Ce travail de thèse a été consacré à l'élaboration d'un nouveau type de membranes de nanofiltration efficaces avec des propriétés améliorées (flux élevé et rétention élevée, et de bonnes propriétés mécaniques) en déposant un revêtement assemblé couche-par-couche (LbL) sur des supports poreux. Après avoir systématiquement étudié le mécanisme de croissance des films assemblés couche par couche des polyélectrolytes choisis et la relation entre les structures de ces films et les performances des membranes résultant, nous avons identifié avec succès les meilleures structures multicouches pour la construction de membranes de nanofiltration de référence avec des performances optimales. En outre, en prenant avantage de la technique LbL, nous avons introduit une couche de diffusion latérale assemblée soit de nanofibrilles de cellulose ou de nanotubes de carbone, qui permet d’augmenter le flux de 30% tout en conservant la même rétention par rapport à la membrane de référence. En plus, les films assemblés à base de chitosan et nanofibrils de cellulose ont montré une forte résistance à la traction allant jusqu’à 450 MPa et un module d’Young jusqu’à 50 GPa. / This thesis work was devoted to the development of a novel and efficient nanofiltration membrane with improved properties (high flux and high retention, good mechanical strength) by coating Layer-by-Layer (LbL) assembled films onto porous membrane support. After having systematically studied the growth mechanism of LbL-assembled films of chosen polyelectrolytes and the relationship between the structures of these films and the membrane performance of the resulting NF membranes, we successfully identified the best multilayer structures for constructing nanofiltration membranes (NF) of reference with optimal membrane performance. Furthermore, taking advantages of the LbL-assembly, we successfully introduced LbL-assembled lateral diffusion layer that is made of either cellulose nanofibrils or carbon nanotubes, which in turn led to membranes with 30% higher flux. In addition, the LbL-assembled films of chitosan and cellulose nanofibrils showed surprisingly strong tensile strength of up to 450 MPa and a high Young modulus of up to 50 GPa.

Träbaserade cellulosananofibriller är intressanta som förstärkande fas i polymera nanokompositer; detta främst på grund av den kristallina cellulosans höga styvhet och på grund av nanofibrillernas förmåga att bilda nätverk. Cellulosananofibriller kan användas i form av mikrokristallin cellulosa, MCC, som har lågt längd/diameter förhållande, eller i form av mikrofibrillerad cellulosa, MFC, med högt längd/diameter förhållande. Målet med det här arbetet är att studera struktur-egenskapsförhållanden för nanofibrillnätverk och kompositer. Nanokompositer baserade på MCC och termoplastisk polyuretan tillverkades genom in-situ polymerisation. Cellulosafibrillerna var väl dispergerade i matrisfasen och kompositen visade ökad styvhet, styrka samt brottöjning. Dessa förbättningar antas bero på stark interaktion mellan polyuretan och cellulosananofibrillerna. En metod som underlättar mikrofibrillering av massafiberns cellvägg under homogenisering har utvecklats. Massan förbehandlades med ett enzym innan homogenisering. Den här metoden förenklade mikrofibrilleringen och mekanismerna diskuteras. De resulterande MFC-nanofibrillerna hade högt längd/diameter förhållande. Filmer har tillverkats av MFC-nanofibriller och filmernas struktur samt mekaniska egenskaper har studerats. Röntgendiffraktion och SEM visar att nanofibrilerna är mer orienterade i planet än i rymden. SEM och densitetsmätningar visar även att filmerna har en porös struktur. Resultaten från dragprovning visade att filmernas brottstyrka är beroende av molekylvikten för cellulosan. Nanofibrillerna med högst molekylvikt visade en E-modul på 13.2 GPa, brottstyrkan var 214 MPa och brottöjningen 10.1%. Kompositer med hög fiberhalt har tillverkats genom tillsats av melaminformaldehyd till MFC-filmer. Dessa kompositer visar ökad styvhet och styrka på bekostnad av brottöjningen. Kompositer har också tillverkats genom impregnering av MFC-nätverk med en hyperförgrenad polymer som tvärbands. DMA visar två Tg för kompositerna med 0.26 och 0.43 volymfraktion nanofibriller; matrisens Tg samt ytterligare ett Tg vid högre temperatur. Detta motsvarar molekyler med lägre mobilitet på grund av ökad interaktion med nanofibrillernas ytor. / The cellulose nanofibril from wood is an interesting new material constituent that can provide strong reinforcement in polymer nanocomposites due to the high stiffness of the cellulose crystals and the network formation characteristics of the nanofibrils. Cellulose nanofibrils can be used either in the form