Decreasing the leachibility of boron wood preservatives

Abstract

The use of boron in wood preservatives has been growing since the 1930s, primarily in various boric acid/borax mixtures. Boron preservatives have several advantages for application as wood preservatives including a broad spectrum of activity against insects and fungi, low mammalian toxicity, low volatility, and cost effectiveness. In addition, they are colorless, odorless and non-corrosive and nonflammable with favorable effects on wood's fire resistance. Boron treatment of wood provides excellent protection for aidoveground uses. However, boron treatment by itself has not been found to give adequate protection when wood is used in ground contact because of its leaching problem. This research examined the potential for decreasing the leachability of boron preservatives using water repellents. Southern pine (Pinus spp.) test samples were impregnated with several types and at different concentrations of borax/boric acid and PEG (Polyethylene glycol) mixture. Leachability performance of these treating solutions was determined. It was found that wood samples treated with boric acid or borax and then treated with PEG-400 or PEG-600 by double treatment method showed a significant increase in their water repellency and resistance to boron leaching. Protection performance of these treating solutions on native wood was also determined by soil-block and agar-block test methods. Weight loss by Lentinus lepideus and Poria monticola fungi and toxic threshold retention point for each treatment solution and biological test method were determined. The type of soil effect on the soil-block test was determined. It was found that it does not appear to be sufficient to choose soils only on the basis of waterholding capacity, pH, and weight as indicated by the ASTM standards. The results found in this research will serve their purpose as far as they are made use of in the wood preservation industry.