The context of this thesis is a research project focused on the investigation of a renewable biopolymer-poly(lactic acid) (PLA) as a potential replacement of petroleum-based polymers in advanced nanocomposites reinforced with Microfibrillated cellulose (MFC). MFC is extracted from wood, which is a renewable, sustainable, carbon neutral and recyclable material. This advanced MFC-PLA bio- based composite material is expected to allow for the substitution of petroleum-based plastics in various markets and applications. The specific objectives of the thesis are: 1) to describe the morphological characterization of MFC used for prototype MFC-PLA composites, and 2) to determine the mechanical properties of the prototype MFC-PLA nanocomposites formulation generated in form of thin transparent films. In order to meet this objective it was necessary to: 2.1) develop a methodology for optical strain measurement in transparent thin films; and 2.2) develop an effective methodology for obtaining multiple mechanical properties from small number of specimens of prototype materials subjected to tensile tests. Two types of MFC, one obtained by courtesy of University of Maine and the other purchased from Innventia AB company, were investigated under a field emission scanning electron microscopy (FESEM). The micrographs obtained from FESEM showed that both types of MFC were of complex hierarchical structures, which did not allow qualitative characterization of the morphological features in terms of particulate composites nor cellular solids. Since prototype formulations of MFC-PLA composites were generated in small amounts (typically one Petri dish) in a form of thin transparent films, there was a need for quick and efficient assessment of their key mechanical properties that would provide feedback and guide further prototyping work. An optical measurement method based on digital image correlation (DIC) principle was developed to measure the deformation and strains of the tensile film samples. In our study, the accuracy and precision of the measurement of deformation were ±1.5 µm and 0.4 µm respectively. The corresponding accuracy and precision in terms of strains were ±30 µstrain and 75 µstrain respectively. This method can be successfully used to determine the critical mechanical properties, such as elastic modulus, toughness and Poisson's ratio, of transparent thin films by a single tensile test, all of which require precise strain measurement. In addition, this optical measurement method makes it possible to significantly simplify the testing for measuring essential work of fracture (EWF), an important material property of thin transparent films. In traditional method, measurement of EWF requires large amount of notched specimens. However, our study showed that only a small amount of notched specimens were needed to measure the EWF of a material. This method could not be successfully used to determine EWF from un-notched tensile specimens. / Graduation date: 2012 / Folder labeled "UMaine MFC aerogel" contains SEM micrographs of MFC from University of Maine (referred as type A MFC in the thesis). Two pieces of leaf-like flakes at different locations were cut by Focused Ion Beam (FIB) in order to observe the internal structure of the flakes. Folder "FIB_01 ": a series of SEM micrographs of FIB-cut flake at different magnification levels. Folder "FIB_02 ": another series of SEM micrographs of FIB-cut flake at various magnification levels. Folder labeled "Swedish MFC aerogel" contains SEM micrographs of MFC from Innventia AB company, Sweden (referred as type B MFC in the thesis). There is a series of SEM micrographs of type B MFC aerogel at various magnification levels in this folder.

