  The antagonistic effect of processing and thermal annealing on both the
filler structure and the polymer matrix is explored in polymer nanocomposites
based on natural rubber with precipitated silica incorporated by coagulation
from aqueous suspension followed by roll-milling. Their structure and linear
and non-linear rheology have been studied, with a particular emphasis on the
effect of high temperature thermal treatment and the number of milling passes.
Small-angle X-ray scattering intensities show that the silica is organized in
small, unbreakable aggregates containing ca. 50 primary nanoparticles, which
are reorganized on a larger scale in filler networks percolating at the highest
silica contents. As expected, the filler network structure is found to be
sensitive to milling, more milling inducing rupture, as evidenced by the
decreasing Payne effect. After thermal treatment, the nanocomposite structure
is found to be rejuvenated, erasing the effect of the previous milling on the
low-strain modulus. In parallel, the dynamics of the samples described by the
rheology or the calorimetric glass-transition temperature remain unchanged,
whereas the natural latex polymer network structure is modified by milling
towards a more fluid-like rheology, and cannot be recovered.
