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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]

Magnesium oxychloride cement (MOC) adhesive has the advantages of being non-formaldehyde and flame retardant and having low energy consumption; however, its poor compatibility with the wood interface results in low bonding strength. Inspired by the H-bonded β-sheets nanoconfinement phase of spider silk, a high-performance inorganic adhesive was developed based on the supramolecular network system of poly (vinyl alcohol)/phytic acid (PVA/PA) with dissolved ions and the synchronous hydration process of MOC. Benefiting from the H-bond crosslinking and chelation confinement effects, the addition of PVA/PA enables MOC to penetrate steadily into the wood. Under this strategy, the compressive strength and softening coefficient of the modified MOC adhesive were 65.07 MPa and 0.84, which were 17.03% and 425% higher than the unmodified MOC adhesive, respectively. In addition, the MOC/PVA/PA adhesive achieved a wet shear strength of 2.02 MPa, 68.3% higher than that of the MOC adhesive. These results demonstrate that the MOC/PVA/PA adhesive would be a promising inorganic adhesive in wood-based building materials. [ABSTRACT FROM AUTHOR]

The development of renewable soy protein (SP) adhesives has aroused growing interest in the wood industry. This research aims to develop a low-cost, sustainable, and high-performance SP adhesive without a petrochemical crosslinker. The hard skin barrier benefits from the dense cross-linked layer of cuticle cells constructed by the peptide bonds between membrane proteins and the dehydration condensation reaction between adjacent hydroxyl groups of polysaccharides. Inspired by the above skin mechanism, a biomimetic strategy of commercially available transglutaminase (TGase) was applied, which constructed Gln-Lys isopeptide bonds within the SP chains. The covalent boroxine structure formed by dehydration of the hydroxyl groups of boronic acid engineered a dense and robust network like skin barrier, converting the SP into a strong, water-resistant, anti-mildew, and flame-retardant adhesive. The resultant adhesive showed outstanding wet shear strength of 1.55 MPa, about 138.5% greater than the pure SP adhesive, and the residual rate increased from 86.19% to 95.99%. The small content of TGase achieved satisfactory performances and low-cost SP adhesive, establishing its usefulness as a crosslinker to replace the petroleum-based modifiers. Notably, the boronic acid mounted on the SP chains by TGase protected proteins from microbial consumption, thus extending the anti-mildew shelf-life of the liquid adhesives from 2 to 15 days. Moreover, the dense and rigid structure containing Gln-Lys isopeptide bonds and boroxine network effectively improved the flame resistance of the cured adhesives, which reduced the peak heat release rate (PHRR) from 95.1 to 84.2 W/g. Therefore, this simple bionic strategy achieved the goal of formulating green, low-cost, high-performance, and multifunctional SP-based adhesives. [ABSTRACT FROM AUTHOR]