Premature yeast flocculation (PYF) is a sporadic problem encountered during industrial brewing fermentations. Current hypothesis states that factors, thought to arise from fungal infection of the barley in the field and/or the malt in the maltings cause yeast to flocculate prematurely and/or heavily before the depletion of the sugars in the wort. This results in poorly attenuated worts, with higher residual extract and lower ABV, flavor abnormalities (i.e. diacetyl, SO2), lower carbonation levels, disruption of process cycle times and potential issues with the re-use of the yeast in subsequent fermentations. Consequently, PYF generates significant financial and logistical problems both to the brewer and the maltster. In the current study a small-scale fermentation assay was developed and optimized to predict the PYF potential of malts, as well as to investigate the importance of yeast strain in the incidence and severity of the phenomenon. Furthermore, the impacts of the PYF factor(s) (i.e. arabinoxylans, antimicrobial peptides) on yeast fermentation performance and metabolite uptake were also studied, whilst the Biolog detection system was investigated as a potential rapid tool which to detect PYF. The results obtained suggested that our in-house assay can be successfully used to predict the PYF potential of malts 69 or 40 h post-pitching depending upon the yeast strain used. Whilst ale yeasts were not found susceptible to PYF, lager yeasts exhibited different degrees of susceptibility even to the same PYF factor(s). More specifically, the more flocculent lager yeast SMA was found to be more susceptible than the medium flocculent lager yeast W34/70. However, interestingly, the fermentation performance of a PYF+ wort could be significantly improved by using a non-flocculent and relatively insensitive to PYF lager yeast. It was also shown that worts with lower amount of glucose and maltose could be responsible for poor fermentation profiles and/or heavy PYF as well as elevated residual sugars and lower fermentability. The observation that linoleic acid (6 mg.l-1) exacerbated PYF (P = 0.047) and made its detection more rapid was found to be contrary to the “titration hypothesis” (Axcell et al., 2000) which hypothesized that the addition of fatty acids might “titrate” out antimicrobial peptides so that they can no longer bind to the yeast cells. High gravity fermentations with worts inducing PYF did not have a significant effect (P > 0.05) on yeast physiological characteristics or fermentation performance suggesting that the PYF+ sample used in this study was inducing PYF though the ‘bridging’ polysaccharide mechanism rather than through the antimicrobial peptides. The Biolog system can be used for the metabolic characterization of different flocculence lager yeasts incubated in different fermentation media, whilst wort composition had a significant effect in redox reduction reactions.

The transport and separation of oil and water is a vital process to the oil and chemical industries. Fluids exiting from oil wells usually consist of gas, oil and water and these three phases need to be transported and separated before they can be processed further. Operation of the primary separators has often proved to be problematic due to the change in composition of the fluids as the well matures, often accompanied by the build up of sand or asphaltenes. These vessels are very expensive to install so there is motivation to improve their design and performance. One major factor affecting separator performance is the phase distribution of the inlet flow, as reflected in the flow pattern and droplet size. In this work, flow pattern boundaries and drop sizes of liquid-liquid dispersions were measured for vertical and horizontal flow of a kerosene and water mixture in a 0.063m tube. Drop size was investigated by using two different laser optical techniques. A laser backscatter technique was employed for concentrated dispersions and a diffraction technique was used at low concentrations. In order to develop a greater understanding of separator performance, a 1/5th-scale model was constructed of diameter 0.6m and length 205m. Residence Time Distributions were obtained for a range of different internal configurations and flow rates using a colorimetric tracer technique. Flow rates of 1.5-4 kg/s oil and 1-4 kg/s water were used and the vessel was equipped with a perforated flow-spreading baffle at the inlet and an overflow weir. Experiments were performed with no internals and with dip or side baffles. The side baffles acted to create quiescent zones within the vessel while the dip baffle caused a local acceleration of both phases. These situations are similar to those that can be caused by blocked internals or existing baffling or structured packing within field separators. A Residence Time Distribution model of a primary separator, the Alternative Path Model, was developed using transfer functions. This model has the ability to reproduce features of the experimental data by representing the flow as a series of continuous stirred tanks in series or in parallel. The model was used to develop parameters that could be used to obtain information about the performance of the separator. This model was also applied to Residence Time Distribution data obtained from field separators by BP Exploration, to relate features of the pilot scale separator to the field vessels.

