Preparation of a durable flame-retardant regenerated cellulose fiber with enhanced mechanical properties

The incorporation of flame retardants into regenerated cellulose spinning solutions is a crucial approach for producing flame-retardant regenerated cellulose fibers. However, this method often encounters challenges such as poor compatibility and inadequate dispersion of the flame retardants within the matrix. In this study, a novel flame retardant (P-TSDPAH) was synthesized using ordinary materials such as tetramethylphosphonium sulfate, dimethyl phosphite, and ammonia solution. The P-TSDPAH contains a lot of -NH- bonds, exhibits compatibility with cellulose and N-methylmorpholine N-oxide (NMMO), and remains good dispersion in the cellulose spinning solution. SEM analysis revealed that the P-TSDPAH was uniformly distributed within the FR-fiber 15 % without aggregation, and EDS results confirmed the presence of substantial phosphorus content. FTIR analysis confirmed the presence of characteristic P-C-O, C N, and N H structures within the FR-fiber 15 %. XRD analysis revealed an enhanced crystallinity in the FR-fiber 15 % upon incorporation of the P-TSDPAH. Compared with pure regenerated cellulose fibers, the peak heat release rate and total heat release of FR-fiber 15 % were reduced by 88.61 % and 30.50 %, respectively, while the char residue at 700 °C increased by 142.79 %. TG and TG-IR analyses demonstrated the flame retardancy of the FR-fiber 15 %, revealing condensed-phase flame retardant mechanism, while limiting oxygen index (LOI) remained at 35.0 % even after 50 washing cycles (NFPA 2112–2012 standard), demonstrating durable performance. Additionally, the incorporation of the P-TSDPAH enhanced the mechanical properties of the regenerated cellulose fibers, which the relative breaking strength and elongation increased by 31.16 % and 48.05 %, respectively. Therefore, the synthesized P-TSDPAH demonstrates application potential for developing durable flame-retardant regenerated cellulose fibers.