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Preparation of soybean meal adhesives offering good water resistance, prepressing adhesion as well as antimildew properties through a green and simple strategy remains challenging. In the present study, a self-assembled nanostructure-based filling enhancement strategy was proposed. Tannic acid (TA) is grafted onto the chitosan framework through free radical grafting, followed by ultrasound induced self-assembly into nanospheres. Chitosan based nanospheres (CS@TA) and ferric chloride (FeCl 3) complexing with nanospheres are combined to modify soybean meal (SM) based wood adhesives synergistically. CS@TA enables interaction with protein chains through hydrogen bonding and Schiff base reactions, which in combination with its nanostructure allows for a more homogeneous dispersion in the SM system. At the same time the Fe (III) ions chelate with the catechol, forming ionic bonds and obtaining a denser structure. The results showed that the dry and wet shear strength (DWSS) of SM/1,2,3-propanetriol triglycidyl ether (GTE) /5%CS@TA/Fe increased by 79% and 693% to 2.28 MPa and 1.27 MPa. At the same time, the residual rate (RD) increased by 9.3–72.5% and prepressing adhesion now reaches 0.71 MPa compared with SM adhesives. And CS@TA nanospheres as well as Fe (III) ions act on the cell membrane of bacteria to provide stronger antibacterial effect, the anti- mildew time has been extended from the initial 2 d to more than 15 d. The construction of multi-network reinforcement strategies through self-assembled nanostructures improves the application potential of SM adhesives and provides ideas for the reinforcement of other engineering materials. [Display omitted] • Self-assembled nanospheres chitosan-based prepared using free radical grafting combined with ultrasonic induction. • Preparation of environmentally friendly adhesives from processing residues soybean meal and biomass materials. • The adhesive has high bond strength, good water resistance and prepressing adhesion. • The anti-mildew of soy protein adhesive was enhanced and extends the storage life. [ABSTRACT FROM AUTHOR]

The preparation of plant protein-based adhesives is one of the potential strategies to mitigate environmental pollution. In this work, the organic-inorganic copolymerization of calcium phosphate oligomer and soy protein was performed by adopting the concept of organic-inorganic polymerization and the physics of polymer adsorption to eliminate the interphase boundary, preparing an adhesive layer with continuous and uniform network structure without using chemical cross-linkers. The participation of ionic and hydrogen bonds improved the mechanical strength. In addition, the Laponite with anisotropic charge distribution was introduced into the cross-linking network to increase the density and cohesion of cross-linking and further improve the bonding performance without complex chemical synthesis. The modified adhesive had an optimum wet shear strength of 1.01 MPa, and excellent water resistance (85.7 % residue rate). The modified adhesive shows good cell compatibility plus flame retardancy. Overall, this biomimetic study has excellent promises for the design of protein-based adhesives with desirable properties for engineering applications. • A soy protein adhesive was formulated by adopting organic-inorganic polymerization concept. • Using physics of polymer adsorption to eliminate the interphase boundary. • The modified adhesive has a wet shear strength of 1.01 MPa, and excellent water resistance. • The modified adhesive shows good cell compatibility plus flame retardancy. [ABSTRACT FROM AUTHOR]

The introduction of 2D graphene into the soybean protein (SP) adhesive is expected to enhance its mechanical performance. However, insufficient binding of the two materials inevitably leads to the resulting composite having limited mechanical strength. Using phytic acid (PA) and a supramolecular self-assembly strategy, hard graphene oxide (GO) was first assembled with PA to form a supramolecular polymer, PA-co-GO, that has a "bricks and mortar" structure as a result of strong non-covalent interactions. PA-co-GO was then further combined with SP in the presence of the long-chain epoxy compound neopentyl glycol diglycidyl ether (NG) to produce a novel biopolymer-based adhesive PA-co-GO/NG/SP. The prepared adhesive has a moisture-insensitive interface as a result of non-covalent/covalent bonds and a "bricks and mortar" microstructure that allows the dissipation of energy, resulting in an enhancement in the water-resistant bonding strength of the material, with a 345% increase in its wet bonding strength compared with the unmodified SP adhesive. Additionally, the combination of the heat shielding of the GO and catalytic carbonization of PA resulted in the adhesive having excellent flame retardant properties. The structure and morphology of the materials were characterized using atomic force microscopy (AFM), dynamic light scattering (DLS), Fourier-transform infrared (FTIR), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and solid-state 13C NMR. Overall, a new clean route for preparing green high-performance biopolymer-based adhesives is described, with potential applications for sustainable agricultural byproducts. [Display omitted] • A supramolecular polymer PA-co-GO was used to improve the performance of adhesive. • The adhesive has a moisture-insensitive interface due to non-covalent/covalent bonds. • A "bricks and mortar" structure increases energy dissipation and improves strength. • The wet bonding strength of the prepared adhesives is greatly improved by 345%. [ABSTRACT FROM AUTHOR]

