Sodium Alginate Synergises with Copper Ion Deposition on Ldh Surface to Enhance the Fire Resistance of Waterborne Epoxy Coatings

Layered double hydroxide (LDH) possesses the effect of interlayer barrier and dilute the concentration of flammable gases due to its unique lamellar structure, which enables it to perform excellent flame retardancy in both gas and condensed phases. In this paper, the abundant hydroxyl and carboxyl groups on the surface of sodium alginate (SA) were utilized to confer excellent hydrophilicity to LDH. Meanwhile, through ion substitution at the carboxyl site of sodium alginate, thus introducing Cu to catalysis charring into LDH@SA for the synthesis of a novel organometallic ion flame retardant (LSCu). Combination of flame retardants with intumescent fireproofing coatings to prepare composite coatings and test them for fire performance. The large panel test indicated that when the LSCu content was 4 %, the backside temperature of the steel panel dropped to 174.7 degrees C, and the char layer surface remained intact, without any holes or cracks. In the furnace test, the composite coating had the highest expansion height (15.6 mm) and expansion rate (13.28 %) with uniform expansion. SEM illustrated that the char layer of the composite coating had a honeycomb structure, which enhanced the adsorption of heat and smoke. In addition, the composite coating retained the highest residual char content (28.1 %), which had to do with the synergistic effect between LDH and Cu complexes. Furthermore, through analyzing the residual char, it was demonstrated that the formation of metal oxides by LSCu at elevated temperatures improved the sustained barrier performance of the char layer.