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The rheological properties of polymer melts and polymer/blowing agent (BA) solutions are determined experimentally and the influences of material rheological properties and crystallization on low-density foaming behaviour of polylactic acid (PLA) are investigated. Understanding the rheological properties of foaming polymers allows the optimization of polymer chemical structure and the development of technologies that produce desired cell morphologies. Although the technology for producing CO2-blown polystyrene (PS) foams is well established, the rheological properties of a PS/CO2 solution, especially its extensional property, are not well understood. In this study, these properties are determined with an in-house developed, online technique, and the measured data are compared with those from commercial rheometers. The online measurement system consists of a tandem foam extrusion system and a die for measuring pressure drops. Shear viscosity is determined from the pressure drop over a straight rectangular channel, while planar extensional viscosity from the pressure drop over a thin hyperbolic channel, taking into account the pressure drop due to shearing. Measured viscosities of the polystyrene without CO2 compare well with those from commercial rheometers. With the presence of dissolved CO2, both the shear and extensional viscosities of the polystyrene are significantly reduced. The influence of CO2 on the two viscosities is found to be similar to an increase of temperature. Polylactic acid is the first mass-produced biodegradable polymer, and has potential to replace petroleum-based polymers in foaming applications. In this study, the influences of material rheological properties and crystallization on the low-density, microcellular extrusion foaming behaviour of polylactic acids (PLAs) are investigated. Comparisons are made between linear and branched PLAs and between amorphous and crystalline PLAs. The branched PLAs are found to produce foams with higher expansion ratios and reduced open-cell content compared to the linear PLA. The foaming behaviour of the linear PLA, then, is significantly improved by adding a small amount of long-chain-branched PLA. The improved cell structure with branched PLAs is attributed to their relatively high melt strength and strain to break. For the first time, it is shown that crystallization, induced by cooling and macroscopic flow during processing, increases melt strength, which aids the production of low-density foams.

Typescript. Includes bibliographical references (leaves 101-105).

Sequencing batch reactor (SBR) systems were used for the development of a system and operating procedures for the high production of polyhydroxyalkanoates (PHAs) by wastewater treatment (activated sludge) bacterial cultures. It was found that unbalanced growth conditions stimulated massive PHA production in activated sludge biomass. Operating conditions had a significant effect on PHA production and the composition of the accumulated copolymer when either laboratory prepared mixtures of organics or a high acetic acid industrial wastewater were used as the organic substrate mixture. Fully aerobic (AE) conditions with nitrogen (N) and phosphorus (P) limitations were the optimum conditions for PHA production when the laboratory prepared mixtures of orgnics were used, while fully AE with the combinations of N, P, and potassium (K) limitations were better for PHA production using a high acetic acid industrial wastewater as the substrate. One nutrient limitation or partial limitation of either N or P as used for commercial production using pure cultures did not promote massive PHA production in activated sludge biomass compared to the combination of nutrient limitations. A maximum cellular PHA accumulation of 70%TSS was obtained under fully AE conditions with multiple alternating periods of growth and N&P limitations. Microaerophilic/aerobic (MAA/AE) or anaerobic/aerobic (AN/AE) cycling promoted less PHA production compared to fully AE conditions. The relative amounts of the PHA copolymers formed, i.e., polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV) were different under different operating conditions, even though the types and amounts of volatile fatty acids (VFAs) in the feed were the same. It was determined that high total phosphorus (TP) content inside the bacterial cells had a significant detrimental impact on PHA production by activated sludge biomass. A two-stage bioprocess was a better approach for obtaining activated sludge PHA accumulation because a growth phase was necessary to grow the bacterial population that contains minimal TP before starting the subsequent PHA accumulation phase. Seeding sludge obtained from a conventional fully aerobic wastewater treatment system was more suitable than seed obtained from a biological phosphorus removal (BPR) system because bacterial populations from BPR systems tended to convert organic substrates to intracellular carbohydrate content rather than PHA under nutrient limitation conditions. The molecular weights and melting point temperatures of PHAs produced by the mixed culture of activated sludge biomass were comparable to those obtained from pure cultures and have the potential to be used for commercial applications. The results of this study indicate that activated sludge biomass has considerable potential for PHA production for commercial purposes, and likely could do so utilizing wastewater sources of organics. In particular organic rich, nutrient limited wastewaters have potential for efficient PHA production. / Ph. D.

