Formation of hydrogels from cellulose nanofibers

We report the preparation of hydrogels from an aqueous suspension of crystalline cellulose nanofibers only by alkaline treatment. The nanofiber suspensions were converted into two kinds of hydrogels with different crystal forms in response to the increasing concentration of sodium hydroxide (NaOH). When treated in 6–9 wt% NaOH, a hydrogel was formed by aggregating the nanofibers with the original morphology and the original crystal form, cellulose I. However, the hydrogel prepared at 15 wt% NaOH had a network formed by the coalescence of cellulose nanofibers and exhibited a highly crystalline cellulose II structure. This gelation process seems to be caused by the axial shrinkage of the cellulose nanofibers in aqueous alkaline solutions.