Volume Resistivity and Mechanical Properties of Electrically Conductive Long Fiber Composites

Abstract

Long, electrically conductive nickel-coated graphite fibers were employed to produce thermoplastic composites by compounding and processing with polypropylene resin. The fibers were blended into the resin in a Brabender mixer and the resulting composite was compression molded into square plaques. The fiber loading was varied from 2 to 20 weight percent. The effects of fiber loading on electrical and impact properties were studied and related to the composite microstructure. A device was constructed to measure the volume resistivity of the samples in two planes, longitudinal and latitudinal. A large initial decrease in resistivity occurs as fibers are added to the insulating matrix. Beyond some critical loading, the resistivity reaches a minimum and begins to level off. The resistivity is identical in the two perpendicular planes. Examination of the microstructure reveals that the fiber orientation is fairly random in the composite, which results in a uniform resistivity in the two planes. Fiber attrition is more significant at low loadings where the mixing shear is greater. Impact tests show that the addition of the fibers results in an increase in sample stiffness, thereby reducing the force and energy needed to break the samples.