The Research On Antistatic And Enhanced Thermal Conductivity Wood-Plastic Composites

In order to eliminate the electrostatic hazard in industrial or domestic environment and improve the heat transfer efficiency of the low-temperature hot water radiant heating floor system,this work takes wood fiber/high density polyethylene(WF/HDPE)wood-plastic composite material as the research object.Firstly,the mechanical properties of WF/HDPE composites were optimized by coupling agent and compatibilizer.Then,multi-walled carbon nanotubes(MWCNTs)with excellent electrical conductivity and thermal conductivity were selected as functional fillers,and antistatic high thermal conductivity wood-plastic composites were prepared by mechanical blending and compression molding.At the same time,the percolation model is used to describe the conductive percolation of MWCNTs in WF/HDPE composites.Finally,the surface modification of MWCNTs was carried out by using coupling agent and surfactant.The effects of dispersibility and compatibility of MWCNTs on the electrical,thermal and mechanical properties of WF/HDPE composites were investigated,and field-emission scanning electron microscopy(FESEM),Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),differential scanning calorimetry(DSC)and other characterization techniques were used to analyze the mechanism of action of surface modifiers on a microscopic scale.The main research results are as follows:1)WF content has a significant effect on the mechanical properties of WF/HDPE composites.The mechanical properties test showed that the composite had the highest flexural strength,elastic modulus and tensile strength when the mass fraction of WF to HDPE was 6:4 without adding any additives other than lubricant.They reached 19.63 MPa,1951 MPa,and 11.10 MPa,respectively.Vinyl trimethoxysilane coupling agent(A-171)and maleic anhydride grafted polyethylene(MAH-g-PE)have obvious improvement on the mechanical properties of WF/HDPE composites.When used alone,the method of using A171 to modify WF in improving the mechanical properties of composites is better than the method of adding MAH-g-PE as a matrix compatibilizer,but the mixed use of the two is better than the single use.SEM and DSC mutually confirmed the improvement of the interfacial properties of composites by A-171 and MAH-g-PE.2)With the increase of MWCNTs loading,the electrical resistivity of WF/HDPE composites decreases,the thermal conductivity increases,and the mechanical properties decrease.When the addition amount of MWCNTs is 0.5?4%,the electrical resistance value of the composite material is 6.56x105-2.73x104 ?,which meets the electrical resistance value of antistatic wall surface and ground of GB50174-2017(2.5×104?1.0×109?).The thermal conductivity increases from 0.35 W/(m·K)to 0.66 W/(m·K),which is 90%higher than that of pure WF/HDPE composites.At the same time,the flexural strength,tensile strength and elastic modulus of WF/HDPE composites decreased to 23.25MPa,14.01 MPa and 1950 MPa,respectively.But they still meet the physical performance requirements of wood-plastic decorative panels specified in GBT24137-2009.(The average bending strength is?20.0 MPa,the minimum value is ?16.0 MPa;the flexural modulus is ?1800 MPa).3)Conductive percolation occurs in WF/HDPE composites with MWCNTs.The electrical resistivity test results show that when the content of MWCNTs reaches 0.5wt%,the resistivity of the composite material drops sharply by 8 orders of magnitude.It can be judged that the conductive percolation threshold of MWCNTs in WF/HDPE composite is 0.5wt%.The classical percolation model was used to fit the conductivity of composites with different MWCNTs content.The calculated conductivity percolation threshold was 0.477vol%(0.473wt%),which is very close to the experimental value.However,the thermal conductivity percolation phenomenon does not appear in the range of 0-8wt%MWCNTs added in this paper.4)Treatment of MWCNTs with silane coupling agent A-171,surfactant PVP,PEG,SEDBS can effectively improve the dispersion and compatibility of MWCNTs in WF/HDPE composites,and thus improve the electrical,thermal and mechanical properties of composites.Among them,A-171 has the greatest effect on reducing the resistivity of MWCNTs/WF/HDPE composites,which makes the resistivity drop by one order of magnitude,which is 87.3%lower than that of untreated,followed by PEG,SEDBS and PVP.PEG has the most significant effect on the improvement of thermal conductivity,which is 85.5%higher than that of MWCNTs,followed by A-171,PVP and SEDBS.The most significant modifier for improving the mechanical properties of composites is A-171.After modification,the flexural strength of the composite is increased to 26.47 MPa,the elastic modulus is increased to 2399 MPa,and the tensile strength is increased to 18.64 MPa.They were increased by 5.8%,13.7%,and 12.9%,respectively,when the MWCNTs were untreated.In practical applications,if there is a higher requirement for antistatic effect,A171 modifier can be used.If the requirement for heat conduction is higher,MWCNTs can be treated with PEG.5)Using A-171 to treat MWCNTs with different mass fractions and then incorporating them into WF/HDPE composites,it is found that the conductivity percolation threshold of modified MWCNTs in the composite is shifted to the left.It shows that MWCNTs can achieve higher conductivity with lower filling amount due to the improved dispersibility and compatibility after A-171 treatment.