Isosorbide, pyrogallol, and limonene-containing thiol-ene photocured bio-based organogels for the cleaning of artworks

Abstract

The development of bio-based gels for the cleaning of historical artworks is an attractive area of research. In this work, we designed thiol-ene photocured organogels by combining five different thiol or allyl functionalized bio-based monomers. Isosorbide, pyrogallol, and limonene were used as the bio-based building blocks for derivatization. The chemical structures of the synthesized monomers were characterized by proton nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared (FTIR) spectroscopy. The organogel structures were examined by FTIR analysis. Thermal and thermomechanical properties of the gels were determined by thermogravimetric analyses (TGA) and dynamic mechanical analysis (DMA), respectively. The swelling behavior of the organogels in various solvents was also investigated. Gels swelled most in dimethyl carbonate (DMC). The confinement of the solvents in the gels decreased their evaporation rate. The organogels displayed a two-stage degradation profile and were found to be thermally stable up to ∼200°C. The gels were evaluated for the cleaning of dammar-based varnish from historical artwork. DMC swollen gels were found to be effective in removing the varnish from the surface of the artwork. None of the prepared gels adhered to the surface layer of the paintings. Scanning electron microscope (SEM) images proved that the surfaces were cleaned without leaving any gel residue.