GAMMA-STERILIZATION EFFECTS AND INFLUENCE OF THE MOLECULAR-WEIGHT DISTRIBUTION ON THE POSTIRRADIATION RESISTANCE OF POLYPROPYLENE FOR MEDICAL DEVICES

In the present study, the dose-rate effects of gamma-irradiation in ai r on two isotactic polypropylene grades of different molecular weight distribution, used for medical devices, were investigated. The thermal , mechanical, rheological, and photometric properties of these materia ls were examined using DSC, stress-strain measurements, MFI, and a yel low index. At low dose rates (0.12 Mrad/h), the oxygen diffusion param eter prevailed. At high dose rates (2.84 Mrad/h), the thermal degradat ion became dominant. However, at high dose rates, an increase in sampl e temperature was monitored. This temperature rise is thought to incre ase the oxygen diffusion rate, peroxide decomposition, and radical mig ration. As a result, intermediate dose rates (in the region of 0.72 Mr ad/h) gave the lowest changes in physical properties in both samples. Furthermore, it was found that the polypropylene grade of broader mole cular weight distribution and lower M(n) had a higher gamma-irradiatio n and postirradiation resistance. (C) 1994 John Wiley & Sons, Inc.