Evaluating the effect of pressure and temperature on hydrogen permeation in semicrystalline polymers using helium as an inherently safer substitute

Polymers with low hydrogen permeability and mechanical resistance to high pressures are required for compressed gas storage. Permeability testing using hydrogen at high pressure is hazardous, thus, this work investigates using helium for screening, with hydrogen reserved for final material qualification. The permeability of high-density polyethylene (HDPE) and polyamide 6 (PA6), plus impact-modified PA6, to helium was measured between 20 and 50 °C, from 10 to 150 bar. Comparison with literature data (including a study on hydrogen permeability in the same samples) showed that the solubility of hydrogen in the polymers was much higher than helium, but with much lower diffusivity, resulting in a hydrogen permeability up to 1.5 times that of helium. By combining hydrogen experiments at low pressure, with helium at high pressure, hydrogen permeability up to 700 bar was predicted to within 5.5% for HDPE and PA6, and within 19.1%, 24.7% and 33.1% for LDPE, MDPE and PA11, respectively.