The role of choline chloride-based deep eutectic solvent and curcumin on chitosan films properties

Non-biodegradable plastics are one of the top environmental threats faced by terrestrial and marine ecosystems. In the field of food packaging, alternative bio-based plastics have been deeply researched because of their good biodegradability, biocompatibility, and the abundance of biomass resources. In this sense, these interesting characteristics allow the use of chitosan, curcumin and green plasticizers such as Deep Eutectic Solvents (DES) as excellent candidates for food packaging applications. Thus, in this work, different percentages of choline chloride-based deep eutectic solvent and curcumin were used as additives to improve chitosan films properties. The film-forming solutions were characterized by rheological techniques and the results were correlated with their morphologies. The addition of plasticizer (DES) and curcumin affected the apparent viscosity of the solutions. Corroborating these results, SEM images of cryo-fractured chitosan solutions appeared as homogeneous surface matrices wherein the pore diameter of which seemed to depend on the use of plasticizer or curcumin in the solution formulation. Transparent chitosan films fabricated from these solutions were prepared by the knife coating technique and their physical properties were assessed. Films with DES presented higher water vapor permeability (WVP), water solubility and water sorption capability. Nevertheless, the incorporation of the curcumin improved the barrier properties of the films leading to a decrease of WVP. In general, improved values of tensile strength (TS) were registered when lower amounts of curcumin were added in the systems. Moreover, non-plasticized films presented the highest values of TS and Young's modulus (YM) whereon agrees with the compact surface images observed by scanning electronic microscopy. Furthermore, the films reported here presented opacity values and yellowness that increased by increasing of pigment concentration.