Citric acid/chitosan adhesive with viscosity-controlled for wood bonding through supramolecular self-assembly.

Developing bio-based sustainable wood adhesives is significant as a substitute for petroleum-derived adhesives. However, the existing bio-based adhesives have disadvantages of complex fabrication, uncontrollable viscosity, and poor water resistance. Herein, we developed a citric acid/chitosan adhesive with viscosity-controlled and water-resistant features by one-step dissolution at room temperature based on the supramolecular self-assembly strategy. Different wood products (plywood, laminated veneer lumber and particleboard) with superior performance were prepared by applying that adhesive on veneer and wood particles (fine and rough particles). The plywood test results showed that the citric acid/chitosan adhesive had dry and wet shear strengths outperforming the China National Standard (GB/T 9846-2015, ≥0.7 MPa), reaching 2.1 and 1.1 MPa, respectively. The adhesion mechanism was mechanical interlocks and cross-linking of citric acid/chitosan in adhesives with those in the cell wall. This work provides high promise for alternatives to traditional unsustainable wood adhesives (urea-formaldehyde, melamine-urea-formaldehyde and phenolic resins) for fabricating different wood products.

Lightweight, strong, moldable wood via cell wall engineering as a sustainable structural material.

Wood is a sustainable structural material, but it cannot be easily shaped while maintaining its mechanical properties. We report a processing strategy that uses cell wall engineering to shape flat sheets of hardwood into versatile three-dimensional (3D) structures. After breaking down wood's lignin component and closing the vessels and fibers by evaporating water, we partially re-swell the wood in a rapid water-shock process that selectively opens the vessels. This forms a distinct wrinkled cell wall structure that allows the material to be folded and molded into desired shapes. The resulting 3D-molded wood is six times stronger than the starting wood and comparable to widely used lightweight materials such as aluminum alloys. This approach widens wood's potential as a structural material, with lower environmental impact for buildings and transportation applications.

Magnetically Driven 3D Cellulose Film for Improved Energy Efficiency in Solar Evaporation.

The architecture of cellulose nanomaterials is definitized by random deposition and cannot change in response to shifting application requirements. Herein, we present a magnetic field-controlled cellulose film derived from wood that exhibits great magnetic properties and reliable tunability enabled by incorporated Fe3O4 nanoparticles and cellulose nanofibers (CNF) with a large length-diameter ratio. Fe3O4 nanoparticles are dispersed in suspensions of CNF so as to enhance the magnetic response. The plane magnetic CNF can be processed to form a three-dimensional (3D) flower-like structure along the magnetic induction line after applying an external magnet. Inspired by the fluidic transport in natural flowers, a bilayer structure was created using the 3D flower-like film as the solar energy receiver and natural wood as the water pathway in a solar-derived evaporation system. Compared with a planar cellulose film decorated with Fe3O4, the 3D structure design can greatly improve the evaporation rate from 1.19 to 1.39 kg m-2 h-1 and the efficiency from 76.9 to 90.6% under 1 sun. Finite element molding further reveals that the 3D structural top layer is beneficial for the formation of a gradient temperature profile and the improvement of the energy efficiency through the reduction of thermal radiation. The magnetically controlled fabrication represents a promising strategy for designing cellulose nanomaterials with a complicated structure and controllable topography, which has a wide spectrum of applications in energy storage devices and water treatment.

A Strong, Tough, and Scalable Structural Material from Fast-Growing Bamboo.

Lightweight structural materials with high strength are desirable for advanced applications in transportation, construction, automotive, and aerospace. Bamboo is one of the fastest growing plants with a peak growth rate up to 100 cm per day. Here, a simple and effective top-down approach is designed for processing natural bamboo into a lightweight yet strong bulk structural material with a record high tensile strength of ≈1 GPa and toughness of 9.74 MJ m-3 . More specifically, bamboo is densified by the partial removal of its lignin and hemicellulose, followed by hot-pressing. Long, aligned cellulose nanofibrils with dramatically increased hydrogen bonds and largely reduced structural defects in the densified bamboo structure contribute to its high mechanical tensile strength, flexural strength, and toughness. The low density of lignocellulose in the densified bamboo leads to a specific strength of 777 MPa cm3 g-1 , which is significantly greater than other reported bamboo materials and most structural materials (e.g., natural polymers, plastics, steels, and alloys). This work demonstrates a potential large-scale production of lightweight, strong bulk structural materials from abundant, fast-growing, and sustainable bamboo.

Single-digit-micrometer thickness wood speaker.

Thin films of several microns in thickness are ubiquitously used in packaging, electronics, and acoustic sensors. Here we demonstrate that natural wood can be directly converted into an ultrathin film with a record-small thickness of less than 10 µm through partial delignification followed by densification. Benefiting from this aligned and laminated structure, the ultrathin wood film exhibits excellent mechanical properties with a high tensile strength of 342 MPa and a Young's modulus of 43.6 GPa, respectively. The material's ultrathin thickness and exceptional mechanical strength enable excellent acoustic properties with a 1.83-times higher resonance frequency and a 1.25-times greater displacement amplitude than a commercial polypropylene diaphragm found in an audio speaker. As a proof-of-concept, we directly use the ultrathin wood film as a diaphragm in a real speaker that can output music. The ultrathin wood film with excellent mechanical property and acoustic performance is a promising candidate for next-generation acoustic speakers.

