Enhanced density separation efficiency of microplastics in presence of nonionic surfactants

Microplastics (MPs) recycling, a promising approach to tackle its pollution, faces significant challenges due to the lack of effective separation methods. Herein, the optimized density separation accompanied with nonionic surfactants was employed to purify single MPs species from mixed systems. By adjusting the flotation fluid density, the single MPs can be separated from their mixtures in equal proportions (e.x., 97 ± 2% pure polyethylene terephthalate (PET) was extracted from polystyrene (PS)/PET mixed system). Under the optimized density separation conditions, nonionic surfactants of Tween 20 (TW20) enhanced the purity of the separated MPs for all MPs mixture systems (from 69%-85% to 76%-96%). The enhanced separations can be mainly attributed to adsorption of surfactant onto the surface of MPs which would alter hydrophilic and hydrophobic properties of MPs. But anionic surfactants could reduce or promote the separated efficiencies of MPs (e.x., the purity of separated polyvinylchloride increased by 4.8% in Thermoplastic polyurethanes/polyvinylchloride group by added sodium dodecyl benzene sulfonate, and the purity of PS decreased by 8.3% in PS/PET group in presence of hexadecyl trimethyl ammonium bromide). The efficient separations have also been obtained in simulated environmental aqueous experiments where TW20 promoted the separated purity of PET from 83.4% to 91.8% in the PS/PET group, consistent with the separation effect in the laboratory environment. This paper provided a convenient and cost-effective method to separate mixed MPs to high-purity MPs, which would be improve the quality of plastic recycling.