Research on the Flame Retardancy Properties and Mechanism of Modified Asphalt with Halloysite Nanotubes and Conventional Flame Retardant

Abstract

The inflammability of asphalt road will promote fire spread in the tunnel and produce lots of toxic smoke. To improve the fire resistance of asphalt pavement, mineral powder flame retardants are generally replaced by flame retardants in equal amounts. In this study, the effects of the synergistic flame retardancy system of halloysite nanotubes (HNTs) and conventional flame retardants (CFR) on the flame retardancy performance and mechanism of asphalt were investigated. Firstly, the flame retardancy properties of the HNTs and CFR composite modified asphalt were investigated based on the Cleveland open cup method (COC), Limiting oxygen index meter (LOI), and Cone calorimeter tests (CCTs). Then, the flame retardancy mechanism of the modified asphalt was studied based on Thermogravimetric analyzer (TGA), Fourier-transform infrared (FTIR), and Scanning electron microscopy (SEM). The results show that adding HNTs could improve the flame retardancy of the CFR modified asphalt binder. When 1 wt % HNTs and 8 wt % CFR were used, the limiting oxygen index of asphalt increased by 40.1%, the ignition temperature increased by 40 °C, while the heat release rate, total heat release, the smoke production rate, total smoke release, and other parameters decreased with varying degrees. Based on TG, FTIR, and SEM, the targeted flame retardancy mechanism and synergistic effect of HNTs/CFR flame retardancy system were revealed and summarized as three stages: (1) Stage 1, aluminum hydroxide (ATH) absorbs heat through thermal decomposition and inhibits the decomposition of lightweight components in asphalt; (2) Stage 2, aluminum diethyl phosphate (ADP) decomposes and produces organic phosphoric acid, which catalyzes crosslinking and ring thickening of asphalt and the quenching effect of phosphorus free radicals to block the combustion; and (3) Stage 3, HNTs plays an important role in increasing the integrity and density of the barrier layer. In addition, the Al2O3 produced by the decomposition of ATH, the carbon layer formed by the ADP catalyzed pitch, and HNTs play a significant synergistic effect in the formation of the barrier layer. Thus, the combination of HNTs and CFR has been proved to be a prospective flame retardancy system for asphalt.

Smoke suppression, flame retardancy, and fire toxicity of polypropylene containing melamine salt of pentaerythritol phosphate halloysite

“…The band at 1016 cm −1 is attributed to CN stretching vibration. [ 14,22 ] The FTIR spectrum of PPH shows absorption bands at 1106, 1009, and 890 cm −1 for POC. The band at 1671 cm −1 is due to phosphoric acid ester group, and the bands at 2890 and 2974 cm −1 are referred to CH 2  of pentaerythritol.…”

“…The band at 1016 cm À1 is attributed to C N stretching vibration. [14,22] The FTIR spectrum of PPH shows absorption bands at 1106, 1009, and 890 cm À1 for P O C. The band at 1671 cm À1 is due to phosphoric acid ester group, and the bands at 2890 and 2974 cm À1 are referred to CH 2 of pentaerythritol. The absorption peaks at 606 and 2325 cm À1 are referred to Si O P. [3,6,11] The FTIR spectrum of MPPH manifests an absorption band at 3419 cm À1 for primary amine.…”

Halloysite Nanotubes and Silane-Treated Alumina Trihydrate Hybrid Flame Retardant System for High-Performance Cable Insulation

“…HNTs are such a nanofiller that could significantly enhance the compactness and thermal stability of the barrier layer and improve the flame retardancy efficiency of different polymer matrices [ 17 , 18 , 19 , 42 ]. The barrier layer covering the polymer matrix surface could effectively cut off the heat and material exchange between the polymer matrix and the combustion flame zone and prevent further degradation [ 48 ]. Such environmentally friendly decomposition of polymer composition containing halogen-free fillers intended for the cable industry is of great interest to both scientific and industrial applications.…”

Environmentally Friendly, High-Performance Fire Retardant Made from Cellulose and Graphite

“…Public concern about fire triggers research activity that has already created effective fire-protective additives for polymers, [ 15 , 16 , 17 , 18 , 19 , 20 ] like hydrated compounds, for example, hydrated salts [ 21 ], oxides (e.g., alumina) and clays that undergo endothermic degradation, carbonates like huntite that decompose forming a CO 2 gas blanket, halogenated paraffins and polymers that emit free-radical suppressants, and chemicals that intumesce like the expandable ammonium phosphates [ 22 ], or still those that form a barrier between air and the substrate, e.g., silica [ 23 , 24 , 25 , 26 ] and clays [ 27 , 28 ], or char as, for example, organophosphorus compounds [ 16 , 29 , 30 , 31 ], polyols and melamine. Graphite (flakes, powder or expanded) has been used as an additive in intumescing coatings [ 19 , 20 , 32 , 33 , 34 , 35 ] and in polymer composites [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ]. Thus, existing fire-retardants explore different approaches and mechanisms.…”