Delignified and Densified Cellulose Bulk Materials with Excellent Tensile Properties for Sustainable Engineering

Biodegradable and Flexible Wood-Gelatin Composites for Soft Actuating Systems

Compliant materials are indispensable for many emerging soft robotics applications. Hence, concerns regarding sustainability and end-of-life options for these materials are growing, given that they are predominantly petroleum-based and non-recyclable. Despite efforts to explore alternative bio-derived soft materials like gelatin, they frequently fall short in delivering the mechanical performance required for soft actuating systems. To address this issue, we reinforced a compliant and transparent gelatin-glycerol matrix with structure-retained delignified wood, resulting in a flexible and entirely biobased composite (DW-flex). This DW-flex composite exhibits highly anisotropic mechanical behavior, possessing higher strength and stiffness in the fiber direction and high deformability perpendicular to it. Implementing a distinct anisotropy in otherwise isotropic soft materials unlocks new possibilities for more complex movement patterns. To demonstrate the capability and potential of DW-flex, we built and modeled a fin ray-inspired gripper finger, which deforms based on a twist-bending-coupled motion that is tailorable by adjusting the fiber direction. Moreover, we designed a demonstrator for a proof-of-concept suitable for gripping a soft object with a complex shape, i.e., a strawberry. We show that this composite is entirely biodegradable in soil, enabling more sustainable approaches for soft actuators in robotics applications.

Optimization of mechanical properties and dimensional stability of densified wood using response surface methodology

Wood has gained popularity as a building and decorative material due to its environmentally friendly and sustainable characteristics. Yet, its long maturation time poses a limitation on meeting the growing demand for wood products. This challenge has led to the plantation of fast-growing wood as an alternative solution. Unfortunately, the poor mechanical properties of fast-growing wood hinder its application. In this study, we developed novel densification-modified wood by combining alkali chemical pretreatment, cyclic impregnation, and mechanical hot-pressing techniques. Additionally, the response surface method was employed to rapidly determine the optimal preparation parameters, reducing the cost of preparation under various conditions. The optimized parameters resulted in densification-modified wood with a flexural strength and modulus of elasticity of 337.04 MPa and 27.43 GPa, respectively. Furthermore, the densified wood achieved excellent dimensional stability by reducing the water-absorbing thickness swelling to 1.15 % for 72-h water soaking. The findings indicated that the densification-modified wood possessed high tensile strength and elastic modulus, along with excellent dimensional stability. The proposed densified wood modification technology in this study offers new perspectives and design guidance for the application of outdoor engineering structures, energy-efficient buildings, and decorative materials.

Lightweight, Strong, and Transparent Wood Films Produced by Capillary Driven Self-Densification

Wood delignification and densification enable the production of high strength and/or transparent wood materials with exceptional properties. However, processing needs to be more sustainable and besides the chemical delignification treatments, energy intense hot-pressing calls for alternative approaches. Here, this study shows that additional softening of delignified wood via a mild swelling process using an ionic liquid-water mixture enables the densification of tube-line wood cells into layer-by-layer sheet structures without hot-pressing. The natural capillary force induces self-densification in a simple drying process resulting in a transparent wood film. The as-prepared films with ≈150 µm thickness possess an optical transmittance ≈70%, while maintaining optical haze >95%. Due to the densely packed sheet structure with a large interfacial area, the reassembled wood film is fivefold stronger and stiffer than the delignified wood in fiber direction. Owing to a low density, the specific tensile strength and elastic modulus are as high as 282 MPa cm3 g-1 and 31 GPa cm3 g-1. A facile and highly energy efficient wood nanotechnology approach are demonstrated toward more sustainable materials and processes by directly converting delignified wood into transparent wood omitting polymeric matrix infiltration or mechanical pressing.

Delignified porous wood as biofilm support for 1,4-dioxane-degrading bacterial consortium

Delignified porous wood samples were used as carriers for biofilm formation of a bacterial consortium with the ability to degrade 1,4-dioxane (DX). The delignification treatment of the natural wood resulted in higher porosity, formation of macropores, increase in surface roughness and hydrophilicity of the treated wood pieces. These superior properties of two types of treated carriers (respectively, A and B) compared to the untreated wood resulted in 2.19 ± 0.52- and 2.66 ± 0.23-fold higher growth of biofilm. Moreover, analysis of the fatty acid profiles indicated an increase in proportion of the saturated fatty acids during the biofilm formation, characterising an enhancement in rigidity and hydrophobicity of the biofilms. DX initial concentration of 100 mg/L was completely degraded (detection limit 0.01 mg/L) in 24 and 32 h using the treated A and B woods, while only 25.84 ± 5.95% was removed after 32 h using the untreated wood. However, fitting the DX biodegradation data to the Monod model showed a lower maximum specific growth rate for biofilm (0.0276 ± 0.0018 1/h) versus planktonic (0.0382 ± 0.0024 1/h), because of gradual accumulation of inactive cells in the biofilm. Findings of this study can contribute to the knowledge of biofilm formation regarding the physical/chemical properties of biofilm carriers and be helpful to the ongoing research on bioremediation of DX.

Fabrication of High-Performance Densified Wood via High-Pressure Steam Treatment and Hot-Pressing

The fabrication of sustainable structural materials with high physical properties to replace engineering plastics is a major challenge for modern industry, and wood, as the most abundant sustainable natural raw material on the planet, has received a great deal of attention from researchers. Researchers have made efforts to enhance the physical properties of wood in order to replace plastics. However, it is also difficult to meet practical demands at a low cost. Herein, we report a simple and efficient top-down strategy to transform bulk natural basswood into a high-performance structural material. This three-step strategy involves partial removal of hemicellulose and lignin via treating basswood by boiling an aqueous mixture of NaOH and Na2SO3, and a high-pressure steam treatment (HPST) was applied to delignified wood followed by hot-pressing, which allowed the wood to absorb moisture uniformly and quickly. HPST-treated dense delignified wood (HDDW) has a tensile strength of ~420 MPa, which is 6.5 times better than natural basswood (~65 MPa). We systematically investigated the various factors affecting the tensile strength of this wood material and explored the reasons why these factors affect the tensile strength, as well as the intrinsic connection between the moisture absorbed through HPST and the increased tensile strength of HDDW. Through our experiments, we realized the enhancement mechanism of HDDW and the optimal experimental conditions for the fabrication of HDDW.

