Fabrication of hydrophobic coatings on paper substrates using silicone oil impregnated silica: a promising sustainable packaging material

Paper substrates possessing features ranging from hydrophobic to oxygen-barrier functional properties are gaining great attention recently due to the global ban on single-use plastics as well as the compulsion to avoid nonbiodegradable polymer packing. In this work, hydrophobic silica carriers are processed first through a direct physical impregnation of silicone oil in various amounts into the 20-nm sized silica nanoparticles and subsequently analyzed for the progressive changes in the surface hydrophobicity by water contact angle measurements. The hydrophobic nano-silica was also systematically analyzed by XRD, TGA, FTIR, SEM, and TEM and the results are presented. It was found that the nano-silica with the bulk BET surface area of 157 m²/g can accommodate 2.5 g of silicone oil per gram of silica, finally resulting in hydrophobic silica with a maximum contact angle of 139°. Later, this hydrophobic nano-silica was dispersed in a polymethylmethacrylate (PMMA) matrix and a coating formulation was prepared to develop water-repellent self-cleaning functional coatings on eco-friendly paper substrates. While applied as topcoats on paper substrates, the hydrophobic silica-PMMA gets embedded into the porous fibrous cellulose network and converts it into an impressive water-repellent packaging material with a contact angle of about 142°. This facile inorganic–organic hybrid topcoat strategy was successfully applied on the fibrous cellulose sludge waste produced by the paper mills to produce lightweight, water/moisture resistance packing material for circular economy.