Heterogeneous deacetylation reaction of chitin under low-frequency ultrasonic irradiation

Low-frequency ultrasonic irradiation was employed as a low cost technique for chitin's deacetylation at a relatively low-temperature range (below 70 °C) and a short reaction times (up to 120 min). Eley-Rideal mechanism and the power-law model were carried out to describe the mechanism of the reaction. The results indicated that the produced chitosan deacetylation degree (DD) was up to 87.73% under the optimum conditions compared to 66.82% using the conventional one (thermo-alkaline process). The Fourier Transform Infrared (FTIR) observations of the produced chitosan presented the same fingerprint as the commercial chitosan, X-Ray Diffraction (XRD), and Differential Scanning Calorimetry (DSC) studies show that the DD induced a lousy impact on the chitosan's thermal degradation and crystallinity index. This work effectively demonstrates that chitin's deacetylation under low-frequency ultrasonic irradiation provides a green process to produce chitosan, and the power-law model, r_DD = k₁(C_R1-NH2)^α; k₁=Aexp-E_aRT, is an excellent model to describe the complex reaction.