Further evidence of crazing and shear banding in the hybrid nanocomposite samples were obtained using optical microscopy. Fig. 7.6 reports the optical microscopy images of P/MT5/CW-CS1 and P/MT5/CW-AH1 hybrid nanocomposites before and after deformation. To better observe the crazes and shear bands, optical microscopy images were conducted using back-illumination. Fig. 7.6 clearly shows crazes forming in the samples after deformation, which look like cracks but characteristically form perpendicular to the draw direction (Arjmandi et al., 2015b). In addition, the formation of shear bands (at 45° to the direction orthogonal to the tensile axis) were also clearly observed in the samples after deformation. These shear bands may also increase the toughness of the nanocomposites through localized yielding of the polymer. High strain within a craze zone and the formation of shear bands could result in an overall increase in the strain to failure of the sample (Arjmandi et al., 2015b).
Figure 7.6 Optical microscopy images prior (left) and after (right) deformation. (A) P/MT5/ CW-CS1; and (B) P/MT5/CW-AH1 hybrid nanocomposites films.
Source: Arjmandi, R., Hassan, A., Eichhorn, S.J., Haafiz, M.M., Zakaria, Z., Tanjung, F.A., 2015b. Enhanced ductility and tensile properties of hybrid montmorillonite/cellulose nanowhiskers reinforced polylactic acid nanocomposites. J. Mater. Sci. 50 (8), 3118—3130.