Electron beam curing of polymer composites

Electron-beam (E-Beam) curing, in the presence of a cationic photoinitiator, of an epoxy polymer matrix and its composite (reinforced with IM7 Carbon fibers) was studied. Photoinitiator concentration, dose, and process temperature were varied to understand their influence on E-beam curing. Optimal photointiator concentration was found to be 5 phr and the curing was due to a primary reaction, with a strong dependence on dose, and a secondary reaction, with a weak dependence on dose and a strong dependence on initiator concentration. The extent of cure increased rapidly with dose until 50 KGy and it approached a plateau value beyond 100 KGy. This plateau value corresponded to incomplete curing by 27% for resin and 22% for composite at a process temperature of 22 degrees C. The causes for incomplete curing appear to be due to the secondary reaction and diffusional limitation. Increase in process temperature resulted in higher extent of cure at a does level. The material used in this study was also found to be thermally curable and the reaction onset temperature (measured in a DSC ramp experiment) reduced from about 150 degrees C at 0 kGy to about 50 degrees C at 30 kGy. This indicates that simultaneous thermal curing during E-beam curing of resin and composite is possible. The T-g of the E-beam cured material increased threefold and the modulus decreased by 10% after thermal post-curing. The service temperature and the modulus of the 100% thermally cured material and the thermally post-cured (after E-Beam irradiation) material were comparable.