Effects of initial polymer properties and nano-silica additions on mechanical performance of styrene-butyl acrylate Pickering copolymers

A set of semicontinuous Pickering emulsion copolymerizations was performed to promote the incorporation of SiO 2 nanoparticles (nSi) into styrene–n-butyl acrylate copolymer matrices with very different initial mechanical behaviors, evaluating their influence on the final mechanical performance. The proposed strategy employed a low percentage of nSi as both a stabilizing and a reinforcing agent, replacing traditional surfactants and enabling the formation of nanocomposite latexes with excellent colloidal stability. By systematically varying comonomer ratios (S/BA, from 70/30 to 40/60, w/w) and feeding profiles, materials exhibiting tunable mechanical responses ranging from rigid to soft behavior were prepared. Tensile testing revealed that the introduction of nSi induced different types of mechanical modifications in the original matrices (e.g., a considerable decrease in rupture strain with non-statistically significant changes in the other parameters, or the rigidization of the original matrix upon nSi incorporation). However, the most pronounced improvements were observed in styrene-rich systems, where simultaneous increases in modulus, yield stress, rupture stress, rupture strain, and toughness were obtained, suggesting that the Pickering process promoted efficient nanoparticle dispersion. These findings highlight the potential of Pickering emulsion copolymerization as a versatile route for producing surfactant-free nanocomposites with adjustable mechanical properties and suitable nanofiller distribution. Besides, the results confirm the wide variety of mechanical modifications that can be induced by the presence of nSi in polymer matrices with different initial mechanical behaviors, despite considering the same chemical system (S/BA).