Akanbi, Muftau Jide; (2018) Design and engineering of electrospun fibres for oil spill clean-up. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The superior oil sorption performance of electrospun polystyrene (PS)/PS-based fibres has rendered its use more competitive than the commercial melt blown polypropylene (PP) fibres. However, on a microscale level, the oil - sorbent interaction and its effect on the sorption behaviour is yet to be fully understood; considering PP polymer is known to have a lower surface energy than polystyrene. Furthermore, the commercialisation of electrospun PS sorbent has been hindered due to the poor mechanical strength of the fibre mats particularly after oil sorption. Therefore, the aim of this thesis is to (1) enhance the understanding of the oil sorption behaviour of electrospun PS fibres (single filament level) and (2) to explore ways to effectively enhance the mechanical properties of the PS fibre mat. The oil adherence potential of filaments of electrospun PS and subsequent comparison with filaments of the commercial melt blown PP sorbent was quantitatively evaluated using drop-on-fibre micro-sorption technique. This was preceded by a systematic optimisation of the electrospinning process, 20%w/w concentration of PS dissolved in DMF/THF (4:1) gave fibres with the best morphology for the micro-sorption test. Further experiments showed single filaments of electrospun PS to exhibit the strongest affinity to the two oils tested, with a mean adhesive energy of 18.0 x 10-13J and 26.2 x 10-13J for sunflower and motor oil respectively. This represents values 3 – 6 times higher than those recorded for single filaments of the PP counterparts. The superior oil adsorptivity of PS fibre was attributed to its chemical structure i.e. the presence of aromatic phenyl group in its structure. For the second aim of this thesis, a single step electrospinning method of blending PS and thermoplastic polyurethane PU polymers in different weight ratio of PSPU polymer blend was explored, using either a Flat Collector (FC) or a Drum Collector (DC) system. This was done in order to enhance the mechanical properties of PS fibres. The method is a simple, cost-effective engineering approach and exhibits great potential. The ultimate tensile strength (UTS) and elongation at UTS were seen to rise with increased PU content. Samples of PSPU ratio 6:4 fabricated using a DC system (PSPU_DC 6:4) and those fabricated using the FC system (PSPU_FC 6:4) recorded a 600% and 1000% increase in tensile strength respectively, in comparison to the pure PS mat. The oil sorption and retention capacities was seen to be dependent on several variables including the fibre collection system. Post treatment of the fibre mat using heat treatment around the polymer glass transition temperature (110ºC) was seen to induce inter-fibre bonds, with the amount of bonds seen to rise with increase in treatment temperature. This causes a simultaneous increase in tensile strength. The work presented in this thesis has pioneered some key aspects that will take electrospinning of polymer fibres further. In terms of characterization, it is the first to quantitatively evaluate the oil adsorptivity of filaments of electrospun PS and melt blown polypropylene sorbents. This creates fundamental insight into the sorption mechanism at a micro-scale level to aid the design of future and improved electrospun sorbents. Also, the electrospinning of PS and PU presented in this thesis, is the first time polymer blend of both polymers is being electrospun for any application, with detailed characterisation of the bi-component fibres presented.

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