http://bura.brunel.ac.uk/handle/2438/231 2013-05-22T20:08:07Z 2013-05-22T20:08:07Z Ng, Thian Hong http://bura.brunel.ac.uk/handle/2438/7417 2013-05-03T13:17:09Z 2013-01-01T00:00:00Z

Title: Twin screw extrusion pre-treatment of wheat straw for biofuel and lignin biorefinery applications Authors: Ng, Thian Hong Abstract: Pre-treatment of wheat straw(lignocellulosic) biomass is a crucial step as it has direct impact on the subsequent yield of enzymatic saccharification and alcohol fermentation processes in the production of biofuel. Twin screw extrusion is a highly feasible pretreatment method and has been received great interest in the recent year pre-treatment studies. Twin screw extrusion is a continuous process, where the biomass feedstock can be subjected to a combination of simultaneous physical, thermal and chemical treatments. Steam explosion is a batch process and is the most commonly used method for lignocellulosic pre-treatment. In the initial stage of this study, the yield of glucose obtained from enzymatic saccharification for both methods (extrusion and steam explosion) were compared to identify the most effective pre-treatment approach. Effectiveness of the conventional steam explosion pre-treatment was used as benchmark for the directions of development of effective extrusion fractionation for wheat straw. In subsequent study, the impact of physical operating parameters (moisture, barrel temperature, compaction, screw speed and size reduction before extrusion) over twin screw extrusion with and without NaOH were studied. Low temperature (50°C) and increased moisture extrusion were preferred extrusion conditions. Yield of glucose can be improved by addition of NaOH (0.04g / g straw) and barrel temperature profile optimisation. Post extrusion washing was recommended. Findings from FTIR and TGA help to understand the chemical and structural changes took place in the pre-treatment and can be correlated with the glucose yield at the end of enzymatic hydrolysis. Characterisation analysis was extended to FT-NIR, morphology, crystallinity and specific surface area analysis to analyse the structural changes of lignocellulose biomass in extrusion pre-treatment and correlation with glucose yield. Chemometric analysis was used to statistically process large amounts of spectral data. The PCA scores plots showed good cluster segregation of the samples and were thus able to distinguish the effects of different pre-treatment conditions. The PLS regression models for both FTIR and FT-NIR showed good statistical regression and predictive ability correlated to the glucose yield. For the lignin ultilisation study, crude lignin was recovered from black liquor and fractionated with solvents. Lignin and the fractions were characterised with solvent solubility, SEC, UV, FTIR, 1H and 13C NMR and evaluated for the antioxidant activity with AAI ranged from 0.3 to 2.4. Reason for the low performance was proposed and experiment was extended to the intended application performance screening. Lignin application study was further extended to assess the feasibility of using lignin as an antioxidant in carboxylated acrilonitrile-butadiene rubber, XNBR glove. Evaluation involved physical observation, mechanical properties and thermal analysis – DSC-OIT after incorporation of lignin into XNBR glove. Lignin antioxidant performance was compared with current chemical antioxidant in used in industry. A part from antioxidant behaviour, lignin was also found can enhance the softness of XNBR film after accelerated heat aging. Description: This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.

2013-01-01T00:00:00Z Wang, Xin http://bura.brunel.ac.uk/handle/2438/7403 2013-04-29T11:01:15Z 2001-01-01T00:00:00Z

Title: Non-destructive characterisation of structural ceramics using impedance spectroscopy Authors: Wang, Xin Abstract: The aim of this project was to explore the potential applications of impedance spectroscopy (IS) in the non-destructive characterisation of structural ceramics. A major advantage in the use of the IS technique is its capability in distinguishing the properties of different microstructural origins in materials, e.g., grains and grain boundaries, etc. In this thesis, a review of the theoretical aspects of IS is presented. An analytical approach and numerical analyses are conducted to illustrate how impedance spectra become resolved and why the spectral resolution is dependent on the representation formalism as well as on the difference between the electrical properties of different microstructural features. Three categories of structural ceramics, i. e. A1203/SiC nanocomposites, thermal barrier coatings and clay-based ceramics, were used as the model materials for this IS study. Both sintering and degradation phenomenon have been examined. Conventional analytical techniques, such as SEM, XRD, EDS, TGA and dilatometry, were used to aid in the understanding of IS and to prove the reliability of impedance measurements. The research results indicate: * For A1203/SiC nanocomposites, IS can be used to examine the conducting mechanisms for the materials containing different quantities of SiC particles. The content of SiC can be correlated to the impedance spectral features and dielectric constant of the material. The oxidation scale formed at the surface gives a separate relaxation process. Based on the capacitive effect of this relaxation process, the thickness can be determined non-destructively using IS. * For thermal barrier coatings, three relaxation processes can be found in the impedance spectra, which correspond to the top coating, oxidation layer and microstructural defects in the top coating, respectively. The thickness of the oxidation layer can be quantitatively related to the diameter of the corresponding semicircle in electrical modulus spectrum. In the meantime, the top coating degradation could also be monitored using IS. * For clay-based ceramics, the impedance spectra consist of a high frequency semicircle and a low frequency tail, which correspond to bulk effect and electrode effect, respectively. The variation of the bulk conductivity with sintering time can be quantitatively correlated to the densification of the material during sintering. The electrode effect tail is directly related to the capacitive effect of the electrode/specimen interface, which could be an effective indicator of the electrode temperature. Therefore IS is a useful technique for non-destructive characterisation of structural ceramics. Description: This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.

