A biomimetic adhesive with high adhesion strength and toughness comprising soybean meal, chitosan, and condensed tannin-functionalized boron nitride nanosheets

A strong and tough supramolecular assembled β-cyclodextrin and chitin nanocrystals protein adhesive: Synthesis, characterization, bonding performance on three-layer plywood

The development of a biomass adhesive as a substitute for petroleum-derived adhesives has been considered a viable option. However, achieving both superior bonding strength and toughness in biomass adhesives remains a significant challenge. Inspired by the human skeletal muscles structure, this study reveals a promising supramolecular structure using tannin acid (TA) functionalized poly-β-cyclodextrin (PCD) (TA@PCD) as elastic tissues and chitin nanocrystals (ChNCs) as green reinforcements to strengthen the soybean meal (SM) adhesive crosslinking network. TA@PCD acts as a dynamic crosslinker that facilitates reversible host-guest interactions, hydrogen bonds, and electrostatic interactions between adjacent stiff ChNCs and SM matrix, resulting in satisfactory strength and toughness. The resulting SM/TA@PCD/ChNCs-2 adhesive has demonstrated satisfactory wet and dry shear strength (1.25 MPa and 2.57 MPa, respectively), toughness (0.69 J), and long-term solvents resistance (80 d). Furthermore, the adhesive can exhibit desirable antimildew characteristics owing to the phenol hydroxyl groups of TA and amino groups of ChNCs. This work showcases an effective supramolecular chemistry strategy for fabricating high-performance biomass adhesives with great potential for practical applications.

Lobster-Inspired Chitosan-Derived Adhesives with a Biomimetic Design

Polysaccharide-based adhesives, especially chitosan (CS)-derived adhesives, serve as promising sustainable alternatives to traditional adhesives. However, most demonstrate a poor adhesive strength. Inspired by the inherent layered structure of marine arthropods (lobsters), a core-shell structure (SiO2-NH2@OPG) with amine-functionalized silica (SiO2-NH2) as the core and oxidized pyrogallol (OPG) as the shell is prepared in this study. The compound is blended with CS to produce a structural biomimetic wood adhesive (SiO2-NH2@OPG/CS) with excellent performance. In addition to thermocompressive curing, this adhesive exhibits a water-evaporation-induced curing behavior at room temperature. With reference to the design mechanism of the lobster cuticle, this microphase-separated structure consists of clustered nanofibers with varying amounts of SiO2-NH2@OPG particles between the fibers. This intriguing microphase structure and its mechanical effects could offer a powerful solution for improving the functional modification of wood composites.

A multiple cross-linking strategy to develop an environment-friendly and water resistance wheat gluten protein wood adhesive

Wheat gluten (WG) shows great promise to synthesize environment-friendly wood adhesives. However, their weak bonding strength and poor water resistance have limited its application in the commercial wood-based panel industry. In this study, a novel WG-based adhesive was developed by constructing a multiple cross-linking network generated by covalent and non-covalent bonds. The potential mechanism was revealed by FT-IR analysis. Furthermore, their surface morphology, thermal stability, viscosity, and residual rate of adhesives with different compositions were systematically characterized and compared. The results showed that the hydrogen bonding, reactions between amine groups and tannin, and ring opening reaction of epoxy, synergistically contributed to generate a highly crosslinked network. The wet/boil water strength of the plywood prepared from WG/tannin/ethylene imine polymer (PEI)-glycerol triglycidyl ether (GTE) adhesive with the addition of 15 % GTE could reach 1.21 MPa and 1.20 MPa, respectively, and a mildew resistance ability was observed. This study provides a facile strategy to fabricate high-performance plant protein-based adhesives with desirable water resistance for practical application.

