Preparation of a multifunctional soybean protein isolate-based adhesive with enhanced mechanical and flame retardancy properties via the synergistic effect between phosphorylated chitosan and quaternary ammonium-functionalized MXene

The pursuit of multifunctional soybean protein isolate (SPI)-based adhesives with high strength, water resistance, and resistance to mildew and flame remains a formidable scientific challenge. Inspired by mussels, in this work, quaternary ammonium salted hyperbranched polyamide (QHBPA) and polydopamine (PDA) were incorporated onto the surface of MXene. The synthesized hybrid material, namely Q-MXene, accompanied with phosphorylated chitosan (PCS), was subsequently integrated into the SPI-based adhesive to synergistically improve its performance via organic-inorganic hybridization techniques. With the addition of 10 % PCS and 5 % Q-MXene, the resultant adhesive (referred to as SPI/PCS/Q-MXene) presented a dramatically increased dry and wet shear strengths, reaching 2.25 MPa and 1.71 MPa, showing an increase of 48 % and 113.8 % compared to that of the pristine SPI-based adhesive (1.52 MPa and 0.8 MPa), respectively. Meanwhile, the incorporation of PCS and Q-MXene enhanced the water resistance, flame retardancy and mildew resistance of the adhesive. This research introduces an efficient and eco-friendly approach for the synthesis of a multifunctional bio-based adhesive.