Enhanced Dissolution of Chitin Using Acidic Deep Eutectic Solvents: A Sustainable and Simple Approach to Extract Chitin from Crayfish shell Wastes as Alternative Feedstocks

Chitin is a natural biomass resource with high potential for a wide variety of applications. However, it remains poorly explored because of its solubility issues. In this work, a large range of acidic deep eutectic solvents (aDESs), combining different hydrogen bond acceptors [betaine (Bet), urea (U), and cholinium chloride (CC)] and hydrogen bond donors [formic acid (FA), acetic acid (AA) propanoic acid (PA), and lactic acid (LA)], were investigated. First, the ability of the aDESs to dissolve commercial chitin was compared and then, based on the solubility data obtained, the most efficient aDESs were chosen to extract chitin directly from red crayfish shell wastes. Considering that up to 10 wt % of commercial chitin was dissolved in the aDES CC:LA 1:2 and Bet:LA 1:2, these were further applied to extract chitin from crayfish shell wastes. Using these aDES as solvents, a high-quality chitin was obtained with a crystallinity index >80%, and a degree of acetylation >90%. The findings demonstrated the suitability of aDESs to enhance dissolution and hence to efficiently extract chitin from different raw biomass without compromising the polymer structural integrity.