There has been a recent surge of interest in biobased foams for applications ranging from building sustainability (insulation) to biomedicine, pharmaceutics, and electronics (scaffolds), with nanocellulose-based foams being particularly promising due to their porous and low-density structure. This study compares the production energy, structure, and properties of foams made from TEMPO-oxidized lignocellulose nanofibers (FTOLCNF) derived from unbleached wood pulp, and TEMPO-oxidized cellulose nanofibers (FTOCNF) from bleached cellulose pulp. Additionally, the incorporation of tannic acid (TA) as a biobased additive is explored for its ability to enhance the mechanical strength of FTOLCNF, contributing to improved performance. This builds upon the inherent advantages of FTOLCNF, which not only demonstrate superior structural integrity and load-bearing capacity (specific Young’s modulus of 37.4 J g–1, compared to 16.4 J g–1 for TOCNF) but also exhibit a higher yield during production due to the minimal processing required for unbleached pulp. Furthermore, FTOLCNF production requires about 18% less cumulative energy than FTOCNF (27 vs 33 MJ kg–1), largely owing to the energy-efficient preparation of TOLCNF from unbleached wood pulp. FTOLCNF also have a significantly lower cumulative energy demand (CED) compared to fossil-based alternatives like expanded polystyrene (EPS) and polyurethane (PU), highlighting their reduced environmental impact. Despite their lightweight nature, FTOLCNF exhibit competitive compressive strength, making them viable candidates for eco-friendly applications across various industries. Overall, this study demonstrates that FTOLCNF are an attractive alternative to other bio- and fossil-based foams, offering a balance of energy efficiency, higher yield, mechanical performance, and sustainability.

The upcycling of discarded garments can help to mitigate the environmental impact of the textile industry. Here, we fabricated hybrid anisotropic foams having cellulose nanocrystals (CNCs), which were isolated from discarded cotton textiles and had varied surface chemistries as structural components, in combination with xanthan gum (XG) as a physical crosslinker of the dispersion used for foam preparation. All CNCs had crystallinity indices above 85 %, zeta potential values below -40 mV at 1 mM NaCl, and true densities ranging from 1.61 to 1.67 g center dot cm(-3). Quartz crystal microbalance with dissipation (QCM-D) measurements indicated weak interactions between CNC and XG, while rheology measurements showed that highly charged CNCs caused the XG chains to change from an extended to a helicoidal conformation, resulting in changes the in viscoelastic properties of the dispersions. The inclusion of XG significantly enhanced the compression mechanical properties of the freeze-casted foams without compromising their thermal properties, anisotropy, or degree of alignment. CNC-XG foams maintained structural integrity even after exposure to high humidity (91 %) and temperatures (100 degrees C) and displayed very low radial thermal conductivities. This research provides a viable avenue for upcycling cotton-based clothing waste into high-performance materials.

This thesis presents novel methods and approaches for designing, preparing/fabricating, and characterizing wood-based nanomaterials. It investigates how modifications in structure, process variables, and composition can enhance functional properties. It employs advanced characterization techniques to analyze process-structure-property relationships and utilizes innovative colloidal processing approaches such as controlled nanoparticle incorporation, Layer-by-Layer self-assembly, and unidirectional ice-templating to improve the functional properties of wood-based nanomaterials.

A novel approach has been developed to fabricate lightweight, highly porous hybrid foams using iron oxide nanoparticles (IONP) and TEMPO-oxidized cellulose nanofibers (TOCNF). The addition of tannic acid (TA) and the application of a magnetic field-enhanced unidirectional ice-templating technique (MFUIT) enhanced processability, mechanical, and magnetic characteristics of the foams. The hybrid foam containing 87% IONPs exhibited a saturation magnetization of 83.2 emu g^–1, which is equivalent to 95% of the magnetization value observed in bulk magnetite.

Hybrid, anisotropic foams have been prepared by incorporation of reduced graphene oxide (rGO) onto the macropore-walls of anisotropic TOCNF foams using a liquid-phase Layer-by-Layer self-assembly method. These hierarchical rGO-TOCNF foams exhibit lower radial thermal conductivity (λ_r) across a wide range of relative humidity compared to control TOCNF foams.