A tough bio-adhesive inspired by pearl layer and arthropod cuticle structure with desirable water resistance, flame-retardancy, and antibacterial property

Petroleum-derived formaldehyde resin adhesives are serious hazards to human health and depend on limited resources. Abundant, cheap and renewable biomass materials are expected to replace them. However, the contradictory mechanisms of high mechanical strength and fracture toughness affect the use of bioadhesives. Herein, a biomimetic soybean meal (SM) adhesive inspired by the structure of insect cuticles and shell pearl layer was proposed. Specifically, chitosan (CS@DA) modified 3,4-dihydroxybenzoic acid (DA, rich in catechol moiety) was anchored on molybdenum disulfide nanosheets (MoS2) to construct a biomimetic structure with copper hydroxide and SM substrate (SM-MoS2/CS@DA-Cu). Schiff base, ionic, and hydrogen bonding strengthened the cohesion of the adhesive. The ordered alternating stacking "brick-mortar" structure stimulated the lamellar sliding and crack deflection of MoS2, synergistically reinforcing the toughness. Compared to SM adhesive (0.57 MPa and 0.148 J), the wet shear strength and adhesion work of the SM-MoS2/CS@DA-Cu were 1.68 MPa and 0.867 J, with 194.7 % and 485.8 % increases, respectively. The multiple antimicrobial effects of CS@DA, Schiff base, and Cu2+ increased the applicability period of the adhesive to 40 days. The adhesive also displayed favorable water resistance and flame retardancy. Therefore, this peculiar and efficient biomimetic structural design inspired the development of multi-functional composites.

Oyster-inspired carbon dots-functionalized silica and dialdehyde chitosan to fabricate a soy protein adhesive with high strength, mildew resistance, and long-term water resistance

Developing multifunctional adhesives with exceptional cold-pressing strength, water resistance, toughness, and mildew resistance remains challenging. Herein, inspired by oysters, a multifunctional organic-inorganic hybrid soybean meal (SM)-based adhesive was fabricated by incorporating amino-modified carbon dots functionalized silica nanoparticles (CDs@SiO2) and dialdehyde chitosan (DCS) into SM matrix. DCS effectively enhanced the interface interactions of organic-inorganic phases and the rigid nanofillers CDs@SiO2 uniformly dispersed in the SM matrix, which provided energy dissipation to improve the adhesive's toughness. Owing to the stiff skeleton structure and enhanced crosslinking density, the crosslinker-modified SM (MSM)/DCS/CDs@SiO2-2 wood adhesive exhibited outstanding cold-pressing strength (0.74 MPa), wet shear strength (1.36 MPa), and long-term water resistance (49 d). Additionally, the resultant adhesive showed superior antimildew and antibacterial properties benefiting from the introduction of DCS. Intriguingly, the fluorescent properties endowed by carbon dots further broadened the application of adhesives for realizing security testing. This study opens a new pathway for the synthesis of multifunctional biomass adhesives in industrial and household applications.

A high-performance bio-based adhesive comprising soybean meal, silk fibroin, and tannic acid inspired by marine organisms

The sustainable development of high-performance bio-based adhesives is both important and challenging for the wood industry. Herein, inspired by the hydrophobic property of barnacle cement protein and the adhesive property of mussel adhesion protein, a water-resistant bio-based adhesive was developed from silk fibroin (SF) rich in hydrophobic β-sheet structures and tannic acid (TA) rich in catechol groups as reinforcing components and soybean meal molecules rich in reactive groups as substrates. SF and soybean meal molecules formed a water-resistant tough structure through a multiple cross-linking network including covalent bonds, hydrogen bonds, and dynamic borate ester bonds constructed by TA and borax. The wet bond strength for the developed adhesive achieved 1.20 MPa, exhibiting its excellent application capabilities in humid environments. The storage period of the developed adhesive (72 h) was 3 times that of pure soybean meal adhesive owing to the enhanced mold resistance of the adhesive by TA. Furthermore, the developed adhesive demonstrated excellent biodegradability (45.45 % weight loss in 30 days) and flame retardancy (limiting oxygen index of 30.1 %). Overall, this environmental and efficient biomimetic strategy provides a promising and feasible route to develop high-performance bio-based adhesives.

