Regenerated isotropic wood

Creation of Wood-Based Hierarchical Superstructures via In Situ Growth of ZIF-8 for Enhancing Mechanical Strength and Electromagnetic Shielding Performance

Given the escalating prevalence of electromagnetic pollution, there is an urgent need for the development of high-performance electromagnetic interference (EMI) shielding materials. Herein, wood-based electromagnetic shielding materials have gained significant popularity due to their exceptional performance as building materials. In this study, a novel wood-based composite with electromagnetic shielding properties is developed. Through the in situ growth of zeolitic imidazolate framework-8 (ZIF-8) crystals on wood fibers, coupled with uniform integration of carbon nanotubes (CNTs), a multifunctional composite named ZIF-8/Poplar-CNT composite is synthesized via a one-step thermoforming process. The incorporation of CNTs endows the composites with excellent EMI shielding effectiveness (EMI SE). Among these elements, despite ZIF-8 crystals not possessing intrinsic electromagnetic shielding functionality, their distinctive dodecahedral structure proves adept at scattering and reflecting electromagnetic waves within the composites, further improving the electromagnetic shielding effect. Hence, the ZIF-8/Poplar-CNT composite (56.95 dB) has ≈10 dB higher EMI SE compared to that of the composites without ZIF-8 crystals. Meanwhile, ZIF-8 crystals endow the materials with excellent tensile strength (54.84 MPa, enhanced by 4 times). Moreover, the introduction of Zn2+ provides superior antibacterial properties. The potential applications of ZIF-8/Poplar-CNT composites extend to diverse areas such as building decoration, electronic products, and medical equipment.

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.

Tough and Moldable Sustainable Cellulose-Based Structural Materials via Multiscale Interface Engineering

All-natural materials derived from cellulose nanofibers (CNFs) are expected to be used to replace engineering plastics and have attracted much attention. However, the lack of crack extension resistance and 3D formability of nanofiber-based structural materials hinders their practical applications. Here, a multiscale interface engineering strategy is reported to construct high-performance cellulose-based materials. The sisal microfibers are surface treated to expose abundant active CNFs with positive charges, thereby enhancing their interfacial combination with the negatively charged CNFs. The robust multiscale dual network enables easy molding of multiscale cellulose-based structural materials into complex 3D special-shaped structures, resulting in nearly twofold and fivefold improvements in toughness and impact resistance compared with those of CNFs-based materials. Moreover, this multiscale interface engineering strategy endows cellulose-based structural materials with better comprehensive performance than petrochemical-based plastics and broadens cellulose's potential for lightweight applications as structural materials with lower environmental effects.

Robust, biodegradable and flame-retardant nanocomposite films based on TEMPO-oxidized cellulose nanofibers and hydroxyapatite nanowires

Flammability is a fatal drawback for sustainable packaging materials made from cellulose and its derivatives. Incorporating inorganic nanomaterials is a viable approach to improve the fire-resistant property. However, due to the aggregation of inorganic fillers and weak interactions between components, incorporating inorganic nanomaterials always had an adverse impact on the mechanical properties and optical transparency of cellulose-based nanocomposites. Herein, we presented a robust, biodegradable, and flame-retardant nanocomposite film composed of TEMPO-oxidized cellulose nanofibers (TOCNFs) and inorganic hydroxyapatite nanowires (HNWs). Both TOCNFs and HNWs possessed one-dimensional microstructure and could form unique organic-inorganic networks microstructure. The organic-inorganic networks interact through physical intertwinement and multiple chemical bonds, endowing nanocomposite film with outstanding mechanical properties. This nanocomposite film showed a tensile strength of 223.68 MPa and Young's modulus of 9.18 GPa, which were superior to most reported cellulose-based nanocomposite. Furthermore, this nanocomposite film demonstrated exceptional thermal stability and flame-retardant feature attributed to the inorganic framework formed by HNWs. This nanocomposite film also possessed a high optical transmittance even when HNWs content reached 30 % and could be decomposed quickly in soil. By employing organic-inorganic interpenetrating network structure design and multiple bonding interaction, cellulose-based nanocomposites can overcome inherent limitations and attain desirable comprehensive properties.

