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The development of a water-retaining soybean flour-based adhesive with high water resistance, interfacial adhesion and mildew resistance is significant in replacing petroleum-based aldehyde-based resin. Drawing inspiration from lobster shells, soybean flour (SF), self-synthesized epoxy hyperbranched hydroxyethyl cellulose (EH) and calcium phosphate (CaP) oligomers were employed to prepare organic-inorganic hybrid composite adhesives based on hyperbranched structure. The EH component, abundant in active groups, enhanced the interfacial adhesion of the adhesives and served as an organic carrier for the mineralization of CaP oligomers. Prior to adhesive solidification, CaP oligomers mineralized to form an inorganic film akin to milk skin, which prevented water evaporation, resulting in a water retention time of 100 min for the adhesive. During adhesive curing, CaP oligomers with fluid-like behavior polymerized and mineralized, ultimately forming a continuous inorganic network of CaP crystals. This network, combined with the organic substrates (SF and EH), constituted an organic-inorganic hybrid structure, which bolstered the water and mildew resistance (20 days) of the adhesives. The prepressing intensity and wet shear strength of the resultant plywood increased by 168% and 396% to 0.67 MPa and 1.39 MPa, respectively, compared to those of the unmodified adhesive. The strength reached the leading level of the reported soybean flour adhesives. The biomimetic strategy employed here can be extended to high-performance gels and membrane materials, offering a novel modification approach for bio-composites. • Organic-inorganic hybrid composite adhesive based on hyperbranched structure was constructed. • Hyperbranched polymers enhanced interfacial adhesion and system compatibility. • CaP oligomers mineralized to form an inorganic film like milk skin to prevented water evaporation. • The adhesive has water retention, water resistance bonding performance and mildew resistance. • The strategy has significant reference for the research of gels, films and composites. [ABSTRACT FROM AUTHOR]

The preparation of a soybean flour adhesive with good bonding and prepressing performance, toughness, mildew resistance, and fire retardancy to address the problem of formaldehyde pollution is crucial; however, it also presents a challenge. The core–shell structure can achieve various properties by tailoring-making the core–shell composition. In this study, a core–shell structure HBPA@TA with hyperbranched polyamide (HBPA) as the core and tannin (TA) as the shell was prepared and used to modify SF adhesives. The results showed that the pyrogallol group of the tannin shell endowed the adhesive with excellent prepressing performance (0.75 MPa of prepressing intension), toughness, and coating performance, rendering the adhesive more suitable for plywood fabrication. Owing to the dense tannins in HBPA@TA, the resultant adhesive exhibited superior mildew resistance (12 d). After closed-mouth placement for 12 d, the prepressing intension was reduced by 17.3% to 0.62 MPa, which still met the usage requirement. The wet shear strength of the plywood prepared using the resultant adhesive was 1.05 MPa—that is, 133.3% higher than that of the unmodified SF adhesive. The synthesized adhesive also showed antibacterial properties (inhibition zone = 8 mm), flame retardancy (LOI = 32.3%), and volatile organic compound release (6.86*106 mg/m2·h) lower than those of commonly used urea–formaldehyde resins and epoxy resins. [Display omitted] • A spherical hyperbranched core-shell structure HBPA@TA with pyrogallol groups was synthesized. • HBPA@TA as toughening and antifungal agent, and flame retardant modify soybean flour adhesive. • The prepared adhesive has good prepressing and coating performance, toughness, bond strength. • The prepared adhesive was mildew proof, antibacterial and flame retardant, low VOCs emission. [ABSTRACT FROM AUTHOR]

Plant-derived biomass adhesives are increasingly in demand to replace traditional non-biodegradable petrochemical materials. However, the insufficient mechanical strengths and poor antibacterial activities of biomaterials severely limit their applicability. Inspired by the amphiphilic characteristics of mussel protein, a dual-crosslinking strategy is reported here for preparing soy meal (SM)-based adhesives with excellent adhesion and antibacterial properties. Specifically, castor oil containing abundant hydroxyl groups was used to prepare the cationic waterborne polyurethane (WPU) dispersion. Subsequently, the dynamic glue bridges were synthesized from the tannic acid-functionalized borax (TA@BA) complexes via multiple coordination bonds. Finally, the enhanced cross-linking network system was then constructed in the protein matrix based on the synergy of dynamic covalent bonds, electrostatic interactions, and hydrogen bonds. As a result, the wet strength of the resultant adhesive significantly increased by 154.77% compared to the SM adhesive. Additionally, the resultant adhesive exhibited remarkably enhanced thermal stability, flame retardancy, and water resistance. Based on the synergistic effect of the cationic WPU, polyphenol components, and borate groups, the SM/WPU/TA@BA adhesive exhibited desirable anti-mildew and antibacterial properties. This biomimetic dual-crosslinking design therefore provides a novel and facile strategy for the preparation of high-performance biopolymer adhesives used in the fields of biology and engineering. [Display omitted] • A bioinspired dual-crosslinking strategy is used to prepare protein-based adhesives. • The cationic waterborne dispersion was synthesized from vegetable castor oil. • A dynamic glue bridge was formed by incorporating tannic acid-functionalized borax. • The water resistance of the protein-based composites was significantly improved. • The hybrid adhesive showed enhanced antibacterial properties and flame retardancy. [ABSTRACT FROM AUTHOR]

Environmentally friendly soybean meal-based (SM) adhesive has been developed to replace harmful formaldehyde-based adhesives in the wood-based panel industry. But, the extensive application of SM adhesives is limited by several deficiencies, including high brittleness, poor coating ability, and poor antibacterial/mildew resistance, etc. In this study, a new SM adhesive has been designed by constructing a hyperbranched cross-linked structure via the Maillard reaction instead of traditional epoxide-based crosslinking structure. Specifically, the hyperbranched poly(ethylenimine)-functionalized carboxymethyl chitosan was synthesized via a one-step procedure using carboxymethyl chitosan and polyethyleneimine, and then mixed with soybean meal and a crosslinker (2,3-butanedione) to develop a wood adhesive. The dry and wet shear strength of plywood bonded by the obtained adhesive was 55% and 357% higher than those of the original SM adhesive, respectively, which were attributed to the formation of Maillard reaction-based crosslinked structure and improvement of adhesive toughness. The corresponding wood failure percentage was increased to 70% compared to pure SM adhesive. Notably, the prepared adhesive exhibited mildew resistance for 240 h and had a uniform coating ability on the wood surface. Construction Maillard reaction based crosslinking structure has potential application in the enhancement of other bio-adhesives and protein-based hydrogels. [Display omitted] [ABSTRACT FROM AUTHOR]