Viscoelastic Characterization of Ethylene-Propylene-Diene Terpolymer Elastomers

Abstract

Abstract A practical range of frequency with the Rheometric mechanical spectrometer for the determination of G′ and G″ was shown to be from 2.5×10−2 to 2.5×102s−1, but one decade lower frequency may be reached routinely. The values G′ and G″ may be calculated from the steady-state viscosity curve obtained with the variable-speed Mooney rheometer. However, with samples having long-chain branching, the calculated G′ and G″ are somewhat higher, the difference being close in magnitude to the error of the measurements. With the variable-speed Mooney rheometer, the highest available shear rate is 16 s−1, about one decade less than that with the Rheometrics instrument. With high-molecular-weight rubbers, the range is further reduced, because of “slipping” or “fracturing” of the polymer. On the other hand, the Mooney rheometer enables one to extend the low-frequency range to 2×10−3s−1 very conveniently. The degree of long-chain branching may be estimated from the viscoelastic behavior by comparing complex viscosity and steady-state viscosity at the same time scale, both measurements being made with a Mooney rheometer at a slow speed with a single charge of sample.