Thermally stimulated discharge current and DC resistivity of ethylene propylene rubberwith various Pb concentrations

Abstract

DC resistivity of extruded ethylene propylene rubber (EPR) samples with various Pb concentration have been measured under wet conditions as a function of electrical field at selected temperatures in a range from 20 to 100°C. The temperature and electrical field coefficients of resistivity have been calculated. Thermally stimulated discharge current (TSDC) has also been measured and a broad positive peak has been observed for three EPR samples. It has been found that the resistivity of EPR is not sensitive to the Pb concentration within the range of 0 to 5 parts per hundred base resin (phr). The results show that the resistivity of EPR varies non-linearly with both temperature and electrical field. The temperature coefficient of resistivity α of EPR has been measured to be ∼0.1 K−1 for all the samples with various Pb concentration. The electrical field coefficient of resistivity β of EPR at room temperature is small and increases with temperature. Increasing Pb content increases slightly the electrical field coefficient β of resistivity. Based on a space charge limited conduction model, the trap depth of EPR has been estimated. TSDC measurements indicate that doping with Pb increases both the density of charge carriers and the number of deep traps simultaneously. The broad TSDC peak reveals that there must be a distribution rather than just a single value of the trap depth.