A quantitative study of acetic acid emissions from historical cellulose acetate at room conditions

Historic objects made of cellulose acetate are potential sources of indoor pollution in heritage collections. As these objects degrade, volatile organic compounds, including acetic acid, are produced and emitted. High concentrations of acetic acid can increase the degradation rate of both organic and inorganic objects stored nearby. In this study, micro-invasive sampling and ion chromatography were used to quantify acetic acid emission rates from objects made of cellulose acetate, including 3D objects and photographic negatives. It was observed that some degrading objects emit acetic acid at high rates, even under standard environmental conditions (20 °C and 30% RH) that are prescribed for storage of objects made of cellulose acetate. The emission rate was found to be governed by the internal diffusion for thicker cellulose acetate objects and by the surface evaporation for thinner objects. In the diffusion-controlled mode of emission, the airflow did not accelerate acetic acid emissions. To compare the storage options for cellulose acetate objects, the emission rates of acetic acid were used as the inputs for models predicting the equilibrium acetic acid concentrations in various enclosures (archival box, surface-coated archival box, metal can, and display case). It was observed that surface-coated boxes contained higher concentrations of acetic acid than other enclosures, mainly due to their low air exchange rates and deposition velocities.