History teaches us that novel materials, such as chlorofluorocarbon and asbestos, can have dire unintended consequences to human and environmental health. The exponential growth of the field of nanotechnology and the products developed along the way provide the opportunity for a new paradigm of design thinking, in which human and environmental impacts are considered early on in product development. In particular, nanocellulose is touted as a promising green nanomaterial, as it is sourced from an effectively inexhaustible feedstock of wood-based cellulose and is assumed to be harmless to the environment since it is derived from a natural material and assumed to be biodegradable. The various forms of nanocellulose possess an impressive diversity of properties, making it suitable for a wide variety of applications such as drug delivery, reinforcement, food additives, and iridescent make-up. However, as nanomaterials can have different properties relative to their bulk form, it is questionable whether they are truly environmentally friendly, particularly in terms of their biodegradability and potential impacts to receiving environments. Given the projected mass-scale application of nanocellulose and the inevitability of its subsequent release into environment, the purpose of this study was to determine the biodegradability of nanocellulose and the response of environmentally-relevant microbial communities. Specifically, it was hypothesized that cellulose in the nano size range would display distinct biodegradation patterns and rates, relative to larger forms of cellulose. Further, it was hypothesized that modification of nanocellulose, in terms of morphology and surface properties (e.g., charge), would further influence its biodegradability. Wetlands and anaerobic digesters were selected as two environmentally-relevant receiving environments that also play critical roles in global carbon turnover. To examine the biodegradability of nanocellulose, two distinct microbial consortia were enriched from wetland (W) and anaerobic digester (AD) inocula and applied in parallel experiments. The consortia were grown under anaerobic conditions with microcrystalline cellulose as the sole carbon substrate over a period of 246 days before being aliquoted to microcosms for subsequent biodegradation assays. Various forms of nanocellulose were spiked into the microcosms and compared with microcrystalline cellulose as a non nano reference. Microcosms were sacrificed in triplicate with time to monitor cellulose degradation as well as various measures of microbial community response. Microbial communities were characterized in terms of gene markers for total bacteria (16S rRNA genes) and anaerobic cellulose degraders (glycoside hydrolase family 48 genes, i.e., cel48) as well as high throughput amplicon sequencing of 16S rRNA genes (V4 region). A series of three studies examined: 1) the effect of nanocrystalline versus microcrystalline cellulose; 2) the effects of nanocellulose morphology (crystalline rod versus filament) and surface functionalization (cationic and anionic); and 3) metagenomic characterization of cellulose degrading communities using next-generation DNA sequencing. It was found that the nano- size range did not hinder cellulose degradation, in fact, nanocrystalline cellulose degraded slightly faster than microcrystalline cellulose according to 1st order kinetics (1st order decay constants: 0.62±0.08 wk-1 for anionic nanocrystalline cellulose versus 0.39±0.05 wk-1 for microcrystalline cellulose exposed to AD culture; 0.69±0.04 wk-1 for anionic nanocrystalline cellulose versus 0.58±0.05 wk-1 for microcrystalline cellulose exposed to W). Experiments comparing the effects of surface functionalization indicated that anionic nanocellulose degraded faster than cationic cellulose (1st order decay constants for cationic nanocrystalline cellulose: 0.48±0.06 wk-1 and 0.58±0.07 wk-1 on exposure to AD and W cultures respectively). Measurements of 16S rRNA and cel48 genes were consistent with this trend of greater biological growth and cellulose-degrading potential in the anionic nanocellulose condition, suggesting that surface properties can influence biodegradation patterns. Taxonomic characterization of 16S rRNA gene amplicons suggested that taxa known to contain anaerobic cellulose degraders were enriched in both W and AD consortia, which shifted in a distinct manner in response to exposure to the different cellulosic materials. This suggests that distinct groups of microbes may drive the biodegradation of different forms of cellulose. Further, metagenomic investigation provided new insight into taxonomic and functional aspects of anaerobic cellulose degradation, including identification of enzymatic families associated with degradation of the various forms of cellulose. Overall, the findings of this study advance understanding of anaerobic cellulose degradation and indicate that nanocellulose is likely to readily degrade in receiving environments and not pose an environmental concern. / Ph. D.