Made available in DSpace on 2017-07-21T20:42:43Z (GMT). No. of bitstreams: 1 Nayana Reggiani Peres.pdf: 6432613 bytes, checksum: 9c46ae14abc57b5978dfcd678165787b (MD5) Previous issue date: 2013-12-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The development of new materials takes into account factors such as need and sustentabilidade.Novas trends in modifying properties of polymeric materials have been observed due to increasing concern about the environment and the constant search by the use of fillers in polymeric materials. Among them, there are the lignocellulosic fibers, which in addition to reinforcing the polymer, are biodegradable low cost, low density and have no abrasive characteristic. The agro-industrial residues are a great source of raw materials, especially in the case of soybean hulls, which is a waste in abundance in our region ( Paraná ). However, it is not always possible to obtain the best features with the Shell Soy Gross ( CSB ) . Thus , in a first step we sought to obtain microfibrillated pulp from the CSB . Conducted to obtain microfibrillated pulp by grinding the colloid mill, proven by analysis of Zeta Potential . And then be obtained twin screw extruder via nanocomposites with the incorporation of 1, 3 and 5% of microfibrillated cellulose. Finally, the nanocomposites were characterized by analysis of tensile test scanning electron microscopy, atomic force microscopy, X-ray diffraction, rheological analysis, thermogravimetry, and mechanical impact tests. Through the zeta potential was proved that the dimensions were namometricas the SEM and AFM demonstrated good adhesion of the microfibrillated cellulose, XRD confirmed the crystallinity. According to rheological analysis showed an increase in molecular weight , with the incorporation of cellulose microfibrillated there was a slight increase in impact strength, and an increase in the stiffness of nanocomposites. / O desenvolvimento de novos materiais leva em conta fatores como necessidade e sustentabilidade. Novas tendências na modificação de propriedades dos materiais poliméricos têm sido observadas devido à crescente preocupação com o meio ambiente e a constante busca pela utilização de cargas em materiais poliméricos. Entre elas, destacam-se as fibras lignocelulósicas, que além de reforçar o polímero, são biodegradáveis, de baixo custo, baixa massa específica e não possuem característica abrasiva. Os resíduos agroindustriais são uma ótima fonte de matériaprima, principalmente no caso da casca de soja, que é um resíduo em abundância em nossa região (Paraná). No entanto, nem sempre é possível obter as melhores características com a Casca de Soja Bruta (CSB). Deste modo, em uma primeira etapa buscou-se a obtenção de celulose microfibrilada, a partir da CSB. Realizou-se a obtenção da celulose microfibrilada através da moagem no moinho coloidal, comprovada pela análise de Potencial Zeta. E em seguida, obtiveram-se via extrusora dupla rosca os nanocompósitos com a incorporação de 1, 3 e 5% de celulose microfibrilada. Finalmente, os nanocompósitos foram caracterizados através das análises de microscopia eletrônica de varredura, microscopia de força atômica, difração de raios X, analise reológica, termogravimetria, ensaios mecânicos de impacto e ensaios mecânicos de tração. Através do potencial zeta provou-se que as dimensões são namometricas, o MEV e MFA comprovou a boa adesão da celulose microfibrilada, o DRX comprovou a cristalinidade. Segundo, a analise reológica houve aumento da massa molar. Com a incorporação da celulose microfibrilada houve um ligeiro aumento na resistência ao impacto, e um aumento na rigidez dos nanocompositos,

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

Microfibrillated cellulose (MFC) is an alternative material that has been widely studied to enhance the mechanical properties of a polymer matrix due to a number of perceived advantages over traditional plant fibre forms. Mechanical properties of MFC networks were found to depend on parameters such as the modulus of fibrils, bonding strength, porosity, degree of crystallinity, contact area of fibrils and possibly the modulus of the cellulose crystals of the raw materials (cellulose I or II). Even though the longer processing time used to produce MFC was found to yield networks with fewer fibre aggregates, finer fibrils and higher density, some properties, for instance thermal stability and degree of crystallinity, decreased due to the degradation of fibrils caused by the harsh treatment. The aims of this thesis were to assess the mechanical properties and interfaces of composites produced using of a range of MFC materials, prepared using different treatments and from different sources. Raman spectroscopy has been used to detect the molecular orientation of cellulose chains within an MFC network, and to monitor the deformation micromechanics of MFC networks. The Raman band initially located at ~1095 cm-1 obtained from MFC networks was observed to shift towards a lower wavenumber position upon the application of tensile deformation. The intensity of this band as a function of rotation angle of MFC networks was similar, indicating randomly oriented networks of fibrils. From the Raman band shift rate data, the effective moduli of MFC single fibrils produced from pulp were estimated to be in the range of 29-41 GPa. Poly(lactic acid) (PLA) composites reinforced with MFC networks were prepared using compression moulding. Enhanced mechanical properties of MFC reinforced composites were reported, compared to neat PLA films. The mechanical properties of these composites were found to mainly depend on the interaction of the PLA matrix and the reinforcement phase. The mechanical properties of the composites reinforced with dense networks were shown to be dominated by the network properties (fibril-fibril interactions), while matrix-fibril interactions played a major role where more opened networks were used to reinforce a polymer matrix. The penetration of the matrix into the network was found to depend on the pore sizes, fibre width and porosity within the network. It was found that the matrix easily penetrates into the network with a range of mean fibril dimensions, rather than for networks with only fine fibrils present. The stress-transfer process in MFC reinforced PLA composites was monitored using Raman spectroscopy. Greater Raman band shift rates with respect to tensile deformation for the composites were observed compared to pure MFC networks. This indicates that stress is transferred from the PLA matrix to MFC fibrils, supporting the enhancement of the mechanical properties of the composites.