High-Strength, High-Swelling-Resistant, High-Sensitivity Hydrogel Sensor Prepared with Wood That Retains Lignin

Wood-derived hydrogels possess satisfactory longitudinal strength but lack excellent swelling resistance and dry shrinkage resistance when achieving high anisotropy. In this study, we displayed the preparation of highly dimensional stable wood/polyacrylamide hydrogels (wood/PAM-Al3+). The alkali-treated wood retains lignin as the skeleton of the hydrogel. Second, Al ions were added to the metal coordination with lignin. Finally, by employing free radical polymerization, we construct a conductive electronic network using polyaniline within the wood/PAM-Al3+ matrix to create the flexible sensor. This approach leverages lignin's integrated structure within the middle lamella to provide enhanced swelling resistance and stronger binding strength in the transverse direction. Furthermore, coordination between lignin and Al ions improves the mechanical strength of the wood hydrogel. Polyaniline provides stable linear pressure and temperature responses. The wood/PAM-Al3+ exhibits a transverse swelling ratio of 3.90% while achieving a longitudinal tensile strength of 20.5 MPa. This high-strength and high-stability sensor is capable of monitoring macroscale human behavior. Therefore, this study presents a simple yet innovative strategy for constructing tough hydrogels while also establishing an alternative pathway for exploring lignin networks in new functional materials development.

Nanocrystalline iron hydroxide lignocellulose filters for arsenate remediation

Harmful levels of environmental contaminants, such as arsenic (As), persist readily in the environment, threatening safe drinking water supplies in many parts of the world. In this paper, we present a straightforward and cost-effective filtration technology for the removal of arsenate from potable water. Biocomposite filters comprised of nanocrystalline iron oxides or oxyhydroxides mineralized within lignocellulose scaffolds constitute a promising low cost, low-tech avenue for the removal of these contaminants. Two types of iron oxide mineral phases, 2-line ferrihydrite (Fh) and magnetite (Mt), were synthesized within highly porous balsa wood using an environmentally benign modification process and studied in view of their effective removal of As from contaminated water. The mineral deposition pattern, minerology, as well as crystallinity, were assessed using scanning electron microscopy, transmission electron microscopy, micro-computed X-ray tomography, confocal Raman microscopy, infrared spectroscopy, and X-ray powder diffraction. Our results indicate a preferential distribution of the Fh mineral phase within the micro-porous cell wall and radial parenchyma cells of rays, while Mt is formed primarily at the cell wall/lumen interface of vessels and fibers. Water samples of known As concentrations were subjected to composite filters in batch incubation and gravity-driven flow-through adsorption tests. Eluents were analyzed using microwave plasma optical emission spectroscopy (MP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). By subjecting the filters to a flow of contaminated water, the time for As uptake was reduced to minutes rather than hours, while immobilizing the same amount of As. The retention of As within the composite filter was further confirmed through energy-dispersive X-ray mappings. Apart from addressing dangerously high levels of arsenate in potable water, these versatile iron oxide lignocellulosic filters harbor tremendous potential for addressing current and emerging environmental contaminants that are known to adsorb on iron oxide mineral phases, such as phosphate, polycyclic aromatic hydrocarbons or heavy metals.

Versatile Mesoporous All-Wood Sponge Enabled by In Situ Fibrillation toward Indoor-Outdoor Energy Management and Conversion

The on-demand regulation of cell wall microstructures is crucial for developing wood as a functional building material for energy management and conversion. Here, a novel strategy based on reactive deep eutectic solvent is developed to one-step in situ fibrillate wood via disrupting the hydrogen bonding networks in cell walls and simultaneously carboxylating wood components, without significantly altering the native hierarchical structures of wood. Benefiting from its distinctive cell wall structure composed of individualized yet well-organized lignocellulose nanofibrils, in situ fibrillated wood exhibits a prominent mesoporous structure with a specific surface area of 81 m2/g. It represents a robust sponge material (5 MPa at 80% strain) with excellent durability. Due to the enhanced compressibility and charge polarization capacity, the in situ fibrillated wood (10 × 11 × 12 mm3) can generate a piezoelectric output voltage of up to 2 V under 221 kPa stress. The favorable microstructural characteristics render in situ fibrillated wood with highly thermal-insulating properties, high solar reflectivity, and mid-infrared emissivity, favoring outdoor passive cooling effects with a subambient temperature drop of 6 °C. Combining its controllable, durable, and eco-friendly attributes, our developed wood sponge represents a versatile structural material suitable for indoor/outdoor energy-saving applications.

Development of super dimensional stable poplar structure with fire and mildew resistance by delignification/densification of wood with highly aligned cellulose molecules

Wood is one of the most popular materials for construction purposes because of its environmentally friendly and sustainable characteristics. However, the use of wood is constrained by the lengthy time it takes for trees to mature. Consequently, fast-growing wood species have become popular as substitute options due to their ability to rapidly reach maturity and high yields. Although the problem of low density and strength has been effectively addressed in recent years by densifying wood, the problem of large thickness swelling due to moisture and water absorption has limited its application. Therefore, we reported an effective modification strategy to overcome the thickness swelling issue of densified wood by preparing a cellulosic reinforced material through the synergistic action of alkaline chemical pretreatment, multi-step cyclic impregnation and high-temperature densification. The results showed that the alkaline chemical pretreatment was effective for removing a large amount of lignin and hemicelluloses, creating a large number of hydrogen bonds among the remaining strong celluloses. The impregnated sodium silicate solution bonded celluloses tightly, and the densification treatment contributed to the production of Si-O-Si structure, forming the shuttle hybridized structure through Si-O-C bonds. The hardness, flexural strength, elastic modulus, and compressive strength of the modified wood increased by 3.9, 6.0, 3.4 and 28.2 times, respectively. In addition, 0 % thickness swelling for 30-day moisture absorption and 1.0 % thickness swelling for 72-hour water absorption were achieved, realizing super dimensional-stable poplar structures. Furthermore, the high-performance densified wood prepared by this method has excellent fire and mildew resistance properties, which lays the foundation for the application of fast-growing wood in outdoor engineering structures.

Wood-based superblack

Light is a powerful and sustainable resource, but it can be detrimental to the performance and longevity of optical devices. Materials with near-zero light reflectance, i.e. superblack materials, are sought to improve the performance of several light-centered technologies. Here we report a simple top-down strategy, guided by computational methods, to develop robust superblack materials following metal-free wood delignification and carbonization (1500 °C). Subwavelength severed cells evolve under shrinkage stresses, yielding vertically aligned carbon microfiber arrays with a thickness of ~100 µm and light reflectance as low as 0.36% and independent of the incidence angle. The formation of such structures is rationalized based on delignification method, lignin content, carbonization temperature and wood density. Moreover, our measurements indicate a laser beam reflectivity lower than commercial light stoppers in current use. Overall, the wood-based superblack material is introduced as a mechanically robust surrogate for microfabricated carbon nanotube arrays.

