Positive and negative temperature coefficient effects of an alternating copolymer of tetrafluoroethylene-ethylene containing carbon black-filled HDPEparticles

A conductive polymer composite was prepared by melt-mixing of an immiscible semicrystalline polymer blend of an alternating copolymer of tetrafluoroet hylene-ethylene (ETFE), high density polyethylene (HDPE), and carbon black (CB). The optical microscopy and time-of-flight secondary mass spectrometry results indicated that the CB particles were selectively localized in the HDPE phase. In addition, it was found that the CB-filled HDPE particles for med a dispersed phase in the ETFE matrix. A double-positive temperature coe fficient (PTC) effect was observed in the composite, caused by the large th ermal expansion due to the consecutive melting of HDPE and ETFE crystallite s. The negative temperature coefficient (NTC) that was observed in this sys tem could not have been caused by the formation of flocculated structures b ecause the size of the CB-filled HDPE particles is significantly large, so that their mobility is extremely limited even at high temperatures. This co nclusion was confirmed by observing the morphology of the composite at temp erature ranging from 25 to 250 degrees C. These results suggest that new me chanisms need to be uncovered to explain the NTC effect of conductive polym er composites. (C) 2000 Elsevier Science Ltd. All rights reserved.