Aging and Degradation Patterns and Life Prediction of Polyethylene Pipes Under Thermal Oxidation and Photo-Oxidation Effects

Polyethylene (PE) pipes are widely used in various gas transmission applications due to their excellent flexibility and other advantages. As high-molecular-weight non-metallic polymeric materials, they inevitably undergo degradation and aging during service under the action of environmental factors such as temperature and ultraviolet (UV) radiation, which impairs their service performance. To investigate the effects of environmental factors on the aging and degradation of PE pipes, a reliable method for predicting their service life was developed in this study. Taking PE80 DN110 pipes as the research subject, an accelerated aging method was adopted to simulate the combined effects of thermo-oxidative and photo-oxidative aging on the pipes. By using Fourier Transform infrared spectroscopy (FTIR) to test and track the carbonyl index (CI), the aging mechanism is explored. Oxidation Induction Time (OIT) and Melt Mass Flow Rate (MFR) tests were used to characterize changes in the pipes’ properties, thermal stability, and melt flow behavior after aging. The Arrhenius equation was used to create a lifetime prediction model under four different temperature conditions. This study estimates the service life of PE pipes under combined photo-oxidative and thermo-oxidative aging conditions. According to research, products produced during the thermo-oxidative and photo-oxidative aging processes of polyethylene pipes can promote secondary reactions and photo-oxygen reactions. The aging rate is 1.87 times higher than that of thermo-oxidative aging alone. The MFR decreased under combined thermo-oxidative and photo-oxidative aging compared with single thermo-oxidative aging, demonstrating impaired melt flowability of polyethylene pipes caused by aging and degradation. Based on the Arrhenius equation, a multi-factor lifetime prediction model for polyethylene pipes was created.