Formulation of a new sustainable hybrid coating for the conservation of street-art: Characterization and application

Street-Art murals are spreading and transforming urban areas worldwide; however, proper and effective conservation procedures for this emerging form of art are lacking. Outdoor murals are made of inorganic pigments or dyes blended with synthetic organic binders applied on inorganic substrates, mainly concrete, and are exposed to serious degradation due to light, temperature, and humidity fluctuations, pollutants, and biological agents that hinder their conservation. This research focuses on the formulation and application of chitosan and nanosilica hybrid coating by exploiting the good film-forming ability, optical and antimicrobial properties, and sustainability of chitosan. The capability of silica to boost the chitosan film properties was investigated, with special reference to the compatibility of hybrid films with paints and concrete substrates. The new formulation was characterized by ATR-FTIR, SEM imaging, DLS, and zeta potential measurements. The hybrid coating was applied on concrete spray paint-coloured mock-ups, and the film properties in terms of adhesion, water vapor permeability, and hydrophobicity are reported. The long-term stability of the coating was assessed by three different accelerated aging tests, and the colorimetric variations were measured. • Development of pH-neutral chitosan-based coatings avoiding formation of harmful salts for application on Cultural Heritage. • Assessment of the stability of chitosan-nanosilica-based hybrid coating through accelerated aging tests. • Physicochemical characterization of chitosan-nanosilica hybrid coating. • Evaluation of the protective action against photo-oxidative, thermal, and hydrothermal degradation.