Multifunctional halogen-free phosphoryl amide derivative boosts fire safety, crystallizability, flexibility, and...

While poly(L-lactic acid) (PLA) exhibits excellent biodegradability, biocompatibility, tensile strength, and processability, its inherent flammability, poor crystallization ability, and brittleness significantly limit its broader application. In this work, a halogen-free phosphoryl amide flame retardant agent (DMPC) was synthesized via a simple one-step nucleophilic substitution reaction to enhance the fire resistance of PLA. The results show that, compared with neat PLA, PLA/1% DMPC composite achieved a 39.0% increase in limiting oxygen index and attained the highest V-0 rating in the vertical burning test, along with self-extinguishing behavior. Cone calorimetry test further reveals an 85.5% longer time to ignition, along with reductions in peak heat release rate (27.9%), total heat release (26.9%), peak smoke production rate (76.4%), total smoke production (85.7%), CO₂ production (34.8%), and fire growth rate index (31.6%), while the residue yield (RY) percentage increased by 26 times. This outstanding flame-retardant performance was primarily attributed to the formation of a compact, thick, and continuous char layer on the composite surface during combustion, which effectively insulated heat, limits oxygen diffusion, and suppressed smoke emission. Additionally, phosphorus‑oxygen radicals generated during pyrolysis scavenged oxygen radicals, thereby interrupting the combustion chain reaction. Beyond flame retardancy, the composite also exhibited exceptional UV-shielding performance, along with improved crystallization kinetics, enhanced hydrophobicity, and increased elongation at break. This work presents a feasible pathway for developing bio-based multifunctional flame-retardant composites and offers a practical solution for expanding the application potential of PLA-based products.