Non-destructive modification of cellulose-based fabrics in aqueous phase for flame-retardant epoxy composite

The flame-retardant modification of plant fiber-reinforced composites (PFRCs) is a fundamental requirement for achieving broader industrial applications. However, commonly used modification methods often compromise the fiber mechanical properties or surface reactivity due to structural damage. In this paper, a water-soluble system consisting of phytic acid imidazole salt and biobased benzoxazine was devised to modify a regenerated cellulose fabric through water-phase immersion. Benefiting from the neutral solution and self-assembly coating, the modified fabric (F-RCF) exhibited a typical self-extinguishing behavior while maintaining good structural integrity and mechanical properties. By further combining F-RCF with a DOPO-containing epoxy resin blend (FEB) to prepare a fiber-reinforced green composite (F-RCF/FEB), the results indicated that the co-curing reaction between the modifier and resin matrix contributed to improved interfacial adhesion. This enabled the simultaneous enhancement of tensile modulus (from 9.82 to 11.29 MPa), impact strength (from 6.58 to 7.26 kJ m⁻²) and interlaminar shear strength (from 11.41 to 13.89 MPa). More importantly, F-RCF/FEB exhibited excellent anti-flammability in terms of a high limiting oxygen index value of 34.3% and a UL-94 V-0 rating, and the peak heat release and total heat release were also markedly reduced by 44.9% and 36.9%, respectively. Mechanism analysis revealed that the modified system effectively prevented the wick effect and provided an inhibitory effect in the gaseous phase, as well as a barrier effect in the condensed phase. This study presents a non-destructive modification strategy for plant fibers, which may also inspire the synchronous enhancement of interfacial compatibility and fire-proof performance of PFRCs.