Study on effect of carbon black on behavior of conductive polymer composites with positive temperature coefficient

Conductive polymer composites showing large positive temperature coefficient (PTC) are made of semi-crystalline polymer as an insulator and a conducting filler, whose concentration is close to the critical volume fraction. In this study, the resistivity and PTC behavior of high density polyethylene (HDPE) filled with different carbon blacks were studied. Among those composites, N660 carbon black filled PE showed the greatest PTC behavior. Carbon black with large particle size, small surface area and small amount of aggregated structure leads to large amplitude of PTC transition (defined as the ratio of maximum resistivity to the resistivity at 25 degrees C). The great PTC behavior is due to some microscopic mechanism under the macroscopic thermal expansion of polymer matrix during melting of polymer crystal.