Fast space charge behavior in heat-treated polypropylene films

In this study, the characterization of the short-circuit current within hundreds of nanoseconds is proposed to study the effect of heat treatment on fast space charge behavior in the polarized biaxially oriented polypropylene (BOPP) films. The BOPP films were cooled either quickly or slowly during the sample preparation. The damped oscillating feature was found in the short-circuit current of all the polarized film samples, but the periods of the oscillating current for the samples prepared by fast cooling rate decrease faster. Bipolar space charge injection in the polarized BOPP films was observed by the thermal pulse (TP) measurement. The variation feature of the short-circuit current was considered to be associated with the varying fast space charge behavior, which depended on the varying structural traps modified by the heat treatment during the sample preparation. The sample subjected to fast cooling process was with relatively shallow trap level revealed by the thermally stimulated current method, which led to higher mobility of the escaping charge in the sample. The TP measurements were utilized to analyze space charge features in the polarized BOPP films.