The Effect of Montmorillonite (MMT) on Structural, Thermal and Optical Properties of Iranian Potato Starch Based Nanobiocomposite Films

In the present study, potato starch nanobiocomposites films plasticized with glycerol and containing four different montemorrillonite loading (0, 1, 3 and 5 wt% starch) were prepared via solution casting method. Differential scanning calorimetry (DSC) confirmed that the melting point and glass transition temperatures were increased and heat stability of the nanocomposites were improved. Upon 5% MMT loading, the glass transition and melting point of PS film were increased from 185.6 and 282.9 to 203.5 and 304.6, respectively. Colorimetry and UV-Vis spectroscopies were employed to evaluate the UV and visible-shielding efficiency of the PS-MMT nanocomposite films. Incorporationof 5% MMT did not have significant effect on color parameters (L*, b* and a*), color differences (E) and whitness index, but decrease yellow index of the films. Presence of 5% MMT in film formulation successfully blocked more than 82, 38 and 11% of UV-A, UV-B and UV-C lights, while opacity and transparency of the films were unchanged. Investigation of chemical structure of nanobiocomposite films by Fourier-transform infrared spectroscopy (FT-IR) and Atomic force microscopy (AFM) and revealed the hydrogen bonds interactions between MMT and starch and uniform dispersion of MMTplatelets in the starch matrix, respectively. Also, AFM topography images were used to study the surface morphology and roughness of starch films. Plasticized starch (PS) film had smoother surfaces and a lower roughness parameter. Adding MMT to starch matrix caused to increase the average roughness (Ra) and the most frequently quantitative parameters of roughness (Rq) from 32.4 nm and 39.9 nm in PS film to 119 nm and 147 nm in PS-5%MMT, respectively. The AFM phase images described the uniformity of the starch-MMT mixtures.