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.