Evaluation of the Viscoelastic Temperature and Pressure Shift Factor Over the Full Range of Shear Rates**

Abstract

A method of determining uniquely the best fitting temperature shift parameters of viscosimetric data over the full range of shear rates, based on the Carreau formula, has been presented in Part I. The method is in accordance with the temperature-time superposition principle of viscoelasticity and works fully numerically, thus providing an objective approximation criterion with optimal compensation of scatter and dispensing with any visual control at all, and includes, if necessary, the Rabinowitsch and Bagley corrections. Evaluations of this kind have been carried out for a multitude of old and new measurements of current types of thermoplastics (PE, PP, PS, PA, PC, PMMA, etc.), for which capillaries as well as rotational systems had been employed. In this way, a comprehensive viscosity data bank is built up containing a 5 or 6-parameter set for each material as a compact information about its flow behaviour and serving as a valuable means for numerical process analyses. At the same time, the usual shift formulas (Arrhenius, WLF, etc.) are compared in respect of their applicability and the typical parameter ranges are marked out. Some attention is given to the physical meaning of the material parameters. Part II deals with the validity of the temperature shift principle in general, the incorporation of correction procedures and the evaluation of the pressure dependence of the viscosity.