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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

PRIVACY-PRESERVING ATTRIBUTE-BASED ACCESS CONTROL IN A GRID

Park, Sang Mork 27 October 2010 (has links)
No description available.
22

Le composite cuivre / nanofibres de carbone / The copper-carbon nanofibers composite

Vincent, Cécile 19 November 2008 (has links)
Le matériau composite Cu/NFC (Nano Fibre de Carbone) peut être utilisé en tant que drain thermique par les industriels de l'électronique de puissance. En remplacement du cuivre, il doit combiner une conductivité thermique élevée et un coefficient de dilatation thermique adapté à celui de la céramique du circuit imprimé (alumine ou nitrure d’aluminium). Après avoir étudié les propriétés de la matrice cuivre et des NFC, plusieurs méthodes de synthèse du composite Cu/NFC ont été développées. Le composite a tout d’abord été élaboré par métallurgie des poudres. Puis, dans le but d’améliorer l’homogénéité, il a été envisagé de revêtir individuellement chaque NFC par du cuivre déposé par voie chimique electroless ainsi que par une méthode originale de décomposition d’un sel métallique. Des mesures de densité et de propriétés thermiques (conductivité et dilatation) ainsi que les caractérisations microstructurales de ces matériaux montrent la complexité de l’élaboration d’un tel composite. En effet, la dispersion des nanofibres, la nature des interfaces fibres/matrice et surtout les phénomènes thermiques à l’échelle nanométrique sont autant de paramètres à contrôler afin d’obtenir les propriétés recherchées. La simulation numérique et analytique, qui a été mise en oeuvre en parallèle a été corrélée aux résultats expérimentaux, afin de prédire les propriétés finales de nos matériaux. / Cu/CNF (Carbon Nano Fiber) composite materials can be used as heat sink in power electronic devices. They can substitute Copper by combining a high thermal conductivity and a coefficient of thermal expansion close to the printed circuit one (alumina or aluminum nitride). After studying the properties of Copper matrix and CNF, three methods were set up for the elaboration of the Cu/CNF composite materials. It was first synthesized by a simple powder metallurgy process. Second, in order to obtain a better homogeneity, CNF were individually coated with Cu by an electroless deposition method. Third, an original technique involving the decomposition of a metallic salt has been used. Measurements of the density, the thermal properties (conductivity and dilatation), and the characterization of the microstructure of the composite materials have been performed. It reveals the complexity of the realization of such a composite. Indeed, the dispersion of CNF and the chemical nature of the Cu/CNF interfaces have to be controlled in order to reach the desired thermal properties. Analytical and numerical simulations have been conducted and correlated with the experimental results to predict final properties of our materials.
23

Carbon nanotube reinforced polyacrylonitrile and poly(etherketone) fibers

Jain, Rahul 23 March 2009 (has links)
The graphitic nature, continuous structure, and high mechanical properties of carbon nanotubes (CNTs) make them good candidate for reinforcing polymer fiber. The different types of CNTs including single-wall carbon nanotubes (SWNTs), few-wall carbon nanotubes (FWNTs), and multi-wall carbon nanotubes (MWNTs), and carbon nanofibers (CNFs) differ in terms of their diameter and number of graphitic walls. The desire has been to increase the concentration of CNTs as much as possible to make next generation multi-functional materials. The work in this thesis is mainly focused on MWNT and CNF reinforced polyacrylonitrile (PAN) composite fibers, and SWNT, FWNT, and MWNT reinforced poly(etherketone) (PEK) composite fibers. To the best of our knowledge, this is the first study to report the spinning of 20% MWNT or 30% CNF reinforced polymer fiber spun using conventional fiber spinning. Also, this is the first study to report the PEK/CNT composite fibers. The fibers were characterized for their thermal, tensile, mechanical, and dynamic mechanical properties. The fiber structure and morphology was studied using WAXD and SEM. The effect of two-stage heat drawing, sonication time for CNF dispersion, fiber drying temperature, and molecular weight of PAN was also studied. Other challenges associated with processing high concentrations of solutions for making composite fibers have been identified and reported. The effect of CNT diameter and concentration on fiber spinnability and electrical conductivity of composite fiber have also been studied. This work suggests that CNT diameter controls the maximum possible concentration of CNTs in a composite fiber. The results show that by properly choosing the type of CNT, length of CNTs, dispersion of CNTs, fiber spinning method, fiber draw ratio, and type of polymer, one can get electrically conducting fibers with wide range of conductivities for different applications. The PEK based control and composite fibers possess high thermal stability with almost no weight loss up to 500 degree C and negligible thermal shrinkage up to 200 degree C. The PEK based fibers showed high toughness which surpassed many of the high-performance fibers like Kevlar(R) and Zylon(R). The 10% FWNT containing fiber is unique in terms of high electrical conductivity and high toughness. The CNT based fibers may be used as structural material, fire-barrier/protection textile, electrode for electrochemical capacitor or fuel cells, and as a template for directional growth of tissues.
24

