Failure Progression and Mechanisms of Irradiated Polypropylenes and Other Medical Polymers

Abstract

This chapter deals with the failure progression and mechanisms of irradiated polypropylenes and other medical polymers. Ionizing sterilization is gaining popularity in medical device and packaging industry because of its convenience and lower cost. The high energy electrons can also initiate ionization events in the material being sterilized. It can create peroxy and hydroperoxy free radicals in the presence of oxygen, and start the degradation cascade. Post irradiated PP material undergoes significant degradation even at ambient temperature, and its rate depends on the copolymer content and the amount and type of stabilizer system. Post radiation failure progression starts from the oxygen initiated surface degradation with residual free radicals in the polymer. An OIT method was found useful in determining the stability of PP at high temperatures, and the data may be extrapolated to ambient temperature to predict the shelf life of PP by following the curvature, non-Arrhenius behavior. This method, if supported by further data, may provide a useful method for shelf life prediction.