In Situ Lignin Adhesion for High-Performance Bamboo Composites

A chitosan-based adhesive with high flame retardancy and superior bonding strength fabricated by interface engineering

With an emphasis on sustainable development, the wood industry faces great challenges, including studies on bio-based, aldehyde-free, high-strength and water-resistant adhesives. Here, a high-strength water-resistant chitosan-based adhesive was prepared by mixing of polyacrylic acid (PAA) and chitosan (CS) with assist of a little Ca2+. Meanwhile, bonding strength was enhanced through wood surface activation caused by wood: adhesive interfacial interaction. The dry and wet bonding strengths of the three-layer plywood were 3.28 MPa and 2.16 MPa, respectively. Bonding strength of the plywood remained 1.38 MPa after a "4 + 4 + 1" harsh test. The main reasons for the excellent performance were: 1) Covalent crosslinking and entanglement between PAA and CS significantly improved the cohesiveness of adhesive. 2) The introduction of Ca2+ formed organic-inorganic hybrid structure, which enhanced the cohesion and interfacial force of adhesive. 3) The active functional groups on wood surface were further cross-linked with adhesive, which greatly enhanced the interfacial bonding. After the adhesive was compounded with ammonium polyphosphate, the plywood exhibited excellent flame retardancy. These strategies have provided valuable ideas for studying high-performance wood adhesives and expanding the functionality of adhesives.

Tough and UV-resistant biodegradable polyurethane elastomers based on extracted lignin and treated wood flour

Polyurethanes are widely utilized across various fields. In the pursuit of sustainable development, current research prioritizes the development of bio-based, environmentally friendly polyurethanes. Wood flour, a type of biomass waste, faces significant challenges in achieving high-value utilization. In this study, wood flour was pretreated with sodium hydroxide solution to generate extracted lignin (Elig) and alkali-treated wood flour (AWF), which were subsequently employed to fabricate biodegradable polyurethane elastomers. Elig was further modified with polycaprolactone (PCL) to enhance its reactivity and flexibility, serving as a biological macromolecule crosslinker in the synthesis of lignin-based polyurethane [PU(Plig)]. Tough polyurethane composite elastomers were then obtained by incorporating AWF into PU(Plig). The resulting PU composite elastomer, PU(Plig@AWF), containing strong interfacial interaction between Elig and AWF, exhibited high toughness (188.15 MJ/m3), excellent UV resistance (with stress and strain retention rates of 77.92 % and 77.07 %, respectively, after 96 h of ultraviolet aging), and outstanding biodegradability (with a mass loss of 19.06 % observed after 50 days of soil degradation testing). Additionally, leveraging the unique characteristics of lignin and wood flour (WF), the elastomer demonstrated remarkable light/thermal-electric conversion capabilities, effectively powering a fan. This study advances the development of biomass-based, multifunctional polyurethane elastomers with enhanced cost-efficiency.

A Natural Lignification Inspired Super-Hard Wood-Based Composites with Extreme Resilience

The growing demand for high-strength, durable materials capable of enduring extreme environments presents a significant challenge, particularly in balancing performance with sustainability. Conventional materials such as alloys and ceramics are nonrenewable, expensive, and require energy-intensive production processes. Here, super-hard wood-based composites (WBC) inspired by the meso-scale homogeneous lignification process intrinsic to tree growth are designed and developed. This hybrid structure is achieved innovatively by leveraging the infusion of low-molecular-weight phenol formaldehyde resin into the cell walls of thin wood slices, followed by a unique multi-layer construction and high-temperature compression. The resulting composite exhibits remarkable properties, including a Janka hardness of 24 382 N and a Brinell hardness of 40.7 HB, along with exceptional antipiercing performance. The created super-hard, sustainable materials address the limitations of nonrenewable resources while providing enhanced protection, structural stability, and exceptional resilience. The WBC approach aligns with UN Sustainable Development Goals (SDGs) by offering extra values for improving personal safety and building integrity across various engineering applications.

