Effect of ionic crosslinking on the water state in hydrogel chitosan membranes

The polyion complex membrane (PEC) composed of chitosan (Ch) and sodium alginate (NaAlg) designated for the separation of water/organic mixtures by pervaporation and/or direct methanol fuel cell technology was synthesized and analysed by FTIR, DSC, DTG and X-ray diffraction. The polyion complex formation between Ch (cationic polyelectrolyte) and NaAlg (anionic polyelectrolyte) was confirmed by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The state of water in pure polyelectrolytes (PE) and PEC was studied by DSC. Results show that freezable and non-freezable water exist in analysed Ch, NaAlg and Ch/NaAlg hydrogels, while there are variations in the amount of non-freezing bound water in PE/water and PEC/water systems. Both ionic crosslinking as well as physical structure influence the state of water, and especially the non-freezable water content, in ionic hydrogel membranes.