Selective hydrophilization based on alkaline-catalyzed alcoholysis: An approach to enhance the flotation of waste polyesters

Polyester plastics, constituting a substantial segment of the global plastic market, offer considerable potential market for the polyesters recycling. This study proposed an efficient separation technology for waste polyesters through flotation assisted by alkaline-catalyzed alcoholysis modification. The alkaline-catalyzed alcoholysis modification facilitates the selective hydrophilization of waste polyesters, regulating their float-sink behavior in flotation. According to the polyester floatability, the hydrophilicity of the modified polyesters is in order of PA6 > PET ≈ PU > PC > PMMA. Due to the different C–O and C–N bond strength, the modification selectively induced alcoholysis on the polyesters surface, enhancing their hydrophilicity by increasing the number of rough structure and hydrophilic functional groups on surfaces rather than introducing heteroatoms. The sinking products in flotation, including polyamide 6 (PA6), polyethylene terephthalate (PET), and polyurethane (PU), could be separated from the floating products, such as polycarbonate (PC), and polymethyl methacrylate (PMMA). The binary separation was achieved under optimum conditions. The recovery and purity of PA6, PET, and PU could reach 100.0 % and 100.0 %, 100.0 % and 85.7 %, 79.9 % and 83.1 %, respectively. Consequently, the heterogeneous alcoholysis reactivity contributes to the selective hydrophilization of waste polyesters. This study established a hydrophilicity order of modified polyesters, and promoted flotation separation of waste polyesters.