Production and characterization of thick, thin and ultra-thin chitosan/PEO films

The current study focused on the functionality of chitosan/PEO films as affected by preparation methods, film composition, and thickness. Mixtures of chitosan and PEO with different blend ratios (100/0–50/50) were dissolved in 1% acetic acid to form 1% blend solutions. Films prepared by casting of 20 g or 10 g film-forming solution per 50-mm diameter polystyrene Petri dish or by using spin-coating method had an average thickness of 87.41 ± 5.44 μm (thick), 37.88 ± 2.41 μm (thin), and 70.47 ± 3.06 nm (ultra-thin), respectively. Development of polymer crystallization was monitored by X-ray diffractometer at ambient temperature; the metal-binding capacity of the films was assessed based on removal of chromium ions from K2CrO4 solution, and the antibacterial properties were tested against Escherichia coli K-12. The crystallization extent of the chitosan/PEO films decreased with decreased thickness as a consequence of faster solvent evaporation during film formation. Decreasing the thickness of the films increased the surface-to-mass ratio, what resulted in higher number of available active sites on the film surface per unit weight of chitosan, and promoted the metal-binding efficiency of the films. Ultra-thin chitosan/PEO films showed a significantly higher chromium-binding capacity [26.47–70.86 mg Cr(VI)/g film] compared to the cast films [0.73–7.59 mg Cr(VI)/g film]. However, these nano-thin films did not show significant antibacterial efficiency, most likely due to their extremely low weight and consequently insufficient chitosan concentration in the inoculated test tubes to kill significant number of bacteria.