Wood-inorganic composites cells

However, the gels in this study must be treated under the temperature at which wood is not thermally degraded. Therefore, in a reaction medium of the metal alkoxide/alcohol (solvent)/acetic acid (catalyst), the moisture-conditioned wood or water-saturated wood is soaked at ambient temperature under reduced pressure or atmospheric pressure. The water present within the wood cells initiates the reaction of the hydrolysis and polycondensation of metal alkoxide. The soaked wood is subsequently treated at a temperature between 50 and 60 C for 24h, and at 105°C for another 24h to prepare wood-inorganic composites (Saka, 1992 Ogjso, 1993). 

A difference in the hydrolysis/polycondensation rate seems to result in the difference in the distribution of inorganic substances within the wood cells (Saka, 1993a). Evidence for this concept can be found in a study of Ti02 wood-inorganic composites prepared with titanium alkoxides and titanium chelates (Miyafuji, 1997). These agents have different rates of hydrolysis and polycondensation, and accordingly result in different distribution of TiOi gels in wood cells. 

Wood-inorganic material composites (WIC) have been developed in Japan [54]. A double-diffusion treatment of wood by two aqueous solutions of inorganic chemicals leads to the formation of water-insoluble deposits within the cell walls and voids. Water-impregnated wood was introduced into solutions (I and II) successively at 50°C for a desired period of time. Saturated aqueous solutions were prepared from (I) barium chloride plus a small amount of boric acid and (II) ammonium phosphate plus a small amount of boric... 

To develop wood with high function and remarkable properties such as dimensional stability, termite resistance, anti-microbial property, photostabihty and fire-resistance, we have tried to prepare inorganic composites ofwood without losing characteristic properties of the wood as seen in its porous structure. In spite ofthe same inorganic substances used, the observed properties are different if inorganic substances are distributed differently in the wood cells. 

Figure 27-1 shows the types of distribution of inorganic substances. Table 27-1 summarizes the results ofits distribution for different metal alkoxide/alcohol reaction systems. The moisture-conditioned specimens refer to wood with only bound water below the fiber saturation point therefore, water is distributed only within the cell walls. Water-saturated specimens have, however, free water in the cell cavities in addition to the bound water within the ceU walls. In this way, the use of these specimens with differently distributed water in the wood cells can make it possible to prepare wood composites with inorganic substances distributed differently (Saica, 1992, 1993a Ogiso, 1993). 

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