Preparation And Properties Of Polypropylene-Based Thermal Conductive Composites

In this article, the formula of polypropylene-based thermal conductivecomposites was determined, and the influence of prescription and processingtechnology on the thermal conductivity of composites was studied throughexperiments. Thermal conductivity of vertical direction and plane directionwas tested, and the thermal diffusicity, electrical conductivity, specific heatand melt flow rate were also tested. The influence of prescription andprocessing technology on the thermal conductivity was investigated bythermal conductivity and thermal diffusivity, and its influence on melt indexwas determined by melt flow rate test. The injection molding of the compositematerials could obtain miniature radiator, which could be applied to LED, andthe heat dissipation effect was studied through experiments.The results were as follows:1. The influence of coupling agent content and lubricant content on thethermal conductivity and melt flow rate of composites was studied. The resultsshowed that when1part of coupling agent was added, the thermalconductivity was highest while the melt flow rate was lowest. It was also found in the experiment that the thermal conductivity of composites displayeda contrary tendency with the melt flow rate, that is, the thermal conductivity ofcomposites was highest, the melt flow rate was lowest.2. The carbon content and particle size of graphite had certain effect onthe thermal conductivity of composites. Higher carbon content would havebetter effect on improvement of the thermal conductivity, but it would nothave significant influence on the electrical conductivity. The effect of particalsize of graphite on thermal conductivity was mainly reflected by the degree ofstack of graphite in the polymer matrix. When contents of the graphite werethe same, the particals having the highest degree of stack would possess higherthermal conductivity. When the flake graphite was added with expandedgraphite or spherical graphite in certain proportion, the thermal conductivity ofcomposites could be improved.3. Different processing had influence on the thermal conductivity ofcomposites. Appropriate screw rotate speed could lead to good dispersion ofthe graphite in the polymer and result in biggest thermal conductivity. With theincreasing of injection speed, thermal conductivity of vertical directiondecreased and pland direction increased. In the process of injection, thedistribution of graphite in the polymer was different, the graphite content washigher in the edge region (except the gate), while the center and gate graphitehad smaller content of graphite.4. Test conditions had an impact on the thermal conductivity of the composites. Thermal conductivity of the composites at30℃was higher thanits thermal conductivity at25℃. During the test, the increase of air humiditywould result in higher thermal conductivity.5. The results of heat radiating experimental of polypropylene/graphitecomposites showed that when the power of LED was10W and the air flux was6L/min, the temperature of LED base plate would be57℃, which was close tothe upper limit temperature of LED.