The Performance of Flame Retardants in Rigid Polyurethane Foam Formulations

The flame retardant properties of rigid polyurethane foam compositions are determined by the type and level of flame retardant, the isocyanate index of the foam and the structure of the polyol.

Three phosphorus-based flame retardant additives are compared using the BS 4735 horizontal burn test and the DIN 4102–B2 vertical burn test in a wide range of polyol types. The results obtained are consistent with the phosphorus content of the additives. Dimethyl methylphosphonate with a phosphorus content of 25% proves to be the most effective flame retardant. Surprisingly, the chlorine content, which accounts for nearly a third of the trismonochloropropyl phosphate molecule, does not appear to exhibit any flame retardant effect above its phosporus content. Reoflam 306, a proprietary halogen-free additive with a phosphorus content of 15·2%, enables polyurethane foams of normal index to be formulated to meet the requirements of DIN 4102–B2 without the addition of a flame retardant polyol

Both test methods clearly showed that the aromatic-based polyols have inherently better flame retardant properties than the aliphatic-based polyether polyols.