Bonding wood with uncondensed lignins as adhesives.

Plywood is widely used in construction, such as for flooring and interior walls, as well as in the manufacture of household items such as furniture and cabinets. Such items are made of wood veneers that are bonded together with adhesives such as urea-formaldehyde and phenol-formaldehyde resins1,2. Researchers in academia and industry have long aimed to synthesize lignin-phenol-formaldehyde resin adhesives using biomass-derived lignin, a phenolic polymer that can be used to substitute the petroleum-derived phenol3-6. However, lignin-phenol-formaldehyde resin adhesives are less attractive to plywood manufacturers than urea-formaldehyde and phenol-formaldehyde resins owing to their appearance and cost. Here we report a simple and practical strategy for preparing lignin-based wood adhesives from lignocellulosic biomass. Our strategy involves separation of uncondensed or slightly condensed lignins from biomass followed by direct application of a suspension of the lignin and water as an adhesive on wood veneers. Plywood products with superior performances could be prepared with such lignin adhesives at a wide range of hot-pressing temperatures, enabling the use of these adhesives as promising alternatives to traditional wood adhesives in different market segments. Mechanistic studies indicate that the adhesion mechanism of such lignin adhesives may involve softening of lignin by water, filling of vessels with softened lignin and crosslinking of lignins in adhesives with those in the cell wall.

High Ion-Conducting PVA Nanocomposite Hydrogel-Based Wearable Piezoelectric and Triboelectric Sensors for Harsh Environments.

Traditional hydrogel-based wearable sensors with flexibility, biocompatibility, and mechanical compliance exhibit potential applications in flexible wearable electronics. However, the low sensitivity and poor environmental resistance of traditional hydrogels severely limit their practical application. Herein, high-ion-conducting poly(vinyl alcohol) (PVA) nanocomposite hydrogels were fabricated and applied for harsh environments. MXene ion-conducting microchannels and poly(sodium 4-styrenesulfonate) ion sources contributed to the directional transport of abundant free ions in the hydrogel, which significantly improved the sensitivity and mechanical-electric conversion of the nanocomposite hydrogel-based piezoelectric and triboelectric sensors. More importantly, the glycerol as an antifreezing agent enabled the hydrogel-based sensors to function in harsh environments. Therefore, the nanocomposite hydrogel exhibited high gauge factor (GF) at -20 °C (GF = 3.37) and 60 °C (GF = 3.62), enabling the hydrogel-based sensor to distinguish different writing letters and sounding words. Meanwhile, the hydrogel-based piezoelectric and triboelectric generators showed excellent mechanical-electric conversion performance regardless of low- (-20 °C) or high- (60 °C) temperature environments, which can be applied as a visual feedback system for information transmission without external power sources. This work provides self-powered nanocomposite hydrogel-based sensors that exhibit potential applications in flexible wearable electronics under harsh environmental conditions.

Preparation and modification of polymer microspheres, application in wastewater treatment: A review.

The removal of various pollutants from water is necessary due to the increasing requirements for the removal of various pollutants from wastewater and the quality of drinking water. Polymer microspheres are regarded as exemplary adsorbent materials due to their high adsorption efficiency, excellent adsorption performance, and ease of handling. Herein, the advantages and disadvantages of different preparation methods, modifications, applications and the current research status of polymer microspheres are summarized at large. Furthermore, the enhanced performance of modified composite microspheres is emphasized, including adsorption efficiency, thermal stability, and significant improvements in physical and chemical properties. Subsequently, the current applications and potential of polymeric microspheres for wastewater treatment, including the removal of inorganic and organic pollutants, heavy metal ions, and other contaminants are summarized. Finally, future research directions for polymer microspheres are proposed, outlining the challenges and solutions associated with the application of polymer microspheres in wastewater treatment.

A robust salt-tolerant superoleophobic aerogel inspired by seaweed for efficient oil-water separation in marine environments.

