Cold plasma-assisted degradation of melamine-resin microplastics: A multiscale analysis of fragmentation and morphological evolution

Microplastics, particularly melamine-resin polymers, are emerging environmental contaminants with high persistence and potential toxicity. Conventional degradation methods are often inefficient in fully breaking down stable carbon backbones of such polymers. Cold plasma technology has recently attracted attention as a non-thermal advanced oxidation process capable of generating highly reactive species under ambient conditions. This study aims to investigate the degradation behavior of melamine-resin microplastics under cold plasma treatment and to characterize the structural transformations, fragmentation dynamics, and degradation efficiency over time. A custom-built cold plasma reactor operating at 10 kV and 3 A was used to treat aqueous suspensions of melamine resin microparticles (2 µm). The plasma reactor enabled gas-liquid phase interactions, enhancing the generation of oxidative species. The degradation process was assessed at different exposure times (5, 20 and 30 min). Structural and morphological changes were analyzed using Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), zeta potential measurements, turbidity analysis, and gravimetric mass loss. Cold plasma treatment induced a progressive reduction in particle size from 2004 ± 93 nm to 119 ± 47 nm after 30 min, accompanied by a 43 % weight loss and increased turbidity (from 2.06 NTU to 7.22 NTU), indicating significant fragmentation. TEM images confirmed morphological transformation from smooth spherical particles to irregular, porous, nano-sized fragments (68–119 nm). Oxidative degradation pathways are attributed to interactions with reactive oxygen species such as •OH, O₃, and H₂O₂ generated within the plasma zone. Cold plasma demonstrates high efficiency in degrading melamine-resin microplastics through advanced oxidative mechanisms, leading to significant fragmentation and nanostructural disruption. The findings support the use of cold plasma as a sustainable and effective method for the remediation of microplastic-contaminated water and offer insights into degradation kinetics and mechanisms of polymer breakdown under plasma exposure.