Effect and mechanism of N-alkoxy hindered amine on the flame retardancy, UV aging resistance and thermal degradation of intumescent flame retardant polypropylene

A multifunctional additive N-alkoxy hindered amine (NOR116) possessed free-radical quenching capability was combined with ammonium polyphosphate/pentaerythritol (APP/PER) to flame-retard polypropylene (PP). The effects of NOR116 on the flame retardancy, ultraviolet (UV) aging resistance and thermal degradation of the PP/APP/PER mixture were investigated by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimetric test (CCT), UV aging test and thermogravimetric analysis (TGA). It was found that NOR116 showed a synergistic effect with APP/PER in flame retardant PP. When the content of APP/PER and NOR116 were 24.5 wt% and 0.5 wt%, respectively, the LOI value of the PP/APP/PER mixture was increased from 31.0% to 35.0% and a UL-94 V-0 rating was achieved. Meanwhile, the UV aging resistance of the PP/APP/PER mixture was improved significantly. The synergistic mechanism between NOR116 and APP/PER was explored and revealed. During the combustion, NOR116 could not only block the radical chain reaction in the gas phase by quenching the active free-radicals, but also promote the formation of the thermostable intumescent char in the condensed phase.