Electret stability related to spherulites in polypropylene

Electret charge stability has been related to the size of the spherulites in polypropylene. As the size of the spherulites is decreased the stability is increased. This is seen for isothermal conditions at 90 and 120 °C as well as for 90 % relative humidity at 50 °C. The charge release temperature is also increased in thermally stimulated voltage discharge experiments as the size of the spherulites is decreased. The size of the spherulites is controlled though the cooling rate from polypropylenes liquid state.