Influence of process parameters on electron beam curing of a polymer composite

The influence of process parameters, viz. dose, dose rate, and temperature, on E-beam (electron beam) curing of an epoxy polymer matrix with a cationic photo-initiator and its composite (with IM7 carbon fibers) was studied. while the extent of curing increased with dose, surprisingly incomplete curing (e.g. 27% residual exothermic heat [measured using DSC] for the pure resin e-beam cured at room temperature) was observed even at a dose of 500 kGy. A comparison of residual exothermic heat flow for 100% thermally cured material with that of samples irradiated with different levels of electron dose revealed that the interaction of the electron beam with the polymer and the photo-initiator led to secondary reactions that are weakly dependent on the electron dose. These reactions appear to be the cause for the incomplete curing. Significant exothermic heat flow (and temperature rise) was observed at a dose between 30 and 40 kGy for all dose rates (i.e. dose / pass). This suggests that a fine control of dose / pass during this crucial period of rapid cure under e-beam s needed to prevent temperature run-off. The fact that the chosen material cured thermally indicates that significant thermal curing can occur during E-beam processing of such cationic formulations. The implications of the above results on E-beam processing of polymer composites are discussed in this paper.