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Styrene-butadiene rubber (SBR) nanocomposites with different organoclay contents (up to 15 phr) were prepared by a melt compounding procedure, followed by a compression-molding step in which the SBR matrix was sulfur crosslinked. The vulcanizates were characterized in respect to their curing, mechanical and viscoelastic properties, and thermal stability. The optimum cure time decreased with increasing organoclay content. This effect was attributed to the ammonium modifier present in the organoclay, which takes part in the curing reaction acting like an accelerator. The results of mechanical test on the vulcanizates showed that the nanocomposites presented better mechanical properties than unfilled SBR vulcanizate, indicating the nanoreinforcement effect of clay on the mechanical properties of SBR/organoclay nanocomposites. The addition of organoclay did not significantly change the glass transition temperature. However, the heights of tan d value at the glass transition temperature for the nanocomposites are lower than that of the unfilled SBR. This suggests a strong interaction between the organoclay and the SBR matrix as the molecular relaxation of the latter is hampered. The temperature at which 50% degradation occurs (T 50 ) and the temperature when the degradation rate is maximum (DTG max ) showed an improvement in thermal stability, probably related to the uniform dispersion of organoclay.

Composites based on styrene-butadiene rubber containing organophilic montmorillonite were produced by melt compounding and conventional sulfur curing. The samples were characterized by X-ray diffraction and both transmission and scanning electron microscopy. The dispersion of the clay and the spacing between the silicate layers revealed the presence of intercalated, aggregated, and partially exfoliated structures. Infrared spectroscopy also provided clear evidence for clay exfoliation and migration of zinc stearate to the surface of the samples. The crosslink density, evaluated through swelling in toluene, decreased with increasing organoclay content. This behavior could be justified by the partial absorption of the curatives on the filler surface. The mechanical properties of nanocomposites significantly increased when compared with those of unfilled rubber. These enhanced properties were attributed to the intercalation/exfoliation of the organoclay.