Structure and Thermoelastic Behavior of Synthetic Rubber/Organoclay Nanocomposites

Nanocomposites of synthetic styrene‐co‐butadiene rubber and three types of organoclay fillers were prepared by melt‐compounding and characterized by small‐angle X‐ray scattering (SAXS), differential calorimetry and stretching calorimetry. The in‐rubber structure of the organoclay particles is characterized by different degrees of intercalation with interlayer distances ranging from 3.1–4.8 nm. In contrast to the pristine rubber, all nanocomposites exhibited irreversibility of both mechanical work and heat effects in stretching/contraction cycles at fairly low elongations. Moreover, at the same filler loading both the mechanical reinforcement effect and the magnitude of specific heat effects proved strongly dependent on the degree of intercalation. In the range of low elongations, significantly earlier onsets of the heat inversion phenomenon (compared to theoretically expected), as well as the overshoots of exothermal heat effects in contraction above the endothermal heat effects in stretching for nanocomposites, suggested the contribution of structural rearrangements at the rubber/filler interface by the mechanism of chain slippage operative in both stretching and contraction regimes. In the range of high elongations, the thermoelastic behavior of nanocomposites could be accounted for quantitatively by the model, which assumed explicitly the contributions of local strain amplification for the rubber matrix and of successive decay of nanoparticle clusters with increasing strain, generating the exothermal effects of external friction between nanoparticles.

Dependency on relative elongation of specific mechanical work (squares) and specific heat effects (circles) for the pristine rubber.