Synthesis of Micro/Nano‐Materials From Fly Ash for Enhancing Flame Retardancy and Smoke Suppression in <scp>PVC</scp>

ABSTRACT The high‐value reuse of waste fly ash (FA) has garnered global attention. In this paper, micron hydroxy‐sodalite (SOD) is synthesized by a simple alkali‐dissolved FA, and further micron aluminum hypophosphite (FA‐AHP) and nano‐silica (FA‐SiO 2 ) are prepared by acid‐dissolved SOD, and their synergistic flame‐retardant mechanism in PVC is revealed. Compared with Pure PVC, the SPR of PVC/SOD (only 5 wt% SOD) decreased by 37.45%. SOD's ion‐exchange capability (OH → Cl) not only neutralizes corrosive HCl but also releases H 2 O, diluting flammable gases. When 5 wt% FA‐SiO 2 ‐AHP is added to PVC, the oxygen index (LOI) is 28.2%; the peak heat release rate (PHRR), carbon monoxide (COP), and carbon dioxide (CO 2 P) decreased by 63.0%, 62.14%, and 65.16%, respectively. The synergistic flame retardant and smoke suppression on PVC of FA‐AHP and FA‐SiO 2 are attributed to the organic combination of micro and nano forms that create a ceramic‐like barrier, the multistage thermal response, and free radicalregulation with gas‐condensation that are coordinated. This work not only provides a new way for the high‐value utilization of FA but also provides theoretical support for the development of environmentally friendly flame retardants.