Aging and pollution studies of EPDM polymers by means of a time-resolved current method in a SEM

In this article, we deal with the charge phenomena of surface-polluted Ethylene Propylene Diene Monomer (EPDM) used in medium-voltage cables. Conductive sodium chloride solutions of varying conductivity were deposited on the surface of both as-received and thermally aged polymers in order to simulate the influence of salt air on cables. These samples were charged under electron irradiation in a scanning electron microscope (SEM). By means of a time-resolved current method implemented in the SEM, we have dynamically studied the degradation of the dielectric properties of EPDM, i.e. how the charging behavior of the polymer changes with the conductivity of the polluted surface. This method allows measurement of both the leakage current of electrons that flow on the specimen surface to the ground and the trapped charge to be measured. The obtained results show that leakage current clearly increases with surface conductivity and that the trapped charge at the steady state decreases as the conductivity increases.