Tesis por compendio / [ES] La presente tesis doctoral tuvo como objetivo desarrollar nuevos materiales biodegradables hechos a base de fibras obtenidas mediante la técnica de electroestirado, denominadas "biopapers" o biopapeles, con barrera a agua y a gases y propiedades de secuestro de oxígeno para su posible aplicación en recubrimientos de papel o como capas intermedias en envases alimentarios basados en papel y cartón. En un primer estudio, se desarrollaron biopapeles de PHB mediante electroestirado, usando dos tipos de colectores, colectores de placa plana y rotativo, para evaluar la influencia del alineamiento de las fibras. Con posterioridad se aplicó un tratamento de recocido por debajo del punto de fusión del polímero a diferentes temperaturas, tiempos y procesos de enfriamiento para obtener películas continuas por coalescencia de las fibras, lo que a su vez condujo a la adhesión entre capas, y a una mejora en las propriedades barrera y ópticas. En un segundo estudio, se depositaron biopapeles monocapa y multicapa hechos de PHB, PVOH y PLA sobre un sustrato de papel no estucado, utilizando los dos colectores citados; y el tiempo de procesamiento por electrospinning se varió para producir espesores diferentes. Para mejorar la adhesión al sustrato de papel, y las propiedades ópticas y de barrera de las multicapas, los biopapeles se sometieron a un proceso de recocido como se describe y optimiza en el primer estudio. Con respecto a la barrera al agua, el sistema de papel/ PVOH/PHB presentó las mejores propriedades. En un tercer estudio, se obtuvieron dos nanopapeles de alta barrera hechos a base de nanofibras de celulosa de dos tipos, nanofibras de celulosa (CNF) y nanofibras de lignocelulosa (LCNF) y se recubrieron con biopapeles de PHA electroestirados con barrera a agua. Como resultado, el carácter hidrófobo de los nanopapeles se mejoró significativamente. Por otra parte, estos también exhibieron un rendimiento mecánico más equilibrado. En un cuarto estudio, se desarrollaron biopapeles de PHA con capacidad activa de secuestro de oxígeno, para lo cual se usaron nanopartículas de paladio (PdNP) como catalizadores de la respuesta activa. La principal dificultad asociada con las nanopartículas es mantenerlas dispersas, por lo que en este trabajo evaluamos el uso de surfactantes CTAB y TEOS como sustancias permitidas en contacto con alimentos para ayudar a la dispersión y distribución de PdNP dentro de las fibras de PHA. Como resultado, se prepararon nanocompuestos electroestirados con capacidad de secuestro de oxígeno hechos de PHB y PdNP, seguidos de un tratamiento de recocido para obtener capas continuas y autoadhesivas. La capacidad de secuestro de oxígeno de los biopapeles, medida a un 100% de humedad relativa (HR), mostró un mejor rendimento para el material en forma de fibra que en forma de film. En cualquier caso, los resultados indicaron una cinética de absorcion relativamente baja. Con el fin de mejorar aún más la cinética de secuestro de oxígeno, incluso a una humedad intermedia y en forma de película, un quinto estudio, desarrolló biopapeles multicapa hechos de PCL y PHA aplicados sobre papel no estucado. Los nanocompuestos de PCL/PdNP mostraron uma cinética de secuestro de oxígeno mucho mayor que la del sistema PHA / PdNP anterior. Este resultado se atribuye a la mayor fración de volumen libre del PCL que permite que la humedad, el hidrógeno y la permeación de oxígeno desencadenen la reacción de eliminación catalítica de forma más eficiente. Finalmente, un sexto estudio, desarrolló un nuevo concepto de capa con capacidad de secuestro de oxígeno y con alta barrera passiva a gases y vapores orgánicos basado en PdNP, CNC y EVOH. Así, CNC y CNC oxidado com TEMPO (TEMPO oxidized CNC), se utilizaron para producir PdNP in situ sobre el nanorefuerzo, que se incorporaron en la matriz del polímero EVOH. El TEMPO oxidized CNC demostró poseer una mayor absorción de oxígeno debido a los grupos car / [CA] La present tesi doctoral va tindre com a objectiu desenvolupar noves capes biodegradables actives obtingudes mitjançant electrospinning, denominades "biopapers" o biopapeles, amb barrera a aigua i a gasos i propietats de segrest d'oxigen per a la seua possible aplicació en recobriments de paper o com a capes intermèdies en envasos alimentaris basats en paper i cartó. En un primer estudi, es van desenvolupar bio-papers de PHB mitjançant electrospinning, utilitzant dos tipus de col·lectors, col·lectors de placa plana i rotatiu, per a avaluar la influència de l'alineament de les fibres. Amb posterioritat es va aplicar un tractament de recuita per davall del punt de fusió del polímer a diferents temperatures, temps i processos de refredament per a obtenir pel·lícules contínues per coalescència de les fibres, la qual cosa al seu torn va conduir a l'adhesió entre capes, i a una millora en les propietats barrera i òptiques. En un segon estudi, es van depositar bio-papers