Special Spherical Shell-shaped Foam deriving from Guanidine Phosphate - Pentaerythritol system and its Intumescent Fire Retardant effects on Polypropylene

An intumescent fire retardant (IFR) system based on guanidine phosphate (GP) and pentaerythritol (PER) was proposed. Decomposition products of GP were studied by thermogravimetric analysis (TGA) combined with pyrolysis gas chromatography-mass spectrometry (Pyrolysis GC-MS) at first. The pure intumescent fire retardant (IFR) GP-PER was studied then. When the IFR was combusted, the special spherical shell-shaped foam was generated. The foam was made up of soluble phosphorus degradation products (PDPs) and insoluble nitrogenous - carbonaceous char consisting of fused ring and heterocyclic ring structures derived from the degradation products of pentaerythritol phosphate esters and condensed cyanamide derivatives. Scanning electron microscopy (SEM) and Raman spectroscopy as well as Ion chromatography (IC) and elemental analysis were used to study the morphology and the moieties of the foam. The mechanism of the special foam formation was proposed with the help of TGA results in the paper. Eventually, mixtures of this IFR blended in polypropylene (PP) matrix were prepared and the fire retardancy was studied. Fourier transform infrared spectroscopy (FTIR) indicated the variation of the foam moieties from 270 °C to 500 °C. Experiments proved the optimal mass ratio of GP and PER is 2:1 to get fire retardancy in PP matrix. With an addition of 25 wt%, the limited oxygen index (LOI) could reach 31% and vertical burning ratings (UL-94 tests) reach a V-0 rating.