Inhomogeneity in acrylonitrile butadiene rubber during hydrogen elimination investigated by small-angle X-ray scattering

To understand the early stage of explosive decompression failure of rubber materials after high-pressure hydrogen exposure, the hydrogen elimination process of hydrogen-saturated peroxide-vulcanized acrylonitrile butadiene rubber (NBR) was investigated by small-angle X-ray scattering. The results were analyzed by the Debye-Bueche equation. Hydrogen-containing NBR samples exhibit a two-phase system with a clear interface, and the low-density phase of NBR samples is considered to be submicron-scale voids. The dimension of the voids in NBR becomes larger with decreasing cross-link density. The inflation of the voids in terms of the penetrated hydrogen contributes to the bulk-volume inflation after decompression. Estimated number densities of voids in the exposed NBR samples were almost constant. Judging from this, the voids in rubber samples after decompression are generated from precursors originally existing in the matrix, which are considered to be the low-density phase, which is attributed to the inhomogeneity of the cross-link density.