Polyphosphazene microspheres modified with transition metal hydroxystannate for enhancing the flame retardancy of polyethylene terephthalate

A novel PZS@CS hybrid structure was synthesized for enhancing the flame retardancy of polyethylene terephthalate (PET). The PZS@CS hybrids showed significant flame retardance. For example, the incorporation of 6 wt% PZS@CS obviously brought about an 8.8% increase of limiting oxygen index value (29.3%) and passed the vertical burning test UL-94 V-0 level, accompanied with the sharp reduction of heat and smoke release. The flame retardant mechanism of PZS@CS hybrids was fully studied by the Thermogravimetric Analysis (TGA), pyrolysis-gas chromatography-mass spectrometry, and Raman methods, and the results showed that the improvement of flame retardancy was mainly ascribed to the synergistic effect of PZS and CS phases in both the condensed and the gas phase. Rheological results showed that PZS@CS hybrids improved the melt complex viscosity of PET composites and the well compatibility of PET matrix and PZS@CS hybrids was also proved by the improvement of mechanical properties.