Development of Functional Polymer-Graphene Nanocomposites

Abstract

This research focuses on the synthesis and characterisation of reduced graphene oxide (GO), systematically varying and identifying factors that are responsible for changing electrical conductivity and integrating the best reduced graphene oxide (rGO) results into a number of composite systems. Five different reducing agents (hydroiodic acid, hydrazine hydrate, hydrobromic acid, sodium borohydride and dextrose) were systematically investigated to identify the type of reducing agent and the process that provides reduced graphene oxide with superior chemical, physical and mechanical properties. Best results were obtained for a graphene oxide film reduced with hydroiodic acid, with the electrical conductivity of 103 S.cm-1 and better flexibility compared to those of films obtained by other reducing agents. Functionalising graphene oxide with electron donor and acceptors further improved the electrical conductivity. This functionalised graphene oxide (fGO) samples have been characterised to understand their physical and chemical properties. Mechanical exfoliation of rGO films using the “scotch tape method” has shown that as films become thinner, conductivity increases. It has been proposed that this is mainly due to the selective removal of less-pure rGO by the tape and this hypothesis has been supported by XPS and confocal microscopy results. Hybrid composites of polymer/polymer/graphene derivatives have been developed focusing on electrical conductivity and mechanical properties. Polypropylene, poly(methyl methacrylate) and polyoxymethylene were used as polymer matrices with polypyrrole and polyaniline as secondary conducting polymers. Graphene (G) and rGO were used as reinforcements. The maximum electrical conductivity of 0.85 S.cm-1 was achieved for a polyoxymethylene/polypyrrole/graphene blend with 2 wt.% and 4 wt.% of polypyrrole and graphene loading. Highly conductive rGO has also been used as a conductive coating on glass, flax and polypropylene yarns using binding materials (epoxy resin and thermoplastic starch solution) and a dip-coating process. Three different dip-coating processes have been developed to identify an efficient method of coating in terms of improving electrical conductivity. Glass fibre yarns (with epoxy binder and rGO) have been identified as having the highest electrical conductivity of 0.1 S.cm-1.