Converting omnipresent environmental energy through the assistance of spontaneous water evaporation is an emerging technology for sustainable energy systems. Developing bio-based hydrovoltaic materials further pushes the sustainability, where wood is a prospect due to its native hydrophilic and anisotropic structure. However, current wood-based water evaporation-assisted power generators are facing the challenge of low power density. Here, an efficient hydrovoltaic wood power generator is reported based on wood cell wall nanoengineering. A highly porous wood with cellulosic network filling the lumen is fabricated through a green, one-step treatment using sodium hydroxide to maximize the wood surface area, introduce chemical functionality, and enhance the cell wall permeability of water. An open-circuit potential of ≈140 mV in deionized water is realized, over ten times higher than native wood. Further tuning the pH difference between wood and water, due to an ion concentration gradient, a potential up to 1 V and a remarkable power output of 1.35 µW cm−2 is achieved. The findings in this study provide a new strategy for efficient wood power generators.

Wood biomass is an important resource in the development ofstrategies towards replacement of fossil-based materials. Woodcomprises cellulose, hemicelluloses and lignin, in amounts thatvary between species. Traditionally, the extraction of cellulose hasbeen prioritized for the production of pulp, paper, and novelmaterials, at the expense of the other two thirds of the woodbiomass. Lignin is an important component of wood, comprising acomplex polymer of aromatic compounds. At the moment, mostof this abundant biopolymer is usually burned for energy or simplydiscarded as a huge waste of the pulp industries, after severemodifications in its already complex structure have rendered itdifficult to valorize. A deeper understanding of the lignin polymerand its properties can guide the design of milder extractiontechniques to obtain specific lignin structures as are needed.In this thesis, fundamental aspects of lignin biosynthesis,structure, and interactions with other cell wall components areinvestigated, employing model biological systems and diversechemical methods. Specifically, a Norway spruce tissue culturethat produces lignin extracellularly, without deposition to theplant cell wall, was used to understand the impact of a secondarycell wall hemicellulose on the production and structure of lignin.The main advantage of this model system is that it enables thecollection of lignin without the need for extraction, which is knownto alter the structure of lignin. The same system was studied viatranscriptomic analysis to elucidate the impact of a hemicelluloseon the lignin biosynthetic pathway and other metabolic processes.The effect of extraction on the structure of lignin was addressedwith the development of mild and green extraction protocols forsoftwood and hardwood species. Different conditions led to thecollection of discrete lignin populations. The results could informthe development of lignin-first biorefinery applications, in whichspecific structural properties of the biopolymer are preserved.Finally, native-like lignin fractions extracted using these mildprotocols were used for the preparation of lignin nanoparticles, toshowcase their potential in high-end applications. Furthermore,the importance of unmodified lignin in the properties of woodaerogel applications was also studied, and was included in thisthesis to demonstrate that lignin modification or even removal isnot always necessary to obtain materials with propertiescompetitive to their fossil-based analogues.

Träbiomassa är en viktig resurs i utvecklingen av strategier för attersätta fossilbaserade material. Trä består av cellulosa,hemicellulosa och lignin, i mängder som varierar mellan arterna.Traditionellt har utvinning av cellulosa prioriterats förframställning av massa, papper och nya material, på bekostnad avövriga två tredjedelar av träbiomassan. Lignin är en viktigkomponent i trä, som består av en komplex polymer av aromatiskaföreningar. För närvarande bränns det mesta av denna rikligabiopolymer vanligtvis för energi eller helt enkelt kasseras som ettenormt slöseri från massaindustrin, efter att allvarligamodifieringar i dess redan komplexa struktur har gjort det svårt attvärdera den. En djupare förståelse av ligninpolymeren och dessegenskaper kan vägleda utformningen av mildareextraktionstekniker för att erhålla specifika ligninstrukturer efterbehov.I denna avhandling undersöks grundläggande aspekter avligninbiosyntes, struktur och interaktioner med andracellväggskomponenter, med hjälp av biologiska modellsystem ocholika kemiska metoder. Specifikt användes en granvävnadskultursom producerar lignin extracellulärt, utan avsättning påväxtcellväggen, för att förstå effekten av en sekundärcellväggshemicellulosa på produktionen och strukturen av lignin.Den största fördelen med detta modellsystem är att det möjliggörinsamling av lignin utan behov av extraktion, vilket är känt för attförändra strukturen av lignin. Samma system studerades viatranskriptomisk analys för att belysa inverkan av en hemicellulosapå ligninbiosyntesvägen och andra metaboliska processer.Effekten av extraktion på strukturen av lignin togs upp medutvecklingen av milda och gröna extraktionsprotokoll för barr- ochlövvedsarter. Olika förhållanden ledde till insamling av specifikaligninpopulationer. Resultaten skulle kunna informera omutvecklingen av lignin-första bioraffinaderiapplikationer, därspecifika strukturella egenskaper hos biopolymeren bevaras.Slutligen användes naturliga ligninfraktioner extraherade meddessa milda protokoll för framställning av ligninnanopartiklar föratt visa upp deras potential i avancerade applikationer. Vidarestuderades också betydelsen av omodifierat lignin i egenskapernahos aerogelapplikationer i trä, och inkluderades i dennaavhandling för att visa att modifiering eller till och med borttagningav lignin inte alltid är nödvändigt för att erhålla material medegenskaper som är konkurrenskraftiga till deras fossilbaseradeanaloger.

