The electrical breakdown properties of low density polyethylene film due to morphological change

In order to investigate the effects of morphological changes on electrical breakdown, we studied direct current and impulse breakdown phenomena of low density polyethylene films annealed at 100°C for 60 minutes in silicone oil and subsequently cooled in various ways. The degree of crystallinity was estimated by infrared absorption and X-ray diffraction measurements for specimens slowly cooled in air, cooled in water, and cooled in liquid nitrogen (LN₂). The crystalline size and distribution of the specimen were measured by differential scanning calorimetry methods. The impulse breakdown strength at 30 and 50°C increased with decreasing crystallinity, suggesting a thermal electronic breakdown process. The impulse breakdown strength decreased with increasing temperature in line with Frohlich-type breakdown theory. The DC breakdown strength was only dependent on crystallinity in the high temperature region