Determination of shear rate and viscosity from batch mixer data

A general analysis allowing the determination of shear rate and viscosity f rom batch mixer rotor speed and torque data is presented. The batch mixer w as represented by two effective adjacent sets of concentric cylinders exert ing the same torque as that obtained from the batch mixer. The effective in ternal radius was determined through a general procedure for calibration us ing non-Newtonian fluid. The effective equivalent internal radius, R-i, was determined for different polymers and processing conditions. The results r evealed that R-i is a universal quantity practically insensitive to the nat ure and to the rheological behavior of the fluid under mixing. In the case of small gaps, it was found that there is a special position in the gap whe re the effective internal radius, the shear rate and viscosity are independ ent of rheological characteristics of the fluid under mixing. This validate s the Newtonian approximation previously used by Goodrich and Porter to ext ract the shear rate-viscosity dependence from batch mixer data. The techniq ue was tested on seven different amorphous and semicrystalline polymers and the results were found to be in reasonable agreement with the data obtaine d independently with cone-and-plate and capillary rheometers. Contributions of both shear stress between the two cylinders and the stress generated at the wall were evaluated. The latter was found predominant. (C) 1999 The So ciety of Rheology. [S0148-6055(99)01102-5].