Transparent and superhydrophobic coating via one-step spraying for cultural relic protection against water and moisture

Paraloid B72, composed of an ethyl methacrylate (70%) and methyl acrylate (30%) copolymer, is widely used in the field of cultural relics protection due to its transparency, durability, and nonyellowing. However, B72 is hydrophilic and the water resistance should be enhanced. Herein, as a further study of the pioneer research by Ntelia et al. [1], transparent superhydrophobic coating was prepared and the durability as well as the protection against moisture will be studied. B72 was mixed with the hydrophobic nanoparticles of SiO2 in xylene and a transparent and superhydrophobic coating was then obtained by spraying onto the substrate of fabric, paper and wood. The fraction of SiO2 in the mixture was optimized to be 2 wt% by taking hydrophobicity, air permeability, transparency, and ultraviolet transmittance into consideration. The optimal coating presented a continuous porous network surface structure with the maximum contact angle of 165 degrees and the minimum sliding angle of 6 degrees. Average transmittance in visible and ultraviolet light range for the composite coating on glass was 72.57% and 19.46%, versus 82.81% and 32.26% for B72, respectively. BS2 coating permeability for different substrates are less than 10%. Contact angle remained above 150 degrees after 4 h of contact with liquids with a pH of 1-13. Water contact angle on the simulated paper relics after exposure to a hot humid (60 degrees C, 85 - 90 RH%) atmosphere for 5 days remained above 150 degrees. In addition, BS2 coating showed good UV resistance after 10 days of UV light irradiation. All these data demonstrated that such a coating may find potential application in the relic protection due to its superhydrophobicity, breathability, transparency, ultraviolet protection, and durability.