| Numerous candidate environmentally-friendly, water-soluble, and non-toxic fire retardants and fire-retarding processes were developed and tested according to the ASTM D 3801 flammability test and the NRL 8093 smoldering test. Flame retardants that passed the ASTM D 3801 flammability test with the highest V0 rating were boron esters of guanidinium hydroxycarboxylate (glycolate, salicylate and dihydroxybenzoate), zinc gluconate borate ester, and cyanoacetate salts of organic bases (melaminium, cyanoguanidinium, and ammonium). Several related compounds pass this test with the lower V1 rating.;Two new synergistic flame and smolder retarding systems were developed in which the individual components were incapable of preventing flame spread or smoldering but in combination they were highly effective. These systems were mixtures of either guanyl urea phosphate and boric acid or beta-alanine and boric acid.;Compositions leading to the maximum solubility of boron oxides in the ammonium borate/sodium borate system were determined at several temperatures and the formation of mixtures exceeding 50% dissolved boric acid equivalents was found possible. These mixtures were applied as flame retardants for wood, paper, and carbon-loaded polyurethane foam both directly and indirectly by in situ precipitation of boric acid or zinc borate by appropriate chemical treatments. These all passed the ASTM flammability test with V0 rating.;The performance of the boron-containing fire retardants is likely due to deposition of protective boron oxide coatings at elevated temperatures except where phosphate was present and a protective boron phosphate was deposited instead. In all cases, the oxidation of carbonaceous char was strongly inhibited. The hydroxycarboxylate groups generally formed intumescent chars during thermal decomposition that also contributed to fire retardancy. |
