA Standard 0112M-1977). On the other hand, a f i l l e r i s d e f i n e d as a non-adhesive substance added to an adhesive to improve i t s working p r o p e r t i e s , permanence, gap f i l l i n g or other q u a l i t i e s ( S h i e l d s , 1975)' Many s t u d i e s concerned' 1 with UF have i n d i c a t e d t h a t t h e i r r e s i s t a n c e to hig h temperatures and humidity can he improved by m o d i f i c a t i o n with s y n t h e t i c or n a t u r a l m a t e r i a l s . M o d i f i c a t i o n o f commercial UF by adding mela-mine and r e s o r c i n o l showed t h a t any f o r t i f i c a t i o n was b e t t e r than the unmodified r e s i n but no a d d i t i o n l e v e l was b e t t e r than s t r a i g h t melamine (Blomquist and Olson, 1964). .Poly-v i n y l a c e t a t e and bloo d used as m o d i f i e r s a l s o improved the d u r a b i l i t y o f UF r e s i n bonds under c o n t r o l l e d c o n d i t i o n s of temperature and humidity f o r f i v e years ( G i l l e p s i e et a l . , 1964). The bes t performances were obtained by modi-f y i n g UF with p o l y v i n y l a c e t a t e at 46:54 r a t i o and with b l o o d at 17:83 r a t i o . Use of m o d i f i e r s at h i g h e r l e v e l s gave l e s s s a t i s f a c t o r y performance due to i n c r e a s e d mois-t u r e s e n s i t i v i t y . The a d d i t i o n o f bloo d albumin a l s o s u b s t a n t i a l l y improved the performance o f UF bonds exposed to h i g h temperatures and moisture (Thomas and T a y l o r , 1962). As the l e v e l o f bloo d was i n c r e a s e d shear s t r e n g t h v a l u e s i n c r e a s e d f o r both unextended and wheat f l o u r extended r e s i n s . Organic m o d i f i e r s , such as f u r f u r y l , a l c o h o l and 7 imidazolidinone have been evaluated at d i f f e r e n t l e v e l s of addition (Steiner and Chow, 1974). R e l a t i v e l y small amounts of modifiers added as monomers to UF resulted i n increased wood-glue bond d u r a b i l i t y and i n increased softening temperature of the cured r e s i n . The influence of other natural products as modifiers and extenders has been reported i n numerous studies. Hirata and Mineura (1974) used various potato starches with UF. They indicated that apart from color and odor drawbacks these starches could s a t i s f a c t o r i l y substitute f o r wheat f l o u r as extender. Rayner (I965) reported that large addi-tions of starch make a UF glue sensitive to moisture and support mould. Wheat f l o u r i s the most accepted extender today but maize, potato and tapioca starches are s t i l l used i n various parts of the world. Blomquist and Olson (1957) pointed out that wheat f l o u r used as UF extender had no pronounced effects on heat resistance. I t has been indicated, however, that addition of other materials, such as walnut-shell f l o u r , improved the d u r a b i l i t y of Douglas-f i r laminates (Steiner, 1973)' Sawdust of various woods has been evaluated as plywood glue f i l l e r (Kubota and Saito, 1974). Results indicated the f e a s i b i l i t y of using sawdust as f i l l e r f o r both UF and phenolic glues. Fine particleboard sander dust performed s a t i s f a c t o r i l y as phenolic extender (Knudson et,al.;, 1978). Mineral f i l l e r s 8 are also used. S t r i c k l e r and Sawyer (1974) developed four phenolic formulations using two types of attapulgite clays as the f i l l e r - e x t e n d e r system. Plant t r i a l s demons-trated the f e a s i b i l i t y of using t h i s material i n commercial production. Successful use of so many d i f f e r e n t materials as f i l l e r s , extenders and modifiers with UF proves the great v e r s a t i l i t y and compatibility of these r e s i n s . Research on the use of bark or bark extracts as adhe-sive!' extender or modifier has been carried out i n several laboratories. McLean and Gardner (1952) indicated the p o s s i b i l i t y of using tannin extracts from western hemlock bark either with formaldehyde or PF as a plywood adhesive. Herrick and Bock (1958) developed thermosetting glues for exterior plywood by combining bark extracts with polyme-thylol-phenol. Formulations containing 49$ bark extract, 34% polymethylol-phenol and 17% f i l l e r produced acceptable exterior grade Douglas-fir plywood. The bark of western hemlock has been recognized as a p o t e n t i a l source of vege-table tannins for many years. Scott (1956) stated that the tannin content i n western hemlock bark amounts 8 to 9%. Anderson et a l . (1974) reported that when paraformal-dehyde is'added to white f i r (Abies concolor Gord. & Glend.) bark p a r t i c l e s and processed into a board, formaldehyde released during the hot-press cycle reacts i n s i t u with 9 bark polyphenolic compounds forming a water r e s i s t a n t bonding agent. The influence of untreated bark on both UF and PF formulations has been investigated. Hamada et a l . (1969) indicated that addition of wattle (Acacia mollissima Willd.) bark powder to PF formed a mix with excellent flow proper-t i e s and that s e t t i n g time was shortened by bark addition. Imura et a l . (1974) used the bark powder of Japanese larch [Larix l e p t o l e p i s (Sieb. and Zucc.) Gord.] with UF for gluing birch (Betula spp.) boards. Bark powder proved ef f e c t i v e i n improving bond- d u r a b i l i t y . More recently, Steiner and Chow (1975) investigated factors influencing use of western hemlock bark extracts as adhesives. Bark age and method of extraction were found to influence adhesive q u a l i t y . They pointed out that bark extracts o f f e r p o t e n t i a l for exterior grade particleboard and plywood, i f e x t r a c t i v e - i n s t a b i l i t y problems are over-come . The u t i l i z a t i o n of fol i a g e as extender or modifier has not been investigated extensively. One of the few studies indicates that phenolic and carbohydrate substances i n f o l i a g e have simpler, smaller molecular structures than wood and that these lower molecular weight components may provide greater chemical r e a c t i v i t y with synthetic resins (Chow, 1977). The same author points out that c e r t a i n 10 f o l i a g e component blends may produce a high-performance polymer mixture with p o t e n t i a l adhesive properties. Furthermore, the addition of fo l i a g e to an adhesive mix may have a humectant function influencing v i s c o s i t y and preventing dry-out of the glueline during assembly. Chow (1977) also examined f o l i a g e as extender f o r both l i q u i d and powdered PF re s i n s . He concluded that f o l i a g e not only can be used as extender, but can also act as a p a r t i a l replacement f o r the r e s i n i t s e l f . More recently, Chow, Steiner and Rozon (1979) reported on the e f f i c i e n c y of coniferous foliage as extender for powdered PF r e s i n . They examined the adhesive p o t e n t i a l of f o l i a g e without addition of PF; the influence of fol i a g e content i n a powdered r e s i n system on the shear strength and i n t e r n a l bond i n plywood-type laminations; and also fabricated experimental waferboard with foliage-phenolic r e s i n s . Results of these experiments reaffirm that f o l i a g e by i t s e l f has inherent adhesive properties. They also showed by scanning electron microscope (SEM) that pure fol i a g e adhesive flows almost l i k e a phenolic mix, and pointed out that t h i s s i m i l a r rheological property demons-trates compatibility of these materials as mixed bonding agents. 11 2.3 Factors A f f e c t i n g Glue Extender Performance The most widely used extender i n i n t e r i o r UF formu-l a t i o n s i s wheat f l o u r . Special wheat f l o u r s have been developed to optimize properties. In consequence, new materials that are to "be used f o r t h i s purpose should have, to a cert a i n extent, s i m i l a r c h a r a c t e r i s t i c s . The fundamental properties required of extenders i s that they b u i l d and maintain a uniform v i s c o s i t y and that they hold the glue on the wood surface. In addition, they should improve performance by increasing pot l i f e and improving the bonding capacity of a s p e c i f i c quantity of mix so l i d s (Robertson, 1966). Robertson (1974) indicated that when using wheat f l o u r as extender i t should meet s p e c i f i c requirements such as: Uniformity; Protein content maximum 10%', Ash content maximum 0.55$; pH about 6 .0; P l a i n (no phosphates or bleaching); Low to medium water requirement; Fine p a r t i c l e size; Stable; Easy mixing; and Minimum lumping tendency. Wheat, i s .."unique i n that i t i s the only cereal containing s i g n i f i c a n t quantities of the protein substance, gluten. Gluten has inherent adhesiveness and has an excellent capacity f o r b u i l d i n g and holding v i s c o s i t y i n an extended mix (Robertson, 1979)* H i l l (1952) had previously indicated that the protein content of wheat i s an i n d i c a t i o n of the amount of gluten present and that i t i s t h i s gluten content 12 which determines i t s q u a l i t y as an extender. Flour con-t a i n i n g excessive gluten causes e r r a t i c v i s c o s i t y behavior and forms sludge which obstructs glue flow. Furthermore, bleached and phosphated f l o u r s can also cause d i f f i c u l t y due to the treatment they have received. They may accele-rate r e s i n curing to a degree that impairs properties of that glue mix. Extender p a r t i c l e - s i z e has been indicated as influ e n c i n g glue properties, e s p e c i a l l y v i s c o s i t y and spreading. Coarse p a r t i c l e - s i z e causes excessive adhesive thickening i n the spreader and s e t t l e s during storage (Knudson et a l . , 1978). Kubota and Saito (1974) reported that f i l l e r p a r t i c l e - s i z e a ffects the temporary bonding strength of urea r e s i n . Wood powder,-/with 90%> of the p a r t i c l e size smaller than 400-mesh, mixed with UF gave plywood strength equivalent to that when wheat f l o u r was used. Stone and Robitscheck (1978) pointed out that such factors as p a r t i c l e - s i z e , drying temperature, weight con-sistency and moisture content of extender materials have r e l a t i v e importance. The most c r i t i c a l f a c t o r i s the inhe-rent chemical nature of the material. 13 2.4 F a c t o r s A f f e c t i n g plywood Bond Q u a l i t y 2.4.1 Veneer q u a l i t y Veneer moisture content, s u r f a c e roughness, s u r f a c e aging, d e n s i t y and l a t h e checks have been d e s c r i b e d as f a c t o r s a f f e c t i n g plywood bond q u a l i t y . Veneer d r y i n g to a moisture content e i t h e r too hig h or too low, s e r i o u s l y a f f e c t s bond q u a l i t y . E x c e s s i v e moisture areas i n the veneer cause steam pr e s s u r e e r u p t i o n s ( b l i s t e r s ) o f plywood laminates d u r i n g or immediately a f t e r hot p r e s s i n g . On the other hand, veneers s u b j e c t e d to exces-s i v e d r y i n g can develop "surface i n a c t i v a t i o n " which produces plywood of poor bond q u a l i t y (Chow et a l . , 1973) • Veneer s u r f a c e roughness i s a s i g n i f i c a n t f a c t o r i n plywood g l u i n g . V a r y i n g roughness causes d i f f e r e n c e s i n optimum glue spread and a l s o r e q u i r e s h i g h e r p r e s s u r e to o b t a i n equal s u r f a c e contact area. Surface roughness due to mechanical p r e p a r a t i o n , c a n i n c e r t a i n s i t u a t i o n s i n c r e a s e bond s t r e n g t h by i n t e r l o c k i n g when t e s t e d i n shear. I n c r e a s i n g roughness, however, produces i n e v i t a b l y t h i c k e r bonds with more d e f e c t s and l o c a l i z e d s t r e s s e s which i n the end reduce s t r e n g t h . Marian _et a l . (1958) found t h a t s t r e n g t h o f edge glued bonds i n c r e a s e d with s u r f a c e roughness u n t i l a p o i n t at which the s i m u l t a n e o u s l y d e c r e a s i n g s t r e n g t h o f the wood and i n c r e a s i n g p o r o s i t y 14 caused the wood to "break. Beyond t h i s p o i n t , f u r t h e r i n c r e a s e i n roughness reduced the shear s t r e n g t h . L a t e l y , Hancock (1980) found t h a t wood f a i l u r e percentage i s a f f e c t e d a l s o by the degree of veneer roughness. Smooth veneer had approximately 17%> h i g h e r wood f a i l u r e than the average of the medium and rough s u r f a c e veneers. The same r e l a t i v e e f f e c t upon wood f a i l u r e with r e s p e c t to roughness was seen r e g a r d l e s s o f the type o f t e s t . Lathe checks are known to reduce veneer q u a l i t y and i n f l u e n c e plywood q u a l i t y . P a l k a (1964) found t h a t p l y -woods made w i t h sawn-veneers (no l a t h e checks) had an average shear s t r e n g t h 1 . 5 times h i g h e r than plywoods made with r o t a r y cut veneers. Chow (1974) gave photo-gr a p h i c evidence t h a t the behavior o f plywoods made wit h r o t a r y cut veneers under l o a d i s completely d i f f e r e n t from t h a t o f sawn-veneer plywoods. He a l s o i n d i c a t e d t h a t shear s t r e n g t h was g r e a t l y i n f l u e n c e d by the depth o f glue p e n e t r a t i o n i n t o l a t h e checks. Aging of the wood s u r f a c e i s another f a c t o r a f f e c t i n g bond q u a l i t y . Stumbo (1964) suggested f o u r p o s s i b l e mechanisms t h a t i n f l u e n c e s u r f a c e g l u i n g p r o p e r t i e s due to agings (1) M i g r a t i o n -to the s u r f a c e o f extraneous m a t e r i a l t h a t i s d e t r i m e n t a l t o wood g l u a b i l i t y ; (2) Che-m i c a l changes of the wood substance or of the extraneous m a t e r i a l a t the s u r f a c e , p r o d u c i n g a l e s s g l u a b l e s u r f a c e ; 15 (3) Decreases i n the s u r f a c e - f r e e energy due to a d s o r p t i o n of a i r b o r n e contaminants and chemical changes or mo l e c u l a r rearrangements; and (4) Decrease i n s t r e n g t h o f the wood f i b e r s due to o x i d a t i o n . The same author i n a study o f D o u g l a s - f i r and redwood [Sequoia sempervirens (D. Don) End l . ] s u r f a c e s p r o t e c t e d a g a i n s t contamination found bond s t r e n g t h reduced by as much as 12 to 50$ over expo-sure p e r i o d s r a n g i n g from 3 "to 5 months. N o r t h c o t t et a l . (1959) r e p o r t e d l i t t l e d i f f e r e n c e when g l u i n g Engelmann spruce ( P i c e a engelmannii P a r r y ) veneer s t o r e d 30 days and t h a t s t o r e d o n l y three days. The above i n d i c a t e s t h a t bond q u a l i t y decreases as the veneer age i n c r e a s e s and, t h e r e f o r e , the time elapsed between p e e l i n g and g l u i n g should be as s h o r t as p o s s i b l e . 