Horowitz & Metzger 식에 의한 DGEBA/MDA/PGE 계의 열분해 속도론

송영욱·심미자．·김상욱

서울시립대학교 화학공학과·．생명과학과

Thermal Decomposition Kinetics of DGEBA/MDA/PGE System

by Horowitz & Metzger Equation

Y. W. Song, M. J. Shim．, and S. W. Kim

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

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

Introduction

Epoxy resin have been applied to various industrial purpose, especially, heavy electrical insulation[1∼3]. Though epoxy resin has good mechanical and electrical properties, it was readily degraded by thermal and electrical stresses. If thermal and electrical stresses concentrated to epoxy resin for long-term, the epoxy resin would be deteriorated during its service life[4,5]. From this view point, preventing large accident of thermal and electrical degradation from occurring, it is very important to resist against thermal and electrical stresses. In this study, the thermal decomposition properties of the epoxy system with diluent was investigated by Horowitz & Metzger equation[2,3,6~8].

Experiment

Epoxy resin was diglycidyl ether of bisphenol A(DGEBA, Epon 828) by Shell Co. Its EEW, MW and viscosity were 188, 385 and 11000∼14000 cps(at 25℃), respectively. Curing agent was 4,4□-methylene dianiline(MDA) and diluent which was used as a toughness agent of epoxy resin was phenyl glycidyl ether(PGE). These curing agent and diluent were provided by Fluka Chemie AG. To make fully crosslink epoxy resin, the mixed content of MDA was 30 phr and PGE was introduced to the system(5∼25 phr). DGEBA/MDA/PGE system was cured for 1 hr at 150℃, after curing for 1.5 hr at 80℃. The sample of DGEBA/MDA/PGE system was decomposed by TGA. Heating rate of TGA was 5, 10 and 15 ℃/min. To prevent the sample from oxidizing, N2 was flowed with the rate of 100 ml/min. Thermal decomposition activation energy of DGEBA/MDA/PGE system was studied by Horowitz & Metzger equation.

Results and Discussion

General feature of decomposition of epoxy resin is one step curve. The patterns of decomposition thermograms for DGEBA/MDA/PGE system were similar to other epoxy resin system. Also, the graphs of DGEBA/MDA/PGE system were similar when the heating rates of TGA were different. The decomposition graphs of DGEBA/MDA/PGE system were shown in Fig. 1.

Fig. 1  Thermal decomposition graph of DGEBA/MDA/PGE system at the heating rates of 5 ℃/min.

Fig. 2  Thermal decomposition graph of DGEBA/MDA/PGE system at the various heating rates.

Decomposition temperature(Td) of the system were found about 350∼380℃, which is respectively stable values for epoxy/diluent system. Td of the system with various PGE contents and heating rates were listed in Table 1.

Though these values were different, it seemed that the decomposition temperature (Td) for DGEBA/MDA/PGE system decreased with the increment of PGE contents and decrement of heating rates.

Table   Td of DGEBA/MDA/PGE System with Various PGE Contents at Various Heating Rates.

Heating rate	System
	D/M/PGE(5)	D/M/PGE(10)	D/M/PGE(15)	D/M/PGE(20)	D/M/PGE(25)
5 ℃/min	359.5℃	357.3℃	352.6℃	352.9℃	353.1℃
10 ℃/min	368.4℃	366.5℃	362.8℃	365.7℃	363.7℃
15 ℃/min	375.5℃	374.1℃	372.0℃	372.8℃	368.8℃

To use Horowitz & Metzger equation, it was required to know weight loss of TG at some temperatures. They obtained from TG curves, as shown in Fig. 1, 2. Horowitz & Metzger equation is

[eqn: ln ln {W_o ~-~W_t `^f } over {W~-~W_t `^f } ~=~ {E theta } over {RT_s ^2 }]

where, Wo is initial sample weight, Wtf is final sample weight, Ts is the temperature of when [eqn: {W_o ~-~W_t `^f } over {W~-~W_t `^f } ~=~ e] , and □ is T１Ts. The parameters calculated by Horowitz & Metzger equation were listed in Table 2.

Table 2  Some Parameters Calculated by Horowitz & Metzger Equation.

Heating rate	W/Wo	Wtf/Wo	lnln[eqn: {W_o ~-~W_t `^f } over {W~-~W_t `^f }]	T	Ts	□
5℃/min	0.8	0.212	-1.228	361.2℃	379.7℃	-18.5
	0.7		-0.736	367.3℃		-12.4
	0.6		-0.345	371.7℃		-8.0
	0.5		0.007	380.6℃		0.9
10℃/min	0.8	0.204	-1.240	375.1℃	390.6℃	-15.5
	0.7		-0.749	380.3℃		-10.3
	0.6		-0.359	385.5℃		-5.1
	0.5		-0.011	392.2℃		1.6
15℃/min	0.8	0.146	-1.321	382.1℃	401.5℃	-19.4
	0.7		-0.838	385.0℃		-16.5
	0.6		-0.459	392.4℃		-9.1
	0.5		-0.127	396.8℃		-4.7

Fig.   Plot of ln ln[eqn: {W_o ~-~W_t `^f } over {W~-~W_t `^f }] vs. □ for DGEBA/MDA/PGE system with various heating rates.

As shown in Fig. 3, thermal decomposition activation energy of DGEBA/ MDA/PGE system was calculated from the slope of fitting curve at various heating rates. The activation energy of the epoxy resin system was listed in Table 3.

Table   Thermal Decomposition Activation Energy of DGEBA/MDA/PGE System.

Heating rate	R	Ts	Ea
5℃/min	8.314 J/mol·K	652.85K	238.6 kJ/mol
10℃/min		663.75K	262.1 kJ/mol
15℃/min		674.65K	281.4 kJ/mol

Conclusion

Epoxy resin system was decomposed in one stage. The thermal decomposition kinetics of DGEBA/MDA/PGE system was investigated by using their gravimetric analysis and Horowitz & Metzger equation. The thermal decomposition activation energy was increased with the increment of heating rates of TGA.

References

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