Flame retardancy working mechanism of methyl-DOPO and MPPP in flexible polyurethane foam

摘要

The chemical nature of flexible polyurethane (flex PU) foams, the low density, the high air permeability and the open cell structure cause this material to be highly flammable. The new phosphorus flame-retardant (FR) methyl-DOPO (9,10-dihydro-9-oxa-methylphosphaphenanthrene-10-oxide) is known to show an excellent flame retarding behavior in flex PU foam by acting mainly in the gas phase. In this study, the FR working mechanism of methyl-DOPO and its ring-opened analogue MPPP (methylphenoxyphenyl-phosphinate) is investigated by TGA, TG-MS, FMVSS 302 and Cone Calorimeter measurements. Under TG-MS conditions comparable concentrations of low molecular weight species such as HPO, CH_3PO or PO_2 are released. These species are able to scavenge the H- and OH-radicals in the radical chain reactions of the flame leading to a significant increase in the CO/CO_2 ratio and the smoke density during cone calorimeter experiments. Finally, the flame retardancy of MPPP is determined to be less efficient in flex PU foam because of the higher vapor pressure compared with methyl-DOPO. Here, the vaporization of methyl-DOPO occurs in the same temperature region as the depolymerization of the urethane and the bisubstituted urea groups during pyrolysis of the foam leading to an optimal interaction.