Construction of thorough cross-linked networks in soybean meal adhesive system by biomimetic boronic acid-anchored cellulose nanofibril for multifunctionality of high-performance, mildew resistance, anti-bacterial, and flame resistance

The soybean meal (SM) adhesive has become the most promising bio-adhesive in wood industry. However, the insufficient mechanical properties and poor water resistance limits their practical applications. Current researches mostly focus on the cross-linking modification of soy protein isolate (SPI) components in SM, whereas ignoring the adverse effects of soy polysaccharide (SPS) components on the SM adhesive system. Herein, inspired of the borate chemistry in the higher plant cell walls, the thorough and strong cross-linked networks were constructed in SM adhesive system by the boronic acid-anchored cellulose nanofibril (BCNF) and tannic acid (TA). The combination of entanglement and interpenetration of polymer backbone molecular chains, dynamic covalent interactions and hydrogen bonds can promote the formation of tough and stable cross-linked network structure in SM adhesive system, and endowed the SM adhesive with excellent wet adhesion strength and water-resistant property. The wet shear strength of resultant SM adhesive increased to 0.92 MPa, which was 3 times of the pristine SM adhesive. Additionally, the resultant SM adhesive exhibited excellent mildew resistance, antibacterial activity, and flame retardance. This biomimetic strategy can achieve the construction of the thorough and strong cross-linked networks in SM adhesive, which provides a novel and versatile route to high-performance and multifunitional bio-adhesive.