Synthesis of <scp>MgAlCu</scp> ‐ <scp>LDH</scp> From Hydrous Magnesium Rhodochrosite by In Situ Substitution Method for <scp>PVC</scp> Flame Retardant Applications

ABSTRACT To address environmental concerns of conventional flame retardants, MgAl‐layered double hydroxide (LDH) was synthesized from hydro‐magnesite. Utilizing hydrotalcite's structural memory effect, Cu was incorporated into LDH through acid activation and reconstruction. The obtained LDH was combined with ammonium polyphosphate (APP) into polyvinyl chloride (PVC). Composite thermal stability and flame retardancy were systematically evaluated. Results demonstrated that MgAlCu‐LDH/APP/PVC exhibited optimal performance, with limiting oxygen index (LOI) increasing from 26.1% (pure PVC) to 31.4%, achieving UL‐94 V‐0 rating. Cone calorimetry tests showed 19.7% and 20.9% reductions in peak heat release rate (PHRR) and total heat release (THR), respectively. Peak smoke production rate (PSPR) and total smoke production (TSP) decreased by 27.8% and 48.9%. These enhancements originated from synergistic dilution of flammable gases by NH 3 (from APP decomposition) and CO 2 (from LDH). Additionally, APP's acidic sites and Cu's catalytic effect jointly promoted PVC dehydrochlorination and aromatization, forming a dense char layer that effectively suppressed heat and mass transfer. This acid activation–in situ replacement method provides a novel strategy for synthesizing MgAlCu‐LDH and other ternary LDHs, demonstrating promising potential for improving polymer fire safety.