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

Microwave energy was investigated to cure nadic-end-capped polyimide precur sors (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 an d hybrid glass cloth-graphite cloth-RP-46 resin composites were studied. Fo r the resin studies, the effect of various parameters, such as power level, sample size, processing temperature, time, and graphite fiber absorber, we re investigated. The variables investigated with the composite study were t he 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 m aterial 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 (5 4-85 ksi) and moduli of 28.7-31.7 GPa (4.2-4.6 Msi) have been fabricated. T his is equivalent to 50 to 80% of the properties of composites fabricated b y conventional means. (C) 1999 John Wiley & Sons, Inc.