Silicic acid/boric acid complexes as ecologically friendly wood preservatives
2005
Yamaguchi, H.
We report a new method for fixing boric acid - a known preservative - in wood. We treated wood with boric acid and colloidal silicic acid solutions (CSAS) or with boric acid and silicic acid monomer solutions (SAMS), and tested for resistance to brown-rot fungus (Fomitopsis palustris) damage, fire resistance, and termite resistance. We also explored the mechanisms by which these compounds prevented fungal damage. Wood treated with a mixture of silicic acid and boric acid showed great resistance to F. palustris decay. At sufficiently high boric acid concentrations, mycelial growth was inhibited completely. If wood was treated only with the silicic acid compounds or only with boric acid and then leached prior to F. palustris exposure, no protection was conferred. When wood was fixed with CSAS, the post-burner combustion time shortened remarkably. After-flaming combustion time was shortened further by addition of borate to CSAS. After-glowing combustion times were similar to those found for after-flaming combustion times. Wood stakes treated with CSAS-boric acid were left in a termite-infested field for 3 years. After 3 years, most of the treated stakes were undamaged, while the control stakes had been eaten by termites. High concentrations of boric acid completely inhibited termite damage. The impregnation procedure required only a single injection of silicic acid/boric acid and conversion of the mixture to a non-leachable solid substance occurred at room temperature. Therefore, silicic acid/boric acid mixtures have great potential as wood preservatives protecting against weather, fire, and termite damage.
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