VOLUME RESISTIVITY AND MECHANICAL-PROPERTIES OF ELECTRICALLY CONDUCTIVE LONG-FIBER COMPOSITES

Long, electrically conductive nickel-coated graphite fibers were emplo yed 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 int o square plaques. The fiber loading was varied from 2 to 20 weight per cent. The effects of fiber loading on electrical and impact properties were studied and related to the composite microstructure. A device wa s constructed to measure the volume resistivity of the samples in two planes, longitudinal and latitudinal. A large initial decrease in resi stivity occurs as fibers are added to the insulating matrix. Beyond so me critical loading. the resistivity reaches a minimum and begins to l evel 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 resisti vity in the two planes. Fiber attrition is more significant at low loa dings where the mixing shear is greater. Impact tests show that the ad dition of the fibers results in an increase in sample stiffness, there by reducing the force and energy needed to break the samples.