Molecular weight and degree of acetylation of high-intensity ultrasonicated chitosan

The influence of high-intensity ultrasonication on the molecular weight and degree of acetylation of chitosan was investigated. High-molecular weight shrimp chitosan was purified by alkaline precipitation and dialysis from aqueous solution. A 1% (w/v) chitosan in 1% (v/v) aqueous acetic acid was sonicated for 0, 0.5, 1, 5, 15, and 30 min at 25 °C at power levels of 16.5, 28.0 and 35.2 W cm−2. Degree of acetylation was determined by high-pressure liquid chromatography with photodiode array at 210 nm, monitoring acetyl groups released after complete hydrolysis and deacetylation of samples. Average molecular weight of ultrasonicated chitosan was determined by measurements of intrinsic viscosity of samples. The degree of acetylation of purified chitosan was 21.5%. Results indicated that neither power level nor sonication time altered the degree of deacetylation of chitosan molecules. Intrinsic viscosity of samples decreased exponentially with increasing sonication time. Rates of intrinsic viscosity decrease increased linearly with ultrasonic intensity. Results were analyzed in terms of molecular weight decreases. The Schmid polymer degradation model was used to analyze the molecular weight decay as a function of sonication time. A first order relationship for the dependence of the reaction rate on the ultrasonic intensity was suggested. Results of this study indicate that high-intensity ultrasonication can be utilized to reduce molecular weight of chitosan while maintaining the degree of acetylation.