Epoxy Resin Chemistry II - American Chemical Society

14 Characterization and Moldability Analysis of Epoxy Reaction Injection Molding Resins Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 1, 2016 | http://pubs.acs.org Publication Date: June 8, 1983 | doi: 10.1021/bk-1983-0221.ch014

J. S. OSINSKI and L. T. MANZIONE Bell Laboratories, Murray Hill, NJ 07974

The interest i n extending the Reaction Injection Mold ing (RIM) process to non-urethane resins has generated need for a greater understanding of the molding beha vior of these fast-cure systems. Epoxy, for example, i s recognized as a candidate for commercial RIM, but its lower reaction rate and high heat of reaction ren der it more difficult to mold than polyurethane. The kinetics and rheology of such a resin must therefore be well characterized i n order to undertstand the molding process and evaluate its feasibility. A method of f u l l y characterizing an epoxy molding system by com bining adiabatic reactor studies, infra-red spectro metry, and viscometer data is therefore described. This provides time-temperature-conversion-viscosity correlations which can be d i r e c t l y u t i l i z e d i n compu ter studies designed to minimize actual molding times while avoiding a damaging exotherm during cure. The particular system studied is a low v i s c o s i t y l i q u i d epoxy cured with aminoethylpiperazine and was found to be moldable over specific temperature ranges. Conducting an analysis of this type on a prospective resin can help determine the value of further invest ment i n experimentation, material development, mold ing equipment, and tooling. R e a c t i o n I n j e c t i o n M o l d i n g (RIM) i s p o l y m e r i z a t i o n and p o l y m e r p r o c e s s i n g i n a s i n g l e c y c l i c o p e r a t i o n . The p r o c e s s c o n s i s t s of m e t e r i n g and m i x i n g l o w v i s c o s i t y r e a c t i v e f l u i d s , mold f i l l i n g , and p o l y m e r i z a t i o n o r c u r e i n t h e m o l d c a v i t y . Although c o m m e r c i a l RIM i s p r i m a r i l y a s s o c i a t e d w i t h p o l y u r e t h a n e due t o i t s wide use i n t h e automotive i n d u s t r y , t h e r e i s c o n s i d e r a b l e i n t e r e s t and a c t i v i t y i n e x t e n d i n g t h e p r o c e s s t o o t h e r r e s i n systems. Epoxy, f o r example, h a s c e r t a i n p r o p e r t i e s and c h a r a c t e r i s t i c s w h i c h make i t d e s i r a b l e f o r u s e i n s u c h a n o p e r a t i o n . C e r t a i n e p o x i e s may b e s u i t a b l e f o r RIM s i n c e t h e y a r e t w o - p a r t , 0097-6156/83/0221-0263$06.00/0 © 1983 American Chemical Society

In Epoxy Resin Chemistry II; Bauer, Ronald S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 1, 2016 | http://pubs.acs.org Publication Date: June 8, 1983 | doi: 10.1021/bk-1983-0221.ch014

264

EPOXY RESIN CHEMISTRY

low v i s c o s i t y s y s t e m s t h a t p r o v i d e a r a p i d , e x o t h e r m i c r e a c t i o n t h a t goes t o c o m p l e t i o n w i t h o u t p r o d u c i n g u n d e s i r a b l e by-products. However, e p o x i e s a r e i n h e r e n t l y l e s s amenable t o t h e RIM p r o c e s s t h a n p o l y u r e t h a n e s . R e f e r r i n g t o F i g u r e 1, we s e e ob v i o u s d i f f e r e n c e s i n the a d i a b i a t i c r e a c t i o n paths of t y p i c a l epoxy and p o l y u r e t h a n e r e a c t i o n s . The epoxy r e a c t i o n , s t a r t i n g a t a h i g h e r t e m p e r a t u r e t h a n t h e p o l y u r e t h a n e , p r o c e e d s much more s l o w l y b u t u l t i m a t e l y r e l e a s e s much more h e a t d u r i n g t h e reaction. These d i f f e r e n c e s w i l l have important i m p l i c a t i o n s i n the molding of the r e s i n . The c o m p a r a t i v e l y s l o w e r r e a c t i o n r a t e o f e p o x i e s means t h a t h i g h e r m o l d i n g t e m p e r a t u r e s a r e r e quired to achieve reasonable cycle times. I t t h e n becomes p o s s i b l e f o r t h e peak t e m p e r a t u r e a c h i e v e d d u r i n g c u r e t o e x c e e d t h e t h e r m a l d e g r a d a t i o n t e m p e r a t u r e o f t h e s y s t e m due t o t h e h i g h h e a t o f r e a c t i o n a s s o c i a t e d w i t h e p o x i e s . The u n d e r s t a n d i n g and p r e d i c t i o n o f s u c h p r o b l e m s i n t r o d u c e d by t h e u s e o f e p o x i e s w i l l y i e l d i n f o r m a t i o n on t h e p r o c e s s a b i l i t y and m o l d a b i l i t y o f a g i v e n r e s i n system i n a p a r t i c u l a r a p p l i c a t i o n , o b t a i n a b l e w i t h o u t e x t e n s i v e e x p e r i m e n t a t i o n . Most s i g n i f i c a n t a r e t h e e f f e c t s of m o l d and f l u i d t e m p e r a t u r e s , p a r t t h i c k n e s s , and f i l l e r l o a d i n g on t h e v i s c o s i t y , c u r e t i m e , and t h e maximum e x o t h e r m tempe rature. Such an a n a l y s i s , however, n e c e s s a r i l y i n v o l v e s t h e a c q u i s i t i o n and c o r r e l a t i o n o f d a t a r e l a t e d t o t h e v i s c o s i t y and k i n e t i c s of t h e c u r i n g polymer. Computer m o d e l i n g o f m o l d f i l l i n g and c u r i n g e v e n t s i s t h e n p o s s i b l e Q , _2, 3 ) . C o u p l i n g t h e s e r e s u l t s w i t h p r a c t i c a l c o n s t r a i n t s such as u l t i m a t e p h y s i c a l p r o p e r t i e s o f t h e cured r e s i n , ease of h a n d l i n g , machine compati b i l i t y , and c o s t , a d i s c r i m i n a t i n g d e c i s i o n c a n h o p e f u l l y be r e a c h e d when c o m p a r i n g d i f f e r e n t r e s i n s , w i t h o u t a c t u a l m o l d i n g t r i a l s of each c a n d i d a t e . T h i s c h a p t e r w i l l d e s c r i b e t e c h n i q u e s f o r e v a l u a t i o n o f an epoxy RIM s y s t e m f r o m t h e a b o v e s t a n d p o i n t s . F i r s t a d e s c r i p t i o n of t h e k i n e t i c and v i s c o s i t y c h a r a c t e r i z a t i o n s w i l l be p r e s e n t e d , f o l l o w e d by a m o l d a b i l i t y a n a l y s i s u s i n g t h e s e d a t a . Most e x p e r i m e n t a l epoxy RIM s y s t e m s c o n s i s t o f a d i g l y c i d y l e t h e r o f b i s p h e n o l A epoxy (DGEBA) w i t h amine o r a n h y d r i d e c u r i n g a g e n t s (4_) . The two p a r t l i q u i d epoxy s y s t e m c h o s e n f o r t h e p r e s e n t a n a l y s i s i s a DGEBA-type r e s i n p l u s r e a g e n t g r a d e aminoe t h y l p i p e r a z i n e (AEP) as a c u r a t i v e . The epoxy h a s a m o l e c u l a r w e i g h t o f 380 and an e q u i v a l e n t w e i g h t , b a s e d on r e a c t i v e epoxy s i t e s , o f 190. AEP i s a t r i f u n c t i o n a l amine o f e q u i v a l e n t w e i g h t 43 c o n t a i n i n g p r i m a r y , s e c o n d a r y , and t e r t i a r y a m i n e s , t h e l a t t e r of w h i c h i s u n r e a c t i v e b u t a c t s as a c a t a l y t i c s i t e . This curing a g e n t was c h o s e n among t h e s e v e r a l t h a t w e r e c o n s i d e r e d b e c a u s e o f i t s r e l a t i v e h i g h r a t e o f r e a c t i o n and i t s p o t e n t i a l f o r u s e as an a c t u a l o f f - t h e - s h e l f RIM component. A l l e x p e r i m e n t s were p e r f o r m e d w i t h t h e n o m i n a l s t o i c h i o m e t r y o f 22.6 p a r t s by w e i g h t per hundred r e s i n ( p h r ) . C e r t a i n l y f a s t e r s y s t e m s a r e a v a i l a b l e t h a n t h e one c h o s e n



