Preparation of DOPO‐Modified Layered Double Hydroxide With Salen–Ni Interlayer and Its Application in Epoxy Resin

ABSTRACT To enhance the flame retardancy and smoke suppression performance of epoxy resins (EP), this study reports the synthesis of a high‐efficiency flame retardant (SLDH‐Ni‐KD) through sequential intercalation modification and surface functionalization of layered double hydroxide (LDH). The optimized design addresses both the flame‐retardant efficacy enhancement and the inherent compatibility limitations of LDH in EP matrices. Comprehensive combustion characterization was conducted through thermogravimetric analysis (TGA), cone calorimetry testing (CCT), limiting oxygen index (LOI) determination, and UL‐94 vertical burning assessment. The underlying flame‐retardant mechanism was systematically investigated using scanning electron microscopy, Raman spectroscopy, and thermogravimetry‐infrared spectroscopy analysis of char residues. Experimental results revealed that the synergistic interaction between LDH and DOPO components, combined with the bi‐phase catalytic charring effects mediated by magnesium/aluminum ions, enabled the 7% SLDH‐Ni‐KD/EP composite to achieve exceptional fire safety performance. Specifically, the composite demonstrated an elevated LOI value of 33.8% ± 0.1%, accompanied by substantial reductions in total heat release (THR) and smoke production rate (SPR). Mechanical property assessments identified 5 wt.% SLDH‐Ni‐KD as the optimal loading for maintaining EP matrix compatibility. This work successfully develops an innovative LDH‐based nano‐flame‐retardant system that integrates high‐efficiency fire‐retardant and smoke‐suppressing functionalities, establishing a novel multielement synergistic strategy for polymer flame retardancy.