Rheological and thermodynamical behavior of styrene/butadiene rubber-organoclay nanocomposites

Organophilic layered silicate (montmorillonite type) was added up to 10 phr to a styrene/butadiene rubber (SBR) cured by an efficient vulcanization system. The compounds were characterized in respect to their curing, rheological and mechanical properties. In addition, attempt was made to consider some thermodynamical aspects of the resulting network. The crosslink density, assessed by the Flory-Rehner equation, increased with increasing organoclay content. This was traced to the accelerator role of the amine functionality of the trialkyl-amine intercalant used. The pronounced structural viscosity (i.e. viscosity decrease as a function of shear rate) and high elongation at break of the compounds caused by the incorporation of organoclay were opposed to the enhanced crosslinking and reinforcing effect of the clay supposed to the exfoliated. To solve the above contradiction a model was proposed according to which the silicate layers are intercalated/exfoliated and encapsulated by a highly crosslinked rubber layer and these "rubberized" platelets are embedded in the lightly crosslinked bulk.