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

Reynolds, Carl and Thompson, Richard and McLeish, Tom (2018) 'Pressure and shear rate dependence of the viscosity and stress relaxation of polymer melts.', Journal of rheology., 62 (2). pp. 631-642.

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.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1122/1.5012969
Publisher statement:© 2018 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Reynolds, Carl, Thompson, Richard & McLeish, Tom (2018). Pressure and shear rate dependence of the viscosity and stress relaxation of polymer melts. Journal of Rheology 62(2): 631-642 and may be found at https://doi.org/10.1122/1.5012969
Date accepted:10 February 2018
Date deposited:06 March 2018
Date of first online publication:02 March 2018
Date first made open access:02 March 2019

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