Exposition of Radiation‐Stabilized Polypropylene Copolymer to Repeated Injection Molding and <i>γ</i> ‐Radiation

ABSTRACT High‐quality requirements for plastic components in healthcare limit their recyclability. This study examined the stability of a representative polypropylene copolymer (PP‐C) containing Tinuvin 622 (T622) as a light stabilizer and calcium stearate (CaSt) as an acid scavenger during successive recycling steps involving γ ‐irradiation, mimicking medical sterilization. Chemical, thermal, rheological and mechanical properties of PP‐C were analyzed throughout various recycling stages. Differential scanning calorimetry and x‐ray scattering revealed little impact of γ ‐irradiation on crystallinity and polymorph formation. The influence of γ ‐irradiation on the chemical and mechanical properties of the PP‐C specimens was large compared to the processing‐related changes to the material properties. T622 content decreased by 22% after four cycles involving γ ‐irradiation, while the formation of volatile substances increased substantially. Zero‐shear viscosity dropped by 80%, indicating a corresponding decrease in molecular weight. Elongation at break increased with each cycle without γ ‐irradiation and decreased with γ ‐irradiation. Since elongation at break did not drop below critical levels, molecular weight likely remained above the threshold for maintaining the required mechanical properties. The decisive influence of γ ‐irradiation over processing effects suggests that although performance declines with γ ‐irradiation, PP‐C retains sufficient stability. These findings support the feasibility of recycling PP‐C for healthcare applications under the conditions considered.