14.

osiNSKi AND MANZiONE

0

20

41

Epoxy

60

00

Reaction

100

Injection

120

140

Molding

160

180

Resins

265

200

TIME (sec)

F i g u r e 1. Typical adiabatic reactions.

t e m p e r a t u r e r i s e o f epoxy a n d p o l y u r e t h a n e


266


here, such as those u s i n g boron t r i f l u o r i d e complexes as a Lewis a c i d c u r i n g agent o r t h o s e i n c o r p o r a t i n g p r o p r i e t a r y c a t a l y s t s . However, b a s e d u p o n p o t e n t i a l p r o c e s s a b i l i t y a s a r e a d i l y a v a i l a b l e o f f - t h e - s h e l f s y s t e m , DGEBA epoxy+AEP l o o k s most p r o m i s i n g .


Resin

Characterization

T h e o r e t i c a l treatment of t h i s polymerization i s d i f f i c u l t b e c a u s e o f t h e p r e s e n c e o f b o t h p r i m a r y and s e c o n d a r y amine r e a c t i o n s a s w e l l a s t e r t i a r y amine c a t a l y z e d epoxy h o m o p o l y m e r i z a tion. To o b t a i n k i n e t i c and v i s c o s i t y c o r r e l a t i o n s , e m p i r i c a l methods were u t i l i z e d . Various techniques that f u l l y or p a r t i a l l y c h a r a c t e r i z e s u c h a s y s t e m b y e x p e r i m e n t a l means a r e d e s c r i b e d i n t h e l i t e r a t u r e (5-9)· T h e s e methods i n c l u d e m e a s u r i n g c u r e b y d i f f e r e n t i a l scanning calorimetry, i n f r a - r e d spectrometry, v i s c o m e t r y , and by m o n i t o r i n g e l e c t r i c a l p r o p e r t i e s . The p r e s e n c e o f m u l t i p l e r e a c t i o n mechanisms w i t h d i f f e r e n t a c t i v a t i o n e n e r g i e s and r e a c t i o n o r d e r s ( 1 0 ) makes a c c u r a t e c h a r a c t e r i z a t i o n s d i f f i c u l t , b u t such c o m p l e x i t i e s s h o u l d be q u a n t i f i e d . A d u a l A r r h e n i u s e x p r e s s i o n was a d o p t e d h e r e f o r t h a t p u r p o s e . Adiabatic Reactor. The d i r e c t measurement o f t h e a d i a b a t i c t e m p e r a t u r e r i s e o f a r e a c t i n g r e s i n a s a f u n c t i o n o f t i m e was u s e d a s a means o f g e n e r a t i n g k i n e t i c d a t a . T h i s method h a s b e e n a p p l i e d t o p o l y u r e t h a n e by L i p s h i t z and Macosko (11) , b u t a com p u t e r i z e d a d a p t a t i o n o f t h e i r method was f o u n d more u s e f u l f o r epoxies. C o m b i n i n g t h e r e s u l t s o f t h i s method w i t h v i s c o m e t e r and I R s t u d i e s , t h e e f f e c t i v e epoxy k i n e t i c s o f a g i v e n s y s t e m a r e r e p r e s e n t e d by:

dC dt

A^ exp

c

1

+ A

2

exp

(1) RT

RT

(see L i s t o f Symbols). Thus, by c o r r e l a t i n g d a t a o v e r s p e c i f i c t e m p e r a t u r e r e g i m e s , t h e d o m i n a t e a c t i v a t i o n e n e r g y and r e a c t i o n o r d e r i n t h a t regime c a n be i n d e p e n d e n t l y e v a l u a t e d . A t y p i c a l epoxy r e a c t i o n c a r r i e d o u t a d i a b a t i c a l l y may h a v e an e x o t h e r m w e l l i n e x c e s s o f 200°C. T h e r e f o r e , much o f t h e r e a c t i o n w i l l be g o v e r n e d b y mechanisms a s s o c i a t e d w i t h h i g h tem p e r a t u r e s , and a s a r e s u l t p r e d o m i n a t e d b y k i n e t i c s d i f f e r e n t f r o m t h o s e i n t h e i n i t i a l r e a c t i o n r e g i o n ( u n d e r 125°C) ( 1 0 ) . I n such a case E q u a t i o n 1 might e f f e c t i v e l y reduce t o

dC dt

—Ε = A exp

A

RT

(2)

and we c o u l d o b t a i n t h e h i g h t e m p e r a t u r e p a r a m e t e r s b a s e d o n t h i s simpler expression. Weighed q u a n t i t i e s o f t h e epoxy r e s i n and c u r i n g a g e n t t o be



