Analysis of Mooney Viscosity Reduction and Carbon Dispersion during Mixing of Natural Rubber

Abstract

Reduction in Mooney viscosity of natural rubber (NR) of the early stage of mixing in an oval-type twin-rotor mixer was measured during three periods characterized by block breaking, granulation, and viscous flow. The reduction rate was constant in each period, and depended on mechanical design and operating condition for the first two periods. The result shows that Mooney viscosity reductions during the two periods are mainly caused by elastic breaking of NR, and molecular break is closely related to elastic deformation. Dispersion of carbon black (CB) into NR was observed in detail. The granulated particles of NR were coated with fine CB particles, which formed striated layers during viscous flow of NR. Styrene-butadiene rubber (SBR) was also examined for comparison. The striation thickness in SBR was larger than in NR, because SBR was not granulated during mixing. Both energy efficiency and final level of CB dispersion in NR was higher than in SBR. The result shows that granulation during mixing is effective for CB dispersion.