Carbon allotropes have taken central stage of nanotechnology in the last two decades. Today, fullerenes, carbon nanotubes (CNTs), and graphene are essential building blocks for nanotechnology. Their superlative electrical, thermal and mechanical properties make them desirable for a number of technological applications ranging from lightweight strong materials to electrical wires and support for catalysts. However, transferring the exceptional single molecule properties into macroscopic objects has presented major challenges. This thesis demonstrates that carbon nanotubes and graphite dissolve in superacids and these solution can processed into macroscopic objects. Chapter 2 reviews neat CNT fiber literature. Specifically, the two main processing methods —solid– state and solution spinning — are discussed. CNT aspect ratio and fibers structure are identified as the main variables affecting fiber properties. Chapter 3 shows that graphite can be exfoliated into single-layer graphene by spontaneous dissolution in chlorosulfonic acid. The dissolution is general and can be applied to various forms of graphite, including graphene nanoribbons. Dilute solutions of graphene can be used to form transparent conductive films. At high concentration, graphene and graphene nanoribbons in chlorosulfonic acid forms a liquid crystal and can be spun directly into continuous fibers. Chapter 4 describes a solution–based method to form a thin CNT network. This network is an ideal specimen support for electron microscopy. Imaging nanoparticles with atomic resolution and sample preparation from reactive fluids demonstrate the unique feature of solution–based CNT support compared to state–of–the–art TEM supports . Chapter 5 describes CNT liquid crystalline phase. Specifically, CNT nematic droplets shape and merging dynamics are analyzed. Despite nanotube liquid crystals having been reported in various CNT systems, a number of anomalies such as low order parameter and spaghetti–like, nematic droplets are reported. However, CNTs in chlorosulfonic acid show elongated, bipolar droplets typical of other rod–like molecules. Moreover, their large aspect ratio allows capturing the transition from homogeneous to bipolar transition expected from scaling arguments.The equilibrium shape and merging dynamics demonstrate the liquid nature of CNT liquid crystals. Chapter 6 describes the CNT/chlorosulfonic acid fiber spinning. The influence of starting material, spinning dope concentration, spin draw ratio and coagulation on fiber properties is discussed. The linear scaling of fiber strength with CNT aspect ratio is demonstrated experimentally, once the best properties from different batches are compared. Moreover, Successful multi–hole spinning demonstrates the intrinsic scalability of wet spinning to meet the typical production output of industrial–scale spinning. Chapter 7 compares acid–spun CNT fibers to other CNTs fibers as well as existing engineered materials. Acid–spun CNT fibers combine the typical specific strength of high–strength carbon fibers to the thermal and electrical conductivity of metals. These properties are obtained because of a highly aligned, dense structure. The combined strength and electrical conductivity allow acid-spun fibers to be used as structural as well as conducting wire while the combined electrical and thermal properties allow for exceptional field emission properties. In conclusion, we demonstrate that multifunctional properties of carbon nanotubes that have fuelled much of the research in the past 20 years, can be attained on a macroscopic level via rational design of fluid–phase processing.

Polyethylene terephthalate is one of the most important engineering thermal plastics used for fibers, films and bottles. Despite its wide applications and vast global market, PET has shortcomings, which limits it usage in many areas. PET has a glass transition temperature (Tg) of 80 DEGREE Celsius, this temperature is too low for certain applications. Increase in glass transition temperature, high temperature mechanical properties, and dimensional stability is of great importance to further expand the applications of PET. Significant research efforts have been made toward this goal, using a variety of approaches. In this work, we attempt to improve the properties of PET melt spun filament. Three strategies has been investigated (i) copolymerization of more rigid comonomer, 4, 4' bibenzoate unit into the PET structure, (ii) UV crosslinking of functionalized PET fiber, and (iii) Reinforcing PET matrix with carbon nanofibers.

