Polymer Latex/MMT Blends Film: Structure And Properties

MMT water-dispersion after sonication was blended with polymer emulsion. Polymer/MMT nanocomposite coating was formed simply by evaporating water, just like in the case of conventional emulsion coating, aiming at producing zero-VOC coatings with excellent mechanical properties. It was demonstrated that polar functional groups introduced on the surface of the polymer particles play a key role to control the morphology and mechanical properties of nano-structured films. In addition, pH of emulsion and drying rate of the film were found to have significant effect on the morphology and properties of nano-structured films.Three kinds of polymer latex with the same main compositions but different surface chemical compositions were synthesized by semi-batch emulsion polymerization. In Latex I, no functional monomer was incorporated on the surface of the polymer particles. In Latex II, the latex surface was covered by the groups of -NH2 while in Latex III, the groups of -COOH were incorporated on the colloidal surface. Although tensile strength and modulus of all the films were dramatically increased with increase of MMT content up to 10wt%. The introduction of-COOH and -NH2 on the polymer colloids were found to improve the mechanical properties significantly, which is consistent with the higher interface interaction between polymer and clay. And the film from Latex III/MMT showed the best mechanical properties. By TEM, the morphologies of the coating film were found to be dependent on the surface composition of the polymer colloids. A unique super network of nanoaggregates of MMT layers could be formed in the Latex III/MMT nano-film which partly contributes to the enhancement of mechanical properties, especially of modulus, of Latex III/MMT nano-film.The concentration of electrolyte and pH value also show profound influence on the mechanical properties of the coating films. The higher concentration of electrolyte and pH value would deteriorate the performance of the coating film.In addition, it was found that the properties of nano-film dried faster is betterthan the properties of film dried slower, but the extent of the influence is dependent on the kind of the latex. The influence is much less significant for Latex III/MMT, which probably attributes to chemical reactions of -OH and -COOH occurred in the interface.The coatings made by the current method have an excellent film forming ability at room temperature as well as excellent mechanical properties. They show very promising use in low VOC (even zero-VOC) coating.