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Understanding light sensitivity of plastics in heritage collections

Pokorska, Anna; (2021) Understanding light sensitivity of plastics in heritage collections. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Through an extensive and in-depth literature review five photostability ‘influencers’ were identified: polymer type, light stabilizers and/or antioxidants, colourants (dyes or pigments), impurities from manufacture and processing, and previous light exposure. Of those five, the effect of several colourants and previous UV exposure on cellulose acetate (CA) and polypropylene (PP) polymers was examined through a series of light-ageing experiments. The selected pigments are known to have a sensitizing effect on those polymers when exposed to UV radiation, however their influence under visible light, as found in a museum environment, has not been explored. Results obtained from these experiments show that, although many of the pigments did indeed accelerate molecular changes of the polymer when compared to uncoloured samples, the effect was not strong enough to lead to mechanical damage or even discolouration even after exposure corresponding to 200 years on display at 200 lux under similar light sources. The final study addressed the question whether previous light exposure of a plastic object can increase its sensitivity to visible light as found in museum displays. The results were similar to the previous experiment in that, although oxidation continued even without UV, its rate was not fast enough to cause significant degradation of the material. However, a growth in a hydroxyl FTIR band caused by UV exposure was linked to light sensitivity of PP when subsequently aged with visible radiation, which allows for simple screening of potentially photosensitive objects. Visible reflectance spectroscopy was also shown to be a promising tool for non-invasive identification of pigments used in plastics, particularly when combined with NIR spectroscopy to identify the polymer type. Finally, all the data and results from the experimental work as well as literature review were made available to the conservation community in the form of an online tool.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Understanding light sensitivity of plastics in heritage collections
Event: UCL (University College London)
Language: English
Additional information: Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of the Built Environment
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of the Built Environment > Bartlett School Env, Energy and Resources
URI: https://discovery.ucl.ac.uk/id/eprint/10127953
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