The adhesives formulated from soy protein (SP) exhibit desirable dry bonding strength needed to eradicate over-reliance on unsustainable petroleum-based formaldehyde adhesives. However, the adhesive full industrial adoption is limited by its inherent poor water resistance, short shelf-life, and proneness to mildew. This study explored a feasible, versatile, green, and sustainable strategy to engineer superior SP-based adhesives using furfuryl alcohol (FA) and 2,5-diamino-1,4-benzenedithiol hydrochloride (DBH). FA/DBH was conjugated via the carbodiimide-mediated addition of DBH under a light-proof condition. The acidity was controlled by NaOH, creating a mildly acidic medium for FA/DBH to develop a strong crosslinked network. The FA and DBH were hybridized by an amide bond, with subsequent SP integration via dynamic covalent linkages and amide bonds. The synergistic interactions between FA/DBH hybrid and the protein chains remarkably enhanced the adhesive properties. Consequently, the added FA/DBH hybrid (6 wt% of SP) achieved high dry and wet shear strengths of 2.38 and 1.43 MPa (plywood), which were 63 % and 200 % higher than the unmodified soy protein adhesive (USPA), respectively. In addition, the constructed organic network improved the adhesive thermal stability, mildew resistance, and shelf-life. Therefore, this sustainable, versatile, and green approach could serve as an alternative crosslinking pathway for developing highly competitive SP-based adhesives. [Display omitted] • A high-performance soybean protein adhesive was constructed without fossil resources. • A development strategy for covalently bonded furfuryl alcohol with sulfhydryl groups was proposed for the first time. • Soybean protein adhesive was crosslinked via dynamic covalent linkages and amide bonds. • The synergistic network enhanced the dry and wet shear strength of the resultant plywood by 63 % and 200 %, respectively. • The anti-mildew and shelf-life of the adhesive were remarkably invigorated. [ABSTRACT FROM AUTHOR]

It is still a great challenge to develop soybean protein adhesives with high strength and antimildew properties through a sustainable and facile strategy. Herein, water-soluble dialdehyde chitosan (DCS) was obtained by oxidizing chitosan (CS) and used to crosslink soybean meal (SM) to fabricate protein adhesives via the Schiff base reaction. This strategy is simple, all-biomass, and without additional crosslinkers. Owing to the covalent imine bonds and non-covalent hydrogen bonds interactions, the adhesion strength of SM/DCS-4 adhesive reached 1.47 MPa, satisfying the requirement for Type II interior plywood (≥ 0.7 MPa). More importantly, the protein adhesives showed excellent antimildew properties due to the amino and aldehyde groups of DCS and the Schiff base formation. The SM/DCS-4 adhesive exhibited long shelf life (7 d), which is beneficial for industrial applications. This study helps in preparing green and fully bio-based adhesives from agricultural and fishery wastes. [Display omitted] • Dialdehyde chitosan (DCS) acted as a functional crosslinker. • Highly dense imine bonds and hydrogen bonds strengthened the adhesive network. • DCS can improve the bonding strength and antimildew properties of the adhesive. • The soybean meal (SM)/DCS adhesive exhibited long shelf life (7 d). • The SM/DCS adhesive made full use of agricultural and fishery wastes. [ABSTRACT FROM AUTHOR]

