Characterizing the Diffusion Property of Hydrogen Sorption and Desorption Processes in Several Spherical-Shaped Polymers

We developed a method for characterizing permeation parameters in hydrogen sorption and desorption processes in polymers using the volumetric measurement technique. The technique was utilized for three polymers: nitrile butadiene rubber (NBR), ethylene propylene diene monomer (EPDM), and fluoroelastomer (FKM). The total uptake ([Formula: see text]), total desorbed content ([Formula: see text] , diffusivity in sorption (D(s)), and diffusivity in desorption (D(d)) of hydrogen in the polymers were determined versus the sample diameter used in both processes. For all the polymers, the diameter dependence was not detected for [Formula: see text] and [Formula: see text]. The average [Formula: see text] and [Formula: see text] at 5.75 MPa were 316 wt∙ppm and 291 wt∙ppm for NBR, 270 wt∙ppm and 279 wt∙ppm for EPDM, and 102 wt∙ppm and 93 wt∙ppm for FKM. The coincidence of [Formula: see text] and [Formula: see text] in the sorption and desorption process indicated physisorption upon introducing hydrogen molecules into the polymers. The larger D(d) in the desorption process than D(s) could be attributed to an increased amorphous phase and volume swelling after decompression. The equilibrium time to reach the saturation of the hydrogen content in both processes was experimentally confirmed as proportional to the squared radius and consistent with the COMSOL simulation. This method could be used to predict the equilibrium time of the sorption time, depending on the radius of the polymers without any measurement.