Nanocelluloses are a novel class of materials, which have drawn significant interest due to their potential for high-performance sustainable materials. Cellulose nanofibrils (CNF) are an important subcategory of nanocelluloses, and this thesis explores possible routes for their processing in orderto achieve novel property combinations. Their morphology and surface properties as chemo-physical substrates are considered central for this purpose. Several polysaccharides adsorb irreversibly on the CNF surface upon mixing in aqueous conditions. Exploiting this tendency, Publication 1 presents a facile strategy for enhancing the properties of CNF-based materials, namely the wet mechanical properties, by physical adsorption of a stimulus-responsive polysaccharide. The CNF surface allows versatile covalent surface modifications. The introduction of surface charge enables CNF to complex with oppositely charged compounds. Publication 2 demonstrates the feasibilityof forming strong continuous CNF-based fibers by interfacial surface complexation with polyelectrolytes. This further enables facile fabrication of strictly compartmentalized bicomponent fibers, which can exhibit humidity-driven shape change. CNF are an attractive material for high-performance fibers, but their uniaxial alignment by stretching results in embrittlement. Publication 3 explores the alignment of CNF by shear forces during extrusion. The use of long extrusion capillaries lead to alignment of the fibrils, and consequently stiff and strong fibers, but in contrast to the literature, without reducing extensibility. The explored processing route leads to CNF-based fibers of high toughness. CNF have a very high persistence length and the fibrils readily bond to each other by hydrogen bonding. Therefore, CNF are well suited to fabricate porous materials, such as aerogels. Publication 4 demonstrates the feasibility of ambient drying of transparent CNF aerogel membranes and their use for fabricating transparent conductors by collecting a network of single-walled carbon nanotubes from a gas-phase synthesis process. A CNF dispersion typically consists of fibrils with a distribution of diameters. Publication 5 demonstrates the tunability of the scattering properties of CNF-based materials by their porosity and constituent diameter distribution. Interestingly, light was shown to undergo superdiffusion in these strongly scattering materials. This thesis gives insight on how the fundamental properties of CNF relate to the possible processing routes, and further to the feasibility of various property combinations, of CNF-based materials. The recognized processing routes offer direct possibilities from the industrial point of view, and the novel property combinations further extend the scope of potential applications of nanocelluloses.
|Translated title of the contribution||Selluloosan nanokuituihin perustuvat materiaalit|
|Publication status||Published - 2018|
|MoE publication type||G5 Doctoral dissertation (article)|
- nanocellulose, cellulose nanofibrils, processing, aerogel, porosity, polyelectrolyte complexation