Biomass adhesives show great potential in developing environment-friendly wood-based panel industry. Among them, soybean protein isolate (SPI) adhesives have a wide source of raw materials, but exploring high-strength, water-resistant, mildew-proof soybean protein-based adhesives remains a tremendous challenge. Inspired by the spatial structure arrangement of spider silk in nature, a facile and efficient bionic approach is adopted to prepare soybean protein adhesive with excellent overall performance by introducing chitosan (CS) and MXene nanosheets in soybean protein. The addition of MXene nanosheets is expected to form the β-sheet crystalline conformation of spider silk, which contributes to the formation of a tightly cross-linked adhesive system that hinders the penetration of moisture. Compared with the 1-SPI adhesive, the prepared 5-SPI/CS/MXene adhesive shows an increase of 175% in wet shear strength (1.76 MPa), indicating excellent adhesion strength and water resistance. Besides, the addition of CS benefits to improve the dispersibility of MXene in the adhesive system. Therefore, the synergy of MXene and CS significantly improves the strength, water resistance of the adhesive and increases the storage time from 7 d to more than 50 d. This research would provide a new idea for the preparation of biomass-based adhesives. [Display omitted] • Aunique β-sheet structure of spider silk is constructed through simple method. • The prepared SPI/CS/MXene adhesive shows excellent wet shear strength (1.76 MPa). • Uniform dispersion of MXene in adhesive improves the toughness via load transfer. • The adhesive possesses excellent mildew resistance due to the CS and MXene. • The synergistic effect of CS and MXene optimizes the structure of the protein. [ABSTRACT FROM AUTHOR]

Natural materials show a special combination of remarkable strength and toughness. Therefore, inspired by nacre's "brick-and-mortar" architecture, high-performance multifunctional plant protein adhesives were constructed through an organic-inorganic hybrid structure and vitrimer networks. Hydroxyl-functionalized boron nitride (BN-OH) nanosheets firstly acted as the "brick" part, and protein chains were thought of as the "mortar" part. BN-OH can not only enhance the toughening through interlayer interface slip, but also achieves synergistic toughening effect with the nanometer effect. Glutaric dialdehyde (GD) acted as a "bridge" between protein chains and BN-OH, which can react with the condensation of hydroxyls in BN-OH or with active amino groups in protein chains to form dynamic covalent bond (vitrimer networks) to dissipate energy. Therefore, the synthesized multiple crosslinked network plant protein adhesives have excellent wet shear strength (1.28 MPa), water resistance, mildew-resistant, flame-retardant, and ultrahigh thermal management capability (3.88 W m−1 K−1), and has wide application potential in green adhesives. [Display omitted] • A high-performance plant protein adhesive was inspired by nacre design. • The BN-OH nanosheets were set as the "brick" part. • Plant protein chains were thought of as the "mortar" part. • Organic-inorganic hybrid and vitrimer networks enhanced the adhesive's strength. • Adhesive shows excellent mold resistance and thermal management capability. [ABSTRACT FROM AUTHOR]

Static electricity and formaldehyde pollution are not only severely harmful to ecological environment but also seriously affecting human health. It is of great importance but still challenging to develop an eco-friendly and multifunctional adhesive for electrostatic shielding. Protein adhesives were considered to be an effective substitute for formaldehyde resin adhesives, but show poor water resistance and conductive, limiting their practical applications in many fields, such as antistatic materials and antistatic floors. Therefore, this study aimed to develop a multifunctional adhesive by a facile organic-inorganic hybrid network to enhance the electrostatic shielding for antistatic materials. As we expected, the volume resistivity of the resultant adhesive for antistatic floors is only 2.73 × 108 Ω·cm, which is five orders of magnitude less than that of soybean meal (SM) adhesive and shows excellent electrostatic shielding performance. After experiencing a rapid thermal shock cycle between two extreme temperature conditions for 30 times, the mechanical performance of adhesive still remained stable. Furthermore, the adhesives are not only eco-friendly and non-formaldehyde, but excellent mildew resistance and flame retardancy. This multifunctional SM-based adhesive opens a new way to replace harmful formaldehyde-based adhesives, which have potential applications in the field of antistatic floors. • A high-performance adhesive was prepared by a facile and green organic-inorganic hybrid strategy for electrostatic shielding. • The multiple bonding structures were formed between protein chains and hydroxylated BT nanoparticles. • The adhesive exhibited mechanical stability under two extreme temperature cycling. • This adhesive could be used for antistatic materials with flame retardance and antimicrobial properties. [ABSTRACT FROM AUTHOR]

