A novel melamine formaldehyde resin coating with phosphoric acid, tannic acid and nano zinc oxide on wood with high flame retardancy and transparency

A novel transparent flame retardant coating was prepared using aqueous melamine formaldehyde resin (MF) as the film-forming resin and gas source, phosphoric acid-tannic acid (H₃PO₄-TA) as the acid and carbon source, and nano zinc oxide (nano-ZnO) as the flame retardant synergist. These coatings were applied to the surface of poplar wood panels to enhance the flame retardancy of wood. After complete drying and curing, the surface of the flame retardant coating was smooth and flat, with an overall light transmission rate exceeding 80 %, and the surface pattern of the wood was clear and visible. The large-plate combustion test showed that the maximum flame retardant time of the sample with 5 % ZnO reached 32 min. The cone calorimeter test showed that the ignition time of the 5 % nano zinc oxide sample increased from 8 s for the coated sample to 310 s, an increase of 3775 %. At the same time, the flame retardant coating, particularly with the addition of nano-ZnO, significantly reduced the heat release rate (HRR) and total heat release (THR) of the wood, demonstrating excellent flame retardant properties. After combustion, the carbon layer showed that the addition of nano zinc oxide increased the graphitization degree of the carbon layer, increased the expansion height of the carbon layer, and formed a denser carbon layer. In summary, this coating has a simple preparation method, low cost, outstanding flame retardant effect, and good transparency, making it a promising application prospects in the flame retardant field of wood products.