Polyacrylate/silica nanoparticles hybrid emulsion (PSHE) with high silica content was produced and used in the preparation of high hardness and dry-wear-resistant coating via a facile and environment-friendly method. Specifically, the surface of alkaline silica sol nanoparticles was modified by cationic polyacrylamide (CPAM), which was then added in an emulsifier-free polymerization system comprised of methyl methacrylate (MMA) and butyl acrylate (BA). Through electrostatic attractions, hydrogen bonds, and van der Waals force, the positive charged silica nanoparticles aggregate around polyacrylate emulsion particles to improve the hardness and dry-wear-resistant of PSHE coating. Our results confirmed an average size of the PSHE particles only 58.6 nm. A bimodal molecular weight distribution (MWD) and consequently two different glass transition temperatures (Tg) were found in such PSHE polyacrylate resin. Due to the presence of modified silica nanoparticles, a reduced polymerization degree of MMA monomer in the aqueous phase of core emulsion leads to a decreased first Tg and the high molecular weight fraction with highly compacted molecular structure, and the improved mechanical properties of the PSHE coating. The chains of relatively low molecular weight fraction of polyacrylate move more easily during film formation, which prevents the structural voids in the coatings. Better adhesion as well as higher hardness, impact resistance, dry-wear-resistance, and thermal stability are found when compared with its pure polyacrylate emulsion (PPE) coating counterparts. Although having high silica content, the PSHE coating still retains 90% transparency rate in visible light range.
Volume 121, August 2018, Pages 30–37