Nanocellulosics, often found in the form of cellulose nanocrystals (CNCs) and nanofibrillated cellulose (NFCs), provide promise as rheological modifiers and reinforcement fillers for composite materials. The biological origin of CNCs promises a bio-renewable resource with the potential to expedite degradation times compared to synthetic polymer species. Additionally, the surface functional groups provide a route for both hydrogen bonding and further chemical modification. While much research is currently investigating the possible uses of these materials, they offer limited aid if their use is not scalable to industrial processing techniques. Common processing techniques such as injection molding subject materials to high temperatures and strain rates upwards of 100000 s-1. Thermal stability is a known challenge that can be increased via chemical modifications, but little is known about the effects of high or extended shear stresses typical of those experienced during typical polymer processing. High shear rates, which proportionally result in high shear stresses, have the potential to influence the alignment, degradation, and overall usability of these materials when employed in consumer applications. In this work, we investigate the rheology and processing of aqueous CNC suspensions at concentrations up to 12.1 wt% and of aqueous NFC suspensions at concentrations up to 20 wt% under capillary shear stresses. Traditional capillary rheology corrections, including the Weissenberg-Rabinowitsch-Mooney (WRM) correction for non-Newtonian fluids, and the Bagley correction for entrance pressure effects, have been applied to determine the true rheological behaviors of these suspensions. Additional analysis using atomic force microscopy (AFM), wide-angle x-ray scattering (WAXS), and conductometric titration assist identification of morphological and chemical changes that affect the CNMs after they have been subjected to industry-relevant shear rates. These studies demonstrate that processing conditions can significantly affect the size and shape of the post-processed nanomaterials by fracturing the CNCs and unwinding the larger bundles of the NFCs. Given the importance of the final aspect ratio of filler and reinforcement materials, the impact of this discovery will substantially influence how these materials are used and processed to create consumer products. / Doctor of Philosophy / As the world struggles with the problem of plastic waste and climate change, it is important to develop biologically friendly solutions to combat these issues. Filler materials such as carbon fibers and glass fibers can help create lightweight materials for cars and transportation containers. However, carbon fibers can be hazardous and expensive to obtain. Glass fibers offer a more cost-effective option, but they often break during processing and are heavy in comparison to carbon fibers. Cellulose nanomaterials (CNMs) can provide a lightweight and more bio-friendly alternative to these fillers. These CNMs can come from a wide variety of sources, such as hardwood trees, bacteria, or tunicates (a type of marine animal). This makes them abundantly available, relatively cheap to produce, and easy for the environment to break down fully. Using these as fillers instead of glass fibers, carbon fibers or other materials could help reduce much of our waste, but we need to be able to process them in the same ways we currently handle other composite materials. This work focuses on characterizing the effect of high-speed flows and the forces those flows put on the cellulose nanomaterials. The following document will show that the smaller, more rigid, cellulose nanocrystals (CNCs) often break under these stresses, while the longer nanofibrillated cellulose (NFCs) unwind and disperse.

Access to clean water is one of the world's foremost challenges that has been addressed on a large scale by membrane-based separation processes for the last six decades. Commercial membrane technology within one operation, reverse osmosis, has remained consistent since the late 1970s, however within the last two decades, access to nanotechnology has created a realm of study involving thin film nanocomposite (TFN) membranes, in which nanoparticles are incorporated into existing membrane designs. Desirable properties of the nanoparticles may positively impact qualities of the membrane like performance, anti-fouling behavior, and physical strength. In the present work, two types of nanoparticles have been evaluated for their potential as TFN additives: cellulose nanocrystals (CNCs) and metal-organic framework (MOF) nanorods. CNCs were chosen due to their high aspect ratios, mechanical strength, and potential for surface functionalization. MOF nanorods are also of interest given their aspect ratios and potential for functionalization, but they also possess defined pores, the sizes of which may be tuned with post-synthetic modification. Both CNCs and MOF nanorods were incorporated into TFN membranes via interfacial polymerization, and the resulting membranes were characterized using a variety of techniques to establish their performances, but also to gain insight into how the presence of each nanoparticle might be affecting the membrane active layer formation. A resulting CNC membrane (0.5 wt% loading) exhibited a 160% increase in water flux and an improvement in salt rejection to 98.98 ± 0.41 % compared to 97.53 ± 0.31 % for a plain polyamide control membrane. Likewise, a MOF nanorod membrane (0.01 wt% loading) with a high