Characterization of chitosan/caseinate films

Films made from sodium caseinate and/or chitosan, using glycerol as plasticizer, were prepared by casting from aqueous solutions. Films cryo-fractured surfaces were examined by SEM. FTIR spectra of the chitosan/ caseinate films showed an increase in the intensity of the amide band, corresponding to the strong interactions developed by the polyelectrolytic complexation of both components. Addition of 28 wt% of glycerol to caseinate films, conditioned at 50% relative humidity (RH), reduced the modulus from 2908 to 250.9 MPa, while the ultimate elongation increased from 4 to 63.2%. Increment to 80% RH further reduced the modulus down to 52.8 MPa. Similar results were found for the glycerol plasticization of chitosan films. The complex films showed a moderate improvement of the tensile strength (19.6 MPa) and an increase of the impact strength (35.6 GPa) with respect to those corresponding of chitosan films (17 MPa and 26.6 GPa, respectively). These properties were markedly improved with respect to those of caseinate (6.2 MPa and 13.4 GPa, respectively). The interactions developed between the cationic polymer chitosan, and the Na-caseinate carboxyl groups, lead to polyelectrolyte complexation in forming the film, which is proposed as the reason for improvement with respect to caseinate or chitosan films.