Influence of high-pressure hydrogen exposure on rubber materials was analyzed using typical rubber models of vulcanized acrylonitrile butadiene rubber(NBR); unfilled(NBR-NF), filled with carbon black(NBR-CB)or silica(NBR-SC). Hydrogen penetrated in rubber affects volume change larger in the order of NBR-CB<NBR-SC<NBR-NF. The late hydrogen elimination in NBR-CB was explained by hydrogen adsorption on carbon black. Deterioration and recovery of elastic modulus is not due to the restraint of rubber molecular mobility but the volume expansion. Cross-linkage was not affected by the repetition of hydrogen exposure. Infrared spectroscope(IR)and solid state NMR showed no chemical structural change such as hydrogenation or chain scissions. Pulsed NMR data suggested that the change of relaxation time(T₂^S)ratio observed only in NBR-SC was caused by detachment or destruction of filler-gel interface or between silica aggregations. In NBR-CB, the bound rubber structure may have stronger interaction to cause no damage of fatigue by the exposure-repetition. Solid state NMR analysis for states of hydrogen penetrated in rubber revealed the existence of hydrogen in two different states; one adsorbed on rubber matrix, the other free hydrogen having no interaction with rubber matrix, which affects the volume expansion and causes deterioration.

Takaishi Industry and Daikin Industries collaboratively developed Fluoroelastomer compound for a sealing material, such as O-ring, in particular, for hydrogen booster of the hydrogen station. No fatal leak of hydrogen gas occurred on the O-ring seal made of the Fluoroelastomer during the endurance cycle test that simulates the hydrogen filling process of fuel cell vehicle (FCV). However, wear damages and extrusion of O-ring seal were observed after the durability test including the cycle of high compression and decompression of hydrogen pressure at high temperature, indicating that developed elastomer still does not have sufficient durability under realistic severe environment. We continue joint development of more desirable Fluoroelastomer compound with less damage even after the durability test.

Hydrogen energy systems have attracted interest in the search for solutions to global energy challenges. One of the technical problems of the rubber O-rings used in high-pressure hydrogen devices is the occurrence of internal fractures known as blisters, which are caused by gas decompression. Our studies revealed that the fracture of the rubber deteriorated sealing property and durability of the O-ring after several pressure cycles. However, the O-rings used in the 70-MPa-class hydrogen vessels of Fuel Cell Vehicles are generally required to withstand 5,500 pressure cycles.
This paper entitled technical issues of rubber materials for high-pressure hydrogen seals reports a fracture behavior and a state change of rubber O-ring. We evaluated the sealing property and durability of rubber O-ring under realistic pressure cycle conditions. Long-term sealing durability tests were successfully performed using 5,500 pressure cycles without fatal leakage, fracture, or change in the elastic modulus. These results indicate that silicone rubber O-ring has good low-temperature seal and long-term durability. The development of the seal technology which this paper reported and accumulation of the knowledge such as the fracture mode become more and more important in future.

Mechanism of fracture in rubber materials for high pressure hydrogen vessels is highly affected by the hydrogen dissolved in rubber during hydrogen exposure. One of the origins of this effect is thought to be the change of higher order structures of the rubber materials by high pressure hydrogen dissolved in these materials. In this work, we focused the dispersion states of zinc stearates in the rubber materials and studied the higher order structure change of the six kinds of rubber materials, EPDM and NBR with and without the silica and carbon fillers, before and after high pressure hydrogen exposure by using FT-IR spectroscopy. We gave the evidence of the higher order structure changes after high pressure hydrogen exposure and these changes depend on the chemical structures of the rubber materials.

Effect of wax on the ozone resistance of vulcanized natural rubber (NR) and vulcanized isoprene rubber (IR) was investigated by exposing to ozone at 40 °C and -30 °C. The vulcanized rubbers were prepared by sulfur vulcanization of NR and IR with sulfur, ZnO, stearic acid, accelerator and wax in the presence of carbon black and they were heated at 40 °C for 72 hours under 20% straining to form wax layer on their surfaces. The ozone exposure test of the vulcanized rubbers was carried out at -30 °C or 40 °C for 24 hours in the presence of 50 pphm ozone and crack propagation of vulcanized rubber was observed by optical microscopy. The crack propagation of the vulcanized rubbers took place at -30 °C, whereas it was suppressed at 40 °C, which were distinguished from the theory of reaction kinetics. It was found that the crack propagation of vulcanized rubbers was caused by the difference in thermal contraction coefficient between wax and the rubbers.