Multiscale Porous Carbon Materials by In Situ Growth of Metal-Organic Framework in the Micro-Channel of Delignified Wood for High-Performance Water Purification

Porous carbon materials are suitable as highly efficient adsorbents for the treatment of organic pollutants in wastewater. In this study, we developed multiscale porous and heteroatom (O, N)-doped activated carbon aerogels (CAs) based on mesoporous zeolitic imidazolate framework-8 (ZIF-8) nanocrystals and wood using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation, in situ synthesis, and carbonization/activation. The surface carboxyl groups in a TEMPO-oxidized wood (TW) can provide considerably large nucleation sites for ZIF-8. Consequently, ZIF-8, with excellent porosity, was successfully loaded into the TW via in situ growth to enhance the specific surface area and enable heteroatom doping. Thereafter, the ZIF-8-loaded TW was subjected to a direct carbonization/activation process, and the obtained activated CA, denoted as ZIF-8/TW-CA, exhibited a highly interconnected porous structure containing multiscale (micro, meso, and macro) pores. Additionally, the resultant ZIF-8/TW-CA exhibited a low density, high specific surface area, and excellent organic dye adsorption capacity of 56.0 mg cm-3, 785.8 m2 g-1, and 169.4 mg g-1, respectively. Given its sustainable, scalable, and low-cost wood platform, the proposed high-performance CA is expected to enable the substantial expansion of strategies for environmental protection, energy storage, and catalysis.

Anisotropic wood-hydrogel composites: Extending mechanical properties of wood towards soft materials' applications

Delignified wood (DW) offers a versatile platform for the manufacturing of composites, with material properties ranging from stiff to soft and flexible by preserving the preferential fiber directionality of natural wood through a structure-retaining production process. This study presents a facile method for fabricating anisotropic and mechanically tunable DW-hydrogel composites. These composites were produced by infiltrating delignified spruce wood with an aqueous gelatin solution followed by chemical crosslinking. The mechanical properties could be modulated across a broad strength and stiffness range (1.2-18.3 MPa and 170-1455 MPa, respectively) by varying the crosslinking time. The diffusion-led crosslinking further allowed to manufacture mechanically graded structures. The resulting uniaxial, tubular structure of the anisotropic DW-hydrogel composite enabled the alignment of murine fibroblasts in vitro, which could be utilized in future studies on potential applications in tissue engineering.

Two-step hot isostatic pressing densification achieved non-porous fully-densified wood with enhanced physical and mechanical properties

A new two-step densification method for wooden materials entitled hot isostatic pressing (HIP) is proposed. This method has the advantage over previous densification methods that can achieved almost the full densification of wood, reaching values up to 1.47 kg/m3, which exceeds any value ever reported for a hardwood species. Furthermore, it can preserve about 35% of the original volume, in comparison to other methods which typically can preserve only 20% of the volume. Although not tested in this investigation, in principle, the HIP method should be capable of densifying any shape of wood including circular and tubular cross sections because the main densification mechanism is based on gas pressure that is equally exerted in the entire surface, rather than localized mechanical compression, which can only be effective with rectangular cross sections. In the first stage of the two-step proposed method, the compressive strength of the anatomical wood structure is reduced by delignification, and, in the second, a full densification is achieved by hot isostatic pressing under argon atmosphere. Three tropical hardwood species with distinct anatomical characteristics and properties were used to test the method. The HIP-densified wood's microstructural, chemical, physical, and mechanical properties were assessed. Apart from the high densification values and volume preservation, the results indicate that proposed method was effective for all the tested species, showing homogenous density patterns, stable densification without noticeable shape recovery, and enhanced mechanical properties. Future research should test the HIP method in softwoods and consider the ring orientation in order to enhance the control of the densified geometry.

Sustainability in Wood Products: A New Perspective for Handling Natural Diversity

Wood is a renewable resource with excellent qualities and the potential to become a key element of a future bioeconomy. The increasing environmental awareness and drive to achieve sustainability is leading to a resurgence of research on wood materials. Nevertheless, the global climate changes and associated consequences will soon challenge the wood-value chains in several regions (e.g., central Europe). To cope with these challenges, it is necessary to rethink the current practice of wood sourcing and transformation. The goal of this review is to address the intrinsic natural diversity of wood, from its origin to its technological consequences for the present and future manufacturing of wood products. So far, industrial processes have been optimized to repress the variability of wood properties, enabling more efficient processing and production of reliable products. However, the need to preserve biodiversity and the impact of climate change on forests call for new wood processing techniques and green chemistry protocols for wood modification as enabling factors necessary for managing a more diverse wood provision in the future. This article discusses the past developments that have resulted in the current wood value chains and provides a perspective about how natural variability could be turned into an asset for making truly sustainable wood products. After briefly introducing the chemical and structural complexity of wood, the methods conventionally adopted for industrial homogenization and modification of wood are discussed in relation to their evolution toward increased sustainability. Finally, a perspective is given on technological potentials of machine learning techniques and of novel functional wood materials. Here the main message is that through a combination of sustainable forestry, adherence to green chemistry principles and adapted processes based on machine learning, the wood industry could not only overcome current challenges but also thrive in the near future despite the awaiting challenges.

Emerging Engineered Wood for Building Applications

The building sector, including building operations and materials, was responsible for the emission of ∼11.9 gigatons of global energy-related CO₂ in 2020, accounting for 37% of the total CO₂ emissions, the largest share among different sectors. Lowering the carbon footprint of buildings requires the development of carbon-storage materials as well as novel designs that could enable multifunctional components to achieve widespread applications. Wood is one of the most abundant biomaterials on Earth and has been used for construction historically. Recent research breakthroughs on advanced engineered wood products epitomize this material's tremendous yet largely untapped potential for addressing global sustainability challenges. In this review, we explore recent developments in chemically modified wood that will produce a new generation of engineered wood products for building applications. Traditionally, engineered wood products have primarily had a structural purpose, but this review broadens the classification to encompass more aspects of building performance. We begin by providing multiscale design principles of wood products from a computational point of view, followed by discussion of the chemical modifications and structural engineering methods used to modify wood in terms of its mechanical, thermal, optical, and energy-related performance. Additionally, we explore life cycle assessment and techno-economic analysis tools for guiding future research toward environmentally friendly and economically feasible directions for engineered wood products. Finally, this review highlights the current challenges and perspectives on future directions in this research field. By leveraging these new wood-based technologies and analysis tools for the fabrication of carbon-storage materials, it is possible to design sustainable and carbon-negative buildings, which could have a significant impact on mitigating climate change.

