Plastic pollution is one of the most pressing environmental issues in today’s world. Addressing this problem calls for the development of environmentally friendly alternatives that would reduce the amount of persistent plastic waste. Wood-based cellulose is an excellent candidate as a renewable and biodegradable alternative to oil-based plastics in a variety of applications. However, for their widespread adoption, cellulosic materials need to perform comparably to their oil-based counterparts, while simultaneously attaining similarly high processing efficiencies. A major challenge today is to produce high-performance cellulosic materials at industrially feasible rates using scalable methods. 

This thesis demonstrates that with a fundamental understanding of fiber chemistry and behavior, cellulose fibers can be tuned to develop sustainable material streams and advanced functional materials at high process rates. First, a new stimuli-responsive cellulosic fiber material called self-fibrillating fibers (SFFs) was developed, where the mechanisms governing the swelling of the fiber wall were thoroughly investigated. The knowledge and understanding obtained from these fundamental studies were utilized to prepare pH-responsive filters. Secondly, the preparation of SFF papers and nanopapers using conventional papermaking methods and equipment was demonstrated within the context of rapid transparent paper preparation. It was shown that SFFs can be rapidly dewatered to obtain papers, where the constituting fibers can be nanofibrillated in situ, resulting in strong, transparent and gas barrier nanopapers without sacrificing processing speed. Thirdly, the use of SFFs was extended to functional nanocomposites. A new and scalable materials processing platform for the rapid preparation of functional cellulose hybrids was developed. The stimuli-responsive self-assembly of chemically nanofibrillated SFFs was studied and utilized to prepare nanopapers and hybrid materials. Finally, SFFs were used as bio-based binders in the fabrication of graphitic Li-ion battery electrodes with improved processing and electrochemistry. Taking advantage of their facile nanofibrillation and favorable chemistry, SFFs were nanofibrillated during slurry mixing then blade-coated on copper supports to create strong electrodes with excellent performance.

The novel materials and methodologies presented herein combine an aqueous fiber modification strategy with excellent processing properties for the preparation of high-performance cellulosic materials that can compete with oil-based plastics in various applications.

Plastföroreningar är en av de mest akuta miljöfrågorna i dagens värld. För att ta itu med problemet krävs en utveckling av miljövänliga alternativ som skulle kunna begränsa mängden icke nedbrytbart plastavfall. I träbaserade, cellulosarika fibrer utgör i detta avseende en utmärkt råvara som kan användas som ett förnyelsebart och biologiskt nedbrytbart alternativ till oljebaserade plaster i en rad olika tillämpningar. Cellulosamaterialen måste naturligtvis ha egenskaper som är i paritet med, eller bättre än, de oljebaserade materialen för att klara konkurrensen och samtidigt ha en konkurrenskraftig tillverkningsekonomi. En stor utmaning idag är därför att producera högpresterande cellulosamaterial med effektiva och skalbara processer.

Föreliggande avhandling visar att det mha grundläggande förståelse för fiberkemi och fibrernas fysikaliska beteende under olika kemiska betingelser att det är möjligt att skräddarsy vedbaserade fibrer så att det är möjligt att utveckla hållbara, avancerade funktionella material tom vid höga tillverkningshastigheter. Initialt utvecklades ett stimuli-känsligt cellulosafibermaterial, sk självfibrillerande fibrer (SFFs), som tillåter att fibrerna kan användas i konventionella arkformningsmetoder för att sedan sönderdelas till fibriller i det tillverkade arket som förvandlar det tillverkade arket till en genomskinlig film. Det visade sig att det var möjligt att snabbt avvattna de självfibrillerande fibrerna och mha en pH-höjning var det sedan möjligt attfibrillera de modifierade fibrerna  in-situ vilket resulterade i starka, transparenta nanopapper med goda barriäregenskaper. Med hjälp av avancerade karakteriseringsmetoder var det också möjligt att klarlägga de mekanismer som styr fibrillfriläggningen och svällningen hos fiberväggen i de modifierade fibrerna. Denna insikt, om hur de modifierade fibrerna sväller under olika betingelser, användes vidare för att tillverka pH-känsliga filter där avskiljningsförmåga och filtreringshastighet enkelt kan styras med enkla pH justeringar. De skräddarsydda, självfibrillerande fibrerna är naturligtvis mycket lämpade för användning i olika typer av kompositer och i avhandlingen visas hur SFF kan användas i olika typer av nanokompositer där de frilagda fibrillernas utmärkta mekaniska egenskaper kan utnyttjas i kombination med tex oorganiska, anisotropa material för att skapa kompositer med mycket goda barriäregenskaper och tex brandsäkra material. Genom att kombinera SFF med energilagrande aktiverat kol visade det sig också vara möjligt att tillverka batterielektroder för användning i Li-jon batterier där konventionella bindemedel kunde ersättas för att skapa elektroder med bättre egenskaper än det som idag finns i kommersiella Li-jon batterier. 

Alla dessa exempel visar att det nya SFF-materialet gör det möjligt att använda konventionella arkformningsmetoder för att skapa nya högpresterande material där det är möjligt att bibehålla en rimlig tillverkningshastighet och att framställa komponenter eller slutgiltiga anordningar som har egenskaper som kan konkurrera med högpresterande material som baseras på fossila råvaror.