Transformation of Bamboo: From Multiscale Fibers to Robust and Degradable Cellulose-Based Materials for Plastic Substitution

Bamboo is an ideal candidate to replace traditional plastics, reduce environmental pollution, and promote harmony between nature and humanity owing to its rapid growth and renewability. However, achieving arbitrary shape-shifting of bamboo while retaining its high strength and degradability remains challenging. This study uses multiscale interface engineering to transform bamboo into a robust, biodegradable, and moldable bamboo cellulose-based material. First, natural bamboo is deconstructed into cellulose fibers, including macro- and nanofibers. Subsequently, the fibers are constructed into high-performance materials using physical and chemical methods, such as surface charge treatment, ion cross-linking, and dense hydrogen bonding networks. The prepared multiscale bamboo cellulose-based materials exhibit excellent properties, with a high specific strength (≈271.8 kN m kg-1), high impact toughness (≈58 kJ m-2), low thermal expansion coefficient (1.19 × 10-6 K-1), excellent formability and biodegradability, and minimal environmental impacts. These properties are superior to those of current commercial plastics and other biomass-derived structural materials. Furthermore, the mechanical properties of the materials can be customized by adjusting the layup configuration, enabling a transition from anisotropic to isotropic characteristics. This transformation demonstrates the significant potential of bamboo for plastic substitution and advances the development of environmentally friendly materials.

Adhesive-Free, Light, and Strong Particle Board

Wood particle boards are massively used in construction and household products. But they often raise health and environmental concerns because of the formaldehyde-based adhesives. More sustainable and high-strength particle boards are developed on a bio-based materials or their derivatives. However, their high density (heavier than that of water) greatly weakens the important light weight properties of natural wood. To address this problem, we realized adhesive-free, light, and strong particle boards assisted by plant macrofibers using big wood particles as raw materials. The challenge of strong connection among big wood particles is achieved by plant macrofibers, which serve as bridges to forming robust linkages between wood particles. The resulting particle boards have densities as low as 0.53 g cm-3 (61.7 MPa) and flexural strengths as high as 114.2 MPa (0.78 g cm-3). This strategy opens a new door for the research and application of wood particle boards for sustainable development of the world.

Effect of W Modification on MoS2 Surface Edge in the Ethanolysis of Lignin into Platform Chemicals

A series of metal-doped MoS2, including W-, V-, and Re-doped MoS2, are prepared via a two-step hydrothermal method, which presents higher activity on the depolymerization of enzymatic hydrolysis lignin (EHL) in ethanol as compared to undoped MoS2. At 320 °C for 6 h, the highest overall aromatic monomer yield of 231 mg/g EHL, including alkylphenols (A-Ps) as the main products with a yield of 126.5 mg/g EHL, is obtained over two-step hydrothermally prepared W-doped MoS2 with the W/Mo molar ratio of 0.1 (Ts-W0.1@MoS2). The W-doped MoS2 sample gives higher enhancement of EHL bio-oils' heating value to 37.1 MJ/kg as compared to Re and V modified MoS2. Large distribution of W atoms on the MoS2 surface in two-step hydrothermally synthesized samples leads to the higher activity of EHL depolymerization than one-step prepared samples. The reduction of W precursors on the MoS2 surface in the preparation process promotes the generation of more Mo5+ and Mo6+, which plays important roles in the improvement of EHL depolymerization activity. The effect of the W-doping modification and the stability of W-doped MoS2 are discussed. The anti-sulfur loss and antioxidant abilities are significantly enhanced after W-doping modification. In the recyclability test, the good incorporation of W atoms with MoS2 surface and the gradual oxidation of W-based sites improve the balance of catalytic cycles among different Mo-based sites, which results in the increase of catalyst stability.

