Developing ionotronic interface layers for zinc anodes with superior mechanical integrity is one of the efficient strategies to suppress the growth of zinc dendrites in favor of the cycling stability of aqueous zinc-ion batteries (AZIBs). Herein, we assembled robust 2D MXene-based hydrogel films cross-linked by 1D cellulose nanofibril (CNF) dual networks, acting as interface layers to stabilize Zn anodes. The MXene-CNF hydrogel films integrated multifunctionalities, including a high in-plane toughness of 18.39 MJ m-3, high in-plane/out-of-plane elastic modulus of 0.85 and 3.65 GPa, mixed electronic/ionic (ionotronic) conductivity of 1.53 S cm-1 and 0.52 mS cm-1, and high zincophilicity with a high binding energy (1.33 eV) and low migration energy barrier (0.24 eV) for Zn2+. These integrated multifunctionalities, endowed with coupled multifield effects, including strong stress confinement and uniform ionic/electronic field distributions on Zn anodes, effectively suppressed dendrite growth, as proven by experiments and simulations. An example of the MXene-CNF|Zn showed a reduced nucleation overpotential of 19 mV, an extended cycling life of over 2700 h in Zn||Zn cells, and a high capacity of 323 mAh g-1 in Zn||MnO2 cells, compared with bare Zn. This work offers an approach for exploring mechanically robust 1D/2D ionotronic hydrogel interface layers to stabilize the Zn anodes of AZIBs.

Cellulose-based aerogels are emerging bio-based materials for a range of applications in the quest toward a circular and carbon-neutral society. Owing to their lightweight nature, high porosity, high specific surface area, biocompatibility, and biodegradability, cellulose aerogels are suitable for packaging, insulation, wound care products, hygiene products, and water purification. However, their commercial use is hampered by complicated time- and energy-consuming fabrication processes. Hence, industrially relevant processes with upscaling opportunities need to be developed for cellulose-based aerogels to reach their full potential. 

This thesis explores different scalable and simple methods for preparing and designing highly porous aerogels with high wet integrity using cellulose-rich fibers and cellulose nanofibrils (CNFs). As wet integrity is crucial for specific applications and enables further functionalization of the aerogels using water-based chemistry, different methods were developed to achieve wet integrity without complicated crosslinking procedures. The effects of the raw materials and processing methods on the final material properties were also carefully studied to optimize the performance for the targeted applications. Moreover, the role of the network-forming ability of CNFs in the development of functional materials with structural integrity was explored by incorporating small amounts of CNFs in aerogel systems based on macroscopic cellulose-rich fibers and nanosized metal-organic frameworks. 

Finally, the potential of the different developed cellulose-based or cellulose-reinforced aerogels with high wet integrity was demonstrated in applications for which the aerogels’ structural integrity and physical and mechanical properties are highly advantageous, such as biomedical applications, gas storage and separation, flame retardancy, and hygiene products. As demonstrated in this thesis, these functional aerogel materials could be a bio-based alternative for today’s fossil-based materials. 

Cellulosabaserade aerogeler har på senare tid visat sig vara användbara biobaserade material för olika tillämpningar i strävan mot ett cirkulärt och kolneutralt samhälle. Materialens mycket låga densitet, höga porositet, höga specifika yta, biokompatibilitet och biologiska nedbrytbarhet innebär att cellulosaaerogeler är lämpliga för förpackningar, isolering, sårvårdsprodukter, hygienprodukter och vattenrening. Den kommersiella användningen har dock bromsats av komplicerade, tid- och energikrävande tillverkningsmetoder. Därmed måste industriellt relevanta processer med uppskalningsmöjligheter utvecklas för att cellulosabaserade aerogeler ska nå sin fulla potential. 

Denna avhandling utforskar olika skalbara och enkla metoder för att bereda och skräddarsy högporösa och våtstabila aerogeler från cellulosafibrer och cellulosananofibriller (CNFer). Eftersom våtstabilitet är avgörande för vissa tillämpningar och möjliggör ytterligare funktionalisering med vattenbaserad kemi, har ett omfattande arbete genomförts för att identifiera nya metoder för att skapa en god våtstabilitet utan att använda komplicerade tvärbindningsprocedurer. Ett stort fokus har även lagts på att klarlägga råvarans och bearbetningsmetodernas inverkan på de slutliga materialegenskaperna för att optimera prestandan för riktade tillämpningar. Dessutom har CNFers unika nätverksbildande egenskaper också utforskats i att skapa funktionella material med strukturell integritet från mycket små mängder CNFer i aerogelsystem baserade på makroskopiska cellulosarika fibrer och nanopartiklar av metallorganiska nätverk.

