Property modellingProcess simulation of laboratory internal mixers

A global, engineering model of the evolution of torque and temperature during the melt processing stage in a laboratory internal mixer is presented, in terms of material properties and processing conditions. The model could be used, not only to estimate melt viscosity from torque and temperature, but to fully simulate the system, predicting both torque and temperature as functions of time. The model requires the experimental determination of a geometric parameter and of the heat transfer coefficients. Test results with several grades of polypropylene, processed at various operating conditions, show that the geometric parameter is an intrinsic characteristic of the mixer/rotor combination, independent of material and processing conditions. Heat transfer coefficients were measured and found to be proportional to the square root of rotor speed.