Influence of post-curing and temperature effects on bulk density, glass transition and stress-strain behaviour of imidazole-cured epoxy network

Abstract

The effects of post-curing and temperature on the glass transition, bulk density and stress-strain behaviour in the glassy and rubbery state of 2-ethyl-4-methyl imidazole-cured epoxy network have been evaluated by differential scanning calorimetry (DSC), water displacement and tensile testing. The glass transition temperature,Tg, was found to increase with increasing post-cure temperature and the size of the base line shift in the glass transition region on the DSC thermogram can serve as an indicator of the extent of cure. At room temperature, the decrease in bulk density with increasing extent of cure may be attributed to the additional cross-linking, adding molecular constraints to the thermal constraints. Thus, a higher free volume atTg can be expected to remain in the glassy state as the sample is slowly cooled through the glass transition temperature. In the investigation on the temperature dependence of the tensile mechanical properties, a fracture envelope was obtained. The tensile strength, Young's modulus and ultimate elongation in the glassy and rubbery state are discussed in detail.