monocapa i multicapa fets de PHB, PVOH i PLA sobre un substrat de paper no estucat, utilitzant els dos col·lectors citats; i el temps de processament per electrospinning es va variar per a produir grossàries diferents. Per a millorar l'adhesió al substrat de paper, i les propietats òptiques i de barrera de les multicapes, els biopapers es van sotmetre a un procés de recuita com es descriu i optimitza en el primer estudi. Respecte a la barrera a l'aigua, el sistema de paper/PVOH/PHB va presentar les millors propietats. En un tercer estudi, es van obtenir dos nano-papers d'alta barrera fets a base de nanofibres de cel·lulosa de dos tipus, nanofibres de cel·lulosa (CNF) i nanofibres de lignocel·lulosa (LCNF) i es van recobrir amb bio-papers de PHA electro-estirats amb barrera a aigua. Com a resultat, el caràcter hidròfob dels nano-papers es va millorar significativament. D'altra banda, aquests també van exhibir un rendiment mecànic més equilibrat. En un quart estudi, es van desenvolupar bio-papers de PHA amb capacitat activa de segrest d'oxigen, per a això es van usar nanopartícules de pal·ladi (PdNP) com a catalitzadors de la resposta activa. La principal dificultat associada amb les nanopartícules és mantenir-les disperses, per la qual cosa en aquest treball avaluem l'ús de surfactants CTAB i TEOS com a substàncies permeses en contacte amb aliments per a ajudar la dispersió i distribució de PdNP dins de les fibres de PHA. Com a resultat, es van preparar nano-compostos electro-estirats amb capacitat de segrest d'oxigen fets de PHB i PdNP, seguits d'un tractament de recuita per a obtenir capes contínues i autoadhesives. La capacitat de segrest d'oxigen dels bio-papers, mesurada a un 100% d'humitat relativa (HR), va mostrar un millor rendiment per al material en forma de fibra que en forma de film. En qualsevol cas, els resultats van indicar una cinètica de absorció relativament baixa. Amb la finalitat de millorar encara més la cinètica de segrest d'oxigen, fins i tot a una humitat intermèdia i en forma de pel·lícula, un cinquè estudi, va desenvolupar bio-papers multicapa fets de PCL i PHA aplicats sobre paper no estucat. Els nano-compostos de PCL/PdNP van mostrar una cinètica de segrest d'oxigen molt major que la del sistema PHA/PdNP anterior. Aquest resultat s'atribueix a la major fracció de volum lliure del PCL que permet que la humitat, l'hidrogen i la permeància d'oxigen desencadenen la reacció d'eliminació catalítica de forma més eficient. Finalment, un sisè estudi, va desenvolupar un nou concepte de capa amb capacitat de segrest d'oxigen i amb alta barrera passiva a gasos i vapors orgànics basat en PdNP, CNC i EVOH. Així, CNC i CNC oxidat com TEMPO (TEMPO oxidat CNC), es van utilitzar per a produir PdNP in situ sobre el nano-reforç, que es van incorporar en la matriu del polímer EVOH. El TEMPO oxidat CNC va demostrar posseir una major absorció d'oxigen degut als grups carboxílics generats. / [EN] The present PhD thesis aimed to develop novel active fiber based biodegradable layers obtained by electrospinning, so-called biopapers, with water and gas barrier and oxygen scavenging properties for their potential use as paper coatings or packaging interlayers in fiber based packaging. In a first study, PHB biopapers were obtained by electrospinning, by means of two types of collectors namely, flat plate and rotation drum collectors, to evaluate the influence of the alignment of fibers. Annealing post-processing below the polymer melting point was carried at different temperatures, isothermal times and cooling processes to obtain transparent and pore free continuous films by fibers coalescence which in turn led to interlayer adhesion, enhanced barrier and optical properties. In a second study, mono and multilayer biopapers comprising PHB, PVOH and PLA were deposited onto a conventional uncoated paper substrate, using the cited two collectors; and the electrospinning processing time was varied to produce different thickneses. To enhance adhesion to the paper substrate, optical and barrier performance of the multilayer, the biopapers were subjected to an annealed process as described and optimized in the first study. Regarding water barrier, the system paper/PVOH/PHB presented the highest barrier performance. In a third study, environmentally friendly materials such as cellulose based nanopapers, i.e. gas barrier layers made of cellulose nanofibrils (CNFs) and lignocellulose nanofibrils (LCNFs), were obtained and coated with the water barrier electrospun PHA biopapers. As a result, the hydrophobic character of the nanopapers was significantly improved by the electrospun biopapers. Moreover, these also exhibited a more balanced mechanical performance. In a fourth study, active oxygen scavenging PHA biopapers were developed, in which palladium nanoparticles (PdNP) were used as catalysts to scavenge oxygen from the headspace. The main difficulty associated with nanoparticles