Translation-based approaches to Conformant Planning

Palacios Verdes, Héctor Luis 03 December 2009 (has links)
Conformant planning is the problem of finding a sequence of actions for achieving a goal in the presence of uncertainty in the initial state and state transitions. While few practical problems are purely conformant, the ability to find conformant plans is needed in planning with observations where conformant situations are an special case and where relaxations into conformant planning yield useful heuristics. In this dissertation, we introduce new formulations for tackling the conformant planning problem with deterministic actions using translations. On the one hand, we propose a translation in propositional logic and two schemes for obtaning conformant plans for it, one based on boolean operations of projection and model counting, the other based on projection and satisfiability. On the other hand, we introduce translations of the conformant planning problem into classical problems that are solved by a modern and effective classical planner. We analyze the formal properties of the translations into classical planning and evaluate the performance of the resulting conformant planners. / La planificación conformante es el problema de encontrar una secuencia de acciones para lograr un objetivo en presencia de información incompleta sobre el estado inicial y en las transiciones entre estados. Aunque pocos problemas son de carácter puramente conformante, la posibilidad de encontrar planes conformantes es necesaria en planificación con observaciones, donde las situaciones conformantes son un caso particular, y donde las relajaciones a planificación conformante dan heurísticas útiles. En esta tesis atacamos el problema de la planificación conformante con acciones determinísticas mediante dos formulaciones basadas en traducciones. Por un lado, proponemos una traducción a lógica proposicional y dos esquemas para obtener planes conformantes a partir de ésta, uno basado en operaciones booleanas de projección y conteo de modelos, y otro basado en projección y satisfacción proposicional. Por otro lado, introducimos traducciones que permiten transformar un problema de planificación conformante en un problema de planificación clásica que es luego resuelto usando planificadores clásicos. También analizamos las propiedades formales de las traducciones y evaluamos el rendimiento de los planificadores obtenidos.
25

Aplicação de nanoceluloses em fibras não branqueadas para obtenção de papéis. / Application of nanocelulose in unbleached fibers for papermaking.

