Properties of cyanate ester-cured epoxy/polyphenylene oxide blends as a matrix material for Kevlar fiber composites

Epoxy/polyphenylene oxide (PPO) blends were cured with multifunctional cyan ate ester resin. The effects of the PPO content on the cure behavior in the cyanate ester-cured epoxy were investigated with Fourier transform infrare d spectroscopy (FTIR). The cure reaction in the epoxy/PPO blends was faster than that of the neat epoxy system. FTIR analysis revealed that the cyanat e functional group reactions were accelerated by adding PPO and that severa l co-reactions had occurred, such as cyanate-hydroxyl addition and epoxy-cy anate addition. This was caused by the reaction of cyanate ester with the P PO phenolic end-group and water yielding imidocarbonate and carbamate inter mediate which can react with cyanate ester to form cyanurate. Then the cyan urate can react further with the epoxy resin. Thermal mechanical analysis s howed that the thermal stability of the epoxy/PPO blends is improved by add ing PPO. The morphology of the fiber-rich areas in the composite is differe nt from that of the epoxy/PPO blend without Kevlar fiber. :In the pure poly mer blends with high PPO content (30 and 50 phr), phase separation and phas e inversion were observed. In the composites, the majority of the epoxy res in migrates to the polar fiber surface, resulting in epoxy-coated fibers. S o the interfacial shear strength (IFSS) between Kevlar fiber and the epoxy/ PPO blends is almost the same as that between Kevlar fiber and neat epoxy. The presence of PPO does not affect the interfacial property in the epoxy/P PO/fiber composite. So the interlaminar shear strength (ILSS) increase with the PPO content is due to an increase in the composite's ductility or toug hness.