Clear Wood toward High-Performance Building Materials

Large-Scale Engineerable Films Tailored with Cellulose Nanofibrils for Lighting Management and Thermal Insulation

Fibrillated cellulose-based nanocomposites can improve energy efficiency of building envelopes, especially windows, but efficiently engineering them with a flexible ability of lighting and thermal management remains highly challenging. Herein, a scalable interfacial engineering strategy is developed to fabricate haze-tunable thermal barrier films tailored with phosphorylated cellulose nanofibrils (PCNFs). Clear films with an extremely low haze of 1.6% (glass-scale) are obtained by heat-assisted surface void packing without hydrophobization of nanocellulose. PCNF gel cakes serve here as templates for surface roughening, thereby resulting in a high haze (73.8%), and the roughened films can block heat transfer by increasing solar reflection in addition to a reduced thermal conduction. Additionally, obtained films can tune distribution of light from visible to near-infrared spectral range, enabling uniform colored lighting and inhibiting localized heating. Furthermore, an integrated simulation of lighting and cooling energy consumption in the case of office buildings shows that the film can reduce the total energy use by 19.2-38.1% under reduced lighting levels. Such a scalable and versatile engineering strategy provides an opportunity to endow nanocellulose-reinforced materials with tunable optical and thermal functionalities, moving their practical applications in green buildings forward.

Preparation of a Flame-Retardant Curing Agent Based on Phytic Acid-Melamine Ion Crosslinking and Its Application in Wood Coatings

To broaden the applications of wood, it is necessary to prepare flame-retardant coatings that can protect wood substrates during combustion. In this study, a bio-based, intumescent, flame-retardant phytic acid-melamine polyelectrolyte (PM) was prepared using phosphorus-rich biomass phytic acid and nitrogen-rich melamine as raw materials through an ion crosslinking reaction. Subsequently, a series of bio-based, flame-retardant wood coatings were prepared by optimizing the structure of urea-formaldehyde resin with the addition of melamine, sodium lignosulfonate, and PM as a flame-retardant curing agent. Woods coated with PM-containing coatings displayed significantly improved flame-retardant performances in comparison to uncoated woods. For PM-cured woods, the measured values of total heat release and total smoke production were 91.51% and 57.80% lower, respectively, compared with those of uncoated wood. Furthermore, the fire growth index decreased by 97.32%, indicating a lower fire hazard. This increase in flame retardancy and smoke suppression performance is due to the dense expanded carbon layer formed during the combustion of the coating, which isolates oxygen and heat. In addition, the mechanical properties of the flame-retardant coatings cured with PM are similar to those cured with a commercial curing agent, NH4Cl. In addition, the prepared flame-retardant coating can also stain the wood. This study proves the excellent flame-retarding and curing effect of ammonium phytate in urea-formaldehyde resin coatings and provides a new approach for the application of bio-based flame retardants in wood coatings.

Molecular-caged metal-organic frameworks for energy management

Metal-organic frameworks (MOFs) hold great promise for diverse applications when combined with polymers. However, a persistent challenge lies in the susceptibility of exposed MOF pores to molecule and polymer penetration, compromising the porosity and overall performance. Here, we design a molecular-caged MOF (MC-MOF) to achieve contracted window without sacrificing the MOF porosity by torsional conjugated ligands. These molecular cages effectively shield against the undesired molecule penetration during polymerization, thereby preserving the pristine porosity of MC-MOF and providing outstanding light and thermal management to the composites. The polymer containing 0.5 wt % MC-MOF achieves an 83% transmittance and an exceptional haze of 93% at 550 nanometers, coupled with remarkable thermal insulation. These MC-MOF/polymer composites offer the potential for more uniform daylighting and reduced energy consumption in sustainable buildings when compared to traditional glass materials. This work delivers a general method to uphold MOF porosity in polymers through molecular cage design, advancing MOF-polymer applications in energy and sustainability.

Synthesis of lignin-based resin and fabrication of sustainable transparent wood based on bio-recycling concept

Transparent wood (TW) has attracted much attention in the field of energy saving building structural materials because of its high light transmittance, good thermal insulation performance and good toughness. However, the polymeric resins used in the present study to impregnate lignin-based wood templates are usually derived from petroleum-based chemical resources, which pose a fatal threat to human beings both in terms of consuming large amounts of resources and causing environmental pollution problems. It is therefore important to develop alternatives to petroleum-derived chemicals in renewable natural resources. Here, we report a green and sustainable TW production process based on the bio-recycling concept. Lignin-based sustainable resin (LSR) was prepared from waste lignin produced during delignification by polymerization of guaiacol. At the same time, according to FT-IR and NMR data analysis combined with previous studies, the synthesis mechanism of LSR was proposed, and this result provided a reference for bio-based resins made from biomass materials. The prepared lignin-based sustainable transparent wood (LSTW) has good light transmittance and good dimensional stability. In addition, the LSTW also shows good thermal insulation and indoor temperature regulation capabilities compared with the common glass.

Cellulose/silica composite microtubular superfoam with excellent flame retardancy, thermal insulation and ablative resistance

Thermal insulation materials with good flame-retardant properties have attracted widespread attention because of their huge application potential. Traditional petrochemical-based polymer insulation materials are flammable and have problems with environmental pollution. The microtubule structure is a perfect microstructure with excellent thermal insulation performance. In addition, the microtubule structure also has low density and high elasticity. Therefore, the microtubule structure is an important reference microstructure for the development of efficient thermal insulation materials. In this paper, a cellulose/SiO2 composite microtube thermal insulation superfoam has been successfully prepared. Cellulose microtubules were successfully prepared from poplar sawdust by chemical methods. The SiO2 aerogel precursor solution can be quickly adsorbed by the delignified cellulose microtubes. The SiO2 aerogel shells are evenly distributed only on the inner and outer walls of the delignified cellulose microtubes. The cellulose/SiO2 microtube composite (CSMC) superfoam exhibits low density, good mechanical properties, and low thermal conductivity (as low as 0.042 ± 0.0018 W m-1 K-1). The CSMC superfoam exhibits excellent self-extinguishing and flame-retardant properties. After being burned by a butane flame, the superfoam still has certain mechanical properties. The thermal conductivity of the B-CSMC superfoam (the CSMC superfoam burned by a butane flame) is about 0.050 W m-1 K-1. The B-CSMC superfoam remained almost unchanged after being continuously ablated by a butane flame for 3600 seconds.

