Methyl-modified silica hybrid fluorinated Paraloid B-72 as hydrophobic coatings for the conservation of ancient bricks

• Preparing the organic-inorganic hydrophobic coatings using a mild method. • The highest contact angle of the coating is 142.3° angle. • The coating has good anti-ultraviolet function. • The coating has improved permeability and physical properties. The ancient brick relics have a great historical and cultural significance. However, under the influence of the physicochemical effect, the bricks have suffered severe weathering and erosion in different climates. A methyl-modified silica hybrid fluorinated Paraloid B-72 as a hydrophobic coating was prepared by a simple and mild process to protect the brick from the erosion of polluted rainwater and the damage of ultraviolet aging. Contact angle and hardness were used to verify the content of fluorinated polymer in the Paraloid B-72 sample and then the fluorinated Paraloid B-72 was characterized by infrared spectroscopy (FT-IR). The methyl-modified silica was analyzed by X-ray powder diffractometer (XRD), FT-IR, scanning electron microscope (SEM), and transmission electron microscope (TEM). After treating with different coatings, we found that the highest contact angle was achieved with the addition of 12% methyl-modified silica in 20% fluorine-containing B-72. The synthesized coating was analyzed by FT-IR and ultraviolet–visible spectroscopy. Furthermore, the physical properties such as the pore size distribution, porosity and water vapor permeability of the bricks before and after coating were also examined. The coating enhanced the brick against weathering from acid, alkali, salt and ultraviolet radiation compared to the untreated bricks.