Topochemistry on the Property Enhancement of Wood with Inorganic Materials

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From our study on wood-inorganic composites by the sol-gel process, SiO_2 wood-inorganic composites from tetraethoxysilane (TEOS) were found to be enhanced in dimensional stability, fire-resistance and so on. To improve their properties further, multicomponent SiO_2-P_2O_5-B_2O_3) wood-inorganic composites were studied in a reaction system of TEOS/EtOH/acetic acid to which trimethylphosphite (TMP) and trimethylborate (TMB) were added. Obtained SiO_2-P_2O_5-B_2O_3 composites were superior in fire-resistance. However, (1) P_2O_5 and B_2O_3 gels are not stable against weathering and (2) TMP is not acceptable in terms of safety in environment for its production due to its offensive oder. For the problem of (1) , HFOETMOS (2-heptafluorooctylethyltrimethoxysilane) was added in a small quantity to the reaction system (1/2,000 in the molar ratio to TEOS). Concomitantly, water-repellent property was added to prevent the composites from a leaching of P_2O_5 and B_2O_3 gels. Furthermore. for (2) … More , silicon alkoxide oligomers instead of TEOS to which TMP and TMB were hydrolized and condensed, were used for preparing SiO_2-P_2O_5-B_2O_3 composites. By doing so, the production environment was improved. Additionally, this modified oligomers are so stable due to covalent bonds among Si, P,and B components that obtained SiO_2-P_2O_5-B_2O_3 gels were resistant against their leaching, and very effective for fire-resistance of wood. SiO_2 wood-inorganic composites prepared from the above reaction system to which phosphorus-containing fire-resistant agents and a small amount of HFOETMOS were added, also revealed antileachability and high fire-resistance of wood.On TiO_2 wood-inorganic composites, composites with various types of TiO_2 distribution were prepared from titanium alkoxides and titanium chelates. Among tem, TiO_2 composites in which TiO_2 gels are distributed only within the cell walls were found to be enhanced in dimensional stability and fire-resistance, indicating that the topochemical effects exist on the property-enhancement of wood. Less