An investigation of the factors affecting the degradation of cellulose acetate artefacts in museum collections
Plastics have had an increasing influence on human activity since the early years of the 20th century and as such are becoming an increasingly important part of museum collections. These plastics are already exhibiting signs of degradation, which raises the question of how they should be stored and treated. However, little is known about the specific degradation processes which occur. Further research is required because the lack of information is hindering the correct approach to plastic conservation. Current interest concerns the degradation of cellulose acetate artefacts; the work carried out and reported here examines this problem by studying artefacts of various ages and degrees of degradation using accelerated ageing and comparing these results to those for naturally aged samples. Initial work has been carried out to investigate the plastic each artefact is made from and also its chemical composition. Various analytical techniques have been used to investigate the additives, impurities and degradation products that may be present. The results from these techniques and further work are discussed. Micro-Fourier Transform Infrared (FTIR) Spectroscopy has been found to be an excellent technique for the identification of the base polymer in a plastic artefact, as minute samples are used. It has also been used to monitor changes in the base polymer of the plastic artefacts. Ion chromatography has been used to study levels of water-extractable acetate and oxalate as well as other significant anions. The presence of oxalate in degraded samples indicates chain scission occurring and high levels of acetate indicate deacetylation is occurring. Non-destructive and destructive sampling for ion chromatography have been used to explore if this is a viable screening process to identify artefacts in the early stages of degradation. Chain scission has been investigated further using gel permeation chromatography. X-ray fluorescence spectroscopy results indicate that trace levels of Se may be important in preventing the initiation of degradation, as so far it has only been detected in undegraded artefacts. Results indicate that deacetylation is the predominant process; while chain scission is secondary or a possible surface reaction. Another factor is plasticiser loss.