Epoxide modification effectively improves the water tolerance of soy protein adhesives, showing great potential in the commercial application as alternatives to petroleum-derived formaldehyde-based adhesives. However, epoxide-modified adhesives still present problematic limitations, such as poor mildew resistance and high hot-pressing temperature. In this study, a curing system based on radical polymerization was designed and developed to prepare soy protein adhesives, instead of building a traditional epoxide cross-linking structure. First, allyl glycidyl ether (G) was grafted onto a soy protein (SP) molecule to obtain soy protein with unsaturated double bonds (G@SP). Allicin (A) was then used as a cross-linker to build a cross-linking structure (G@SP/A) via free-radical polymerization to enhance the bond performance of the adhesive. Relative to that of pure SP adhesive, the wet shear strength (WSS) and dry shear strength (DSS) of plywood bonded with the G@SP/A adhesive increased by 108% and 45%, reaching 1.08 MPa and 1.84 MPa, respectively, at 120 °C pressing temperature. Notably, the G@SP/A adhesive showed superior antibacterial (Escherichia coli and Staphylococcus aureus) activity, high mildew resistance (35 d shelf life), good cytocompatibility, and biodegradability (30 d). Moreover, the WSS of plywood bonded with the G@SP/A adhesive at 80 °C for 6 min and 20 °C for 72 h reached 1.08 MPa and 1.12 MPa, respectively, indicating the sufficient low-temperature curing ability of the resultant adhesive. Thus, building a cross-linking structure by free-radical polymerization can be extended to improve the performance of film composites, other adhesives, and engineering materials. • Free radical polymerization curing system was used to prepare soy protein adhesive. • The resultant adhesive has excellent antibacterial and mildew proof ability. • The resultant adhesive has good cytocompatibility and biodegradability. • The wet shear strength of resultant plywood increased by 108% to 1.08 MPa. • The resultant adhesive has good low temperature curing ability. [ABSTRACT FROM AUTHOR]

For improving the water resistance, bonding performance, and anti-mildew property of the soy protein-based adhesive (SPA), in this research, based on cross-linking enhancement theory, soybean meal flour as the main raw material, self-synthesizing triglycidylamine (TGA), and larch tannin (LT) were used to build efficient crosslinking water-resistant structure and develop SPA. The effect of LT addition on the physical properties, bonding strength, and anti-mildew property of the resultant adhesive was investigated. The results showed that the residual rate of SPA with 4 % LT and 3 % TGA was improved by 2.1 % and the corresponding moisture absorption rate was reduced by 20.1 % compared with the SPA only modified by 3 % TGA. In addition, the SPA with 4 % LT and 3 % TGA had a 42.3 % increase in bonding strength, reaching 1.11 MPa, which satisfied the standard requirements of interior use plywood (≥ 0.7 MPa). The improved water-resistant bonding performance is mainly because interaction forces, such as hydrogen bonds, ionic bonds, and covalent bonds, formed between tannin and protein, and under the cross-linking effect of TGA, the whole cross-linking system forms a dense network structure. LT not only had a reinforcing effect on the SPA but also could prolong the pot life of the adhesive for 60 h due to the phenolic hydroxyl groups of tannin. Compared with the commercial anti-mildew agents, the mildew resistance before and after curing is the following: 1,2-benzisothiazole in-3-one > LT > sodium tetraborate > potassium sorbate. [Display omitted] • An easy-to-produce, high-performance, and environmentally friendly bio-adhesive was developed. • The incorporation of larch tannin enhanced the cohesion and mechanical properties of adhesives. • The resultant adhesive has better water-resistant bonding performance and an anti-mildew effect. • Effectively extend durability of plywood prepared by adhesive and storage period of the SPAs. [ABSTRACT FROM AUTHOR]