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The production of long, thin polymeric fibers is a main objective of the textile industry. Melt-spinning is a particularly simple and effective technique. In this work, we shall discuss the equations of melt-spinning in viscous and viscoelastic flow. These quasilinear hyperbolic equations model the uniaxial extension of a fluid thread before its solidification. We will address the following topics: first we shall prove existence, uniqueness, and regularity of solutions. Our solution strategy will be developed in detail for the viscous case. For non-Newtonian and isothermal flows, we shall outline the general ideas. Our solution technique consists of energy estimates and fixed-point arguments in appropriate Banach spaces. The existence result for a simple transport equation is the key to understanding the quasilinear case. The second issue of this exposition will be the stability of the unforced frost line formation. We will give a rigorous justification that, in the viscous regime, the linearized equations obey the ``Principle of Linear Stability''. As a consequence, we are allowed to relate the stability of the associated strongly continuous semigroup to the numerical resolution of the spectrum of its generator. By using a spectral collocation method, we shall derive numerical results on the eigenvalue distribution, thereby confirming prior results on the stability of the steady-state solution. / Ph. D.

This work is concerned with mechanical property improvements to poly(ethylene terephthalate), PET, fibers by the addition of layered silicate nanoparticles and by drawing the un-oriented nanocomposite filaments in a second step. No previous studies on PET fibers filled with montmorillonite (MMT) nanoclay examined fiber drawability at temperatures above the glass transition. Therefore, the primary objective of this research was to determine 1) if PET nanocomposite fibers could be drawn to finer diameters and 2) whether drawing imparted improved Young's modulus and tenacity (i.e. strength) relative to un-filled PET fibers. Of equal importance to this work, the subsequent objective was to discern and understand the role of nanoclay in 1) the production of improved or reduced mechanical properties and 2) the ability to draw PET to lower or higher than normal draw ratios. In the first part of this thesis, the improvements in Young's modulus and tenacity of PET fibers filled with various types of organically modified montmorillonite is shown and the method to produce them is discussed. Greater improvements in mechanical properties occurred when the MMT stacks were intercalated with PET. A nominal 1 wt% loading of dimethyl-dehydrogenated tallow quaternary ammonium surface modified MMT in drawn PET fiber showed a 28% and 63% increase in Young's modulus and strength, respectively. Relative to an un-filled PET fiber, these results exceeded the upper-bound of the rule of mixtures estimate. Therefore, both the type of surface modification and concentration of MMT were shown to affect the degree of PET orientation and crystallinity. Furthermore, drawability above Tg and elongation-at-break increased upon the addition of organically modified MMT to un-oriented PET fibers, which was a key distinction of this work from others examining similar systems. Interestingly, the mechanical properties of modulus and tenacity showed a maximum with concentration of alkyl modified clay, but drawability did not show significant variation with increasing nanoclay content. Thermal analysis and Raman spectroscopy was used to examine the role of nanoclay in creating this maximum in mechanical properties. At low loadings, nanoclay was shown to intercalate with PET and enhance amorphous orientation. At higher concentrations of nanoclay the presence of large agglomerates prevented efficient orientation to the fiber axis and acted as stress concentrators to aid in cavitation and failure during testing. Raman spectroscopy showed that the as-spun unfilled PET fibers possessed significantly more trans conformer content of the ethylene glycol moiety than the nanocomposite fibers. The greater gauche content of the nanocomposite fibers delayed crystalline development during non-isothermal DSC scans to higher temperatures was associated with the increased drawability. / Ph. D.

The spinning process of hollow fiber membranes was investigated with regards to two fundamental phenomena: flow (shear and elongation) and phase separation. Quantitative analysis of phase separation kinetics of binary (polymer/solvent) and ternary (polymer/solvent/volatile co-solvent) polymer solution was carried out with a newly developed microfluidic device. The device enables visualization of in situ phase separation and structure formation in controlled vapor and liquid environments. Results from these studies indicated that there was a weak correlation between phase separation kinetics and macroscopic defect (macrovoid) formation. In addition, the effect of shear and elongation on membrane morphology was tested by performing fiber extrusion through microfluidic channels. It was found that the membrane morphology is dominated by different factors depending on the rate of deformation. At high shear rates typical of spinning processes, shear was found to induce macrovoid formation through normal stresses, while elongation suppressed macroscopic defect formation. Furthermore, draw resonance, one of the key instabilities that can occur during fiber spinning, was investigated. It was found that draw resonance occurs at aggressive elongation condition, and could be suppressed by enhanced phase separation kinetics. These results can be used as guidelines for predicting hollow fiber membrane spinnability.