14.

osiNSKi

AND

Epoxy

MANZIONE

Reaction

Injection

Molding

Resins

267

t e s t e d a r e heated s e p a r a t e l y i n a c o n v e c t i o n oven t o t h e d e s i r e d i n i t i a l t e m p e r a t u r e o f a p p r o x i m a t e l y 50°C. P r i o r t o d a t a a c q u i s i t i o n , t h e r e s i n i s t r a n s f e r r e d t o a s t a t i c o v e n h e l d a t t h e same i n i t i a l temperature t o m i n i m i z e subsequent heat l o s s e s . Because h i g h temperatures a r e reached, t h e r e a c t i o n i s c a r r i e d out i n an FEP T e f l o n b e a k e r s u r r o u n d e d b y a s t y r o f o a m j a c k e t . A f a s t r e s p o n s e (45 ms t i m e c o n s t a n t ) C h r o m e l - A l u m e l t h e r m o c o u p l e i s sub merged i n t h e f l u i d and t h e s i g n a l i s s e n t t o a s m a l l a m p l i f i e r and t h e n i n p u t d i r e c t l y t o a d e s k t o p - c o m p u t e r c o n t r o l l e d d a t a a c q u i s i t i o n s y s t e m . T h i s s y s t e m c a n a c c u r a t e l y sample d a t a p o i n t s a t i n t e r v a l s r a n g i n g from l e s s t h a n a m i l l i s e c o n d t o an i n d e f i n i t e time p e r i o d . G e n e r a l l y t h e sampling r a t e used f o r the p r e s e n t s y s t e m was ~1 p e r s e c . At t h i s p o i n t a s t o i c h i o m e t r i c q u a n t i t y o f c u r i n g agent i s q u i c k l y added t o t h e c o n t a i n e r and v i g o r o u s l y s t i r r e d f o r a p p r o x i m a t e l y 15 s e c a s t e m p e r a t u r e d a t a a r e o b t a i n e d . M i x i n g c a n be c a r r i e d o u t m a n u a l l y a n d i s f o u n d t o be e f f e c t i v e . Heat l o s s e s n e a r t h e end o f t h e r e a c t i o n a r e n o t e n t i r e l y n e g l i g i b l e and a r e accounted f o r i n t h e subsequent d a t a r e d u c t i o n r o u t i n e a s d e s c r i b e d below. A heat b a l a n c e o f an a d i a b a t i c r e a c t i o n based on E q u a t i o n 2 y i e l d s an e x p r e s s i o n o f t h e form: P

In

C

P

(

T

)

(-AH)C (C/C ) ο ο

dT n d

t

n _ 1

= In A C ο

-

~

RT

(3)

P l o t t i n g t h e l e f t s i d e o f t h i s e q u a t i o n a g a i n s t 1/T s h o u l d t h e r e fore y i e l d a straight l i n e , enabling c a l c u l a t i o n of the activation e n e r g y and p r e - e x p o n e n t f r o m t h e s l o p e and i n t e r c e p t , r e s p e c t i v e l y . M a t e r i a l d e n s i t y i s measured and assumed c o n s t a n t ; t h i s i s r e a sonable because t h e s m a l l i n c r e a s e i n d e n s i t y due t o p o l y m e r i z a t i o n i s p a r t i a l l y o f f s e t by t h e s i m u l t a n e o u s d e c r e a s e due t o h i g h t e m p e r a t u r e . Cp a s a f u n c t i o n o f t e m p e r a t u r e ( s e e T a b l e I ) was o b t a i n e d f r o m a n a p p r o x i m a t e p o l y n o m i a l f i t t o t h e d a t a o f Kamal and Ryan ( 6 ) f o r t h e i r epoxy s y s t e m , w h i c h i n c l u d e s t h e e f f e c t o f i n c r e a s i n g c h e m i c a l c o n v e r s i o n . Heat l o s s e s a r e c o r r e c t e d f o r by d e t e r m i n i n g t h e downward s l o p e o f t h e t a i l o f t h e r a w t e m p e r a t u r e v s . t i m e c u r v e and c a l c u l a t i n g t h e e f f e c t i v e o v e r a l l h e a t t r a n s f e r coefficient. The h e a t l o s s a t e a c h t i m e i n c r e m e n t c a n t h e n be c a l c u l a t e d and added b a c k i n t o t h e s y s t e m m a t h e m a t i c a l l y . ΔΗ and o t h e r v a l u e s c a n be c a l c u l a t e d from t h e a d j u s t e d d a t a . The d e r i v a t i v e i ^ . a t e a c h p o i n t i s o b t a i n e d b y a f o u r t h o r d e r c e n t r a l d i f f e r e n c e e q u a t i o n , then an a r b i t r a r y but approximate v a l u e o f η i s c h o s e n and a l l p o i n t s o t h e r t h a n v e r y e a r l y and p l a t e a u p o i n t s a r e c o r r e l a t e d by a l e a s t - s q u a r e s l i n e a r r e g r e s s i o n u s i n g E q u a t i o n 3. The i n d e x η i s i n c r e m e n t e d o r d e c r e m e n t e d s y s t e m a t i c a l l y u n t i l the best c o r r e l a t i o n c o e f f i c i e n t i s obtained. D a t a f r o m a s i n g l e e x p e r i m e n t a l r u n c a n be r e d u c e d a l o n e o r com b i n e d w i t h o t h e r d a t a f i l e s o f t h e same s y s t e m . Employment o f



22.6

AEP (Lo-temp)

ο

4682

4682

-524 + 6.29T + .000686T .

No e n t r y means n o t m e a s u r e d .

