Mildly delignified softwood holocellulose fibers featuring native tracheid fiber cell wall structure and high hemicellulose content are prominent building blocks for wood derived fiber-based materials. However, preserving the natural alignment of long softwood fiber is challenging since top-down structure-retaining delignified softwood is unstable as extensive removal of lignin from intercellular space induces cracking and disintegration of wood structure. Here we report the use of chemical crosslinking pretreatment to improve the intercellular bonding between softwood fibers, therefore preserving the integrity of the naturally aligned softwood fibers after delignification. The crosslinked softwood veneer was delignified with peracetic acid and further densified into transparent and high-density film by thermal compression. The obtained transparent film of naturally aligned softwood holocellulose fibers showed high optical transmittance of 71 %, high haze of 85 %, strong optical anisotropy, as well as high tensile strength of 449 ± 58 MPa and high Young's modulus of 49.9 ± 5.6 GPa. This study provides a facile approach to preserve the natural alignment of softwood fibers for the fabrication of high performance holocellulose fibers-based materials.

Plastic pollution is an environmental emergency and finding sustainable alternatives to traditional plastics has become a pressing need. Seaweed-based bioplastic has emerged as a promising solution, as it is biodegradable and made from renewable biomass, while seaweed cultivation itself provides various environmental benefits. However, the feasibility of implementing a brown seaweed-based bioplastic supply chain in a realistic setting remains unclear, as previous research focused either on single processing steps or on virtual supply chains aggregating data from different studies. This study describes a case study for seaweed-based bioplastic within the PlastiSea research project: from seaweed cultivation to biomass processing and bioplastic and composite material development at the lab and pilot scale, thus providing insights into its feasibility. Adopting a multidisciplinary approach, the study employs multiple methods to characterize each stage in the supply chain and provides an overall life cycle assessment (LCA) as well as lessons learned throughout the process. The analysis showed potential for producing and utilizing multiple co-products from the same seaweed source, including biopolymer extracts with varying degrees of refinement for use in low-cost (bioplastic films) and high-cost (microfiber composites) applications. The use of residual biomass as a source of alginates for producing bioplastics offers a low-cost and sustainable biomass supply currently not competing with other markets. The LCA results indicate the potential for reducing the environmental impact of seaweed-based bioplastic production through upscaling and increasing process efficiency.

Cultivated brown algae represent an important potential source of carbohydrate polymers for packaging and other biobased materials. However, their exploitation is currently limited by a short harvest season and a lack of cost-effective and sustainable methods to preserve biopolymer quality. In the present study, cultivated Saccharina latissima (SL) and Alaria esculenta (AE) were preserved with formic acid at 4, 13 and 20 degrees C for up to 16 weeks prior to extraction and characterization of alginate and cellulose. The data show up to 40 % increased yield of alginate from preserved biomass compared with fresh and non-preserved biomass, primarily due to removal of minerals and other soluble compounds during the acid wash. Acid preservation and storage caused a reduction in alginate weight average molecular weight (Mw) that was mainly dependent on storage temperature and to a lesser extent on storage time; storage at 4 degrees C maintained the Mw of alginates at 350-500 kDa. Preservation had no effect on the guluronate block structure of the extracted alginates, but guluronic acid content and block length increased in the non-preserved samples, presumably due to enzymatic degradation of the alginate's M-rich re-gions. Preservation of the seaweed resulted in an increased cellulose yield compared with fresh and non -preserved biomass, again due to the biomass being reduced during acid wash. The molecular weight and crys-tallinity of cellulose were not altered by the process. Altogether our findings demonstrate that acid preservation at low temperatures can effectively stabilize seaweed biomass while preserving alginate and cellulose quality for biomaterials and other applications.

Nature has evolved elegant ways to alter the wood cell wall structure through carbohydrate-active enzymes, offering environmentally friendly solutions to tailor the microstructure of wood for high-performance materials. In this work, the cell wall structure of delignified wood is modified under mild reaction conditions using an oxidative enzyme, lytic polysaccharide monooxygenase (LPMO). LPMO oxidation results in nanofibrillation of cellulose microfibril bundles inside the wood cell wall, allowing densification of delignified wood under ambient conditions and low pressure into transparent anisotropic films. The enzymatic nanofibrillation facilitates microfibril fusion and enhances the adhesion between the adjacent wood fiber cells during densification process, thereby significantly improving the mechanical performance of the films in both longitudinal and transverse directions. These results improve the understanding of LPMO-induced microstructural changes in wood and offer an environmentally friendly alternative for harsh chemical treatments and energy-intensive densification processes thus representing a significant advance in sustainable production of high-performance wood-derived materials.

