Acrylate hybrid nanocomposite coatings based on SiO2 nanoparticles by in-situ batch emulsion polymerization

Waterborne acrylate/SiO2 nanocomposites were synthesized by in situ emulsion polymerization using batch process. Polymethyl methacrylate (PMMA), acrylic acid (AA) and butyl acrylate (BA) were copolymerized in the presence of nanosilica particles of 7 nm size. Nanosilica was added up to 3% gig and the emulsions thus obtained were stable for at least 6 months in storage at room temperature. The results showed that when the concentration of nanosilica was increased, the degree of conversion decreased, and the percent of coagulum slightly increased. Interestingly, in the presence of nanosilica the latex particle size continually decreased as the polymerization reaction progressed until reaching a nearly constant value of 150 nm. Conversely, the neat acrylic latex particles exhibited the typical continuous increase of particle size as polymerization time increased. Steady shear rheology showed that the viscosity of the nanostructured emulsions was shear thinning, exhibiting a power-law behavior. As cast coatings were optically transparent and no evidence of aggregation was detected by SEM and AFM, and EDS analysis confirmed the presence of silica throughout the coatings. The nanosilica induced significantly higher thermal stability, as decomposition temperatures, Td, of the nanostructured acrylics increased by as much as 40 C relative to the neat acrylic. The glass transition temperature T-g was increased up to 10 degrees C at only 1 wt% SiO2 nanoparticle concentration, but at higher concentrations it was slightly reduced. As cast films exhibited higher shear modulus and shift of maximum of tan B denoting a modification of macromolecular dynamics by the SiO2 nanoparticles. The results are contrasted with those obtained on acrylate-SiO2 coatings with equal formulation but polymerized by semi-batch process (Romo-Uribe et al., 2016). (C) 2016 Elsevier B.V. All rights reserved.