Surface alcoholysis induced by alkali-activation ethanol: A novel scheme for binary flotation of polyethylene terephthalate from other plastics

Although waste plastic was defined as potential resources, heterogeneous components and low separation efficiency severely blocked plastic recycling. Based on polyesters alcoholysis, we proposed a novel surface modification process with ethanol solution and sodium hydroxide (NaOH) catalyst to assist the flotation separation of waste plastics. After surface alcoholysis, hydrophilic polyethylene terephthalate (PET), as a sinking product, was separated from the floating plastics of hydrophobic polystyrene (PS), polyvinyl chloride (PVC), and polymethyl methacrylate (PMMA). The recovery and purity of PET reached ca. 100% under optimal conditions. Then, we systematically illuminated the hydrophilization mechanism and established surface reactions for PET plastics with the aid of scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS). Exposed moieties containing oxygenated groups devoted a hydrophilic surface to PET plastics when some immobilizing segments were substituted with ethanol after surface alcoholysis. A layer of water film dissociated the hydrophilic PET surface from air bubbles, endowing its different trajectory from other hydrophobic plastics in flotation. To our knowledge, this study first proposed alkali-activation ethanol for the wettability regulation and flotation separation of plastic mixtures. Surface alcoholysis without metal and heteroatom contaminants can enrich modification operation, promote plastic flotation, and improve the recycling of waste plastics.

Automated summary

The study introduced a novel surface modification process with ethanol solution and NaOH catalyst for flotation separation of waste plastics, achieving a recovery and purity of PET of approximately 100%. The hydrophilization mechanism was systematically illuminated and surface reactions for PET plastics were established using various analytical techniques.