Oil-water separation has recently become an important subject due to the increasing incidence of oil spills. Materials with underwater superoleophobic properties have aroused considerable interest due to their cost-effectiveness, environmental friendliness and anti-fouling properties. This paper presents a robust salt-tolerant superoleophobic aerogel inspired by seaweed used without any further chemical modification for oil-seawater separation. The green aerogel is prepared by freeze-drying of sodium alginate (SA)-nanofibrillated cellulose (NFC) using Ca2+ ions as the crosslinking agent. The three-dimensional (3D) interconnected network structure of the developed aerogel ensures its high mechanical strength and good flexibility. The natural hydrophilicity of the polysaccharides contained in the aerogel ensures its excellent underwater superoleophobicity, antifouling and salt-tolerance properties. More impressively, the as-prepared aerogel can even keep its underwater superoleophobicity and high hydrophilicity after being immersed in seawater for 30 days, indicating its good stability in marine environments. Furthermore, the aerogel could separate oil-seawater mixtures with a high separation efficiency (of up to 99.65%) and good reusability (at least 40 cycles). The facile and green fabrication process combined with the excellent separation performance and good reusability makes it possible to develop engineering materials for oil-water separation in marine environments.

A Cellulose/Chitosan Dual Cross-Linked Multifunctional and Resilient Hydrogel for Emergent Open Wound Management.

Adhesive hydrogel holds huge potential in biomedical applications, such as hemostasis and emergent wound management during outpatient treatment or surgery. However, most adhesive hydrogels underperform to offer robust adhesions on the wet tissue, increasing the risk of hemorrhage and reducing the fault tolerance of surgery. To address this issue, this work develops a polysaccharide-based bioadhesive hydrogel tape (ACAN) consisting of dual cross-linking of allyl cellulose (AC) and carboxymethyl chitosan (CMCS). The hygroscopicity of AC and CMCS networks enables ACAN to remove interfacial water from the tissue surface and initializes a physical cross-link instantly. Subsequently, covalent cross-links are developed with amine moieties to sustain long-term and robust adhesion. The dual cross-linked ACAN also has good cytocompatibility with controllable mechanical properties matching to the tissue, where the addition of CMCS provides remarkable antibacterial properties and hemostatic capability. Moreover, compared with commercially available 3 M film, ACAN provides an ultrafast wound healing on tissue. The ACAN hybrid hydrogels have advantages such as biocompatibility and antibacterial, hemostatic, and wound healing properties, shedding new light on first-aid tape design and advancing the cellulose-based materials technology for high-performance biomedical applications.

Sustainable, super-stable thermochromic material by coupling hydroxypropyl cellulose and sodium carboxymethyl cellulose.

Hydroxypropyl cellulose (HPC) is a green thermochromic material in energy-saving buildings, anti-counterfeiting, and data security fields. However, the high lower critical solution temperature (LCST) of HPC, around 42 °C (higher than the human thermal comfort temperature), limits its thermochromic sensitivity, poor stability, and short lifespan. Herein, we developed a durable, high-performance cellulose-based thermochromic composite with a lower LCST and easy preparation capability by combining HPC with sodium carboxymethyl cellulose (CMC). In such thermochromic cellulose, CMC constructs a hydrophilic skeleton to enable uniform dispersion of HPC, and functions as a stronger competitor to attract the water molecules compared to HPC, both of which trigger high thermochromic sensitivity and low LCST (just 32.5 °C) of our CMC/HPC. In addition, CMC/HPC shows superior stability, such as 100-day working capability and 60-time recyclability. This advancement marks a significant step forward in creating sustainable, efficient thermochromic materials, offering new opportunities for energy conservation in the building.

Electrospun chitosan nanofiber constructing superhigh-water-flux forward osmosis membrane.

Forward osmosis (FO) technology exhibits great potential in seawater desalination and wastewater treatment due to its negligible energy consumption and high antifouling, however, the weak desalination capability, especially low water flux, remains challenging. Herein, a cost-effective and high-desalination-performance chitosan (CS)-based FO membrane is developed via coupling the electrospinning CS nanofibers and interfacial-polymerized polyamide (PA). The electrospun nanofibers construct the porous and hydrophilic CS layer with the large pore-diameter of ~274 nm and low thickness of ~10 µm, enabling the effective transport of water molecules, specifically, a superhigh water flux of 107.53 LMH at a low salt-water ratio of 0.24 g·L-1. In addition, such superior desalination performance of the as-prepared FO membrane is universal for the various salt species and concentrations. Our CS nanofiber-based membrane with the high separation capability of water-salt, desirable antibacterial activity, as well as the low cost, offers a roadmap toward the sustainable membrane materials.

