Effect of hydrogen on the mechanical properties of amorphous polyethylene: a molecular dynamics study with microstructural analysis

Abstract

With the development of hydrogen-blended natural gas pipeline transportation technology, the stability of pipeline materials in a long-term hydrogen environment has become an increasingly prominent concern. The mechanical properties of non-metallic materials in hydrogen environments have not been widely discussed, posing potential risks to the safe operation of pipelines. In this work, molecular dynamics simulations were used to investigate the variations in mechanical properties and microstructural changes of amorphous polyethylene under typical urban gas pipeline conditions (0.1–4 MPa, 100–400 K) in both pure hydrogen and hydrogen-methane environments. The influence of hydrogen on the mechanical properties showed different trends. Under the simulation conditions, the presence of hydrogen led to an approximate 10% enhancement in the yield strength of PE. Specifically, at 0.1 MPa and 100 K, the elastic modulus of polyethylene was 1.568 GPa in a pure hydrogen environment, compared with 1.495 GPa in the absence of hydrogen. Energy analysis showed that the initial potential energy of amorphous PE was only weakly affected by hydrogen under low-pressure conditions. Only slight perturbations in the microstructure were observed, and overall structural integrity was not compromised. During tensile deformation, hydrogen mainly affected the variations in bond angle energy and dihedral torsional energy. The total energy of the system was affected only to a limited extent. Microstructural analysis suggested that the mechanical properties of amorphous PE were influenced by the combined effects of temperature, pressure, and hydrogen molecule concentration, resulting in fluctuations within a certain range. A moderate amount of hydrogen was found to enhance interchain cohesion, reduce the variation rate of large cavity diameter and free volume fraction, and thereby improve the overall mechanical performance. Simulation under hydrogen-blended conditions indicated that the effect of hydrogen content on the mechanical behavior of amorphous PE was not significant and could be considered negligible.