Fast Curing Epoxy-Episulfide Resin for Uses at ... - ACS Publications

8 Fast Curing Epoxy-Episulfide Resin for Uses at Room Temperature Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 28, 2016 | http://pubs.acs.org Publication Date: June 8, 1983 | doi: 10.1021/bk-1983-0221.ch008

WENHSIUNG KU and JAMES P. BELL University of Connecticut, Institute of Materials Science, Storrs, CT 06268

A fast curing epoxy-episulfide resin system has been developed which has important advantages over standard room temperature formulations. Rheo vibron and thermomechanical measurements show two transition temperatures, at approximately 75°C and 135°C, when the polyamide curative Versamide 140 is used. The area under the tan δ curve is very broad and indicates good toughness. The heat of polymerization i s very low. Water absorption is lower than for a control system without episulfide. The presence of the episulfide homopolymer network in the standard epoxy matrix has a slight lowering effect on the shear strength, but the difference between wet and dry properties is small.

Development o f an epoxy-type r e s i n system which w i l l become hard i n 5-20 minutes f o r s m a l l q u a n t i t i e s a t room temperature, without l o s s o f p r o p e r t i e s r e l a t i v e to standard room temperature epoxy r e s i n s , has been a goal o f epoxy research f o r many years (1). Such a r e s i n would appear to have use i n a v a r i e t y of a p p l i c a t i o n s near room temperature, from d e n t i s t r y and orthopedic bone cement, to i n d u s t r i a l and e l e c t r o n i c assembly operations where high room temperature curing r a t e s and good p r o p e r t i e s are required. Our approach has been to s y n t h e s i z e the d i e p i s u l f i d e r e s i n corresponding to the normal b i s p h e n o l A type diepoxide r e s i n s . A polyamide type c u r i n g agent (Versamide 140) was used because o f our p a r t i c u l a r i n t e r e s t i n orthopedic adhesives, i . e . "bone cement". Some o f the p r o p e r t i e s were therefore t a i l o r e d to be optimum near body temperature. We have found very l i t t l e p r i o r l i t e r a t u r e on d i e p i s u l f i d e r e s i n s . As prepared, the d i e p i s u l f i d e r e s i n analog o f DGEBA i s a c r y s t a l l i n e s o l i d which must be heated above i t s m e l t i n g temperature f o r r e a c t i o n . Charlesworth (2) has reported mechanical r e l a x a t i o n behavior of e p o x y - e p i s u l f i d e p o l y 0097-6156/83/0221-0153$06.00/0 © 1983 American Chemical Society

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

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mers p r e p a r e d a t e l e v a t e d t e m p e r a t u r e . L e u e t a l . (.3,4) h a v e r e p o r t e d i n t h e p a t e n t l i t e r a t u r e t h a t such polymers have an accelerated rate of cure. Experimental

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 28, 2016 | http://pubs.acs.org Publication Date: June 8, 1983 | doi: 10.1021/bk-1983-0221.ch008

A s t a n d a r d b i s p h e n o l A t y p e e p o x y r e s i n , Epon 828 f r o m S h e l l C h e m i c a l Co. U.S.A., a n d a n amine t y p e c u r i n g a g e n t , V e r s a m i d 140 f r o m G e n e r a l M i l l s C h e m i c a l , U.S.A., w e r e u s e d a s r e c e i v e d . The d i e p i s u l f i d e r e s i n was s y n t h e s i z e d f r o m Epon 8 2 8 . S y n t h e s i s a n d F o r m u l a t i o n , The s y n t h e s i s method i s b a s e d upon t h e w o r k o f V. C a l o e t a l . ( 5 ) , i n w h i c h o x i r a n e s were c o n v e r t e d into thiiranes:

0 /\

/ \

CH -CH

-CH-CH

0

2

s / \

CH -CH

-CH-CH

S

3

2

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/ \

CF C00H

+

C=S

2

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0

DEPPE

S NMBTL To a r o u n d b o t t o m f l a s k c o n t a i n i n g 13.6g. n - m e t h y l b e n z o t h i a z o l - 2 - t h i o n e (NMBTT), 17 gm C f ^ O J E L a n d 100 m l . C H C 1 , was added s l o w l y a s o l u t i o n o f 14.5 g. Epon 828 i n 100 m l . C H C 1 w h i c h h a d b e e n p l a c e d i n a 250 m l . séparatory f u n n e l . The r e a c t i o n was c a r r i e d o u t w i t h s t i r r i n g a t room t e m p e r a t u r e (22°C) f o r t h i r t y minutes. G r o u n d s o d i u m c a r b o n a t e ( 2 0 g.) was t h e n added i n t o t h e f l a s k a n d t h e e n t i r e s y s t e m was s t i r r e d f o r 3 hours. T h e a d d i t i o n o f s o d i u m c a r b o n a t e was n o t o n l y t o n e u t r a l i z e the CF C00H i n the r e a c t i o n m i x t u r e , b u t a l s o t o i n i t i a t e t h e f o r m a t i o n o f e p i s u l f i d e p r o d u c t . The s o d i u m t r i f l u o r o a c e t a t e f o r m e d d u r i n g n e u t r a l i z a t i o n was f i l t e r e d o u t b y means o f a Buchner f u n n e l . The f i l t r a t e was d r i e d u n d e r vacuum t o f o r m a v e r y v i s c o u s y e l l o w i s h l i q u i d w h i c h was r e a d y f o r p u r i f i c a t i o n . 2

2

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S i l i c a g e l ( S i l i c a r CC-7 f r o m M a l l i n c k r o d t C h e m i c a l , I n c . ) was p o u r e d i n t o a c o l u m n (575 mm l o n g and 1 cm d i a m e t e r ) and was t i g h t l y packed w i t h t h e a i d o f a v i b r a t o r . T h i s c o l u m n was u s e d to i s o l a t e the d i e p i s u l f i d e r e s i n . Two grams o f v i s c o u s l i q u i d o b t a i n e d a s i n t h e a b o v e s e c t i o n was d i l u t e d b y t h e a d d i t i o n o f 10 m l . o f s o l v e n t m i x t u r e o f t o l u e n e and a c e t o n e (100:1 b y v o l ume). The d i l u t e d s a m p l e was t h e n p o u r e d i n t o t h e c o l u m n . After t h e s a m p l e was c o m p l e t e l y a b s o r b e d b y s i l i c a g e l , t h e e l u t i o n s o l v e n t ( t o l u e n e : a c e t o n e = 100:1) was r u n t h r o u g h t h e column. The s o l v e n t e f f l u e n t was c h e c k e d a t v a r i o u s t i m e i n t e r v a l s by a t h i n l a y e r c h r o m a t o g r a p h i c (TLC) t e c h n i q u e . The f i r s t e l u t e d p r o d u c t was c o l l e c t e d and d r i e d u n d e r vacuum. A w h i t e powder l i k e p r o d u c t (DEPPE r e s i n ) was o b t a i n e d w i t h an o v e r a l l y i e l d o f a p p r o x i m a t e l y 80%. I n f r a r e d and NMR s p e c t r a c o n f i r m e d t h e p r o d u c t s t r u c t u r e , as shown i n F i g u r e 1 and 2. For p r o d u c t i o n of l a r g e r q u a n t i t i e s , t h e c h r o m a t o g r a p h i c p u r i f i c a t i o n method was t e d i o u s and i t was f o u n d t h a t t h e p r o d u c t c o u l d be p u r i f i e d by r e p e a t e d w a s h i n g s o f t h e p r o d u c t w i t h a s o l u t i o n c o n t a i n i n g 50 p a r t s m e t h a n o l t o one p a r t w a t e r . The p r o d u c t d i e p i s u l f i d e was a c r y s t a l l i n e s o l i d . I t was found a f t e r s e v e r a l t r i a l s t h a t i t c o u l d be m a i n t a i n e d i n s o l u t i o n f o r a f e w h o u r s w i t h o u t c r y s t a l l i z a t i o n i n a m i x e d epoxy r e s i n system. The s y s t e m was c o m p r i s e d o f 90% E p o n 828 , 5% Epon 836 and 5% Epon 1001. These t h r e e r e s i n s a r e a l l of the 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 t y p e , d i f f e r i n g o n l y i n t h e number o f b i s p h e n o l A r e p e a t u n i t s i n t h e m o l e c u l e . By u s i n g s u c h a m i x t u r e a b e t t e r c o h e s i v e e n e r g y d e n s i t y m a t c h i s o b t a i n e d , and t h e b r o a d m o l e c u l a r w e i g h t d i s t r i b u t i o n may a l s o i n h i b i t c r y s t a l l i z a t i o n o f the d i e p i s u l f i d e . The f i n a l r e s i n s y s t e m t h u s c o n t a i n s t h e l i q u i d d i e p i s u l f i d e - d i e p o x i d e m i x t u r e , and l i q u i d c u r i n g a g e n t unit. G e l a t i o n Time Measurement. A m o d i f i e d method f r o m t h a t d e s c r i b e d i n ASTM D2471 was a d o p t e d f o r t h e measurement o f g e l a t i o n t i m e f o r t h i s new r e s i n s y s t e m . E p o x y - e p i s u l f i d e r e s i n and V e r s a m i d 140 w e r e w e i g h e d i n t o s e p a r a t e r e g i o n s o f one s m a l l aluminum d i s h and b r o u g h t t o room t e m p e r a t u r e (23°C). The two r e s i n s w e r e n o t p e r m i t t e d to c o n t a c t each o t h e r i n the d i s h . The two components w e r e t h e n m i x e d t h o r o u g h l y f o r 30 s e c . b y t h e u s e o f a s p a t u l a . The r e s u l t i n g r e s i n was t r a n s f e r r e d t o a s i l i c o n r u b b e r m o l d w h i c h m e a s u r e d 1/4" X 3/16" X 3/16". The r u b b e r m o l d c o n t a i n i n g t h e s a m p l e was p l a c e d on an i n s u l a t e d c a r d b o a r d s u r f a c e i n s t i l l a i r a t 23°C. The r e s i n was t h e n p r o b e d w i t h a wooden a p p l i c a t o r s t i c k (6 i n c h e s l o n g , f r o m TOR S c i e n t i f i c ) , h o l d i n g t h e s t i c k perpendicular to the r e s i n surface. The g e l a t i o n t i m e was t a k e n as t h e p o i n t a t w h i c h t h e r e s i n no l o n g e r a d h e r e d t o t h e end o f the probe. Sample P r e p a r a t i o n . F o r an e p o x y r e s i n s y s t e m , a t y p i c a l method o f s a m p l e p r e p a r a t i o n f o r m e c h a n i c a l t e s t i n g i s as f o l l o w s : r e s i n





