Thiol-assisted bioinspired deposition of polyurethane onto cellulose as robust elastomer for reinforcing soy protein-based composites

The development of natural fiber-reinforced composites is environmentally friendly and therefore presents great potential; however, these composites are characterized by poor water resistance and interfacial bonding, which therefore limits its practical applications. This study reported a facile and novel approach for the construction of a high-performance microfibrillated cellulose (MFC) elastomer using thiol-functionalized polyurethane (PU-SH) with the assistance of a bioinspired dopamine platform. This elastomer was then employed as a reactive reinforcer to improve soy protein isolated (SPI) adhesive. The surface modification of MFC included the formation of a polydopamine (PDA) layer and Michael addition reactions between PU-SH and PDA, which were characterized by the Fourier-transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy measurements. It was found that the high-functional MFC elastomer served as a reactive cross-linker that gave rise to multiple physical and chemical interactions with the SPI matrix. This resulted in the optimization of the crosslinking system, which ultimately contributed to the solution of the bottleneck issues for natural fiber-reinforced composites. Consequently, the modified SPI-based adhesives notably enhanced the shear strength to 1.38 MPa, displaying a 236.6% increment compared to the unmodified adhesive. This strategy may provide a new insight into the design and preparation of superior natural plant-reinforced composites.