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  • (2009) Jayawardena, Menuk Birendra
    During the last few decades, systems incorporating immobilised enzymes have been used prevalently in many industrial and commercial applications. Normally, enzyme-based applications are expensive and have limited operating times, hence low cost operating systems and reusability of the biocatalyst are valuable factors that need consideration. All biocatalytic coatings are composed of two distinct components, categorised as the catalytic and the non-catalytic component. In order to have a stable and long lasting biocatalytic system both these components need to withstand varying conditions and to operate synergistically. Two commercially produced lipases, Greasex (LIPHLL) and NS81042 (LIPCA) were scrutinised for their ability to operate as immobilised biocatalysts in household based paint coatings. The two enzymes were first characterised in solution and in paint to determine their ability to withstand conditions that are considered foreign. The capability of these enzymes to withstand thermal denaturation was then analysed both in paint (in-can stability) and after entrapment in paint coatings, demonstrating significantly greater stability in the latter. The first part of the work described in this thesis was aimed at improving the thermostability of both lipases (the catalytic component). Chemical modifications were chosen over more expensive genetic modification techniques. The chemically modified variants showed improved thermostability both in buffer and in paint emulsion. The second part of the thesis addressed the modification and optimisation of the non-catalytic component (the support). Two strategies were successfully implemented to overcome the mass transfer limitations commonly experienced by many immobilised biocatalysts, including enzymes. The surfactant and solvent based improvements provided compelling evidence that they were practical approaches to direct the location of enzymes to a desired position in the surface layer of the polymer coating. The third part involved the use of the optimised lipase-based paint coatings to determine their detergency against natural substrates such as oils and ester/fat-based commercial stains. The lipase-based paint coatings indicated increased hydrolysis of oils and increased detergency towards the removal of ester-based stains on polymer surfaces. Overall, self-cleaning paint coatings were developed in this project to target fouling by fat material and these films offer great potential in a variety of applications and surroundings. It is proposed that the initial steps required for the development of a commercially available household paint with self-cleaning capabilities have been successfully undertaken.