Kissinger 식에 의한 천연 Zeolite/Epoxy 복합재료의 열분해속도론

김양림, 심미자*, 김상욱

서울시립대학교 화학공학과, *생명과학과

Thermal Decomposition Kinetics of Zeolite/Epoxy Composites

by Kissinger Equation

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

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

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

Introduction

Zeolites are crystalline aluminosilicate minerals and have large internal surface area due to the channels and pores available for the adsorption of low weight molecules. Therefore, zeolites have been used in many industrial fields as catalysts, molecular sieves, sorptive agents, ion exchange material, etc.[1]

The purpose of this paper is to investigate the thermal stability with the addition of zeolite for the diglycidyl ether of bisphenol A(DGEBA)/4,4'-methylene dianiline(MDA)/neopentyl glycol(NPG) system. Thermal decomposition kinetics of the DGEBA/MDA/NPG system filled with 5, 10, 15 and 20 phr of natural zeolite were analyzed by thermogravimetry(TG).

In this study, the expression derived by Kissinger equation was used to investigate the thermal decomposition kinetics. This expression allowed the calculation of kinetic parameters through the relationship between heating rates and the peak temperatures where maximum conversion rate occurred.[2~6]

Kissinger equation is

[eqn: rm -ln LEFT ( beta over {T }_{m } ^2 RIGHT )={{{E}_{d }}} over {{R} {T}_{m}} - ln( { { A}_{d } R } over { { E}_{d } } )]

where, □: heating rate, Tm: a temperature where maximum decomposition rate occurs on derivative thermogravimetry(DTG) curve, Ed: thermal decomposition activation energy, A: pre-exponential factor for thermal decomposition and R: gas constant.

Experiment

DGEBA(Epon 828, Shell Co.) was used as a base resin, MDA(Fluka Chemie. AG) was used as a curing agent and NPG(Aldrich Chemi. Co. Inc.) was used accelerator. Natural zeolite from Kampo area in Korea was used as a filler.

DGEBA and NPG(10 phr) were well mixed with dried natural zeolite(0, 5, 10, 15 and 20 phr) at 100oC and MDA(30 phr) was added to the mixtures at 80oC. The samples were cured at 150oC for 1 hr after curing at 80oC for 1.5 hr. The weighed sample (5-7 mg) was placed in TG furnace and the weight loss was measured at the heating rates of 5, 10, 15, and 20 oC/min from room temperature to 600oC. Nitrogen gas was flowed at 50 ml/min.

Results and Discussion

Fig. 1 TG and DTG curves for DGEBA/MDA/NPG system filled                  with  zeolite(10 phr) at 10oC/min

Fig. 1 shows TG and DTG curves for DGEBA/MDA/NPG system filled with zeolite(10 phr) at the heating rate of 10 oC/min. On the TG curve, the thermal decomposition temperature, Td was 364.4oC. The sample was stable below about 250oC and showed noticeable weight loss above the Td. On the DTG curve, thermal decomposition took place in one stage.

Dynamic DTG curves for DGEBA/MDA/NPG/zeolite(10 phr) system at various heating rates were shown in Fig. 2. A temperature where maximum decomposition rate occurs on DTG curve, Tm is 363.2, 373.2, 382.7 and 388.0oC at 5, 10, 15, and 20 oC/min, respectively. Tm increased with the increment of heating rate.

From the relationship between Tm and □ obtained from Fig. 2, -ln(□/Tm2) vs. 1/Tm × 103 were plotted in Fig. 3. Thermal decomposition activation energy was calculated from the slope and pre-exponential factor was obtained from the intercept. The slope and intercept were 21.76 and -22.14, respectively. So activation energy was 43.24 kcal/mol and pre-exponential factor was 1.50 □ 1012 sec-1.

By the same method in Fig. 2, Tm and □ of DGEBA/MDA/NPG system with other zeolite contents were obtained. From the relationship between Tm and □, the slope and intercept which were obtained from plot of -ln(□/Tm2) vs. 1/Tm × 103 for DGEBA/MDA/NPG system with other zeolite contents were listed in Table 1. With the increment of zeolite content, slope was increased and intercept was decreased. The activation energies and pre-exponential factors for the system with various contents of zeolite were also listed in Table 1. The values of activation energy and pre-exponential factor increased with the increment of zeolite contents.

Fig. 2. Dynamic DTG curves for DGEBA/MDA/NPG(10 phr) at various           heating rates.

Fig. 3. Plot of -ln(□/Tm2) vs. 1/Tm for DGEBA/MDA/NPG(10 phr) system.

Table 1.  Slope, Intercept, Activation Energy and Pre-exponential Factor for the                DGEBA/MDA/NPG(10 phr) System with Various Zeolite Contents.

Zeolite Contents (phr)	Slope	Intercept	Ed (kcal/mol)	Ad (sec-1)
0	17.23	-15.87	34.24	2.24 □ 109
5	20.45	-20.91	40.63	4.11 □ 1011
10	21.76	-22.14	43.24	1.50 □ 1012
15	24.01	-26.38	47.71	1.15 □ 1014
20	28.68	-33.51	56.69	1.71 □ 1017

To look into rate constant of thermal decomposition with the addition of zeolite for the DGEBA/MDA/NPG system, Arrhenius equation was used. The overall rate constant, kd was expressed as follows.

kd= A exp (- Ed/RT)

kd was 1.95 □ 10-4, 1.30 □ 10-4, 4.80 □ 10-5, 7.30 □ 10-5 and 3.10 □10-5 sec-1 at 300oC for the systems with 0, 5, 10, 15 and 20 phr of zeolite content, respectively. It was observed that rate constant of thermal decomposition of the system without zeolite higher than those of the system with zeolite. These results lead to the conclusion that thermal stability of the system with zeolite was higher than those of the system without zeolite.

Conclusion

1.  Activation energy and pre-exponential factor increased with the increment of          zeolite content.

2.   Thermal stability of the system with zeolite was higher than those of the system      without zeolite.

References

1.  Jan F. Rabek, Exp. Meth. Polym. Chem., 556(1980).

2.  H. e. Kissinger, Analyt. Chem., 29, 1702(1957)

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

4.  Roger l. Blaine, Du Pont Co., DE19898, number TA-84

5.  J. Y. Lee, M. J. Shim and S. W. Kim, J. Kor. Iod. & Eng. Chem., 731(1994)

6.  J. Y. Lee, M. J. Shim and S. W. Kim, J. Kor. Iod. & Eng. Chem., 904(1994)