Effects of drying methods and plasticizer concentration on some physical and mechanical properties of edible chitosan films

In order to alleviate shortcomings of edible chitosan films, which are rigid and brittle in nature, an idea of using advanced drying methods, in combination with appropriate concentration of plasticizer, to improve the mechanical properties of the films was proposed and tested. Physical (thickness and color) and mechanical (tensile strength and percent elongation) properties of edible chitosan films plasticized at four glycerol concentrations (0%, 25%, 75% and 125% w/w chitosan) and prepared by three drying methods, namely, hot air drying (≈40 °C), vacuum drying and low-pressure superheated steam drying (LPSSD) (90 °C, 10 kPa) were investigated. Dynamic mechanical thermal analysis (DMTA) was used to determine the glass transition temperature to verify the compactness of edible chitosan films. It was found that the drying methods and plasticizer concentration significantly affected the drying time, tensile strength, percent elongation and glass transition temperature of the films. On the other hand, the drying methods and plasticizer concentration did not affect the thickness and final moisture content of the film samples at lower glycerol concentrations. In the cases of vacuum drying and LPSSD, there was a limiting value of plasticizer concentration (25% w/w) beyond which the effect of the plasticizer concentration on the mechanical properties was negligible. In all cases, the color of all tested films was not significantly different.