Relations between aging, space charge and polarization of polyethylene

The relations between aging, space charges and polarization of polyethylene (PE) under the influence of high electrical fields (above 20 kV/mm) are discussed in light of our electrical aging model. Below a so-called critical field, the activation volume of the aging process is dependent on the field-induced strain. It is our contention that strong charge injection occurs only after nanocavity formation, i.e. above the critical field. Above the critical field, the amorphous phase is significantly deformed and weak van der Waals bonds are broken, leading to another faster aging regime. This corresponds to the onset of permanent electroluminescence and also to the formation of the wave packets observed in space charge measurements. The possible relation between the nanocavity formation at moderate fields and bonds breaking at higher fields proposed in our aging model and various polarization measurements is discussed. It seems that the wave packets and the negative resistance observed above ∼70 to 100 kV/mm in PE are associated with a steady state in the field-induced defect formation. Some calculations of the space charge concentrations based on the basic principles of our aging model and on the above discussed assumptions show an excellent agreement with experimental results.