Rubber-clay nanocomposites. From nanostructures to material properties

In this presentation are discussed rubber/clay nanocomposites prepared by compounding either synthetic or natural isoprene rubber with pristine and organo-modified montmorillonite (MMT), and also by mixing the isoprene rubber with pristine MMT and the organic modifier (OM), an ammonium salt bearing organic radicals. Nanocomposites were characterized by X-ray diffraction measurements, Differential Scanning Calorimetry and by Transmission Electron Microscopy. Montmorillonite was delaminated by compounding with either synthetic or natural poly-isoprene and a progressive reduction of the number of the packed clay-layers without any polymer intercalation was observed. A delamination process is proposed for nanocomposites in isoprene rubbers: complete separation between clay-layers can be achieved not only by the well-known intercalation-exfoliation mechanism. Pristine MMT was delaminated in isoprene rubber and was re-aggregated by aging in the presence of the organic-modifier, leading to a MMT/OM intercalate structure. The basal spacing of the intercalate prepared in Natural Rubber was found to be nearly double with respect to the usual MMT/OM intercalate, obtained by direct treatment of MMT with OM in a polar solvent or in synthetic isoprene rubber3. As far as the reinforcement of rubber matrix is concerned, a comparison with traditional fillers is presented.