Characterization and performance improvement of tough hydrogels based on cellulose and chitin nanofibers

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Cellulose and chitin exist in nature as highly crystalline nanofibers. First, this study prepared the hydrogels from an aqueous suspension of cellulose nanofibers only by NaOH treatment. The nanofiber suspensions were converted into two kinds of hydrogels with different crystal forms in response to the increasing concentration of 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. However, the hydrogel prepared at 15 wt% NaOH had a network formed by the interdigitation of nanofibers and exhibited a highly crystalline cellulose II structure. This method can be applied to chitin nanofibers. In the case of chitins, the use of ethanol voided the dissolution during neutralization and enabled the preparation of a higher strength hydrogel. These unique hydrogels are expected to further expand the application area of natural polymer hydrogels by capturing the features of crystalline networks.