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.

Separating mixtures into their components is a ubiquitous feature of industry, and these separations are necessary for every facet of life down to the simple functions of breathing clean air and drinking potable water. These chemical separations account for a large portion of the total energy use both in the United States and globally. Polymer membrane based separations are desirable when applicable due to their lower energy requirements relative to thermal methods such as distillation. This has led to increases in membrane usage to reduce energy costs; however, membrane separations are not without limitations relating to the membrane material and application requirements. Herein I will address membrane separation technologies, their limitations, and the impact of incorporation of high aspect ratio cellulose nanocrystals (CNCs) on the performance of the resulting polymer composite membranes for desalination and gas phase separations. Lack of available drinking water is an increasing problem across the world with much of the world living in water scarce regions. Desalination using reverse osmosis (RO) membranes is one of the most effective methods of producing clean drinking water. Aromatic polyamide based thin film composite membranes (TFCs) are the most commonly used for commercial desalination and have been since the late 1970s. These TFCs suffer from drawbacks including irreversible performance reduction from fully drying the membrane before use and susceptibility to biological fouling. One technique to mitigate issues with TFCs is to utilize the desirable properties of nanoparticles through their incorporation in the TFC selective layer to create thin film nanocomposite membranes (TFNs). CNCs were selected for this work due to their high aspect ratio, potential for surface modification, attractive mechanical properties, sustainable feedstock, and low toxicity. Membranes containing as received CNCs, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNs), tertiary amine functionalized cellulose nanocrystals (aCNCs), or zwitterionic functionalized cellulose nanocrystals (zCNCs) were synthesized to investigate the effects of nanoparticle functionality and loading level on the brackish water desalination, drying behavior, and fouling resistance of polyamide based TFNs. Loading level was investigating using TOCN containing TFNs which exhibited an increase in water flux and sodium salt rejection up to a maximum when the m-phenylenediamine monomer to TOCN ratio was 20:1 followed by a decrease in both water flux and salt rejection with more TOCN added to the membrane. At the optimal loading level there was a 25% increase in the water flux and 0.2% increase in salt rejection relative to the unloaded control for the membranes kept hydrated and a 146% increase in water flux and 1.6% increase in salt rejection relative to the unloaded control for membranes that were dried. These increases yielded equivalent water flux and salt rejection for the membranes kept hydrated and those dried prior to use at the optimal loading level. The changes in desalination performance are attributed to the introduction of a new water transport pathway at the interface of the TOCN nanoparticle and the polymer matrix and a structural reinforcement effect preventing the collapse of pores present in the polymer during the drying process. The optimal loading level from the previous investigation was used for all work with the other CNC functionalities. The TFNs containing CNCs yielded a 10% increase in water flux and no change in salt rejection relative to the unloaded control while those containing aCNCs and zCNCs yielded no change in water flux and a 0.6% and 0.3% decrease in salt rejection respectively. These differences in behavior relative to the TOCN loaded TFNs are attributed to the transport pathway and structural reinforcement effects being subject to the interaction between the polymer and functionality of the nanoparticle as well as the size and shape of the functional group leading to the differences for each CNC functionality. There were no changes in the foulant resistance for any of the membranes when exposed to water containing bovine serum albumin and sodium alginate as probe foulants. This is attributed to the synthesis procedure in which the nanoparticles are added to the membrane in the denser aqueous phase of the interfacial polymerization. The CNCs will not diffuse well through the polymer as it begins to form, so they would be likely to be concentrated deeper in the membrane while fouling is a surface sensitive behavior, so if the nanoparticles aren't near the surface they will not affect that behavior. Gas separations are of interest for investigation into the effects of high aspect ratio nanoparticles in composite membranes as it allows for investigating more fundamental information through control of the membrane morphology and mixture composition. The range of molecule sizes in the separation is much smaller for gas separations compared to desalination with kinetic diameter differences on the order of 0.1-1 Å compared to 4.5Å. Additionally, with the lower pressure requirements for gas transport relative to reverse osmosis, simple membrane geometries can be investigated using dense films rather than TFNs. In this investigation, dense film composite membranes were made consisting 0, 0.07, 0.7, 3.6, 7.2% or 15% CNCs by volume in a thermoplastic polyurethane (TPU) matrix. The addition of TPU showed increased structural strength in the film with loading modulus increasing from 10 MPa for the unloaded TPU to 58 MPa for 3.6% CNC loaded TPU and 105 MPa for 7.2% CNC loaded TPU. The gases tested during this investigation are CO2, He, Ar, O2, and N2. As the CNC loading level increased, the gas permeability for each gas decreased. For the gases other than CO2, there 0.07, 0.7, and 3.6% CNC films all had the same permeability with all, but Ar, 47 ± 3 % less than the unloaded film permeability. The 15% CNC permeabilities were all 44 ± 1 % less than that of the 0.07, 0.7, and 3.6% CNC films. For CO2, the permeability decreased with each addition of CNC. None of these decreases are described by simple space filling by an impermeable particle. This indicates that the structural reinforcement providing strength to the membrane may be limiting some of the chain mobility inhibiting the diffusion of gases through the membrane which is seen in the diffusion coefficient of CO2 which decreases with increasing CNC loading. / Doctor of Philosophy / Mixtures often need to be separated into their individual parts. These mixtures are often difficult to separate like salt from water or pollution from air. These are important problems as everyone needs clean air to breath and clean water for drinking, cleaning, and watering crops and there are places all over the world without enough clean air and water. A common way to separate these difficult mixtures involves boiling the liquids to become gases and then cooling the gases back down to form a purified liquid. Unfortunately, these methods take immense amounts of energy at a time in which energy demand is at an all-time high. It is important to improve the performance of the low energy demand methods such as membrane separations, where a thin material acts as a filter on scale small enough to conduct these difficult separations. Membranes come with their own drawbacks that must be addressed such as a tradeoff between the rate of separation and product purity as well as a tendency to be blocked by contaminants that get stuck to the membrane surface. One method people have tried to address these drawbacks is the introduction of incredibly small particles called nanoparticles that have properties the membrane material lacks. This can lead to improved separation performance, but it is important to expand the separation conditions, the form of membranes tested, and the type of mixture separated to better understand how the nanoparticles work within the membrane. A better understanding of how nanoparticles work will allow for more widespread application and increased efficiency lowering energy demands and improving access to needs such as clean air and water. In this work we have included long, thin nanoparticles produced from wood into desalination and gas separation membranes to investigate the changes in the rate and purity of clean water produced, the resistance to contaminates, and rate that gases can cross the membrane.

