Anomalies between Microwave and Thermal Cure Kinetics of Epoxy-Amine Resin Systems

Abstract

The cure of the epoxy systems MY721/27% DDS at 160 °C and MY721/32% DDM at 120 °C have been investigated in both rectangular and cylindrical microwave cavities and thermally. The cure rates were monitored by FT-NIR spectroscopy over the region 4750–7250 cm-1. The rates of cure in the microwave cavities, estimated from both the primary and epoxy group concentrations, were found to be different, and different from the rate observed for thermal cure in a heated aluminium block. This anomalous behaviour has been attributed to spatial inhomogeneity in the temperature of the epoxy samples, arising from inhomogeneity in the microwave field in the cavity, rather than to specific absorptions of the microwave radiation by the reactive groups in the epoxy samples, as has been suggested previously by some other authors.