(307a) Effect of Foaming on Fiber Orientation and Electrical Conductivity of Polymer Carbon Fiber Composites in Injection Molding

Abstract: Numerous applications of electrically conductive polymer composites have initiated a very active research area to develop these materials. Addition of conductive fillers such as carbon fiber and carbon black to a non-conductive thermoplastic matrix by melt mixing is one of the common approaches to produce conductive polymer composites. Injection molding is the favoured method to produce electrically conductive parts. Flow induced fiber orientation during mold filling and packing results in anisotropic properties for molded composites [1]. Previous studies show that anisotropic fiber orientation exhibit anisotropic conductivity changes by up to 3 orders of magnitude, parallel and perpendicular to the flow direction [2-3]. Therefore tailoring of fiber orientation distribution to obtain the desired electrical conductivity in the preferred direction is a requirement in the processing of electrically conductive polymer/carbon fiber composites. In this research we have investigated the impact of foaming along with processing conditions on fiber orientation and electrical conductivity of cyclic olefin copolymer (COC)/carbon fiber (CF)-carbon black (CB) hybrid composites in injection molding process. A fractional factorial design was used to screen the effects of injection speed, melt temperature and mold temperature with and without foaming. Cell size distribution, fiber orientation distribution, fiber length and electrical conductivity in three dimensions were characterized. The results revealed that foaming can enhance the conductivity in the transverse and normal direction to the mold flow. Foaming reduces injection shot size and viscosity resulting in lower injection pressure; therefore foaming can expand the application of injection molding for composites with high filler loading.