Linking Antioxidant Depletion with Material Properties for Polyethylene Pipes Resins

Abstract

Plastic pipes used in gas distribution networks are typically made from polyethylene (PE) and are stabilized against degradation by antioxidants. Over time, the antioxidant is consumed and the polymer integrity can become compromised. The rate of antioxidant depletion can be dependent on the specific grade of PE and the surrounding environment. In this research, the crystallinity, tensile strength, Young's modulus, and strain at break were measured for the four most commonly used PE pipe resins in the Australian natural gas distribution network as a function of antioxidant content. A relationship between the changes in material properties with antioxidant consumption was established. By measuring the carbonyl index (CI), which quantifies the amount of degradation products present, and linking this with the oxygen induction time (OIT), it was found that three clear regions exist for all investigated PE resins. These distinct regions of the OIT–CI relationship correlate with regions of substantially different rate of change in material properties, and hence indicate a measure of the integrity of the PE. POLYM. ENG. SCI., 60: 323–329, 2019. © 2019 Society of Plastics Engineers