Anisotropic materials based on carbohydrate polymers: A review of fabrication strategies, properties, and applications

Anisotropic structures exist in almost all living organisms to endow them with superior properties and physiological functionalities. However, conventional artificial materials possess unordered isotropic structures, resulting in limited functions and applications. The development of anisotropic structures on carbohydrates is reported to have an impact on their properties and applications. In this review, various alignment strategies for carbohydrates (i.e., cellulose, chitin and alginate) from bottom-up to top-down strategies are discussed, including the rapidly developed innovative technologies such as shear-induced orientation through extrusion-based 3D/4D printing, magnetic-assisted alignment, and electric-induced alignment. The unique properties and wide applications of anisotropic carbohydrate materials across different fields, from biomedical, biosensors, smart actuators, soft conductive materials, to thermal management are also summarized. Finally, recommendations on the selection of fabrication strategies are given. The major challenge lies in the construction of long-range hierarchical alignment with high orientation degree and precise control over complicated architectures. With the future development of hierarchical alignment strategies, alignment control techniques, and alignment mechanism elucidation, the potential of anisotropic carbohydrate materials for scalable manufacture and clinical applications will be fully realized.

Mismatched Refractive Index Strategy for Fabricating Laser-Driven Wood Diffusers from Bulk Wood for Illumination Applications

Laser-diode-based solid-state lighting is primarily used in state-of-the-art illumination systems. However, these systems rely on light-converting inorganic phosphors, which have low quantum efficiencies and complex manufacturing conditions. In this study, a mismatched refractive index strategy is proposed to directly convert natural bulk wood into a laser-driven wood diffuser using a simple delignification and polymer infiltration method. The resulting material has the potential to be used in laser-driven diffuse illumination applications. The optical performance of the laser-driven wood diffuser is optimized by changing the density of natural wood. The optimal coefficient of illuminance variation of the wood diffuser is as low as 17.7%, which is significantly lower than that of commercial diffusers. The illuminance uniformity is larger than 0.9, which is significantly higher than the ISO requirements for indoor workplace lighting. The laser damage threshold is 7.9 J cm-2, which is considerably higher than those of the substrates of commercially available phosphors. Furthermore, the optimized wood diffuser exhibits outstanding mechanical properties, excellent thermal stability, tolerance to harsh environmental conditions, and low speckle contrast. These results show that the laser-driven wood diffuser is a promising laser-color converter that is suitable for indoor, long-distance outdoor, undersea, and other high-luminance laser lighting applications.

Fabrication of carbon dots-embedded luminescent transparent wood with ultraviolet blocking and thermal insulating capacities towards smart window application

To expand functions of transparent wood (TW) including fluorescence, ultraviolet blocking, heat preservation and insulation, we adopted carbon quantum dots (CQDs) to prepare luminescent transparent wood. CQDs with yellow/red fluorescence (YCD/RCD) were prepared by chitosan and o-phenylenediamine. Afterwards, Balsa woods were pretreated to obtain wood frameworks (DW/LW), which were further combined with epoxy resin for achieving transparent woods (DW-TW/LW-TW). Results showed LW retained more lignin, the LW-TW blocked more ultraviolet light, displaying the better visible transmission and mechanical strength than DW-TW. After adding YCD and RCD to LW-TW, the yellow and red fluorescence transparent woods with outstanding mechanical and ultraviolet blocking properties were prepared, especially the red fluorescence transparent wood (RTW). Specifically, the tensile strength and elongation at break of RTW reached up to 19.39 MPa and 5.35 %, respectively. Moreover, RTW could block 78.8 % of UV-B light and 78 % of UV-A light, respectively. Besides, RTW possessed excellent visible transmission (70.3 %) and UV blocking (88.87 %). Significantly, both RTW and YTW displayed outstanding water repellency, excellent durability, good thermal stability and insulation. Predictably, luminescent transparent woods certainly will enhance the adaptability of wood, and broaden its applications in green decoration, lighting setup, sensor and other fields.

Modulating Smart Mechanoluminescent Phosphors for Multistimuli Responsive Optical Wood

Mechanoluminescence is a smart light-emitting phenomenon in which applied mechanical energy is directly converted into photon emissions. In particular, mechanoluminescent materials have shown considerable potential for applications in the fields of energy and sensing. This study thoroughly investigates the mechanoluminescence and long afterglow properties of singly doped and codoped Sr2 MgSi2 O7 (SMSO) with varying concentrations of Eu2+ and Dy3+ ions. Subsequently, a comprehensive analysis of its multimode luminescence properties, including photoluminescence, mechanoluminescence, long afterglow, and X-ray-induced luminescence, is conducted. In addition, the density of states mapping is acquired through first-principles calculations, confirming that the enhanced mechanoluminescence properties of SMSO primarily stem from the deep trap introduced by Dy3+ . In contrast to traditional mixing with Polydimethylsiloxane, in this study, the powders are incorporated into optically transparent wood to produce a multiresponse with mechanoluminescence, long afterglow, and X-ray-excited luminescence. This structure is achieved by pretreating natural wood, eliminating lignin, and subsequently modifying the wood to overall modification using various smart phosphors and epoxy resin composites. After natural drying, a multifunctional composite wood structure with diverse luminescence properties is obtained. Owing to its environmental friendliness, sustainability, self-power, and cost-effectiveness, this smart mechanoluminescence wood is anticipated to find extensive applications in construction materials and energy-efficient displays.

