ケイ酸塩を用いた木材の無機質複合化 第４報 水ガラス‐ホウ素化合物系による無機質複合体の接着性と難燃性

Abstract

The glueability and fire resistance of wood-mineral composites were investigated, which were made by introducing inorganic substances into wood (buna) veneer using the water glass (sodium silicate)-boron compound system (double treatment). The composites were also made with boron compounds alone (single treatment), and two-ply plywoods were prepared by bonding with a phenol-resorcinol resin adhesive. Dry gluejoint strength was determined by tensile-shear test, and fire resistance was evaluated by burning test using a microburner.The glue-joint strength was reduced by both single and double treatments in comparison with the untreated wood, and the values for the double treatment were 44% to 65% of the value for the untreated wood. Besides the bulking of the composites and the deterioration resulting from soaking in an alkaline solution, the lessening of a mechanical anchoring effect was considered to be one of the main reasons for the reduction of glue-joint strength by combination of wood and mineral. There was a negative correlation between glue-joint strength and weight percent gain; the strength reduced linearly with an increase in weight percent gain.The wood-mineral composites showed a good wettability, but it did not contribute to enhance the bonding strength because there was a tendency for the bonding strength to reduce with an increase in contact angles (cosθ). However, the high values of wood failure indicate that the wood-mineral composites have a sufficiently good glueability for practical use in spite of the reduction of bonding strength.Plywoods prepared from wood-mineral composites had heat-resisting and flame-resisting effects of the single and double treatments. Particularly, the double treatments with boron trioxide, ammonium borate, and boric acid were confirmed to show an excellent fire-resistance effect.