O amido termoplástico (TPS) é um material biodegradável que tem sido bastante estudado em função do seu baixo custo e pelo fato de ser derivado de fontes renováveis. Contudo, o TPS apresenta limitações mesmo para aplicação em produtos de baixos requisitos devido a conjunto de fatores como sua baixa propriedade mecânica, térmica, e de resistência à umidade, além de possuir baixa compatibilidade com outros polímeros sintéticos. Nesse trabalho foi testada a modificações do TPS com ácido cítrico e com 4,4-difenil metano diisocianato (MDI) e as blendas desses materiais com polietileno de baixa densidade (PEBD) e o efeito da modificação do PE com anidrido maleico (MA) e da adição de ceras de polietileno não modificada e modificada com anidrido maleico como agente compatibilizante. A modificação do amido com ácido cítrico e com MDI não afetou de forma significativa a sua hidrofilicidade. O uso de MDI se mostrou eficaz na melhoria das propriedades mecânicas do amido não modificado com AC. A compatibilização com cera se mostrou extremamente promissora, tendo no caso da blenda 50/50 de polietileno e TPS compatibilizada com 5 % de cera resultando em um composto com propriedades mecânicas (módulo e resistência à tração) muito similares às do polietileno de origem. / Thermoplastic starch (TPS) is a biodegradable material that has been extensively studied due to its low cost and because it is derived from renewable sources. However, TPS present several drawbacks even for application in products of low performance due to its poor mechanical properties, thermal properties and moisture resistance, and also due to its low compatibility with other synthetic polymers. In this work we studied the modification of TPS with citric acid and with 4,4 \'- diphenyl methane diisocyanate (MDI) and the blends of these materials with low density polyethylene (LDPE) and the effect of modification of PE with maleic anhydride (MA) and the addition of polyethylene waxes unmodified and modified with maleic anhydride as compatibilizing agent. The modification of starch with citric acid and MDI did not affect significantly its hydrophilicity. The use of MDI is effective in improving mechanical properties of unmodified starch with AC. The compatibility with wax showed very promising with the case of blend 50/50 TPS and polyethylene compatibilized with 5% wax results in a material with mechanical properties very similar to those of polyethylene (modulus and tensile strength) .

No description available.

Thesis (M.Ch.E.)--University of Delaware, 2006. / Principal faculty advisor: Eric M. Furst, Dept. of Chemical Engineering. Includes bibliographical references.

Carbon nanotubes were dispersed and functionalized with polyethylene imine (PEI) before incorporation in a polyvinyl acetate matrix. The resulting samples exhibit air-stable N-type characteristics with electrical conductivities as great as 1600 S/m and thermopowers as high as 100 microV/K. Thermopowers and electrical conductivities correlate, in a reversal of the trend found in typical materials. This phenomenon is believed to be due to the increase in the number of tubes that are evenly coated in a better dispersed sample. Increasing the amount of PEI relative to the other constituents positively affects thermopower but not conductivity. Air exposure reduces both thermopower and conductivity, but a stable value is reached within seven days following film fabrication. The atmospheric effects on the electrical conductivity prove to be reversible. Oxygen is believed to be the primary contributor to the decay.

Because engineered tissue constructs are inherently limited by their lack of microvascularization, which is essential to provide oxygen for cell survival, this thesis presents rationally designed materials and cell culture techniques capable of supporting functional tubule formation and stabilization. Combining a synthetic scaffold material with cells and their cell-secreted signals instigated tubule formation throughout the scaffold. Poly(ethylene glycol) (PEG) based hydrogels, biocompatible polymers which resist protein adsorption and subsequent nonspecific cellular adhesion, were modified to induce desired cell characteristics. Human umbilical vein endothelial cells were used as a reproducible and readily available cell type. Several tubule-stabilization signals, including platelet derived growth factor-BB (PDGF-BB) and ephrinA1, were covalently immobilized via conjugation to PEG to enable prolonged bioactive signaling and controlled local delivery. All hydrogels were further tested in a mouse cornea micropocket angiogenesis assay, a naturally avascular tissue for easy imaging in a reproducible and quantifiable assay. Hydrogels containing soluble growth factors induced vessel formation in the hydrogel, and the resulting vessel morphology was modulated using different growth factor concentrations. Immobilized PDGF-BB led to tubule formation in two dimensions, three dimensions, and in the mouse cornea while immobilized ephrinA1 stimulated secretion of extracellular matrix proteins laminin and collagen IV to stabilize the newly formed tubules. Finally, a co-culture of endothelial and pericyte cells encapsulated into hydrogels formed tubules that anastomosed to the host vasculature and contained red blood cells. PEG-based hydrogels represent a promising technique to induce microvascular formation in engineered constructs, leading to stable and functional vessel formation using covalently immobilized growth factors and encapsulated cells. These materials can be used for replacement of damaged or diseased tissues as the current supply of cadaveric donations cannot meet the demand of tissues for the 110,000 people awaiting an organ in the US.

