New measurements of the flow-curves for Carbopol dispersions without slip artefacts |
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Authors: | Geraint P Roberts Howard A Barnes |
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Institution: | (1) Unilever Research Port Sunlight Wirral CH63 3JW, United Kingdom e-mail: Howard.Barnes@Unilever.com, GB |
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Abstract: | The thickening properties of many commercial thickeners are difficult to measure because of wall slip artefacts. Here we
report a series of experiments on a typical thickener where these artefacts have been successfully eliminated. As a result,
complete, steady-state flow-curves of aqueous Carbopol 980 (the toxicologically preferred version of the older and more well-known
Carbopol 940) dispersions are reported for a range of concentrations of 0.045–1.0 wt%. The vane-and-basket flow geometry was
used to avoid slip problems at low shear stress, with the geometry housed in a TA AR1000-N controlled-stress rheometer, whilst
a Haake RV2 viscometer with an SV2P and MV2P concentric-cylinder geometries were used at higher shear rates. The flow-curves
obtained show a smooth but steep transition from a very high Newtonian viscosity at low shear stress to a much lower viscosity
at high shear stress. No real yield stresses were detected, but the higher shear rate results can be fitted to the Herschel-Bulkley
model, which assumes an apparent yield stress. The various model parameters are displayed as a function of Carbopol concentration.
Received: 29 November 2000/Accepted: 26 February 2001 |
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Keywords: | Wall slip Carbopol Dispersion Herschel-Bulkley Vane Controlled-stress rheometer |
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