The synergism between chitosan/tartaric acid/bentonite, metal cations and thymol in antioxidant and antimicrobial activities of films.

In recent years, antimicrobial materials have been investigated as a response to resistance antibacterial. In the present study, chitosan films containing 10% Zn(II) and Cu(II) bentonite were obtained by casting and reticulation with tartaric acid. Thymol was incorporated at 3 and 10% w/w in the film ex situ. Structural, morphological, thermal, and physicochemical properties were investigated to follow the formation and performance of the films. Their antioxidant action and antimicrobial properties against Gran positive and Gran negative bacteria were also evaluated by the agar diffusion method. The incorporation of Zn(II) and Cu(II) exchanged bentonites improved mechanical resistance and stiffness, while their combination with thymol modulated water solubility and swelling. FT-IR indicated hydrogen bonding between amino groups of chitosan, clay OH groups, and thymol, with possible electrostatic interactions. CHN analysis indicated higher thymol incorporation in films with Cu(II), confirmed by thermogravimetry. The presence of metal-cation bentonites improved the mechanical properties of the films independently of the ions in the clay. Fast release of thymol in 1.5 h by copper- and zinc-based films. The films were slightly more effective against E. coli. Mechanisms were associated with antioxidant activity, especially at 10% thymol. In summary, the combination of chitosan, Zn(II), or Cu(II) bentonites reticulate by tartaric acid resulted in stable films and adsorbed thymol. The functional systems behaved as interesting antioxidant and antimicrobial materials. The route was promising for the development of bioactive chitosan films.