Photodegradation of polyester films

  • Fiona Horne

Student thesis: Doctoral Thesis

Abstract

Poly(ethylene terephthalate) (PET) is well known for its excellent properties, but when exposed to ultra-violet (UV) light PET films have the tendency to degrade, which in some applications can be a shortcoming. Many groups have studied the different degradation pathways that can occur in PET during outdoor exposure, however, the effect of specific narrow band wavelength ranges of light have received little attention.To begin, this research programme was concerned with understanding the effects of exposing PET films to narrow and broad band wavelength ranges of light. The narrow band wavelength ranges used were 302 and 365 nm light and the broad band wavelength range was 290-800 nm. Single films were analysed as well as stacks of films, to investigate whether these could be used to depth profile a single film of the same thickness, during exposure.When using narrow band wavelength ranges, oxidative and non-oxidative conditions (under nitrogen) were used. This fundamental study concluded that PET degrades more extensively under short wavelength light (302 nm) compared to longer wavelength light (365 nm) of the same intensity and when exposed under oxidative conditions compared to non-oxidative conditions. During exposure, various degradation products were proven to be produced, including carboxylic acid end groups, dimers, quinone species, monohydroxy terephthalate groups and mono-substituted terephthalic rings.Another area of this research was focused on using a novel way to study the reactions that take place as a consequence of different wavelengths of light, while still replicating outdoor exposure. Exposing samples to the full spectrum of light means that photodegradation reactions taking place as a consequence of short and long wavelengths of light, happen simultaneously. Whereas, if samples were exposed to different wavelengths of light consecutively, the reactions that happen simultaneously outdoors could be studied.Samples were therefore exposed to one wavelength of light followed by another wavelength of light (302 nm light followed by 365 nm light and vice versa). This study showed that long wavelength light (365 nm) can cause more damage to a film than previously reported, especially when a film has already been photodegraded using short wavelength light (302 nm) before being exposed to longer wavelength light.Finally, the photodegradation behaviour of poly(diethylene glycol terephthalate) (PDEGT) homopolymer was studied. Although the thermal degradation of PDEGT has been previously reported, the photodegradation of PDEGT has received no attention. The effects of temperature, atmosphere, and wavelength of light were considered, resulting in the PDEGT showing a higher extent of degradation compared to PET, exposed under the same conditions. A mechanistic pathway for the photodegradation reactions occurring in PDEGT during exposure has been proposed.
Date of Award17 May 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorJohn Liggat (Supervisor) & Peter Skabara (Supervisor)

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