Littérature scientifique sur le sujet « Carbon microfibrils »

Cellulose is the most abundant naturally occurring polymer and has diverse applications in biology, energy and engineering. The cellulose nanostructure has implications on the mechanical strength of natural materials such as wood and nanocelluloses are also being used to create high-performance composite materials with properties comparable to aramid fibres and carbon nanotubes. The efficiency of breakdown of cellulose into ethanoic alcohols for biofuels is also strongly linked to the aggregation of cellulose fibres into microfibrils. Despite this, the nanostructure of cellulose microfibrils is not well understood. Neutron scattering is a powerful way to distinguish order and disorder in biological fibres, wherever the disordered regions are accessible to deuterium exchange. The aggregation of microfibrils in plant cell walls, coupled to the benefits of deuterium exchange and increased scattering contrast using neutrons gives rise to a small-angle Bragg reflection allowing the size of microfibrils to be deduced. Applying these measurements with a range of spectroscopic techniques and wide-angle X-ray and neutron scattering (WAXS, WANS) has enabled us to develop a model for the structure for the microfibrils of cellulose microfibrils in a range of plant species. The scattering data were consistent with 3nm fibrils with both hydrophobic and hydrophilic surfaces exposed. Disorder in chain packing and hydrogen bonding were shown to increase outwards from the microfibril centre. Axial disorder could be explained in terms of twisting of the microfibrils, with implications for their biosynthesis. The disorder aspects of these microfibrils are directly related to the mechanical strength of wood and the natural variation in microfibril angle reflects this. We will present the outcome of in-situ stretching measurements of cellulose microfibrils with insights into the mechanism of the absorption of strain to further probe this mechanical strength.

Annually, plants produce about 180 billion tons of cellulose making it the largest reservoir of organic carbon on Earth. Cellulose is a linear homopolymer of beta(1-4)-linked glucose residues. The coordinated synthesis of glucose chains is orchestrated by specific plasma membrane-bound cellulose synthase complexes (CelS). The CelS is postulated to be composed of approximately 36 cellulose synthase (CESA) subunits. The CelS synthesizes 36 glucose chains in close proximity before they are further organized into microfibrils that are further associated with other cell wall polymers. The 36 glucose chains in a microfibril are stabilized by intra- and inter-hydrogen bonding which confer great stability on microfibrils. Several elementary microfibrils come together to form macrofibrils. Many CESA isoforms appear to be involved in the cellulose biosynthetic process and at least three types of CESA isoforms appear to be necessary for the functional organization of CelS in higher plants.

The concept of microfibrillar composite (MFC) has been used to create a new type of polymer composites, in which the reinforcing microfibrils are loaded with carbon nanotubes (CNT). Polyamide 66 (PA66) has been melt blended with polypropylene in a twin screw extruder with and without CNT, and thereafter cold drawn to create a fibrillar state as well as to align the CNT in the PA66 microfibrils. The drawn bristles were compression moulded at 180°C to prepare MFC plates. The scanning electron microscope (SEM) observations indicate near perfect distribution of CNT in the reinforcing PA66 microfibrils. Although the fibrillated PA66 is able to improve the tensile stiffness and strength as expected from the MFC structure, the incorporation of CNT does not exhibit any further enhancing effect. It rather adversely affects the mechanical properties due to poor interface adhesion between the matrix and the reinforcing microfibrils with the presence of CNT, as demonstrated by SEM. However, the resulting highly aligned CNT within the MFC are expected to affect the physical and functional properties of these composites.

In this work, carbon black (CB)/polyamide 6 (PA6)/polypropylene (PP) microfibrillar composites (MFCs) were fabricated through an extrusion (hot stretching) heat treatment process. The CB-coated conductive PA6 microfibrils with high aspect ratio were in situ generated as a result of the selective accumulation of CB at the interface. At the proper temperature, a 3D entangled conductive structure was constructed in the PP matrix, due to topological entanglement between these conductive microfibrils. This unique conductive structure provided the PP composites with a low electrical conductivity percolation threshold. Moreover, the electromechanical properties of conductive MFCs were investigated for the first time. A great stability, a high sensitivity and a nice reproducibility were achieved simultaneously for CB/PA6/PP MFCs. This work provides a universal and low-cost method for the conductive polymer composites’ (CPCs) fabrication as sensing materials.