2001-01-01T00:00:00Z Sartori, Celine http://bura.brunel.ac.uk/handle/2438/7399 2013-04-29T09:55:28Z 1997-01-01T00:00:00Z

Title: The characterisation of alginate systems for biomedical applications Authors: Sartori, Celine Abstract: This research project focused on a range of polysaccharides, including sodium alginates (with varying mannuronic (M)/guluronic (G) acid ratio), pectin and sodium carboxymethylcellulose (CMC), for wound dressing applications. The samples were prepared as mixed salts such as sodium/calcium salts as Ca2+ ions are known to promote faster healing. The aims of this research were: 1- to provide a greater insight into the nature of binding between various ions (NaT, Ca2+ as well as Zn2+ and Ag+) and the polysaccharide molecules. Interactions between alginate/pectin and alginate/CMC molecules were also studied. This was achieved using a range of analytical techniques such as Fourier transform infrared spectroscopy, Raman spectroscopy and neutron spectroscopy, thermogravimetric analysis, microprobe analysis, X-ray diffraction and atomic absorption spectroscopy. It was found that sodium ions were bound to the carboxyl groups of the alginate molecules, whilst calcium ions attached themselves onto COO- as well as onto the alginate backbone, leading to crosslinked structures. Appearance of OH ... -OOC to the detriment of OH ... OH bonding was also observed. Addition of zinc ions involved greater constraint in the alginate network and the silver ions were believed to produce insoluble alginate salts, due to their larger ionic radius; furthermore hydroxyl-hydroxyl interactions in the silver alginate were rather between the polymer molecules than with the water. The addition of pectin to alginate led to partial binding between the two polysaccharides via hydrogen bonds. By contrast, carboxymethylcellulose molecules were found to act as independent entities in contact with alginate, and therefore suggested incompatibility. 2- to determine the performance of sodium/calcium alginate systems as well as Na/Ca alginate/pectin and Na/Ca alginate/CMC systems, in order to improve properties such as absorbency, gel strength and calcium release (to assess the haemocompatibility) in a simulated serum solution. A greater calcium and guluronic acid content was found to improve the gel strength of alginate samples, but decrease the swelling ability. Calcium release was favoured with a low G and a high calcium content. Addition of a second polysaccharide enhanced these gel properties. For example, the gel strength could be significantly increased with a 25 % pectin addition, while addition of CMC up to 50 % increased both the swelling and the calcium release. 3- to develop a new model of the ion release process for a polysaccharide system brought into contact with a simulated serum solution. It was based on a "hoppingtrapping" mechanism for the calcium ions, whereby different release rates are due to different affinities with the polysaccharide blocks. Description: This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.

1997-01-01T00:00:00Z Butt, M Taqi Zahid http://bura.brunel.ac.uk/handle/2438/7389 2013-04-26T14:24:45Z 1990-01-01T00:00:00Z

Title: Study of gold-based alloy phase diagrams Authors: Butt, M Taqi Zahid Abstract: The partial constitutions of the Au-Ge-X and Au-Pb-X ternary alloys have been investigated, where X is a metallic element, selected from the sub-groups period 1m and rrm of the periodic table (In, Ga, Zn, or Cd), which forms one or more stable compounds with gold, but which forms no stable compound with Ge and Pb. The Smith Thermal Analysis Method, supplemented by metallographic and X-ray techniques, was used to determine the constitutions of the ternary systems. Eutectiferous, pseudobinary systems were found between Ge and the stable congruent intermediate compounds, AuIn, Auln2' AuGa, AuGa2' AuZn and AuCd. The solubility of Ge in the AuX compounds was not determined directly. However, it was 1.3 at.% Ge for Zn and Cd containing alloys and less than 1.0 at. % Ge for In and Ga containing alloys at the eutectic temperatures, which is in accordance with the Hume-Rothery rule. Ternary eutectic points were also determined in the Auln-AuIn2-Ge, Auln2-In-Ge and AuGa-AuGa2-Ge partial ternary systems. No evidence of liquid immiscibility was found in any of these ternary systems. The experimental results obtained were in good agreement with computed features of the diagrams. However, pseudobinary systems were not found between Pb and the stable congruent melting intermediate compounds, AuGa, AuGa2, AuZn and AuCd (the AuIn-Pb and AuIn2-Pb sections had already been investigated). The evidence of an extensive liquid immiscibility was found in each of these systems. The miscibility in the liquid state was found to decrease progressively down group IV when the elements of this group react with AuX compounds, which can be attributed to the progressive increase of the atomic size and decrease in electronegativities and solubility parameters of the elements, down this group. Two rules were derived to relate the liquid immiscibility/miscibility of ternary systems. One of the rules based upon the atomic sizes and melting points of the constituent elements showed a fair agreement with many systems. However, the other rule based upon the solubility parameter and electronegativities of the constituent elements showed good agreement with immiscible systems, but gave a poor predictability for miscible systems. The lower temperature equilibria of the Au-rich portion of the Au-Sn binary phase diagram are not well defined. So, long term heat treatment of samples at appropriate temperatures and compositions was carried out. Optical microscopy and SEMIEDAX techniques were employed and hence the low temperature equilibria of the Au-Sn binary system have been amended. Description: This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.

1990-01-01T00:00:00Z