Poly(styrene-co-butyl acrylate)-Brazilian montmorillonite nanocomposites, synthesis of hybrid latexes via miniemulsion polymerization

In this work hybrid latexes of poly(styrene-co-butyl acrylate)/montmorillonite were synthesized via miniemulsion polymerization using a Brazilian organically modified montmorillonite. The natural clay was previously treated with Cetyltrimethyl ammonium chloride (CTAC) in order to increase the interaction between the clay and the monomer phase. Three different methodologies to modify the clay and their influence on the final properties of the composites obtained were evaluated in this work. The modified clays were characterized by X-ray diffraction (XRD). The films obtained after drying the latexes were characterized by dynamicmechanical thermal analyses (DMTA), small amplitude oscillatory shear (SAOS), transmission electronic microscopy (TEM) and Cobb test. The X-ray diffractograms, showed an increase of basal spacing after organic treatment indicating the introduction of CTA(+) within the clay interlamelar space. This interlamelar space was further increased after polymerization for all of the three differently modified clays studied, indicating that in situ polymerization occurred. The introduction of organically modified clays did not influence the kinetics of polymerization. Stable latexes were obtained. The DMTA presented improved mechanical properties for the materials charged with two of the modified clays studied when compared to a conventional composite. SAOS analysis revealed that an exfoliated structure might have been obtained when adding one of the modified clays to the reacting medium. Cobb tests showed that the permeability to water was reduced by the incorporation of clays to the copolymer.