Ageing of radiation-sterilized polypropylene: changes in semicrystallinity

Area of Science:

• Polymer Science
• Materials Science
• Biomedical Engineering

Background:

• Isotactic polypropylene is a semicrystalline polymer with applications in biomedical devices.
• Radiation sterilization is a common method for sterilizing medical polymers.
• Understanding the effects of sterilization on polymer properties is crucial for ensuring device safety and efficacy.

Purpose of the Study:

• To investigate the effects of radiation sterilization on the relative crystallinity and stiffness of isotactic polypropylene.
• To compare the aging effects on uncovered and covered samples of isotactic polypropylene.
• To elucidate the role of polymer branching and oxygen diffusion in property changes.

Main Methods:

• Samples of isotactic polypropylene (uncovered and covered) were subjected to radiation sterilization.
• Changes in relative crystallinity were measured to assess the impact of aging.
• The formation of branches in the polymer backbone and oxygen diffusion were analyzed.

Main Results:

• Radiation sterilization and subsequent aging altered the relative crystallinity of isotactic polypropylene.
• Covered samples exhibited a higher degree of branching, attributed to increased energized oxygen diffusion.
• Covered samples demonstrated greater long-duration stiffness compared to uncovered samples.
• Changes in relative crystallinity were more rapid in uncovered samples (70% max; 34% min) than in covered samples (87% max; 43% min).

Conclusions:

• The semicrystalline nature of isotactic polypropylene leads to changes in crystallinity upon radiation sterilization and aging.
• Polymer branching significantly influences the transition between short- and long-duration stiffness.
• Covered samples are more susceptible to oxygen diffusion, resulting in enhanced long-duration stiffness.
• These findings are critical for optimizing radiation sterilization protocols for biomedical polypropylene applications.