Rubber-clay nanocomposites. The control of nanostructured to steer material properties

Novel nanostructures are presented formed by a smectite clay and ammonium salts in a hydrocarbon polymer and the correlation of said nanostructures with the properties of composite material is discussed. Clay intercalates with organic mono-layers and bi-layers were prepared by mixing the clay and various ammonium salts in poly-1,4-cis-isoprene, either synthetic or naturally occurring. Experimental evidences are reported, based on X-ray diffractions and transmission electron microscopy. The formation of the two different kinds of clay intercalates was found to be dependent on the substituents of the ammonium salts and on the polar substances present in the rubber used as the reaction medium and is interpreted as driven by the need of achieving an inter-layer density high enough for a stable crystalline structure. Both kinds of clay intercalates were found to be thermally stable, maintaining their intra-layer crystalline order up to 250°C. A delamination process for said nanostructures was observed, upon thermomechanical mixing: complete separation between clay-layers can be thus achieved not only by the well-known intercalation-exfoliation mechanism. Rheological properties of composite materials were investigated through strain sweep, frequency sweep and stress relaxation tests and dynamic mechanical properties of cured compounds is discussed as well.