Adhesives from Renewable Resources - American Chemical Society

Downloaded by CORNELL UNIV on June 2, 2017 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch028

Chapter 28 Thermosetting Adhesive Resins from Whey and Whey Byproducts T i t o Viswanathan Department of Chemistry University of Arkansas at Little Rock Little Rock, A R 72204

The disposal of whey and whey byproducts derived from the cheese industry represents a serious economic and enviromental problem due to the high biological oxygen demand of lactose-the major con stituent of whey solids. Maillard and caramelization reactions asso ciated with the thermal degradation and polymerization of the milk sugar can be exploited to convert lactose in whey to a thermosetting resin that can serve as an adhesive for binding solid lignocellulosic materials. The resin synthesis may be accomplished in one step using a batch reaction (Phase I) or prepared more readily using a continuous plugflow reaction with a two-step synthesis (Phase II). Resins have been shown to perform well as adhesives for sawdust and/or rice hull reinforced boards. Preliminary thermal studies in dicate an exothermic polymerization occurring at around 200 ° C for the Phase I resin preparation. A waste d i s p o s a l p r o b l e m o f significant p r o p o r t i o n s exists because o f t h e 23 b i l l i o n p o u n d s o f excess whey p r o d u c e d i n t h e U n i t e d States each year as a b y p r o d u c t o f the cheese i n d u s t r y (1). T h e n u t r i t i o u s proteins present i n w h e y m a y b e separated b y u l t r a f i l t r a t i o n , r e s u l t i n g i n large v o l u m e s o f u l t r a f i l t r a t e or " p e r m e a t e , " consisting o f 5 % lactose a n d traces o f i n o r g a n i c s a l t s . T h i s per meate s t r e a m is essentially useless a n d exacerbates t h e d i s p o s a l p r o b l e m due t o i t s h i g h b i o l o g i c a l oxygen d e m a n d (25,000 m g / L ) m a i n l y o w i n g t o lactose. I n a d d i t i o n , salt whey ( r e s u l t i n g f r o m pressing cheese c u r d after s a l t i n g ) r e p resents a p a r t i c u l a r l y difficult d i s p o s a l p r o b l e m due t o t h e added presence o f s o d i u m chloride. T h e generation o f excess whey permeate i n t h e U n i t e d States is d e p i c t e d i n F i g u r e 1. T y p i c a l c o m p o s i t i o n o f wheys a n d permeates i s s h o w n i n T a b l e I . T a b l e I I shows t h e a m o u n t o f t o t a l whey solids available for use throughout the world. 0097-6156/89Λ)385-0395$06.00/0 ° 1989 American Chemical Society

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

396

ADHESIVES FROM RENEWABLE RESOURCES


Milk

Cheese

Whey: 46 billion lbs. in the U.S. (5% lactose, 1% proteins and traces of salts)

26 billion lbs. (56%) used as food additives, cattle feed, etc.

20 billion lbs. (44%) excess

Pollution Problem!

Ultrafiltration

19 billion lbs. (Whey Permeate)

220 million lbs. of protein (Sold as a 35% concentrate)

I drying process 1.1 billion lbs. of dry permeate F i g u r e 1. G e n e r a t i o n o f w h e y a n d w h e y p e r m e a t e f r o m t h e cheese i n d u s t r y i n the U n i t e d S t a t e s . Reprinted with permission from ref. 17. Copyright 1987 Technomic Publishing.


28.

Adhesive Resins from Whey and Whey Byproducts

viSWANATHAN

397

T o a large e x t e n t , the u t i l i z a t i o n of w h e y a n d w h e y b y p r o d u c t s ( i n c l u d i n g salt w h e y a n d w h e y permeate) is a p r o b l e m of u t i l i z i n g the m i l k sugar, lactose. Since the excess lactose p r o d u c e d i n the U n i t e d States each year a m o u n t s to m o r e t h a n a b i l l i o n p o u n d s , one m u s t consider i t s use i n large v o l u m e p r o d u c t s . O n e s u c h p r o d u c t is lactose-based p o l y e t h e r - p o l y o l used i n the m a n u f a c t u r e of l o w - d e n s i t y r i g i d p o l y u r e t h a n e foams (2).