of low aspect ratio microcrystalline cellulose, MCC, or as high aspect ratio microfibrillated cellulose, MFC. The objective is to study structure-property relationships for cellulose nanofibril networks and composites. Nanocomposites based on MCC and thermoplastic polyurethane were prepared by in-situ polymerization. The cellulose nanofibrils were successfully dispersed in the matrix and the composites showed improvements in stiffness, strength, as well as in strain-to-failure. Cellulose nanofibrils reinforce the physical rubber network by strong molecular interaction with the rubber. A method that facilitates microfibrillation of the pulp cell wall during homogenization has been developed. The pulps were treated with a combination of beating and enzymatic treatment prior to homogenization. The enzymatic pretreatment was found to facilitate the microfibrillation and the mechanisms are discussed. The resulting MFC nanofibrils were of high aspect ratio. Cellulose nanofibril networks of high toughness were prepared from MFC and studied with respect to the structure and mechanical properties. These films have a porous structure and the nanofibrils are more in-plane than in-space oriented. Tensile testing showed that the strength is dependent on the average molecular weight of the cellulose. The MFC of the highest molecular weight showed a modulus of 13.2 GPa, tensile strength as high as 214 MPa and 10.1% strain-to-failure, at a porosity of 28%. Composites of high fiber content have been prepared by addition of melamine formaldehyde to MFC films. These composites show increased stiffness and strength, at the cost of strain-to-failure. Composites were also prepared by impregnating MFC nanofibril networks with a hyperbranched polymer. The matrix was crosslinked and strong interactions with the nanofibrils were formed. By DMA two Tg’s were observed for the composites with 0.26 and 0.43 volume fraction nanofibrils. The Tg of the matrix was observed as well as a Tg at higher temperatures. This corresponds to molecules with constrained mobility by increased interactions with the cellulose nanofibril surfaces. / QC 20100810

Non-spherical particles are present all around us, in biological, industrial and environmental processes. Making predictions of their impact on us and systems in our vicinity can make life better for everyone here on earth. For example, the ash particles from a volcano eruption are non-spherical and their spreading in the atmosphere can hugely impact the air traffic, as was also proven in 2010. Furthermore, the orientation of the wood fibres in a paper sheet influences the final properties of the paper, and the cause of a specific fibre orientation can be traced back to the fluid flows during the manufacturing process of the paper. In this thesis, experimental and numerical work is presented with the goal to understand and utilize the behavior of elongated particles in fluid flows. Two different experimental setups are used. The first one, a turbulent half channel flow, aims at increasing the understanding of how particles with non-zero inertia behave in turbulence. The second setup is an attempt to design a flow field with the purpose to align nanofibrils and create high performance cellulose filaments. Experiments were performed in a turbulent half channel flow at different flow set- tings with dilute suspensions of cellulose acetate fibres having three different aspect ratios (length to width ratio). The two main results were firstly that the fibres agglom- erated in streamwise streaks, believed to be due to the turbulent velocity structures in the flow. Secondly, the orientation of the fibres was observed to be determined by the aspect ratio and the mean shear, not the turbulence. Short fibres were oriented in the spanwise direction while long fibres were oriented in the streamwise direction. In order to utilize the impressive properties (stiffness comparable to Kevlar) of the cellulose nanofibril in a macroscopic material, the alignment of the fibrils must be controlled. Here, a flow focusing device (resulting in an extensional flow), designed to align the fibrils, is used to create a cellulose filament with aligned fibrils. The principle is based on a separation of the alignment and the assembly of the fibrils, i.e. first align the fibrils and then lock the aligned structure. With this process, continuous filaments were created, with properties similar to that of the wood fibre at the same fibril alignment. However, the highest alignment (lowest angle) of the fibrils in a filament created was only 31o from the filament axis, and the next step is to increase the alignment. This thesis includes modeling of the alignment process with the Smoluchowski equation and a rotary diffusion. Finding a model that correctly describes the alignment process should in the end make it possible to create a filament with fully aligned fibrils. / <p>QC 20140908</p>

