Catalyzing carbonization function of α-ZrP based intumescent fire retardant polypropylene nanocomposites

The catalyzing carbonization function of alpha-zirconium phosphate (α-Zr(HPO4)2·H2O, α-ZrP) based on an intumescent fire retardant (IFR) polypropylene (PP) system is reported. The IFR system consists of ammonium polyphosphate and pentaerythritol. The morphology of the PP/organophilic ZrP nanocomposites is characterized by X-ray diffraction and high resolution transmission electron microscopy (HRTEM). The results indicate that an intercalated structure is formed. Thermogravimetric analysis, limiting oxygen index (LOI) and UL-94 are used to characterize the thermal stability and the flame retardant properties. It is found that there is a transformation of the char microstructure and an increment of LOI value in the PP systems with the OZrP, and the UL-94 level is improved, from failure, to a V-0 rating. The synergistic effect improves the flame retardant properties of PP remarkably. The morphology and structure (HRTEM and selected area electron diffraction) of the char residue also indicate the presence of graphite sheets. A possible mechanism for catalyzing carbonization is discussed.