Organophosphorus-hydrazides as potential reactive flame retardants for epoxy

For structural composites used in vehicles and aircraft, flame retardant chemistries which enhance char formation and reduce heat release are preferred. Phosphorus-based and phosphorus-nitrogen flame retardants for epoxies have been well studied to date, but phosphorus hydrazides have not been studied for their flame-retardant potential in epoxy. These hydrazides offer some novel structures and they can potentially offer a combination of vapor and condensed phase flame retardant action. A series of eight compounds were systematically investigated in this study as reactive flame retardants in a bisphenol F epoxy/aliphatic amine resin system at a level of 2.5 wt% phosphorus. Results suggest that the phosphorus hydrazides react with the epoxy during thermal decomposition, and they also release nitrogen during flaming combustion of the epoxy matrix. The observed reactions resulted in increased char yields and reduced total heat release, while simultaneously lowering heat of combustion and total smoke release.