Sustainable Biobased Polyurethane Organogels for the Cleaning of Paintings

Abstract

The removal of aged varnishes and coatings is a recurrent task in the preservation of Cultural Heritage (CH), often performed using organic solvents. However, solvents are difficult to control as they evaporate, diffuse inside the artifact, and spread at the surfaces of the painted layer. Here, we report the synthesis and characterization of biobased organogels, which constitute a novel class of advanced sustainable materials designed to maximize the confinement and retention of the solvents, allowing for safe applications on sensitive painted layers and other artistic surfaces. The polyurethane gel network is obtained by reacting castor oil with a biobased isocyanate through an easy one-pot solvent-free synthetic route. The gels’ mechanical properties and nanoscale structure can be controlled by playing on the ratio between polyol and isocyanate groups, as demonstrated by rheology and X-ray scattering. The gels can be swollen with different solvents, showing that they are versatile tools that can interact with various types of varnishes/coatings in a controlled way. After preliminary tests on mockups, the gels were used to remove an aged varnish from the surface of a modern metaphysical painting masterpiece belonging to the Peggy Guggenheim Collection of Venice. The new tools grant safe and effective varnish removal within short exposure times (30–60 s), providing enhanced control and time-effectiveness compared to traditional conservation methodologies based on cotton swabs and solvent thickeners.