Effect of morphology and traps on DC conductivity and breakdown of polyethylene nanocomposites

MgO/LDPE nanocomposites with various nanofiller loadings are fabricated and the morphology and trap properties are characterized to investigate their effect on DC conductivity and electrical breakdown strength. It is found that DC conductivity depends on both shallow and deep traps. As the nanofiller loading increases, the density of shallow traps increases, leading to higher shallow trap-controlled hopping conductivity, while the deep traps increase firstly due to the formation of isolated interfacial regions and then decreases caused by the overlapping of interfacial regions, resulting in the variation in charge trapping-detrapping dynamics. An equation considers both the shallow trap-controlled hopping and the charge trapping-detrapping processes is derived to calculate the DC conductivity of MgO/LDPE nanocomposites, and the calculation results are consistent with experiments. The DC electrical breakdown strength is influenced by both the morphology and deep trap properties. At low nanofiller loadings, higher crystallinity and smaller crystallite size may block the motion of molecular chains in LDPE nanocomposites, and deep traps formed in interfacial regions hinder the charge transport. The synergetic effects of nano-doping on morphology structure and charge carrier transport enhances the DC electrical breakdown strength of MgO/LDPE nanocomposites.