Effect of nano-aluminum hydroxide on mechanical properties, flame retardancy and combustion behavior of intumescent flame retarded polypropylene

In view of the relatively low efficiency of intumescent flame retardants compared to that of traditional flame retardants, nano-aluminum hydroxide (nano-ATH) was added to polypropylene (PP), along with ammonium polyphosphate (APP) and dipentaerythritol (DPER), to prepare intumescent flame retarded polypropylene (IFR-PP). The effect of nano-ATH on the mechanical properties, flame retardancy and combustion behavior of the IFR-PP was investigated. The mechanical properties of the IFR-PP were enhanced by the partial replacement of APP with nano-ATH. The results of the limiting oxygen index (LOI) test, the UL-94 vertical burning test and cone calorimetry tests demonstrated that the flame retardancy of the IFR-PP was optimized when 2 wt.% APP was replaced by the nano-ATH. In this case, the LOI value of the IFR-PP increased from 26.6% to 31.2% and the sample passed V-0 rating in the UL-94 test. The peak heat release rate (PHRR) decreased by 56%. Investigation of the char residues from the cone calorimetry tests indicated that the incorporation of the nano-ATH contributed to the formation of a more intact and homogeneous char during combustion. Based on these results, the flame retardant mechanism was proposed.