Lin Chia-Feng, Karlsson Olov, Das Oisik, Mensah Rhoda Afriyie, Mantanis George I, Jones Dennis, Antzutkin Oleg N, Försth Michael, Sandberg Dick
Wood Science and Engineering, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Forskargatan 1, SE-931 77 Skellefteå, Sweden.
Structural and Fire Engineering, Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, SE-971 87 Luleå, Sweden.
ACS Omega. 2023 Mar 14;8(12):11381-11396. doi: 10.1021/acsomega.3c00146. eCollection 2023 Mar 28.
The exterior application of fire-retardant (FR) timber necessitates it to have high durability because of the possibility to be exposed to rainfall. In this study, water-leaching resistance of FR wood has been imparted by grafting phosphate and carbamate groups of the water-soluble FR additives ammonium dihydrogen phosphate (ADP)/urea onto the hydroxyl groups of wood polymers via vacuum-pressure impregnation, followed by drying/heating in hot air. A darker and more reddish wood surface was observed after the modification. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, solid-state C cross-polarization magic-angle-spinning nuclear magnetic resonance (C CP-MAS NMR), and direct-excitation P MAS NMR suggested the formation of C-O-P covalent bonds and urethane chemical bridges. Scanning electron microscopy/energy-dispersive X-ray spectrometry suggested the diffusion of ADP/urea into the cell wall. The gas evolution analyzed by thermogravimetric analysis coupled with quadrupole mass spectrometry revealed a potential grafting reaction mechanism starting with the thermal decomposition of urea. Thermal behavior showed that the FR-modified wood lowered the main decomposition temperature and promoted the formation of char residues at elevated temperatures. The FR activity was preserved even after an extensive water-leaching test, confirmed by the limiting oxygen index (LOI) and cone calorimetry. The reduction of fire hazards was achieved through the increase of the LOI to above 80%, reduction of 30% of the peak heat release rate (pHRR), reduction of smoke production, and a longer ignition time. The modulus of elasticity of FR-modified wood increased by 40% without significantly decreasing the modulus of rupture.
由于阻燃（FR）木材可能会暴露在降雨中，因此其外部应用需要具有高耐久性。在本研究中，通过真空压力浸渍将水溶性FR添加剂磷酸二氢铵（ADP）/尿素的磷酸酯和氨基甲酸酯基团接枝到木材聚合物的羟基上，然后在热空气中干燥/加热，赋予了FR木材耐水浸性。改性后观察到木材表面颜色变深且更偏红。傅里叶变换红外光谱、X射线光电子能谱、固态碳交叉极化魔角旋转核磁共振（C CP-MAS NMR）和直接激发磷MAS NMR表明形成了C-O-P共价键和聚氨酯化学桥。扫描电子显微镜/能量色散X射线光谱表明ADP/尿素扩散到细胞壁中。热重分析结合四极质谱分析的气体逸出揭示了从尿素热分解开始的潜在接枝反应机制。热行为表明，FR改性木材降低了主要分解温度，并促进了高温下炭渣的形成。通过极限氧指数（LOI）和锥形量热法证实，即使经过广泛的水浸试验，FR活性仍得以保留。通过将LOI提高到80%以上、将峰值热释放速率（pHRR）降低30%、减少烟雾产生以及延长点火时间，实现了火灾危险性的降低。FR改性木材的弹性模量提高了40%，而断裂模量没有显著降低。
