Role of Atmospheric Gases in the Space Charge Polarization of Low-Density Polyethylene in a Divergent AC Field

Charge injection into lowdensity polyethylene by a divergent ac field at room temperature has been investigated using a high-resolution ther mally stimulated discharge current technique. It was observed that TSDC spectra obtained after charging with ac fields were dissimilar to those obtained with dc fields of similar magnitude and were influenced by sam ple history and by the nature of the gaseous charging environment. Thoroughly outgassed samples charged in a high vacuum showed little change in charge release characteristics for ac and dc charging fields. Evidence of additional large polarizations was found in samples charged with ac fields only in a gaseous environment. It is suggested that this is due to the trapping of electrons by ionized gas molecules adsorbed by the polymer. The presence of oxygen gas initiated irreversible changes in the polarization behavior of LDPE by interaction with an ac field.