Promoting degradation of polyamide-microplastic fibers using hydroxy radical

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 high-performance oxidizing ability in water, allowing MPFs to be degraded in an aqueous environment. Herein, we investigated the degradation of polyamide 6/6 (PA6/6), as a common MPF. Fourier-transform infrared spectroscopy analysis confirmed that the signal of amide bonds (-CONH-) were reduced and new signal of carboxyl groups (-COOH) were formed in the sample after degradation. In addition, gas chromatography-mass spectrometry 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.