Flame retardancy and thermal degradation properties of polypropylene/wood flour composite modified with aluminum hypophosphite/melamine cyanurate

In this study, aluminum hypophosphite (AP) and melamine cyanurate (MCA) were used as flame retardant in polypropylene (PP)/wood flour (WF) composite. The flammability of the PP/WF composites was examined by the limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter test. When the PP/WF composite was loaded with 20% AP/MCA (the mass ratio of AP and MCA was 5: 1), the UL-94 achieved V-0 rating and the LOI was increased to 29.5%. In addition, the flexural strength was increased by about 11.0%. The results of cone calorimeter test revealed that the heat release rate and heat release rate peak of the PP/WF composite with AP/MCA were significantly reduced. The thermal degradation mechanism of PP/WF composites was investigated by thermo-gravimetric analysis, Fourier transform infrared spectrometry, energy-dispersive X-ray spectroscopy and scanning electron microscopy. The results indicate that AP/MCA had the effect of gas-phase and condensed-phase flame retardancy during the combustion and degradation of PP/WF composite. Consequently, a thermal property reinforcing mechanism of the PP/WF composite with AP/MCA was presented.