Freeman & Carroll식과 Kissinger식에 의한 DGEBA-CTBN/MDA계의

열분해 활성화 에너지

송영욱, 심미자．, 김상욱

서울시립대학교 화학공학과, 생명과학과．

Thermal Decomposition Energy of DGEBA-CTBN/MDA System

by Freeman & Carroll Equation and Kissinger Equation

Y. W. Song, M. J. Shim． and S. W. Kim

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

Dept. of Life Sci., Seoul City Univ.．

Introduction

In these days, many materials are demanded some characteristics such as anti- chemicals, electrical insulation, thermal stability for various industrial purposes and testing methods have been proposed by many investigators. In this paper, rubber copolymer was introduced to epoxy resin system as toughening agent and thermal decomposition activation energy of this system was studied by Freeman & Carroll equation[1,2] and Kissinger equation[2∼4].

Freeman & Carroll equation is

[eqn: rm-{ DELTA ln (dw/dt)} over { DELTA ln W_r}~=~ Ea over R {DELTA T^-1 }over{ DELTA ln W_r} ~- ~n] (1)

where, dw/dt is rate of weight loss, W r is weight loss at a time, Ea is activation energy, R is gas constant, T -1 is inversion of temperature, and n is reaction order. Kissinger equation is

[eqn: rm -ln left( beta over T_m ^2 right)~=~ Ea over R 1over T_m ~-~ ln left(AR over Ea right)] (2)

where, q is heating rate, T m is peak temperature of DTG graph, and A is pre-exponential factor.

Experiment

Epoxy resin was diglycidyl ether of bisphenol A(DGEBA, Epon 828) obtained from Shell Co., curing agent was 4,4'-methylene dianiline(MDA) supplied by Fluka Chemie AG. and toughening agent was carboxyl-terminated butadiene acrylonitrile copolymer(CTBN, 1300×8) by B. F. Goodrich. To modify epoxy resin with rubber copolymer, DGEBA was reacted with CTBN at 150℃, for 30 min. After this, the compound was cured with MDA and it was analyzed by TGA. Then, thermal decomposition activation energy was calculated by Freeman & Carroll equation and Kissinger equation.

Results and Discussion

When DGEBA-CTBN/MDA system was analyzed by TGA, thermograms of this system at the heating rate of 50 ℃/min were shown in Fig. 1.

Fig. . TG and DTG graphs for DGEBA-CTBN/MDA system at the heating rate of  50 ℃/min.

TG was almost stable in initial state and the graph sharply decreased from 356.6℃. Total weight loss of this system was 86.39 % and the fraction of weight loss from 356.6℃ to 501℃ was 80.72 %. Thermal decomposition temperature(Td) was about 370℃. The DTG curve presented the thermal decomposition reaction rate with the assumption that the rate of weight loss was proportional to the rate of thermal decomposition. The temperature of peak on DTG graph that is the temperature of maximum decomposition rate(Tm) was 406.2℃.

Fig. . Fitting curve of Freeman & Carroll parameters for DGEBA-CTBN/MDA system with the heating rates of     50 ℃/min.

From the relationship between [eqn: DELTA]TG and [eqn: DELTA]DTG, Freeman & Carroll parameters were obtained and they depicted in Fig. 2. The fitting curve formula is Y=-0.21X +1.30. From this fitting curve, thermal decomposition activation energy was calculated from slope. Thermal decomposition activation energy increased with the increment of heating rates of TGA and the values were listed in Table 1. So, it was confirmed that thermal stability of DGEBA-CTBN/MDA system was more excellent when the heating rate of TGA was high.

Table . Thermal Decomposition Energy of DGEBA-CTBN/MDA         System with the Various Heating Rates.

Heating rate (℃/min)	5	10	20	50
Activation energy (kJ/mol)	87.5	133.2	148.0	174.8

Fig. . Plot of heating rates vs. peak temperatures on DTG curves for DGEBA-CTBN/MDA sysem by TGA analysis.

To use Kissinger equation, heating rates vs. Tm was plotted in Fig. 3. Because heating rates effected on decomposition weight loss rate, Tm increased with the increment of heating rates. From Fig. 3, Kissinger parameters were depicted in Fig. 4. In Fig. 4, fitting curve was obtained similar to Freeman & Carroll parameters to use the relation between -ln(□/Tm2) and 1/Tm × 103. Decomposition activation energy was calculated from the slope of fitting curve and pre-exponential factor was calculated from Y intersect. The fitting curve formula was Y=21.70X -22.77. Then, decomposition activation energy was 180.4 kJ/mol and pre-exponential factor was [eqn: rm 1.67×10^8~ s^-1]. Decomposition activation energy of DGEBA-CTBN/MDA system was larger than that of DGEBA/MDA/CTBN system and pre-exponential factor of DGEBA-CTBN/MDA system was larger than that of DGEBA/MDA/CTBN system, too. From this results, it confirmed that thermal stability of pretreated DGEBA-CTBN/MDA system was excellent than that of DGEBA/MDA/CTBN system.

References

1. E. S. Freeman and B. Carroll, J. Phys. Chem., 62, 394(1958)

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

3. T. Ozawa, J. Therm. Anal., 2, 301(1975)

4. Y. W. Song, M. J. Shim and S. W. Kim, J. Korean Ind. & Eng. Chem., 7, 356(1996)

Fig. . Plot of -ln(□/Tm2) vs. 1/Tm × 103 for DGEBA-CTBN/MDA system with the various heating rates of TGA.