On the interpretation of data from Converging Flow Rheometers

Abstract

A reappraisal of data obtained from a Converging Flow Rheometer (CFR) is presented, together with new results for a specific polymer solution.Particular emphasis is placed on the interpretation of the experimental pressure data in terms of a planar extensional viscosity. It is suggested that previous interpretations, while yielding viscosity levels that appear reasonable, nevertheless fail to give the qualitative behaviour that might be expected on the basis of predictions from well accepted constitutive models. This, in the authors' opinions, arises because certain fluids, i.e. those that are highly tension-thickening, cease to flow in accordance with the assumed kinematics at high flow rates.By adapting a recently proposed approximate analysis for flow through a contraction it is shown that better qualitative behaviour, for the planar extensional viscosity, can be obtained from the Converging Flow Rheometer.

Effect of convergent–divergent flow on thermal and crystallization properties of PP/MWCNTs nanocomposites

“…The extensional deformation in the C‐D die will change periodically when materials flow through the convergent plates. Jones and Binding and Kim et al . have used planar hyperbolic‐shaped dies to analyze the extensional flow on the properties of polymer blends.…”

Melt rheological properties of ETFE: an attempt to illuminate the fluorine-substitution effect

“…By means of Binding and Cogswell's theory [38][39][40][41], extensional viscosity can be determined from entrance effect of the capillary rheometry. Several assumptions are made in their theory: first, the polymer melt adopts a coni-cylindrical flow pattern as it passes from the reservoir into the capillary to minimize the entrance pressure drop; second, the shear viscosity of the polymer melt can be described in terms of a power law model.…”

Rheological study on tetrafluoroethylene/hexafluoropropylene copolymer and its implication for processability

“…When a fluid flow from the barrel of a capillary rheometer into a capillary die, converging flow occurs, and the fluid is stretched at the die entrance along the direction of its axis. The stretching brings to extra pressure drops (Δ P ent ) localized at the entry of the die 15–18. The converging flowing is a complex flow, which combines extensional with shear flow component.…”

“…However, this technique can only effectively characterize extensional flow behavior at low strain rate and is difficult to operate. Alternatively, capillary rheometer with a set of dies can be used to determine elongational viscosity on the basis of Cogswell and Binding's work on converging flow and entry flow 15–18. Such technique is easy to operate, needs no extra instruments, and has relatively better accuracy, especially at high elongational strain rate 19–23.…”