Submitted by Ronildo Prado (ronisp@ufscar.br) on 2017-08-23T14:10:16Z No. of bitstreams: 1 DissPICC.pdf: 9243099 bytes, checksum: d5c4984be722eda91236fbec51d566f6 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-08-23T14:10:24Z (GMT) No. of bitstreams: 1 DissPICC.pdf: 9243099 bytes, checksum: d5c4984be722eda91236fbec51d566f6 (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-08-23T14:10:29Z (GMT) No. of bitstreams: 1 DissPICC.pdf: 9243099 bytes, checksum: d5c4984be722eda91236fbec51d566f6 (MD5) / Made available in DSpace on 2017-08-23T14:10:35Z (GMT). No. of bitstreams: 1 DissPICC.pdf: 9243099 bytes, checksum: d5c4984be722eda91236fbec51d566f6 (MD5) Previous issue date: 2017-02-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / New materials from cellulose have been developed, such as cellulose nanocrystals (CNC) and cellulose nanofibrils (CNF). Different morphologies of the cellulose can lead to the formation of films with different thermal, mechanical and optical properties in relation to conventional cellulose films. The objective of this work was to evaluate the effect of different dimensional scales of cellulose, micro and nanometric, on the production of cellulose films from two vegetable species and their thermal, mechanical, morphological and optical properties. Eucalyptus fibers and pineapple leave fiber (curauá) (PALF) were used as cellulosic fibers for this study. The films of eucalyptus and pineapple cellulosic fibers were prepared by filtration and casting, and the CNC and CNF films were obtained by continuous casting. The CNC and CNF films showed mechanical tensile strength in the order of 9 to 35 MPa higher than the films of cellulose fibers, regardless of the origin of the fiber. The continuous casting process produced CNC and CNF films that presented different mechanical resistance in the longitudinal direction of the process with respect to the transverse direction. This behavior may be related to how hydrogen bonds and mechanical anchorages occur between nanofibers. The thermal stability of the nanocellulose films was lower in the order of 20 to 150 ºC than in the films of fibers due to the routes of obtaining the CNC and CNF. Nanofiber films presented lower opacity in the order of 3 to 60% lower than the films of fibers due to the diameter of the nanocelluloses. Curauá fibers had the highest crystallinity index (Ic) reaching 87%. It is concluded that the properties studied were influenced by the type of nanocellulose (CNC or CNF), the origin of the cellulose (eucalyptus or pineapple), and the micro and nanometric scale of the fibers. / Novos materiais a partir da celulose tem sido obtidos, como os nanocristais de celulose (CNC) e as nanofibrilas de celulose (CNF). Diferentes morfologias da celulose podem levar a formação de filmes com propriedades térmicas, mecânicas e ópticas diferentes de filmes de celulose convencional. O objetivo deste trabalho foi avaliar o efeito de diferentes morfologias de fibras de celulose, micro e nanométricas, na obtenção de filmes - provenientes de duas espécies vegetais – e em suas propriedades térmicas, mecânicas, ópticas e morfológicas. Utilizou-se como fibras celulósicas para este estudo as fibras de eucalipto e fibras de folhas de abacaxi (curauá) (PALF). Os filmes de fibras celulósicas de eucalipto e de abacaxi foram confeccionados por filtragem e casting, e os filmes de CNC e CNF foram obtidos por continuous casting. Os filmes de CNC e CNF apresentaram resistência mecânica à tração, na ordem de 9 a 35 MPa superior aos filmes de fibras de celulose, independente da origem da fibra. O processamento por continuous casting produziu filmes de CNC e CNF que apresentaram resistência mecânica diferente no sentido longitudinal ao processo com relação ao sentido transversal. Este comportamento pode estar relacionado de que forma ocorrem às ligações de hidrogênio e os emaranhamentos mecânicos entre as nanofibras. A estabilidade térmica dos filmes de nanofibra foi menor na ordem de 20 a 150 ºC do que aos filmes de fibras devido às rotas de obtenção das CNC e CNF. Os filmes de nanofibra apresentaram menor opacidade, na ordem de 3 a 60% inferior, que os filmes de fibras devido ao diâmetro das nanofibras. As fibras de curauá apresentaram o maior índice cristalinidade (Ic) chegando a 87%. Conclui-se que a propriedades estudadas foram influenciadas pelo tipo de nanofibra (CNC ou CNF), pela origem da celulose (eucalipto ou abacaxi), e pela escala micro e nanométrica das fibras.

