Acetic acid and cellulose acetate films: artificial ageing and preliminary risk assessment of climate-induced impact

Most cellulose acetate film archives are affected by the vinegar syndrome (Bigourdan, et al., 2000). This spontaneous and self-catalytic process leads to a rapid (i.e., in a few years) deterioration of film materials, which rate increases under unfavourable thermo-hygrometric storage conditions. Therefore, the actual problem facing archives is the preservation of collections that are not yet in acetic syndrome (or in its early stage), since films in advanced stages of decay are unrecoverable and can only be handled and digitised before their definite loss. This paper presents a study in laboratory in which the ageing of films in real storages has been reproduced in a climate chamber under different conditions of temperature (T), relative humidity (RH), and acetic acid concentration. Some laboratory tests have been conducted to investigate the state of conservation and deterioration before and after different ageing experiments. Subsequently, specific dose response functions (Fenech, et al., 2013) (Menart, et al., 2014) related to archival materials have been exploited for assessing the climate-induced risk predicted specifically for cellulose acetate films in an acetic acid polluted environment. Selected samples of virgin cellulose acetate films were artificially aged in a climate chamber (i.e., with constant RH and variable T) with known concentrations of acetic acid (i.e., order of magnitude 101, 102, 103, 104 parts per billion). To qualitatively detect the presence of gaseous acidic compounds, Acid Detection (A-D) strips (developed and produced by the Image Permanence Institute - IPI) were used. Then, the state of conservation of the materials before and after the different ageing experiments was evaluated by means of non-destructive UV-visible spectrophotometry and contact surface pH measurement coupled with Fourier Transform InfraRed spectroscopy (FTIR), in order to quantify the degree of (de)polymerization of the cellulose. The impact of different acetic acid concentrations under variable thermo-hygrometric conditions was estimated. The change in colorimetric features of the cellulose acetate films was measured by UV-visible spectrophotometry, while the chemical degradation was obtained in terms of the acidification (pH) of the material associated with the appearance of characteristic peaks of aldehyde and ketone compounds in the FTIR spectra as a consequence of cellulose hydrolysis. The results are expressed in terms of the retention percentage of the capacity to handle and display the film after artificial ageing. The life expectancy calculation method was deduced from existing dose-response functions applied to the experimental data obtained. These data reproduce real archival conditions, in which films in excellent condition and films suffering acetic syndrome (i.e., contaminating the surrounding atmosphere with acetic acid) are stored in the same space. Therefore, the research outcomes are useful for estimating life expectancy of cellulose acetate films in real case studies. References - Bigourdan J.L., Reilly J.M., Effectiveness of storage conditions in controlling the vinegar syndrome: preservation strategies for acetate base motion-picture film collections, in: Aubert M., & Billeaud R., Proceedings of the 5th Joint Technical Symposium - JTS, Paris (2000) 14-34. - Fenech A., Dillon C., Ntanos K., Bell N., Barrett M., Strlič M., Modelling the Lifetime of Colour Photographs in Archival Collections, Studies in Conservation, 58(2) (2013) 107-116. - Menart E., de Bruin G., Strlič M., Effects of NO2 and acetic acid on the stability of historic paper, Cellulose, 21(5) (2014) 3701-3713.