Synthesis of water-based polystyrene-nanoclay composite suspension via miniemulsion polymerization

A stable water-based polystyrene nano-saponite composite suspension was synthesized via miniemulsion polymerization. The stability of the suspension and the intercalation degree of clay were strongly affected by the pretreatment of saponite-Ca with cationic surfactant OTAB (octadecyltrimethylammonium bromide). This pretreatment process not only intercalated the clay layers but also converted the nanoclay particles from hydrophilic (waterlike) to hydrophobic (monomerlike). The organophilic clay obtained by the above treatment could be well dispersed in the monomer phase by sonication at low saponite concentration (< 5%), but formed a high-viscosity solution or a gel in the organic monomer at higher concentration of saponite. The effects of saponite modification conditions on the stability of the miniemulsion were studied, and the optimum conditions for preparing stable emulsions are reported. The final products resulting from the subsequent polymerization were characterized using light scattering, transmission electronic microscopy (TEM), and X-ray diffraction (XRD). It was found that the particle size of the prepared suspensions is in the range of 90-120 nm, and the final latex of nano-saponite composite is stable for months. It was also found that the addition of clay slightly reduced both the reaction rate and the conversion.