Graphene/Thermoplastic Based Composites

Mass-produced Graphene (GN) nanoplatelets provided by NanoXplore Inc, Ethylene Vinyl Acetate (EVA) copolymer and various grades of Polyethylene (PE), were used for the preparation of graphene-composites with single-phase and multi-phase polymer matrices. All the composites were prepared by melt-compounding using a twin-screw extruder. The electrical properties were measured with a two-electrode frequency domain setup as well as a 4-point system in order to measure the conductivity both out-of-plane and in-plane. The rheological properties were measured by a rotational rheometer operating in a parallel-plate configuration and the composites morphologies were evaluated by Transmission Electron Microscopy (TEM). The electrical percolation threshold was found to be dependent on the viscoelastic properties, the matrix morphology, and even the processing sequence. Overall, a good correlation was observed between rheological and electrical percolation thresholds, despite of the different physical natures of electrical networks and elastic networks. Besides, it was found that the electrical percolation threshold tends to increase with decreasing melt flow rate of the matrix, most likely due to slower diffusion of GN nanoplatelets and formation of conductive networks. Moreover, the multi-phase morphology of the blend composites that induces selective localization of GN nanoplatelets at the interface or in one phase depending on the processing sequence, resulted in lower percolation threshold compared to single-phase composites. Anisotropy in the electrical conductivity was also observed, the in-plane conductivity being higher than the out-of-plane conductivity mainly due to the combination of the filler shape factor and the processing method.