Tensile Properties and Swelling Behavior of Sealing Rubber Materials Exposed to High-Pressure Hydrogen Gas

Abstract

Rubber O-rings exposed to high-pressure hydrogen gas swell, and the volume increase induced by swelling influences tensile properties of the O-rings. Samples of nonfilled (NF), carbon black-filled (CB), and silica-filled (SC) sulfur-vulcanized acrylonitrile-butadiene rubber were exposed to hydrogen at 30 °C and pressures of up to 100 MPa, and the effect of hydrogen exposure on the volume increase, hydrogen content, and tensile properties was investigated. The residual hydrogen content, measured 35 minutes after decompression, increased with increasing hydrogen pressure in the range 0.7-100 MPa for all three samples. In contrast, the volumes of NF, CB, and SC barely changed at pressures below 10 MPa, whereas they increased at pressures above 10 MPa. This nonlinear volume increase is probably related to the free volume of the rubber structure. The volume increase of the CB and SC samples was smaller than that of the NF samples, possibly because of the superior tensile properties of CB and SC. As the volumes of the NF, CB, and SC samples increased, their tensile elastic moduli decreased as a result of a decrease in crosslink density and elongation by volume increase. Although the true fracture stress of NF was barely dependent on the volume of the specimen, those of CB and SC clearly decreased as the volume increased. The decrease in the true fracture stress of CB and SC was related to the volume increase by swelling, showing that the boundary structure between the filler and the rubber matrix was changed by the volume increase.