2.4.2 Glue v i s c o s i t y Glue v i s c o s i t y i s a rough index o f r e s i n m o l e c u l a r s i z e or degree o f p o l y m e r i z a t i o n which a f f e c t s flow, transfer?;: p e n e t r a t i o n and w e t t i n g ( R i c e , I965). A f t e r glue has been spread on wood, i t must pass through s e v e r a l flow stages b e f o r e a s t r o n g bond can be formed. I t must: (1) Flow l a t e r a l l y to form a continuous f i l m ; (2) T r a n s f e r from the wood s u r f a c e on which i t was spread to the oppo-s i t e , unspread s u r f a c e ; (3) P e n e t r a t e i n t o both s u r f a c e s of the j o i n t ; (4) Wet the wood s u r f a c e ; and (5) S o l i d i f y 16 into a strong substance (Brown et a l . , 1952). These stages, except the f i f t h , involve flow and, therefore, are greatly influenced by adhesive f l u i d i t y . High v i s c o s i t y o ffers resistance to spreading and reduces glue flow. On the other hand, i f a condition of too low v i s c o s i t y e x i s t s , then excessive glue migration away from the surface occurs and t h i s may a f f e c t bond qua-l i t y . V i s c o s i t y influences eventual bond q u a l i t y . Rice (I965) has indicated the dependence of bond qua l i t y on v i s c o s i t y . High v i s c o s i t y extended UF resins produced thicker gluelines, which were s i g n i f i c a n t l y more durable than those made with low unextended resin s . Ramos Garcia (1965)* however, obtained higher shear strength values with lower v i s c o s i t y PF resins than with higher v i s c o s i t y ones. The ef f e c t of v i s c o s i t y on bond qu a l i t y appears controversial. This e f f e c t should not be viewed indepen-dently but along with other factors, such as a r e s i n type, wood moisture content and assembly and pressing times. 2.4.3 Glue application, assembly time and pressing Spread l e v e l s and mix formulations vary according to glue type and wood. There are useful maximum and minimum l i m i t s to spread l e v e l . H i l l (1952) indicates that when 2 hot pressing these l i m i t s are 11 to 16 kg/100 m (24 to 17 35 lb /1000 f o r unextended r e s i n s and 16 to 20 kg /100 m^ (35 "to kk lb /1000 f t ) o f s i n g l e g l u e l i n e f o r extended ones. High spread l e v e l s are prone to e x c e s s i v e squeeze-out and b l i s t e r f o r m a t i o n due to h i g h g l u e l i n e m o i s t u r e . I n a d d i -t i o n , h i g h e r amounts o f water' must be absorbed by the wood or i t must be evaporated f o r complete c u r i n g ^ thus l o n g e r p r e s s i n g time i s n e c e s s a r y . On the other hand, i f the spread l e v e l i s too low the water d i f f u s e s r a p i d l y i n t o the wood and adhesion i s reduced (Kollmann et a l . , 1975)' Assembly time i s the l e n g t h o f time elapsed between glue s p r e a d i n g and p r e s s u r e a p p l i c a t i o n . T h i s i s d i v i d e d as open assembly time, where the spread glue i s exposed on open veneer, and c l o s e d assembly time, the p e r i o d b e t -ween the making up_ o f an assembly, and the a p p l i c a t i o n o f p r e s s u r e . Assembly time allows f o r some moisture absorp-t i o n by the veneer and some r e d u c t i o n i n v i s c o s i t y due to moisture l o s s . The p a r t i c u l a r c h a r a c t e r i s t i c s o f a glue system have c o n s i d e r a b l e e f f e c t on assembly time. Veneer d e n s i t y , moisture content and spread l e v e l a l s o p l a y important r o l e s . Dense veneers r e t a i n more water i n the g l u e l i n e than do l e s s dense veneers and h i g h spread l e v e l s are conducive to l o n g e r assembly times, whereas low spread l e v e l s are a s s o c i a t e d with s h o r t e r assembly times ( H i l l , 1952). The e f f e c t s of r e s i n age and veneer moisture content 18 on assembly time have been reported (Marra, 1964). "A fresh mix with a short - assembly time tended to produce a starved state on high moisture veneer, but was optimum for d r i e r veneer. As assembly time increased, however, the optimum passed from dry veneer to higher moisture veneer. Furthermore, as the age of the mix increased, higher moisture veneers and shorter assembly times were required. Driehuyzen and Wellwood (i960) investigated the effects of glue room temperature and humidity on open assembly time. They indicated that at the same tempera-ture, high r e l a t i v e humidities permitted longer assembly times than low r e l a t i v e humidities. Lowering the tempe-rature and increasing the r e l a t i v e humidity simultaneously resulted i n a substantial increase i n maximum allowable open assembly time. Adequate pressure i s required i n gluing f o r various reasons, such as to: (1) Bring surfaces into as close contact as possible, thereby producing a thi n glueline, squeezing out excess glue and increasing penetration to undamaged portions of the adherend; (2) Ensure good trans-f e r to the unspread veneer face; and (3) Maintain good contact between veneers of normal roughness during f i n a l glue cure. Pressure i s applied according to wood com-pressive strength. Pressures usually applied are 200 p s i 19 f o r Douglas-fir. Excessive pressure leads to compression loses i n plywood thickness (Kennedy, 1965)• -During-pressing, heat i s applied for various reasons, such as to (1) Increase rate of chemical reaction i n the curing of thermosetting glues; (2) Decrease v i s c o s i t y and increase penetration; (3) Increase wood p l a s t i c i t y ; and (4) Remove solvent from the glueline by evaporation, d i f f u -sion or c a p i l l a r y movement (Kollmann et a l . , 1975)' Heating of the wood involves simultaneous heat and mass transfer peculiar to wood. Changes i n temperature induce moisture movements i n wood. For optimum bonding, veneer should contain a d e f i n i t e amount of moisture. Fisher and Bensend (1969) have indicated that with short hot press times the glue does not receive a s u f f i c i e n t quantity of thermal energy to a t t a i n a complete cure; but at long hot press times several factors can lower panel q u a l i t y . The veneer can be over-dried causing not only severe i n t e r -f a c i a l stresses while i n the press, but severe stresses during reconditioning of the panel to the desired moisture content. Also by producing a complete cure i n the hot press instead of allowing the cure to continue i n a hot stacking period, stresses may be introduced i n the glueline i t s e l f . Chow et a l . (1973) indicated that the curing tempera-ture for a glueline depends on the adhesive used among other factors. Inadequate curing temperature and i n s u f f i -20 cient pressing time are causes f o r undercured bonds. They also reported that with phenolic resins a minimum inner glueline temperature of about 120°C i s necessary to pass the CSA wood f a i l u r e standard when the vacuum pressure-soak method of t e s t i n g i s used. 2.5 Glue Cure Indicators A n a l y t i c a l methods, such as u l t r a v i o l e t spectroscopy (UV), thermal gravimetric analysis (TGA), d i f f e r e n t i a l scanning calorimetry (DSC) and other technigues are useful for determining degree of cure, curing properties and thermal s t a b i l i t y of thermosetting r e s i n s . Chow and Hancock (1969) developed a simple spectro-photometry method for measuring the degree of cure of phenolic r e s i n s . They indicated that t h i s method i s good for p r e d i c t i n g bond undercure and d u r a b i l i t y . In addition, the influence of pressing time and temperature on glue bond formation can be determined. D i f f e r e n t i a l thermal analysis (DTA) has been found useful f o r t r a c i n g d i r e c t l y the chemical r e a c t i v i t y of a glue. Chow and Steiner (1975) also examined the thermal reactions of UF by DTA during various stages of r e s i n synthesis. The effects of ammonium chloride concentration, storage time and addition of extra urea also were examined. They concluded that the exothermic peak temperature of UF 21 i n the presence of ammonium chloride catalysts i s important to the pot l i f e , assembly time tolerance and curing of the r e s i n . Chow and Steiner (1979) compared d i f f e r e n t i a l scanning calorimetry (DSC) thermograms of both l i q u i d and powdered commercial PP r e s i n s . They found that the mechanism of cure f o r these resins i s d i f f e r e n t . 2.6 Some Aspects of"Wood Adhesion Adhesion i s a complex science i n v o l v i n g chemical, physical and mechanical p r i n c i p l e s . The wood bonding pro-cess i s especially complex, because the adherend i s a heterogeneous system. The surface of wood i s usually weakened by tools or exposure and the glue has to pene-trate beyond the surface to form a bond. In hot-setting operations the s i t u a t i o n becomes even more complex because the glue v i s c o s i t y changes, wood extractives may migrate to the surface and i n t r i n s i c moisture steams the surface (Meyer, 1979). Brown et a l . (1952) indicated that i n wood bonding two types of adhesion operate as: (1) Mechanical adhesion caused by anchorage r e s u l t i n g from hardened tentacles of glue extending into the wood; and (2) S p e c i f i c adhesion caused by anchorage r e s u l t i n g from forces of adhesion acting between molecules and atoms of the wood and glue. 22 The mechanism of mechanical adhesion i s explained by assuming that the glue, while s t i l l i n l i q u i d form penetrates into the wood c e l l c a v i t i e s . Thereupon, i t s o l i d i f i e s and the bond strength i s due, at l e a s t i n part, to i n t e r l o c k i n g of the two s o l i d s , the wood and the glue embedded i n the wood (Brown et a l . , 1952). When r e f e r r i n g to mechanical adhesion, Truax (1929) and other researchers have pointed out that mechanical adhesion alone would be quite inadequate to account f o r the strength of wood j o i n t s . Marian and Stumbo (1962) indicated that mechanical adhesion only contributes about 10 to 20%, of the t o t a l adhesive strength. Mechanical adhesion can operate with, wood, depending on j o i n t type and surface condition of the adherend member. Rough or damaged surfaces w i l l influence mechanical adhesion, but f o r smooth and undamaged surfaces t h i s influence i s minimal. S p e c i f i c or chemical adhesion i s explained on the basis of molecular or atomic a t t r a c t i o n between the adhesive and the wood surface. S p e c i f i c adhesion i s caused by p r i -mary valence forces or secondary valence (van der Waal's) forces (Marian and Stumbo, 1962). Kollmann et a l . (1975) stated that primary valences, ranging from 10 to 100 or more k cal/mole, are strong forces of a t t r a c t i o n between atoms. They determine the structure of molecules and appear i n some chemical processes. They are not important 23 f o r the phenomenon o f a d h e s i o n . The weaker s e c o n d a r y v a l e n c e s (2 t o 4 k c a l / m o l e ) d e c i d e the amount o f a d h e s i o n . A n o t h e r a u t h o r ( Z i s m a n , 1963) remarked t h a t a d h e s i o n i s c a u s e d by f o r c e s between m o l e c u l e s i n o r n e a r t h e s u r f a c e o f t h e two c o n t a c t i n g m a t e r i a l s and t h a t t h e s e a r e p r i m a -r i l y o f van d e r W a a l ' s and h y d r o g e n b o n d i n g t y p e s . H y d r o g e n b o n d i n g i s one t y p e o f s e c o n d a r y c h e m i c a l b o n d i n g i n w h i c h h y d r o g e n i o n s a r e m u t u a l l y s h a r e d by r e a c t i v e p o l a r g r o u p s , u s u a l l y c a r b o x y l o r h y d r o x y l . K l e i n (1975) has i n d i c a t e d t h a t the p o t e n t i a l f o r h y d r o g e n b o n d i n g depends upon t h e number o f r e a c t i v e groups i n r e s i n and wood m o l e c u l e s , w e t t a b i l i t y o f the a d h e s i v e and i t s a b i l i t y to c u r e i n p l a c e w i t h a minimum o f s h r i n k a g e and i n t e r n a l s t r e s s e s , w h i l e r e a c t i v e s i t e s on the r e s i n and wood m o l e c u l e s are s h a r i n g h y d r o g e n i o n s . I n a n a l y z i n g the f a c t o r s t h a t i n f l u e n c e t h e b o n d i n g p r o c e s s i n wood, M a r r a ( c i t e d i n M e y e r , 1979) has i n d i c a t e d t h a t t h e t r u e bond f o r m i n g p o t e n t i a l o f a g l u e must i n v o l v e b o t h bond f o r m a t i o n and bond p e r f o r m a c e . Bond f o r m a t i o n i n c l u d e s e s t a b l i s h i n g a d h e s i o n and a c h i e v i n g s t r e n g t h . Bond p e r f o r m a n c e i s r e f l e c t e d i n bond s t r e n g t h and p e r m a -n e n c e . He e x p l a i n e d t h a t t h e c o n d i t i o n s under w h i c h t h e s e f a c t o r s combine i n v o l v e f o u r s y s t e m s : (1) The b a s i c c h e m i c a l , p h y s i c a l and m e c h a n i c a l n a t u r e s o f the l i q u i d and s o l i d g l u e ; (2) The c o r r e s p o n d i n g p r o p e r t i e s o f t h e a d h e r e n d ; 2h (3) The consolidation conditions, including pressure, temperature, humidity and time; and (4) The exposure or service conditions of the f i n a l product. 2.7 Assessing Plywood Bond Quality The Canadian Standards Association (CSA) uses percen-tage wood f a i l u r e as the basis for assessing plywood bond qua l i t y . CSA defines wood f a i l u r e as "the area of wood f i b r e remaining at the glueline following completion of the s p e c i f i e d shear t e s t . Wood f a i l u r e i s determined by means of v i s u a l examination and expressed as a percentage of the unit test area." The reasoning behind the concept of wood f a i l u r e i s that the test specimen must have a glue bond strength at l e a s t equal to that' of the wood i n the specimen (Yavorski _et a l . , 1955) • ip^g v a l i d i t y of using percentage wood f a i l u r e has been questioned i n several cases. Marian and Stumbo (1962) pointed out that shear tests f o r wood are unsuitable because of the v a r i a t i o n i n density from l o g to l o g which makes wood f a i l u r e an a r b i t r a r y f i g u r e . Wood f a i l u r e as such i s a function of springwood-summerwood ratio' and d i s t r i b u t i o n . Plywood made of veneers -from a fast-grown l o g w i l l show d e f i n i t e l y higher wood f a i l u r e percentages than that from a slow-grown l o g . Shen (1958) indicated that certain variations i n the wood, glue, gluing procedure or i n t e s t i n g 25 and measurement methods may cause wood f a i l u r e to vary considerably. In pra c t i c e , the reading of percentage wood f a i l u r e i s a highly developed s k i l l subject to operator v a r i a b i l i t y . Some countries (Japan, Germany) use shear strength as the sole c r i t e r i o n f o r assesing plywood bond q u a l i t y . Shear strength i s defined i n terms of the ultimate shear strength (N/mm , lb/sq in) required to break a test plywood specimen i n tension shear. The rela t i o n s h i p between wood f a i l u r e and shear strength i s not well defined. Northcott (1952, 1955) postulated that there was poorer c o r r e l a t i o n between breaking load and service l i f e than between wood f a i l u r e and service l i f e . Shen (1958) indicated that breaking load i n Engelmann spruce (Picea engelmannii Parry) plywood was a better i n d i -cator of bond q u a l i t y than wood f a i l u r e . Palka (1964) found that an increase of shear strength was associated with higher wood f a i l u r e . Chow and Warren (1972) found that wood f a i l u r e i s a more sensitive measure of glue bond undercure than was shear strength. Chow (1974) explained that i n properly assembled*plywood with bonds having an optimum degree of cure, f i n a l shear strength has no d i r e c t r e l a t i o n s h i p with percentage wood f a i l u r e , but i s intimately influenced by the depth of lathe checks or veneer q u a l i t y . Chow and Chunsi (1979) derived an i n t r i n s i c r e l a t i o n s h i p 26 between shear strength and wood f a i l u r