The Role of Protein-Plasticizer-Clay Interactions on Processing and Properties of Thermoplastic Zein Nanocomposites

Bionanocomposites (BNCs) based on ther- moplastic zein (TPZ) and unmodified sodium montmoril- lonite (MMT), at 1, 2.5, 5, and 10 wt % loading, were prepared by using an internal mixer. The nanocomposites were characterized by using the following analytical meth- ods: small-angle and wide-angle X-ray diffraction, ther- mogravimetric, dynamic-mechanical and mechanical analyses. Results evidenced that the efficient dispersion of the inorganic reinforcement, as proved by X-ray diffrac- tion, allowed for an effective improvement of thermal and mechanical properties of the BNCs with respect to the neat TPZ. In particular, a significant increase of the storage modulus in the whole temperature range was observed in dynamic-mechanical experiments. A dramatic increase of mechanical properties has also been observed, with Young’s modulus increasing from 296MPa for neat TPZ to 1205MPa at 5wt% and to 1478 at 10wt% of MMT. The observed dependencies are explained by means of three concurring mechanisms: (i) the stiffening by exfoliated MMT platelets, (ii) the development of strong interactions between the nanoparticles and the protein macromolecules, promoted by the low-molecular weight plasticizer, (iii) the occurrence of possible plasticizer sequestration by MMT and the corresponding reduction of plasticizing effect on the protein.