Constructing An All-Natural Bulk Structural Material from Surface-Charged Bamboo Cellulose Fibers with Enhanced Mechanical and Thermal Properties

Bamboo is widely distributed, rapidly regenerable, and incorporates long cellulose fibers, which make it one of the most lightweight and strong natural materials. Processing bamboo into a high-performance structural material for plastic replacement is highly promising but challenging. In this study, an all-natural, high-performance structural material is derived from natural bamboo with superior mechanical and thermal properties that benefit from the introduction of surface charge and further layer-by-layer assembly of bamboo cellulose fibers. The obtained modified bamboo fiber plate (MBFP) transcends the constraints of the natural size and anisotropy of bamboo, showing high flexural strength (ca. 179 MPa) and flexural modulus (ca. 12 GPa). Moreover, the product has an extremely low coefficient of thermal expansion (ca. 11.3×10^-6  K^-1 ), high thermal stability, and superior fire resistance. The excellent mechanical and thermal properties combined with the efficient and rational manufacturing process make MBFP a powerful plastic alternative for furniture, construction, and automotive industries.

An All-Natural Wood-Inspired Aerogel

The oriented pore structure of wood endows it with a variety of outstanding properties, among which the low thermal conductivity has attracted researchers to develop wood-like aerogels as excellent thermal insulation materials. However, the increasing demands of environmental protection have put forward new and strict requirements for the sustainability of aerogels. Here, we report an all-natural wood-inspired aerogel consisting of all-natural ingredients and develop a method to activate the surface-inert wood particles to construct the aerogel. The obtained wood-inspired aerogel has channel structure similar to that of natural wood, endowing it with superior thermal insulation properties to most existing commercial sponges. In addition, remarkable fire retardancy and complete biodegradability are integrated. With the above outstanding performances, this sustainable wood-inspired aerogel will be an ideal substitute for the existing commercial thermal insulation materials.

Preparation of Cellulose Nanofibers from Corn Stalks by Fenton Reaction: A New Insight into the Mechanism by an Experimental and Theoretical Study

Agricultural biomass wastes are an abundant feedstock for biorefineries. However, most of these wastes are not treated in the right way. Here, corn stalks (CSs) were assigned as the raw material to produce cellulose nanofibers (CNFs) via in situ Fenton oxidation treatment. In order to probe the formation mechanism of an in situ Fenton reactor, the bonding interaction of hydrated Fe²⁺ ions and fiber has been systemically studied based on adsorption experiments, IR spectroscopy, density functional theory (DFT) calculations, and Raman spectroscopy. The results indicate that the coordination of the hydrated Fe²⁺ ion to the fiber generates a quasi-octahedral-coordinated sphere around the Fe center. The Jahn-Teller distortion effect of the Fe center promotes the Fe-O₂H₂ bonding interaction via reduction of the energy gap of the d_z² orbital of the Fe center and π_2py/π_2pz orbitals of the H₂O₂ molecule. The oxidation treatment of the pretreated CS by the in situ Fenton process shows the formation of a new carboxyl group on the fiber surface. The scanning electron microscopy image shows that the Fenton-treated fiber was scattered into the nanosized CNFs with a diameter of up to 50 nm. Both experimental and theoretical studies show that the pseudo-first-order kinetic reaction could describe the in situ Fenton kinetics well. Moreover, the proposed catalytic cycle shows that the large thermodynamic barrier is the cleavage of the O-O bond of H₂O₂ to generate the ^•OH radical, and the whole catalytic cycle is found to be spontaneous at room temperature.

Multifunctional cellulosic materials prepared by a reactive DES based zero-waste system

Energy consumption and post-treatment of chemical reagent residues are important issues that hinder the sustainable production of the natural building blocks of cellulose nanofibrils (CNFs). In this study, we realize a low-energy, zero-waste process for CNF production by designing a novel reactive deep eutectic solvent (DES), the residue of which can be directly used as a plant growth regulator. After pretreatment with the DES, cellulose fibers self-delaminate into thin layers referred to as pseudo-CNFs, as their strength, toughness and transmittance are comparable to those of CNFs. Pseudo-CNFs break into smaller particles during recycling and thus display unique mechanical upcycling. After facile fibrillation, the obtained CNFs can independently form freestanding sub-micrometer films that show a strong, full coloration, which is demonstrated for the first time. Our concept can enable a green process, and the developed cellulosic materials may find various applications as structural materials and optical coatings.

Engineered Cellulose Nanofiber Membranes with Ultrathin Low-Dimensional Carbon Material Layers for Photothermal-Enhanced Osmotic Energy Conversion

As a promising clean energy source, membrane-based osmotic energy harvesting has been widely investigated and developed through optimizing the membrane structure in recent years. For chasing higher energy conversion performance, various external stimuli have been introduced into the osmotic energy harvesting systems as assistant factors. Light as a renewable and well-tunable energy form has drawn great attention. Normally, it needs massive photoresponsive materials for improving the energy conversion performance and this hinders its wide applications. Herein, we fabricate a cellulose nanofiber (CNF) membrane with an ultrathin layer of low-dimensional carbon materials (LDCMs) for photothermal-enhanced osmotic energy conversion. The ultralow loading carbon quantum dot, carbon nanotube, and graphene oxide (LDCM/CNF = 1:200 wt) are used for light-to-heat conversion to build the heat gradient across the membrane. The output power density of the osmotic energy generator has increased from ∼3.55 to ∼7.67 W/m² under a 50-fold concentration gradient with light irradiation. This work shows the great potential of the CNF as a nanofluidic platform and the photothermal enhancement in osmotic energy conversion, and the ultralow loading design provides a practical and economical way to fully utilize other energy resources for enhancing osmotic energy conversion.