Robust flexural performance and fracture behavior of TiO2 decorated densified bamboo as sustainable structural materials

High-performance, fast-growing natural materials with sustainable and functional features currently arouse significant attention. Here, facile processing, involving delignification, in situ hydrothermal synthesis of TiO₂ and pressure densification, is employed to transform natural bamboo into a high-performance structural material. The resulting TiO₂-decorated densified bamboo exhibits high flexural strength and elastic stiffness, with both properties more than double that of natural bamboo. Real-time acoustic emission reveals the key role of the TiO₂ nanoparticles in enhancing the flexural properties. The introduction of nanoscale TiO₂ is found to markedly increase the degree of oxidation and the formation of hydrogen bonds in bamboo materials, leading to extensive interfacial failure between the microfibers, a micro-fibrillation process that results in substantial energy consumption and high fracture resistance. This work furthers the strategy of the synthetic reinforcement of fast-growing natural materials, which could lead to the expanded applications of sustainable materials for high-performance structural applications.

Autonomous self-burying seed carriers for aerial seeding

Aerial seeding can quickly cover large and physically inaccessible areas¹ to improve soil quality and scavenge residual nitrogen in agriculture², and for postfire reforestation^3-5 and wildland restoration^6,7. However, it suffers from low germination rates, due to the direct exposure of unburied seeds to harsh sunlight, wind and granivorous birds, as well as undesirable air humidity and temperature^1,8,9. Here, inspired by Erodium seeds^10-14, we design and fabricate self-drilling seed carriers, turning wood veneer into highly stiff (about 4.9 GPa when dry, and about 1.3 GPa when wet) and hygromorphic bending or coiling actuators with an extremely large bending curvature (1,854 m^-1), 45 times larger than the values in the literature^15-18. Our three-tailed carrier has an 80% drilling success rate on flat land after two triggering cycles, due to the beneficial resting angle (25°-30°) of its tail anchoring, whereas the natural Erodium seed's success rate is 0%. Our carriers can carry payloads of various sizes and contents including biofertilizers and plant seeds as large as those of whitebark pine, which are about 11 mm in length and about 72 mg. We compare data from experiments and numerical simulation to elucidate the curvature transformation and actuation mechanisms to guide the design and optimization of the seed carriers. Our system will improve the effectiveness of aerial seeding to relieve agricultural and environmental stresses, and has potential applications in energy harvesting, soft robotics and sustainable buildings.

Green, Sustainable Architectural Bamboo with High Light Transmission and Excellent Electromagnetic Shielding as a Candidate for Energy-Saving Buildings

Currently, light-transmitting, energy-saving, and electromagnetic shielding materials are essential for reducing indoor energy consumption and improving the electromagnetic environment. Here, we developed a cellulose composite with excellent optical transmittance that retained the natural shape and fiber structure of bamboo. The modified whole bamboo possessed an impressive optical transmittance of approximately 60% at 6.23 mm, illuminance of 1000 luminance (lux), water absorption stability (mass change rate less than 4%), longitudinal tensile strength (46.40 MPa), and surface properties (80.2 HD). These were attributed to not only the retention of the natural circular hollow structure of the bamboo rod on the macro, but also the complete bamboo fiber skeleton template impregnated with UV resin on the micro. Moreover, a multilayered device consisting of translucent whole bamboo, transparent bamboo sheets, and electromagnetic shielding film exhibited remarkable heat insulation and heat preservation performance as well as an electromagnetic shielding performance of 46.3 dB. The impressive optical transmittance, mechanical properties, thermal performance, and electromagnetic shielding abilities combined with the renewable and sustainable nature, as well as the fast and efficient manufacturing process, make this bamboo composite material suitable for effective application in transparent, energy-saving, and electromagnetic shielding buildings.

Bamboo-Inspired Renewable, Lightweight, and Vibration-Damping Laminated Structural Materials for the Floor of a Railroad Car

It is important for the floor of railroad cars to be fitted with vibration- and noise-reducing, fire-resistant, and durable materials. In this study, inspired by a delicate and ordered bamboo gradient structure and excellent multilevel interfaces, we fabricated a laminated composite with characteristics similar to those of the bamboo structure using a simple and effective "top-down" method by laminating fast-growing wood, waste rubber, and bamboo charcoal plastic sheets made of bamboo processing residues. This composite material combines the unique advantages of a laminated structure design and composite interface bionics. The low density (0.73 g/cm³) of the laminated composite results in a specific modulus of 13.03 GPa cm³/g, a vibration damping ratio of 6.61%, and an impact toughness of 14.16 J/cm², which is significantly higher than that of other wood-based composites used for high-speed rail floors, such as Birch plywood (BP). In addition, we also investigated the laminated composite bonding property, fire resistance, and fatigue performance. This biomimetic bamboo-wood composite material has great potential for application in fitting the floor of eco-friendly railway cars.

Modification of Poplar Wood via Polyethylene Glycol Impregnation Coupled with Compression

Wood permeability and compressibility are affected by cell wall structure and chemical composition. These properties can be improved by appropriate wood pretreatments. Low-density poplar wood was converted to a more dense structure by the following steps: First, lignin and hemicellulose were removed using a mixture of NaOH and Na2SO3. Second they were impregnated with polyethylene glycol (PEG, mean molecular weight of 1200), nano-SiO2, and a silane coupling agent at atmospheric temperature and pressure. Finally, impregnated wood was compressed at 150 °C. Results showed that the tracheid lumens on the transverse section of the compressed wood almost vanished. Specifically, the lumens in the wood cells, especially those that were compressed, were almost completely filled with PEG. In FTIR, the asymmetric absorption peaks of Si–O–Si at 1078–1076 cm−1 were clearly observed, which confirms the existence of bonding between nano-SiO2 and wood. The highest melting enthalpy and crystallization enthalpy showed a heat storage capacity of modified wood, which were 20.7 and 9.8 J/g, respectively. Such phase change capabilities may have potential applications in regulating the rate of change of room temperature. In summary, the modified wood could be utilized as material for construction to conserve energy.

Selected Properties of Densified Hornbeam and Paulownia Wood Plasticised in Ammonia Solution

The aim of the study was to densify samples of Paulownia Clone wood in vitro 112 and hornbeam (Carpinus betulus L.) by compression in the radial direction. Before the specimens were densified, they were subjected to plastic treatment in an ammonia solution. After densification, the compressive strength in the radial direction and the determination of the Brinell hardness in all three anatomical directions of the wood were determined. The wood swelling in humid air (98% RH) and liquid water was also determined. Paulownia wood density increased by about 280% and hornbeam wood density by 40%. The Brinell hardness parallel to the fibres increased by 49 and 390%, perpendicular by 80 and 388% for hornbeam and Paulownia, respectively. A significant increase in the compressive strength of wood in the radial direction was also observed. Densified hornbeam wood exposed to water showed a high swelling value of 153, while Paulownia wood exhibited 107%.

