Dynamic and viscoelastic behavior of natural rubber/layered silicate nanocomposites obtained by melt blending

Vulcanized natural rubber/layered silicate (montmorillonite)
nanocomposites prepared by melt blending with
different contents of organoclay (0, 5, 10, 20 wt%) were
investigated. The morphological characteristics of
the materials were studied by transmission electron
microscopy (TEM), wide angle X-ray diffraction, and
dynamic mechanical thermal analysis (DMTA). X-ray
spectra evidence some intercalation of the clay, while
TEM results show a good dispersion of the clay and
the occurrence of partial delamination. DMTA analysis
with varying temperature shows that the peak of the
loss modulus broadens by increasing the clay content
within the material, though the peak temperature is
scarcely affected. Mechanical reinforcement induced
by the presence of the clay is evidenced by static tensile
tests. At every clay content explored, dynamic
experiments show a nonlinear behavior (Payne effect),
which strongly increases with the amount of clay incorporated
and is considerably more pronounced than in
natural rubber filled with comparable amounts of conventional
fillers. The viscoelastic behavior of the materials
is investigated by recovery tests of low amplitude
storage modulus, carried out after the application of a
large strain perturbation, and by stress relaxation
experiments.