Thermal degradation behavior and flammability of polyurethanes blended with poly(bispropoxyphosphazene)

Abstract

Polyurethanes containing different amount of flame retardant, poly(bispropoxyphosphazene), were synthesized by a two-step polymerization. The thermal degradation behaviors of these polyurethanes were then studied by the thermal gravimetric analysis (TGA), TGA coupled with Fourier transform infrared analysis and elemental analysis. A limiting oxygen index was used to evaluate the flammability of these polyurethanes. For these modified polyurethanes under nitrogen, a two-stage thermal degradation behavior was observed. The first stage was caused by the degradation of hard segments, whereas the soft segments were responsible for the second-stage degradation. The thermal degradation activation energies were calculated by using Ozawa's method. It was found that the addition of flame retardant caused a decrease of the activation energy in the first stage, but an increase in the second stage, which was probably due to the formation of a thermal stable structure. As for the flame retardancy, the modified polyurethanes have a higher char yield at 550°C, and a higher limiting oxygen index than the neat polyurethane.