Investigation of the influence of natural deep eutectic solvents (NaDES) in the properties of chitosan-stabilised films

In the present work, the plasticising effect of the natural deep eutectic solvents (NaDESs) choline chloride/lactic acid and betaine/lactic acid in the formation of chitosan-stabilised films is investigated. The films were prepared by the casting technique, dissolving chitosan in 1% w/v solution of choline chloride and lactic acid or betaine and lactic acid in water, either as a pre-formed NaDES or as separately added components (physical mixture), without the addition of acetic acid. The physicochemical and mechanical properties of the formed films were studied. High concentration of the NADES (83%) increases the weight and thickness of the films. The reference chitosan films containing acetic acid or lactic acid are inelastic and very resistant to burst. On the other hand, the addition of betaine increases significantly the elongation capacity of the film prior to burst. The water vapour permeability of the films prepared from the NaDES solutions presents a 4.5 and a 2.6-fold increase, respectively, in comparison with acetic acid containing films. The materials prepared using the NaDESs have distinct differences to those prepared using the physical mixture of the NADESs' components, as shown from the thermal and FT-IR spectroscopic analyses data. Finally, SEM imaging revealed differences among the surfaces of the films.