Evaluation of Hydrogen Permeability of Polymer Membranes

We conducted a gas permeation test on polyether ether ketone (PEEK), polyimide (PI), polycarbonate (PC), polypropylene (PP), and cellophane (PT) membranes at room temperature using Gas Transmission-rate Measuring Equipment (GTME) designed by ourselves and determined their permeability coefficient. Among the five types of test pieces, PP shows the largest hydrogen permeability coefficient of 2.24×10-15 [mol / m･s･Pa] and PT does the smallest one of 5.78×10-17 [mol / m･s･Pa]. All of the permeability coefficients are almost the same as the results of other researchers. Generally, the hydrogen permeability coefficient is considered to be a parameter that does not depend on the film thickness. The measurements of PEEK and PI with different thicknesses showed that the coefficients were affected by the film thickness. Since the state of the polymer chains in the thickness direction also affects the diffusion as the film thickness increases, in such a case, it is considered effective to add the hydrogen permeation amount to the evaluation parameters. The hydrogen permeability coefficient of PEEK and PI increased with increasing temperature in the temperature range of this experiment. In particular, PEEK with a glass transition temperature of 140°C to 220°C changed the tendency of the hydrogen permeability coefficient in this temperature range, because the diffusion characteristics of hydrogen are improved by the increase in free volume caused by the initiation of Micro Brownian motion in the molecular chain of the non-crystalline part.