Research On Thermal Conductivity And Electrical Properties Of PP/SEBS/BN Composite Insulation Materials

At present,electric power equipment is developing in the direction of high power,miniaturization and light weight.The long operation of the equipment will inevitably lead to a large amount of heat accumulation in the cable insulation materials,which will affect the accuracy and service life of the equipment.In serious cases,it will lead to safety accidents.For example,insulation materials of charging pile cables,supercomputer power lines and some large-capacity electrical equipment lines need strong heat dissipation capacity.Therefore,it is of great practical significance to research and develop composites with high thermal conductivity and excellent electrical insulation properties.In this thesis,PP/SEBS/BN composites are prepared by changing the ratio of PP/SEBS and the blending order of BNNSs,using PP/SEBS as the matrix and boron nitride nanosheets(BNNSs)as the thermal conductivity filler,then the influence of BNNSs on the thermal conductivity and insulation properties of the composites is explored.The microscopic features of the composites are characterized by scanning electron microscopy(SEM)and polarized light microscopy(PLM),and the dispersion of BNNSs is analyzed;the thermal conductivity and crystallization properties of the composites are tested,and the construction of internal thermal conductivity pathways and melt crystallization behavior of the materials are analyzed;the conductivity properties and breakdown properties are tested under different temperature conditions,and the carrier migration behavior is analyzed;the dielectric properties at different frequencies are tested,and the internal interface polarization behavior of the materials is analyzed.The experimental results show that the selective distribution of BNNSs thermal conductive fillers in PP/SEBS matrix can be achieved by adding BNNSs in different blending order.When the BNNSs content is fixed at 20 phr and the PP/SEBS ratio is4:6,the(SEBS+BNNSs)+PP composite prepared by blending SEBS with BNNSs first and then adding PP has the best thermal conductivity of 0.4254 W/(m·K),which is0.1885 W/(m·K)compared with the PP/SEBS matrix material at the same ratio.The thermal conductivity is improved by 225%.In the matrix material PP/SEBS,with the increase of SEBS content,the spherical crystal size gradually decreases,the crystallization temperature gradually decreases,the breakdown field strength gradually decreases,and the conductivity change is not obvious.After the addition of BNNSs,the spherical crystals of PP/SEBS/BN composites are refined into grains,the melt peak area is reduced,and the crystallization temperature increased by 10°C on average compared with the matrix material in the same ratio;the total potential barrier of ionic conductivity of the composites becomes smaller at 20～140°C,and increases at 140～160°C.Moreover,at 60～160°C,the conductivity of the composites is two orders of magnitude lower than that of the PP/SEBS matrix material in the same ratio,and the electrical insulation performance is better than that of the matrix material.The addition of BNSS improves the breakdown field strength of the composites,among which(SEBS+BNSS)+PP composites have the best breakdown performance,with the highest breakdown field strength of 92.62 k V/mm,which is increased by 30.24%compared with the same proportion of matrix materials.At the same time,BNNSs thermal conductive filler will slightly reduce the dielectric properties of the composites,but the relative dielectric constants are between 2.46 and 2.64,and the loss angle tangent value under working frequency is less than 0.001.The PP/SEBS/BN composite prepared in this paper has excellent thermal conductivity and insulation properties,which lays a research foundation for the development of insulating cable materials with high thermal conductivity.