Evaluation of hydrogen dissolved in rubber materials under high-pressure exposure using nuclear magnetic resonance

Abstract

Hydrogen molecules dissolved in rubber due to high-pressure hydrogen gas exposure have been analyzed using 1 H nuclear magnetic resonance (NMR) with solution and solid-state probes. To analyze the characteristics of dissolved hydrogen in rubber materials and to compare them with gaseous phase hydrogen, we measured the NMR spectra of gaseous phase hydrogen and evaluated the chemical shifts and pressure dependency. Measurement using a sealed tube and liquid phase probes enabled the simultaneous analysis of dissolved hydrogen in rubber and gaseous phase hydrogen eliminated from the rubber. Two peaks at 4.3 and 4.8 p.p.m. were observed in the 1 H MAS NMR of the rubber samples after high-pressure hydrogen exposure. Using information from the chemical shift of the free hydrogen gas and the time dependency of hydrogen quantification in the rubber, both of these peaks were confirmed to be attributable to dissolved hydrogen. Their differences in relaxation time confirmed that their mobilities were different. In conclusion, the hydrogen dissolved in acrylonitrile butadiene rubber exists in two different forms with different mobilities. The ratio of those two hydrogens differs and is affected by the exposure pressure and elimination process time.

Volume Dependence of Hydrogen Sorption and Desorption Diffusion in Cylindrical Polymers

“…The general behavior illustrated in Fig. 3 showing that high-pressure hydrogen exposure does not cause any chemical structure changes in NBR by nuclear magnetic resonance analysis 22,23 . The reversible adsorption phenomenon of hydrogen is usually observed in the literature 24,25 .…”

Fracture Behaviour of Ethylene Propylene Rubber for Hydrogen Gas Sealing under High Pressure Hydrogen

“…Blister fracture and extrusion fracture due to volume increase of the rubber were identified as features of O-ring fracture. In the light of these findings, investigations aimed at developing high pressure hydrogen seals are currently focussing on the changes in structure and properties that accompany dissolution of hydrogen in rubber materials [9][10][11][12].…”

“…Based on factor analysis of the observed fracture behaviours and analysis of changes in chemical structure [9], along with the results of an NMR analysis of the dissolution of hydrogen in the rubber material [10][11][12], research is now being directed towards establishing guidelines for the molecular design and compound design of rubber materials for hydrogen gas sealing.…”

A Review on Applicability, Limitations, and Improvements of Polymeric Materials in High-Pressure Hydrogen Gas Atmospheres

“…They identified new peaks, which were originated from dissolved hydrogen molecules in the material after the exposure to 100 MPa of hydrogen gas for 24 h at RT, and they could assume the existence of hydrogen molecules in the free volume of rubber as well as constrained by the molecular chains of the rubber material. [50,53,96] Simmons et al [97] also conducted similar tests on NBR exposed up to 28 MPa hydrogen gas for 24 h at RT and detected the dissolved hydrogen within the matrix observing the peaks in the NMR spectrum. Further investigations of bubbling and initiation of cracks at RGD were conducted by identifying the change of submicron-scale morphological structures during the hydrogen elimination process by Ohyama et al [98] In this study, they used a SAXS, observing the submicron-scale voids in peroxide-vulcanized NBR composites during hydrogen elimination after exposure to 90 MPa of high-pressure hydrogen gas at 30 C for 24 h. Based on the SAXS and Debye-Bueche function, they managed to identify two phases in NBR with a clear interface, which originated from penetrated hydrogen; one phase corresponds to voids with hydrogen, which is identified as a low-density phase and the other phase is from rubber chain molecules, which are closely packed and identified as a high-density phase.…”

“…[95] This research work led them to conclude that it is probable that isolated hydrogen molecules exist between matrix polymer chains rather than a coalition of more than one hydrogen molecule at high-pressure hydrogen exposure. [95] Further, for identifying the origin of a bubble, Nishimura and Fujiwara [50,96] attempted to detect the dissolved hydrogen in rubber material by solid-state nuclear magnetic resonance (NMR). They identified new peaks, which were originated from dissolved hydrogen molecules in the material after the exposure to 100 MPa of hydrogen gas for 24 h at RT, and they could assume the existence of hydrogen molecules in the free volume of rubber as well as constrained by the molecular chains of the rubber material.…”