Finishing Process to Improve Interfacial Bonding in SiC/BMI Composites

High-temperature (HT) polymer matrix composites (PMCs) are desired for many aerospace and military applications. Silicon carbide (SiC) fibers provide a potentially attractive reinforcement for HT PMCs for applications ranging from propulsion systems to structures for the orbiting space plane. The sizings routinely added to commercial SiC fibers are not compatible with the new HT matrix resins. The result is that the thermo-oxidative stability (TOS) and mechanical properties of composites made with such fibers are compromised. A need exists for a SiC fiber adhesion promoting finish that is compatible with high-temperature bismaleimide (BMI) and polyimide (PI) chemistries. Previous work at Adherent Technologies, Inc. has revealed chemistries that chemically bond to fiber surfaces and high-temperature curing matrix resins. Composites fabricated with finishes based on reactive coupling agent chemistries show substantially higher interface-dependent properties, TOS, and moisture resistance. Those chemistries will be modified to function with the SiC fiber surface and BMI and AFR-PE-4 PI moieties during cure. SiC/PMC composites will be fabricated for mechanical testing and moisture and thermal aging studies. Results are expected to show superior interfacial strength and environmental durability. It is also expected that the finishes will serve as weaving and prepregging aids.