Medical devices differ from other polymer applications in one major aspect: that the product frequently needs to be sterilized. Due to simplicity and cost effectiveness, sterilization by ionizing radiation has become increasingly popular. Of course, the ionizing radiation that disrupts biological macromolecular structures (bio-burden) can and frequently does damage synthetic polymer chains. We have examined several polypropylenes (PP) subjected to long term ambient storage for up to 18 years after gamma irradiation at different doses. Many of the samples in thin film form have completely disintegrated. However, in many cases the degradation reaction was not homogeneous, with an apparent distinct skin-core structure and very different properties. These results and interpretations with an oxygen diffusion limited degradation reaction model will be presented.
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