Epoxy resin flame-retarded via a novel melamine-organophosphinic acid salt: Thermal stability, flame retardance and pyrolysis behavior

A melamine-organophosphinic acid salt (MDOP) was synthesized via neutralization of dibenzo[c,e][1,2]oxaphosphinic acid (DOPA) with melamine, and used as an additive-type flame retardant for epoxy resin (EP). Thermal stability and flame retardance was comprehensively evaluated via thermogravimetric analysis (TGA), UL-94 vertical burning test, limiting oxygen index (LOI) and cone calorimetry. The cured epoxy easily passed UL-94 V-0 rating with 0.33% content of P (5 phr MDOP); and LOI value of 38.0% was further achieved with 10 phr MDOP. The peak heat release (PHRR), total heat release (THR), total smoke production (TSP) and fire growth rate (FIGRA) were all reduced with the incorporation of MDOP. The pyrolysis behavior of the flame-retardant EP systems from Py-GC/MS and TG-FTIR suggested that MDOP played the role of flame retardance in both condensed and gaseous phases. Interestingly, the incorporation of MDOP did not deteriorate the mechanical properties of epoxy resin.