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Zinc {ONO} complexes for the chemical recycling of PET and PLA
Summary
Researchers synthesized zinc complexes with tridentate ONO ligands and demonstrated their effectiveness in chemically recycling both PLA and PET waste plastics into valuable monomers like methyl lactate and BHET. The most active catalyst achieved sequential PLA and PET degradation under mild conditions while tolerating common plastic contaminants like HDPE and PVC, making it a promising tool for mixed-plastic recycling.
Nine {ONO} ligands were prepared and treated with ZnEt 2 to form a range of complexes. The resulting complexes were characterised in solution through 1 H and 13 C{ 1 H} NMR spectroscopy, and in the solid state through single-crystal XRD and elemental analysis. Moderate reactivity towards lactide polymerisation was demonstrated, with hydroxyl complexes reaching high conversion in 1–2 minutes at 300: 1: 1. All complexes successfully degraded PLA to methyl lactate and the effect of reaction time, temperature and catalyst loading was explored. Zn( 4 ) 2 successfully produced ethyl and n-butyl lactate and was shown to work in ambient conditions, albeit with reduced yield and selectivity. The production of BHET from waste PET was demonstrated with a selection of the most active catalysts. Zn( 4 ) 2 was shown to be capable of sequential PLA/PET degradation and to be tolerant of HDPE/PVC contaminants. • Characterisation of zinc complexes by NMR and crystallography. • Zinc complexes effective for chemical recycling of commodity polyesters. • Inert hydrocarbon polymers not affected by reaction. • Selective and sequential chemical recycling demonstrated.