Effect Of Modified Micro-nano ZnO On LDPE Insulation Performance

Low-density polyethylene(LDPE),due to its simple processing,has outstanding insulation properties and good ductility and it has become a common material for the insulation layer of high-voltage DC cables.However,long-term exposure to high-voltage field strength will cause the performance of LDPE to deteriorate,and the insulation layer will fail with time.In order to meet the needs of human daily life for electricity,higher requirements have been placed on LDPE in engineering.In order to obtain materials with better insulation and better aging resistance,LDPE was cross-linked modified,filled with nanoparticles and blended with other polymers.At present,it is mainly modified by adding metal nano oxides to LDPE,such as MgO,SiO2,TiO2 and so on.However,nanoparticles will form agglomeration in LDPE,so it is necessary to modify the surface of nanoparticles so as to give full play to the role of nanoparticles in LDPE.In this paper,a series of micro-nano ZnO with different particle sizes were first prepared,and then the surface of ZnO was modified with octyltriethoxysilane(C8)and octadecyltrimethoxysilane(C18).Modified C8-ZnO and C18-ZnO are obtained;finally,LDPE is filled with surface modified nano-ZnO with different mass fractions by solvent method to prepare ZnO/LDPE composite material.The structure,morphology and crystalline state of ZnO were characterized by TEM,XRD and TGA.The results showed that micro-nano ZnO with different particle sizes were successfully prepared,and the prepared ZnO contained no impurities and had a good crystalline form.The morphology and chemical structure of the surface modified zinc oxide were characterized by HRTEM,FT-IR,TGA and DSC.The results show that both C8 and C18 have been successfully grafted on the surface of ZnO,and combined with DSC and HRTEM,it is found that C18-ZnO is crystalline,the thickness of the coating on the surface of ZnO is 1.6nm,C8-ZnO is not crystalline,coated The thickness is 1.1 nm.The effect of nanoparticles on the crystallinity of LDPE was studied by DSC and polarized light microscope.The results show that for pure ZnO,the crystallinity increases with the increase of ZnO mass fraction,and it is higher than the crystallinity of pure LDPE;for C8-ZnO and C18-ZnO,the crystallinity is lower than pure LDPE and after C18 change ZnO has the lowest crystallinity.Finally,the mechanical properties and insulation properties of the composite materials were tested,and the mechanical properties of different ZnO/LDPE were tested using a universal tensile machine.It was found that under the same strain,the stress of LDPE increased with the increase of ZnO mass fraction Increase,that is to say the increase of ZnO concentration weakens the toughness of LDPE.Next,the effects of mass fraction,particle size and different modified ZnO on the volume resistivity and current density of LDPE composites were compared using a high resistance meter.It is found that nano-ZnO(n)has higher volume resistivity and lower current density than micro-ZnO(?).Modified ZnO/LDPE have higher volume resistivity than unmodified ZnO/LDPE.And as the concentration of ZnO increases,the volume resistivity first increases and then decreases,but the current density is just the opposite.The maximum volume resistivity is C8-ZnO(n)/LDPE with a mass fraction of 3%.Compared with the addition of 3%unmodified ZnO(n),the resistivity of the composite material is increased by 2 times.The maximum volume resistivity is 8.2×1015 Q·m.And tested the relative dielectric constant of different composite materials,and found that the relative dielectric constant of ZnO/LDPE composites modified with C8 and C18 is lower than that of unmodified ZnO/LDPE.