Cruces Cerro, Jorge 18 August 2016 (has links)
Atualmente, o Brasil é o maior fabricante de celulose branqueada de eucalipto do mundo. Geralmente as fibras virgens de Eucalyptus spp. são utilizadas na fabricação de papéis para imprimir, tissue e especiais. Papéis para embalagens, tipicamente Kraftliners, precisam de uma grande resistência mecânica e são produzidos principalmente a partir de pastas Kraft de coníferas não branqueadas. Por outro lado, nanoceluloses fabricadas a partir de biomassa são consideradas um dos materiais sustentáveis mais interessantes para o século, com excelentes propriedades como baixa densidade, elevadas propriedades mecânicas, alta hidrofilicidade, grande área superficial com reatividade química e elevado valor econômico. Desde 2012 o uso de nanoceluloses na fabricação de papel ganhou impulso. As nanoceluloses têm sido adicionadas em pastas mecânicas e Kraft branqueadas para fabricação do papel, incrementando notavelmente as suas propriedades mecânicas, mas há preocupações sobre a diminuição da drenabilidade, da porosidade e da opacidade do papel. Poucos estudos foram desenvolvidos visando a aplicação de nanoceluloses em fibras não branqueadas, ainda que tenham aplicações em pastas branqueadas e/ou mecânicas. Portanto, o presente trabalho visa desenvolver o uso de nanoceluloses para melhorar as propriedades mecânicas em fibras não branqueadas. Em primeiro lugar, tomaram-se os finos primários do branqueamento de celulose de Pasta Kraft de Eucalipto como a matéria-prima para produzir dois tipos de nanocelulose. A celulose microfibrilada (MFC) é produzida diretamente por homogeneização mecânica utilizando equipamento Masuko. A celulose nanofibrilada (CNF) é produzida por oxidação mediada por TEMPO e homogeneizada por GEA. Em segundo lugar, selecionaram-se com as fibras virgens de Pasta Kraft Marrom de Pinho (PKPM) com número Kappa 36,1 e Pasta Kraft de Eucalipto Não Branqueada (PKEP), obtida na saída de estágio de deslignificação com oxigênio, com número Kappa 9,21, e todas as fibras foram refinadas até atingir o mesmo grau Shopper-Riegler (33±1 SR). Os experimentos com PKPM são conduzidas como uma referência a papéis Kraftliners tradicionais, com ou sem nanocelluloses. Também obteve folhas manuais com pasta branqueada Kraft de eucalipto, adicionando nanoceluloses, para compreender o efeito da lignina presente em PKEP. A receita e os aditivos químicos aplicados aqui são os mesmos que na produção industrial. Os principais resultados são: o uso de CNF (ou MFC) e agentes químicos, separadamente, na pasta PKEP, aumenta as resistências mecânicas dos papéis, no entanto, quando aplicadas CNF (ou MFC) em PKMP sem aditivos químicos, as resistências à tração e a estouro diminuem, e a resistência ao rasgo permanece constante. Como a terceira parte do estudo, delineamento de experimentos teve a configuração composto central com o ponto central em 1% de CNF (ou MFC) e 1% de agentes químicos (polímero+amido+cola), e seus pontos axiais foram 0,3%-1,7% de CNF (ou MFC), e 0,15%-0,85% de agentes químicos. O ponto ótimo de equilíbrio dos índices de rasgo (mN.m2/g) /estouro (kPa.m2/g) /tração (N.m/g) de (10,00/2,25/36,56 para CNF e 12,88/4,25/57,62 para MFC), obteve-se com a adição de 1,03% de CNF e 0,65% de amido, ou com a adição de menos de 0,01% de MFC e de 1% de amido. Finalmente, foram aplicadas CNF ou MFC por impregnação direta no centro da direção-z, considerando que o papel tem forças que interagem em 3D. Os resultados mostram que a PKEP atinge a qualidade do Kraftliner de pinus obtendo um índice de tração de 52,58 N.m/g utilizando 1% de CNF, ou 47,40 N.m/g utilizando 1% de MFC. Também, o custo de utilização do CNF ou MFC na fabricação do papel é avaliado, resultando em estimativas de 0,9494 US$/kg ou 0,3036 US$/kg, com a adição de 1% de CNF ou 1% de MFC, respectivamente, em pasta PKEP. Este trabalho mostra que a aplicação de nanocelulose em Kraftliner tradicional com fibras de pinus com todos os agentes químicos não tem vantagens reais. No entanto, o uso de CNF e MFC tecnicamente e economicamente tem vantagens superiores em pasta Kraft de eucalipto não branqueada (e deslignificada com oxigênio), obtendo-se propriedades superiores às de fibras longas. / Nowadays, Brazil is the largest manufacturer of Bleached Eucalyptus Kraft Pulp in the world. Mostly the Eucalyptus spp. virgin fibres are used in papermaking to manufacture printing, tissue and specialty papers. Packaging papers, typically Kraftliners, have high demands for mechanical strength and are made mostly from Unbleached Softwood Kraft Pulp. Other side, nanocelluloses from biomass are considered one of the most interesting sustainable materials for the Century, with excel properties such as low density, high mechanical properties, high hydrophilicity, large surface area with chemical reactivity and high economic value. Since 2012 the use of nanocellulose in papermaking experienced a great momentum. Nanocelluloses are added in bleached or mechanical pulp in papermaking to increase significantly the mechanical properties, but there are concerns about the decreasing of the drainability, the porosity and the opacity of the paper. A very few studies were developed on the application of nanocelluloses in an unbleached Kraft pulp, even there are its applications on bleached pulps and mechanical pulps. Therefore, the present work aims to develop the application of nanocelluloses to increase the mechanical properties of the unbleached fibers, specifically for Kraftliners, and show the way to replace the softwood fibers with the low-cost hardwood fibers. Firstly, the primary fines from bleaching area of Eucalyptus Kraft pulp, obtained from an industrial residue, was the raw material for nanocellulose production of two nanocelluloses. The microfibrillated celluloses (MFC) are produced with direct mechanical homogenization using Masuko. The nanofibrillated cellulose (NCF) is produced with oxidation mediated by TEMPO and homogenization using GEA. Secondly, as virgin fibers were selected the Unbleached Pine Kraft Pulp (USKP) with Kappa number 36.1 and the Unbleached Eucalyptus Kraft Pulp (UEKP) just after the oxygen delignification stage with the Kappa number 9.21. All the fibres (USKP and UEKP) was refining at the same Shopper-Riegler (33±1 SR). USKP experiments are conducted as reference to traditional Kraftliners, with or without nanocelluloses. Also the virgin bleached Eucalyptus Kraft pulp with nanocelluloses addition for the handsheet paper helps to understand the role of lignin in UEKP. The recipe and chemicals applied here are the same of the industrial production. The main results are: the use CNF (or MFC) and chemical agents, separately, in UEKP, promote the mechanical resistances, however when applied CNF (or MFC) in UPKP without chemicals, the tensile and burst properties decreased and tear remains constant. As the third group of the study, the design of the experiments was conducted in the star configuration with centre point as 1% CNF (or MFC) and 1.00% chemical agents (polymers+starch+chemical agents) and, the axial points were 0.3%-1.7% NCF (or MFC) and 0.15%-0.85 of chemical agents. The optimum point from the balanced tear (mN.m2/g) /burst (kPa.m2/g) /tensile (N.m/g) index point of view with 10.00/2.25/36.56 for (1.03% CNF and 0.65% starch) and 12.88/4.25/57.62 for (<0.001% MFC and 1% starch). Finally, it is applied here the direct impregnation of the center of z-direction with 1% of CNF and MFC, considering that the paper has 3D interacting forces. The results show that the UEKP reaches the pinus Kraftliner quality with 52.58 N.m/g (Tensile Index) using 1% CNF or 47.40 N.m/g using 1% MFC. Also, the cost of use CNF or MFC in papermaking is evaluated, resulting in the estimates of 0.9494 US$/kg or 0.3036 US$/kg, the addition of 1% CNF or 1% MFC in UEKP. This work shows that the application of nanocellulose in traditional Kraftliner with pinus fibres with all chemical agents has no real advantages. However, the use of CNF and MFC technically and economically has superior advantages in Eucalyptus unbleached (and oxygen delignified) Kraft pulp, resulting in such properties superior to those of long fibres.
26

