Concurrent space charge and current density measurements in additive-free LDPE

The authors report an initial investigation into space charge dynamics in insulating polymers. In particular, consideration is given to the effect of electrode materials on space charge accumulation and conduction processes in low density polyethylene. Based on the Pulsed Electro-acoustic (PEA) technique a new system which is capable of measuring space charge and current simultaneously in a planar sample has been constructed. Space charge distribution and current in additive-free Low Density Polyethylene (LDPE) films with different electrode materials under dc electric stress at room temperature were monitored. The materials used for the electrode are Semicon and Aluminium. Aluminium (Al) electrode was evaporated onto the sample and the Semicon (Sc) press-moulded from granules was attached to the LDPE sample. Experiments were carried out using combinations of these two types of electrodes. The homo charge observed is believed to be originated from charge injection across the electrode/LDPE interfaces. It has been found that both space charge formation and conduction characteristic are affected by the electrode materials. It has also become clear that space charge and current measurements are the essential tools to characterize the behaviours of polymeric materials.