Preparation and Application of a Urea–Formaldehyde-Blended Guanidinium Azole–Phytic Acid–Copper Flame-Retardant Resin Coating

In this study, environmentally friendly flame retardants capable of efficient flame retardancy at low concentrations in wood were developed. Urea-formaldehyde (UF) resin and guanidinium azole (GZ)-phytate (PA)-copper hydroxide (Cu(OH)₂) flame-retardant resin coating blends were prepared using urea, formaldehyde, 3,5-diamino-1,2,4-triazole (GZ), phytanic acid (PA), and copper hydroxide (Cu(OH)₂). Employing dioctyl phthalate as the plasticizer and tannic acid as the curing agent, a three-stage reaction was performed to obtain the desired UF-GZ/PA/Cu as a bio-based flame retardant. Thermal evaluations demonstrated that UF-GZ/PA/Cu lost 5% of its mass through decomposition at a temperature of 195.5 ± 2.1 °C, with its maximum decomposition rate being observed at 300.6 ± 1.5 °C, and 29.8 ± 2.5 wt.% of dense residual charcoal being obtained at 800 °C. When applied as a flame retardant coating on wood, the prepared UF-GZ/PA/Cu exhibited excellent flame-retardant properties, forming a continuous dense charcoal residual layer, with a limiting oxygen index of 32.0%, and passing the UL-94 V-0 test. In addition, the heat release rate and total heat release rate of the flame retardant were determined to be reduced by 87.7 and 83.66%, respectively. Overall, this study provides a green and effective method for the preparation of flame-retardant wood.