Wood-based capillary enhancers for accelerated moisture capture and solar-powered release

The pressing need to address the global water crisis has spurred research efforts toward exploring alternative sources and technologies, and harvesting atmospheric water from the humid air emerges as a promising solution. Liquid desiccants, known for their high absorption capacity, have been widely utilized for moisture capture, but their water yield is mainly restricted by sluggish adsorption and desorption dynamics. To address this limitation, we present a facile strategy to promote the absorption/desorption dynamics of moisture by virtue of capillary transport and enlarged interfaces in a photothermal wood enhancer. These enhancers are fabricated via partial delignification of natural balsa woods followed by low-temperature carbonization to endow them with photothermal properties. The moisture absorption rate shows a notable increase of 103% and 84% under the relative humidity (RH) of 60% and 90%, respectively, within the initial two hours by applying the three enhancers. On the other hand, the desorption efficiency is doubled, reaching 80% in two hours under 60 °C with the enhancers. Moreover, the desorption can be driven by solar energy with an evaporation rate of 1.217 kg·m-2·h-1. This work provides a design strategy combining capillary and interfacial effects to enhance moisture harvesting without altering hygroscopic materials.

Mechanically strong, hydrostable, and biodegradable all-biobased transparent wood films with UV-blocking performance

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 optical properties for plastic replacement. Here, we report a simple and efficient method to manufacture high-performance all-biobased structural materials from cellulosic wood skeleton (WS) and gelatin via oxidation and densification. Specifically, gelatin was grafted to the oxidized cellulose wood skeletons (DAWS) and then physically crosslinked via Tannic acid (TA), resulting in a significant enhancement of the material properties. Notably, only a mild pressure was applied during the drying process to form a densified TA/Gelatin/transparent wood film(TWF). The developed TA/Gelatin/TWF (thickness:100 ± 12 μm) exhibited a desirable combination of high strength (∼154.59 MPa), light transmittance (86.2 % at 600 nm), low haze (16.7 %), high water stability (wet strength: ∼130.13 MPa) and ultraviolet blocking efficacy which surpass most of the petroleum-based plastics. In addition, due to the all bio-based origins (wood and gelatin), TA/Gelatin/TWF are easily biodegradable under natural conditions, leading to less impact on the environment. These findings would hold promises for exploring high-quality all bio-based wood composites as eco-friendly alternatives to substitute plastics with wide applications, e.g. anti-counterfeiting, UV protection, and flexible electricals.

Redesigning Natural Materials for Energy, Water, Environment, and Devices

The United Nations Framework Convention on Climate Change (UNFCCC) acknowledges that global cooperation is paramount to mitigate climate change and further warming. The global community is committed to renewable energy and natural materials to tackle this challenge for all humankind. The widespread use of natural materials is embraced as one such action to reach net-zero carbon emissions. Given the hierarchical framework and earth abundance, cellulose-based materials extend their negative carbon benefits to our daily products and accelerate our pace toward carbon neutrality. Here, we present an overview of recent developments of cellulose-based materials in upsurging applications in radiative cooling, thermal insulation, nanofluidics, and wearable devices. We also highlight various modifications and functionalized processes that transform massive amounts of cellulose into green products. The prosperous development of functionalized cellulose materials aligns with a circular economy. Expedited interdisciplinary fundamental investigations are expected to make fibrillated cellulose penetrate more into carbon downdraw at speed and scale.

Insulative Biobased Glaze from Wood Laminates Obtained by Self-Adhesion

The combination of optical transparency and mechanical strength is a highly desirable attribute of wood-based glazing materials. However, such properties are typically obtained by impregnation of the highly anisotropic wood with index-matching fossil-based polymers. In addition, the presence of hydrophilic cellulose leads to a limited water resistance. Herein, this work reports on an adhesive-free lamination that uses oxidation and densification to produce transparent all-biobased glazes. The latter are produced from multilayered structures, free of adhesives or filling polymers, simultaneously displaying high optical clarity and mechanical strength, in both dry and wet conditions. Specifically, high values of optical transmittance (≈85.4%), clarity (≈20% with low haze) at a thickness of ≈0.3 mm, and highly isotropic mechanical strength and water resistance (wet strength of ≈128.25 MPa) are obtained for insulative glazes exhibiting low thermal conductivity (0.27 W m-1 K-1 , almost four times lower than glass). The proposed strategy results in materials that are systematically tested, with the leading effects of self-adhesion induced by oxidation rationalized by ab initio molecular dynamics simulation. Overall, this work demonstrates wood-derived materials as promising solutions for energy-efficient and sustainable glazing applications.

Advances in the research of carbon-, silicon-, and polymer-based superhydrophobic nanomaterials: Synthesis and potential application

With the rapid development of science and technology, superhydrophobic nanomaterials have become one of the hot topics from various subjects. Due to their distinct properties, such as superhydrophobicity, anti-icing and corrosion resistance, superhydrophobic nanomaterials are widely used in industry, agriculture, defense, medicine and other fields. Hence, the development of superhydrophobic materials with superior performance, economical, practical features, and environment-friendly properties are extremely important for industrial development and environmental protection. Aimed to provide a scientific and theoretical basis for the subsequent study on the preparation of composite superhydrophobic nanomaterials, this paper reviewed the latest progress in the research of superhydrophobic surface wettability and the theory of superhydrophobicity, summarized and analyzed the latest development of carbon-based, silicon-based and polymer-based superhydrophobic nanomaterials in terms of their synthesis, modification, properties and structure sizes (diameters), discussed the problems and unique application prospects of carbon-based, silicon-based and polymer-based superhydrophobic nanomaterials.