is to keep them dispersed, so in this work we assessed the use of CTAB and TEOS surfactants as food contact permitted substances to help dispersion and distribution of the PdNP within the PHA fibers. As a result, oxygen scavenging nanocomposite biopapers made of electrospun PHB and PdNP were prepared, followed by annealing treatment to obtain homogeneous and continuous active layers. The oxygen scavenging capacity at 100% relative humidity (RH) of the biopapers in fiber form showed better performance than their annealed specimens as expected, but in general this was not considered optimal. In order to improve further the oxygen scavenging capacity, even at a low relative humidity and in film form, a fifth study, developed multilayered biopapers made of PCL and PHA coated on conventional cellulose paper. The PCL/PdNP nanocomposites showed much more enhanced oxygen scavenging performance in comparison with the above PHA/PdNP system. This result is attributed to the higher fractional free volume of the PCL polymer that allows moisture, hydrogen and oxygen permeation to trigger the catalytic scavenging reaction. Finally, a sixth study, developed a solvent casting high gas barrier and active oxygen scavenging layer concept based on PdNP, CNC and EVOH. Thus, CNC and TEMPO oxidized CNC, were used to produce in situ PdNP, which were incorporated into the EVOH polymer matrix. The TEMPO oxidized CNC exhibited higher oxygen absorption due to the generated carboxylic groups. / Spanish Ministry of Economy and Competitiveness (MINECO) project AGL2015-63855-C2-1-R for financial support. A. Cherpinski also would like to thank the Brazilian Council for Scientific and Technological Development (CNPq) of Brasilian Government for her predoctoral grant (205955/2014-2). A. Cherpinski also acknowledges the European Cooperation in Science and Technology (COST) Action FP1405 for funding through a Short Term Scientific Mission (STSM) / Cherpinski Correa, A. (2019). NOVEL ELECTROSPUN POLYHYDROXYALKANOATE BASED HIGH BARRIER AND ACTIVE BIOPAPERS OF INTEREST IN FOOD PACKAGING [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/123064 / TESIS / Compendio

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In conjunction with ongoing studies to develop a method for quantifying potentially biodegradable organic carbon (Rectanus et al 2005), this research was conducted to evaluate the extent to which organic carbon extracted using this method will biodegrade in anaerobic environments. The ultimate goal is to use this method for the evaluation of chloroethene contaminated sites in order to estimate the long-term sustainability of monitored natural attenuation (MNA) as a remediation strategy. Although relatively recalcitrant under aerobic conditions, the breakdown of chlorinated solvents primarily occurs through the anaerobic process of reductive dechlorination. The biodegradation of organic carbon in these anaerobic environments drives the system to reducing conditions conducive for reductive dechlorination. The extraction procedure developed by Rectanus et al. (2005) has been tested in several series of aerobic bioassays to determine the biodegradable fraction of carbon extracted. This study seeks to show that the carbon removed from the sediment by this extraction process will also degrade in anaerobic environments. Three aquifer sediment samples characterized by low, medium, and high carbon concentrations were taken from Naval Submarine Base Kings Bay, Georgia. Two sites were also sampled from Naval Amphibious Base Little Creek, Virginia. MLS20 is a site located inside of a chloroethene plume, and MLS10 is located outside of the plume. For approximately 12 weeks aqueous total organic carbon (TOC), headspace carbon dioxide (CO2), volatile fatty acids (VFAs), and headspace hydrogen concentrations were monitored for evidence of the biodegradation of organic carbon. Although few VFAs were observed throughout the experiments, their presence as early as 8 days after inoculation indicated that the bioassays were anaerobic. The fewest VFAs were seen in the MLS20 bioassays, while the most VFAs were observed in the MLS10 bioassays. MLS20 exhibited low levels of TOC loss and the low VFA levels indicate that complex organic matter was not highly degraded in these bioassays. The higher level of VFAs observed in MLS10 bioassays corresponded with little TOC degradation, indicating that although more complex organics were being broken down, conditions were not reduced enough to further oxidize the organic carbon. As much as 50% TOC loss was observed in the Kings Bay bioassays with few VFAs detected. Loss of TOC was accompanied by CO₂ generation which provides supporting evidence that organic carbon was being oxidized. Hydrogen was observed in the bioassays, suggesting that VFAs resulting from organic carbon breakdown were being oxidized. This indicates that organic carbon removed from sediment using the extraction process is biodegraded anaerobically and could lead to conditions capable of sustaining reductive dechlorination. / Master of Science

