Abstract
Non-isothermal crystallization kinetics of Poly(4-methyl-1-pentene) samples irradiated by γ-ray in air and vacuum with 100-400 kGy was studied using Differential Scanning Calorimeter (DSC). Different cooling rates at 2.5, 5, 7.5, 10, 15 and 20 ℃/min were applied to investigate the exothermic behavior of crystallization. According to the heat flow along the continuous cooling temperature, the heat flow is related to the degree of crystallization. However, we found double peaks in the diagram of the heat flow versus the cooling temperature. Two crystalline processes were expected to coexist. It is possible that the phenomenon comes from the up-down disorder in crystal structure. In this research, we separated the double peaks by curve fitting. We used the probability density function of the inverse Gaussian distribution to separate two peaks with different parameters. After that, Avrami approach modified by Jeziorny and Ozawa approach were applied to analyze the non-isothermal crystallization kinetics. Generally speaking, the exponent n of Avrami approach is around 1.5~2 for Peak 1 and 1~1.5 for Peak 2 at different cooling rates when TPX samples are irradiated by γ-ray with different doses in air and vacuum. The exponent n of Ozawa approach decreases from 2~3 to 0.5~1 for peak 1 and peak 2 with the decreasing crystallization temperature. The activation energy of non-isothermal crystallization were computed by Kissinger’s approach. The crystallization activation energy for peak 1 decreases from 667.01 KJ/mol to 452.63 KJ/mol and 407.75 KJ/mol with the increasing dose of γ-ray in air and in vacuum, respectively. The crystallization activation energy for peak 2 decreases from 484.18 KJ/mol to 420.97 KJ/mol and to 342.17 KJ/mol with the increasing dose of γ-ray in air and in vacuum, respectively.