Copper-centered Anderson-type polyoxomolybdates as high-efficiency flame retardants for epoxy resins

The increasing severity of fire-related hazards necessitates the development of advanced polymeric materials with integrated flame retardancy and smoke suppression. In this work, metal-centered Anderson-type polyoxomolybdates (POMos) are explored as multifunctional additives for epoxy resins (EP) to address both flammability and toxic fume emissions. A comparative study of a main-group aluminum-centered Anderson-type POMo (AlMo₆) and its transition-metal copper-centered analogue (CuMo₆) reveals the superior performance of the copper-containing system. Specifically, EP composites incorporating CuMo₆ exhibit markedly improved limiting oxygen index (LOI), significantly reduced peak heat release rate (p‑HRR), and substantially suppressed carbon monoxide emissions during combustion. Raman spectroscopy of the residual chars indicates that CuMo₆ promotes a higher degree of graphitization, supporting copper-catalyzed carbonization. Furthermore, encapsulation of the inorganic POM clusters with hexadecyltrimethylammonium bromide (CTAB) markedly enhances their dispersion within the hydrophobic epoxy matrix, as confirmed by scanning electron microscopy (SEM). Thermogravimetric analysis (TGA) coupled with FTIR spectroscopy demonstrates that CTAB-modified CuMo₆ not only improves the thermal stability of the EP composites but also effectively reduces the release of flammable volatile decomposition products. This enhanced performance is primarily attributed to the catalytic action of CuMo₆, which facilitates the formation of a dense, continuous, and thermally stable char barrier that limits heat and mass transfer during combustion.