TOPOCHEMISTRY OF SiO2 WOOD-INORGANIC COMPOSITES FOR ENHANCING WATER-REPELLENCY

Abstract

Methyltrimethoxysilane (MTMOS) was used to prepare the SiO2 wood-inorganic composites. To enhance the properties of these composites, 2-heptadecafluorooctylethyltrimethoxysilane (HFOETMOS) as a property enhancer was added to this reaction system for SiO2 wood-inorganic composites. To elucidate the mechanism for enhancing the water-repellent property in the HFOETMOS-SiO2 wood-inorganic composites, the composites with various weight percent gains (WPGs) were prepared, and the prepared composites with the lower WPG revealed the better property in water-repellency, whereas those with the higher WPG could not attain the high water-repellent property. SEM-EDXA analysis on these composites revealed that the HFOETMOS-derived residues were concentrated on the boundary between the cell wall and cell lumen in both composites with the lower and higher WPGs, while SiO2 gels were almost uniformly distributed within the cell walls in the composites with lower WPG. SiO2 gels in the composites with higher WPG were distributed in a similar manner but slightly higher in its concentration at the boundary between the cell wall and cell lumen. From these results, it was assumed that for the composites with lower WPG, the cell wall would be covered with the long hydrophobic alkyl residue of the HFOETMOS, whereas for the composites with higher WPG, SiO2 gels formed in the cell lumen would have prevented HFOETMOS-derived residues from being exposed uniformly over the surface of cell wall. This may be why the different water-repellent properties were shown between the composites with higher and lower WPGs. These results suggest that the topochemical effects of the SiO2 gels and HFOETMOS-derived residues exist for the enhancement of water-repellent property.