Recently introduced perfluorinated polyether rubbers have been found to be useful materials for use as o-rings in harsh environments. They have a very broad range of thermal utility, -55°C to 200°C, and exhibit strong resistance to harsh chemical environments over the entire temperature range. The data presented here demonstrate the excellent high and low temperature performance of perfluorinated polyether rubbers after extended exposures to jet fuel and synthetic hydraulic fluids. Demonstration of an appreciable degree of retained sealing force by molded o-rings down to -40°C is shown in a compression stress relaxation device. Perfluorinated polyether o-rings are demonstrated to offer significant improvement in performance over current nitrile-based o-ring materials. POLYM. ENG. SCI., 45: 1622-1629, 2005.
After discovery of failed Viton™ B Fluoroelastomer gaskets at the Salt Waste Processing Facility (SWPF) in early calendar 2021, a short-term (27 day) compatibility test was conducted between SWPF process solutions including Average Salt Simulant, 1 mM nitric acid, 10 mM boric acid, Caustic-Side Solvent Extraction (CSSX) solvent, and Next Generation Solvent (NGS) and the following four polymers: Viton™ B, Viton™ Extreme™ ETP-600S, expanded polytetrafluoroethylene (ePTFE), and Garlock ® Blue-Gard ® 3700. To the aqueous solutions, 20 mg/L of the following organics were added to represent impurities: Dibutyl phosphate, n-butanol, 2butanone, ethyl acetate, 4-secbutyl phenol, and N-(3,7-dimethyloctyl) amine. The 1 mM nitric acid, 10 mM boric acid, NGS, and CSSX solvent exposure tests were performed at 35 °C, with NGS, CSSX, and Average Salt Simulant Solution tests also performed at ambient temperature. The physical characteristics of the polymeric gaskets, their surface chemistry and the chemistry of the solutions were monitored.The gasket material behavior is summarized. Viton™ B Fluoroelastomer showed low swelling (less than 2%) with the test solutions due to the presence of a surface treatment or barrier layer, presumed talc (magnesium silicate hydroxide). However, if the talc layer was removed, Viton™ B is susceptible to fast caustic hydrolysis as noted in the literature (expect significant swelling). The talc surface treatment is generally applied by gasket manufacturers to reduce friction during gasket installation and to prevent sticking between materials, not for chemical protection. It is possible that a combination of over-torquing the gaskets and breaking of the protective talc layer led to gasket degradation in the facility. The degree to which each factor contributed to the failure cannot be determined based on the data available at this time. It is noted that reliance on a surface treatment for chemical resistance is less desirable than having sufficient inherent resistance. Fourier Transform Hydrogen Nuclear Magnetic Resonance (FT-HNMR) indicated that Viton™ B did not absorb 2butanone, dibutyl phosphate, and secbutylphenol in 1 mM nitric acid and in10 mM boric acid.The ETP-600S Fluoroelastomer gained weight and volume during testing (swelling less than 5%), with some hardness loss in Average salt simulant, 10 mM boric acid and 1 mM nitric acid solutions. This was expected based on the literature and information provided by the polymer manufacturer (The Chemours Company). The free volume available in this polymer explains the rate of mass gain in such a short period (27 days of contact) and it should be considered for long-term performance of this gasket. The extent of the swelling in Average salt simulant, in 1mM nitric acid, and in 10 mM borica was less than 5% which is considered as "little effect" by the manufacturer (The Chemours Company). Longer-term exposures are recommended to better assess this behavior. The ETP-600S did better when exposed to CSSX or NGS solvent with a volume swelling of 2% or l...
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