A comprehensive review of lignocellulosic biomass derived materials for water/oil separation

With rapid socioeconomic development, oil is widely used in all aspects of modern society. However, the extraction, transport, and processing of oil inevitably lead to the production of large quantities of oily wastewater. Traditional oil/water separation strategies are often inefficient, costly, and cumbersome to operate. Therefore, new green, low-cost, and high-efficiency materials must be developed for oil/water separation. As widely sourced and renewable natural biocomposites, wood-based materials have become a hot field recently. This review will focus on the application of several wood-based materials in oil/water separation. The state of research on wood sponges, cotton fibers, cellulose aerogels, cellulose membranes, and some other wood-based materials for oil/water separation over the last few years and provide an outlook on their future development are summarized and investigated. It is expected to provide some direction for future research on the use of wood-based materials in oil/water separation.

H2O2 Solution Steaming Combined Method to Cellulose Skeleton for Transparent Wood Infiltrated with Cellulose Acetate

Hydrogen peroxide (H2O2) steaming, a green and highly efficient delignification method, has been demonstrated to provide a wood skeleton with a very low content of residual lignin in the manufacturing of transparent wood. It usually requires a long reaction time and a large amount of H2O2 because the piece of wood is treated using steaming equipment. Herein, a H2O2 solution steaming method was developed for the highly efficient removal of lignin from wood. Specifically, several wood samples were simultaneously immersed in a hot H2O2 solution to obtain delignified wood with a relatively high content of residual lignin, which provided a high strength and preserved the cellulose skeleton. Subsequently, the delignified wood with a relatively high content of residual lignin was further treated with H2O2 steam to obtain a very low lignin delignified wood. Compared with the previous H2O2 steaming method, the reaction time and used H2O2 volume of the H2O2 solution steaming method was reduced by 37.3% and 52.7%, respectively. All-biomass transparent wood could be obtained by infiltrating the delignified wood with cellulose acetate, which showed both a high transmittance of 83.0% and a low thermal conductivity of 0.30 Wm−1K−1.

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.

Research and Application of Biomass-Based Wood Flame Retardants: A Review

Wood is widely used as a construction material due to its many advantages, such as good mechanical properties, low production costs, and renewability. However, its flammability limits its use in construction. To solve the problem of wood flammability, the most common method to improve the fire safety of wood is to modify the wood by deep impregnation or surface coating with flame retardants. Therefore, many researchers have found that environmentally friendly and low-cost biomass materials can be used as a source of green flame retardants. Two aspects of biomass-based intumescent flame retardants are summarized in this paper. On the one hand, biomass is used as one of the three sources or as a flame-retardant synergist in combination with other flame retardants, which are called composite biomass intumescent flame retardants. On the other hand, biomass is used alone as a feedstock to produce all-biomass intumescent flame retardants. In addition, the potential of biomass-based materials as an environmentally friendly and low-cost FR source to produce high-performance biomass-based flame retardants with improved technology was also discussed in detail. The development of biomass-based intumescent flame retardants represents a viable and promising approach for the efficient and environmentally friendly production of biomass-based flame retardants.

Potential new material for optical fiber: Preparation and characterization of transparent fiber based on natural cellulosic fiber and epoxy

In order to reduce the dependence on fossil energy products, natural fiber/polymer hybrid composites have been increasingly researched. The high price of the quartz optical fibers and glass optical fibers has greatly inspired researchers to engage in the research on polymer optical fibers. Herein, transparent fibers based on plant fibers were innovatively prepared for the first time by delignification and impregnating epoxy diluted with acetone. The epoxy improved the thermal stability of the fiber without deteriorating its mechanical properties, and also endowed the fiber with the property of transparency. The tensile strength of transparent fibers of three diameters were 34.5, 58.6 and 100.3 MPa, respectively and the corresponding Young's modulus reached 1.1, 1.7 and 2.3 GPa, respectively. In addition, the light-conducting properties of transparent fibers were displayed with a green laser and the fibers displayed good light transmission along the fiber growth direction. Transparent fibers are expected to be used in optical fibers because of their high thermal stability, good mechanical properties and light-conducting properties.

Fully recyclable multifunctional adhesive with high durability, transparency, flame retardancy, and harsh-environment resistance

Recyclable/reversible adhesives have attracted growing attention for sustainability and intelligence but suffer from low adhesion strength and poor durability in complex conditions. Here, we demonstrate an aromatic siloxane adhesive that exploits stimuli-responsive reversible assembly driven by π-π stacking, allowing for elimination and activation of interfacial interactions via infiltration-volatilization of ethanol. The robust cohesive energy from water-insensitive siloxane assembly enables durable strong adhesion (3.5 MPa shear strength on glasses) on diverse surfaces. Long-term adhesion performances are realized in underwater, salt, and acid/alkali solutions (pH 1-14) and at low/high temperatures (-10-90°C). With reversible assembly/disassembly, the adhesive is closed-loop recycled (~100%) and reused over 100 times without adhesion loss. Furthermore, the adhesive has unique combinations of high transparency (~98% in the visible light region of 400-800 nm) and flame retardancy. The experiments and theoretical calculations reveal the corresponding mechanism at the molecular level. This π-π stacking-driven siloxane assembly strategy opens up an avenue for high-performance adhesives with circular life and multifunctional integration.

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.

