THE POSITIVE TEMPERATURE-COEFFICIENT EFFECT OF LOW-DENSITY POLYETHYLENE CHLORINATED POLYETHYLENE/CARBON BLACK ELECTRICAL CONDUCTIVE COMPOSITES/

The temperature dependence of electric resistivity of low density poly ethylene (LDPE)/chlorinated polyethene (CPE)/carbon black (CB) composi tes we studied in the temperature range from room temperature to 140 d egrees C. Based on the morphological observations, a new model capable of explaining both the PTC (positive temperature coefficient) and the NTC (negative temperature coefficient) effects is proposed, according to which the PTC effect is the combined result of transformation from crystalline to amorphous phase and thermal expansion, and the NTC eff ect is mainly related to the agglomeration of CB at high temperature. The influences of each component concentration and heat treatment on P TC effect are also discussed. It shows that the maximum PTC intensity occurs at the CB concentration near the percolation shreshold. The pre sence of CPE and TiO2 filler leads to the decrease of PTC effect. Upon repeated thermal cycling, the PTC effect decreases, When samples are annealed at appropriate temperatures, the room-temperature resistivity is reduced and the PTC effect is enhanced.