A review of PIN FRs for polyurethane foams notes the synergy of N and P FRs as an “eco-friendly”, low smoke solution. Nitrogen-containing FRs can be additive or reactive in polyurethane foams (PUF) and are considered, with other PIN FRs, to provide future solutions with low toxicity, high thermal stability and low smoke, especially in PIN FRs combining nitrogen with phosphorus. Mechanisms of N-FRs are reviewed in detail. (1) N-FRs decompose with an exothermic reaction, absorbing heat. Melamine, for example, absorbs high amounts of heat. (2) N-FRs release ammonia, nitrogen, nitrogen oxides and/or carbon dioxide, which dilute fire gases. APP (ammonia polyphosphate) also releases water vapour. (3) Melamine compounds decompose to produce melamine salts (e.g. melem, melam, melon) which contribute to char stability. (4) Melamine compounds can react and modify the polyurethane decomposition process in fire, resulting in slower burning. (5) Some N-FRs in fire release radicals such as nitroxyl, alkyl, aminyl and alkoxy which inhibit the gas phase fire reactions. Combined with phosphorus, which causes char formation by release of phosphoric acid and can also act in the gas phase, nitrogen-based PIN FRs can delay ignition, reduce the release of heat and smoke.
“Nitrogen-Based Ecofriendly Flame Retardants for Polyurethane Foams”, N. Arastehnejad et al., chapter 6 in ‘Polyurethane Chemistry: Renewable Polyols and Isocyanates’, Gupta & Kahol, ACS Publications, 2021 https://dx.doi.org/10.1021/bk-2021-1380.fw001