Intumescent flame-retardant system of phosphates and 5,5,5′,5′,5″,5″-hexamethyltris (1,3,2-dioxaphosphorinanemethan)amine 2,2′,2″- trioxide for polyolefins

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A new halogen-free intumescent flame-retardant system was developed using melamine phosphates and 5,5,5′,5′,5″,5″- hexamethyltris (1,3,2- dioxaphosphorinanemethan) amine 2,2′,2″-trioxide (XPM-1000, Monsanto Co.). This intumescent system, optimally at a weight ratio of about 1 : 2, showed effective flame retardancy by oxygen index (OI) and UL 94 tests in ethylene–vinyl acetate (EVA) and polyolefin formulations. At a constant loading and a constant weight ratio of phosphate/XPM-1000, the flame-retardant effectiveness was influenced by the phosphates in the order of melamine pyrophosphate > melamine phosphate ≈ dimelamine phosphate > melamine amyl phosphate. The rate of char formation, as measured under flaming conditions, appeared to correlate better than did the char yield to the observed flame-retardant effectiveness of the different phosphate/XPM-1000 combinations and to the different ratios of phosphate/XPM-1000. A test procedure was developed to measure the char-forming rate which proved to be well correlated with flame retardancy. The possible composition of intumescent char was suggested based on infrared, XPS, and elemental analysis. The presence of polycondensed phosphorus acids with some PNH bonds appears likely. Such phosphorus-nitrogen species may help explain the observed synergism, since their formation could reduce the volatility of the phosphorus acids and enable them to better protect the char.



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