Upcycling of polyethylene waste to biodegradable polyesters via oxidative conversion

Converting waste polyethylene into valuable monomer compounds represents an ideal strategy to mitigate the accumulation of plastic waste. However, the chemical stability of the C–C backbone poses a formidable challenge for chain scission—state-of-the-art technologies are confined to specific polymers and lack practical utility. In this work, we used low-concentration nitric acid as an oxidant to convert low-density polyethylene (LDPE) waste into high-value-added dicarboxylic acids using a one-step hydrothermal method and used it for novel polyester synthesis. The degradation mechanism under nitric acid oxidation was systematically investigated by multiple characterization techniques. Under the conditions of 160°C and 0.20 g/mL nitric acid concentration with a 5 h, dicarboxylic acid was obtained with a high yield of 93% and a carbon yield of 37%. The resulting product was subsequently subjected to ring-opening polymerization with epoxy resin monomers, including the structurally rigid bisphenol A diglycidyl ether (DGEBA) and the flexible aliphatic polyethylene glycol diglycidyl ether (DGEG), yielding a novel degradable polymer with tailorable rigidity-flexibility properties. Systematic variation of the DGEBA:DGEG molar ratio from 1:1 to 9:1 produced corresponding changes in mechanical properties, with tensile strength increasing from 1.37 MPa to 24.69 MPa and elongation at break decreasing from 864.90% to 28.48%. This study breaks the exclusive dependence of polyester synthesis on petrochemical-based monomers. By partially replacing petrochemical monomers with those derived from waste polyethylene, it realizes the leap of waste polyolefin resources from low-level recycling to high-value feedstock utilization.