Transparent and Flexible Electromagnetic Interference Shielding Materials by Constructing Sandwich AgNW@MXene/Wood Composites

Electromagnetic interference (EMI) shielding materials have attracted intensive attention with the increased electromagnetic pollution, which are required to possess high transparency and flexibility for applications in visualization windows, aerospace equipment, and wearable devices. However, it remains a challenge to achieve high-performance EMI shielding while maintaining excellent light transmittance. Herein, a sandwich composite is constructed by coating the core material of transparent wood (TW) with silver nanowire (AgNW)@MXene, exhibiting a maximum transmittance of 28.8% in the visible range and a longitudinal tensile strength of 47.8 MPa. The average EMI shielding effectiveness can reach up to 44.0 dB under X-band (8-12.4 GHz), ascribed to the increased absorption shielding induced by the multireflection of electromagnetic waves within microchannels of the TW layer and the interfacial polarization between AgNW and MXene. Simultaneously, large-scale EMI shielding films can be conveniently produced by our proposed method, which provides inspiration for the development of advanced EMI shielding materials for wide applications.

Green-Manufactured and Recyclable Coatings for Subambient Daytime Radiative Cooling

Passive daytime radiative cooling, which reflects sunlight and simultaneously emits heat into space to cool surfaces without energy input, is a promising strategy for energy conservation. Integrating radiative cooling with building systems can tremendously alleviate electrical cooling, but manufacturing high-efficient and eco-friendly coatings remains an urgent and challenging task. Here, we present a simple and scale-up strategy for fabricating ultrawhite coatings consisting of porous ethyl cellulose matrix-random BaSO₄ nanoparticles utilizing green solvents. With the synergistic effect of the ideal intrinsic properties of the materials and the strong Mie scattering of the porous structure, the ultrawhite coating possesses a record solar reflectance of 98.6% and a thermal emittance of 98.1%, resulting in a subambient temperature drop of over 2.5 °C under a solar intensity of ∼920 W m^-2. Better yet, our coatings can be conveniently brushed, rolled, or sprayed onto various types of substrates, with excellent durability, self-cleaning, and cost-effectiveness, paving an attractive and viable pathway for large-scale applications in practical buildings.

Characterization of a Translucent Material Produced from Paulownia tomentosa Using Peracetic Acid Delignification and Resin Infiltration

Paulownia tomentosa, a tree species that allows for efficient production of translucent wood, was selected as an experimental wood species in this study, and a two-step process of delignification and polymer impregnation was performed. For delignification, 2–4 mm thick specimens were immersed in peracetic acid for 8 h. The delignified-wood specimens were impregnated using epoxy, a commercial transparent polymer. To identify the characteristics of the resulting translucent wood, the transmittance and haze of each type of wood section (cross- and tangential) were measured, while bending strength was measured using a universal testing machine. The translucent wood varied in properties according to the wood section, and the total transmittance and haze were 88.0% and 78.5% for the tangential section and 91.3% and 96.2% for the cross-section, respectively. For the bending strength, untreated wood showed values of approximately 4613.5 MPa modulus of elasticity (MOE), while the epoxy impregnation to improve the strength of the wood had increased the MOE up to approximately 6089.9 MPa, respectively. A comparative analysis was performed in this study with respect to the substitution of balsa, which is used widely in the production of translucent wood. The results are anticipated to serve as baseline data for the functionalization of translucent wood.

Highly Flexible and Broad-Range Mechanically Tunable All-Wood Hydrogels with Nanoscale Channels via the Hofmeister Effect for Human Motion Monitoring

Wood-based hydrogel with a unique anisotropic structure is an attractive soft material, but the presence of rigid crystalline cellulose in natural wood makes the hydrogel less flexible. In this study, an all-wood hydrogel was constructed by cross-linking cellulose fibers, polyvinyl alcohol (PVA) chains, and lignin molecules through the Hofmeister effect. The all-wood hydrogel shows a high tensile strength of 36.5 MPa and a strain up to ~ 438% in the longitudinal direction, which is much higher than its tensile strength (~ 2.6 MPa) and strain (~ 198%) in the radial direction, respectively. The high mechanical strength of all-wood hydrogels is mainly attributed to the strong hydrogen bonding, physical entanglement, and van der Waals forces between lignin molecules, cellulose nanofibers, and PVA chains. Thanks to its excellent flexibility, good conductivity, and sensitivity, the all-wood hydrogel can accurately distinguish diverse macroscale or subtle human movements, including finger flexion, pulse, and swallowing behavior. In particular, when "An Qi" was called four times within 15 s, two variations of the pronunciation could be identified. With recyclable, biodegradable, and adjustable mechanical properties, the all-wood hydrogel is a multifunctional soft material with promising applications, such as human motion monitoring, tissue engineering, and robotics materials.

Energy saving thermal adaptive liquid gating system

Thermal transfer systems involving temperature control through heating, ventilation, and air conditioning applications have emerged as one of the largest energy issues in buildings. Traditional approaches mainly comprise closed and open systems, both of which have certain advantages and disadvantages in a single heating or cooling process. Here we report a thermal adaptive system with beneficial energy-saving properties, which uses functional liquid to exhibit high metastability, providing durability in a temperature-responsive liquid gating system. With an efficient use of energy, this system achieves smart “breathing” during both heating and cooling processes to dynamically tune the indoor temperature. Theoretical modeling and experiments demonstrate that the adaptive, sandwich-structured, membrane-based system can achieve temperature control, producing obvious advantages of energy saving compared with both closed and open systems through the bistable interfacial design of the liquid gating membrane. Further energy saving evaluation of the system on the basis of simulation with current global greenhouse plantation data shows a reduction of energy consumption of 7.9 × 10¹³ kJ/year, a percentage change of ∼11.6%. Because the adaptive system can be applied to a variety of thermal transfer processes, we expect it to prove useful in a wide range of real-world applications.

