Research On The Characteristics Of Low Density Polyethylene/Silica Dioxide Nanocomposites Under Tensile And Thermal Aging

Polyethylene nanocomposites not only have good tensile strength,high breakdown strength,low dielectric constant,and low conductance properties,but also improve the crystallinity of the material and electric field distribution,and inhibit the growth of electric branches.The space charge accumulation in the material can also be reduced,and the voltage level and capacity of the DC transmission can be improved.It is expected to become a new generation of high-voltage electrical insulation materials of high voltage direct current cable.In the process of operation,the cable will be subjected to the electrical,thermal,mechanical stressand chemical etching,leading to the deterioration of the insulation material,partial discharge,electrical tree and threatening the reliability of power supply.Therefore,the degradation characteristics of insulating materials under the influence of various factors are the focus of current research,and exploring whether polyethylene nanocomposites can keep good mechanical and electrical insulation performance in practical application environment is an important prerequisite for its popularization and application in high voltage power equipment.This paper combined with molecular simulation and theoretical models to research different concentration of LDPE/SiO₂ nanocomposite material’s physicochemical properties,dielectric properties and space charge characteristics,under the condition of mechanical stretching and thermal aging.The main work is as following:（1）The SiO₂ nanoparticles,which were handled by A-171（vinyl trimethoxy silane coupling agent）,were used to prepare LDPE/SiO₂ nanocomposites material with doping concentration of 0.5wt%,1wt%,3wt%and 5wt%.Study on the physicochemical properties,dielectric properties and space charge characteristics of composite materials,from the morphology,thermal stability,optical performance analysis,and high electric insulation properties on the polyethylene nanocomposites were explored,the optimal concentration ratio of nanoparticles was found out.（2）Research on the polyethylene nanocomposites’properties under condition of tensile was developed.The space charge distribution and dielectric properties under the tensile state was analyzed.According to the structure changes of polyethylene material and the test results,this paper researches and analysis the carrier injection,migration and accumulation in the tensile materials,and found that LDPE/SiO₂ nanocomposites have the ability of tensile resistance,and still maintain the ability of nanocomposites to restrain the space charge in the tensile state.（3）Based on the morphology,structural and electrical insulation properties of polyethylene nanocomposites after thermal aging,the thermal ageing reaction time and product types of pure LDPE and polyethylene nanocomposites were found.The dielectric properties and the distribution space charge of nanocomposites after aging were studied by using the molecular simulation.And the effect of aging products on trap depth within the material was also analyzed.An important conclusion was that LDPE/SiO₂ nanocomposites have the ability of anti-thermal ageing.（4）According to the results of experiment and simulation,the aging mechanism of polyethylene with SiO₂ nanoparticle,combing with the physical,physicochemical and dielectric properties of the nanoparticles and polyethylene was studyed.According to the quantum effect,small size effect,high surface energy and the properties of interface between LDPE matrix and the SiO₂ nanoparticles,this paper introduced an in-depth interpretation about the ability of the anti-thermal ageing and space charge inhibition in polyethylene nano composite material after aging,using the specific models and theories.