Preparation Of Graphite/resin Composite Material And The Research On Its Thermal Conductive Properties

With the broadening of the applications of thermal conductive polymer materialsthese years, the reports about the thermal conductivity of polymer materials haveconstantly increased. Currently, high thermal conductive fillers are often used toimprove the poor thermal conductive properties of polymer materials. Graphite hasbeen an ideal filler for thermal conductive polymer materials due to its high thermalconductivity and other excellent properties. Epoxy is characterized by its outstandingadhesive property, processability and formability, which contributes it to be the matrixmaterial of thermal adhesion agent, paint, potting material to make up for the poorcorrosion resistance of metal material. In the present manuscript, we report asystematic investigation of the graphite/epoxy thermal conductive material.Meanwhile, another common thermosetting phenolic resin has features of good heat,flame and electrical resistance and self-curing property, which can simplify themodeling process. Therefore, graphite/phenolic resin thermal conductive material wasstudied.We examined the thermal and mechanical properties affected by various factorssuch as the amount of graphite, size, size ratio and the amount of carbon black. Itindicates that with the increase in graphite, the thermal conductivity improvesobviously, though the grow rates are varied. As with the former, when the additionpercent of graphite is15%, the grow rate of thermal conductivity is increased. Thethermal conductivity reaches the peak when graphite makes up45%, and remain thesame ever since. The later keeps increasing. When it comes to the compressivestrength, the former increases firstly and then decreases, always less than that of pureepoxy. The latter keeps decreasing. And the electrical property also firstly increasesand then decreases. The size of graphite has a great influence on the property ofcomposite material. For graphite/Epoxy material, when the amount of graphite is setas35%, the thermal property increases with the growth of the size when graphite failsto form a thermal conductive network in the matrix; With the decline of the size,graphite foam a conductive net through the matrix, and the thermal conductivity isimproved. The compressive strength tends to increase firstly and decrease then withlarger size of graphite. In terms of graphite/phenolic resin materials, as the sizeincreases, the conductivity increases firstly and reduced subsequently, and the compressive strength keeps reducing. The thermal conductivity reaches the highestpoint when the size of graphite is38μm. A small amount of fine particles couldincrease the thermal conductivity, while an excess amount would bring an oppositeresult. Two kinds of composite materials began to increase with the increase of carbonblack, and then to decrease. It has the best thermal conductivity when1%carbonblack is added.Regarding graphite/epoxy material, when it is added a small amount of graphite,the Maxwell model can well predict the thermal conductivity of the compositematerial. When the amount becomes larger, the measured value is greater than thepredicted value. The measured value of natural flake graphite is less than the Hattatheoretical model plane predictive value, but greater than the fitting value along thethickness direction. The ability to improve the thermal conductivity of epoxy of flakegraphite is greater than that of spherical graphite. For graphite/phenolic resincomposite material, the measured value is closer to the planar predicted value byHatta model, but lager than theoretical value, which shows that the flakes mainlystretch in the matrix under the modeling pressure and it contributes to better thermalconductivity.In addition, we also discussed the coupling agent’s effect in the thermalconductivity of graphite/epoxy material and the processing condition’s effect in that ofgraphite/phenolic resin material. The result presents that when added1.5%silanecoupling agent, the graphite/epoxy material can own both the best thermal andmechanical property. Increasing the molding pressure can increase the thermal andelectrical conductivity and compressive strength of graphite/phenolic resin material,but too large pressure would bring a poorer electrical conductivity. Appropriateextension of curing time when the intense reaction happens, can improve the thermalconductivity of graphite/phenilic resin material.