22.6

phr curative

(Hi-temp)

AEP

System

1090

1090

ρ

-

129000

-ΔΗ

.3603

3.977

A

4640

7991

A

E /R

Table I Reaction K i n e t i c Parameters

2.0

2.80

η

233

ΔΤ ad


.49

gel

.9996

.9987

Η

GO

§

Χ m

ο

M

00

ON


14.

osiNSKi AND MANZIONE

Epoxy

Reaction

Injection

Molding

Resins

269

t h i s r o u t i n e on a t e s t f i l e g e n e r a t e d by an η order Arrhenius expression e a s i l y reproduces the parameters used, c o r r e c t to f o u r o r more s i g n i f i c a n t d i g i t s . Sample o u t p u t s f o r epoxy + AEP a r e shown i n F i g u r e s 2 and 3. Figure 2 i l l u s t r a t e s the t y p i c a l f i t that i s p o s s i b l e using data from a s i n g l e experiment. K i n e t i c c o n s t a n t s o b t a i n e d f r o m one t r i a l do n o t s a t i s f a c t o r i l y p r e d i c t o t h e r e x p e r i m e n t s a t d i f f e r e n t s t a r t i n g t e m p e r a t u r e s , however. T h e r e f o r e , i t i s a d v a n t a geous t o c o r r e l a t e s e v e r a l f i l e s o f d a t a s i m u l t a n e o u s l y , a s i n F i g u r e 3. The e q u a t i o n o b t a i n e d when t h i s i s done r e p r e s e n t s t h e adiabatic reaction kinetics:

| £ = 3.977

exp -7991

c

2.80 equiv. m3-sec

(4)

V i s c o m e t r y and I n f r a r e d S p e c t r o m e t r y . To o b t a i n a l o w tem p e r a t u r e k i n e t i c e x p r e s s i o n a s w e l l as r h e o l o g i c a l d a t a f o r epoxy + AEP, t h e v i s c o s i t y o f t h e c u r i n g r e s i n as a f u n c t i o n o f t i m e and t e m p e r a t u r e was o b t a i n e d on a F e r r a n t i - S h i r l e y c o n e and p l a t e v i s c o m e t e r and m a t c h e d w i t h c o n v e r s i o n d a t a a c q u i r e d t h r o u g h IR s p e c t r o m e t r y . No a t t e m p t was made t o a c c o u n t f o r nonNewtonian e f f e c t s s i n c e i n p r a c t i c e mold f i l l i n g s h o u l d t a k e p l a c e i n t h e r e a s o n a b l y Newtonian r e g i o n o f low c o n v e r s i o n . The m a t e r i a l was f o u n d t o be N e w t o n i a n o v e r t h e r a n g e where c a v i t y f i l l i n g w o u l d be e x p e c t e d t o t a k e p l a c e . The s h e a r r a t e u s e d was a p p r o x i m a t e l y 150 s e c ~ ^ . Isothermal g e l times at temperatures f r o m 30 t o 90°C a t 10° i n t e r v a l s w e r e f o u n d by e x t r a p o l a t i n g t h e asymptotic v i s c o s i t y curve to i n f i n i t e v i s c o s i t y (see F i g u r e 4 ) , representing gelation. Assuming t h e c o n v e r s i o n of r e a c t i v e spe c i e s a t t h e g e l p o i n t t o be i n d e p e n d e n t o f t h e i s o t h e r m a l c u r e t e m p e r a t u r e , a p l o t o f I n t g ^ v s . 1/T s h o u l d t h e n g i v e a s t r a i g h t l i n e of s l o p e _A . T h i s i s indeed the case f o r t h e data o b t a i n e d . L e a s t s q u a r e s l i n e a r r e g r e s s i o n o f s e v e n d a t a p o i n t s gavg a c o r r e l a t i o n c o e f f i c i e n t o f 0.9996 and an a c t i v a t i o n e n e r g y A o f 4640?K. I t c a n be shown t h a t t h e i n t e r c e p t o f t h i s l i n e ^Ls u s e f u l as w e l l , a s s u m i n g n order Arrhenius k i n e t i c s . I n t e g r a t i o n of E q u a t i o n 2 f o r c o n s t a n t t e m p e r a t u r e g i v e s , f o r t = t g e l E

e

t n

a t

C =

c

g

e

l

:

In

t

gel

In

J-n "gel (1-n) A

+ ^ RT

η φ

1

(5)

representing the equation of a l i n e . To make u s e o f t h e i n t e r c e p t t e r m o f t h e a b o v e t o s o l v e f o r t h e p r e - e x p o n e n t i a l f a c t o r A, t h e c o n c e n t r a t i o n a t t h e g e l p o i n t Cgel d e t e r m i n e d by o b t a i n i n g t h e c o n v e r s i o n c a l c u l a t e d by IR a b s o r b a n c e c h a n g e s a t 920 cm~l wavenumbers (12) a t t h e c o r r e s p o n d w

a

s




Ο

Ν)

osiNSKi AND MANZiONE 100

Epoxy

Reaction

Injection

Molding

Ρ

1

ΔΤ =41.0 °C 0


271

Resins

3

1/T x10 (1/DEG K) F i g u r e 3. D a t a c o r r e l a t i o n f o r t h r e e epoxy + AEP e x p e r i m e n t s . ΔΤ = 41.0°C, [ ] Τ = 51.9°C, 0 Τ = 53.2°C. ο ' ο ο


272


i n g t e m p e r a t u r e and g e l t i m e f o u n d o n t h e v i s c o m e t e r . A P e r k i n E l m e r M o d e l 567 s p e c t r o m e t e r w i t h h e a t e d c e l l c a r r i e r and sodium c h l o r i d e p l a t e s was u s e d t o m o n i t o r t h i s a b s o r b a n c e peak c o r r e s ponding t o t h e r e d u c t i o n i n t h e epoxide group. The r e a c t i v e m i x t u r e was m i x e d a t room t e m p e r a t u r e and p l a c e d i n a t h i n f i l m b e t w e e n t h e two h e a t e d N a C l p l a t e s whereupon t h e c l o c k was s t a r t e d . B e e r ' s Law was assumed. T h r e e t r i a l s a t 4 0 , 60 and 80°C y i e l d e d gel 2400 e q u i v / m ^ + 7% ( X g i 0 . 4 9 ) , and a n a c t i v a t i o n e n e r g y i n good agreement w i t h t h a t o b t a i n e d o n t h e v i s c o m e t e r , a l t h o u g h w i t h a lower c o r r e l a t i o n c o e f f i c i e n t . A reasonable value of η = 2 was c h o s e n t o o b t a i n t h e l o w t e m p e r a t u r e k i n e t i c e x p r e s s i o n : c

=

=


e

-4640

- j ^ - = .3603 exp

^2 e q u i v 3 m -sec

(6)

