Preparation Of Functionalized Boron Nitride Nanosheets And Their Application In Thermal Conductive Composites

Boron nitride nanosheets（BNNS）have excellent thermal,electrical,optical and mechanical properties.They are often added into polymers as fillers to prepare packed thermal conductive composites,which are used in the field of thermal management materials such as electronic packaging.Except for van der Waals force,there are some ionic bond forces between hexagonal boron nitride（h-BN）layers,which result in high energy consumption and small transverse size during the exfoliation process.In addition,h-BN has stable structure,smooth basal plane and few active sites,which makes BNNS easily agglomerate and limits its application scope.In order to overcome the above problems,functional boron nitride nanosheets were prepared by means of mechanical sand-milling exfoliation and interface chemical modification,and were added into thermoplastic polyurethane（TPU）by solution mixing and hot-pressing methods to prepare thermal conductive composites.The main research contents are as follows:（1）L-lysine（Lys）graft-functionalized BNNS（Lys@BNNS）was prepared by mechanical sand-milling,and then the Lys@BNNS/TPU composites were prepared by solution blending and hot-pressing.The effects of functionalized BNNS content（0.1 wt%to 5 wt%）on the thermal conductivity and mechanical properties of the composites were investigated.The addition of Lys enhances the interfacial interaction between Lys@BNNS and TPU,resulting in better thermal conductivity and mechanical properties of the composites.When the Lys@BNNS content is 3 wt%,the thermal conductivity and tensile strength of the obtained composites are 90%and 16%higher than those of pure TPU,respectively.Lys@BNNS/TPU with better thermal and mechanical properties can be used as a heat dissipation material and has application potential in the field of thermal management materials.（2）PEI@BNNS with a transverse size of about 600 nm and a thickness of about 2.5nm was successfully prepared by sand-milling with polyethyleneimine（PEI）as a sanding aid.Different contents of PEI@BNNS（0.1 wt%to 5 wt%）were added to TPU to prepare composites,and the relationship between thermal and mechanical properties with filler content was deeply explored.The larger diameter-thickness ratio of PEI@BNNS increases its contact area with TPU,which weakens the interface phonon scattering.And the higher graft content increases the hydrogen bond density between PEI@BNNS and TPU.Thus,the thermal and mechanical properties of the composites have been improved.When the amount of PEI@BNNS is 1 wt%,the composite has high thermal conductivity(0.61W·m^-1·K^-1)while maintaining the insulation and tensile properties,providing a new material for effective heat dissipation of electronic devices.