Making a robust carbon nanotube-based conductor as a replacement of copper in electricity grids can initiate a paradigm shift in energy transmission. This dissertation identifies four fundamental factors for making carbon nanotube-based conductors as functionalization, dispersion, concentration and processing. These four factors are discussed in detail by studying four separate systems: nanotube/epoxy composites, nanotube/porous medium density polyethylene (MDPE) composites, nanotube/high density polyethylene (HDPE) composites and pure nanotube cables. In nanotube/epoxy composites, homogeneous dispersion of nanotubes and a strong interface between nanotubes and epoxy matrix were simultaneously achieved through the development of a novel nanotube functionalization. While the degree of functionalization was high, the process was non-destructive to the mechanical properties of the nanotubes. In addition, the functional groups constructed covalent bonds with the epoxy matrix and also made dispersing the nanotubes much easier. As a result, the composites reinforced by the functionalized nanotubes had better mechanical properties than the samples reinforced by the raw nanotubes. In nanotube/porous MDPE composites, the degree of nanotube dispersion reached a level of 1 micron for nanotube agglomerate size within the matrix. This successful dispersion was primarily attributed to creating the porous MDPE. The pore size was tuned to be as small as 1 micron so that the sub-micron long HiPco nanotubes could easily penetrate into the matrix. The nanotube/porous MDPE composites obtained enhancement both in mechanical strength and electrical conductivity compared to the control samples. In nanotube/HDPE composites, the nanotube conducting networks were studied. Conductivity of the composites with the loading ratio at the percolation threshold was not sufficiently high for conductor applications. Nanotube/HDPE composite wires with higher loading ratios up to 40 wt% were prepared. Key factors for improving the formation of the conducting networks were identified. Through optimization in processing, maximum conductivity of ∼10 3 S/m was achieved. Pure nanotube cables were prepared by a solid spinning procedure, which showed the potential to make macroscopic cables of various length and thickness. The pure nanotube cables circumvented the bottleneck in improving conductivity for composite systems, in which polymer in-between the nanotubes caused high contact resistance. The pure nanotube cables reached conductivity as high as ∼10 6 S/m. Through iodine doping, conductivity further was enhanced so that the specific conductivity of the doped cables exceeded that of metals such as copper. As a result of applying the knowledge learned from study of the four fundamental factors, a macroscopic carbon-nanotube cable was created. It reached an unprecedented conductivity as high as ∼10 7 S/m. Mechanically it was more robust than steel, but with 1/6 the weight. This advanced nanotube-based conductor can have a wide spectrum of applications such as transmission lines and low dimensional connecting wires.

L'objectif de cette thèse est d'observer la modification du comportement rhéologique dedifférents polyéthylènes branchés, suite à un traitement de cisaillement. Après avoir décrit lesmatériaux et les moyens utilisés, nous avons caractérisé le plus complètement possible lecomportement rhéologique des différents matériaux, aussi bien en cisaillement qu'en élongation.Nous avons également déterminé des données calorimétriques et des informations sur lescaractéristiques moléculaires, permettant entre autres de définir la masse entre enchevêtrements.Nous avons ensuite mesuré l'évolution de la viscosité dans différentes conditions de pré‐cisaillement,en faisant varier le temps et le taux de cisaillement dans un rhéomètre cône‐plan et dans unegéométrie de Couette montée en amont d'un rhéomètre capillaire. Nous avons montré que lesmécanismes de désenchevêtrement sont complexes et qu'ils ne sont pas directement explicables parun seul paramètre, comme la masse entre enchevêtrements. Enfin, l'observation des extrudats à lasortie de la filière nous a permis de mettre en évidence la modification des défauts d'extrusion sousl'effet d'un pré‐cisaillement.

