Poly (diallyldimethylammonium) and polyphosphate polyelectrolyte complexes as an all-in-one flame retardant for polypropylene

Poly (diallyldimethylammonium chloride) (PDDA) and ammonium polyphosphate (APP) deionized chloride ions and ammonium ions by ionizing in aqueous solution respectively, then combined to form poly (diallyldimethylammonium) and polyphosphate (PAPP) polyelectrolyte complexes as an all-in-one flame retardant for polypropylene and its composites were characterized by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy. One flame retardant system composed of PAPP and PP, the other flame retardant system composed of PAPP, Polyamide-6 (PA6) and PP were tested by limiting oxygen index (LOI), UL-94, cone calorimeter tests and thermogravimetric analysis (TGA) and compared with pure PP. The results showed that the LOI value of PP/PAPP composite can reach 27.5%, and UL-94 V-2 rating can be reached at 25 wt% PAPP loading. Meanwhile the cone calorimetry results displayed that the peak heat release rate (PHRR) and total heat release (THR) were reduced up to 69.3% and 22.5%, respectively, compared with those of pure PP. After adding 5 wt% PA6, the carbon source missing due to the early PAPP decomposition can be made up, and PHRR and THR can be further reduced slightly. The flame retardant mechanism of PAPP was studied by FTIR spectroscopy and X-ray photoelectron spectroscopy. Six-membered ring of C─N containing conjugate double bonds, cross-linked phosphate structure formed stable, intumescent, compact char layer which greatly improved the flame retardancy of PP.