Synthesis and application of recyclable plant-based benzimidazole phytate for flame retardant PA6 filaments with excellent anti-dripping performance

In this study, a novel benzimidazole-modified phytate (PMI) was synthesized through the reaction of plant-derived phytic acid with benzimidazole derivatives, subsequently applied as an eco-friendly flame retardant for polyamide 6 (PA6). A series of flame-retardant PA6 composites (FR-PA6s) with different PMI loadings were prepared via melt-blending. The thermal stability, flame retardancy, and recyclability of these composites were systematically investigated through comprehensive characterization. Thermogravimetric analysis (TGA) indicated that PMI incorporation maintained the thermal degradation profile of PA6 while remarkably improving its char residue yield from 0% to 7.3% under air atmosphere. Particularly, the PA6/PMI-9 composite containing 9 wt% PMI demonstrated superior flame-retardant performance, achieving a limiting oxygen index (LOI) of 29.3% and attaining UL-94 V-0 rating with significant suppression of melt dripping. Cone calorimetry test results revealed substantial reductions in peak heat release rate (p-HRR, 40.4%) and total heat release (THR, 33.1%) compared with PA6, accompanied by the emergence of characteristic anti-dripping behavior in HRR profile. Notably, PMI exhibited excellent recyclability through a closed-loop recovery process achieving recovery efficiency of 62%. The recycled PMI (R-PMI) retained effective flame retardancy, as evidenced by comparable performance of re-blended composites (R-FR-PA6s) to their virgin counterparts. Especially, successful melt-spinning of PA6/PMI-9 into continuous filaments demonstrated its processability for textile applications. The enhanced fire safety originated from the formation of intumescent char layer that effectively isolates heat and oxygen, as well as free radical scavenging effect and NH 3 dilution effect in the gas phase. This multi-phase protection strategy provided new insights for developing sustainable flame-retardant polyamides.