Polymer-layered silicate nanocomposites: an overview

An overview of polymer–clay hybrid nanocomposites is provided with emphasis placed on the use of alkylammonium exchanged smectite clays as the reinforcement phase in selected polymer matrices. A few weight percent loading of organoclay in nylon 6 boosts the heat distortion temperature by 80°C, making possible structural applications under conditions where the pristine polymer would normally fail. A similar loading of clay nanolayers in elastomeric epoxy and polyurethane matrices dramatically improves both the toughness and the tensile properties of these thermoset systems. Glassy epoxy nanocomposites exhibit substantial improvement in yield strength and modulus under compressive stress–strain conditions. The latest development in polypropylene hybrids have yielded nanocomposites with improved storage moduli. Polyimide hybrids in thin-film form display a 10-fold decrease in permeability toward water vapor at 2 wt.% clay loading. In situ and melt intercalation processing methods are effective in producing reinforced polystyrene hybrids. Nitrile rubber hybrids show improved storage moduli and reduced permeabilities even toward gases as small as hydrogen. Poly(ε-caprolactone)–clay nanocomposites prepared by in situ polymerization of ε-caprolactone in organoclay galleries show a substantial reduction in water adsorption. Polysiloxane nanocomposites produced from poly(dimethylsiloxane) and organoclay mixtures have improved in tensile properties, thermal stability and resistance to swelling solvents. Organoclay-poly(l-lactide) composite film was obtained by solvent casting technique. Clay nanolayers dispersed in liquid crystals act as structure directors and form hybrids composites that can be switched from being highly opaque to highly transparent by applying an electric field of short duration.