DGEBA/MDA/SN/천연 Zeolite 계의 열분해 특성

김유정, 김상욱

서울시립대학교 화학공학과

Thermal Degradation Characteristics of DGEBA/MDA/SN/Natural Zeolite System

Y. J. Kim and S. W. Kim

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

Introduction

Epoxy resin has the good properties of dimensional stability, chemical resistance, electrical insulation, high mechanical strength, etc., and it has been used in many industrial fields. Especially, as the society is developed rapidly to the industrial community, large capacity of electric power is needed. Therefore the demands for good insulating materials were expanded, and many researchers has studied polymer insulating composites by introducing the inorgnic fillers such as metal powder, mica, silica, aluminium oxide, etc[1∼4]. Zeolites are crystalline aluminosilicate minerals and have the characteristics of low density and large porosity, and have been applied in many fields of catalysis, molecular sieve, ion exchange mineral, and so forth.

In this study, to develope the electrical insulating material, zeolite was added to the diglycidyl ether of bisphenol A(DGEBA)/4,4'-methylene dianiline(MDA)/succino- nitrile(SN) system with various contents and the thermal properties of the cured composite was analyzed by thermogravimetry(TG) and differential scanning calorimetry(DSC). Kissinger equation is used to calculate the kinetic parameters through the relationship between heating rates and the peak temperatures where maximum degradation rate occurred.

Kissinger equation is

[eqn: rm -ln LEFT (beta over T_m ^2 RIGHT )~= ~E_d over{R ~T_m}~-~ln LEFT ({A_d ~R}overE_d RIGHT )]

where, □: heating rate, Tm: the temperature where maximum degradation rate occured on derivative thermogravimetry(DTG) curve, Ed: thermal degradation activation energy, A: pre-exponential factor for thermal degradation and R: gas constant[5].

Experiment

DGEBA(Epon 828, Shell Co.) was used as a base resin, MDA(Fluka Chemie. AG) was used as a curing agent and SN(Acros Org.) was used as a reactive additive for the purpose of improving toughness by extending the chain length. Natural zeolite from Kampo area in Korea was used as a filler.

DGEBA and SN(10 phr) were well mixed with dried natural zeolite(0, 20, 40, 60, and 80 phr) at 80℃ and MDA(30 phr) was added to the mixtures. The mixtures were cured at 150℃ for 1 hr after curing at 80℃ for 1.5 hr. The weighed sample(5∼7 mg) was tested by TG and DSC analysers. Nitrogen gas was flowed into the furnace at 80 ml/min.

Results and Discussion

The distance between zeolite particles filled in the specimens was obtained by Lange's equation and was shown in Table 1. Lange's equation[6] is

[eqn: rm d={2D LEFT (1-Vp RIGHT )} over 3Vp]

where, d: interparticle distance, D: the diameter of particle, Vp: volume fraction of particles. The average particle diameter of zeolite is 20.03 □.

Table 1. Interparticle distance of zeolite filled in epoxy matrix

Zeolite Content (phr)	Density of Specimen (g/□)	Vp	d(□)
20	1.195	0.063	198
40	1.334	0.125	93.47
60	1.432	0.181	60.42
80	1.549	0.238	42.75

Dynamic DSC curves for DGEBA/MDA/SN with zeolite contents(0, 20, 40, 60, 80 phr) were shown in Fig.1. With the increment of zeolite content, Tg increased. It was due to the buckling up the chain segment by the pore of zeolite filler. For Tg is a characteristic temperature to determine the motion of chain segments.

Fig.1 Glass transition temperature of DGEBA/MDA/ SN/zeolite system.

Fig.2 shows TG curves for DGEBA/MDA/SN system filled with or without zeolite(80 phr) at the heating rate of 10 ℃/min. In the initial state, the system without zeolite was decomposed earlier than the system with zeolite. This suggests that the system with zeolite be more stable than the system without zeolite.

Fig.2 TG curves for DGEBA/MDA/SN with or

without zeolite(80 phr) system

Fig.3 shows the dynamic DTG curves for DGEBA/MDA/SN/zeolite(20 phr) system at various heating rates. The temperature where maximum degradation rate occured on DTG curve, Tm increased with the increment of heating rate.

From the relationship between Tm and □ obtained from Fig.3, -ln(□/Tm2) vs. 1/Tm ×103 were plotted in Fig.4. Thermal decomposition activation energy was calculated from the slope and pre-exponential factor was obtained from the intercept. The slope and intercept were 6.97 and -8.92. Therefore, activation energy was 57.94 kJ/mol and pre-exponential factor was 8.69 × 105 sec-1.

By the same method, the activation energies and pre-exponential factors of DGEBA/MDA/SN system with other zeolite contents were obtained, and they were listed in Table 2. With the increment of zeolite content, the values of activation energy and pre-exponential factor decreased.

To investigate the rate constant of thermal degradation with the addition of zeolite for the DGEBA/MDA/SN system, Arrhenius equation was applied. The expression of the equation was below.

Kd = Ad exp (-Ed/RT)

In table 2, the rate constant of thermal degradation of the system with various content of zeolite at 573 K was shown. As the content of zeolite was increased, the rate constant was decreased. These results showed that thermal stability of the system with zeolite was higher than those of the system without zeolite.

Fig.3 Dynamic DTG curves for

DGEBA/MDA/SN/zeolite(20

phr) system

Fig.4 -ln(q/Tm2) vs. 1/Tm×103 of

DGEBA/MDA/SN/zeolite(20

phr) system

Conclusion

1. Tg increased with the increment of zeolite content due to the buckling up the chain segments by the pore of zeolite.

2. Pre-exponential factor and activation energy decreased with the increment of zeolite content.

3. DGEBA/MDA/SN/zeolite system was more stable to heat than the system without zeolite.

Table 2. Activation Energy, Pre-exponential Factor and Rate Constant

for DGEBA/MDA/SN System with Various Content of Zeolite

Zeolite Content (phr)	Activation Energy Ea (kJ/mol)	Pre-exponential Factor A (sec-1)	Rate Constant Kd (sec-1)
0	61.773	2.6×106	6.075
20	57.948	8.69×105	4.526
40	54.290	2.5×105	2.809
60	49.385	4.3×104	1.354
80	52.211	1.1×105	1.913

References

1. H. Lee and K. Neville, "Handbook of Epoxy Resins", McGraw-Hill, Inc., New York(1983)

2. M. J. Shim and S. W. Kim, Polymer J., 30, 73(1998).

3. D. W. Breck, "Zeolite Molecular Sieves", John Wiley & Sons, New York(1974)

4. H. S. An, M. J. Shim and S. W. Kim, Kor. J. Mater. Res., 7, 733(1997)

5. H. E. Kissinger, Analyt. Chem., 29, 1702(1957)

6. F. F. Lange and K. C. Radford, J. Mater. Sci., 6, 1197(1971)