Unusual positive temperature coefficient effect of polyolefin/carbon fiber conductive composites

The high-density polyethylene/carbon fiber (HDPE/CF) and isotactic polypropylene/carbon fiber (iPP/CF) conductive composites were prepared by melting blending and unusual positive temperature coefficient (PTC) effects were observed. For HDPE/CF composites, the sharp increase of resistivity happened in an extremely narrow temperature range and hardly any negative temperature coefficient (NTC) effect was observed when the temperature increased. Especially, the conductive network became more sensitive with increasing thermal cycles which manifested as obviously ever-increasing PTC intensity with the increase of thermal cycles. For the iPP/CF composites, the PTC transition temperature decreased with increasing thermal cycles. In addition, the onset resistivity of each thermal cycle obviously increased during the continuous thermal processes.