The true stress vs. strain curves for unfilled natural rubber
matrix and up to 8.3 wt% carbon nanotubes NR composites at 20 C are represented in Fig. 2. In all cases the typical non-linear ‘‘S curve’’ described in the kinetic theory of rubber
elasticity [1] is observed. It is useful in that case to plot a socalled reduced (or Mooney) stress ½r ¼ r=ða 1 a2Þ as a function of the extension ratio a, or a1 (Fig. 3)