The overall aim of this research project was to expand the understanding of the deposition of titanium and the nickel-based superalloy Inconel 718 by spray deposition methods. The spray processes employed were cold spraying and high velocity oxy-fuel (HVOF) thermal spraying. The first part of the work was undertaken to expand the understanding of the deposition of titanium by cold spraying; the HVOF process is unsuitable for Ti because of the metal's high reactivity. The deposits were produced from commercially pure titanium using cold spray equipment designed in the University. Using helium gas, the effects of different powder particle size ranges, types of substrate, substrate preparation methods, and spray parameter conditions on deposit formation were investigated. Using a simple one-dimensional model of compressible gas flow and particle acceleration, particle velocity distributions were calculated to aid interpretation of experimental data. Results show that titanium can be successfully cold sprayed onto substrates of Ti6AI4V and mild steel, with the critical velocity for deposition of this powder type of approximately 690 m s-1. The level of porosity was generally in the range of 13-23% and the adhesive bond strength was dependent on surface preparation but independent of gas pressure with values ranging from 22 MPa to 10 MPa for ground and grit blasted substrates respectively. This compares with a value of around 80 MPa which is typical for well adhered HVOF sprayed coatings. The second part of the study was concerned with comparing the deposition of Inconel 718 by cold spraying and HVOF thermal spraying; the latter employed a JP5000 liquid fuel gun. A Tecnar DPV-2000 instrument was used to systematically investigate the effect of changes in spray parameters (spraying stand-off distance, oxygen/fuel ratio, total mass flow rate, combustion pressure), on particle velocity and temperature during HVOF spraying. It was found that generally the particle velocity was more strongly affected by the stand-off distance and combustion pressure of the spraying gun whereas the particle temperature was mostly influenced by the particle size and combustion pressure. The microstructures of coatings sprayed under 4 different well controlled conditions were investigated and changes in the morphology of splats and partially melted particles in the coating were related to the particle temperature and velocity at impact. The HVOF had high bond strength and low oxygen level of typically 0.45 wt% (corresponding to an oxide content of less than 1.6 wt.%). By contrast, in the cold sprayed coatings, the bonding was considerably low (-14 MPa), independently from the process conditions. It was found that the process parameter that mainly affected the properties of the cold sprayed deposits was the gas pressure. More specifically, the microhardness of the coatings increased with the pressure whereas the relative porosity decreased.

The aim of the project was to understand the science behind rapid cooling of chocolate used in the Frozen Cone® process. Differential scanning calorimetry was used to study the effect of slow and rapid cooling on tempered chocolate. On rapid cooling, lower melting polymorphs of cocoa butter were generated. Upon heating these recrystallised into the more stable Form V. Results were confirmed by similar observations with tempered chocolate fats. A hypothesis was formed whereby upon rapid cooling, lower melting polymorphs nucleate and grow at the expense of Form V nuclei produced during tempering. Upon subsequent warming, these polymorphs melt and recrystallise into Form V. Rapid cooling on untempered chocolate did not show any recrystallisation during warming; proving that tempering is required for the formation of Form V crystals in the final matrix. These results were confirmed by temperature-controlled X-ray diffraction on cocoa butter and chocolate fats. The polymorph generated upon rapid cooling was identified as Form I. This co-existed and eventually transformed to Form II and Form V upon warming. X-ray results showed that following rapid cooling, Form V crystals created during tempering did not grow until above 5 °C. Direct contact cooling at different temperatures was carried out to mimic the Frozen Cone® process. It was found that above -15 °C, the adhesion of the sample to the holder increases and seems to be correlated to the presence of Form II. These results suggest that the molecular structure and adhesive property of the polymorphs formed at specific temperatures are important for the release of chocolate. Stepscan differential scanning calorimetry was used to separate the simultaneous melting and recrystallisation events occurring in chocolate following slow and rapid cooling, by deconvoluting the total heat flow into reversing and non-reversing components. The general applicability and limitations of Stepscan DSC are also discussed.

