Shear effects on the properties and separation characteristics of whey protein precipitates

Selective isoelectric whey protein precipitation and aggregation is carried out at laboratory scale in a standard configuration batch agitation vessel. Geometric scale-up of this operation is implemented on the basis of constant impeller power input per unit volume and subsequent clarification is achieved by high speed disc-stack centrifugation. Particle size and fractal geometry are important in achieving efficient separation while aggregates need to be strong enough to resist the more extreme levels of shear that are encountered during processing, for example through pumps, valves and at the centrifuge inlet zone. This study investigates how impeller agitation intensity and ageing time affect aggregate size, strength, fractal dimension and hindered settling rate at laboratory scale in order to determine conditions conducive for improved separation. Particle strength is measured by observing the effects of subjecting aggregates to moderate and high levels of process shear in a capillary rig and through a partially open ball-valve respectively. The protein precipitate yield is also investigated with respect to ageing time and impeller agitation intensity. A pilot scale study is undertaken to investigate scale-up and how agitation vessel shear affects centrifugal separation efficiency. Laboratory scale studies show that precipitates subject to higher impeller shear-rates during the addition of the precipitation agent are smaller but more compact than those subject to lower impeller agitation and are better able to resist turbulent breakage. They are thus more likely to provide a better feed for more efficient centrifugal separation. Protein precipitation yield improves significantly with ageing, and 50 minutes of ageing is required to obtain a 70 - 80% yield of α-lactalbumin. Geometric scale-up of the agitation vessel at constant power per unit volume results in aggregates of broadly similar size exhibiting similar trends but with some differences due to the absence of dynamic similarity due to longer circulation time and higher tip speed in the larger vessel. Disc stack centrifuge clarification efficiency curves show aggregates formed at higher shear-rates separate more efficiently, in accordance with laboratory scale projections. Exposure of aggregates to highly turbulent conditions, even for short exposure times, can lead to a large reduction in particle size. Thus, improving separation efficiencies can be achieved by the identification of high shear zones in a centrifugal process and the subsequent elimination or amelioration of such.

Advanced polymer membrane development in pervaporation dehydration and lateral flow diagnostics

The work in this thesis concerns the advanced development of polymeric membranes of two types; pervaporation and lateral-flow. The former produced from a solution casting method and the latter from a phase separation. All membranes were produced from casting lacquers. Early research centred on the development of viable membranes. This led to a supported polymer blend pervaporation membrane. Selective layer: plasticized 4:1 mass ratio sodium-alginate: poly(vinyl-alcohol) polymer blend. Using this membrane, pervaporation separation of ethanol/water mixtures was carefully monitored as a function of film thickness and time. Contrary to literature expectations, these films showed increased selectivity and decreased flux as film thickness was reduced. It is argued that morphology and structure of the polymer blend changes with thickness and that these changes define membrane efficiency. Mixed matrix membrane development was done using spherical, discreet, size-monodisperse mesoporous silica particles of 1.8 - 2μm diameter, with pore diameters of ~1.8 nm were incorporated into a poly(vinyl alcohol) [PVA] matrix. Inclusion of silica benefitted pervaporation performance for the dehydration of ethanol, improving flux and selectivity throughout in all but the highest silica content samples. Early lateral-flow membrane research produced a membrane from a basic lacquer composition required for phase inversion; polymer, solvent and non-solvent. Results showed that bringing lacquers to cloud point benefits both the pore structure and skin layers of the membranes. Advancement of this work showed that incorporation of ethanol as a mesosolvent into the lacquer effectively enhances membrane pore structure resulting in an improvement in lateral flow rates of the final membranes. This project details the formation mechanics of pervaporation and lateral-flow membranes and how these can be controlled. The principle methods of control can be applied to the formation of any other flat sheet polymer membranes, opening many avenues of future membrane research and industrial application.

Development of low-cost sensing and separation devices based on macro, micro and nano technology for health applications

The work presented in this thesis described the development of low-cost sensing and separation devices with electrochemical detections for health applications. This research employs macro, micro and nano technology. The first sensing device developed was a tonerbased micro-device. The initial development of microfluidic devices was based on glass or quartz devices that are often expensive to fabricate; however, the introduction of new types of materials, such as plastics, offered a new way for fast prototyping and the development of disposable devices. One such microfluidic device is based on the lamination of laser-printed polyester films using a computer, printer and laminator. The resulting toner-based microchips demonstrated a potential viability for chemical assays, coupled with several detection methods, particularly Chip-Electrophoresis-Chemiluminescence (CE-CL) detection which has never been reported in the literature. Following on from the toner-based microchip, a three-electrode micro-configuration was developed on acetate substrate. This is the first time that a micro-electrode configuration made from gold; silver and platinum have been fabricated onto acetate by means of patterning and deposition techniques using the central fabrication facilities in Tyndall National Institute. These electrodes have been designed to facilitate the integration of a 3- electrode configuration as part of the fabrication process. Since the electrodes are on acetate the dicing step can automatically be eliminated. The stability of these sensors has been investigated using electrochemical techniques with excellent outcomes. Following on from the generalised testing of the electrodes these sensors were then coupled with capillary electrophoresis. The final sensing devices were on a macro scale and involved the modifications of screenprinted electrodes. Screen-printed electrodes (SPE) are generally seen to be far less sensitive than the more expensive electrodes including the gold, boron-doped diamond and glassy carbon electrodes. To enhance the sensitivity of these electrodes they were treated with metal nano-particles, gold and palladium. Following on from this, another modification was introduced. The carbonaceous material carbon monolith was drop-cast onto the SPE and then the metal nano-particles were electrodeposited onto the monolith material