Melt Processing and Properties of Polyamide 6/Graphene Nanoplatelet Composites

In this paper, the processing and characterization of Polyamide 6 (PA6) / graphite nanoplatelets<br/>(GNPs) composites is reported. PA6/GNPs composites were prepared by melt-mixing using an<br/>industrial, co-rotating, intermeshing, twin-screw extruder. A bespoke screw configuration was used<br/>that was designed in-house to enhance nanoparticle dispersion into a polymer matrix. The effects of<br/>GNPs type (xGnP® M-5 and xGnP® C-500), GNPs content, and extruder screw speed on the bulk<br/>properties of the PA6/GNPs nanocomposites were investigated. Results show a considerable<br/>improvement in the thermal and mechanical properties of PA6/GNPs composites, as compared with<br/>the unfilled PA6 polymer. An increase in crystallinity (%Xc) with increasing GNPs content, and a<br/>change in shape of the crystallization exotherms (broadening) and melting endotherms, both suggest a<br/>change in the crystal type and perfection. An increase in tensile modulus of as much as 376% and<br/>412% was observed for PA6/M-5 xGnP® and PA6/C-500 xGnP® composites, respectively, at filler<br/>contents of 20wt%. The enhancement of Young’s modulus and yield stress can be attributed to the<br/>reinforcing effect of GNPs and their uniform dispersion in the PA6 matrix. The rheological response<br/>of the composite resembles that of a ‘pseudo-solid’, rather than a molten liquid, and analysis of the<br/>rheological data indicates that a percolation threshold was reached at GNPs contents of between 10–<br/>15wt%. The electrical conductivity of the composite also increased with increasing GNPs content,<br/>with an addition of 15wt% GNPs resulting in a 6 order-of-magnitude increase in conductivity. The<br/>electrical percolation thresholds of all composites were between 10–15wt%.