A comparison of SPS  and HP sintered, electroless copper plated carbon nanofibre composites for heat sink applications

Ullbrand, Jennifer January 2009 (has links)
<p>The aim of this study is to synthesize a material with high thermal conductivity and a low coefficient of thermal expansion (CTE), useful as a heat sink. Carbon nanofibres (CNF) are first coated with copper by an electroless plating technique and then sintered to a solid sample by either spark plasma sintering (SPS) or hot pressing (HP). The final product is a carbon nanofibre reinforced copper composite. Two different fibre structures are considered: platlet (PL) and herringbone (HB). The influence of the amount of CNF reinforcement (6-24 %wt), on the thermal conductivity and CTE is studied. CNF has an excellent thermal conductivity in the direction along the fibre while it is poor in the transverse direction. The CTE is close to zero in the temperature range of interest. The adhesion of Cu to the CNF surface is in general poor and thus improving the the wetting of the copper by surface modifications of the fibres are of interest such that thermal gaps in the microstructure can be avoided. The poor wetting results in CNF agglomerates, resulting in an inhomogeneous microstructure. In this report a combination of three different types of surface modifications has been tested: (1) electroless deposition of copper was used to improve Cu impregnation of CNF; (2) heat treatment of CNF to improve wetting; and (3) introduction of a Cr buffer layer to further enhance wetting. The obtained composite microstructures are characterized in terms of chemical composition, grain size and degree of agglomeration. In addition their densities are also reported. The thermal properties were evaluated in terms of thermal diffusivity, thermal conductivity and CTE. Cr/Cu coated platelet fibres (6wt% of CNF reinforcement) sintered by SPS is the sample with the highest thermal conductivity, ~200 W/Km. The thermal conductivity is found to decrease with increasing content of CNFs.</p>
27