One portion of this work was concerned with injection molding pregenerated microcomposites composed primarily of poly(ethylene terephthalate) (PET) as the matrix and HX1000 as the thermotropic liquid crystalline polymer (TLCP). Several factors were examined to maximize the mechanical properties of these composites, including injection molding temperature, matrix viscosity, and nozzle tip exit diameter. In addition, concentrated strands of HX1000/PET (50/50 wt%) were diluted using both an injection molding grade of PET and an injection molding grade of PBT. From this work, it was determined that the best mechanical properties were produced when the microcomposites were processed at the lowest injection molding temperatures, diluted with PBT, and injection molded using a large nozzle tip exit diameter. The pregenerated microcomposite properties were compared against theoretical predictions as well as glass-filled PET. It was found that the pregenerated microcomposites had tensile moduli of approximately 70% of theoretical expectations in the machine direction. Additionally, the comparisons against glass-filled PET revealed that at the same weight fraction of reinforcement, the pregenerated microcomposites had lower properties. Still, the composites were found to have smoother surfaces than glass-filled PET and at temperatures up to 150° C the storage and loss moduli of the pregenerated microcomposites were similar to those of glass filled PET. It was concluded that if the theoretically expected levels of reinforcement could be attained, the pregenerated microcomposites processing scheme would be a viable method of producing light weight, wholly thermoplastic composites with smoother surfaces than are obtained with glass reinforcement. An additional focus of this research was to evaluate the ability to modify the crystallization behavior of a high melting TLCP (HX6000, Tm = 332° C) with a lower melting TLCP (HX8000, Tm = 272°C). It was found that it was possible to tailor the crystallization behavior of these TLCP/TLCP blends by varying the weight fraction of each component, as determined by rheological cooling scans and differential scanning calorimetric cooling tests. Based on the analysis of these TLCPs at the maximum injection molding temperature of 360° C, it was speculated that they had reacted with one another. / Ph. D.

A new concept of a "fiber sorbent" has been investigated. The fiber sorbent is produced as a pseudo-monolithic material comprising polymer (cellulose acetate, CA) and zeolite (NaY) by applying hollow fiber spinning technology. Phase separation of the polymer solution provides an appropriately porous structure throughout the fiber matrix. In addition, the zeolite crystals are homogeneously dispersed in the polymer matrix with high loading. The zeolite is the main contributor to sorption capacity of the fiber sorbent. Mass transfer processes in the fiber sorbent module are analyzed for hydrogen recovery and compared with results for an equivalent size packed bed with identical diameter and length. The model indicates advantageous cases for application of fiber sorbent module over packed bed technology that allows system downsizing and energy saving by changing the outer and bore diameters to maintain or even reduce the pressure drop. The CA-NaY fiber sorbent was spun successfully with highly porous structure and high CO2 sorption capacity. The fiber sorbent enables the shell-side void space for thermal moderation to heat of adsorption, while this cannot be applied to the packed bed. The poly(vinyl alcohol) coated CA-NaY demonstrated the thermal moderation with paraffin wax, which was carefully selected and melt at slightly above operating temperature, in the shell-side in a rapidly cycled pressure swing adsorption. So this new approach is attractive for some hydrogen recovery applications as an alternative to traditional zeolite pellets.

This disseration covers the processing and characterization of nanocellulose polymer composites. In this disseration, two fiber spinning methods were developed to create high stiffness nanocomposite fibers from renewably-sourced materials and the properties of these nanocomposites were evaluated. Additionally, bulk nanocomposites were created and some of the properties of these materials, for different types of nanoparticles, are also discussed. Evaluation of nanocellulose as a nucleation agent in poly(lactic acid) is also presented for very small concentrations of nanocelluloses in a plasticized polymer.