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Item Restricted Understanding the Biophysics of Plant Yarn Dissolution in Ionic Liquids(Saudi Digital Library, 2025) Alrefaei, Nora; Ries, Michael; Hine, PeterThis thesis investigates the dissolution behaviour of natural and pre-treated plant-based yarns (hemp, cotton, and flax) in the ionic liquid 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]), with a focus on understanding the roles of molecular weight, composition, and crystallinity in their dissolution. A combination of mercerization (sodium hydroxide treatment) and electron beam irradiation (EBI) was applied to alter the structural and chemical properties of the yarns. While mercerization was found to affect both composition and molecular weight, electron beam irradiation was found to predominantly reduce molecular weight, allowing these two important factors to be separately evaluated. The dissolution behaviour of these yarns in the ionic liquid was evaluated across different dissolution times and temperatures. Optical microscopy, wide-angle X-ray diffraction (WAXD), and mechanical testing were employed to investigate structural and mechanical properties. The most important finding of this work is that molecular weight is the dominant factor governing both the rate of dissolution and the dissolution activation energy (Eα). A direct linear relationship was identified between Eα and molecular weight (MW). This correlation, consistent across all yarn types and treatment conditions, establishes molecular weight as the primary factor governing both the rate of dissolution and the energy barrier that must be overcome for dissolution to take place. The growth of a partially dissolved and coagulated fraction surrounding an undissolved core was tracked using optical microscopy. Time–temperature superposition was applied across all yarn types, allowing for the determination of the dissolution activation energies. Pre-treatments had a significant impact on dissolution behaviour: mercerisation led to reductions in both lignin content and molecular weight, whereas EBI primarily caused a notable decrease in molecular weight. EBI-treated yarns consistently exhibited the lowest activation energies compared to their natural counterparts. Optical microscopy confirmed that dissolution followed time–temperature superposition and diffusion-limited kinetics, with the growth of the coagulated layer being proportional to the square root of time. Overall, this work provides an understanding of the dissolution of different cellulosic yarns in ionic liquids and establishes molecular weight as a predictive parameter for dissolution kinetics. The findings offer valuable insights for optimising pre-treatment strategies to improve the processing of cellulose-based materials, with potential applications in sustainable textiles, all-cellulose composites, packaging, and biodegradable products.15 0Item Restricted Understanding the Dissolution Behaviour of Flax Yarn in Ionic Liquids(University of Leeds, 2025-03) Albarakati, Fatimah Ahmed; Hine, Peter J; Ries, Michael EThe purpose of this thesis is to study the dissolution of flax fibres in imidazolium based ionic liquids and anti-solvent mixtures. This is an important area of study, helping to understand the mechanism of cellulose solvation and the ways in which the properties of ILs (in particular different anion and cation combinations) can influence their ability to dissolve cellulose at the micro- and macro level, and how different IL features affect the dissolution process. This study investigates the dissolution behaviour of flax yarns in three distinct imidazolium based ILs:1-ethyl-3-methylimidazolium acetate ([C2mim]+[OAc]- ),1- butyl-3-methylimidazolium acetate ([C4mim]+[OAc]-), and 1-ethyl-3-methylimidazolium octanoate ([C2mim]+[Oct]-). The first two of these had the same anion ([OAc]-) but a different cation, while the third had the same cation ([C2mim]+), as the first but a different anion. This work was able to reveal the role of the cation and the anion on the dynamics of cellulosic yarn dissolution. The dissolution process involved submerging the yarns in the pure ILs for a range of temperatures and times, followed by coagulation in water. The coagulated material called coagulated fraction (CF) produced an outer ring that surrounded the centre yarn fibre. Optical microscopy was used to follow the growth of this ‘dissolved’ region and it showed an Arrhenius behaviour, enabling the determination of the dissolution activation energy from this simple measurement. The dissolution activation energies of the ILs [C2mim][OAc], [C4mim][OAc] and [C2mim] [Oct] were found to be 64 ± 5 kJ/mol, 67 ± 1 kJ/mol and 79 ± 1 kJ/mol, respectively. In addition, the growth of the outer coagulated ring's thickness of the coagulated material