Preparation of a strong, mildew-resistant, and flame-retardant biomimetic multifunctional soy protein adhesive via the construction of an organic-inorganic hybrid multiple-bonding structure

It is important but challenging to develop multifunctional soy protein adhesives with high bonding strength to replace toxic formaldehyde-based adhesives used in the wood-based panel fabrication industry. In this study, inspired by arthropod cuticles, the epoxide-crosslinked soy protein isolate (SPI) was used to form the covalently-bonded network, and dopamine-functionalized waste paper fiber (WPF-PDA) was synthesized as the catechol groups donor to form the hydrogen bond network and physically-enhancement, copper hydroxide was used as an inorganic material that chelated with the catechol groups of WPF-PDA to form the ionic bond network. This formed an organic-inorganic hybrid multiple-bonding structure in the soy protein adhesive. The results showed that the dry/wet shear strength of the plywood prepared by the resultant adhesive increased by 46% and 144% to 2.0 and 1.22 MPa, respectively, compared with SPI adhesive. The fracture toughness increased by 145%, and the residual rate of the adhesive increased by 18.6%, indicating that the bonding strength, toughness, and water resistance of the adhesive were significantly improved. In addition, the anti-mildew time of the adhesive increased from 1 d to more than 40 d, while the maximum heat release rate and total heat release decreased by 32.5% and 5.8%, respectively. This strategy provides a potential method to develop high-performance and multifunctional bio-adhesives, composites, and hydrogels.