Effects of freezing on the condensed state structure of chitin in alkaline solution

Chitin powder was soaked in concentrated sodium hydroxide solution (45%, w/w), and freezed at −18/−35 °C for further modification (the ratio of chitin and sodium hydroxide solution was 1:10, w/v). The degree of deacetylation (DDA) was determined by acid–base titration while the structural changes of the regenerated chitin after alkali-freezing treatment were investigated by X-ray diffraction (XRD), infrared spectroscopy (IR) and differential scanning calorimetry (DSC). The results showed that the formation and growth of ice crystal during the slowly freezing process could break the intra- and inter-molecular hydrogen bonds, disorganize the ordered molecular structure, destruct the compact crystal structure and decline the crystallinity. However, such structural damage was unstable and reversible. Nevertheless, the study explained that the alkali-freezing treatment was beneficial for further modification of chitin, which could significantly promote its solubility and accelerate the chemical reaction rate, while it could also keep its main molecular chains completely.