Structural Characterization and Properties of Deep Eutectic Solvents Plasticized Chitosan Films

In this study chitosan (CS) films were prepared from a deep eutectic solvent (DES) composed of choline chloride and malonic acid by solvent casting, and the influence of DES content on the structure and properties of the CS films was investigated in detail. It was confirmed by the spectral data that hydrogen bonds and ionic bonds were formed between the CS chains and DES. Structural analysis demonstrated that the crystallization of the CS was greatly hampered and the CS chains were stacked disorderly in films with high DES content. Differential scanning calorimetry (DSC) results indicated that DES exerted a significant plasticizing effect. In the case of the plasticized film containing 80 wt% of DES it showed a low glass transition temperature (Tg) of 20 degrees C. With increasing DES content, the water content of the plasticized films also increased, evidenced by the TGA results. Meanwhile, a structural change from granular to lamellar structure was observed by SEM. In addition, compared with pure CS film, the DES plasticized CS films possessed good fracture toughness and hydrophilicity. These observations suggest that the structure and properties of the CS films can be controlled by changing their DES content.