L’originalité de ce travail est d’étudier la contribution des nanocelluloses pour limiter deux défauts courant dans les papiers sécurités: le froissage et les “cornes”, où plis qui se manifestent dans les angles des papiers. Ces défauts sont principalement causés par une manipulation quotidienne de ces papiers à haute valeur ajoutée, et sont responsables d’une perte en qualité visuelle et mécanique ainsi que de troubles économiques. Les nanocellulose peuvent être divisées en deux différentes familles de matériaux : les nanofibrilles de celluloses (NFCs) et les nanocristaux de cellulose (NCCs). Les NFCs sont longues et flexibles et peuvent facilement s’enchevêtrer pour former un réseau cohésif maintenu par de nombreuses liaisons hydrogènes. Les NCCs sont des matériaux petits et rigides, et leurs impressionantes propriétés mécaniques font d’eux des candidats intéressants pour être utilisés en renfort de polymère. Dans cette étude, deux stratégies sont proposées pour incorporer ces deux types de nanocellulose dans la fabrication du papier sécurité. Premièrement, il est question d’introduire une couche de NFCs à l’intérieur du papier afin d’augmenter la résistance de ce papier au froissage. Ensuite, il est question d’imprégner ce papier avec de l’alcool polyvinylique renforcé par des NCCs afin d’augmenter la résistance aux cornes. Enfin, ces approches sont testées à l’échelle pilote et industrielle. / The original feature of this work is the use of nanocellulose for limiting two security paper defects: corner folds, also called “dog-ears”, and crumpling. These defects, caused principally by daily handling of these high added value documents, are responsible for a decrease of paper visual and mechanical quality and constitute an economic loss. Nanocellulose can be divided into two different families: cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs). CNFs are long and flexible materials with the ability to entangle and form a network strongly maintained by hydrogen bonds. CNCs are short and rigid materials whose outstanding mechanical properties make them good candidates for reinforcement in a polymer matrix. In this study, two strategies are proposed to incorporate these two kinds of nanocellulose in the security paper process. First, it is question to introduce a CNF layer within the paper substrate in order to increase the paper crumpling resistance. Then, it is question to impregnate the paper with CNCs-reinforced polyvinyl alcohol (PVOH) in order to increase the dog-ears resistance. Finally, these approaches are tested at pilot and industrial scales.

Submitted by Milena Rubi ( ri.bso@ufscar.br) on 2017-10-17T16:37:26Z No. of bitstreams: 1 SILVA_Barbara_2017.pdf: 2018251 bytes, checksum: 6dab58bc6d22c81d23f1cfb7011353bf (MD5) / Approved for entry into archive by Milena Rubi ( ri.bso@ufscar.br) on 2017-10-17T16:37:37Z (GMT) No. of bitstreams: 1 SILVA_Barbara_2017.pdf: 2018251 bytes, checksum: 6dab58bc6d22c81d23f1cfb7011353bf (MD5) / Approved for entry into archive by Milena Rubi ( ri.bso@ufscar.br) on 2017-10-17T16:37:47Z (GMT) No. of bitstreams: 1 SILVA_Barbara_2017.pdf: 2018251 bytes, checksum: 6dab58bc6d22c81d23f1cfb7011353bf (MD5) / Made available in DSpace on 2017-10-17T16:38:00Z (GMT). No. of bitstreams: 1 SILVA_Barbara_2017.pdf: 2018251 bytes, checksum: 6dab58bc6d22c81d23f1cfb7011353bf (MD5) Previous issue date: 2017-03-15 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / The application of cellulose nanofibrils to the production of composites has been studied and presents promising results, mainly due to the abundance of the material, which is of a renewable source, and to its low cost. However, the presence of the hydroxyl groups in their chain and their storage in aqueous solutions limits their application as reinforcement in nonpolar matrix composites. In this context, this work aimed to modify the wettability and adhesion properties of films of cellulose nanofibrils to apolar matrices, through plasma treatment. For this, nanocellulose films with thickness of 38 ? 8 ?m were produced by the casting method, from a suspension of nanofibrils in water. The atomic force microscopy characterization (AFM) of the suspended nanofibrils indicated that most of them have an average diameter of less than 75 nm. Each film obtained, after drying the suspension, was then cut into 13 samples with 2 x 1 cm, 12 of which were exposed to plasma and one stored as untreated. Three films were treated with oxygen plasma, with excitation power of 150 W, for 30 minutes and pressure of 0.1, 0.3 and 0.5 Torr. Another three films were treated with sulfur hexafluoride plasma at pressures of 0.1, 0.2 and 0.3 Torr, with a power of 150 W for 15 minutes. It was observed that weight loss was greater than 40% for the films treated with the most extreme conditions oxygen and sulfur hexafluoride. The results also showed that the treatments with sulfur hexafluoride promoted the reduction of the receptivity of the samples to the