The applicability of colloidal silica for producing a wood-mineral composite by impregnation was investigated, and its properties such as dimensional stability and decay and fire resistances were evaluated.
The colloidal silica solution was prepared by mixing silicic acid anhydride (30.4%), boric acid, and chitosan with a low molecular weight (0.3%). Instead of boric acid, metal ions of Cu, Ag, or Ti (1000ppm) were added to the solution. The solution was diffusion-penetrated into the water-saturated specimens of Sugi (Cryptomeria japonica D. Don), followed by drying to solidify the colloidal silica for a combination. The formation of silicic acid gel in the composites made by using the colloidal silica solution system was proved to be mostly insoluble.
The composites showed an antiswelling efficiency with the greatest value of 23% due to the bulking effect despite being hygroscopic and a good reduction in water absorptivity. Also, the composites, particularly those by using the colloidal silica-boric acid system, were found to improve greatly the decay and fire resistances.
For practical use, the composites were manufactured with boards of yellow poplar (Liriodendron tulipifera L.) applying the colloidal silica-boric acid system. They showed the enhancement of bending strength and modulus of elasticity to some extent of apparent weight percent gains. The absorbed energy in impact bending became greater than that of the untreated wood.