Tato diplomová práce se zabývá přípravou nových kompozitů na bázi mikrofibrilované celulozy a multi-walls carbon nanotubes (MFC/MWCNTs). Tři různé metody byly použity pro modifikaci MWCNTs. Byl zkoumán vliv použitých modifikací na kvalitu MWCNTs suspense. Dále byly připraveny kompozity obsahující MFC a MWCNTs a vliv MWCNTs na mechanické a elektrické vlastnosti a morfologii byl zkoumán. MWCNTs suspense byly charakterizovány za použití UV-VIS spektrofotometrie, Rastrovacího elektronového mikroskopu (SEM) a Termogravimetrické analýzy (TGA). Elektrické vlastnosti byly měřeny pomocí Keithly Electrometer/High Resistivity Meter. Mechanické vlastnosti v tahu byly měřeny za použití Miniature Materials Tester a pro studium morfologie byl použit SEM. Žádný významný vliv MWCNTs na mechanické vlastnosti nebyl pozorován. Hodnoty získané z měření rezistivity vykazují typický perkolační trend a výrazného snížení rezistivity bylo dosaženo přidáním 1 – 2 wt.% MWCNTs. Nicméně hodnoty se velice liší pro horní a spodní stranu téhož vzorku. Ze získaných výsledků vyplývá, že klíčovým krokem ke zdokonalení vlastností materiálu jsou dobrá suspense MWCNTs a také dosažení vzájemné kompatibility obou složek.

The potential to use acidic hydrogen peroxide in the presence of ferrous ions (Fenton’s reagent) as a pre-treatment when producing microfibrillar cellulose (MFC) from a fully bleached birch (Betula verucosa) kraft pulp was investigated and the properties of the produced MFC was compared to the properties of a MFC produced with enzymatic pre-treatment with a monocomponent endoglucanase (FiberCare® R). The mechanical treatment to MFC was performed in a laboratory colloid mill or in a pilot high-pressure homogeniser and the pre-treated pulps as well as the produced MFCs were chemically and morphologically characterised. Additionally, the MFCs produced in the colloid mill were evaluated as strength enhancers in test sheets representing the middle ply of paperboard. From the chemical characterisation, it was concluded that the Fenton pre-treatment caused a decrease in the degree of polymerisation (DP) and an increase in both carboxyl- and carbonyl groups. The increase in carbonyl groups could not be explained by the formation of new reducing end groups due to depolymerisation which indicates that carbonyl groups are introduced along the cellulose chain. The enzymatic pre-treatment as performed in this study caused less impact on the cellulosic material, i.e. resulted in a pulp with a higher DP and a much lower amount of carbonyl- and carboxylic groups compared with the Fenton pre-treated pulps. In the subsequent mechanical treatment in a colloid mill, the Fenton pre-treated pulps were easier to process mechanically i.e. reached a higher specific surface area and a higher surface charge at a given mechanical treatment time compared to enzymatic pre-treated pulps and pulps not subjected to any pre-treatment. These findings were confirmed when MFCs were produced by homogenisation at high pressure in multiple passes; the birch kraft pulp was either pre-treated with Fenton’s reagent or the combined mechanic and enzymatic pre-treatment methodology used at the Centre Technique du Papier (CTP, France). By size fractionation, rheological measurements and scanning electron microscopy, it was revealed that Fenton pre-treatment resulted in MFC suspension containing a significantly higher proportion of small sized material (< 0.2 mm). When the MFCs were evaluated as strength enhancers in test sheets produced from a furnish consisting of a spruce (Picea abies) chemithermomechanical pulp, MFC and a retention system containing cationic starch and an anionic silica sol, Fenton pre-treated MFCs increased the strength properties more than the enzymatic pre-treated MFCs. Addition of 5 wt% Fenton pre-treated MFC resulted in an increase in z-directional strength of about 50%, an increase in tensile stiffness index of about 25% and an increase in tensile index of 35% compared to test sheets prepared without MFC addition. / The potential to use acidic hydrogen peroxide in the presence of ferrous ions (Fenton’s reagent) as a pre-treatment when producing microfibrillar cellulose (MFC) from a bleached birch kraft pulp was investigated and the properties of the produced MFC was compared to the properties of a MFC produced with enzymatic pre-treatment. Additionally, the MFCs evaluated as strength enhancers in test sheets representing the middle ply of paperboard. From the chemical characterisation, it was concluded that the Fenton pre-treatment caused a decrease in the degree of polymerisation (DP) and an increase in both carboxyl- and carbonyl groups. In the subsequent mechanical treatment in a colloid mill, the Fenton pre-treated pulps were easier to process mechanically indicating a potential to lower the energy consumption. When the MFCs were evaluated as strength enhancers in test sheets, Fenton pre-treated MFCs increased the strength properties more than the enzymatic pre-treated MFCs at a given mechanical treatment time. Addition of 5 wt% Fenton pre-treated MFC resulted in an increase in z-directional strength of about 50%, an increase in tensile stiffness index of about 25% and an increase in tensile index of 35% compared to test sheets prepared without MFC addition.

