A new way to determine the three-dimensional solubility parameters of hydrogenated nitrile rubber and the predictive power

In order to understand the swelling behavior of hydrogenated nitrile rubber (HNBR) more fully, the total solubility parameters (δt) of HNBR (Therban 2568) were determined by equilibrium swelling tests. Then, the swelling responses were analysed by a computer program to determine the Hansen three-dimensional solubility parameter (HSP). The HSP values - determined from lightly cured rubber samples - were estimated as δd = 18.4 (J/cm3)1/2, δp = 6.0 (J/cm3)1/2, δh = 4.5 (J/cm3)1/2 and δt = 19.9 (J/cm3)1/2. The energy difference (Ra) between HNBR and solvents or solvent mixtures have been calculated by their HSP values and proven to be useful for predicting the swelling behaviour of HNBR. The swelling volume decreases with increasing Ra values. Using blended solvents, a clear correlation between Ra values and the rubber swelling response was established. Thus, it may be possible to use the Hansen three-dimensional solubility parameters to predict swelling phenomena of cured rubber articles in mixed fluids such as bio-fuels or lubricants. Also, the HSP values may be used to predict the response of rubber seals or gaskets when replacing toxic or expensive fluids with more favorable environmentally friendly or inexpensive ones.