Phosphorous-Based, Halogen-Free Flame Retardants for Thin, Flexible Polyurethane Artificial Leathers

Polyurethane (PUR)-based artificial leathers are often used as interior materials in public area, making flame retardants (FRs) necessary. The mode of action of different FRs varies depending on the chemical class and the structure of the supplied material. Usually, FRs are designed for bulk materials like foams, e.g., for upholstery, the main application of PUR. However, in thin materials, FRs act differently, thus leaving the PUR without sufficient flame resistance. In this study, PUR films and artificial leathers were equipped with twelve commercially available, halogen-free FRs in various concentrations and combinations. Fire resistance was tested with LOI measurements, cone calorimetry, horizontal burning behavior, and thermogravimetric analyses. An organophosphorus FR proved to be the most suited for flame-resistant artificial leather. The LOI was increased from 20 to 24.2%, the peak heat release rate was reduced by about 30%, and the sample was self-extinguishing in horizontal burning behavior. Phosphinates and aluminum trihydroxide were the least efficient FRs. Combinations of bentonite with phosphorus-based FRs showed synergistic effects in reducing the probability of igniting the material. The results demonstrate that sufficient flame retardancy for PUR-based thin materials can be achieved with commercially available halogen-free FRs, paving the way for more sustainable and greener materials by substituting ecologically harmful and health-damaging FRs.