Polyoxomolybdate-based nanocoating on flexible polyurethane foams for efficient flame retardancy and smoke suppression

Flexible polyurethane foams (FPUF) are commercially used cushioning materials, but severely suffer from fire risks due to their inherent flammability. Surface coating can localize flame-retardant functionality at the polymer-air interface without altering bulk properties. However, developing a facile nanocoating strategy beyond the layer-by-layer technique for FPUF remains challenging. This work reports novel flame-retardant FPUF@PMo-PPy composites, fabricated by uniformly depositing phosphomolybdic acid (H₃PMo₁₂O₄₀, PMo₁₂) clusters encapsulated within polypyrrole (PPy) via in situ polymerization onto the FPUF skeleton surface, based on electrostatic interactions. The PMo-PPy coating significantly mitigates the fire hazards of FPUF, exhibiting a maximum reduction of 66.7% in peak heat release rate (pHRR) and 73.5% in peak smoke production rate (pSPR). Notably, the maximum smoke density (D_max) and smoke density at 10 min (D_{10 min}) were reduced by 55.7% and 60.8%, respectively, accompanied by lower pyrolysis gas toxicity (HCN and CO). This enhancement is attributed to decomposition products—phosphoric acid and MoO₃—generated from the PMo-PPy coating, which improve the stability and compactness of the char layer. This PMo-PPy nanocoating strategy provides a security assurance for cushioning materials in industrial engineering, ensuring the security of life and property.