T a b l e I . T y p i c a l C o m p o s i t i o n (%)


Component

Fluid Sweet W h e y

pH T o t a l solids Moisture Fat Total protein Lactose Ash Lactic acid S o d i u m choride SOURCE:

5.9-6.3 6.35 93.7 0.5 0.8 4.85 0.5 0.05

of W h e y s a n d P e r m e a t e Fluid

Acid Whey

Salt Whey

Whey Permeate

4.4-4.6 6.5 93.5 0.04

5.2 10.7 89.26 0.04

4.5-5.8 6.1 94.2

0.75 4.90 0.8 0.4

0.7 4.35 5.25

0.1

-

4.7

-

4.9 0.7 0.4

Reprinted from ref. 13. Copyright 1984 American Chemical Society.

Table II. A m o u n t of T o t a l W h e y Solids A v a i l a b l e for Use W o r l d w i d e i n 1981 [ T h o u s a n d T o n s (18)} Country EEC Other Western Europe Canada USA Australia Japan New Zealand Czechoslavakia Hungary Poland USSR O t h e r countries Total world

Whey Solids

1

Production

2141 322 104 1144 80 40 53 66 25 176 411 1499 6065

W h e y solids c a l c u l a t e d u s i n g 10 l b w h e y / l b of cheese m a d e t i m e s 6 % t o t a l solids. 1

SOURCE:

Reprinted with permission from ref. 18. Copyright 1984

Dairy Science Association.