Recognising the difficulties encountered in measuring the adsorption of hydrogen at high pressure, a reliable volumetric differential pressure method of high accuracy and good repeatability has been developed for measurement up to ca 100 bar. The apparatus used has two identical limbs, a sample and a blank limb, between which a high accuracy differential pressure cell measures changes in pressure. By simultaneously expanding the two limbs and closely controlling the temperature of the entire system, many of the errors due to expansion of the gas can be avoided. In addition, helium blank measurements are used as a base line correction, which substantially reduces the effects caused by the rapid expansion of gas through a small port. Using this method, the hydrogen storage capacities of relatively small samples (1.0-2.5 g) of a selection of carbon materials have been accurately measured to a conservative limit of detection of 0.05 wt% and an accuracy of +/-0.02 wt%. The accuracy of the apparatus has been proven using lanthanide nickel (LaNi5), which has a known hydrogen storage capacity of 1.5 wt%, as a standard. The method has also been developed in order to analyse samples at elevated temperatures of up to 270 C. This has been demonstrated using lithium nitride (Li3N) compounds. The carbon materials studied include a series of activated carbons, carbon nanofibres (CNF) and carbon nanotubes (CNT). The activated carbons have displayed almost instantaneous hydrogen uptake independent of the degas method used, which indicates that sorption occurs via a physisorption mechanism. The series of powdered activated carbons have displayed direct correlation between the BET surface area and the hydrogen sorption capacity. The largest hydrogen sorption capacity observed for activated carbons was for a chemically activated carbon with a surface area of 3100 m2 g-1, achieving an uptake of 0.6 wt%. The preparation of CNF, grown from ethylene over mixed copper, iron and nickel alloy catalysts, has been extensively investigated. Control of the parameters of preparation has allowed the formation of CNF with surface areas of 10 - 500 m2 g-1, diameters of 100 - 1000 nm, lengths of 1-10s nm, gas conversions of 0-90 % and the formation of herringbone and platelet CNF structures. The CNF studied have been observed to be capable of adsorbing a maximum of 0.5 wt% hydrogen at 100 bar and ambient temperature. Only one of the materials studied was observed to break by a significant amount the trend of surface area vs hydrogen sorption capacity, observed for the activated carbons. This was a single-walled nanotube (SWNT) sample which achieved ca 1.6 wt% after slow carbon dioxide activation at low temperature. This larger sorption is hypothesised to result from the hydrogen slowly diffusing into the SWNT through defects in the structure and between the graphite planes in the CNF.

Nanofiltration has many potential applications as a separation technology for processes that use mixtures of aqueous and organic solvents, for example alcohol/water mixtures. Membrane systems are well established for separations carried out in aqueous media, however they have seen a much slower rate of uptake in non-aqueous processes or with aqueous/organic mixtures. This is because the interaction between membrane and solvent(s) dictates both the permeability and selectivity, and there is currently limited criterion for identifying the theoretical performance of a membrane based on the properties of a bulk polymeric material. The small numbers of commercial successes to date have arisen from empirical findings, with no agreed methodology by which new candidate membrane materials can be identified. New membrane materials are required to exhibit a high permeability along with the selectivity demanded by the application. Permeability can be relatively easily manipulated using engineering solutions such as large surface areas, or very thin active separation layers. Selectivity, however cannot be manipulated in such an intuitive fashion, with the mixture type and composition, pressure and polymer characteristics all reported to be major factors. This work investigates the factors which influence the inherent selectivity of polymeric materials, and the link to nanofiltration processes. The aims of this study are to investigate the effectiveness of current theoretical and predictive tools, and to establish a technique to evaluate polymeric materials without having to fabricate a membrane. Two polymers were chosen for study which are at opposing ends of the permeability/selectivity spectrum. Polydimethylsiloxane (PDMS) and poly (vinyl alcohol) (PVA) membranes have been previously investigated in several separations involving organic-water mixtures. The materials were characterized using GPC and ATR-FTIR techniques, with ATR-FTIR further used to quantify the crosslinking content of the polymers. The total swelling degree and the inherent separation that occurs upon swelling with solvent mixtures was studied for a range of model and industrially-relevant systems, using polymer materials fabricated under different conditions. It was found that the selectivity of the polymer was a highly non-linear function of mixture type and concentration. PDMS and PVA were shown to change their affinity toward mixture components depending on the concentration, and it was hypothesized that this is due to competing mechanisms based on both molecular size and polarity. Selectivity was shown to be less dependent on the applied pressure and the degree of crosslinking, with the polymer type and mixture composition the two most dominant factors. The Flory-Huggins model was evaluated and found to give an extremely poor prediction of the selectivity in all the polymer-solvent systems studied. Further analysis was carried out using chemical potential and activity coefficient models in order to establish the sorption coefficient for future comparison with membrane filtration data. One of the key outcomes of this work is the measurement of sorption coefficients at varying composition and pressure, which can subsequently be used with existing Solution-Diffusion and Pore-Flow filtration models with greater confidence than has been possible to date.

