Valorization of fly ash as a harmless flame retardant via carbonation treatment for enhanced fire-proofing performance and mechanical properties of silicone composites.

Owing to the environmental and economic problems arising from fly ash (FA), there have been various ongoing efforts over the past decades to find a use for it. Among the various applications of FA, its use as a filler in polymer composites has gained much attention. However, most studies have applied FA as a semi-reinforcing filler, which only marginally improves mechanical properties arising from the poor surface wettability of FA with polymer matrices. To solve this problem and to explore new applications, FA was carbonated by bubbling CO in water in this study. The carbonated FA was adopted as a fire-proofing filler in silicone rubber (SR). The surface properties and compositional changes of FA by carbonation were thoroughly examined. Mechanical and thermal properties of carbonated FA-filled SR were evaluated. In particular, the gas torch test confirmed that the carbonation of FA increased the penetration time of SR composites by 11%. In addition, the penetration time of the carbonated FA-filled SR composite was 2-3 times greater than that of the composites filled with commercially available fillers.