American

398

ADHESIVES F R O M RENEWABLE RESOURCES


A n o t h e r p r o b l e m o f a seemingly u n r e l a t e d n a t u r e is the f o r m a l d e h y d e e m i s s i o n f r o m b u i l d i n g b o a r d s t h a t are c u r r e n t l y m a n u f a c t u r e d u s i n g u r e a - f o r m a l d e hyde adhesive resins. F o r m a l d e h y d e has been i m p l i c a t e d as a carcinogen a n d c a n also cause severe u p p e r r e s p i r a t o r y p r o b l e m s a n d contact d e r m a t i t i s i n some i n d i v i d u a l s (3-5). T h e use o f formaldehyde-free adhesive resins f r o m w h e y a n d w h e y b y p r o d ucts for m a n u f a c t u r i n g c o n s t r u c t i o n - q u a l i t y b o a r d s c o u l d resolve these p r o b l e m s s i m u l t a n e o u s l y . T h e d e m a n d for formaldehyde-based t h e r m o s e t t i n g adhesive resins i n the U n i t e d States was e s t i m a t e d t o be 1.9 b i l l i o n p o u n d s i n 1983 (6). T h e a n t i c i p a t e d r e q u i r e m e n t for resins a n d the p o t e n t i a l a v a i l a b i l i t y of r a w m a terials f r o m w h e y are a f o r t u i t o u s c o m b i n a t i o n . R e s e a r c h b y others has established the f e a s i b i l i t y o f u s i n g sugars a n d starches for b i n d i n g w o o d . S u c h uses have been investigated b y S t o f k o ( 7 - 0 ) , U s m a n i a n d S a l y e r (10), G i b b o n s a n d C h i a n g (11), a n d G i b b o n s a n d W o n d o l o w s k i (12), a m o n g others. T h e w o r k o f G i b b o n s i n c o l l a b o r a t i o n w i t h C h i a n g (11) a n d W o n d o l o w s k i (12) has dealt w i t h the p a r t i a l replacement of f o r m a l d e h y d e i n resins by sugars or starches. Because of the fluid n a t u r e o f the a v a i l a b l e r a w m a t e r i a l a n d the desire t o prepare resin s o l u t i o n s w i t h h i g h solids content, a s l i g h t l y different a p p r o a c h is r e q u i r e d f r o m t h a t e m p l o y e d i n the use o f starches or cellulose as resin ingredients. I n the a u t h o r ' s research, a m m o n i u m n i t r a t e was used t o c a t a l y z e t r a n s f o r m a t i o n o f lactose t o p o l y m e r i c c o m p o u n d s . T h e a m o u n t of a m m o n i u m n i t r a t e was kept at 8 % ( w / w o f final s o l u t i o n ) because t h i s a m o u n t was sufficient t o p r o d u c e a final p H o f 2 t o 3 w h i l e y i e l d i n g a n i n s o l u b l e p o l y m e r (13). (Lower p H values w o u l d be d e t r i m e n t a l t o s t r e n g t h r e t e n t i o n over a p e r i o d o f t i m e ) . T a i l o r i n g o f the resin was possible b y a d d i n g condensing agents s u c h as u r e a a n d / o r p h e n o l to p r o d u c e c o n c e n t r a t e d s o l u t i o n s of v a r i a b l e v i s c o s i t y a n d p H . ( T h e a d d i t i o n o f these crosslinkers, however, resulted i n increased cure t i m e for resin p r e p a r a t i o n ) . M i n o r a m o u n t s of copper salts (e.g., C u C b or CUSO4) were a d d e d t o the r e a c t i o n m i x t u r e d u r i n g resin synthesis t o c a t a l y z e M a i l l a r d b r o w n i n g reactions, w h i c h are k n o w n t o result i n h i g h m o l e c u l a r weight heteroc y c l i c p o l y m e r s . F i g u r e 2 shows the proposed r e a c t i o n p a t h w a y s for synthesis o f w h e y - b a s e d resins. E v e n t h o u g h the s t r u c t u r a l aspects o f the p o l y m e r s have not been w o r k e d o u t due t o the m a n y possible r e a c t i o n p r o d u c t s , i t is safe t o propose a general l i n e a r s t r u c t u r e w i t h a large n u m b e r o f c a r b o n y l s due t o the o x i d a t i o n o f - C - O H groups i n a n o x i d i z i n g HNO3 e n v i r o n m e n t . Size e x c l u s i o n c h r o m a t o g r a p h y o f the m e t h a n o l - i n s o l u b l e b u t water-soluble w h e y - r e s i n f r a c t i o n i n d i c a t e s a m o l e c u l a r weight i n the range o f 10,000 t o 80,000 [in c o m p a r i s o n t o proteins o f k n o w n m o l e c u l a r weight used as s t a n d a r d s (14)]- T h i s m o l e c u l a r weight is consistent w i t h the c o n s t i t u e n t s i n cane sugar refiner's final molasses (15) t h a t are k n o w n t o result f r o m advanced M a i l l a r d b r o w n i n g reactions, a m o n g others. In a recent s t u d y , a two-step m e t h o d was used t o m a k e w h e y permeate resin (16,17). T h e process consisted o f i n j e c t i o n o f gaseous a m m o n i a i n t o a r e a c t i o n


viswANATHAN


399


28.

F i g u r e 2. P r o p o s e d r e a c t i o n p a t h w a y s for t h e synthesis o f w h e y - b a s e d resins. A m m o n i a gas m a y be used i n a two-step r e a c t i o n scheme. S t r u c t u r e s o f p o l y m e r s s h o w n here are h y p o t h e t i c a l . Reprinted from ref. 13. Copyright 1984 American Chemical Society.