Facile Fabrication of Nanofibrillated Chitin/Ag2O Heterostructured Aerogels with High Iodine Capture Efficiency.

Nanofibrillated chitin/Ag2O aerogels were fabricated for radioiodine removal. Chitin was first fabricated into nanofibers with abundant acetyl amino groups (-NHCOCH3) on the surface. Then, highly porous chitin nanofiber (ChNF) aerogels were obtained via freeze-drying. The ChNF aerogels exhibited a low bulk density of 2.19 mg/cm3 and a high specific surface area of 179.71 m2/g. Ag2O nanoparticles were evenly anchored on the surfaces of ChNF scaffolds via strong interactions with -NHCOCH3 groups, subsequently yielding Ag2O@ChNF heterostructured aerogels. The composites were used as efficient absorbents to remove radioiodine anions from water and capture a high amount of I2 vapor in the forms of AgI and iodine molecules. The adsorption capacity of the composite monoliths can reach up to 2.81 mmol/g of I- anions. The high adsorbability of the composite monolithic aerogel signifies its potential applications in radioactive waste disposal.

Coherent-Interface-Assembled Ag2O-Anchored Nanofibrillated Cellulose Porous Aerogels for Radioactive Iodine Capture.

Nanofibrillated cellulose (NFC) has received increasing attention in science and technology because of not only the availability of large amounts of cellulose in nature but also its unique structural and physical features. These high-aspect-ratio nanofibers have potential applications in water remediation and as a reinforcing scaffold in composites, coatings, and porous materials because of their fascinating properties. In this work, highly porous NFC aerogels were prepared based on tert-butanol freeze-drying of ultrasonically isolated bamboo NFC with 20-80 nm diameters. Then nonagglomerated 2-20-nm-diameter silver oxide (Ag2O) nanoparticles (NPs) were grown firmly onto the NFC scaffold with a high loading content of ∼500 wt % to fabricate Ag2O@NFC organic-inorganic composite aerogels (Ag2O@NFC). For the first time, the coherent interface and interaction mechanism between the cellulose Iß nanofiber and Ag2O NPs are explored by high-resolution transmission electron microscopy and 3D electron tomography. Specifically, a strong hydrogen between Ag2O and NFC makes them grow together firmly along a coherent interface, where good lattice matching between specific crystal planes of Ag2O and NFC results in very small interfacial straining. The resulting Ag2O@NFC aerogels take full advantage of the properties of the 3D organic aerogel framework and inorganic NPs, such as large surface area, interconnected porous structures, and supreme mechanical properties. They open up a wide horizon for functional practical usage, for example, as a flexible superefficient adsorbent to capture I- ions from contaminated water and trap I2 vapor for safe disposal, as presented in this work. The viable binding mode between many types of inorganic NPs and organic NFC established here highlights new ways to investigate cellulose-based functional nanocomposites.

Poly(vinyl alcohol) films reinforced with nanofibrillated cellulose (NFC) isolated from corn husk by high intensity ultrasonication.

This work was aimed at fabricating and characterizing poly(vinyl alcohol) films that were reinforced by nanofibrillated corn husk celluloses using a combination of chemical pretreatments and ultrasonication. The obtained nanofibrillated celluloses (NFCs) possessed a narrow width ranging from 50 to 250 nm and a high aspect ratio (394). The crystalline type of NFC was cellulose I type. Compared with the original corn husks, the NCF crystallinity and thermal stability increased due to the removal of the hemicelluloses and lignin. PVA films containing different NFC concentrations (0.5%, 1%, 3%, 5%, 7% and 9%, w/w, dry basis) were examined. The 1% PVA/NFC reinforced films exhibited a highly visible light transmittance of 80%, and its tensile strength and the tensile strain at break were increased by 1.47 and 1.80 times compared to that of the pure PVA film, respectively. The NFC with high aspect ratio and high crystallinity is beneficial to the improvement of the mechanical strength and thermal stability.

Fabrication and characterization of nanofibrillated cellulose and its aerogels from natural pine needles.

To obtain the nanofibriled cellulose from natural pine needles, a combination of chemical pretreatments and subsequently ultrasonic treatments was employed for removing the hemicelluloses and lignins and splitting the bundled cellulose into pine needle nanofibers. Using SEM and diameter distribution method, it was confirmed that the obtained pine needle nanofibers had a narrow diameter from 30 to 70 nm. The crystalline type of the pine needle nanofibers was the cellulose I type. The crystallinity reached 66.19%, which was increased by 7.61% as compared with the raw material pine needles. The TGA and DTG results showed that the degradation temperature of the nanofibers was increased to approximately 267 and 352°C compared with 221 and 343°C of the raw material fibers, respectively. Furthermore, the highly flexible and ultralight pine needle nanofibers aerogels were prepared from the aqueous pine needle nanofibers solution using the freezing-drying technique. Aerogels were studied by SEM observation and nitrogen gas adsorption. The mechanical properties were measured in compression for aerogels. This study provides a new opportunity to fabricate novel nanomaterials from waste biomass materials, which is crucial for the fully utilizing of abundant biomass resources.