3840 EVALUATION OF SHEAR RATE AND VISCOSITY IN TORQUE RHEOMETER T. S. Valera, S. M. Toffoli, N. R. Demarquette Departamento de Engenharia Metalúrgica e de Materiais da Escola Politécnica da USP Av. Prof Mello Moraes, 2463, CEP: 05508-900 - São Paulo/SP E-mail: nick@usp.br ABSTRACT A torque rheometer is a batch mixer that measures the torque on the blades as a function of the mixing time. It is very useful to extract more fundamental information using this kind of rheometer. In this work it was used a model developed by Bousmina to investigate the rheological properties of polymer melts in a torque rheometer. This model was developed from a previous model proposed by Goodrich and Porter, who developed a correlation based on the rheometer dimensions, and which converts torque and the rotational speed of the rotors into apparent viscosity and shear rate. The viscosity as a function of the shear rate of the polymers was obtained using Bousmina’s model. To check the effectiveness of the model of Bousmina, the viscosities as a function of shear rates have also been measured in a capillary rheometer. Good agreement between the behavior of the curves viscosity x shear rate evaluated in both capillary and torque rheometer was observed for most polymers tested, although the universal value for R i was not achieved. Key-words: torque rheometer, internal mixer, capillary rheometer, rheological properties, model INTRODUCTION A torque rheometer is a batch mixer that measures the torque applied to the mixing blades as a function of the mixing time. It is widely used in laboratories working on polymer processing. Using torque to obtain other fundamental pieces of information, like viscosity, can be of great help, not only to the scientists, but also to the industry. The curve viscosity as a function of the shear rate is usually obtained using a capillary rheometer. However, this instrument can not always be available at research laboratories. On the other hand, a torque rheometer can be used to evaluate the preliminary behavior of mixtures, to evaluate changes occurring during the processing, and even to determine the effect of additives on new formulations, with the advantage that all this valuable information can be obtained from a single equipment, which does not require a person bearing deep rheology knowledge to operate it. There are few experimental studies that correlate the results obtained by torque rheometry and capillary rheometry (1-5) . These correlations can be divided into two groups: the research groups (5) that found a universal quantity β (the ratio between the chamber radius and the inner equivalent radius), practically insensitive to the nature and rheological behavior of polymer melts and others (1-4) that calculated β by empirical methods, and did not obtain a single universal value for all the polymer. Theory Among all the theories correlating the properties obtained in the torque and capillary rheometers, it was adopted in this paper the model proposed by Bousmina (5) , that calculated the value of β using non-empirical methods. His model was developed from a previous model proposed by