Preparation and flame retardancy of intumescent flame-retardant polypropylene

Polypropylene(PP) was flame retarded with an intumescent flame retardant(IFR) system containing 1, 2, 3-tri(5, 5-dibromomethyl-1, 3-dioxaphosphorinanyl-2-oxy)benzene(FR), polyphosphate(APP ) and melamine(MEL).The effect of content on flame retarding properties such as limited oxygen index(LOI)measurements, thermal gravimetric analysis(TGA), UL-94 and cone tests was studied. The results demonstrate that IFR is effective on improving the flame retardancy of polypropylene. The limited oxygen index value could reach 36.2% for the sample containing 30% IFR(FR∶APP∶MEL, 4∶8∶3, mass ratio). The cone experimental results show that the peak heat release rate(pk-HRR), average heat release rate(av-HRR), average effective heat of combustion(av-EHC), average specific extinction area(av-SEA), average mass loss rate(av-MLR) and average CO release rate(av-CO) of the PP are reduced 75.9%, 71.7%, 76.4% , 74.6%, 58.3% and 50.0% respectively than those of the pure PP. The release rate of soot and poisonous gas are reduced, which reaches to about zero at burning time of 300 s. In addition, SEM observation reveales that the IFR can promote the formation of strong charred layers in the early stage of burning of the composite.