Investigation on the Viscosity–Temperature Properties for Various EPDM Solutions Based on Three-Dimensional Solubility Parameters and Flory–Huggins Interaction Parameters

Three organic solvents, cyclohexane, n-hexane and n-heptane were selected to dissolve the Ethylene-Propylene-Diene Monomer (EPDM) to keep the mass fractions of EPDM solution at 5 wt% and 10 wt%, respectively. The viscosities of three EPDM solutions at different temperatures were measured by a rotary viscometer. The experimental results show that the concentration and temperature exert significant influences on the viscosities of the EPDM solutions, compared with the rotor type and rotational speed having no obvious effect on the viscosities. An EPDM solution with higher concentration shows remarkable higher viscosity. The viscosities show almost linear decline with increasing temperature within the experimental temperature range, which is also called a viscosity–temperature curve. However, the temperature dependences of viscosity are varied for the three different EPDM solutions. The compatibility between EPDM and solvents could be characterized by the energy difference (Ra) and Flory–Huggins interaction parameter (χ), which has also been attempted to be correlated with the viscosity–temperature curve and solvent molar volume. It is found that the smaller Ra value relates to better compatibility of the EPDM solution and greater slope of the viscosity–temperature curve. Furthermore, the viscosity of EPDM solution and the slope of the viscosity–temperature curve are affected more significantly by the molar volume of solvent when the Ra value is similar. A formula for predicting the viscosity of EPDM solution has been established by using a new Flory–Huggins interaction parameter (χHSP), which can also be used to calculate the viscosity at the extreme temperature that is difficult to be measured. Finally, for the three EPDM solutions, the different dissolution temperatures corresponding to the same viscosity can be obtained by formula calculations with the achieved prediction formulas.