Pressure and shear rate dependence of the viscosity and stress relaxation of polymer melts

Reynolds, Carl; Thompson, Richard; McLeish, Tom

Abstract

The pressure dependencies of polymer viscosity and stress relaxation are an important but often overlooked aspect of the material processing and postprocessing properties. We show how these dependencies can be isolated in a single measurement and can be related to the characteristic relaxation times of the material. Using a multipass rheometer (a small volume double piston rheometer), a polystyrene melt was confined at 170 °C and pressure range 1–100 bar. The pressure drop over a contraction-expansion geometry and stress birefringence were monitored as a function of shear rate, shear history, and applied pressure. Relaxation times, extracted from the stress decays correspond closely to the Rouse and reptation times of the polymer and the contributions of each mode are determined by the relationship between the shear rate and relaxation times established from linear rheology. Increasing the applied pressure caused an increase in viscosity and the measured relaxation time, but no effect on relaxation times was observed with shear rate. The technique allows the extraction of relaxation data following deformation at high shear rates and pressures, conditions more akin to industrial processing than conventional shear rheology.

Citation

Reynolds, C., Thompson, R., & McLeish, T. (2018). Pressure and shear rate dependence of the viscosity and stress relaxation of polymer melts. Journal of Rheology, 62(2), 631-642. https://doi.org/10.1122/1.5012969

• Journal Article Type: Article
• Acceptance Date: Feb 10, 2018
• Online Publication Date: Mar 2, 2018
• Publication Date: Mar 2, 2018
• Deposit Date: Mar 6, 2018
• Publicly Available Date: Mar 6, 2018
• Journal: Journal of Rheology
• Print ISSN: 0148-6055
• Electronic ISSN: 1520-8516
• Publisher: American Institute of Physics
• Peer Reviewed: Peer Reviewed
• Volume: 62
• Issue: 2
• Pages: 631-642
• DOI: https://doi.org/10.1122/1.5012969
• Public URL: https://durham-repository.worktribe.com/output/1365628