e which was applicable to 50 South Asian hardwoods (SG O.33 to 1.01). They i n d i -cated that i f a sound wood substrate i s used, the wood f a i l u r e percentage i s a good representation of bond strength, regardless of i t s d i r e c t or i n d i r e c t c o r r e l a t i o n with absolute strength. From the l i t e r a t u r e above, i t appears that a. r e l a t i o n -ship between shear strength and-wood f a i l u r e may e x i s t . This subject i s s t i l l c o ntroversial. I t has been suggested (Chow, 1974; Chow and Chunsi, 1979) that adoption of both shear strength and wood f a i l u r e as c r i t e r i a i n plywood-bond qu a l i t y control could be the best safeguard f o r ensuring a sa t i s f a c t o r y bond. 27 3.0 MATERIALS AND METHODS 3.1 Experimental Plan The experimental plan included four variables: Two wheat f l o u r extended UF resins; Two modifiers; Two pressing times; and Three modifier addition l e v e l s . The plan was as follows. Two UF resins: 1) Commercial plywood UF r e s i n (UF); and a 2) Laboratory synthesized, low mole-cular weight UF r e s i n (UFi). Two modifiers: 1) Ground white spruce f o l i a g e ; and 2) Ground western hemlock bark. Two pressing times: Six; and Ten min. Three modifier addition l e v e l s : 15; 30; and k5%. The experiment was divided into two stages. The f i r s t stage comprised evaluation of fol i a g e and bark as modifiers f o r the commercial UF r e s i n . The above variable combinations gave 12 treatments, two controls of wheat f l o u r extended commercial UF r e s i n were used giving a t o t a l of 14 treatments. Two panels were made f o r each treatment. The second stage evaluated fo l i a g e and bark as modifiers for a laboratory synthesized low molecular weight UF r e s i n (UFi). The variable combinations used gave four treatments, 28 two controls of wheat f l o u r extended low molecular weight UP r e s i n were used giving a t o t a l of six treatments. Only 30% modifier addition was evaluated i n t h i s case. From both stages a t o t a l of 20 treatments and 40 plywood panels were included i n the study. Plywood panels were prepared under the following conditions: 1) Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] veneer, 3.17 mm thickness; 2) Five-ply, 38 x 38 cm test panels; 3) Glue spread 32 kg/100 m2 (70 lb /1000 f t 2 ) of double glueline; 4) Closed assembly time 20-min; 5) Pressure 1.38 MPa; 6) ~ Pressing times 6 or 10-min; 7) Platen temperature l49°C; and 8) One panel per opening. Bond qua l i t y was evaluated by: 1) Dry tes t , following conditioning to atmospheric EMC; 2) Vacuum pressure-one cycle'! 3) Vacuum pressure-five cycles; and 4) B o i l - d r y - b o i l t e s t . Wood f a i l u r e percentage (CSA-0121-M1978). and-shear strength data, were used to assess bond: q u a l i t y . Wood f a i l u r e was read by the author of the study. 29 3.2 Veneer Dry, rotary-cut, 3.17 mm thickness, grade *A' Douglas-f i r veneers obtained from MacMillan Bloedel Ltd. were supplied by Forintek Canada Corp. (Western Forest Products Laboratory, Vancouver). These were cut into 38 x 38 cm squares and stored i n a controlled temperature-humidity room which approximated 5°$ r e l a t i v e humidity (dry bulb 26.7°C and EMC of about 6%), P r i o r to gluing, moisture content of i n d i v i d u a l veneers was checked by using an electronic moisture meter (Moisture Reg. 'L' Co.). A randomly selected sample of 5° veneer pieces was used f o r these measurements (Table 1). Veneer thickness v a r i a t i o n was estimated p r i o r to gluing by using an apparatus activated by a i r pressure and equipped with a micrometer (0.001-in accuracy). At random, f i f t y 38 by 38-cm veneer pieces were selected for these measurements. Veneer thickness was obtained by averaging f i v e readings on each piece (Table 1). Veneer roughness was estimated p r i o r to gluing by means of a v i s u a l veneer roughness scale developed by Northcott and Walser (1965). Randomly, f i f t y 38 by 38-cm veneer pieces were used for th i s t e s t (Tables.l. and 2). The depth of lathe checks was measured on a 2.54-cm cross section from the deepest point of lathe check. Depth of the three longest lathe checks was averaged and divided 30 by veneer thickness to give a percentage depth of lathe check. F i f t y randomly selected pieces (38 by 10-cm) were used for t h i s t e s t . Each piece and section was submerged i n a dye solution (gential v i o l e t ) and then l i g h t l y sanded. This permitted the stained part to be more e a s i l y observed and provided accurate measurements (Table 1 ) . Lathe-check angles were measured on a 2.54-cm cross section with a transparent protractor. Angle of the three longest lathe checks was averaged to represent the piece. The same veneer pieces used f o r lathe-check depth were used for these measurements (Table 1 ) . 3.3 UF Resins The commercial standard UF r e s i n (Casco UF 109) i s a high so l i d s (63^2.0$), aqueous r e s i n s o l u t i o n . I t i s a clear to s l i g h t l y cloudy viscous l i q u i d when fresh, becoming increasingly cloudy on storage. Casco UF 109 r e s i n , as indicated by the manufacturer meets i n d u s t r i a l need for a durable glue' that i s water r e s i s t a n t , fungus proof and can be used i n gluing both hardwoods and softwoods. The laboratory synthesized low molecular UF r e s i n (UFi) was used i n th i s study on the assumption that i t could provide a system with p o t e n t i a l f o r chemical reaction with fo l i a g e and bark low molecular weight phenolic compounds. I t i s generally agreed that the size of polymer molecules increase 31 at d i f f e r e n t stages of condensation-polymerization. Also, molecular growth occurs at the expense of reactive (methylol) groups, as the degree of polymerization increases the number of free reactive groups decreases (Parkes .and Taylor . 1 9 6 6 ) . Thus, a low molecular' weight -resin,-'product of low degree of condensation should have more available reactive groups to undergo reaction with eventual modifiers. The low molecular weight UF r e s i n (UFi) of molar r a t i o F/U=2 was prepared by placing 1500 g of 46.3% formaldehyde solution and 695 g of urea i n a reaction vessel, and pH was adjusted to about 8 with 50% sodium hydroxide (NaOH) solu-t i o n . The solution was heated to 70°C and the temperature was maintained 45-min. The solution was made s l i g h t l y a c i d i c (pH about 6) with 10% HC1 and then refluxed f o r 30-min. F i n a l l y , the mixture was cooled and neutralized with NaOH solution. Total s o l i d s content was about 63%. 3.4 Foliage and Bark White spruce f o l i a g e (95% needles) and western hemlock bark dried and pulverized were provided by Forintek Canada Corp. These materials were coll e c t e d approximately one year before used i n t h i s experiment. Foliage was col l e c t e d from a commercial logging s i t e (Princeton area) i n the i n t e r i o r of B r i t i s h Columbia while bark was collected from Eburne Sawmills D i v i s i o n , Vancouver, B.C. P r i o r to use as 32 modifiers, f o l i a g e and bark were a i r - d r i e d and put through a hammer m i l l , they were then oven-dried at 103 - 2°C u n t i l moisture content was about Q%. F i n a l l y , both materials were ground using a Pallman grinder 'L' 18. Moisture con-tent of f o l i a g e and bark was checked p r i o r to use i n the glue\mixes by oven-drying two f i v e g samples of powders (Table 3 ) . P a r t i c l e - s i z e d i s t r i b u t i o n s of fol i a g e and bark powders were determined by screen analyses using a shaker (100, 200 and 325-mesh screens) with 100 g samples. The screens were f i r s t shaken for 15-min and the weight of sample retained on each screen was recorded. The screens were then re-stacked, shaken for another 15-min and weighed again. The average value of two analyses was recorded. Foliage and bark pH was determined by using a standard Corning pH meter 125. The tests were conducted by mixing f i v e g sample of dry, powdered material and 200 ml of fr e s h l y d i s t i l l e d water. The average pH value of two measurements was recorded (Table 3)• Ash content data on foliage and bark was obtained from previous research at Forintek Corporation (Table 3 ) . The tests were performed i n accordance with ASTM D 1102-56 (1977). 33 3.5 G l u e M i x P r o p e r t i e s The- c o m m e r c i a l p l y w o o d UF g l u e m i x was p r e p a r e d f o l l o w i n g t h e m a n u f a c t u r e r ' s i n s t r u c t i o n s a n d t h i s was u s e d w i t h i n t h e recommended w o r k i n g p o t l i f e . The same i n s t r u c t i o n s w e r e f o l l o w e d t o p r e p a r e a l l o t h e r m i x e s i n c l u d i n g t h e l a b o r a t o r y s y n t h e s i z e d r e s i n . F o l i a g e a n d b a r k w e r e a d d e d t o t h e m i x a t 15, 30 and l e v e l s b a s e d o n r e s i n s o l i d s c o n t e n t ( o r 20, ^0 a n d 60% b a s e d o n e x t e n d e r c o n t e n t ) . The s t a n d a r d m i x f o r m u l a t i o n i s g i v e n i n A p p e n d i x I . G l u e m i x i n g was p e r f o r m e d w i t h a m e c h a n i c a l - e l e c t r i c a l m i x e r e q u i p p e d w i t h a s t e e l s t i r r e r . S t i r r e r r o t a t i o n s p e e d was 700 r.p.m. A f i v e g a l l o n . - p l a s t i c c o n t a i n e r was u s e d f o r m i x i n g g l u e c o m p o n e n t s . V i s c o s i t y m e a s u r e m e n t s w e r e p e r f o r m e d i n a c c o r d a n c e w i t h ASTM D2556-69 (1977) o n e - h r a f t e r m i x i n g a t 22±1°C. A B r o o k f i e l d s y n c h r o e l e c t r i c L V F v i s c o m e t e r w i t h s p i n d l e No. 4 a t 30 r.p.m. was u s e d . A 600 m l b e a k e r a nd 400 m l g l u e m i x w e r e u s e d f o r t h i s t e s t . PH was d e t e r m i n e d u s i n g a s t a n d a r d C o r n i n g pH m e t e r 125 f o u r - h r a f t e r m i x i n g . P r i o r t o pH d e t e r m i n a t i o n , t h e m i x (300 m l ) was s t i r r e d m a n u a l l y t o r e a c h i e v e h o m o g e n e i t y D e n s i t y was d e t e r m i n e d f o u r - h r a f t e r m i x i n g a t 2 2-l°C, u s i n g a 1000 m l g r a d u a t e d c y l i n d e r t a r e d a n d 1000 m l m i x . D e n s i t y was c a l c u l a t e d f r o m t h e w e i g h t / v o l u m e r a t i o . G e l a t i o n t i m e was m e a s u r e d f o u r h o u r s a f t e r m i x i n g . . 34 F i f t e e n grams o f m i x were p l a c e d i n a 25 m l t e s t t u b e and s t i r r e d r e g u l a r l y w h i l e s u s p e n d e d i n a h o t . w a t e r b a t h a t 60°C. The g e l a t i o n t i m e as a v e r a g e v a l u e f o r two s a m p l e s was r e c o r d e d f o r e a c h m i x . M i x s t a b i l i t y was d e t e r m i n e d b y v i s c o s i t y m e a s u r e m e n t s a t o n e , 24- and 4 8 - h r . A B r o o k f i e l d s y n c h r o e l e c t r i c LVF v i s c o m e t e r w i t h s p i n d l e N° 4 r o t a t e d a t 30 r.p.m. -was u s e d . 3.6 D i f f e r e n t i a l S c a n n i n g C a l o r i m e t r y D i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y (DSC) was u s e d t o e x a m i n e c u r i n g p r o p e r t i e s o f g l u e m i x e s p r e p a r e d f o r t h e s t u d y . The m e t h o d dep'erids'on m e a s u r i n g d i f f e r e n t i a l p o w e r o r h e a t i n p u t n e c e s s a r y t o k e e p a s a m p l e a n d a r e f e r e n c e s u b s t a n c e i s o t h e r m a l as t e m p e r a t u r e i s c h a n g e d l i n e a r l y ( B a u e r e t a l , , 1978). A l l d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y a n a l y s e s w e r e p e r f o r m e d on a P e r k i n - E l m e r DSC -2 i n s t r u m e n t . A s a m p l e o f a b o u t 2 mg was p l a c e d i n a n a l u m i n u m s a m p l e p a n and s e a l e d w i t h a c o v e r l i d . The s a m p l e was t h e n h e a t e d i n a DSC s a m p l e c e l l t o 250°C a t a c o n s t a n t r a t e o f 10°C/min ( F i g u r e 1) . Time r e q u i r e d f o r e a c h a n a l y s i s was a p p r o x i m a t e l y 30-m i n . 3 5 3 . 7 Plywood Manufacture The glue mixes were spread at about 3 2 k g / 1 0 0 nl ( 7 0 l b / 1 0 0 0 f t 2 ) of double glueline. This i s within the l i m i t s ( 3 0 - 40 k g / 1 0 0 m ) used i n i n d u s t r i a l p ractice and recommended by H i l l ( 1 9 5 2 ) . A mechanical spreader was used for glue ap p l i c a t i o n . Five-ply, 3 8 by 38.cm panels, were prepared. Each panel was comprised of f i v e randomly selected veneers. Standard plywood shear specimens were cut from each panel to have lathe checks pulled closed. Chow ( 1 9 7 * 0 found when te s t i n g white spruce plywood that shear strength was lower f o r specimens i n which lathe checks were pulled open rather than closed. For each treatment, two plywood panels were assembled. Each panel was coded with respect to glue type and pressing time, modifier and addition l e v e l . Twenty min closed assembly time (CAT) was used. This i s within the l i m i t s ( 1 0 to 30-min) used i n hot pressing operations. Rose ( 1 9 5 7 ) reported that when veneers of moderate moisture content ( 5 to Q%) are used, UF glue deve-lops maximum bond strength at CAT of 2 0 to 3 0 min. Two pressing times, 6 and 10-min, were used. In indus-t r i a l operations pressing time ranges from 6 to 10-min. In this case both times were used to insure proper glue cure. 2 Following i n d u s t r i a l practice a press pressure of 14 kg/cm ( 2 0 0 psi) and 149°C platen temperature were used. Chow et a l . 3 6 ( 1 9 7 3 ) reported that at about 1 5 0?C platen temperature, the inner center, gluellne reachest,120°G* T h e y a l s o indicated that with phenolic glues a minimum inner glueline temperature of 120°C i s needed to pass the CSA 80$ wood f a i l u r e stan-dard, when the vacuum pressure method i s used. 3.8 Bond-Quality Testing Shear test specimens were prepared from each test panel i n accordance with CSA Standard 0121-M1978 for Douglas-f i r plywood. An average of 4 0 shear specimens were obtained from each panel, from which ten specimen were randomly assigned f o r each of the three conditioning cycles. Shear specimens were coded by panel and experimental va r i a b l e s . One set of specimens was tested following conditioning to ambient temperature and r e l a t i v e humidity (dry t e s t ) . A second set was placed i n a pressure vessel and immersed i n cold tap water. A vacuum of 8 5 KPa ( 6 3 5 mm mercury) • was drawn by water vacuum and maintained f o r 3 0-min, followed immediately by application of 4 5 0 to 480 KPa ( 6 5 - 7 0 p s i ) pressure. Specimens were then removed from the vessel and tested while s t i l l wet. The vacuum pressure-five cycle conditioning i s not included i n the CSA 0121-M1978. I t was carried out here as a treatment intermediate between vacuum pressure and b o i l - d r y - b o i l t e s t s . I t was assumed that t h i s would better 3 7 indicate plywood bond d u r a b i l i t y , e s p e c i a l l y with UP glue mixes which are known to have .good water resistance. The method follows the same procedures as the vacuum pressure t e s t , except that i t involves f i v e vacuum pressure-drying (at 5°°C) cycles. Samples were tested wet. The fourth set of specimens was boiled f o r four-hr and then dried f o r 2 0-hr at 6 3 - 3 ° C . Specimens were boiled again for four hours, cooled i n room temperature water and tested while wet. Shear test specimens representing 4 0 panels were tested by tension loading to f a i l u r e i n a standard Globe shear tes t i n g machine. This was operated at a loading rate of 2 7 2 to kg/min. Following shear t e s t , wood f a i l u r e was read a f t e r the wet specimens were oven-dried to prevent reading errors since water makes wood.fibers transparent. 