Cellulose nanocrystals (CNC) are great candidates for composite materials. The reasons why CNCs are such attractive materials for them are due to their great mechanical properties, high aspect ratio and low density. On the other hand, hydroxyapatite (HAp) is a kind of calcium phosphate and a main component of bones and teeth. The purpose of the present study is to make oriented nano-sized composites with CNC and HAp. Although some researchers carried out to make CNC composites with HAp for biomedical materials, nano-sized and oriented ones haven’t been achieved yet. Also, films made of CNC and other compounds are known to be transparent and have good oxygen permeability. Especially when CNCs’ direction is in parallel, they show high strength. However most previous researches dealt with particles or plate-like minerals in inorganic/CNC films, so there is no case that coated CNCs themselves were aligned in the films. Therefore fabrication of composite-oriented thin films is quite unique and it will be a potential step for bone-like hierarchical structure. In experiment, certain amount of CNC suspension with functional groups were put into revised simulated body fluid (r-SBF) solutions which were adjusted between pH 6.9-7.9 to make the molar ratio of calcium ion per functional groups on CNC surfaces between 30-230. The suspensions were put into the ultrasonic bath for 15 minutes and stirred in the thermostatic oven at 37 ⁰C for 1 hour. The process of ultrasound and stirring in oven was repeated 1-3 times depending on conditions. Precipitated products were collected with the centrifuge instrument and dried with the freeze dryer. Functional groups induced HAp’s nucleation and the HAp/CNC composites could be obtained under control of molar ratio of calcium ions per functional groups on CNC and pH. Morphology of the composites could be determined by pH and HAp content could be controlled between 25-75 wt% by initial molar ratio. The suspension having the composites synthesized in pH 7.9 with low initial molar ratio was dropped on superhydrophilic glass substrates. At the moment, the substrates were set with leans of 20 degrees. Then they were dried at 60 oC for 3 hours and transparent films containing 25-40 wt% of HAp were obtained. The transmittances of the films were more than 90 % and their thicknesses were 2.2-4.2 μm. The films were suggested to have oriented structure by polarization microscope when the shape of the composites were needle-like homogeneously and independent each other. From the results from SEM, they were aligned longitudinally at both ends of the film and laterally at the upper middle part of the films. It is considered that controlling drying direction influenced on the orientation. The current study should become a promising step to build up a bone-like hierarchical structure artificially.

This thesis investigates the effect of reaction media on the efficiency of grafting hydrophobic polymers from cellulose nanocrystals (CNCs) via surface-initiated atom transfer radical polymerization (SI-ATRP), with the goal of producing highly-modified CNCs for incorporation into latex-based pressure sensitive adhesives (PSAs). A latex is a dispersion of polymer particles in water made by emulsion polymerization; latexes are commonly used in paints, coatings, elastomers, inks/toners, household products, cosmetics, and adhesives. However, latex-based PSAs often underperform compared to their organic solvent-polymerized counterparts due to a lack of cohesive strength in the cast latex films. The environmental benefit of using latex-based PSAs synthesized in water is significant, but the development of strategies to improve their performance are required. CNCs are hydrophilic rod-shaped nanoparticles with high mechanical strength. Adding CNCs to latex-based PSAs has been shown to improve both adhesive (i.e., tack and peel strength) and cohesive (i.e., shear strength) properties and offers a degree of sustainability because CNCs are derived from natural cellulose sources such as wood pulp. However, their hydrophilicity, particularly relative to the hydrophobic polymers used in PSAs, has constrained CNCs to the continuous (i.e., water) phase of the latex. To improve CNC compatibility with the dispersed (i.e., polymer) phase and improve their distribution in cast latex films, hydrophobic polymers can be grafted from CNCs. However, CNCs with a high polymer graft density are required to ensure their compatibility with monomers/polymers during latex synthesis. To begin, grafting poly(butyl acrylate) (PBA) from CNCs using SI-ATRP in polar dimethylformamide (DMF) versus non-polar toluene was directly compared. The enhanced colloidal stability of initiator-modified CNCs in DMF led to improved accessibility to surface initiator groups during polymer