  The mechanical properties of non-vulcanized natural rubber and dialyzed
natural rubber-clay nanocomposites have been studied by uniaxial deformations
to evaluate the reinforcement efficiency of the clay. We show that while
non-rubber molecules contribute to auto-reinforcement, removal of these
molecules improves significantly the performance of clay as reinforcement
agent. These mechanical properties are discussed in relation to morphological
aspects of the clay characterized by TEM and SANS. The nanocomposites prepared
by "latex-mixing" with aqueous dispersions of clay are found to contain
completely exfoliated clay lamellae in coexistence with tactoids. Improved
mechanical properties of the nanocomposites can be modeled by the high aspect
ratio of exfoliated clay platelets coupled with immobilized rubber matrix.
Interestingly, presence of tactoids does not appear to compromise the excellent
reinforcement properties of the exfoliated platelets. At high deformations,
strain-induced alignment of the clay exhibits anisotropic scattering, with
anisotropy increasing with clay concentration and stretching.
