Study on time-dependent resistance of carbon black-loaded high-density polyethylene composites during the isothermal course

Carbon black (CB)-loaded high-density polyethylene composites were prepared using conventional blending. The resistance and temperature (R-T) relation s under constant heating rates and the resistance and time (R-t) relations at different isothermal temperatures have been studied. The results of the R-T and differential scanning calorimetry (DSC) curve demonstrated a correl ation between the positive temperature coefficient/negative temperature coe fficient transition and the melting course. At isothermal temperatures belo w T-PTC/NTC,T- the resistance displayed a sharp increase and thereafter a m ild decrease with time. The time to reach the highest resistance became sho rter with rise in the isothermal temperature. The ratio between highest res istance and initial resistance was maximum at T-peak of the DSC curve. When the isothermal temperature was higher than T-PTC/NTC, the resistance atten uated with time. The attenuation fits to a first order exponential decay fu nction. The calculated time constant tau decreased with rise in isothermal temperature. The attenuation discrepancy under different isothermal tempera tures reduced as the heating rate before the isothermal courses was higher. A model based on polymer chain diffusion and CB movements at high temperat ure is proposed. The model can explain the results obtained in R-T and R-t measurements. (C) 2001 John Wiley & Sons. Inc.