Starch nanocrystal nanocomposite films

Nominal (a) elongation at break, (b) strength, (c) nominal strength vs nominal elongation at break (the starch nanocrystal contents are indicated in panel) and (d) tensile modulus for waxy starch nanocrystals/ NR nanocomposite films vs starch content. 

Figure 14.15 Typical nominal stress vi nominal strain curves of waxy maize starch nanocrystals/NR nanocomposite films. The starch nanocrystal contents are indicated in the figure.

Starch nanocrystals also reduced the oxygen diffusion through the nanocomposite films as shown from the decrease of diffusion coefficient values upon filler content increase in Table 14.3. It is believed that the platelet-like low permeable structures of the starch stand in the way of the oxygen molecules (O2 diameter 3.47 A), increasing the tortuosity of the diffusion path. The... 

Table 14.3 Water vapour transmission rate (WVTR), diffusion coefficient (D), permeability coefficient (P) and solubility (S) of oxygen for starch nanocrystal/NR nanocomposite films.

The Mullins effect is characterized by stress softening. In order to demonstrate the presence of the Mullins effect in NR nanocomposites, three successive tensile cycles were performed for each sample. For the unfilled NR matrix, curves corresponding to the successive cycles were perfectly superposed, to a few per cent (6-8%) (Figure 14.22(a)).For nanocomposites, a significant decrease in G o can be observed between the first and the second cycle, for films reinforced with 30 wt% starch nanocrystals (Figure 14.22(b)).Similar to the Payne effect, the magnitude of the Mullins effect also increases with filler content. Furthermore, this increase was almost proportional to the filler content. 

The glycerol content was fixed at 36 wt% based on the dry starch matrix. Then this mixture was poured into a flask equipped with a stirrer and heated at 100 °C for 30 min to gelatinize starch. The same procedure is used for the fabrication of the Hemp Cannabis sativa) cellulose nanocrystals and potato starch nanocomposite films S/HC-NC (Cao et al. 2008b). 

Slavutsky et al. (2014) prepared starch/cellulose nanocrystals (CNCs) films and their water barrier properties were studied. The measured film solubility, contact angle, and water sorption isotherm indicated that reinforced starch/CNC films have a lower affinity to water molecules than starch films. Permeability, dififusivity, and solubility coefficients indicated that the permeation process was controlled by the water diffusion and was dependent on the tortuous pathway formed by CNC incorporation. The decrease in surface hydrophilicity and the improvement in water vapor barrier properties with the addition of CNC showed that these nanocomposites present excellent potential as a new biomaterial for application in food packaging and conservation. 

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