An aneurysm is a balloon-like bulge in the wall of blood vessels, occurring in major arteries from the heart and brain. Biodegradable stent-assisted coiling is expected to be the ideal treatment of wide-neck complex aneurysms. A number of biodegradable stents are promising, but also with issues and/or several limitations to be addressed. From the design point of view, biodegradable stents are typically designed without structure optimization. The drawbacks of these stents often cause weaker mechanical properties than native arterial vessels. From the fabrication point of view, the conventional methods of the fabricating stent are time-consuming and expensive, and also lack precise control over the stent microstructure. As an emerging fabrication technique, dispensing-based rapid prototyping (DBRP) allows for more accurate control over the scaffold microstructure, thus facilitating the fabrication of stents as designed. This thesis is aimed at developing methods for fabrication and optimal design of biodegradable stents for treating aneurysms. Firstly, a method was developed to fabricate biodegradable stents by using the DBRP technique. Then, a compression test was carried out to characterize the radial deformation of the stents fabricated. The results illustrated the stent with a zigzag structure has a higher radial stiffness than the one with a coil structure. On this basis, the stent with a zigzag structure was chosen to develop a finite element model for simulating the real compression tests. The result showed the finite element model of biodegradable stents is acceptable within a range of radial deformation around 20%. Furthermore, an optimization of the zigzag structure was performed with ANSYS DesignXplorer, and the results indicated that the total deformation could be decreased by 35% by optimizing the structure parameters, which would represent a significant advance of the radial stiffness of biodegradable stents. Finally, the optimized stent was used to investigate its deformation in a blood vessel. The deformation is found to be 0.25 mm in the simulation, and the rigidity of biodegradable stents is 7.22%, which is able to support the blood vessel all. It is illustrated that the finite element analysis indeed helps in designing stents with new structures and therefore improved mechanical properties.

Gold nanoparticles have received significant interest recently due to their utility in biomedical imaging and therapy. Nanoparticles which exhibit intense extinction in the near infrared (NIR) region, where blood and tissue absorb light weakly, are of great interest as contrast agents for biomedical imaging applications. While strong NIR extinction often requires sizes greater than ~20-30 nm, effective clearance from the body to avoid toxic accumulation necessitates sizes below ~6 nm. Moreover, effective clearance depends upon lack of adsorption of serum proteins in the bloodstream onto the particles. Herein, this conflict is addressed by assembling sub-5 nm gold nanoparticles into clusters with controlled size and morphology, in order to provide intense NIR extinction. Furthermore, the surfaces of the primary gold nanoparticles are designed such that the particles avoid the adsorption of any serum proteins. Binary ligand monolayers of anionic citrate and appropriate amounts of either cationic lysine or zwitterionic cysteine are synthesized to completely prevent serum protein adsorption from undiluted fetal bovine serum. A mechanism is proposed whereby the zwitterionic tips which are present on both the lysine and cysteine ligands limit the interactions between serum proteins and the "buried" charges on the nanoparticle surfaces. These primary nanoparticles are subsequently assembled into biodegradable nanoclusters via "quenched assembly", wherein nanoclusters are assembled and subsequently quenched by the adsorption of a biodegradable polymer on the cluster surface. The sizes of completely reversible "quenched equilibrium" nanoclusters formed from gold nanoparticles coated with a mixture of lysine and citrate are tuned from 20 nm to 40 nm, and nanocluster size is semi-quantitatively predicted by a free-energy model. Additional control over nanocluster size and extinction is demonstrated by adding NaCl, which is shown to decrease the polymer adsorption on the clusters and thus decrease polymer bridging interactions. This nanocluster formation platform is extended to nanospheres capped with citrate and the thiolated, zwitterionic cysteine ligand. A general paradigm is presented whereby the sizes and optical properties of biodegradable gold nanoclusters formed from nanospheres which do not adsorb any serum proteins are tuned via control over van der Waals, electrostatic, depletion, and polymer bridging colloidal interactions. / text