The role of nano‐ <scp> Fe ₂ O ₃ </scp> crystal structure on the thermal stability, flame retardancy, and smoke suppression of intumescent flame‐retarded epoxy resins

Abstract Nano‐Fe 2 O 3 is well known to has a synergistic effect with intumescent flame retardants in reducing the fire hazard of polymeric materials, but the role of nano‐Fe 2 O 3 geometry on the synergistic effect of the intumescent system has not been thoroughly investigated. In this study, a series of pentaerythritol phosphate melamine salt (PPMS)‐grafted iron oxide with different crystal configurations (PPMS‐α‐Fe 2 O 3 and PPMS‐γ‐Fe 2 O 3 ) were successfully synthesized. The role of nano‐Fe 2 O 3 geometry on the thermal stability, flame retardancy, and smoke suppression of intumescent flame‐retarded epoxy resins (EP) was investigated by thermogravimetric analysis, cone calorimeter test, and smoke density test. The results showed that PPMS‐α‐Fe 2 O 3 flame retardant substantially improved the thermal stability and char formation of intumescent flame‐retarded EP compared to PPMS‐γ‐Fe 2 O 3 flame retardant. Additionally, α‐Fe 2 O 3 exerts a better role in improving the flame retardancy and smoke suppression properties compared to that of γ‐Fe 2 O 3 . It is notable that the incorporation of 5 wt% α‐Fe 2 O 3 as a flame retardant confers a 78.9% reduction in peak heat release rate (PHRR) value and an 81.8% reduction in peak smoke production rate (PSPR) value compared to pure EP. Char residue analysis revealed that α‐Fe 2 O 3 performs positively in enhancing the compactness of the char layer, thereby leading to an improved synergistic flame retardant effect. Highlights Successful synthesis of flame retardants (PPMS‐α‐Fe 2 O 3 and PPMS‐γ‐Fe 2 O 3 ). α‐Fe 2 O 3 and PPMS have superior synergistic flame retardant effect. α‐Fe 2 O 3 remarkably enhances thermal stability and char formation of EP. Compared to γ‐Fe 2 O 3 , α‐Fe 2 O 3 contributes more to the smoke suppression of EP. Designing improved EP fire performance based on the role of nano‐Fe 2 O 3 .