Intercellular Matrix Infiltration Improves the Wet Strength of Delignified Wood Composites

Delignified wood (DW) represents a promising bio-based fibrous material as a reinforcing component in high-performance composites. These cellulose composites possess excellent strength and stiffness in the dry state, which are significantly higher than for natural wood. However, in the wet state, a penetrating water layer enters the intercellular regions and disrupts the stress transfer mechanisms between cell fibers in fully DW. This water layer initially facilitates complex shaping of the material but imparts DW composites with very low wet stiffness and strength. Therefore, a sufficient stress transfer in the wet state necessitates a resin impregnation of these intercellular regions, establishing bonding mechanisms between adjacent fibers. Here, we utilize a water-based dimethyloldihydroxyethylene urea thermosetting matrix (DMDHEU) and compare it with a non-water-based epoxy matrix. We infiltrate these resins into DW and investigate their spatial distribution by scanning electron microscopy, atomic force microscopy, and confocal Raman spectroscopy. The water-based resin impregnates the intercellular areas and generates an artificial compound middle lamella, while the epoxy infiltrates only the cell lumina of the dry DW. Tensile tests in the dry and wet states show that the DMDHEU matrix infiltration of the intercellular areas and the cell wall results in a higher tensile strength and stiffness compared to the epoxy resin. Here, the artificial compound middle lamella made of DMDHEU bonds adjacent fibers together and substantially increases the composites' wet strength. This study elucidates the importance of the interaction and spatial distribution of the resin system within the DW structure to improve mechanical properties, particularly in the wet state.

Interpretation of Strengthening Mechanism of Densified Wood from Supramolecular Structures

In this study, densified wood was prepared by hot pressing after partial lignin and hemicellulose were removed through alkaline solution cooking. The tensile strength and elastic modulus of densified wood were improved up to 398.5 MPa and 22.5 GPa as compared with the original wood, and the characterization of its supramolecular structures showed that the crystal plane spacing of the densified wood decreased, the crystallite size increased, and the maximum crystallinity (CI) of cellulose increased by 15.05%; outstandingly, the content of O(6)H⋯O(3′) intermolecular H-bonds increased by approximately one-fold at most. It was found that the intermolecular H-bond content was significantly positively correlated with the tensile strength and elastic modulus, and accordingly, their Pearson correlation coefficients were 0.952 (p < 0.01) and 0.822 (p < 0.05), respectively. This work provides a supramolecular explanation for the enhancement of tensile strength of densified wood.

Changes in Chemical and Thermal Properties of Bamboo after Delignification Treatment

Bamboo delignification is a common method for studying its functional value-added applications. In this study, bamboo samples were delignified by treatment with sodium chlorite. The effects of this treatment on the bamboo’s microstructure, surface chemical composition, and pyrolysis behaviour were evaluated. Field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were conducted to evaluate these parameters. The FTIR results demonstrated that the lignin peak decreased or disappeared, and some hemicellulose peaks decreased, indicating that sodium chlorite treatment effectively removed lignin and partly decomposed hemicellulose, although cellulose was less affected. The XPS results showed that, after treatment, the oxygen-to-carbon atomic ratio of delignified bamboo increased from 0.34 to 0.45, indicating a lack of lignin. XRD revealed increased crystallinity in delignified bamboo. Further pyrolysis analysis of treated and untreated bamboo showed that, although the pyrolysis stage of the delignified bamboo did not change, the maximum thermal degradation rate (R_max) and its corresponding temperature (from 353.78 to 315.62 °C) decreased significantly, indicating that the pyrolysis intensity of the bamboo was weakened after delignification. Overall, this study showed that delignified bamboo develops loose surfaces, increased pores, and noticeable fibres, indicating that alkali-treated bamboo has promising application potential due to its novel and specific functionalities.

Upscaling 3D Engineered Trees for Off-Grid Desalination

More than 70% of the population without access to safe drinking water lives in remote and off-grid areas. Inspired by natural plant transpiration, we designed and tested in this study an array of scalable three-dimensional (3D) engineered trees made of natural wood for continuous water desalination to provide affordable and clean drinking water. The trees took advantage of capillary action in the wood xylems and lifted water more than 1 foot off the ground with or without solar irradiation. This process overcame some major challenges of popular solar-driven water evaporation and water harvesting, such as intermittent operation, low water production rate, and system scaling. The trade-off between energy transfer and system footprint was tackled by optimizing the interspacing between the trees. The scaled system has a ratio of surface area (vapor generation) to project area (water transport) up to 118, significantly higher than the prevailing flat-sheet design. The extensive surface area evaporated water at a temperature cooler than the surrounding air, drawing on multiple environmental energy sources including solar, wind, or ambient heat in the air and realized continuous operation. The total energy for evaporation reached over 300% of the one-sun irradiance, enabling a freshwater production rate of 4.8 L m^-2 h^-1 from an array of 16 trees in an enclosed room and 14 L m^-2 h^-1 under a 3 m/s airflow. Furthermore, we found that the ambient heat in the air contributed 60%-70% of the total latent heat of vaporization when energy sources were decoupled. During long-term desalination tests, the engineered trees demonstrated a self-cleaning mechanism with daily cycles of salt accumulation and dissolution. Combining the quantification from an evaporation model and meteorology data covering the globe, we also demonstrated that the 3D engineered trees can be of particular interest for sustainable desalination in the Middle East and North Africa (MENA) regions.

Properties of Multilayer Transparent Bamboo Materials

The objective of this study is to solve the shortcomings of the current transparent bamboo veneer with a small thickness and low light transmittance by means of lamination. The delignified bamboo templates were vacuum impregnated with an epoxy resin, and the impregnated bamboo templates were laminated with the same radial texture using the viscosity of the epoxy resin to obtain multilayer transparent bamboo (MLTB). The multilayer stacking method can greatly improve the optical and mechanical properties of transparent bamboo. The transparent bamboo with a thickness of 1.2 mm and the delignified bamboo with a volume fraction of 44.8% prepared by multilayer stacking exhibited an improved total optical transmissivity of up to 78.6%, while the highest transmittance of bamboo (0.9 mm thick) without multilayer stacking treatment was only 10.4%. Compared with the single-layer transparent bamboo with a thickness of 2.1 mm, the maximum tensile strength of the seven-layer transparent bamboo was 4 times that of the single-layer transparent bamboo. Therefore, MLTB can compensate to a certain extent for the low light transmission and poor mechanical properties of single-layer transparent bamboo. Overall, MLTB shows a richer and more layered texture, which has more esthetic value. It is a kind of natural transparent material with good light transmittance and excellent mechanical properties, which has a good development prospect as a structural material in the fields of construction, household, and electronic products.

