title: Cellulose Filaments, A novel Nanocellulose for Advanced Colloidal Applications
Creators: name: Varamesh, Amir
Publisher: name: Graduate Studies
Year: 2024
Subjects: subject: Nanocellulose
subject: Colloids
subject: Emulsions
subject: Aerogels
subject: Porous Materials
subject: Biobased materials
subject: Water treatment
subject: Thermal insulation
subject: Engineering--Chemical
subject: Engineering--Environmental

description: With growing global awareness of sustainability, environmental protection, and the harmful effects of fossil fuel-derived materials, biorenewable sources, such as nanocellulose, have gained considerable attention over the past decades. This thesis explores the potential applications of a less studied yet more economically viable and scalable form of nanocellulose, cellulose filaments (CFs). Specifically, the thesis investigates CFs' role in different colloidal systems including emulsion stabilization and the development of aerogels for water treatment and fire-retardant thermal insulation. The application of CFs in oil in water Pickering emulsion stabilization was explored and compared with conventional nanocellulose including cellulose nanofibrils (CNFs) and TEMPO-oxidized CNFs (TEMPO-CNFs), and nanocrystals (CNCs). Emulsion stability analysis revealed that CFs outperform CNCs and TEMPO-CNFs in forming stable emulsions. Investigations into the stabilization mechanism suggest that the superior performance of CFs is likely due to the high viscosity of the aqueous phase and the formation of an entangled network of fibrils within the continuous phase. Furthermore, CFs exhibit strong adsorption at the oil-water interface, providing enhanced emulsion stability under environmental stresses such as varying pH (2–10) and ionic strength (0–500 mM NaCl). These findings indicate that CFs are a promising nanocellulose for the sustainable and cost-effective formulation of stable Pickering emulsions, with potential applications across a wide range of industries. The application of CFs in creating fully biobased aerogels (FBAs) for water treatment and fire-retardant thermal insulation was also explored. CFs, combined with chitosan (CS) and citric acid (CA), were used to develop mechanically robust composite aerogels. The resultant aerogels were tested for their ability to remove three major water pollutants: dyes, heavy metals, and oil/organic solvents. Due to the unique structure and the abundance of active sites provided by the biobased composite system, the aerogels exhibited exceptionally high adsorption capacities for methylene blue (619 mg/g) and copper (206 mg/g). Surface modification through silanization rendered the FBAs highly efficient for oil-water separation, achieving over 96% separation efficiency. Additionally, the FBAs demonstrated excellent reusability, recyclability, and antibacterial properties, making them an ideal adsorbent for water treatment applications. Finally, the application of the developed FBAs was extended to fire-resistant thermal insulation via layer-by-layer (LBL) assembly using oppositely charged biomaterials, namely phytic acid and chitosan. Aerogels with six bilayer depositions (LBL6) exhibited an outstanding peak heat release rate (pHRR) of 6.0 kW·m−2 and a total heat release (THR) of 0.4 MJ·m−2, significantly lower than previously developed cellulose-based aerogels and foams. LBL6 also demonstrated immediate self-extinguishing behaviour with an impressive limiting oxygen index (LOI) of 63%, the highest reported for a biobased aerogel. Furthermore, the aerogels showed a superior Young’s modulus of up to 4.5 MPa, outperforming other flame-retardant aerogels, and exhibited excellent thermal insulation properties, with a thermal conductivity of less than 38.2 mW·m−1·K−1, on par with or even better than commercial thermal insulators. Given the simplicity of the fabrication process and the inherent benefits of a fully biobased system, these aerogels represent a sustainable and environmentally friendly alternative to current petroleum-based thermal insulators.