ELECTRICAL-PROPERTIES OF POLYETHYLENE HIGHLY FILLED WITH CARBON

Carbon-filled polyethylene composites were fabricated and tested to es tablish the practical lower limit of their electrical resistivity at r oom temperature and to investigate the trade-offs between low resistiv ity and the magnitude of the resistance anomaly (i.e., a large positiv e temperature coefficient of resistivity) that appears when such compo sites are heated through the polyethylene crystalline melting transiti on. Carbon blacks with large particle size and low surface area provid ed low-resistivity composites having large resistance anomalies. The l argest resistance anomalies were found in composites that were well mi xed, but the room-temperature resistivity also increased in composites that were cycled repetitively through the crystalline-melting transit ion. A mixture of carbon blacks of two different sizes provided a lowe r resistance than was found in a material with the same fill of only t he coarser black. By controlling the composition and the processing, c omposites were made with room-temperature resistivities lower than 0.2 ohm cm and resistance changes of at least 2 orders of magnitude. A re sistance change of as much as 5 orders of magnitude was obtained for c omposites with room-temperature resistivities of only 1 ohm cm.