Thermomechanical and acidic treatments to improve plasticization and properties of chitosan films A comparative study of acid types and glycerol effects

Plasticized and unplasticized chitosan films were successfully prepared by thermomechanical treatment, as a possible alternative route to solvent casting method. Acetic acid and lactic acid were used as solvents and glycerol was used as plasticizer with a fixed concentration of 25 wt.-%. The properties of the prepared samples were investigated demonstrating the effects of acid type and the addition of glycerol. Microstructure analysis results revealed a homogeneous and cohesive matrix, indicating a smooth surface without pores, cracks and irregularities. Unplasticized samples with lactic acid showed lower stiffness, higher elongation at break, more thermal stability, higher water uptake and water vapor permeability compared to the samples prepared with acetic acid. The introduction of glycerol affected all properties of the samples, but the samples prepared with lactic acid were more influenced. The rheological and mechanical properties (tensile strength and elongation at break) were improved when glycerol was added, resulting in a ductile behavior with a small plastic deformation and higher elongation at break compared to unplasticized films. On the other side, thermal properties were negatively affected by a decrease in the thermal stability. The water uptake and WVP measurements verified that the hydrophilic character of the material was enhanced by the addition of glycerol