Preparation And Thermal Conductivity Of BN/Polymer Composites

With the rapid development of electronic equipment,the heat emission of electronic equipment has become one of the most critical problems.In recent years,polymer-based thermal management materials have been widely used for heat dissipation materials in electronic devices,because they are easy to process and have low cost.However,the thermal conductivity of polymers is very low,so it is urgent to enhance the thermal conductivity of polymer.Hexagonal boron nitride as a high thermal conductivity filler has been paid more attention,it can show higher thermal conductivity by coupling with the compound of metal filler.This thesis has tried to establish a thermal conductivity path by means of the functional h-BN and metal nanoparticles and nanowires composite.Thus,it can improve the thermal conductivity of polymer matrix composites.The main research contents of this thesis are as follows:（1）A new strategy for the preparation of BN-Ni/epoxy resin composites（hm BN-Ni/EP）by the synergistic effect of magnetic field and hot pressing on the orientation of BN-Ni composite fillers is proposed.Compared with other BN/EP composites obtained only by hot pressing or magnetic field orientation,hm BN-Ni/EP composites have better BN orientation in the in-plane direction.At a load of 30 wt%BN-Ni,the thermal conductivity of hm BN-Ni/EP reaches 2.42 W·m^-1K^-1,1145%higher than that of pure EP.The increased thermal conductivity of hm BN-Ni/EP is attributed to the high in-plane orientation of BN-Ni through the synergistic action of magnetic field orientation and hot pressing.At the same time,the prepared hm BN-Ni/EP composite material has good insulation and mechanical properties,which is conducive to its industrial application in electronic packaging.（2）A new BN/Ag NWs@Ni boron nitride hybridization strategy was constructed,and on this basis,BN/Ag NWs@Ni/EP composites were prepared,which were placed in an external magnetic field to dynamically improve the in-plane or out-of-plane thermal conductivity of the composites in real time by changing the direction of the magnetic field.Due to their large aspect ratio,Ag NWs can be used as"bridges"to connect different two-dimensional BN sheets to form a heat conduction path.By changing the direction of the magnetic field,the Ag NWs@Ni will be oriented in either an in-plane or out-of-plane direction.At 40 wt%BN/Ag NWs@Ni,the thermal conductivity of the composites is 0.824W·m^-1K^-1 in the out-of-plane direction and 0.723 W·m^-1K^-1 in the in-plane direction,and the corresponding of thermal conductivity enhancement is 429%and 359%,Respectively.at the same time,BN/Ag NWs@Ni/EP has good mechanical and dielectric properties,which is conducive to its industrial applications in electronic packaging.（3）Flexible thermally conductive materials are often required in industrial applications,so BN-Ag NWs/PVA composite films with good thermal and mechanical properties are prepared by solvent evaporation.At 40 wt%mass fraction,the out-of-plane thermal conductivity of the composite reached the highest level,which was 0.81 W·m-1K-1,which was 224%higher than that of pure PVA film,indicating that the thermal conductivity of composite film was greatly improved because BN-Ag NWs formed a continuous heat conduction channel in the composite film.Moreover,the addition of BN-Ag NWs has a positive effect on the mechanical properties of BN-Ag NWs/PVA composite films.