Interactive Effects of Antioxidants, Acid Scavengers, and HALS on the Material Properties of Polypropylene Copolymer Considering γ‐Radiation Sterilization and Recycling for Medical Devices

Global plastic production and consumption have risen continuously over past decades, increasing the need for sustainable end‐of‐life strategies. The present study provides a systematic assessment of how repeated processing and γ‐irradiation affect the stability, additive consumption, and performance of polypropylene copolymers (PP‐C) intended for closed‐loop recycling in medical technology. Applying a design of experiments approach with Irganox 1010, Irgafos 168, Tinuvin 622, and calcium stearate (CaSt), the results identify γ‐irradiation as the dominant factor dominating additive depletion, molecular degradation, and optical aging. Phenolic and phosphite antioxidants were rapidly consumed after irradiation, frequently falling below quantifiable levels, whereas processing alone caused only moderate degradation. Pronounced synergistic interactions between Irganox 1010 and Irgafos 168 were confirmed, particularly in combination with CaSt, enabling both stabilizers to remain effective over multiple cycles. Tinuvin 622 exhibited fluctuating behavior consistent with regeneration mechanisms associated with the Denisov cycle. Changes in yellowness, tensile properties, and zero shear viscosity further demonstrate that irradiation, rather than mechanical recycling, drives deterioration and rheological instability. These findings underline that successful recycling of γ‐sterilized PP‐C requires tailored additive systems and highlight stabilizer engineering as a key factor for ensuring material safety, performance, and sustainability in circular medical plastics.