THERMAL EFFECTS OF HEAT-RESISTANT RUBBER BLENDS .1. JOULE HEATING EFFECTS IN CARBON BLACK-LOADED NR/SBR BLENDS

A heat‐resistant rubber blend of natural rubber NR and styrene butadiene rubber (SBR‐1502) was prepared according to the standard techniques. The rubber blend was loaded with different concentrations of LAMP black and general purpose furnace (GPF) black for obtaining conductive rubber composites. The obtained vulcanizates were subjected to electrical conductivity measurements over a wide range of temperature and electric field. It was found that all samples showed negative values of temperature coefficient of conductivity (TCC). The temperature developed inside the samples by the Joule heating effect was recorded as a function of time (T–t) at different values of the initial applied DC‐electric power. The T–t dependence was found to obey an exponentially growing function with a time constant (τ), which was found to be dependent on the concentrations as well as the type of carbon black and the value of the initial applied power. The current–voltage characteristics of the samples showed a negative resistance behavior after a characteristic voltage (V*). It was noticed that V* decreases as the carbon black concentration increases. Copyright © 1990 John Wiley & Sons, Inc.