Methacrylated gellan gum microgels: A further step in the gel-based cleaning system

• Gellan gum polymer has been chemically modified via methacrylation. • Methacrylated gellan gum-based (GGMA) microgels have been developed. • GGMA microgels have been used to clean ancient and modern paper samples. • GGMA microgels efficiently remove both hydrophilic and hydrophobic byproducts from samples. • GGMA micro- and macro-gel cleaning performances have been compared. Paper has been entrusted with a large portion of humanity's recorded knowledge in recent centuries, therefore its preservation is fundamental for maintaining cultural heritage. Indeed, cellulose—the primary material of these artifacts— goes through irreversible degradation processes as it ages, leading to a weakening of paper stability and color changes. In order to slow down ageing, several restoration strategies involving the use of wet cleaning by hydrogels can be found in literature. Multi-step treatments are often required to complete the cleaning procedure, as the properties of contaminants greatly vary from a chemical–physical point of view (i.e. hydrophilic, hydrophobic or, as for adhesives, polymeric compounds). In this article, we propose a cleaning strategy that accounts for the inherent roughness of paper by developing microgel particles made of methacrylated gellan gum. Microgel particles are smaller than their macroscopic counterparts, hydrogels, and as a result, they can clean paper more quickly, a few minutes as opposed to hours. Moreover, the chemical modification performed on deacylated gellan gum makes the polymer more hydrophobic, as compared to the unmodified one. In this way, the proposed microgels are able to interact with and adsorb not only hydrophilic by-products of cellulose degradation, as gellan gum-based microgels do, but also hydrophobic materials or synthetic adhesives. This procedure represents a valid strategy, safe for operators, for the cleaning of paper artworks as it avoids the use of potentially dangerous organic solvents for hydrophobic material removal.