Structure, Rheological Behavior, and in Situ Local Flow Fields of Cellulose Nanocrystal Dispersions during Cross-Flow Ultrafiltration

Abstract

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.

Breakdown and buildup mechanisms of cellulose nanocrystal suspensions under shear and upon relaxation probed by SAXS and SALS

“…Rheometric measurements were carried out using a shear rate controlled rheometer (DHR3, TA Instrument) with a cone-plate geometry of 65 mm diameter and angle of 2° in the same conditions as in scattering experiments. These values of shear thinning index n were deduced from our previous results (Gicquel et al, 2019;Rey et al, 2019). Measurements were performed at a fixed temperature of 25 ± 1 °C.…”

“…In order to improve the development of nanocellulosebased materials, several processes involving shear flow or pressure forces have been subject of in situ structural investigations. For example, time-resolved in situ small-angle X-ray scattering (SAXS) was successfully employed to access the structural organization and growth of accumulated particles near the membrane surface during cross-flow ultrafiltration (Jin et al, 2015;Rey et al, 2019;Semeraro et al 2020). In situ and real time grazing-incidence wide-angle X-ray scattering (GIWAXS) was used to investigate the influence of suspension concentration, shear-cast velocity, and drying temperature on the ordering of the CNCs during the casting process (Sanchez-Botero et al, 2018).…”

Build-up and relaxation of membrane fouling deposits produced during crossflow ultrafiltration of casein micelle dispersions at 12 °C and 42 °C probed by in situ SAXS

“…Refs. [48][49][50]70,71,79]). It corresponded to wall shear stress τ w ≈ 0.2 Pa (at 12 • C) and 0.1 Pa (at 42 • C).…”

“…This can be explained by an instant shift of the flexible polymeric filtration membrane away from the rigid membrane support due to the instant reduction of TMP [70,71] (although a low TMP of 10 kPa was maintained in order to reduce this effect during the pressure relaxation). The shift of the membrane towards positive z brought the inner sublayer of casein micelles, which was localized close to the membrane surface (z < 20 μm) and was not accounted for in the calculations of m ex and h g during the earlier filtration step, into the scope of SAXS analysis (z > 20 μm) [70,71], resulting in an apparent increase of m ex and h g . According to Fig.…”

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

“…This confirmed the theoretical prediction of a confinement-induced anisotropy of the pair correlation function of a fluid. SAXS allowed the characterization of microstructure within the concentration polarization layer during the cross-flow ultrafiltration process of cellulose nanocrystal dispersions, including the orientation and packing as a function of the distance from the membrane, and link to the concentration polarization and identifying the fouling layer near the membrane [123].…”