Solid particles can be used as stabilizers for oil/water (o/w) emulsions instead of the conventional surfactants. Emulsion polymerization of styrene, as an example of polymerizable oil, was started in the current study after ultrasonication of the monomer into aqueous phase with aid of montmorillonite nanoplatelets as solid stabilizer. Imaging using a field emission scanning electron microscopy equipped with energy dispersive X-ray unit as well as transmission electron microscopy proved the formation of polystyrene/montmorillonite as core-shell hybrid latex particles via Pickering mode of emulsification. The mechanical properties of polypropylene (PP) and ethylene vinyl acetate copolymer (EVA) were studied after addition of various loadings of these hybrids (2, 4, 8, 12, and 14 wt%). It could be ensured that the tolerance of PP towards phase separation caused by the insertion of the core-shell particles was higher than that of EVA, which translates into different extents of reinforcements. POLYM. ENG. SCI., 55:1546-1552, 2015. (c) 2015 Society of Plastics Engineers