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 behaviour of polyethylene filled with different carbon blacks were studied. Among the composites filled with different carbon blacks, N660 carbon black filled PE showed the greatest PTC behaviour. Large particle size, small surface area and small amount of the aggregate structure lead to large amplitude PTC behaviour (defined as the ratio of maximum resistivity to the resistivity at room temperature). The large PTC behaviour is due to some microscopic mechanism under the macroscopic thermal expansion of the polymer matrix during the melting of polymer crystal.