Packet-like space charge dynamics in polyethylene with various crystallinity

Packet-like space charge behavior in polyethylene was firstly indentified in the early 1990´s. Much effort has been done to clarify it in physical essence. The space charge density and migrating velocity of space charge packet are of the two main parameters to characterize this phenomenon. The micro-structure could significantly influence charge trap density and trap level, which therefore influence the space charge migration. In this study, linear low density polyethylene (LLDPE) samples with various crystalline rate and gradient crystalline were prepared by hot pressing process with controlling cooling rate. The evolution of space charge packet in the LLDPE samples sandwiched by semiconducting electrodes under DC 40MV/m stress at 40degC was monitored by pressure wave propagation (PWP) method. The influence of crystallinity and micro-morphology on charge injecting rate, mobility and decaying procedure in LLDPE are discussed. The results show that the heating process history could significantly influence the dynamics of packet-like space charge.