Influence of Metals on Thermo Oxidative Degradation of Polypropylene and Its Evaluation Methods

Abstract

The effects of copper-based metals on thermal oxidative degradation and the evaluation methods to analyze different degrees of thermo oxidative degradation with polypropylene (PP) wrere invesigated. In the state of inserting the terminal into the connector of molded PP, thermal aging took place at 140°C for 120 hours. Four types of terminal components (cartridge brass, high copper alloy, tinning cartridge brass, and tinning high copper alloy) and PP with different thermal stability were used. From SEM observations of tin-copper alloy in the tinning layer and the ICP quantification of copper in PP, the influence of the PP thermal stability and terminal components on PP thermo oxidative degradation could be quantitatively identified. The convenient high-temperature GPC, ATR-FTIR, Oxidation Onset Temperature (OOT) with DSC, and iodometric hydroperoxide determination were used as methods to analyze oxidative degradation. Due to the master curve for the degree of degradation, OOT was effective for evaluating the degree of PP thermo oxidative degradation, ranging from the initial to increased degradation and correlated with the molecular-weight change behavior. Rapid decreases of the molecular weight could be sensitively predicted by the iodometric method in a simple manner.