Abstract: Polypropylene (PP) composites filled with exfoliated graphite (EG) were prepared by roll mixing and hot press method. The effects of filler content, particle sizes, and hybrid filling on the thermal conductivity of the composites were investigated. The thermal conductivity of composites was improved with increasing EG filler contents. When the filling rate was over 30%, the thermal conductivity increased faster, achieving percolation threshold. When the filling rate was 50%, the thermal conductivity of composite material reached 1.791 W/(m·K). The large size filler particles were more beneficial to improve the thermal conductivity of composites than small size particles. If the mixture of hybrid particles was at a preferable mass ratio, the composites exhibited the highest thermal conductivity.

Key words: exfoliated graphite, hybrid filling, polypropylene, thermal conductivity, composite