How the Interplay of Accelerated Aging and Sterilization by γ ‐Irradiation Influences the Recyclability of Medical Polypropylene Copolymer

Recycling of medical‐grade plastics remains challenging due to stringent quality and safety requirements. We investigated the combined effects of two injection molding/ γ ‐irradiation (25 kGy) cycles and accelerated aging simulating 1 year of service life on two compounds consisting of isotactic polypropylene copolymer containing less than 10 mol‐% ethylene (PP‐C) and different stabilizer compositions. One composition comprised the primary antioxidant Irganox 1010 (I1010), the secondary antioxidant Irgafos 168 (I168), the radiation stabilizer Tinuvin 622 (T622), and calcium stearate (CaSt) as acid scavenger, while the second composition was lacking I1010. For comparison, both compounds were subjected to the same treatments without γ ‐irradiation. We analyzed additive consumption, radiolysis product formation, molar mass evolution, rheological behavior, and crystallinity. High‐performance liquid chromatography (HPLC) and gas chromatography combined with mass spectrometry (GC–MS) revealed pronounced degradation of I1010 and I168, particularly after γ ‐irradiation. The presence of I1010 mitigated the depletion of I168, indicating synergistic stabilization. The radiolysis product 1,3‐di‐tert‐butylbenzene (DTBB) formed upon γ ‐irradiation, confirming additive decomposition. Gel permeation chromatography (GPC) and oscillatory rheometry showed a reduction in PP‐C molar mass and zero‐shear viscosity reflecting chain scission. The slope of the relation of the PP‐C radius of gyration and its molar mass M indicated that γ ‐irradiation primarily induced long chain branching in the absence of I1010. In contrast, X‐ray diffraction (XRD) revealed only minor changes in crystallinity, suggesting that the crystalline phase remained largely unaffected by the irradiation and injection molding history. Overall, irradiation effects exceeded those of reprocessing and accelerated aging, indicating that sterilization crucially impacts recyclability of PP‐C in medical products.