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An energy saving thermal adaptive liquid gating system is constructed

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The system uses functional liquid to exhibit high metastability, providing durability

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The system is used as an energy saving patch to greenhouse by sandwich configutration

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The system shows energy consumption reduction of ∼11.6% than traditional greenhouse

Highly Transparent Nanofibrous Membranes Used as Transparent Masks for Efficient PM0.3 Removal

Currently, the quest for highly transparent and flexible fibrous membranes with robust mechanical characteristics, high breathability, and good filtration performance is rapidly rising because of their potential use in the fields of electronics, energy, environment, medical, and health. However, it is still an extremely challenging task to realize transparent fibrous membranes due to serious surface light reflection and internal light scattering. Here, we report the design and development of a simple and effective topological structure to create porous, breathable, and high visible light transmitting fibrous membranes (HLTFMs). The resultant HLTFMs exhibit good optical performance (up to 90% transmittance) and high porosities (>80%). The formation of such useful structure with high light transmittance has been revealed by electric field simulation, and the mechanism of fibrous membrane structure to achieve high light transmittance has been proposed. Moreover, transparent masks have been prepared to evaluate the filtration performance and analyze their feasibility to meet requirement of facial recognition systems. The prepared masks display high transparency (>80%), low pressure drop (<100 Pa) and high filtration efficiency (>90%). Furthermore, the person wearing this mask can be successfully identified by facial recognition systems. Therefore, this work provides an idea for the development of transparent, breathable, and high-performance fibrous membranes.

Preparation of Transparent Fast-Growing Poplar Veneers with a Superior Optical Performance, Excellent Mechanical Properties, and Thermal Insulation by Acetylation Modification Using a Green Catalyst

There has been growing interest in transparent conductive substrates due to the prevailing flexible electron devices and the need for sustainable resources. In this study, we demonstrated a transparent fast-growing poplar veneers prepared by acetylated modification, followed by the infiltration of epoxy resin. The work mainly focused on the effect of acetylation treatment using a green catalyst of 4-Dimethylpyridine on the interface of the bulk fast-growing poplar veneer, and the result indicated that the interface hydrophobicity was greatly enhanced due to the higher substitute of acetyl groups; therefore, the interface compatibility between the cell wall and epoxy resin was improved. The obtained transparent fast-growing poplar veneers, hereafter referred to as TADPV, displayed a superior optical performance and flexibility, in which the light transmittance and haze were 90% and 70% at a wavelength of 550 nm, respectively, and the bending radius and bending angle parallel to grain of TADPV were 2 mm and 130°, respectively. Moreover, the tensile strength and tensile modulus of the TADPV were around 102 MPa and 198 MPa, respectively, which is significantly better than those of the plastic substrates used in flexible electron devices. At the same time, the thermal conductivity tests indicated that TADPV has a low coefficient of thermal conductivity of 0.34 Wm⁻¹ K⁻¹, which can completely meet the needs of transparent conductive substrates. Therefore, the obtained TADPV can be used as a candidate for a flexible transparent substrate of electron devices.

Sustainable and Superhydrophobic Lignocellulose-Based Transparent Films with Efficient Light Management and Self-Cleaning

Light-management (LM) films that can regulate transmitted light are significant to diverse fields, such as optoelectronics and energy-efficient buildings. However, for conventional LM films made from petroleum-based polymers, the nonbiodegradability and complicated fabrication process remain a challenge. Herein, we prepare sustainable lignocellulose-based films with excellent light-management capability by facile dissolution and regeneration of wood pulp and the corncob residue from xylitol production (CRXP). The obtained films exhibit high transparency (78%), high haze (61%), and especially remarkable UV-blocking performance (99.94% for UVB and 98.04% for UVA). They achieve consistent indoor light distribution and UV radiation shielding by light management for the application of smart buildings. Furthermore, by spray-coating with SiO₂ nanoparticles to construct hierarchical networks, the films are endowed with a superhydrophobic surface with a self-cleaning function to mitigate dust accumulation. Our work provides novel insights into the conversion of lignocellulosic waste to desirable and sustainable functional materials.

Wood-Derived Composites with High Performance for Thermal Management Applications

Fabricating advanced polymer composites with remarkable mechanical and thermal conductivity performances is desirable for developing advanced devices and equipment. In this study, a novel strategy to prepare anisotropic wood-based scaffolds with a naturally aligned microchannel structure from balsa wood is demonstrated. The wood microchannels were coated with polydopamine-surface-modified small graphene oxide (PGO) nanosheets via assembly. The highly aligned porous microstructures, with thin wood cell walls and large voids along the cellulose microchannels, allow polymers to enter, resulting in the fabrication of the wood-polymer nanocomposite. The tensile stiffness and strength of the resulting nanocomposite reach 8.10 GPa and 90.3 MPa with a toughness of 5.0 MJ m^-3. The thermal conductivity of the nanocomposite is improved significantly by coating a PGO layer onto the wood scaffolds. The nanocomposite exhibits not only ultrahigh thermal conductivity (in-plane about 5.5 W m^-1 K^-1 and through-plane about 2.1 W m^-1 K^-1) but also satisfactory electrical insulation (volume resistivity of about 10¹⁵ Ω·cm). Therefore, the results provide a strategy to fabricate thermal management materials with excellent mechanical properties.

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.

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.

