Preparation of chitosan-sodium alginate films through layer-by-layer assembly and ferulic acid crosslinking: Film properties, characterization, and formation mechanism.

Chitosan-alginate films were prepared through layer-by-layer assembly combined with ferulic acid crosslinking. Their mechanical properties, opacity, and hydrophobicity were compared to films prepared by direct mixing, crosslinking alone, and LBL assembly alone. Thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectroscopy were used to characterize the films and analyze their formation mechanism. The results indicated that the layer-by-layer assembly and ferulic acid crosslinking combination increased the tensile strength and light-blocking ability of the films. In addition, the films had a lower water vapor transmission rate, swelling degree, and water solubility, as well as higher hydrophobicity. Scanning electron microscopy showed a good compatibility between the film components of the film prepared by the combination technique. The structural characterization results revealed some strong interactions among the amino, carboxyl, and hydroxyl groups of the ferulic acid, chitosan, and sodium alginate in the film. The driving force for film formation was the generation of non-covalent bonds among the film components rather than covalent bonds.