Promoting Degradation of Polyamide-Microplastic Fibers Using Hydroxy Radical Generated by Electrochemical Advanced Oxidation Processes

Microplastic fibers (MPFs) generated by washing textile products made of synthetic fibers cannot be removed at sewage treatment plants and are released into rivers and oceans. In this study, we proposed using hydroxy radical (•OH) to degrade MPF. •OH exhibits strong oxidizing ability, allowing MPFs to be degraded. Herein, electrochemical advanced oxidation processes, which combines electrochemical oxygen reduction in water and UV irradiation, was used to generate •OH. In this paper, we investigated the degradation of polyamide 6/6 (PA6/6), as a common MPF. After 120 h degradation process, the sample thickness and fiber diameter decreased 32.0% and 13.7% respectively. After only 12 h, the sample toughness decreased 78.9%. Infrared spectroscopy confirmed that the signal of amide bonds (–CONH–) were reduced and new signal of carboxyl groups (–COOH) were formed in the sample after degradation. Gas chromatography confirmed that several short-chain amide compounds were released into the degraded solution. These results suggest that the amide bonds in the PA6/6 molecular structure are cleaved by the •OH, thereby accelerating the degradation of PA6/6. The proposed degradation method achieved a much faster degradation rate than other methods using microorganisms, and is expected to be a novel MPF degradation method.