Structure and properties of hydrogels prepared from cellulose in NaOH/urea aqueous solutions

Hydrogels have been successfully prepared from cellulose in NaOH/urea aqueous solution by using epichlorohydrin (ECH) as a cross-linker, and via heating and freezing methods. Structure and properties of the hydrogels were measured with UV–vis spectroscopy, SEM, XRD, solid-state 13C NMR, rheometry and water absorption testing. The results indicated that hydrogels prepared by heating displayed macroporous inner structure, while fiber-like structure could be observed in the hydrogels prepared by freezing. The light transparency and equilibrium swelling ratio of the hydrogels decreased, while the reswelling water uptake and the storage modulus increased, with an increase of the cellulose content. Compared with the hydrogels post-treated by freezing, the hydrogels prepared by heating displayed better light transmittance, higher equilibrium swelling ratios and reswelling water uptakes, and relatively weaker mechanical strength. Therefore, the structure and properties of the hydrogels could be adjusted by changing the cellulose content and the post-treatment methods.