AbstractWe have used field emission scanning electron microscopy (FESEM) to study the high-resolution organization of cellulose microfibrils in onion epidermal cell walls. We frequently found that conventional “rule of thumb” conditions for imaging of biological samples did not yield high-resolution images of cellulose organization and often resulted in artifacts or distortions of cell wall structure. Here we detail our method of one-step fixation and dehydration with 100% ethanol, followed by critical point drying, ultrathin iridium (Ir) sputter coating (3 s), and FESEM imaging at a moderate accelerating voltage (10 kV) with an In-lens detector. We compare results obtained with our improved protocol with images obtained with samples processed by conventional aldehyde fixation, graded dehydration, sputter coating with Au, Au/Pd, or carbon, and low-voltage FESEM imaging. The results demonstrated that our protocol is simpler, causes little artifact, and is more suitable for high-resolution imaging of cell wall cellulose microfibrils whereas such imaging is very challenging by conventional methods.

Aramid fibers with low density and high strength, modulus, and thermal resistance are widely used in applications such as bulletproof vests and cables. However, owing to their chemical structure, they are sensitive to ultraviolet light, which degrades the fibers’ useful mechanical properties. In this study, titanium dioxide (TiO2) nanoparticles were synthesized both on the aramid III fiber surface and in the interfacial space between the fibrils/microfibrils in supercritical carbon dioxide (scCO2) to improve the UV resistance of aramid fibers. The effects of scCO2 treatment pressure on the TiO2 structure, morphology, surface composition, thermal stability, photostability, and mechanical properties were investigated using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, ultraviolet–visible spectroscopy, and single-fiber test. The results show that amorphous TiO2 formed on the fiber surface and the interface between fibrils/microfibrils, and decreased the photodegradation rate of the aramid III fiber. Moreover, this modification can also improve the tensile strength via treatment at low temperature and without the use of a solvent. The simple synthesis process in scCO2, which is scalable, is used for mild modifications with a green solvent, providing a promising technique for synthesizing metal dioxide on polymers.

To contrast enhance unidirectional (45° angle) 15-18Å thick Pt/C coated cellulose specimens backed with 100-173Å thick carbon films, micrographs were contrast reversed on Kodak 7302 fine grain positive film. In addition to increasing the contrast of 10-20Å features, the Pt/C coated surfaces are now white and the molecular details are modulated on this background in blacks and shades of grey for easy structural interpretation. By shooting a tilt series at 10° intervals at 105X on a JEM 100CX at 80KV with a 5mm focal length and a 40μ objective aperture, a 6.6Å resolution and a 2710Å depth of field are achieved in the picture series. The tilt series is generally visualized stereoscopically and then a single image representing the correct 3-D structure is shown.

The extensive experimental investigation aimed to assess the effects of hybrid epoxy resin with micro-fibrillated cellulose on tensile quasi-static and fatigue behaviour of open hole carbon plain weave composites. The hybridization of the matrix allowed an improved damage tolerance of the composite leading to increase of the quasi-static tensile strength and extension of the fatigue life. The enhanced mechanical performance of the notched composites was connected to the bridging effect of cellulose microfibrils preventing or delaying the cracks propagation in the matrix and along the fibres interface. The better distribution of the stress state was assessed by digital image correlation strain maps around the hole and the imparted fatigue damage was analysed by scanning electron microscope and X-ray micro-computed tomography visualizations.

Hydrophobic dipeptide crystals recently emerged as novel “organic zeolites” featuring tailorable pore size. In fact, seven out of nine pairwise combinations of L-isoleucine, L-valine and L-alanine amino acids crystallize according to the same charge-assisted hydrogen bond pattern, generating a family of microporous materials with right-handed 1D channels, having diameters in the sub-nanometer domain (<6Å), aliphatic environment and different degrees of helicity. The relationship between pore size and material properties was investigated with respect to gas separation, exploiting the affinity of carbon dioxide for the hydrophobic nanochannels of L-alanyl-L-valine (AV), L-isoleucyl-L-valine (IV) and L-valyl-L-isoleucine (VI). Reversible CO2 capture from an equimolar mixture of CO2 and methane, at room temperature and 1 atmosphere, was demonstrated with increasing purification performance with decrease in pore size. Dipeptide were also used as nanovessels in radical polymerizations with the aim of controlling otherwise non-specific reactions. Diene monomers (trans-1,3-pentadiene and isoprene) only yield linear 1,4-trans polymer in accordance with 1-dimensional pore geometry, while poly(acrylonitrile) (PAN) could be obtained as a stereoregular isotactic product by acrylonitrile polymerization in AV dipeptide. Finally, taking advantage of the dipeptide lability and unique thermal properties of poly(acrylonitrile), AV-PAN nanocomposites were used as a scaffold to obtain carbon replicas of the starting nanocomposite crystals (carbon micro-fibrils) showing anisotropic arrangement of the graphite domains.

