SEM images of the cross-section for the neat NR film and NR5% nanocomposite film are presented in Fig. 4. A smooth and uniform morphology is observed for unfilled NR, whereas the CNC/NR nanocomposite gives the impression of being composed of two layers, one rougher phase and another smoother phase. They possibly correspond to the lower CNC-rich face and upper NR-rich face, respectively. Nevertheless, it was not possible to observe the presence of microscale CNC aggregates, even for 5 wt% CNC content, with the magnification utilized.
The viscoelastic behavior of the films was analyzed in the linear range using DMA. Figs. 5a and 5b show the isochronal evolution at 1 Hz of the logarithm of the tensile storage modulus (log E') and tangent of the loss angle (tan δ), measured as a function of temperature, for the neat NR film and nanocomposite films with different loading levels (1, 2.5 and 5 wt%) of CNCSH. The temperature corresponding to the maximum of tan δ (associated to Tg of the NR matrix) and storage modulus value at 25 °C are reported in Table 1.