Exfoliation of graphite and expanded graphite by melt compounding to prepare reinforced, thermally and electrically conducting polyamide composites

High performance composites based on a thermoplastic polyamide matrix containing well dispersed graphene nanoplatelets were prepared, by delaminating expanded graphite (EG) into its constituent graphene nanoplatelet (GNP) layers, by melt compounding. Results from scanning electron microscopy, transmission electron microscopy, and 3D tomography showed good dispersion of the GNP, while contact angle measurements revealed that the polyamide and graphene-based constituents had excellent interfacial interactions. Compared to flake graphite, exfoliation of EG into graphene nanoplatelets substantially improved the electrical, thermal and mechanical properties at low filler volume fractions: the electrical percolation threshold was attained at 1.9 vol%, the thermal conductivity increased by 1300% at 8 vol%, and the flexural modulus by 270% at 15 vol%. Substantial improvements in the impact properties of the composites were imparted by adding a maleated elastomeric impact modifier, which was well-dispersed within the PA matrix, resulting in excellent toughening performance. This research achieves composites with superior properties, using an industrially relevant, easy to implement melt compounding method.