Les performances exceptionnelles des composites naturels comme la nacre ou le bois émergent de l’arrangement précis d’éléments souples et rigides à l’échelle nanométrique. L’assemblage couche-par-couche permet la fabrication de films avec un contrôle nanométrique de l’organisation et de la composition. Ce travail décrit l’assemblage et les propriétés de nouveaux nano-composites contenant des nano-renforts 1-D (fibrilles de cellulose) et 2-D (plaquettes d’argile). Nous avons combiné les argiles avec une matrice extrêmement souple de poly(diméthylsiloxane) dans une architecture lamellaire imitant celle de la nacre. Nous avons étudié des composites à base de fibrilles de cellulose aléatoirement orientées dans le plan, puis alignées dans une direction pour mieux imiter les parois cellulaires du bois. Les propriétés mécaniques de ces composites bio-inspirés égalent ou surpassent celles de leurs homologues naturels, tout en étant transparents et dans certains cas auto-réparants. / Natural materials such as nacre or wood gain their exceptional mechanical performances from the precise organisation of rigid and soft components at the nano-scale. Layer-by-layer assembly allows the preparation of films with a nano-scale control over their organisation and composition. This work describes the assembly and properties of new nano-composites containing 1-D (cellulose nano-fibrils) and 2-D (clay nano-platelets) reinforcing elements. The clay platelets were combined with an extremely soft matrix (poly(dimethylsiloxane)) to mimic the lamellar architecture of nacre. Cellulose based composites with a random in plane orientation of the fibrils were studied first, later we aligned the fibrils in a single direction to mimic further the cell wall of wood. The mechanical properties of these bio-inspired composites match or surpass those of their natural counterparts, while being transparent and in one case self-repairing.

This thesis contributes to a development of a method for rheological characterization of microfibrillated cellulose. The intended use of the method is to be able to distinguish between different grades of microfibrillated cellulose. The method that was developed had preparation procedure of suspensions, pH, dry content and conductivity as well as measuring geometry and measuring sequence in mind. The method resulted in using a propeller mixer for sample preparation and the most suitable properties of the samples for comparison of different qualities of microfibrillated cellulose was evaluated to be pH 8 with a dry content of 2.0 wt% and a conductivity of 110 µS/cm. The rheology of the microfibrillated cellulose suspensions was examined by using a dynamic rotational rheometer and a splined bob and cup (C25G/PC25G). The complex viscosity from amplitude sweeps is used as the parameter to distinguish between different grades of 2 wt% microfibrillated cellulose suspensions. At 1.0 wt% the pH of the suspensions appeared to have a very small impact on the results from rheological measurements while an increased conductivity of the suspensions resulted in an increased complex viscosity. The dry content dependency appeared to be exponential in the range of 0.5 to 3.0 wt% and it was thus easier to distinguish between different grades of microfibrillated cellulose when the dry content is 2.0 wt% compared to 1.0 or 1.5 wt%.

This work describes three alternative processes for producing microfibrillated cellulose (MFC) in which pulp fibres are first pre-treated and then homogenized using a high-pressure homogenizer. In one process, fibre cell wall delamination was facilitated with a combined enzymatic and mechanical pre-treatment. In the two other processes, cell wall delamination was facilitated by pre-treatments that introduced anionically charged groups into the fibre wall, by means of either a carboxymethylation reaction or irreversibly attaching carboxymethyl cellulose (CMC) onto the fibres. All three processes are industrially feasible and enable production with low energy consumption. Using these methods, MFC can be produced with an energy consumption of 500–2300 kWh/tonne, which corresponds to a 91–98% reduction in energy consumption from that presented in earlier studies. 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. / <p>QC 20120928</p>

