Preparation of UV-opaque, Vis-transparent acrylic–silica nanocomposite coating with promising physico-mechanical properties via miniemulsion polymerization

Here, waterborne coatings with enhanced physico-mechanical properties were prepared by incorporation of modified silica nanoparticles into an acrylic matrix through miniemulsion polymerization. In order to circumvent the inherent incompatibility of organic and inorganic portions, methylene diphenyl diisocyanate and 2-hydroxyethyl methacrylate molecules were chemically coupled to the surface of silica nanoparticles to alter the hydrophilic nature of inorganic nanoparticles to hydrophobic ones. Also, for investigating the effect of the exploited surface modification process, unmodified silica nanoparticles were used in preparing acrylic latex via miniemulsion polymerization. The optical and physico-mechanical properties of the acrylic–silica nanocomposite films with 0–10 wt% of unmodified and modified SiO₂ were characterized by measuring their surface roughness, haziness, gloss values, UV–Vis transmittance, scratch resistance, tensile, and pendulum hardness. It was found that by using modified SiO₂ nanoparticles, due to their better dispersion state and ability for establishing covalent linkage with acrylic polymer chains, it is possible to obtain nanocomposite coatings with improved physico-mechanical properties, high transparency in Vis region, considerable UV adsorption, and comparable surface roughness, glossiness, and haziness with pure acrylic film. However, unmodified silica nanoparticles formed many aggregates in the polymer matrix which deteriorated optical and different physico-mechanical properties of acrylic latex. It was found that the greatest improvement in properties is achieved by incorporation of 7 wt% modified silica nanoparticles in acrylic polymer.