Shelf Life Failure Prediction Considerations for Irradiated Polypropylene Medical Devices

Abstract

This chapter examines the various important parameters that need to be taken into consideration when a specific method is applied to predict the shelf life of a product made of polypropylene material. Factors governing polypropylene's post radiation shelf life to maintain the mechanical ductility were identified. It is proposed to incorporate the surface brittle layer thickness into an overall model based on stress concentration factor and the strain rate dependence for device and component shelf-life prediction. Technique used in this study includes ASTM D3895-92 isothermal oxidative induction time (OIT) from Dupont 1090 thermal analyzer with 910 differential scanning calorimetry (DSC) cell. OIT was conducted under air flow condition of 100 CC/min. The high energy gamma photons or accelerated electrons (from the e-Beam source) interact with the atoms in the material, creating a secondary high energy electron and a recoiling photons or electrons. These electrons can lead to a series of secondary ionization events in localized spurs. The cascade is propagated until all the excess energy above the ionization threshold is dissipated. Catastrophic failures have been reported during the PP shelf life storage period. Intense investigation has come to the hypothesis that long lived free radicals trapped in the crystalline domains slowly migrate towards the crystalline /amorphous interface where they react with available oxygen to form peroxy and hydroperoxy radicals and initiate degradation near the interface.