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

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.

A diagnostic tool for assessing the conservation condition of cellulose nitrate and acetate in heritage collections: quantifying the degree of substitution by infrared spectroscopy

“…A vast percentage of European cultural heritage can be found in cinematographic films and photography produced since 1899 [1][2][3][4][5]. Images are obtained through a complex stratigraphy that is depicted in Scheme 1 [6].…”

“…The base for these images is made of cellulose derivatives, which depending on their history of manufacture, storage and use may reveal a high degree of instability [1][2][3][4][5]. For this reason, more than 120 years of visual memories, based on cellulose nitrate (CN) and cellulose acetate (CA) materials, are in danger to be lost [1][2][3][4][5]. To overcome this risk, the European project NEMOSINE aims at improving the traditional storage solutions based on cold storage, by developing a modular package with the main goal of energy-saving and extent conservation time (https :// nemos inepr oject .eu).…”

Removing of the Sulfur Compounds by Impregnated Polypropylene Fibers with Silver Nanoparticles-Cellulose Derivatives for Air Odor Correction

“…The films used in that period can be classified according to several criteria: geometric dimensions (see next paragraph); purpose (negative and positive films, counter type, or sound films, etc. ); spectral sensitivity (un-sensitized, orthochromatic, panchromatic, infra-chromatic, and color) [ 86 , 87 ].…”

Plasticiser loss in heritage collections: its prevalence, cause, effect, and methods for analysis

“…Others recommend ventilated storage or scavengers to minimise a build-up of acidic species arising from hydrolysis of CA and CN [25,26]. However, a recent study suggests replication as the only viable long-term preservation method for triacetate film [27]. Plasticiser migration occurs alongside the deacetylation of CA; although, its relative rate, importance, and impact is understudied.…”

“…However, higher emission rates would be expected versus stagnant environments. For CA, the relative rates of polymer deacetylation and plasticiser loss are unknown; therefore, the effectiveness of ventilated containers has been questioned [27].…”