Preparation And Performance Research Of Composite With High Thermal Conductive And Insulating Which Have BN-MWCNT Isolated Thermally Conductive Network

At present,the preparation of polymer-based insulating and high thermal conductivity composite usually needs fill a large amount of insulating and thermally conductive fillers,which leads to reducing of processability and mechanical properties.Filling carbon-based high thermal conductivity fillers and insulating thermally conductive fillers to polymers were achieved more higher thermal conductivity,but that also causes significant decrease in volume resistivity.In this study,polycarbonate（PC）as the polymer matrix,multi-walled carbon nanotubes（MWCNT）and hexagonal boron nitride（h-BN）as carbon-based high thermal conductivity fillers and insulating thermally conductive fillers.Construct isolated thermally conductive network by layered coating two types fillers,to preparation insulating and high thermal conductivity composites with low filling content and well mechanical propertiesThe results showed that the PC@MWCNT@BN composites was prepared by double-layer coating had well thermal conductivity at low fillers content.hen the content of MWCNT is 1.2wt%and h-BN is 15.3wt%,the diffusivity and thermal conductivity of composites are 0.56mm²/s and 0.77W/m·K,which are 4.3 times and3.7 times than pure PC.But the volume resistivity of composites was reduced from1.4*10¹⁶Ω·cm to 3.2×10⁹Ω·cm.The PC@MWCNT@BN/PA6 composites was prepared by double-layer coating under low-temperature hot pressing.The diffusivity and thermal conductivity of composites are 1.05m²/s and 1.64W/m·K which are 8.1 times and 7.8 times than pure PC.At the same composition,the thermal conductivity and volume resistivity of PC@MWCNT@BN/PA6 composites was higher than composites which prepared by melt blending and single-layer coating.Observation of the microscopic morphology of the composites by SEM proved that the MWCNT-BN isolated thermally conductive network was formed inside.The dielectric test showed that the dielectric constant of the composite material was 7.54 at 10³ Hz,and the dielectric loss was 0.69.However,the tensile strength and flexural strength of the composites were obviously lower than the composites prepared by melt blending and pure PC.In further work,different sizes of PC particles and microspheres were prepared,and then PC（1mm）@MWCNT@BN/PA6 and PC（30μm）@MWCNT@BN/PA6 comp-osite materials were prepared by electrostatic adsorption with low-temperature hot pressing.The results showed that the diffusivity of PC（1mm）@MWCNT@BN/PA6 and PC（30μm）@MWCNT@BN/PA6 composites were reached 0.63mm²/s and 0.69 mm²/s,which are 4.8 times and 5.3 times that of pure PC.The thermal conductivity has reached0.9W/m·K and 1.03W/m·K,which are 4.28 times and 4.9 times that of pure PC;The volume resistivity of composites can reach 4.28×10¹⁵Ω·cm and 3.26×10¹⁵Ω·cm respectively.Observing the microscopic morphology of the composites by SEM,it is found that the isolated thermally conductive network with smaller network unit size is formed inside.The dielectric test showed that the dielectric constants are 5.68 and 6.28at 10³ Hz,and the dielectric loss are 0.074 and 0.054.The mechanical properties of composites that prepared with smaller PC microspheres have been significantly enhanced.The tensile strengths of PC（1mm）@MWCNT@BN/PA6 and PC（30μm）@MWCNT@BN/PA6 composites are 36.2MP and 44.5MPa,which are 56%and 69%of the tensile strength of pure PC,and the flexural strength is 79.5MPa and 81.4MPa respectively,which are the same as the flexural strength of pure PC.