Cellulose nanofibril (CNF) hybrid materials show great promise as sustainable alternatives to oil-based plastics owing to their abundance and renewability. Nonetheless, despite the enormous success achieved in preparing CNF hybrids at the laboratory scale, feasible implementation of these materials remains a major challenge due to the time-consuming and energy-intensive extraction and processing of CNFs. Here, we describe a scalable materials processing platform for rapid preparation (<10 min) of homogeneously distributed functional CNF-gibbsite and CNF-graphite hybrids through a pH-responsive self-assembly mechanism, followed by their application in gas barrier, flame retardancy, and energy storage materials. Incorporation of 5 wt % gibbsite results in strong, transparent, and oxygen barrier CNF-gibbsite hybrid films in 9 min. Increasing the gibbsite content to 20 wt % affords them self-extinguishing properties, while further lowering their dewatering time to 5 min. The strategy described herein also allows for the preparation of freestanding CNF-graphite hybrids (90 wt % graphite) that match the energy storage performance (330 mA h/g at low cycling rates) and processing speed (3 min dewatering) of commercial graphite anodes. Furthermore, these ecofriendly electrodes can be fully recycled, reformed, and reused while maintaining their initial performance. Overall, this versatile concept combines a green outlook with high processing speed and material performance, paving the way toward scalable processing of advanced ecofriendly hybrid materials. 

Cellulose nanofibers (CNFs) are bio-sourced nanomaterials, which, after proper chemical modification, exhibit a unique ability to disperse carbon-rich micro- and nanomaterials and can be used in the design of mechanically strong functional nanocomposites. When used in the preparation of graphite anodes for Li-ion batteries, they have the potential to outperform conventional binders such as carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) both electrochemically and mechanically. In this study, cellulose-rich fibers were subjected to three different chemical modifications (including carbonyl-, carboxyl-, and aldehyde-functionalization) to facilitate their fibrillation into CNFs during the preparation of aqueous slurries of graphite and carbon black. Using these binders, graphite anodes were prepared through conventional blade coating. Compared to CMC/SBR reference anodes, all anodes prepared with modified cellulosic fibers as binders performed better in the galvanostatic cycling experiments and in the mechanical cohesion tests they were subjected to. Among them, the aldehyde- and carboxyl-rich fibers performed the best and resulted in a 10% increase in specific capacity with a simultaneous two- and three-fold increase of the electrode material's stress-at-failure and strain-at-break, respectively. In-depth characterizations attributed these results to the distinctive nanostructure and surface chemistry of the composites formed between graphite and these fiber-based binders. 

Thorough characterization and fundamental understanding of cellulose fibers can help us develop new, sustainable material streams and advanced functional materials. As an emerging nanomaterial, cellulose nanofibrils (CNFs) have high specific surface area and good mechanical properties; however, handling and processing challenges have limited their widespread use. This work reports an in-depth characterization of self-fibrillating cellulose fibers (SFFs) and their use in smart, responsive filters capable of regulating flow and retaining nanoscale particles. By combining direct and indirect characterization methods with polyelectrolyte swelling theories, it was shown that introduction of charges and decreased supramolecular order in the fiber wall were responsible for the exceptional swelling and nanofibrillation of SFFs. Different microscopy techniques were used to visualize the swelling of SFFs before, during, and after nanofibrillation. Through filtration and pH adjustment, smart filters prepared via in situ nanofibrillation showed an ability to regulate the flow rate through the filter and a capacity of retaining 95% of 300 nm (diameter) silica nanoparticles. This exceptionally rapid and efficient approach for making smart filters directly addresses the challenges associated with dewatering of CNFs and bridges the gap between science and technology, making the widespread use of CNFs in high-performance materials a not-so-distant reality.

Cellulose nanofibrils (CNFs) prepared from wood biomass are promising candidates to replace oil-based materials in, for example, packaging applications. However, CNFs' affinity for water combined with their small size leads to very slow and energy-demanding processes for handling and removal of water. To a large extent, this is the major roadblock that prevents a feasible production of dry CNF-based materials on an industrial scale. In this work, self-fibrillating fibers (SFFs) from wood, where the fibrils can be liberated by external stimuli, were prepared via sequential TEMPO and periodate oxidation reactions. Papers made from these modified fibers using conventional laboratory papermaking methods were then in situ nanofibrillated via a modest pH increase. With a dewatering time of less than 10 s for a 3 g/L dispersion, SFFs represent a major improvement over conventional CNF nanopapers that take approximately 6 h to dewater. Moreover, 100 g/m2 nanopapers obtained through in situ fibrillation exhibited comparable, if not superior, properties to those reported for conventionally made CNF films. A tensile strength of 184 MPa, a Young's modulus of 5.2 GPa, a strain at break of 4.6%, 90% optical transmittance, and an oxygen permeability of 0.7 cm3 μm m-2 d-1 kPa-1 at 50% RH were measured for SFF nanopapers. Furthermore, in situ nanofibrillation of the SFFs can also be achieved from already dried papers, facilitating numerous possibilities in terms of logistics and handling for an industrial scale-up and transportation of nanomaterials. Overall, stimuli-induced SFFs indeed enable a rapid production of strong, transparent, gas barrier nanopapers, which likely can be industrially scaled up and eventually compete with the oil-based plastics in the market for packaging materials.