Condensed Tannins as Substitutes for Resorcinol in Bonding

Downloaded by RUTGERS UNIV on November 30, 2016 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch018

Chapter 18 Condensed Tannins as Substitutes for Resorcinol in Bonding Polyester and Nylon Cord to Rubber G a r y R . H a m e d and K y u n g H. C h u n g Institute of Polymer Science University of Akron Akron, O H 44325 R i c h a r d W. Hemingway Southern Forest Experiment Station Forest Service, U.S. Department of Agriculture Pineville, L A 71360

Nylon and polyester cords used to reinforce tires are coated with a reactive resorcinol-formaldehyde-latex (RFL) adhesive dip to strongly couple the rubber and cord. Condensed tannins from pecan nut pith, bark of southern pine trees, or peanut skins can be used to replace some or all of the resorcinol in a standard RFL dip. When the tire cord adhesion test (TCAT) geometry is used, pullout forces for dipped nylon cords embedded in a typical styrene-butadiene rubber (SBR) vulcanizate nearly equaled those obtained with the standard dip when resorcinol was replaced with tannins from peanut skins or pine bark sulfite extracts. When bonding polyester cord, resins formulated with pecan pith sulfite extracts and purified pine bark tannins gave pullout forces substantially higher than the standard RFL dip. Resins made with peanut skin tannins or pine bark sulfite extracts as substitutes for resorcinol were marginally inferior to the standard RFL dip. When bonding to nylon cord, tannin preparations of low molecular weight appear to provide the stronger bonds. Bond strength was not influenced by the presence of sulfite ion or carbohydrates in nylon adhesion. Tannin preparations containing low proportions of carbohydrates gave the higher bond strengths in adhesion to polyester cord. 0097-6156/89/0385-0242$06.00/0 © 1989 American Chemical Society

Hemingway et al.; Adhesives from Renewable Resources ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


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N y l o n a n d polyester cords are c o m m o n l y used i n tire b o d y plies t o i m p a r t s t r e n g t h a n d d u r a b i l i t y . T o f u n c t i o n p r o p e r l y , the cords m u s t be f i r m l y b o n d e d t o the s u r r o u n d i n g r u b b e r . S o m e c o u p l i n g o f c o r d t o r u b b e r occurs because o f s i m p l e m e c h a n i c a l i n t e r l o c k i n g o f r u b b e r t h a t has p e n e t r a t e d i n t o the c o r d . However, t h i s t y p e o f b o n d i n g is insufficient, a n d a n adhesive i n t e r l a y e r is re q u i r e d . T y p i c a l l y , the c o r d f a b r i c is d i p p e d i n t o a w a t e r - b a s e d adhesive, t h e n d r i e d before c a l e n d e r i n g i n t o a r u b b e r ply. T h e o r i g i n for the adhesives c u r r e n t l y used dates t o a patent b y C h a r c h a n d M a n e y (1). T h i s class o f adhesives is based o n reactive m i x t u r e s o f r e s o r c i n o l , f o r m a l d e h y d e , a n d a r u b b e r y l a t e x ( R F L ) d i p s . A representative R F L c o m p o s i t i o n (2) s u i t a b l e for b o n d i n g n y l o n t o a diene elastomer is d e t a i l e d i n T a b l e I. I n the adhesive, the r e s o r c i n o l a n d f o r m a l d e h y d e react t o f o r m a p r o d u c t t h a t reinforces the r u b b e r y m a j o r p o r t i o n (3). It is also the R F p a r t o f the adhesive t h a t is t h o u g h t t o be p r i n c i p a l l y responsible for the adhesive's s t r o n g i n t e r a c t i o n w i t h the c o r d (4). D u r i n g the v u l c a n i z a t i o n of a c o r d - R F L - r u b b e r c o m p o s i t e , c o - c u r i n g across the r u b b e r adhesive interface is expected (5). O n e f u n c t i o n o f the p y r i d i n e m o i e t y o f the s t y r e n e - b u t a d i e n e - v i n y l p y r i d i n e p o l y m e r is t o increase the i n t e r a c t i o n between the l a t e x r u b b e r a n d the R F , thereby e n h a n c i n g the cohesive s t r e n g t h o f the d i p (6).

