Optimizing PVA hydrogel characteristics and properties through physical and chemical crosslinking for oil-painting restoration

Polymer gels have presently been employed instead of cotton wool soaked with organic solvents to clean artwork in cultural heritage restoration since they are less harmful to the artwork’s surface and more efficient in safe cleaning. A lack of insight into the characteristics and properties of polymer gels produced by various materials and methods leads to misuse and might cause damage to artwork. In this work, poly(vinyl alcohol) (PVA) was employed to produce a cleaning gel. Different crosslinking agents, sodium tetraborate (borax), borax plus polyethylene glycol (borax-PEG), and glutaraldehyde, were studied together with various gel formation methods, solely casting, casting plus freeze-thawing, and casting plus freeze-thawing and solvent soaking. Characterization and property tests were carefully conducted to understand the behavior of produced materials. The porosity of the PVA gel crosslinked with borax-PEG significantly increased by freeze-thawing. After being loaded with water, the porous structure was maintained even as it swelled, and its confined water was slowly released when the gel was left on an oil painting. The 4 wt% PVA gel crosslinked with 5% borax and 0.5% PEG, after freeze-thawing and water soaking, exhibited the most suitable rigidity and elasticity for the required cleaning gel properties and provided better cleaning efficiency on oil paintings than other gels. These results indicated that PVA crosslinked with borax plus PEG and formed by the casting plus freeze-thawing and solvent soaking could be an alternatively suitable material for a cleaning gel in oil-painting restoration.