Electret properties of ethylene–propylene random co-polymer

Thermally stimulated current (TSC) spectra were examined for ethylene–propylene (EP) random co-polymer at different charging voltages V p with positive and negative polarities. Observed TSC spectra showed two well-separated TSC bands, B L and B H, which respectively appeared in the temperature regions below and above 100 °C. Observed V p dependence of B L was quite different from that of typical polypropylene homo-polymer: As V p increased, B L band grew keeping its peak position same at 65 °C, and the band shape unchanged, as if the traps responsible for the B L band are a single set of traps with the same trap depth and capture cross section. The trap depth of B L was about 1.9 eV and 1.7 eV for positively charged EP and talc-containing EP samples, respectively. EP samples also showed unique TSC bands above 100 °C: one is a narrow TSC band peaked at 120 °C and the other is an unusual TSC band which was non-vanishing even at 165 °C just before destruction of samples by their melting. Consequently, the utmost stable charge density in EP co-polymer above 100 °C was found to be 3.5 × 10 −4 C/m 2 and 6.0 × 10 −4 C/m 2 for positively and negatively charged samples, respectively. These equivalent surface charge densities are much larger than those of usual polypropylene homo-polymer.