Preparation and characterization of sodium silicate impregnated Chinese fir wood with high strength, water resistance, flame retardant and smoke suppression

To improve the properties and added value of Chinese fir wood, sodium silicate-modified Chinese fir wood (SSMCF) was prepared by respiratory impregnation method. Phenol formaldehyde oligomer-modified Chinese fir wood (PFOMCF) as control sample, the impregnation and reinforcement effects, water resistance of PFOMCF and SSMCF were compared. The results showed that the weight percentage gain, density growth rate, bending strength, compressive strength, and dimensional stability of SSMCF were clearly higher than those of PFOMCF, and the SSMCF showed a lower water absorption rate within 60 h. The impregnation and reinforcement effects, for SSMCF were better than those for PFOMCF. FT-IR, XRD, CONE, and TGA examinations were used to analyze the chemical structure, crystalline structure, flame retardancy, and heat resistance of these modified woods. The results indicated that SiOSi chemical bonding with high bond energy was formed in SSMCF, and there are possessed more hydrogen bonds in SSMCF than PFOMCF and that SiOSi chemical bonding with high bond energy was formed. Meanwhile, the weakened degree of the diffraction peak of SSMCF was much less than that of PFOMCF. These results explained the better mechanical properties and water resistance of SSMCF. Compared with PFOMCF, SSMCF had lower heat release rate (HRR), peak-HRR, mean-HRR, total heat release, smoke production rate, and total smoke production, and showed higher thermal decomposition temperature and residual rate. Inorganic sodium silicate was shown to be a better flame retardant, while SSMCF had good smoke suppression effects, thermal stability, and safety performance in the case of fire.