This thesis deals with processing of nanocellulose originating from pulps, with focus on mechanical pulp fibres and fines fractions. The nanocellulose materials produced within this research project were tested for different purposes ranging from strength additives in paper and paperboard products, via composite films to foam materials. TAPPI (Technical Association of Pulp &amp; Paper Industry) has recently suggested a standard terminology and nomenclature for nanocellulose materials (see paper I). In spite of that we have decided to use the terms nano-ligno-cellulose (NLC), microfibrillated cellulose (MFC), nanofibrillated cellulose (NFC) and nanocellulose (NC) in this thesis . It is well-known that mainly chemical pulps are used as starting material in nanocellulose production. However, chemical pulps as bleached sulphite and bleached kraft are quite expensive. One more cost-effective alternative can be to use fibres or fines fractions from thermo-mechanical pulp (TMP) and chemi-thermomechanical pulp (CTMP).   In paper II-IV, fractionation has been used to obtain fines fractions that can easily be mechanically treated using homogenisation. The idea with this study was to investigate the possibility to use fractions of low quality materials from fines fractions for the production of nanocellulose. The integration of a nanocellulose unit process in a high-yield pulping production line has a potential to become a future way to improve the quality level of traditional products such as paper and paperboard grades.   Paper III describes how to utilise the crill measurement technique as a tool for qualitative estimation of the amount of micro- and nano-material produced in a certain process. The crill values of TMP- and CTMP-based nanocelluloses were measured as a function of the homogenisation time. Results showed that the crill values of both TMP-NLC and CTMP-NLC correlated with the homogenisation time. In Paper V pretreating methods, hydrogen peroxide and TEMPO are evaluated. Crill measurement showed that hydrogen peroxide pretreatment (1% and 4%) and mechanical treatment time did not improve fibrillation efficiency as much as expected. However, for TEMPO-oxidised nanocelluloses, the crill value significantly increased with both the TEMPO chemical treatment and mechanical treatment time. In paper V-VII TEMPO-mediated oxidation systems (TEMPO/NaBr/NaClO) are applied to these fibres (CTMP and Sulphite pulp) in order to swell them so that it becomes easy to disrupt the fibres into nanofibres with mechanical treatment.   The demand for paperboard and other packaging materials are steadily increasing. Paper strength properties are crucial when the paperboard is to withstand high load. A solution that are investigated in papers IV and VI, is to use MFC as an alternative paper strength additive in papermaking. However, if one wish to target extremely higher strength improvement results, particularly for packaging paperboards, then it would be fair to use MFC or cationic starch (CS). In paper VI CS or TEMPO-based MFC was used to improve the strength properties of CTMP-based paperboard products. Results here indicate significant strength improvement with the use of different levels of CS (i.e., 20 and 10 kg t–1) and 5% MFC. The strengthening impact of 5% MFC was approximately equal to that of 10 kg t–1 of CS.   In paper VII, NFC and nanographite (NG) was used when producing composite films with enhanced sheet-resistance and mechanical properties. The films produced being quite stable, flexible, and bendable. Realising this concept of NFC-NG composite film would create new possibilities for technological advancement in the area of high-yield pulp technology.  Finally, in paper VIII, a new processing method for nanocellulose is introduced  where an organic acid (i.e., formic acid) is used. This eco-friendly approach has shown to be successful, a nanocellulose with a uniform size distribution has been produced. / <p>Vid tidpunkten för disputationen var följande delarbeten opublicerade: delarbete 5 och 7 inskickade, delarbete 6 och 8 manuskript.</p><p>At the time of the doctoral defence the following papers were unpublished: paper 5 and 7 submitted, paper 6 and 8 manuscripts.</p>

