(35d) Dynamic Relaxation Spectra Reveal Changes in Polymer Melt Properties in Natural Gas Environments

Modern natural gas pipelines are commonly manufactured from plastics feedstocks due to their ease of processing, low cost, and high mechanical integrity. Historically, however, pipelines were made from cast iron or untreated steel, resulting in significant corrosion and degradation over the last decades. This decreased performance has dramatic impacts on safety and environmental stewardship, but replacing these aging pipelines can be prohibitively expensive in certain municipalities. To alleviate these costs, cast iron pipelines can be rehabilitated using either cured-in-place (thermoset) or sliplining (thermomelt) approaches. On the regulatory side, these approaches are not accepted as a an alternative to replacement because of the lack of information regarding pipeline liner performance in the presence of natural gas molecules. Here, we evaluate evaluate how polymer melts plasticize in the presence of small molecule penetrants. We show that small molecules have no significant impact on the modulus of polymer melts but can significantly accelerate terminal relaxations. We quantify these accelerated dynamics through the activation energy of time-temperature superposition plots and find that the accelerated dynamics are reversible when allowed to off-gas. Overall, our findings indicate that polymers maintain their mechanical integrity to a sufficient extent to be used as liner materials but that long-time failure modes such as creep will be accelerated.