Synergistic flame retardant properties of a layered double hydroxide in combination with zirconium phosphonate in polypropylene

High-performance flame retardant nanocomposites were prepared for polypropylene (PP). The nanocomposites consisted of an organic-modified layered double hydroxide (LDH) in combination with zirconium 2-(2-(2-aminoethylamino)ethylamino)ethylphosphonate (ZrP) compounds containing phosphorus and nitrogen. The composition, thermal stability and mechanical properties of the nanocomposites combined with PP were studied by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and differential scanning calorimetry. The flame retardant behavior was observed using a microscale combustion calorimeter. As an effective synergistic flame retardant, the addition of the nanocomposites resulted in a significant decrease in the heat release rate compared with pure PP. When the load of LDH in combination with ZrP was 5 and 15% (a ratio of 1 : 3), the peak heat release rate was reduced by 28.2%. The flame retardant showed good dispersion in the PP matrix. The improved flame retardant performance may be because LDH and ZrP decomposed to produce noncombustible gases, which diluted the combustible gases, and a compact char layer that acted as a fire barrier.