Preparation And Properties Of Hexagonal Boron Nitride Thermal Conductive Composites

Polymer materials are widely used in daily life due to their advantages of light weight,low manufacturing cost,easy processing,and excellent chemical stability.However,the thermal conductivity of polymers is incommensurably lower,which greatly limits their application in thermal management materials.A simple and effective method at this stage is to fill the polymer matrix with a certain high thermal conductivity filler to improve the thermal conductivity of the polymer material.Hexagonal boron nitride(h-BN)is similar to graphite in chemical structure and physical properties.It has the advantages of high thermal conductivity,excellent thermal stability,stable chemical properties,corrosion resistance and excellent electrical insulation of thermally conductive fillers.It is an ideal thermal conductivity filler.In this paper,h-BN was used as thermal conductivity filler,h-BN/PDA@PEI/epoxy resin(h-BN/PDA@PEI/EP)composite and h-BN/PDA@PEI/polyvinyl alcohol(h-BN/PDA@PEI/PVA)composite were prepared by hot pressing curing and melting extrusion,respectively,so as to be capable of good thermal conductivity.The main research contents are as follows:The chemical stability of hexagonal boron nitride is relatively high,resulting in poor interfacial compatibility between its lamellae and the polymer matrix.Surface modification of hexagonal boron nitride sheets is required to improve the dispersion of h-BN nanosheets in polymers,thereby reducing interface phonon scattering and improving the thermal conductivity of composites.In this paper,the surface of h-BN nanosheets was first modified by using PDA and PEI co-modifier to prepare h-BN/PDA@PEI filler.The amino group(-NH₂)is grafted on the surface of hexagonal boron nitride,which can produce chemical bond interaction with the polymer matrix,so that the interfacial bonding force between the polymer matrix and h-BN is improved.SEM results showed that PDA and PEI are uniformly deposited on the surface of h-BN when the content of PDA and PEI are both0.2 wt%,indiacating the surface modification effect is the best.Then,epoxy resin composites with different h-BN nanosheets and h-BN/PDA@PEI contents were prepared,and the thermal stability,thermal conductivity,and mechanical properties of the composites were compared.By analyzing the brittle fracture surface morphology of epoxy resin composites.The result showed that the h-BN/PDA@PEI has better dispersibility in the matrix,compared with the original h-BN nanosheets after surface modification treatment According to the experimental results,It is found that the thermal conductivity of epoxy resin composites increases with increasing the amount of thermally conductive filler,and the thermal conductivity of h-BN/PDA@PEI/EP composites is higher than that of pure epoxy resin and h-BN/EP composites material.The experimental results display that the thermal conductivity is 1.392 W m^-1K^-1when the mass fraction of h-BN/PDA@PEI reaches 40 wt%,which is 596%higher than that of epoxy resin(EP).Meanwhile,the prepared epoxy resin composite has good thermal stability and electrical insulation properties.In this paper,h-BN/PDA@PEI/PVA composite fibers were prepared by melt blending and extrusion using glycerol/PEG200 as plasticizer,h-BN/PDA@PEI as thermally conductive filler,and polyvinyl alcohol as matrix.The surface-modified h-BN/PDA@PEI can improve the compatibility of h-BN and polyvinyl alcohol interface and reduce the interfacial thermal resistance of the two phases.Comparing the thermal conductivity and mechanical properties of h-BN/PDA@PEI/PVA composite fibers and h-BN/PVA composite fibers,it is found that the enhancement effect of h-BN/PDA@PEI is better than that of h-BN.When the content of h-BN/PDA@PEI is 20 wt%,the thermal conductivity is1.311 W m^-1K^-1,which is 496%higher than that of pure PVA.In addition,the addition of filler improves the water resistance of the polymer,and the mechanical properties are also improved.In order to further demonstrate the practical application of the two composite materials prepared in this paper,we put the above two composite materials on a hot stage to conduct heating experiments,and use an infrared thermal imager to observe and record the surface temperature changes of the composite materials.The results show that under the same filler content,h-BN/PDA@PEI/EP composites and h-BN/PDA@PEI/PVA composites have faster heating rate,higher temperature and higher thermal conductivity than the corresponding pure epoxy resin and pure PVA.Above all,the composites prepared in this paper have certain application in the fields of electronic information industry,electronic packaging industry and functional clothing.