Structural Characteristics and Swelling Mechanism of Two Commercial Nitrile-Butadiene Elastomers in Various Fluids
Abstract
Results on the structural characteristics and swelling mechanisms of the two commercial elastomers viz. N0674-70 and peroxide cured N0741-75 in a variety of fluids are reported here. The fluids used in these investigations included toluene, o-xylene, p-xylene, mesitylene, HISOL-15, n-hexane, ethanol, tert-butyl alcohol, acetone, JP-8, S-8 and blends of S-8 plus HISOL-15 and S-8 plus toluene. Both changes in mass and volume of the rectangular disks of the samples were monitored as a function of time. Structural characterization of the elastomer was done using x-ray diffraction and FTIR spectroscopy. Time dependence of the recovery of swelling after the elastomers are taken out of the fluids was monitored by x-ray diffraction and changes in mass. In general swelling of the peroxide cured N0741-75 was less than that of N0674-70, percentage changes in mass were less than the percentage changes in volume, and the swelling is strongly fluid dependent. For initial times, the swelling is interpreted in terms of diffusion of the fluid into the elastomer. However, diffusion is not strictly Fickian in that the exponent differs from 0.5 for Fickian diffusion, instead varying between 0.4 and 0.6 for different fluids. It is shown that the results of maximum swelling can be interpreted in terms of compatibility of the Hansen Solubility Parameters (HSP's) of the fluid and the elastomer, swelling decreasing on a Gaussian curve as the HSP of the fluid deviates from that of the elastomer. Also, swelling is determined by the polybutadiene component of the elastomer. In HISOL-15, a commercial aromatic solvent, nitriles swell by about 55% and mixing of HISOL-15 with S-8 produces swelling linearly proportional to the % of mixed HISOL-15. The observed few percent decrease in swelling on long-term exposure may be related to loss of material and so eventual failure of the nitrile O-rings.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 06, 2012
- Accession Number
- ADA554219
Entities
People
- M. S. Seehra
- M. Yalamanchi
- Vibhor Singh
Organizations
- West Virginia University