Emily Noake

‘Identifying, Characterising and Mapping the Deterioration of Cellulose Nitrate in Museum Collections: An Archaeological Adhesive Case Study’ (PhD in Cultural Materials Conservation, 2018).

Introduced in the 1870s, cellulose nitrate (CN) has been widely used as a plastic, in film, coatings and adhesives. Research has shown CN to be an inherently unstable material, subject to rapid, irreversible deterioration. It also has the potential to produce degradation products that may catalyse further deterioration in CN materials and impact neighbouring artefacts. Consequently, CN presents ongoing challenges for conservators and allied professionals managing artefacts in gallery, library, archive and museum environments. In response to these concerns, this thesis investigates whether an in-depth understanding of CN’s deterioration trajectory and characteristics could be used to develop a model for strategically managing this material’s preservation and conservation. CN has been used as a primary polymer in adhesives in archaeology and conservation for more than 100 years. More recently it has been revealed as a secondary polymer in commercially available adhesives. As an initial step towards understanding the potential breadth of CN’s presence within museum collections, this project identified, characterised and mapped the deterioration of CN using historic, real-time aged CN materials found in the archaeological context. Commercially available products and adhesives introduced to archaeological artefacts post-excavation were used to historically study the presence of CN. The University of Melbourne’s Middle Eastern and Cypriot archaeological collections were used as a case study. Adhesive samples removed from repairs and labels were used to locate CN, identify formulation variances and examine degradation. Diachronic changes in the selection and application of these materials in archaeological and conservation practice were mapped. A range of analytical techniques including infrared spectroscopy, gas chromatography-mass spectroscopy, x-ray photoelectron spectroscopy, chemical testing, colorimetry and multivariate analysis were used to analyse and interpret samples. Unambiguous identification methodologies were developed for identifying CN in collections. CN was found to be present as a primary or secondary polymer in adhesive repairs and labels. Plasticisers camphor and di-butyl phthalate were associated with the CN based adhesives. The deterioration trajectory of this unstable material was explored using accelerated ageing studies of commercially available adhesives. CN’s presence as a primary or secondary polymer, and its associated plasticisers were used to explore how formulation variances may influence the deterioration profile of this material. A U-shaped trajectory of deterioration was mapped for UV radiation aged adhesive samples using IR spectra and principle component analysis (PCA). Comparative analyses of ageing trajectories for adhesives containing CN as a primary or secondary polymer, and with two different plasticisers showed that variations in adhesive formulations influence the rate and extent of sample deterioration. The results have suggested that IR spectroscopy and PCA can be used to map a trajectory of CN deterioration. It is recommended that additional analytical techniques be used to fully characterise and interpret the underlying chemistry that is recorded in the IR spectra. This thesis establishes a base methodology for identifying and characterising CN in collections which may function as a starting point for further research, extension and development. It has demonstrated that variations in formulation and physical characteristics can influence the way CN ages. It is suggested that there is potential for an in-depth understanding of the deterioration trajectory and characteristics of CN to be used to develop a model for predicting its deterioration to aid strategic management of its preservation and conservation.

Supervisors: Dr Petronella Nel, and Ms Deborah Lau (CSIRO).