Clay delamination in hydrocarbon rubbers

Apolar-rubber/clay composites obtained by rubber compounding with pristine and organo-modified montmorillonite (MMT) have been characterized by X-ray diffraction measurements. By reducing the clay content in the rubber, the (00l) reflections progressively reduce their intensity, with respect to (hk0) reflections, while their spacing remains unaltered. These results indicate the occurrence of a progressive reduction of the number of the packed clay layers without any polymer intercalation. This delamination process, different from the usual intercalation - exfoliation process, is more efficient for pristine rather than for organo-modified MMT. In particular, pristine MMT, as observed for contents lower than 10% by weight, can be fully delaminated by mixing with natural rubber. Moreover, MMT delaminated by compounding with natural rubber can be aggregated by aging in the presence of suitable organic modifiers (OM), leading to MMT/OM intercalate structures with basal spacing nearly double with respect to the usual MMT/OM intercalate, obtained by direct intercalation of OM in MMT. These results have been rationalized by assuming the formation in the rubber of intercalates comprising organic bilayers rather than organic monolayers.