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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]

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]

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]

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]

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]