Selective Upcycling of Waste PET into Di(2-ethylhexyl) Terephthalate via a Hybrid Organometallic Catalytic Strategy for PVC Plasticizer Applications.

The selective conversion of post-consumer polyethylene terephthalate (PET) into value-added plasticizers offers a promising pathway for advancing polymer circularity within the scope of the circular economy approach. Herein, waste PET bottles were directly upcycled into di(2-ethylhexyl) terephthalate (DOTP) via degradative alcoholysis/transesterification with 2-ethylhexanol using four organometallic catalyst systems: butylstannic acid (F), monobutyltin tris(2-ethylhexanoate) (TK), titanium tetraisopropoxide (T), and a hybrid organotin-titanium system (TKT). PET conversion ranged from 84 to 94%, with the T catalyst affording the highest conversion (94%). Notably, the hybrid TKT catalyst provided the most favorable overall performance, achieving an 81% isolated yield and 85.4% selectivity. GC-FID analysis revealed that DOTP-TKT achieved a 92.0% chromatographic area, while GPC confirmed that this product had the lowest proportion of residual oligomers (15.13%) among all PET-derived samples. FTIR and 1H-NMR spectroscopy further confirmed efficient PET-to-DOTP transformation, with DOTP-TKT displaying the closest structural correspondence to commercial DOTP. Amongst the PET-derived products, DOTP-TKT exhibited the most favorable thermal behavior, with a principal maximum degradation temperature (Tmax) of approximately 283.5 °C. When incorporated into PVC, PET-derived DOTP-TKT showed enhanced tensile strength, elastic modulus, and elongation at break compared with commercial DOTP. These findings demonstrate that the combined Ti-Sn catalyst system simultaneously promotes selective PET depolymerization and product formation while limiting oligomeric residues, providing an effective route for converting post-consumer PET into functional, high-value PVC plasticizers within a circular polymer economy.