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(+), Zn(2+), Cu(2+), and Fe(3+) 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 Cu(2+) or Fe(3+) ions strongly promoted the depolymerization rate of chitosan using a solution plasma treatment. However, chitosan-Ag(+) and chitosan-Zn(2+) 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-Fe(3+) complex with the plasma treatment time of 180 min.