liquids, with contact angles of approximately 60º for water and 50º for diiodomethane. The profilometry technique revealed that the roughness of the films varied after the treatment with oxygen and sulfur hexafluoride, but the high error bars impede a definitive conclusion on the tendency of these variations. The X-ray diffraction analysis (XRD) indicated no significant change in the crystallinity of the samples with the treatments. In the Fourier Transform Infrared absorption spectra (FTIR), a C-F bonding related peak appeared for the 0.3 Torr sulfur hexafluoride treated sample, indicating the presence of fluorine in that sample. The scanning electron microscopy (SEM) allowed the visualization of the changes in the topography of the films, due to the etching processes resulting from the action of the plasma and the films ruptures caused by the high removal of surface material. In order to test the incorporation of treated films into composites using polyolefins as the matrix, polyethylene pellets were solubilized in xylene for the production of composite films. The treated and untreated nanocellulose films were placed in Petri dish jointly to the polyethylene films still dissolved and left at room temperature. After drying, adhesion between the films was tested through the adhesive tape test, resulting in class-zero adherence, according to the technical standard. It is believed that the lack of adhesion is a result of the composite production method that should be optimized for future work, in order to provide a better investigation of the effects of plasma on the surface properties of the film of cellulose nanofibrils. / A aplicação de nanofibrilas de celulose à produção de compósitos vem sendo estudada e apresenta resultados promissores, principalmente devido à abundância do material, que é de fonte renovável, e ao seu baixo custo. Contudo, a presença dos grupos hidroxila em sua cadeia e o seu armazenamento em soluções aquosas impede sua aplicação como reforço em compósitos de matrizes apolares. Nesse contexto, esse trabalho buscou modificar as propriedades de molhabilidade e aderência de filmes de nanofibrilas de celulose a matrizes apolares, através de tratamento a plasma. Para isso, filmes de nanocelulose com espessura de 38 ? 8 ?m foram produzidos pelo método de casting, a partir de uma suspensão de nanofibrilas em água. A caracterização por microscopia de força atômica (AFM) das nanofibrilas em suspensão indicou que a maior parte destas apresenta diâmetro médio inferior a 75 nm. Cada filme obtido, após a secagem da suspensão, foi então cortado em 13 amostras de 2 x 1 cm, sendo 12 destas expostas ao plasma e uma armazenada como não tratada. Três filmes foram tratados com plasma de oxigênio, com potência de excitação de 150 W, por 30 minutos e pressão de 0,1, 0,3 e 0,5 Torr. Outros três filmes foram tratados com plasma de hexafluoreto de enxofre, nas pressões 0,1, 0,2 e 0,3 Torr, com potência de 150 W por 15 minutos. Observou-se que houve perda de massa superior a 40% para os filmes tratados com as condições mais extremas de oxigênio e hexafluoreto de enxofre. Os resultados demonstraram também que os tratamentos com hexafluoreto de enxofre promoveram a diminuição da receptividade a líquidos das amostras, com ângulos de contato de aproximadamente 60º para água e 50º para o diiodometano. A técnica de perfilometria revelou que a rugosidade dos filmes variou após o tratamento com oxigênio e hexafluoreto de enxofre, porém as elevadas barras de erro impediram uma conclusão definitiva sobre a tendência dessas variações. As análises de difração de raios X (DRX) indicaram não haver alteração significativa na cristalinidade das amostras com os tratamentos. Nos espectros de absorção no infravermelho por transformada de Fourier (FTIR), foi observado o surgimento de um pico relacionado à ligação C-F para a amostra tratada com 0,3 Torr de hexafluoreto de enxofre, que indica a presença de flúor nessa amostra. As análises de microscopia eletrônica de varredura (MEV) permitiram visualizar as alterações na topografia dos filmes, devido aos processos de ecthing decorrentes da ação do plasma e os rompimentos ocasionados pela elevada remoção de material da superfície. A fim de testar a incorporação dos filmes tratados em compósitos que utilizam poliolefinas como matriz, pellets de polietileno foram solubilizados em xileno para produção de filmes compósitos. Os filmes de nanocelulose tratados e não tratados foram dispostos em placa de Petri junto aos filmes de polietileno ainda dissolvidos e deixados em temperatura ambiente. Depois de secos, a adesão entre os filmes foi testada através do teste de fita-cola, resultado em adesão classe zero, conforme a norma técnica. Acredita-se que a falta de adesão é resultado do método de produção do compósito que deve ser otimizado para trabalhos futuros, com o objetivo de proporcionar uma melhor investigação dos efeitos do plasma sobre as propriedades da superfície do filme de nanofibrilas de celulose.

