THERMAL-STABILITY RELATIONSHIPS BETWEEN PMR-15 RESIN AND ITS COMPOSITES

A study was conducted to investigate the relationships between the the thermo-oxidative stability of PMR-15 matrix resin and the stability o f graphite-fiber reinforced composites that contain this resin as the matrix material. Three areas were investigated. The first was the effe ct of fiber/matrix interfacial bond strength on the isothermal aging w eight loss of composites. By using type-A graphite fibers produced by Hercules, it was possible to study composites reinforced with fibers t hat were processed to receive different surface treatments. One of the fibers was untreated, a second fiber was treated by oxidation to enha nce fiber/matrix bonding, and the third type of fiber was coated with an epoxy sizing. These treatments produced three significantly differe nt interfacial bond strengths. The epoxy sizing on rite third fiber wa s quickly oxidized from the bare fiber surfaces at 288, 316, and 343 d egrees C. The weight loss due to the removal of the sizing was constan t at 1.5 percent. This initial weight loss was not observed in thermo- oxidative stability studies of composites. The PMR-15 matrix satisfact orily protected the reinforcement at all three temperatures.