Non-ionic, poly(ethylene oxide)-based surfactants as intercalants/dispersants/exfoliants for poly(propylene)-clay nanocomposites

Poly(propylene) (PP)-clay nanocomposites were prepared from unmodified montmorillonite clays (NaMMT), with poly(ethylene oxide)-based nonionic surfactants as dispersants/intercalants/exfoliants. The primary objective of this research was to find dispersants that (a) allow PP nanocomposites to be formed by direct melt mixing; (b) are effective with unmodified clays and (c) comprise of only a minor component with respect to both the clay and the overall composition. Linear, branched, gemini and sugar-based surfactants and structures containing poly(dimethyl siloxane) and poly(methyl methacrylate) blocks were examined. These additives were found to be effective in breaking down the clay agglomerates to tactoids, giving some expansion of the clay structure and partial exfoliation and providing substantially improved clay dispersion. The properties of the derived nanocomposites depend on the level of additive and its structure. Tensile and impact properties show significant improvement over the precursor PP. Also notable are the significantly better thermal and thermo-oxidative stabilities, as compared to both PP and "clay alone" composites. For optimal properties, it is both necessary and desirable that the surfactant should only be a minor constituent (20-50%) of the composition, with respect to the clay. A preferred surfactant is linear PE-block-PEO, with a short PEO block and an alkyl chain with approximately 30 carbon atoms (C-30).