Study On Preparation,Structure And Properties Of Polyolefin Nanocomposites

High-voltage direct current(HVDC)electrical insulating materials show great advantages due to low loss in long-distance and large-capacity power transmission,but space charge accumulation easily causes breakdown under high-voltage DC electric fields,thereby reducing the reliability and service life of insulating materials.Therefore,the study of HVDC insulation materials has great theoretical significance and practical application.In this paper,linear low-density polyethylene(LLDPE),polystyrene(PS),polyethylene grafted polystyrene(PES)and ethylene acrylic acid copolymer(EAA)are used as the main substrates,and graphene(GR)and hexagonal boron nitride(h-BN)are used as nano-fillers to prepare HVDC insulating polyolefin nanocomposites,and their space charge accumulation and breakdown field strength characteristics were studied.The preparation of the nanocomposites provides a new idea for the development of new HVDC polyolefin nanocomposites.4-[4-(p-toluenesulfonyloxy)phenoxy] phenyl 2-methyl-acrylic acid(MTE)containing active double bonds was synthesized from 4,4’-dihydroxydiphenyl ether(HDE),methacryloyl chloride and p-toluenesulfonyl chloride.Then,MTE and styrene(St)were solution-polymerized to prepare St-MTE copolymer(PSM).LLDPE/PES/PSM/GR nanocomposites were prepared by melt blending technology using LLDPE,PES and PSM as raw materials and GR as nano-filler.And the effect of GR on the properties of LLDPE/PES/PSM/GR nanocomposites was studied.The fluorescence emission spectra showed that there was a strong π-π interaction between GR and the aromatic rings in matrix.DSC test analysis showed that the introduction of GR had no significant effect on the crystalline of LLDPE.Dielectric properties analysis shows that LLDPE/PES/PSM/GR nanocomposites doped with a small amount of GR had good dielectric properties.The electrical insulating properties of LLDPE/PES/PSM/GR nanocomposites were significantly improved due to the introduction of a large number of deep traps by GR,and the internal space charge was significantly suppressed.When the GR content was 0.005 wt%,the DC breakdown strength of LLDPE/PES/PSM/GR nanocomposites reached 400.1 k V/mm,which was 8.5 % higher than that of LLDPE/PES/PSM blends,and the cumulative increase was 41.6% higher than that of pure LLDPE.Modified h-BN(T-BN)containing reactive groups was prepared by etching h-BN with thionyl chloride,and then T-BN was further covalently modified with succinic acid(named C-BN).Three nanocomposites,LLDPE/EAA/h-BN,LLDPE/EAA/T-BN and LLDPE/EAA/C-BN,were prepared by melt blending using LLDPE and EAA as raw materials.The FT-IR and XPS spectra analysis proved that T-BN and C-BN with active groups on the surface were successfully prepared.The space charge accumulation of nanocomposites can be effectively inhibited by the introduction of unmodified/modified h-BN.When the T-BN content was 0.5 wt%,the DC breakdown strength of LLDPE/EAA/T-BN nanocomposites reached 464.1 k V/mm,which was 12.9 % higher than that of LLDPE/EAA blends.When the C-BN content was 0.5 wt%,the DC breakdown strength of LLDPE/EAA/C-BN nanocomposites reached 480.8 k V/mm,which was 17.0 %higher than that of LLDPE/EAA blends.This study opens up a new way for the development and application of GR and covalently modified h-BN in HVDC polyolefin insulated cable materials.