Solvent-free epoxy coatings with enhanced cross-linking networks towards highly-efficient flame retardancy, water resistance and anticorrosion

Developing robust flame-retardant epoxy-based coatings that provide protection against fire, high temperatures, and prolonged exposure to wet environments remains a significant challenge. In this work, a facile and effective strategy is developed to enhance the cross-linking network and charring ability while reducing VOCs emissions in epoxy (EP) coatings. By exploiting a charring agent-derived active diluent, pentaerythritol glycidyl ether (PTGE), in combination with ammonium polyphosphate (APP) and EP, a solvent-free EP coating with enhanced flame retardancy, water resistance, and anticorrosion properties is constructed. With its low viscosity and multifunctionality, PTGE, anchored by four epoxy groups, reduces the coating's viscosity and strengthens the cross-linking network, thereby improving water resistance and anticorrosion properties, achieving an adhesion force that meets the ASTM 5B standard. The ring-opening of PTGE produces abundant hydroxy groups, and the synergistic effect of PTGE and APP provides excellent flame retardancy to wood, as evidenced by a limiting oxygen index of 29.2 % and a 40.0 % reduction in peak heat release rate. With the formation of a dense and hard char layer, the maximum back temperature of coated structural steel remains as low as 75 °C after 2600 s of flame exposure. This study provides a feasible strategy for constructing multifunctional, solvent-free, flame-retardant protective coatings.