Effects of gamma radiation on cyclic olefin copolymers with varied norbornene content: Impacts on structure and properties at sterilization doses

Cyclic olefin copolymer (COC) is a transparent amorphous plastic known for its chemically inertness, biocompatibility, low density, and easy processability. These qualities have led to its widespread adoption in various cutting-edge applications, including the medical, packaging, optical and microelectronics. Radiation sterilization, utilizing high-energy irradiation, is a method for achieving highly effective sterilization of medical products. However, this process can induce changes in the color and properties of the COC materials. In order to comprehend the effects of ionizing radiation on COC, it is crucial to investigate the underlying reaction mechanisms. In this work, the effects of gamma-ray irradiation on COC with different norbornene contents were examined. The finding revealed that tertiary alkyl radical content and the degree of oxidative degradation increased with an increase in norbornene content. Furthermore, the macroscopic properties experienced notable shifts, including decreased thermal stability, lower glass transition temperature and the change in color from colorless and transparent to yellow-green . Analysis of the melt index indicated a dominance of cross-linking phenomena with increased absorbed dose for COC with a norbornene content of 35%, while the melt flow rate steadily accelerated with the increase of absorbed dose for COC with norbornene content of 46%, 52% and 57%, leading to a predominant cracking behavior. The variation in tensile properties of the four COCs before and after irradiation were minimal, not exceeding 3%. Overall, this investigation sheds light on the intricate effects of ionizing radiation on COC and highlights the importance of understanding these mechanisms for practical applications.