Bio-mediated MOF-derived Core–shell Flame Retardant: Towards Styrene–butadiene–styrene Asphalt with Enhanced Flame Safety and Pavement Performance

In order to improve the flame retardancy of magnesium hydroxide (MH) in styrene- butadiene-styrene (SBS) asphalt, two hierarchically structured bio-based flame retardants (FRs) (MH@SA-MOF and MH@SA-LDH) with MH as the core as well as metal organic framework (MOF) or derived layered double hydroxide (LDH) as the shell, were engineered via an alginate-mediated assembly and etching strategy in this study. The flame retardancy and smoke suppression properties of SBS asphalt were found to be remarkably improved by the addition of the bio-based FRs. In addition, the SBS asphalt with added MH@SA-MOF had a higher limiting oxygen index (LOI) than the SBS asphalt samples to which had been added the same amount of MH or MH@SA-LDH. The peak heat release rate (pHRR) and total heat release (THR) of the bio-based MH@SA-MOF FR asphalt (FRA) was 32.9% and 8.9% lower, respectively, than those of the MH FRA. The MH@SA-MOF and MH@SA-LDH FRs had similar impacts on the flame retardancy of SBS asphalt, but the MH@SA-LDH FR had a stronger smoke suppression effect. In addition, bio-based FRs can enhance the anti-aging and anti-deformation performance of SBS asphalt. Moreover, hierarchical catalytic charring structure was observed, suggesting application prospects in flame-retardant asphalt tunnel pavement for the new FRA designs based on bio-remediation of conventional hydroxide flame retardants.