EFFECTS OF LEACHING MEDIUM ON LEACHABILITY OF WOOD PRESERVING N ' N-HYDROXYNAPTHALIMIDE (NHA)

Abstract

Laboratory leaching test procedures usually call for the use of distilled or deionized water; however, treated wood is generally exposed to different types of water, soil, and weather conditions. Thus, factors such as salinity, hardness, pH, temperature etc. might be important in the release of different amounts of biocide compounds. This study evaluates the release of the sodium salt of the calcium precipitating and wood preserving agent N'N-hydroxynapthalimide (NHA) from treated wood specimens exposed to different types of leaching media. Scots pine wood specimens were treated with NHA at three different solution strengths. Treated specimens were then leached with distilled water, tap water, rain water, synthetic sea water, natural sparkling water, or 1% CaCO3 solutions for 2 weeks. Leaching with higher ion concentrations reduced NHA losses from the specimens in comparison with that of distilled water and rain water leaching trials. Microscopic evaluations were in good accordance with the results from leaching trials, revealing NHA precipitation onto the tori of pit elements and tracheids. In distilled water and rain water leaching trials, less NHA precipitation on to the tori of pit membranes and tracheid surfaces was observed, whilst the specimens leached with tap water, 1% CaCO3, sea water, and sparkling water showed higher NHA precipitations on the cell elements. We conclude that the leaching of NHA from treated wood can be decreased by precipitation with ions coming from tap water, sea water, sparkling water, and 1% CaCO3 solutions as leaching media rather than distilled water or rain water with no or much less ion composition.