Equilibrium swelling test is employed to study the swelling responses of natural rubber (NR) in various solvents, and to determine the total Hildebrand solubility parameter (δt) of NR. The three‐dimensional solubility parameters (HSP) of NR is obtained by virtue of software package as the result of being δd = 17.50 MPa1/2, δp = 3.20 MPa1/2, δh = 1.40 MPa1/2, and δt = 17.85 MPa1/2, respectively. The swelling ratio (q) is correlated with the energy difference (Ra) in order to deeply understand the swelling principle of NR, and the results turn out that q decreased with the increase of the Ra and it can be used to explain the abnormal swelling phenomena of methyl acetate and ethyl acetate. One of the possible applications of Ra is the prediction or explanation of diffusion behaviors of small liquids in the rubber matrix. Therefore, the diffusion coefficient (D) is calculated in accordance with the Fick's law model and attempted to correlate with the Ra value. Two qualitative relationships between D and Ra and χHSP can be preliminarily established now, which can provide an easy way to predict the diffusion behavior of fluids in rubber matrix.

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To enrich the research on the solubility parameter of rubber blends, equilibrium swelling tests combined with computer software, Hansen solubility parameter in practice (HSPiP), were employed to deeply investigate the three‐dimensional solubility parameters (HSP) of hydrogenated nitrile rubber/ethylene propylene diene monomer rubber (HNBR/EPDM) blends. And the transport behaviors of four ester solvents have been studied through the calculation of sorption and permeation coefficients. It is found that the HSP values of HNBR/EPDM blends show linear relationships with the mass fraction of HNBR. And a linear equation has been obtained for the calculation of the solubility parameters of HNBR/EPDM blends. Sorption and permeation coefficients show two‐stage upward linear relationships with the HNBR concentration, which can be attributed to the sea phase in the blend playing a decisive role in the transport behaviors of solvents. Moreover, the trend of the selective adsorption of the solvent is more obvious in the permeating process than that at the final equilibrium swelling state. The achievements can provide important guidance for evaluating the liquid resistance of the HNBR/EPDM‐based rubber products in industrial and automotive applications.