grafting. As such, PBA-grafted CNCs produced in DMF had up to 30 times more grafted polymer chains than PBA-grafted CNCs produced in toluene. The PBA-grafted CNCs produced in DMF showed high contact angles when cast in a film and formed stable suspensions in toluene. This work highlights that optimizing CNC colloidal stability in a given solvent prior to polymer grafting is a more crucial consideration than solvent–polymer compatibility in the context of obtaining high graft densities and thus hydrophobic CNCs via SI-ATRP. The improved polymer grafting method in DMF was then used to produce PBA and poly(methyl methacrylate) (PMMA)-grafted CNCs at two polymer chain lengths. Polymer grafted CNCs were incorporated in situ during a seeded semi-batch emulsion polymerization to produce PBA latex nanocomposite PSAs. Viscosity measurements revealed significant differences between latexes prepared with CNCs versus polymer-grafted CNCs, with the lower viscosities of the latter suggesting their incorporation inside the polymer particles. When CNCs with short polymer grafts were introduced into PSAs at 1 wt. % loading, they exhibited comparable tack and improved peel strength compared to unmodified CNCs (and all properties improved relative to the base latex without any CNCs). This is attributed to their improved distribution throughout the PSA, the enhanced wettability of the substrate with the CNC containing latex, and the increased polymer chain mobility achieved based on the low molecular weight of the grafts. CNCs with long polymer grafts aggregated in the latex and did not improve PSA properties. PMMA-grafted CNCs slightly outperformed PBA-grafted CNCs likely due to the higher glass transition temperature of PMMA. These results provide insight into future optimization of more sustainable latex-based PSA formulations as well as new commercial CNC-latex products, where the presence of low molecular weight grafts on CNC surfaces could improve polymer mobility and tack and peel strength. / Thesis / Master of Applied Science (MASc) / When the adhesives used in tapes, labels or sticky notes are produced using water-based reactions, they normally underperform compared to conventional adhesives produced using toxic solvents. To improve such water-based adhesives, adding nanocellulose (tiny particles derived from wood pulp) during synthesis has been shown to be an asset. Nanocellulose can be chemically modified to improve its compatibility with adhesive ingredients, and thus change the role of nanocellulose during adhesive manufacturing. In this thesis, modified nanocelluloses were added to water-based adhesives to evaluate their effect on performance (i.e., strength and stickiness). It was found that the reaction conditions during nanocellulose modification were crucial for obtaining highly modified particles that are compatible with adhesive ingredients. This work aims to provide insight for future production of less environmentally taxing adhesives made in water and expand the use of nanocellulose in new commercial products.

This thesis has as its principal goal the development of sustainable pressure-sensitive adhesives (PSAs). To that end, we examined polymer reaction engineering practices and polymer formulations through the lens of the 12 Principles of Green Chemistry. To begin with, we employed emulsion polymerization as our polymer synthesis method because of its use of water instead of hazardous solvents. We also replaced various petroleum-based components with bio-based alternatives (e.g., starch, cellulose nanocrystals), thereby reducing synthesis hazards, increasing product safety and increasing the amount of sustainably sourced raw materials in the PSA. However, changing the synthetic method as well as key components in the formulation presented significant challenges to maintaining PSA performance. This thesis illustrates the challenging path taken towards developing a fully renewable PSA. PSAs should display a specific balance of adhesion and cohesion. Typically, petroleum-based additives (which are often hazardous/toxic) such as tackifiers, cross-linkers, chain transfer agents and rheology modifiers are added to tailor latex properties to fit the intended application. However, because of their inherently opposing effects, an additive used to increase adhesion will weaken the cohesive forces of the polymer, and vice versa. Cellulose nanocrystals (CNCs) are sustainable nanomaterials that have been shown to be effective to resolve the adhesion/cohesion conundrum. In the first part of this project, we developed a new technique to increase CNC loading in emulsion-based PSA formulations beyond the 1-2% limits previously encountered due to high latex viscosity, colloidal instability, and poor film properties. The higher CNC loadings were