열분석에 의한 DGEBA/MDA/MDA-endcapped CTBN

계의 경화반응 연구

이재영, 심미자*, 김상욱

서울시립대학교 화학공학과, 생명과학과*

Calorimetric Study of Cure Reaction for DGEBA/MDA/

MDA-endcapped CTBN System

J. Y. Lee, M. J. Shim* and S. W. Kim

Dept. of Chem. Eng., Seoul City University

Dept. of Life Sci., Seoul City University*

Introduction

There have been many methods to enhance the toughness of cured epoxy resin and one of the well-known methods is to incorporate various amounts of reactive liquid rubber such as carboxyl-terminated butadiene acrylonitrile(CTBN) copolymer, amine-terminated butadiene acrylonitrile(ATBN) copolymer, epoxy-terminated butadiene acrylonitrile(ETBN) copolymer and hydroxyl-terminated butadiene acrylonitrile(HTBN) copolymer1∼4. However, the compatibility between epoxy resin and rubber compounds is low and the rubber compounds do not take part in the cure reaction effectively. Due to the incompatibility, the properties of cured epoxy system can't reach the required values, so the end chains of rubber compound should be capped with proper compound. In this study, CTBN was endcapped with 4,4'-methylene dianiline(MDA).

To study cure kinetics of the epoxy system, autocatalytic cure rate expressions5∼7 were used and they were

[eqn: rmdot□ ~= ~ d□ over dt ~=~ (ｏ sub1 + ｏ sub2 □ sup m )(1-□) sup n]             (1)

[eqn: rm k sub1 ~=~ ({d alpha} overdt ) sub t=0]	(2)

[eqn: rm m ~+ ~n~=~2]	(3)

[eqn: rm m ~ = ~ {ln{({ dot□`sub p /(1-□ sub p ) sup 2-m ~ - ~ ｏ sub 1} over {(2-m) ｏ sub 1 □ sub p sup 1-m / (m-2□ sub p )})}} over {ln□ sub p}]	(4)

[eqn: rm ｏ sub 2 ~ = ~ {(2-m)ｏ sub 1 □ sub p sup 1-m} over {m-2□ sub p }]	(5)

Where, □ : cure rate, □ : cure degree of monomers, k1, k2 : cure rate constants, m, n : reaction orders, □p : degree of cure at exothermic peak and □p : cure rate at exothermic peak.

Experiment

Diglycidyl ether of bisphenol A(DGEBA, Epon 828 grade) supplied by Shell Co. was used as a base resin and 4,4'-methylene dianiline(MDA) was used as a curing agent. Carboxyl-terminated butadiene acrylonitrile copolymer(CTBN) manufactured by B. F. Goodrich Co. under the trade name of Hycar 1300×8 was used as a toughener8,9. To give better compatibility between epoxy resin and CTBN rubber, CTBN was capped with MDA by the formation of amide linkage formed by the reaction between primary amine in MDA and carboxylic acid in CTBN.

DGEBA and MDA-endcapped CTBN(0, 10 phr) were well mixed at 80□ for 5 mins and MDA(30 phr) was added to the mixture under 80□ to prevent the cure reaction during the mixing. To study the cure kinetics, the sample was analyzed by isothermal DSC method at 80, 90, 100, 110 and 120□ and the data were introduced to Eqs.(1∼5).

Results and Discussion

Fig.1 shows the isothermal cure curves for DGEBA/MDA system without MDA-endcapped CTBN at five different temperatures. With the increment of cure temperature, cure rate increased and the time to be the exothermic peak decreased. k1 can be obtained from the Fig.1 and Eq.2, and the values are listed in Table 1. As cure temperature increases, k1 value increases. From the assumption that the area of the curve in Fig.1 is proportional to the heat evolved during the cure and the heat is

Table 1. Kinetics parameters for DGEBA/MDA system with and without

Fig. Isothermal cure curves for DGEBA/MDA system without

MDA-endcapped CTBN.

MDA-endcapped CTBN(10 phr).

MDA-endcapped CTBN Content (phr)	Temp (K)	□px102	□p	k1x102 (min-1)	Ea1 (kcal/mol)	k2x102 (min-1)	Ea2 (kcal/mol)	m	n
0	353	1.30	0.42	0.3	12.86	4.32	10.49	0.91	1.09
	363	1.83	0.41	0.37		6.20		0.88	1.12
	373	2.73	0.39	0.56		9.31		0.84	1.16
	383	4.18	0.41	1.01		14.52		0.89	1.11
	393	5.94	0.39	1.89		18.91		0.88	1.12
10	353	1.39	0.41	0.52	11.21	4.35	11.09	0.94	1.06
	363	2.01	0.34	1.10		5.41		0.88	1.12
	373	3.13	0.35	1.21		9.85		0.82	1.18
	383	4.59	0.36	1.91		13.48		0.86	1.14
	393	6.90	0.34	2.98		20.68		0.82	1.18

proportional to the extent of conversion. Therefore, isothermal conversion curves can be obtained and are shown in Fig.2. When k1, □p and □p are introduced to Eq.3∼5, k2, m and n can be obtained and they are also listed in Table 1. To get activation energy for k1 and k2 by Arrhenius equation, the relationship between -ln(k) and 1/T x 103 is plotted in Fig.3 and two straight lines are obtained. From the

activation energy can be calculated and also listed in Table 1. By the same method, kinetic parameters for DGEBA/MDA/MDA-endcapped CTBN(10 phr) are calculated and listed in Table 1.

Fig. Conversion vs. time for DGEBA/MDA system without

MDA-endcapped CTBN.

References

1. A. Takemura, K. Shiozawa, B. I. Tomita and H. Mizumachi, J. Appl. Polym. Sci.,

31, 1351(1986)

2. C. Domenici, G. Levita, A. Marchetti and V. Frosini, ibid., 34, 2285(1987)

3. S. Varughese and D. K. Tripathy, ibid., 49, 1115(1993)

4. L. T. Manzione and J. K. Gillham, ibid., 26, 889(1981)

5. M. E. Ryan and A. Dutta, Polymer, 20, 203(1979)

6. A. Dutta, M. E. Ryan, J. Appl. Polym. Sci., 24, 635(1979)

7. M. R. Keenan, ibid., 33, 1725(1987)

8. J. Y. Lee, M. J. Shim and S. W. Kim, Mater. Chem. & Phys., 44, 74(1996)

9. J. Y. Lee, M. J. Shim and S. W. Kim, Proc. of IUMRS-ICA-'94, Taiwan,

699(1995)

Fig. -ln k vs. 1/T x 103 for DGEBA/MDA system without

MDA-endcapped CTBN.