Freeman & Carroll 식에 의한 EPDM의 열분해 활성화 에너지

송영욱, 박장호, 심미자*, 김상욱

서울시립대학교 화학공학과, 생명과학과*

Thermal Decomposition Activation Energy of EPDM

by Freeman & Carroll Equation

Y. W. Song, J. H. Park, M. J. Shim* and S. W. Kim

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

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

Introduction

To test thermal properties, various thermal analyzers have been used for polymer materials, especially DSC and TGA have been used. TGA analysis provided thermal decomposition data for polymer materials as functions of  time, temperature, and heating rates. Because thermal decomposition for electrical polymer insulator is important, TGA analysis is often utilized in electrical fields.

Ethylene propylene diene terpolymer(EPDM) rubber has good properties such as heat resistance, oxidation resistance, ozone resistance, weather resistance, low temperature flexibility, high resilience, and radiation resistance and its applications are various. Especially, it is used in electrical insulator, because of its low dielectric constant and power factor, corona resistance, water resistance, wet electrical stability, and high temperature performance.

In this study, to test the thermal properties of EPDM rubber, its thermal decomposition activation energy was calculated by Freeman & Carroll equation.

Experiment

EPDM was Nordel 1040(PE 54 %, PP 42 %, and diene polymer 4 %) and antioxidants were polymerized 1,2-dihydro-2,2,4-trimethylquimoline(ARD), zinc-2- mercapto-toluimidazole(ZMTI), and zinc-methylmercaptobenzimidazole(ZMMBI). Their contents were 0, 0.5, 1 and 2 phr. The rubber was mixed in open two roll mill at 70℃ for 20 min, and cured in 150 kg heating press at 170℃ for 10 min. Cured sample was investigated by TGA and its thermal decomposition activation energy was calculated by Freeman & Carroll equation. In Table 1, the composition of EPDM rubber were shown.

Table 1. Composition of EPDM Rubber(phr)

No.	EPDM	White filler	Oil	Plasticizer	DCP	ARD	ZMMBI	ZMTI
# 1	100	100	10	3	4	0.5	-	-
# 2	100	100	10	3	4	1.0	1.0	-
# 3	100	100	10	3	4	1.0	-	1.0
# 4	100	100	10	3	4	-	2.0	-

Results and Discussion

When EPDM was decomposed by TGA, the TG and DTG thermograms for EPDM rubber(#1) as a function of time were shown in Fig. 1.

Fig. .  TG and DTG thermograms of EPDM rubber(#1) with the heating rate of   10 ℃/min

As shown in Fig. 1, EPDM rubber was decomposed at 2-steps. Generally, it was known that white filler was decomposed during first step and the degradation of EPDM was progressed in second step.

To calculate thermal decomposition activation energy of EPDM, Freeman & Carroll equation was used. It was caused that Freeman & Carroll equation[1,2] has been utilized in thermal analysis for various materials, include polymer. This equation is like below

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

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. These data obtained from DTG curve were useful not only using the expression but also calculating decomposition activation energy. From DTG curve, Freeman & Carroll equation parameters were plotted and the scattered points were fitted by linear curve. Thermal decomposition activation energy of EPDM rubber was calculated from the slope of fitting curve.

In Fig. 2 and 3, DTG curves at various heating rates for various EPDM rubber samples were shown.

Fig. .  DTG curves of EPDM rubber(#1) with various heating rates.

Fig. .  DTG curves of EPDM rubber samples with the heating rate of 20 ℃/min.

From Fig. 2, DTG curve has two peaks which caused by 2-step thermal decomposition of EPDM. Second peak was maximum value and it was used in Freeman & Carroll equation. The temperature at maximum value of DTG curve decreased with the increment of heating rate. However, for various samples, the shapes of DTG curve of EPDM were similar, as shown in Fig. 3.

After calculating thermal decomposition activation energy, the results were listed in Table 2. When heating rate was 20 ℃/min, sample #3 had highest thermal decomposition activation energy. But, sample #3 was lowest energy at the heating rate of 50 ℃/min. It seemed that the case of antioxidant ARD had high decomposition energy and ZMMBI was similar, too. However, when ARD, ZMMBI and ZMTI were mixed with EPDM in #2 and #3, thermal decomposition activation energies were low. Also, it was considered that the effect of ZMTI on thermal decomposition energy was decreased with the increment of heating rate.

Table . Thermal Decomposition Activation Energy of EPDM Rubber at the Various Heating Rates.

Heating rates	Sample No.	Decomposition Energy
20 ℃/min	# 1	108.5 kJ/mol
	# 2	85.4 kJ/mol
	# 3	126.1 kJ/mol
	# 4	102.7 kJ/mol
50 ℃/min	# 1	181.5 kJ/mol
	# 2	100.7 kJ/mol
	# 3	56.9 kJ/mol
	# 4	132.3 kJ/mol

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)