Preparation of stable acrylate/montmorillonite nanocomposite latex via in situ batch emulsion polymerization: Effect of clay types

Nanocomposites based on acrylic (butyl acrylate-co-methyl methacrylate-co-acrylamide) terpolymer and various commercial montmorillonites were synthesized by an “in situ” batch emulsion polymerization method. A complex emulsifier system containing sodium dodecyl sulphate (SDS) and a polymeric stabilizer was used in the polymerization. The minimum emulsifier concentration necessary to obtain stable latex depended on nanoparticle type and was established by several trials. Based on the experimental data two groups of stable latexes were obtained and characterized. The first nanocomposite latex group (Group A) was obtained by using lower emulsifier content and included Cloisite 93A, Cloisite 30B, Nanomer I.31 PS, Cloisite Na+ clays while the second group (Group B) had higher emulsifier content including Cloisite 15A, Cloisite 20A, Dellite 67G and Nanomer I.44P clays. The nanocomposite emulsions were characterized by means of particle size and zeta potential analyzes. The intercalation/exfoliation of the nanoparticles in acrylic latex was assessed by XRD and SEM. The structural characterizations of the nanocomposite films were performed by FTIR, mechanical properties were tested by DMTA and thermal behavior was analyzed by DSC and TGA. ta potential and particle size analysis showed that nanocomposite latexes were electrostatically stable and they had fine particle sizes varying between 94 and 174 nm with narrow distributions. DMTA results indicated significantly enhanced elastic moduli values for the nanocomposites except of those containing the clays having a relatively more hydrophilic nature (C30B, CNa+). The nanocomposite films also exhibited increased thermal stabilities. It was concluded that the clay type used in the preparation of nanocomposites and the emulsifier content in emulsion polymerization play important roles in determining latex and polymer properties of the nanocomposites and they should be predetermined for each application field.