ELECTRICAL-CONDUCTIVITY OF BARIUM-FERRITE-VULCANIZED POLYCHLOROPRENE FILLED WITH SHORT CARBON-FIBER

Short-carbon-fiber-filled polychloroprene composites, prepared by mill-mixing and cement-mixing methods were vulcanized by barium ferrite. The effects of concentration and aspect ratio (L/D) of short carbon fiber on volume resistivity have been studied. Composites prepared by the cement mixing method having high fiber aspect ratio (L/D 100) show higher hardness and modulus accompanied by lower elongation and volume resistivity than the composites prepared by the mill mixing method, which give low fiber aspect ratio (L/D 25). Experimental values of volume resistivity agreed reasonably well with the calculated values from the theory based on probability of formation of conductive network. The temperature dependence of volume resistivity of the composite shows a positive temperature coefficient. The shape of the hysteresis loop, observed during the heating and cooling cycle in the variation of volume resistivity with temperature, depends on the concentration and aspect ratio of short carbon fiber. Hall-effect studies indicate that increase in fiber concentration and aspect ratio in the composites causes increase in carrier concentration and decrease in mobility of the carriers. With increase in temperature, both conductivity and carrier concentration decrease and mobility of the carriers increases.