Polyamide/MDA의 비율에 따른 에폭시수지 계의 경화반응 속도론

김양림, 최형기*, 김상욱

서울시립대학교 화학공학과, *국립기술품질연구원 화학부

Cure Kinetics of Epoxy System with Different Ratio of Polyamide/MDA

Y. L. Kim, H. K. Choi* and S. W. Kim

Dept. of Chem. Eng., The Univ. of Seoul., Seoul 130-743

*Div. of Chem., NITQ, Kwachon 427-010

Introduction

Cured bisphenol A type epoxy resins with MDA are fairly brittle. This brittleness is evidently due to the existence of a highly crosslinked structure. Most efforts to modify the toughness involve the addition of other polymer materials. The line between resinous modifiers in this sense and curing agents is not always sharp, since the modifying resins often have functional groups capable of reacting with the epoxy resin.

In this study, diglycidyl ether of bisphenol A(DGEBA) was mixed with different ratio of 4,4ˇ-methylene dianiline(MDA) and Polyamide, and the cure kinetics were analyzed by DSC. To calculate and compare the values of activation energy, pre-exponential factor and rate constant, Kissinger and Arrhenius equations were used and they are.

[eqn: -ln( {q } over { { T}`_{p} ^{2 } } ) { }^{ } = { }^{ } { { E}_{ a} } over { R} { 1} over { { T}_{p } } { }^{ } - { }^{ } ln( { AR} over { { E}_{ a}} )]     : Kissinger equation

[eqn: k { }^{ } = { }_{ } A { }^{ } exp (- { { E}_{a } } over {RT} )]                        : Arrhenius equation

where, [eqn: q] : heating rate, [eqn: { T}_{p }] : a temperature where maximum conversion rate occurs on DSC curve, [eqn: { E}_{a }] : curing activation energy, [eqn: A] : pre-exponential factor, [eqn: R] : gas constant and [eqn: k] : rate constant.

Experiment

DGEBA(Epon 828, Shell, Co.) was used as a base resin, MDA(Fluka Chemie, AG) and Polyamide(LA 0331, Lucky) were used as a curing agent. Various equivalent weights(Table 1) of MDA and Polyamide which had melted at 100℃ were mixed with DGEBA and the sample was placed at -13℃ to prevent the cure reaction during store. The sample(3∼5□) was placed in DSC cell and DSC analyzer was operated at the heating rates of 5, 10, 15 and 20 ℃/min. Nitrogen gas was flowed at 80 □/min to prevent the oxidation of the sample.

Table 1. The Equivalent Weight of Between MDA and Polyamide for DGEBA(10g)

	System Ⅰ	System Ⅱ	System Ⅲ	System Ⅳ	System Ⅴ
MDA	2.60g	1.95g	1.30g	0.65g	0g
PA	0g	3.23g	2.15g	3.23g	4.30g

Results and Discussion

Fig.1 Dynamic DSC curves for System Ⅱ at various heating rates.

Fig.2 Dynamic DSC curves for System Ⅳ at various heating rates.

Fig.1 shows DSC curves for System Ⅱ at various heating rates. All of DSC curves showed one maximum peak and with the increment of heating rate, the temperature at the maximum peak was increased and the shape of peak was elevated.

Fig.2 shows DSC curves for System Ⅳ at various heating rates. All of DSC curves showed two maximum peak. The first step is appeared in the range of 110.4 ∼ 141.5℃ and the second step is in the range of 141.8 ∼ 186.5℃. As shown in Fig.1, the temperature at the maximum peak of first and second steps were increased  with the increment of heating rate, and the shape of peak was elevated. Other systems were also analyzed by DSC at various heating rates and temperatures at maximum cure peak, [eqn: { T}_{p }]  were listed on Table 2.

Kissinger equation has merits that it is easy to apply and can easily obtain activation energy as well as pre-exponential factor from the relationship between heating rate, [eqn: q] and the temperature at the maximum peak, [eqn: { T}_{p }]. To calculated the activation energy and pre-exponential factor,[eqn: -ln(q/ { T}`_{p } ^{2 } )] as a function of  [eqn: 1/{ T}_{ p} × { 10}^{ 3}] for DGEBA/MDA/Polyamide(10 phr) system was plotted in Fig.3. The slope of the straight line was 5.70 and the intersection was -3.12. Therefore, the     Table. 2 [eqn: { T}_{p }] Values for All Systems

	System Ⅰ	System Ⅱ	System Ⅲ	System Ⅳ		System Ⅴ
5 oC/min	149.5℃	146.9℃	144.1℃	107.6℃	151.1℃	105.2℃
10 oC/min	168.0℃	165.7℃	163.4℃	121.8℃	174.5℃	119.8℃
15 oC/min	180.1℃	177.8℃	176.3℃	133.4℃	188.2℃	128.5℃
20 oC/min	189.1℃	187.4℃	185.3℃	139.3℃	196.5℃	135.1℃

Fig.3 Plot of -ln(q/Tp2) vs. 1/Tp × 103 for System Ⅱ by Kissinger equation.

Fig.4 Plots of -ln(q/Tp2) vs. 1/Tp × 103 for System Ⅳ by Kissinger equation.

activation energy was 11.33 Kcal/mol and the pre-exponential factor was 2151 sec-1. These parameters were introduced to Arrhenius equation and the kinetic rate constant, [eqn: k] was expressed as follows.

[eqn: k = 2151 exp(-11.33× { 10}^{ 3} /RT)]

From the above equation, [eqn: k] at 80℃ was 2.09 × 10-4 sec-1.

By the same method in Fig.3, the relationship between [eqn: -ln(q/ { T}`_{p } ^{2 } )] and [eqn: 1/ { T}_{ p} × { 10}^{ 3}] for System Ⅳ was plotted in Fig.4. The activation energy and pre-exponential factor were also calculated from the slopes and the intersections, respectively and those values were listed in Table 3. The kinetic rate constant at 80℃ of the first peak was 2.05 × 10-4 sec-1 and that of the second peak was 3.71 × 10-4 sec-1. To calculate and compare the value of activation energy, pre-exponential factor and rate constant, other systems were interpreted by Kissinger and Arrhenius equations and those parameters were listed on Table 3. The kinetic rate constant was increased with the increment of equivalent weight of Polyamide.

Table 3. Slope, Intersection, Activation Energy, Pre-exponential Factor and Kinetic             Rate Constant for DGEBA System with Different Ratio of Polyamide/MDA

	System Ⅰ	System Ⅱ	System Ⅲ	System Ⅳ		System Ⅴ
Slope	5.95	5.70	5.52	5.11	5.93	6.36
Intersection	-3.60	-3.12	-2.80	-1.54	-5.34	-6.56
Ea (Kcal/mol)	11.84	11.33	10.97	10.15	11.78	12.64
A (sec-1)	3630	2151	1513	397	20612	74880
k × 104 (sec-1)	1.71	2.09	2.43	2.05	3.71	10.48

Conclusion

All of the DSC curves for System Ⅳ showed two maximum peaks and those for the others systems showed one maximum peak. The temperature of maximum peak of all system increased with the increment of heating rate. The rate constants, k at 80℃ were 1.71 × 10-4, 2.09 × 10-4, 2.43 × 10-4 and 10.48 × 10-4 sec-1 for System Ⅰ, Ⅱ, Ⅲ and Ⅴ, respectively and the rate constant of the first peak for System Ⅳ was 2.05 × 10-4 and that of the second peak for System Ⅳ was 3.71 × 10-4.

References

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