3 . 9 S t a t i s t i c a l Analyses Analysis of variance (ANOVA) were performed on both shear strengths and wood f a i l u r e percentages. This allowed f o r comparison among treatments. The Duncan's Multiple Test was used to test f o r s i g n i f i c a n t differences between tr e a t -ments . To f a c i l i t a t e i n t e r p r e t a t i o n of r e s u l t s , the same number of shear te s t specimens ( 2 0 ) was tested f o r a l l treatments. Each treatment was coded f o r i d e n t i f i c a t i o n as shown i n Appendix I I . 38 4.0 RESULTS Thermograms of the commercial UF r e s i n with wheat f l o u r , 3 0 $ f o l i a g e and 3 0 $ "bark, are i l l u s t r a t e d i n Figure 1. Foliage and bark powder properties such as moisture content, ash content, pH and p a r t i c l e size d i s t r i b u t i o n are presented i n Table 3. Glue mix physical properties such as v i s c o s i t y j pH, density and gelation time are presented i n Table 4. .4.1 Modified Commercial UF Glue Table 5 summarizes average shear strengths and wood f a i -lure percentages f o r the 14 glue mix (M) and pressing time (PT) treatment combinations following three conditioning treatments. Figures 2, 3 and 4 i l l u s t r a t e r e s u l t s of dry, vacuum pressure-one cycle and vacuum pressure-five cycles as shear strengths and wood f a i l u r e percentages. The b o i l -dry-boil test resulted i n complete delamination of shear test specimens. No values were recorded. 4.2 Modified Laboratory UF Glue (UFi) Table 6 summarizes average shear strengths and wood f a i l u r e percentages for the s i x treatment combinations of M and PT following three conditioning treatments. Figures 5 , 6 and 7 i l l u s t r a t e r e s u l t s of dry, vacuum pressure-one cycle and vacuum pressure-five cycles as shear strengths 39 and wood f a i l u r e percentages. As i n the case of the commercial UF glue, the b o i l - d r y - b o i l test resulted i n complete delamination of shear test specimens. 4.3 S t a t i s t i c a l Analyses Results of dry-shear strength and wood f a i l u r e percen-tage analysis of variance (ANOVA) for treatments bonded with the commercial UF glue are summarized i n Table 7« The table shows the s i g n i f i c a n t main and i n t e r a c t i n g effects at 0.01 and 0.05 p r o b a b i l i t y l e v e l s . The interactions M x PT are depicted i n Figure 8. Table 8 summarizes ANOVA resu l t s of vacuum pressure-shear strengths and wood f a i l u r e percentages for treatments bonded with the commercial UF glue. The interactions M x PT are depicted i n Figure 9« Table 9 summarizes ANOVA re s u l t s of vacuum pressure-f i v e cycles shear strengths and wood f a i l u r e percentages for treatments bonded with the commercial UF glue. The interactions are depicted i n Figure 10. S i m i l a r l y , Table 10 summarizes ANOVA re s u l t s of dry shear strengths and wood f a i l u r e percentages for treatments bonded with the laboratory UFi glue. Table 1 ! summarizes ANOVA resu l t s of vacuum pressure-one cycle shear strengths and wood f a i l u r e percentages for treatments with the UFi glue. F i n a l l y , Table 12'summarizes ANOVA re s u l t s of vacuum 40 p r e s s u r e - f i v e c y c l e s s h e a r s t r e n g t h s a nd wood f a i l u r e p e r c e n t a g e s f o r t r e a t m e n t s w i t h t h e U F i g l u e . The i n t e r -a c t i o n s M x PT a r e d e p i c t e d i n F i g u r e s 11, 12 a n d 13. T a b l e s 13 and 14 p r e s e n t r e s u l t s o f D u n c a n ' s m u l t i p l e r a n g e t e s t f o r t r e a t m e n t s b o n d e d w i t h t h e c o m m e r c i a l UF g l u e . T a b l e s 15 and 16 p r e s e n t r e s u l t s f o r t r e a t m e n t s b o n d e d w i t h t h e U F i g l u e . 41 5.0 DISCUSSION 5.1 F o l i a g e and B a r k P r o p e r t i e s As shown i n T a b l e 3 w h i t e s p r u c e f o l i a g e had a s l i g h t l y l o w e r p a r t i c l e - s i z e d i s t r i b u t i o n t h a n w e s t e r n hemlock b a r k . F o l i a g e had 81.8% p a s s i n g t h r o u g h t h e 200-mesh s c r e e n w h i l e b a r k had 78.3%' When d r i e d t o a m o i s t u r e c o n t e n t below 10%, b o t h m a t e r i a l s were e a s i l y p u l v e r i z e d t o the f i n e p a r -t i c l e - s i z e . The t y p e o f g r i n d e r c o u l d a f f e c t f o l i a g e and b a r k r e s u l t s . Chow (1977) compared P a l l m a n r i n g g r i n d e r e f f i c i e n c y w i t h t h a t o f a S p r o u t - W a l d r o n g r i n d e r and found t h a t t h e f o r m e r was much more e f f e c t i v e i n g r i n d i n g f o l i a g e to p a r t i c l e - s i z e below 200-mesh. The P a l l m a n g r i n d e r was used i n t h i s s t u d y . As i n d i c a t e d e a r l i e r t h e p a r t i c l e - s i z e o f m a t e r i a l s used as g l u e e x t e n d e r s o r f i l l e r s i n f l u e n c e s g l u e p h y s i c a l p r o p e r t i e s (Knudson e t a l . , 1978; K u b o t a and S a i t o , 1972; Stone and R o b i t s c h e c k , 1 9 7 4 ) . F i n e p a r t i c l e - s i z e i s r e p o r -t e d to be a r e q u i r e m e n t f o r h i g h q u a l i t y e x t e n d e r s . C o a r s e p a r t i c l e - s i z e a f f e c t s g l u e v i s c o s i t y , s p r e a d i b i l i t y , p o t l i f e and u l t i m a t e l y bond q u a l i t y . The s c r e e n a n a l y s e s t e s t s c a r r i e d out i n t h i s s t u d y i n d i c a t e d t h a t b o t h f o l i a g e and b a r k can be ground to a f i n e p a r t i c l e - s i z e s u i t a b l e f o r use as e x t e n d e r s o r f i l l e r s . The m o i s t u r e c o n t e n t s o f w h i t e s p r u c e f o l i a g e and 42 w e s t e r n h e m l o c k b a r k w e re 6.2 a n d 8 .0$, r e s p e c t i v e l y ( T a b l e 3)« H i g h e r m o i s t u r e c o n t e n t s may a f f e c t g l u e p r o p e r t i e s e s p e c i a l l y v i s c o s i t y . As shown i n T a b l e 3 th 5e pH o f w h i t e s p r u c e f o l i a g e a n d w e s t e r n h e m l o c k b a r k w e r e k.3 and k.7 r e s p e c t i v e l y . Chow (1977) r e p o r t e d a s i m i l a r pH f o r w h i t e s p r u c e f o l i a g e . The pH o f f o l i a g e a n d b a r k a r e a c i d i c a n d c o m p a t i b l e w i t h UF r e s i n s w h i c h a r e t y p i c a l l y a c i d c u r i n g r e s i n s . The a s h c o n t e n t s o f w h i t e s p r u c e f o l i a g e a n d w e s t e r n h e m l o c k b a r k w e r e 3«7 and 2.3$ r e s p e c t i v e l y ( T a b l e 3)• Low a s h c o n t e n t i n a n e x t e n d e r i s a q u a l i t y c r i t e r i a a n d a s e l e c t i o n f a c t o r . R o b e r t s o n (1974) p o i n t e d o u t t h a t f o r wh e a t f l o u r e x t e n d e r s a n optimum a s h c o n t e n t s h o u l d be a b o u t 0.55$« O t h e r m a t e r i a l s u s e d a s g l u e e x t e n d e r s s u c h as g r o u n d o a t , r i c e a n d c o r n c o b h u l l r e s i d u e s h a v e a s h c o n t e n t s i n t h e r a n g e o f 8 t o 20$ ( S t o n e a n d R o b i t s c h e c k , 1974). The a s h c o n t e n t s o f f o l i a g e and b a r k a r e r e l a t i v e l y l o w and a d e q u a t e f o r u s e w i t h g l u e s y s t e m s . 5.2 M o d i f i e d C o m m e r c i a l UF G l u e P r o p e r t i e s As shown i n T a b l e 4, m i x e s UF - F 1 5 a n d UF-F30 g a v e l o w e r v i s c o s i t i e s t h a n t h e c o n t r o l m i x . The v i s c o s i t y o f UF-F30 was s i m i l a r t o t h a t o f t h e c o n t r o l . H i g h e r f o l i a g e a d d i t i o n (UF - F 4 5 ) p r o d u c e d h i g h e r v i s c o s i t y t h a n t h e c o n t r o l a n d e x h i b i t e d u n s u i t a b l e f l o w p r o p e r t i e s . T h i s m i x was 43 s t i l l spreadable a f t e r two-hours but showed a tendency to lump during spreading. The mixes with bark additions UF -B15 and UF - B 3 0 exhibited higher v i s c o s i t i e s than the control mix but were suitable f o r spreading. Mix UF-B45. as i n the case of f o l i a g e additions, had too high a v i s c o s i t y and was unsui-table for spreading. I t has been reported that bark addition to UF resins increases glue v i s c o s i t y and that t h i s i s more pronounced when highly-condensed UF r e s i n i s used (Hamada et a l . , 1969)• I t was observed during v i s c o s i t y measurements that a l l mixes exhibited * a- drop i n v i s c o s i t y when subjected to cons-tant shearing but reached t h e i r f i n a l value within one-min. This phenomenon i s known -as thixotropy and can be attributed to the presence of wheat f l o u r and f o l i a g e or bark i n the mix. The importance of glue v i s c o s i t y was reviewed e a r l i e r . Optimum v i s c o s i t y ensures proper glue flow and helps glue transfer from the spread veneer surface to the unspread surface. I t also affects glueline thickness and glue penetration into the veneer surfaces. Results 'from- t h i s study indicat'e that large additions of untreated f o l i a g e and bark powder produce high and unsuitable v i s c o s i t i e s . This occurs because large additions absorb considerable amounts of water from the mix, thus 44 increasing v i s c o s i t y . I t has been found (Steiner, 1980) that white spruce foliage and Douglas-fir bark water absorbency rate i s about 180$, while wheat f l o u r rate i s 80$. The higher v i s c o s i t y produced by bark additions compared with lower v i s c o s i t y by f o l i a g e additions indicates that bark has a greater chemical i n t e r a c t i o n a l th the UF r e s i n . Evidence of considerable r e a c t i v i t y between western hemlock bark tannin constituents and formaldehyde has been reported (Hamada et. a l . , ' 1969; Steiner and Chow, 1975) • In the case of f o l i a g e additions, Chow (1977) reported that foliage might.have a humectant function that influences glue v i s c o s i t y . Also, Chow et a l . (1979) found that a mix of pure foliage exhibits s i m i l a r flow properties to phenolic r e s i n . This f o l i a g e humectant property may explain the lower v i s c o s i t y produced by f o l i a g e additions up to the 30$ l e v e l . As shown i n Table 4 the mixes with f o l i a g e and bark additions had lower densities than the control mix. In both cases the glue density was found to decrease with increased addition. The r e s u l t s suggest that, since the mixes with f o l i a g e and bark additions have lower density than the control, these mixes w i l l give more glue volume per unit area than the control when spread at equivalent l e v e l s . Also,, these mixes may have an improved gap f i l l i n g property because of t h e i r greater volume. 4 5 Table 4 shows that mixes with foliage and bark addi-tions had lower pH values than the control mix. This was expected since f o l i a g e and bark have 4 . 3 and 4 . 7 pH values, resp e c t i v e l y . Mix pH decreased with an increase of addition l e v e l . I t has been indicated that"glue v i s c o s i t y and pot l i f e are dependant on rate of pH f a l l with time (Rose, I 9 6 7 ) . Gelation time provides a means for evaluating s e t t i n g rate and potential speed of reaction of crosslinked polymer systems during t h e i r transformation from l i q u i d to s o l i d phase (Steiner,and Chow, 1 9 7 5 ) ' I t i s shown (Table 4 ) that mixes with fo l i a g e exhibited s l i g h t l y longer gelation times than the control mix. Con-versely, mixes with bark gave shorter gelation times than the control. From these re s u l t s i t appears that higher bark additions increased glue r e a c t i v i t y , thus shortening gelation time. In a s i m i l a r study with phenolic resins Hamada et a l . ( 1 9 6 9 ) reported that glue se t t i n g time was shortened by bark addition. Glue mix s t a b i l i t y as indicated by v i s c o s i t y measure-ments at one-hour, 2 4 and 48-hr a f t e r mixing i s shown i n Table 4 . Mixes UF - F 1 5 and UF - F 3 0 had a s i g n i f i c a n t v i s c o -s i t y increment a f t e r 24-hr but were lower than the control. Mix UF - F 4 5 had too high a v i s c o s i t y which indicated low mix s t a b i l i t y . Mixes with bark additions UF-B15 and UF-B30 46 also showed substantial increase i n v i s c o s i t y but remained workable under a g i t a t i o n . Mix UF-B45, as with f o l i a g e , developed excessively high v i s c o s i t y which made the glue unworkable aft e r 24-hr. Over a period of 48-hr mixes UF-F15 and UF - F 3 0 v i s c o -s i t i e s increased further but were s t i l l workable. Mix UF-F45 was so thick that v i s c o s i t y measurements were not possible. Mixes UF-B1.5 and UF-B30 had higher v i s c o s i t i e s than those of UF-foliage mixes and were s i m i l a r to the control. The re s u l t s indicate that 48-hr a f t e r mixing, f o l i a g e additions UF-F15 and UF - F 3 0 exhibited better s t a b i -l i t y than the control mix. Mixes UF-B15 and UF-B30 exhibited s i m i l a r s t a b i l i t y to the control. Large additions of fol i a g e and bark produced mixes with low s t a b i l i t y , unworkable a f t e r 24-hours. From the re s u l t s i t appears that glue pot l i f e i s dependent to a certa i n extent on the i n i t i a l v i s c o s i t y , mix formulation and rate of pH f a l l . 5.3 D i f f e r e n t i a l Scanning Calorimetry Chow and Steiner ( 1 9 7 5 ) investigated the exothermic reaction of UF r e s i n . Supported by res u l t s from d i f f e r e n -t i a l thermoanalysis, thermogravimetric analysis, i n f r a r e d spectra and softening temperature measurements they indicated that the exothermic peak i s associated with r e s i n cure. The endothermic peak i s related to the heat of water evaporation. 47 As shown i n Figure 1 the thermogram for the UF r e s i n shows an exothermic peak at 64°C and an endothermic peak at about 100°C. The UF-wheat', f l o u r thermogram shows the peaks sh i f t e d to a higher temperature, exothermic at 82°C and endothermic at l l 6°C. Foliage addition s l i g h t l y s h i f t e d the exothermic peak (96°) and the endothermic peak (120°C). UF-bark exhibited a s i m i l a r thermogram to UF-foliage. The s l i g h t temperature s h i f t to the exothermic peak with f o l i a g e and bark additions may be important to glue pot l i f e . Increased exothermic peak temperature may retard glue pre-cure, since higher energy i s needed to i n i t i a t e curing. Figure 1 also shows the influence of the glue extender. The exothermic peaks of UF-wheat f l o u r , UF-fo l i a g e and UF-bark mixes occur at higher temperatures than that of the UF r e s i n alone. This suggests that exten-ders improve glue assembly time tolerance and pot l i f e . 5 . 4 Bond Quality of Modified Commercial UF glue 5 . 