On the stability and properties of the polyacrylate/Na-MMT nanocomposite obtained by seeded emulsion polymerization

Abstract

For high performance waterborne coatings usually polymer latexes with low emulsifier content are more preferred. Although polymer/clay nanocomposites offer improved properties, it is difficult to produce clay based nanocomposite latexes containing low emulsifier due to the stabilization problems especially caused by organoclays. Present study deals with the preparation of a tBA/BA/MAA ternary copolymer/clay nanocomposite containing 3wt.% sodium montmorillonite (Na+-MMT) via seeded emulsion polymerization. Experimentally it was observed that even the usage of hydrophilic clay caused stabilization problem and a certain amount of emulsifier (>1wt.%) was necessary to obtain stable latexes. In addition, the usage of a low molecular weight water soluble polymer as steric barrier was found to increase the stability of system. Obtained nanocomposite latex showed fine particle size diameter (127nm) and very narrow size distribution (PDI=0.06). The WAXD and TEM investigations indicated that a mostly exfoliated nanocomposite was obtained. Thermal analyses (DSC, DMTA and TGA) showed that there was no change at Tg of the copolymer while very high improvement was obtained for elastic modulus and a slight increase in thermal stability. According to the rheological measurements, the nanocomposite latex showed a higher low shear viscosity, a stronger shear thinning behavior and an improved physical stability in comparison to the reference latex.