Influence of degree of crystallinity on DC-conduction of polypropylene

Abstract

Aim of this work was to study how degree of crystallinity influences the DC conduction characteristics of capacitor grade polypropylene (PP). PP pellets were pressed to 0.3 mm plates using two different cooling rates in order to vary the degree of crystallinity. The DC conduction currents were measured at 50 and 70 °C at 8-55 kV/mm. 3 h polarization and 15 h depolarization times were used. It turned out that temperature and the dielectric stress played a more dominant role regarding DC-conductivity than the obtained ~4 wt-% difference in crystallinity. Especially at 39-55 kV/mm, when temperature increased from 50 to 70 °C the DC-conductivity increased 10-15 times. There was however a trend related to the degree of crystallinity: the increase in crystallinity (more slowly sample cooling) led to lower conductivity values.