This
study focuses on investigating the phenomena involved in the
formation of the concentration polarization and fouling layer during
the cross-flow ultrafiltration process of cellulose nanocrystal (CNC)
suspensions. Thanks to new cross-flow ultrafiltration cells specially
designed, experiments of first time-resolved in situ Small Angle X-ray Scattering (SAXS) and second time-resolved in
situ micro Particle Image Velocimetry (micro-PIV) at the vicinity
of the membrane surface during filtration were performed. These two
methods have given access to the concentration profiles and the velocity
field as a function of the distance z from the membrane
surface within the concentration polarization layers. The results
obtained show an increase in particles concentration related to a
decrease in the velocity within the layers formed during the process.
This information linked to the rheological behavior of the suspensions
permitted access to the calculated stress field within the concentrated
layers during the cross-flow ultrafiltration process. Three different
areas of shear stress/shear rate behaviors near the membrane surface
have been emphasized. The important role of the rheological behavior
and interparticle interaction in the dynamic evolution in space and
time of the accumulated layers has been highlighted.
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