Processing natural bamboo into white bamboo through photocatalyzed lignin oxidation

Scalable and highly efficient bamboo whitening remains a great challenge. Herein, an effective bamboo whitening strategy is proposed based on photocatalyzed oxidation, which involves H2O2 infiltration and UV illumination. The as-prepared white bamboo well maintains the nature structure of natural bamboo and demonstrates high whiteness and superior mechanical properties. The absorbance value is significantly decreased to 3.5 and the transmittance is increased to 0.04 % in UV-visible wavelength range due to the removal of light-absorbing chromospheres of lignin, resulting in a high whiteness when the UV illumination time is 8 h. In addition, the white bamboo displays a high tensile strength of 30 MPa and a high flexural strength of 36 MPa due to the well-preserved lignin units (lignin preservation is about 89 %). XRD patterns and analysis show that photocatalyzed oxidation has no effect on the crystal parameters of cellulose. Compared with the traditional bamboo whitening technology, our photocatalyzed oxidation strategy demonstrates significant advantage including chemical and time conservation, high efficiency, environment friendliness, and mechanical robustness. This highly efficient and environmentally friendly photocatalyzed oxidation strategy for the fabrication of white bamboo may pave the way of bamboo-based energy-efficient structural materials for engineering application.

Desirable Strong and Tough Adhesive Inspired by Dragonfly Wings and Plant Cell Walls

The production of wood-based panels has a significant demand for mechanically strong and flexible biomass adhesives, serving as alternatives to nonrenewable and toxic formaldehyde-based adhesives. Nonetheless, plywood usually exhibits brittle fracture due to the inherent trade-off between rigidity and toughness, and it is susceptible to damage and deformation defects in production applications. Herein, inspired by the microstructure of dragonfly wings and the cross-linking structure of plant cell walls, a soybean meal (SM) adhesive with great strength and toughness was developed. The strategy was combined with a multiple assembly system based on the tannic acid (TA) stripping/modification of molybdenum disulfide (MoS2@TA) hybrids, phenylboronic acid/quaternary ammonium doubly functionalized chitosan (QCP), and SM. Motivated by the microstructure of dragonfly wings, MoS2@TA was tightly bonded with the SM framework through Schiff base and strong hydrogen bonding to dissipate stress energy through crack deflection, bridging, and immobilization. QCP imitated borate chemistry in plant cell walls to optimize interfacial interactions within the adhesive by borate ester bonds, boron-nitrogen coordination bonds, and electrostatic interactions and dissipate energy through sacrificial bonding. The shear strength and fracture toughness of the SM/QCP/MoS2@TA adhesive were 1.58 MPa and 0.87 J, respectively, which were 409.7% and 866.7% higher than those of the pure SM adhesive. In addition, MoS2@TA and QCP gave the adhesive good mildew resistance, durability, weatherability, and fire resistance. This bioinspired design strategy offers a viable and sustainable approach for creating multifunctional strong and tough biobased materials.

Valorization of sewage sludge for facile and green wood bio-adhesives production

A method is presented herein for the design of wood bio-adhesives using sewage sludge extracts (SSE). SSE was extracted from SS using deep eutectic solvents and processed with glycerol triglycidyl ether (GTE) to disrupt the secondary structure of proteins. An additive was also used to improve mechanical performance. The resulting bio-adhesive (SSE/GTE@TA) had a wet shear strength of 0.93 MPa, meeting the Chinese national standard GB/T 9846-2015 (≥0.7 MPa). However, the high polysaccharide content in SSE would weaken the mechanical properties of wood bio-adhesives. The key to improve bio-adhesive quality was the formation of a strong chemical bond via Maillard reaction as well as higher temperatures (140 °C) to reduce polysaccharide content via dehydration. This approach has lower environmental impact and higher economic efficiency compared to incineration and anaerobic digestion of sewage sludge. This work provides a new perspective on the high-value utilization of SS and offers a novel approach to developing bio-adhesives for the wood industry.