Anomalous attenuation and structural origin of positive temperature coefficient (PTC) effect in a carbon black (CB)/poly(ethylene terephthalate) (PET)/polyethylene (PE) electrically conductive microfibrillar polymer composite with a preferential CB distribution

This article reports the positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects of a carbon black (CB)-filled electrically conductive microfibrillar poly(ethylene terephthalate) (PET)/polyethylene (PE) composite (FCMC). The composite contains in situ polymer microfibrils in the matrix of another polymer with CB particles selectively localized at microfibrils' surfaces. Anomalous attenuations of PTC and NTC intensities (IPTC and INTC) of FCMC were observed during heating–cooling runs (HCRs) and long-term isothermal treatments. Particularly, when the isothermal treatment time was 32 h, the IPTC decreased from 5.5 in the original sample to only 0.5, showing a tremendous attenuation ratio of up to 91%, and the NTC effect was completely eliminated. On the contrary, attenuations of PTC and NTC effects in a common conductive polymer composite (CCPC) were so weak as to be negligible through the same thermal treatments. Microstructural changes of the conductive network by Brownian motion and large size of the conductive component-CB coated PET microfibrils are both responsible for the great reductions in IPTC and INTC. The present results strongly suggest that thermal field induced microstructural transformation by Brownian motion helps to reveal the origin of PTC and NTC effects. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012