Synergistic flame retardancy and thermal insulation properties of silicotungstic acid intercalated ZnAl-LDH with IFRs on epoxy-polyamide coatings

Epoxy resin, known for its excellent mechanical properties, chemical resistance, and dimensional stability, has been widely employed in advanced electronic packaging, high-performance coatings, and aerospace engineering. However, its inherent flammability has limited its applications. To address this issue, a ZnAl-NO₃-LDH was synthesized via co-precipitation and subsequently modified by ion-exchange intercalation with [SiW₁₂O₄₀]⁴⁻ to form ZnAl-SiW₁₂O₄₀-LDH (SiW-LDH). The obtained SiW-LDH was then combined with AMP intumescent flame retardants composed of APP, MEL, and PER to enhance the fire resistance properties of the epoxy–polyamide resin (EP). The resulting 2 %SiW-LDH/AMP/EP coatings containing 24.5 wt% AMP and 2 wt% SiW-LDH exhibited excellent flame-retardant properties, achieving an LOI value of 35.3 % and a UL-94 V-0 rating. Additionally, the total heat release (THR) and total smoke production (TSP) recorded during cone calorimeter tests decreased by 69.7 % and 70.9 %, respectively. Moreover, further analysis of the residual char of SiW-LDH/AMP/EP demonstrated that the catalytic carbonization co-effect of AMP and SiW-LDH promoted the formation of a dense and continuous char layer with aromatic structures containing AlO, WO, SiO, WC, Zn²⁺, P–O–C, and PN moieties. Notably, these structures enhanced the flame retardancy, smoke suppression, charring, and thermal insulation properties of the EP. These properties also originated from the dilution of non-combustible gases and the heat-absorbing action upon the thermal decomposition of SiW-LDH/AMP during combustion. Overall, these results demonstrate that the incorporation of SiW-LDH and AMP into epoxy matrices effectively enhances the flame retardancy and thermal insulation properties of polymer systems.