Manufacturing and characterisation of multifunctional polymer–graphene oxide nanocomposites

Abstract

Composites with polymer matrices and nano-sized exfoliated fillers demonstrate significant enhancement in mechanical and functional properties over those of monolithic polymers at extremely low filler loadings. From the variety of nano-fillers utilised by researchers to develop commercially viable nanocomposites, carbon based nano-fillers are prominently used to render electrical conductivity in addition to mechanical strength. Amongst these, graphene oxide (GO) is electrically insulating contrary to the rest of carbon-based fillers, and hence not much investigated as a nano-filler so far. However, chemical and/or thermal reduction of GO can restore the electrical conductivity. This transitional behaviour makes GO a promising nano-filler for electronic applications. Besides, the thermal stability and mechanical strength of GO are comparable to graphene at temperate conditions. This research work is aimed at preparation of multifunctional polymer-GO nanocomposite thin films. The multi-layered films are constructed as a sandwich of plain polymer facing sheets supporting an electrospun polymer-GO nano-fibre core. The material formulation is divided into two parts, viz., development of a simple and less hazardous process for synthesizing conductive GO nano-fillers, and manufacturing of polymer-GO nano-fibre mats with electrospinning. The characterisation techniques employed to assess the structure and morphology of synthesized GO include X-ray diffractometry, Fourier transform infrared spectroscopy and scanning electron microscopy and the results confirm the effectiveness of the developed GO synthesis process. Additionally, the partial chemical reduction lead to a severe drop in electrical resistivity of GO sheets, and the observed average resistivity values are amongst the lowest reported till date. An orthogonal experimental design as per Taguchi method was devised to analyse the process parameter effects on the average resistivity value of GO sheets. Poly(methyl methacrylate) was selected as the polymer matrix for this work and plymer-GO nano-fibre mats were generated with electrospinning under controlled environmental conditions, to produce well-dispersed nano-fibres with uniform diameter. Vacuum forming was used to manufacture the sandwich films with electrospun cores. Additionally, electrically conducting, monolayer polymer-GO nanocomposite films were prepared through solution casting. The nanocomposite sandwich films demonstrate very high gas barrier with permeation values of nearly zero, measured during oxygen permeation testing. Modelling of gas barrier property is accomplished with analytical and finite element based numerical modelling tools. The observed high gas barrier is attributed to multi-layered structure, fibrous core and presence of impermeable GO fillers in the nano-fibres. Based on the experimental results, these films are found highly suitable for applications in food and beverage packaging and chemical processing plants. Analytical modelling of electromagnetic interference shielding capability of the solution cast polymer-GO films was conducted. The shielding effectiveness values predicted by the models are positive, but significantly lower than the commercial requirements. However, the theoretical cases for nanocomposite films with moderate improvement in electrical conductivity and increased film thickness yield commercially required EMI SE values, thus confirming the potential of these films as EMI shields This thesis thus reports a comprehensive work covering the synthesis of GO nano-fillers, manufacturing of sandwich thin films with electrospun polymer-GO nano-fibre cores and the experimental characterisation of the fillers and nanocomposite specimens.