The e x a c t v a l u e o f t h e i n d e x η i s n o t c r i t i c a l f o r o u r p u r p o s e s and t h e c h o i c e o f η = 2 f i t s t h e d a t a w e l l . Note t h e v e r y d i f f e r e n c e a c t i v a t i o n e n e r g y compared t o t h e h i g h t e m p e r a t u r e e x p r e s s i o n ( E q u a t i o n 4 ) . C e r t a i n l y t h i s d i s c r e p a n c y i s beyond any e x perimental e r r o r , i n d i c a t i n g t h e presence of a d i f f e r e n t c u r i n g mechanism a t t h e s e t e m p e r a t u r e s . The v a l u e o f = 4640°K com p a r e s w e l l w i t h v a l u e s quoted by o t h e r s f o r e p o x V ~ i systems s t u d i e d by i s o t h e r m a l g e l t i m e measurements a t l o w t e m p e r a t u r e s (13). The l o w and h i g h t e m p e r a t u r e e x p r e s s i o n s c a n t h e n be com b i n e d i n t o one e q u a t i o n u s i n g e m p i r i c a l l y d e t e r m i n e d w e i g h t i n g f a c t o r s on each term: a m

dC dt

= 2.704 exp

ο on

-7991 C

n e

-4640

(7)

+ .05405 exp

Sample a d i a b a t i c r e a c t i o n p a t h s d e t e r m i n e d by t h i s e q u a t i o n a r e shown i n F i g u r e 5. K i n e t i c p a r a m e t e r s o b t a i n e d i n t h i s w o r k a r e summarized i n T a b l e I . Viscosity Correlations. The i n i t i a l v i s c o s i t y o f DGEBA epoxy + AEP a s a f u n c t i o n o f t e m p e r a t u r e and a t e s s e n t i a l l y z e r o c o n v e r s i o n c a n be d e s c r i b e d b y a n a c t i v a t e d p r o c e s s a s w e l l . L i n e a r r e g r e s s i o n o f I n η v s . 1/T t o f i t t h e e q u a t i o n (8)

yields the expression η = 7.309x10

-10

6960 exp

poise

w i t h a c o r r e l a t i o n c o e f f i c i e n t o f 0.9985.


(9)


14.

OSINSKI A N D M A N Z I O N E

Epoxy

Reaction

Injection

Molding

Resins

273

m A EXPERIMENTAL — CORRELATED

I ι ι ι ι ι ι ι ι ι I ι ι ι ι ι ι ι ι ι I j ' ι ι '

200

300 TIME (sec)

400

» • I

500

'

F i g u r e 5. Two a d i a b a t i c r e a c t i o n p a t h s f o r epoxy 4- AEP, a t Τ = 41.0°C and Τ = 51.9°C. S o l i d c u r v e s a r e p r e d i c t i o n s b a s e d o n como plex k i n e t i c s (Equation 7 ) .


274


F o r p u r p o s e s o f m o d e l i n g t h e f i l l i n g s t a g e o f t h e R.IM m o l d i n g operation, i t i s also generally desirable to quantify the increase i n v i s c o s i t y due t o p o l y m e r i z a t i o n . T h e r e f o r e , t o c o r r e l a t e t h e v i s c o s i t y w i t h a d e v e l o p i n g p o l y m e r m a t r i x , a c o n v e r s i o n t e r m was added t o E q u a t i o n 8, a d a p t e d f r o m C a s t r o and Macosko ( 1 4 ) . Since i t h a s been shown t h a t t h e f l o w a c t i v a t i o n e n e r g y Εη d o e s n o t n e c e s s a r i l y remain constant w i t h c o n v e r s i o n ( 7 ) , t h e e x p r e s s i o n became X


n =

exp

E* RT

X

gel

1 gel - - X

(10)

where E* i s a c o m p l e x f u n c t i o n o f c o n v e r s i o n , and i n t h e p r e s e n t case, temperature as w e l l : E* R

• 6 + 2.754x10 0

R

7 I ; /

1 Λ

-2400 exp — - —

Χ °K

(11)

N o t e t h a t E q u a t i o n 10 r e d u c e s t o E q u a t i o n 9 f o r X = 0. Equation 10, d e s c r i b i n g v i s c o s i t y a s a f u n c t i o n o f t e m p e r a t u r e and c o n v e r s i o n , i s p l o t t e d i n F i g u r e 6, a n d , i n c o m b i n a t i o n w i t h E q u a t i o n 6, p r e d i c t s v i s c o s i t y and t i t o w i t h i n a few p e r c e n t ( s e e F i g u r e 4) over t h e temperature range e x p l o r e d . Mold f i l l i n g should n o t take p l a c e o u t s i d e t h e r a n g e o f l o w c o n v e r s i o n and m o d e r a t e t e m p e r a t u r e i f f l o w s e i z u r e i s t o be a v o i d e d , so t h e s e e q u a t i o n s a r e a p p l i cable. The d i s c r e p a n c y b e t w e e n t h e v i s c o m e t e r d a t a and t h e p r e d i c t e d v a l u e s a t 40°C i n F i g u r e 4 i s p r o b a b l y due t o s l i g h t d e v i a t i o n f r o m 40°C o n t h e v i s c o m e t e r d u r i n g t h e d a t a a c q u i s i t i o n , s i n c e t h e r e s i n c u r e and v i s c o s i t y a r e v e r y t e m p e r a t u r e sensitive at l o w e r t e m p e r a t u r e s . g

Resin

e

Moldability

S e v e r a l s i g n i f i c a n t a s p e c t s o f t h e RIM o p e r a t i o n d e t e r m i n e t h e moldability of a resin i n a particular application. These a r e m i x i n g , m o l d f i l l i n g , and r e s i n c u r i n g . I n a d d i t i o n , t h e p r e s e n c e o f f i l l e r s i s o f i m p o r t a n c e and c a n make t h e d i f f e r e n c e between a m o l d a b l e and non-moldable system as t h e f i l l e r a f f e c t s each o f t h e above s t e p s . RIM m i x i n g s t u d i e s h a v e b e e n c a r r i e d o u t by L e e , e t a l . ( 1 5 ) , and s u g g e s t t h a t t h e R e y n o l d s number o f t h e f l u i d t h r o u g h t h e i n j e c t i o n o r i f i c e s be a t l e a s t 250 f o r c o m p l e t e m i x i n g . For the present system t h i s i s e a s i l y o b t a i n a b l e by a d j u s t i n g t h e temper a t u r e o f t h e epoxy a b o v e 35°C t o r e d u c e t h e v i s c o s i t y t o b e l o w 30 p o i s e o r s o . T h i s i s n o t done w i t h o u t i n some way a f f e c t i n g t h e s u b s e q u e n t f i l l i n g and c u r i n g s t a g e s , however, a s d i s c u s s e d b e l o w . AEP v i s c o s i t y i s n o m i n a l l y 0.2 p o i s e a t room t e m p e r a t u r e and need n o t be l o w e r e d .



