Structuring Of Cellulose Nanocrystal Deposit Layers During Crossflow Membrane Filtration

Date

2025-8-26

Author

Barış, Bengisu

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This study investigates the formation of deposit layers from TEMPO (2,2,6,6- Tetramethylpiperidin-1-yl)oxyl)-oxidized cellulose nanocrystals (TEMPO-CNCs) and how their structures are affected by TEMPO-CNC concentration, salt concentration and deposition duration. TEMPO-CNCs obtained by TEMPO-oxidation of CNCs synthesized via sulfuric acid hydrolysis were deposited onto porous support membranes using crossflow filtration. 0.2 M AlCl3 was used for the stabilization of the formed cake layers, followed by rinsing with ultrapure water. Characterization techniques including polarized optical microscopy (POM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were employed to investigate flux behavior, resistance, optical behavior, and solid content in the cake. AlCl3 permeation raised solid content without significantly affecting cake resistance, which is attributed to a highly concentrated concentration polarization layer with comparable resistance to the cake layer. Polarized optical microscopy revealed a transition from nematic to cholesteric structure with longer deposition times, indicating structural reorganization in the cake layer. Filtration of TEMPO-CNC suspension with 100 mM NaCl concentration resulted in aggregation on the cake surface. At 5 mM NaCl, cakes prepared with different TEMPO-CNC concentrations exhibited both nematic and cholesteric ordering. The samples prepared with the suspensions of 0.30% TEMPO-CNC and various NaCl concentrations showed both nematic and cholesteric symmetries in their structures. Gel layer concentrations were vi estimated around 1 wt.% from limiting flux data, while higher solid contents were calculated using the Kozeny-Carman equation and TGA. This study enabled a better understanding of the relationship between deposition durations, TEMPO-CNC concentration, salt concentration and the structural properties of TEMPO-CNC deposit layers.

Subject Keywords

TEMPO-CNC, Crossflow membrane filtration, Cake formation, Cholesteric phase, Nematic phase

URI

https://hdl.handle.net/11511/115641

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Graduate School of Natural and Applied Sciences, Thesis