Electret properties of ethylene-propylene random co-polymer

Thermally stimulated current (TSC) spectra were examined for ethylene-propylene (EP) random copolymer 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 degrees 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 degrees 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 degrees C: one is a narrow TSC band peaked at 120 degrees C and the other is an unusual TSC band which was non-vanishing even at 165 degrees C just before destruction of samples by their melting. Consequently, the utmost stable charge density in EP co-polymer above 100 degrees C was found to be 3.5 x 10(-4) C/m(2) and 6.0 x 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. (C) 2009 Elsevier B.V. All rights reserved.