Flame retardation behavior of polybenzoxazine/α-ZrP nanocomposites

Flame retardation behaviors of polybenzoxazine (PBa) nanocomposites containing various levels of exfoliated alpha-zirconium phosphate (alpha-ZrP) nanoplatelets were prepared and confirmed by transmission electron microscopy. Thermogravimetric analysis (TGA) and cone calorimetry results indicate that exfoliated alpha-ZrP could drastically enhance the thermal stability of PBa and promote high char formation of PBa. Additionally, alpha-ZrP greatly enhances the flame retardancy of PBa. The time to ignition was increased to 91 s for PBa/alpha-ZrP-4.6 wt% as opposed to 73 s for pristine PBa. The peak heat release rate value of PBa was significantly reduced by nearly 50% with 8.4 wt% addition of alpha-ZrP. The char residue analyses using scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy suggest the participation of alpha-ZrP in the charring process. The volatile products formed in the thermal degradation processes of PBa and PBa/alpha-ZrP were analyzed by a TGA-Fourier transform infrared spectrometer and found that exfoliated alpha-ZrP facilitate the formation of a compact and homogeneous char layer, which contains flame retardant elements (N, P and Zr) on the surface of the materials, during burning. The improved flame retardancy of PBa/alpha-ZrP is mainly attributed to a combination of the greatly increased melt viscosity of PBa and matrix fast swelling due to the formation of the pyrolytic gases. Additionally, exfoliated alpha-ZrP is found to greatly reduce the amount of toxic gases containing C-O groups. Instead, it releases phosphorous-containing species to achieve flame retardancy in the gas phase. The implication of the present study for the preparation of fire retardant polymers is discussed.