4 .1 Dry test Figure 2 and Table 5 shows that treatments with foliage additions (UF-F15-10, UF-F45 at 6 and lG-min PT) gave higher shear strengths than the control while treatments with 30% f o l i a g e at 6 and 10-min pressing time (PT) gave sim i l a r strengths to the control. Bark additions, with exception of treatment UF-B15-10, produced higher shear strengths 48 than the control. The analysis of variance (ANOVA) for the shear strength data (Table 7) shows the i n t e r a c t i o n between glue mix (M) and pressing time (PT) as highly s i g n i f i c a n t . This i n t e r -action (Figure 8), indicates that there was a d i f f e r e n t response among glue mixes to PT l e v e l s . Except f o r t r e a t -ment with 15$ f o l i a g e , PT did not appear to influence shear strength of treatments bonded with UF-foliage glue. In the case of bark, higher shear strengths were produced at 6 than at 10-min PT. In general, treatments with foliage (UF-F15-10) and bark (UF-B45-6) gave the highest shear strengths at 2.08 MPa (302 psi) and 2.02 MPa (293 p s i ) . Duncan's multiple range test for multiple comparisons (Table 13).indicates that these re s u l t s were 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 p r o b a b i l i t y l e v e l . Treatments UF-C-6 (Control), UF-F15-6 and UF-B15-10 gave the lowest values at 1.48 MPa ( 2 1 4 p s i ) , 1.55 MPa (225 psi) and 1 .-59 MPa (217 p s i ) , respectively. '. Figure 2 and Table 5 also show that one treatment with foliage (UF-F30-6) gave higher wood f a i l u r e percentage than the -control. Treatments with bark additions (UF-B15-10, UF-B30 at 6 and 10-min PT) gave higher wood f a i l u r e percen-tages than the control. The ANOVA for the dry-wood f a i l u r e data (Table 7) shows, as i n the case of the shear strength t e s t , that the j+9 i n t e r a c t i o n M x PT was highly s i g n i f i c a n t . Figure 8 depicts t h i s i n t e r a c t i o n . Except for treatments with 4 5 % f o l i a g e , higher values were produced at 6 than at 10-min.PT. In the case of hark, higher wood f a i l u r e values were pro-duced at 10-min PT which contradicts the shear strength test i n which higher values were produced at 6-min PT. In general, treatment with hark (UF - B 3 0 - 1 0 ) gave the highest wood f a i l u r e at 9 8 % . The Duncan's test (Table 1 1 ) shows that, except f o r treatment UF - B 4 5-6, the above r e s u l t was 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 rest of the t r e a t -ments. This indicates that bond quality i n terms of wood f a i l u r e was high for most treatments regardless of addition l e v e l . The lowest value ( 6 l % ) was given by treatment UF - B 4 5-6. I t can be noted that shear strength and wood f a i l u r e r e s u l t s are contradictory. As indicated e a r l i e r the relationship between shear strength and wood f a i l u r e i s not well defined and i s s t i l l a subject of controversy. The dry test provides a measure of i n i t i a l bond strength. High i n i t i a l bond strengths for the commercial r e s i n were observed following addition of foliage or bark. This i s important since UF resins are used for i n t e r i o r applications where d u r a b i l i t y (resistance to heat and moisture) may not be primordial. In terms of wood f a i l u r e a l l treatments, except UF - B 4 5-6, met the minimum 8 0 % wood f a i l u r e required by CSA Standards. The low wood f a i l u r e value f o r treatment 50 UF-B45-6 can be explained by the high glue v i s c o s i t y . As noticed during wood f a i l u r e readings there was an evident lack of proper glue transfer between veneers,. In terms of shear strength, with exception of two treatments, higher i n i t i a l strengths were produced by foliage and bark mixes than with the control mix. From the above, the use of UF r e s i n with f o l i a g e or bark appears advantageous when i n t e r i o r applications are contemplated. 5.4.2 Vacuum pressure-one cycle Figure 3 and Table 5 show that treatments with f o l i a g e additions (UF-F15-10 and UF-F45 at 6 and 10-min PT) gave higher shear strengths than the control. Treatments with 30% f o l i a g e had s i m i l a r values to the control. Treatments with bark additions UF-B'30-6 and UF-B45-6 gave higher shear strength values than the control. Treatments with 15% f o l i a g e gave somewhat lower values than the cont r o l . The ANOVA for the shear strength data (Table 8) shows the i n t e r a c t i o n M x PT highly s i g n i f i c a n t . This i n t e r a c t i o n (Figure 9) implies that there was a d i f f e r e n t response among glue mixes to PT l e v e l s . PT did not appear to i n -fluence adhesion strength with UF-foliage treatments. Except f o r treatments with 15% f o l i a g e , s i m i l a r values were produced at both PT l e v e l s . In the case-of bark addi-tions, PT appears to have influenced adhesive strength of 51 treatments with 30 and 45$ additions. Higher values were produced at 6-min. In general, treatments UF - B 3 0 - 6 , UF -B45-6 and UF - F 1 5 - 1 0 produced the highest shear strengths at 1 . 9 4 MPa (281 p s i ) , 1 . 9 2 MPa (279 psi) and I . 8 5 MPa (268 p s i ) , r espectively. In addition, Duncan's test (Table 13) shows that the above resu l t s 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 O .05 proba-b i l i t y l e v e l . The lowest values were produced by treatments with 15$ bark and those with 30$ f o l i a g e . Figure 3 and Table 5 also show that treatments with 30 and 45$ f o l i a g e produced s i m i l a r wood f a i l u r e percentages to the control. Treatments with 15$ additions gave s l i g h t l y lower wood f a i l u r e than 8 0 $ . Treatments with 15 and 30$ bark produced si m i l a r values to the control which were higher than the minimum 80$ required by CSA Standard. The ANOVA for the wood f a i l u r e data (Table 8) shows that the i n t e r a c t i o n M x PT i s s i g n i f i c a n t at the 0 . 0 5 l e v e l . Figure 9 depicts t h i s i n t e r a c t i o n . As i n the case of the dry test, PT did not seem to influence bond d u r a b i l i t y of UF-foliage treatments. Similar values were produced at both PT l e v e l s . In the case of bark additions, higher values were produced at 10-min PT. This indicates that with foliage additions the glue bonds a t t a i n a high degree of cure at 6-min while bark additions require higher energy. Chow (1972) has indicated that for plywood PF bonds, the 52 vacuum pressure test i s more c r i t i c a l i n detecting under-cured bonds than the dry, 24-hr cold soak and b o i l - d r y - b o i l tests on the basis of wood f a i l u r e evaluation. Furthermore, he emphasized that wood f a i l u r e i s a more sensitive measure of glue bond undercure than shear strength. In general, the highest wood f a i l u r e values were produced by treatments UF"-C-6 (93$), UF-C-10 (89$); UF - F 3 0 -10(89$); UF - F 4 5 -6( 8 7 $ ), UF - F 4 5 - 1 0 ( 8 0 $ ); UF - B 1 5 -6 (83$) , UF - B 1 5-10 (90$), UF-B30-6(85$) and UF - B 3 0 -10(90$). In addi-ti o n , Duncan's test (Table 14) shows that these r e s u l t s > 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 p r o b a b i l i t y l e v e l . The lowest values were produced by UF-B45-6 (57$) and UF-B45-10 (70$) which were s i g n i f i c a n t l y lower than the other r e s u l t s . As i n the case of the dry te s t , r e s u l t s of shear strength and wood f a i l u r e tests are contradictory. However, shear strength re s u l t s from dry and vacuum pressure followed the same pattern. The UF-£oliage treatments showed a s l i g h t l y steady decrease i n shear strength when submitted to vacuum pressure. The same occurred with UF-bark t r e a t -ments, but there was not a s i g n i f i c a n t decrease i n shear strength i n the cases of treatments with 30 and 45 $ bark at 6-min PT. Figures 2 and 3 show that wood f a i l u r e percentage-dry and vacuum pressure-one cycle test data followed the same 5 3 pattern as above. Among the UF-foliage treatments only 1 5 % f o l i a g e addition gave s i g n i f i c a n t decrease i n bond qu a l i t y . The same occurred with the UF-bark treatments, where only 4 5 % bark addition showed a s i g n i f i c a n t decrease i n bond qua l i t y a f t e r the vacuum- pressure cycle. The wood f a i l u r e percentage r e s u l t s indicate that with two exceptions (treatments with 1 5 % foliage and 4 5 % bark), treatments with f o l i a g e and bark additions exhibited good bond quality s i m i l a r to the control. The s l i g h t l y lower values given by treatments with 1 5 % foliage may be due to veneer quality factors rather than glue properties, since mix formulation and properties were close to those of the control. These good r e s u l t s may be explained, i n part, as due to the p l a s t i c i z i n g action of water i n reducing stress concentrations on the specimens g l u e l i n e . I t i s also possible that additives such as wheat f l o u r , f o l i a g e and bark enhance adhesion by better d i s t r i b u t i n g stresses during exposure. The poor bond quality produced by mix with 4 5 % bark can be explained by the high, unsuitable v i s c o s i t y of t h i s glue which did not allow proper spreading and transfer on the veneer surfaces. 5 . 4 . 3 Vacuum pressure-five cycles Figure 4 and Table 5 show that treatments with low 5 4 f o l i a g e a d d i t i o n s ( U F - F 1 5 - 6 and U F - F 1 5 - 1 0 ) g a v e s h e a r s t r e n g t h s h i g h e r t h a n t h e c o n t r o l . T r e a t m e n t s U F - F 3 0 - 6 and U F - F 4 5 - 6 h a d somewhat l o w e r v a l u e s t h a n t h e c o n t r o l . I n t h e c a s e o f b a r k a d d i t i o n s , t r e a t m e n t UF-B30 -6 h a d h i g h e r s h e a r s t r e n g t h t h a n t h e c o n t r o l . T r e a t m e n t s UF-B30 - 1 0 , U F - B 4 5 a t 6 and 1 0 - m i n showed s i m i l a r s t r e n g t h s t o t h e c o n t r o l , w h i l e t r e a t m e n t s w i t h l o w b a r k a d d i t i o n s (UF-BI5 - 6 and UF-B15 - 1 0 ) p r o d u c e d t h e l o w e s t v a l u e s . The ANOVA f o r t h e s h e a r s t r e n g t h d a t a ( T a b l e 9 ) i n d i c a t e s t h a t t h e M and PT f a c t o r s a r e h i g h l y s i g n i f i c a n t . The i n t e r a c t i o n M x PT ( F i g u r e 1 0 ) was n o t s i g n i f i c a n t i m p l y i n g t h a t t h e r e was a s i m i l a r r e s p o n s e among t r e a t m e n t s t o PT l e v e l s . E x c e p t f o r t r e a t m e n t UF-B30 - 6 , t h e r e s u l t s w e r e h i g h e r f o r a l l t r e a t m e n t s a t 1 0-min PT. I n g e n e r a l , t h e h i g h e s t s h e a r s t r e n g t h v a l u e s w e r e p r o d u c e d b y t r e a t m e n t s U F - F 1 5 - 1 0 ( 1 . 3 7 MPa, 1 9 9 p s i ) , U F - F 1 5 - 6 ( 1 . 3 4 MPa, 1 9 5 p s i ) , U F - F 4 5 - 1 0 ( 1 . 2 6 MPa, 1 8 3 p s i ) ; UF-B30 -6 ( 1 . 4 9 MPa, 216 p s i ) , UF-B30 -10 ( 1 . 3 1 MPa, 1 9 0 p s i ) a nd t h e c o n t r o l UF-C - 1 0 ( 1 . 3 5 MPa, 1 9 6 p s i ) . I n a d d i t i o n , D u n c a n ' s t e s t ( T a b l e 1 3 ) i n d i c a t e s t h a t t h e s e r e s u l t s a r e 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 t h e O . 0 5 p r o b a -b i l i t y l e v e l . The l o w e s t v a l u e s w e r e p r o d u c e d b y t r e a t m e n t s U F - F 3 0 - 6 ( 0 . 9 0 MPa, 1 3 0,>psi), U F - F 4 5 - 6 ( 0 . 8 6 MPa, 1 2 4 p s i ) ; UF-B15 -10 ( 0 . 9 5 MPa, 1 3 8 p s i ) a n d UF-B15 -6 ( 0 . 7 0 MPa, 1 0 2 p s i ) . 55 Figure 4 and Table 5 also show that treatment with 3 0 $ foliage gave s i m i l a r wood f a i l u r e percentage to the control at 10-min PT and lower at 6-min. Treatments with 1 5 and 4 5 $ f o l i a g e gave lower values than the control at both PT l e v e l s . In the case of bark additions, treatments with 1 5 and 3 0 $ bark gave s l i g h t l y higher values than the control at 10-min PT and similar at 6-min. Treatment with 4 5 $ bark gave su b s t a n t i a l l y lower wood f a i l u r e percentage than the control. The ANOVA f o r the wood f a i l u r e percentage data (Table 9 ) shows that the M and PT factors are highly s i g n i f i c a n t . The in t e r a c t i o n M x PT (Figure 10) was not s i g n i f i c a n t implying that there was a response among treatments to PT l e v e l s . The PT factor appeared to influence bond quality, a l l treatments produced higher values at 10-min PT. This suggests that stronger or more durable bonds are formed at longer PT and that co-reaction of UF r e s i n with f o l i a g e or bark requires higher thermal energy to a t t a i n a high degree of cure. In general, the highest wood f a i l u r e values were produced by treatments UF-F30-10 ( 5 9 $ ) ; UF-B15-10 ( 6 3 $ ) , UF-B30-10 ( 6 3 $ ) and UF-C-10 ( 6 0 $ ) . Duncan's test (Table 1 4 ) indicates that these r e s u l t s 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 . 0 5 p r o b a b i l i t y l e v e l . The lowest values were produced by treatments UF - F 4 5 - 6 ( 1 5 $ ) and UF - B 4 5 - 6 5 6 ( 1 9 % ) . I t can be noted that large additions of either f o l i a g e or bark beyond 3 0 % gave the lowest wood f a i l u r e percentages. Thevvacuum pressure-five cycles test i s not included i n the CSA Standards. I t i s a much more severe test than the vacuum pressure-one cycle, therefore, can provide a measure of bond degradation under more extreme conditions. Both, the veneer and the glue are submitted to severe stresses due to shrinking and swelling throughout the cycles. This treatment can be considered intermediate between vacuum pressure-one cycle and b o i l - d r y - b o i l for evaluating - bond d u r a b i l i t y . I t was noted while conducting the test that delamina-tions resulted a f t e r the second cycle with UF - F 1 5 - 6 ( 5 delaminations) and UF - F 4 5 - 6 ( 7 delaminations). After the t h i r d cycle, delaminations resulted i n treatments UF - F 1 5 - 6 ( 4 ) , UF-F15-10 ( 3 ) , UF - F 4 5 - 6 ( 6 ) and UF -F45-10 ( 3 ) . After the fourth cycle only UF - B 4 5 - 6 showed delaminations ( 7 ) . At the end of the f i f t h cycle the remaining specimens showed severe s p l i t s but were s t i l l suitable f o r shear t e s t i n g . The above indicates that most delaminations occurred with foliage additions and that, as shown i n Figure 4 , stronger bonds were formed with bark additions. The r e s u l t s of UF-bark ( 1 5 and 3 0 % additions) are i n agreement with those of Hamada et a l . ( 1 9 6 9 ) who found 57 that cold soak bond strength of UF resins was increased by wattle bark addition. 5 . 4 . 4 B o i l - d r y - b o i l test This test was conducted as s p e c i f i e d by CSA Standards. A l l treatments, including the control delaminated completely i n the f i r s t b o i l i n g cycle. This test was included on the assumption that UF r e s i n modification with f o l i a g e and bark additions could improve bond d u r a b i l i t y to the point of r e s i s t i n g heat and moisture. The results indicate that no modifying improvements were made by these additions. 58 5 - 5 Modified Laboratory UF Glue (UFi) Properties As shown i n Table 4 mix with 30$ f o l i a g e addition (UFi-F30) lowered v i s c o s i t y below the control, while treatment with bark addition (UFi-B30) raised i t above the control. As with the commercial UF r e s i n , f o l i a g e addi-t i o n to the mix resulted i n decreased v i s c o s i t y while bark tended to increase i t . The lower v i s c o s i t y of the UFi mix, compared with the standard UF, may be due to the r e l a t i v e l y low v i s c o s i t y of the UFi r e s i n caused by i t s low molecular weight. Table 4 also shows that the pH and density values of UFi mixes were lower than of commercial UF mixes. The gelation times were s i g n i f i c a n t l y shorter than those of UF mixes. This indicates that glue assembly time tolerance and pot l i f e were reduced with UFi r e s i n . Mix s t a b i l i t y as indicated by v i s c o s i t y measurements decreased s i g n i f i c a n t l y a f t e r 24-hr. At such time only the mix with fo l i a g e addition remained workable. The mix with bark addition had too high v i s c o s i t y and was unsuitable for spreading. After 48-hr a l l mixes were unworkable and v i s c o s i t y measurements were not possible. Again, these res u l t s indicate the low s t a b i l i t y of UFi mixes. From the re s u l t s i t appears that both v i s c o s i t y and s t a b i l i t y were affected by the low molecular weight of the r e s i n . As indicated by gelation time and s t a b i l i t y tests the glue pot l i f e was reduced considerably. 