A comparison of SPS  and HP sintered, electroless copper plated carbon nanofibre composites for heat sink applications

Ullbrand, Jennifer January 2009 (has links)
The aim of this study is to synthesize a material with high thermal conductivity and a low coefficient of thermal expansion (CTE), useful as a heat sink. Carbon nanofibres (CNF) are first coated with copper by an electroless plating technique and then sintered to a solid sample by either spark plasma sintering (SPS) or hot pressing (HP). The final product is a carbon nanofibre reinforced copper composite. Two different fibre structures are considered: platlet (PL) and herringbone (HB). The influence of the amount of CNF reinforcement (6-24 %wt), on the thermal conductivity and CTE is studied. CNF has an excellent thermal conductivity in the direction along the fibre while it is poor in the transverse direction. The CTE is close to zero in the temperature range of interest. The adhesion of Cu to the CNF surface is in general poor and thus improving the the wetting of the copper by surface modifications of the fibres are of interest such that thermal gaps in the microstructure can be avoided. The poor wetting results in CNF agglomerates, resulting in an inhomogeneous microstructure. In this report a combination of three different types of surface modifications has been tested: (1) electroless deposition of copper was used to improve Cu impregnation of CNF; (2) heat treatment of CNF to improve wetting; and (3) introduction of a Cr buffer layer to further enhance wetting. The obtained composite microstructures are characterized in terms of chemical composition, grain size and degree of agglomeration. In addition their densities are also reported. The thermal properties were evaluated in terms of thermal diffusivity, thermal conductivity and CTE. Cr/Cu coated platelet fibres (6wt% of CNF reinforcement) sintered by SPS is the sample with the highest thermal conductivity, ~200 W/Km. The thermal conductivity is found to decrease with increasing content of CNFs.
28

Acquisition de connaissances et raisonnement en logique propositionnelle

Zanuttini, Bruno 04 July 2003 (has links) (PDF)
Nous étudions l'algorithmique de deux problèmes centraux d'Intelligence Artificielle, pour des bases de connaissances représentées, notamment, par des formules propositionnelles de Horn, bijonctives, Horn-renommables ou affines. Nous traitons tout d'abord l'acquisition de connaissances à partir d'exemples : nous donnons notamment un algorithme efficace et général pour l'acquisition exacte, complétons l'état de l'art pour l'approximation et donnons un algorithme pour le PAC-apprentissage des formules affines. Nous étudions ensuite des problèmes de raisonnement : nous donnons un algorithme général pour l'abduction, qui nous permet d'exhiber de nouvelles classes polynomiales, et posons de premières pierres pour l'étude de ce processus lorsque la base de connaissances est approximative. L'étude des formules affines pour la représentation de connaissances n'avait jamais été réellement menée. Les résultats présentés dans ce mémoire montrent qu'elles possèdent de nombreuses bonnes propriétés.
29

Aplicação de nanoceluloses em fibras não branqueadas para obtenção de papéis. / Application of nanocelulose in unbleached fibers for papermaking.