shown to continuously improve shear strength but resulted in eventual decreases to tack and peel strength. In the second part of this project, we replaced the sulfated CNCs with carboxylated CNCs (cCNCs), which are produced by a process using a “greener” catalyst (i.e., hydrogen peroxide instead of sulfuric acid). The cCNCs’ carboxylate surface groups interacted strongly with the polymer matrix, ultimately leading to catastrophic coagulation. The interactions between cCNCs and other standard latex components were studied and through the creative manipulation of the emulsion polymerization process, a reproducible method to incorporate the cCNCs in a seeded semi-batch reaction yielded stable, high-quality latexes. In the third part of this project, the effect of the cCNCs on the adhesive properties of the nanocomposite latex films was studied and compared to the effects of the sulfated CNCs. AFM imaging revealed that cCNCs interact with latex particles and each other; thus, omitting ultrasonication at the preparation stage was shown to preserve these interactions and lead to greater property enhancements. In the fourth part of this project, starch nanoparticles (SNPs) were used to displace some of the petroleum-based monomer in the production of core-shell (SNP cores, acrylic shell) latexes. SNPs are renewably sourced, inexpensive, and biodegradable. The challenge of locating the SNPs into the particle cores was overcome by crosslinking the SNPs using a food grade cross-linker (sodium trimetaphosphate) and functionalizing them using a sugar-based monomer (EcoMer™). To tune the PSA properties to rival a range of commercial tapes, a method to incorporate CNCs to the SNP-latexes in situ was developed. In addition, because monomers such as 2-octyl acrylate (2OA), styrene, and acrylic acid can be bio-sourced, they were selected as the acrylic shell monomers to encapsulate the SNPs in the nanocomposite latexes. Due to supply chain challenges, n-octyl acrylate was used as a model monomer for 2OA to produce latexes with ~80% bio-content that rivaled commercial Post-It™ notes, masking tapes, and duct tapes. After addressing the sustainability of the polymerization method and polymer components, we posed the question: what are the effects of using renewably sourced and bio-sourced materials on the end-of-life of the PSAs? Because the infrastructure for biodegradation studies at the lab scale via composting does not exist in Canada (to our knowledge), we designed an in-house aerobic composting set-up consisting of a series of bioreactors and sensors capable of measuring the aerobic biodegradability of our polymers in a simulated composting environment. Although not fully tested, the composting setup was designed, and its construction was begun. Steps to complete the construction and validate its operation are detailed. The path towards sustainability is often long and complex. In this four-year study, the re-design of an adhesive synthesis process using a more sustainable approach, emulsion polymerization, along with an 80% bio-sourced formulation required significant corrective measures. Overcoming the technical challenges required mustering all the polymer reaction engineering tools at our disposal. Despite the time and effort required, achieving a more sustainable process is indeed within our grasp.

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Colloidally-stable zero valent iron nanoparticles (nZVI) were synthesized through a classical redox reaction of iron sulfate with minor modifications using cellulose nanocrystals (CNCs) as stabilizers. We obtained spherical nZVI particles with high surface roughness and a mean size of 130nm. Particles remain colloidally stable after more than two months. Cellulose nanocrystals play a dual role in nZVI stability: a foreign surface to encourage stable nucleation over fast aggregation and a stabilizer to prevent iron nanoparticles aggregating into fractal colloids. Our results highlight the impact of the presence of CNCs on the rates and mechanisms of nucleation, growth, aggregation, and aging of nZVI particles, indicating promise in controlling size and morphology of similarly redox-generated nanoparticles. Cellulose nanocrystal-stabilized nZVI nanoparticles demonstrate properties well-suited for enhanced soil and groundwater remediation. //Nanocomposites composed of carboxylated cellulose nanocrystals and iron (Fe-oxCNC) were prepared through a classical redox reaction of iron sulfate using TEMPO-oxidized cellulose nanocrystals (oxCNCs) as a template and stabilizer. Morphological control over Fe-oxCNC nanoparticles was realized by varying the amount of oxCNC added to the redox process. As the molar ratio between oxCNC and Fe was increased from 1 to 8, the morphology of Fe-oxCNC nanoparticles evolved from rounded iron aggregates supported by cellulose nanocrystals to thin film iron-coatings on cellulose nanocrystals. Transmission electron microscopy (TEM), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), and chemical analyses (EDX, EELS) revealed that oxCNCs were coated by iron. Small changes to the density and type of functional groups on the CNC surface have large impacts on the morphology and the oxidation state of adsorbed iron nanoparticles. / Thesis / Master of Applied Science (MASc)