Today, the focus lies on the state of the environment and how we can choose more sustainable alternatives to oil based materials. One material of interest is microfibrillated cellulose (MFC).The microfibril exhibits interesting properties, which one is its excellent barrier properties, that is expected to come in good use for the conversion to a more sustainable society. It is believed that the use of biobased barriers will increase with these new materials and MFC is showing promising results. But in order to develop the material to its full potential, it is important to investigate how MFC behaves in different situations, which can be examined with rheological measurements. The aim of the thesis is to examine how the rheological properties of suspensions containing MFC are affected by temperature and time storing and how the learning from this work can be used for influencing dispersion properties. Four samples were investigated, containing different amounts of MFC and modified waxy maize starch. The samples were analyzed with a dynamic rotational rheometer (Kinexus Pro +) with a splined cup and bob. The following steps were included in the method development used in this work: sample preparation, the repeatability, rest time and statistical analysis. An oscillatory shear and steady shear measurement was performed on the samples, and selected samples were studied with microscopy. The results show that the temperature has affected the samples. The shear viscosity of all samples decreased with increasing temperature and the samples followed the temperature dependence of Arrhenius' equation. For samples containing MFC, the structure was affected, and the initial viscosity was not recovered. The complex viscosity did also decrease at the beginning to then suggestively increase, creating a stronger network at higher temperatures. With the raised temperature the bonding between the fibrils became weaker, which in turn made the dispersion less viscous. Then, depending on the applied force, the shear viscosity and complex viscosity acted differently. To conclude, both the shear viscosity and the complex viscosity in these dispersions containing MFC are dependent on the temperature and time storing. By the learnings from this work, a method has been developed to understand how to use temperature and storing time to lower the shear viscosity and lower, or increase, the complex viscosity. / Idag ligger det ett stort fokus på miljöns tillstånd och hur vi kan välja mer hållbara alternativjämfört med oljebaserade material. Ett material av intresse är mikrofibrillerad cellulosa (MFC).Denna mikrofibrill besitter intressanta egenskaper, varav en är enastående barriäregenskaper,som förväntas komma till god användning i omställningen till ett mer hållbart samhälle. Det tros att biobaserade barriärer kommer att användas mer i dessa nya material och här visar MFC lovande resultat. Men för att kunna utveckla materialet till sin fulla potential är det viktigt att undersöka hur MFC beter sig i olika situationer, som kan undersökas genom reologiska mätningar. Syftet med arbetet är att undersöka hur de reologiska egenskaperna för suspensioner innehållande MFC påverkas av temperatur och lagringstid samt hur lärdomen från det här arbetet kan användas för att påverka dispersionsegenskaper. Fyra prover undersöktes,innehållande olika mängd MFC och modifierad majsstärkelse. Proverna analyserades med en dynamisk rotations reometer (Kinexus Pro +) med räfflad kopp och bob. Följande steg ingick i metodutvecklingen som användes i detta arbete: provberedning, repeterbarhet, vilotid och statistisk analys. En oscillerande skjuvning och jämn skjuvmätning utfördes på de olika proverna samt att utvalda prover studerades med mikroskopi. Resultatet visade att temperaturen hade påverkat proverna. Skjuvviskositeten för alla prover minskade med en ökande temperatur och proverna följde temperaturberoendet av Arrhenius ekvation. För prover innehållande MFC påverkades strukturen och startviskositeten återficks inte. Den komplexa viskositeten minskade också till en början för att sedan suggestivt öka, vilket skapade ett starkare nätverk vid högre temperaturer. Med en högre temperatur blev bindningarna mellan fibrillerna svagare, vilket bidrog att dispersionerna blev mindre viskösa. Beroende på den applicerade kraften, verkade skjuvviskositeten och den komplexa viskositeten olika. Slutsatsen var att både skjuvviskositeten och den komplexa viskositeten i dessa prover innehållande MFC beroende av temperaturen och lagringstid. Från lärdomen av arbetet har en metod tagits fram för att kunna använda temperatur och lagringstid för att sänka skjuvviskositeten och sänka, eller öka, den komplexa viskositeten.