Alginate‐Iron ( III ) Complex for Flame‐Retardant Epoxy Composites With Enhanced Mechanical Properties

Developing eco‐friendly bio‐based flame retardants (FRs) via simple, green routes is vital for sustainable polymers. Alginic acid (Alg) offers promising metal‐chelating ability, yet conventional alginate FRs often suffer from limited efficiency. Here, we report a straightforward aqueous synthesis of an alginate‐iron complex (AF) via Fe (III) coordination. Adding just 5 wt% AF to epoxy resin achieves a UL‐94 V‐1 rating and a limiting oxygen index of 28.2%. Remarkably, cone calorimetry reveals substantial fire safety enhancements: peak heat release rate, total smoke production, and peak CO production decrease by 33.3%, 20.0%, and 29.4%, respectively, versus neat EP. These improvements originate from a condensed‐phase mechanism, in which AF catalyzes the formation of a dense char layer with a higher structural ordering degree, as confirmed by TG‐IR, SEM, Raman and XPS analyses, which effectively suppresses heat and mass transfer. Additionally, the composite exhibits improved mechanical properties. This study offers a simple and potentially useful strategy for developing more sustainable epoxy composites.