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Fourier transform rheometry was used to investigate the nonlinear viscoelastic behavior of a series of gum polybutadiene and styrene–butadiene rubbers. A commercial torsional rheometer [the rubber process analyzer (RPA®, Alpha Technologies)] was suitably modified for capturing strain an torque signals, using appropriate software developed in Lab View® (National Instruments). Proprietary programs, written in MathCad® (MathSoft Inc.), were used to perform Fourier transform (FT) calculations and other data treatments. Results showed that FT rheometry provides not only the same information as standard dynamic testing in the linear region, although with a better accuracy, but gives valuable information about the nonlinear behavior of materials. Using a four‐parameter equation to model the variation of the relative 3rd‐harmonic component with strain amplitude, it was found that the strain sensitivity of the materials was adequately quantified, with results apparently consistent with their processing shear sensitivity. The only material parameters that were found to significantly affect the strain sensitivity are the chemical nature of the elastomers (i.e., polybutadiene versus styrene–butadiene rubber) and the molecular weight. No clear effect of the microstructure was seen, however, likely because the sampling was not discriminating enough in this respect. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 90–106, 2005

Strong interactions between elastomer and filler particles result in the so-called bound rubber (BdR), i.e. the fraction of polymer not extractable from uncured filled rubber compounds by a good solvent of the gum elastomer. BdR is an essential characteristic of uncured compounds and a key element in understanding the flow properties of such materials. After a brief review of works that demonstrate how BdR is involved in the particular morphology of uncured filled rubber compounds, the molecular origin of this phenomenon is explained. A kinetic extraction method to assess BdR is described that yields the absolute value of BdR with a compensation for experimental scatter. Results that further demonstrate how bound rubber is related with the rheological properties of filled rubber materials are reported. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1542–1550, 2000