Synergic effect between α-zirconium phosphate nanohybrid and aluminum hypophosphite to achieve eco-friendly high fire safety and mechanical strength

Abstract

The simple addition of conventional flame retardants has made it difficult to achieve a balance between fire safety, smoke suppression, smoke toxicity and mechanical properties in flame-retardant polyurethanes. How to effectively integrate flame-retardant elements to synergize with traditional flame retardants while keeping the preparation process simple remains a major research challenge. Here, an in-situ supramolecular self-assembly organic-inorganic hybrid strategy was proposed. α-ZrP as an assembly aid, phosphorus-nitrogen integrated two-dimensional nanosheets (ZAMP) was prepared to work synergistically with aluminum hypophosphite (AHP), enhancing fire safety, smoke suppression, and anti-dripping properties of thermoplastic polyurethane (TPU). Due to the radical scavenging, gas dilution and physical barrier effects, and catalytic carbonization promoted by the 2D hybrid nanosheets, the flame-retardant polyurethane achieves a V0 rating in UL-94, self-extinguishes quickly without melt dripping, and exhibits a high limiting oxygen index (27.5 %), along with reduced peak heat release rate (74.8 %) and peak smoke production rate (54.55 %). Compared to single AHP addition (TPU/7 %AHP), TPU/6 %AHP/1 %ZAMP shows enhanced fire safety, lower smoke toxicity and better retention of mechanical properties. This straightforward supramolecular self-assembly flame-retardant strategy, using α-ZrP as an anchoring layer, provides new insights into designing highly effective nano flame-retardant synergists with broad fire protection performance.