Preparation And Properties Of Functionalized Boron Nitride Thermally Conductive Composites

With the advent of the 5G era,various highly integrated electronic and electrical devices have posed unprecedented requirements and challenges for thermally conductive materials.New filler type thermally conductive polymer materials with high thermal conductivity,high integration and high density have become the favorites in the thermally conductive material industry.Hexagonal boron nitride is highly preferred due to its graphene-like structure and unique electrical insulation properties.In this thesis,functionalized boron nitride nanosheets are used as thermally conductive fillers to construct heat conduction channels in composites through the design of different thermally conductive microstructures,thus improving the thermal conductivity of the composites.The main work and results of the thesis are as follows:（1）The hydroxyl-functionalized BNOH nanosheets were prepared by ball milling method with glucose as ball milling agent,followed by settling and cleaning process.After freezing and immobilizing the BNOH nanosheets in the NFC gel using the complexation reaction of calcium ions with NFC,the gel was directly freeze-dried to obtain BNOH/NFC/Ca²⁺aerogel,followed by impregnation of PDMS into the aerogel to prepare PBXCa composites.The results showed that the maximum planar thermal conductivity of the obtained PB10Ca composites was 0.699 W·m^-1·K^-1,which increased the thermal conductivity by about 240%over that of the pure PDMS material,indicating that the BNOH nanosheets successfully constructed a three-dimensional network of interconnected structures with the assistance of NFC to form continuous heat transfer channels and enhance the thermal conductivity of the composites.（2）PVA/BNNH₂ composite films with BBNH₂nanosheets oriented and aligned in-plane were prepared by using the salt precipitation effect of saturated sodium sulphate solution on aqueous PVA solution.When the content of BBNH₂ nanosheets was 30 wt%,the in-plane thermal conductivity of the PVA/BNNH₂ composite film was 3.089 W·m^-1·K^-1,which was977.57%higher than that of the pure PVA film,indicating that the in-plane thermal conductivity of the composite film could be well improved due to the oriented arrangement of BBNH₂ nanosheets in the composite film,which formed a continuous heat conduction channel in the in-plane direction.can be well improved.Moreover,the mechanical properties of the composite films were tested,indicating that the incorporation of BNNH₂ nanosheets had a positive effect on the mechanical properties of the PVA/BNNH₂ composite films.（3）The PBI-BNOH composite filler was prepared by heating and stirring,and the PBI-BNOH/NFC composite film with anisotropic high thermal conductivity was prepared as a thermally conductive filler using vacuum filtration technique.When the content of PBI-BNOH composite filler was 35 wt%,the maximum in-plane thermal conductivity of the composite film was up to 3.85 W·m^-1·K^-1,which was increased by 902.01%compared with the pure NFC film,and the increase in thermal conductivity could be attributed to the arrangement of PBI-BNOH composite filler in the composite film along the laminar structure to form efficient and continuous heat conduction channels,thus improving the thermal conductivity of the composite film.thermal conductivity of the composite film.Meanwhile,the results of mechanical and dielectric properties tests show that the PBI-BNOH/NFC composite films have good mechanical properties and excellent dielectric properties,which are expected to be widely used in the field of electronic devices.