Hydrogen Permeation in Polyethylene: Effect of Crystallinity on Gas Transport Coefficients at Different Temperatures

Semicrystalline polymers such as high-density polyethylene (HDPE) are increasingly adopted as liners in compressed hydrogen storage tanks, due to low weight, easy processing, and high durability, together with good mechanical properties and low hydrogen permeability. Hydrogen gas permeation experiments were performed in three polyethylenes with different degrees of crystallinity through the time lag method, allowing the determination of the permeability, diffusivity, and solubility coefficients at different temperatures, between 30°C and 50°C, in a pressure range between 1 and 10 bar. A simple empirical model is proposed to account for the effect of temperature and crystallinity on permeability, diffusivity, and solubility coefficients, allowing the description of experimental data coming from different literature sources within an ambient temperature range. Finally, the model was extended to include the reduction in crystallinity occurring at the elevated temperatures of on-board filling. In HDPE, heating from 30°C to 85°C decreases volume crystallinity by up to 7%, which increases hydrogen permeability by nearly one order of magnitude due to the combined effects of Arrhenius-type behavior and partial melting.