Electrical conductivity of polymer blends containing liquid crystalline polymer and carbon black

This paper presents results of a study of melt-processed immiscible polymer blends of high impact polystyrene (HIPS), liquid crystalline polymer (LCP) and carbon black (CB). Relationships between composition, electrical resistivity and morphology of the blends produced by Brabender mixing followed by compression molding, extrusion through a capillary rheometer, extrusion through a single-screw extruder and injection molding were investigated. The LCP phase morphology in the blends was found sensitive to the processing conditions. A blend composition of at least 20 wt% LCP and 2 phr CB is necessary to preserve the conductivity of filaments produced over a wide range of shear rates. Enhancement of conductivity of blends containing CB and 30 wt% or more LCP was observed, under processing at 270degreesC and increasing levels of shear rate. An important role of the skin region in determining the resisitivy of injection molded samples was found. A good agreement between resistivity values of extruded or injection molded blends with resistivity values of filaments produced at similar conditions by a capillary rheometer was shown. Hence, the study of shear rate effect on resistivity of capillary rheometer filaments may serve as a predictor of resistivity behavior in real processing procedures.