Investigation of charge transport and trapping in LDPE and HDPE through space charge and conduction current measurements

Space charge observation and conduction current measurements have proved to be fundamental tools for the characterisation of the behaviour under electrical field of insulating materials. They provide complementary information on the processes of charge injection and transport, from the threshold for space charge formation to the conduction mechanism, which can help in understanding the relation between chemical-physical-microstructural properties and the electrical properties. Even apparently simple and widely-used materials such as low-density polyethylene (LDPE) and high-density polyethylene (HDPE) have not been exhaustively investigated as regards injection and transport mechanisms. The purpose of this paper is to provide a contribution to the investigation of charge trapping and transport mechanisms under DC electrical field, using both space charge and charging current measurements. The information obtained by these two techniques allows the correlation between charge accumulation and transport to be discussed. In particular, the threshold characteristics, which provide the behaviour of trapped charge and conductivity as a function of electrical field, are determined.