Dual Flame-Retardant and Curing-Agent Effects of Phytic Acid–Guanazole as an Additive in Fire-Protective Coatings for Wood

Recent research has focused on developing environmentally friendly flame-retardant coatings to improve the fire resistance of wood. In this study, phytic acid–guanazole (PG), a dual-functional compound synthesized through an ionic reaction between phytic acid and guanazole, was added to KH550-modified urea–formaldehyde resin (KUF) as both a curing agent and flame retardant. The−PO43−groups from phytic acid act as an acid source to accelerate char formation during combustion, while the −NH2groups introduced by guanazole release non-combustible gases to dilute oxygen in the air, synergistically enhancing flame retardancy. Additionally, the hygroscopic−PO43−groups absorb free water in the resin, reducing the curing temperature and accelerating coating solidification. The KH550 coupling agent improves compatibility between KUF and PG while introducing silicon, which forms SiO2during combustion to strengthen the char layer and further enhance flame resistance. Evaluations showed that PG outperforms conventional tannic acid (TA) in curing efficiency and fire resistance. Comprehensive analyses, including Differential Scanning Calorimetry (DSC), Limiting Oxygen Index (LOI), vertical flame tests, and cone calorimetry, confirmed PG’s dual functionality. Scanning Electron Microscope (SEM) and Raman spectroscopy revealed that PG-modified coatings form denser post-combustion char layers, directly linked to improved fire resistance. As a multifunctional additive, PG eliminates the need for separate curing agents and utilizes bio-based phytic acid, offering cost-effective and sustainable advantages for industrial applications.