Tensile behavior and morphology studies of glass-fiber-reinforced polymeric in situ hybrid composites

The morphology and tensile behavior of an in situ hybrid composite system, based on E-glass-fibers, liquid-crystalline polymers, and Noryl (a modified polyphenylene ether/polystyrene blend) with a hierarchical microstructure containing reinforcements with an order-of-magnitude difference in size, were studied. The primary reinforcement was short E-glass fibers, and the secondary reinforcement was formed by LCP inclusions with submicrometer dimensions generated in situ during fabrication. With an increase in the LCP content, both the geometry and dimensions of the LCP phase in the composites changed, from spherical droplets to ellipsoidal droplets and then to fibrils or lamellar structures. The orientation of the short E-glass fibers was influenced by this change, and the breakage of the glass fibers during processing was less intensive. The tensile strength of the composites increased moderately with the addition of LCPs and the reduction of the glass-fiber content. The elastic modulus of the composites did not follow rule-of-mixture predictions. This more complicated hybrid effect was attributed to several competing mechanisms. Tensile fractography analysis indicated that the tensile fracture of the composites was dominated by fiber/ matrix-interface failure.