14.

osiNSKi

20

40

AND

MANZiONE

G0

Epoxy

80

Reaction

Injection

Molding

Resins

100

TEMPERRTURE ( C ) F i g u r e 6. V i s c o s i t y o f epoxy + AEP a s a f u n c t i o n o f t e m p e r a t u r e and conversion (Equation 10).


275


276


Mold F i l l i n g . Since f o r very r e a c t i v e r e s i n s the time r e q u i r e d f o r m o l d f i l l i n g (8 o r more s e c o n d s f o r l a r g e p a r t s ) may be a s i g n i f i c a n t p o r t i o n of t h e a d i a b a t i c g e l time of t h e r e s i n , con s i d e r a b l e c o n v e r s i o n can o c c u r d u r i n g t h i s s t e p . Indeed, f o r p o l y u r e t h a n e s f l o w s e i z u r e due t o g e l a t i o n i s a m a j o r c o n c e r n when establishing processing conditions. Due t o t h e n o n - u n i f o r m i t y o f d e v e l o p i n g v e l o c i t y , t e m p e r a t u r e , and c o n c e n t r a t i o n g r a d i e n t s d u r i n g mold f i l l i n g , however, i t i s not a s i m p l e m a t t e r t o p r e d i c t t h i s event. F u r t h e r m o r e , t h e n o n - u n i f o r m t e m p e r a t u r e and c o n c e n t r a t i o n p r o f i l e s t h a t r e s u l t may h a v e i m p o r t a n t i n f l u e n c e s on t h e s u b s e q u e n t c u r e . T h e r e f o r e k n o w l e d g e o f t h e s e p a r a m e t e r s as a f u n c t i o n o f l o c a t i o n i n t h e mold i s v a l u a b l e i n p r e d i c t i v e modeling. A n u m e r i c a l a n a l y s i s o f c a v i t y f i l l i n g was d e v e l o p e d t o e v a l u a t e and o p t i m i z e t h e u s e o f r e a c t i v e f l u i d s i n RIM. This method, w h i c h h a s b e e n p r e v i o u s l y d e s c r i b e d i n d e t a i l ( 3 ) , em p l o y s t h e m a r k e r and c e l l method f o r t r e a t i n g t r a n s i e n t f l u i d flows i n c o n j u n c t i o n w i t h f i n i t e d i f f e r e n c e s o l u t i o n s of the con v e r s i o n and t e m p e r a t u r e f i e l d s i n t h e p r e - p o l y m e r and t h e m o l d wall. The t i m e - t e m p e r a t u r e - c o n v e r s i o n - v i s c o s i t y c o r r e l a t i o n s shown e a r l i e r f o r epoxy + AEP w e r e t h e n u s e d i n t h e m o l d f i l l i n g simulation. R e s u l t s o f epoxy m o d e l i n g i n d i c a t e t h a t u n l i k e w i t h p o l y u r e t h a n e s , however, g e n e r a l l y v e r y l i t t l e c o n v e r s i o n o c c u r s d u r i n g mold f i l l i n g . T h i s s u g g e s t s two p o i n t s : f l o w s e i z u r e due t o p r e m a t u r e g e l a t i o n s h o w l d n o t be a p r o b l e m i n epoxy RIM, and an e s s e n t i a l l y u n i f o r m i n i t i a l c o n d i t i o n o f χ = 0.0 w i l l u s u a l l y s u f f i c e f o r modeling t h e mold c u r i n g sequence under moderate con ditions. O f t e n , h o w e v e r , s e v e r e m o l d i n g c o n d i t i o n s ( T > 140°C f o r t h i s system) a r e u t i l i z e d t o a c h i e v e lower mold r e s i d e n c e times. The t e m p e r a t u r e p r o f i l e s d e v e l o p e d a c r o s s t h e f l u i d due t o t h e f i l l i n g o f t h e c a v i t y may o n l y t h e n be s u f f i c i e n t l y n o n u n i f o r m t o h a v e s i g n i f i c a n t e f f e c t s on t h e r e s u l t i n g c u r e . In such c a s e s , p r e d i c t i o n o f t h e s e p r o f i l e s f o r use as t h e i n i t i a l c o n d i t i o n i n t h e s u b s e q u e n t c u r e may be n e c e s s a r y f o r a c c u r a t e m o d e l i n g even i f t h e c o n v e r s i o n throughout t h e c a v i t y i s n e g l i gible. Shown i n F i g u r e 7 a r e t h e t e m p e r a t u r e p r o f i l e s o f epoxy + AEP at t h e c o n c l u s i o n o f a 12 s e c f i l l i n a 0.476 cm t h i c k by 12 cm l o n g by i n f i n i t e l y w i d e c a v i t y , w i t h Τ = 70°C and T = 125°C. The g a t e c o r r e s p o n d s t o Z/L = 0.0 i n t n e p l o t . Minimal conversion has o c c u r r e d ( p l o t n o t shown) t h u s t h e s e p r o f i l e s a r e a l m o s t e n t i r e l y due t o c o n d u c t i o n and n o t h e a t o f r e a c t i o n . Only m i l d a x i a l v a r i a t i o n o f t e m p e r a t u r e i s e v i d e n t h e r e , and even l e s s w o u l d o c c u r w i t h more m o d e r a t e m o l d i n g t e m p e r a t u r e s . Under s u c h c i r c u m s t a n c e s , a one r a t h e r t h a n two d i m e n s i o n a l s o l u t i o n o f t h e curing stage should s u f f i c e , s i m p l i f y i n g the modeling procedure. w

w

M o l d C u r i n g . A d j u s t i n g component and m o l d t e m p e r a t u r e s f o r processing reasons s i g n i f i c a n t l y a f f e c t s the r e s i n c u r i n g stage.



