Modified LDHs for Long-Lasting Fire Safety in Polypropylene: Simultaneous Flame Retardancy and Smoke Toxicity Reduction

A bio-based phytate (PA)-intercalated Mg-Al layered double hydroxide (LDH-PA) was successfully synthesized via a calcination-reconstruction method and incorporated into polypropylene (PP) as an efficient flame retardant. LDH-C precursors were first prepared by co-precipitation combined with hydrothermal treatment, followed by calcination at 500°C to obtain layered double oxides (LDO). Subsequent anion exchange with phytate under a nitrogen atmosphere reconstructed the LDH structure, introducing PA anions into the interlayer. The results from multiple characterization techniques confirmed the successful incorporation of phytate anions. The PP/LDH-PA composites exhibited markedly enhanced thermal stability. At a loading of 15 wt% LDH-PA, the maximum thermal decomposition rate decreased by 19.0%, and the residual char yield increased to 12.72 wt%. The composite achieved a limiting oxygen index (LOI) of 26.8% and attained a UL-94 V-1 rating. Cone calorimeter tests showed that, compared with pure PP, the PP/LDH-PA 15 composite reduced the peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR), total smoke release (TSR), peak CO release rate, and peak CO 2 release rate by 29.6%, 19.2%, 41.2%, 13.4%, 35.3%, and 32.4%, respectively. These enhancements can be mainly ascribed to three factors: (i) the compact char layer catalyzed by LDH-PA offers a physical barrier effect; (ii) during the LDH decomposition, the carbon dioxide and crystalline water released generate a dilution effect; (iii) PA brings about a radical-quenching mechanism.