Study On The Dielectric Properties Of Polymer Matrix Composites With Low Dielectric Loss And High Thermal Conductivity

At present,due to dielectric properties polymer matrix materials have excellent processing and thermal conductivity,its attracted much attention in the field of industry and military.However,the research on the dielectric properties composites with great thermal conductivity has not been carried out.The existing dielectric properties polymer matrix materials have been unable to meet the requirements of high thermal conductivity and high dielectric properties under high performance and extreme conditions.In this paper,alumina（Al₂O₃）as conductive filler,polypropylene（PP）as the matrix,high dielectric properties barium titanate ceramics（BT）would be filled and modified.Thermal conductive filler/dielectric ceramic/polymer matrix composites will be prepared and tested.The main conclusions are as follow:（1）In the thermally conductive filler/polymer two-phase composite,when the Al₂O₃/PP=1:1（volume fraction）,Its dielectric constant from pure PP 2.74 to 5.00 increase of 82%（1000Hz）,dielectric loss from PP 0.0055 to 0.0011 drop of 80%.Breakdown strength reached 42MV/m,thermal conductivity from 0.176W/（m·k）increased to0.346W/（m·k）.（2）In order to improve the dielectric properties of the thermal conductive composites further,a series of thermally conductive filler/dielectric ceramic/polypropylene composites were prepared by adding high dielectric constant barium titanate ceramics.The results show that,when Al₂O₃:BT=1:4,the volume fraction of the filler is 50%,the dielectric constant of the composite peaked at 15.59,it is about 4.7times of the pure polypropylene material,and the dielectric loss of the composites is generally small,and it stay around0.05.The thermal conductivity increased from polypropylene 0.176W/（m·k）to 0.898W/（m·k）enhance the rate of 4.1 times.The breakdown strength reached 47.35MV/m,the energy density reaches maximum.（3）The barium titanate ceramics were modified by chemical coating method using tartaric acid as chelating agent.A modified BT/Al₂O₃/PP composite was prepared.The results show that,when Al₂O₃:modified BT=1:4,the volume fraction of the filler is 50%,the dielectric constant from unmodified composite15.59 to modified composite20.73increase of 33%（1000Hz）,Dielectric loss from unmodified composite0.0030 to modified composite0.0015 drop of 50%.The thermal conductivity increased from unmodified composite 0.898W/（m·k）to 1.239W/（m·k）enhance the rate of 31%.However,the breakdown strength after modification decreased to 44.87MV/m.The experimental results show that the polymer composites with low dielectric loss and high thermal conductivity can be prepared by adding thermal conductive fillers and high dielectric ceramics to the polymer matrix,and the surface treatment of the filler also has the same function.