More than half of platform petrochemicals are aromatic, whereas the only large-scale, naturally-occurring, renewable source of aromatics is lignin. Chemical depolymerization of lignin requires extreme conditions, and results in extensive destruction of the aromatic rings and/or char formation. By contrast, enzymatic lignin depolymerization occurs under mild conditions with retention of the aromatic nuclei. Therefore, laccase from Agaricus bisporus (LAB) and from Trametes versicolor (LTV) with the mediator, ABTS (2,2'-azino-bis(3 ethyl benzthiazoline-6-sulphonic acid)) were used to depolymerize lignin (sodium Iignosulphonate) under mild reaction conditions with the aim to obtain high concentrations of value-added chemicals. The depolymerization in the presence of LTV was higher than LAB, which resulted from the high catalytic activity of LTV. Lignin degradation resulted in formation of complex product mixtures. Therefore the products were fractionated and analyzed by different analytical techniques including GPC (for preliminary screening), HPLC and GCMS (for product characterization and quantification), and NMR (for fingerprint analysis). Products included guaiacol, vanillin, acetovanillone, vanillic acid, homovanillyl alcohol, phenol, 4- methyl benzaldehyde, catechol, p-toluic acid, 4- hydroxybenzaldehyde, tyrosoI, isovaniIIin, and 3-hydroxy-1-(4-hydroxy-3 -methoxyphenyl) propan-1-one, and the total yield of monomers from lignin was 9.8 % in the presence of LTV. The parameters involved in the depolymerization process were optimized to increase the yield of monomers. The efficiency of laccase mediators was also explored by the use of 2,2,6,6-tetramethylpiperidin-1-yloxy (TEMPO), 1-hydroxybenzotriazole (HBT), N-hydroxyphthalimide(HPI) and violuric acid (VLA) in the depolymerization of sodium lignosulphonate. However, the catalytic depolymerization in the presence of these mediators was lower than ABTS. In order to improve the solubility of the substrate for the depolymerization process, screening of ionic liquids that are compatible with LAB was deployed in order to find laccase-friendly ionic liquids for further use in lignin depolymerization. The study has found [C4mim] [L-tartrate] as the best ionic liquid tested, that increased the activity of LAB by 90 %. In conclusion, enzymatic depolymerization of lignin offers a greener process than the chemical methods, and also provides a more efficient method to obtain monomers of valuable specialty chemicals under mild reaction conditions.

Predicting flavour perception is complicated by interactions occurring both within and across sensory modalities, but understanding these interactions and the resulting multimodal integration is crucial to the formulation of successful products. Despite the commercial appeal of carbonated soft drinks, few studies have examined the effects of tastant: aroma: carbonation interactions on sensory perception. To facilitate these investigations, a citrus flavoured model beverage was created containing ingredients common in commercial beverages; water, aroma volatiles, sugar (glucose or fructose; equi-sweet levels), and acid (citric and lactic acid; equi-sour levels). The complexity of the beverage was gradually increased (influence of carbonation and caffeine) until the model beverage contained elements capable of stimulating gustatory, olfactory and trigeminal systems. Samples, selected according to D-optimal designs, were evaluated instrumentally (APCI-MS measuring volatile release, rheological measures of viscosity), and sensorially (using a trained panel of assessors). Predictive polynomial models were generated from mean panel data to explain variations in the attributes as a function of the design factors. The model beverages provided evidence that multi-modal interactions occurred within this model beverage system. Increasing both sugars and acids resulted in an increase in perceived citrus flavour which was not related to any alteration in volatile release measured instrumentally. Intriguingly, glucose and fructose showed different flavour perception enhancement profiles despite being used at perceptually equi-sweet levels. This difference between the monosaccharides was also evident in the predictive models generated for mouthfeel attributes. 'Overall fizziness' was dependant only on carbonation level and unaffected by levels of tastants. However, varying levels of glucose impacted on 'tingling', a relationship not mimicked by fructose. Addition of carbonation increased perceived sourness, in agreement with previous literature, but results also demonstrated a suppressive effect on perceived sweetness. Interestingly, evaluation of non-caffeinated beverages revealed the perception of a bitter aftertaste, which was primarily driven by CO2 level, enhanced by citric acid, and suppressed by increasing sugar concentration. In caffeinated beverages, however, caffeine concentration was the main influence on 'bitterness' and 'bitter aftertaste' attributes. Despite beverage manufacturers including caffeine as 'flavouring' there was little evidence to suggest caffeine concentration modified perception of citrus flavour in this system. This project provides a comprehensive assessment of the sensory profile of a model carbonated beverage. Combining instrumental and sensorial analysis provided novel evidence of the influence of multi-modal interactions on sensory perception, and highlights the differential effects of two monosaccharides on several key sensory attributes.

