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

纤维素和甲壳素在自然界中以高度结晶的纳米纤维的形式存在。首先，本研究仅通过NaOH处理从纤维素纳米纤维的水悬浮液中制备了水凝胶。随着NaOH浓度的增加，纳米纤维悬浮液转变为两种不同晶型的水凝胶。当在6-9wt%NaOH中处理时，纳米纤维以原始的形貌和原始的晶型聚集在一起形成水凝胶。然而，在15wt%NaOH下制备的水凝胶具有由纳米纤维交错形成的网络结构，并显示出高度结晶的纤维素II结构。该方法可应用于甲壳素纳米纤维的制备。在几丁质的情况下，使用乙醇消除了中和过程中的溶解，并能够制备出更高强度的水凝胶。这些独特的水凝胶通过捕捉结晶网络的特征，有望进一步扩大天然聚合物水凝胶的应用领域。

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.