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Guanyl-urea phosphate (GUP) was introduced into furfurylated wood in order to improve fire retardancy. Modified wood was produced via vacuum-pressure impregnation of the GUP–furfuryl alcohol (FA) aqueous solution, which was then polymerized at elevated temperature. The water leaching resistance of the treated wood was tested according to European standard EN 84, while the leached water was analyzed using ultra-performance liquid chromatography (UPLC) and inductively coupled plasma–sector field mass spectrometry (ICP-SFMS). This new type of furfurylated wood was further characterized in the laboratory by evaluating its morphology and elemental composition using optical microscopy and electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX). The chemical functionality was detected using infrared spectroscopy (FTIR), and the fire resistance was tested using cone calorimetry. The dimensional stability was evaluated in wet–dry soaking cycle tests, along with the mechanical properties, such as the Brinell hardness and bending strength. The fire retardancy of the modified furfurylated wood indicated that the flammability of wood can be depressed to some extent by introducing GUP. This was reflected in an observed reduction in heat release rate (HRR2) from 454.8 to 264.9 kW/m2, without a reduction in the material properties. In addition, this leaching-resistant furfurylated wood exhibited higher fire retardancy compared to conventional furfurylated wood. A potential method for producing fire-retardant treated furfurylated wood stable to water exposure has been suggested., Validerad;2022;Nivå 2;2022-05-02 (hanlid);Funder: CT WOOD, Luleå University of Technology; European Structural and Investment Fund, OP RDE (CZ.02.1.01/0.0/0.0/16_019/0000803);Part of special issue: Performance and Application of Novel Biocomposites II, Advanced Research Supporting the Forestry and Wood Processing Sector’s Adaptation to Global Change and the 4th Industrial Revolution

Maleic anhydride (MA) is a cyclic anhydride capable of forming an ester bond with wood constituents, providing enhanced dimensional stability and fungal resistance of wood. However, the weight gain through treatment was lost during wet-dry cycle, which indicates that the ester bonds in maleated wood is susceptible to hydrolysis. This study focuses on improving the stability of the maleated product through the use of sodium hypophosphite. Studies have shown the combined treatment resulted in improved anti-swelling efficiency (ASE), lower weight loss and smaller saturated volumes than untreated or specimens treated with maleic anhydride along. In order to better understand the relationship between the modified wood and water, low-field nuclear magnetic resonance (LFNMR) spectroscopy was used to determine the influence of moisture in wood. The modification process resulted in a weak wood–water interaction using LFNMR, suggesting an increased T2 relaxation time of capillary water. However, the weak wood–water interaction did not seem to be related to the accessible hydroxyl groups because the modification reaction resulted in a similar number of hydroxyl groups as present in unmodified wood. This finding would appear to agree with the concept of MA modification resulting in the “ring opening” of the anhydride, creating a carboxylic acid group for each hydroxyl group modified within the wood., Funder: Northern European network for wood science and engineering (WSE); Advanced research supporting the forestry and wood-processing sector’s adaptation to global change and the 4th industrial revolution, OP RDE, (CZ.02.1.01/0.0/0.0/16_019/0000803)

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.