Flame-retardant mechanism of a novel polymeric intumescent flame retardant containing caged bicyclic phosphate for polypropylene

A novel polymeric intumescent flame retardant, named poly(ethanediamine-1,3,5-triazine-o-bicyclic pentaerythritol phosphate) (PETBP), was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), solid-state C-13 nuclear magnetic resonance (C-13 NMR), P-31 NMR and elemental analysis (EA). The effects of PETBP on the flame retardancy and thermostability of polypropylene (PP) were investigated by limiting oxygen index (LOI), vertical burning test (UL-94V), cone calorimetric test (CCT), thermogravimetric analysis (TGA) and TG-FTIR, respectively. The results showed that PETBP could significantly improve the flame retardancy and thermostability of PP. When the content of PETBP was 25.0 wt%, the PP/PETBP mixture could achieve a LOI value of 29.5% and a UL-94 V-0 rating, and its peak heat release rate (PHRR), total heat release (THR), average mass loss rate (av-MLR), smoke production rate (SPR) and total smoke production (TSP) were considerably decreased. The flame-retardant mechanism of PETBP was investigated by TGA, FTIR, TG-FTIR and scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDXS). The results revealed that during the combustion PETBP could quench the free radicals of PP chain scission, and form a continuous and compact intumescent char on the substrate, thus effectively retard the degradation and combustion of PP. (C) 2015 Elsevier Ltd. All rights reserved.