5 9 5 . 6 Bond Quality of Modified Laboratory UF Glue (UFi) 5 - 6 . 1 Dry test As explained e a r l i e r , i t i s possible that a low mole-cular weight r e s i n could provide a system with p o t e n t i a l f o r reaction with f o l i a g e and bark low molecular weight phenolic compounds. To examine th i s a bond qua l i t y evalua-t i o n was made of UFi r e s i n mixed with f o l i a g e and bark at the 3 0 $ addition l e v e l . Figure 5 and Table 6 show that treatments with 3 0 % f o l i a g e gave higher shear strength values than the control while treatments with bark gave s i m i l a r values to the control. The ANOVA for the shear strength data (Table 1 0 ) shows the main factor glue mix (M) as highly s i g n i f i c a n t . The i n t e r a c t i o n M x PT (Figure 1 1 ) was not s i g n i f i c a n t , implying that there was a response among treatments to PT l e v e l s . A l l treatments including the control, produced higher shear values at 6-min PT. Treatments U F i - 3 0 at 6 and 1 0-min PT gave the highest values of 1 . 6 MPa ( 2 3 2 psi) and 1 . 5 4 MPa ( 2 2 3 p s i ) , respectively. Duncan's test (Table 1 5 ) shows these re s u l t s as 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 . 0 5 l e v e l and that they are s i g n i f i c a n t l y d i f f e r e n t than those of the control and bark treatments. The lowest value of 1 . 2 2 MPa ( 1 7 7 psi) was given by the control mix. 60 In'general, shear strength data were r e l a t i v e l y low i n d i c a t i n g that the i n i t i a l bond strength was reduced when the low molecular weight r e s i n was used. In terms of wood f a i l u r e percentage, Figure 5 shows that treatments with bark addition gave the highest values, while fo l i a g e additions gave s i m i l a r values to the control. The ANOVA f o r the wood f a i l u r e percentage data shows the main M and PT factors as highly s i g n i f i c a n t . The i n t e r a c t i o n M x PT was not s i g n i f i c a n t . As with the shear strength test, there was a response among treatments to PT l e v e l s . Higher r e s u l t s were produced at 6-min P-T. The highest wood f a i l u r e values were given by treatments UFi-B 3 0 - 6 (93%) and UFi-F30-6 (89%). Duncan's test shows these re s u l t s as not s i g n i f i c a n t l y d i f f e r e n t from those produced by UFi-C-6?:(82%) and UFi -B30-10 (86%). A l l treatments, with exception of UFi-C-10 (72%) and UFi-F30-10 (78%) met the minimum CSA bond qu a l i t y requirements. The o v e r a l l r e s u l t s of t h i s test are lower than those produced by the commercial UF treatments at equivalent addition l e v e l s . As indicated e a r l i e r , an explanation f o r decreased i n i t i a l bond qua l i t y with UFi r e s i n treatments would be the lower cohesive strength of t h i s r e s i n r e s u l t i n g from i t s smaller i n i t i a l molecular s i z e . However, i t should be noted that better r e s u l t s were obtained with bark and foliage than with the control. This suggests that some 61 degree of reaction between the r e s i n and fol i a g e or bark was attained. 5 . 6 . 2 Vacuum pressure-one cycle Figure 6 and Table 6 show that treatments with f o l i a g e and bark produced, higher shear strength values than the control. The ANOVA f o r -the shear strength data (Table 11) shows the M and PT factors as highly s i g n i f i c a n t . The i n t e r a c t i o n M x PT (Figure 12) was not significant-which indicates s i m i l a r responses among treatments to PT l e v e l s . Higher r e s u l t s were produced at 10-min PT. The highest shear strength r e s u l t was given by treatment UFi-B30-10 (1.37 MPa, 199 p s i ) . Duncan's test (Table 16) shows t h i s r e s u l t as s i g n i f i c a n t l y d i f f e r e n t than those of the other treatments. The lowest values were given by the control treatments UFi-C-6 (0 .92 MPa, 134 p s i ) and UFi-C-10 (1 .01 MPa, 1^7 p s i ) . In terms of wood f a i l u r e percentage, Figure 6 also shows that the highest values were produced by treatments UFi - F 3 0 - 6 ( 8 6 $ ) , UFi -F30-10 (87$) and UFi-B30-6 ( 9 2 $ ) . Duncan's test shows these r e s u l t s as s i g n i f i c a n t l y higher than those of the control. The lowest values were given by the controls UF-C-6 (59$) and UF-C-10 ( 6 6 $ ) . The ANOVA for the wood f a i l u r e percentage data shows the i n t e r a c t i o n M x PT (Figure 12) as not s i g n i f i c a n t . 62 Treatments with f o l i a g e and the control gave higher values at 6-min PT while those with bark gave s i m i l a r values at both PT l e v e l s . Following vacuum pressure-one cycle bond q u a l i t y i n terms of shear strength decreased sub s t a n t i a l l y f o r t r e a t -ments with f o l i a g e and the control. In terms of wood f a i l u r e , f o l i a g e and bark additions gave higher bond q u a l i t y than the control. This suggests that foliage and bark components take up residual formaldehyde and react with the r e s i n r e s u l t i n g i n improved adhesion. 5«6.3 Vacuum pressure-five cycles Figure 7 and Table 6 show that treatments with bark gave higher shear strength values than-the control while f o l i a g e additions (at 6j-min PT) gave the lowest values. The ANOVA for the shear strength data (Table 13) shows the i n t e r a c t i o n M x PT as highly s i g n i f i c a n t . This i n t e r a c t i o n , shown i n Figure 1 3 ,-indicates a d i f f e r e n t response among treatments to PT l e v e l s . The highest shear strength values were produced by treatments UFi-B30-6 (O.56 MPa, 81 psi) and UFi-B30-10 (0 . 6 l MPa, 84 psi) 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 at the 0.05 l e v e l . The lowest value of 0.40 MPa (58 psi) was given by UFi-F30 -6 . The ANOVA for wood f a i l u r e percentage data (Table 14) 63 shows the i n t e r a c t i o n M x PT as s i g n i f i c a n t which indicates a d i f f e r e n t response among treatments to PT l e v e l s (Figure 13). As shown i n Figure 7 the highest wood f a i l u r e percen-tage was produced by treatment UF-F30-10 (36%) which 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 those of treatments UFi-C-10 (20$) and UF-B30-6 (20$). Treatment UFi-B30-10 gave the lowest value at 9$. In general, a l l treatments produced low r e s u l t s . An examination of ruptured shear specimens showed glue hydro-l y s i s . I t appears clear that the low molecular weight glue had lower-cohesive strength as r e s u l t of i t s low degree of polymerization. Cohesive forces are generally high i n commercial synthetic r e s i n s . Also, i t has been pointed out e a r l i e r that v i s c o s i t y i s a function of molecular weight. Low molecular weight glues usually give low visco-s i t y which may cause undesirable glue overpenetration into the veneer a f f e c t i n g "bond qu a l i t y . Conversely, high mole-cular 'weight glues generally give high v i s c o s i t y which affects glue flow and transfer on veneer surfaces r e s u l t i n g i n decreased adhesion. Consequently, a glue should have a proper molecular weight d i s t r i b u t i o n to produce a high cohesive strength and suitable v i s c o s i t y which i n turn develops strong wood-glue bonds. The b o i l - d r y - b o i l test as i n the case of the commercial UF glue resulted i n complete delamination of test specimens. 6k 5 . 7 Use of Foliage and.Bark with UF Resins Results from bond.quality evaluation indicated that f o l i a g e and bark action as modifiers i s l i m i t e d . No UF mix survived b o i l i n g treatment, which implies that exterior glueline d u r a b i l i t y can not be achieved by these modifica-tions. Because of t h i s r e s u l t the vacuum pressure-five cycle became the c r i t i c a l test f o r evaluating bond durabi-l i t y . In t h i s case formulations with the commercial UF r e s i n and bark(-15 =and. 30%) yielded 3 to' 12% higher wood f a i l u r e than the control, while 30% f o l i a g e gave s i m i l a r r e s u l t s to the control. This indicates that under accelerated aging conditions d u r a b i l i t y was not sub s t a n t i a l l y improved. Conversely, following dry and vacuum pressure-one cycle treatments, most formulations containing foliage and bark yielded high bond q u a l i t y (above 80% wood f a i l u r e ) . This c l e a r l y indicates that UF r e s i n bond q u a l i t y i s well main-tained by fo l i a g e and bark additions even when exposed to high moisture conditions. From the above, i t appears evident that f o l i a g e and bark action follows that of glue extenders rather than of modifiers. As indicated e a r l i e r , a modifier involves glue bond d u r a b i l i t y improvement, while an extender i s added to improve the adhesive action of the glue mix." Extenders improve v i s c o s i t y control and pot l i f e , reduce dry-out and f a c i l i t a t e spread of active glue s o l i d s on a s p e c i f i c surface area. 65 Special--wheat f l o u r s possess i d e a l properties fo r use as UF extenders which includes inherent adhesive-ness, f i n e p a r t i c l e s i z e , uniformity, and low ash content. Some physical tests conducted i n t h i s study demonstrated that f o l i a g e and "bark impart good properties to UF glues s i m i l a r to those mentioned above. In addition, i n the case of f o l i a g e , i t was found that t h i s material was e f f e c t i v e i n maintaining glue s t a b i l i t y , v i s c o s i t y increased more slowly over a 48-hr period. The inherent adhesiveness of foliage has been proven already by Chow, Steiner and Rozon (1979) who reported that foliage alone without addition of synthetic r e s i n can develop strong adhesive properties. Bark also has important properties and has been used as a f i l l e r f or phenolic glues f o r a long time. Bark i s espec i a l l y a t t r a c t i v e f o r i t s high phenolic content (30 to 70$) which are highly reactive components. Special attention has been given for a long time to the use of bark extractives as wood adhesives. The f e a s i b i l i t y of using formaldehyde and various bark extracts to bond plywood and particleboard has been demonstrated (Hall et a l . , 1970; Anderson e_t a l . , 1974; Steiner and Chow, 1975) •, In thi s study bark addition to UF r e s i n increased r e a c t i v i t y and s l i g h t l y improved bond d u r a b i l i t y under c y c l i c a l t e s t i n g . The above indicates that f o l i a g e and bark have good properties and can be used successfully as part of the 66 extender system i n UF formulations. As mentioned e a r l i e r both materials can substitute f o r wheat f l o u r up to k0% (extender weight basis) without a f f e c t i n g glue mix proper-t i e s . In addition, use of these materials includes other benefits, such as: 1) More complete tree u t i l i z a t i o n ; 2) Use of l a r g e l y unused, non-food materials; 3) Simple pro-cessing for use as extenders in v o l v i n g raw material c o l l e c t i o n , drying and grinding; and 4) Use of extenders made from l o c a l materials i s important, e s p e c i a l l y f o r countries where imported wheat f l o u r and r e s i n costs are a great burden. 67 6.0 CONCLUSIONS U n t r e a t e d w h i t e s p r u c e f o l i a g e a n d w e s t e r n h e m l o c k h a r k p o w d e r s e x h i b i t e d p h y s i c a l p r o p e r t i e s c o m p a t i b l e w i t h UF g l u e s . B o t h m a t e r i a l s w e re e a s i l y p u l v e r i z e d t o f i n e p a r t i c l e - s i z e when d r i e d t o m o i s t u r e c o n t e n t s b e l o w 10%. T h e s e f o l i a g e a n d b a r k a r e a c i d i c (pH 4.3 and 4.7> r e s p e c t i v e l y ) a n d a s h c o n t e n t s w e r e r e l a t i v e l y l o w (3.7 a n d 2.3%). UF g l u e m o d i f i c a t i o n w i t h f o l i a g e t o 30% l e v e l ( b a s e d on r e s i n s o l i d s ) g a v e l o w e r v i s c o s i t y t h a n t h e c o n v e n -t i o n a l w h e a t f l o u r e x t e n d e d UF g l u e . C o n v e r s e l y , b a r k a d d i t i o n t o t h e same l e v e l i n c r e a s e d v i s c o s i t y . T h e s e v i s c o s i t i e s , h o w e v e r , were a l l w i t h i n s u i t a b l e l i m i t s a n d d i d n o t a f f e c t g l u e w o r k a b i l i t y s i g n i f i c a n t l y . F o l i a g e a n d b a r k a d d i t i o n s a t 45% l e v e l s , h o w e v e r , i n c r e a s e d v i s c o s i t y t o a p o i n t t h a t a f f e c t e d g l u e f l o w , s p r e a d a b i l i t y a n d p o t l i f e . The l a b o r a t o r y UF g l u e m o d i f i e d w i t h 30% f o l i a g e a n d b a r k g a v e l o w e r v i s c o s i t y t h a n t h e m o d i f i e d commer-c i a l UF g l u e m i x e s . G l u e d e n s i t y a n d pH d e c r e a s e d w i t h f o l i a g e a n d b a r k a d d i t i o n s a n d were l o w e r t h a n t h o s e o f t h e c o n t r o l . F o l i a g e a d d i t i o n s g ave s i m i l a r g e l a t i o n t i m e s a s t h e c o n t r o l w h e r e a s , b a r k s h o r t e n e d t i m e s . The m o d i f i e d l a b o r a t o r y UF g l u e g a v e s i g n i f i c a n t l y 68 shorter gelation times than the modified commercial UF mixes. UF mix s t a b i l i t y , as indicated by v i s c o s i t y tests a f t e r one,. 24 and 48-hr was best maintained by fol i a g e addition to a 30$ l e v e l . S t a b i l i t y of mixes with bark additions to a 30$ l e v e l was si m i l a r to the control. Higher fo l i a g e and bark addition l e v e l s decreased mix s t a b i l i t y and a f t e r 48-hr were unworkable DSC analyses examining the influence of fo l i a g e and bark on UF glue curing properties showed a s l i g h t i n -crease of exothermic peak temperature when these materials were added to a UF mix. This ef f e c t may rel a t e to improved assembly time tolerance and glue pot l i f e . Treatments bonded with the commercial UF glue produced higher shear strength and wood f a i l u r e percentage res u l t s than treatments bonded with- the laboratory glue Treatments bonded with the commercial glue produced high i n i t i a l shear strength and wood f a i l u r e percentage i n the dry t e s t . Bond quality i n terms of wood f a i l u r e percentage was highest for treatment with 3°$ foliage at 6-min PT, and treatments with 15 and 3°$ bark at 10-min PT. The vacuum pressure-one cycle did not reduce bond quality s i g n i f i c a n t l y . In terms of wood f a i l u r e 69 percentage treatments with 30$ foliage and 15 and 30$ hark produced the highest bond qualit y , s i m i l a r to the control. Following vacuum pressure -5 cycles bond strength was reduced s i g n i f i c a n t l y . In terms of wood f a i l u r e , treatments with 15 and 30$ bark had s l i g h t l y higher bond quality than the control; treatment with 3°$ f o l i a g e at 10 min PT had s i m i l a r bond quality to the control. Influence of the PT factor became evident i n t h i s test as bond quality was best at 10-min PT f o r a l l treatments. The b o i l - d r y - b o i l test used to assess d u r a b i l i t y improvement of UF glue by modification with f o l i a g e and bark resulted i n complete delamination. This r e s u l t indicates that no improvement to the usual poor performance under heat and moisture conditions accom-panied these modifications. Dried and pulverized foliage and bark were used successfully to replace up to 40$ of the conventional wheat f l o u r extender. 