Este trabalho trata do estudo da introdução de fibras poliméricas como agente porogênico na manufatura de membranas cerâmicas de alta resistência mecânica. Membranas cerâmicas são utilizadas para a separação de substâncias onde a estabilidade química e a resistência à alta temperatura são requeridas; na engenharia mecânica é também aplicada como mancais aerostáticos. A escolha do processo de manufatura destas membranas e o projeto da porosidade da estrutura cerâmica é de grande importância. Quando se utiliza da adição de elementos porogênicos, que são substâncias que se decompõem durante a queima deixando poros (abertos e fechados), altera não somente a porosidade como também a seletividade e permeabilidade da membrana, bem como diminui suas propriedades mecânicas. Este trabalho objetiva membranas com poros micrométricos e submicrométricos para aplicações em microfiltração ou em mancais aerostáticos, porém que tenham a maximização da sua resistência mecânica. Para isso foi idealizada a obtenção de membranas permeáveis com a menor porosidade possível. Então, propôs-se a adição de fibras poliméricas (fibras de polipropileno, fibras de carbono e fibras de álcool polivinílico) como agentes porogênicos em uma massa cerâmica de alumina que após granulada foi prensada na forma de pastilhas e sinterizadas. As membranas foram caracterizadas por ensaios de permeabilidade ao ar, resistência mecânica por flexão a 3 pontos, volume de poros pelo Princípio de Arquimedes e morfologicamente por MEV. A caracterização morfológica das membranas e os resultados de porosidade indicaram que a percolação foi melhorada pela adição de fibras em relação a trabalhos equivalentes que se utilizaram de particulados. As melhores condições de permeação, integridade da matriz e resistência mecânica foram encontradas para as membranas com 1 vol. % de fibras de álcool polivinílico, seguida das membranas com 2 vol. % de fibras de carbono. Com base nos resultados obtidos, foi comprovado que a morfologia alongada das fibras aumenta a probabilidade de contato entre os poros, pois com apenas 2 vol. % de fibras de PVAl, obteve-se uma porosidade total de 33,3%, porosidade aparente de 17,4% e permeabilidade específica de 6,32x10-12 m², apresentando resistência à flexão de 134,3 MPa, valor este o dobro de quando utilizado 50 vol. % de sacarose como agente precursor com equivalente permeabilidade. As propriedades físicas do agente porogênico como: expansão térmica, dimensões, relação comprimento versus diâmetro afetam enormemente a porosidade, percolação dos poros e integridade da matriz.<br>This work deals with the study of the introduction of polymeric fibers as porogenic agent in the manufacture of ceramic membranes with high mechanical strength. Ceramic membranes are used for separation of substances where chemical stability and high temperature resistance are required, in mechanical engineering is also applied as an aerostatic bearings. The choice of these membranes manufacturing process and design the porosity of the ceramic structure is of great importance. When using addition of porogenic components, which are substances that decompose during the burning leaving pores (open and closed), not only alters the porosity and also the permeability and the selectivity of the membrane, as well as decreases their mechanical properties. This work aims membranes with micrometric pores and submicrometrics for microfiltration applications or aerostatic bearings, however they having the maximization their mechanic strength. To this was designed to obtain porous membranes with the lowest porosity possible. Then proposed the addition of polymeric fibers (polypropylene fiber, carbon fiber and polyvinyl alcohol fiber) as porogenic agents on a ceramic alumina mass that was granular and pressed the form of discs and sintered. The membranes were characterized by testing the air permeability, mechanical strength by three points flexural, pore volume by Archimedes principle and morphologically by SEM. Morphological characterization of membrane and the results of porosity indicated that the percolation has been improved by adding fibers in relation to the corresponding work where particulates were used. The best conditions of permeation, matrix integrity and mechanical strength were found for the membranes with 2 vol. % of polyvinyl alcohol fibers and membranes with 2 vol. % carbon fibers. Based on these results, it was proven that the elongated morphology of the fibers increases the probability of contact between the pores, because with only 2 vol. % of PVAl fibers, we obtained a total porosity of 33.3%, apparent porosity of 17.4% and the specific permeability of 6.32x10-12 m², flexural strength of 134.3 MPa, this value is twice than when it is used 50 vol. % sucrose as a precursor agent with equivalent permeability. The physical properties of porogenic agent such as thermal expansion, dimensions and relation length versus diameter affect greatly the porosity, pore percolation and integrity of the matrix.

