The charge states in polypropylene doped with ZrO2 nanoparticles and their changes at heat treatment

Charge states of polypropylene doped with zirconium oxide nanoparticles and their changes during heat treatment at different temperatures are studied by the method of thermally stimulated depolarization (TSD) current. It is shown that two peaks associated with the release of charge from different types of traps appear on the TSD thermograms for both pure polypropylene and composites. With an increase in the concentration of the filler, the intensity of the peaks increases up to 3 vol.%. A further increase in concentration leads to a decrease in the intensity of the peaks. The activation energy of charge release from traps, temperature of maximum of the peaks, and the magnitude of the accumulated charge in the traps have also maximal value at nanoparticle concentration of 3 vol.%. The study of charge characteristics of the nanocomposite with concentration of 3 vol.% after heat treatment shows that the intensity of TSD peaks, the temperature of peak maxima, and the activation energy of charge release increase with increasing pre-treatment temperature. The magnitude of the charge accumulated in traps at low treatment temperatures is practically unchanged but has a maximal value at treatment temperature of 140 °C owing to the increase in the number of traps.