The search for alternatives to the fossil-based products has dramatically surged during past few decades primarily due to the problems associated with the scarcity of these sources and global environmental concerns. Among those many alternatives, exploitation of cellulose, as a raw material to develop novel products has been a constant attempt since it has never lost its both economic and industrial impact. Cellulose is known for its significant contribution as a raw material and as a fascinating sustainable macromolecule, which exhibits wide availability and versatile chemical reactivity to discover novel derivatives for broad range of applications. Conversion of cellulose C2/C3 secondary hydroxyl groups to dialdehyde groups in the presence of periodate is an extremely useful method for regioselective oxidation of cellulose and to activate the polymer for further derivatization. This thesis is primarily focused on synthesis and characterization of wide range of cellulose derivatives exploiting facile periodate oxidation methodology. The first study investigated the use of periodate oxidation as a potential method to synthesize a novel water soluble derivative of cellulose from bleached hardwood Kraft pulp. The work focused on the effect of periodate oxidation and sulfonation reaction on water solubility, morphology and structure of cellulose fibers. The results showed a significant increase in water solubility (2.85 -28.5 g/L) and complete change in surface morphology of the fibers due to the introduction of sulfonic acid groups. In the second study, the same reaction scheme was employed on bead cellulose to prepare anionic 2,3-disulfonated beads. Due to the presence of negatively charged sulfonic acid groups, the beads were found to be agglomerated in presence of cationic starch, exhibiting their future application in chromatographic separation. In the third study, model primary amine compounds such as methyl and butyl amines were grafted to nanowhisker surfaces following periodate oxidation and reductive amination. Then, based on the grafting procedure, in the following study, gamma aminobutyric acid (spacer) and syringyl alcohol (linker) was attached to periodate oxidized nanowhiskers to synthesize a novel drug delivery system. The final study investigated the application of periodate oxidized nanowhiskers as chemical cross-linkers to stabilize gelatin gels. It was concluded that the chemical cross-linking has a significant effect on relative increase in percentage of rigid protons, reduced water uptake ability and reduced pore size of the gels. Not only did the chemical cross-linking improve the storage modulus of the gels (150%) and but it also increased the thermal resistance until 50 oC.

We studied PLA-microcrystalline cellulose composites, focusing on the effects of processing, particle size and surface modification. The thermal and mechanical properties of these PLA based composites were studied and the effect of cellulose addition on PLA degradation was analyzed. For our system, the degradation rate was found to depend on initial sample crystallinity, pH of the degradation media and cellulose content of the composite. Composites were prepared using solution processing and melt mixing methods. The processing methods influenced the polymer's ability to crystallize affecting the mechanical properties. Isothermal crystallization studies carried out to study the kinetics of crystallization showed melt processed samples to have lower half time for crystallization and higher value for the Avrami exponent. The crystallization rate of PLA was also found to depend on surface chemical composition of cellulose particles and the particle size. Influence of filler surface modification on the composite properties was studied via grafting of lactic acid and polylactic acid to cellulose particles and the effect of filler size was studied using hydrolyzed microcrystalline cellulose particles. A simple esterification reaction that required no external catalyst was used for surface modification of cellulose particles. Surface modification of cellulose particles enhanced the static and dynamic mechanical properties of the composite samples due to improvement in the PLA-cellulose compatibility that resulted in better interfacial interactions. The utility of cellulose, available from a renewable resource, as an effective reinforcement for PLA is demonstrated.

Esta Dissertação discorre sobre a pesquisa de caracterização de palha de milho e a sua utilização como matéria prima para a obtenção de nanocelulose. Segundo o IBGE, este resíduo agrícola foi produzido no Brasil, no ano de 2013, em cerca de seis milhões de toneladas. As amostras deste resíduo lignocelulósico utilizadas neste trabalho foram coletadas na forma cotidiana de descarte mais frequentemente encontrada em supermercados e feiras livres. Procedeu-se, então, ao beneficiamento mecânico, beneficiamento químico (mercerização e branqueamento) e hidrólise ácida dessas amostras, o que produziu os seguintes materiais: palha de milho beneficiada mecanicamente, palha de milho beneficiada quimicamente e nanocelulose. Cada um destes materiais foi caracterizado, conforme o tipo, por menos ou mais dos seguintes ensaios: determinação de densidade, determinação de umidade, determinação do teor de cinzas, resistência à tração, determinação do teor de extraíveis, determinação