The packaging does not serve as a mere containment but also can be designed to play a key role in preserving the product from quality-deteriorating factors, including oxygen, light irradiation, and foodborne pathogenic microorganisms (e.g., Escherichia coli). There has been a growing interest in employing ultra-porous metal-organic frameworks (MOF) with visible light-responsive antibacterial mechanisms to generate reactive oxygen species (ROS) that can eliminate bacteria via an oxidative burst. MOF is made of inorganic metal ions/nodes/clusters/secondary building units linked by organic bridge ligands, where titanium dioxide (TiO2) and tetrakis(4-carboxyphenyl)porphyrin) (TCPP) were selected for these components, respectively. TiO2 is an exceptional UV-A/B/C-blocker; meanwhile, TCPP dye performs a remarkable photocatalytic ability even under visible light, on top of its macro-heterocyclic structure that is ideal as a MOF linker. Both have good compatibility but suffer from the notorious tendency to self-quench/aggregate. The incorporation of MOF-based conjugates into a polymeric matrix, like cellulose, is among the proven-successful solutions. Cellulose is the Earth's most abundant and naturally biodegradable, and cellulose nanofibril (CNF) was particularly chosen for its high specific surface area and surface activity. However, a straightforward, cheap, and environmentally friendly approach of multicycle homogenization (0-25 passes) was conducted to solve neat cellulose's challenge of natural hydrophilicity, where low pressure (<10 MPa) was applied to prevent the common over-shearing effect. The antibacterial efficacy of CNF films functionalized with TiO2-TCPP conjugate on inhibiting E. coli growth was analyzed with and without light of different intensities (3000 and 6000 lux). The positive impacts of CNFs' promoted fibrillation and subsequent inter/intra-molecular hydrogen bonding post-homogenization were evidenced in an array of functional properties, i.e., crystallinity, TiO2-TCPP conjugate dispersion, surface smoothness, mechanical properties, thermal stability, hydrophobicity, oxygen barrier (comparable to ethylene-vinyl alcohol (EVOH), a commercial high-barrier polymer), and 100%-antibacterial rate (under 6000 lux after 72 hours). Varying optimum cycles of homogenization demonstrated the prospect of the proposed homogenization approach in preparing CNF with diverse processability and applicability. These findings also exhibited a promising potential for a myriad of high-barrier, UV-blocking, and/or visible light-responsive antibacterial film applications, including food packaging and biomedical. / Doctor of Philosophy / Packaging is useful not only as a container but can also be designed to help prevent products from being spoiled due to various reasons such as oxidation, light, and bacterial contamination. Researchers have discovered the promising antibacterial feature of the metal-organic framework (MOF). Packaging made with MOF technology can harness light and oxygen in the environment to produce a special form of oxygen called reactive oxygen species (ROS) that can kill unwanted bacteria. MOF is an extremely porous sponge-like material made of two ingredients: an inorganic metal cluster and an organic linker; in this study, titanium dioxide (TiO2) and a porphyrin called TCPP were selected, respectively. TiO2 is an excellent ultraviolet blocker, while TCPP has a unique, ring-like geometry that is ideal for use as a linker and an antimicrobial feature that works well under the visible light spectrum. The pair are compatible but still suffer from MOF's notorious challenge, where it tends to clump together because of its tiny size. To resolve this problem, TiO2-TCPP MOF can be deposited evenly in a cast made of polymer. Cellulose has been proven to work effectively as a polymeric cast; moreover, it is natural, biodegradable, and in abundant supply. A type of nanosized cellulose—cellulose nanofibril (CNF)—was specifically chosen because its high surface area and activity are useful when blended with other materials. However, cellulose is naturally a poor water-repellant that is not ideal for packaging applications. As a solution, cellulose can be treated with a homogenization technique by passing the material through a very narrow hole under high pressure. Homogenization can be problematic as it possibly damages the cellulose's structure, and its high pressure can also be expensive and energy consuming. Therefore, low pressure with multiple cycles was applied in this work. CNF-TiO2-TCPP films were tested for their ability to slow down E. coli bacteria growth with and without light of varying brightness to compare its light-sensitive antimicrobial feature. Homogenization was found helpful in producing higher-quality CNF, which improved several of the film's final characteristics, including an even material dispersion, structural order, smoothness, strength, heat resistance, and water repellency. Most importantly, it produced films with oxygen barrier ability comparable to commercial high-barrier plastics and completely eliminated bacteria after 72 hours. The optimum number of homogenization cycles was found to be dependent on the desired characteristics and application. Overall, these findings carry a promising potential for a variety of applications, including food packaging and the biomedical field.