Natural organic-inorganic hybrid structure enabled green biomass adhesive with desirable strength, toughness and mildew resistance

Plant based proteins are green, sustainable, and renewable materials that show the potential to replace traditional formaldehyde resin. High performance plywood adhesives exhibit high water resistance, strength, toughness, and desirable mildew resistance. Adding petrochemical-based crosslinkers is not economically viable or environmentally benign; this chemical crosslinking strategy makes the imparted high strength and toughness less attractive. Herein, a green approach based on natural organic-inorganic hybrid structure enhancement is proposed. The design of soybean meal-dialdehyde chitosan-amine modified halloysite nanotubes (SM-DACS-HNTs@N) adhesive with desirable strength and toughness enhanced by covalent bonding (Schiff base) crosslinking and toughened by surface-modified nanofillers is demonstrated. Consequently, the prepared adhesive showed a wet shear strength of 1.53 MPa and work of debonding of 389.7 mJ, which increased by 146.8 % and 276.5 %, respectively, due to the cross-linking effect of organic DACS and toughening effect of inorganic HNTs@N. The introduction of DACS and Schiff base generation enhanced the antimicrobial property of the adhesive and increased the mold resistance of the adhesive and plywood. In addition, the adhesive has good economic benefits. This research creates new opportunities for developing biomass composites with desirable performance.

Chitosan-tannin adhesive: Fully biomass, synthesis-free and high performance for bamboo-based composite bonding

Inspired by phenol-amine chemistry of mussels, a synthesis-free and fully biomass adhesive composed of chitosan and tannin (CST) was successfully developed by a facile method. The performance of CST adhesive for bonding bamboo, wood and bamboo-wood substrates were tested. When 160 °C hot-press temperature was used, dry lap shear strength above 5.00 MPa was obtained. The CST adhesive has remarkable water resistance and low cure temperature as high wet shear strength of 2.37 MPa for plybamboo specimens was achieved after 3 h boiling in water even though low hot-press temperature of 100 °C was applied. Further, high strength of 1.78 MPa remained after 72 h boiling. With higher hot-press temperatures used, wet shear strength above 3.60 MPa was achieved. The adhesion performance for wood substrate was also superior to other phenol-amine adhesives reported in literatures. The bamboo-wood composites assembled with CST adhesive show excellent mechanical performance, specifically modulus of rupture (MOR) of 100-133 MPa and modulus of elasticity (MOE) of 10-13 GPa were achieved with different hot-press temperatures used. Given the advantages including outstanding water resistance, facile preparation, fully biomass, and low cure temperature, CST adhesive exhibited great potential to be an ideal alternative to formaldehyde-based resin for wood and bamboo bonding.

Novel ammonia-responsive carboxymethyl cellulose/Co-MOF multifunctional films for real-time visual monitoring of seafood freshness

Nowadays, ammonia-responsive biopolymer-based intelligent active films are of great interest for their huge potential in maintaining and monitoring the freshness of seafood. However, it is still a challenge to create biopolymer-based intelligent active films with favorable color stability, antibacterial and visual freshness indication functions. Herein, cobalt-based metal-organic framework (Co-MOF) nanosheets with ammonia-sensitive and antibacterial functions were successfully synthesized and then embedded into carboxymethyl cellulose (CMC) matrix to develop high performance and multifunctional CMC-based intelligent active films. The influence of Co-MOF addition on the structure, physical and functional characters of CMC film was comprehensively studied. The results showed that the Co-MOF nanofillers were homogeneously embedded within the CMC matrix, bringing about remarkable promotion on tensile strength (from 45.3 to 62.2 MPa), toughness (from 0.7 to 2.3 MJ/m³), water barrier and UV-blocking performance of CMC film. Notably, the obtained CMC/Co-MOF nanocomposite films also presented excellent long-term color stability, antibacterial activity (with the bacteriostatic efficiency of 99.6 % and 99.3 % against Escherichia coli and Staphylococcus aureus), and ammonia-sensitive discoloration performance. Finally, the CMC/Co-MOF nanocomposite films were successfully applied for real-time visual monitoring of shrimp freshness. The above results demonstrate that the CMC/Co-MOF nanocomposite films possess huge potential applications in intelligent active packaging.