Farmakalidis H.V., Douvas, A.M. Karatasios, I. Sotiropoulou S., Boyatzis S., Argitis P., Chryssoulakis Y., Kilikoglou V. Accelerated Ageing of Acrylic, Cyclohexanone-Based and Urea-Aldehyde Polymers Used in Paintings Conservation. International Symposium on Archaeometry (ISA), 15 – 21 May 2016, Kalamata, Greece.
Natural resins have been used for centuries as varnishes on painted artifacts. During the 1950’s, synthetic polymers were introduced in paintings conservation due to their superior resistance to degradation, while presenting optical properties comparable to those of traditionally used natural resins. However, after prolonged service times, these polymers also undergo deterioration. The objective of this research is to assess the durability and workability of four commonly used polymers after accelerated ageing, in order to finally estimate their service life using a combination of analytical techniques. Among the polymers which are commonly used in paintings conservation, Paraloid B72, Primal AC33 (both acrylic resins), Ketone Resin N (a cyclohexanone-based resin) and Laropal A81 (a urea-aldehyde resin) were selected for this study. Accelerated ageing parameters involved relatively high temperature levels, daylight radiation and high humidity levels. An analytical methodology was established aiming at the study of molecular changes in the artificially aged materials in the form of films (using FT-IR and UV-Vis spectroscopy), and the impact of these changes on their film surface morphology (Scanning Electron Microscopy, SEM), on their solubility (solubility and swelling tests) and on colour changes (spectro-colorimetry). The results provided information on the polymers’ degradation mechanisms and their possible products as a result of accelarated ageing. More specifically, the two acrylic polymers and the aldehyde resin were found highly stable with regard to their molecular condition, as compared to the cyclohexanone-based polymer, while all four polymers displayed changes in their colour and film thickness. Morphological examination with SEM revealed features (such as cracking) on the polymer films, which significantly limit their use under unstable environmental conditions. Furthermore, the role of common inorganic additives (such as TiO2) in the commercially available materials was investigated by comparing their performance with the presence and absence of TiO2.