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Tesis por compendio / [ES] La presente tesis doctoral está basada en el aprovechamiento de residuos de biomasa para la obtención de celulosa y otros compuestos de interés con el objetivo de desarrollar estructuras aplicables en el envasado alimentario. El uso masivo de los plásticos convencionales derivados del petróleo genera una cantidad ingente de residuos debido a su mínima degradabilidad y baja eficacia de las estrategias de reciclaje actuales, provocando así su acumulación en los ecosistemas terrestres y marinos. En este contexto, el uso de biopolímeros (y más en concreto, la celulosa) juega un papel crucial puesto que ofrecen una alternativa abundante, renovable y biodegradable que permite reducir y reemplazar el uso de estos materiales tradicionales. Para ello, se ha seleccionado como fuente de celulosa los residuos de hojas de Posidonia oceanica (planta acuática endémica del mar Mediterráneo) debido a su abundancia y problemática asociada: sus hojas se acumulan en las playas generando mal olor, teniendo las autoridades locales que retirarlas sin un uso específico posterior. Por tanto, además de proponer una solución a un problema de gestión, el aprovechamiento de dicho residuo está en línea con las políticas actuales de economía circular y "residuo cero" que permiten una utilización más sostenible de los recursos naturales. De esta forma, la valorización de residuos de biomasa respecto a otras fuentes tradicionales de celulosa como la madera u otros cultivos específicos es beneficiosa por ambas partes. En la primera parte de la tesis, se demuestra el potencial de las hojas de P. oceanica como fuente de celulosa (¿30% contenido). Dicha celulosa, así como otras dos fracciones celulósicas intermedias se utilizaron para formar films mediante filtrado a vacío y como aditivos de refuerzo en matrices de almidón comercial mediante mezclado en fundido y prensa. En paralelo, tanto la celulosa como las fracciones celulósicas de interés fueron sometidas a un tratamiento ácido para la obtención de nanocristales. La presencia de compuestos adicionales recalcitrantes tuvo un efecto positivo en las propiedades de estos, cuya obtención fue escalada a nivel planta piloto para la producción de bandejas mediante termoformado de mezclas con almidón. Por último, se obtuvieron extractos bioactivos mediante técnicas en base acuosa (ultrasonidos y calor) para una valorización integral del residuo de hojas de P. oceanica con el objetivo de reducir el uso de disolventes orgánicos. En una segunda parte de la tesis, se aplicaron los protocolos simplificados de extracción de celulosa a otros residuos de biomasa como los sarmientos de vid, la paja de arroz y la cáscara de arroz. Cabe destacar que se purificaron con éxito fracciones y nanocristales celulósicos en todas las biomasas evaluadas. Esto demostró que es posible simplificar los procesos de extracción de celulosa para disminuir costes y aumentar la sostenibilidad de la metodología pese a la posible heterogeneidad de la(s) fuente(s) de partida. En la última parte de la tesis, estos nanocristales celulósicos se utilizaron como material de partida para la formación de aerogeles mediante un proceso de liofilización. Para paliar la baja resistencia mecánica y al agua de estos materiales, se diseñó un método patentado de inmersión en una disolución de ácido poliláctico (PLA) que recubría el aerogel celulósico mejorando tanto su resistencia mecánica como su resistencia al agua. Estos aerogeles puramente biopoliméricos fueron ampliamente caracterizados mediante distintas metodologías, destacando la microscopía Raman y confocal. Finalmente, se obtuvieron aerogeles bioactivos mediante la incorporación de los extractos de P. oceanica más prometedores (previamente obtenidos y caracterizados). Por tanto, la presente tesis muestra la valorización de residuos de biomasa mediante protocolos simplificados para el desarrollo de estructuras de envasado alimentario. / [CA] La present tesi doctoral està basada amb l'aprofitament de residus de biomassa per a l'obtenció de cel·lulosa i altres compostos d'interès amb l'objectiu de desenvolupar estructures aplicables a l'envasat alimentari. L'ús massiu de plàstics convencionals derivats del petroli genera una quantitat ingent de residus degut a la seua mínima degradabilitat i baixa eficàcia de les estratègies de reciclatge actuals, provocant d'aquesta manera la seua accumlació als eocisistemes terrestres i marins. Dins d'aquest context, l'ús de biopolímers (i més concretament, la cel·lulosa) juga un paper crucial ja que oferix una alternativa abundant, renovable i biodegradable que permet reduir i