Hydrogen Permeation Characteristics of PET Liners Used for Type IV High Pressure Hydrogen Tanks

The hydrogen gas permeation through polymer materials is due to two different mechanisms : molecular and atomic diffusion. Indeed, this overall gas diffusion is strongly affected by the microstructural composition of the material, the production process, and also the experimental conditions. Consequently, the hydrogen permeation parameters, when available in the literature, are changing and unreliable. The need of an accurate knowledge of these parameters for a specific polymer, after complete process, leads us to design an experimental apparatus based on the manometric method and its corresponding numerical model. From initial approximate values roughly deduced from a first experiment, the numerical model implemented in Matlab language, allows a refining of the parameters, by fitting the simulated values to the experimental ones on successive experiments. These experiments are carried out on a sample with increasing upstream pressures from 25 bar up to 150 bar. Because of the high pressure values, the beginning of permeation experiments are affected by the gas flow disturbance due to the sharp pressure rising. Considering this delay time induced by the pressure increase, the permeation parameters are evaluated more accurately. In fact, with a single experiment the phenomenon cannot be readily separated from the so-called time-lag parameter occurring in gas diffusion through a material.