UV and IR dual light triggered cellulose-based invisible actuators with high sensitivity.

Actuators are widely used in bionic devices and soft robots, among which invisible actuators have some unique applications, including performing secret missions. In this paper, highly visible transparent cellulose-based UV-absorbing films were prepared by dissolving cellulose raw materials using N-methylmorpholine-N-oxide (NMMO) and using ZnO nanoparticles as UV absorbers. Furthermore, transparent actuator was fabricated by growing highly transparent and hydrophobic polytetrafluoroethylene (PTFE) film on regenerated cellulose (RC)-ZnO composite film. In addition to its sensitive response to Infrared (IR) light, the as-prepared actuator also shows a highly sensitive response to UV light, which is attributed to the strong absorption of UV light by ZnO NPs. Thanks to the drastic differences in adsorption capacity between the RC-ZnO and PTFE materials for water molecules, the asymmetrically- assembled actuator demonstrates extremely high sensitivity and excellent actuation performance, with a force density of 60.5, a maximum bending curvature of 3.0 cm-1, and a response time of below 8 s. Bionic bug, smart door and the arm of excavator made from the actuator all exhibit sensitive responses to UV and IR lights.

Design of asymmetric-adhesion lignin reinforced hydrogels with anti-interference for strain sensing and moist air induced electricity generator.

Flexible hydrogels with integration of excellent mechanical and electrical properties are well suited for applications as wearable electronic sensors, and others. Self-adhesion is an important feature of wearable sensors. However, the usual isotropic- adhesion hydrogels have the drawback of poor anti-interference, which negatively affects their applications. In this study, we developed asymmetric-adhesion and tough lignin reinforced hydrogels in a facile two-step process: 1) PAA hydrogels, with lignin as the binder and conductive filler, were first prepared; 2) the asymmetric-adhesion property was imparted to lignin reinforced hydrogel by simple soaking of the top portion of the hydrogel in CaCl2 solution. The as-obtained asymmetric-adhesion lignin reinforced hydrogel was assembled into a wearable sensor, which shows excellent anti-interference and accurate and stable collections of sensing signals, with its gauge factor (GF) of 2.51 (in the strain range of 0-51.5%). In addition, the tough hydrogel is capable of generating electricity upon moist air sweeping through it, showing excellent energy conversion capabilities, with open-circuit voltage of as high as 306.6 mV. These results provided new prospects for the application of polyelectrolyte hydrogel materials in the fields of wet-to-electric conversion and wearable electronic sensors.

Design of asymmetric-adhesion lignin-reinforced hydrogels based on disulfide bond crosslinking for strain sensing application.

Soft and elastic polymer hydrogel materials are booming in the fields of wearable biomimetic skin, sensors, robotics, and bioelectrodes. Currently, many researchers are exploring new chemistries for the preparation of hydrogels to improve their performance. In the present study, we design and develop a strategy to prepare lignin reinforced hydrogels based on disulfide bond crosslinking mechanisms, and resultant hydrogels exhibit excellent stretchability, with tensile strain of up to 1085.4%, and high adhesion (with the highest T-peel strength of up to 432.2 N/m to pigskin). The underlying mechanism is based on the disulfide bonds that act as crosslinkers in the as-prepared hydrogel, and they can be easily cleaved and re-formed under mild conditions. Thanks to the presence of lignin, the as-obtained hydrogels also have excellent UV shielding effect. When assembled into a strain sensor, they can output stable and sensitive sensing signals, with gauge factor (GF) of 2.72 (strain: 0-72.8%). Furthermore, a simple and effective strategy to construct asymmetric adhesive hydrogels was adopted, which is based on directional soaking of the top portion of the hydrogel in a high-concentrated calcium chloride solution. The asymmetric hydrogel strain sensor transmits accurate and stable signals without the interference of various contaminants.

