A selective paper artwork cleaning process using modified Gellan hydrogel

Paper manuscripts are among the most valuable historical artifacts, but they are also very fragile. Furthermore, they were often strengthened by gluing external materials (like wooden or cardboard lining paper) to the original piece and the used glue underwent to structural transformations that accelerates the degradation processes of the artwork itself. Wet cleaning is one of the most important and critical steps in a paper artwork restoration process, and in the last years innovative cleaning methodologies have been proposed based on application of suitable hydrogels. Unfortunately often, to remove contaminants from paper artworks like glues or hydrophobic material components, additional specific procedures are required. In this work we present innovative multi-component materials able to remove in a single, simple and not invasive treatment, specific contaminants from paper artworks. The materials are based on rigid Gellan hydrogel; after investigating the cleaning ability of the Gellan gel “per se”, indeed, we also evaluated the possibility of using Gellan gel as a carrier of tuned cleaning agent. More in detail, Gellan hydrogel carrying alpha-amylase or proteinase K enzymes has been applied on several paper samples to remove starch paste or animal glues respectively. In this system, the enzyme works as selective cleaning agent, hydrolyzing not easily removable glues into smaller fragments soluble into the gel, which, in turn, plays the role of support and removal matrix for the enzymatic products. Finally, Gellan gel could be a not suitable agent to remove hydrophobic contaminants, due to its hydrophilic nature; to this end, we performed preliminary experiments by preparing a “mixed Gellan gel” carrying opportune polimeric surfactants.To assess the effectiveness and safety of the proposed cleaning method on the several samples under examination, we have employed a multitechnique approach, using high-performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and pH measurements