| Phthalonitrile resins are widely used in aerospace,ships,electronic and new energy fields,but their low thermal conductivity seriously restricts their further application.In order to solve this problem,a simple and efficient method is to fill thermally conductive and electrically insulating fillers to the resins.Phthalonitrile composites with high thermal conductivity,electrical insulation and good thermal stabilities were prepared by using new types of fillers,designing the composite structures and adjusting the direction of fillers.In this paper,alumina-coated graphite core-shell structure particles were obtained by coating the graphite surface with a uniform and dense alumina insulation layer,using a liquidphase chemical precipitation method with aluminum nitrate nonahydrate as alumina source and sodium dodecyl sulfate as the anionic surfactant.Polymer-based composites were prepared by filling new core-shell particles into phthalonitrile resins.The thermal conductivity of the composites increases with the increase of the content of fillers,and the composite can still maintain good electrical insulation under the content of 20 wt%core-shell particles.Compared with the glass transition temperature of pure phthalonitrile resin(46?),the glass transition temperature of the composites decreased slightly but still high(above 450?).The ceramic insulation layer is covered on the surface of carbon material to combine the advantages of high thermal conductivity of carbon material and electrical insulation of ceramic material.The application of new fillers has greatly broadened the application field of phthalonitrile resins.The bulk boron nitride(BN)was successfully exfoliated into few-layered boron nitride nanosheets(BNNSs)by wet ball-milling.This physical exfoliation method can prepare BNNSs on a large scale and high quality.Phthalonitrile microspheres with low crosslinking density were prepared by reaction-induced phase separation methods.By controlling the crosslinking density of phthalonitrile microspheres,thermosetting microspheres could be melted and reshaped at high temperatures.Using uncross-linked phthalonitrile resin as adhesive,the BNNSs-coated phthalonitrile core-shell microspheres were prepared by coating the surface of phthalonitrile microspheres with BNNSs,and then the core-shell microspheres were hotpressed into composites with a three-dimensional(3D)continuous BNNSs thermal conductive network.The composites with 3D continuous thermal conductive network have a phase separation structure and the thermally conductive filler was a continuous phase,and it can greatly reduce the fillers content.At 40 vol%BNNSs content,the thermal conductivity of the composite was increased to 4.282 W·m-1·K-1,which was 16.16 times of the pure phthalonitrile resin and 2.21 times of the same content of randomly distributed filler composite;in addition,the weight loss temperature(Ts and T10)and the char yield at 100?(Yc)of the composite increased to 567?,684? and 85.3%,respectively,which were 50?,121? and 13.3%higher than the pure phthalonitrile resin.The uniform dispersion and directional arrangement of high content BNNSs in the matrix of phthalonitrile resin were achieved by the solution mixing method and hot-pressing method.Compared with random fillers distribution,directional fillers can show more special physical properties and higher performance.The microstructure of the directional BNNSs composites prepared show that BNNSs is oriented in the direction perpendicular to the pressure.For 40 vol%oriented BNNSs composite,the thermal conductivity along the filler alignment was 7.835 W·m-1·K-1,and the thermal conductivity perpendicular to the filler direction was 1.622 W·m1·K-1,which was 29.6 and 6.12 times of the pure phthalonitrile resin,respectively.The simple and efficient hot-pressing method provides a feasible approach for adjusting the orientation of 2D fillers,which is of great significance to realize the anisotropic thermal conductivity of composites. |
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