Orientador: Edson Cocchieri Botelho<br>Resumo: Esta pesquisa visa o processamento de compósitos termorrígidos laminados multifuncionais, via moldagem por compressão a quente, constituídos por fibras de carbono, resina epóxi e mantas de poli(butadieno) (BR) produzidas via processo de eletrofiação. Estas mantas têm como função proporcionar maior tenacidade ao compósito obtido, aumentando sua tolerância ao dano e consequentemente, elevando sua aplicabilidade no setor aeroespacial. Para o desenvolvimento deste trabalho de pesquisa, primeiramente, foram produzidas mantas de poli(butadieno) por eletrofiação. Todas as condições de processamento foram avaliadas nesta etapa do projeto. Posteriormente, estas mantas foram utilizadas para a obtenção de diferentes compósitos com resina epóxi e fibra de carbono, utilizando-se oito distintas configurações, processados via moldagem por compressão a quente. A qualidade dos compósitos fabricados foi avaliada a partir de ensaios de digestão ácida, microscopia, análise dinâmico mecânica (DMA) e inspeção acústica por ultrassom. Com o intuito de se avaliar eventuais ganhos na tenacidade à fratura dos laminados, foram realizados ensaios de excitação por impulso e resistência ao impacto, o qual foi seguido pela técnica de ultrassom. Também foram realizados ensaios de End-Notched Flexure (ENF) pelo modo II de fratura (modo de deslizamento) e ensaios de cisalhamento interlaminar (ILSS) e após os respectivos ensaios, os compósitos também foram avaliados por microscopia. A partir da técnica de eletr... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: This research aims the processing of multifunctional laminated thermosetting composites by hot compression molding, consisting of carbon fibers, epoxy resin and polybutadiene (BR) mats produced by electrospinning. These mats can provide greater toughness to the composite obtained, increasing its damage tolerance and consequently increasing its applicability in the aerospace field. For the development of this research, polybutadiene mats were produced by the electrospinning process. All processing conditions were evaluated at this stage of the project. Subsequently, these mats were used to obtain different epoxy resin/ carbon fiber composites with 8 distinct configurations, processed by hot compression molding process. The quality of the manufactured composites was evaluated using acid digestion tests, microscopy, dynamic mechanical analysis (DMA) and acustic inspection by ultrasound. After processing, in order to evaluate possible gains in fracture toughness, these laminates were submitted impulse excitation tests, impact resistance, and after tests the specimens were analyzed by ultrasound. Also, End-Notched Flexure (ENF) testes were performed using mode II fracture (sliding mode) and interlaminar shear tests (ILSS) and after the respective tests, the composites were also evaluated by microscopy. Using the electrospinning technique, it was possible to manufacture polybutadiene microfibers successfully, and use them to process laminated composites consisting of carbon fibers ... (Complete abstract click electronic access below)<br>Doutor