<div> <p><a>Polymer nanocomposites are envisioned for use in many advanced applications, such as structural industries, aerospace, automotive technology and electronic materials, due to the improved properties like mechanical strengthening, thermal and chemical stability, easy bulk processing, and/or light-weight instigated by the filler-matrix combination compared to the neat matrix. In recent years, due to increasing environmental concerns, many industries are inclining towards developing sustainable and renewable polymer nanocomposites. Cellulose nanomaterials (CNs), including cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), have gained popularity due to their excellent mechanical properties and eco-friendliness (extracted from trees, algae, plants etc.). However, to develop CN-reinforced nanocomposites with industrial applications it is necessary to understand impact of hygroscopic swelling (which has very limited </a>quantitative study at present), aspect ratio, orientation, and content of CNs on the overall performance of nanocomposites; and overcome the low dispersibility of CNs and improve their compatibility with hydrophobic matrix. In this work, we attempt to understand the influence of single nanocrystals in the hygroscopic and optical response exhibited by nanostructured films; effect of CNCs on the properties of PVA/CNC fibers by experimental evidence with mathematical modeling predictions; and hydrophobized CNFs using a facile, aqueous surface modification to improve interfacial compatibility with epoxy. </p><p><br></p> <p>To evaluate the effect of CNC alignment in the bulk response to hygroscopic expansion, self-organized and shear-oriented CNC films were prepared under two different mechanisms. The coefficient of hygroscopic swelling (CHS) of these films was determined by using a new contact-free method of Contrast Enhanced Microscopy Digital Image Correlation (CEMDIC) that enabled the characterization of dimensional changes induced by hygroscopic swelling of the films. This method can be readily used for other soft materials to accurately measure hygroscopic strain in a non-destructive way. By calculating the CHS values of CNC films, it was determined that hygroscopic swelling is highly dependent on the alignment of nanocrystals within the films, with aligned CNC films showing dramatically reduced hygroscopic expansion than randomly oriented films. Finite element analysis was used to simulate moisture sorption and kinetics profile which further predicted moisture diffusion as the predominant mechanism for swelling of CNC films. </p> <p><br></p><p>To study the effects of different types and aspect ratios of CNCs on mechanical, thermal and morphological properties of polyvinyl alcohol (PVA) composite <a>fibers, CNCs extracted from wood pulp and cotton were reinforced into PVA to produce fibers by dry-jet-wet spinning. The fibers were collected as-spun and with first stage drawing up to draw ratio 2. </a>The elastic modulus and tensile strength of the fibers improved with increasing CNC content (5 – 15 wt. %) at the expense of their strain-to-failure. The mechanical properties of fibers with cotton CNC were higher than the fibers with wood CNC when the same amount of CNCs were added due to their higher aspect ratio. The degree of orientation along the spun fiber axis was quantified by 2D X-ray diffraction. As expected, the CNC orientation correlates to the mechanical properties of the composite fibers. Micromechanical models were used to predict the fiber performance and compare with experimental results. Finally, surface and cross-sectional morphologies of fibers were analyzed by scanning electron microscopy and optical microscopy.</p><p><br></p> <p>To improve the dispersibility and compatibility of CNFs with epoxy, CNFs were modified by using a two-step water-based method where tannic acid (TA) acts as a primer with CNF suspension and reacts with hexadecylamine (HDA), forming the modified product as CNF-TA-HDA. The modified (-m) and unmodified (-um) CNFs were filled into hydrophobic epoxy resin with a co-solvent (acetone), which was subsequently removed to form a solvent-free two component epoxy system, followed by addition of hardener to cure the resin. Better dispersion and stronger adhesion between fillers and epoxy were obtained for m-CNF than the um-CNF, resulting in better mechanical properties of nanocomposites at the same loading. Thermal stability and the degradation temperature of m-CNF/epoxy improved when compared to neat epoxy. </p> </div> <br>

