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Are we overestimating the permanence of cellulose triacetate cinematographic films? A mathematical model for the vinegar syndrome

Ahmad, IR; Cane, D; Townsend, JH; Triana, C; Mazzei, L; Curran, K; (2020) Are we overestimating the permanence of cellulose triacetate cinematographic films? A mathematical model for the vinegar syndrome. Polymer Degradation and Stability , 172 , Article 109050. 10.1016/j.polymdegradstab.2019.109050. Green open access

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Abstract

Among the earliest signs of degradation in cellulose triacetate cinematographic films is the generation of acetic acid due to hydrolytic deacetylation of the polymer, marked by an increase in the acidity of the films and emissions of acetic acid leading to a characteristic vinegar odour. We propose a mathematical model for predicting the onset of the vinegar syndrome which accounts for the autocatalytic effect of acetic acid on the deacetylation reaction. Model parameters are estimated from previously published experimental data from other research groups. These show free acidity changes in cellulose triacetate films subjected to accelerated ageing at temperatures of 70–100 °C. The model is validated against a different set of previously published experimental data of cellulose triacetate films aged at 21 °C and 35 °C, at 20, 35 and 50% relative humidity. The model demonstrates good quantitative agreement with the published experimental data. Predictions of film permanence at lower temperatures, similar to those present in the archives in which the films are typically stored, are made and compared with the predictions of film conservation guidelines. The results indicate that film permanence may be overestimated by existing guidelines, which do not account for autocatalysis in their modelling of the deacetylation rate. Our results suggest that cold storage, a common film conservation strategy, may be less effective at inhibiting degradation than previously thought. As cold storage typically requires film to be kept in confined spaces with limited air movement, conditions which promote autocatalysis, the inclusion of autocatalysis in our model is highly applicable to simulating this environment.

Type: Article
Title: Are we overestimating the permanence of cellulose triacetate cinematographic films? A mathematical model for the vinegar syndrome
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.polymdegradstab.2019.109050
Publisher version: https://doi.org/10.1016/j.polymdegradstab.2019.109...
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: cellulose acetate; acetic acid; cinematographic films; kinetics; autocatalysis; mathematical modeling; lifetime prediction; Arrhenius; hydrolysis; deacetylation
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 Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
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/10089012
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