Recyclable Universal Solvents for Chitin to Chitosan with Various Degrees of Acetylation and Construction of Robust Hydrogels

Chitin and chitosan are enticing natural polymers derived from seafood wastes, and their applications mostly depend on the degree of acetylation (DA). For their efficient utilization, a series of universal solvents for the direct dissolution from chitin to chitosan with various DA ranged from 5 to 94% were designed, and robust hydrogels were constructed from their solution via a physical regeneration, for the first time. The NMR results demonstrated that K+ of KOH interacted easily with C═O group to break the NH...O═C intermolecular hydrogen bonds of chitin, whereas Li+ of LiOH could bound with NH2 group to promote the destruction of NH...O6 hydrogen bonds of chitosan. Thus, a series of LiOH/KOH/urea aqueous solutions with weight ratios of LiOH to KOH from 0 to 2.5 were developed to directly dissolve these biomacromolecules with DAs ranging from 5 to 94%. Subsequently, a series of coagulants were also exploited for the regeneration of these chitin/chitosan solutions to construct the robust hydrogels with ...