Electret properties of PP/ZnO and PP/CuO composite films

In the present paper the influence of both time and storage temperature on the surface potential decay of polypropylene (PP) composite films was investigated. We have investigated the 200 μm PP composite films with different weight concentrations of the particles (ZnO or CuO) - 0 wt.%, 2 wt.% and 4 wt.%. The samples were charged in a corona discharge by means of a corona triode system for 1 minute under room conditions. Positive or negative 5 kV voltage was applied to the corona electrode and 1 kV voltage of the same polarity as that of the corona electrode was applied to the grid. After charging, the surface potential was measured using the method of the vibrating electrode with compensation. The results obtained show a significant change in the electret behavior of the composite films after the inclusion of ZnO or CuO particles with different concentration into the PP matrix. The possible surface potential decay mechanisms responsible for the electret´s behavior were discussed. It was established that the surface potential decay depended on the corona polarity, the particles concentration and the type of the particles. It has been experimentally demonstrated that the normalized surface potential of PP composite films with different concentrations of ZnO or CuO particles decays faster than the one of the pure PP films.