T a b l e I. S t a n d a r d R F L - T y p e A d h e s i v e D i p Composition Component

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F o r m a l i n s o l ' n (37%) N a O H s o P n (10%) D i s t i l l e d water Styrene-butadiene-vinylp y r i d i n e l a t e x ( 4 1 % solids)

3.0 g 236 g 244 g

T h e r e a c t i v i t y o f resorcinol w i t h f o r m a l d e h y d e is essential for d e v e l o p i n g the cohesive s t r e n g t h o f the interlayer a n d i t s b o n d i n g c h a r a c t e r i s t i c s . C o n densed t a n n i n s are k n o w n t o be very reactive w i t h f o r m a l d e h y d e (7-9), so these renewable p h e n o l i c p o l y m e r s are g o o d candidates as r e s o r c i n o l replacements. Indeed, condensed t a n n i n s f r o m w a t t l e a n d pine b a r k e x t r a c t s have been suc cessfully used i n c o l d - s e t t i n g , w o o d - l a m i n a t i n g adhesives, a n d the f o r m e r are used e x t e n s i v e l y i n the c o m m e r c i a l p r o d u c t i o n o f l a m i n a t e d t i m b e r s i n S o u t h A f r i c a ( P i z z i , Α . , N a t i o n a l T i m b e r Research I n s t i t u t e , P r e t o r i a , S o u t h A f r i c a , p e r s o n a l c o m m u n i c a t i o n , 1982) (10-13). T h e purpose o f the research described here was t o explore the f e a s i b i l i t y o f u s i n g condensed t a n n i n s as replacements for resorcinol i n R F L - t y p e adhesive


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d i p s for b o n d i n g of c o r d t o r u b b e r p r o d u c t s . Success i n t h i s effort w o u l d g r e a t l y increase the m a r k e t s for condensed t a n n i n s , since far m o r e resorcinol is used i n the r u b b e r i n d u s t r y t h a n i n b o n d i n g of w o o d p r o d u c t s .