reemplaçar l'ús d'aquests materials tradicionals. Per a aquest fet, s'ha seleccionat com a font de cel·lulosa els residus de fulles de Posidonia oceanica (planta aquàtica endèmica del mar Mediterrani) degut a la seua abundància i a la problemàtica associada: les seues fulles s'acumulen a les platges generant mal olor i tenint que retirar-les les autoritats locals sense u ús posterior. Per tant, a més de proposar un solució a un problema de gestió, l'aprofitament del residu en qüestió està en la línia de les polítiques actuals d'economia circular i "residu zero" que permeten una utilització més sostenible dels recursos naturals. D'aquesta manera, la valorització de residus de biomassa respecte d'altres fonts tradicionals de cel·lulosa com la fusta i altres cultius específics és beneficiosa per ambdues parts. En la primera part de la tesi, es demostra el potencial de les fulles de P. Oceanica com a font de cel·lulosa (30% del contingut) al purificar-se amb èxit mitjançant l'aplicació d'un protocol convencional. Aquesta cel·lulosa, així com altres dues fraccions cel·lulòsiques intermitges es van emprar per a formar pel·lícules mijançant mescla en fos i premsa. Paral·lelament, tant la cel·lulosa com les fraccions cel·lulòsiques d'interès van ser sotmeses a un tractament àcid per a l'obtenció de nanocristals. La presència de compostos adicionals recalcitrants va tenir un efecte positiu en les seues propietats. La obtenció resultant va ser escalada a nivell de planta pilot per a la producció de safates a través termoformat de mescla amb almidó. Per últim, es van obtenir extractes bioactius amb tècniques amb base d'aigua (ultrasons i calor) per a la valorització integral del residu de fulles de P. Oceanica amb l'objectiu de reduir la utilització de dissolvents orgànics. En la segona part de la tesi es van aplicar els protocols simplificats d'extracció de cel·lulosa a altres residus de biomasa com els sarments de vinya, la palla d'arròs i la closca de l'arròs. Hem de destacar que es van purificar amb èxit les fraccions i els nanocristals cel·lulòsics en totes les biomasses avaluades. Es va demostrar que és possible simplificar els procesos d'extracció de cel·lulosa per a disminuir costos i augmentar la sostenibilitat de la metodologia malgrat la possible heterogeneïtat de le(s) font(s) del punt de partida. En la última part de la tesi, aquestos nanocristals cel·lulòsics es va emprar com a material de partida per a la formació de aerogels mitjançant un procés de liofilització. Per a paliar la baixa resistència mecànica i l'aigua d'aquests materials, es va dissenyar un mètode patentat de immersió en una dissolució d'àcid polilàctic (PLA) que recobria l'aerogel cel·lulòsic millorant tant la seua resistència mecànica com la seua resistència a l'aigua. Aquestos aerogels purament biopolimèrics van ser ampliament caracteritzats a través distintes metodologies, destacant la microscopia Raman i confocal. Finalment, es van obtenir aerogels bioactius mitjançant la incorporació dels extractes de P. Oceànica més prometedors (prèviament obtinguts i caracteritzats). Per tant, la present tesi mostra la valoració de residus de biomassa mitjançant protocols simplificats per al de / [EN] The following Ph. D thesis is based on the waste biomass valorization for obtaining cellulose and other relevant compounds aimed to develop food packaging structures. The massive use of fossil-fuel derived conventional plastics generates an excessive number of residues due to their low degradation rates and inefficient current recycling strategies, which makes them accumulate in both terrestrial and marine ecosystems. In this context, the use of biopolymers (concretely cellulose) plays a key role in offering an abundant, renewable and biodegradable alternative that allows to reduce and even replace the use of these conventional materials. For this aim, Posidonia oceanica (an endemic aquatic plant from the Mediterranean Sea) dead leaves have been selected as the main cellulose source due to their abundance and problematic associated: dead leaves are accumulated in beaches and seashores causing bad odours and must be removed by local authorities without any further use. Thus, the valorization of this residue provides a solution in line with current circular and "zero-waste" economy policies which enables more sustainable exploitation of natural resources. As a result, waste biomass valorization for obtaining cellulose with regards to other more conventional sources is doubly beneficial. In the first part of the thesis, the potential of P. oceanica leaves as a cellulosic source was shown (¿30% cellulose content) after successfully applying a conventional