High-Performance Joule Heating and Electromagnetic Shielding Properties of Anisotropic Carbon Scaffolds

Highly efficient electrical heaters along with excellent electromagnetic interference (EMI) shielding properties are urgently required for the progress of miniaturization electronics, artificial intelligence, and smart heating management setups. Herein, lignin removal, which comprises two efficient and versatile steps, followed by carbonization produces multifunctional carbon monoliths derived from natural wood. The obtained carbonized wood exhibits a high specific surface area (655.14 m²/g) and electrical (17.5 S/cm) and thermal conductivity (0.58 W/m·K), superhydrophilicity (contact angle of ∼0°), and excellent EMI shielding ability and Joule heating performance. The high electrical conductivity renders a low-voltage-actuated Joule heating performance and fascinating EMI shielding effectiveness of 55 dB, primarily resulting from the absorption mechanism. Moreover, regulation of the carbonized woods derived from the longitudinal to the radial direction enables transformation of hydrophilicity, strong thermal conductivity, and absorption-dominated EMI shielding to hydrophobicity, thermal insulation, and reflection-dominated EMI shielding. This is attributed to the unique anisotropic microstructure of carbon scaffolds. It is believed that these multifunctional carbon scaffolds can be used for intelligent electronics, EMI shielding, and thermal heating instruments.

Bioinspired Cellulose Foam with Excellent Water Wicking and Flux Properties Prepared Using Ice Template

The application and functionalization of cellulose has been attracting increased attention in academic and industrial studies because of its wide range of sources, short renewable cycle, and low environmental impact. In order to enhance the application field of cellulose and decrease the environmental pollution for organic solvent associated with its preparation, cellulose foam with a vertically hierarchically porous structure similar to wood was designed and fabricated successfully from a cellulose aqueous solution using an ice templated in this study. The cellulose foam prepared using a 3 wt % concentration possessed a uniform vertical hierarchically porous structure, which could provide a pathway for the flow of water or air based on the capillary effect. The highest water wicking rate and flux were 7.8184 mm·s^-1 and 29.49 mL·min^-1·g^-1, respectively, for the porous foam prepared using a 3 wt % concentration. The mechanical testing experiment showed that the porous structure did not reduce the amount of stress that the sample could endure before being damaged. The compression strength increased with increasing cellulose concentration in solution. Therefore, the hierarchical structure formed in the prepared cellulose foam effectively improved the water flux behavior and provided a structural basis for future applications of cellulose scaffolds.

High Performance, Fully Bio-Based, and Optically Transparent Wood Biocomposites

The sustainable development of engineering biocomposites has been limited due to a lack of bio-based monomers combining favorable processing with high performance. Here, the authors report a novel and fully bio-based transparent wood biocomposite based on green synthesis of a new limonene acrylate monomer from renewable resources. The monomer is impregnated and readily polymerized in a delignified, succinylated wood substrate to form optically transparent biocomposites. The chemical structure of the limonene acrylate enables diffusion into the cell wall, and the polymer phase is both refractive index-matched and covalently linked to the wood substrate. This results in nanostructured biocomposites combining an excellent optical transmittance of 90% at 1.2 mm thickness and a remarkably low haze of 30%, with a high mechanical performance (strength 174 MPa, Young's modulus 17 GPa). Bio-based transparent wood holds great potential towards the development of sustainable wood nanotechnologies for structural applications, where transparency and mechanical performance are combined.

Self-Densified Optically Transparent VO2 Thermochromic Wood Film for Smart Windows

Optically transparent wood has emerged as a promising glazing material. Thanks to the high optical transmittance, strong mechanical properties, and excellent thermal insulation capability of transparent wood, it offers a potential alternative to glass for window applications. Recently, thermo-, electro-, and photochromic transparent woods that dynamically modulate light transmittance have been investigated to improve building energy efficiency. However, it remains challenging to widely replace windows with transparent wood because of its poor weather resistance. In this study, an environment-friendly thermochromic transparent wood film (TTWF) with thermal switching of transmittance is proposed and demonstrated. To achieve thermochromism, the bleached wood is impregnated with the vanadium dioxide (VO₂)/polyvinyl alcohol composite. Due to the self-densification of cellulose microfibrils during the evaporation of solvents, the transparent wood is in the form of thin films, which can be attached on the inner face of a window to protect it from severe weather conditions, making the installation convenient and low-cost. Furthermore, the surface of VO₂-TTWF is modified by octadecyltrichlorosilane to enhance the waterproof ability and achieve self-cleaning and antidust functions. The proposed VO₂-TTWF shows great potential for application in energy-efficient buildings using sustainable materials with advanced optical properties (i.e., T_lum = 50.5%, ΔT_sol = 3.4%, and haze = 70%) that are mechanically robust (i.e., σ = 130.6 MPa along the wood growth direction), have low-thermal conductivity (i.e., K = 0.29 W m^-1 K^-1 along the perpendicular direction to the wood fibers), and demonstrate hydrophobic self-cleaning and antidust functions (i.e., contact angle: 121.9°). An experiment, using a model house, showed that the VO₂-TTWF attached on the inner face of the window could significantly reduce the indoor air temperature by 33.9 °C compared with a bare glass panel, proving that VO₂-TTWF has potential to be applied as a new-generation energy-efficient material for smart windows.

Fast Preparation of High-Performance Wood Materials Assisted by Ultrasonic and Vacuum Impregnation

In the absence of high-quality hardwood timber resources, we have gradually turned our attention from natural forests to planted fast-growing forests. However, fast-growing tree timber in general has defects such as low wood density, loose texture, and poor mechanical properties. Therefore, improving the performance of wood through efficient and rapid technological processes and increasing the utilization of inferior wood is a good way to extend the use of wood. Densification of wood increases the strength of low-density wood and extends the range of applications for wood and wood-derived products. In this paper, the effects of ultrasonic and vacuum pretreatment on the properties of high-performance wood were explored by combining sonication, vacuum impregnation, chemical softening, and thermomechanical treatments to densify the wood; then, the changes in the chemical composition, microstructure, and mechanical properties of poplar wood before and after treatment were analyzed comparatively by FT-IR, XRD, SEM, and mechanical tests. The results showed that with ultrasonic pretreatment and vacuum impregnation, the compression ratio of high-performance wood reached its highest level and the MOR and MOE reached their maximums. With the help of this method, fast-growing softwoods can be easily prepared into dense wood materials, and it is hoped that this new material can be applied in the fields of construction, aviation, and automobile manufacturing.

