Preparation, structure and properties of thermoplastic starch-clay nanocomposite films

Thermoplastic starch (TPS)-clay nanocomposite films were prepared by a solution method, followed by gelatinisation and compression moulding using urea as the plasticiser. XRD and FT-IR results showed that the TPS formed nanocomposites with both an organoclay and a natural montmorillonite clay, with the organoclay having a higher degree of exfoliation and stronger interactions with the TPS compared to the natural clay. Pre-mixing the organoclay with urea before introduction of starch modified the clay surfaces and helped formation of nanocomposites between the hydrophobic commercial organoclay and hydrophilic starch. Additions of clay did not induce occurrence of new types of crystalline structure of the TPS but changed its crystallinity slightly. The hardness, elastic modulus and water resistance of the TPS increased with the presence of clay, and the organoclay provided much better property enhancements compared to the natural clay confirming the formation of nanocomposites between the TPS and the organoclay. With the addition of 5 wt.% organoclay, the hardness and elastic modulus of the TPS increased by 125% and 91% respectively, and the amount of water absorbed at equilibrium was reduced by 40%.