400

ADHESIVES F R O M R E N E W A B L ERESOURCES

m i x t u r e c o n t a i n i n g d e g r a d a t i o n p r o d u c t s of w h e y solids p r o d u c e d b y s u l f u r i c a c i d at h i g h t e m p e r a t u r e a n d pressure i n a n enclosed P a r r reactor. T h e first step consists of a c i d - c a t a l y z e d h y d r o l y s i s a n d d e h y d r a t i o n of sugars at p H 0.5 a n d h i g h t e m p e r a t u r e s . F i g u r e 3 shows the f o r m a t i o n of the m e t h a n o l - i n s o l u b l e p r o d u c t ( M I P ) as the r e a c t i o n progresses. T h e M I P p o r t i o n of the r e a c t i o n was d e t e r m i n e d b y w i t h d r a w i n g a l i q u o t s of the r e a c t i o n m i x t u r e (1.25 g), m i x i n g w i t h 100 m L of m e t h a n o l , filtering, a n d d r y i n g . T h e value of a p p r o x i m a t e l y 5 0 % M I P o b t a i n e d for t i m e zero is p r o b a b l y due t o i m m e d i a t e h y d r o l y s i s of lactose t o galactose a n d glucose o n a d d i t i o n of a c i d . O v e r t i m e , d e h y d r a t i o n of the monosaccharides s h o u l d t a k e place, p r o d u c i n g m e t h a n o l - s o l u b l e p r o d u c t s such as h y d r o x y m e t h y l f u r f u r a l d e h y d e . T h i s i n t u r n w o u l d l e a d to a decrease i n m e t h a n o l - i n s o l u b l e f r a c t i o n . If the r e a c t i o n is c o n t i n u e d , the M I P f a l l s to a m i n i m u m value a n d is t h e n followed b y a n increase i n the value, i n d i c a t i n g form a t i o n of higher m o l e c u l a r weight p r o d u c t s t h a t t e n d t o be generally i n s o l u b l e in methanol. A t the p o i n t where the M I P is at a m i n i m u m , i n j e c t i o n of a m m o n i a gas results i n a steep increase i n the a m o u n t of h i g h - m o l e c u l a r - w e i g h t m a t e r i a l s w i t h a c o n c u r r e n t rise i n p H value. B o t h these processes are h i g h l y desirable. A m m o n i a is a d d e d u n t i l the desired p H value is o b t a i n e d ( « 3.5 t o 4.0). A t t h i s p o i n t , the resin p r e p a r a t i o n is a viscous e m u l s i o n of d a r k b r o w n color. T h e advantage of t h i s m e t h o d of resin p r e p a r a t i o n is its a d a p t a b i l i t y t o continuous plug-flow r e a c t i o n , u n l i k e the P h a s e I r e s i n , w h i c h is m o r e s u i t e d t o b a t c h r e a c t i o n . T a b l e I I I shows the properties of p a r t i c l e b o a r d s p r e p a r e d w i t h P h a s e I w h e y permeate-based r e s i n . T a b l e I V shows the properties of r i c e - h u l l - r e i n f o r c e d b u i l d i n g b o a r d s u s i n g P h a s e II r e s i n . L o w - q u a l i t y b o a r d s are p r e p a r e d w i t h rice h u l l s , b u t t h e i r q u a l i t i e s m a y be i m p r o v e d b y u s i n g g r o u n d h u l l s or a d d i n g sawdust t o the f o r m u l a t i o n . A l t h o u g h whey-based resins have been f o u n d to be excellent adhesives for b i n d i n g s o l i d lignocellulosic m a t e r i a l s , these resins t e n d t o require higher cure t e m p e r a t u r e s a n d longer cure t i m e s as c o m p a r e d to f o r m a l d e h y d e - b a s e d resins. T h i s chapter describes p r e l i m i n a r y i n v e s t i g a t i o n i n t o the t h e r m o s e t t i n g p r o cess o f one w h e y - b a s e d resin p r e p a r a t i o n u s i n g differential s c a n n i n g c a l o r i m e t r y (DSC). Experimental

Methodology

A M e t t l e r T A 3000 s y s t e m c o n s i s t i n g o f a T C 1 0 A T A processor a n d a D S C 20 m e a s u r i n g cell was used t o investigate the c u r i n g r e a c t i o n of the whey-based resin p r e p a r e d as follows. A m i x t u r e of 171-g w h e y permeate, 73.2-g NH4NO3, 2.85-g C u C b , a n d 2 0 0 - m L H2O was placed i n t o a P a r r pressure reactor a n d heated w i t h s t i r r i n g at 125 ° C for 90 m i n . T h e p H of the final p r e p a r a t i o n was 3.6. A p p r o x i m a t e l y 7- t o 10-mg samples of t h i s resin were weighed i n sealed-glass, high-pressure crucibles. Pressure cells were used t o c o n t a i n any v o l a t i l e , reactive



