Extraction, characterization, and kinetics of N-deacetylation of chitin obtained from mud crab shells

This study focuses on the isolation, chemical and crystalline structures, and the kinetics of heterogeneous deacetylation of chitin from mud crab shells (Scylla serrata). The independent variables in this work are temperature, NaOH concentration, and reaction time. The degree of deacetylation (DD) of the resulting chitosan was determined for different reaction times. It was found that the DD increases nonlinearly with the reaction time. The deacetylation of the chitin followed pseudo first-order kinetics and it occurred in two stages, which are respectively attributed to the reaction of acetamide groups in the amorphous region on the external layer, and in the crystalline region inside the chitin particles. The rate constants for the latter stage of the deacetylation at 35°C, 75°C, and 105°C were 4.67×10⁻⁴ min⁻¹, 3.00×10⁻³ min⁻¹, and 4.61×10⁻³ min⁻¹, respectively. Based on this temperature-dependent rate constant, the activation energy of the slow deacetylation stage was estimated to be 32.6 kJ mol⁻¹.