Further Studies on Oxidative Induction Test on Medical Polymers

Abstract

We have published previously initial results on the application of the oxidative induction test to a wide variety of medical polymers. This is a continuation and further elaboration on the earlier study. For medical flexible polyvinyl chloride (PVC) compounds, the traditional measure of degree of degradation by color formation was found to correlate to measured oxidative induction times. Furthermore, three distinct regimes were also detected. In the initial phase of degradation, little color formation was detected for significant decreases in the induction time. This is followed by a nearly linear regime. Finally in the terminal regime, where the stabilizer were nearly exhausted the color increased exponentially. This observation was interpreted by the established mechanism of PVC degradation. In another series with polyolefins, several subtle phenomena were observed that may have utility in either optimizing the stabilization package or predicting long term shelf life. It was found that significant antioxidant losses occurred at typical experimental temperatures above 200°C. Much better shelf life predictions can be obtained by collecting data at lower temperatures. And the inflection point on the activation energy plot corresponded to the antioxidant volatilization temperature.