Thermal-Aging Behavior of Bo-Pp Films

The variation in electrical properties and morphology of biaxially-oriented polypropylene (BO-PP) films with thermal aging is discussed, using two kinds of BO-PP films. It was found that the thermal aging behavior of those two types of films depends on their initial morphology. The thermal aging gives rise to an increase in the degree of cyrstallinity due to crystallization of a part of the amorphous phase in BO-PP films. Crystal re-organization was also in-dicated, resulting in the improvement of the crystal perfection and the thermal stability. The increase in crystallinity enhances selective morphological change and also selective degradation in the amorphous phase. The morphological change due to the thermal aging manifested itself clearly in dielectric and electrical conduction properties in the form of an increase in primary relaxation loss peak and an increase in ionic conduction loss.