Composite strategy for improving fire-retardancy of furfurylated wood

Furfurylated wood has been used widely for exterior purposes due to its superior dimensional stability and biological durability, though its fire resistance is not enhanced. Here, Scots pine (Pinus sylvestris L.) sapwood was impregnated with a hygroscopic fire-retardant guanyl-urea phosphate (GUP) and furfuryl alcohol (FA) by a vacuum-pressure impregnation followed by curing in elevated temperature. The water-resistance of such treated material was evaluated according to European standard EN 84. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) revealed the penetration of GUP into the cell wall. The hydrophobic FA polymerised in-situ within the wood structure, and this enhanced the water-resistance of GUP. Fourier-transform infrared spectroscopy (FTIR) showed that the chemical functionalities changed such as formation of methylene bridges attributed to the polymerised FA and ketone groups attributed to GUP. Thermal gravimetric analysis (TGA) showed that GUP enhanced thermal stability at elevated temperature by promoting char formation. Fire stability test examined by limiting oxygen index (LOI) showed the improvement of fire-retardancy by the incorporation of GUP. Mechanical properties examined by Brinell hardness and three-point bending test indicated that GUP has a low impact on the properties of surface hardness, modulus of elasticity (MOE) and modulus of rupture (MOR) of the furfurylated wood. The work suggests that GUP/FA treatment has the prospective to impart substantial fire-retardancy to the furfurylated wood with small reduction in other properties, thus increasing the potential for exterior applications.