Space Charge Characteristics And Electrical Properties Of Three-layered MgO/LDPE Nanocomposites

Nano-doping modification is an effective way to improve the electrical properties of polymer insulation materials,however in the actual doping process,the nano-size effect is not better reflected due to the unavoidable clustering of nanoparticles.The multi-layer dielectrics have attracted much attention because of their special interface structure,which makes the multi-layer dielectrics have some special electrical properties.The study of the interface charge and dielectric properties can help to reveal the mechanism of the electrical properties of the multilayer polymer nanocomposite.The main effort is devoted to the investigations on the space charge characteristics and the trap energy levels of different structured three-layer Mg O/LDPE nanocomposites.By taking the space charge characteristics and the trap energy levels as the entry point,the mechanisms corresponding to the electrical properties of three-layer films are studied.The single-layer LDPE and Mg O/LDPE nanocomposite films,and three-layer composite films with different compositions were prepared by melt blending and hot-pressing.The dispersion of nanoparticles and the microstructure and morphology of the three-layer cross-sections were investigated by SEM and FTIR,which can confirm nano-composite and interfacial delamination effect.The results show that the monolayer and three-layer nanocomposite films of the nanocrystalline Mg O particles dispersed and layered uniformly can be prepared by controlling the temperature and pressing time of the hot-pressing process.The space charge characteristics of three-layer nanocomposite films with different structures were investigated by the pulsed electro-acoustic technique(PEA).The results show that a large number of trap distribution at the interface of thethree-layer structure sample plays an important role in charge injection and dissipation,and these traps at the interface between the layers may capture moving charge to form interface charge layer.The accumulation of charge greatly reduces the electric field at the interface,and forms barrier at the interface,which reduces the charge injection and dissipation rate and restrains the further injection and dissipation of charge.Nano-doping and three-layer composite structure effectively improves the dielectric properties of LDPE.Both the nano-doping and the inter-layer interface structure brings new dipole moments into the LDPE matrix,which improve the relative permittivity and dielectric loss of three-layer composite films.The results of PSD show that 1wt% nano-Mg O doping has little effect on the trap depth,but it greatly increases the trap density in the nanocomposite.The introduction of the inter-facial layer structure of polyethylene makes the three-layer produce a large number of shallow trap relatively with depths of 3.55-5.13 e V in the films.The Weibull distribution of the dielectric breakdown strength of the three-layer and single-layer dielectrics shows that the carrier trapping at the interface between the dielectric layers and the blocking action of the potential barrier can effectively improve the breakdown strength of the three-layer composite film.To a great extent,this effect overcomes the degradation of breakdown of nano-composite dielectric because of nano-doping.