Effects of plasticizers on the structure and properties of starch–clay nanocomposite films

Biodegradable nanocomposites were successfully fabricated from corn starch and montmorillonite (MMT) nanoclays by melt extrusion processing. The structure and morphology of the nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and film properties such as barrier, mechanical and thermal properties were also measured. As a conventional plasticizer, the influence of glycerol content was first investigated. As the glycerol content decreased from 20% to 5%, the degree of clay exfoliation increased. Films with 5% glycerol exhibited the lowest water vapor permeability (0.41 g mm/kPa h m2), highest glass transition temperature (53.78 °C), and highest tensile strength (35 MPa), but low elongation at break (2.15%). Urea and formamide were tested as alternative plasticizers for the starch–clay nanocomposites. The results indicated that the use of new plasticizers increased the degree of clay exfoliation. The formamide plasticized starch–clay nanocomposite films exhibited lower water vapor permeability (0.58 g mm/kPa h m2), higher glass transition temperature (54.74 °C), and higher tensile strength (26.64 MPa) than the other two plasticizers when used at the same level (15 wt%).