Study on the flame retardancy of reactive PU modified in situ using ammonium polyphosphate

Herein, a simple and efficient inorganic particle surface modification strategy was developed to improve the flame retardancy of flammable polyurethane (PU) materials while avoiding the serious degradation of their mechanical properties due to the incorporation of inorganic particles. Novel organic–inorganic hybrid hydroxylation ammonium polyphosphate (OHAPP) was fabricated via an ion-exchange reaction between APP and diethanolamine, and a PU/OHAPP film was prepared by crosslinking OHAPP with reactive PU via in situ polymerization. The curing properties, flame retardancy, and mechanical properties of materials were evaluated. Results showed that the addition of 15 wt% OHAPP in PU increased the tensile strength of the sample by 16% compared to PU alone. The peak heat release rate, total heat released, and total smoke produced from the materials measured via the conical calorimetric method were 337.2 kW/m², 78.1 MJ/m², and 8.9 m², respectively, which were 63.8%, 43.6%, and 15.2% lower than those of PU. Additionally, the flame-retardant mode of action of the PU/OHAPP film was verified. This study is a useful reference for further studies on flame-retardant materials.