Conductivity And Trap Properties Of Zeolite/LDPE Nanocomposites

With the rapid development of modern electric power industry,the performance of high voltage cables,especially insulation materials,is becoming more and more demanding.The common polymer materials are becoming more and more difficult to meet the needs of the future electric and electronic industry.The using of nanomaterials to modify polymers is an effective way to improve dielectric strength of insulating materials,and is also a hot topic in the field of engineering dielectric.In this paper,we selected nanozeolites with special porous nanostructures which are different from ordinary nanoinorganic oxides as dopants,and prepared many kinds of nanozeolites composite polyethylene(LDPE)materials.The preparation process of composite materials with stable quality and uniform dispersion of nanoparticles has been mastered.The conductivity and trap properties of the composites doped with 4A and Na Y type nanozeolites in LDPE were studied.The porous structure and the specific surface area of nanozeolite far exceed the specific surface area of ordinary materials,which enhance the role of nanoparticles in composite and interfacial effect in nanodielectric.Dielectric properties of zeolite/LDPE nanocomposites were investigated by dielectric spectroscopy,conductive current test,isothermal discharge test and space charge distribution test.At the same time,an isothermal space charge decay method is proposed to calculate the trap level parameters of composite materials.The results are compared with the trap parameters calculated by the isothermal discharge current method,and the same laws and conclusions are obtained.Through dielectric spectroscopy experiment,it was found that at room temperature and high temperature,the dielectric constant of 4A zeolite/LDPE nanocomposites is slightly larger than LDPE,while the dielectric constant of Na Y zeolite/LDPE nanocomposites is slightly smaller than LDPE.This is related to the porous structure and the dielectric constant of nanozeolites.At the same time,the low frequency loss of zeolite/LDPE nanocomposites is related to zeolite particles and internal residual water molecules.Through the study of conductive current properties of zeolite/LDPE composites,it is found that nanozeolites effectively enhance the threshold field strength of space charge limited current.Meanwhile,trap level parameters of nanocomposites were calculated by isothermal discharge current experiment.It was found that a large number of trap levels were introduced into nanocomposites.The number of traps in the composites was significantly higher than that in pure polyethylene and increased with the doping concentration increased.This reduces the carrier mobility in the composite,prevents the charge injection,and reduces the conductivity of nanocomposites.The space charge suppression of composite materials is studied by the electro acoustic pulse method and trap energy level distribution is calculated by using space charge decay in short circuited state.It is found that the doping of nanozeolite can effectively inhibit the accumulation of space charge at high field and reduce the number of hetero-polar charge.The variation of trap energy level distribution of zeolite/LDPE nanocomposites is consistent with isothermal space charge decay method and isothermal discharge current method.Therefore,the method proposed in this paper is effective to calculate trap energy level by space charge decay,and the validity of the space charge distribution test is also verified.