do teor de holocelulose, determinação do teor de hemicelulose, determinação do teor de alfacelulose, determinação do teor de lignina, análise termogravimétrica (TGA), espectroscopia por infravermelho por transformada de Fourier (FTIR), índice de cristalinidade por difração de raios-x (CrI), medição do tamanho de partícula por espalhamento de luz dinâmico (DLS), morfologia por microscopia eletrônica de varredura (SEM) e determinação do rendimento dos produtos de hidrólise. Nesta pesquisa também se estudou, empregando a técnica de planejamento de experimento fatorial com ponto central, a influência dos fatores razão fibra/ácido e tempo da reação na obtenção da nanocelulose, conseguida com êxito em todos os experimentos executados com a palha de milho que foi branqueada de forma efetiva neste trabalho / The present research focuses on the characterization of corn husks and its use as a raw-material for the cellulose Nanowhiskers production. According to the IBGE (Brazilian Institute of Geography and Statistics), in 2013 about six million tons of this agricultural waste were produced in Brazil. The samples from this lignocellulosic waste used in this research were collected in the most usual form of discard found in supermarkets and street markets. After that, the mechanical processing, chemical processing (mercerization and bleaching) and acid hydrolysis of these samples were carried out, yielding the following materials: mechanically processed corn husk, chemically processed corn husk and cellulose nanowhiskers. Each one of these materials, according to the type, was characterized by the following standardized tests (some by fewer, others by almost all of the tests): density; moisture; ash; mechanical property; extractible, hemicellulose, cellulose and lignin contents; thermal behavior by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), crystallinity index (CrI) by X-ray diffraction (XRD), distribution of particle size by dynamic light scanning (DLS); morphology by scanning electron microscopy (SEM) and determination of the yield of the hydrolysis products. The influence of the factors fiber/acid ratio and reaction time in the production of cellulose nanowhiskers was also studied in this research, using the factorial experiment design. The obtention of cellulose nanowhiskers was successfully achieved in all experiments performed with corn husk that was bleached effectively in this work

Esta Dissertação discorre sobre a pesquisa de caracterização de palha de milho e a sua utilização como matéria prima para a obtenção de nanocelulose. Segundo o IBGE, este resíduo agrícola foi produzido no Brasil, no ano de 2013, em cerca de seis milhões de toneladas. As amostras deste resíduo lignocelulósico utilizadas neste trabalho foram coletadas na forma cotidiana de descarte mais frequentemente encontrada em supermercados e feiras livres. Procedeu-se, então, ao beneficiamento mecânico, beneficiamento químico (mercerização e branqueamento) e hidrólise ácida dessas amostras, o que produziu os seguintes materiais: palha de milho beneficiada mecanicamente, palha de milho beneficiada quimicamente e nanocelulose. Cada um destes materiais foi caracterizado, conforme o tipo, por menos ou mais dos seguintes ensaios: determinação de densidade, determinação de umidade, determinação do teor de cinzas, resistência à tração, determinação do teor de extraíveis, determinação do teor de holocelulose, determinação do teor de hemicelulose, determinação do teor de alfacelulose, determinação do teor de lignina, análise termogravimétrica (TGA), espectroscopia por infravermelho por transformada de Fourier (FTIR), índice de cristalinidade por difração de raios-x (CrI), medição do tamanho de partícula por espalhamento de luz dinâmico (DLS), morfologia por microscopia eletrônica de varredura (SEM) e determinação do rendimento dos produtos de hidrólise. Nesta pesquisa também se estudou, empregando a técnica de planejamento de experimento fatorial com ponto central, a influência dos fatores razão fibra/ácido e tempo da reação na obtenção da nanocelulose, conseguida com êxito em todos os experimentos executados com a palha de milho que foi branqueada de forma efetiva neste trabalho / The present research focuses on the characterization of corn husks and its use as a raw-material for the cellulose Nanowhiskers production. According to the IBGE (Brazilian Institute of Geography and Statistics), in 2013 about six million tons of this agricultural waste were produced in Brazil. The samples from this lignocellulosic waste used in this research were collected in the most usual form of discard found in supermarkets and street markets. After that, the mechanical processing, chemical processing (mercerization and bleaching) and acid hydrolysis of these samples were carried out, yielding the following materials: mechanically processed corn husk, chemically processed corn husk and cellulose nanowhiskers. Each one of these materials, according to the type, was characterized by the following standardized tests (some by fewer, others by almost all of the tests): density; moisture; ash; mechanical property; extractible, hemicellulose, cellulose and lignin contents; thermal behavior by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), crystallinity index (CrI) by X-ray diffraction (XRD), distribution of particle size by dynamic light scanning (DLS); morphology by scanning electron microscopy (SEM) and determination of the yield of the hydrolysis products. The influence of the factors fiber/acid ratio and reaction time in the production of cellulose nanowhiskers was also studied in this research, using the factorial experiment design. The obtention of cellulose nanowhiskers was successfully achieved in all experiments performed with corn husk that was bleached effectively in this work

