Haruhiko Yamaguchi

Low molecular weight silicic acid – inorganic compound complex as wood preservative

Abstract A new wood preservative containing low molecular weight and low-toxicity silicic acid (LWSA) was investigated. To prevent environmental pollution with the wood preservative, a silicic acid monomer aqueous solution (SAMS) or colloidal silicic acid solution (CSAS) was combined with various metal compounds or boric acid. Agents where SAMS or CSAS was combined with boric acid gave good protection against decay caused by the brown-rot fungus Fomitopsispalustris, the treated wood (Cryptomera japonica D. Don) specimens after the leaching test maintained a high resistance to decay. The leaching and decay tests revealed high quantities of chemicals leaching from wood treated with SAMS-metal agents. However, when wood was treated with SAMS-boric acid, there was little leaching of agent in either test. The mechanism of resistance of wood, which was treated with boric acid mixed with CSAS or SAMS, to the brown-rot fungus F. palustris were investigated. When the concentration of boric acid was high, mycelial growth was inhibited completely and no protein production was detected. When the amount of boric acid was low, the xylanase, mannase and cellulase activities were lower than with control wood powder. When powdery boric acid was combined with CSAS, it was considered that the treated woods have higher anti-weather properties than when boric acid-methanol solution was mixed with CSAS. The agent-preparation method adopted should be considered carefully after taking the treatment process and the intended use of the preservative-treated wood into account.

Influence of tannin-copper complexes as preservatives for wood on mechanism of decomposition by brown-rot fungus Fomitopsis palustris

Summary The mechanism of preservation by chemically modified tannin and tannin-ammonia-copper agents was examined. Wood decay by F. palustris was markedly suppressed by processing wood with agents made by mixing chemically modified tannins with ammonia and cupric chloride. When wood powder was treated with these agents, mycelial growth and generated protein increased to some extent. The preservative effects of the chemically modified tannins (RMT and CMT) or compound agents composed of the tannins and ammonia-copper were considered to be due to inhibition of the activities of xylanase, mannase and Cx-cellulase. In the culture medium in which treated wood powder was brought in with these agents, drop of pH by oxalic acid, which F. palustris produces, is not generated. The potency of the effect was thought to be due to chelation of copper, an essential trace element for wood decay by F. palustris, by the tannin, and/or neutralization or suppression of oxalic acid production by ammonia-copper.

Termite resistance and wood-penetrability of chemically modified tannin and tannin-copper complexes as wood preservatives

We examined the ability of chemically modified tannin and tannin-copper complexes to penetrate wood and the ability of the treated wood to resist termites. Only the tannin-treated wood retained the agents after treatment. Wood with untreated mimosa tannin (MT) retained the least amount, followed by wood with resorcinolated tannin (RMT) and that with catecholated tannin (CMT). When RMT or CMT was mixed with ammonia-copper, the wood retained twice as much of these solutions as the MT -ammonia-copper solution. The degree of retention of RMT-NH3-Cu and CMT-NH3-Cu ranged from 268 to 326kg/m3. The solutions penetrated 2–13 mm from the tangential sections of the logs. We also measured the termite resistance conferred by these solutions. Most of the tannin-NH3-Cu solutions showed contact lethality for termites in the contact toxicity test. However, the termites were fed cellulose treated with those solutions and most survived the oral toxicity test (14 days). Moreover, these solutions reduced the amount of damage to the wood by termites. However, the mortality rate of the termites during the eating-damage test (>21 days) did not reach 100% for any of the solutions except for RMT. As a result of the field stake test with the same logs used for the penetrability test, the mass loss of wood treated with RMT or CMT alone or with RMT + NH3 + CuCl2, was about one-third to one-half that of the controls. Because these solutions have good wood penetrability and good termite resistance, they have potential use as low-toxicity wood preservatives.