An appraisal of rheological models as applied to polymer melt flow

Summary

An attempt is made at giving an appraisal of some representative rheological models of both differential and integral type, using the standard rheological measurements of six polymer melts. Experimental data obtained were the steady shear viscosity and the first normal stress difference by means of aWeissenberg rheogoniometer over the range of shear rates: 10⁻² ~ 10 sec⁻¹, and by means of aHan slit/capillary rheometer over the range of shear rates: 10 ~ 10³ sec⁻¹. Also measured by means of theWeissenberg rheogoniometer were the dynamic viscosity and dynamic elastic modulus over the range of frequencies: 0.3 × 10⁻² ~ 3 × 10² sec⁻¹. Rheological models chosen for an appraisal are theSpriggs 4-constant model, theMeister model, and theBogue model.

It is found that the capability of the three models considered is about the same in their prediction of the rheological behavior of polymer melts in simple shearing flow. It is pointed out however that, due to the ensuing mathematical complexities, the usefulness of these models is limited to the study of flow problems associated with simple flow situations. Therefore, in analysing the complex flow situations often encountered with various polymer processings, the authors suggest use of the empirical models of the power-law type for both the viscosity and normal stress functions.