Silk fibroin, a widely used natural biopolymer, presents remarkable flexibility and biodegradability, making it of great interest as a polymer matrix for functional composite materials. Herein, composites of silk nanofibrils and metal-organic framework (MOF) nanosheets were successfully fabricated by a coincubation and coassembly process. Under heat incubation, silk fibroin self-assembled into one-dimensional nanofibrils, while MOF nanosheets simultaneously covered or wrapped on the silk nanofibrils in a water suspension. Transparent composite membranes were obtained from their water suspensions by the solution casting method. The regenerated silk nanofibrils formed a network structure, and the integrated MOF nanosheets (0.1 to 3.0 wt %) endowed the composites with aggregation-induced emission luminogen (AIEgen)-based fluorescence. The fluorescence intensity of the composites was significantly enhanced owing to the interfacial interactions between silk nanofibrils and MOF nanosheets. The composite membranes also offer excellent UV shielding while maintaining optical transparency in the visible spectrum. This work provides an efficient pathway to fabricate luminescent silk protein-based composites for functional materials such as fluorescence sensing and anticounterfeiting.

Improving the redispersion and recycling of dried cellulose nanofibrils (CNFs) without compromising their nanoscopic dimensions and inherent mechanical properties are essential for their large-scale applications. Herein, mixed-linkage (1,3;1,4)-beta-D-glucan (MLG) was studied as a rehydration medium for the redispersion and recycling of dried CNFs, benefiting from the intrinsic affinity of MLG to both cellulose and water molecules as inspired from plant cell wall. MLG from barley with a lower molar ratio of cellotriosyl to cellotetraosyl units was found homogeneously coated on CNFs, facilitating rehydration of the network of individualized CNFs. The addition of barley MLG did not impair the mechanical properties of the CNF/MLG composites as compared to neat CNFs nanopaper. With the addition of 10 wt% barley MLG, dry CNF/MLG composite film was successfully redispersed in water and recycled with well-maintained mechanical properties, while lichenan from Icelandic moss, cationic starch, and xyloglucan could not help the redispersion of dried CNFs.

Optically transparent wood has been fabricated by structure-retaining delignification of wood and subsequent infiltration of thermo- or photocurable polymer resins but still limited by the intrinsic low mesopore volume of the delignified wood. Here we report a facile approach to fabricate strong transparent wood composites using the wood xerogel which allows solvent-free infiltration of resin monomers into the wood cell wall under ambient conditions. The wood xerogel with high specific surface area (260 m2 g–1) and high mesopore volume (0.37 cm3 g–1) is prepared by evaporative drying of delignified wood comprising fibrillated cell walls at ambient pressure. The mesoporous wood xerogel is compressible in the transverse direction and provides precise control of the microstructure, wood volume fraction, and mechanical properties for the transparent wood composites without compromising the optical transmittance. Transparent wood composites of large size and high wood volume fraction (50%) are successfully prepared, demonstrating potential scalability of the method.

Lytic polysaccharide monooxygenase (LPMO)-catalysed oxidation of cellulose has emerged as a green alternative to chemical modifications in the production of cellulose nanofibrils (CNFs) from wood pulp fibres. The effect of the hemicellulose content of the starting pulp fibres on the oxidation capabilities of cellulose-active LPMO is important and has not been investigated previously. In this study, the production of LPMO-oxidised CNFs was evaluated on two commercial softwood pulp fibres with different hemicellulose contents. Thin and colloidally stable CNFs were readily obtained from kraft pulp with a hemicellulose content of 16%. The preserved hemicellulose fraction in the kraft pulp enhanced the access of LPMO into the fibre cell wall, enabling the production of homogeneous CNFs with a thin width of 3.7 ± 1.7 nm. By contrast, the LPMO-oxidised dissolving pulp with a lower hemicellulose content of 4% could only be partially disintegrated into thin CNFs, leaving a large amount of cellulose microfibril aggregates with widths of around 50 to 100 nm. CNFs disintegrated from the LPMO-oxidised kraft pulp could be processed into nanopapers with excellent properties including an optical transmittance of 86%, tensile strength of 260 MPa, and Young's modulus of 16.9 GPa. Such CNFs also showed acid-triggered nanofibril gelation owing to the introduced carboxyl groups on cellulose microfibril surfaces. These results indicate that the inherent hemicelluloses present in the wood cell wall are essential for LPMO-mediated CNF production from wood pulp fibres.

