Thermally Resilient Polymeric Antioxidants that Improve PET Stabilization with Reduced Additive Leaching

Abstract

Antioxidants are incorporated into plastics to enhance their resistance to oxidative degradation. With rising concerns of leaching of additives and/or their degradation products into packaged goods and the environment, the development of antioxidants that maintain function while mitigating leaching is an important step for a sustainable plastics industry. In this work, we developed a suite of phenol-containing polymeric antioxidants and incorporated them into PET via twin-screw extrusion to investigate their performance against a commercial small-molecule phenolic antioxidant, Irganox 1010. The antioxidants were generated via uncontrolled free-radical copolymerization of styrene (S) with 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propyl methacrylate (BHPM). PS/BHPM copolymer size and composition were systematically varied, targeting 10 or 30 mol % BHPM and M_n values between 7–20 kg/mol. Thermogravimetric analyses revealed size- and composition-dependent T_d,5% values in the range of 340–359 °C, significantly higher than that of Irganox 1010. PET extrudates with PS/BHPM demonstrated better antioxidant performance (i.e., higher oxidative induction times, OITs) and drastically less leaching than PET extrudates with Irganox 1010. Size and composition trends emphasized a trade-off between OIT enhancement and mitigation of leaching (e.g., higher additive M_n resulted in less leaching but lower OITs). Extrudate discoloration was quantified via yellowness index (YI), revealing a minor composition trend and overall comparable or lower discoloration than Irganox 1010. These PS/BHPM copolymers outperform our first-generation additives, demonstrating that chemical structure is key to optimizing performance (OIT, YI, and leaching potential) and showing the importance of careful additive design for future plastic formulations.