Saudi Cultural Missions Theses & Dissertations
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Item 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.25 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.17 0Item Restricted The Dissolution of Regenerated Cellulose Multifilament Bundles in Ionic Liquid of 1- ethyl-3-methyl- imidazolium acetate [C2mim]+ [OAc]-(University of Leeds, 2023-04-23) Alanazi, Maer; Ries, Mike; Hine, PeterRegenerated cellulose fibres like Cordenka and Lyocell have been studied for their potential use as reinforcement in polymer composites. These fibres are attractive candidates for improving the mechanical and environmental characteristics of various polymer materials. In our research group we have devolved the idea of manufacturing ‘all-cellulose’ composites from a single cellulosic source. The idea is to create the ‘matrix’ of all cellulose composite by selectively dissolving the surface of each fibre or filament, which on coagulation forms the matrix. Being also cellulose, this should give excellent compatibility/adhesion between the phases. This thesis has studied the dissolution of two commercial regenerated cellulose yarns, namely Cordenka™ and Lyocell™. Optical microscopy, Wide angle X-ray diffraction (WAXS) and mechanical testing techniques have been used to track the dissolution of these multifilament bundles in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate [C2mim]+ [OAc]- for different times and temperatures. This allowed both the speed of the dissolution to be determined at different temperatures as well as the dissolution activation energy Ea from time-temperature superposition. The different nature of the multifilament bundles (Cordenka™, which was untwisted and Lyocell™ where the bundles were twisted) resulted in different techniques being most suitable for their study. For Cordenka, WAXS and mechanical measurements on partially dissolved composite filaments proved most successful. In the dissolution process, the oriented cellulose II crystals in the regenerated cellulose fibres dissolve and then reform into randomly oriented crystals to form a matrix phase. This change in orientation enabled the dissolution process to be followed and hence determine the growth of the dissolved matrix fraction of 𝑣𝑚 with time and the dissolution activation energy. On the other hand, optical microscopy was found to work very well with the Lyocell multifilament bundles to directly determine the dissolved matrix volume fraction 𝑣𝑚. Mechanical measurements of Young’s Modulus and ultimate tensile strength on partially dissolved composites proved successful for both Cordenka and Lyocell multifilament yarns. The change in the average molecular orientation 𝑃2 determined from an azimuthal (𝛼) X-ray scan, allowed the growth of the matrix volume fraction 𝑣𝑚to be calculated with time and temperature. This is an indirect measurement and relies on using a rule of mixtures approach. The optical microscopic method offered a direct method to measure the growing area of the dissolved and coagulated fraction for the Lyocell multifilament bundle with increasing time and temperature. The twisted fibres meant that the dissolved fraction formed a ring on the outside of the multifilament, allowing a measurement of the decrease of the inner core (the undissolved original fibre fraction) and the increase in the area and thickness of the dissolved and coagulated outer ring. The decrease of the inner core and the growth of coagulation fraction C.F. and the thickness and area of the dissolved and coagulated outer ring was found to follow time temperature superposition, with an Arrhenius behaviour, giving consistent values for the activation energy of Ea= 141 ± 15, Ea= 141 ± 16 and Ea= 127 ± 14 respectively. Young’s modulus and ultimate tensile stringth was measured on all the resulting processed composites for Cordenka and Lyocell multifilament bundles. The fall of Young’s modulus and ultimate tensile strength with dissolution time and temperature was found to follow time-temperature superposition for the Cordenka multifilament bundle, with an Arrhenius behaviour giving a value for Ea= 198± 29 kJ/mol. The Young’s Modulus and ultimate tensile strength results were plotted against 𝑣𝑚 determined from the WAXS measurements and were found to agree well to the Voigt upper bound parallel Rule of Mixtures. This suggests that the resulting composites are well bonded and that the dissolved Cordenka material (which has a higher molecular weight compared to the Lyocell material) is a suitable matrix material for to make all a cellulose composite. For the Lyocell multifilament bundle, the Young’s modulus of the processed composites was found to be quite scattered and so it could not be ascertained if this followed time-temperature superposition. However, the fall of the ultimate tensile strength of the composites with dissolution time and temperature was found to follow time-temperature superposition, with an Arrhenius behaviour giving a value for Ea= 144± 27 kJ/mol. The ultimate tensile strength results plotted against 𝑣𝑚 determined from the optical microscopic method was found to lie significantly below the Voigt rule of mixtures. This suggests that either the dissolved Lyocell material is less successful as a matrix, or that the twisted nature of the Lyocell multifilaments does not allow dissolution to happen in the interior of the bundle as the ionic liquid cannot penetrate. In terms of the difference between the Cordenka and Lyocell multifilament bundles, it was found from the Optical microscopic results, that the geometry of the Cordenka multifilament bundle is untwisted with a few hundred individual multifilaments, which appeared as a loose microstructure with significant inner spaces in between. On the other hand, the geometry of Lyocell multifilament bundle is twisted with few hundred individual fibres that are close to each other without significant inner spaces. The Cordenka multifilament bundle has higher average orientation, and a higher Young’s modulus, ultimate tensile strength, and activation energy compared to the Lyocell multifilament bundle, which we attribute to the fibres being untwisted. The Lyocell bundle has lower average orientation, which was shown to be due to the significant twist of the bundle. These findings, especially the geometry and molecular weight lead to the Cordenka multifilament bundle having a faster dissolution rate than the Lyocell multifilament bundle. The comparative geometry (untwisted fibres), the speed of dissolution and the higher molecular weight, lead to the important result that the Cordenka multifilament bundle would make an excellent basis for an all cellulose regenerated fibre composite (ACC). However, it is appreciated that if woven cloth is to be used to manufacture all-cellulose composites (ACC) then some degree of twist will be required to stop the individual fibres from breaking during the weaving process, so there is maybe an optimum bundle twist to be discovered in any future work.20 0