Preparation of waterborne intumescent flame-retardant coatings using adenosine-based phosphonates for wood surfaces

Here, organic solvent-free adenosine-based waterborne flame retardant curing agents were synthesized and introduction into a melamine urea-formaldehyde resin (MUF) to construct flame-retardant coatings for wood surfaces. Adenosine-based phosphonate (APU), composed of adenosine, urea, formaldehyde, and phosphorous acid, was synthesized by the Mannich reaction. The chemical structure of APU was investigated by Fouriertransform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and 31P nuclear magnetic resonance (NMR) spectroscopy. In contrast to MAW0, the coatings containing APU exhibited similar physical characteristics. MAW4 achieved a vertical combustion (UL-94) V-0 rating and an impressive limiting oxygen index (LOI) of 54.5 %. Cone calorimetry indicated that the time to ignition (TTI) of MAW4 was 89 s, an increase of 790 % compared with MAW0, which may significantly prolong the escape time from a fire. Scanning electron microscopy (SEM), thermal infrared imaging, and Raman spectroscopy all confirmed that continuous and dense char layers reduced the transport of heat, ignitable gases, and smoke. This limited the further pyrolysis and combustion of wood, showing that the waterborne intumescent flame-retardant coatings proposed in this research endowed wood with excellent flame retardancy.