Alenezi, Hussain A Kh M D; (2022) Manufacturing Multi-layer Core-sheath Polymeric Fibres Using Novel Gyrospinning. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Polymeric fibres are used for essential and sophisticated practical applications such as nanosensors, tissue engineering scaffolds, and fibre-reinforced composites. This thesis presents a substantial move forward in comprehending the physics underpinning their formation. Polymeric fibres can be generated through centrifugal spinning and the pressurised gyration processes of a polymer solution within a reservoir. The core difference between these processes is that pressure is employed as a control parameter with the rotation speed in the latter. For both processes, experimental and numerical investigations were conducted into the behaviour exhibited by the polymeric solution inside a transparent reservoir. Fibre generation took less than one second. Polyethylene oxide was used as the model polymer and distilled water as the solvent. For centrifugal spinning, the experiments were conducted at three rotational speeds (7000, 8500, and 10000 rpm). The investigation was conducted at three nitrogen gas pressures (0.1, 0.2, and 0.3 MPa) at a set rotational speed (10000 rpm) for pressurised gyration. High-speed camera images were used to depict the behaviour of the fluid within the reservoir. Increasing the gas pressure to 0.3 MPa significantly enhanced the homogeneity of the fibre distribution, morphology, and production yield. Forming of polymeric core-sheath nanofibres where the sheath contains functional additives is gaining prominence due to their numerous potential applications, most notably in functional scenarios such as antiviral filtration, attracting significant attention due to the Covid pandemic. This research pursued core-sheath fibre production. A novel vessel was successfully purpose-designed and constructed to generate core-sheath polymeric fibres. Investigations were conducted into numerous water-insoluble and water-soluble polymer solutions. As core materials, polyethylene oxide (PEO) and polyvinyl alcohol (PVA) were used. Poly (lactic acid) (PLA) and poly(caprolactone) (PCL) were used as sheath materials, whereas PLA and PCL were used as core and sheath materials, respectively. The fluid behaviour of the core-sheath within the vessel was studied with and without applied pressure using computational fluid dynamics to simulate the core-sheath flow within the chamber. A high-speed camera was used to observe the behaviour of jetted solutions at core-sheath generation vessel openings, and the best scenario was achieved using 6000 rpm spinning speed with 0.2 MPa (twice atmospheric) applied pressure. The surface morphology of core-sheath fibres was studied using a scanning electron microscope, and focused ion beam milling assisted scanning electron microscopy was used to investigate the cross-sectional features of the produced fibres. Laser confocal scanning microscopy was also used to verify the core-sheath structure of the fibres, which were further characterised by Fourier transform infrared spectroscopy and differential scanning calorimetry. The results obtained confirmed the presence of core-sheath fibre materials in examined samples. Thus, using a variety of polymer solutions, both theoretically and experimentally, how core-sheath fibres evolve in a vessel that can serve as scalable manufacturing pressurised gyration production process was elucidated. As the final instalment to this thesis, a gyrospinning device capable of producing multi-layer (≥3) core-sheath polymeric fibres using a novel vessel consisting of a tri-chamber and a novel rotary union capable of continuously infusing three fluids was successfully designed and constructed. Furthermore, it precisely controls crucial process parameters such as spinning speed, gas pressure, polymer solution flow rates, temperatures, humidity, and fibre collectors. Moreover, the manufacturing process is controlled by an industrial automation system for continuous operation to meet the lack of mass production and reduce waste.

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