Investigation of the microwave curing of the PR500 epoxy resin system

Microwave heating has been used to cure a resin system, PR500 (3M). The same resin has been cured using a conventional oven. The cured resins have been compared using a number of techniques including modulated differential scanning calorimetry (MDSC), dynamic thermal analysis, infrared spectroscopy (IR) and solid-state NMR spectroscopy. The reaction path appears to be slightly different depending upon the nature of the heating. The epoxy-amine reaction occurs to a greater extent than the epoxy-hydroxyl reaction in the microwave cured resin compared to the thermally cured resin. The dielectric properties for the thermally and microwave cured materials were measured for degrees of cure greater than 75% and over this range are similar for materials cured by the two techniques and thus not sensitive to this change. Broadening of the glass transition for microwave-cured epoxy resins was observed. Since the IR and solid-state NMR results show small differences as does the DMA behaviour of materials cured using the two routes the broadening is attributed to a difference in network structure.