purification protocol. This cellulose, as well as two intermediate cellulosic fractions (with the presence of additional components such as hemicelluloses and/or lignin), were used for developing films both by vacuum filtration and melt mixing and hot pressing in starch composites. In parallel, both cellulose and cellulosic fractions were submitted to acid treatment in order to obtain nanocrystals, being these protocols upscaled at a pilot-plant level for the development of thermoformed trays by injection moulding. Interestingly, the presence of the aforementioned additional components had a positive effect on their performance. Lastly, water-based extracts were successfully obtained from P. oceanica dead leaves by ultrasounds and hot-water extraction methodologies, providing a complete valorization of the residue with the aim of minimizing the use of organic solvents. In a second part, simplified cellulose extraction protocols were applied to other waste sources such as vine shoots, rice straw and rice husks. Both cellulosic fractions and nanocrystals were successfully purified regardless of the source, being the initial composition (holocellulose, lignin, ashes, lipids and proteins) and the monosaccharide profile the key factors which defined the final properties of the materials (evaluated in film form). In the last part of the thesis, these cellulosic nanocrystals were used for developing aerogels by freeze-drying. In order to overcome their inherent poor mechanical performance and low water resistance, a novel and patented dipping method using polylactic acid (PLA) was designed. These biopolymeric aerogels were broadly characterized by means of several techniques such as Raman and Confocal microscopies. Finally, bioactive aerogels were developed by incorporating some of the most promising P. oceanica bioactive extracts (previously obtained and characterized). Then, the following Ph. D. thesis shows the valorization of several waste biomasses by applying simplified protocols for developing food packaging structures. The presence of additional compounds in the resulting materials has been shown not only to reduce associated costs by increasing the total mass yield but also to present improved performance in comparison to more conventional materials, being in line with current circular economy policies. As a result, a more sustainable and viable alternative for the massively used conventional plastics is proposed. / Benito González, I. (2021). Waste Biomass Valorization for the Production of Cellulosic Fractions of Interest in Food Packaging Applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/177358 / Compendio

Decentralized electrochemical production of hydrogen peroxide (H₂O₂) is an attractive alternative to the industrial anthraquinone process, the application of which is hindered by the lack of high-performance electrocatalysts in acidic media. Herein, a novel catalyst design strategy is reported to optimize the Pd sites in pure metallic aerogels by tuning their geometric environments and electronic structures. By increasing the Hg content in the Pd–Hg aerogels, the Pd–Pd coordination is gradually diminished, resulting in isolated, single-atom-like Pd motifs in the Pd₂Hg₅ aerogel. Further heterometal doping leads to a series of M–Pd₂Hg₅ aerogels with an unalterable geometric environment, allowing for sole investigation of the electronic effects. Combining theoretical and experimental analyses, a volcano relationship is obtained for the M–Pd₂Hg₅ aerogels, demonstrating an effective tunability of the electronic structure of the Pd active sites. The optimized Au–Pd₂Hg₅ aerogel exhibits an outstanding H₂O₂ selectivity of 92.8% as well as transferred electron numbers of ≈2.1 in the potential range of 0.0–0.4 V/RHE. This work opens a door for designing metallic aerogel electrocatalysts for H₂O₂ production and highlights the importance of electronic effects in tuning electrocatalytic performances.

The work presented in the thesis is focused on the synthesis of diverse colloidal semiconductor NCs in organic media, their surface design with tiny inorganic and hybrid capping species in solution phase, and subsequent assembling of these NC building units into two-dimensional close-packed thin-films and three-dimensional non-ordered porous superstructures.

The work presented in the thesis is focused on the synthesis of diverse colloidal semiconductor NCs in organic media, their surface design with tiny inorganic and hybrid capping species in solution phase, and subsequent assembling of these NC building units into two-dimensional close-packed thin-films and three-dimensional non-ordered porous superstructures.

