Cross-slot extensional rheometry and the steady-state extensional response of long chain branched polymer melts

Auhl, D.; Hoyle, David M.; Hassell, D.; Lord, T.D.; Mackley, M.R.; Harlen, O.G.; McLeish, T.C.B.

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.

Citation

Auhl, D., Hoyle, D. M., Hassell, D., Lord, T., Mackley, M., Harlen, O., & McLeish, T. (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

• Journal Article Type: Article
• Publication Date: Jul 1, 2011
• Deposit Date: Feb 16, 2012
• Publicly Available Date: Jul 31, 2017
• Journal: Journal of Rheology
• Print ISSN: 0148-6055
• Electronic ISSN: 1520-8516
• Publisher: American Institute of Physics
• Peer Reviewed: Peer Reviewed
• Volume: 55
• Issue: 4
• Pages: 875-900
• DOI: https://doi.org/10.1122/1.3589972
• Public URL: https://durham-repository.worktribe.com/output/1514114