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Danesh, Marziyeh

University of British Columbia

Colloidal gels of cellulose nanocrystals (CNCs) were prepared by increasing ionic strength. The ultimate objective was to investigate stabilization of zirconia suspensions by using a small amount of CNC by changing electrolyte concentration or pH. First, the rheological behavior of CNC hydrogels in the presence of a monovalent electrolyte (NaCl) as a function of CNC and salt concentration was explored using a variety of linear and nonlinear rheological tests. Two step-yielding behavior was observed for CNCs in the presence of high electrolyte concentration from amplitude sweep experiment. The first yielding corresponds to the maximum in the loss modulus at the crossover point between storage and loss modulus due to disconnection of link between CNC clusters. The second yield stress is due to the deformation of clusters to smaller flocs and individual nanorods (corresponding to the change in the slope of loss modulus at higher shear strains). Small angle light scattering measurements, confocal laser scanning microscopy and polarized microscopy images confirmed the gradual breakup of clusters to smaller ones and eventually to nearly individual fibers with an increase in the applied shear strain and rate. CNCs were used as a dispersant to stabilize water-based zirconia suspensions. The zirconia suspensions as functions of solid content, pH and CNC concentration were studied to produce stable highly concentrated suspensions. The achieved stability was found to be due to the adsorption of CNC nanofibers around the zirconia particles revealed by Scanning Electron Microscopy (SEM) images. Suspensions with the lowest viscosity and highest stability over 24 h achieved at pH 4 i.e., 30 wt.% zirconia particles stabilized with the addition of 1 wt.% CNC. Finally, the effect of CNC and NaCl concentration was studied on the stability, adsorption, zeta potential, size, and rheology of slurries. The results confirm that the adsorption capacity of CNC on the surface of zirconia particles increases as salt concentration increases, associated with rise in the viscoelastic properties and denser structure on the surface of adsorbent. It has been concluded that zirconium oxide suspensions of high concentration (>30 wt.%) can be effectively stabilized by using a small amount of CNC (<1 wt.%).

Text

2022-06-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/81799

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/