Eco-friendly preparation of high-quality mineralized wood via thermal modification induced silica sol penetration

Application of wood as a green and sustainable material is restricted due to its easy wrapping property, deformation, biological degradation and thermal instability. Coupling thermal treatment and silica sol penetration could overcome the weakness of natural wood, and synergistically improve the overall performance. Thermal treatment showed a significant effect on hydrophobicity, hygroscopicity, surface color and compressive strength. It reduced the compressive strength to some extent due to the degradation of cell wall polymers (hemicellulose, lignin and cellulose). At above 200 ℃, the degradation of cell wall polymers, rather than hornification, was in the leading position, dominating the compressive strength. Changes in the component and structure of cell walls (chemical and physical environment) helped the penetration and deposition of silica sol owing to extra channels and enlarged pore size. Satisfied silica sol incorporation in thermally treated wood further improved the surface hydrophobicity, dimensional stability, surface hardness, and compensated the reduction on compressive strength. It was attributed to the -OH consumption (cell wall polymers degradation) and filling effect caused by silica sol networks (Si-O-Si and Si-O-C bonds) in wood. The improved thermal stability was ascribed to the coverage effect of silica sol on the inner-surfaces of wood, which could be treated as a physical barrier to prevent heat conduction. Eventually, we proposed a mechanism concerning the combination treatment for preparing silica-mineralized wood. This work opens an eco-friendly way to produce bio-based materials with high quality to be used in outdoor applications or humid environments.