Cure kinetics of an epoxy-anhydride-imidazole resin system by isothermal DSC

The cure kinetics of a dimethyl imidazole catalyzed diglycidyl ether of bisphenol A methyltetrahydrophthalic anhydride resin system was examined. Degree of conversion versus cure time was obtained using isothermal DSC over the temperature range from 80 degrees C to 140 degrees C. The kinetic data were analysed using both nth order and autocatalytic kinetic models. The results indicated that the epoxy curing process could be described satisfactorily by Kamal's four-parameter generalised autocatalytic model modified with an exponential function of conversion defined as the diffusion factor. The curing process was predominantly autocatalytic in nature. The autocatalytic rate constant of the resin system was 10 to 60 times larger than the nth order rate constant. The corresponding activation energies obtained from Arrhenius equation were 78.1 kJ/mol and 67.6 kJ/mol, respectively. The approximate order of reaction was 0.39 for the autocatalytic reactions and 1.0 for the nth order reactions.