This thesis is concerned with fused filament fabrication (FFF) of cellulose nanocrystal (CNC) and thermoplastic polyurethane (TPU) nanocomposites, focusing on preliminary optimization of a processing window for 3D printing of mechanically responsive composites and the influence of temperature on mechanical adaptivity, thermal stability, and rheology. CNC thermoplastic nanocomposites are a water responsive, mechanically adaptive material that has been gaining interest in additive manufacturing for 4D-printing applications. Using a desktop FlashForge Pro 3D printer, we first established a viable processing window for a nanocomposite comprising 10 wt% CNCs in a thermoplastic urethane (TPU) matrix, formed into a filament through the combination of masterbatch solvent casting and single screw extrusion. Printing temperatures of 240, 250, and 260°C and printing speeds of 600, 1100, and 1600 mm/min instituted a consistent 3D-printing process that produced characterizable CNC/TPU nanocomposite samples. To distinguish the effects of these parameters on the mechanical properties of the printed CNC/TPU samples, a design of experiments (DOE) with two factors and three levels was implemented for each combination of printing temperature and speed. Dynamic mechanical analysis (DMA) highlighted 43 and 66% increases in dry-state storage moduli values as printing speed increases for 250 and 260°C, respectively. 64 and 23% increases in dry-state storage moduli were also observed for 600 and 1100 mm/min, respectively, as temperature decreased from 260 to 250°C. For samples printed at 240°C and 1600 mm/min, it was determined that that parameter set may have fallen out of the processing window due to inconsistent deposition and lower dry-state storage moduli than what the slower speeds exhibited. As a result, the samples printed at 240°C did not follow the same trends as 250 and 260°C. Further analysis helped determine that the thermal energy experienced at the higher end printing temperatures coupled with the slower speeds decreased the dry-state storage moduli by nearly 50% and lead to darker colored samples, suggesting CNC degradation. Isothermal thermogravimetric analyses (TGA) demonstrated that the CNC/TPU filament would degrade at relative residence times in the nozzle for all the chosen printing temperatures. However, degradation did not eliminate the samples' ability to mechanically adapt to a moisture-rich environment. DMA results verified that mechanical adaptivity was persistent for all temperature and speed combinations as samples were immersed in water. However, for the higher temperatures and slower speeds, there was about a 15% decrease in adaptability. Optimal parameters of 250°C and 1600 mm/min provided the highest dry-state storage modulus of 49.7 +/- 0.5 MPa and the highest degree of mechanical adaptivity of 51.9%. To establish the CNC/TPU nanocomposite's use in 4D printing applications, shape memory analysis was conducted on a sample printed at the optimal parameters. Multiple wetting, straining, and drying steps were conducted to highlight 76% and 42% values for shape fixity and shape recovery, respectively. Furthermore, a foldable box was printed to serve as an example of a self-deployable structure application. The box displayed shape fixity and recovery values of 67% and 26%, respectively, further illustrating significant promise and progress for CNC/TPU nanocomposites in 4D-printed, shape adaptable structures. Further analysis of the effect of degradation during FFF of the CNC/TPU nanocomposite was conducted using rotational rheometry, Fourier-Transform Infrared Spectroscopy (FTIR), and polymer swelling experiments. A temperature ramp from 180 to 270°C showed a significant increase in complex viscosity (h*) at the chosen printing temperatures (240, 250, and 260°C). Moreover, h* of neat TPU suddenly increases at 230°C, indicating a potential chemical crosslinking reaction taking place. 