Natural polymers as alternative consolidants for the preservation of waterlogged archaeological wood

Abstract

In recent years, there has been increased interest in examining alternative polymers for the conservation of archaeological artefacts, particularly waterlogged timbers, providing better, renewable, greener alternatives to poly(ethylene glycol) (PEG). The degradation of PEG consolidants in the timbers of the sixteenth century warship Mary Rose has been examined and the rheological and thermal properties of PEG have been compared with its monomethyl and dimethyl ethers and several polysaccharide consolidants (chitosan, guar, and 2-hydroxyethyl cellulose) in order to evaluate their potential as alternative consolidants for the conservation of waterlogged wooden artefacts. Additionally, the effect of the polymers on the archaeological wood was characterised by thermogravimetric analysis and solid-state nuclear magnetic resonance spectroscopy. The results suggest that the future of conservation technologies lies with polysaccharide consolidant materials, which show enhanced compatibility with wooden artefacts with no detectable side effects while also being cheap, with extremely low toxicity, renewable, and sustainably resourced.

Multifunctional supramolecular polymer networks as next-generation consolidants for archaeological wood conservation

“…Guar shares the gelling ability of chitosan and is amenable to dynamic functionalization through the diol unit. Neither polymer forms acidic byproducts on degradation (11).…”

“…This supramolecular "handcuff" is particularly effective in joining together polymer chains to form 3D networks (22,24). Aqueous solutions of chitosan and guar, two naturally sourced polymers, have been shown to provide enhanced structural support and stability at reduced concentrations (11). Functionalizing these polymers created a material tailored toward hindering biological activity and chelating catalytically active Fe 3+ .…”

“…1). Natural polymers provide the additional benefit of removing the plasticizing effect of consolidants on the timbers (11,25). Although none of the constituent materials of the polymer are themselves extraordinary or novel, the interaction of the various units and their assembly to form a multifunctional chemotactic consolidant material is completely innovative, to both this field and supramolecular chemistry in general, and results in a consolidant material that addresses the three most pressing issues facing conservators of waterlogged archaeological timbers.…”

“…Finally, the action of bacteria, Fe 3+ , natural acids, temperature, and humidity on PEG can cause its degradation to acidic byproducts over time (9). It is clear from the examination of PEG consolidants that another conservation strategy is necessary (11).…”

“…Recently, alternative consolidants have appeared in the literature with the focus moving toward oligoamides and natural polymers such as chitosan, guar, and 2-hydroxyethyl cellulose (11)(12)(13)(14). These consolidants represent renewable and environmentally friendly alternatives to PEG with no acidic degradation products, enhanced timber compatibility, and a significantly reduced cost as they are often sourced as waste products from industrial processes.…”