Programming material compliance and actuation: hybrid additive fabrication of biocomposite structures for large-scale self-shaping

We present a hybrid approach to manufacturing a new class of large-scale self-shaping structures through a method of additive fabrication combining fused granular fabrication (FGF) and integrated hygroscopic wood actuators (HWAs). Wood materials naturally change shape with high forces in response to moisture stimuli. The strength and simplicity of this actuation make the material suitable for self-shaping architectural-scale components. However, the anisotropic composition of wood, which enables this inherent behavior, cannot be fully customized within existing stock. On the other hand, FGF allows for the design of large physical parts with multi-functional interior substructures as inspired by many biological materials. We propose to encode passively actuated movement into physical structures by integrating HWAs within 3D-printed meta-structures with functionally graded stiffnesses. By leveraging robotic manufacturing platforms, self-shaping biocomposite material systems can be upscaled with variable resolutions and at high volumes, resulting in large-scale structures capable of transforming from flat to curved simply through changes in relative humidity.

Characterization of Microstructure, Chemical, and Physical Properties of Delignified and Densified Poplar Wood

Wood is an attractive and inherently sustainable alternative to many conventional materials. Recent research on improving wood mechanical strength emphasizes wood densification through the partial removal of lignin and hemicelluloses, therefore the chemical and physical properties of delignified and densified wood require further investigation. In this study, poplar wood samples were subjected to alkali and maleic acid hydrotropic delignification with varying degrees of lignin and hemicellulose removal followed by hot pressing, and the microstructure, chemical properties, and dimensional stability of densified wood through delignification were evaluated. The results showed that the complete wood cell collapse was observed near the surface of all the delignified wood blocks, as well as some micro-cracks in the cell walls. The chemical analysis indicated that delignification occurred mainly near the surface of the wood blocks and enhanced hydrogen bonding among the aligned cellulose fibers. For dimensional stability, the set recovery decreased with the increase in alkali dosage, and the considerable fixation of compressive deformation was obtained by a post-densification hydrothermal treatment at 180 °C. These results have demonstrated that the densified wood with delignification can be easily fabricated using the proposed method, and the densified wood exhibited great potential to be used as a sustainable material.

Hydrogen-Bonding-Aided Fabrication of Wood Derived Cellulose Scaffold/Aramid Nanofiber into High-Performance Bulk Material

Preparing a lightweight yet high-strength bio-based structural material with sustainability and recyclability is highly desirable in advanced applications for architecture, new energy vehicles and spacecraft. In this study, we combined cellulose scaffold and aramid nanofiber (ANF) into a high-performance bulk material. Densification of cellulose microfibers containing ANF and hydrogen bonding between cellulose microfibers and ANF played a crucial role in enhanced physical and mechanical properties of the hybrid material. The prepared material showed excellent tensile strength (341.7 MPa vs. 57.0 MPa for natural wood), toughness (4.4 MJ/m³ vs. 0.4 MJ/m³ for natural wood) and Young’s modulus (24.7 GPa vs. 7.2 GPa for natural wood). Furthermore, due to low density, this material exhibited a superior specific strength of 285 MPa·cm³·g⁻¹, which is remarkably higher than some traditional building materials, such as concrete, alloys. In addition, the cellulose scaffold was infiltrated with ANFs, which also improved the thermal stability of the hybrid material. The facile and top-down process is effective and scalable, and also allows one to fully utilize cellulose scaffolds to fabricate all kinds of advanced bio-based materials.

Sustainability in wood materials science: an opinion about current material development techniques and the end of lifetime perspectives

Wood is considered the most important renewable resource for a future sustainable bioeconomy. It is traditionally used in the building sector, where it has gained importance in recent years as a sustainable alternative to steel and concrete. Additionally, it is the basis for the development of novel bio-based functional materials. However, wood's sustainability as a green resource is often diminished by unsustainable processing and modification techniques. They mostly rely on fossil-based precursors and yield inseparable hybrids and composites that cannot be reused or recycled. In this article, we discuss the state of the art of environmental sustainability in wood science and technology. We give an overview of established and upcoming approaches for the sustainable production of wood-based materials. This comprises wood protection and adhesion for the building sector, as well as the production of sustainable wood-based functional materials. Moreover, we elaborate on the end of lifetime perspective of wood products. The concept of wood cascading is presented as a possibility for a more efficient use of the resource to increase its beneficial impact on climate change mitigation. We advocate for a holistic approach in wood science and technology that not only focuses on the material's development and production but also considers recycling and end of lifetime perspectives of the products. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Advanced materials design based on waste wood and bark

Trees belong to the largest living organisms on Earth and plants in general are one of our main renewable resources. Wood as a material has been used since the beginning of humankind. Today, forestry still provides raw materials for a variety of applications, for example in the building industry, in paper manufacturing and for various wood products. However, many parts of the tree, such as reaction wood, branches and bark are often discarded as forestry residues and waste wood, used as additives in composite materials or burned for energy production. More advanced uses of bark include the extraction of chemical substances for glues, food additives or healthcare, as well as the transformation to advanced carbon materials. Here, we argue that a proper understanding of the internal fibrous structure and the resulting mechanical behaviour of these forest residues allows for the design of materials with greatly varying properties and applications. We show that simple and cheap treatments can give tree bark a leather-like appearance that can be used for the construction of shelters and even the fabrication of woven textiles. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Twist and lock: nutshell structures for high strength and energy absorption

Nutshells achieve remarkable properties by optimizing structure and chemistry at different hierarchical levels. Probing nutshells from the cellular down to the nano- and molecular level by microchemical and nanomechanical imaging techniques reveals insights into nature's packing concepts. In walnut and pistachio shells, carbohydrate and lignin polymers assemble to form thick-walled puzzle cells, which interlock three-dimensionally and show high tissue strength. Pistachio additionally achieves high-energy absorption by numerous lobes interconnected via ball-joint-like structures. By contrast, the three times more lignified walnut shells show brittle LEGO-brick failure, often along the numerous pit channels. In both species, cell walls (CWs) show distinct lamellar structures. These lamellae involve a helicoidal arrangement of cellulose macrofibrils as a recurring motif. Between the two nutshell species, these lamellae show differences in thickness and pitch angle, which can explain the different mechanical properties on the nanolevel. Our in-depth study of the two nutshell tissues highlights the role of cell form and their interlocking as well as plant CW composition and structure for mechanical protection. Understanding these plant shell concepts might inspire biomimetic material developments as well as using walnut and pistachio shell waste as sustainable raw material in future applications.

Nanoscale Ion Regulation in Wood-Based Structures and Their Device Applications

Ion transport and regulation are fundamental processes for various devices and applications related to energy storage and conversion, environmental remediation, sensing, ionotronics, and biotechnology. Wood-based materials, fabricated by top-down or bottom-up approaches, possess a unique hierarchically porous fibrous structure that offers an appealing material platform for multiscale ion regulation. The ion transport behavior in these materials can be regulated through structural and compositional engineering from the macroscale down to the nanoscale, imparting wood-based materials with multiple functions for a range of emerging applications. A fundamental understanding of ion transport behavior in wood-based structures enhances the capability to design high-performance ion-regulating devices and promotes the utilization of sustainable wood materials. Combining this unique ion regulation capability with the renewable and cost-effective raw materials available, wood and its derivatives are the natural choice of materials toward sustainability.