Plant Cellulose Nanofiber-Derived Structural Material with High-Density Reversible Interaction Networks for Plastic Substitute

Ubiquitous petrochemical-based plastics pose a potential threat to ecosystems. In response, bioderived and degradable polymeric materials are being developed, but their mechanical and thermal properties cannot compete with those of existing petrochemical-based plastics, especially those used as structural materials. Herein, we report a biodegradable plant cellulose nanofiber (CNF)-derived polymeric structural material with high-density reversible interaction networks between nanofibers, exhibiting mechanical and thermal properties better than those of existing petrochemical-based plastics. This all-green material has substantially improved flexural strength (∼300 MPa) and modulus (∼16 GPa) compared with those of existing petrochemical-based plastics. Its average thermal expansion coefficient is only 7 × 10^-6 K^-1, which is more than 10 times lower than those of petrochemical-based plastics, indicating its dimension is almost unchanged when heated, and thus, it has a thermal dimensional stability that is better than those of plastics. As a fully bioderived and degradable material, the all-green material offers a more sustainable high-performance alternative to petrochemical-based plastics.

Sustainable Cellulose-Nanofiber-Based Hydrogels

Hydrogel materials have many excellent properties and a wide range of applications. Recently, a new type of hydrogel has emerged: cellulose nanofiber (CNF)-based hydrogels, which have three-dimensional nanofiber networks and unique physical properties. Because CNFs are abundant, renewable, and biodegradable, they are green and eco-friendly nanoscale building blocks. In addition, CNF-based hydrogel materials exhibit excellent mechanical properties and designable functions by different preparation methods and structure designs, demonstrating huge development potential. In this Perspective, we summarize the recent progress in the development of CNF-based hydrogels and introduce their applications in elastic hydrogels, ionic conduction, water purification, and biomedicine, highlighting future trends and opportunities for the further development of CNF-based hydrogels as emerging materials systems.

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.

Bio-Inspired Lotus-Fiber-like Spiral Hydrogel Bacterial Cellulose Fibers

Hydrogel materials with high water content and good biocompatibility are drawing more and more attention now, especially for biomedical use. However, it still remains a challenge to construct hydrogel fibers with enough strength and toughness for practical applications. Herein, we report a bio-inspired lotus-fiber-mimetic spiral structure hydrogel bacterial cellulose fiber with high strength, high toughness, high stretchability, and energy dissipation, named biomimetic hydrogel fiber (BHF). The spiral-like structure endows BHF with excellent stretchability through plastic deformation and local failure, assisted by the breaking-reforming nature of the hydrogen bonding network among cellulose nanofibers. With the high strength, high stretchability, high energy dissipation, high hydrophilicity, porous structure, and excellent biocompatibility, BHF is a promising hydrogel fiber for biomedicine. The outstanding stretchability and energy dissipation of BHF allow it to absorb energy from the tissue deformation around a wound and effectively protect the wound from rupture, which makes BHF an ideal surgical suture.

An all-natural bioinspired structural material for plastic replacement

Petroleum-based plastics are useful but they pose a great threat to the environment and human health. It is highly desirable yet challenging to develop sustainable structural materials with excellent mechanical and thermal properties for plastic replacement. Here, inspired by nacre’s multiscale architecture, we report a simple and efficient so called “directional deforming assembly” method to manufacture high-performance structural materials with a unique combination of high strength (281 MPa), high toughness (11.5 MPa m^1/2), high stiffness (20 GPa), low coefficient of thermal expansion (7 × 10⁻⁶ K⁻¹) and good thermal stability. Based on all-natural raw materials (cellulose nanofiber and mica microplatelet), the bioinspired structural material possesses better mechanical and thermal properties than petroleum-based plastics, making it a high-performance and eco-friendly alternative structural material to substitute plastics.

It is desirable yet challenging to develop sustainable structural materials to replace petroleum-based plastics. Here, the authors report a facile assembly method for manufacturing high-performance structural materials with a unique combination of high strength, toughness and stiffness.