Preparation And Dielectric Properties Of LDPE/zeolite Nanocomposite

The rapid development of modern cable industry for high voltage cable especially the insulation material requires higher insulating properties,however the common polymer materials difficult to meet the future development of power and electronic industry needs.Taking advantage of nano materials apply on the polymer modified research is an effecient way to improve the dielectric material performance,and it is also becoming the research focus in the field of engineering dielectric as well.Especially with the condition of nano dielectric correlation theory model is still not clear,and the existing theories have poor universality,sufficient nano dielectric and its related properties researches have very important application significance and theoretical value.In this article,type 4A and NaY zeolite nanoparticles with special porous structure are doped in low-density polyethylene(LDPE)by melt blending and the dielectric properties of LDPE/zeolite nanocomposite are studied intensively.Using the porous structrure of nano zeolite and its enormous specific surface area which is far more than in the ordinary materials,in order to enhance the special properties of the effect nanoparticles in the composite,increase the nano of dielectric interface effect,and establish the relevance between microstructure and dielectric properties,discusse the mechanism of LDPE/zeolite nanocomposite performance.The main achievements of this article are as follows:1.Using type 4A and NaY nano Zeolite particles composites with Low-density Polyethylene(LDPE)material,prepared different doping concentrations for the LDPE/Zeolite nanocomposites.In order to enhance nanoparticles dispersion effect,the preparation process is improved by using solution as a carrier of nanoparticles in blending process.Microstructure characterization of nanocomposite found tha the zeolite nanoparticles' dispersion is relatively uniform,especially in NaY type zeolite particle dispersion effect,and can not find any obvious reunion phenomenon;Infrared spectrum test found that nano zeolite doping does not affect to polyethylene matrix molecular chain composition,and at the same time,it does not find other impurities and groups,especially does not find residual hydroxy group which could be induced in the preparation process by ethanol solution carrier;DSC test found that nanocomposites' crystallinity degree decreased,which is due to nano zeolite doping reduced the number of spherulites with large size,and then reduce the gaps between the molecular chains,reduces the structural defects to improve the polyethylene molecular chain group distribution.2.The dielectric spectra of LDPE/zeolite nanocomposites and pure LDPE are tested by broadband dielectric spectrometer,at two different temperatures 20 ? and 80?,.The study found that nanocomposites' dielectric constant generally decline,which is relative with the nano zeolite porous structure.At the same time,it shows that the dielectric loss at low frequency is relative with the Low-Frequency-Dispersion phenomenon induced by zeolite and the residual water in nanocomposites.The law of the dielectric loss in middle frequency range is in according with the Maxwell-Wagner(M-W)theory.The loss peak position calculated from M-W equation is consistent with the experimental curve Using Arrhenius equation calculation,it shows that the loss peak of nanocomposites move to higher frequency at high temperature.The dielectric loss at high frequency is applied to the Na+ irons' relaxation behavior in the zeolite super cage which can make long range movement.3.Space charge distributions of LDPE/zeolite nanocomposite are tested using pulse eletro-acoustic(PEA)method at high electric field and short circuit,respectively,and trap distribution are analyzed by thermal stimulation current test as well.The results indicate that the zeolite doping can effectively improve the space charge distribution in LDPE/zeolite nanocomposite,suppress the charge injection and greatly reduce the amount of heterocharges.The charge decay in LDPE/zeolite is significantly weaker than that in LDPE,which indicates that the space charges in LDPE/zeolite nanocomposite belong to deep trapping states.The result of thermal stimulation current test further verifies the results of space charge distribution test:most of traps in LDPE/zeolite nanocomposite belong to deep trapping states and the quantity of traps is much larger than that in LDPE.It can be explained that the zeolite nanoparticles increase the interface regions and introduce small size cavity traps from the porous surface of zeolite,which results in the increase of deep traps.These deep traps capture homocharges at high electric field near the electrodes,raise the potential barrier for charge injection,which suppress the space charge injection.4.Through the LDPE/zeolite nanocomposite AC and DC breakdown performance testing it is found that nanocomposites' breakdown field strength significantly improved,4a type zeolite and NaY type zeolite doping make LDPE/zeolite nanocomposites' AC breakdown field strength increased by 15%and 20%,respectively.DC breakdown test found that DC breakdown field strength of nanocomposites with a certain doping concentrations make 6-10%of the ascension,but the shape parameter declined,which means the material uniformity and stability will be descended.Only the DC breakdown field strength of LDPE/zeolite nanocomposite with zeolite NaY type raised and make the shape parameter remain stable for its execellent dispersion of zeolite nanoparticles.5.The conductive current characteristics of LDPE/zeolite nanocomposite were studied.The result showed that nano doping improves the space charge injection threshold value,which verified the space charge distribution phenomenon;At the same time traps and trap levels introduced by nano zeolite doping make carrier mobility reduced,suppress the charge injection and restrain the charge mobile of impurity ionization,and reduce the conductance of nanocomposite effectively.