Effects of Adding Nanosilica on Acrylic and Siloxane Hydrophobic Coatings to Protect Calcite Stones

Hypothesis: Both acrylic and siloxane polymers show good water-repellency when applied on the surface of mineral materials, such as bricks and stones. This property makes them an option to protect the porous surfaces of mineral, such as stone artworks. Another advantage of using these polymers is their water-based feature and biodegradability. Methods: In this study, substrate was selected from calcium carbonate rocks of the stone artworks of Persepolis. By adding silica nanoparticles to acrylic and siloxane polymers, changes in the properties of coatings, applied on the surface of the mineral substrate, were investigated. For this purpose, the samples were subjected to various experimental tests, such as water absorption at different time intervals, color changes resulted from accelerated aging, hydrophobic behavior study using contact angle measurement, hardness test and TGA. Morphology and surface area of coatings were studied by scanning electron microscopy (SEM). Characterization of these materials was done by various analysis methods.Findings: The effectiveness of acrylic and siloxane polymers alone and also in comparison with each other and after adding nanosilica was evaluated by different tests. This study showed that the addition of silica particles to both polymers improved surface hydrophobic properties. In addition, the silica nanoparticles altered the surface morphology of the coating and increased surface roughness. In addition, silica nanoparticles improved the stability of coatings against accelerated aging conditions, resulting in less color changes after aging. The increase in nanosilica content also increased the average hardness and the thermal resistance of both polymer coatings