Freeman & Carroll 식에 의한 DGEBA/MDA/GN 계의 열분해 활성화에너지

안현수, 양영석*, 심미자**, 김상욱

서울시립대학교 화학공학과, *한국원자력 연구소,

**서울시립대학교 생명과학과

Thermal Degradation Activation Energy of DGEBA/MDA/GN System by Freeman & Carroll Eqaution

H. S. An, Y. S. Yang*, M. J. Shim** and S. W. Kim

Dept. of Chem. Eng., The Univ. of Seoul

*Korea Atomic Energy Research Institute

**Dept. of Life Sci., The Univ. of Seoul

1. Introduction

Epoxy resin system has not only good mechanical properties but also excellent electrical insulating property. Therefore, it has been used as electrical insulating materials with the form of coating, casting, molding and encapsulation, etc. It is usually operated at high temperature under high electrical field. The excess of the temperature rise in the insulator is one of the main causes of dielectric failure. For the stable supply of electric power, the thermal stability of the insulator is so important that many studies have been investigated by researchers in order to prolong the service and expectancy life under high temperature and electric field.

To investigate the thermal stability of polymeric insulators, thermogravimetry analyzer(TGA) which measures the weight loss as a function of temperature or time has been used. TGA experiments provide information on the characteristics of the thermal decomposition and thermal degradation kinetics of polymers. In thermal deagradtion kinetics, there are many equations such as Freeman's equation, Kissinger equation and Toop's equation, etc.1∼4). These equations provide the activation energy of materials and estimate their thermal stability.

In this study, the thermal degradation activation energy of diglycidyl ether of bisphenol A(DGEBA)/4,4'-methylene dianiline(MDA)/gluatronitrile(GN) system was estimated by Freeman & Carroll equation.

Freeman & Carroll equation is as follows.

[eqn: {DELTA~log dC/dt} over {DELTA~log(1-C)} ~=~n- LEFT ( {E over 2.3R} RIGHT ) LEFT ( DELTA(1/T) over {DELTA log(1-C)} RIGHT )]

where, [eqn: DELTA] : the difference value for the constant [eqn: DELTA](1/T), C : the fraction of weight loss, T : temperature,  E : activation energy, R : gas constant and n : the order of the reaction.

2. Experiment

In this study, base resin was DGEBA type epoxy and curing agent was MDA. GN was used as a reactive additive and its role was to improve toughness.

Well mixed DGEBA, MDA(30 phr) and various contents of GN were cured at 150℃ for 1.0 hr after curing at 80℃ for 1.5 hr. To investigate thermal degradation kinetics, TGA was performed at various heating rates. Under the nitrogen atmosphere, their experimental temperature ranges were from 50℃ to 600℃.

3. Results and Discussion

Fig.  TGA and DTG curves of DGEBA/MDA/GN(0 phr) system at the heating rate of 10 ℃/min

Typical curves of TG and derivative thermogravimetry(DTG) for DGEBA/MDA/GN(0 phr) system at the heating rate of 10 ℃/min was shown in Fig. 1.  On the TG curves, the weight of the sample is almost stable below a temperature and above the temperature, the weight loss increases rapidly in the short temperature range. The total weight loss at 600℃ was about -73%.

To obtain degradation activation energy by means of Freeman & Carroll equation, the values of [eqn: {DELTA log(dC/dt)} over {DELTA log(1-C)}] and [eqn: - {DELTA (1/T)} over {DELTA log(1-C)}] could be calculated from TG and DTG curves in Fig. 1 and the relationship between two terms was displayed in Fig. 2.

Fig.  The relationship bewteen □log(dC/dT)/□log(1-C) and □(1/T)/□log(1-C) in DGEBA/MDA/GN(0 phr) system at the heating rate of 10 ℃/min.

Fig.  Activation energy of DGEBA/MDA/GN system with the different GN contents at the heating rate of 10 ℃/min.

Fig. 3 shows the activation energies of DGEBA/MDA/GN system with the different GN contents at the heating rate of 10 ℃/min. In the GN contents of 0, 5, 10 and 15 phr, the activation energies are 1.04×103, 1.43×103, 0.57×103. and 0.40×103 kJ/mol, respectively. In the GN content of 5 phr, the activation energy increased. But above 5 phr, the activation energy decreased with the increment of GN contents. It assumed as follows. As GN contents increased, the crosslinked density of the samples decreased. Thus, the thermal decomposition increased.

References

1. M. Day, J. D. Cooney and D. M. Wiles, J. Appl. Polym. Sci., 38, 323(1989)

2. E. S. Freeman and B., J. Carrol, Phys. Chem., 62, 394(1958)

3. D. J. Toop, IEEE Trans. Dielectr. Electr., Insul., EI-7, 32(1972)

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