70 LITERATURE CITED Anderson, A.B., Wong, A. and K-T. Wu. 1974. U t i l i z a t i o n of white f i r hark i n particleboard. Forest Prod. J . 24(1): 51-54. American Society f o r Testing Materials. 1978. Annual book of ASTM standards. Part 22. Wood; Adhesives. Philadelphia. 1062 pp. Bauer, H.H., Chr i s t i a n , G.D. and J.E. O'Reilly. 1978. Instrumental Analysis. A l l y n and Bacon, Inc. Boston. 832 pp. Barton, G.M., Mcintosh, J.A. and S. Chow. 1978'. The pre-sent status of fo l i a g e u t i l i z a t i o n . Reprint from AICHE Symposium Series No. 177. 74: 124-131. Blomquist, R.F. and W.Z. Olson. 1957 • D u r a b i l i t y of urea-r e s i n glues at elevated temperatures. Forest Prod. J . 7(8): 266-272. . =1964. D u r a b i l i t y of urea-r e s i n glues exposed to exterior weathering. Forest Prod. J . 14(10): 4 6 1 - 4 6 6 . Brown, H.P., Panshin, A.J. and C.C. Forsaith. 1952. Text-book of Wood Technology. Vol. I I . Mac Graw-Hill Book Co., New York. pp. 185-208. 71 Canadian Standards Association. 1977. Wood adhesives. CSA 0112M-1977. Rexdale, Ont. 104 pp. ' 1978. Douglas-fir plywood. CSA 0121M-1978. Rexdale, Ont. 37 pp. Chow, S. 1974. Lathe-check influence on plywood shear strength. Information Report VP-X-122. Dept. of the Environment, Can. Forest Serv., Western For. Prod. Lab., Vancouver. 13 pp. . I975. Bark boards without synthetic r e s i n s . Forest Prod.. J . 25(11).: 32-37. . 1977> Foliage as adhesive extender: A progress report. Symposium on Particleboard.- Pullman, Washington, pp.. 89-98. and K.S. Chunsi. 1979• Adhesion strength and wood f a i l u r e r e l a t i o n s h i p i n wood-glue bonds. J . Japan Wood Res. Soc- 25(2): . 125-131. and W.V. Hancock. 1969. Method f o r determining degree of cure of phenolic r e s i n . Forest Prod. J . 19(4): .21-29. and P.R. Steiner. 1975• C a t a l y t i c , exothermic reactions of UF r e s i n . Holzforsch. 29: 5-10« , \ . 1979. Comparison of the cure of PF novolac and r e s o l systems by DSC. J . Appl. Polymer S c i . 23: 1973-1985. 72 Chow, S., Steiner, P.R. and L. Rozon. 1979 • E f f i c i e n c y of coniferous f o l i a g e as extenders f o r powdered th phenolic r e s i n . 13 Particleboard Symposium. Pullman, Washington, pp. 329-342.. and G E. Troughton. 1975* Thermal reactions of phenol-formaldehyde resins i n r e l a t i o n to molar r a t i o and bond q u a l i t y . Wood Science 8(1): 343-349. , Troughton, G-.E., Hancock, W.V. and H .N . Mukai. 1973. Quality control i n veneer drying and p l y -wood gluing. Information Report VP-X-113. Dept. of the Environment, Can. Forest Serv., Western For. Prod. Lab., Vancouver. 33 PP• and W.G. Warren. 1972. E f f i c i e n c y of plywood bond-quality t e s t i n g methods. Information Report VP-X-104. Dept. of the Environment, Can. Forest Driehuyzen, H.W. and R.W. Wellwood. i960. E f f e c t of tem-perature and humidity of glue room on open assembly time. Forest Prod. J . 10(5): 254-259. Fisher, C. and D.W. Bensend. 19^9. Gluing of southern pine veneer with blood modified phenolic r e s i n glues. Forest Prod. J . 19(5): 32-37* 73 G i l l e p s i e , R.H., Olson, W.Z. and R.F. Blomquist. 1964. D u r a b i l i t y of urea-resin glues modified with po l y v i n y l acetate and blood. Forest Prod. J . 1 4 ( 8 ) : 343-349. H a l l , R.B., Leonard, J.H. and G.A. N i c h o l l s . i 9 6 0 . Bonding particleboard with bark extracts. Forest Prod. J . 10(5) « 2 4 3-272. Hamada, R., Ikeda, S. and Y. Satake. I 9 6 9 . U t i l i z a t i o n of wood bark f o r plywood adhesive. I I . J . Japan Wood Res. Soc. 15(8)': J 171-175. Hancock,"W.V. .1980. Veneer Roughness. Forintek Corp. Western For. Prod. Lab., Vancouver. Private communication. Herrick, F.W. and L.H. Bock. 1958. Thermosetting exterior plywood type adhesives from bark extracts. Forest Prod. J . 8: 269-274. H i l l , R. 1952. Urea and melamine adhesives. J . Forest Prod. Res. Soc. 2 ( 3 ) : 104-116. Hirata, S. and N. Mineura. 1974. The u t i l i z a t i o n of starch wastes as a f i l l e r f o r adhesives. J . Hokkaido Forest Prod. Res. Inst. 2 2 ( 7 ) : 10-14. 74 Imura, S., Sato, M., Nakamura, H. and I. Abe. 1974. E f f e c t s of bark on the adhesive strength of UF r e s i n . J . Hokkaido Forest Prod. Res. Inst. 23(3): 10-14. Kennedy, E.I. 1965« Strength and related properties of wood grown i n Canada. Publ. 1104. Can. Dept. Forestry. 51 PP* Kl e i n , J.A. 1975' Chemical aspects of gluing plywood with phenolic r e s i n s . FPRS Meeting, Portland. 7 PP-Knudson, R.M., 'Stout, R.M.T. and Rogerson, D.E. 1978. Plywood glue extender from particleboard sander-dust. Forest Prod. J . 28(9): 44. Kollmann, F.F.P., Kuensi, E.W. and A.J. Stamm. 1975* P r i n c i p l e s of Wood Science and Technology. I I . Wood Based Materials. Springer Verlag, New York. 703 PP. Kubota, M. and M. Saito. 1974. The u t i l i z a t i o n of saw-dust as f i l l e r f or plywood adhesives. J . Hokkaido Forest Prod. Res. Inst. 23(8): 5-9. McLean, H. and J.A.F. Gardner. 1952. Bark extracts i n adhesives. Pulp Paper Mag. Can. 53('8): 111-114. 75 Marra, G.G. 1964. Functional components of wood adhesion. Proceedings of the conference on theory of wood adhesion. U. Michigan, Ann Arbor. 1:3:1. Marian, J.E. and D.A. Stumbo. 1962. Adhesion i n wood. I. Physical factors. Holzforsch. 16:134-148. and C.W. Maxey. 1958. Surface texture of wood as related to glue-joint strength. Forest Prod. J . 8(12): 345-351. Meyer, B. 1979* Urea formaldehyde r e s i n s . Addison-Wesley Pub. Co., London. 423 pp. Northcott, P.L. 195 2» The development of the glu e l i n e -cleavage t e s t . J . Forest Prod. Res. Soc. 2(5): 216-224. . 1955. Bond strength as indicated by wood f a i l u r e or "mechanical t e s t . Forest Prod. J . 5(2): 118-123. , Colbeck, H.G.M., Hancock, W.V. and K.C. Shen. 1959. Undercure: casehardening i n plywood, Forest Prod. J . 9(12): 442-451. and D.C. Walsfer. 1965- Veneer-roughness scale. B.C. Lumberman 780-82. 76 Palka, L.C. 1 9 6 4 . Factors influencing the strength properties of Douglas f i r plywood normal to glueline. Unpuhl. MF thesis, Dept. of Forestry, The University of B.C., 7 3 pp. Parkes, R.S.R. and P. Taylor. 1 9 6 6 . Adhesion and Adhesives. Pergamon Press, Oxford. 1 4 2 pp. Rayner, C.A.A. I 9 6 5 . Synthetic organic adhesives. Adhesion and Adhesives, V o l . I. E l s e v i e r Pub. Co., New York. pp. I 8 7 - 3 3 7 . Ramos--Garcia, J.M. I 9 6 5 . . Bleedtrough of adhesive i n t r o p i c a l hardwood plywood. Unpubl. MF th e s i s . University of Washington, Seattle. 9 3 PP• Rice, J.F. 1 9 6 5 . The effect of urea formaldehyde r e s i n v i s c o s i t y on plywood bond d u r a b i l i t y . Forest Prod. J . 1 5 ( 3 ) : 1 0 7 - 1 1 2 . Robertson, J.E. 1 9 6 6 . Let-'s analyze the glue extender problem. Plywood and Panel 7 ( 1 ) : 3 0 . . 1 9 7 4 . P l a n t - s i t e observations of Asian plywood glue extenders. Forest Prod.- J . 2 4 ( 1 1 ) : 3 5-41. and R.R. Robertson. 1 9 7 9 . F i l l e r s and extenders i n plywood production: U.S. and Foreign pra c t i c e s . Forest Prod. J . 2 9 ( 6 ) : 15-21. 77 Rosales, D.A. 1980. Comparison of plywood manufacture i n Peru and the i n t e r i o r of B r i t i s h Columbia. Unpubl. FRST 580 report. Dept. of Forestry, The University of B.C., 51 pp. Rose, A. 1957« Chemical control of hot press UF glue mixes. Forest Prod. J . 7 ( H ) : 30A-33A. S e l l e r s , T. 1976. A plywood review and i t s chemical i m p l i -cations. Symposium on chemical aspects of s o l i d wood and board technology. Reichhold chemicals, Inc., Tuscalosa. pp. 11-14. Shen, K.C. 1958. The effe c t of dryer temperature, sapwood and heartwood, and time elapsing between drying and gluing on the gluing properties of Engelmann spruce veneer. Unpubl. MF thesis, Dept. of Forestry, The University of B.C., 36 pp. Shields, J . 1975. Adhesives Handbook. SIRA. Ministry of technology, Ohio. 355 PP• Scott, D.S. 1956. Recovery of tannins from western hemlock bark. I. Extraction rates with water as solvent. Pulp Paper Mag. Can. 57(4): 139-141. Steiner, P.R. 1973. D u r a b i l i t y of urea formaldehyde adhe-sives: E f f e c t s of molar r a t i o , second urea, and f i l l e r . Forest Prod. J . 23(12): 32-38. 78 Steiner, P.R. 1980. Foliage and bark water uptake. Forintek Corp., Western Forest. Prod. Lab., Vancouver. Personal communication. and S. Chow. 1974. Comparison of modifiers fo r d u r a b i l i t y improvement of urea-formaldehyde r e s i n . Wood and Fiber 6 ( 1 ) : 5 7 - 6 5 ' . 1975« Factors influencing western hemlock bark use as adhesives. Information Report VP-X-153« Dept. of the Environment, Can. Forest Serv., Western For. Prod. Lab., Vancouver. 13 pp. Stone, M.D. and P. Robitscheck. 1978. Factors a f f e c t i n g the performance of plywood glue extenders. Forest Prod. J . 28 ( 6 ) : .32 - 3 5 . S t r i c k l e r , M.D. and E.W. Sawyer. 1974. Attapulgite clay-a f i l l e r f or exterior plywood adhesives. Forest Prod. J . 24(11): 17-22. Stumbo, D.A. 1964. Influence of surface aging p r i o r to gluing on bond strength of Douglas-fir and red-wood. Forest Prod. J . 23(12): 3 2 -38. Thomas., R.J. and F.W. Taylor. I 9 6 2 . Urea formaldehyde resins modified with water-soluble blood. Forest Prod. J . 1 3 ( 3 ) : 111-115• 79 Troughton, G.E. I968. Accelerated aging of glue-wood bonds. Wood Science 1: 172-176. Truax, T .R. ' 1929. The gluing of wood. Bui. 1500. U.S .D.A., 23 pp. Yavorski, J.M., Cunningham, J.H., and N.G. Hundley. 1955« Survey of factors a f f e c t i n g strength tests of glue j o i n t s . Forest Prod. J . 5' 306-311. Zisman, W.A. 1963« Influence of constitution on adhesion. I. & E.C. 55(10): 19-38. 80 Table 1. Veneer q u a l i t y analyses. (3.17 mm Douglas-fir veneer) Mean •8-SD Max Min Rangi 1. Roughness (n=50) (mm) 0.33 0.08 0.51 0.13 0.38 2. Thickness (n=50) (mm) 3.20 0.04 3.27 3.09 0.18 3 . Moisture content (n=50) (%) 6.6 0.6 7.8 5.3 2.5 4 . Lathe-check depth (n=50) {%) 75 10 90 60 30 5- Lathe-check angle (n=50) (deg.) 60 ' 5 70 50 20 Standard deviation Measured from three longest lathe-checks Table 2. Veneer roughness measurements (n=50). Roughness Scale mm-;. equivalent Frequency number Frequency (fo) 0 0.00 0 0.0 1 0.13 3 6.0 2 0.25 16 32.0 3 0.38 30 60.0 4 0.51 1 50 2.0 100.0 82 Table 3 . Foliage -and Bark powder properties. Ioisture content Ash content pH(n=2) (n=2) W {%) White spruce f o l i a g e Western hemlock bark 6.2 8 .0 3-7 2.3 4 . 3 4 . 7 P a r t i c l e size d i s t r i b u t i o n (#) White spruce f o l i a g e (n=2) P a r t i c l e sizes Retained on 100 mesh Retained on 200 mesh Retained on 325 mesh Smaller than 325 mesh Western hemlock bark (n=2) Retained on 100 mesh Retained on 200 mesh Retained on 325 mesh Smaller than 325 mesh weight (%] 3 . 4 1 4 . 8 4 0 . 6 4 1 . 2 3-9 1 7 . 8 3 4 . 8 4 3 - 5 Data obtained from Forintek Canada Corp. 83 Table 4. Glue mix physical properties. Glue mix 1 hr V i s c o s i t y (cps) 24-hr 48-hr PH * Density (g/cc) Gelation Time(min UF-C 5,100 9,700 12,800 6.4 1.14 23.0 UF - F 1 5 4,600 7,900 10,500 5.7 1.11 23.5 UF-F30 4,300 7,100 9,250 5.6 0.96 23.5 UF-F45 5,600 ## 5.3 0.98 25.5 UF-B15 6,200 9,750 10,900 6.1 1.08 20.0 UF-B30 7,200 10,300 5.9 1.06 21.0 UF-B45 7,800 5.2 1.03 1-7.0 UFi-C 4,400 11,600 6.1 1.10 10.0 UFi-F30 3,900 9,4oo 5.3 0.92 11.0 UFi-B30 4,700 12,400 5.5 1.02 ' 8.0 Measured without NH^Cl ca t a l y s t . Glues developed too high v i s c o s i t y to record on viscometer scale (> 20,000 cps). Table 5« Average (n=20) shear strengths and wood f a i l u r e percentages of UF glue treatment combinations. DRY TEST VACUUM PRESSURE TEST VACUUM PRESSU.RE-5. CYCLES Mean Mean Mean Mean Mean Mean Treatments Shear Wood Shear Wood Shear Wood Strength (psi) F a i l u r e Strength (psi) F a i l u r e (*) Strength (psi) F a i l u r e (*) UF-C-6 214 92 199 93 - 152 51 UF-C-10 238 91 225 89 196 60 UF-F15-6 225 89 208 79 195 19 UF-F15-10 302 85 268 78 199 39 UF -F30 -6 244 95 195 88 130 24 UF-F30-10 242 91 194 89 152 59 UF-F45-6 269 81 241 87 124 15 UF-F45-10 268 90 240 80 183 33 UF-B15-6 232 88 190 83 102 47 UF-B15-10 217 96 I85 90 138 63 UF-B30-6 283 95 281 85 216 44 UF-B30-10 265 98 226 90 190 63 UF-B45-6 293 61 279 57 158 19 UF-B45-10 263 87 222 70 169 29 Note: 1. Figures rounded to the nearest unit. 2. Treatment codes are shown i n Appendix I I . Table 6. Average (n=20) shear strengths and wood f a i l u r e percentages of UFi glue treatment combinations. DRY TEST VACUUM PRESSURE TEST VACUUM PRESSURE -5 CYCLED Treatments Mean Shear Strength (psi) Mean Wood Fail u r e (*) Mean Shear . Strength (psi) Mean Wood Failure (*) Mean Shear Strength (psi) Mean Wood Fai l u r e UFi-C-6 196 82 134 66 79 18 UFi-C-10 177 72 147 59 77 20 UFi-F30-6 232 89 178 86 58 18 UFi-F30-10 223 78 179 87 92 36 UFi-B30-6 196 93 174 92 81 20 UFi-B30-10 194 86 199 78 84 9 UFi, Low molecular weight UF r e s i n . Note: 1. Figures rounded to the nearest unit. 2. Treatment codes are shown i n Appendix I I . 86 Table 7. Analysis of variance f o r dry-shear strengths and wood f a i l u r e percentages for t e s t i n g the effect of glue mix and pressing time on the UF-glue bond qu a l i t y . Shear Strength Source Degrees of Freedom Sum of • Square Mean Square F Ratio: Glue mix (M) 6 0.12198xl06 20330.0 30.10' Pressing time(PT) 1 1555-7 1555-7 2.30 Panel (P) 1 488.93 488.93 0.72 MxPT 6 78629.O 13105.O 19.40' PTxP 1 300.36 300.36 0.44 MxP " 6 16931.0 2821.8 4.18 MxPTxP 6 37590.0 6264.9 9.28 Residual 252 0.17020x10° 0.42768xl06 675.42 Total 279 Wood Fai l u r e Source Degrees of Freedom Sum of Square Mean Square F Ratio: Glue mix (M) 6 13010.0 2168.4 10.48' Pressing time(PT) 1 1966.3 1966.3 9.51 Panel (P) 1 276.01 276.01 1.33 MxPT 6 6692.3 1115.4 5-39 PTxP 1 565.73 565-73 2.73 MxP 6 5123.6 853.93 4.13 MxPTxP 6 2848.9 474.81 2.30 Residual 252 52104.0 206.76 Total 279 82587.0 S i g n i f i c a n t at the 0.05 l e v e l . S i g n i f i c a n t at the 0.01 l e v e l . 87 Table 8. A n a l y s i s o f v a r i a n c e f o r vacuum p r e s s u r e - s h e a r s t r e n g t h s and wood f a i l u r e percentages f o r t e s t i n g the e f f e c t o f glue mix and p r e s s i n g time on the UF glue bond q u a l i t y . Shear Strength Source Degrees Sum of Mean F o f Square Square Ratioi Freedom Glue mix (M) 6 0.17729x10° 29549.0 29.09 P r e s s i n g time(PT) 1 1462.9 1462.9 1.44 Panel (P) 1 8803.2 8803.2 8.66' MxPT 6 0.10504x10° 17507.0 17.23 PTxP 1 300.36 300.36 0.30 MxP 6 21182.0 3530.3 3.47 MxPTxP 6 83720.0 13953.0 13.73 R e s i d u a l 252 0.25597x10° I O I 5 . 8 T o t a l 279 •K-3S-Wood F a i l u r e Source Degrees of Freedom Sum of Square Mean Square F Ratios Glue mix (M) 6 20929.0 .3488.1 16.251 P r e s s i n g time(PT) 1 260.36 260.36 1.21 Panel (P) 1 '38.629 38.629 0.18 MxPT 6 3228.9 538.16 2.50' PTxP 1 6 6 O .36 660.36 3.07 MxP 6 5502.9 917.15 4.27' MxPTxP 6 6110.3 1018.4 4.74' R e s i d u a l 252 54075.0 214.58 T o t a l 279 9O8O5.O S i g n i f i c a n t at the 0.05 l e v e l . ** S i g n i f i c a n t at the 0.01 l e v e l . 