Electrical breakdown in polyethylene and its morphology

Dielectric properties in semicrystalline polymers, especially electrical conductivity, thermally stimulated current or electrical breakdown have been often explained by analogous model of an inorganic crystal which has vacancies or interstitials for electron or hole traps, or an electronic band model of an amorphous semiconductor which should have a diffused edge of state density in a forbidden gap. However, a semicrystalline polymer has its own morphology, e.g. microbrownian motion in its rubber state, free volume, lamellae or spherulite structure, glass transition or crystal melting temperature and so on. Electronic properties, such as conductivity or breakdown strength must be closely related to those morphological properties. In this report, the relation between the unique morphology of polymers and breakdown strength is investigated for the case of Polyethylen (PE) where morphology changes could be created by mechanical drawing or annealing.