14.

osiNSKi AND MANZIONE

Epoxy

Reaction

Injection

Molding

Resins

280 h

240 h

0

.2

.4 .6 X/W

.8

1

F i g u r e 7· Temperature p r o f i l e s a t t h e c o n c l u s i o n o f mold f i l l i n g i n a s l a b g e o m e t r y w i t h epoxy + AEP. 12 s e c f i l l t i m e , 0.476 section width,

12 cm l e n g t h , Τ

= 70°C, Τ ο

= 125°C. w


277


278


Heat e f f e c t s a r e more i m p o r t a n t i n epoxy RIM t h a n i n p o l y u r e t h a n e p r o c e s s i n g b e c a u s e o f t h e u s u a l l y h i g h e r a c t i v a t i o n e n e r g y as w e l l a s t h e much h i g h e r h e a t o f r e a c t i o n . Degradation i s r a r e l y i f e v e r e n c o u n t e r e d i n u r e t h a n e r e a c t i o n s , w h e r e a s a 250°C epoxy exotherm can r e c o g n i z a b l y degrade a p a r t t h a t i s n e a r l y a d i a b a t i c . M o l d and component t e m p e r a t u r e s as w e l l as p a r t d e s i g n must t h e r e f o r e be c h o s e n c a r e f u l l y when u s i n g e p o x i e s . S i n c e e p o x i e s a r e g e n e r a l l y slower than urethanes, i n i t i a t i v e e x i s t s f o r reducing t h e i r m o l d i n g t i m e s , b u t a b a l a n c e must be m a i n t a i n e d i n o r d e r t o minimize c y c l e time w h i l e avoiding thermal degradation. The n u m e r i c a l t r e a t m e n t o f c a v i t y f i l l i n g c a n be e x t e n d e d t o m o d e l c u r i n g o f t h e r e s i n t o examine h e a t e f f e c t s d u r i n g c u r e . A one d i m e n s i o n a l s o l u t i o n , a s m e n t i o n e d , i s o f t e n s u f f i c i e n t t o p r e d i c t t h e t e m p e r a t u r e s a c h i e v e d d u r i n g c u r e and t h e t i m e r e q u i r e d t o d e m o l d . DemoId t i m e i s f o u n d by d e t e r m i n i n g t h e p o i n t a t w h i c h t h e e n t i r e c r o s s s e c t i o n h a s a c h e i v e d a minimum e j e c t able conversion. S i n c e t h e h i g h e s t t e m p e r a t u r e o f a p a r t w i l l u s u a l l y be reached i n the c e n t e r of i t s c r o s s s e c t i o n w i t h a h i g h l y exother m i c s y s t e m s u c h a s epoxy, t h i s i s t h e c r i t i c a l l o c a t i o n t o m o n i t o r the t e m p e r a t u r e . P r e d i c t e d and e x p e r i m e n t a l l y o b t a i n e d c e n t e r l i n e t e m p e r a t u r e s f o r epoxy c u r e d w i t h AEP i n 0.476 and 0.635 cm t h i c k c a v i t i e s a r e shown i n F i g u r e s 8 and 9 f o r a m o l d t e m p e r a t u r e o f 110°C and a component t e m p e r a t u r e o f 55°C. E x p e r i m e n t a l d a t a w e r e a c q u i r e d by m o u n t i n g a 0.013 cm t h e r m o c o u p l e i n t h e c e n t e r o f a 7.5 cm d i a m e t e r c a v i t y formed by two 0.635 cm t h i c k s t e e l p l a t e s s e p a r a t e d by an 0 - r i n g s e a l . T h i s u n i t was p l a c e d i n a t e m p e r a t u r e c o n t r o l l e d l a b o r a t o r y o i l b a t h and epoxy was i n j e c t e d t h r o u g h a s m a l l s p a c e i n t h e s e a l , whereupon t e m p e r a t u r e s were o b t a i n e d t h r o u g h t h e same d a t a a c q u i s i t i o n s y s t e m d e s c r i b e d previously. H e a t c o n d u c t i o n d u r i n g t h e c a v i t y f i l l i n g o f *2 s e c was n e g l e c t e d i n t h e m o d e l , b u t a n o n - i s o t h e r m a l s o l u t i o n t o t h e m o l d w a l l t e m p e r a t u r e d u r i n g c u r e was i n c l u d e d . E x c e l l e n t agree ment i s shown b e t w e e n t h e m o d e l p r e d i c t i o n and e x p e r i m e n t , b o t h i n t h e shape o f t h e c u r v e and t h e t i m e and m a g n i t u d e o f t h e peak. The i n f l e c t i o n i n t h e e x p e r i m e n t a l d a t a i n t h e e a r l y p o r t i o n o f t h e c u r v e i s p r o b a b l y due t o c o n v e c t i v e f l o w o f t h e r e s i n i n t h e c a v i t y , b u t t h i s a p p a r e n t l y h a s no g r e a t i n f l u e n c e on s u b s e q u e n t temperature p r o f i l e s . The c u r e m o d e l assumes a s t a t i c f l u i d . S i m u l a t i o n s o v e r a w i d e r a n g e o f c a v i t y w i d t h s and i n i t i a l component and m o l d t e m p e r a t u r e s a r e p o s s i b l e o n c e we a r e c o n f i d e n t o f t h e m o d e l . T h i s e x e r c i s e w i l l be met w i t h v a r y i n g d e g r e e s o f s u c c e s s as t h e c o n d i t i o n s d e v i a t e f a r f r o m t h o s e d e s c r i b e d a b o v e due t o e r r o r s i n t h e k i n e t i c e x p r e s s i o n and t h e r m a l p a r a m e t e r s such as t h e heat t r a n s f e r c o e f f i c i e n t . The t r e n d s , h o w e v e r , a r e c o r r e c t and c a n be u s e d t o e x p l o r e a l l p o s s i b l e m o l d i n g c o n d i t i o n s on t h e c o m p u t e r i n a few h o u r s r a t h e r t h a n a few weeks o r months i n the laboratory. S i n c e t h e t e m p e r a t u r e and c o n v e r s i o n a t any point i n the r e s i n are i n t i m a t e l y r e l a t e d f o r a given cure h i s t o r y , a good agreement w i t h t e m p e r a t u r e d a t a s h o u l d a l s o p r o -


osiNSKi AND MANZiONE

Epoxy

Reaction

Injection

Molding

279

Resins

260

•

220h ?

\Q0\-

/ / h

UJ


3

140

§140

I M

UJ Û.

Iioo 601 20

1

I

I

I

I

40

I

I

80

120

TIME (sec) F i g u r e 9· As a b o v e , 0.635 cm c a v i t y .


