Antioxidant-Containing Polymeric Additives for Improved Mechanical Recycling of PET

Functional additives such as antioxidants and chain extenders are important mitigators of the thermo-oxidative degradation that occurs during the high-temperature reprocessing of poly(ethylene terephthalate) (PET), yet leaching of these additives into packaged goods or the environment can pose risks to environmental or human health. In this work, we prepared a series of polymeric antioxidants with molar masses in the range of 3–12 kg/mol by free radical copolymerization of styrene (S) and 2.5–10 mol % of a phenol-containing methacrylate monomer (BHM). These additives were incorporated into PET via extrusion, and we investigated their ability to impart oxidative stability as well as their propensity to leach into solvents of different polarities. Additive performance was benchmarked against that of Irganox 1010, a commercially available phenolic antioxidant, and Joncryl ADR 4400, a polymeric chain extender that rebuilds polymer chains through cross-linking. Extrusion trials revealed similar performance between all polymeric additives and Irganox 1010, whereas oxidative induction time (OIT) tests revealed that the 5–10 mol % incorporation of BHM afforded similar or better performance than Irganox 1010, with little to no dependence on the polymer molar mass. Minimal leaching of the polymeric antioxidants was observed in methanol, whereas experiments in acetone revealed that ca. 3 kg/mol polymers leached between 2 and 5 times more than their ca. 12 kg/mol counterparts across all polymer compositions. This systematic study provides valuable insights for the design of future antioxidants that effectively stabilize recycled plastics without increasing risks to the environment or human health.