Kinetic methods to study isothermal and nonisothermal epoxy-anhydride cure

Abstract

The kinetics of epoxy-anhydride cure were studied by differential scanning calorimetry under isothermal and nonisothermal conditions. The data were fitted to single-step and to two-step kinetic models. In both cases the activation energies derived from nonisothermal measurements differ from the values obtained for the isothermal cure data. Unlike the model-fitting methods, a model-free isoconversional method of kinetic analysis yields matching dependencies of the activation energy on the extent of conversion for isothermal and nonisothermal experiments. For both dependencies, the effective activation energy increases from 20 kJ·mol–1 at the beginning of cure to 70 kJ·mol–1 when the process is near completion. The occurrence of the dependence suggests that the cure kinetics is determined by competing reactions. The model-fitting methods have not been capable of reliably detecting the complex character of the cure kinetics.