Construction of a network structure in Chinese fir wood by Na2SiF6 crosslinked Na2SiO3

The mechanical properties, dimensional stability, and fire resistance of fast-growing Chinese fir wood was improved using a silicate-impregnation modification of Chinese fir as a green, safe and non-toxic method. However, the high leaching rate of silicate from impregnated wood has remained a problem. This study was aimed to prepare sodium silicate (Na2SiO3)-modified Chinese fir wood with leaching resistance using a cyclic increasing-pressure method, with sodium fluorosilicate (Na2SiF6) solution as the curing agent. Scanning electron microscopy and weight percentage gain results indicated that silicate effectively adhered to the wood interior and leaching tests showed that the weight leaching ratio of Na2SiO3/Na2SiF6-modified wood was increased by 25.97% and the water absorption rate reduced by 15.80%, compared to Na2SiO3-modified wood. Compressive and bending strength enhancements of 210 and 40.1%, over than that of natural wood, were observed. In addition, silica impregnation inside the cell walls and lumens were confirmed using Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). Thermogravimetric analysis (TGA) and cone calorimetry (CONE) analyses showed that the addition of sodium fluosilicate alleviated thermal decomposition and complete combustion of this treated wood and enhanced its flame retardancy.