28.

viswANATHAN


401

F i g u r e 3. Percentage o f m e t h a n o l - i n s o l u b l e p r o d u c t o b t a i n e d d u r i n g t h e r e a c t i o n of 233.4 g o f d r y w h e y permeate a n d 90.3 m L o f s u l f u r i c a c i d i n a n enclosed reactor at 145 ° C . A m m o n i a was injected after a r e a c t i o n t i m e o f 21 m i n u t e s to increase the p H t o 4.0.


402

ADHESIVES F R O M R E N E W A B L E RESOURCES

species a n d t o s i m u l a t e the pressure c o n d i t i o n s at w h i c h the resin m i g h t be cured i n p r a c t i c e . A n e m p t y sealed-glass c r u c i b l e was used as a n i n e r t reference. T h e D S C sensor used was a five-part A u / N i t h e r m o c o u p l e h a v i n g a s e n s i t i v i t y of a p p r o x i m a t e l y 20 m i c r o v o l t s per K . T e m p e r a t u r e scan rates of 5 t o 10 K / m i n were generally used t o scan the t e m p e r a t u r e range f r o m 30 t o 250 ° C .

T a b l e I I I . P r o p e r t i e s of P a r t i c l e b o a r d s P r e p a r e d w i t h the W h e y P e r m e a t e R e s i n


1

Resin ( D r y Basis)

Temperaturepressed

Density

IB

(% ) 7

(»c) 165

(lb/ft ) 55.7

(psi)

10

185 165 185

53.7 53.9 61.6

Thickness Swell 24 h r 2hr

2

3

(% ) 50

81 125 92 132

11 19 7.4

(%) 20 25 18

Dried Strength (psi) 4

-

21

-

30

S i n g l e - l a y e r b o a r d s of l o c a l p i n e s a w d u s t , 3 / 8 i n t h i c k . V a l u e s represent the average of d u p l i c a t e tests. T h e p a r t i c l e b o a r d m a t ( m o i s t u r e content 6%) was pressed at 500 p s i for 7 min. P o u n d s per square i n c h . T h e i n t e r n a l b o n d s t r e n g t h recovery was d e t e r m i n e d after the specimens (24 h r w a t e r i m m e r s e d ) were d r i e d i n a n oven at 103 ± 2 ° C u n t i l a p p r o x i m a t e l y constant weight was o b t a i n e d . 2

3

4

SOURCE:

Reprinted from ref. 13. Copyright 1984 American Chemical Society.

Results a n d Discussion T h e D S C t h e r m o g r a m of the whey-based resin prepared above i n d i c a t e d a n e x o t h e r m i c p e a k o c c u r r i n g at a p p r o x i m a t e l y 185 t o 190 ° C . T h e s o l i d mass o b t a i n e d p r i o r t o the e x o t h e r m is r u b b e r y , b u t becomes b r i t t l e after t h i s t r a n s i t i o n . T h e change i n e n t h a l p y d u r i n g the course of p o l y m e r i z a t i o n , w h i c h corresponds t o the a m o u n t of heat l i b e r a t e d d u r i n g the e x o t h e r m i c process, m a y be determ i n e d b y the area u n d e r the D S C curve. A c o m p u t e r p r o g r a m w r i t t e n as p a r t of the T A processor's k i n e t i c m e t h o d i n d i c a t e d E = 633.44 k J / m o l . A s s u m i n g t h a t the heat change is p r o p o r t i o n a l t o the extent of r e a c t i o n , the area under the curve m a y serve as a n a n a l y t i c a l p a r a m e t e r , a n d the r e a c t i o n k i n e t i c s m a y be d e r i v e d i n a s t r a i g h t f o r w a r d m a n n e r . I n the case of w h e y - b a s e d resins, h o w ever, the sequence of reactions o c c u r r i n g d u r i n g the p o l y m e r i z a t i o n process is sufficiently c o m p l e x t h a t o n l y q u a l i t a t i v e aspects of the D S C t h e r m o g r a m m a y be considered. a

T h e c o m p l e x i t y of the whey-based resin t h e r m o s e t t i n g process c a n be i l l u s t r a t e d b y c o n s i d e r i n g several i s o t h e r m a l i n v e s t i g a t i o n s . S a m p l e s of the resin


28.

