Study On Thermal Conduction Modification And Preparation Process Of Epoxy Based On Double Percolation Effect

With the increasing demand for lightweighting in various fields of industry,carbon fiber reinforced epoxy-based composite materials have a lot of applications due to their advantages such as low density,easy processing and molding,high strength,and corrosion resistance.However,carbon fiber reinforced epoxy-based composite material has the defect of poor thermal conductivity in the thickness direction,which limits its application to structures with high thermal conductivity requirements.By adding a thermally conductive filler such as graphene to epoxy resin,its thermal conductivity can be improved.However,there are still some drawbacks for filled thermally conductive polymer materials.When the content of thermally conductive fillers is low,the thermal conductivity of polymer composites is poor and cannot meet the requirements of practical use.When the content of thermally conductive fillers is high,the thermal conductivity is good.However,thermally conductive polymer materials have the disadvantages of significantly reduced mechanical properties and filling difficulties.Therefore,the current research focus is mainly on how to obtain higher thermally carbon fiber reinforced epoxy-based thermally conductive composites with lower filler content.Double percolation effect provides a new approach that allows the material to form thermally conductive paths with less thermally conductive filler.It refers to the use of two resin matrixes to form a two-phase incompatible matrix structure,so that the thermally conductive filler is selectively distributed on one of the continuous phase resins.Based on the double percolation effect,epoxy resin/ phenolphthalein polyaryletherketone(PEK-C)/grapheme nanoplates(GR)three-phase composites were prepared,and epoxy resin and PEK-C were used as the two-phase incompatible resin matrix,and GR was used as the thermally conductive filler.The gel point and phase transition time of epoxy resin and PEK-C were tested,and the curing process was formulated.The solution method was used to prepare epoxy/PEK-C/GR composites.The contact angles of each phase of the composite material were tested,and the selective distribution of the GR filler was predicted based on the Young's theory.The microstructure of the composite under different matrix compositions and GR fillers were observed under electron microscope to verify the selective distribution and explore the micro-mechanism of changes in material properties.A series of thermal conductivity tests were performed on the double percolation structure matrix-based composites and pure epoxy-based composites under different GR fillers loading to investigate the effect of the double percolation effect on thermal conductivity.The composites and pure epoxy were compared on glass transition temperature,thermal stability and thermal expansion properties.Through dynamic morphology observation,it was found that phase separation in epoxy resin/PEK-C blended matrix occurred at 61 minutes at150?.The rheological test results showed that the gelation reaction in epoxy resin/PEK-C blended matrix begins at 90 minutes at 150?.Through the contact angle test and the Young's equation,the wetting coefficient ?? was calculated to be 1.57,and graphene will be preferentially distributed on the PEK-C phase.Observed through microscopic morphology,when the mass ratio of epoxy resin to PEK-C was 90 to 10,PEK-C was dispersed in the epoxy resin in the shape of sea-islands.When the mass ratio of epoxy resin to PEK-C was 80 to 20,the composite material matrix formed a phase inversion structure.Thermal conductivity test showed that the thermal conductivity of the matrix of epoxy resin blended with PEK-C with a mass ratio of 80:20(referred to as 80EP20PEK-C)is higher than that of epoxy resins as a whole.Even at a very low filler content of 0.1phr,the thermal conductivity was significantly improved(increased by 25.4%)compared to composites with epoxy resin matrix(increased by 8.3%).In the range of 0.1-1.0phr of filler in this study,the amount of filler with the best thermal conductivity modification effect could be reduced by 50% through the double percolation effect.The glass transition temperature test showed that the glass transition temperature of pure epoxy resin is 213.1 oC,and that of the composites with a mass ratio of epoxy resin to PEK-C to GR which is 80 to 20 to 0.5(referred to as 80EP20PEK-C0.5GR)is 227.2 oC.According to the results of the thermal stability test(TGA),compared with pure epoxy resin,the thermal decomposition temperature T5% of the composite 80EP20PEK-C0.5GR was reduced from 322.7 oC to 320.1oC,but T10% increased from 352.6 oC to 354.9oC.And the carbon residue rate increased from 24.2% to 30.5%.According to the thermal expansion performance test analysis,below the glass transition temperature,the average CTE(coefficient of thermal expansion)of pure epoxy resins,EP80PEK-C20GR0.3 and EP80PEK-C20GR0.5 are respectively 6.77*10-5,6.71*10-5 and 6.38*10-5,and the thermal expansion coefficient of composite materials is lower than that of pure epoxy as a result.