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Fluorescent polyphosphate delivers early fire warning in epoxy
Researchers have developed a fluorescent ammonium polyphosphate-based hybrid that provides epoxy composites with thermochromic early-warning functionality, high flame retardancy and improved mechanical performance. The multifunctional approach addresses several long-standing trade-offs in epoxy-based systems.
Epoxy resins are widely used as structural polymers in adhesives, coatings, civil construction, electrical insulation and aerospace applications. However, their high flammability, limited fire safety and the loss of mechanical properties following flame-retardant modification remain persistent challenges. A recent study presents a strategy that combines effective flame retardancy, fire early-warning functionality and mechanical robustness in a single epoxy system.
The authors developed a fluorescent flame-retardant hybrid, APP@ZnQ2, by assembling a quinoline-zinc complex (ZnQ2) on the surface of ammonium polyphosphate (APP). The hybrid was subsequently incorporated into an epoxy-curing system to produce multifunctional composites. Above 160 °C, the composites showed a distinct change in their characteristic chartreuse fluorescence, providing a thermochromic early-warning signal for elevated temperatures.
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Flame retardancy, smoke suppression and mechanical improvement
An epoxy composite containing 6 wt.-% APP@ZnQ2 achieved a limiting oxygen index (LOI) of 29.6 % and reached the highest V-0 rating in vertical burning tests. Compared with the pure epoxy reference, the peak heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) were reduced by 72 %, 67 % and 72 %, respectively, indicating a significant improvement in overall fire safety.
Beyond flame retardancy, the improved compatibility of APP@ZnQ2 within the epoxy matrix supported the mechanical performance of the composites. Tensile strength was comparable to that of the neat resin, while impact strength exceeded that of pure epoxy. The results demonstrate a straightforward yet effective approach for producing epoxy composites that combine fire safety with intrinsic early-warning capability, offering potential for applications in coatings, adhesives and other structural systems where both protection and hazard detection are required.
Source: Ma, T.-L. et al., A fluorescent polyphosphate hybrid for multifunctional epoxy resins: Thermochromic early warning, fire safety and mechanical robustness. Progress in Organic Coatings (2026). https://doi.org/10.1016/j.porgcoat.2026.110247
