Influence of TiO2 particles and APP on combustion behavior and mechanical properties of flame-retardant thermoplastic polyurethane

The experimental investigation on combustion behavior and mechanical properties of flame-retardant thermoplastic polyurethane were performed in the article. By the masterbatch-melt blending technique, the TiO₂ particles were well dispersed in TPU/APP composites. The microscopic morphology structure was observed by TEM and SEM. TEM images of TPU–TiO₂ masterbatch material showed that the grain sizes of TiO₂ particles were 200–400 nm. The SEM result indicated that the TiO₂ particles could enhance compatibility and dispersion of APP in TPU. The mechanical properties of TPU composites were characterized by dynamic mechanical analysis (DMA) and tensile tests, respectively. The DMA results indicated that TiO₂ particles could improve the viscoelastic property of the TPU/APP composites. The tensile strength achieved a significant improvement with addition of TiO₂ particles. APP/TiO₂-5 obtains a better value of 344% than APP-1 (277%). Also, the flame-retardant property and thermal stability of the TPU composites were characterized using cone calorimeter test (CCT) and thermogravimetric analysis (TGA), respectively. The CCT results revealed that TiO₂ particles could enhance the flame-retardant property of APP in TPU. The peak heat release rate of APP/TiO₂-4 containing 0.5% TiO₂ decreased to 157.27 kW m^?2 from 225.5 kW m^?2 of APP-1 sample without any TiO₂. The TiO₂ particles could promote the formation of carbon layers which restrict the diffusion of fuels into combustion zone and access of oxygen to the underlying materials. The TGA results indicated that TiO₂ can improve the thermal stability of TPU/APP composites.