Preparation And Properties Of Boron/polyurethane Thermally Conductive Composites

Hexagonal boron nitride has outstanding thermal conductivity,insulation properties and chemical stability,therefore,it is considered as an ideal thermal conductivity filler.However,blending it with polyurethane（PU）can result in weak interface effects,hindering its large-scale application.To address this issue,this study utilized non-solvent induced phase separation（NIPS）in mixed solvents to optimize the interface properties between filler particles and polyurethane.As a result,a flexible and high thermal conductivity boron nitride/polyurethane（h-BN/PU）composite material was developed.Three preparation methods were tested and analyzed to optimize the development of the insulating material:（1）The structure and properties of h-BN/PU composite films fabricated using mixed solvent via NIPS method was investigated.Unmodified h-BN was used as a thermal conductive filler to prepare the h-BN/PU composite film,and the effects of h-BN content on the microstructure and properties of the resulting PU were studied.The results show that the interface between the unmodified h-BN and PU is optimized by using the mixed solvents.When the h-BN content is 60wt%,the h-BN/PU composite film exhibit good mechanical properties and thermal conductivity.The stress,strain,and thermal conductivity of the 60%h-BN/PU composite film prepared using the proposed method were 307.59%,1466.12%,and70.85%higher than those of 60%h-BN/PU-NIPS（traditional method）,and 175.46%,9122.16%and 28.24%higher than those of 60%h-BN/PU-SE（traditional method）,respectively.Moreover,the thermal conductivity of the 60%h-BN/PU composite film was 218.71%higher than that of PU alone.The resistance value of the 60%h-BN/PU composite film was 23.9×10¹²Ω·cm,which exceeded the electrical insulation standard（10⁹Ω·cm）.（2）In the second method,the structure and properties of h-BN/PU composite films using modified h-BN surfaces were investigated.By modifying the surfaces of h-BN,the interfacial compatibility between the filler and the matrix is improved,resulting in the formation of more heat conduction pathways.Four different silane coupling agents,specifically 3-Aminopropyl-triethoxysilane（APTES）,3-Glycidoxypropyltrimethoxysilane（GOPTS）,3-（Trimethoxysilyl）pr-opylmethacrylate（TMSPMA）and 3-Mercaptopropyltriethoxysilane（MPTS）were used to modify h-BN,and the resulting h-BN/PU composite films were prepared and characterized.Upon further analysis of the modified h-BN/PU composite films resulting from each silane coupling agent,it became evident that the composite film prepared with TMSPMA exhibited superior mechanical properties and thermal conductivity.The stress and strain of the T-BN/PU composite film were 9.65±1.40 MPa and 759.88±67.93%,respectively,indicating outstanding flexibility.The thermal conductivity of the T-BN/PU composite film was 407.06%higher than that of PU.Furthermore,the resistance value of the T-BN/PU composite film was 36.3×10¹²Ω·cm,indicating remarkable insulation properties.（3）The structure and properties of the modified T-BN/PUF-BNNS composite fibers prepared using T-BN and BNNS were studied and analyzed.T-BN/PUF-BNNS composite fibers were prepared by incorporating T-BN in the wet spinning process,where mechanical induction was used to align the h-BN along the drafting direction.Results showed that the stress of T-BN/PUF-BNNS composite fiber was 5.28%higher than that of T-BN/PU composite membrane.The heat dissipation capacity of the T-BN/PUF-BNNS composite fiber was significantly improved compared to that of the T-BN/PU composite film,exhibiting superior thermal conductivity stability in the temperature range of 2～80℃.