Microplastic Separation via Interfacial Trapping in Aqueous Multiphase Systems

Microplastics are distributed in environmental matrices but their separation remains challenging because samples contain particles with different polymer types, sizes, shapes, densities, and surface properties. Conventional flotation and filtration can recover plastics from mixed streams, yet their selectivity is limited for particles with similar physical characteristics. Therefore, a separation medium that uses tunable liquid–liquid interfaces as trapping sites is needed. In this study, aqueous multiphase systems (AMPSs), formed from mutually immiscible polymer aqueous solutions, are investigated for microplastic separation. In AMPSs, multiple polymer-containing aqueous phases coexist, and the interfaces between phases can be controlled by polymer composition and concentration. This interfacial concept is first examined in a PEG/Dextran system using polystyrene particles as model microplastics. Under designed phase-density conditions, the particles localize at the PEG-rich/Dextran-rich interface rather than remaining in either phase, indicating that the interface serves as a trapping region. The same interfacial trapping behavior is further evaluated using irregular commercial plastic fragments, which also accumulate at the interface and support the applicability of the system beyond ideal spherical particles. To expand the separation range, AMPSs are formulated from multiple immiscible polymer aqueous solutions, allowing phase-density gradients with fine intervals. Density differences on the order of 0.01 g cm⁻³ can be introduced, allowing plastic particles to occupy designed positions within the multiphase structure. These results suggest that polymer-solution-based AMPSs provide a tunable aqueous platform for microplastic separation through controlled interfacial trapping under aqueous conditions.
This research was supported by the Korea Environmental Industry & Technology Institute (KEITI) funded by the Ministry of Climate, Energy and Environment.