The energy distribution of trapped charges on the surface of cross-linked polyethylene thermally aged at different temperatures

In this paper, the energy distribution of trapped charges on the surface of cross-linked polyethylene (XLPE) thermally aged at 100 °C and 160 °C were studied by the isothermal surface potential decay method. It was found that the surface traps of unaged XLPE were mainly deep ones of both electron-type and hole-type. In the process of thermal aging at 100 °C, the surface traps of XLPE were still mainly deep traps. As the aging time increased, the density of shallow traps increased, and the density of deep traps didn't change much. In the process of thermal aging at 160 °C, the density of shallow traps of both electron-type and hole-type ones increased greatly, and the density of deep traps of both electron-type and hole-type ones decreased sharply. At the same time, the energy levels of hole-type traps decreased. Under the thermal stress, the increase in the density of shallow traps may be due to an increase in aging products such as carbonyl (C=O); the decrease in the density of deep traps should be due to a decrease in chemical defects in the crystalline regions because of the destruction of spherulites. Differences of the energy distribution of trapped charges on the surface of XLPE aged at two different temperatures may be caused by the differences in the way that crystal structures deteriorate.