Experimental Study On Preparation And Comprehensive Properties Of Boron Nitride/coconut Shell Carbon/polyethylene Composites

Good thermal conductivity,insulation,thermal stability and mechanical properties are very important for high density polyethylene（HDPE）composites in electronic and electrical fields.HDPE has the advantages of light material,low cost and long applicati on period;Boron nitride（BN）has good thermal conductivity,mechanics,thermal stability and insulation properties;Natural fiber is widely used in polymer composites because of its renewability,degradability and environmental protection.In this paper,BN and coconut shell carbon（CSC）were selected as fillers and HDPE as matrix.In order to improve the comprehensive properti es of HDPE composites,t heir mechanical properties,thermal stability,electrical properties and thermal conductivity were experimentally studied.In this paper,HDPE/BN,HDPE/CSC and HDPE/BN/CSC composite systems were prepared by melt blending and hot pressing.The microstructur e of the composites was characterized by X-ray diffraction（XRD）and scanning electron microscope;The tensile strength and Young’s modulus are used to measure the mechanical properties of the samples;The thermal stability of the sample was evaluated by t he initial decomposition temperature and the temperature at the maximum weight loss;The storage modulus,loss modulus and composite viscosity are used to measure the microstructure of the samples in the molten state;The electrical properties of samples are measured by volume resistivity,dielectric constant and dielectric loss;The thermal conductivity,crystallini ty and infrared thermal imaging were used to measure the thermal conductivity of the samples,and the thermal conductivity of HDPE/BN and HDPE/BN/CSC samples were theoretically calculated by EMA and Agari formula.The main work and corresponding results of this paper are as follows:（1）The mechanical proper ties and thermal stability of HDPE/BN/CSC composites are better than those of HDPE/BN and HDPE/CSC composites.After adding CSC,the void density of the filler decreases,delaying the mov ement of the polymer chain and enhancing t he tensile strength.The tensile strength of HDPE/25BN/3CSC（25wt%BN,3wt%CSC）samples was 23.76 MPa,which was18.92%higher than that of the matrix,and higher than that of HDPE/3CSC and HDPE/30BN binary composites;The blocking effect of CSC and BN hybrid network is enhanced,and the thermal stability of HDPE/25BN/3CSC sample is7.86℃higher than that of the substrate and 3.36℃higher than that of HDPE/30BN.（2）The filler network structure of HDPE/BN/CSC composite system is better than that of binary composite system,and has good dielectric and insulating properties.The storage modulus,l oss modulus and composit e viscosity of HDPE/BN/CSC composites are higher than those of binary composites,which reflects that there is a good filler network in HDPE/BN/CSC composites;Because the network structure restricts the movement of polymer chain and weakens the polarization of filler,the dielectric constant of HDPE/25BN/3CSC sample is lower than that of HDPE/25BN,and lower than that of pure HDPE,and the dielectric loss is also lower than that of pure HDPE;At 10⁵～10⁷ Hz,the volume resistivity of HDPE/25BN/3CSC sample is lower than that of HDPE/25BN,but still higher than that of pure HDPE.At 10⁷～10⁸ Hz,the volume resistivity of HDPE/25BN/3CSC sample is higher than that of HDPE/25BN,maintaining good insulation performance.（3）Due to the synergistic effect between BN and CSC,the thermal conductivity of HDPE/BN/CSC composite system is higher than that of HDPE/BN and HDPE/CSC composite systems.The thermal conductivity enhancement effect of CSC on HDPE is much less than that of BN.When a small amount of CSC is added to HDPE/BN system,the thermal conductivity enh ancement effect is higher than that of BN.The normal and in-plane thermal conductivity of HDPE/25BN/3CSC samples(0.94 W·m^-1K^-1、4.28 W·m^-1K^-1)are higher than that of HDPE/28BN samples(0.86 W·m^-1K^-1、3.61 W·m^-1K^-1).The in-plane thermal conductivity of HDPE/40BN/4.8CSC samples reached 5.29 W·m^-1K^-1,which was1222.5%higher than that of the matrix.XRD and melting property test results showed that CSC did not change the crystal structure of the composites.The result s of infrared thermal imaging are consistent with those of thermal conductivity test.In addition,EMA equation and Agari equation can predict the thermal conductivity of HDPE/BN and HDPE/BN/CSC composites in a small error range.