Investigations into the mechanism of electron-beam curing of an epoxy resin

Electron-beam (E-beam) curing of composite materials has a number of advantages over conventional thermal curing, one of which is the fact that it is not necessary to heat the mould in order to achieve the cure. However, since the crosslinking process involves exothermic reactions governed by chemical kinetics, it is clear that temperature does play an important role. The object of this study was to develop a better understanding of the mechanism of the E-beam curing process and the effect of temperature. Samples of a typical E-beam epoxy resin system (Tactix 123 + 3 phr CD1012) were partially or fully cured under varying conditions and characterized by different techniques, including the monitoring of temperature during the irradiation, differential scanning calorimetry, infrared spectroscopy, and dynamic mechanical thermal analysis. The results indicate that the main E-beam reactions proceed reasonably fast at moderate temperatures (50-150degreesC), but that the process parameters like dose rate and total dose should be chosen in such a way as to ensure that the temperature developed internally is high enough to achieve sufficient curing in the time allowed. The results also suggest that E-beam irradiated samples contain "trapped" active sites that remain stable for a long time at room temperature. In the case of partially cured samples, these sites promote further crosslinking, when the sample is subsequently heated above room temperature. With the proper choice of conditions, E-beam curing of the system investigated (Tactix 123, + CD1012) can give a product with a glass transition temperature around 190degreesC.