Preparation and Characterization of Corn Starch/Clay Nanocomposite Films: Effect of Clay Content and Surface Modification

Sodium montmorillonite (Na+-MMT) and Cloisite 30B (C30B) were modified with silver and copper metal ions using cation exchange process in solution. The modified clays were characterized by Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis. The modified clays were then used to prepare corn starch (CS)/clay nanocomposite films via solution casting method. The effect of clay content and surface modification on the microstructure, antibacterial activity (against Escherichia coli and Staphylococcus aureus), tensile properties, water vapor permeability and UV irradiation absorption, and transmittance of the CS-based nanocomposite films were systematically studied. XRD patterns showed the formation of an intercalated structure of clays in the nanocomposite films, and scanning electron microscopy (SEM) evidenced the presence of tactoids in the films. Nanocomposites films containing modified clays revealed improved antibacterial properties compared to those of control. When a combination of silver- and copper-modified clays was used in the preparation of films, antibacterial activity, and lower water vapor permeability were enhanced. The nanocomposites exhibited higher UV-Vis absorption compared with that of pure starch with the highest absorption for films containing silver-modified clay. The use of clay nanoparticles significantly increased tensile modulus and ultimate strength of the films at the expense of a decrease in strain at break. Nanocomposites films containing silver-modified clays showed the highest stiffness and strength.