Self-assembly of phosphorus-containing ionic liquids on black phosphorus nanosheets for enhancing the fire safety of ethylene-vinyl acetate copolymers

This study presents the design and synthesis of a novel phosphorus-containing ionic liquid flame retardant, DV, which serves as both a surfactant and a synergistic flame retardant. DV self-assembled onto the surface of BP nanosheets through electrostatic interactions, forming a polymerized ionic liquid coating via radical initiation. Simultaneously, DOPO-derived groups were incorporated into the polymer matrix by ionic bonding with imidazole groups, further enhancing the structural integrity of the composites. The resulting composite was used to develop EVA-based materials with outstanding mechanical properties and flame retardancy. At a low loading of 3 wt% DVBP, the synergistic effect of phosphorus and nitrogen, combined with the two-dimensional structure of BP, facilitated char formation at elevated temperatures, effectively inhibiting the transfer of oxygen and flammable substances. Additionally, the gas-phase flame-retardant mechanism reduced the release of pyrolysis products. The composite achieved a V-0 rating in the UL-94 test, a 22.3 % reduction in peak heat release rate (PHRR), and an 8.1 % increase in tensile strength, highlighting its potential for application in cables used in critical transport equipment.