Effect of sorbitol content on microstructure and thermal properties of chitosan films.

In this work, the influence of sorbitol content on the microstructure and thermal properties of chitosan films was investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC). It showed that the addition of sorbitol weakened the hydrogen bonding between chitosan molecules as well as the electrostatic interactions existed in chitosan films. Structural analysis revealed that a small amount of sorbitol (~10 wt%) could facilitate the crystallization of chitosan, whereas it was seriously hindered at high content of sorbitol (~50 wt%). The thermal behavior of composite films indicated that the sorbitol addition did not reduce the thermal stability of polymer films. When the sorbitol content rose to above 30 wt%, phase separation may occur and two glass transitions presented in composite films. The lower temperature transition was associated with the glass-rubber transition of sorbitol-rich phase, and the higher one was related to chitosan-rich phase. These results implied that the microstructure as well as properties of the plasticized chitosan films can be controlled by adding sorbitol, which is important for their usage as packaging materials.