ZnO coated nanoparticles based on acrylic copolymer for protecting historic calcareous stone monuments

Abstract

Historical calcareous stone surfaces may undergo unwanted changes due to the exposure to many physical and chemical deterioration factors. This paper evaluates the use of zinc oxide nanoparticles, dispersed in a laboratorial prepared acrylic copolymer [polyethylmethacrylate/methylacrylate (70:30) (Poly EMA/MA)], as a nanocomposite coating material with hydrophobic, consolidating and protecting properties against artificial aging by relative humidity/temperature, UV radiation and dirt accumulation. The obtained nanocomposites have been characterized by transimition electron microscopy (TEM) to ensure the homogenous dispersion of ZnO nanoparticles in the polymer matrix and the average crystal size. Marble stone blocks have been prepared and coated by the nanocomposite material, the efficiency of the treatments has been evaluated after coating and artificial aging, through capillary water absorption, Ultraviolet-light exposure to evaluate photo-induced and the hydrophobic effects of the coated surface. Thermal aging, colorimetric measurements have been performed to evaluate the optical appearance. All the results confirmed that the nanocomposite coating enhanced the durability of stone surfaces toward UV aging, and improved their resistance to relative humidity and temperature compared to the samples coated with the acrylic polymer without ZnO nanoparticles.