A comparative study of organic nanoparticles coatings for enhanced stone protection

Conservation of historical buildings is an important issue; the environmental conditions seriously affect the monumental stones. The protection of cultural heritage buildings and monuments by surface treatment with polymers is a common practice due to their ability to form a protective layer on the monumental surface as well as to control the transport of different fluids from the surface to the inner part [1–3]. Moreover, in the last few years, nanomaterials have been frequently applied for restoration and conservation of artworks. It is worth noting that inorganic nano-oxides, such as silica and titania, improve the performances of materials used in conservation field [4]. In particular, the application of photocatalytic coatings on stone has been investigated for providing surface protection and self-cleaning properties [5]. In this work three different substrates were used: Carrara/Botticino marbles, and Angera stone. Commercially available siloxanes and acrylic polymers were used as protective agents to improve the hydrophobicity features of the different tested materials. Then the conservation effectiveness of inorganic nanoparticles dispersions was evaluated when applied on the porous stone substrates. The strengthening effect of the nanoparticles-based treatments is compared to that exhibited by the well-known consolidant polymers. Morphological (SEM-EDS), structural (XRD), thermal (TGA) and spectroscopic (FTIR and DRS) analyses were carried out on coated and uncoated stones to establish the changes of appearance, color, and water absorption. Static/dynamic contact angle measurements and surface free energy determinations were adopted to evaluate the final wettability and self-cleaning properties before and after UV-light exposure and artificial ageing.