Composite polymer hydrogels are of significant interests for high optical transparency and mechanical performance. In this work, a strong and transparent composite hydrogel is developed from a highly mesoporous cellulose network prepared from wood via top-down delignification followed by TEMPO-mediated oxidation and in situ polymerization of PNIPAM. Individualization of cellulose microfibrils inside the wood cell wall is critical for the fabrication of free-standing composite hydrogel with high water content of 94.9 wt% and high optical transmittance of 85.8% with anisotropic light scattering behavior. The composite hydrogel also showed anisotropic mechanical properties with a tensile strength, Young's modulus and toughness of 317 kPa, 5.4 MPa, and 39.2 kJ m- 3 in axial direction, and 152 kPa, 0.31 MPa and 57.1 kJ m- 3 in the transverse direction, respectively. It also showed thermochromic behavior, i.e., reversibly changing between transparent and brightly white by a temperature change between 25 and 40 degrees C, demonstrating great potential for optical applications.

Recently emerged top-down processing concept has provided new insights into the chemical modification of wood at the nanoscale. Nanostructured wood with naturally aligned cellulose microfibrils, cell wall nanoporosity, and precisely tuned chemical composition has opened up numerous possibilities for advanced design of functional materials. In this thesis, novel chemical modification strategies have been developed to obtain nanostructural control and surface functionalization of nanostructured wood. Functional biocomposite materials with superior mechanical and optical performance, high CO₂ adsorption capacity, and immobilized protein have been fabricated using the novel chemically modified nanostructured wood. 

The direct preparation of nanostructured wood from hardwood balsa was achieved by structure retaining delignification using acidic sodium chlorite. Crosslinking of the matrix polysaccharides using a homobifunctional epoxide compound was necessary as a pretreatment step for softwood spruce to maintain its structure integrity after complete delignification. Further chemical modification of delignified balsa wood through 2,2,6,6-tetrametylpiperidin-1-oxyl (TEMPO)-mediated oxidation selectively oxidized surface hydroxyls to carboxyl groups and induced fibrillation of cellulose microfibrils within the cell wall. Therefore, TEMPO-oxidized wood (TO-wood) with high carboxylate content (0.78 mmol g^-1), high specific surface area (249 m² g^-1), and large mesopore volume (0.78 cm³ g^-1) was successfully produced. Tunable microstructure of TO-wood was subsequently obtained by incorporating different counterions (H⁺, Cu²⁺, Al³⁺, Zn²⁺) or by employing different drying methods (super critical drying and freeze drying). In addition, surface amination method was also developed on highly mesoporous delignified spruce cellulose scaffold to introduce a reactive handle for immobilization of biomolecules. These chemically modified nanostructured wood have inspired the fabrication of wood-based biocomposites with new functionalities that are not possible with traditional wood materials.

Delignified balsa wood showed stronger hydrophilicity and larger porosity, which allowed the formation of composite hydrogels through infiltration of gelatin and crosslinking with genipin. The composite hydrogels showed high mechanical strength under compression and low swelling in physiological condition. The preserved cellular structure and fibrillated cellulose microfibrils in TO-wood enabled facile fabrication of compressible aerogel and exceptionally strong film (tensile strength of 449 MPa and Young’s modulus of 51 GPa) upon different drying conditions. Fibrillation of cellulose microfibrils was also found critical to the inter-penetration between cell wall and poly(N-isopropylacrylamide) (PNIPAM) hydrogel network, producing tough and highly transparent composite hydrogel with a total transmittance of 85.8% at thickness of 2 mm. The TO-wood/PNIPAM hydrogel was able to reversibly switch between transparent and brightly white in response to environmental temperature change between 25 and 40 °C. Surface carboxyl groups of TO-wood also facilitated the surface coordination of cell wall to multivalent metal ions, which subsequently enhanced the in situ synthesis of metal organic frameworks (MOFs). The resulting TO-wood/Cu₃(BTC)₂ (copper benzene-1,3,5-tricarboxylate) composite aerogel showed high specific surface area of 471 m² g^-1 and high CO₂ adsorption capacity of 1.46 mmol g^-1 at 25 °C under atmosphere pressure. The highly mesoporous and mechanical robust spruce derived cellulose scaffold laden with reactive amine groups allowed covalent immobilization of functional biomolecules, such as a lectin protein concanavalin A, which demonstrated potential glycoprotein-binding and separation applications.