Wood Derived Cellulose Scaffolds-Processing and Mechanics

Wood-derived cellulose materials obtained by structure-retaining delignification are attracting increasing attention due to their excellent mechanical properties and great potential to serve as renewable and CO₂ storing cellulose scaffolds for advanced hybrid materials with embedded functionality. Various delignification protocols and a multitude of further processing steps including polymer impregnation and densification are applied resulting in a large range of properties. However, treatment optimization requires a more comprehensive characterization of the developed materials in terms of structure, chemical composition, and mechanical properties for faster progress in the field. Herein, the current protocols for structure-retaining delignification are reviewed and the emphasis is placed on the mechanical characterization at different hierarchical levels of the cellulose scaffolds by experiments and modeling to reveal the underlying structure-property relationships.

Structural and Ecofriendly Holocellulose Materials from Wood: Microscale Fibers and Nanoscale Fibrils

Mildly delignified wood holocellulose fibers show well-preserved cellulose nanofibril (CNF) structure in the fiber cell wall. Fibers, paper, biocomposites, and compression-molded fiber materials demonstrate excellent mechanical properties. Here, wood holocellulose fibers and corresponding CNFs are discussed with respect to nanostructure, mechanical performance, and advanced materials potential. Functionalization routes are discussed, as well as materials selection, nanoscience of recycling, and the embodied energy in cellulosic candidates for multifunctional structural materials.

Mechanics Design in Cellulose-Enabled High-Performance Functional Materials

The abundance of cellulose found in natural resources such as wood, and the wide spectrum of structural diversity of cellulose nanomaterials in the form of micro-nano-sized particles and fibers, have sparked a tremendous interest to utilize cellulose's intriguing mechanical properties in designing high-performance functional materials, where cellulose's structure-mechanics relationships are pivotal. In this progress report, multiscale mechanics understanding of cellulose, including the key role of hydrogen bonding, the dependence of structural interfaces on the spatial hydrogen bond density, the effect of nanofiber size and orientation on the fracture toughness, are discussed along with recent development on enabling experimental design techniques such as structural alteration, manipulation of anisotropy, interface and topology engineering. Progress in these fronts renders cellulose a prospect of being effectuated in an array of emerging sustainable applications and being fabricated into high-performance structural materials that are both strong and tough.

Sustainable Wood Nanotechnologies for Wood Composites Processed by In-Situ Polymerization

The development of large, multifunctional structures from sustainable wood nanomaterials is challenging. The need to improve mechanical performance, reduce moisture sensitivity, and add new functionalities, provides motivation for nanostructural tailoring. Although existing wood composites are commercially successful, materials development has not targeted nano-structural control of the wood cell wall, which could extend the property range. For sustainable development, non-toxic reactants, green chemistry and processing, lowered cumulative energy requirements, and lowered CO2-emissions are important targets. Here, modified wood substrates in the form of veneer are suggested as nanomaterial components for large, load-bearing structures. Examples include polymerization of bio-based monomers inside the cell wall, green chemistry wood modification, and addition of functional inorganic nanoparticles inside the cell wall. The perspective aims to describe bio-based polymers and green processing concepts for this purpose, along with wood nanoscience challenges.

Effect of UV Radiation on Optical Properties and Hardness of Transparent Wood

Optically transparent wood is a type of composite material, combining wood as a renewable resource with the optical and mechanical properties of synthetic polymers. During this study, the effect of monochromatic UV-C (λ—250 nm) radiation on transparent wood was evaluated. Samples of basswood were treated using a lignin modification method, to preserve most of the lignin, and subsequently impregnated with refractive-index-matched types of acrylic polymers (methyl methacrylate, 2-hydroxyethyl methacrylate). Optical (transmittance, colour) and mechanical (shore D hardness) properties were measured to describe the degradation process over 35 days. The transmittance of the samples was significantly decreased during the first seven days (12% EMA, 15% MMA). The average lightness of both materials decreased by 10% (EMA) and 17% (MMA), and the colour shifted towards a red and yellow area of CIE L*a*b* space coordinates. The influence of UV-C radiation on the hardness of the samples was statistically insignificant (W+MMA 84.98 ± 2.05; W+EMA 84.89 ± 2.46), therefore the hardness mainly depends on the hardness of used acrylic polymer. The obtained results can be used to assess the effect of disinfection of transparent wood surfaces with UV-C radiation (e.g., due to inactivation of SARS-CoV-2 virus) on the change of its aesthetic and mechanical properties.

Wood Sponge Reinforced with Polyvinyl Alcohol for Sustainable Oil-Water Separation

The excellent oil absorption capacity and sustainability advantages of adsorbent-type oil-absorbing products have become the primary method to deal with marine oil spills and organic pollution at this stage, especially aerogel products. However, this type of material also has some problems, such as secondary pollution during nanocellulose preparation. Lignin and hemicellulose were removed from the natural wood, and followed by the action of freeze drying, the wood sponge was prepared. Then, followed by immersing the wood sponge into polyvinyl alcohol solution (PVA) and dipping it in polydimethylsiloxane solution, the target PVA-reinforced wood sponge with better mechanical compressibility and hydrophobic properties was obtained. The new wood sponge showed high mechanical compressibility (reversible compression rate of 40%) and elastic recovery rate (the height retention rate was about 100% after 200 cycles of 30% strain). It also showed excellent hydrophobic and oleophilic properties, and the water contact angle was up to 138°, and the oil absorption capacity was 25 g·g^-1. The ability of oil absorption can be recovered by compression, and the high absorption rate was maintained after 50 cycles. The wood sponge has great potential in reusable oil-water separation due to low cost, high efficiency, high performance, biodegradability, environmental friendliness, and other advantages.

Strong, Hydrostable, and Degradable Straws Based on Cellulose-Lignin Reinforced Composites

The huge consumption of single-use plastic straws has brought a long-lasting environmental problem. Paper straws, the current replacement for plastic straws, suffer from drawbacks, such as a high cost of the water-proof wax layer and poor water stability due to the easy delamination of the wax layer. It is therefore crucial to find a high-performing alternative to mitigate the environmental problems brought by plastic straws. In this paper, all natural, degradable, cellulose-lignin reinforced composite straws, inspired by the reinforcement principle of cellulose and lignin in natural wood are developed. The cellulose-lignin reinforced composite straw is fabricated by rolling up a wet film made of homogeneously mixed cellulose microfibers, cellulose nanofibers, and lignin powders, which is then baked in oven at 150 °C. When baked, lignin melts and infiltrates the micro-nanocellulose network, acting as a polyphenolic binder to improve the mechanical strength and hydrophobicity performance of the resulting straw. The obtained straws demonstrate several advantageous properties over paper straws, including 1) excellent mechanical performance, 2) high hydrostability, and 3) low cost. Moreover, the natural degradability of the cellulose-lignin reinforced composite straws makes them promising candidates to replace plastic straws and suggests possible substitutes for other petroleum-based plastics.

