CURING KINETIC MODEL OF THE 2-ETHYL-4-METHYLIMIDAZOLE/EPOXY SYSTEM

Abstract

The system of bisphenol-A diglycidyl ether type epoxy resin(DGEBA) cured with 2-ethyl-4-methylimidazole(2,4-EMI) was studied by means of differential scanning calorimetry(DSC) in isothermal mode.Analysis of DSC curves indicated that the curing reaction could be separated into two stages,the addition reaction and the catalytic polymerization,as proposed in the literatures.The catalytic polymerization reaction has an induction period which decreases with the increasing of curing temperature(T_c).The rate constants for the catalytic polymerization stage were calculated from DSC studies.A curing kinetic model separated into two steps by the induction period was developed based on the reaction mechanism.The model can predict part of the experimental results,but some deviations are observed at the higher values of curing degree(α).A critical value of curing degree(α_c) and a diffusion factor were introduced,and a diffusion controlled curing kinetic model was developed.For the systems of various concentrations of 2,4-EMI cured in the temperature range of 90～120℃,the values of α_c were calculated.The studies show that the diffusion factors affect the curing kinetics greatly in the higher values of α.When the value of α is low,the reaction is controlled by the chemical factors,but it is controlled by diffusion,when α is high.The value of α_c is mainly affected by the glass transition of the system.With the increase of T_c,the curing degree at the glass transition increases and thus the value of α_c increases too.