Importance of the homogenization method for natural rubber characterization by variable speed mooney viscometer

The Mooney viscometer is an industrial tool that is widely used to characterize elastomers. Cantaloube and Cocard [1] recently showed that the classical rotor speed, 2 rpm, leads to misleading information on natural rubber (NR) due to structural failure during the test by shearing at high speed. It was recommended to using rotor speeds under 0.2 rpm for NR characterization. Our main objective was to evaluate the influence of the two main homogenization methods used (ISO and SMR) on Mooney viscosity determined at different speeds (0.02 - 4 rpm). The study was done on model samples of raw NR which structure was characterized by SEC-MALLS. The results showed that though the differences in Mooney viscosity between the two methods of homogenization were small at 2 rpm, they could be very large at low speeds (< 0.2 rpm). The main reason would be the difference in structures of NR homogenized by different methods, differences in temperature and number of passes.