Resin/fiber thermo‐oxidative interactions in pmr polyimide/graphite composites

Abstract The amounts of resin weight loss and fiber weight loss in four PMR polyimide/graphite fiber composites were calculated from the composite weight losses and the fiber/resin ratios of the composites after long term thermo‐oxidative aging in 600° F air. The accelerating effect of graphite fiber on resin weight loss, compared to neat resin weight loss, indicated the presence of a deleterious resin/fiber thermo‐oxidative interaction, presumably due to fiber impurities. Similarly, the declerating effect of the protective matrix resin on fiber weight loss, compared to bare fiber weight loss, was also demonstrated. The amount of hydrazine indigestible resin and the amount of loose surface graphite fiber that formed during 600° F exposure of the composites were quantitatively determined. The indigestible residual resin was also qualitatively studied by scanning electron microscopy.