Fort d’une croissance annuelle de l’ordre de 6%, le secteur des matériaux composites est actuellement en pleine expansion et se doit de répondre aux exigences d’un marché en constante évolution. Dans le même temps, la raréfaction des ressources pétrolières et l’augmentation de la conscience environnementale, conduisent à une demande croissante en matériaux bio-composites. Le remplacement des fibres synthétiques (fibre de verre en particulier) par des fibres naturelles engendre un intérêt certain dont les motivations principales sont la réduction de l’impact environnemental, la diminution des coûts et l’obtention d’un matériau plus léger à volume égal. Néanmoins, la faible compatibilité existante entre les fibres de cellulose hydrophiles et les matrices polymères hydrophobes, est un des inconvénients majeurs qui nuit au bon développement de ces matériaux. L’objectif de cette thèse est de développer une alternative aux fibres de verre pour l’élaboration de matériaux composites à matrice thermoplastique. Pour ce faire, l’intégration de filaments de cellulose (FC), fournis par Kruger notre partenaire industriel, a été étudiée. En plus d’apporter un côté « vert » au matériau final, les FC permettent de réduire le poids des composites par rapport à leurs homologues synthétiques. Néanmoins, la faible compatibilité entre les filaments polaires et la matrice apolaire ainsi que la grande capacité d’absorption d’eau des FC nous a conduit à développer différentes stratégies de modification chimique des FC, afin d’en accroitre le caractère hydrophobe. Ces modifications ont permis de renforcer les matériaux composites grâce à l’amélioration de l’adhésion entre les FC et la matrice, le tout en minimisant la perte de résistance mécanique causée par l’absorption d’eau. Les résultats obtenus après acétylation, alkylation et encollage sont décrits dans ce manuscrit. / Over the past two decades, the increase of environmental concerns and shortage of petroleum resources have provoked a growing interest in the use of natural fibers as an alternative to synthetic fibers for the reinforcement of composites. Natural fibers possess desirable specific properties including biodegradability, renewability and low-cost. In addition, they have densities much lower than synthetic fibers, which makes them interesting for different applications ranging from automotive parts to packaging. Despite their benefits, certain drawbacks such as incompatibility with the hydrophobic polymer matrix, a tendency to form aggregates during processing and a poor resistance to moisture absorption, reduce the potential of these fibers to be used as a reinforcement of hydrophobic thermoplastic matrices.This thesis aims to substitute glass fibers by cellulose fibers for their use in fiber-reinforced composites. Reinforcement of LDPE composites with cellulose filaments (CF), supplied by our industrial partner Kruger, was studied. CF appear to an interesting alternative to glass fibers because they possess desirable specific properties including biodegradability, low density, high tensile strength and modulus as well as providing a low-cost and renewable option. However, the weak interfacial adhesion between CF and LDPE, and the high moisture absorption of CF led us to carry out several chemical modifications of CF in order to increase their hydrophobicity. Modified CF-composites exhibit higher mechanical properties and lower water uptake than unmodified CF-composites. Results obtained from acetylation, alkylation and paper sizing are described in this manuscript.

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

This work describes three alternative processes for producing microfibrillated cellulose (MFC; also referred to as cellulose nanofibrils, CNF) in which bleached pulp fibres are first pretreated and then homogenized using a high-pressure homogenizer. In one process, fibre cell wall delamination was facilitated by a combined enzymatic and mechanical pretreatment. In the two other processes, cell wall delamination was facilitated by pretreatments that introduced anionically charged groups into the fibre wall, by means of either a carboxymethylation reaction or irreversibly attaching carboxymethylcellulose (CMC) to the fibres. All three processes are industrially feasible and enable energy-efficient production of MFC. Using these processes, MFC can be produced with an energy consumption of 500–2300 kWh/tonne. These materials have been characterized in various ways and it has been demonstrated that the produced MFCs are approximately 5–30 nm wide and up to several microns long. The MFCs were also evaluated in a number of applications in paper. The carboxymethylated MFC was used to prepare strong free-standing barrier films and to coat wood-containing papers to improve the surface strength and reduce the linting propensity of the papers. MFC, produced with an enzymatic pretreatment, was also produced at pilot scale and was studied in a pilot-scale paper making trial as a strength agent added at the wet-end for highly filled papers. / <p>QC 20150126</p>