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and c u r i n g agent are mixed, t r a n s f e r r e d to the mold, vacuumed f o r about 40 min. to e l i m i n a t e a i r i n the system, and then cured a t a given temperature. I t i s , however, extremely d i f f i c u l t to o b t a i n good samples f o r an e p o x y - e p i s u l f i d e system by t h i s method because the system cures so r a p i d l y that there i s no way to vacuum the a i r out of the sample b e f o r e i t g e l s . Since a c o n s i d e r a b l e amount of a i r i s trapped during mixing, one method of a i r e x c l u s i o n i s to mix the r e s i n s and c u r i n g agent under vacuum. Figure 3 shows the scheme o f a mechanical mixer used i n t h i s work. The mixing blades were made of T e f l o n and were trimmed and bent to match the curvature of the vacuum f l a s k . The e p o x y - e p i s u l f i d e r e s i n was weighed i n t o the vacuum f l a s k and the c u r i n g agent was s t o r e d i n the c a l i b r a t e d separatory f u n n e l . Under vacuum, the T e f l o n stop cock of the separatory f u n n e l was opened to permit the c u r i n g agent to be p u l l e d i n t o the vacuum f l a s k , and the r e s i n s were mixed by the r o t a t i n g mixing b l a d e s . The mixed sample was then poured i n t o a g l a s s mold and cured i n a room maintained at 37°C. A l l samples were cured f o r 7 days a t 37°C. The wet specimens were prepared by soaking the cured samples i n a s a l i n e s o l u t i o n (0.9 Ν NaCl s o l u t i o n ) at 37°C. The water absorption was measured p e r i o d i c a l l y u n t i l no measurable weight change was observed. Thermal C h a r a c t e r i z a t i o n . The DuPont 941 Thermal Mechanical Ana l y z e r (TMA), attached to a model 900 thermal a n a l y z e r , was used f o r the measurement of g l a s s t r a n s i t i o n temperature (Tg). The h e a t i n g r a t e was s e t a t 10 °C/min. For wet samples, about 0.05 ml o f d i s t i l l e d water was dropped i n t o the TMA sample holder tube b e f o r e running the experiments, to maintain the sample i n a water saturated s t a t e during the measurement. The DuPont 990 Thermal Analyzer w i t h a DuPont DSC c e l l p l u g - i n module was used f o r the measurement of heat of r e a c t i o n . E p o x y - e p i s u l f i d e r e s i n and Versamid 140, which were weighed i n t o an aluminum d i s h , were mixed by s p a t u l a f o r 20 sec. and quenched with l i q u i d n i t r o g e n at once. At the same time, the DSC c e l l was cooled down to -50°C w i t h the a i d of l i q u i d n i t r o g e n . One p i e c e (about 10-20 mg) of quenched sample was t r a n s f e r r e d to a p r e weighed hermetic cup which had already been cooled i n l i q u i d n i t r o g e n . The sample was then placed on the sample p l a t f o r m i n s i d e the DSC c e l l and the experiment was performed by program ming the temperature from -50°C to 140°C w i t h a h e a t i n g r a t e of 5°C/min. The heat o f r e a c t i o n , ΔΗ, was then c a l c u l a t e d by the comparison w i t h the heat of f u s i o n of Indium, which was measured at the same c o n d i t i o n s . P h y s i c a l P r o p e r t y E v a l u a t i o n . A Rheovibron ( d i r e c t reading dyna mic v i s c o e l a s t o m e t e r , model RHEO-200, manufactured by Toyo Measuring Instruments Co.) was used to measure the temperature dependence o f the complex modulus and damping, tan 6, at 11 Hz. An O s c i l l o s c o p e OS-46 A/U ( S e n t i n e l E l e c t r i c Inc., P h i l a d e l p h i a ,