<p>Stress relaxation in tin films can result in microstructural changes visible on the surface, referred to as “surface defects,” and can include whisker and hillock formation, cracking, nucleation of new grains, and grain growth. Sn whiskers are of particular concern for microelectronics reliability in which Sn whiskers growing from component surface and cause catastrophic short-circuiting. While prior research has identified the conditions and mechanisms for surface defect evolution during aging and thermal cycling, the response of tin films due to mechanical stress, especially high frequency vibration, is not fully understood. In practical terms, high frequency vibration is an important source of mechanical stress generation in microelectronics for automotive and aerospace applications. This research, based on high frequency vibration of cantilevers, adds to the existing mechanisms for stress relaxation process in metal thin films, not just for tin films, as well as proposed new mechanisms for such processes.</p> <p>In the first study, the piezoelectric drive of small atomic force microscopy (AFM) cantilevers vibrated at resonance are used for high frequency cyclic bending experiments. Intermetallic (IMC) formation as well as initial film morphology and thickness (corresponding to surface grain size) all influence the response of tin films for cyclic bending. A laser doppler vibrometer (LDV) system was used to identify the real-time strain along the cantilever during cycling, suggesting that the small strains are responsible for the limited nucleation and growth for defects though the defect density increases with the number of cycles and strain distribution along the cantilever.</p> <p>In the second study, the effect of larger strains on defect evolution was determined using vibration of larger cantilevers at resonance as a function of number of cycles, frequency, temperature, and whether the vibration was continuous or interrupted for SEM characterization of defect type and density. In addition to typical micro-sized whiskers and hillocks, intragranular breakup (IGB) with intrusions and extrusions and nanowhiskers (NWs) with diameters < 1 𝜇m were observed. Both increasing number of cycles and strain amplitude/rate promote defect formation for a fixed frequency, with the defect density being strongly frequency dependent.Vibration at low temperature and interrupting measurements for SEM characterization affected the relative densities. The density of larger surface defects is strongly influenced by interruptions while NW density is almost unaffected. </p><p>Both low resonant frequency and low T (223 K) promote IGB formation during cyclic bending due to large maximum strain amplitude and slower diffusion/creep at low T, respectively. Though the overall defect density for low T is smaller than that at room temperature (RT), the response of films is similar to that at RT, indicating the same mechanisms. The defect density decrease at low T is mainly determined by NW formation, and there is a transition from micro-sized surface defects to IGBs for cyclic bending at low T.</p><p>This research demonstrated that cyclic bending of cantilevers can be used to quantify the stress relaxation of tin films in an important stress regime for microelectronics and to develop defect mitigation strategies to improve the reliability of interconnects in electronic applications.</p>

Die vorliegende Dissertation befasst sich mit dem Wachstum und der Charakterisierung von Silizium- und Germanium-Nanodrähten. Diese Strukturen gelten als aussichtsreiche Komponenten für zukünftige Bauelemente. Für die Anwendung ist die genaue Kenntnis der Größe, der kristallographischen Orientierung und der Position der Nanodrähte erforderlich. Ziel dieser Arbeit war daher die Untersuchung von Si- und Ge-Nanodrähten im Hinblick auf ihre Größe, Orientierung und Position. Die Herstellung erfolgte durch Physikalische Gasphasenabscheidung (PVD) im Ultrahochvakuum nach dem Vapor-Liquid-Solid (VLS)-Verfahren, das auf dem Wachstum aus Lösungsmitteltröpfchen basiert. Die Größe der Nanodrähte konnte im Falle von Silizium auf Si(111) mit Gold als Lösungsmittel durch die Parameter des Experiments reproduzierbar bestimmt werden. Höhere Goldbedeckung und höhere Substrattemperaturen führten zu Tröpfchen mit größerem Duchmesser und somit zu dickeren Drähten. Längere Si-Verdampfungszeiten und höhere Si-Verdampfungsraten führten zu längeren Drähten. Dünnere Drähte wuchsen schneller als dickere. Als zweites Lösungsmittel wurde Indium untersucht, da es sich im Vergleich zu Gold nicht nachteilig auf die elektronischen Eigenschaften von Silizium auswirkt. Basierend auf den Ergebnissen zur Tröpfchenbildung konnten die besseren Wachstumsresultate mit Gold erklärt werden. Germanium-Nanodrähte, die aus Goldtröpfchen auf Ge(111) gezüchtet wurden, zeigten im Gegensatz zu den Si-Nanodrähten nicht die kristallographische [111]-Orientierung des