Submitted by Marilene Donadel (marilene.donadel@unioeste.br) on 2017-09-29T01:08:32Z No. of bitstreams: 1 Andressa_G_Rosenberger_2017.pdf: 2187152 bytes, checksum: eeb5c275b57d9c489c86178a66925400 (MD5)<br>Made available in DSpace on 2017-09-29T01:08:32Z (GMT). No. of bitstreams: 1 Andressa_G_Rosenberger_2017.pdf: 2187152 bytes, checksum: eeb5c275b57d9c489c86178a66925400 (MD5) Previous issue date: 2017-03-01<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES<br>Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Estado do Paraná (FA)<br>Water is a vital element in human health and a determining factor in the pace of human evolution; however, the presence of emerging pollutants threatens its quality and may endangers the well-being of people and the environment. This work stands out for the development of a composite material based on nanotechnology to be used as an electroanalitic sensor in aqueous solutions with the Metronidazole drug which is considered an emerging pollutant. Initially the polymeric fibers were produced based on ecovio® and carbon nanotubes multilayer (MWCNT’s). In order to evaluate the parameters that could interfere in the process of electrospinning and to understand the interaction between the polymer and the MWCNT’s, a fractional factorial design and physicochemical characterizations analysis were used, which were: optical micrography scanning electron microcopy (SEM), mechanical analysis, wettability by contact angle, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential thermal analysis (DSC) and X-ray diffraction. For the porpuse of fabricating the sensor, the fibers were calcinated and the obtained residue was characterized by SEM and FTIR. The statistical data and the images of optical microscopy and SEM showed that the addition of MWCNT’s is the parameter that most influences the diameter of the obtained microfibers (1.16 ± 0.22 µm) so that their presence decreases the diameter and results in fibers more uniform and homogeneous. After selecting the ideal conditions an experiment was done with the following process and solution parameters: concentration of ecovio® 15,00% (m/v) and MWCNT’s 0,60% (m/v); flow: 1.80 mL.h-1; distance: 16 cm and applied voltage: 18 kV. The morphology and diamater os the fibers was obtained using SEM images and showed an average diameter of 1.59±0.61 µm. It was also demonstrated a better mechanical performance after the addition of MWCNT’s to the fibers, so that they presented greter elasticity (180%) and significant increase on the elastic resistance (163%) and tensile strength (107%), besides the analysis of wettability from the contact angle suggest that the carbon-based nanomaterial is inside the polymeric microfibers. The interactions between the MWCNT’s and the polymer were better evaluated by vibracional aspects by Fourier transform infrared spectroscopy (FTIR) and showed the interaction between the MWCNT’s and the functional group C=O characteristic of the group ester of the polymers. The analysis of thermogravimetry (TGA) demonstrated a higher stability. The thermogravimetric analysis (TGA) showed a higher stability of the poly (lactic acid) component and lower resistances of the poly (butylene adipate co-terephtalate) component in the polymer blend. Besides it was necessary a constant temperature of 550 ºC during 50 minutes to the total degradation of the polymer. By differential thermal analysis (DSC) it was possible to confirm the interactions proposed by FTIR and TGA, which indicate that the interaction occurs preferentially with the aliphatic chains of the ecovio® polymer. After the calcination of the fibers, the obtained residue was characterized by FTIR and MEV and variations in the characteristics of pure MWCNT's can be observed, with reduction of the corboxylic groups for the calcined and electrospun/calcined MWCNT's, as well as the formation of lamella for the MWCNT's electrospun/calcined. The electrochemical measurements using the cyclic voltammetry technique showed that the sensor is promising for determination of Metronidazole.<br>A água é um elemento vital e determinante no ritmo da evolução humana, contudo a presença de poluentes emergentes ameaça sua qualidade e põe em risco o bem estar humano e ambiental. O presente trabalho destaca-se por desenvolver um material compósito formado por poli (butileno adipato co-tereftalato) (PBAT) e poli (ácido lático) (PLA) para ser utilizado como sensor eletroanalítico em soluções aquosas contendo o fármaco metronidazol. Inicialmente produziu-se fios poliméricos a base de ecovio® e nanotubos de carbono de paredes múltiplas (MWCNT’s). A fim de avaliar os fatores interferentes do processo e compreender a interação entre o polímero e os MWCNT’s utilizou-se um planejamento fatorial fracionário e análises de caracterização físico-química tais como: micrografia ótica, microscopia eletronica de varredura (MEV), análise mecanica, molhabilidade por angulo de contato, espectroscopia vibracional de infravermelho por transformada de Fourrier, análise termogravimétrica (TGA), calorimetria exploratória diferencial (DSC) e difratometria de raio X (DRX).Para a construção do sensor eletroquímico as fibras foram calcinadas e o resíduo obtido foi caracterizado pelas ténicas de MEV e FTIR. Os resultados estatísticos em conjunto com as imagens de microscopia ótica e MEV demonstram que a adição de MWCNT’s é o parâmetro que mais influência no diâmetro das microfibras (1,16 ± 0,22 µm) obtidas, de modo, que sua inserção diminui este parâmetro deixando as fibras mais uniformes e homogêneas. Após a escolha das condições ideais procedeu-se um experimento com os seguintes parâmetros da solução e do processo de eletrofiação: ecovio® 15,00% (m/v) e MWCNT’s 0,60% (m/v); fluxo: 1,80 mL.h-1; distância: 16 cm e tensão: 18 kV. A morfolagia e o diâmetro das fibras foram realizadas usando as imagens de MEV e apresentam diâmetro médio de 1,59±0,61 µm. Foi evidenciado também um melhor desempenho mecanico após a inserção de MWCNT’s às fibras de modo que as fibras apresentam maior elasticidade (180%) e um aumento significativo da resistência elástica (163%) e tensão de ruptura (107%). Ademais a análise de molhabilidade por ângulo de contato sugere que o nanomaterial a base de carbono encontra-se no interior das microfibras poliméricas. As interações entre o MWCNT’s e os polímeros foram melhor avaliadas pelos espectros vibracionais de infravermelho por transformada de Fourrier (FTIR) e evidenciam a interação entre MWCNT’s e o grupamento funcional C=O, característicos dos grupamentos ésteres dos polímeros. As análises de termogravimetria (TGA) demonstram uma maior estabilidade do componente poli (ácido lático) e uma menor estabilidade do poli (butileno adipato co-tereftalato) na blenda polimérica, além disso, foi necessário uma temperatura constante de 550 ºC durante 50 minutos para degradar totalmente o polímero.Pela análise térmica diferencial (DSC) foi possível confirmar as interações propostas pelo FTIR e TGA, que indicam que a interação ocorre preferencialmente com as cadeias alifáticas do polímero ecovio®. Após a calcinação das fibras, para o preparo do sensor, o resíduo obtido foi caracterizado por FTIR e MEV e pode-se observar mudanças na caracteristica dos MWCNT’s puros com diminuição dos grupos carboxilicos para os MWCNT’s tratados termicamente e eletrofiados/calcinados, além da formação de lamelas para o MWCNT’s eletrofiados/calcinados. As medidas eletroquímicas usando a tecnica de voltametria cíclica, mostram que o sensor é promissor para determinação de metronidazol.