20-minute time sweeps further verified that h* increases along with steady increases in storage (G') and loss (G'') moduli. From these results, it was hypothesized that crosslinking is occurring between CNCs and TPU. Preliminary characterization with FTIR was used to probe the molecular structure of thermally crosslinked samples. At 1060 and 1703 cm-1, there are significant differences in intensities (molecular vibrations) as the temperature increases from 180 to 260°C related to primary alcohol formation and hydrogen bonded carbonyl groups, respectively. The hypothesis is the disassociation of TPU carbamate bonds into soft segments with primary alcohols and hard segments with isocyanate groups. The subsequent increasing peaks at 1060 and 1703 cm-1 may indicate crosslinking of CNCs with these disassociated TPU segments. To quantify potential crosslinking, polymer swelling experiments were implemented. After being submerged in dimethylformamide (DMF) for 24 hours, CNC/TPU samples thermally aged for 15 minutes at 240, 250, and 260°C retained their filament shape and did not dissolve. The 240 and 250°C aged samples had relatively similar crosslink densities close to 900 mole/cm3. However, from 250 to 260°C, there was about a 36% increase in crosslink density. These results suggest that crosslinking is occurring at these printing temperatures because both CNCs and TPU are thermally degrading into reactive components that will lead to covalent crosslinks degradation. Additional characterization is needed to further verify the chemical structure of these CNC/TPU nanocomposites which would provide significant insight for CNC/TPU processing and 3D printing into tunable printed parts with varying degrees of crosslinking. / Master of Science / This thesis is concerned with the development of a processing window for mechanically adaptive cellulose nanocrystal (CNC) and thermoplastic polyurethane (TPU) nanocomposites with fused filament fabrication (FFF) and, evaluating the influence of elevated temperatures on the mechanical, thermal, and rheological properties of said nanocomposite. CNC thermoplastic nanocomposites are a water responsive, mechanically adaptive material that has been gaining interest in additive manufacturing for 4D-printing. Using a desktop 3D-printer, an initial processing window for a 10 wt% CNC in TPU was established with printing temperatures of 240, 250, and 260°C and printing speeds of 600, 1100, and 1600 mm/min. A design of experiments (DOE) was implemented to determine the effects of these parameters on the mechanical properties and mechanical adaptability of printed CNC/TPU parts. Dynamic mechanical analysis (DMA) suggests that combinations of higher temperatures and lower speeds result in reduced storage moduli values for printed CNC/TPU parts. However, mechanical adaptation, or the ability to soften upon water exposure, persists for all the printed samples. Additionally, there was significant discolorations of the printed samples at the higher temperature and slower speed combinations, suggesting thermal degradation is occurring during the printing process. The decrease in storage moduli and discoloration is attributed to thermal energy input, as thermogravimetric analysis indicated thermal degradation was indeed occurring during the printing process regardless of printing temperature. Using the parameters (250°C and 1600 mm/min) that displayed the superior mechanical properties, as well as mechanical adaptivity, shape memory analysis was conducted. The optimal printed part was able to hold 76% of the shape it was strained to, while recovering 42% of the original unstrained shape once immersed in water, indicating potential for shape memory and 4D-printing applications. Furthermore, a foldable box was printed with the optimal parameters and it displayed similar shape memory behavior, illustrating promise for CNC/TPU self-deployable shape adaptable structures. To further study the effect of degradation on the CNC/TPU system, melt flow properties, molecular structure, and polymer swelling were investigated. At the printing temperatures (240, 250, and 260°C), the complex viscosity of the CNC/TPU filament experienced an exponential increase, indicating potential network formation between the CNCs and TPU. Fourier-Transform Infrared Spectroscopy (FTIR) highlighted changes in the molecular structure for the CNC/TPU filament as temperature increased from 240 to 260°C, which suggests that chemical structure changes are occurring because of degradation. The hypothesis is TPU is disassociated into free soft and hard segments that the CNCs can covalently crosslink with, which can potentially be explained by the increases in the FTIR intensities relating to TPU and CNC's chemical structure. To further quantify potential crosslinking between CNCs and TPU, polymer swelling experiments were implemented. The results from these experiments suggest that increasing printing temperatures from 240 to 260°C will lead to higher degrees of crosslinking. Further investigation could yield the validity of this crosslinking and additional optimization of FFF printing with CNC/TPU nanocomposites.

