Thermal degradation and combustion behavior of novel intumescent flame retardant polypropylene with N-alkoxy hindered amine

• The synergism and mechanism of NOR116 on the flame retardancy and thermal degradation of PP/APP/Si-MCA were studied.
• NOR116 could significantly improve the flame retardancy, smoke suppression ability and thermostability of PP/APP/Si-MCA.
• NOR116 could effectively quench the active free-radicals and promote the formation of thermostable intumescent char layer.

How to effectively improve the flame retardancy of polypropylene (PP) is one of the key problems needed to be resolved to promote its development and application. In this work, an efficient synergist—N-alkoxy hindered amine (NOR116) was combined with a novel intumescent flame retardant (IFR, i.e., ammonium polyphosphate/silicone-containing macromolecular charring agent) to flame-retard PP. The effects of NOR116 on the thermal degradation and combustion behavior of the PP/IFR composites were investigated. It was found that a small amount of NOR116 could effectively improve the flame retardancy and thermal stability of the composites. When the content of NOR116 was 0.3 wt%, the limiting oxygen index (LOI) value of the composite was increased from 35.0% to 42.5%, and the vertical burning (UL-94) test reached a V-0 rating. Meanwhile, the heat release rate (HRR), total heat release (THR), average mass loss rate (av-MLR) and smoke production rate (SPR) of the composite were also significantly reduced. Thermogravimetric analysis (TGA), Thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR), scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDXS) and Laser Raman Spectroscopy (LRS) results revealed that NOR116 could change the thermal degradation of the PP/IFR composites, and promote the charring performance of IFR at lower temperature and enhance the quantity and quality of the intumescent char at high temperature. The possible synergistic mechanism between NOR116 and IFR in PP was also discussed.