[ES] Esta memoria de tesis presenta una contribución al estudio de los materiales textiles en el campo de la absorción sonora. En concreto, se ha trabajado con la asociación de una capa absorbente fibrosa constituida por una estructura laminar no tejida cuya composición es poliéster y una capa resistiva a base de tejido de calada también compuesta de poliéster. El objetivo de este trabajo consiste en evaluar las variaciones que provocan los cambios en distintos parámetros de construcción de la capa resistiva, sobre el comportamiento del conjunto ante el sonido. Para abordar el problema se emplean distintos tejidos de calada, tales como telas simples, múltiples, acolchadas y rizo, con diferentes parámetros de construcción. Se mide el coeficiente de absorción de sonido al aplicarlas a diferentes espesores de estructura no tejida de poliéster, empleando el tubo de ondas estacionarias. Tras analizar los resultados obtenidos, se observan diferencias en los coeficientes de absorción de sonido alcanzados, las cuales se explican atendiendo al espesor del no tejido, pero también se observa la influencia de las características constructivas de los tejidos empleados. Finalmente, se emplea el diseño de experimentos para obtener la combinación óptima de parámetros que proporciona el mayor coeficiente de absorción de sonido para un tipo de tejido dado en todas las frecuencias estudiadas. Se concluye que, la modificación en la absorción de sonido de una estructura no tejida al aplicar una capa resistiva de tejido de calada, es lo suficientemente significativa como para ser tenida en cuenta a la hora de diseñar productos textiles para acondicionamiento acústico y que el diseño de experimentos constituye una herramienta de gran utilidad a este fin.<br>[CAT] Aquesta memòria de tesi presenta una contribució a l'estudi dels materials tèxtils en el camp de l'absorció sonora. En concret, s'hi ha treballat amb l'associació d'una capa absorbent fibrosa constituïda per un no teixit de polièster i una capa resistiva a base de teixit de calada de composició polièster. L'objectiu d'aquest treball consisteix a avaluar les variacions que provoquen els canvis en diferents paràmetres de construcció de la capa resistiva, sobre el comportament del conjunt davant el so. Per a abordar el problema s'empren diferents teixits de calada, com ara teles simples, múltiples, encoixinats i ris, amb diferents paràmetres de construcció. Es mesura el coeficient d'absorció en aplicarles a diferents grossàries de no teixit de polièster, emprant el tub d'ones estacionàries. S'observen diferències en els coeficients d'absorció de so obtinguts, les quals s'expliquen atenent la grossària del no teixit, però també a les característiques constructives dels teixits emprats. Finalment, s'empra el disseny d'experiments per a obtenir la combinació òptima de paràmetres que proporciona el major coeficient d'absorció de so per a un tipus de teixit donat en totes les freqüències estudiades. Es conclou que la modificació en l'absorció de so d'un no teixit en aplicar una capa resistiva de teixit de calada és prou significativa per a ser tinguda en compte a l'hora de dissenyar productes tèxtils per a condicionament acústic i que el disseny d'experiments constitueix una eina de gran utilitat a aquest efecte.<br>[EN] This thesis report presents a contribution to the study of textile materials in the field of sound absorption. Specifically, we have worked with the association of a fibrous absorbent layer consisting of a polyester nonwoven and a resistive layer based on openwork fabric. The objective of this work is to evaluate the variations that cause the changes in different construction parameters of the resistive layer, on the behaviour of the whole before the sound. To address the problem, different openwork fabrics are used, such as single, multiple, quilted and curl fabrics, with different construction parameters. The absorption coefficient is measured when applied to different thicknesses of polyester nonwoven, using the standing wave tube. Differences are observed in the sound absorption coefficients obtained, which are explained according to the thickness of the nonwoven, but also to the constructive characteristics of the fabrics used. Finally, the design of experiments is used to obtain the optimal combination of parameters that provides the highest sound absorption coefficient for a given type of tissue at all frequencies studied. It is concluded that the modification in the sound absorption of a nonwoven when applying a resistive layer of openwork fabric is significant enough to be taken into account when designing textual products for acoustic conditioning and that the design of experiments constitutes a very useful tool for this purpose.<br>Al departamento de Ingeniería Textil y Papelera y a la unidad docente de Alcoy del departamento de Mecánica de los Medios Continuos y Teoría de Estructuras, por facilitarme los medios necesarios para realizar todas las actividades que han sido necesarias. A Jaime Ramis Soriano, por recibirme en el laboratorio de Grupo de Acústica Aplicada del IUFACyT de la Universidad de Alicante.<br>Segura Alcaraz, MDP. (2020). Empleo de textiles en aplicaciones de absorción sonora [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/159786<br>TESIS

