Sustainable, high-performance, flame-retardant waterborne wood coatings via phytic acid based green curing agent for melamine-urea-formaldehyde resin

Developing sustainable, high-performance, and flame-retardant wood coating is significantly important for effective utilization of wood. In this work, a bio-based flame-retardant curing agent of ammonium hydrogen phytate (AHP) was synthesized by controlling the reaction molar ratio of phytic acid and urea. This synthetic AHP displayed appropriate pH which is beneficial for curing melamine-urea-formaldehyde (MUF) resin aqueous solution, and the curing rate could be freely adjusted by changing the weight ratio of AHP to MUF, which was convenient for the operation of wood coating. Compared to the control sample of wood coating prepared by the commercial curing agent of ammonium chloride, except the greatly improved thermal stability and flame retardancy, the resultant wood coating (MP) exhibited comparable Tg, hardness, adhesion, and water resistance, and its preparation process was facile, easy scale-up, and the solvent is eco-friendly water. Especially, the optimized MP-3 wood coating presented a high LOI value of 39.1% and UL-94 rating of V-0, and this LOI value was superior higher than that of previously reported flame-retardant coatings. The CONE tests and thermal imagery further confirmed this MP-3 coating could form tough intumescent char layer to effectively suppress the transmission of heat and oxygen and reduce the smoke production. And the outstanding flame retardancy of MP3 wood coating was ascribed to N/P synergistic intumescent flame-retardant mechanism. Therefore, this research presents a sustainable, eco-friendly approach to construct high-performance, flame-retardant wood coating, which has great potential in the wood and furniture industries.