Synthesis of a novel polyphosphazene/triazine bi-group flame retardant in situ doping nano zinc oxide and its application in poly (lactic acid) resin

A novel polyphosphazene/triazine bi-group flame retardant in situ doping nano ZnO (A4-d-ZnO) was synthesized and applied in poly (lactic acid) (PLA). Fourier transform infrared (FTIR), solid state nuclear magnetic resonance (SSNMR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and energy dispersive spectrometer (EDS) were used to confirm the chemical structure of A4-d-ZnO. The thermal stability and the flame-retardant properties of the PLA composites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), limiting oxygen index (LOI), vertical burning test (UL-94), and micro combustion calorimeter (MCC) test. The results of XPS showed that A4-d-ZnO has been synthesized, and the doping ratio of ZnO was 7.2% in flame-retardant A4-d-ZnO. TGA results revealed that A4-d-ZnO had good char forming ability (40 wt% at 600 degrees C). The results of LOI, vertical burning test, and MCC showed that PLA/5%A4-d-ZnO composite acquired a higher LOI value (24%), higher UL94 rating, and lower pk-HRR (501 kW/m(2)) comparing with that of pure PLA. It indicated that a small amount of flame-retardant A4-d-ZnO could achieve great flame-retardant performance in PLA composites. The catalytic chain scission effect of A4-d-ZnO could make PLA composites drip with flame and go out during combustion, which was the reason for the good flame-retardant property. Moreover, after the addition of A4-d-ZnO, the impaired mechanical properties of PLA composites are minimal enough.