Manganese‐Doped Phosphonitride/Polyammonium Phosphate Compounds Toward Synergistic Flame Retardation of Polylactic Acid

ABSTRACT Polylactic acid (PLA), a biodegradable thermoplastic, finds extensive applications in packaging, textiles, and medical fields. However, its inherent flammability limits its utilization in scenarios with stringent fire safety requirements. To address this issue, an intumescent flame retardant (IFR) system is constructed using ammonium polyphosphate (APP) and manganese ion‐doped phosphonate sulfonamide salt (PASAS‐Mn). The latter is synthesized via ion exchange and complexation reactions, with sulfathiazole, aminotrimethylphosphonic acid, and manganese acetate tetrahydrate as raw materials. Subsequently, the IFR is incorporated into a toughened PLA/thermoplastic polyamide elastomer (TPAE) blend through melt compounding to prepare flame‐retardant PLA/TPAE/IFR blends. At an IFR loading of 22.5 wt%, the PLA/TPAE/IFR blend achieves a UL‐94 V‐0 rating and a limiting oxygen index (LOI) of 29%. Compared with the PLA/TPAE blend, the total heat release (THR) and peak heat release rate (PHRR) are reduced by 93% and 91%, respectively. The excellent flame retardancy of the PLA/TPAE/IFR blends is attributed to a biphasic flame‐retardant mechanism. We envision that the design of biphasic flame retardants provides valuable insights for developing halogen‐free, high‐efficiency, and environmentally friendly flame retardants for PLA, and is expected to broaden the application scope of PLA in electronic devices, automotive interiors, etc.