All-biobased transparent-wood: A new approach and its environmental-friendly packaging application

Transparent-wood (TW) is an emerging research topic that can be applied to biobased products. However, it is necessary to fill pores in TW with natural substances to prepare all-biobased TW. This paper reports an all-biobased TW by infiltrating cellulose nanofiber (CNF) and chitosan (CTS) suspensions into the bleached wood. CNF was isolated by combining the chemical and physical methods, and CTS was dissolved in acetic acid, and they were infiltrated into the pores of the bleached Fir veneer wood using a vacuum jar. The CNF and chitosan effects on the mechanical properties of the TW were studied, and the morphologies, crystallinity index, water contact angle, antioxidant, thermal degradation, and UV-shielding properties were investigated. The prepared TW showed 80 % total transmittance and 30-60 % haze, suitable for solar cell application. The all-biobased TW showed good thermal stability up to 315 °C and excellent UV shielding property for UV-B and UV-C. The antioxidant property of the CTS-TW significantly increased as compared to the original wood. The CNF-TW showed considerable tensile strength and yield strength of more than 200 % improved from the original wood. The potential for environment-friendly packaging applications was demonstrated by making a bag, medicine packaging, and straw for a drink.

Alignment of Cellulose Nanofibers: Harnessing Nanoscale Properties to Macroscale Benefits

In nature, cellulose nanofibers form hierarchical structures across multiple length scales to achieve high-performance properties and different functionalities. Cellulose nanofibers, which are separated from plants or synthesized biologically, are being extensively investigated and processed into different materials owing to their good properties. The alignment of cellulose nanofibers is reported to significantly influence the performance of cellulose nanofiber-based materials. The alignment of cellulose nanofibers can bridge the nanoscale and macroscale, bringing enhanced nanoscale properties to high-performance macroscale materials. However, compared with extensive reviews on the alignment of cellulose nanocrystals, reviews focusing on cellulose nanofibers are seldom reported, possibly because of the challenge of aligning cellulose nanofibers. In this review, the alignment of cellulose nanofibers, including cellulose nanofibrils and bacterial cellulose, is extensively discussed from different aspects of the driving force, evaluation, strategies, properties, and applications. Future perspectives on challenges and opportunities in cellulose nanofiber alignment are also briefly highlighted.

Optically Transparent Bamboo with High Strength and Low Thermal Conductivity

The objective of this study is to convert bamboo into a transparent material with great optical transmittance and good strength. Bamboo has a much faster regeneration rate than wood, but its high density and high extractive content make it challenging to produce transparent products. This study presents a simple and effective approach that could address this challenge. Pretreatment of bamboo with low concentration sodium hydroxide greatly improved the preparation efficiency of transparent bamboo. The transparent bamboo with a thickness of 1 mm and cellulose volume fraction of 22% made from the pretreated bamboo exhibited an improved total optical transmissivity up to 80%, which was 60% higher than that of untreated bamboo. Compared to transparent wood (TW), although the transmissivity of transparent bamboo was slightly lower, its mechanical strength was almost doubled. Besides, the developed transparent bamboo exhibited a low heat conductivity of 0.203 W m^-1 K^-1, being about 10% lower than that of TW (0.225 W m^-1 K^-1) and approximately 80% lower than that of common glass material (0.974 W m^-1 K^-1). The transparent bamboo would significantly enhance energy-saving performance, being a promising alternative to traditional glass.

Wood-Nanotechnology-Based Membrane for the Efficient Purification of Oil-in-Water Emulsions

With increasing amounts of oily water discharged from industrial and domestic sources, purifying oily emulsions using effective and eco-friendly methods is of great significance. Although functional membranes with selective wettabilities have been extensively explored for the efficient purification of oil-in-water emulsions, the development of functional membranes that use green and inexpensive materials, are simple to fabricate, and are easy to scale up remains very challenging. Herein, we report a simple approach that uses biomass to prepare a membrane for the purification of emulsions. A simple top-down approach was used to partially remove lignin and hemicellulose fractions in wood sheets, resulting in a highly porous and flexible wood membrane. The obtained wood membrane shows excellent water-absorbing and underwater anti-oil adhesion properties due to the removal of the hydrophobic lignin. The wood membrane is durable and stable, thereby maintaining its selective wettability in harsh environments. Selective wetting properties along with a porous structure enable the wood membrane to purify surfactant-stabilized oil-in-water emulsions. Such a biomass-derived membrane, which is green, inexpensive, easy to fabricate, and scalable, along with its selective wettability and durability, shows great potential for use as a substitute for existing filter media in diverse industries.

Crystalline stability of cellulose III nanocrystals in the hydrothermal treatment and NaOH solution

To better understand the system and conversion of cellulose allomorphs, cellulose III nanocrystals (CNC-III) were used to investigate the crystalline stability of cellulose III in the hydrothermal condition and a lower concentrated NaOH-water system. It was shown that H₂O or alkali played an important role in the process of polymorphic transformation. The CNC-III allomorph turned back to cellulose I with an extremely low crystallinity (∼4.18 %) during hydrothermal process at 90-95 °C, or cellulose II when the temperature excessed boiling point (≥100 °C). Furthermore, CNC-III could be rapidly dissolved in an aqueous NaOH (∼7 wt.%) without a pre-cooled treatment to obtain its stable solution. Afterwards, cellulose II with a steady average crystallite size (∼34) was acquired after the regeneration process via dialysis with distilled water. The polymorphic transformation was also analyzed by X-ray diffraction (XRD), solid-state ¹³C nuclear magnetic resonance (¹³C NMR).