Inhibitory effects of developed composite flame retardant on bituminous combustion and volatile emissions

Abstract

Bituminous materials release plenty of heat and hazardous volatiles when exposed to high temperature. To develop a sustainable and efficient composite flame retardant (CFR) of bituminous materials, new compositional formulation proportions of selected Ca–Al hydrotalcite (CAHC), ammonium polyphosphate (APP), coated red phosphorus (CRP) and expanded vermiculite (EV) in the prepared CFR were confirmed. Then the inhibitory effects of CFR on non-isothermal combustion kinetics characteristics of bitumen and the dynamic release processes of various volatile constituents were discussed using thermogravimetry/differential scanning calorimeter-mass spectrometer-Fourier transform infrared spectroscopy (TG/DSC- MS-FTIR) combined approach. Test results suggest that the combustion processes of bitumen and CFR bitumen mainly include obvious multistage exothermic reactions. When the heating rate is elevated, the incomplete combustion of bitumen and CFR bitumen is increased, and more heat and volatiles are emitted. Further, as the bituminous temperature is gradually raised, the CAHC, APP, CRP and EV in added CFR are decomposed in turn to inhibit the multistage combustion process of bitumen, showing comprehensive and synergistic flame retarding effects due to dilution, cooling, and insulation. Therefore, the combustion of bituminous four components is correspondingly inhibited by the matched flame retardant in CFR so that the bituminous thermal stability is obviously improved by added CFR. Additionally, the CFR produces thicker intumescent layer on bitumen, which insulates bitumen with oxygen, and decreases the volatile release and molten droplet formation. Fewer macromolecular volatiles are emitted from CFR bitumen than those from bitumen. Moreover, the dynamic release process of various volatile constituents during the bituminous combustion is efficiently suppressed by CFR. The developed CFR plays an important role of flame retarding and smoke suppressing functions, providing an efficient and green flame retardant for bituminous materials when exposed to a fire.