Emily Cranston

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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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.

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Bio-based materials are promising alternatives to less sustainable materials (i.e., petroleum-based chemicals), however, very few have been commercialized in advanced material roles. In addition to formulation development, new processing methods must be established to allow bio-based materials to make the leap from lab-scale to industrial-scale processing. In this work, we investigated the use of cellulose nanocrystals (CNCs) in the microencapsulation of oils. First, drying techniques including freeze drying, spray freeze drying, and spray drying were compared for producing corn oil-filled powders stabilized by CNCs, methyl cellulose (MC) and tannic acid. All three techniques produced dry oil powders with high encapsulated oil content (>90%). The oil powders could be redispersed in water to reform an emulsion and could be stored dry for weeks (in the fridge) without oil leakage. The three drying techniques imparted different surface morphologies that were linked to powder redispersibility and oil release properties. Spray freeze dried powders displayed the most tunable oil release when tested on a hydrophobic substrate. It was demonstrated that spray drying could be used to encapsulate a variety of oils that have different interfacial tensions and volatilities, including jojoba, lavender, and tea tree oil. Next, a dry jet wet spinning apparatus was designed and fabricated to use the same CNC and oil encapsulation system to produce oil-filled fibres. Coaxial extrusion provided a continuous spinning process whereby an external CNC-MC “shell” and internal oil “core” led to fibres with discrete oil-filled beads measuring ca. 2 mm in width along the fibre. The spun fibres were stable under ambient conditions, relatively flexible, and exhibited interesting optical properties. The encapsulated oil could be released by shearing or by re-wetting the fibres. Both the oil-filled powders and fibres were prepared using scalable processing techniques, employed plant-based and industrially-produced “building blocks”, worked with commercially-relevant oils, and will hopefully contribute to the development of environmentally sustainable emulsions, powders, and fibres for food, cosmetic, biomedical, pharmaceutical, agricultural and construction applications.

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