Experimental

Methodology

M a t e r i a l s . T w o types of s t a n d a r d t i r e c o r d o b t a i n e d f r o m G e n C o r p o r a t i o n were used i n t h i s i n v e s t i g a t i o n : polyester, 1 3 0 0 / 3 , a n d n y l o n 66, 1 2 6 0 / 3 . T h e r u b b e r c o m p o s i t i o n t o w h i c h the adhesively d i p p e d cords were b o n d e d h a d the f o l l o w i n g c o m p o s i t i o n i n p a r t s b y weight: styrene-butadiene r u b b e r ( S B R ) 1502, 100; N 3 3 0 c a r b o n b l a c k , 50; z i n c oxide, 5; stearic a c i d , 0.5; s u l f u r , 1.7; 2m o r p h o l i n o t h i o - b e n z o t h i a z o l e , 2. M a s t e r batches were m i x e d 7 m i n i n a 3 5 0 - m l B r a b e n d e r P l a s t i c o r d e r , a n d curatives were a d d e d o n a cool t w o - r o l l m i l l . C u r e characteristics at 155 ° C were d e t e r m i n e d w i t h a n o s c i l l a t i n g disc rheometer ( A S T M D 2084). T h e t i m e t o reach 9 0 % of the f i n a l cure state was 23 m i n , a n d the S h o r e A hardness o f the final v u l c a n i z a t e was a p p r o x i m a t e l y 60. F o u r types o f condensed t a n n i n s were s t u d i e d i n the adhesive d i p s : 1) ext r a c t s f r o m pecan n u t p i t h o b t a i n e d b y d i g e s t i o n w i t h aqueous s o d i u m sulfites o d i u m c a r b o n a t e s o l u t i o n s , 2) p u r i f i e d t a n n i n s f r o m s o u t h e r n p i n e b a r k , 3) e x t r a c t s f r o m s o u t h e r n pine b a r k o b t a i n e d b y digestion w i t h aqueous s o d i u m s u l f i t e - s o d i u m c a r b o n a t e s o l u t i o n s , a n d 4) t a n n i n s e x t r a c t e d w i t h acetone-water solutions from peanut skins. T h e sulfite e x t r a c t o f the p e c a n nut p i t h was o b t a i n e d by e x t r a c t i n g the finely g r o u n d r e d powder (509 g m ) w i t h s o d i u m sulfite (20.4 g m ) a n d s o d i u m c a r b o n a t e (2.0 g m ) i n 2549 m L of water. A p p r o x i m a t e l y 1 h r was r e q u i r e d to reach reflux t e m p e r a t u r e , a n d t h e suspension was heated at reflux for 2 h r . T h e suspension was cooled, the v o l u m e adjusted t o a constant b y a d d i t i o n o f w a t e r , a n d i t was filtered twice t h r o u g h glass w o o l . A l i q u o t s (100 m L ) of the recovered l i q u o r were freeze-dried t o determine the e x t r a c t y i e l d . T h e r e m a i n d e r was also freeze-dried t o recover a d a r k b r o w n s o l i d . T h e p u r i f i e d p i n e b a r k t a n n i n was o b t a i n e d i n the f o l l o w i n g m a n n e r . T h e p h l o e m o f freshly felled l o b l o l l y p i n e trees was removed b y carefully p e e l i n g the outer b a r k away at the cork c a m b i u m a n d t h e n p e e l i n g the w h i t e p h l o e m f r o m the x y l e m c a m b i u m . S t r i p s of p h l o e m were cut i n t o sections of a b o u t 2 t o 5 i n a n d i m m e d i a t e l y i m m e r s e d i n acetone-water (70:30, v / v ) . T h e e x t r a c t i o n flasks were kept at a m b i e n t t e m p e r a t u r e , p r o t e c t e d f r o m exposure t o l i g h t , for 48 h r , after w h i c h the solvent was recovered b y filtration. T h e acetone was removed u n d e r v a c u u m o n a r o t a r y e v a p o r a t o r , a n d the aqueous s o l u t i o n was e x t r a c t e d four t i m e s w i t h a n a p p r o x i m a t e l y e q u a l v o l u m e of e t h y l acetate t o remove low m o l e c u l a r weight phenolics. T h e r e m a i n i n g water-soluble e x t r a c t was freezed r i e d . A l i q u o t s ( a b o u t 50 g m ) were redissolved i n m e t h a n o l - w a t e r (1:1, v / v ) , a n d the s o l u t i o n s were a p p l i e d t o 2.4 X 90 c m Sephadex L H - 2 0 c o l u m n s packed i n t h i s same solvent. T h e c o l u m n s were e l u t e d w i t h m e t h a n o l - w a t e r u n t i l no m o r e colored m a t e r i a l was e l u t e d . T h e condensed t a n n i n p o l y m e r s absorbed 2


