Analytical studies of the degradation of cellulose nitrate artefacts
The deterioration of cellulose nitrate artefacts in museum and art collections is a complex problem facing conservators and conservation scientists. This study has looked at several aspects of the degradation by analysing artefacts and model samples. Initial work concentrated on a survey of a collection of artefacts, many of which showed active degradation, by visual inspection and FTTR spectroscopy. A more thorough analysis of the artefacts was carried out, using ion chromatography, xray fluorescence spectroscopy and atomic absorption spectroscopy, to identify compositional differences between samples, which may relate to degradation. The results of these studies suggested that residual sulphate in the plastics is a cause of increased degradation. The presence of oxalate in degraded artefacts also indicated that chain scission is occurring during deterioration. Later work using gel permeation chromatography confirmed this. Work has also involved the use of accelerated ageing tests to study the effect of sulphate in the degradation and also the influence of inorganic fillers, iron and humidity. It has been concluded that the degradation of cellulose nitrate artefacts is dependent on the presence of sulphate and humidity. The process is diffusion controlled which indicates that loss of plasticiser is a vital factor. This work also suggests simple procedures that can be used to assess an artefact's stability.