Influence of structural effects of halogen and phosphorus polyol mixtures on flame retardancy of flexible polyurethane foams

Abstract

AbstractThe role of mixtures of reactive bromine and phosphorus flame‐retardant polyol intermediates as well as the individual bromine and phosphorus reagents in suppressing combustion of flexible polyurethane foams was investigated by means of the oxygen index flame test and charring techniques. Bromine alone appears to contribute to flame retardancy in the solid as well as the vapor phase. A substantial portion of the bromine from both aliphatic and aromatic bromide flame retardants was accounted for in the char, and this is also true when phosphorus is present. Ionic bromine appears to be the most effective elemental form. Like phosphorus, bromine alone in foams is also observed to increase the yield of char. Aliphatic bromide in mixture with phosphonate or phosphate gave enhanced flame retardancy, whereas, mixtures with phosphite are not beneficial. Maximum flame retardancy and char yields correlate well for bromine mixed with phosphate and phosphonate, whereas the relationship does not hold with phosphites. Charring experiments at 500°C with foams containing both phosphorus and bromine generally afforded a constant P/Br ratio, suggesting a specific chemical interaction for flame retardancy. Phosphate flame‐retardant efficiency was sensitive to concentration of phosphorus in the foams. On the other hand, phosphonate and phosphite exhibited a constant level of fire resistance at phosphorus levels greater than 0.3%.