Ce travail porte sur l'incorporation de nanorenforts biosourcés, c'est-à-dire des nanofibrilles de cellulose (NFC), dans les matériaux composites à matrice polymère et les mousses. Ces nouveaux matériaux biosourcés peuvent par exemple être utilisés pour la conception de structures sandwich. L'étude à caractère expérimental, théorique et numérique s'articule autour de trois axes visant à optimiser tant les procédés d'élaboration que les propriétés en service de ces matériaux.Dans un premier temps, la rhéologie des suspensions concentrées de NFC, fluides à seuil thixotropes, a été étudiée aux échelles macro- et mésoscopiques en utilisant un dispositif original de rhéométrie couplé à des mesures de champs cinématiques par vélocimétrie ultra-sonore. Nous montrons ainsi que l'écoulement des suspensions de NFC est fortement hétéro-gène et présente des glissements aux parois, de multiples bandes de cisaillement couplés avec des écoulements de type « bouchon ». Sur la base de cette étude, un modèle rhéolo-gique multi-échelles est proposé. Ce modèle tient compte d'une part de l'architecture aniso-trope des réseaux connectés de NFC dans ces suspensions, et d'autre part des interactions mécaniques et physico-chimiques aux échelles nanométriques. Il permet de montrer que les interactions colloïdales et hydrodynamiques, ainsi que la tortuosité et l'orientation des NFC jouent un rôle majeur sur la contrainte seuil et sur le comportement rhéofluidifiant de ces suspensions.Dans un deuxième temps, des nanocomposites à matrice polymère ont été élaborés sous forme de films en faisant varier sur une très grande plage la fraction volumique de NFC. En utilisant d'une part des techniques de microscopie (AFM, MEB) et de diffraction aux rayons X, et d'autre part des essais mécaniques (traction, DMA) nous montrons (i) que les NFC ont une orientation plane et s'organisent en réseaux connectés par des liaisons hydro-gènes, (ii) que ces réseaux jouent un rôle majeur sur le comportement mécanique des nano-composites et (iii) que le comportement élastique des nanocomposites est bien en deçà des prévisions données par les modèles micromécaniques de la littérature. De là, nous proposons un modèle multi-échelles alternatif où les principaux nano-mécanismes de déformation sont ceux se produisant dans les parties amorphes des NFC et au niveau des très nombreuses interfaces entre NFC.Enfin, nous avons étudié l'influence des conditions d'élaboration, de la nature et de la con-centration des NFC sur les microstructures (microtomographie synchrotron à rayons X), les propriétés mécaniques (essais de compression) et les micro-mécanismes de déformation (essai in situ en microtomographie) de mousses préparées par cryodessiccation de suspensions aqueuses de NFC. / This study focuses on the use of cellulose nanofibrils (NFCs) as bio-based nano-reinforcement in polymer composites and foams. These renewable materials can be used in place of traditional materials such as for instance to produce sandwich panels. This experi-mental, theoretical and numerical work aims at optimizing the processing of these NFC-based materials as well as their use properties.In the first part of this work, the rheology of concentrated NFC suspensions, that behave as thixotropic yield stress fluids, is investigated at macro- and mesoscales using an original rheo-ultrasonic velocimetry (rheo-USV) setup allowing the local flow kinematic to be obtai-ned. We show that the flow of NFC suspensions is highly heterogeneous and exhibits com-plex situations with the coexistence of wall slippage, multiple shear bands and plug-like flow bands. Using this experimental database, we develop an original multiscale rheological model for the prediction of the rheology of NFC suspensions. The model takes into account the anisotropic fibrous nature of NFC networks as well as colloidal and mechanical interaction forces occurring at the nanoscale. The model predictions prove that colloidal and hydrody-namic interaction forces together with the orientation and the wavy nature of NFCs play a major role on the yield stress and shear thinning behaviour of the suspensions.In the second part of this work, NFC-reinforced polymer nanocomposite films are processed for a wide range of NFC contents. Using advanced microscopy techniques (AFM, SEM), X-ray diffraction and mechanical tests (tensile and DMA tests), we show (i) that NFCs form highly connected nanofibrous structures with in-plane random orientation, (ii) that these connected NFC networks play a leading role on the mechanical behaviour of the nanocompo-sites and (iii) that the elastic properties of nanocomposite films are much lower than those predicted from the micromechanical models of the literature. In light of these observations, we propose an alternative multiscale model in which the main involved deformation nano-mechanisms are those occurring both in the amorphous segments of the nanofibers and in the numerous nanofiber-nanofiber contact zones.Finally, in a third part we focus on the influence of the processing conditions, the suspension type and the NFC concentration on the microstructure (using X-ray synchrotron microto-mography), the mechanical properties (using compression tests) and the deformation micro-mechanisms (using in situ compression test with X-ray microtomography) of various foams prepared from NFC suspensions by freeze-drying.

<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>