Water-Soluble Biobased Modifier Toward Epoxy/Cellulose Fabric Composite with Simultaneous Enhancement of Flame Retardancy and Interface Adhesion

Natural plant fibers, as green and lightweight alternatives to traditional fibers in fabricating green composites, have attracted much interest in recent years. However, their hydrophilic and flammable natures severely limit the interfacial adhesion and flame resistance of the composite, and the synchronous improvement of both remains a considerable challenge. Herein, a combined modifier consisting of a water-soluble benzoxazine (HGB) with high carbonization and phytic acid (PA) containing phosphorus elements and acid groups was devised to treat regenerated cellulose fabric (SF). The treated fabric (F-SF) not only could realize self-extinguishing from the fire, which helps to avoid the wick effects, but also exhibited an optimized interfacial property of the composites. After being combined with an intrinsic flame-retardant epoxy resin (F-EP), the composite material (F-SF/F-EP) achieved a V-0 rating in the UL-94 test and an excellent limiting oxygen index (LOI) value of 33.8% due to the flame-retardant effect in both the gaseous and condensed phases. Simultaneously, benefiting from the improved interfacial compatibility, both the tensile modulus and impact strength were enhanced from 9.82 GPa and 6.58 MPa to 11.29 GPa and 7.21 MPa, respectively, compared with untreated SF/EP composite, especially the interlaminar shear strength (ILSS) dramatically increased by 21.7%. This work provided an integrated strategy for synchronously enhancing interfacial compatibility and the fire-proof performance of plant fiber-reinforced composites.