Study on filler content dependence of the onset of positive temperature coefficient (PTC) effect of electrical resistivity for UHMWPE/LDPE/CF composites based on their DC and AC electrical behaviors

Composites of carbon fibers (CF) filled with ultrahigh molecule weight polyethylene/low density polyethylene blend matrix (UHMWPE/LDPE) were prepared by kneading method. The positive temperature coefficient (PTC) effect of electrical resistivity of UHMWPE/LDPE/CF composites was investigated by direct current (DC) and alternating current (AC) measurements over the frequency range of 100–106.5 Hz from 30 to 150 °C. The onsets of PTC effect were found to be strongly depended upon the CF content even the melting behaviors were almost same for all composites. To interpret this phenomenon, a master curve of temperature–frequency–resistivity superposition was constructed for composites with different CF contents based on the AC resistivity. The CF content dependence of correlation length was related to the onset of PTC effect. The transitions of conductor–insulator were studied quantitatively by complex planes of AC impedance, and the calculated capacitances and resistances showed a similar PTC effect under DC. Based on the analysis of AC capacitance, the average distances between CFs were calculated using a plane capacitance model which varied with CF concentration and temperature, and the tendency was consistent to the PTC effect.