The temperature calibration of a parallel plate rheometer and evaluation of the thermal lags during polymer solidification

Parallel plate rheometers are often employed for analysing the effect of small amplitude oscillations, with different frequencies, on the crystallization of polymers. Practical problems associated to this application are analysed and discussed with emphasis on those involved with the temperature measurements and the true sample temperature evaluation. A temperature calibration method of these devices, for nominally isothermal and cooling experiments, is tested through simultaneous measurements of the sample temperature performed with an additional thermocouple. The magnitude and errors of the isothermal correction are evaluated and their effect on the recorded experimental data is also discussed. For isothermal and nonisothermal experiments, the additional thermal effects ascribed to the sample thermal resistance and to the heat of crystallization released during the solidification are also evaluated. The effect of these corrections over DSC and rheometer results is analysed and discussed.