Effect Of Doping Boron Nitride On The Thermal Properties Of Polymer Based Composites

Polymer materials are widely used in electronic,electrical,microelectronic packaging and other fields because of their excellent properties such as corrosion resistance,low dielectric constant,light weight,high strength and low insulation resistance.However,the thermal conductivity of polymer materials is generally very low,which makes it difficult to rapidly dissipate the heat generated by electronic devices,and therefore limits the polymer materials.Further development in this field.How to effectively improve the thermal conductivity of polymer materials to improve the efficiency and life of electronic and electrical insulation devices has become a very important research topic.Hexagonal boron nitride(h-BN)has graphite-like layered crystal structure and many excellent properties: insulation,low thermal expansion coefficient,stable chemical properties and high thermal conductivity,so it is considered as an excellent thermal conductivity filling material.(1)Epoxy resin is chosen as the base material because of its good mechanical properties,easy processing,good thermal stability and low price.The existing BNNSs and BNNPs in the laboratory were selected as inorganic fillers to prepare polymer composites with high thermal conductivity.The effects of different morphologies of hBN and surface functionalization of h-BN on thermal conductivity of composites were also studied.The experimental results show that the thermal conductivity of the composites increases with the increase of filler mass fraction,and the thermal conductivity of the composites can reach 1.7 W/(m·K)when the content of untreated boron nitride microsheets reaches 70%.On the other hand,considering the interfacial wettability of inorganic-organic materials,we used silane coupling agent KH-540(3-aminopropyl trimethoxysilane)to functionalize the surface of two kinds of boron nitride and compared them with pure boron nitride filling to study the effect of surface functionalization on the thermal conductivity of composite materials.(2)After a lot of experiments,it is found that there is a serious interfacial thermal resistance between inorganic filler BN and epoxy resin,and there is a large number of phonon scattering at the interface of the two phases,thus reducing the thermal conductivity.At the same time,the dispersion of micrometer boron nitride sheets with "bulk" morphology in the resin matrix is not uniform,and the effective overlap of heat conduction network paths between BN molecules is not satisfactory.The above two problems are well solved by the experimental study of ball milling assisted boric acid functionalization of h-BN.On the one hand,more active functional groups are ·grafted on the edge of boron nitride lattice,which improves both of them.The wettability of the interface,on the other hand,properly peeled the bulk boron nitride microsheets,formed more efficient heat conduction pathways,effectively improved the thermal conductivity.The thermal and mechanical properties of the composites were tested.(3)At present,the latest research idea of filling thermal conductive insulating polymer materials is to construct a three-dimensional thermal conductive network framework,and then encapsulate the resin into the framework to form high thermal conductive composites.In this chapter,by using BN suspension and melamine foam to co heat and dry it,build a three-dimensional structure heat conduction path with melamine foam grid as carrier,and then encapsulate the epoxy resin.The thermal conductivity of composites formed at a very low filling content of BN is obviously improved,which provides a new way of thinking for the preparation of high thermal conductivity composites.