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o n the c o l u m n p a c k i n g were t h e n e l u t e d w i t h acetone-water (50:50, v / v ) . T h e acetone was r e m o v e d b y e v a p o r a t i o n u n d e r v a c u u m o n a r o t a r y e v a p o r a t o r , a n d the aqueous s o l u t i o n was freeze-dried. T h e s o d i u m s u l f i t e - s o d i u m c a r b o n a t e e x t r a c t s of p i n e b a r k were p r e p a r e d f r o m s o u t h e r n p i n e tree b a r k s o b t a i n e d f r o m logs at a p l y w o o d p l a n t i n c e n t r a l L o u i s i a n a . T h e b a r k was collected f r o m transfer chains i m m e d i a t e l y f o l l o w i n g the debarkers. A f t e r a i r - d r y i n g , the b a r k was first processed i n a g a r d e n m u l c h e r a n d t h e n refined i n a S p r o u t - W a l d r i n disk refiner fitted w i t h breaker plates. T h e finely g r o u n d b a r k was d i v i d e d i n t o lots of a p p r o x i m a t e l y 30 l b (100 p a r t s b y w e i g h t ) , w h i c h were t h e n e x t r a c t e d w i t h 4.0 p a r t s o f s o d i u m sulfite a n d 0.4 p a r t s of s o d i u m c a r b o n a t e i n 700 p a r t s of water i n a 4 0 - g a l c a p a c i t y stainless steel t a n k . T h e s o l u t i o n was heated t o 95 t o 100 ° C over 1 h r a n d m a i n t a i n e d at t e m p e r a t u r e for 2 h r . T h e suspension was cooled, adjusted t o a constant v o l u m e , a n d the e x t r a c t l i q u o r was filtered twice t h r o u g h fiberglass m a t s . T y p i c a l l y , 6 0 % o f the a d d e d l i q u o r was recovered f r o m the p u l p . A p p r o x i m a t e l y 100 g a l of e x t r a c t were d r i e d i n a hot p a n e v a p o r a t o r . F o r the p r e p a r a t i o n of the peanut s k i n t a n n i n , the red s k i n s were separated f r o m r e s i d u a l n u t a n d h u l l m a t e r i a l by h a n d s o r t i n g , a n d t h e n a b o u t 30 l b of s k i n s were e x t r a c t e d w i t h acetone-water (60:40 v / v ) at a l i q u o r - t o - s k i n s r a t i o of 5 t o 1 at 50 ° C for 4 h r i n a stainless steel t a n k . T h e e x t r a c t was filtered t h r o u g h a fiberglass m a t , the acetone was r e m o v e d u n d e r v a c u u m o n a r o t a r y e v a p o r a t o r , a n d the aqueous s o l u t i o n was freeze-dried. A d h e s i v e P r e p a r a t i o n . T h e s t a n d a r d R F L d i p t h a t was used is g i v e n i n T a b l e I. I n the d i p s c o n t a i n i n g the t a n n i n s , a l l ingredient a m o u n t s were h e l d constant except the r a t i o o f resorcinol t o t a n n i n . S t a r t i n g w i t h the c o n t r o l d i p ( T a b l e I), t a n n i n was s i m p l y s u b s t i t u t e d for r e s o r c i n o l , such t h a t d i p s c o n t a i n i n g r e s o r c i n o l / t a n n i n of 1 0 0 / 0 , 7 5 / 2 5 , 5 0 / 5 0 , 2 5 / 7 5 , a n d 0 / 1 0 0 were p r e p a r e d as follows. R e s o r c i n o l , t a n n i n , f o r m a l i n , N a O H s o l u t i o n , a n d d i s t i l l e d water were m i x e d together a n d allowed t o react for 2 h r . T h e n , the s t y r e n e - b u t a d i e n e - v i n y l p y r i d i n e l a t e x ( G e n t a c 118 f r o m G e n C o r p o r a t i o n ) was a d d e d , a n d the d i p was allowed t o age 24 h r before use. I n some cases, the adhesive b e c a m e a soft gel. T h i s , however, c o u l d be " b r o k e n " b y m i x i n g , a n d i t was s t i l l possible t o coat the d i p o n t o the test c o r d . T h e d i p was a p p l i e d t o a c o r d b y i m m e r s i n g the c o r d i n the d i p for 30 s. T h e c o r d was t h e n removed a n d d r i e d 5 h r at r o o m t e m p e r a t u r e before p r e p a r i n g p u l l o u t test specimens. I n i n d u s t r y , a short heat t r e a t m e n t after d i p a p p l i c a t i o n is often e m p l o y e d , however, t h i s was n o t done i n the present i n v e s t i g a t i o n . P u l l o u t T e s t s . T h e m e t h o d t o determine the adhesion between the d i p p e d cords a n d the S B R v u l c a n i z a t e was the tire c o r d adhesion test (14,15), F i g u r e 1. H e r e , t w o cords are embedded (to a d e p t h of 10 m m ) i n t o o p p o s i t e ends of a r u b b e r b l o c k (76 m m χ 13 m m χ 6.4 m m ) . S a m p l e s are t h e n cured 23 m i n at 155 ° C a n d allowed t o rest 1 day. B o n d strengths are d e t e r m i n e d b y c l a m p i n g the t w o free c o r d ends i n a n I n s t r o n a n d p u l l i n g at the rate of 50 m m / m i n .


246


F a i l u r e occurs w h e n one of the cords is p u l l e d - o u t ; the s t r e n g t h is denoted by the m a x i m u m force d u r i n g c o r d p u l l o u t .


