Characterizing Traps Distribution in LDPE and HDPE through Isothermal Surface Potential Decay Method

The energy distribution of trapped charges and traps in low density polyethylene (LDPE) and high density polyethylene (HDPE) were investigated based on isothermal surface potential decay (ISPD) method in this paper. Corona charging measurement was conducted by a non-contact setup, which was specially designed to obtain the decay characteristics of thin polymer films with varied charging polarity implying the dynamics of electrons or holes. Considering space charge profile of polymers under high dc electric field and detrapping mechanism after removing the field, a model based on ISPD was proposed to obtain the trap distribution of polymers. By assuming different charge spatial distribution features, two kinds of trap energy distributions of LDPE and HDPE were achieved respectively, which reveal similar distribution characteristics. It is shown that there are mainly deep traps in LDPE and HDPE both for electron-type and hole-type traps. The mean trap depth of hole-type traps is lower than that of electron-type ones in LDPE, whereas the situation in HDPE is reversed. Additionally, more trapped charges are accumulated in HDPE with deeper trap depth than that of LDPE. It is indicated that the obtained results may imply essentially nature of hole/electron traps, i.e., the electron-type traps show an inter-chain character whereas the character of hole-type traps is intra-chain. Furthermore, the energy distribution of traps is further related to the unique aggregation structure of LDPE and HDPE.