에폭시 수지의 반응속도에 미치는 경화제의 영향

이재영, 최형기*, 김상욱

서울시립대학교 화학공학과, *국립기술품질원 화학부

Effect of Mixed Hardners on the Cure Rate of Epoxy System

Jae-Young Lee, Hyeong-Ki Choi* and Sang-Wook Kim

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

*Dept. of Chem., NITQ, Kwachen 427-101

Introduction

There are many useful equations to estimate the cure rate of epoxy system by differential scanning calorimetry(DSC) with the assumption that the heat evolved during the cure reaction is proportional to the monomer conversion[1∼3]. The well-known equations are Kissinger equation[1], isoconversional equation[2], autocatalytic cure rate equation[3] and so on. In this study, Kissinger equation was used.

-ln(q/Tp2) = Ea/RTp - ln(AR/Ea)

where, q was heating rate, Tp, the temperature at the maximum peak, Ea,  activation energy R, gas constant and A was gas constant. The relationship between -ln(q/Tp2) and 1/Tp was obtained from the DSC thermograms at different heating rates, and the activation energy and pre-exponential factor could be calculated from the slope and y-intersection.

Experiment

Epoxy formulation was the complex mixture of diglycidyl ether of bisphenol A(DGEBA, Epon 828 grade, Shell Co.), 4,4'-methylene dianiline(MDA, Fluka Chemie. AG.) and hexamethylene dianiline(HMDA, Hayashi Pure Chemical Industries Ltd.)

The weight ratios of DGEBA : MDA : HMDA were 100 : 15 : 6.35. The sample was analyzed by dynamic DSC run at the heating rates of 5, 10, 15 and 20 ℃/min. In order to prevent the oxidation of the sample, nitrogen gas flowed at 40 ml/min.

Results and Discussion

Fig.1 shows the dynamic DSC thermogram for the sample at the heating rate of 10 ℃/min. The thermogram shows two exothermic peaks, and the temperature of the first maximum peak, Tp1 is 110.1℃ and that of the second maximum peak, Tp2 is 159.7℃. This result said that the cure reaction of the system took place in two separated steps. The first peak was due to the HMDA hardner and the second was due to the MDA hardner.

Fig.2 shows the dynamic DSC thermograms for the sample at various heating rates. All the thermograms separated into two regardless of heating rate and the temperature at the maximum peak was increased with the increment of heating rate. Tp1 was about 46∼52℃ higher than Tp2.

Fig. DSC thermogram for the sample at the heating ratio of

10 ℃/min.

To use Kissinger equation, Tp1 and Tp2 values at various heating rates were listed on Table 1 and 2. The values of -ln(q/Tp2) and 1/Tp were also listed on these Tables. The relationship between -ln(q/Tp2) and 1/Tp was plotted in Fig.3 to get

Fig. Dynamic DSC thermograms for the sample at

various heating rates.

Table . Data of Thermal Analysis and Kinetic Parameters for

the first peak.

q (℃/min)	Tp1 (℃)	1/Tp1 (K-1)	-ln(q/Tp12)	A1 (sec-1)	Ea1 (kJ/mol)	Rate Constant at 25℃, k1(25) (sec-1)
5 10 15 20	94.7 110.1 120.8 128.3	2.72×103 2.61×103 2.54×103 2.49×103	10.20 9.59 9.24 8.99	5.40×103	43.73	1.20×10-4

Table . Data of Thermal Analysis and Kinetic Parameters for

the second peak.

q (℃/min)	Tp2 (℃)	1/Tp2 (K-1)	-ln(q/Tp22)	A2 (sec-1)	Ea2 (kJ/mol)	Rate Constant at 25℃, k2(25) (sec-1)
5 10 15 20	141.0 159.7 171.9 180.6	2.41×103 2.31×103 2.25×103 2.20×103	10.44 9.84 9.49 9.24	2.99×103	47.89	1.24×10-5

activation energy and pre-exponential factor. The linear expressions for Tp1 and Tp2 were

-ln(q/Tp12) = 5.26×103/Tp1 - 4.12

-ln(q/Tp22) = 5.76×103/Tp2 - 3.44

Fig. Plots of 1/Tp × 103 vs. -ln(q/Tp2)

Therefore, the activation energy was obtained from the slope and the pre-exponential factor was from y-intersection, and these values were listed on Table 1 and 2. To compare the rate constant, these values were introduced to Arrhenius equation and the rate constants at 25℃ were also listed on Table 1 and 2. The rate constant of HMDA is 10 times faster than that of MDA.

Conclusion

The kinetic parameters for DGEBA/MDA/HMDA system was studied by Kissinger equation. All the thermograms separated into two regardless of heating rate and the temperature at the maximum peak was increased with the increment of heating rate. The peak at lower temperature was due to the HMDA hardner and the peak at higher temperature was due to the MDA hardner. The rate constant of HMDA was 1.20×10-4 sec-1 and that of MDA was 1.24×10-5 sec-1.

References

1. J. Y. Lee, M. J. Shim and S. W. Kim, Mater. Chem. & Phys., 44, 74(1996)

2. S. Montserrat, C. Flaqu□, P. Pag□s and J. M□lek, J. Appl. Polym. Sci., 56,

1413(1995)

3. J. Y. Lee, M. J. Shim and S. W. Kim, Mater. Chem. & Phys., 48, 36(1997)