Mass transport of liberated lignin fragments from pits and fiber walls into black liquor is considered a determining step in the delignification process. However, our current understanding of the diffusion of lignin through cellulose and the influential parameter on this process is very limited. A comprehensive and detailed study of lignin mass transport through cellulosic materials is, therefore, of great importance. In this study, diffusion cell methodology is implemented to systematically investigate the transport of fractionated kraft lignin molecules through model cellulose membranes. Pulping is a complex process and lignin is very heterogenous material therefore to perform a more detailed study on lignin diffusion, we included an additional solvent fractionation step. One of the benefits of this method is that the setup can be adjusted to various experimental conditions allowing the complex chemical reactions occurring during pulping, which would affect the mass transfer of lignin, to be avoided. Here, the effects of the alkalinity of the aqueous solution and molecular weight of the kraft lignin molecules on their diffusion were investigated. Additionally, NMR spectroscopy, size exclusion chromatography, and UV/Vis spectroscopy were used to characterize the starting material and the molecules that passed through the membrane. Lignin molecules detected in the acceptor chamber of the diffusion cells had lower molecular weights, indicating a size fractionation between the donor and acceptor chamber. UV/Vis showed higher concentrations of ionized conjugated kraft lignin molecules in the acceptor chamber, which is a sign of chemical fractionation. This study suggests that the diffusion of lignin through small cellulose pores can be enhanced by decreasing the average molecular weight of the diffusing kraft lignin molecules and increasing alkalinity.

Understanding the structure of hardwoods can permit better valorization of lignin by enabling the optimization of green, high-yield extraction protocols that preserve the structure of wood biopolymers. To that end, a mild protocol was applied for the extraction of lignin from ball-milled birch. This made it possible to understand the differences in the extractability of lignin in each extraction step. The fractions were extensively characterized using 1D and 2D nuclear magnetic resonance spectroscopy, size exclusion chromatography, and pyrolysis-gas chromatography-mass spectrometry. This comprehensive characterization highlighted that lignin populations extracted by warm water, alkali, and ionic liquid/ethanol diverged in structural features including subunit composition, interunit linkage content, and the abundance of oxidized moieties. Moreover, ether- and ester-type lignin-carbohydrate complexes were identified in the different extracts. Irrespective of whether natively present in the wood or artificially formed during extraction, these complexes play an important role in the extractability of lignin from ball-milled hardwood. Our results contribute to the further improvement of lignin extraction strategies, for both understanding lignin as present in the lignocellulosic matrix and for dedicated lignin valorization efforts.

Polymer shape-memory aerogels (PSMAs) are prospects in various fields of application ranging from aerospace to biomedicine, as advanced thermal insulators, actuators, or sensors. However, the fabrication of PSMAs with good mechanical performance is challenging and is currently dominated by fossil-based polymers. In this work, strong, shape-memory bio-aerogels with high specific surface areas (up to 220 m2/g) and low radial thermal conductivity (0.042 W/mK) were prepared through a one-step treatment of native wood using an ionic liquid mixture of [MTBD]+[MMP]−/DMSO. The aerogel showed similar chemical composition similar to native wood. Nanoscale spatial rearrangement of wood biopolymers in the cell wall and lumen was achieved, resulting in flexible hydrogels, offering design freedom for subsequent aerogels with intricate geometries. Shape-memory function under stimuli of water was reported. The chemical composition and distribution, morphology, and mechanical performance of the aerogel were carefully studied using confocal Raman spectroscopy, AFM, SAXS/WAXS, NMR, digital image correlation, etc. With its simplicity, sustainability, and the broad range of applicability, the methodology developed for nanoscale reassembly of wood is an advancement for the design of biobased shape-memory aerogels.

Renewable resources such as wood are an important candidate towards the replacement of fossil-based materials with bio-based materials. Lignin, comprising up to 40% of woody biomass, has shown great potential in the preparation of nanoparticles (LNPs), which can be used in diverse material applications. Typically, LNPs are prepared from technical lignins, deriving from pulping processes. Their formation is thought to be driven by the hydroxyl content and molecular weight of lignin. However, other equally important parameters are the monolignol composition and the concentration of lignin used. In this study, we used native-like lignin fractions from hardwood and softwood to investigate the impact of lignin structure on LNP formation. We identified a synergistic effect between 7C-7C stacking and hydroxyl group content in nanoparticle formation. Our LNPs exhibited different morphologies, including compact, collapsed spheres, and 'snowman' aggregates. The results described herein provide an in-depth perspective on the formation and structure-property relationship of LNPs from native -like lignin fractions. With this study we aim to promote biorefinery concepts, in which the lignin structure is preserved during extraction.