The shear-induced orientations and relaxations of multi-component dispersions containing cellulose nanocrystals (CNC) and montmorillonite nanoplatelets (MNT) have been studied by rheological small-angle X-ray scattering (Rheo-SAXS). The addition of MNT resulted in gelation and changes in flow behavior, shear responses, and relaxation dynamics. Rheo-SAXS measurements showed that CNC and MNT aligned under shear, creating aligned structures that relaxed upon shear removal. Gaining insights into shear-induced orientations and relaxation dynamics can aid in the development of advanced wood-based nanocomposite materials.

Transmission Electron Microscopy (TEM) was employed to characterize lignin oleate nanoparticles (OLNPs) derived from abundant lignin waste. TEM analysis revealed that the OLNPs had a spherical shape and a core-shell structure. Upon drying, the particles tended to agglomerate due to the loss of electrostatic repulsion forces. This agglomeration behavior indirectly supports the hypothesis that oleate chains act as a hydration barrier, preventing water permeation into the particles. 

Finally, a comprehensive study showed that TEMPO-oxidized lignocellulose nanofibers (TOLCNF)-based foams made from unbleached pulp can be used to prepare anisotropic, light-weight ice-templated foams with high mechanical strength. TOLCNF foams utilize lignin and hemicellulose to enhance properties while require less energy for production compared to TOCNF-based foams. This study emphasizes the potential for developing sustainable wood-based nanomaterials using TOLCNF.

The results presented in this thesis offer valuable insights for further advancements of wood-based nanomaterials. 

Denna avhandling presenterar nya metoder och tillvägagångssätt för design, beredning/tillverkning och karakterisering av träbaserade nanomaterial. Den undersöker hur förändringar i struktur, processvariabler och sammansättning kan förbättra funktionella egenskaper. Avancerade karaktäriseringstekniker används för att analysera samband mellan process, struktur och egenskaper, och innovativa kolloidala bearbetningsmetoder såsom kontrollerad nanopartikelinkorporering, lager-på-lager-självmontering och unidirektionell is-templering används för att förbättra de funktionella egenskaperna hos träbaserade nanomaterial.

En ny metod har utvecklats för att tillverka lätta, högporösa hybridskum med järnoxidnanopartiklar (IONP) och TEMPO-oxiderade cellulosa nanofibrer (TOCNF). Tillsatsen av tanninsyra (TA) och användningen av en magnetfältförstärkt unidirektionell is-templeringsteknik (MFUIT) förbättrade bearbetningsbarheten, de mekaniska egenskaperna och de magnetiska egenskaperna hos skummen. Hybridskummet med 87 % IONP uppvisade en mättnadsmagnetisering på 83,2 emu g^–1, vilket motsvarar 95 % av magnetiseringsvärdet hos bulk magnetit.

Hybrida, anisotropa skum har framställts genom att införliva reducerad grafenoxid (rGO) på makroporernas väggar av anisotropa TOCNF-skum med hjälp av en flytande fas Layer-by-Layer självmonteringsmetod. Dessa hierarkiska rGO-TOCNF-skum uppvisar lägre radial termisk ledningsförmåga (λ_r) över ett brett relativt fuktighetsområde jämfört med kontroll-TOCNF-skum.

Skjuvinducerade orienteringar och relaxationer av multikomponentdispersioner innehållande cellulosananokristaller (CNC) och montmorillonitnanoplattor (MNT) har studerats med hjälp av reologisk röntgenstrukturanalys med små vinklar (Rheo-SAXS). Tillsatsen av MNT resulterade i gelbildning och förändringar i flödesbeteende, skjuvresponser och relaxationsdynamik. Rheo-SAXS-mätningar visade att CNC och MNT linjerades upp under skjuvning, vilket skapade linjerade strukturer som slappnade av efter att skjuvningen avlägsnats. Att få insikt i skjuvinducerade orienteringar och relaxationsdynamik kan hjälpa vid utvecklingen av avancerade träbaserade nanokompositmaterial.

