Cross-slot extensional rheometry and the steady-state extensional response of long chain branched polymer melts
(2011) Journal of Rheology — Vol. 55, n° 4, p. 875-900 (2011)
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- Abstract
- Stress-optical measurements at a flow stagnation point in confined geometries such as the cross-slot provide an elegant way to perform extensional testing for polymer melts. This technique is especially useful for samples which have a steady-state that cannot be reached (easily) in standard elongational rheometry, for example, highly branched polymers which show a non-homogeneous deformation that occurs in stretching experiments for Hencky strains above 4. In contrast to filament stretching, the cross-slot provides one point at which steady-state extensional flow may be sustained indefinitely. In this study, a Cambridge multi-pass rheometer [Coventry, K. D., and M. R. Mackley, J. Rheol. 52, 401-415 (2008)] is used to generate planar elongational flow in a cross-slot geometry for different polyethylene melts. The experimental results are compared to finite element flow simulations using the multi-mode Pompom constitutive equations. The steady-state elongational viscosity at the stagnation point is computed from the flow-induced stress birefringence and the strain-rate determined from numerical calculations of the flow field. We apply this technique to a range of different branched high- and low-density polyethylene melts. This demonstrates both the effectiveness of this technique and shows how the stress distribution in a complex flow depends on molecular structure. Cross slot extensional rheometry therefore provides a very promising technique for parameterizing molecular constitutive equations for LCB melts. © 2011 The Society of Rheology, Inc.
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Auhl, D., Hoyle, D. M., Hassell, D., Lord, T. D., Harlen, O. G., MacKley, M. R., & McLeish, T. C. B. (2011). Cross-slot extensional rheometry and the steady-state extensional response of long chain branched polymer melts. Journal of Rheology, 55(4), 875-900. https://doi.org/10.1122/1.3589972 (Original work published 2011)