Jorge Cruces Cerro 18 August 2016 (has links)
Atualmente, o Brasil é o maior fabricante de celulose branqueada de eucalipto do mundo. Geralmente as fibras virgens de Eucalyptus spp. são utilizadas na fabricação de papéis para imprimir, tissue e especiais. Papéis para embalagens, tipicamente Kraftliners, precisam de uma grande resistência mecânica e são produzidos principalmente a partir de pastas Kraft de coníferas não branqueadas. Por outro lado, nanoceluloses fabricadas a partir de biomassa são consideradas um dos materiais sustentáveis mais interessantes para o século, com excelentes propriedades como baixa densidade, elevadas propriedades mecânicas, alta hidrofilicidade, grande área superficial com reatividade química e elevado valor econômico. Desde 2012 o uso de nanoceluloses na fabricação de papel ganhou impulso. As nanoceluloses têm sido adicionadas em pastas mecânicas e Kraft branqueadas para fabricação do papel, incrementando notavelmente as suas propriedades mecânicas, mas há preocupações sobre a diminuição da drenabilidade, da porosidade e da opacidade do papel. Poucos estudos foram desenvolvidos visando a aplicação de nanoceluloses em fibras não branqueadas, ainda que tenham aplicações em pastas branqueadas e/ou mecânicas. Portanto, o presente trabalho visa desenvolver o uso de nanoceluloses para melhorar as propriedades mecânicas em fibras não branqueadas. Em primeiro lugar, tomaram-se os finos primários do branqueamento de celulose de Pasta Kraft de Eucalipto como a matéria-prima para produzir dois tipos de nanocelulose. A celulose microfibrilada (MFC) é produzida diretamente por homogeneização mecânica utilizando equipamento Masuko. A celulose nanofibrilada (CNF) é produzida por oxidação mediada por TEMPO e homogeneizada por GEA. Em segundo lugar, selecionaram-se com as fibras virgens de Pasta Kraft Marrom de Pinho (PKPM) com número Kappa 36,1 e Pasta Kraft de Eucalipto Não Branqueada (PKEP), obtida na saída de estágio de deslignificação com oxigênio, com número Kappa 9,21, e todas as fibras foram refinadas até atingir o mesmo grau Shopper-Riegler (33±1 SR). Os experimentos com PKPM são conduzidas como uma referência a papéis Kraftliners tradicionais, com ou sem nanocelluloses. Também obteve folhas manuais com pasta branqueada Kraft de eucalipto, adicionando nanoceluloses, para compreender o efeito da lignina presente em PKEP. A receita e os aditivos químicos aplicados aqui são os mesmos que na produção industrial. Os principais resultados são: o uso de CNF (ou MFC) e agentes químicos, separadamente, na pasta PKEP, aumenta as resistências mecânicas dos papéis, no entanto, quando aplicadas CNF (ou MFC) em PKMP sem aditivos químicos, as resistências à tração e a estouro diminuem, e a resistência ao rasgo permanece constante. Como a terceira parte do estudo, delineamento de experimentos teve a configuração composto central com o ponto central em 1% de CNF (ou MFC) e 1% de agentes químicos (polímero+amido+cola), e seus pontos axiais foram 0,3%-1,7% de CNF (ou MFC), e 0,15%-0,85% de agentes químicos. O ponto ótimo de equilíbrio dos índices de rasgo (mN.m2/g) /estouro (kPa.m2/g) /tração (N.m/g) de (10,00/2,25/36,56 para CNF e 12,88/4,25/57,62 para MFC), obteve-se com a adição de 1,03% de CNF e 0,65% de amido, ou com a adição de menos de 0,01% de MFC e de 1% de amido. Finalmente, foram aplicadas CNF ou MFC por impregnação direta no centro da direção-z, considerando que o papel tem forças que interagem em 3D. Os resultados mostram que a PKEP atinge a qualidade do Kraftliner de pinus obtendo um índice de tração de 52,58 N.m/g utilizando 1% de CNF, ou 47,40 N.m/g utilizando 1% de MFC. Também, o custo de utilização do CNF ou MFC na fabricação do papel é avaliado, resultando em estimativas de 0,9494 US$/kg ou 0,3036 US$/kg, com a adição de 1% de CNF ou 1% de MFC, respectivamente, em pasta PKEP. Este trabalho mostra que a aplicação de nanocelulose em Kraftliner tradicional com fibras de pinus com todos os agentes químicos não tem vantagens reais. No entanto, o uso de CNF e MFC tecnicamente e economicamente tem vantagens superiores em pasta Kraft de eucalipto não branqueada (e deslignificada com oxigênio), obtendo-se propriedades superiores às de fibras longas. / Nowadays, Brazil is the largest manufacturer of Bleached Eucalyptus Kraft Pulp in the world. Mostly the Eucalyptus spp. virgin fibres are used in papermaking to manufacture printing, tissue and specialty papers. Packaging papers, typically Kraftliners, have high demands for mechanical strength and are made mostly from Unbleached Softwood Kraft Pulp. Other side, nanocelluloses from biomass are considered one of the most interesting sustainable materials for the Century, with excel properties such as low density, high mechanical properties, high hydrophilicity, large surface area with chemical reactivity and high economic value. Since 2012 the use of nanocellulose in papermaking experienced a great momentum. Nanocelluloses are added in bleached