Flynn & Wall 식에 의한 DGEBA/MDA/Polyamide 계의 열분해속도론

김양림, 박장호, 김상욱

서울시립대학교 화학공학과, *생명과학과

Thermal Decomposition Kinetics of DGEBA/MDA/Polyamide System by Flynn & Wall Equation

Y. L. Kim, J. H. Park and S. W. Kim

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

Introduction

With the increasing demands for polymer materials in the high temperature applications, it is important to estimate the thermal decomposition characteristics, thermal stability, limited temperature for use, etc. before their applications. Numerous differential or integral methods have been proposed to obtain kinetic parameters with thermogravimetric analyzer(TGA) which is a powerful instrument to investigate complex degradation processes. In this study, the effect of polyamide(PA) on thermal degradation of diglycidyl ether of bisphenol A(DGEBA)/4,4'-methylene dianiline(MDA) system  was studied by using the weights loss curves obtained by TGA instrument and the parameters of thermal decomposition was obtained by Flynn & Wall equation.

This expression had the advantages that this method was very simple and easy, and relatively exact activation energy could be obtained at each decomposition conversion. Flynn & Wall expression was

[eqn: rm{ E}_{d }= { -R} over {0.457 } { d(log□)} over {d( { T}^{-1 } ) }]

where, [eqn: rm{E }_{d }] was activation energy of thermal decomposition, [eqn: rm R] was gas constant, [eqn: rm □] was heating rate and [eqn: rm {T }^{-1 }] was inversion of absolute temperature. To get[eqn: rm{E }_{d }], the straight relationship between [eqn: rm log□] and[eqn: rm {T }^{-1 }] at a selected fraction of thermal decomposition was displayed and the[eqn: rm{E }_{d }] value was calculated from the slope. The selected fraction was various from 0.05 to 0.4 and each activation energy for the each fraction was obtained and compared.

Experiment

DGEBA(Epon 828, Shell Co.) was used as a base resin, MDA(Fluka Chemie. AG) and PA(LA 0331, Lucky) were used as curing agents. Various contents of MDA and PA were well-mixed with DGEBA at 80oC and then the sample were cured thoroughly. The equivalent ratio of DGEBA to curing agent was 1 to 1. The formulations were shown in Table 1. TGA(ATI CAHN, TG121) was operated in order to measure the weight loss curves. The weighed sample (5-7 mg) was placed in the furnace and were heated in the temperature range of 20oC to 600oC at the heating rates of 5, 10, 15 and 20 oC/min, respectively. To prevent the oxidation of the sample, nitrogen gas was flowed at the rate of 80 ml/min.

Table 1. The Formulations of the Equivalent Ratio of DGEBA, MDA and PA.

Sample NO.	DGEBA	MDA	PA
Ⅰ	100g	26g	0g
Ⅱ	100g	19.5g	10.8g
Ⅲ	100g	13g	21.5g
Ⅳ	100g	6.5g	32.3g
Ⅴ	100g	0g	43g

Results and Discussion

Fig. 1 Thermal decomposition curves of system Ⅱ        at various heating rates.

Fig.1 shows TG curves for system Ⅱ at four different heating rates. With the increment of heating rate, the curves shifted to right-hand side and decomposition temperature, Td were 351.6oC, 361.0oC, 366.9oC and 376.4oC at 5, 10, 15 and 20 oC/min, respectively. Td could be obtained from the point where weight loss abruptly increased. The temperatures at □= 0.15 for four heating rate were measured from the cross points of dotted line and the TG curves, and the values were 360.7oC, 337.0oC, 376.8oC and 385.2oC at 5, 10, 15, and 20 oC/min, respectively. To get thermal decomposition activation energy, these data were listed on Table 2. By the same method, temperatures at different □ were obtained and log □ and 1/T × 103 were also listed on Table 2. The fixed conversion were selected from 0.05 to 0.4.

Table 2. Isoconversional Data of System Ⅱ for Flynn & Wall Equation.

□ log□	0.05	0.1	0.15	0.2	0.25	0.3	0.35	0.4
0.699	1.623	1.596	1.578	1.568	1.559	1.549	1.541	1.533
1	1.596	1.569	1.555	1.545	1.536	1.528	1.520	1.512
1.176	1.574	1.551	1.539	1.528	1.520	1.511	1.504	1.495
1.301	1.556	1.530	1.519	1.510	1.501	1.493	1.485	1.477

Fig. 2 Isoconversionl polts of System Ⅱ          by Flynn & Wall equation.

Straight lines for various □ were created by the relationships between log□ and 1/T × 103 of Table 2, and they were listed table 3. The slope of the straight lines for □= 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 and 0.4 were 15.29, 15.47, 16.55, 17.13, 17.09, 17.43, 17.40 and 17.25, respectively. Therefore, thermal decomposition activation energies for □= 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 and 0.4 were 278.2, 281.5, 301.1, 311.7, 311.0, 317.1, 316.6 and 313.9 kJ/mol, respectively. As the thermal decomposition proceeded, the activation energy increased steeply in the initial stage until □=0.20, and after that the activation energy was almost constant. This meant that the molecules of week bonding for thermal stress were removed in the initial stage, and after that the strong bonding molecules affected on the high activation energy.

From the TG curves of other systems, the relationship between log□ and 1/T ×103 were obtained, and activation energy were calculated by Flynn and Wall equation and listed on Table 3. It indicated that activation energy increased until system Ⅱ and then decreased in the same decomposition fraction(□). So DGEBA were synthesized by the rate of equivalent of MDA(75%) and polyamide(25%) is more stable than any other system.

Table 3. Activation Energy Obtained from Flynn & Wall Equation.

□	Ea (kJ/mol)
	0.05	0.1	0.15	0.2	0.25	0.3	0.35	0.4
System Ⅰ	249.2	257.8	274.7	280.2	280.2	277.3	276.0	274.5
System Ⅱ	278.2	281.4	301.1	311.6	310.9	317.1	316.6	313.8
System Ⅲ	265.2	278.0	282.2	295.1	296.4	294.4	288.5	285.3
System Ⅳ	253.4	260.0	263.8	263.4	260.5	258.7	257.8	259.2
System Ⅴ	218.1	223.6	226.7	243.8	250.7	257.8	266.5	261.6

References

1. Ozawa, T., bull. Chem. Soc. Japan, 38, 1881 (1965)

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

3. Cooney, J. D., Day, M. and Wiles, D. M., J. of Appl. Polym. Sci., 28, 2887        (1983).

4. Song, Y. W., Shim, M. J. and Kim, S. W., korean J. of Master. Res., 7, 386        (1997).