88 Table 9 . Analysis of variance f o r vacuum-pressure f i v e cycle-shear strengths and wood f a i l u r e percen-tages for t e s t i n g the effect of glue mix and and pressing time on the UF glue bond q u a l i t y . Shear Strength Source Degrees Sum of of Square Freedom Mean Square F Ratios Glue mix (M) 6 Pressing time(PT) 1 Panel (P) 1 MxPT 6 PTxP 1 MxP 6 MxPTxP 6 Residual 252 Total 279 0.21257X101" 32342.0 211.04 48449.0 4204.7 0.20018x10^ 60050.0 0.10859xl0( 0.16438x10^ 35428.0 32342.0 211.04 8074.8 4204.7 33364.0 10008.0 4309.O 8.22 7.51 0.48x10 1.87 0.97 7.74 -1 2.32 •3S-Wood Fail u r e Source Degrees of Freedom Sum of Square Mean Square F Ratios Glue mix (M) 6 Pressing time(PT) 1 Panel (P) 1 MxPT 6 PTxP 1 MxP 6 MxPTxP 6 Residual 252 Total 279 51447.0 23461.0 10.032 746.81 1449.2 14618.0 14959.0 0 .15808x l0 ( 0.26851x10* 8574.6 23461.0 10.032 746.81 1449•2 2436.3 2493.2 627.3 13.66 37.39 0.15x10' 1.19 2.31 3.884 3.97 S i g n i f i c a n t at the 0.05 l e v e l S i g n i f i c a n t at the 0.01 l e v e l 89 Table 10. Analysis of variance f o r dry-shear strengths and wood f a i l u r e percentages f o r t e s t i n g the effec t of glue mix and pressing time on the UFi glue bond qu a l i t y . Shear Strength Source Degrees of Freedom Sum of Square Mean Square F Ratios Glue mix (M) -2 36487.0 18243.0 22.06 Pressing time(PT) 1 2900.8 2900.8 3.50 Panel (P) 1 7-5 7.5 0.90x10" MxPT 2 15^1.7 770.83 o.93 PTxP 1 607.5 607.5 0.73 MxP 2 845.0 422.5 0.51 MxPTxP 2 605.0 302.5 0.36 Residual 108 89315.0 826.99 Total 119 0.13231x10° Wood Fai l u r e Source Degrees of Freedom Sum of Square Mean Square F Ratios Glue mix (M) 2 3227.8 1613.9 4.84** Pressing time(PT) 1 2585.4 2585.4 , T r /r 7.76 Panel (P) 1 106.41 106.41 0.31 MxPT 2 115.82 57.908 0.17 PTxP 1 57.408 57.408 0.17 MxP 2' 256.32 128.16 0.38 MxPTxP 2 816.32 408.16 1.22 Residual 108 35962.O 332.98 Total 119 43128 S i g n i f i c a n t at the 0.05 l e v e l . S i g n i f i c a n t at the 0.01 l e v e l . 2 90 Table 11. Analysis of variance f o r vacuum pressure-shear strengths and wood f a i l u r e percentages f o r tes t i n g the eff e c t of glue mix and pressing time on the UFi glue bond qu a l i t y . Shear Strength Source Degrees of Freedom Sum of Square Mean Square F Ratios Glue mix (M) 2 48701.0 24351.0 ** 43.73 Pressing time(PT) 1 5005.2 5005.2 8.98 Panel (P) 1 1300.2 1300.2 2.33 MxPT 2 2587.9 1294.0 2.32 PTxP 1 16.875 16.875 0.30x10" MxP 2 2240.4 1120.2 2.01 MxPTxP 2 908.75 454.37 0.81 Residual 108 60137.0 556.83 Total 119 0.12090x10° Wood Fail u r e Glue mix (M) 2 14382.0 7190.9 ** 16.50 Pressing time(PT) 1 1280.5 1280.5 2.93 Panel (P) 1 5.633 5.633 0.12x10 MxPT 2 1022.5 511.23 1.17 PTxP 1 554.70 554.70 1.27 MxP 2 67.267 33.63 0.77x10 MxPTxP 2 178.40 89.20 0.20 Residual 108 47051.0 435.66 Total 119 64542 S i g n i f i c a n t at the 0, 05 l e v e l . S i g n i f i c a n t at the 0.01 l e v e l . -1 -1 91 Table 12. Analysis of variance f o r vacuum pressure f i v e cycle-shear strengths and wood f a i l u r e percen-tages f o r t e s t i n g the effect of glue mix and pressing time on the UFi glue bond q u a l i t y . Shear Strength Source Degrees of Freedom Sum of Square Mean Square F Ratios Glue mix (M) 2 '1096.3 548.13 1.32 Pressing time(PT) 1 3910.2 1910.2 9.41 Panel (P) 1 1300.2 1300.2 3.13 MxPT 2 7632.9 3816.5 9.19 PTxP 1 200.21 2700.2 0.48 MxP 2 5400.4 2700.2 •K--35-6.50 MxPTxP 2 3100.4 1550.2 3.73 Residual 108 44857.0 415.35 Total 119 67498.0 Wood Fai l u r e Source Degrees of Freedom Sum of Square Mean Square F . Ratios Glue mix (M) 2 2930.4 1465.2 2.40 Pressing time(PT) 1 226.88 226.88 0.37 Panel (P) 1 75.208 75.208 0.12 MxPT 2 4366.2 2183.1 3.58* PTxP 1 91.875 91.875 0.15 MxP 2 125.42 62.708 0.10 MxPTxP 2 11.25 5.625 0.92x10 Residual 108 65837.0 609.61 Total 119 73665.0 S i g n i f i c a n t at the 0.05 l e v e l . S i g n i f i c a n t at the 0.01 l e v e l . -2 92 Table 1 3 . Duncan's multiple range tests f o r shear strengths of treatments bonded with UF glue. T R E A T M E N T R A N K I N G* Dry Test ]_ 10 3 9 2 6 5 14 1 2 8 7 1 1 13 4 Treatment 214 217 225 232 238 242 244 263 265 268 .269 283 293 302 Mean Vacuum Pressure test Treatment 10 9 5 6 1 3 14 2 1 2 8 7 4 1 3 H Mean 1 8 5 1 9 0 1 9 ^ 1 9 9 2 0 8 2 2 2 2 2 5 2 2 6 ^ 2 6 8 2 7 9 2 8 1 Vacuum Pressure-5 Cycles test 9 7 5 10 6 1 13 14 8 12 3 2 4 11 Treatment** 102 124 1 3 0 138 1 5 2 1 5 2 1 5 8 I 6 9 183 190 1 9 5 196 199 216 Mean Means underscored by the same l i n e 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 5% l e v e l of s i g n i f i c a n c e . Means above r e f e r to treatments as follows: 1 UF-C-6 5 UF-F30-r6 9 UF - B 1 5 - 6 13 UF - B 4 5 - 6 2 •'•'UF-C-10 6 UF-F30-10 10 UF-B15-10 14 UF-B45-10 3 UF - F 1 5 - 6 7 UF-F45-6 11 UF - B 3 0 -6 4 UF-F15-10 8 UF-F45-10 12 UF-B30-10 93 Table 14. Duncan's multiple range tests f o r wood f a i l u r e percentages of treatments bonded with UF glue. T R E A T M E N T R A N K I N G * Dry Test # # 13 7 4 14 9 3 8 2 6 1 5 11 10 12 T r 8 M e a n n t 6 1 8 1 8 5 8 7 8 8 8 9 9 ° 9 1 9 1 9 2 9 5 9 5 9 6 9 8 Vacuum Pressure Test w 13 14 4 3 8 9 11 7 5 2 6 12 10 1 i i Mean Treatment ^ ? 0 7 Q ? 9 8 o 83 85 87 88 89 89 90 90 93 Vacuum Pressure-5 Cycles Test # # 7 13 3 5 14 8 4 11 9 1 6 2 10 12 Treatment ± 5 ±(? 1 ? ^ 2 g 33 3 9 ^ ^ 5 ± 5 9 6 o 6 3 6 3 Mean . •3S--5S-Means underscored by the same l i n e 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 5% l e v e l of s i g n i f i c a n c e . Means above r e f e r to treatments as follows: 1 UF-C-6 5 UF-F30-6 9 UF-B15-6 13 UF-B45-6 2 UF-C-10 6 UF-F30-10 10 UF-B15-10 14 UF-B45-10 3 UF-F15-6 7 UF-F45-6 11 UF-B30-6 4 UF-F15-10 8 UF-F45-10 12 UF-B30-10 94 Table 15• Duncan's multiple range tests for shear strengths of treatments bonded with UFi glue T R E A T M E N T R A N K I N G * D r v T e s t 2 6 5 1 4 3 Treatment Mean 177 194 196 196 223 232 Vacuum Pressure Test 1 2 . 5 3 4 6 Treatment Mean** 134 147 174 178 179 199 Vacuum Pressure-5 Cycles Test 3 2 1 5 6 4 Treatment Mean 58 77 79 81 84 92 Means underscored by the same l i n e 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 5$ l e v e l of si g n i f i c a n c e . Means above r e f e r to treatments as follows: 1. UFi-C-6 2. UFi-C-10 3. UF1-F30-6 4. UFi-F30-10 5. UF1-B30-6 6. UFi-B30-10 9 5 T a b l e 1 6 . Duncan's m u l t i p l e range t e s t f o r wood f a i l u r e percentages o f treatments bonded with U Fi g l u e . T R E A T M E N T R A N K I N G * D r y T e s t 2 4 1 6 3 5 Treatment Mean 72 78 82 86 -89 9 3 Vacuum Pr e s s u r e T e s t 2 1 6 3 4 5 Treatment Mean 66 5 9 78 86 87 9 2 Vacuum P r e s s u r e - 5 C y c l e s T e s t 6 3 1 2 5 4 Treatment Mean 9 18 18 2 0 2 0 3 6 Means underscored by the same l i n e 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 5 $ l e v e l o f s i g n i f i c a n c e . Means above r e f e r to treatments as f o l l o w s : 1. U F i - C - 6 2 . UFi-C-10 3 . U F i - F 3 0 - 6 4 . UFi-F30-10 5 . UFi-B30 - 6 6 . UFi-B30-10 96 i l l : • ' : 1 • • -HEATING RATE 10°c/min I 1 1 1 ! 1 I T-40 60 80 100 120 140 160 180 temperature (°C) Figure 1. DSC thermograms of UF r e s i n with wheat f l o u r , 30% f o l i a g e and 30% bark. 100 J hi H <: fe Q o o 90 J 80 70 ~\ 60 J 50 300 • H CQ ,5? 250 E H E H w 200 -4 cc : <: w 0 97 [ j 6 min pressing time j j j] 10 min pressing time % FOLIAGE % BARK • 1 5 30 4-5 - - 15 30 15 30 45 ~ 15 30 45 " 45 UF GLUE MIXES Figure 2. Dry-shear strengths and wood f a i l u r e percentages f o r treatments bonded with the commercial UF glue. 100 -90 -w 80 _J w Pi H 70 < § 60 o 5 0 -o i 98 jf J 6 min pressing time 10 min pressing time % FOLIAGE 15 30 45 $ BARK -15. , 30 4 5 -300 _, 250. •H to EH EH 200-4 < W 150. 15 30 45 - 15 30 45 UF GLUE MIXES Figure 3 . Vacuum pressure-shear strengths and wood f a i l u r e percentages f o r treatments bonded with the commercial UF glue. 99 6 min pressing time 10 min pressing time % FOLIAGE 15 30 4 5 " $ BARK 15 30 45 -- 15 30 45 - 15 30 45 " UF GLUE MIXES Figure 4 . Vacuum pressure-five cycle shear strengths and wood f a i l u r e percentages f o r treatments bonded with the commercial UF glue. 100 i—i Q o o 100 90 80 70 60-50 A •:> 0 % 6 min pressing time 10 min pressing time FOLIAGE 30% BARK 30% K E H 00 PC < w 00 0 % 30% 30% 250 • H ra £ 200. E H O 150. UFi GLUE MIXES Figure 5« Dry shear strengths and wood f a i l u r e percentages f o r treatments bonded with the laboratory UF glue (UFi). 101 100 -, 9 0 J w 80-PC 3 70-fe Q 8 60 5o4 > 0 0 $ [ [ 6 min pressing time [ | || 10 min pressing time FOLIAGE 30$ BARK 30$ 0 % 30$ 30$ 200 -. 150 w 100 J 0 UFi GLUE MIXES gure 6. Vacuum pressure-shear strengths and wood f a i l u r e percentages f o r treatments "bonded with the .laboratory UF glue (UFi). 102 50 -I 0 % j J 6 rain pressing time 10 min pressing time FOLIAGE BARK 30% 30% 40 w K 30 -!=> Hi H . 20-Q O S 10-0 0 % 30% 30% m 100 EH EH Ui te < w w 50 UFi GLUE MIXES Figure 7. Vacuum pressure f i v e cycle-shear strengths and wood f a i l u r e percentages f o r treatments bonded with the laboratory UF glue (UFi). 100 —i fe tt H < fe Q O o 90 80 J 70 6 0 J 103 f o l i a g e "bark 6 min p r e s s i n g time 10 min p r e s s i n g time 300 CQ ft 250 _ « EH r j W tt EH GO tt < H GO 200 J A / \ > 0 0 F i g u r e 8 . 15 30 45 15 $ MODIFIER ADDITION r 30 45 Dependence o f plywood bond q u a l i t y on the UF glue mix and p r e s s i n g time i n t e r a c t i o n a c c o r d i n g to d r y - s h e a r s t r e n g t h s and wood f a i l u r e percentages 1 0 0 w M < fe 9 0 80 Q 7 0 o o 6 0 J 104 0 O f o l i a g e b a r k 6 min p r e s s i n g t i m e 1 0 min p r e s s i n g t i m e 300 ra 2 5 0 EH a EH 2 0 0 Ul 3 DQ 1 5 0 - I J L 1 5 3 0 4 5 1 5 % MODIFIER ADDITION 30 4 5 Figure 9< Dependence o f plywood bond q u a l i t y on t h e UF g l u e mix and. p r e s s i n g t i m e i n t e r a c t i o n a c c o r d i n g t o vacuum p r e s s u r e - s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s . . 7 0 - - , 1 0 5 6 0 J 5 0 H a 4 0 >A M SS 30 Q o g 2 0 1 0 0 f o l i a g e "bark 6 min p r e s s i n g t i m e — 1 0 min p r e s s i n g t i m e 200 J ra P. w 150-1 EH EH C O g 1 0 0 -w co 1 5 3 0 4 5 1 5 $ MODIFIER ADDITION 3 0 4 5 F i g u r e 1 0 , Dependence o f plywood "bond q u a l i t y on t h e UF g l u e mix and p r e s s i n g t i m e i n t e r a c t i o n a c c o r d i n g t o vacuum p r e s s u r e f i v e c y c l e s - s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s . 100 106 9 0 -« 3 80. < fe P o o 70-4 0 O f o l i a g e © ba r k 6 min p r e s s i n g t i m e 10 min p r e s s i n g t i m e 250-, •H ca 200-4 E H E H C O te < 00 150-4 > 0" 30 % MODIFIER ADDITION 30 F i g u r e 11. Dependence o f plywood bond q u a l i t y on t h e U F i g l u e mix and p r e s s i n g t i m e i n t e r a c t i o n a c c o r d i n g t o d r y - s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n -t a g e s . 107 100 H 90 80 J 70 J Q 8 60 5 0 -0 ? o f o l i a g e b a r k 6 min p r e s s i n g t i m e 200 J •H CQ P. w EH C J EH C O < C O 150 100-J — 10 min p r e s s i n g t i m e > 30 $ MODIFIER ADDITION 30 Figure 12 . Dependence o f plywood bond q u a l i t y on t h e U F i g l u e mix and p r e s s i n g t i m e i n t e r a c t i o n a c c o r d i n g t o vacuum p r e s s u r e one c y c l e - s h e a r s t r e n g t h s and wood f a i l u r e p e r c e n t a g e s . 108 40 30 H « H-l M fe 20 Q O o 1 0 - J 0 o o \ \ \ \ \ \ f o l i a g e bark 6 min pressing time 10 min pressing time 150-1 •H CQ PH EH C5 EH 00 10CM w 50-| . 1 T 0 30 % MODIFIER ADDITION 30 Figure 13 Dependence of plywood bond q u a l i t y on the UFi glue mix and pressing time i n t e r a c t i o n according to vacuum pressure f i v e cycles-shear strengths and wood f a i l u r e percentages. 109 APPENDIX I. S p e c i f i c a t i o n and mixing directions for the standard Casco UF 109 glue. •fir -\\ \ ; L..* >v . . . A ' V \ j — 7 i— j I V l , 110 A D H E S I V E S AND RESINS PRODUCT T Y P E : A P P E A R A N C E : P R O P E R T I E S : CASCO UF 109 A P P L I C A T I O N : S TORAGE & HANDLING: UF109 i s a high solids, aqueous, urea-formaldehyde r e s i n solution. A cl e a r to sl i g h t l y cloudy, viscous l i q u i d when f r e s h , bee inc r e a s i n g l y cloudy on storage. oming Specifications Test Method M M 26D Centipoise s 44 I 5 525 ± 75 63. 8. 0 \ 0% 4 -+0. 2 1.302- 0.003 2.0-0.5 F-302 F-302. 4 F-303. 1(WCAV. F-304 F-301 F-305. 1 1 5 - 2 mins. 23 - 3 mins. 4 2 - 4 mins. V i s c o s i t y at 70° F. V i s c o s i t y at 77°F. % Solids Content pH (Beckman Model H2) S p e c i f i c g r a v i t y 60°/60 F % F r e e Formaldehyde G e l Time at 110° F. With 5 cc 10% "Y" catalyst per 100 gms. UF109 With 10 gms 109ARNhardener per 100 gms UF109 With 10 gms 221 hardener per 100 gms UF109 The manufacture of plywood; veneering, lumber Laminating, edge gluing, and general assembly gluing when formulated with the appropriate catalysts and/or extenders and f i l l e r s . The storage l i f e of UF109 i s approximately 6 months at 70° F. Low temperatures w i l l i n crease the storage l i f e and, conversely, higher temperatures w i l l decrease the storage l i f e appreciably. UF109 is c l a s s i f i e d as a l i q u i d r e s i n , e s s e n t i a l l y non-volatile and non-flammable. The free formaldehyde present i n UF109 can cause derm a t i t i s and i t i s recommended that gloves and goggles be used when handling this r e s i n . Contamination with i r o n w i l l tend to darken most urea-formaldehyde resins and to avoid this o c c u r r i n g i n UF109 it i s recommended that the r e s i n be stored i n heresite, polyethylene, or equivalent lined drums or tanks. "hose recommendations ."ind siigr .estions for the use of our materials ore based on our best experience ,md knowledge b u t w e U-> not -.uarantee the results to be obtained in customer's processes. Prices subject to change without notice. B O R D E N C H E M I C A L W E S T E R N DIVISION OF THE BORDEN COMPANY, LIMITED III t'HONI C'.O.I! :'(•! 0.(51, I'lllI'MONI I 1(1 il '..!«() I l l •3f"» Standard Plywood UF Glue Mix Mixing Directions Water - 851 g Sterox - 3«3 g Start mixing Wheat f l o u r - 700 g Mix 2-4 minutes Resin (63$ UF 109) - 1500 g (945 g r e s i n s o l i d s ) * * Mix u n t i l smooth Ammonium chloride - 12 g Aqua ammonia - 12 g 3078 g Resin s o l i d s as % t o t a l _ - a n 7 mix Total s o l i d s as % t o t a l -~ g mix ' Spread, MDGL, approx. - 70 lb/MDGL* ? (32 kg/100 in ) MDGL: 1000 square foot of double glueline 1 5 i 30 and 45$ f o l i a g e and bark additions were based on r e s i n s o l i d s weight. 112 APPENDIX I I . Code for treatments i d e n t i f i c a t i o n 113 Code for Treatments I d e n t i f i c a t i o n Treatment Glue Modifier addition ($) Pressing time (min) Code F i r s t stage 1 UF 0 6 UF-C -6(Control) 2 0 10 UF-C-10(Control) 3 Foliage 15$ 6 UF-F15-6 4 Foliage 15$ 10 UF-F15-10 5 Foliage 30$ 6 UF-F30-6 6 Foliage 30$ 10 UF-F30-10 7 Foliage 45$ 6 UF - F 4 5 - 6 8 Foliage 45$ 10 UF-F45-10 9 • Bark 15$ 6 UF-B15-6 10 Bark 15$ 10 UF-B15-10 11 Bark 30$ 6 UF-B30-6 12 Bark 30$ 10 UF-B30-10 13 Bark 45$ 6 UF - B 4 5 - 6 14 Bark 45$ 10 UF-B45-10 Second Stage * 0 1 UFi 6 UFi-C - 6(Control) 2 0 10 UFi-C-10(Control 3 Foliage 30$ 6 UFi-F30 -6 4 Foliage 30$ 10 UFi-F30-10 5 Bark 30$ 6 UFi-B30-6 6 Bark 30$ 10 . UFi-B30-10 * UFi, laboratory-formulated low molecular weight UF r e s i n . Examp e: UF-F15-6 pressing time •addition l e v e l UF r e s i n type 

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