Inkjet printing has generated considerable interest as a technique for the patterning of functional materials in the liquid phase onto a substrate. Despite its high promise, the phenomena associated with inkjet printing remain incompletely understood. This research project investigates inkjet printing of cellulose nanocrystals (CNCs) as a possible method for the fabrication of cellulose micropatterns. CNCs were prepared from wood pulp by H₂SO₄ hydrolysis and characterized in terms of length, width, and thickness distributions by atomic force microscopy (AFM) and dynamic light scattering. Aqueous CNC suspensions were characterized in terms of shear viscosity with a rheometer. Glass substrates were cleaned with a detergent solution, aqua regia, or a solvent mixture, and characterized in terms of surface chemical composition, surface free energy, polarity, roughness, ζ-potential, and surface charge distribution in air by X-ray photoelectron spectroscopy, contact angle measurements, AFM, streaming potential, and scanning Kelvin probe microscopy (SKPM). Additionally, poly(ethylene glycol)-grafted glass substrates were prepared and characterized in terms of surface free energy, polarity, and roughness. Aqueous CNC suspensions were printed in different patterns onto the different glass substrates with a commercial, piezoelectric drop-on-demand inkjet printer. Inkjet deposited droplet residues and micropatterns were analyzed by AFM, scanning electron microscopy, and polarized-light microscopy. At low CNC concentrations (0.05 wt %), inkjet-deposited droplets formed ring-like residues due to the "coffee drop effect". The "coffee drop effect" could be suppressed by the use of higher CNC concentrations. The resulting dot-like droplet residues exhibited Maltese cross interference patterns between crossed polarizers, indicating a radial orientation of the birefringent, elongated CNCs in these residues. The observed Maltese cross interference patterns represent unprecedented indirect evidence for a center-to-edge radial flow in drying droplets. The degree of definition of the micropatterns depended strongly on the surface properties of the glass substrates. Well-defined micropatterns were obtained on aqua regia-cleaned substrates. In addition to the surface free energy and polarity, other factors seemed to play a role in the formation of the inkjet-printed micropatterns. If these factors can be identified and controlled, inkjet deposition of CNCs could become an attractive method for the fabrication of cellulose micropatterns. / Ph. D.

The purpose of this research was to determine the effects of cellulose nanocrystals (CNCs), as potential additives, on the properties and performance of phenol–formaldehyde (PF) adhesive resin. The steady-state viscosity of a commercial PF resol resin and three CNC–resin mixtures, containing 1–3 wt % CNCs, based on solids content, was measured with a rheometer as a function of shear rate. The viscosity of the PF resin itself was independent of shear rate. The viscosity–shear rate curves of the CNC–resin mixtures showed two regions, a shear thinning region at lower shear rates and a Newtonian region at higher shear rates. The low-shear-rate viscosity of the resin was greatly increased by the CNCs. The structure of the CNC–resin mixtures under quiescent conditions was analyzed by polarized light microscopy. The mixtures contained CNC aggregates, which could be disrupted by ultrasound treatment. The curing progressions of the resin and CNC–resin mixtures were analyzed by non-isothermal differential scanning calorimetry (DSC). The DSC curves showed two exotherms followed by an endotherm. The energy of activation for the first exotherm was reduced by the CNCs whereas the energy of activation for the second exotherm was not affected by the CNCs. Increasing CNC contents caused higher degrees of reaction conversion during the first curing stage and a greater loss of sample mass, attributed to formaldehyde release during resin cure. For analysis of the mechanical properties during and after cure, sandwich-type test specimens were prepared from southern yellow pine strips and the resin and CNC–resin mixtures. The mechanical properties of the test specimens were measured as a function of time and temperature by dynamic mechanical analysis (DMA). The time to incipient storage modulus increase decreased and the rate of relative storage modulus increase increased with increasing CNC content. The ultimate sample stiffness increased with increasing CNC content for CNC contents between 0 and 2 wt %, which was attributed to mechanical reinforcement of the resin by the CNCs. At a CNC content of 3 wt %, the ultimate sample stiffness was lower than at a CNC content of 2 wt % and the second tan δ maximum occurred earlier in the experiment, indicating an earlier onset of vitrification. The lower ultimate sample stiffness was attributed to premature quenching of the curing reactions through CNC-induced depression of the vitrification point. For analysis of the fracture performance, double cantilever beam test specimens were prepared from southern yellow pine beams and the resin and CNC–resin mixtures, using different hot-pressing times. Fracture energies were measured by mode I cleavage tests. Bondline characteristics were analyzed by light microscopy. At a hot-pressing time of 10 min, the fracture energy decreased with increasing CNC content, whereas it stayed constant for CNC contents between 1 and 3 wt % at a hot-pressing time of 8 min. The bondlines of resin mixtures containing CNCs exhibited voids, whereas those of the pure resin did not. CNCs had both benefitial and detrimental effects on the properties and performace of PF resin. / Master of Science