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F i g u r e 3.

Photograph o f apparatus f o r mixing s m a l l q u a n t i t i e s of r e s i n s w i t h c u r i n g a g e n t u n d e r vacuum.


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PA) was attached to help the phase adjustment and to monitor the preset o f optimum t e n s i o n . The shear s t r e n g t h measurement was conducted with an I n s t r o n t e n s i l e t e s t machine o f the constant-rate-of-crosshead movement type. A shear t o o l described i n ASTM D732 was used. The samples were run at a crosshead speed of 0.05 in/min.


Results and D i s c u s s i o n E v a l u a t i o n of E p o x y - E p i s u l f i d e Resin System. A p l o t of g e l a t i o n time with respect to the DEPPE content i n the sample, with the same numbers of equivalents of Epon 828 and Versamid-140, i s shown i n Figure 4. G e l a t i o n time i s d r a m a t i c a l l y reduced when a s m a l l amount of DEPPE i s introduced. The c u r i n g r e a c t i o n of a conventional epoxy r e s i n system i s governed by the n u c l e o p h i l i c a d d i t i o n of amine to the epoxide group. In the case of the e p o x y - e p i s u l f i d e r e s i n system, the r e a c t i o n of amine with the e p i s u l f i d e r i n g i s a l s o i n c l u d e d . K i n e t i c measurements, which w i l l be discussed i n a separate p u b l i c a t i o n , have shown that the a n i o n i c p o l y m e r i z a t i o n of the DEPPE i t s e l f p l a y s an important r o l e i n the high c u r i n g r a t e of t h i s system. Water absorption decreases as the amount of DEPPE i n the mixture i n c r e a s e s , as shown i n F i g u r e 5. Note that the data are f o r e q u i l i b r i u m water absorption i n s a l i n e s o l u t i o n not at room temperature, but a t 37°C. I t seems reasonable that the product formed i n the e p o x y - e p i s u l f i d e system, which i n v o l v e s many — S — l i n k a g e s , i s l e s s p o l a r than the product from a standard epoxy r e s i n system c o n t a i n i n g many hydroxyl groups a f t e r r e a c t i o n . I n c r e a s i n g the DEPPE content i n c r e a s e s both the dry and water-saturated g l a s s t r a n s i t i o n temperatures as measured by Thermomechanical Analyzer, as i l l u s t r a t e d i n Figure 6. Rheo v i b r o n data (Figures 7-10) g i v e a more d e t a i l e d understanding of the g l a s s t r a n s i t i o n of the e p o x y - e p i s u l f i d e system; a second t r a n s i t i o n a t vL35°C i s present and becomes more s i g n i f i c a n t as a greater p o r t i o n of DEPPE was introduced i n t o the sample. The two g l a s s t r a n s i t i o n temperatures correspond to two incompatible p o l y mer s t r u c t u r e s formed i n the amine cured e p o x y - e p i s u l f i d e r e s i n : one i s a conventional epoxy-amine r e s i n which has a Tg at approxi mately 75°C; the other seems to be an e p i s u l f i d e homopolymer which has a Tg above 130°C. Rheovibron data a l s o show that the system p o t e n t i a l l y has a higher upper use temperature than the Epon 828 - Versamid 140 system, s i n c e the e l a s t i c modulus, E', drops more s l o w l y . The area under the tan δ curve f o r t h i s system i s greater than that of a corresponding epoxy system. The areas under the damping curves are l i s t e d i n Table I . The data imply improved energy absorption c a p a b i l i t y f o r the new system.


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F i g u r e 5. E q u i l i b r i u m water a b s o r p t i o n f o r e p o x y - e p i s u l f i d e r e s i n system w i t h one e q u i v a l e n t of each of Epon 828 and Versamid-140 at 37°C.


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Fast Curing Epoxy-Episulfide Resin for Uses at ... - ACS Publications

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