Solvent-confining organogels offer a viable alternative for the cleaning of water-sensitive works of art, which cannot withstand the application of water, even if confined in highly retentive hydrogels. In this work, we present a solvent-free and cost-effective synthesis of castor oil-based xerogels derived from natural resources using polyurethane crosslinking chemistry. The curing mechanism was studied by Attenuated total reflection Fourier Transformation Infrared (FTIR-ATR) spectroscopy and rheological measurements, which illustrate the development of covalent polyurethane bonds during the curing process and simultaneous changes in the viscoelastic properties. Different formulations have been prepared, showing a significant tunability in the final properties of the obtained xerogels, whose characteristics can be adapted to match those required by specific applications. These xerogels can be swollen in several organic solvents in a broad range of polarities, such as aliphatic and aromatic hydrocarbons, oxygenated solvents (alcohols, ketones, aldehydes, ethers, esters), as well as halogenated solvents. Organogels exhibit a different swelling degree for each organic solvent and significantly increase in size upon solvents’ uptake, without a significant alteration in their transparency, which is an important feature for conservators as it allows them to visually inspect the artwork’s surface during application. The viscoelastic properties of swollen systems, especially the elastic modulus, can be finely tuned by varying the ratio between castor oil and poly(hexamethylene diisocyanate). Small-angle X-ray scattering (SAXS) and Small-angle Neutron scattering (SANS) were used to detail the mesoporosity and the nanoscale structure of the 3D polymeric network before and after solvents’ uptake. Overall, these organogels, which can adapt to surfaces having different roughness and be easily peeled off without leaving any residues on the original artwork, have demonstrated to be an advanced tool for the safe and efficient removal of unwanted coatings from modern and contemporary works of art.

Adaptive castor-oil based organogels: Synthesis, characterization and use for the selective and controlled cleaning of works of art

ACS Spring Meeting 2021

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