A comparative study on heterogeneous deacetylation of chitin to chitosan under various ultrasound irradiation and characterization

Chitosan, a semi-synthetic polymer derived from the deacetylation of chitin, is a basic polysaccharide widely applied in biomedicine, packaging, and environmental fields. To improve the inefficiency of the conventional heterogeneous deacetylation method relying on prolonged heating under alkaline circumstances, ultrasound-assisted approaches, such as low-frequency probe or ultrasound baths, have been explored as a novel technologies. This study innovatively explores various ultrasound systems as alternative strategies to assist rapid and efficient chitin deacetylation. Different ultrasound set-ups were systematically compared under standardized treatments: low-frequency ultrasound probe (US-L), high-frequency ultrasound plate (US-H), and ultrasound-microwave combination reactor (US-MW) with further structure analysis. Results showed that US-H and US-MW successfully achieved effective deacetylation under the bi-functioning of cavitation and heat effect, while US-L exhibited limited deacetylation performance. Further structural and functional characteristics of the chitosan analogues were confirmed through FTIR, XRD, SEM, TGA-DSC, and HP-SEC, demonstrating a comparable structure of chitosan analogues obtained by US-H and US-MW to conventional deacetylation (CVN), with deacetylation duration significantly reduced from 3 h to 15 min. This work provides foundational insights into potentially scalable and efficient chitosan production, highlighting the potential of US-H and US-MW in sustainable biopolymer manufacturing.