STUDIES OF THERMALLY STIMULATED CURRENT IN POLYPROPYLENE CALCIUM-CARBONATE SURFACTANT SYSTEMS

Thermally stimulated polarization (TSP) and depolarization (TSD) experiments have been performed with two grades of polypropylene and some respective CaCO3-filled composites containing small amounts of nonionic surfactant (0-2wt%). The effects of electrode blocking, electrode materials on the thermally stimulated currents, and reproducibility of the measurements have been studied. The effect of water vapor adsorbed from the ambient air on the AC dielectric properties and on the thermally stimulated polarization behavior has been determined. The addition of either CaCO3 or surfactant to PP decreases the intensity of the alpha(c) depolarization current peak in the pre-melting region, while the presence of both components increases the current. Partial discharges are present in poly-propylene/CaCO3 composites under high voltages if neither water vapor nor a coherent surfactant layer is present at the matrix/filler interface. A short literature survey is presented on the TSC studies of polyolefins and their composites, and various mechanisms responsible for the observed changes are discussed, including interfacial polarization, trap redistribution through nucleation, and oriented adsorption.