Sheet-like Iron Hydroxyl Phosphate as an effective flame retardant and smoke suppressant for Polyacrylonitrile

A novel, one-step, facile and low-cost strategy was successfully designed to synthesize iron hydroxyl phosphate (IP) nanosheets via solvothermal method using iron (II) sulfate heptahydrate, ethylene glycol, and phosphoric acid. Then, for the first time, the flame retardant and smoke suppressant properties of the IP were studied. The synthesized IP nanosheets were added into the polyacrylonitrile (PAN) matrix, by a solvent blending method, to prepare PAN/IP nanocomposite. The structure and morphology of the IP nanosheets were carefully characterized by X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). In addition, the thermal stability, flame retardancy and fire hazard of the PAN/IP nanocomposite were investigated by thermogravimetric analysis (TGA), cone calorimetry, and UL-94 vertical burning test. The PAN/IP nanocomposite exhibited significantly higher smoke suppression and flame retardancy capability as well as less fire hazards than those of the pure PAN. Moreover, incorporation of the IP into the PAN matrix increased the residual char. These improvements were attributed to the ability of the IP to contribute in formation of effective barrier char layer on the PAN, sheet-like morphology of the IP as well as catalytic activity of the IP in carbon monoxide (CO) oxidation.