Effect of hydration on water state, glass transition dynamics and crystalline structure in chitosan films.

The influence of water uptake on water state, glass transition dynamics and crystalline structure in chitosan films was investigated by differential scanning calorimetry (DSC), X-ray diffraction and infrared spectroscopy (FTIR) techniques. DSC result indicated that two types of water, i.e., non-freezable water and freezable water, appeared in turn with the gradual increase of water content. Only the non-freezable water was responsible for the reduction of glass transition temperature (Tg), which leveled off at higher hydration levels. Structural analysis revealed that moisture could bring about a slight increase in the crystallinity of polymer due to alignment of hydrated and relaxed chitosan chains in the amorphous region. FTIR result showed that the hydrogen bonds and electrostatic forces existing in chitosan films varied slightly with water content. These observations suggest that changing the water content in such systems offers the possibility to control the microstructure as well as properties of polymers.