Sunlight curable boehmite/siloxane-modified methacrylic nano-composites: An innovative solution for the protection of carbonate stones

The application of hydrophobic polymers to stone materials is an effective way to preserve stone artifacts and to protect them from decay. To improve the characteristics and performance of water-repellent treatments, and to avoid the use of harmful solvents, new solutions have recently been explored. As a recent example, a sunlight photopolymerizable siloxane-modified methacrylic formulation, containing organically modified boehmite (OMB) nano-particles, was developed and characterized. In this paper, the protective characteristics of the latter nano-composite product applied on stone were assessed. To this aim, different analytical techniques (contact angle, colorimetric and water absorption measurements, ESEM-EDS analyses) were employed to characterize the water-repellent sunlight-polymerizable coating applied on two calcareous stone substrates typical of Apulia Region (Leccese stone, PL and Gentile stone, PG). A theoretical model able to predict the pores radius of each stone after the treatment, was proposed and verified. The experimental results evidenced that the properties of the innovative free-solvent sunlight-polymerizable protective coating, in terms of hydrophobicity and durability, are excellent and comparable to those of the commercial products.