PIN FRs for polyurethane elastomers

Data on mechanisms, effectiveness and properties of additive and reactive PIN FRs are analysed from 140 publications. The authors consider that halogenated FRs are decreasingly used because of environmental concerns and release of corrosive gases in fires. PIN FRs discussed include primarily phosphorus-based FRs, because of compatibility with polyurethane elastomers and effective performance. They act both in the gas phase (releasing radicals which inhibit burning) and in the solid phase (generating a fire-protective char layer). Nitrogen-based PIN FRs, including melamine compounds, triazoles, tetrazoles and imidazoles, act by diluting fire gases and by stabilising the char layer (e.g. by forming carbonised graphite nitride). Silicon-based PIN FRs, e.g. POSS (Polyhedral oligomeric silsesquioxane) generate dense carbon char embedded with silicon dioxide. Boron-based PIN FRs generate boron-carbon layers in char which inhibit heat transfer. Selenium-containing PIN FRs remove radicals in fire gases, inhibiting burning. Reactive PIN FRs, often with chain extenders, can act in polyurethane elastomers by cross-linking the polymer, so reducing flammability.

“Review. Strategy for Constructing Phosphorus-Based Flame-Retarded Polyurethane Elastomers for Advanced Performance in Long-Term”, Y. Luo et al. Polymers, 2023, 15, 3711. https://doi.org/10.3390/polym15183711