In this article, we report the use of a variety of analytical methods, in particular, solid-state 1H-NMR and 13C-NMR to characterize the relationship between the condensed-phase chemistry and burning behavior as determined by a series of combustion tests for two commercially derived flexible polyurethane foams, one combustion-modified. The combustion tests showed that the foams met several regulatory requirements in terms of their fire performance, whether or not they were combustion-modified. Both foams passed the MV SS 302 and CAL 117 small-flame tests. The nonmodified foam failed the Crib 5 test, but this test had a much larger ignition source. The particular problem with the nonmodified foam was melt drip into the flame zone. This led to a steady maintenance of the fuel feed and a rapid escalation of the fire. In contrast, the combustion-modified foam showed little melt drip and self-extinguished. Thermal analysis data for the two foams showed that melamine acted in part as an endothermic heat sink. This alone did not account for the much reduced melt flow and drip of the combustion-modified foam, but the solid-state 1H-NMR data clearly showed that the molecular mobility of the combustion char from combustion-modified foam was lower than the unmodified foam char, which indicated that the flame-retardant formulation in the combustion-modified foam acted by a condensed-phase mechanism

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The aim of this investigation is to ascertain whether the mode of action of melamine in exible polyurethane (PU) involves condensed phase chemistry in terms of promoting char formation. A combination of in situ 1 H NMR analysis, solid state 13 C NMR characterization of chars prepared ex situ, and normal TGA and DSC has been employed. Solid state 13 C NMR indicates that there is no major discernible difference in the structure of the dichloromethane-insoluble chars prepared with and without melamine, the remaining polyol only accounting for 20±25 % of the total carbon at 350°C, but still being quite mobile. However, in situ 1 H NMR provides de®nitive evidence that melamine acts in the condensed phase in terms of promoting the formation of rigid char which forms in more signi®cant quantity by 450°C. No increase in the residue yields is observed by TGA upon melamine addition, probably due to a combination of the small sample size and open sample holder in relation to the in situ 1 H NMR analysis which also involves fairly slow heating.

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