Cleaning Works of Art: Tuning Hydrogels properties by Blending PVA-based Systems

The choice of the most suitable system for the cleaning of cultural heritage artifacts is a challenging issue due to the great variety of materials and textures that can be encountered during restoration. High control and selectivity are the main features that should characterize an ideal cleaning system. At present, the use of cleaning fluids confined in gelled structures is considered one of the most performing strategies to face concerns related to an excessive penetration of the liquid phase within the porous matrix of the artwork. In the last decades several gel formulations were introduced in restoration practice, most of them pertaining to class of physical gels, while, more recently, also some chemical gel formulations were adopted. Physical gels have usually a jam-like texture and permit to attain homogenous cleaning thanks to their complete adaptability and adhesion to the surface they are put in contact with. However, they present important drawbacks related to left residues after treatment. Chemical gels are characterized by strong cohesion forces, which permit their easy and complete removal and, thus, a residue-free treatment. Their cleaning performances, in terms of homogeneity, might be compromised in case that the irregularities of the surface to be treated don’t permit an appropriate adhesion of the gel. Blended PVA-based hydrogels, obtained through two different synthesis methods, are innovative systems that permit both, homogenous adhesion, thanks to their mechanical adaptability, and an easy and complete removal thanks to strong cohesion forces. Hydrogel synthesis is performed through cast-drying or repeated freezing and thawing of neat or blended PVA aqueous solutions. Gelification process involves the formation of crystalline regions that act as tie- points, contributing to formation of the three-dimensional network. A physico- chemical characterization was carried out on several formulations to investigate synthesis parameters that affect the final properties of the hydrogels. Water content and free water index (FWI) were quantified through thermal analysis (DTG, DSC). The crystallinity degree was determined by means of ATR-FTIR, DSC and XRD. Information about hydrogels porosity were obtained from SEM images, while networks structure was investigated through SAXS analysis. Finally, some preliminary application tests are presented.