Catalyst-Free Upcycling of Polyethylene Waste Into Oxidized Polyethylene Wax

Polyethylene (PE) accounts for 36% of the total plastic waste by mass. However, its inherent chemical stability poses significant challenges for chemical recycling, including energy-intensive processing, costly catalysts, and thermodynamic constraints that result in low-value hydrocarbon products. Herein, we present a catalyst-free, one-pot hydrothermal oxidation strategy for the efficient upcycling of waste PE into high-value oxidized polyethylene wax (OPEW). Notably, under optimized conditions (160°C, 1.5 MPa O₂), low-density polyethylene (LDPE, 1.0 g) is converted to OPEW within 0.5 h, achieving an OPEW/PE mass ratio of 103.3% and a carbon yield of 99.8%. The resulting OPEW exhibits a tunable acid number (20-70 mg KOH/g) and saponification number (5-80 mg KOH/g), covering industrial specifications for commercial wax products. Mechanistic studies reveal that the superoxide radical (·O₂ ^-) plays a key role in mediating the reaction. Furthermore, 30-fold scale-up trials and successful application to various types of PE waste feedstocks demonstrate the great potential of this methodology for industrial viability. This strategy establishes a sustainable, catalyst-free pathway for upcycling plastic waste into functional materials.