Rapid fabrication of bionic pyrogallol-based self-adhesive hydrogel with mechanically tunable, self-healing, antibacterial, wound healing, and hemostatic properties.

Hydrogels are functional materials that are similar to human skin and have received much attention in recent years for biomedical applications. However, the preparation of nontoxic, highly adhesive, and antimicrobial hydrogels in an efficient way remains a great challenge. Inspired by adhesive mussel foot proteins (mfps) which consist of abundant catecholic amino acids and lysine (Lys) residues, gallic acid-modified ε-poly-L-lysine (EPL/GA) was synthesized, and an active functional monomer (AA-EPL/GA) was then created through a reaction with acrylic acid (AA). The polymerization of AA-EPL/GA occurred rapidly (30-160 s) under blue light (λ = 405 nm) irradiation to produce a biomimetic PAA-EPL/GA hydrogel under mild conditions. The biomimetic pyrogallol-Lys distribution endowed the PAA-EPL/GA hydrogels with superior adhesion in humid environments (with an adhesive strength of 50.02 kPa toward wet porcine skin) and tunable mechanical and self-healing properties. Additionally, the PAA-EPL/GA hydrogels exhibited outstanding antibacterial ability due to the inherent characteristics of GA and EPL. In a mouse model, PAA-EPL/GA adhered firmly around the wound tissues. Photographs of the wound and the histological results demonstrated the ability of the hydrogel to promote wound healing, control wound infection, and suppress scar formation. Moreover, the hydrogel had a good hemostatic effect on liver bleeding. Our results highlighted the promising application potential of GA-based hydrogels, which were easily, harmlessly, and efficiently fabricated by blue light irradiation.

Engineered Janus cellulose membrane with the asymmetric-pore structure for the superhigh-water flux desalination.

Membranes are the dominant material for seawater desalination and clean-water harvesting, which are commonly composed of synthetic polymers, showing low hydrophilicity and environmental hazard. Herein, we developed a low-cost, intrinsically green, superhigh-water flux Janus cellulose membrane (CEM) via a facile cellulase etching strategy. Coating cellulase on the single surface of cellulose membrane (such as top surface), triggers effective etching on its top section rather than bottom section, which architects an asymmetric-pore structure of the Janus CEM including porous top-and dense bottom-layer. Such distinction endows the Janus CEM with an unprecedented high-water flux of 135.75 LMH and a low salt-water ratio of 0.29 g·L-1 for 1 M NaCl solution, which is 17-time higher and 62-time lower than that of the pristine CEM. Our Janus CEM enables a promising participant for the advanced membrane materials toward versatile separation engineering.

A Green Catechol-Containing Cellulose Nanofibrils-Cross-Linked Adhesive.

Traditional adhesives with strong adhesion are widely applied in the fields of wood, building, and electronics. However, the synthesis and usage of commercial adhesives are not eco-friendly, which are harmful to human health and to the environment. In this study, a green cellulose nanofibrils/poly(hydroxyethyl methacrylate-co-dopamine methacrylamide) (CNFs/P(HEMA-co-DMA)) adhesive with excellent biocompatibility and strong bonding strength has been fabricated. P(HEMA-co-DMA) with a catechol content of 7.1 mol % was synthesized using dopamine methacrylamide and hydroxyethyl methacrylate. The CNFs/P(HEMA-co-DMA) adhesive was generated by cross-linking P(HEMA-co-DMA) solution using cellulose nanofibrils (CNFs). Strong adhesion was realized on various substrates, with a maximum lap shear strength of 5.50 MPa on steel. The NIH 3T3 cells test demonstrated that the adhesive possessed excellent biocompatibility. The green catechol-containing CNFs-cross-linked adhesive has promising potential for applications in medicine, electronic, food packaging, and engineering.

Mild depolymerization of the sinocalamus oldhami alkali lignin to phenolic monomer with base and activated carbon supported nickel-tungsten carbide catalyst composite system.

