The use of organogels represents a valid option for the cleaning of works of art that cannot withstand the application of water-based cleaning fluids even when confined in highly retentive carrier, such as hydrogels. With the aim of overcoming the limitation of available materials, we have developed a solvent-free and cost-effective synthesis of a new class of gels derived from natural resources, based on castor oil and isocyanates mixtures. The development of covalent polyurethane bonds during the curing process induces significant changes in the viscoelastic properties of the systems which result in strong gels with good mechanical properties. Changes in the castor oil and isocyanates ratio and the use of fillers or other additives allowed us to prepare several formulations whose final properties can be tuned to match those required by specific applications. For applicative purposes, castor oil-based gels can be swollen in organic solvents having 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 different swelling degrees in the selected organic solvents and increase in size upon solvents’ uptake, without a significant alteration in their transparency, which is a pivotal feature for conservators as it allows the visual inspection of the artwork’s surface during application. The viscoelastic properties of swollen systems, especially the elastic modulus, can be finely tuned by varying the composition of the pre-gel mixture. 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 adapt to surfaces having different roughness and are easily peeled off from cleaned surfaces without leaving any residues on the original artwork, have demonstrated to be an advanced tool for the safe and efficient removal of unwanted materials from modern and contemporary works of art.

Castor oil-based organogels as advanced and adaptive tools for the selective and controlled cleaning of works of art

ACS Fall 2021

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