Antibacterial, hydrophobic, and dyeable homogeneous flame-retardant regenerated cellulose fiber

Blending methods for flame-retardant regenerated cellulose fibers often show poor compatibility, primarily due to insufficient hydrogen bonding between the flame retardant and the cellulose spinning system. This results in migration and aggregation that compromise both the mechanical properties and flame retardancy of the resulting fibers. In this study, a reactive liquid flame retardant (rrPNm) achieved homogeneous dispersion with cellulose, N-methylmorpholine N-oxide (NMMO), and water through strong hydrogen bonding interactions (NH donor, P=O/N acceptor). Chemical crosslinking occurred during coagulation without phase separation or migration/aggregation, ensuring good mechanical properties and durable flame retardancy. The resulting flame-retardant regenerated cellulose fiber (Cationic-Fr-rcf 20%) achieved a limiting oxygen index (LOI) of 33.5%, a 72.03% reduction in total heat release (THR), and a 138.2% increase in char residue relative to pure fiber (rcf). The analysis reveals that rrPNm plays a condensed-phase role in flame retardancy. After 50 washing cycles (AATCC 61-2013 3 A), its LOI remained at 30.2%, and it demonstrated enhanced mechanical properties, including a 20.5% increase in elongation at break. The fiber also showed multifunctional properties: antibacterial activity, hydrophobicity, and dyeing performance. This work provides a versatile, energy-efficient strategy for developing multi-functional flame-retardant regenerated cellulose fibers for fire resistance, healthcare, and wearable products.