VISWANATHAN


403

were heated i s o t h e r m a l l y at various t e m p e r a t u r e s r a n g i n g f r o m 140 t o 185 ° C , a n d the r e a c t i o n was m o n i t o r e d w i t h respect t o t i m e . W h e n the resin s a m ple was heated i s o t h e r m a l l y at 140 ° C for 15 m i n , no e x o t h e r m was observed. T h e s a m p l e was allowed to c o o l slowly to r o o m t e m p e r a t u r e a n d t h e n heated i s o t h e r m a l l y at 185 ° C for 15 m i n . A g a i n , no e x o t h e r m was observed.

T a b l e I V . P r o p e r t i e s of P a r t i c l e b o a r d s P r e p a r e d w i t h P h a s e I I R e s i n [ W h e y P e r m e a t e / H S 0 / N H 3 (17) ]


2

Resin ( D r y Basis)

4

Thickness

(%)

Press Cycle (min)

Rice

10

8

(lb/ft ) 57.0

75% Ground rice & 2 5 % dust

7

7

Dust

7

50% Ground rice h 5 0 % dust G r o u n d rice

Composition

IB (psi)

MOR (psi)

Swell

12.9

864

125.9

53.2

49.8

984

37.8

7

55.9

144.4

2047

27.0

7

7

56.9

79.8

838

49.4

7

7

54.3

29.4

Density 3

(%)

38.8

^ i n a l p H = 3. T h e b o a r d s are a single layer of p i n e dust a n d / o r rice h u l l s ( g r o u n d a n d u n g r o u n d ) . V a l u e s given represent average o f d u p l i c a t e r u n s . F i n a l thickness o f the b o a r d s was 1/4 i n c h . 2

Reprinted with permission from ref. 17. Copyright 1987

S O U R C E :

Technomic

Publishing. However, w h e n a fresh s a m p l e of the resin was heated i s o t h e r m a l l y at 185 ° C , there was a n e x o t h e r m i c process evident t h a t peaked w i t h i n the first m i n u t e a n d reached c o m p l e t i o n w i t h i n a p p r o x i m a t e l y 4 t o 5 m i n . T h u s , i t is e v i d e n t t h a t the cure m e c h a n i s m m a y change w i t h change i n r e a c t i o n c o n d i t i o n s , r e v e a l i n g the c o m p l e x i t y of the whey-based resin t h e r m o s e t t i n g process. Since a d y n a m i c r u n described earlier revealed a n e x o t h e r m i c p o l y m e r i z a t i o n at a r o u n d 185 t o 190 ° C , crosslinkers were a d d e d i n a n a t t e m p t to lower the t e m p e r a t u r e for p o l y m e r i z a t i o n . T h e c r o s s l i n k i n g agents ( 1 0 % w / v of resin p r e p a r a t i o n ) used were p h t h a l i c a n h y d r i d e , m a l e i c a n h y d r i d e , t a l l o w d i a m i n e , a n d p-toluenesulfonic a c i d . W e were u n a b l e t o lower the t e m p e r a t u r e of i n i t i a t i o n o f p o l y m e r i z a t i o n b y the a d d i t i o n of the first three reagents, b u t d i d observe a shift t o a lower t e m p e r a t u r e ( « 165 ° C ) i n the presence of ])-toluenesulfonic a c i d . T h e ρ H of the m i x t u r e p r i o r to h e a t i n g was a r o u n d 2.0, whereas, the Hemingway et al.; Adhesives from Renewable Resources ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

