Anomalous thermally stimulated currents in polypropylene films

摘要

Thermally stimulated current (TSC) spectra were observed in open-circuit condition for corona-charged polypropylene films from room temperature to about 160 u000b0;C. In these TSC spectra, two kinds of reversal currents I1 and I2 were found: I1 appeared at room temperature and rapidly decreased with increasing temperature, whereas I2 increased with temperature to form a TSC band. These anomalous currents practically appeared only for the positively charged samples because of their strong charging-polarity dependence. After I1 decayed, the same sample was exposed to the humid ambient air for less than 100 s, and then I1 revived again. Whereas, I2 was not observed in the sample, which was quickly cooled in, the ambient air just after I2 was once observed, and reheated again from room temperature. To explain these anomalous behaviors of I1 and I2, a simple model was made and three discriminants were also derived from the model for determining hetero-charge''s contribution to I1 and I2. From these discriminants, most of I1 and I2 were concluded to be due to direct charge flow from the charged surface of the sample to the current-measuring electrode placed above the sample. A tentative explanation for the source of the reversal currents was also made.