Study On Preparation And Properties Of Thermal Conductive And Insulating Paper-based Materials Of Boron Nitride Nanosheets/Aramid Nanofibers

With the rapid development of science and technology,electronic components are gradually developing towards the high integration.The heat output of the equipment increases sharply with the enhancement of power density and integration,and the heat dissipation efficiently has become the core of the safe and effective operation of the equipment.The conventional thermal conductive material will no longer be applicable to new generation of electronic equipment due to its high quality,processing resistance and high coefficient of expansion.Aramid nanofibers(ANFs)paper-based material shows the characteristics of light weight,insulation,excellent mechanical strength and good flexibility,etc.,and it is widely used in the field of electrical insulation protection.However,the low thermal conductivity restricts its further development.Therefore,it is significant to develop the ANFs paper-based material which possesses good thermal conductivity and promote its application and development in the field of thermal conductive field,especially in electronic packaging and thermal interface materials.In this study,boron nitride nanosheets(BNNS)were used as thermal conductive fillers to improve the thermal conductivity of ANFs paper-based materials in two aspects of interface bonding and structural design.The interface bonding was enhanced by the introduction of"thiol-ene" click chemistry.And the density of heat conduction network was improved by building a double heat conduction network structure.The the ANFs thermal conductive and insulation paper-based materials were prepared by vacuum-assisted filtration technology.The effects of click chemistry and double network on the thermal conductive and insulating properties of the paper-based materials were studied,and the thermal conductivity mechanism of paper-based materials was explored.Firstly,ANFs and BNNS were prepared by chemical splitting method and exfoliating method,respectively,and the BNNS/ANFs paper-based material was fabricated by vacuum-assisted filtration technology.The results showed that the diameter of ANFs was about 20 nm.The diameter of BNNS exfoliated by molten hydroxide intercalation,hydrothermal method and microwave-assisted hydrothermal method was ranged from 200 nm to 500 nm.And the microwave-assisted hydrothermal method exhibited high yield with 19.4%.The prepared BNNS/ANFs paper-based composites exhibited good flexibility and layered structure,and its thermal conductivity and insulation properties increased gradually with the addition of BNNS.The results showed that the highest thermal conductivity,breakdown strength and volume resistivity of BNNS/ANFs paper-based composites reached 0.079 W/(m·K),123 kV/mm and 5.34×1015?·cm respectively with the 50 wt.%BNNS loading.The thermal conductivity increased by about 126%,which was ascribed to the establishment of effective thermal conduction pathway by BNNS.Besides,the mechanical properties of BNNS/ANFs pape-based composites decreased with the addition of BNNS.The tensile strength was about 39 MPa with 50 wt.%BNNS loading.Subsequently,the interface bonding between BNNS and ANFs was promoted by functionalized modification and "thiol-ene" click chemistry,and the f-BNNS/s-ANFs paper-based composites were prepared.The results showed that the thermal conductivity of f-BNNS/s-ANFs paper-based composites reached 0.224 W/(m·K),which was about 540%and 185%higher than that of pure ANFs(0.035 W/(m·K))and BNNS/ANFs paper-based composites respectively with the content of f-BNNS of 50 wt.%.And it still maintained good electrical insulating property with the breakdown strength and volume resistivity of 93.50 kV/mm and 1.24×1014 ?·cm.In addition,the tensile strength of f-BNNS/s-ANFs paper-based composites increased to 50 MPa,which was about 28%higher than that of the same content of BNN/ANFs paper-based composites.Considering the tensile strength,it is considered that when f-BNNS content is 50 wt.%,the thermal conductivity of paper-based material is the best,and the mechanical properties are effectively improved.The "thiol-ene" click chemistry effectively promoted the dispersion of BNNS in ANFs,and the synergistic effect of hydrogen bonding and covalent bonding significantly enhanced the thermal conductivity and interfacial bonding of paper-based composites,improving the mechanical properties.Finally,the SiO2 nanospheres were introduced to construct a double thermal conductive network.The morphology and size of SiO2@BNNS composite filler that designed by in-situ growth method and click chemical assembly method were investigated and the SiO2@BNNS/ANFs paper-based composites were prepared.The results displayed that the thermal conductivity of SiO2@BNNS/ANFs paper-based composites reached 0.196 W/(m·K),which increased about 460%and 149%compared with pure ANFs and BNNS/ANFs paper-based composites with 50 wt.%SiO2@BNNS loading.Importantly,the breakdown strength and volume resistivity of SiO2@BNNS/ANFs paper-based composites possessed 114 kV/11 and 6.30×1015 ?·cm,presenting satisfying insulating property.The SiO2@BNNS composite filler increased the density of the thermal conductivity network and perfected the structural of paper-based composites,improving the thermal conductivity.