Depolymerization of chitosan–metal complexes via a solution plasma technique

Chitosan–metal complexes were depolymerized under acidic conditions using a solution plasma system. Four different types of metal ions, including Ag+, Zn2+, Cu2+, and Fe3+ ions, were added to the chitosan solution at a metal-to-chitosan molar ratio of 1:8. The depolymerization rate was affected by the types of metal ions that form complexes with chitosan. The complexation of chitosan with Cu2+ or Fe3+ ions strongly promoted the depolymerization rate of chitosan using a solution plasma treatment. However, chitosan–Ag+ and chitosan–Zn2+ complexes exhibited no change in the depolymerization rate compared to chitosan. After plasma treatment of the chitosan–metal complexes, the depolymerized chitosan products were separated into water-insoluble and water-soluble fractions. The water-soluble fraction containing low-molecular-weight chitosan was obtained in a yield of less than 57% for the depolymerization of chitosan–Fe3+ complex with the plasma treatment time of 180 min.