Relations Between High-Temperature Mastication and Mooney Viscosity Relaxation in Natural Rubber

Mastication of natural rubber (NR) is undertaken as a preliminary step towards the preparation of NR-based vulcanizates, a process during which the elastomer is broken down to a homogeneous matrix of lower viscosity. Several tests and indicators are in use for characterizing the behavior of elastomers but these have mostly been adopted for the nonmasticated product. This study uses coefficients generated from modeled Mooney relaxation data, as indicators of elasticity, to examine the effect of high-temperature mastication on the processability of the masticated rubber. Some derived coefficients such as the terminal relaxation time (T) from Maxwell's triexponential model, the elastic component (a) from Wu-Abbott model [Y = 1 + a* ln(t) - bt/(c + t)], and the constant (b) from the Power law model (Y = at(-b)), adequately characterized the effect of mastication on NR. Although the NR grades studied were quite different with respect to their initial molar mass distributions, they followed a similar response to the mechanical models before and after mastication, indicating therefore that mastication decomposes to a similar extent, the various components (long isoprene chains, densely crosslinked solvent-insoluble gel, etc.) that account for the viscoelastic behavior of the raw elastomer. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 2785-2790,2009