Hygrothermal stability of plasma modified graphite fiber/epoxy composite

When fiber reinforced polymeric composites are exposed to high temperature and wet environment, mechanical properties become gradually deteriorated, which normally proceeds from the fiber/resin interphase. This paper reports the hygrothermal stability of graphite fiber/epoxy interphase, the structure of which are altered though plasma modification of fiber surface. Fortafil-3 fibers were treated with plasma of acrylonitrile, styrene, ethylene, and styrene/air mixed gases. Treated fibers were cast into single filament composites, and the interfacial shear strength was estimated from the fragmented fiber lengths when the composite is under uniaxial tension. Overall, the interfacial shear strength decrease gradually with water immersion time at 55 degree C. Among the specimens, styrene/air plasma treated specimens exhibit the best performance in terms of absolute strength values at well as %-retention of the strength after water exposure. Ethylene plasma treated samples also showed relatively high level of wet strength retention. Hygrothermal stability of the interface region is examined in terms of the presence of primary bondings and the non-polar nature at the interface, which can be effectively generated by plasma polymerization