Distinctive Viewpoint on the Rapid Dissolution Mechanism of α‑Chitin in Aqueous Potassium Hydroxide–Urea Solution at Low Temperatures

To develop a green solvent for chitin dissolution, the most fundamental aspects of its mechanism must be elucidated. In this work, an aqueous KOH/urea solution was utilized for the rapid dissolution of α-chitin without performing freeze–thaw cycles. It was found that the mechanism of α-chitin dissolution involved not only the fast expansion of its crystalline regions and hierarchical structure but also direct and strong interactions between K⁺ ions and chitin carbonyl oxygens. The relatively high flexibility and deformability of the K⁺ hydration shells allowed fast exchange between water molecules and carbonyl oxygens, which induced the cleavage of strong inter- and intramolecular hydrogen bonds, resulting in the rapid swelling and destruction of the chitin crystal and dissolution of α-chitin. Moreover, the additional urea mitigated the hydrophobicity of chitin chains, which prevented self-aggregation and increased the mobility of chitin chains. The described α-chitin dissolution mechanism can help achieve a better understanding of biomacromolecule dissolution.