The objectives of this research programme were to examine the influence of manufacturing and processing parameters on the environmental stability of aqueous acrylic based latices and to also extend the programme to an assessment of the behaviour of various stabiliser types suitable to such materials through either end-group modification or direct in-situ addition. During the research programme a number of physical and chemical techniques were assessed to routinely characterise and monitor the photochemical and thermal degradation of acrylic latices. These were based on emulsion polymerised formulations of methyl methacrylate and butyl acrylate. In the first instance, acrylic latices based on different formulations were chosen as homopolymers and copolymers. Here the nature of impurities and oxidation products generated during various stages of their manufacture have to be characterised and inter-related to their influence on subsequent environmental degradation. This involved the use of reflectance FT-IR spectroscopy to show functional group changes together with colourimetric U.V. analysis to determine photochemical generation of hydroperoxides. The early chemical changes and their subsequent influence on the physical and chemical properties of the latices during the later stages of environmental degradation were found to exhibit a close inter-relationship. In this regard the formation and the manufacturing temperatures and periods were crucial. Thermal methods of analysis were also used to characterise differences in the properties of the latices before and during thermal and photochemical oxidation. The nature of the residual persulphate initiator and the compositions of the latices in terms of end group modification were important parameters. De-esterification and hydroperoxide formation were found to be important processes during latex degradation while the use of low levels of co-monomer addition. such as methacrylic acicL to the emulsion reaction gave latices with improved light stability. Subsequent aspects of the research programme involved a detailed investigation into the behaviour and performance of various stabiliser types and formulations. Thus, while coreactive hindered piperidine stabilisers was found to be effective, the incorporation of simple terminal dialkyl acrylamide/methacrylaroide groups were also found to be effective. The efficiency of dialkylamide groups operating through a sacrificial mechanism is discussed. The influence of these processing operations on subsequent stabiliser activity provides valuable information on the mode of action of these stabilisers in such complex media. Further work involved a study into the effect of fluorinated methacrylates used in emulsion polymerised formulations. Here, the presence of residual starting materials in the monomer was found to have a detrimental effect in terms of photostability. Subsequent analysis of acrylic resins, based on solution polymerised formulations of methyl methacrylate and fluorinated methacrylates, was undertaken. The influence of reactive stabiliser types on these resins was important and to improve stabiliser perfonnance, synergistic stabiliser formulations were studied. This project will provide important fundamental information on the behaviour of active chromophores produced during the manufacturing process and hopefully resuh in the development of monitoring methodologies to establish paint quality.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:337183 |
| Date | January 1997 |
| Creators | Regan, Christopher James |
| Publisher | Manchester Metropolitan University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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