Browsing by Author "Paulse, Lambert Owen"
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- ItemPorous carbon and ceramic nanofibres(Stellenbosch : Stellenbosch University, 2020-03) Paulse, Lambert Owen; Mallon, Peter Edward; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: In this study, a series of polyacrylonitrile (PAN)/polyvinylpyrrolidone (PVP) nanofibre blends with and without TiO2 nanoparticles as well as ceramic TiO2 composite nanofibres were successfully fabricated via the electrospinning process. The amounts of the PVP polymer within the blend ratios were 0 wt. %, 30 wt. %, 50 wt. %, 70 wt. %, and 100 wt. %. By altering the blend ratios of the PAN and PVP polymers, controllable porous morphologies were obtained. Two approaches were used to fabricate porous carbon nanofibres. The first involves the direct carbonisation of the precursor fibres while the second includes the leaching of the sacrificial PVP phase followed by the carbonisation process. Scanning electron microscopy (SEM) images showed a decrease in mean fibre diameter as well as change in the surface texture as a function of increased wt. % PVP. The former is explained by the decrease in solution viscosity while the latter is due to the phase inversion of blends; the matrix phase and the dispersed phase inverts into the dispersed phase and matrix phase as the amount of the dispersed phased is increased. With incorporation of the TiO2 nanoparticles, a significant increase in the fibre diameter is observed throughout the blend series and is explained by the restricted polymer chains segmental motion by the TiO2 nanoparticles during the fibre formation. TEM images showed that the TiO2 nanoparticles are homogenously dispersed along the fibre with some agglomerates present for the 0 wt. % PVP/TiO2 fibre. The increase in PVP content results in a drastic decrease in TiO2 particle dispersion with evidence of agglomerates within the fibre matrix. In conjunction with the electrospinning process, this is attributed as PAN being a good dispersing agent for the particles. According to the author’s knowledge, there are no studies on the solution ageing effects of PAN fibre blends. The results show an increase in the mean fibre diameter as well as solution viscosity are as a function of solution ageing time. This effect was found to be more pronounced for the pure PAN than PVP fibres. Precursor PAN/PVP films were prepared via solvent cast and rapid solvent evaporation preparation methods. The cast films were porous and the rapid solvent evaporation films were more homogenous in surface morphology. The resultant films showed different structures after direct carbonisation and PVP extraction followed by carbonisation. It was found that the film preparation methods have a significant effect on the resultant morphology. The precursor, direct carbonised, PVP extracted, PVP extracted followed by carbonisation samples were all analysed by FE-SEM, EDS-SEM, XRD, DSC, and TEM to quantify the effect of each step of this study. Decreased fibre diameters were observed after each of these steps. It was also found that the porosity was more apparent for the PVP leached samples with increased porosity as a function of PVP content. TEM images showed that the TiO2 nanoparticles were still embedded within the polymer matrix following both carbonisation routes with increase particles exposure on the fibre surface for the carbon 30 wt. % to 70 wt. %/TiO2 nanocomposite nanofibres. Ceramic TiO2 nanofibres were fabricated from hybrid carbonisation-calcination thermal treatment of PVP/TiO2 composite precursor fibres. The SEM and TEM images showed spine-like structures after the thermal treatment which is explained by the crystallization of the TiO2 and formation of amorphous carbon residue (partial thermalisation) from the PVP phase. XRD analysis showed that rutile TiO2 nanofibres were obtained.