Flame retardancy and thermal degradation behaviors of polypropylene composites with novel intumescent flame retardant and manganese dioxide

•The synergistic effects of manganese dioxide (MnO2) on the flame retardancy of the PP/IFR systems were studied.•A small amount of MnO2 could dramatically improve the flame retardancy properties of PP/IFR system.•MnO2 could change the degradation behavior and increase the char residue of the IFR and PP/IFR.•MnO2 could help to form continuous and compact intumescent char layer on the outer surface of PP/IFR.•The existence of MnO2 could promote to remain more P and O in the char layer.

The flame retardancy and thermal degradation behavior of polypropylene composites containing ammonium polyphosphate (APP), novel charring agent (CNCA-DA) and manganese dioxide (MnO2) were characterized by limiting oxygen index (LOI), UL-94 measurement, cone calorimeter test (CCT), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). It was found that a small amount of MnO2 could dramatically increase the LOI value, UL rating of the PP/IFR systems, and reduce the combustion parameters of PP/IFR system from CCT test, including peak heat release rate (p-HRR), total heat release (THR), and smoke production rate (SPR). The catalytic effectivity (CAT-EFF) results showed that when 1 wt% MnO2 was added, it had the highest CAT-EFF, and could promote the LOI value of the composites from 27.1 to 30.7. The TGA data revealed that MnO2 could change the degradation behavior of the IFR and PP/IFR, improve the thermal stability of the PP/IFR systems at high temperature and increase the char residue. The morphological structures observed by digital photos and SEM indicated that MnO2 could effectively help to form more continuous and compact intumescent char layer on the outer surface to protect the underlying materials from burning. The EDS results illustrated that the existence of MnO2 could promote to remain more P and O in the char layer.