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

<p dir="ltr">Food packaging plays a crucial part, yet the use of petroleum-based plastics has led to environmental concerns. Researchers have been exploring sustainable alternatives using CNMs. This dissertation includes three parts, each focusing on using CNF or CNC for packaging applications. In the first project, CNF/CMC coated MP trays were achieved via over-molding. Mechanical, Gurley air porosity and water vapor transmission rate testing showed that the coating improved the overall performance. Coated samples showed the highest oil and grease resistance level. Fresh fruit testing showed that the coating helps elongate the shelf life of fruits. In the second project study, to overcome the problem of relatively poor water barrier performance of CNF/CMC coatings in high humidity conditions, coatings were chemically modified by crosslinking with PAE and incorporated with Cloisite-Na⁺ nano-clay and PVA. The chemical modification enhanced both water and oxygen barrier performance and reduced Cobb value. The formulated CNF-coated MP trays maintained the same level of oil and grease resistance. Mechanical testing showed reduced Young’s modulus, similar UTS, and higher strain at break for formulated CNF-coated tray samples compared to the un-crosslinked samples. In the third project, a transparent tri-layer PLA-CNC/PVA-PLA film was successfully fabricated using blade coating and lamination. The CNC/PVA coating (~ 6μm) showed a high degree of CNC alignment and significantly enhanced the gas barrier properties. Furthermore, these laminates were formed into bags where a fruit storage test showed that the PLA-CNC/PVA-PLA could elongate the shelf life of fresh apple slices based on weight loss and enzymatic browning.</p>