Preparation, fire behavior and thermal stability of a novel flame retardant polypropylene system

In this study, a novel spirocyclic pentaerythritol bisphosphorate disphosphoryl-di-prop-2-en-1-amine (SPSA) compound containing a functional double bond (C=C) was synthesized and characterized by Fourier transform infrared spectroscopy and H-1 nuclear magnetic resonance spectroscopy (H-1 NMR). In this paper, a new intumescent flame retardant (IFR) was designed by combining ammonium polyphosphate (APP) and SPSA (mass ratio of APP and SPSA was 2:1) and this IFR was mixed with polypropylene (PP) via twin-screw extruder to prepare a series of flame retardant PP composites. The thermal stability and fire behaviors of these flame retardant PP composites were investigated by thermogravimetric analysis, limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter test. Furthermore, the morphology of the char residues of flame retardant PP composites after cone calorimeter test was studied by scanning electron microscopy with energy dispersive X-ray analysis (EDS). Aiming to further improve the thermal stability of the composites, electron beam irradiation has been used to treat these composites. The results showed that LOI value of flame retardant PP composite containing 30 % IFR was 24.0 and passed UL 94 V-0. In the cone calorimeter test, both peak heat release rate and total heat release results of PP/IFR system were lower than those of PP/APP system. In addition, this IFR provided relatively good quality of char residue in the combustion. Moreover, electron beam treatment of the composites improved the thermal stability of these designed flame retardant PP composites.