Miljövänliga top-down-metoder som börja med trä har gett ny insikt i forskning om kemiskmodifiering i nanoskalan. Nanostrukturerat trä med naturligt orienteradecellulosamikrofibriller, nanoporösa cellväggar och exakt avstämd kemisk sammansättninghar öppnat många möjligheter för avancerad design av funktionella material. I dennaavhandling har nya kemiska modifieringsstrategier utvecklats för att erhålla nanostrukturellkontroll och ytfunktionalisering av nanostrukturerat trä. Funktionella biokompositmaterialmed höga mekaniska egenskaper och hög optisk prestanda, hög CO2-adsorptionskapacitetoch immobiliserat protein har tillverkats med det nya kemiskt modifieradenanostrukturerade träet.

Den direkta beredningen av nanostrukturerat trä från balsa uppnåddes genom delignifieringsom bevarar träets naturliga struktur. Tvärbindning av matrispolysackariderna medanvändning av det homofunktionella tvärbindningsmedlet butandiol-diglycidyleter varnödvändig som ett förbehandlingssteg för gran för att bibehålla dess strukturella integritetefter fullständig delignifiering. Ytterligare kemisk modifiering av delignifierat balsa genom2,2,6,6-tetrametylpiperidin-1-oxyl (TEMPO)-medierad oxidation selektivt oxideradeythydroxyler till karboxylgrupper och inducerad fibrillering av cellulosamikrofibriller icellväggen. Därför framställdes framgångsrikt TEMPO-oxiderat trä (TO-trä) med högkarboxylathalt (0,78 mmol g-1), hög specifik yta (249 m2 g-1) och stor mesoporvolym (0,78 cm3g-1). Avstämbar mikrostruktur av TO-trä erhölls därefter genom att inkorporera olikamotjoner (H+, Cu2+, Al3+, Zn2+) eller genom att använda olika torkningsmetoder (superkritisktorkning och frystorkning). Dessutom var ytan amineringsmetod också utvecklat på mycketmesoporöst delignifierade grancellulosa ställning för att införa ett reaktivt handtag förimmobilisering av biomolekyler. Dessa kemiskt modifierade nanostrukturerade trä harinspirerat tillverkningen av träbaserade biokompositer med nya funktioner som inte ärmöjliga med traditionella trämaterial.

Delignifierat balsaträ visade starkare hydrofilicitet och större porositet, vilket möjliggjordebildandet av komposithydrogeler genom infiltrering av gelatin och tvärbindning med genipin.Komposithydrogelerna uppvisade hög mekanisk hållfasthet under kompression och lågsvullnad i fysiologiskt tillstånd. Den bevarade cellulära strukturen och fibrilleradecellulosamikrofibriller i TO-trä möjliggjorde enkel tillverkning av kompressibel airgel ochexceptionellt stark film (draghållfasthet 449 MPa och Youngs modul på 51 GPa) vid olikatorkningsförhållanden. Fibrillering av cellulosamikrofibriller visade sig också vara kritisk förinterpenetrationen mellan cellvägg och poly(N-isopropylakrylamid) (PNIPAM)hydrogelnätverk, vilket producerar tuff och mycket transparent komposithydrogel med entotal transmittans på 85,8% vid en tjocklek av 2 mm. TO- trä/PNIPAM hydrogel kunde växlamellan transparent och vitt som svar på temperaturförändringar mellan 25 och 40 °C.Ytkarboxylgrupper av TO-trä underlättade också ytkoordinering av cellvägg till multivalentametalljoner, vilket därefter förbättrade in situ-syntesen av metallorganiska ramar (MOFs).Den resulterande TO-trä/Cu3 (BTC)2 (kopparbensen-1,3,5-trikarboxylat) komposit-aerogelenuppvisade hög specifik yta på 471 m2 g-1 och hög CO2-adsorptionskapacitet på 1,46 mmol g-1vid 25 °C under atmosfärstryck. Den mycket mesoporösa och mekanisk robust gran härleddcellulosa nätverk lastat med reaktiva amingrupper är tillåtna kovalent immobilisering avfunktionella biomolekyler, såsom ett lektin protein konkanavalin A, som visade potentiellaglykoprotein-bindande och separationstillämpningar.