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Recently, soy protein has attracted extensive attention from wood industries and consumers in the production of wood adhesives as it is non‐toxic, biodegradable, low cost, and easy to process. There are a variety of reactive groups namely OH, NH2, COOH, and SH, in protein molecules, which offer possibilities for protein denaturation, chemical modification, and increased ionic interactions. The research in protein denaturation, crosslinking modification, biomimetic modification, and organic–inorganic hybrid formulation not only focuses on enhancing the mechanical properties and tolerance to water of the adhesives but also considers its toughness, mildew resistance, and flame retardancy to further optimize the performances of the adhesives. In this paper, soy protein chemical composition, soy protein denaturation, and reinforced modification are discussed to understand these methods and further develop into a multifunctional soy protein‐based adhesive. Given the potential of bio‐based adhesives, these modification methods not only provide the theoretical basis for its development at full scale, but also the possibility for the multifunctional applications of bio‐based adhesives. [ABSTRACT FROM AUTHOR]

Soy protein (SPI) adhesives are non‐toxic and eco‐friendly that can potentially replace traditional formaldehyde‐based adhesives to ease toxic gas emissions. The development of strong and toughness SPI adhesive benefits its bonding stability but is challenging. In this study, inspired by nacre structure, a soft–hard double network structure was constructed in SPI adhesive. The triglycidylamine (TGA) cross‐linked protein served as the hard phase to provide cohesion. In addition, the self‐synthesizing epoxidized rubber (ER) as soft phase cross‐linked protein and enhanced the interfacial force between hard and soft phase to dissipate energy during fracture, which improved the toughness of adhesive. The results showed that: compared with original SPI adhesive, the residue rate of SPI/4%TGA/3%ER adhesive increased by 7.9%, and the moisture absorption rate decreased by 16.7%. The dry and wet shear strength of the plywood prepared by SPI/4%TGA/3%ER adhesive increased by 58.9% and 160.4% to 1.86 and 1.38 MPa, which was higher than commercial polyamide‐epichlorohydrin modified SPI adhesive. The elongation at break increased by 55.2%–45%, the fracture energy increased by 233% to 2.96 MJ/m2, and the cracks on the adhesive surface disappeared, indicating that the strength, toughness, and water resistance of the adhesive were significantly improved. In this research, a soft–hard double network structure is constructed in a bio‐based adhesive to obtain excellent performance, this eco‐friendly adhesive opens up a new way to replace harmful formaldehyde‐based adhesives. [ABSTRACT FROM AUTHOR]

Nanoparticle enhancement has been used as an effective means to improve the performance of biomass adhesives. However, there is an inevitable problem of stress concentration caused by particle agglomeration and thus the adhesive layer is susceptible to damage. Therefore, in this paper, a sol–gel method was used to generate uniformly distributed manganese dioxide (MnO2) nanoparticles on the surface of diatomite (Dia) and used for the modification of soybean meal based wood adhesives. The results showed that MnO2 nanoparticles have been successfully anchored on the surface of Dia during the sol–gel process without agglomeration. MnO2/Dia particles could fill in the adhesive gaps and form hydrogen bonds with soy protein molecules, which ensured that the adhesive wet shear strength was increased by 33% to 0.89 MPa. This study provided an idea for the preparation of highly dispersed nanoparticle reinforced adhesives. [ABSTRACT FROM AUTHOR]

Soybean protein adhesives are environmentally friendly biomass‐based aldehyde‐free adhesives that have good economic value for the wood industry; however, it remains challenging to produce soybean protein adhesives with excellent water resistance, toughness, and mildew resistance through a simple modification method. In this work, inspired by plant polyphenols, a novel crosslinked soybean meal adhesive (SMPT) is obtained using a facile economic method. Polyamidoamine‐epichlorohydrin (PAE) and tannic acid (TA) are combined with a soybean meal matrix to form a tough co‐crosslinked network through strong intermolecular forces (covalent bonds, ionic bonds, and hydrogen bonds) in adhesive system. The results show that the wet bonding strength of SMPT adhesives for plywood is 134.1% higher than the unmodified soybean meal adhesive. The adhesion properties met the standard requirements for interior‐use plywood. And the compact cross‐linking network structure is accelerated the greater energy dissipation, which improves the toughness of adhesive. Moreover, cationic azetidinium groups in PAE and phenol hydroxyl groups in TA synergistically not only exhibit the good antibacterial activities but also improve mildew resistance for SMPT adhesives. This facile strategy provides an economic sustainable method to prepare high‐performance environmentally friendly wood adhesives. [ABSTRACT FROM AUTHOR]

Crosslinking modification can effectively improve the water resistance of soy protein isolate (SPI) adhesive, but it often depends on petroleum‐based reagents, violating the concept of green environmental protection. Here, inspired by the breaking and recombination of the disulfide bond in the perm process, a high‐performance wood adhesive is prepared by incorporation of SPI (modified by sodium sulfite to cleave the disulfide bonds of protein chains) and feather keratin (FK, extracted from waste chicken feathers by breaking the disulfide bond) without using any other crosslinkers. The crosslinking reaction occurs by disulfide bonds derived from the sulfhydryl group of FK and SPI. Thus the wet shear strength of the SPI/FK‐20 adhesive is improved from 0.57 to 1.18 MPa, an increment of 107%. This study provides a green strategy to prepare high‐performance protein‐based adhesive from the waste products‐chicken feathers, which will contribute to the development of the environmentally friendly wood adhesive industry. [ABSTRACT FROM AUTHOR]