Effects of metal chelates on a novel oligomeric intumescent flame retardant system for polypropylene

A novel oligomeric phosphorus–nitrogen containing intumescent flame retardant, poly(4,4-diamino diphenyl methane-O-bicyclicpentaerythritol phosphate-phosphate) (PDBPP), was synthesized and characterized. Effects of metal chelates on flame retardancy of polypropylene (PP)/PDBPP systems were studied and the results showed that the presence of metal chelates considerably enhanced the fire retardant performance as evidenced by the increase of LOI values and a great reduction in peak heat release rate of PP/PDBPP system. Raman spectroscopy, infrared spectroscopy and scanning electron microscopy demonstrated that metal chelates could react with polyphosphoric acid, a decomposition product of PDBPP, to form crosslinked network. Through salt bridges a more compact char layer was formed which was responsible for the improved thermal and flame retardancy properties of PP/PDBPP system.