Results and Discussion I n the p r e s e n t a t i o n of d a t a a n d discussion t h a t follows, the four types of c o n densed t a n n i n e x t r a c t s are designated: pecan p i t h sulfite e x t r a c t (1), p u r i f i e d pine b a r k t a n n i n (2), p i n e b a r k sulfite e x t r a c t (3), a n d p e a n u t s k i n t a n n i n (4). P u l l o u t strengths for the polyester a n d n y l o n cords coated w i t h dips c o n t a i n i n g the four t a n n i n s are given i n F i g u r e s 2 to 7. A l l d a t a p o i n t s are the average of s i x p u l l o u t forces. P u l l o u t forces as a f u n c t i o n of percent resorcinol (based o n the t o t a l of resorcinol a n d t a n n i n ) i n the d i p are given i n F i g u r e s 2 a n d 3 for the polyester a n d n y l o n c o r d , respectively. T h e r i g h t m o s t d a t a p o i n t s are values for the c o n t r o l d i p c o n t a i n i n g no t a n n i n . It is w o r t h w h i l e t o note first t h a t m a n y of the d i p s c o n t a i n i n g the condensed t a n n i n s h a d p u l l o u t strengths n e a r l y e q u a l t o or exceeding those o f the c o n t r o l c o n t a i n i n g o n l y r e s o r c i n o l . T h i s is especially t r u e w i t h the polyester c o r d . T h e t y p e of t a n n i n m a r k e d l y influences the p u l l o u t force. W i t h the polyester c o r d , the highest p u l l o u t force was o b t a i n e d w i t h a d i p c o n t a i n i n g 2 5 / 7 5 , res o r c i n o l / p e c a n p i t h sulfite e x t r a c t . However, t h i s same d i p gave a m o n g the lowest strengths w h e n a p p l i e d t o t h e n y l o n c o r d . O n the other h a n d , q u i t e g o o d b o n d i n g t o n y l o n was o b t a i n e d w i t h a 5 0 / 5 0 , r e s o r c i n o l / p e a n u t s k i n t a n n i n d i p , w h i l e t h i s c o m p o s i t i o n led t o a q u i t e low p u l l o u t force w i t h the polyester c o r d . A c o m p a r i s o n between the b e h a v i o r o f n y l o n a n d polyester w i t h the v a r i o u s d i p s is better s h o w n i n F i g u r e s 4 t o 7, where p u l l o u t forces for each of the four types o f t a n n i n - c o n t a i n i n g dips are presented. G e n e r a l l y , the pecan p i t h sulfite e x t r a c t a n d p u r i f i e d p i n e b a r k t a n n i n give s u p e r i o r results w i t h polyester c o r d , whereas, j u s t the o p p o s i t e is true for the pine b a r k sulfite e x t r a c t a n d the p e a n u t skin tannin. T h e t a n n i n e x t r a c t s e x a m i n e d i n t h i s p r e l i m i n a r y s t u d y represent a w i d e range o f properties. F o r e x a m p l e , b o t h the p e a n u t s k i n a n d p u r i f i e d p i n e b a r k t a n n i n e x t r a c t s are p r e d o m i n a n t l y p o l y m e r i c p r o c y a n i d i n s (3,5,7,3',4'-pentah y d r o x y f l a v a n s ) , b u t the peanut s k i n t a n n i n is m u c h lower i n m o l e c u l a r weight (16-19). I n b o n d i n g t o n y l o n , the resins f o r m u l a t e d w i t h p e a n u t skins p e r f o r m e d m u c h b e t t e r t h a n those m a d e w i t h p u r i f i e d pine b a r k t a n n i n s . T h e condensed t a n n i n s f r o m p i n e b a r k undergo i n t e r f l a v a n o i d b o n d cleavage w i t h the f o r m a t i o n of flavan- or p r o c y a n i d i n - 4 - s u l f o n a t e s w h e n reacted w i t h sulfite i o n (SO); so, even t h o u g h e x p e r i m e n t a l evidence is l a c k i n g for the m o l e c u l a r weight of sulfite e x t r a c t s of b a r k , i t seems p r o b a b l e t h a t the sulfite e x t r a c t s f r o m pine b a r k are of a lower m o l e c u l a r weight t h a n the p u r i f i e d t a n n i n s . T h e sulfite e x t r a c t p e r f o r m e d n e a r l y as w e l l as the p e a n u t s k i n t a n n i n i n b o n d i n g t o n y l o n . Use of a t a n n i n sulfonate d e r i v a t i v e does not seem t o h i n d e r the development o f s t r o n g b o n d s ( c o m p a r e peanut s k i n a n d sulfite e x t r a c t s f r o m p i n e b a r k ) . L i k e w i s e , the presence of c a r b o h y d r a t e s i n the t a n n i n e x t r a c t s does


