The properties of hydrated nanocellulose network structures
Time: Fri 2024-05-24 10.00
Location: F3 (Flodis), Lindstedtsvägen 26
Language: English
Subject area: Fibre and Polymer Science
Doctoral student: Rebecca Östmans , Fiberteknologi, Wallenberg Wood Science Center, Wallenberg Wood Science Center, Fibre Technology
Opponent: Professor Monika Österberg, Department of Bioproducts and Biosystems, School of Chemical Engineering, Aalto University, Vuorimiehentie 1, Espoo, 02150, Finland
Supervisor: Professor Lars Wågberg, VinnExcellens Centrum BiMaC Innovation, Linné Flow Center, FLOW, Fiberteknologi, Wallenberg Wood Science Center; Doktor Tobias Benselfelt, Wallenberg Wood Science Center, Ytbehandlingsteknik, Fiberteknologi; Universitetslektor Torbjörn Pettersson, VinnExcellens Centrum BiMaC Innovation, Fiber- och polymerteknologi
QC 2024-04-30
Embargo godkänt av skolchef Amelie Eriksson Karlström via e-post 2024-04-18.
Abstract
Long, slender cellulose nanofibrils (CNF) are unique with their high axial modulus, small diameter, high flexibility, and the possibility of chemical tailoring of, among other things, their surface charge density. The objective of this work has been to elucidate how the hydrogel network properties and how their related deformation mechanisms depend on CNF properties, concentration, and chemical environment. In addition, the influence of CNF characteristics on the formation of the structure and properties of isotropic hydrogels, anisotropic hydrogels, and aerogels has been studied.
This was done by combining theoretical models describing the CNF network's topology and mechanics with high-resolution experiments to validate the theoretical models. Furthermore, the properties of the fibrils have been characterized in detail and linked to the material properties of materials formed from the fibrils. Finally, the CNF networks in this work have been functionalized in two different ways. In the first case, a flow channel was created within the hydrogel network at extremely low CNF concentrations, that could be surface treated with a Layer-by-layer (LbL) methodology with a consecutive addition of oppositely charged polyelectrolytes/nanoparticles to add new functionalities to the channels. Secondly, wet stable aerogels, prepared at higher concentrations of CNFs, were treated using the LbL methodology to adjust the aerogels' surface structure and surface energy, thereby controlling the liquid spreading rate properties of the formed networks.
The most important findings in this work are that CNF network topology and network mechanics can be described using theoretical, rather non-complicated, elastoplastic models. Furthermore, at lower concentrations of CNFs, the network structure is formed in a more organized way, meaning that the fibrils have the time and freedom to seek their optimal contact points during the network formation from a thermodynamic free energy point of view. It has also been shown that the low-density, wet fibrillar network structures formed by neutralizing the charges of the fibrils deform by sliding in fibril/fibril contacts upon straining the network structure above a critical stress. These fibril/fibril contacts are also shown to be re-established when the stress is released, provided that the networks have not been subjected to a macroscopic collapse. Finally, these cellulose networks show great potential for further functionalization using the LbL modification methodology.