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synopsisThe role of mixtures of reactive bromine and phosphorus flameretardant 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 substantid portion of the bromine from both aliphatic and aromatic bromide flame retardants w q accounted for in the char, and this is also true when phosphorus is preseqt. 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 generdy 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%.

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This article presents an up-to-date review of chemical compositions, particularly those bearing the elements of halogen and phosphorus, and structural features of flame retardants which have been chemically incorporated in polyurethane foams. Particular Anthony J. Papa is project scientist with the Chemicals and Plastics Division, Union Carbide Corp., South Charleston, W. Va. He received his Pk.D. degree from Washington State University in 1960, and did postdoctoral work at Purdue University in 1961 and exploratory research on polyurethanes as leather substitutes at Du Pont from 1962 to 1966. He has had experience in the areas of urethane, isocyanurate, and phenolic foams, and since 1966 has worked in the fields of rigid and flexible foams.directed toward the construction marketplace, but at the present time the biggest outlet for flame-retardant rigid polyurethanes is still as insulation for the transportation industry. Test MethodsA review of all flammability test methods applicable to polyurethane foams is beyond the intent of this article. The most commonly employed small and medium scale tests for rigid foams include the ASTM D 1692 test, the Butler chimney test, the Bureau of Mines flame penetration test, the ASTM E 162 radiant panel test, and the ASTM D 568 vertical bar test. The ASTM E 84