Synergistic enhancement of flame retardancy of epoxy resin by layered zirconium phenylphosphate modified layered double hydroxides

Abstract

While water-based epoxy coatings have been welcomed by the market due to their excellent environmental performance and low volatile organic compounds emission, its poor flame retardancy has led to limited applications. Herein, the catalytic char formation effect of zirconium phenylphosphonate (ZrPP) and the excellent flame retardant properties of layered double hydroxide (LDH) were fully combined to obtain a high-performance composite flame retardant coating. Specifically, polydopamine (PDA) with excellent adhesion properties was encapsulated on the surface of LDH to enhance its dispersibility in water. The introduction of PDA provided abundant active sites for the adsorption of ZrPP precursor cations, which contributed to the uniform loading of ZrPP on LDH to obtain well-structured LDH@PDA@ZrPP (LPZP) hybrids. The synergistic effect of LDH and ZrPP on the flame retardant properties of the epoxy resin matrix was investigated. The LPZP4%/EP sample showed the lowest backside temperature (173.6 °C), maximum expansion height (25.10 mm) and expansion rate (20.10), proving its highest thermal insulation effect. In the TGA test, the residual char of LPZP4%/EP increased to 26.8 %, proving the excellent thermal stability of the coating. The SEM images showed that the internal char layer of the composite coating formed a honeycomb network structure, which increased the heat absorption property of the char layer.