TEMPERATURE EFFECT OF ELECTRICAL-RESISTIVITY OF CARBON-BLACK FILLED POLYMERS

In this review paper, the author is concerned with the relationship between electric resistivity and temperature in carbon black-filled SRR and silicone rubber as well as in crystallizing polymers, such as polyethylene or ethylene-vinyl acetate polymers. It is shown that very large positive temperature coefficients of resistivity (PTC) found in a narrow temperature range with dispersions of carbon blacks in noncrystallizing polymers are caused by an increase in average particle or aggregate distances of the dispersed black. This effect is the result of their deagglomeration upon temperature increase, induced by the increased Brownian motion, predominantly caused by the large reduction in vehicle viscosity and aided by the increase in segmental motion of the polymeric molecules. Highest PTC effects are found in the range of the steepest resistivity-concentration curves for the carbon black dispersion, differing markedly for each black and each polymer. The effects of crosslinking the polymer as well as the influence of strain on PTC effects are considered. The decline in PTC effects above the peak temperature is discussed.