Preparation of CNTs/PP@Gr composites with a segregated structure and enhanced electrical and thermal conductive properties by the Pickering emulsion method

Abstract

Conductive and thermal conductive polymer composites have significant advantages in corrosion resistance and mechanical and processing properties. To improve the integrity of the network structure of the conductive filler in a polypropylene (PP) matrix, PP@Graphite (Gr) with segregated single-network structure, PP@(carbon nanotubes (CNTs)/Gr) with segregated double-network structure, and (x wt%-CNTs/PP)@Gr with segregated hybrid double-network structure were prepared by the Pickering emulsion method. The original irregular powder was converted into spherical shape by the Pickering emulsion method. Among these composites, the (2 wt%-CNTs/PP)@Gr composite had the highest conductivity and thermal conductivity. The electrical and thermal conductivity of the (2 wt%-CNTs/PP)@Gr composite reached 1.45 S/m and 0.82 W/m·K, respectively, at a Gr loading of 13.01 wt%, and the electrical conductivity was 3 and 0.5 times higher than that of PP@Gr and PP@(CNTs/Gr) composites, respectively. The CNTs acted as "bridges" to form a denser conductive network, and significantly improved the conductivity. The interfacial thermal resistance of the (2 wt%-CNTs/PP)@Gr composite was between 1.5×10-7 and 1×10-6 m2K/W according to the effective medium theory (EMT) fitting results. Additionally, the crystalline peaks of the PP@Gr and PP@(CNTs/Gr) composites showed a significant left shift, while the (2%-CNT/PP)@Gr composite showed a significant right shift, which indicated that the hybridization of CNTs with Gr caused a "bridge effect" and increased the thermal conductivity. This method provides a convenient and time-saving new approach for the study of segregated structural thermally conductive composites by encapsulating the filler on the matrix through a one-step process while meeting the requirements of green environment.