Tailoring the interface in graphite‐reinforced polycarbonate

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Abstract
Pronounced effects of thermal treatment on the properties of graphite fiber/polycarbonate and glass fiber/polycarbonate composites have been demonstrated and explained. At 20 volume percent loading of random‐in‐a‐plane, discontinuous fibers, both specimen strength and modulus in both fiber systems were found to increase dramatically upon molding above 260–265°C, whereas only the graphite system was further improved by subsequent annealing. In the latter case, property improvement is due to generation of a crystalline innerlayer at the interface, which apparently transfers the stresses more effectively from fiber to fiber. Regardless of the type of fiber, molding at 275°C (slightly above 260–265°C, the melting point of crystalline polycarbonate) results in improved properties due to better wetting of the fibers by the resin. Hot forming of graphite reinforced polycarbonate composites between the molding and annealing steps takes advantage of the higher processability of the unannealed material in addition to providing increased modulus and strength in the final molded article.