Quantifying degradation in cellulose acetate-based historic artefacts: a new approach using 1H NMR spectroscopy
High-resolution liquid state nuclear magnetic resonance (NMR) spectroscopy is an analytical technique widely used in the field of Chemistry to aid molecular structure determination of unknown organic molecules, among several other applications. However, whereas very common in the field of Chemistry, in the heritage field, this technique is still underused, particularly in the analysis of contemporary modern materials involving plastics.
Motivated to overcome this, our team has developed new methodologies based on NMR spectroscopy which can contribute to the study of the degradation of historic cellulose acetate (CA)-based artefacts, such as the comb in Fig 1. As it is well-known, these artefacts can suffer from stability issues associated with the loss of their plasticisers to the environment, in addition to the degradation caused by the reaction between CA and moisture. Thus, understanding these degradation processes and their relationship with environmental conditions is important for defining optimal conditions for storage and display, and simultaneously minimising degradation signs, such as warping, crazing, cracking and increased brittleness, which could impact on an artefact’s historic, aesthetic or information value.
Fig. 1 – Cellulose acetate comb.
However, until now, methods available for studying these degradation processes could be very time-consuming and require the separation between the CA polymer and its plasticisers prior to analysis. Published in the Polymer Degradation and Stability Journal [1], our work demonstrates how NMR spectroscopy can be applied for quantifying diethyl phthalate plasticiser content and monitoring degradation in historic CA artefacts while presenting no such requirement. In addition, the method suitability is illustrated by the analysis of a series of historic samples, involving CA sheets produced in the 1960s and combs kindly donated by Colin Williamson and Jen Cruse, respectively.
Fig. 2 – NMR instrument carousel with sample tubes.
Moreover, identifying plastic types from different artefacts in museum collections can also represent a challenge for defining suitable storage conditions. Our research further shows how NMR spectroscopy can be used to identify the presence of CA and additional chemical additives in plastic pieces of unknown origin, as obtained signals are characteristic of atoms’ positions in the analysed chemical molecules. As a result, the technique can be used to determine complex chemical compositions from plastic artefacts (not limited to CA).
Therefore, we hope our work can not only contribute to ongoing efforts to investigate the impact of environmental conditions on the conservation of valued CA items in museum collections and archives, but also inspire the heritage science community to make more use of this analytical tool.
This research was carried out as part of COMPLEX [2], a European Research Council funded project under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 716390) at the UCL Institute for Sustainable Heritage.
- Simoní Da Ros, Abil E. Aliev, Isabella del Gaudio, Rose King, Anna Pokorska, Mark Kearney, Katherine Curran, Characterising plasticised cellulose acetate-based historic artefacts by NMR spectroscopy: A new approach for quantifying the degree of substitution and diethyl phthalate contents, Polymer Degradation and Stability, 2020, 109420, https://doi.org/10.1016/j.polymdegradstab.2020.109420.
- www.ucl.ac.uk/bartlett/heritage/complex (Follow us on Twitter: @complexplastic)
Written by Simoní Da Ros ([email protected])1 and Katherine Curran ([email protected]), UCL Institute for Sustainable Heritage, University College London
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