In this study, the sinocalamus oldhami alkali lignin was depolymerized into phenolic products in a combined system by using the composite alkali and Ni-W2C/activated carbon (AC) as catalysts. FT-IR, GPC, TG, 2D-HSQC and GC-MS were used to analyze the composition, structure and distribution of degradation products, and the synergistic effect of metal and alkali catalysts on the depolymerization of lignin was also studied. The results showed that Ni-W2C/AC and composite alkali could effectively improve the catalytic degradation efficiency of lignin under mild conditions, 94.4% of lignin was converted and 17.18% of phenolic monomers were obtained under 260 °C for 5 h. In this composite system, the synergism of the basic sites, the metal active sites and the Lewis acid sites could promote the cleavage of C-O bonds in the lignin molecule and lower the char formation during the base-catalyzed solvolysis. Phenolic monomers were mainly composed of phenol, 2-methyl-phenol and p-cresol etc.

Nature-inspired self-powered cellulose nanofibrils hydrogels with high sensitivity and mechanical adaptability.

It is still a challenge to integrate high sensitivity, mechanical adaptability, and self-powered properties for hydrogels. Herein, we report a conductive polyvinyl alcohol (PVA) hydrogel based on natural nanoclay and cellulose nanofibrils (CNFs). The CNFs and PVA chains could construct a double network structure, resulting in a high mechanical composite hydrogel. Meanwhile, the nanoclay could be well dispersed and immobilized in the network of the hydrogel, thus improving mechanical adaptability of the hydrogel for curved and dynamic surfaces. Moreover, the conductive ions (Al3+) imparted the hydrogel with high conductivity (6.67 S m-1) and gauge factor (1.17). Therefore, the composite hydrogel exhibited high sensitivity to tiny pressure changes, enabling recognition of the complicated sounding and handwriting. More importantly, the composite hydrogel possessed self-powered property, which could generate an output voltage of up to 78 mV. In summary, the multi-functional composite hydrogel may have giant applications in artificial electronic skins or wearable devices.

An oriented Fe3+-regulated lignin-based hydrogel with desired softness, conductivity, stretchability, and asymmetric adhesiveness towards anti-interference pressure sensors.

The development of conductive, soft, ultra-stretchable, and asymmetrically adhesive hydrogels is difficult and essential for both wearable electronics and anti-adhesion tissue dressings. In particular, there is still no simple, effective and universal approach to construct an asymmetrically adhesive multifunctional hydrogel. Here, we first synthesized lignosulfonate sodium (LS)-doped PAA hydrogels with uniform adhesion (adhesive strength: ~30.5 kPa), conductivity (~0.45 S/m), stretchability (up to ~2250%), and low compressive modulus (~20 kPa). In the second step, an oriented soaking of Fe3+ onto the upper surface of the resultant composite hydrogel renders the upper surface non-adhesive. This novel strategy masterfully delivers asymmetric adhesion behavior to the upper and bottom surfaces of the same hydrogel (~0 kPa adhesive strength for the upper surface; strong adhesive strength of ~27 kPa for the bottom surface). The asymmetric adhesive hydrogel has proven to adhere well onto the human skin and achieve waste-barrier. Importantly, this hydrogel assembled pressure sensor demonstrates excellent anti-interference and wearable comfort.

Preparation of lignosulfonate ionic hydrogels for supercapacitors, sensors and dye adsorbent applications.

Lignin, an abundant natural polymer but presently under-utilized, has received much attention for its green/sustainable advantages. Herein, we report a facile method to fabricate lignosulfonate (LS) ionic hydrogels by simple crosslinking with poly (ethylene glycol) diglycidyl ether (PEGDGE). The as-obtained LS-PEGDGE hydrogels were comprehensively characterized by mechanical measurements, FT-IR, and SEM. The rich sulfonic and phenolic hydroxyl groups in LS hydrogels play key roles in imparting multifunctional smart properties, such as adhesiveness, conducting, sensing and dye adsorption, as well as superconductive behavior when increasing the moisture content. The hydrogels have a high adsorption capacity for cationic dyes, using methylene blue as a model, reaching 211 mg·g-1. As a moist-induced power generator, the maximum output voltage is 181 mV. The LS-PEGDGE hydrogel-based flexible strain sensors exhibit high sensitivity when detecting human movements. As the hydrogel electrolyte, the assembled supercapacitor shows high specific capacitance of 236.9 F·g-1, with the maximum energy density of 20.61 Wh·kg-1, power density of 2306.4 W·kg-1, and capacitance retention of 92.9% after 10,000 consecutive charge-discharge cycles. Therefore, this multifunctional LS hydrogels may have promising applications in various fields, providing a new platform for the value-added utilization of lignin from industrial waste.

