Boron Phosphates In Situ Generated From Bilayer Coating Approach for Flame‐Retardant Applications

Abstract

Intumescent flame‐retardant coatings offer excellent passive fire protection for flammable materials and steel. However, a key challenge is the conflict between increased melt viscosity from additive catalyst and chemical foaming behavior. Herein, “interfacial autocatalytic” strategy‐guided design of a double dopant‐free epoxy coating is reported with a 100 µm boron‐rich upper layer and a 300 µm phosphorus‐rich bottom layer. This coating generates BPO4 catalyst in situ at the interface during combustion, synergistically catalyzing charcoal formation with the expansion process. BPO4, with its better lattice arrangement, is able to form a dense ceramic layer of 5.5 µm ceramic layer from a stack of 10–40 nm nanoparticles, encapsulating an underlying 1.8 cm intumescent char layer. The coating demonstrates the superior thermal insulation with the heat‐resistant time for up to 50 min, a 271% delay in ignition time, an ultra‐low fire growth rate with 58% reduction, and a 33% reduction in total heat release. In addition to high transparency, this coating presents easy self‐healing, good mechanical properties, and water resistance. This autocatalytic strategy in a confined space‐time introduces a new method for enhancing catalytic charring flame retardancy.