Substrates, sondern eine -Orientierung, was durch Berechnungen von Keimbildungsenergien auf verschiedenen Kristallflächen erklärt werden konnte. Zur Anordnung von Metalltröpfchen und damit von Nanodrähten wurden Substrate mithilfe von fokussierten Ionenstrahlen (FIB) vorstrukturiert, um die Tröpfchenbildung an bestimmten Stellen zu begünstigen. Es gelang, aus angeordneten Goldtröpfchen epitaktisch gewachsene Si- und Ge-Nanodrähte zu züchten. / This dissertation deals with the growth and the characterization of silicon and germanium nanowhiskers, also called nanorods or nanowires. The investigation of these structures is of great interest as they represent promising building blocks for future electronic devices. With regard to a possible application, the knowledge of size, crystallographic orientation and position of the nanowhiskers is essential. The purpose of this work was, therefore, to investigate the growth of Si and Ge nanowhiskers with regard to their size, orientation and position. The nanowhiskers were grown via physical vapor deposition (PVD) in ultra-high vacuum using the vapor-liquid-solid (VLS) mechanism which is based on growth from solution droplets. The size of the nanowhiskers could be reproducibly determined by the experimental parameters in the case of Si nanowhiskers on Si(111) with gold as the solvent. A higher gold coverage as well as a higher substrate temperature led to larger droplet diameters and thus to thicker whiskers. A longer silicon evaporation time and a higher silicon rate led to longer whiskers. Thinner whiskers grew faster than thicker ones. A second material used as the solvent was indium as it is more suitable for electronic application compared to gold. Based on results of droplet formation of the two solvents on silicon, the better results of whisker growth using gold could be explained. Ge nanowhiskers grown from gold droplets on Ge(111) did not show the [111] orientation of the substrate as in the case of Si nanowhiskers on Si(111) but a orientation. By calculating nucleation energies on different crystal facets, the experimental findings could be explained. To position nanodroplets of the solvent material and thus to obtain a regular arrangement of nanowhiskers, substrates were pre-structured with nanopores by focused ion beams (FIB). Silicon and germanium nanowhiskers could be epitaxially grown from ordered arrays of gold droplets.

El presente trabajo tiene por objetivo estudiar las aplicaciones de los nanocristales o ¿nanowhiskers¿ extraídos mediante hidrólisis ácida de celulosa bacteriana (BCNW) para el desarrollo de materiales poliméricos y biopoliméricos con propiedades mejoradas para su uso en aplicaciones de envasado de alimentos. En primer lugar se estudió y optimizó el proceso de extracción de BCNW. Se desarrolló un procedimiento de extracción con ácido sulfúrico, que permitió obtener nanocristales con elevada relación de aspecto y cristalinidad y al mismo tiempo, un elevado rendimiento de extracción. Este procedimiento comprende una posterior etapa de neutralización que resultó ser necesaria para garantizar la estabilidad térmica de los nanocristales. El siguiente paso consistió en la formulación de materiales nanocompuestos con propiedades mejoradas incorporando BCNW en diferentes matrices plásticas, en concreto copolímeros de etileno-alcohol vinílico (EVOH), ácido poliláctico (PLA) y polihidroxialcanoatos (PHAs). Mediante las técnicas de electroestirado y estirado por soplado se generaron fibras híbridas de EVOH y PLA con BCNW. La incorporación de BCNW en las disoluciones empleadas para producir fibras modificó significativamente sus propiedades (viscosidad, tensión superficial y conductividad) y por tanto, la morfología de las fibras se vio afectada. Además, se generaron fibras con propiedades antimicrobianas mediante la incorporación de aditivos, maximizando el efecto antimicrobiano con la adición de sustancias de carácter hidrofílico. Seguidamente, se produjeron nanocompuestos por mezclado en fundido y se desarrollaron técnicas de pre-incorporación de BCNW para evitar la aglomeración de los mismos no sólo en matrices hidrofílicas como el EVOH, sino también en matrices hidrofóbicas como el PLA. La dispersión óptima de BCNW resultó en una mejora de las propiedades mecánicas y de barrera de los nanocompuestos. También se estudió la modificación de la superficie de los nanocristales mediante copolimerización con poli(glicidil metacrilato) para mejorar la compatibilidad de BCNW con una matriz hidrofóbica como el PLA. Se incluyen además los primeros resultados obtenidos en cuanto a la producción de nanobiocompuestos sintetizados por microorganismos, que consisten en PHAs con diferentes contenidos de hidroxivalerato reforzados con BCNW. Por último, se desarrollaron películas con propiedades de alta barrera basadas en películas de BCNW recubiertas con capas hidrofóbicas. El recubrimiento mediante la deposición de fibras por electrospinning seguido de homogeneización por calentamiento garantizó una buena adhesión entre las diferentes capas, protegiendo así las películas de BCNW del efecto negativo de la humedad. / Martínez Sanz, M. (2013). Bacterial cellulose nanowhiskers to enhance the properties of plastics and bioplastics of interest in food packaging [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/30312 / Premios Extraordinarios de tesis doctorales