Mechanical properties improvement of chitosan films via the use of plasticizer, charge modifying agent and film solution homogenization

Glycerol, charge modifying agent (NaCl) and high-pressure homogenization were used to prepare chitosan film-forming solution prior to drying to improve mechanical properties of the resulting films. Zeta potential and viscosity of each film solution were measured, while mechanical properties viz. tensile strength and percent elongation of the films were assessed. X-ray diffraction analysis, Fourier transform infrared spectroscopy and dynamic mechanical analysis results of the films were obtained and used to explain the mechanical property data. Combined use of glycerol, NaCl and homogenization led to increased zeta potential but decreased viscosity of the solution. Electrostatic repulsion led to extended chitosan chains and lower film crystallinity and glass transition temperature due to weaker hydrogen bonding and increased amide-I band interactions. A film with the best mechanical properties (tensile strength of 50 MPa and percent elongation of 47) was from the solution with 25% (w/w) glycerol, 15-mM NaCl and homogenized at 10/5 MPa.