No abstract

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.

Nanocomposites were prepared based on diene rubbers and layered clays modified with an alkyl quaternary ammonium cation (organoclay). A diene rubber, either polybutadiene, or synthetic or naturally occurring polyisoprene or styrene-butadiene copolymer, was melt blended with either a preformed organoclay or with a mixture of pristine clay and ammonium cation. Besides isolated lamellae, nanocomposites showed the presence of crystalline organoclays with intercalated organic layers made only by low molecular mass substances, essentially the ammonium cation, and no evidences for the intercalation of polymer chains were observed. Dynamic-mechanical properties of sulphur cured compounds with carbon black as the main filler and a minor amount of organoclay were investigated. The organoclay was found to bring about a reduction of Mooney viscosity, an increase of storage modulus at low temperature as well as an increase of thermoplasticity.

Summary: The g-ray induced ''grafting'' of polybutadiene olygomers onto precipitated silica and the radiation induced crosslinking of the blends prepared with the modified silica in SBR matrices have been investigated in the dose range up to 290 kGy. Enhanced mechanical properties have been detected for the SBR blends containing the modified silica after g-ray induced crosslinking. The comparison with the analogue mixtures containing pristine silica, supported by EPR measurements, suggests that the PB coating is effective in enhancing the mechanism of formation of filler-rubber chemical links.