A CALIBRATION TECHNIQUE TO EVALUATE THE POWER-LAW PARAMETERS OF POLYMER MELTS USING A TORQUE-RHEOMETER

In this work we develop an empirical method to calibrate the measuring head of a torque-rheometer to obtain the power-law parameters of poly mer melts. This method is based on a similar analysis developed by Lee and Purdon. However, in this work, only one geometrical parameter, wi th well-defined physical limits, is needed for calibration, instead of the two arbitrary parameters proposed by the previous authors. Moreov er, this parameter is closely related to the ordinate of the logarithm ic relationship between the torque (M(T)) and the angular velocity (S- 1), obtained from the torque-rheometer data. This allows us to define a calibration function for this parameter, which is used to evaluate t he consistency index (m) of the melt. On the other hand, experimental results confirm the equivalence between the slope of the logarithmic v alues of torque and angular velocity obtained from the torque-rheomete r data and those of shear stress vs. shear rate obtained from capillar y rheometry. This further highlights the feasibility of evaluating the melt flow index (n) and the consistency index (m) from the torque-rhe ometer data.