Flame Retardancy and Thermal Stability of Polypropylene Composite Containing Ammonium Sulfamate Intercalated Kaolinite

Ammonium sulfamate (AS) intercalated kaolinite (K) was successfully prepared through a three-step method, and then, it was introduced in association with intumescent flame retardants (IFR) into polypropylene (PP). The structure of intercalated kaolinite (AS-K) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and X-ray photoelectron spectrometry (XPS). The flammability evaluation by limit oxygen index (LOI), vertical burning test (UL-94), and cone calorimeters test (CCT) revealed that the LOI value was increased to 35.3, and UL-94 grade reached V-0 rating for the PP/IFR (23.5 wt %)/AS-K (1.5 wt %) sample; the heat release rate (HRR) value was lower than other PP composites. The thermostability analysis by TGA demonstrated that the addition of AS-K could enhance the thermal stability and the formation of char residue. It was proposed that AS-K could react with P, N, and polyaromatic rings to form a ceramic-like compact and continued to char during burning.