or mechanical pulp in papermaking to increase significantly the mechanical properties, but there are concerns about the decreasing of the drainability, the porosity and the opacity of the paper. A very few studies were developed on the application of nanocelluloses in an unbleached Kraft pulp, even there are its applications on bleached pulps and mechanical pulps. Therefore, the present work aims to develop the application of nanocelluloses to increase the mechanical properties of the unbleached fibers, specifically for Kraftliners, and show the way to replace the softwood fibers with the low-cost hardwood fibers. Firstly, the primary fines from bleaching area of Eucalyptus Kraft pulp, obtained from an industrial residue, was the raw material for nanocellulose production of two nanocelluloses. The microfibrillated celluloses (MFC) are produced with direct mechanical homogenization using Masuko. The nanofibrillated cellulose (NCF) is produced with oxidation mediated by TEMPO and homogenization using GEA. Secondly, as virgin fibers were selected the Unbleached Pine Kraft Pulp (USKP) with Kappa number 36.1 and the Unbleached Eucalyptus Kraft Pulp (UEKP) just after the oxygen delignification stage with the Kappa number 9.21. All the fibres (USKP and UEKP) was refining at the same Shopper-Riegler (33±1 SR). USKP experiments are conducted as reference to traditional Kraftliners, with or without nanocelluloses. Also the virgin bleached Eucalyptus Kraft pulp with nanocelluloses addition for the handsheet paper helps to understand the role of lignin in UEKP. The recipe and chemicals applied here are the same of the industrial production. The main results are: the use CNF (or MFC) and chemical agents, separately, in UEKP, promote the mechanical resistances, however when applied CNF (or MFC) in UPKP without chemicals, the tensile and burst properties decreased and tear remains constant. As the third group of the study, the design of the experiments was conducted in the star configuration with centre point as 1% CNF (or MFC) and 1.00% chemical agents (polymers+starch+chemical agents) and, the axial points were 0.3%-1.7% NCF (or MFC) and 0.15%-0.85 of chemical agents. The optimum point from the balanced tear (mN.m2/g) /burst (kPa.m2/g) /tensile (N.m/g) index point of view with 10.00/2.25/36.56 for (1.03% CNF and 0.65% starch) and 12.88/4.25/57.62 for (<0.001% MFC and 1% starch). Finally, it is applied here the direct impregnation of the center of z-direction with 1% of CNF and MFC, considering that the paper has 3D interacting forces. The results show that the UEKP reaches the pinus Kraftliner quality with 52.58 N.m/g (Tensile Index) using 1% CNF or 47.40 N.m/g using 1% MFC. Also, the cost of use CNF or MFC in papermaking is evaluated, resulting in the estimates of 0.9494 US$/kg or 0.3036 US$/kg, the addition of 1% CNF or 1% MFC in UEKP. This work shows that the application of nanocellulose in traditional Kraftliner with pinus fibres with all chemical agents has no real advantages. However, the use of CNF and MFC technically and economically has superior advantages in Eucalyptus unbleached (and oxygen delignified) Kraft pulp, resulting in such properties superior to those of long fibres.
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THE INFLUENCE OF CELLULOSE NANOCRYSTALS ON PERFORMANCE AND TRANSPORT PROPERTIES OF CEMENTITIOUS MATERIALS AND GYPSUM

Anthony Paul Becerril (9669782) 16 December 2020 (has links)
<p>Concrete is in everyday life such as parking lots, buildings, bridges, and more. To keep concrete and its constituents together, binders such as cement are used. Cement’s production process is responsible for 8% of global carbon dioxide emissions as of 2018. With global warming being a severe global issue, the challenge of reducing cement carbon dioxide emissions can be greatly beneficial with even slight improvements. Various solutions to this challenge have developed over the years in the form of processing efficiency, material substitution, or material additives. Of the additives for cement and concrete that have been ventured, nanomaterials have had a strong development in recent years. Specifically, cellulose nanomaterials in the form of nanocrystals, nanofibrils, and more have demonstrated great improvement in cement’s performance resulting in a reduction in cement produced and reduction in emissions. This study expands on the knowledge of cellulose nanocrystals as an additive for cement using the formation factor methodology. Formation factor is a resistivity ratio of the specimen and pore solution that can be used in correlation to the diffusion of chloride ions through the use of the Nernst-Einstein equation. This study also investigates the effect that cellulose nanomaterials have on the mechanical properties and thermogravimetric analysis of gypsum, a material commonly used in cement production that delays the hardening of cement. </p>

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