The mechanical properties of a model hydrogenated nitrile butadiene rubber (HNBR) following simulated sweet oil exposure at elevated temperature and pressure

Abstract

a b s t r a c tA typical carbon black reinforced hydrogenated nitrile butadiene rubber (HNBR) was exposed to a mix of hydrocarbons (toluene, heptane and cyclohexane) at elevated temperatures and pressure in order to chemically age the material. The effect of this exposure on the mechanical properties is reported; the most significant change is a dramatic increase in tensile stiffness for specimens exposed at 160 C for 12 weeks. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) revealed changes in the glass transition behaviour of this material, with a general reduction in the magnitude of the glass transition with increasing ageing time. In addition, gravimetric studies of the swollen specimens after removal from the hydrocarbon mix showed that the more aged specimens underwent significantly slower drying rates compared to less aged specimens. These results may be explained by an increase in crosslink density in the materials being the main mechanism occurring during chemical ageing of these HNBR compounds.

The effect of hydrocarbon ageing on the mechanical properties, apparent crosslink density and CO2 diffusion of a hydrogenated nitrile butadiene rubber (HNBR)

“…6 shows the relationship between the saturation swelling shown in Fig. 3, and tensile modulus results of these specimens (after drying), as presented previously [11], while Fig. 7 shows the relationship between apparent crosslink density as calculated using Equation (4).…”

“…Of the solvents investigated here, it is clear that chloroform gives the highest saturation swelling for the HNBR, and the test solvent mix does not give a very strong swelling of this HNBR. It is interesting to note that the test solvent mix leads to a saturation swelling in ambient pressure and temperature of 10.7% (from Table 4), while exposure to the same solvent environment at elevated temperature and pressure was previously shown to yield a higher saturation swelling of at least 14% [11] when exposed in pressure vessels at elevated temperature and 100 bar of pressure.…”

“…The procedure of exposure of HNBR samples to organic solvents at elevated temperature and pressure has been described in detail in a previous publication [11], but will be summarized here for completeness. The HNBR samples were placed in a hydrocarbon liquid phase (variation classification A.1.ii) with a gas phase (variation classification A.2.i), as suggested by ISO 23936-2:2011 Annex A, and as summarised here in Table 2.…”

“…Previous work by the same authors has shown that an aggressive chemical environment at elevated temperature and pressure can be used in the laboratory to age HNBR specimens [11], and the main mechanism active in the ageing of HNBR appears to be an increase in the apparent crosslink density. In a continuation of that study, HNBR specimens which have been aged to varying degrees are now subjected to further analyses to determine the relationship between the stiffness measurements (which require a specific test geometry and, therefore, cannot be easily applied to retrieved seals) and saturation solvent swelling tests (which do not require specific test geometries and so could be applied to any retrieved parts).…”

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.…”