Transmissionselektronmikroskopi (TEM) användes för att karakterisera nanopartiklar av ligninoleat (OLNP) som härstammar från rikligt förekommande ligninavfall. TEM-analysen visade att OLNP hade en sfärisk form och en kärna-skal-struktur. Vid torkning tenderade partiklarna att agglomerera på grund av förlusten av elektrostatiska repulsionskrafter. Denna agglomerationsbeteende stöder indirekt hypotesen att oleatkedjorna fungerar som en hydratiseringsbarriär, vilket förhindrar vatteninträngning i partiklarna.

En omfattande studie visade att skum baserade på TEMPO-oxiderade lignocellulosa nanofibrer (TOLCNF) tillverkade av obelagd massa kan användas för att förbereda anisotropa, lätta is-templaterade skum med hög mekanisk styrka. TOLCNF-skum utnyttjar lignin och hemicellulosa för att förbättra egenskaper samtidigt som de kräver mindre energi för produktion jämfört med TOCNF-baserade skum. Studien betonar potentialen för att utveckla hållbara träbaserade nanomaterial med hjälp av TOLCNF.

Resultaten som presenteras i denna avhandling erbjuder värdefulla insikter för ytterligare framsteg inom träbaserade nanomaterial.

Anisotropic cellulose nanofiber (CNF) foams represent the state-of-the-art in renewable insulation. These foams consist of large (diameter >10 μm) uniaxially aligned macropores with mesoporous pore-walls and aligned CNF. The foams show anisotropic thermal conduction, where heat transports more efficiently in the axial direction (along the aligned CNF and macropores) than in the radial direction (perpendicular to the aligned CNF and macropores). Here we explore the impact on axial and radial thermal conductivity upon depositing a thin film of reduced graphene oxide (rGO) on the macropore walls in anisotropic CNF foams. To obtain rGO films on the foam walls we developed liquid-phase self-assembly to deposit rGO in a layer-by-layer fashion. Using electron and ion microscopy, we thoroughly characterized the resulting rGO-CNF foams and confirmed the successful deposition of rGO. These hierarchical rGO-CNF foams show lower radial thermal conductivity (λ_r) across a wide range of relative humidity compared to CNF control foams. Our work therefore demonstrates a potential method for improved thermal insulation in anisotropic CNF foams and introduces versatile self-assembly for postmodification of such foams.

Lightweight and mechanically robust hybrid foams based on cellulose nanocrystals (CNC) and multi-walled carbon nanotubes (MWCNT) with an anisotropic structure are prepared by directional ice-templating. The anisotropic hybrid CNC-MWCNT foams displayed a combination of highly anisotropic thermal conductivity and an orientation-dependent electromagnetic interference (EMI) shielding with a maximum EMI shielding efficiency (EMI-SE) of 41–48 dB between 8 and 12 GHz for the hybrid foam with 22 wt% MWCNT. The EMI-SE is dominated by absorption (SE_A) which is important for microwave absorber applications. Modelling of the low radial thermal conductivity highlighted the importance of phonon scattering at the heterogeneous CNC-MWCNT interfaces while the axial thermal conductivity is dominated by the solid conduction along the aligned rod-like particles. The lightweight CNC-MWCNT foams combination of an anisotropic thermal conductivity and EMI shielding efficiency is unusual and can be useful for directional heat transport and EMI shielding. 

Lightweight iron oxide nanoparticle (IONP)/TEMPO-oxidized cellulose nanofibril (TOCNF) hybrid foams with an anisotropic structure and a high IONP content were produced using magnetic field-enhanced unidirectional ice-templating. Coating the IONP with tannic acid (TA) improved the processability, the mechanical performance, and the thermal stability of the hybrid foams. Increasing the IONP content (and density) increased the Young's modulus and toughness probed in compression, and hybrid foams with the highest IONP content were relatively flexible and could recover 14% axial compression. Application of a magnetic field in the freezing direction resulted in the formation of IONP chains that decorated the foam walls and the foams displayed a higher magnetization saturation, remanence, and coercivity compared to the ice-templated hybrid foams. The hybrid foam with an IONP content of 87% displayed a saturation magnetization of 83.2 emu g⁻¹, which is 95% of the value for bulk magnetite. Highly magnetic hybrid foams are of potential interest for environmental remediation, energy storage, and electromagnetic interference shielding.