Slutligen demonstrerades potentialen av de framställda cellulosabaserade och cellulosaförstärkta aerogelerna med utmärkt våtstyrka i tillämpningar där deras strukturella integritet, fysikaliska och mekaniska egenskaper kan användas på ett mycket fördelaktigt sätt, till exempel biomedicinska applikationer, gaslagring och -separering, flamskydd, och hygienprodukter. Mot bakgrund av dessa resultat är det alltså rimligt att slå fast att dessa funktionella aerogeler kan utgöra möjliga biobaserade alternativ till dagens fossilbaserade material.

Highly anisotropic cellulose nanofibrils can solidify liquid water, creating self-supporting structures by incorporating a tiny number of fibrils. These fibrillar hydrogels can contain as much as 99.99 wt% water. The structure and mechanical properties of fibrillar networks have so far not been completely understood, nor how they solidify the bulk water at such low particle concentrations. In this work, the mechanical properties of cellulose fibrillar hydrogels in the dilute regime from a wt% perspective have been studied, and an elastoplastic model describing the network structure and its mechanics is presented. A significant insight from this work is that the ability of the fibrils to solidify water is very dependent on particle stiffness and the number of contact points it can form in the network structure. The comparison between the experimental results and the theoretical model shows that the fibrillar networks in the dilute regime form via a non-stochastic process since the fibrils have the time and freedom to find contact points during network formation by translational and rotational diffusion. The formed, dilute fibrillar network deforms by sliding fibril contacts upon straining the network beyond its elastic limit. Our results also show that before macroscopic failure, the fibril contacts are restored once the load is released. The exceptional properties of this solidified water are exploited to host fluidic channels, allowing directed fluid transportation in water. Finally, the microfluidic channels formed in the hydrogels are tailored by the layer-by-layer technique to be interactive against external stimuli, a characteristic envisioned to be useful in biomedical applications.

Tunable dynamic networks of cellulose nanofibrils (CNFs) are utilized to prepare high-performance polymer gel electrolytes. By swelling an anisotropically dewatered, but never dried, CNF gel in acidic salt solutions, a highly sparse network is constructed with a fraction of CNFs as low as 0.9%, taking advantage of the very high aspect ratio and the ultra-thin thickness of the CNFs (micrometers long and 2–4 nm thick). These CNF networks expose high interfacial areas and can accommodate massive amounts of the ionic conductive liquid polyethylene glycol-based electrolyte into strong homogeneous gel electrolytes. In addition to the reinforced mechanical properties, the presence of the CNFs simultaneously enhances the ionic conductivity due to their excellent strong water-binding capacity according to computational simulations. This strategy renders the electrolyte a room-temperature ionic conductivity of 0.61 ± 0.12 mS cm−1 which is one of the highest among polymer gel electrolytes. The electrolyte shows superior performances as a separator for lithium iron phosphate half-cells in high specific capacity (161 mAh g−1 at 0.1C), excellent rate capability (5C), and cycling stability (94% capacity retention after 300 cycles at 1C) at 60 °C, as well as stable room temperature cycling performance and considerably improved safety compared with commercial liquid electrolyte systems.

Fibrillar hydrogels are remarkably stiff, low-density networks that can hold vast amounts of water. These hydrogels can easily be made anisotropic by orienting the fibrils using different methods. Unlike the detailed and established descriptions of polymer gels, there is no coherent theoretical framework describing the elastoplastic behavior of fibrillar gels, especially concerning anisotropy. In this work, the swelling pressures of anisotropic fibrillar hydrogels made from cellulose nanofibrils were measured in the direction perpendicular to the fibril alignment. This experimental data was used to develop a model comprising three mechanical elements representing the network and the osmotic pressure due to non-ionic and ionic surface groups on the fibrils. At low solidity, the stiffness of the hydrogels was dominated by the ionic swelling pressure governed by the osmotic ingress of water. Fibrils with different functionality show the influence of aspect ratio, chemical functionality, and the remaining amount of hemicelluloses. This general model describes physically crosslinked hydrogels comprising fibrils with high flexural rigidity - that is, with a persistence length larger than the mesh size. The experimental technique is a framework to study and understand the importance of fibrillar networks for the evolution of multicellular organisms, like plants, and the influence of different components in plant cell walls.

