Anderson-type polyoxometalate-based hybrid with high flame retardant efficiency for the preparation of multifunctional epoxy resin nanocomposites

Transition metal oxides based catalytic carbonization have been proved to be a promising way to enhance polymer flame retardancy, but finding better way to introduce organic phosphorus and transition metal oxide hybrids into polymer matrix to form nanocomposites is still a great challenge. In this work, an organic phosphorus and metal oxide hybrid compound named P-MnMo6 was prepared through combining 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with polyoxometalate (POM). The as-prepared P-MnMo6 had a center of [MnMo6O18](3-) and was used as the precursor of transition metal oxides to improve the flame retardancy of epoxy resin (EP). With the aid of the organic modification, the addition of P-MnMo6 not only maintained the transparency of EP but also enhanced the dynamic mechanical properties. Notably, the then mogravimetric analysis showed that the char yield of EP/P-MnMo6 composite increased significantly. Besides, epoxy with 8 wt% addition of P-MnMo6 passed the vertical burning grade (UL-94) V-0 rating with the limiting oxygen index (LOI) value of 30.4%. Cone calorimeter test indicated the peak heat release rate of EP/P-MnMo6-4 decreased by 41%. Meanwhile, smoke products and CO were greatly suppressed. In addition, the potential flame retardancy mechanism of P-MnMo6 in epoxy matrix was proposed.