Cooperative flame retardancy of ammonium polyphosphate and magnesium–aluminum-layered double hydroxide (LDH) in EVA blends

Abstract

To address the issue of excessive magnesium aluminum layered double hydroxides (MgAl-LDH) required in ethylene vinyl acetate copolymer (EVA) to achieve effective flame retardancy, which severely impairs the material's mechanical properties, this study explored the synergistic flame retardant effect of ammonium polyphosphate (APP) and MgAl-LDH. A series of EVA blends were prepared via melt blending, with MgAl-LDH as the primary additive and a small amount of APP as the auxiliary flame retardant. The flame-retardant properties, mechanical performance, and char residue characteristics of these blends were systematically evaluated using the limiting oxygen index (LOI) test, UL-94 vertical burning test, cone calorimeter test (CCT), tensile test, and char residue analysis. The results indicated that when the APP content was 8% and the MgAl-LDH content was 47%, the EVA blend achieved a UL-94 V-0 rating, exhibited an LOI value of 29.3%, and demonstrated an elongation at break 52.8% higher than that of the neat EVA (EVA0). This superior performance is primarily attributed to the strong cooperative flame retardant effect of the APP/MgAl-LDH combination, which effectively reduces heat and smoke release during combustion. Furthermore, the incorporation of APP promotes the formation of a dense and continuous char layer on the composite surface, thereby significantly enhancing flame retardant performance. This study is expected to provide a valuable reference for the practical application and green development of flame-retardant EVA materials in the wire and cable industry and construction sector.