In order to develop more economic uses of lignin, greater knowledge regarding its native structure is required. This can inform the development of optimized extraction methods that preserve desired structural properties. Current extraction methods alter the polymeric structure of lignin, leading to a loss of valuable structural groups or the formation of new non-native ones. In this study, Norway spruce (Picea abies) tissue-cultured cells that produce lignin extracellularly in a suspension medium were employed. This system enables the investigation of unaltered native lignin, as no physicochemical extraction steps are required. For the first time, this culture was used to investigate the interactions between lignin and xylan, a secondary cell wall hemicellulose, and to study the importance of lignin-carbohydrate complexes (LCCs) on the polymerization and final structure of extracellular lignin (ECL). This has enabled us to study the impact of xylan on monolignol composition and structure of the final lignin polymer. We find that the addition of xylan to the solid culture medium accelerates cell growth and impacts the ratio of monolignols in the lignin. However, the presence of xylan in the lignin polymerization environment does not significantly alter the structural properties of lignin as analyzed by two-dimensional nuclear magnetic resonance (NMR) spectroscopy and size exclusion chromatography (SEC). Nevertheless, our data indicate that xylan can act as a nucleation point, leading to more rapid lignin polymerization, an important insight into biopolymer interactions during cell wall synthesis in wood. Lignin structure and interactions with a secondary cell wall hemicellulose were investigated in a model cell culture: we found that the polymerization and final structure of lignin are altered when the hemicellulose is present during cell growth and monolignol production. The physicochemical interactions between lignin and xylan partly define the extractability and utility of native lignin in high value applications, so this work has implications for lignin extraction as well as fundamental plant biology.

Mechanical milling of lignocellulose has been used in several studies as a key pretreatment enabling the extraction of lignin from various sources for structural analysis. It is also applied as an alternative to wet chemical methods for lignin valorization. However, the changes caused to the plant cell walls at different hierarchical scales and how they relate to the molecular events are still poorly understood. In this context, we sought to gain deeper insights into molecular heterogeneity in milled cell walls, with a primary focus on lignin. A novel fractionation protocol was developed to enable the advanced analysis (1D and 2D NMR, SEC, XRD) of molecular populations in ball milled fiber walls. The methodology was applied to follow the emergence of such populations through the milling process, and in different milling environments. Lignin heterogeneity in the ball milled fibers was found to consist of distinct populations of small and large fractions of lignin carbohydrate complexes and pure lignin fractions, both with differences in lignin inter-unit abundances. Lignin-carbohydrate bonds of benzyl ester type were unequivocally demonstrated for the first time by combination of HSQC-HMBC NMR analysis. γ-Ester LCC and phenyl glycoside LCCs were also detected. Furthermore, an important branching point in lignin, previously controversial, namely the 4-O-etherified 5-5′ substructure, is unequivocally shown here by HSQC-HMBC analysis of the milled wood isolates, and supported by biomimetic lignin (DHP) to originate from the native structure. Based on the advanced characterization, the origin of lignin heterogeneity in ball milled fibers is proposed to result from the uneven distribution of the applied mechanical energy, where synergistic effects between crystalline and amorphous states play a central role. Accordingly, a plant cell wall model is proposed and a complete mechanism of its disintegration during the milling exercise is presented. The unveiled heterogeneity model of ball milled cell walls can serve as a useful guide for future studies on mechanical fractionation and valorization of lignocellulose based polymers.

An intense effort has been put into replacing fossil- with bio-based materials. To achieve this goal in a  sustainable manner, renewable resources such as wood can be used. Lignin makes up around % of  woody biomass and has shown great potential in the preparation of nanoparticles (LNPs) of use in  diverse material applications. Typically, LNPs are prepared from so-called technical lignins deriving  from the pulping process, with formation thought to be driven by the hydroxyl content and molecular  weight of lignin. However, other equally important parameters are the lignin concentration and  monolignol composition. In this study, we used native-like lignins extracted from hardwood and  softwood under mild conditions to investigate the impact of lignin structure on the formation of LNPs.  We identified a synergistic effect between π-π stacking and hydroxyl group content in nanoparticle  formation. LNP morphology, including compact and collapsed spheres or ‘snowman’ aggregates,  seemed to depend mainly on monolignol composition. The results described herein provide an in depth perspective on the formation of LNPs from non-technical lignins and take us closer to  understanding their structure-property relationship. With this study we aim to promote lignin-first  biorefinery concepts, in which the lignin structure is preserved during extraction