Influence of liquid media on lifetime predictions of nitrile rubber

Abstract

Evaluating a material's suitability for an application includes determination of its expected service lifetime. For alternative fuels, this entails assessing, inter alia, their effect on the durability of polymeric engine components, e.g., seals, gaskets, and O-rings. When this is governed by thermally activated chemical deterioration, the conventional approach to characterizing aging is laboratory measurements of property changes of the polymer subjected to accelerated conditions (usually higher temperatures), with the data analyzed by an Arrhenius analysis. However, this method is inefficient and time-consuming when the number of candidate alternative fuels is large. Herein, we test the hypothesis that the activation energy governing thermal oxidation of elastomeric engine components is independent of the fuel; thus, while the aging rate may vary, the effect of temperature is independent of the contacting liquid. Accelerated testing of the thermal oxidation of nitrile rubber O-rings were carried out in three liquids, including a fossil fuel and a bio-fuel. The activation energy obtained from changes in crosslink density, 5 82 kJ/mol, was the same for all liquids and consistent with the broad range of literature values for similar compounds aged in air. This result suggests the possibility that estimates of the lifetime of polymeric engine components require only a single accelerated aging test, with the known activation energy used to predict the durability at the service temperature. This would represent at least an order of magnitude reduction in testing requirements. The extension of the approach to the general aging of polymers exposed to different environments is obvious. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40296.

Effects of medium phases on the thermal degradation of hydrogenated nitrile rubber O‐rings under compression

“…When the O-rings were exposed to air at high temperatures, the volatile additives and residual monomers gradually migrated from the inside to the surface, and then volatilized into the atmosphere, resulting in weight loss. 10 However, for the compressed samples subjected to oil, the oil can extract the soluble components (such as additives and residual monomers) of the samples. 11,18 Thus, solvent extraction caused an initially rapid decrease in the weight of the samples after exposure to oil.…”

“…Hydrogenated nitrile butadiene rubber (HNBR) O‐rings are well known for their resistance to thermal oxidation, chemical mediums and mechanical stress, and are usually applied in hydraulic systems to inhibit leaks of liquids or gases . However, under actual service conditions, the O‐rings are often subjected to harsh environments, such as mechanical stress (often compressive stress), high temperatures (up to 150 °C) and both gaseous (air) and liquid (hydraulic oil) environments, leading to substantial degradation of the chemical structure and mechanical properties of the seals . The degradation of these seals causes sealing failures in the hydraulic system, resulting in leakages of air or hydraulic oil.…”

“…[4][5][6] However, under actual service conditions, the O-rings are often subjected to harsh environments, such as mechanical stress (often compressive stress), high temperatures (up to 150 8C) and both gaseous (air) and liquid (hydraulic oil) environments, leading to substantial degradation of the chemical structure and mechanical properties of the seals. [7][8][9][10] The degradation of these seals causes sealing failures in the hydraulic system, resulting in leakages of air or hydraulic oil. Thus, understanding the degradation behaviors and mechanisms of seals exposed to air and hydraulic oil can lead to improvements in the reliability and security of the hydraulic system by timely replacement and maintenance.…”

Stress–thermal oxidative aging behavior of hydrogenated nitrile rubber seals

“…Some applications, for example, in hydraulic servo valves of hydraulic servo control systems, often need to satisfy long service life due to some actual requirement for the seals. However, under actual service conditions, rubber seals are sensitive to heat, oxygen, chemical mediums, and mechanical stress leading to the subsequent degradation in chemical structures and mechanical properties . Accompanied by aging, seals gradually lose elasticity and the ability to recover automatically, which result in leakage of gas and/or liquid due to sealing failure.…”

Lifetime prediction of nitrile rubber under compression stress in transformer oil

“…[18][19][20][21] Buckley et al [21] studied the influence of liquid media on lifetime predictions of nitrile rubber and it was determined that the activation energy for oxidative degradation of a particular NBR O-ring had a value, 82 kJ/mol, that was invariant to the immersion liquid.…”