A multifunctional soft material with high ionic and electrical conductivity, combined with high mechanical properties and the ability to change shape can enable bioinspired responsive devices and systems. The incorporation of all these characteristics in a single material is very challenging, as the improvement of one property tends to reduce other properties. Here, a nanocomposite film based on charged, high-aspect-ratio 1D flexible nanocellulose fibrils, and 2D Ti3C2Tx MXene is presented. The self-assembly process results in a stratified structure with the nanoparticles aligned in-plane, providing high ionotronic conductivity and mechanical strength, as well as large water uptake. In hydrogel form with 20 wt% liquid, the electrical conductivity is over 200 S cm−1 and the in-plane tensile strength is close to 100 MPa. This multifunctional performance results from the uniquely layered composite structure at nano- and mesoscales. A new type of electrical soft actuator is assembled where voltage as low as ±1 V resulted in osmotic effects and giant reversible out-of-plane swelling, reaching 85% strain.

Metal–organic frameworks (MOFs) are hybrid porous crystalline networks with tunable chemical and structural properties. However, their excellent potential is limited in practical applications by their hard-to-shape powder form, making it challenging to assemble MOFs into macroscopic composites with mechanical integrity. While a binder matrix enables hybrid materials, such materials have a limited MOF content and thus limited functionality. To overcome this challenge, nanoMOFs are combined with tailored same-charge high-aspect-ratio cellulose nanofibrils (CNFs) to manufacture robust, wet-stable, and multifunctional MOF-based aerogels with 90 wt% nanoMOF loading. The porous aerogel architectures show excellent potential for practical applications such as efficient water purification, CO2 and CH4 gas adsorption and separation, and fire-safe insulation. Moreover, a one-step carbonization process enables these aerogels as effective structural energy-storage electrodes. This work exhibits the unique ability of high-aspect-ratio CNFs to bind large amounts of nanoMOFs in structured materials with outstanding mechanical integrity—a quality that is preserved even after carbonization. The demonstrated process is simple and fully discloses the intrinsic potential of the nanoMOFs, resulting in synergetic properties not found in the components alone, thus paving the way for MOFs in macroscopic multifunctional composites. 

Multifunctional, light-weight, responsive materials show promise in a range of applications including soft robotics, therapeutic delivery, advanced diagnostics and charge storage. This paper presents a novel, scalable, efficient and sustainable approach for the preparation of cellulose nanofibril-based aerogels via a facile ice-templating, solvent exchange and air-drying procedure, which could replace existing inefficient drying processes. These ambient-dried aerogels (similar to 99% porosity) exhibit a high specific compressive modulus (26.8 +/- 6.1 kPa m(3) kg(-1), approaching equivalence of carbon-nanotubereinforced aerogels), wet stability and shape recovery (80-90%), favorable specific surface area (90 m(2) g(-1)) and tunable densities (2-20 kg m(-3)). The aerogels provide an ideal nanofibrillar substrate for in-situ growth of metal-organic frameworks (MOFs), via co-assembly of MOF precursors with proteins in aqueous solutions. The resulting hybrid aerogels show a nine-fold increase in surface area (810 m(2)g(-1)), with preserved wet stability and additional protein biofunctionality. The hybrid aerogels facilitate a pH-controlled release of immobilized proteins, following a concomitant disassembly of the surface grown MOFs, demonstrating their use in controlled delivery systems. The colorimetric protein binding assay of the biofunctionalized hybrid aerogel also demonstrates the potential of the material as a novel 3D bioassay platform, which could potentially be an alternative to plate-based enzyme-linked immunosorbent assay.

This paper investigates a strategy to convert hydrophilic cellulose nanofibrils (CNF) into a hydrophobic highly cross-linked network made of cellulose nanofibrils and inorganic nanoparticles. First, the cellulose nanofibrils were chemically modified through an esterification reaction to produce a nanocellulose-based macroinitiator. Barium titanate (BaTiO3, BTO) nanoparticles were surface-modified by introducing a specific monomer on their outer-shell surface. Finally, we studied the ability of the nanocellulose-based macroinitiator to initiate a single electron transfer living radical polymerization of stearyl acrylate (SA) in the presence of the surface-modified nanoparticles. The BTO nanoparticles will transfer new properties to the nanocellulose network and act as a cross-linking agent between the nanocellulose fibrils, while the monomer (SA) directly influences the hydrophilic-lipophilic balance. The pristine CNF and the nanoparticle cross-linked CNF are characterized by FTIR, SEM, and solid-state 13C NMR. Rheological and dynamic mechanical analyses revealed a high dregee of cross-linking.

A strategy is devised to synthesize zwitterionic acetylated cellulose nanofibrils (CNF). The strategy included acetylation, periodate oxidation, Schiff base reaction, borohydride reduction, and a quaternary ammonium reaction. Acetylation was performed in glacial acetic acid with a short reaction time of 90 min, yielding, on average, mono-acetylated CNF with hydroxyl groups available for further modification. The products from each step were characterized by FTIR spectroscopy, ζ-potential, SEM-EDS, AFM, and titration to track and verify the structural changes along the sequential modification route.