Construction Of Thermally Conductive Networks In Boron Nitride/Epoxy Composites And Their Effectiveness

With the development of electronic devices towards miniaturization,high integration,and versatility,the heat generated by electronic devices during high-power operation cannot be dissipated in a timely manner,which will affect the service life of electronic devices.Therefore,developing efficient thermal conductive polymer materials to adapt to the development of the electronic packaging industry is of great significance.Due to the low phonon transport capacity of polymer materials,they present low thermal conductivity defects in applications due to phonon scattering defects,making it difficult to meet the demand for fast thermal performance of electronic components.One of the effective ways to enhance the thermal conductivity of polymers is based on the filling of high thermal conductivity fillers.Boron nitride（BN）has excellent thermal conductivity（200 W/m K）,thermal stability and electrical insulation properties,and the use of BN to enhance the performance of thermally conductive materials has become a recent research hotspot.Previous studies have found that due to the extremely large surface area/thickness ratio of boron nitride,it is difficult to disperse it uniformly in epoxy resin,making the preparation of boron nitride/epoxy resin composites very difficult.In addition,the interfacial bond between boron nitride and epoxy resin is weak,and voids or microscopic holes are easily formed between the boron nitride particles and the epoxy resin matrix,which affects heat transfer,generates thermal resistance and reduces the thermal conductivity of the composites.This paper uses boron nitride as the thermal conductivity raw material and epoxy resin as the matrix.In response to the poor dispersion of boron nitride in epoxy resin and the interface thermal resistance between boron nitride and epoxy resin,this paper modifies the surface of boron nitride,blends it with epoxy resin,and constructs a three-dimensional thermal conductivity network within the epoxy resin using salt templates and carbonization synergistic modification methods,two efficient BN/epoxy resin composite thermal conductive materials were prepared separately.Studying the effect of surface modification of boron nitride and constructing a three-dimensional network on the thermal conductivity of composite materials,using the Y.Agari model to evaluate the rationality of the thermal conductivity of the produced composite materials,the research results can enrich the design ideas and preparation routes of thermal conductive composite materials.The important research results obtained are as follows:1.The BN@TACu/epoxy composites were prepared by a filler surface modification method by tannic acid-copper（TACu）synergistic modification of the boron nitride surface,using epoxy resin（E51）as the matrix and by co-blending.Tannic acid（TA）was adsorbed on the surface of the boron nitride nanosheets throughπ-πinteraction,and then formed a TACu cladding layer on the boron nitride surface through the coordination of TA with copper ions(Cu²⁺)to finally obtain BN@TACu filler particles.The results show that TACu successfully adheres to the BN surface,enhances the filler surface activity,improves the interfacial compatibility with the E51 matrix,constructs a continuous thermal diffusion network with excellent dispersion,and effectively improves the thermal conductivity of the boron nitride/epoxy composite.The thermal conductivity of the boron nitride/epoxy composite increases with increasing boron nitride content,reaching 1.61W/m K at a filler content of 30 wt%,which is 7.3 times higher than that of pure E51（0.22W/m K）.The thermal conductivity network factors（C₂）of BN@TACu/EP and BN/EP were 0.932 and 0.325 respectively,calculated by Y.Agari model analysis,indicating that the surface-modified boron nitride filler formed a reasonable thermal conductivity network in the composite system.And the thermal stability performance and mechanical properties of BN@TACu/EP epoxy composites were also improved.2.The aforementioned surface modification of boron nitride can effectively solve the problem of poor dispersion,but there is still room to improve the density of the thermally conductive network formed by the filler.Based on the above work,this work further explores the construction of a three-dimensional continuous and efficient thermally conductive BN network skeleton by using salt template and carbonisation co-modification method to prepare EP polymer-based thermally conductive composites with excellent performance.In this work,sodium chloride pellets,benzoxazine（PH-DDM）monomer and BN flakes were firstly mixed,pressurised and moulded,and then the salt pellet template was dissolved to form a porous structural material with a honeycomb shape.The resulting porous material was further carbonised at high temperature,benzoxazine was carbonised and covered on the BN network,and epoxy resin was added for curing to obtain three-dimensional carbonised epoxy thermally conductive composites（3D BN/C/EP）,and their structure,morphology and properties were characterized analytically.The results showed that the pre-constructed 3D BN skeleton could effectively improve the thermal conductivity of the composites and significantly reduce the internal interfacial thermal resistance of the composites,and the thermal conductivity of the composites 3D BN/PH-DDM/EP and 3D BN/C/EP increased accordingly with the increase of the boron nitride content,and when the boron nitride content in the composites was 38.86 wt%,the thermal conductivity of the composites 3D BN/PH-DDM/EP and 3D BN/C/EP was significantly enhanced.The thermal conductivity of 3D BN/PH-DDM/EP and 3D BN/C/EP was 3.02 W/m K and 4.27 W/m K,respectively.According to the Y.Agari model analysis and calculation,the thermal conductivity network factors（C₂）of3D BN/PH-DDM/EP and 3D BN/C/EP are 1.612 and 1.714,respectively,indicating the formation of stronger thermal conductivity network structures in the 3D BN/C/EP composite material system.A comparison of the thermal conductivity of the 3D BN/C/EP composites with that of commercial thermally conductive gaskets confirmed the superior thermal performance of the 3D BN/C/EP composites.The proposed method for the preparation of 3D BN/C/EP composites with synergistic salt template and carbonisation is able to build an effective 3D BN/C/EP network structure and achieve high thermal conductivity at the same time,which has a great potential for application in the field of electronic device fabrication.