Preparation and characterization of hydrogels obtained from chitosan and carboxymethyl chitosan

Chitosan and carboxymethyl chitosan-based hydrogels were prepared by crosslinking the biobased polymers with hexamethylene diisocyanate (HDI). The hydrogels were obtained in a simple one-pot route, using water as solvent, at room temperature and without the use of other additives. The obtained materials were characterized using Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TG/DTG), X-ray diffraction (XRD), elemental analysis (CHN) and scanning electron microscopy (SEM) techniques. The water absorption capacity and absorption kinetics were also studied at different pH values. The comparison between the hydrogels obtained from the different biopolymers showed remarkable differences including water absorption capacity (swelling ratio) which is up to ~ 15 for the chitosan-based hydrogel and reached ~ 64 for the carboxymethyl chitosan-based hydrogel. In addition, the morphologies obtained for each sample were also considerably different. The chitosan-based hydrogels did not present pores before the swelling process, and after that, only the presence of a heterogeneous pores structure was observed. On the other hand, for the CMC-based hydrogels a homogeneous porous structure was noticed before and after the swelling process, and a significant increase in pore size was observed after water absorption. Since the two kinds of hydrogels obtained here were prepared through an easy and efficient route, using water as solvent and present potential biodegradability, simultaneously with a good swelling capacity, particularly for the CMC-based hydrogels, the obtained materials can find application in different areas such as agricultural or biomedical.