Highly effective preparation of low molecular weight chitosan by enhanced chemical degradation applying high gravity technology

Abstract

To effectively prepare value-added low molecular weight chitosan with improved molecular weight uniformity, a novel high-gravity reactor—the Rotating Foam Stirrer Reactor (RFSR)—is proposed to enhance the chemical degradation process of chitosan. The study reveals that the combined H₂O₂-Vc degradant significantly increases degradation efficiency compared to H₂O₂ or Vc alone, attributed to synergistic effects in hydroxyl radical production. Specifically, the degradation efficiency of the H₂O₂-Vc combination increased by 56.41 % and 32.88 %, respectively, within 5 min. Increased rotational speed improves degradation efficiency and narrows the molecular weight distribution, particularly at higher chitosan concentrations. The weight-average molecular weight rapidly decreases within the first 30 min and then stabilizes, while maintaining a more uniform distribution. Positioning the degradant feed at the stirrer's outer edge further enhances degradation. The RFSR outperforms traditional reactors, producing chitosan with lower molecular weight and better uniformity. Additionally, a predictive correlation for the reaction rate constant, incorporating mass transfer effects, shows good agreement with experimental results, with an error margin of approximately ±20 %, supporting large-scale industrial applications in polysaccharide degradation.