Abstract: In this study, the effects of three different preparation methods, acid dissolution followed by alkali regeneration (CS-Na), alkali-urea dissolution followed by hot water regeneration (CS-60 ℃), and alkali dissolution followed by alcohol regeneration (CS-C2H6O) on the properties (mechanical strength, light transmittance, water vapor transmission rate (WVTR)) and structure (groups, crystalline structure and microstructure) of chitosan film were investigated. It was found that the tensile strength of the CS-Na film was 0.064 MPa, and the elongation at break was 34.72%. The tensile strength and elongation at break of the two chitosan films prepared with alkali-urea system were significantly improved, indicating better mechanical properties. All three chitosan films had excellent ultraviolet (UV) barrier capacity; the CS-C2H6O film had the highest UV transmittance, the CS-60 ℃ film was in the middle, and the CS-Na film had the lowest UV transmittance. The WVTR of these films under saturated NaCl and MgCl2 conditions decreased in the following order: CS-60 ℃ < CS-C2H6O < CS-Na, indicating that the CS-60 ℃ film had the best water vapor barrier capacity. The results of Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) indicated that alkali-urea system could enhance the hydrogen bonding between chitosan molecules to the largest extent. Molecular chain rearrangement occurred in all these chitosan films during the dissolution-regeneration process, and hot water bath at 60 ℃ was more conducive to the formation of nanofiber structure in chitosan films. Scanning electron microscopy (SEM) results suggested that the cross-section of CS-60 ℃ presented a denser and more uniform porous structure. Moreover, the surface of this film was much smoother than that of the CS-C2H6O and CS-Na films. Overall, the CS-60 ℃ film had better mechanical properties and a more uniform porous structure, and therefore could have better application prospects in the field of food packaging.

Key words: chitosan; high-strength chitosan film; alkali-urea system; microstructure