Defects in polyethylene film are often caused by contaminant particles in the polymer melt. In this research, particle properties obtainable from in-line melt monitoring, combined with processing information, are used to predict film defect properties. “Model” particles (solid and hollow glass microspheres, aluminum powder, ceramic microspheres, glass fibers, wood particles, and cross-linked polyethylene) were injected into low-density polyethylene extruder feed. Defects resulted when the polyethylene containing particles was extruded through a film die and stretched by a take-up roller as it cooled to form films 57 to 241mm in thickness. Two off-line analysis methods were further developed and applied to the defects: polarized light imaging and interferometric imaging. Polarized light showed residual stresses in the film caused by the particle as well as properties of the embedded particle. Interferometry enabled measures of the film distortion, notably defect volume. From the images, only three attributes were required for mathematical modeling: particle area, defect area, and defect volume. These attributes yielded two ”primary defect properties”: average defect height and magnification (of particle area). For all spherical particles, empirical correlations of these properties were obtained for each of the two major types of defects that emerged: high average height and low average height defects. Analysis of data for non-spherical particles was limited to showing how, in some cases, their data differed from the spherical particle correlations. To help explain empirical correlations of the primary defect properties with film thickness, a simple model was proposed and found to be supported by the high average height defect data: the “constant defect volume per unit particle area” model. It assumes that the product of average defect height and magnification is a constant for all film thicknesses. A numerical example illustrates how the methodology developed in this work can be used as a starting point for predicting film defect properties in industrial systems. A limitation is that each prediction yields two pairs of primary defect property values, one pair for each defect type. If it is necessary to identify the dominant type, then measurement of a length dimension of sufficient defects in the film is required.

Aluminum complexes, specifically those employing bulky ligand frameworks such as sal (sal = 2-[CH═N(2,6-iPr2-C6H3)]-4,6-tBu2-phenoxide) and alpha-diimine (alpha-diimine = [(2,6-iPr2-C6H3)N═C(Me)]2) derivatives are studied in various contexts. During ethylene polymerization with LCu(II) catalysts in the presence of methylaluminoxane (MAO), ligand (L) transfer is observed from the copper centre to the aluminum centre present in MAO. In the alpha-diimine case, an (imino-amido)AlMe2 complex is formed by alpha-diimine ligand transfer to aluminum followed by alkylation of one imino moiety in the ligand backbone. These ligand transfer products are then shown to be active as ethylene polymerization catalysts, bringing into question the role of the copper species. The (sal)AlMe2, (sal)AlMeCl and (imino-amido)AlMe2 complexes were also used as initiators in the ring-opening polymerization of epsilon-caprolactone. Polymerization was studied with and without addition of tert-butanol as a co-initiator to determine its role and necessity in the catalytic cycle. Finally, the (imino-amido)AlMe2 complex was also used as the starting complex in attempts at forming a mononuclear aluminum(I) target species. Reaction of (imino-amido)AlMe2 with excess I2 proved successful in forming the isolable precursor, (imino-amido)AlI2. Attempts at reducing (imino-amido)AlI2 with excess potassium were carried out in hopes of forming a very rare example of a mononuclear aluminum(I) species.

Defects in polyethylene film are often caused by contaminant particles in the polymer melt. In this research, particle properties obtainable from in-line melt monitoring, combined with processing information, are used to predict film defect properties. “Model” particles (solid and hollow glass microspheres, aluminum powder, ceramic microspheres, glass fibers, wood particles, and cross-linked polyethylene) were injected into low-density polyethylene extruder feed. Defects resulted when the polyethylene containing particles was extruded through a film die and stretched by a take-up roller as it cooled to form films 57 to 241mm in thickness. Two off-line analysis methods were further developed and applied to the defects: polarized light imaging and interferometric imaging. Polarized light showed residual stresses in the film caused by the particle as well as properties of the embedded particle. Interferometry enabled measures of the film distortion, notably defect volume. From the images, only three attributes were required for mathematical modeling: particle area, defect area, and defect volume. These attributes yielded two ”primary defect properties”: average defect height and magnification (of particle area). For all spherical particles, empirical correlations of these properties were obtained for each of the two major types of defects that emerged: high average height and low average height defects. Analysis of data for non-spherical particles was limited to showing how, in some cases, their data differed from the spherical particle correlations. To help explain empirical correlations of the primary defect properties with film thickness, a simple model was proposed and found to be supported by the high average height defect data: the “constant defect volume per unit particle area” model. It assumes that the product of average defect height and magnification is a constant for all film thicknesses. A numerical example illustrates how the methodology developed in this work can be used as a starting point for predicting film defect properties in industrial systems. A limitation is that each prediction yields two pairs of primary defect property values, one pair for each defect type. If it is necessary to identify the dominant type, then measurement of a length dimension of sufficient defects in the film is required.