Electrical conductivity and rheology of carbon fiber/liquid crystal polymer composites

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One emerging market for electrically conductive resins is for bipolar plates for use in fuel cells. Adding carbon fillers to thermoplastic resins increases composite electrical conductivity and viscosity. Current technology often adds as much of a single type of carbon filler as possible to achieve the desired conductivity, while still allowing the material to be extruded and molded into a bipolar plate. In this study, varying amounts of two different types of polyacrylonitrile (PAN) based carbon fiber (Fortafil 243 and Panex 30) were added to Vectra A950RX liquid crystal polymer. The resulting single fiber composites were then tested for electrical conductivity and rheological properties. The electrical conductivity followed the behavior typically seen in composites with a percolation threshold at 5 vol% for Fortafil 243 and at 13 vol% for Panex 30. Viscosity increased with increasing filler volume fraction for all shear rates, but was more rapid for the Fortafil 243 composites. Over the range of shear rates studied, the viscosity followed a shear-thinning power law model with power-law exponent (n - 1) = -0.5 for neat Vectra A950RX. Panex 30 had no effect on the power-law exponent and Fortafil 243 changed (n - 1) to -0.6. © 2007 Society of Plastics Engineers.

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Polymer Composites