Synergistic flame retardant and smoke suppression effects of ferrous powder with ammonium polyphosphate in thermoplastic polyurethane composites

In this paper, ferrous powder has been used as flame retardant and smoke suppression synergism with ammonium polyphosphate (APP) in flame retardant thermoplastic polyurethane (TPU) composites. The synergistic flame retardant and smoke suppression effects between ferrous powder and APP have been studied using cone calorimeter test (CCT), smoke density test (SDT), and limiting oxygen index (LOI). The CCT results showed that appropriate amount of ferrous powder can greatly decrease heat release rate, total heat release, mass loss, smoke production rate, total smoke release, and smoke factor. The SDT results indicated that ferrous powder can greatly improve the luminous flux of flame retardant TPU composites in the test with flame; however, the luminous flux decreases with the addition of ferrous powder in the test without flame. And the LOI results showed that the LOI value of the samples with ferrous powder is higher than that of the sample with only APP. The above results imply there are synergistic flame retardant and smoke suppression effects between ferrous powder and APP in TPU composites. Then, the thermo-gravimetric (TG) and scanning electron microscopy (SEM) were used to investigate the synergistic flame retardant and smoke suppression mechanism between ferrous powder and APP in TPU composites. The TG and DTG results showed that ferrous powder can decrease the initial decomposition temperature and improve the thermal stability at high temperature for flame retardant TPU composites. The SEM results showed that ferrous powder can improve the quality of char residues after CCT, resulting good flame retardant and smoke suppression properties for TPU composites containing both APP and ferrous powder. This is a very meaningful result in fire safety materials fields.