Effect of graphene structure, processing method, and polyethylene type on the thermal conductivity of polyethylene-graphene nanocomposites

In this chapter, we have reported on the thermal conductivity of highly loaded reduced graphene-polyethylene (PE) nanocomposites. The impact of the graphene structure and functionalization, the PE grade, and the processing method and conditions on the nanocomposite morphology and thermal conductivity is investigated. Low-density polyethylene (LDPE)-based nanocomposites exhibited a higher enhancement in thermal conductivity than the corresponding high-density polyethylene (HDPE) at the same graphene loading due to improve processability. The solution blending method was superior to melt blending in terms of thermal conductivity enhancement. Moreover, the nanocomposites produced via a two-solvent precipitation method exhibited better thermal conductivity and thermal stability due to the improved dispersion of graphene particles compared to the conventional solution blending. The impact of graphene loading was not substantial at very high loading that led to marginal enhancement compared to moderate loading due to the increased polymer-graphene interfaces. Also, the state of graphene dispersion in the PE matrix led to a slight rise in the thermal conductivity of the nanocomposites processed at higher compounding speed. Moreover, improved thermal conductivity was observed using graphene with a higher surface area and lower oxygen-to-carbon ratio. Furthermore, graphene nanocomposites with an immiscible blend of LDPE and HDPE did show a synergistic effect on the thermal conductivity of the nanocomposite. Finally, the stiffness and strength of the PE-graphene nanocomposites have significantly improved, but the ductility was reduced.