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% Resorcinol F i g u r e 2. P u l l o u t forces o f polyester cords for v a r i o u s t a n n i n - c o n t a i n i n g adhesive d i p s as a f u n c t i o n o f percent resorcinol. 1, p e c a n p i t h sulfite e x t r a c t ; 2, p u r i f i e d p i n e b a r k t a n n i n ; 3, p i n e b a r k sulfite e x t r a c t ; 4, p e a n u t s k i n t a n n i n .

American Chemical Society Library 1155 15th St., N.W.

Hemingway et al.; Adhesives from Renewable Resources Washington, D.C. 20036 ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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100

F i g u r e 3. P u l l o u t forces o f n y l o n cords for various t a n n i n - c o n t a i n i n g adhesive d i p s as a f u n c t i o n of percent r e s o r c i n o l . D e s i g n a t i o n same as F i g u r e 2.

F i g u r e 4. C o m p a r i s o n of the p u l l o u t forces of polyester a n d n y l o n cords for d i p s c o n t a i n i n g p e c a n sulfite e x t r a c t . Hemingway et al.; Adhesives from Renewable Resources ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

18.

100


249


H A M E D ET AL.

r

25

50 %

75

100

Resorcinol

F i g u r e 5. C o m p a r i s o n o f the p u l l o u t forces o f polyester a n d n y l o n cords for dips containing purified pine bark t a n n i n .

100

0

25

50 %

75

100

Resorcinol

F i g u r e 6. C o m p a r i s o n of the p u l l o u t forces o f polyester a n d n y l o n cords for dips c o n t a i n i n g pine b a r k sulfite e x t r a c t . Hemingway et al.; Adhesives from Renewable Resources ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


250

ADHESIVES F R O M RENEWABLE

0

25

50 %

75

RESOURCES

100

Resorcinol

F i g u r e 7. C o m p a r i s o n of the p u l l o u t forces of polyester a n d n y l o n cords for dips containing peanut skin tannin.



18.

HAM ED ET A L

251


not seem t o reduce b o n d s t r e n g t h . T h e p u r i f i e d pine b a r k e x t r a c t c o n t a i n s no m e a s u r a b l e a m o u n t s o f c a r b o h y d r a t e s , whereas, the e x t r a c t s f r o m p e a n u t s k i n s a n d sulfite e x t r a c t s f r o m p i n e b a r k c o n t a i n between 15 a n d 2 0 % o f c o - e x t r a c t e d carbohydrates. A t t h i s t i m e , i t is not possible to p i n p o i n t the reason for the p o o r perf o r m a n c e o f the p e c a n p i t h e x t r a c t i n b o n d i n g t o n y l o n . T h e t a n n i n is pred o m i n a n t l y a p r o d e l p h i n i d i n (3,5,7,3,',4',5'- h e x a h y d r o x y f l a v a n ) i n s t e a d of p r o c y a n i d i n ( H e m i n g w a y , R . W . , S o u t h e r n Forest E x p e r i m e n t S t a t i o n , u n p u b l i s h e d results), b u t t h a t w o u l d not seem t o be a reasonable cause for s u c h a large difference i n b e h a v i o r . A c o m p a r i s o n o f e l e m e n t a l c o m p o s i t i o n a n d c a r b o h y d r a t e s o b t a i n e d after h y d r o l y s i s shows m u c h lower a m o u n t s o f c a r b o h y d r a t e s i n the p e c a n p i t h e x t r a c t ( T a b l e I I ) . T h e low p r o p o r t i o n of c a r b o h y d r a t e o b t a i n e d after h y d r o l y s i s is consistent w i t h c o m p a r a t i v e l y h i g h S t i a s n y p o l y p h e n o l content o f 8 7 % for the p e c a n p i t h e x t r a c t .

