Microwave irradiation of nadic-end-capped polyimide resin (RP-46) and glass-graphite-RP-46 composites: cure and process studies

Abstract

Microwave energy was investigated to cure nadic-end-capped polyimide precursors (RP-46 resin) using a Cober Electronics Model LBM 1.2A/7703 microwave oven at a frequency of 2.45 GHz. Both neat resin samples and glass cloth and hybrid glass cloth-graphite cloth-RP-46 resin composites were studied. For the resin studies, the effect of various parameters, such as power level, sample size, processing temperature, time, and graphite fiber absorber, were investigated. The variables investigated with the composite study were the power level, mold material, vacuum, and low pressure. The results showed that microwave energy was effective in curing both neat resin samples and composite specimens. The presence of a small quantity of absorber (chopped carbon fiber) accelerates the cure dramatically. Moreover, soapstone mold material was found to be an efficient absorber for glass and glass-graphite composite processing, causing an effective cure in less than 1 h. Glass and glass-graphite hybrid composites with flexural strengths of 372-588 MPa (54-85 ksi) and moduli of 28.7-31.7 GPa (4.2-4.6 Msi) have been fabricated. This is equivalent to 50 to 80% of the properties of composites fabricated by conventional means.