Abstract
A rheometric method based on velocity profiling by
optical coherence tomography (OCT) was used in the
analysis of rheological and boundary layer flow
properties of a 0.5% microfibrillated cellulose (MFC)
suspension. The suspension showed typical shear thinning
behaviour of MFC in the interior part of the tube, but
the measured shear viscosities followed interestingly two
successive power laws with an identical flow index
(exponent) and a different consistency index. This kind
of viscous behaviour, which has not been reported earlier
for MFC, is likely related to a sudden structural change
of the suspension. The near-wall flow showed existence of
a slip layer of 2-12 µm thickness depending on the flow
rate. Both the velocity profile measurement and the
amplitude data obtained with OCT indicated that the slip
layer was related to a concentration gradient appearing
near the tube wall. Close to the wall the fluid appeared
nearly Newtonian with high shear rates, and the viscosity
approached almost that of pure water with decreasing
distance from the wall. The flow rates given by a simple
model that included the measured yield stress, viscous
behavior, and slip behavior, was found to give the
measured flow rates with a good accuracy.
Original language | English |
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Pages (from-to) | 4715-4728 |
Number of pages | 14 |
Journal | Cellulose |
Volume | 24 |
Issue number | 11 |
DOIs | |
Publication status | Published - 2017 |
MoE publication type | A1 Journal article-refereed |
Keywords
- shear viscosity
- yield stress
- lubrication layer
- slip velocity
- velocity profile
- optical coherence tomography