Table II. Elemental Composition and Carbohydrate C o n t e n t o f Sulfite E x t r a c t s f r o m P e c a n N u t P i t h and Southern Pine Bark Property Yield P e r c e n t o f d r y weight

Pecan

Pine

52

18

Elemental Composition Carbon Hydrogen Sodium Sulfur

46.2 4.4 7.2 4.4

45.4 4.7 5.8 3.8

—

Carbohydrates Glucose Xylose Galactose

4.5 0.7

Arabinose Mannose T o t a l sugars after h y d r o l y s i s

1.4 6.6

4.9 2.4 4.5 3.0 4.4 18.2

Stiasny polyphenols

87

52

—

T h e p e c a n p i t h e x t r a c t was the best of the t a n n i n e x t r a c t s e x a m i n e d i n b o n d i n g t o polyester c o r d . P u l l o u t forces u s i n g t h i s e x t r a c t t o t o t a l l y replace resorcinol were n e a r l y twice as h i g h as i n the s t a n d a r d d i p . T h e p u r i f i e d p i n e b a r k e x t r a c t also gave very g o o d results. O n e c o m m o n a l i t y i n these t w o e x t r a c t s



252


was the low p r o p o r t i o n o f c a r b o h y d r a t e s . B o n d strengths t o polyester c o r d usi n g resins based o n p e a n u t s k i n t a n n i n s a n d p i n e b a r k e x t r a c t s o b t a i n e d b y e x t r a c t i o n w i t h s o d i u m sulfite were a b o u t the same a n d o n l y m a r g i n a l l y lower t h a n those o b t a i n e d u s i n g the s t a n d a r d R F L d i p . A s was n o t e d i n b o n d i n g t o the n y l o n c o r d , s u l f o n a t i o n seems t o have l i t t l e influence o n b o n d s t r e n g t h . T h e s e types of e x t r a c t s have also p r o v e n t o be g o o d resorcinol s u b s t i t u t e s for c o l d - s e t t i n g , w o o d - l a m i n a t i n g adhesives. E v e n t h o u g h the e x t r a c t s c a r r y s u l fonic a c i d f u n c t i o n s , d u r a b l e water-resistant b o n d s are p r o d u c e d (13,21). The results w i t h the polyester c o r d are p a r t i c u l a r l y e n c o u r a g i n g , since the s i m p l e R F L c o n t r o l d i p is n o t t h a t w e l l s u i t e d for greige polyester c o r d . It s h o u l d be n o t e d t h a t t h i s research effort has m a d e n o a t t e m p t t o o p t i m i z e the f o r m u l a t i o n of d i p s c o n t a i n i n g condensed t a n n i n s . R a t h e r , the procedure for the d i p m o d i f i c a t i o n was a s i m p l e s u b s t i t u t i o n b y weight of t a n n i n for r e s o r c i n o l . T h e r a t i o of ingredients is expected t o g r e a t l y influence viscosity, cure rate, a n d p H , as w e l l as the b o n d i n g characteristics. I n a p a t e n t search f o l l o w i n g t h i s p r e l i m i n a r y w o r k , a 1967 Japanese patent (22) was discovered t h a t h a d not been p r e v i o u s l y n o t e d . T h e influence of t y p e of t a n n i n e x t r a c t or m o d i f i c a t i o n s i n resin f o r m u l a t i o n were n o t disclosed i n t h i s patent either. Therefore, a d d i t i o n a l studies t o e x a m i n e these effects are p l a n n e d . T h i s a d d i t i o n a l w o r k w i l l h o p e f u l l y allow a better u n d e r s t a n d i n g of the b o n d i n g properties t h a t w i l l l e a d t o i m p r o v e d s t r e n g t h a n d d u r a b i l i t y of adhesion of c o r d t o r u b b e r m a t r i c e s . Conclusions C o n d e n s e d t a n n i n s have considerable p r o m i s e as substitutes for resorcinol used i n resin f o r m u l a t i o n s for b o n d i n g of n y l o n or, p a r t i c u l a r l y , polyester c o r d t o r u b b e r . A l t h o u g h m u c h m o r e w o r k needs t o be done, p r e l i m i n a r y results suggest t h a t refinement of e x t r a c t properties a n d adhesive f o r m u l a t i o n s c o u l d l e a d t o a large, h i g h - v a l u e m a r k e t for condensed t a n n i n e x t r a c t s . A cknowledgment s A u t h o r s H a m e d a n d C h u n g are g r a t e f u l t o the S o u t h e r n Forest E x p e r i m e n t S t a t i o n , U S D A Forest Service, for a cooperative grant (19-86-037) s u p p o r t i n g t h i s w o r k . W e t h a n k B o i s e C a s c a d e C o r p o r a t i o n for supplies of s o u t h e r n p i n e b a r k , the R o b e r t s o n C o r p o r a t i o n for supplies of pecan n u t p i t h , A s s o c i a t e s R e s e a r c h M a n a g e m e n t C o r p o r a t i o n for peanut s k i n s , a n d G e n C o r p o r a t i o n for resins a n d c o r d m a t e r i a l s .

