Open Collections

Hallman, Madeleine Therese

University of British Columbia

The commercial production of cellulose nanocrystals (CNCs) has increased dramatically in recent years in response to the growing demand for sustainably-sources materials. CNCs have proven to be versatile nanomaterials, endorsed for their colloidal stability, rheology, and optical properties, which make them useful as flow modifiers, reinforcing agents in composites, and property modifiers in coatings, etc. To successfully develop functional materials with CNCs, a fundamental understanding of their properties is necessary. In this thesis work, commercially produced carboxylated CNCs (DextraCel™ from Anomera) were directly compared to the more extensively studied and commercially produced sulfated CNCs (CelluRods™ from CelluForce). The colloidal stability window for CNCs in water as a function of ionic strength and pH was established to inform best handling conditions; all CNCs were colloidally stable between pH 3 and 11 with less than 5 mM of added NaCl. The primary factors that increased colloidal stability were decreasing CNC suspension concentration and increasing CNC surface charge. The rheological behavior of carboxylated CNCs as a function of concentration, surface charge and ionic strength was in line with sulfated CNCs. One key difference was that ordered microdomains (tactoids) of carboxylated CNCs were easier to disrupt under shear which resulted in self-assembly not impacting viscosity until higher concentrations than the critical concentration determined visually for liquid crystalline phase separation. CNC self-assembly lends interesting optical properties to suspensions and films; however, the presence of tactoids can be detrimental in some circumstances, e.g. where uniform distribution of CNCs is needed and when flow behavior needs to be consistent over long time periods. CNC tactoids in suspension were successfully disassembled through heating (to 50 °C) for CNCs with low surface charge. Dilution to below the critical concentration and the addition of salt also led to tactoid disassembly. Elucidating this material behavior under a large range of conditions will ideally guide researchers in the development of bioproducts incorporating CNCs.

Text

2025-02-28

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87409

Chemical and Biological Engineering

University of British Columbia

UBCV

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