Mussel-inspired adhesives are designed based on a bio-polymer backbone including chitosan 25, gelatin 22, hyaluronic acid 26, and vegetable protein 27. Generally, available methodologies can be roughly sorted to three categories: 1) designed or functionalized synthetic or natural polymers with 3,4-dihydroxyphenyl-L-alanine (DOPA) or catechol-based monomers produced via organic/polymer synthesis technologies 21, 22, 2) the direct conversion of protein tyrosine residues to DOPA-o-quinones via Fremy’s salt oxidation 23, and 3) the replication and production of MAPs in bio-systems via the technique of genetic engineering 24. The mussel-inspired artificial adhesive-based catecholamine chemistry has been extensively developed to facilitate strong and reversible adhesion under various “extreme” (e.g., humid, underwater, or with polar substrate surface) conditions 20. Recently, many researchers have been inspired to explore catechol-containing molecules by the robust bioadhesive ability of mussel adhesive proteins (MAPs) 18, 19. These reaction conditions, cost, and safety of organic compounds are unfavorable, however 17. Cross-linking modification includes the use of formaldehyde-based resin 13, maleic anhydride 14, epoxy groups 15, epoxy resin, and monomer (e.g., ethylene glycol diglycidyl ether and 1,2,3-propanetriol-diglycidyl-ether) 10, 16. The formation of cross-linking network has been acknowledged as an effective approach to fabricate high-adhesion soy protein-based adhesives by incorporating reactive cross-linkers and synthetic resins per their high reactivity with the amino (–NH 2), carboxyl (–COOH), and other exposed groups of polypeptide side chains 12. Typically, the fabrication of wood composites using non-formaldehyde bio-adhesives necessitates enhanced bonding strength this is typically accomplished by modifying the biomass matrices 4, 5.Īs a notable example 6, 7, soybean-derived bio-adhesives generally exhibit low adhesion strength and low water resistance due to their poor chemical resistance and inherent amphiphilic nature 8, 9, 10, 11. In recent studies, bio-based adhesives have shown remarkable potential in manufacturing industry applications due to their numerous advantages in terms of low cost, biodegradability, renewability, and environmental friendliness in comparison to petroleum-based adhesive materials 1, 2, 3. The proposed STP adhesive may be a promising cost-effective and wet-resistant bio-adhesive for the application in the wood composites industry.

Moreover, the thermal stability of the resultant STP adhesive exhibited a significant improvement. Both the solid content and residual mass analysis also confirmed that the enhancement in the STP adhesive was attributable to the network crosslinking density and stiffness after integrating the TAPI system. The adhesion meets standard requirements for interior-use plywood. As expected, TAPI-modified SM adhesives showed a 156.1% increase in wet bonding strength compared to the control SM adhesive. The results showed that a dense, robust, and water-resistant adhesive layer was constructed between network-bound catechol moieties in the TAPI and SM system, endowing the STP adhesive with high wet bonding strength for plywood. The multiple physico-chemical interactions (including intermolecular H-bonding and covalent bonding) between the TAPI co-crosslinking system and SM matrices were examined by the Fourier transform infrared spectroscopy, solid-state 13C nuclear magnetic resonance, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Novel soybean meal-based biomimetic (STP) adhesives were fabricated via soybean meal (SM) and enhanced by tannic acid (TA) and polyetheylenimine (PEI) (TAPI) co-crosslinking network based on natural polyphenol-inspired chemistry.

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