Synthesis of APP@MOFs integrated hybrids flame retardants for reducing flammability of thermoplastic polyurethanes

In this manuscript, the UiO-66-NH₂(Zr) (MOFs) was adopted to modify ammonium polyphosphate (APP), and the novel synergistic integrated flame retardant system (APP@MOFs) was formed. The flame retardants were incorporated to the thermoplastic polyurethanes (TPU) matrix, and the effects of APP@MOFs on reducing flammability of thermoplastic polyurethanes were compared and investigated. The results show that the flame retardant and smoke suppression performances of TPU/APP@MOFs composites are improved significantly. The pHRR, THR, SPR, TSP, Y_CO, and Y_CO2 of TPU/APP@MOFs composites decreased by 75.76%, 86.19%, 69.74%, 86.34%, 57.14%, and 76.37% in comparison with pure TPU. Furthermore, the char residues increased from 0.11 (pure TPU) to 32.3% (TPU/APP@MOFs composites). Generally, the APP@MOFs have great effect on improving the flame retardant and smoke suppression performances of TPU due to the catalytic carbonization and dilution effects of APP, the synergistic and catalysis effects of MOFs. Through the char structure analysis, the mechanism of the TPU/APP@MOFs composites during the combustion processes was also investigated and proposed.