Thesis

Thermal, oxidative and hydrolytic degradation studies of poly(ethylene naphthalate)

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Awarding institution
  • University of Strathclyde
Date of award
  • 2013
Thesis identifier
  • T13500
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Abstract
  • Degradation of PEN is a particular problem above its melt temperature and is generally inevitable during synthesis and processing as the material is subjected to high thermal and mechanical stress. Whilst the literature is replete with studies on the degradation of PET, PEN has received little attention. In our research, we report on the thermal, thermal-oxidative and hydrolytic degradation of PEN, in comparison to PET, with particular emphasis on degradation under model processing conditions. Despite evidence of increased thermal stability of PEN in contrast to PET, thermal degradation studies of PET and PEN highlighted strong similarities in their degradation behaviour. Identical primary and secondary thermal degradation mechanisms have been proposed for PET and PEN, with radical processes thought to dominate at high temperatures. Under thermo-oxidative conditions, the dominant degradation reaction in PEN has been revealed as oxidative cross-linking with more extensive chain scission thought to occur in PET. A reduction in the formation of cross-linked species in both polyesters has been demonstrated only in the presence of significant levels of moisture due to competing thermo-oxidative and hydrolytic degradation reactions. Cross-linking reactions in PET and PEN have been proposed to result in the formation of interconnected rings, with a high degree of conjugation, contributing to the extensive discoloration observed following thermo-oxidative degradation, particularly in PEN. Finally, the extent of degradation has been shown to differ quite significantly during low temperature ageing studies of PET and PEN. Degradation of PET was largely influenced by the ageing environment and temperature with the dominant degradation reaction shown to differ with ageing temperature. However, all ageing environments and temperatures were found to have no detrimental effect on the physical properties of PEN. Embrittlement of both PET and PEN after ageing has been proposed to originate from secondary crystallisation developed upon ageing, causing remarkable changes to mechanical properties.
Advisor / supervisor
  • Liggat, John
Resource Type
DOI
Date Created
  • 2013
Former identifier
  • 995958

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