was investigated, enabling the IL's diffusion coefficients to be determined. NMR study (pulsed- field gradient self- diffusion measurements), viscosity, density, and Stokes-Einstein analysis provided further understanding of the properties of the pure ILs. The calculated diffusion activation energies of the ILs [C2mim][OAc], [C4mim][OAc] and [C2mim][Oct], were found to be 64 ± 5 kJ/mol, 69 ± 5 kJ/mol and, 77 ± 3 kJ/mol, respectively. The resultant data shows that the dissolution rate goes from fastest to slowest in the order [C2mim][OAc] >[C4mim][OAc] >[C2mim][Oct]. Our key result is that the dissolution of the flax yarns (in all three ILs) is controlled by the diffusion of the IL, through a region of swollen cellulose/IL solution around each fibre as the thickness of the dissolved and coagulated layer increases with the square root of time and so is diffusion controlled. The effect of adding small amount of water on the activation energy and dissolution speed of ionic liquids ILs [C2mim][OAc] and [C4mim][OAc] was investigated separately. For the IL [C2mim][OAc], three different water contents have been used 1%, 2% and 4% by weight and for the IL [C4mim][OAc], four different water concentration have been used 1%, 2%, 4%, and 8% by weight. The resultant data has also been compared to the results from chapter 3 (the pure IL [C2mim][OAc] was found to consist of 0.2% water), and chapter 4 (the pure IL [C4mim][OAc] was found to consist of 0% water). As expected, the coagulated outer layer was seen to form around the undissolved core fibre for the water systems of 1%, 2%, and 4%. However, there was no sign of dissolution showed by the IL [C4mim][OAc]-water system of 8%. For the IL[C2mim][OAc], the activation energies were found to be 77 ± 5 kJ/mol, 97 ± 3 kJ/mol and 116 ± 6 kJ/mol for the system containing 1%, 2% and 4% water respectively. For the IL [C4mim][OAc], the activation energies were found to be 78 ± 7 kJ/mol, 83 ± 7 kJ/mol and 110 ± 6 kJ/mol for the system containing 1%, 2% and 4% water respectively. The dissolution rate was found to exponentially decrease as a function of water content for [C2mim][OAc]; however, the dissolution rate at 1% water was found to be higher than that of 0% water for [C4mim][OAc]. This shows a level of effectiveness at 1% water could make it a viable option for both research and industrial use.39 0Item Restricted Photocatalytic Reforming of Lignocellulosic Feedstocks for H2 Production using TiO2-based Catalyst(The University of Manchester, 2024-06-26) Aljohani, Meshal; Fan, Xiaolei; Christopher, HardacreThe demand for energy has increased massively, mainly supplied by fossil fuels with significant carbon emissions. Hydrogen (H2) emerges as an efficient and clean energy carrier, having many promising characteristics (such as higher heating value and zero carbon emission after combustion) to replace fossil fuels. Solar-driven photocatalytic reforming (photoreforming, PR) of biomasses (such as cellulose and lignin) at ambient conditions presents a promising solution to produce renewable H2 due to the use of (i) biomass (widely abundant in nature, sustainable and theoretically carbon neutral) and (ii) solar energy (i.e., the sun as the largest energy resource driving the catalysis). Current PR processes mainly employ cellulose and bio-derived chemicals such as bioethanol. Comparatively, although it is very challenging, the direct use of lignin for H2 production via PR can be advantageous. This PhD thesis employed platinised TiO2 catalysts to study the PR of model aromatic compounds, purified and IonSolv-extracted lignin and cellulose, and raw biomass feedstocks to produce H2. While PR of aromatic compounds and lignin yields comparable and low levels of H2 production (4.8−6.6 μmol gcat−1 h−1) compared to cellulose (~62.8 μmol gcat−1 h−1) due to poisoning by intermediates, alternating between anaerobic and aerobic atmospheres resulting in a threefold enhancement in H2 production from the PR of lignin. In addition, Pt nanoparticles loaded on TiO2 using an in-situ photodeposition method enhanced the production of H2 significantly from the PR of lignin and aromatic substrates compared to ex-situ methods. The PR of isolated cellulose pulps from various bioenergy crops showed the highest H2 production, while derived lignin was the lowest. The variations in H2 production from bioenergy crops were found to be unrelated to the differing composition of cellulose, hemicellulose and lignin. The interaction strength of bioenergy crops with water, as observed by NMR relaxometry, was determined to influence H2 production, correlating with H2 production. In summary, this thesis investigates the challenges of lignin PR, proposes mitigation strategies, and identifies factors impacting the PR of lignocellulosic feedstocks for efficient H2 production.19 0