Study On Exfoliated Graphite/Polypropylene Thermal Conductive Polymer Composites

With the industrial development and social progress, the application of thermalconductive materials is more and more extensive. Because of good chemical corrosionresistance and insulation, easyforming, excellent anti-fatigue performance, polymer materialsget people’s wide attention. To improve polymer materials’ thermal conductivity, usingthermal-conductive fillers became the main research direction.Polypropylene(PP) filled with exfoliated graphite(EP) were investigated by roll mixingand hot press method. The effects of filler content,particle sizes, mixed filling, surfacetreatment and sisal fiber coated with exfoliated graphite on the thermal conductivity,mechanical properties and thermal stability were discussed detailedly by the apparatusmeasuring the thermal conductivity of polymeric materials and other moden analyticalmethods, such as electronic universal testing machine, thermogravimetric analyzer(TGA), andscanning electron microscopy(SEM). Experimental research found that:The addition of EP filler into the PP material increases its thermal conductivity. Whenthe filling rate is over30%, thermal conductivity rises faster, and it achieves “percolation”threshold. When the filling rate is50%, the thermal conductivity of composite material up to1.791W/(m·K) and it is9.43times that of pure PP. The mechanical properties increase andthen decrease. When the filling rate is between30%and40%, it achieves the best overallmechanical properties. Small size particles can improve the heat resistance of compositematerials, but the change of amount has little effect on the thermal stability. The larger fillerparticles can more easier to improve the thermal conductivity whereas the mechanicalproperties and heat resistance properties are superior to that filled with larger size. When themixture of hybrid particles is at a perferable mass ratio, composite material can exhibit thehighest thermal conductivity. The tensile and flexural properties of composite materialincorporated with hybrid particles are higher than the cases where only filler with single largesize particles are used. When the EP particles are treated with coupling agent, the thermalconductivity and mechanical properties of composite materials are improved. But when the coupling agent is overdose, the properties will decrease. Coupling agent treatment has littlehelp on improving composite materials’ thermal stability. Using sisal fiber(SF) exfoliatedgraphite can improve the thermal conductivity of composite materials, but the mechanicalproperties decrease.