Stability assessment of a commercial polypropylene copolymer and Irgafos 168 under repeated injection molding and γ‐irradiation cycles

Abstract

Despite the increasing importance of recycling, the medical sector is hardy engaged at this time due to regulatory issues. The aim of this study was to evaluate the influence of γ‐radiation sterilization (48–52 kGy) on the repetitive injection molding of a polypropylene copolymer for medical applications. For this purpose, the material was analyzed after injection molding and irradiation. To evaluate the irradiation and reprocessing influence, optical, rheological, and mechanical properties were investigated in addition to chromatography. The latter comprised the quantitative determination of Irgafos 168 and the qualitative comparison of volatile degradation products formed, including the radiolysis product 1,3‐di‐tert‐butylbenzene. The influence of irradiation on the content of Irgafos 168, volatile organic compounds, and 1,3‐di‐tert‐butylbenzene was greatest after the first irradiation, with a decrease of Irgafos 168 content by 40%. The yellowness index and melting enthalpy were influenced by irradiation and processing, but showed no direct relationship to the individual process steps. The zero viscosity correlated directly with gas chromatography–mass spectrometry results and decreased by 80% after the first irradiation. In addition, the elongation at break was reduced by 95% after the second irradiation. The influence of irradiation on the studied characteristics was high, whereas the influence of repetitive processing did not show any measurable differences