Research On The Dielectric And Space Charge Properties Of LDPE Nanocomposites After Thermal Aging

Compared with the neat low density polyethylene（LDPE）,LDPE/MgO nanocomposites have the higher dielectric strength and mechanical properties and the ability to suppress space charge accumulation,which are expected to be the neat generation insulation.However,during the long-term operation of high-voltage power equipment,the thermo-oxidative degradation of polymer insulation may be accelerated by the thermal aging,leading to theβ-scission of polymer chains and producing a large amount of free radicals,which may decrease the insulation of materials.Therefore,it is necessary to research the polyethylene based nanocomposites with anti-thermal aging ability.In this paper,we chose LDPE/MgO nanocomposites to do the research and also chose LDPE/SiO₂ and LDPE/ZnO nanocomposites as the control groups.The sectional morphology,molecular structure,breakdown strength,dielectric properties and space charge behavior of nanocomposites before and after thermal aging were researched.The results revealing the anti-thermal aging ability of nanocomposites.The main innovative achievements of this paper are as following:（1）The sectional morphology,physicochemical properties,dielectric properties and space charge behavior of LDPE/MgO,LDPE/ZnO and LDPE\SiO₂ nanocomposites were researched in this paper,which showed the best percentage for the insulation nanocomposites.The results pointed out how nanoparticles affect the insulation properties of nanocomposites.（2）The effect of thermal aging on the insulation properties of nanocomposites were researched in this paper.The results revealed the best percentage of nanoparticles for the insulation nanocomposites during thermal aging,which provided guidance for preparing the nanocomposites with anti-thermal aging ability.（3）The dielectric properties of nanocomposites before and after thermal aging were researched in this paper.The results showed whether nanocomposites can remain low dielectric loss after thermal aging.Furthermore,according to the Debye fitting of imaginary permittivity,the effect of thermal aging on the DC conductivity nanocomposites during thermal aging were analyzed,which revealed the mechanism that nanocomposites can remain low dielectric loss after thermal aging.（4）The space charge behavior of nanocomposites before and after thermal agingwere researched in this paper.According to the calculation of space charge amount and charge mobility,we analyzed whether nanocomposites have the ability to suppress space charge accumulation in matrix after thermal aging.The depth and density of charge traps during thermal aging were calculated in this paper.The results revealed the mechanism that nanocomposites can suppress space charge accumulation during thermal aging.（5）The hydrogen bonds between nanoparticles and polyethylene matrix,the active energies of nanocomposites,the oxygen diffusion of nanocomposites and the reactive energies between nanoparticles and polyethylene chains were calculated in this paper.The results revealed the mechanism that nanoparticles can enhance the anti-thermal ability of polyethylene,which provided guidance for preparing nanocomposites with anti-thermal aging ability.Additionally,by calculating the density of state（DOS）of polyethylene with C=O bonds,how the thermal aging affect the charge traps of materials was discussed in this paper.This paper shows that MgO and ZnO nanoparticles can improve the anti-thermal aging ability of polymer matrix,and can also protect the insulation properties of materials during thermal aging.Additionally,based on the hydrogen bond interaction,activation energy,oxygen diffusion,and interaction energy of materials,the mechanism that nanoparticles can enhance the anti-thermal ability of polyethylene matrix was discussed in this paper,which provided guidance to select the proper nanoparticles and concentrations for the nanocomposites with anti-thermal aging ability.