Inorganic Glass Forming Systems as Intumescent Flame Retardants for Organic Polymers

This paper describes the development of several inorganic-based, non- halogenated, intumescent flame retardant additives for organic polymers. Low melting phosphate-sulfate glasses, borate/carbonate glass forming systems and ammonium pentaborate are discussed with respect to their role in converting otherwise flammable polymers into heat resistant, ablative materials. Ammonium pentaborate is shown to be particularly effective as an intumes cent, char-forming additive for thermoplastic polyurethanes. The pentaborate undergoes relatively low temperature thermal decomposition accompanied by in situ glass formation. When subjected to an open flame, the pentaborate/poly urethane composition generates an intumescent char. The resulting glassy foam approximates an ideal char structure in that it provides virtually instantaneous, thermal insulative protection to a substrate and is able to resist thermo- oxidative degradation due to the inorganic, glassy nature of the char.