Rubber-clay nanocomposites: from nanostructures to properties

In this contribution are discussed rubber-clay nanocomposites composed of a diene rubber and layered clays. Synthetic and natural poly-1,4-cis-isoprene and styrene/butadiene copolymers are used as the rubbers and a montmorillonite, either pristine or modified with a quaternary ammonium salt, is the layered clay. Montmorillonite was delaminated by compounding with either synthetic or natural poly-isoprene. Moreover, (00l) reflections in XRD patterns of both pristine and organo-modified MMT were found to reduce their intensity, with respect to (hk0) reflections, as they were mixed with the diene rubbers (styrene/butadiene as well), while their spacing remained unaltered, thus indicating a progressive reduction of the number of the packed clay-layers without any polymer intercalation. A delamination process is thus observed for nanocomposites in diene rubbers: complete separation between clay-layers can be thus achieved not only by the well-known intercalation-exfoliation mechanism. Reaction between pristine MMT and the organic modifier (OM) was performed by using rubber as a reaction medium. Unique results were obtained using natural polyisoprene: the basal spacing of the OM-intercalated structure prepared in this rubber was found to be nearly double with respect to the basal spacing of OM-intercalated clays obtained by direct treatment of MMT with OM in a polar solvent or in synthetic rubbers. Physical-mechanical testing of sulfur cured compounds showed a remarkable increase of storage modulus, an increase of thermoplasticity and of hysteresis as well as of Payne Effect. Rubber clay nanocomposites with organic-modifier-intercalated (OM-intercalated) crystalline structure seem thus to promote a higher dissipation of energy in sulfur cured compounds.