404

ADHESIVES F R O M R E N E W A B L E RESOURCES

CURVE A"=PRESS TEMR = l65 C.,PRESS =500?5l, MAT MOISTURE » CURVE"B-PRESS TEMP-IftS't./PRESS.-SOOPSl,MAT MOISTUKEg g>7* e


1

0

1

ε

3

4-

5

7

T I M E

F i g u r e 4. T h e influence o f press t e m p e r a t u r e , pressure, a n d t i m e o n core t e m p e r a t u r e rise d u r i n g hot pressing. A m o u n t o f resin used was 7 % (by d r y weight) i n the b o a r d . T h e resin a p p l i e d h a d 6 5 % solids content. M a t m o i s t u r e content was 6 % p r i o r t o pressing.


28.

viswANATHAN

405


ΙςυκνεΆ": PRESS ΤΕΜ& - ;*o c ASSURE SOOPSL'MAT MOISTURE^ e

200


"A"

4 ο ο

U: Σ tu

/

UJ

ο ο

>

TIME

F i g u r e 5. T h e influence of press t e m p e r a t u r e , pressure, a n d t i m e o n core t e m p e r a t u r e rise d u r i n g h o t pressing. T h e a m o u n t of resin used was 7% (by d r y weight) i n t h e b o a r d . T h e resin a p p l i e d h a d a 6 5 % s o l i d content w i t h 1 0 % w / v of p h t h a l i c a n h y d r i d e . M a t m o i s t u r e content was 6 % p r i o r t o pressing.


406

ADHESIVES F R O M RENEWABLE RESOURCES

others h a d a p H a r o u n d 3.0 t o 3.5. W h e n t h e p H o f t h e m i x t u r e c o n t a i n i n g p-toluenesulfonic a c i d w a s r a i s e d t o 3.5, t h e advantage i n t e r m s o f lower t e m p e r a t u r e for t h e i n i t i a t i o n o f p o l y m e r i z a t i o n was lost.


S i n c e we (19) have r e p o r t e d t h a t there is a n i m p r o v e m e n t i n i n t e r n a l b o n d s t r e n g t h o f h i g h - d e n s i t y p a r t i c l e b o a r d s o n a d d i t i o n o f p h t h a l i c a n h y d r i d e , we decided t o investigate t h e influence o f press t e m p e r a t u r e , pressure, a n d t i m e o n core t e m p e r a t u r e rise d u r i n g h o t pressing. F i g u r e s 4 a n d 5 i n d i c a t e t h e results o b t a i n e d under t h e c o n d i t i o n s s t a t e d . T h e a m o u n t o f p h t h a l i c a n h y d r i d e i n F i g u r e 5 w a s 1 0 % w / v o f a 6 5 % resin s o l u t i o n . T h e m a t thickness w a s threeeighths o f a n i n c h , a n d t h e b o a r d w a s p r e p a r e d b y pressing u n d e r continuous pressure w i t h o u t stops. It is clear f r o m t h e results o b t a i n e d t h a t t h e core t e m p e r a t u r e rises above the p l a t e n t e m p e r a t u r e i n the presence o f p h t h a l i c a n h y d r i d e . Since n o u n u s u a l differences i n t h e D S C t h e r m o g r a m o f w h e y - b a s e d resin i n t h e presence a n d i n the absence o f p h t h a l i c a n h y d r i d e were seen, t h e e x o t h e r m i c p h e n o m e n o n b e i n g observed u n d e r c o n d i t i o n s o f b o a r d p r e p a r a t i o n deserves f u r t h e r i n v e s t i g a t i o n . Conclusion W o r k done w i t h w h e y - b a s e d resins so f a r h a s d e m o n s t r a t e d t h e f e a s i b i l i t y o f u s i n g t h e t h e r m a l d e g r a d a t i o n / p o l y m e r i z a t i o n p r o d u c t s o f lactose as a n adhesive for b i n d i n g l i g n o c e l l u l o s i c m a t e r i a l s . T h i s offers a n e x c i t i n g s o l u t i o n t o t h e w h e y d i s p o s a l p r o b l e m , w h i c h takes o n n o t o n l y n a t i o n a l b u t i n t e r n a t i o n a l s i g nificance. T h e m a j o r d r a w b a c k i n b o a r d m a n u f a c t u r e u s i n g w h e y - b a s e d resins is the p r o l o n g e d cure t i m e a n d d a r k e r color. T h e m a j o r advantages are t h e lower cost a n d t h e lower f o r m a l d e h y d e emissions. B o t h s h o u l d encourage t h e forest p r o d u c t s i n d u s t r y t o consider t h i s v i a b l e a l t e r n a t i v e . G o v e r n m e n t a l decisions r e g a r d i n g f o r m a l d e h y d e t o x i c i t y w i l l have a n enormous b e a r i n g o n the f u t u r e o f research o n adhesives f r o m renewable resources. Acknowledgments T h e a u t h o r t h a n k s the A r k a n s a s Science a n d T e c h n o l o g y A u t h o r i t y for f u n d i n g a n d t h e Office o f R e s e a r c h i n Science a n d Technology, U n i v e r s i t y o f A r k a n s a s at L i t t l e R o c k for assisstance i n t h e p r e p a r a t i o n o f t h i s m a n u s c r i p t . Literature