Literature Cited 1. Charch, W. H.; Maney, D. G. U.S. Patent 2 128 299, 1938. 2. Doyle, G. M. I.R.I. Transactions. 1960, 36, 177. 3. Moult, R. H. In Handbook of Adhesives; Skeist, I., Ed.; Van Nostrand Reinhold: New York, 1977, pp 661-688.


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4. 5. 6. 7.

Iyenger, Y. J. Appl. Polym. Sci. 1978, 22, 801. Takeyama, T.; Matsu. J.RubberChem.Technol. 1969, 42, 159. Reeves, L. N.RubberWorld. 1955, 132, 764. Pizzi, A. In Wood Adhesives: Chemistry and Technology; Pizzi, Α., Ed.; Marcell Dekker: New York, 1983, pp 177-246. 8. Hemingway, R. W.; McGraw, G. W. J. Liquid Chrom. 1978, 1, 163. 9. Kiatgrajai, P.; Wellons, J. D.; Gollub, L.; White, J. D. J. Org. Chem. 1982, 47, 2913. 10. Pizzi, Α.; Rossow, du T.; Knuffel, W. E.; Singmin, M. Holzforschung und Holzverwertung. 1980, 32, 140-150. 11. Pizzi, Α.; Cameron, F. A. Forest Prod. J. 1984, 34, 61-68. 12. Kreibich, R. E.; Hemingway, R. W. Forest Prod. J. 1985, 35, 23-27. 13. Kreibich, R. E.; Hemingway, R. W. Forest Prod. J. 1987, 37, 43-46. 14. Nicholson, D. W.; Livingston, D. I.; Fielding-Russell, G. S. Tire Science and Technol ogy. 1978, 6, 114. 15. Hamed, G. R.; Donatelli, T. Rubber Chem. Technol. 1983, 56, 450. 16. Karchesy, J. J.; Hemingway, R. W. J. Agric. Food Chem. 1980, 28, 222-228. 17. Hemingway, R. W.; Foo, L. Y.; Porter, L. J. J. Chem. Soc. Perkin Trans.I1982, 1209-1216. 18. Williams, V. M.; Porter, L. J.; Hemingway, R. W. Phytochemistry 1983, 22, 275-281. 19. Karchesy, J. J.; Hemingway, R. W. J. Agric. Food Chem. 1986, 34, 966. 20. Foo, L. Y.; McGraw, G. W.; Hemingway, R. W. J. Chem.Soc.,Chem. Commun. 1983, 672-673. 21. McGraw, G. W.; Laks, P. E.; Hemingway, R. W. J. Wood Chem.Technol.,in press. 22. Matsushita, T. Japanese Patent8227/67,1967. RECEIVED June 2, 1988


Condensed Tannins as Substitutes for Resorcinol in Bonding

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