Estudos sistemáticos utilizando a técnica de SAXS foram realizados no síncrotom do LURE (Orsay) com feixe intenso de geometria pontua:, para descrever a cinética e as estruturas obtidas durante as etapas de transformação sol -> gel úmido -> gel seco -> vidros de sílica . As análises foram feitas em termos de uma lei de potência I = q-? cujo expoente está relacionado a dimensão fractal de massa ou de superfície das estruturas. Devido a polidispersividade das unidades espalhadoras as dimensões fractais verificadas podem ser resultados de dimensões reais encobertas por uma distribuição de tamanhos. As curvas obtidas para a cinética de gelificação e envelhecimento dos géis úmidos mostram expoentes que indicam fractalidade de massa e, posteriormente, de superfície. Uma microestrutura composta, que pode resultar de uma agregação limitada por difusão (DLA) seguido de agregação de agregados (C-C) foi observado nas soluções básicas. Por outro lado, os agregados ácidos parecem surgir do crescimento contínuo de cadeias até atingir a interligação com outros agregados com uma cinética que pode ser descrita pelo modelo DLA. No estado de aerogeis outras técnicas como picnometria de mercúrio e hélio, microscopia eletrônica de transmissão e adsorção de gás de nitrogênio, foram também aproveitadas. Nestes materiais encontramos em uma faixa estreita de escala, um expoente indicando fractalidade de massa, embora com superfície lisa. Os resultados estão de acordo com um modelo de estrutura que tem uma matriz de SiO2 densa. A estrutura fractal desaparece durante o tratamento térmico de densificação devido ao rearranjo estrutural. / Systematic SAXS studies have been performed at the LURE synchrotron (Orsay) using an intense beam of point-like cross-section to describe the kinetic and the structure obtained during the sol-> humid gel -> dry gel ->silica glass. The analysis were done in terms of a power law, I = q-? , whose exponent is related to mass and surface fractal dimensions of the structures. Due to polidispersity of the scattering units the found fractal dimensions can be \"smeared\" dimensions that result from a size distribution. All the kinetic and aging humids curves showed evidenced of fractal structures. A composed microstructure that can be originated by clustering of clusters (C-C) of primary units grown by diffusion limited-aggregation (DLA), was observed for basic gels. By other hand, the acidic cluster seems to grow continuously reaching gelation through crosslinking of the clusters. The DLA model seems to describe this process. In the aerogels study others techniques like density measurements using Hg and He, TEM and adsorption of N2 gas were done along with SAXS measurements. Here we could find a narrow range in which the system is a mass fractal, although its surface has been already smoothened. The results agree with a dense SiO2 matrix model. During the densification no fractal structure was verified due to structural rearrangements at high temperature.

La cellulose étant l'un des biopolymères les plus abondants, elle est employée dans ce travail de thèse sous sa forme nano-fibrille (2 à 5nm de diamètre et plusieurs microns de long) pour préparer des nanomatériaux durables. Les microfibrilles de cellulose (MFC) chargées positivement ou négativement sont assemblées en couches minces dans ces nanomatériaux par la méthode « Layer by Layer » (LbL) par trempage, pulvérisation ou spin assisté. Les différences entre ces films LbL à base de MFC et les films LbL à base de polymères standards sont discutées brièvement et sont reliées à la forme nanofibrillaire de la cellulose. Les MFC réagissent comme des nano-objets anisotropes et rigides. Les films LbL de MFC sont ensuite intégrés à des membranes de séparation, entre la couche polymérique de séparation et le support poreux, pour améliorer le débit à travers ces membranes. Ces films minces sont également déposés sur des aérogels de cellulose pour améliorer la stabilité de ces aérogels en milieu aqueux. Dans les deux applications, les résultats était encouragent et montre une validation de principe. / Cellulose, one of the most abundant biopolymers, is used in this PhD work in its nanofibrillated form, 2-5 nm in diameter and microns long, to prepare sustainable nanomaterials. Both positively and negatively charged microfibrillated celluloses (MFC) are assembled in these nanomaterials using the versatile Layer by Layer (LbL) assembly methods: dipping, spray assisted-deposition and spin-assisted deposition. A brief comparison between the MFC based LbL assembled films and the standard polymeric LbL films is carried out. Thedifferences between the two species are related to the fibrillar form of cellulose. MFC behaves like rigid anisotropic nano-objects. MFC LbL assembled films are then integrated in separation membranes between active polymeric separation layers and a mechanically stable porous support to improve the flux through these membranes. MFC LbL assembled films are also coated on cellulosic aerogels to improve the wet stability of these aerogels. In both cases, results were encouraging and showed a proof of concept.