Developing eco-friendly soy protein-based adhesives instead of the extensively used aldehyde-based adhesives to fabricate wood-based panels can reduce environmental hazards and benefit human health. However, traditional soy protein-based adhesives lack long-term antibacterial and antimildew properties, reducing their bond strength and durability. Here, 3,4-dihydroxybenzaldehyde-grafted chitosan was prepared as a catechol structure donor and then introduced into the soy protein isolate (SPI) adhesive for the in situ reduction of silver ions to stable silver nanoparticles (Ag NPs); a biomineralization system was thus established. Notably, the catechol–quinone reversible redox reaction in the system endowed the resultant adhesive with excellent antibacterial (more than 99.99% bactericidal rate against Staphylococcus aureus and Escherichia coli , 91.67% bactericidal rate against Candida albicans) and long-term antimildew properties (40 d). The wet shear strength (1.24 MPa) and prepressing bond strength (0.80 MPa) of the plywood prepared with the adhesive were increased by 63.27% and 129.63%, respectively, relative to the SPI adhesive. The volatile organic compounds release of the adhesive was 1–2 orders of magnitude lower than that of commonly used commercial adhesives. This strategy provides inspiration for reinforcing antibacterial or antimildew bio-based adhesives, hydrogels, and composites. [Display omitted] • A system of biomineralized Ag NPs was built in the soy protein-based adhesive. • CS and SPI are used as stabilizers to avoid aggregation and agglomeration of Ag NPs. • The wet shear strength of plywood bonded by the adhesive was improved by 129.63%. • The adhesive has long-term antibacterial, mildew resistance, and low VOCs release. [ABSTRACT FROM AUTHOR]

Plant-derived protein adhesives have attracted extensive research interest in recent years as effective alternatives to nonrenewable and nonbiodegradable formaldehyde-based adhesives. However, owing to their insufficient bonding strength and poor mildew resistance, it has been challenging for biopolymer adhesives to achieve strong and durable adhesion performance. Inspired by insect cuticles, we report a green and versatile strategy for the fabrication of a strong, mildew-resistant, antibacterial soy protein (SP)-based adhesive via phenol-amine synergy and biomineralization reinforcement. Gallic acid (GA), as a phenolic glue molecule, was co-assembled with hydroxyapatite (HAP) through Ca2+–phenolic coordination bonds to prepare GA-functionalized HAP (GA@HAP) nanoparticles. Moreover, ε -polylysine (PL) with abundant amino groups was used for grafting to the phenolic GA@HAP nanoparticles through a Schiff base reaction. Owing to multiple cross-linking and the inorganic–organic hybrid system, the wet shear strength of the SP/PL/GA@HAP adhesive increased considerably to 1.09 MPa, 127% higher than the unmodified SP adhesive. The cationic PL polymer endowed the protein adhesive with desirable antifungal and antibacterial properties, synergistically with the phenolic components in GA@HAP. In addition, the resultant adhesive exhibited enhanced flame retardation, thermal stability, and water resistance. This simple and versatile strategy could lead to advances in the development of high-performance biopolymer materials for biological and engineering applications including adhesives, hydrogels, and films. [Display omitted] • A mineral–organic hybrid network was constructed in a biopolymer system. • Hydroxyapatite nanoparticles were functionalized with phenolic glue molecules. • Multifunctional soy protein adhesive was fabricated via phenol-amine chemistry. • The wet shear strength of the prepared adhesive was significantly improved by 127%. • Biopolymer adhesive showed enhanced anti-mildew and antibacterial properties. [ABSTRACT FROM AUTHOR]

Bioinspired strategies for preparing multifunctional hydrogels have drawn attention. Among these hydrogels, the adhesive types have been extensively studied, However, most of them exhibit poor mechanical properties, short-term adhesion, and no antibacterial activity. Inspired by the mussel adhesion mechanism, an adhesive hydrogel made from tannic acid (TA), acrylamide (AM), and soy protein isolate (SPI) is presented in this study. The adhesive hydrogel showed a large tensile strain (932%), high tensile strength (45.8 kPa), high toughness (155.15 kJ·m−3), and ideal compressive properties owing to the formation of a hybrid double network (DN). This hydrogel exhibited satisfactory adhesion to various materials, including muscle tissue, metal, rubber, glass, plastic, and wood. The TA-PAM-SPI hydrogel also showed good antibacterial properties against Escherichia coli and Staphylococcus aureus , in addition to self-healing properties and biocompatibility. With these characteristics, the TA-PAM-SPI hydrogel was used as a wound dressing to accelerate wound healing and skin tissue regeneration. This study provides a convenient approach to preparing multifunctional hydrogels and promoting the application of SPI in biomedical materials. [Display omitted] • Inspired by mussels, a hybrid double-network soy protein-based composite hydrogel was developed. • The incorporation of SPI enhanced the cohesion and mechanical properties of hydrogel. • Hydrogel exhibited extremely high adhesiveness to hydrophilic/hydrophobic surface. • The resultant hydrogel has high biocompatibility and promotes wound healing. [ABSTRACT FROM AUTHOR]