Cited

1. United States Department of Agriculture, Dairy Products Annual Summary 1982. Statistical Reporting Service, Washington, DC, 1983; pp. 17, 33. 2. Viswanathan, T.; Burrington, D.; Richardson, T. J. Chem. Tech.Biotechnol.,1984, 34B, 52. 3. Fisher, A. Contact Dermatitis, 3rd ed., Lea and Fibiger, Pa, 1986; p. 36. 4. Cronin, E . Contact Dermatitis, Churchill Livingstone, London, 1986; p. 622.


28.

viswANATHAN


407

5. Adam, R. M., Occupational Skin Disease, Grune and Stratton, Inc., New York, 19B3; p. 250. 6. White, J. T. Paper presented at Wood Adhesives Research, Application and Needs Symposium held in Madison, WI, Sept. 23-25, 1980. 7. Stofko, J. L. U.S. Patent 4 107 379, 1978. 8. Stofko, J. L. U.S. Patent 4 183 997, 1980.


9. Stofko, J. L. "Carbohydrate Transformation Bonding of Lignocellulosic Materials," paper presented at the Wood Adhesive-Research, Application and Needs Symposium, Madison, WI, 1980. 10. Usmani, A. M.; Salyer, I. O. "Resin Bonded Bagasse Composite," In Polymer Applications of Renewable-Resource Materials, Carraher C. E . , Sperling L. A. Eds., Plenum Press: New York 1983. 11. Gibbons, J. P.; Chiang, M. T. U.S. Patent 4 085 075, 1978. 12. Gibbons, J. P.; Wondolowski, L. U.S. Patent 4 085 076, 1978. 13. Viswanathan, T.; Richardson, T. Ind. Eng. Chem. Product Res. Dev., 1984, 23, 644-647. 14. Viswanathan, T. Ind. Eng. Chem. Product Res. Dev., 1985, 24, 176-177. 15. Tsuchida, H.; Komoto, M . Proc. Res. Soc. Japan Sugar Refin. Technol., 1970, 22, 66-76. 16. Viswanathan, T. Phase II Final Report on the development of thermosetting resins from whey and whey byproducts 121 pages. Submitted to the EPA for contract No. 68-02-4098 (1985). 17. Viswanathan, T.; Smith, M.; Palmer, H. J. Elastomers & Plastics, 1987, 19, 99-108. 18. Zall, R. J. Dairy Sci., 1984, 67, 2621-2629. 19. Viswanathan, T.; Gilton, T. Ind. Eng. Chem. Product Res. Dev., 1986, 25, 313-315. RECEIVED June2,1988


Adhesives from Renewable Resources - American Chemical Society

Recommend Documents