Estudos sistemáticos utilizando a técnica de SAXS foram realizados no síncrotom do LURE (Orsay) com feixe intenso de geometria pontua:, para descrever a cinética e as estruturas obtidas durante as etapas de transformação sol -> gel úmido -> gel seco -> vidros de sílica . As análises foram feitas em termos de uma lei de potência I = q-? cujo expoente está relacionado a dimensão fractal de massa ou de superfície das estruturas. Devido a polidispersividade das unidades espalhadoras as dimensões fractais verificadas podem ser resultados de dimensões reais encobertas por uma distribuição de tamanhos. As curvas obtidas para a cinética de gelificação e envelhecimento dos géis úmidos mostram expoentes que indicam fractalidade de massa e, posteriormente, de superfície. Uma microestrutura composta, que pode resultar de uma agregação limitada por difusão (DLA) seguido de agregação de agregados (C-C) foi observado nas soluções básicas. Por outro lado, os agregados ácidos parecem surgir do crescimento contínuo de cadeias até atingir a interligação com outros agregados com uma cinética que pode ser descrita pelo modelo DLA. No estado de aerogeis outras técnicas como picnometria de mercúrio e hélio, microscopia eletrônica de transmissão e adsorção de gás de nitrogênio, foram também aproveitadas. Nestes materiais encontramos em uma faixa estreita de escala, um expoente indicando fractalidade de massa, embora com superfície lisa. Os resultados estão de acordo com um modelo de estrutura que tem uma matriz de SiO2 densa. A estrutura fractal desaparece durante o tratamento térmico de densificação devido ao rearranjo estrutural. / Systematic SAXS studies have been performed at the LURE synchrotron (Orsay) using an intense beam of point-like cross-section to describe the kinetic and the structure obtained during the sol-> humid gel -> dry gel ->silica glass. The analysis were done in terms of a power law, I = q-? , whose exponent is related to mass and surface fractal dimensions of the structures. Due to polidispersity of the scattering units the found fractal dimensions can be \"smeared\" dimensions that result from a size distribution. All the kinetic and aging humids curves showed evidenced of fractal structures. A composed microstructure that can be originated by clustering of clusters (C-C) of primary units grown by diffusion limited-aggregation (DLA), was observed for basic gels. By other hand, the acidic cluster seems to grow continuously reaching gelation through crosslinking of the clusters. The DLA model seems to describe this process. In the aerogels study others techniques like density measurements using Hg and He, TEM and adsorption of N2 gas were done along with SAXS measurements. Here we could find a narrow range in which the system is a mass fractal, although its surface has been already smoothened. The results agree with a dense SiO2 matrix model. During the densification no fractal structure was verified due to structural rearrangements at high temperature.

Cette thèse décrit le développement de procédés utilisables pour valoriser des extraits de bois afin de préparer : (1) des combustibles (hydrocarbures) liquides ; (2) des matériaux poreux avec des applications potentielles dans les domaines de l’énergie et l’environnement, notamment isolation thermique, catalyse, piégeage et séparation de micropolluants. Les extraits de bois en question sont des lignines, associées ou non à des tannins. Les deux types de matériaux sont actuellement peu valorisés, et l’on montre qu’ils peuvent être source de valeur ajoutée au travers des procédés rapportés dans ce mémoire / The present thesis describes the development of processes which can be used for valorizing wood extracts in the aim of preparing: (1) liquid (hydrocarbon) fuels; (2) porous materials with potential energy and environmental applications, namely thermal insulation, catalysis, abatement or separation of micropollutants. The wood extracts in question are lignins, associated or not with tannins. Both kinds of materials are presently poorly valorized, and it is shown here that they can lead to high added-value products through the processes reported in this PhD dissertation