The effect of the addition of cellulose microfibrils, water soluble polymer, nanoclays and carbon nanotubes to the cement paste was studied. The hydration kinetic was determined by means of an adiabatic rise temperature method. The addition of polymer to the cement paste produced the highest delay in the hydration kinetic followed by the addition of organically modified montmorillonites in a polymer solution. Flexion and compression strength were determined. Some admixtures produced an increase of the cement paste’s void content. Cellulose produced a change in the rheology and a delay in the hydration kinetic of the cement paste. The use of heat for curing increased the mortar’s mechanical properties. Carbon nanotubes also were added to the cement paste in order to study the effect on electric conductivity and hydration kinetic.

Cartilage defects, which are caused by a variety of reasons such as traumatic injuries, osteoarthritis, or osteoporosis, represent common and severe clinical problems. Each year, over 6 million people visit hospitals in the U.S. for various knee, wrist, and ankle problems. As modern medicine advances, new and novel methodologies have been explored and developed in order to solve and improve current medical problems. One of the areas of investigation that has thus far proven to be very promising is tissue engineering [1, 2]. Since cartilage matrix is nanocomposite, the goal of the current work is to use nanomaterials and nanofabrication methods to create novel biologically inspired tissue engineered cartilage scaffolds for facilitating human bone marrow mesenchymal stem cell (MSC) chondrogenesis. For this purpose, through electrospinning techniques, we designed a series of novel 3D biomimetic nanostructured scaffolds based on carbon nanotubes and biocompatible poly(L-lactic acid) (PLLA) polymers. Specifically, a series of electrospun fibrous PLLA scaffolds with controlled fiber dimension were fabricated in this study. In vitro hMSC studies showed that stem cells prefer to attach in the scaffolds with smaller fiber diameter. More importantly, our in vitro differentiation results demonstrated that incorporation of the biomimetic carbon nanotubes and poly L-lysine coating can induce more chondrogenic differentiations of MSCs than controls, which make them promising for cartilage tissue engineering applications.