An Investigation on the Enhancement of Electromechanical Performance of Polymer Composites using Supercritical Carbon Dioxide for Electroactive Applications

Electroactive polymers (EAPs), also known as artificial muscles, are a type of polymer which responds to an electric field with structural or mechanical changes. However, current plastic research and manufacturing sectors are still lacking the use of EAP’s for smart applications, due to their diverse thermal, mechanical and electrical behavioural changes depending on small variations in their processing conditions. Therefore, this research investigated the effects of novel supercritical carbon dioxide (scCO2) fluid assisted polymer processing techniques on the thermal, mechanical and electrical properties of EAPs. Semi-crystalline polymer Pebax and rubber elastomer Poly(styrene-ethylene-butylene-styrene) - SEBS was chosen as the base polymeric material; and in order to enhance the electroactive properties, graphene-graphene oxide were used as filler material. The research begins with preliminary investigations of the scCO2 processing of polymers at various critical pressures. This initial study indicated that both polymers resulted in increased microphase formation producing a more homogeneous co-polymer base material and decreased the mechanical properties due to the foaming effect. In order to enhance the electroactive properties of the base polymers, graphene-based filler materials at low concentrations (<2.5% wt.) were used, processed with and without scCO2. Clear enhancement with respect to mechanical properties and crystallisation kinetics were observed below 1% filler loading and additional information on the exfoliation and agglomeration effects were drawn. Finally, the effects of reprocessing scCO2 processed composites were investigated. Various crystallisation kinetics theories were used to understand the effects of scCO2 processing on the crystallisation process; these results were validated using X-ray diffraction through crystallite size calculation. An in-depth understanding of results obtained from thermal, mechanical and electrical behaviour were co-related. The thesis concludes that the use of scCO2 processing induced rearrangement of polymer chains into favourable configurations resulting in exfoliation of filler particles with improved homogeneity, mechanical and electrical properties. Bending capabilities were evaluated by sulfonation of the manufactured SEBS graphene oxide composites. The sSEBS graphene oxide composites processed with scCO2 demonstrated a maximum bending actuation of 27 degrees.