The soybean meal (SM) adhesive has become the most promising bio-adhesive in wood industry. However, the insufficient mechanical properties and poor water resistance limits their practical applications. Current researches mostly focus on the cross-linking modification of soy protein isolate (SPI) components in SM, whereas ignoring the adverse effects of soy polysaccharide (SPS) components on the SM adhesive system. Herein, inspired of the borate chemistry in the higher plant cell walls, the thorough and strong cross-linked networks were constructed in SM adhesive system by the boronic acid-anchored cellulose nanofibril (BCNF) and tannic acid (TA). The combination of entanglement and interpenetration of polymer backbone molecular chains, dynamic covalent interactions and hydrogen bonds can promote the formation of tough and stable cross-linked network structure in SM adhesive system, and endowed the SM adhesive with excellent wet adhesion strength and water-resistant property. The wet shear strength of resultant SM adhesive increased to 0.92 MPa, which was 3 times of the pristine SM adhesive. Additionally, the resultant SM adhesive exhibited excellent mildew resistance, antibacterial activity, and flame retardance. This biomimetic strategy can achieve the construction of the thorough and strong cross-linked networks in SM adhesive, which provides a novel and versatile route to high-performance and multifunitional bio-adhesive. [Display omitted] • The thorough and strong cross-linked networks were formed in soy meal adhesive. • The boronic acid-anchored CNF and tannic acid served as effective crosslinkers. • The wet adhesion strength of resulting adhesives was significantly improved. • The adhesive showed mildew resistance, antibacterial ability, and flame resistance. [ABSTRACT FROM AUTHOR]

Soy protein-based adhesives show great prospects in replacing aldehydes resin adhesives to fabricate wood-based panels, however, high doses of synthetic resins as crosslinkers must be used to obtain good bonding performance. To reduce overreliance upon crosslinkers derived from fossil resources, a 100% bio-derived crosslinker-xylitol epoxide (EX) was synthesized from epichlorohydrin and xylitol, followed by blending with soy protein isolate (SPI) to create a functional biological adhesive. After using EX, the wet and dry shear strengths of plywood prepared by the SPI/4%EX adhesive increased by 138.6% and 55.6%, respectively, compared with the pure soy protein adhesive. This was attributable to the crosslinked network formed in adhesive and the enhanced adhesive toughness. The optimized process parameters of plywood prepared with EX-modified soy protein adhesive were 110 ℃, 1.3 min/mm and 0.8 MPa. The addition of EX also improved the mildew-resist property of the adhesive to 10 days, which prolonged the adhesive storage life and the service life of the resultant plywood. Therefore, EX could be utilized to enhance the mechanical and mildew-resist properties of protein-based materials, and shows great potential applications in adhesive, film, and hydrogel. • Xylitol was epoxidized to form a bio-based crosslinker (EX). • Using soy protein and 4% EX develops a 100% bio-derived wood adhesive. • The wet and dry shear strength of plywood increased by 138.6% and 55.6%. • The mildew resistance of resultant adhesive is more than ten days. [ABSTRACT FROM AUTHOR]

The aim of this study was to improve the water resistance of soybean meal-based adhesive with heat treatment after hot pressing. The effects of four different heat-treatment processes on plywood bonded with soybean meal-based adhesive were examined. Five-ply plywood specimens were fabricated to measure the adhesive's water resistance. Extending the hot press time allowed the adhesive to cure more completely and improve its water resistance. The surface and core layer wet shear strength of plywood at a 70 s/mm hot press time increased by 18.8% and 109%, respectively, compared with that of a 60 s/mm hot press time. The surface and core layer wet shear strength improved by 56.3% and 102.3%, respectively, with 4 min low pressure heat treatment, which makes it practical for use in industrial applications. Heat treatment could also improve the water resistance of the adhesive by improving the cross-linking density of the adhesive layer in plywood and releasing its interior force, according to a vertical density profile analysis. Therefore, 8 h oven drying heat treatment at 120 °C, the surface and core layer wet shear strength improved by 60.0% and 175.0%, respectively. [ABSTRACT FROM AUTHOR]