In this study, a novel flame retardant designated as SFD, which contains phosphorus (P), nitrogen (N), and sulfur (S), was successfully synthesized via a one-pot method utilizing 2-aminobenzothiazole, furfural, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as raw materials. This flame retardant was subsequently incorporated as an additive into epoxy resin (EP), with various formulations prepared using dicyandiamide (DDM) as the curing agent. The epoxy formulations containing only 3 wt% of SFD exhibited an improved Limiting Oxygen Index (LOI) of 34% and achieved UL-94 V-0 ratings. The Peak Heat Release Rate (PHRR), Total Heat Release (THR), and Total Smoke Production (TSP) for the EP/SFD composites were reduced by 28.0%, 30.1%, and 30.0%, respectively, in comparison to pure EP. Mechanical property assessments of the SFD/EP composites indicated that the incorporation of SFD had minimal impact on the mechanical properties of EP; thus, SFD can enhance the flame retardancy of EP without compromising its mechanical integrity. Analysis of the flame retardant mechanism revealed a significant P-N synergistic effect between the benzothiazole moiety and the phosphorus heterophenanthrene moiety present in SFD. The addition of SFD effectively mitigates heat release and smoke production during combustion processes involving EP while demonstrating excellent flame-retardant characteristics along with smoke suppression capabilities; furthermore, it promotes carbon layer formation. This research presents a straightforward strategy for synthesizing a multi-element synergistic flame retardant system that holds promise for application across a broad spectrum of thermoset plastics.
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