Thermal, mechanical, and dielectric properties of radiation sterilized mesomorphic PP: Comparison between gamma and electron beam irradiation modalities

Polypropylene (PP) is widely used in the medical industry to produce syringes, vials, and numerous other singleuse biopharmaceutical devices. The need to sterilize these products has led to intensive use of high-energy radiation, even though PP is known to undergo excessive oxidative degradation and deterioration in properties upon irradiation in air. In recent years, a shortage in 60Co supply, as a main source for gamma sterilization, is pushing radiation sterilization of polymeric medical products to electron beam (EB) and/or X-ray modalities as preferable. Some questions related to the equivalence of these methods remain open and are mostly related to changes in the material structure caused by different types of radiation and processing conditions, such as dose rates. This research compares electron beam and gamma irradiation modalities employed on the low crystalline (quenched) PP. In the case of EB irradiation, the typical dose rates are on the order of 104 kGy/h, while in the case of gamma radiation dose rates are lower for three or more orders of magnitude. Since gamma irradiation covers a wide range of dose rates, the difference between samples gamma irradiated with relatively fast (8 kGy/ h) and slow (0.08 kGy/h) dose rates was also analyzed in detail. Comparative investigation of crystallinity, oxidative degradation, thermal, dielectric, and mechanical properties provide a clearer picture of the impact of different modalities and dose rates on mesomorphic PP and are of interest in the practical application of ionizing radiation in the sterilization of PP-based medical devices.