Tendon-inspired fibers from liquid crystalline collagen as the pre-oriented bioink.

Nature provides rich bionic resources for the construction of advanced materials with excellent mechanical properties. In this work, inspired by animal tendons, a bionic collagen fiber was developed using collagen liquid crystals as the pre-oriented bioink. The texture of liquid crystalline collagen observed from polarized optical microscopy (POM) showed the specific molecular pre-orientation. Meanwhile, the collagen spinning liquids exhibited a minimal rise in viscosity upon increasing concentration from 60 to 120 mg/mL, indicating the feasible processability. The collagen fiber, which was prepared via wet spinning without being denatured, exhibited the favorable orientation of fibrils along its axis as observed with FESEM and AFM. Thanks to the synergistic effects between pre-orientation and shearing orientation, the maximum tensile strength and Young's modulus of collagen fibers reached 9.98 cN/tex (219.29 ± 22.92 MPa) and 43.95 ± 1.11 cN/tex (966.20 ± 24.30 MPa), respectively, which were also analogous to those of tendon. In addition, the collagen fiber possessed a desirable wet strength. Benefiting from the natural tissue affinity of collagen, the as-prepared bionic collagen fiber possessed excellent wound suture performance and biodegradability in vivo, which offers a new perspective for the potential of widespread applications of collagen fibers in biomedical fields.

Transparent, smooth, and sustainable cellulose-derived conductive film applied for the flexible electronic device.

A high-performance flexible conductive substrate is one of the key components for developing promising wearable devices. Concerning this, a sustainable, flexible, transparent, and conductive cellulose/ZnO/AZO (CZA) film was developed in this study. The cellulose was used as the transparent substrate. The added AZO was as the conductive layer and ZnO functioned as an interface buffer layer. Results showed that the interface buffer layer of ZnO effectively alleviated the intrinsic incompatibility of organic cellulose and inorganic AZO, resulting in the improvement of the performance of CZA film. In compared with the controlled cellulose/AZO (CA) film with 365 Ω/sq sheet resistance and 87% transmittance, this CZA film featured a low conductive sheet resistance of 115 Ω/sq and high transmittance of 89%, as well as low roughness of 1.85 nm Moreover, the existence of conducive ZnO buffer layer enabled the conductivity of CZA film to be stable under the bending treatment. Herein, a flexible electronic device was successfully prepared with the biomass materials, which would be available by a roll-to-roll production process.

Mussel-inspired cellulose-based adhesive with biocompatibility and strong mechanical strength via metal coordination.

Inspired by marine mussel, catechol-containing materials, such as adhesives, self-healing hydrogels, and antifouling coatings, have been developed with wide applications in chemical, biomedical, and electronics industries. Conventionally, petrochemicals or organic solvents are widely used for preparation and dissolution of adhesives, which makes the adhesives are not eco-friendly and biocompatible. To develop environmentally friendly and biocompatible adhesives with desired properties, here we report catechol-containing cellulose-based tissue adhesives, synthesized by incorporating catechol groups onto cellulose. The structures of the adhesives with different catechol contents were analyzed by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H NMR) spectroscopy. The adhesion strengths were examined using porcine skin by lap shear tensile tests. The adhesion strength of the as-prepared adhesive with catechol content of 16.5 mol% was 20.0 kPa. Fe3+ was used as crosslinker to enhance the adhesion strength and accelerate the solidification of adhesives. Through the Fe3+-catechol coordination, the adhesion strength of adhesive was increased to 88.0 kPa, showing strong mechanical strength compared to the fibrin adhesive. NIH 3T3 cells test demonstrates that the adhesive is favorable for cell attachment and proliferation, possessing excellent biocompatibility. The catechol-containing cellulose-based adhesive has promising application in bioengineering field.