Low-density foams and aerogels based on upcycled and bio-based nanofibers and additives are promising alternatives to fossil-based thermal insulation materials. Super-insulating foams are prepared from upcycled acid-treated aramid nanofibers (upANF_A) obtained from Kevlar yarn and tempo-oxidized cellulose nanofibers (CNF) from wood. The ice-templated hybrid upANF_A/CNF-based foams with an upANF_A content of up to 40 wt% display high thermal stability and a very low thermal conductivity of 18–23 mW m⁻¹ K⁻¹ perpendicular to the aligned nanofibrils over a wide relative humidity (RH) range of 20% to 80%. The thermal conductivity of the hybrid upANF_A/CNF foams is found to decrease with increasing upANF_A content (5–20 wt%). The super-insulating properties of the CNF-upANF_A hybrid foams are related to the low density of the foams and the strong interfacial phonon scattering between the very thin and partially branched upANF_A and CNF in the hybrid foam walls. Defibrillated nanofibers from textiles are not limited to Kevlar, and this study can hopefully inspire efforts to upcycle textile waste into high-performance products.

By forming and directionally freezing an aqueous foam containing cellulose nanofibrils, methylcellulose, and tannic acid, we produced a stiff and tough anisotropic solid foam with low radial thermal conductivity. Along the ice-templating direction, the foam was as stiff as nanocellulose–clay composites, despite being primarily methylcellulose by mass. The foam was also stiff perpendicular to the direction of ice growth, while maintaining λ_r < 25 mW m^–1 K^–1 for a relative humidity (RH) up to 65% and <30 mW m^–1 K^–1 at 80% RH. This work introduces the tandem use of two practical techniques, foam formation and directional freezing, to generate a low-density anisotropic material, and this strategy could be applied to other aqueous systems where foam formation is possible. 

The development of robust production processes is essential for the introduction of advanced materials based on renewable and Earth-abundant resources. Cellulose nanomaterials have been combined with other highly available nanoparticles, in particular clays, to generate multifunctional films and foams. Here, the structure of dispersions of rod-like cellulose nanocrystals (CNC) and montmorillonite nanoplatelets (MNT) was probed using small-angle X-ray scattering within a rheological cell (Rheo-SAXS). Shear induced a high degree of particle orientation in both the CNC-only and CNC:MNT composite dispersions. Relaxation of the shear-induced orientation in the CNC-only dispersion decayed exponentially and reached a steady-state within 20 seconds, while the relaxation of the CNC:MNT composite dispersion was found to be strongly retarded and partially inhibited. Viscoelastic measurements and Guinier analysis of dispersions at the shear rate of 0.1 s⁻¹ showed that the addition of MNT promotes gel formation of the CNC:MNT composite dispersions. A better understanding of shear-dependent assembly and orientation of multi-component nanoparticle dispersions can be used to process materials with improved mechanical and functional properties.

Time-resolved small-angle X-ray scattering (SAXS) was used to probe the assembly of cellulose nanocrystals (CNC) and montmorillonite (MNT) over a wide concentration range in aqueous levitating droplets. Analysis of the SAXS curves of the one-component and mixed dispersions shows that co-assembly of rod-like CNC and MNT nanoplatelets is dominated by the interactions between the dispersed CNC particles and that MNT promotes gelation and assembly of CNC, which occurred at lower total volume fractions in the CNC:MNT than in the CNC-only dispersions. The CNC dispersions displayed a d proportional to phi(-1/2) scaling and a low-q power-law exponent of 2.0-2.2 for volume fractions up to 35%, which indicates that liquid crystal assembly co-exists and competes with gelation.