Radical adducts formation mechanism of CHCO∙ and CHCO∙ realized decomposition of chitosan by plasma catalyzed peracetic acid.

High-molecular-weight chitosan has limited applications due to unsatisfactory solubility and hydrophilicity. Discharge plasma coupled with peracetic acid (PAA) oxidation ("plasma+PAA") realized fast depolymerization of high-molecular-weight chitosan in this study. The molecular weight of chitosan rapidly declined to 81.1 kDa from initial 682.5 kDa within 60 s of "plasma+PAA" treatment, and its reaction rate constant was 12-fold higher than single plasma oxidation. Compared with O, ∙CH, CHO·, and O∙, CHCO∙ and CHCO∙ played decisive roles in the chitosan depolymerization in the plasma+PAA system through mechanisms of radical adduct formation. The attacks of CHCO∙ and CHCO∙ destroyed the β-(1,4) glycosidic bonds and hydrogen bonds of chitosan, leading to generation of low-molecular-weight chitosan; the main chain structure of chitosan was not changed during the depolymerization process. Furthermore, the generated low-molecular-weight chitosan exhibited greater antioxidant activities than original chitosan. Overall, this study revealed the radical adduct formation mechanisms of CHCO∙ and CHCO∙ for chitosan decomposition, providing an alternative for fast depolymerization of high-molecular-weight chitosan.