Effect of flake graphite orientation on thermal conductivity of flake graphite/polypropylene, flake graphite/nylon66 composites

The flake graphite/polypropylene (PP) and flake graphite/nylon66 (PA66) thermal conductive composites were prepared by twin screw extrusion and injection molding to study the effect of the flake graphite orientation on the thermal conductivity especially thermal conductivity in different directions of flake graphite/PP and flake graphite/PA66 composites. The results were analyzed by SEM and ultrasonic test. The results show that the smaller particle size is, the higher planar orientation degree is, which makes the difference between the planar and vertical thermal conductivity of the composites bigger. The excessive shear of twin screw extruder can destroy lamella structure of flake graphite, influence the formation of the heat conducting network and reduce the thermal conductivity, but improve the uniformity of heat conducting in different directions of the composites. The moderate shear can open the lamellar structure of flake graphite and improve the thermal conductivity of the composites, the injection molding influences the anisotropy of heat conducting of composites at a large degree.