Sustainable Double-Network Structural Materials for Electromagnetic Shielding

Electromagnetic interference (EMI) shielding materials with excellent EMI shielding efficiency (SE), lightweight property, and superb mechanical performance are vitally important for modern society, but it is still a challenge to realize these performances simultaneously on one material. Here, we report a sustainable bioinspired double-network structural material with excellent specific strength (146 MPa g^-1 cm³) and remarkable EMI SE (100 dB) from cellulose nanofiber (CNF) and carbon nanotubes (CNTs), which demonstrates remarkable and outstanding performance to both typical metal materials and reported polymer composites. In particular, the bioinspired double-network structure design simultaneously achieves an extremely high electrical conductivity and mechanical strength, which makes it a lightweight, high shielding efficiency, and sustainable structural material for real-life electromagnetic wave shielding applications.

Review of Functional Treatments for Modified Wood

Wood modification is now widely recognized as offering enhanced properties of wood and overcoming issues such as dimensional instability and biodegradability which affect natural wood. Typical wood modification systems use chemical modification, impregnation modification or thermal modification, and these vary in the properties achieved. As control and understanding of the wood modification systems has progressed, further opportunities have arisen to add extra functionalities to the modified wood. These include UV stabilisation, fire retardancy, or enhanced suitability for paints and coatings. Thus, wood may become a multi-functional material through a series of modifications, treatments or reactions, to create a high-performance material with previously impossible properties. In this paper we review systems that combine the well-established wood modification procedures with secondary techniques or modifications to deliver emerging technologies with multi-functionality. The new applications targeted using this additional functionality are diverse and range from increased electrical conductivity, creation of sensors or responsive materials, improvement of wellbeing in the built environment, and enhanced fire and flame protection. We identified two parallel and connected themes: (1) the functionalisation of modified timber and (2) the modification of timber to provide (multi)-functionality. A wide range of nanotechnology concepts have been harnessed by this new generation of wood modifications and wood treatments. As this field is rapidly expanding, we also include within the review trends from current research in order to gauge the state of the art, and likely direction of travel of the industry.

Enhanced mechanical energy conversion with selectively decayed wood

Producing electricity from renewable sources and reducing its consumption by buildings are necessary to meet energy and climate change challenges. Wood is an excellent "green" building material and, owing to its piezoelectric behavior, could enable direct conversion of mechanical energy into electricity. Although this phenomenon has been discovered decades ago, its exploitation as an energy source has been impaired by the ultralow piezoelectric output of native wood. Here, we demonstrate that, by enhancing the elastic compressibility of balsa wood through a facile, green, and sustainable fungal decay pretreatment, the piezoelectric output is increased over 55 times. A single cube (15 mm by 15 mm by 13.2 mm) of decayed wood is able to produce a maximum voltage of 0.87 V and a current of 13.3 nA under 45-kPa stress. This study is a fundamental step to develop next-generation self-powered green building materials for future energy supply and mitigation of climate change.

Identifying Efficient Transport Pathways in Early-Wood Timber: Insights from 3D X-ray CT Imaging of Softwood in the Presence of Flow

Wider use of timber has the potential to greatly reduce the embodied carbon of construction. Improved chemical treatment could help overcome some of the barriers to wider application of timber, by furthering the durability and/or mechanical properties of this natural material. Improving timber treatment by treating the whole volume of a piece of timber, or tailored sections thereof, requires sound understanding and validated modelling of the natural paths for fluid flow through wood. In this study we carry out a robust analysis of three-dimensional X-ray CT measurements on kiln-dried softwood in the presence of flow and identify small portions of early-wood which are uniquely capable of transporting fluids—herein ‘efficient transport pathways’. We successfully model the effects of these pathways on the liquid uptake by timber by introducing a spatial variability in the amount of aspiration of the bordered pits following kiln drying. The model demonstrates that fluid advances along these efficient transport paths between 10 and 30 times faster than in the remainder of the timber. Identifying these efficient transport pathways offers scope to improve and extend the degree to which timber properties are enhanced at an industrial scale through processes to impregnate timber.

In Situ Lignin Modification toward Photonic Wood

Lignin serves as a binder that forms strong matrices of the cell walls of wood. However, it has many photolabile chromophore groups that create a monotonic brownish color and make wood susceptible to photodegradation. Herein, a new strategy is reported for modifying lignin using an in situ, rapid, and scalable process that involves the photocatalytic oxidation of native lignin in wood by H₂ O₂ and UV light. The reaction selectively eliminates lignin's chromophores while leaving the aromatic skeleton intact, thus modulating the optical properties of wood. The resulting "photonic wood" retains ≈80% of its original lignin content, which continues to serve as a strong binder and water-proofing agent. As a result, photonic wood features a much higher mechanical strength in a wet environment (20-times higher tensile strength and 12-times greater compression resistance), significant scalability (≈2 m long sample), and largely reduced processing times (1-6.5 h vs 4-14 h) compared with delignification methods. Additionally, this in situ lignin-modified wood structure is easily patterned through a photocatalytic oxidation process. This photocatalytic production of photonic wood paves the way for the large-scale manufacturing of sustainable biosourced functional materials for a range of applications, including energy-efficient buildings, optical management, and fluidic, ionic, electronic, and optical devices.

Nanocellulose: Recent Fundamental Advances and Emerging Biological and Biomimicking Applications

In the effort toward sustainable advanced functional materials, nanocelluloses have attracted extensive recent attention. Nanocelluloses range from rod-like highly crystalline cellulose nanocrystals to longer and more entangled cellulose nanofibers, earlier denoted also as microfibrillated celluloses and bacterial cellulose. In recent years, they have spurred research toward a wide range of applications, ranging from nanocomposites, viscosity modifiers, films, barrier layers, fibers, structural color, gels, aerogels and foams, and energy applications, until filtering membranes, to name a few. Still, nanocelluloses continue to show surprisingly high challenges to master their interactions and tailorability to allow well-controlled assemblies for functional materials. Rather than trying to review the already extensive nanocellulose literature at large, here selected aspects of the recent progress are the focus. Water interactions, which are central for processing for the functional properties, are discussed first. Then advanced hybrid gels toward (multi)stimuli responses, shape-memory materials, self-healing, adhesion and gluing, biological scaffolding, and forensic applications are discussed. Finally, composite fibers are discussed, as well as nanocellulose as a strategy for improvement of photosynthesis-based chemicals production. In summary, selected perspectives toward new directions for sustainable high-tech functional materials science based on nanocelluloses are described.