160



280

v i d e a good agreement w i t h c o n v e r s i o n p r o f i l e s , w h i c h a r e d i f f i c u l t i f not i m p o s s i b l e t o measure e x p e r i m e n t a l l y . This can pro v i d e t h e minimum d e g r e e o f c u r e i n t h e p a r t a t a n y t i m e , and t h e r e f o r e t h e t i m e r e q u i r e d f o r e j e c t i o n . By n o t i n g t h e m o l d i n g c o n d i t i o n s a t w h i c h t h e peak t e m p e r a t u r e r e a c h e s t h e maximum t o l e r a b l e d e g r a d a t i o n p o i n t ( a b o u t 265°C i n t h i s c a s e ) , o p t i m a l m o l d i n g c o n d i t i o n s f o r a g i v e n m o l d g e o m e t r y c a n be d e r i v e d . T h i s w i l l g e n e r a l l y o c c u r by b o o s t i n g m o l d a n d / o r r e s i n t e m p e r a t u r e t o decrease cure time w h i l e remaining subject t o temperature requirements. F o r epoxy + AEP i n 0.476 cm c a v i t y , a m o l d t e m p e r a t u r e o f 125°C and a r e s i n t e m p e r a t u r e o f 70°C w i l l p r o v i d e a d e m o l d t i m e o f a b o u t 45 s e c and a peak t e m p e r a t u r e o f 2 6 2 ° C In a 0.635 cm c a v i t y t h e same m a t e r i a l w i l l p r o c e s s b e s t o n t h e b a s i s o f minimum demold t i m e and a v o i d a n c e o f t h e r m a l d e g r a d a t i o n w i t h a mold t e m p e r a t u r e o f 115°C and a r e s i n t e m p e r a t u r e o f 55°C. T h i s r e s u l t s i n a minimum demold t i m e o f a b o u t 75 s e c and a maximum t e m p e r a t u r e o f 265°C. The p r e s e n c e o f f i l l e r s a f f e c t s t h e r e s u l t s by i n c r e a s i n g h e a t c o n d u c t i o n ( u s u a l l y ) and d e c r e a s ing t h e e f f e c t i v e r e a c t i o n exotherm. Summary To d e t e r m i n e t h e m o l d a b i l i t y o f a p r o s p e c t i v e r e a c t i o n i n j e c t i o n molding r e s i n , i t i s u s e f u l t o e m p i r i c a l l y c h a r a c t e r i z e the given r e s i n system by t i m e - t e m p e r a t u r e - c o n v e r s i o n - v i s c o s i t y correla tions. I t i s t h e n p o s s i b l e t o choose between d i f f e r e n t r e s i n systems based on t h e s e c o r r e l a t i o n s i n c o n j u n c t i o n w i t h computer s i m u l a t i o n s o f t h e i r b e h a v i o r and w i t h c o n s i d e r a t i o n t o p r o c e s s requirements. Epoxy i s s e e n a s a v i a b l e c a n d i d a t e f o r RIM, b u t s i g n i f i c a n t d i f f e r e n c e s w i t h polyurethane e x i s t . Most i m p o r t a n t l y , t h e s l o w e r r e a c t i o n r a t e and h i g h e r h e a t o f r e a c t i o n o f e p o x i e s mean t h a t t h e m o l d i n g o p e r a t i o n i s l i m i t e d by p a r t d e g r a d a t i o n during cure rather than flow s e i z u r e during f i l l i n g . DGEBA epoxy w i t h AEP a s t h e c u r i n g a g e n t i s c o n c l u d e d t o be a v i a b l e o f f - t h e - s h e l f epoxy RIM s y s t e m w i t h p o t e n t i a l c y c l e t i m e s of 2 minutes o r l e s s . S p e c i f i c a p p l i c a t i o n s are subject to the p h y s i c a l p r o p e r t y r e q u i r e m e n t s , o f c o u r s e , w h i c h c a n be i n f l u e n c e d by t h e a d d i t i o n o f f i l l e r s , r e i n f o r c e m e n t s , o r m o d i f i e r s . List

o f Symbols

A

pre-exponential

factor,

(equiv/m^)*

C

concentration of r e a c t i v e species,

n

sec *

3 equiv/m 3

C^ ^ e

c o n c e n t r a t i o n a t g e l p o i n t , equiv/m 3

C C

Q

i n i t i a l concentration of reactive species,

equiv/m

h e a t c a p a c i t y , J/kg-°K



14.

osiNSKi AND

MANZIONE

Epoxy

Reaction

Injection

E^

r e a c t i o n a c t i v a t i o n energy,

E^

v i s c o u s f l o w a c t i v a t i o n energy,

ΔΗ

heat o f r e a c t i o n ,

η

r e a c t i o n index, dimensionless

r

correlation c o e f f i c i e n t , dimensionless

R

u n i v e r s a l gas c o n s t a n t ,

t

time, sec

t -L

time t o g e l , sec

Τ

temperature,

g e

T Τ Τ

initial

Q

wall

w

ο ΔΤ ^

X

gel

_

281

J/equiv J/gm-mol

J/equiv

J/equiv-°K

temperature,

°C

(mold) t e m p e r a t u r e ,

°C

(mold) t e m p e r a t u r e ,

a d i a b a t i c temperature r i s e ,

X

Resins

°Κ

i n i t i a l wall

w

Molding

°C

°K

C —C conversion of reactive species — - — , dimensionless ο conversion at g e l , dimensionless 3

ρ

density,

kg/m

η

Newtonian v i s c o s i t y ,

poise

pre-exponential factor,

poise

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8.

Domine, J . D.; Gogos, C. G. Polym. Eng. and Sci., 1980, 20, 847. Lee, L. J . ; Macosko, C. W. Int. J . of Heat Transfer, 1980, 23, 1479. Manzione, L. T. Polym. Eng. and Sci., 1981, 21, 1234. Kubiak, R. S.; Harper, R. C. SPI Preprints, 35th Annual Technical Conference, 1980, 22-C-l. Levy, N. ACS ORPL Preprints, 1981, 45, 485. Kamal, M. R.; Ryan, M. E. Polym. Eng. and Sci., 1980, 20, 859. Kamal, M. R. Polym. Eng. and Sci., 1974, 14, 231. Kamal, M. R.; Sourour, S. Polym. Eng. and Sci., 1973, 13, 59.



282


9. Haran, E. N.; Gringras, H.; Katz, D. J . Appl. Polym. S c i . , 1965, 9, 3305. 10. Saunders, T. F.; Levy, M. F.; Sevino, J . F. J. Polym. S c i . , 1967, 5, 1609. 11. Lipshitz, S. D.; Macosko, C. W. J . Appl. Polym. S c i . , 1977, 21, 2029. 12. Lee and Neville, "Handbook of Epoxy Resins"; McGraw-Hill 1967 13. Holtzman, Κ. Α., B e l l Laboratories, Murray Hill, N.J.; Manzione, L. T., B e l l Laboratories, Murray Hill, N.J.; unpublished results. 14. Castro, J . M.; Macosko, C. W. SPE Preprints, 38th Annual Technical Conference (May, 1980). 15. Lee, L. J . ; Ottino, J . M.; Ranz, W. E.; Macosko, C. W. Polym. Eng. and S c i . , 1980, 20, 868. RECEIVED

December 2,

1982


Epoxy Resin Chemistry II - American Chemical Society

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