ratio of acid chain modification exhibited a 95% flux increase with maintained high salt rejection. For the CNCs, the flux increase is attributed to the formation of nanoscale voids along the length of each particle that form during the interfacial polymerization. These nanochannels introduce new rapid water transport pathways within the active layer of each membrane while maintaining ion rejection. The proposed mechanism for the MOF nanorods also introduces nanochannels into each membrane, but the presence of each nanorod's pore structure may offer another transport pathway for water molecules, one that varies with pore size. In combination, these results have allowed the study of molecular transport of water molecules and various ion species within the active layer of a thin film composite RO membrane. Understanding these phenomena will allow the development of smarter membrane materials to address present-day and future separations challenges. Carbon nanotubes are also demonstrated as surface modifiers for forward osmosis (FO) membranes to address issues unique to the FO process, namely reverse solute flux (RSF). This method shows promise, as a coating density of 0.97 g/m2 reduced RSF for many draw solution species, including a 55% reduction for sodium chloride. / Doctor of Philosophy / Access to clean water is one of the world's foremost challenges that has been addressed on a large scale by membrane-based separation processes for the last six decades. Commercial membrane technology within one operation, reverse osmosis, has remained consistent since the late 1970s, however within the last two decades, access to nanotechnology has created a recent realm of study in which nanoparticles are incorporated into existing membrane designs. It is desired to use nanotechnology, or nanoparticles to improve membrane performance, i.e. create a membrane with better rejection of unwanted ions or contaminants or improve the amount of water that passes through the membrane. In the present work, two types of nanoparticles have been evaluated for their potential as TFN additives: cellulose nanocrystals (CNCs) and metal-organic framework (MOF) nanorods. Both CNCs and MOF nanorods were incorporated into membranes and the resulting membranes were characterized using a variety of techniques to establish how the nanoparticles affected performance. A resulting CNC membrane (0.5 wt% loading) exhibited a 160% increase in water flux (the amount of water passing through an area in a given amount of time) and an improvement in salt rejection. Likewise, a MOF nanorod membrane with a high ratio of acid chain modification exhibited a 95% flux increase with maintained high salt rejection. For both the CNCs and the MOFs, these performance changes are attributed to new pathways within each membrane for water flow that exist due to the presence of the nanoparticles in each system. In combination, these results have allowed the study of transport of water molecules and various ion species in each membrane. Understanding these results will allow the development of smarter membrane materials to address present-day and future separations challenges.

With the rapid development of concrete 3D printing for construction projects, it is crucial to produce sustainable 3D-printed cementitious composites that meet the required fresh and hardened properties. This study investigates the application of cellulose-based nanomaterials (CN) (i.e., abundant natural polymers) that can improve the mechanical properties of cement-based materials – in 3D-printed cementitious composites of ordinary portland cement (OPC) and alkali-activated materials (AAMs). A combination of low calcium fly ash and ground granulated blast-furnace slag was used as the precursor in AAM systems. This work examines the 3D-printed mixtures with varying binders and mixture proportions and with different dosages of cellulose-based nanomaterial known as cellulose nanocrystals (CNC) to optimize the formulation for the production of sustainable high-performance 3D-printed elements. A suite of experimental techniques was applied to study the impact of CNC on the fresh and hardened properties of the 3D-printed samples. The buildability of the alkali-activated mixtures was improved by increasing the CNC content, suggesting that the CNC performs as a viscosity-modifying agent in AAMs. The inclusion of CNCs up to 1.00% (by volume of the binder) improves the overall mechanical performance and reduces the porosity of 3D-printed OPC and heat-cured AAM samples. Further, the addition of CNC (up to 0.30%) in sealed-cured AAM samples improves their flexural strength due to the crack-bridging mechanism of CNCs. The addition of CNC densifies the microstructure of OPC samples by increasing the degree of hydration, however, no significant impact on the microstructure of AAMs is noticed. The OPC sample with CNC has approximately 25% increase in the degree of hydration at inner depths which can be attributed to the internal curing potential of CNC materials. The initial water absorption rate of heat-cured AAM samples is lower than the sealed-cured AAM samples and comparable to the OPC system. The developed printable “alkali-activated-CNC” composites can provide an overall reduction in the environmental impacts of the 3D-printed cementitious composites by eliminating/reducing the need for different chemical admixtures to improve 3D-printed material consistency and stability, and replacing 100% of portland cement with fly ash and slag. / Civil Engineering