Effect of an antioxidant additive on morphology and space-charge characteristics of low-density polyethylene

The effect of an antioxidant additive on the morphology and internal charge distribution under DC electric stress of low-density polyethylene (LDPE) is considered. Two batches of polyethylene samples are studied, one containing no additives and the other containing about 1% antioxidant. Samples from each batch were electrically aged at a stress of 60 kV mm(-1) for 48 h and allowed to discharge in a closed circuit for a further 48 h. Measurements of the bulk-charge distributions and associated internal electric-stress distributions were made using a laser-induced pressure-pulse technique. Material characterisation techniques were used to relate these measured bulk-charge distributions to the morphologies of the polymers. It is shown that the inclusion of the antioxidant had a significant effect on the morphology of the polymer. Moreover, the space-charge distributions for each of the polyethylene types is shown to be remarkably different after DC electrical ageing. These charge distributions are also shown to cause significant changes in the interface stresses of the samples. Results indicate that the microstructure of the dielectric has perhaps second-order effects on the trapping/detrapping and transportation of charge. On the other hand, the macrostructure of the polymer, such as defect or impurity content, seems to have a significant effect on space-charge formation.