Development of waterborne transparent intumescent coatings for timber buildings: influence of phosphoric acid ratio

Timber, as a sustainable and eco-friendly construction material, has gained increasing attention in civil engineering. However, its poor fire resistance significantly limits its broader application in fire prone areas. Transparent intumescent fire-retardant coatings have emerged as a promising solution, offering reliable fire protection without compromising the aesthetic appearance of timber. This study presents a systematic synthesis method for a transparent intumescent fire-retardant coating based on bisphenol-A epoxy resin. Compared to epoxy resin-based transparent fire-retardant coatings reported in the literature, the proposed coating demonstrates better performance with superior fire resistance. These improvements are obtained by the removal of urea and the adjustment of the phosphoric acid ratio to result in simplified synthesis procedures and significantly enhanced transparency. Notably, when the ratio of epoxy resin, diethanolamine, and phosphoric acid is optimised at 1:2:4, the 1.2 mm coating achieves optimal fire performance. In a simulated big panel method lasting 45 min, the backside temperature stabilised at approximately 148°C. This work provides a promising strategy for the development of highly transparent and effective fire-retardant coatings for timber applications.