Soft, Peelable Organogels from Partially Hydrolyzed Poly(vinyl acetate) and Benzene-1,4-diboronic Acid: Applications to Clean Works of Art

Abstract

We have developed soft, peelable organogels from 40% hydrolyzed poly(vinyl acetate) (40PVAc) and benzene-1,4-diboronic acid (BDBA). The organic liquids gelated include dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, 2-ethoxyethanol, and methanol. The rheology of these soft materials can be tuned by altering the concentration of the polymer and/or crosslinker. Insights into the mechanisms leading to gelation were obtained from H NMR experiments, fluorescence measurements, and studies comparing properties of materials made from BDBA and phenylboronic acid, a molecule incapable of forming covalent crosslinks between the polymer chains. These organogels can be easily peeled off a surface, leaving no residue detectable by UV-vis spectroscopy. They are demonstrated to be effective at softening and removing deteriorated coatings from water-sensitive works of art and delicate surfaces. They have the needed characteristics to clean topographically complex surfaces: good contact with the surface, easy removal, and little to no residue after removal. A 2-ethoxyethanol organogel was used to remove oxidized varnish from a 16th century reliquary decorated with painted gold leaf, and an ethanol gel was used to remove solvent-resistant coatings from 16th and 18th century oil paintings.

Characterization of polyvinyl alcohol-borax/agarose (PVA-B/AG) double network hydrogel utilized for the cleaning of works of art

“…To address these issues, so-called 'solvent-gels' were developed as a carrier for solvents and cleaning agents as a more controllable and selective cleaning tool [6]. Since then, conservation scientists have been exploring and developing variable types of gels to meet the different cleaning requirements [7][8][9][10]. In these studies, the gels were loaded with the desired cleaning agents and successfully employed to remove variable deposits from artwork surfaces.…”

Boronate sol–gel method for one-step fabrication of polyvinyl alcohol hydrogel coatings by simple cast- and dip-coating techniques

“…Molecules having more than two boronic acid groups such as DBA, benzene-1,3-diboronic acid, and biphenyl-4,4 0 -diboronic acid are known to crosslink PVA in solutions through boronate esterication to form gels with three dimensional network structures at room temperature. [33][34][35] Interestingly, the resultant gels exhibit excellent durability in aqueous solutions over a wide pH range due to the strong binding of the boronic acid groups to the 2,4-pentanediol motifs, 36 while boronic acid inherently shows reversible covalent bonding with diols based on the relatively small free energy barriers of the reverse reactions. [37][38][39][40][41] Therefore, such boronate gels have been utilized as platforms for adsorbing materials, 42,43 microcapsules, 44 and solid-based chemosensors 45 functioning in aqueous solutions even under basic conditions.…”

Structural, rheological and dynamics insights of hydroxypropyl guar gel-like systems

“…In the last decades, several advanced and innovative systems for the conservation of cultural heritage have been proposed [40][41][42]. In particular hydro and organogels have been proposed as a feasible alternative to overcome the limits of traditional methods for the selective removal of patinas from surfaces of artistic and historical interest [43][44][45][46][47].…”