Long term (>2 years) failure of UHMWPE components in-vivo is predominantly caused by wear of the UHMWPE component. The surface properties of UHMWPE greatly influence the adhesive and abrasive mechanisms of wear that occur in the hip. However, there is not a clear understanding of how in-vivo wear mechanisms influence surface mechanical properties of UHMWPE. In addition, previous researchers have reported wear rates for Charnley UHMWPE acetabular components that vary considerably between patients. It is conceivable that these variations in wear are a result of variations in the surface mechanical properties of UHMWPE. This study used a combination of instrumented indentation testing and Ff-IR imaging to assess the depth dependent micromechanical and chemical properties of 32 retrieved UHMWPE acetabular components. Significant variations in the mechanical and chemical properties of samples taken from worn and unworn regions of retrieved UHMWPE acetabular components were found. In unworn regions, these variations were principally caused by post-irradiation ageing. However, in worn regions, the variation in properties was primarily caused by the wear process.

Photocuring of polymers and polymer composites, from epoxy resin based formulations, has been of growing interest over the past two decades. The photocuring occurs when an epoxy formulation is exposed to electromagnetic radiation, usually ultraviolet (UV) radiation. This process has been explored widely and it can be described as an open mould process by which the epoxy formulation is exposed directly to the radiation. However, for a closed mould process, thermal curing, rather than radiation curing, typically is employed. The potential of using photocuring for a closed mould process has not yet been investigated in detail. The challenge in photocuring of polymers and polymer composites in a closed mould is directing the radiation into the mould to activate the photocuring process, which is not possible using the conventional methods. Hence, for this reason the present work is focused on the development of a closed mould photocuring system using side emitting optical fibres. This photocuring system using side emitting optical fibres relies upon the optimisation of epoxy based resins. As a result, an extensive characterisation of different types of UV curable cationic epoxy resins is carried out using two pre-formulated commercial resins, formulations from bisphenol A/F, and formulations from cycloaliphatic epoxy. The formulations showed different reactivity and hardness. An important result is that the cycloaliphatic epoxy resin formulations cured much faster than the other bisphenol A/F formulations, having a more uniform hardness distribution and UV radiation transparency during the curing. Side emitting optical fibres are adopted to photocure epoxy in a closed mould. Different types of side emitting optical fibres are characterised to determine irradiation efficiency. The optical fibres had either a silica core or a PMMA core. The silica core fibres have a silicone cladding containing radiation scattering particles (either ZnO or Al2O3) and diffuser (either PA6 or ETFE). The PMMA core polymer optical fibres (PMMA POFs) have a PVDF cladding with micro-perforations as a side emission mechanism. Silica core fibres with the Al2O3 scattering particles and the PMMA core fibre are more suitable for the closed mould application as they transmitted efficiently in the UV radiation band. The high side emission characteristics of the PMMA POF compared to the silica core fibre showed higher potential for use in the closed mould photocuring process. As the polymerisation speed is influenced by the amount of flux density of the radiation source, a high flux lamp (Hg lamp, 40 W/cm2) is coupled to the side emitting optical fibres. This lamp caused thermal degradation to the PMMA POF at the launch point when in use. A cooling device is made to minimise the thermal degradation generated by radiation absorption. After improving the optical transmission stability of the PMMA POF, its side emission is enhanced by various treatments, such as permanent modification of the fibre geometry with adjusted bend radii as well as by mechanically embedding silica scattering particles into the fibre and applying micro-cuts. The developed, closed mould photocuring system consists of: enhanced side emitting PMMA POF, a cooling device, high emission Hg lamp, and a closed mould setup. 1.5 mm and 5 mm thick components, made from an optimised epoxy formulation (based on cycloaliphatic epoxy), are cured using the photocuring system. The 1.5 mm thick component (20 mm wide and 245 mm long) is cured in 45 minutes using a single PMMA POF treated with silica particles (side emission of ~81 % of the total launched emission). The 5 mm thick component (75 mm wide and 170 mm long) partly cured in 45 minutes by simultaneously using three PMMA POFs treated with silica particles and geometric modification (side emission of ~96 % of the total launched emission). This sample eventually cured with time (up to 36 hours) due to dark reaction. The efficiency of the developed closed mould photocuring system is validated by curing a 1.5 mm thick component made from a pre-formulated polyester resin formulation. This component cured in 7 minutes (30 mm wide and 245 mm long) using a single PMMA POF treated with silica particles.