Kinetics and mechanism of fixation of Cu-Cr-As wood preservatives. Part 5: Effect of wood species and preservative composition on the leaching during storage
Conversion reactions during storage of CCA treated wood take place even at and below the fiber saturation point as long as ion transport is possible. Increase in drying temperature increases the final pH of the treated wood and the leachability of Cu and decreases slightly the leachability of Cr, while the leachability of As is not affected. This temperature effect is considered to be of no technical importance, but may be of importance when preparing material for biological testing. The length of the wet fixation period before the drying does not influence the results. The presence of alkali sulfates in some preservatives affects the pH of the unleached wood but not the leachability of the active elements. The natural pH of the wood determines to a considerable extent the final pH and the leachability. A correlation was established between the leachability of Cu and As versus the final pH in wood. When treated with 2-2.5% preservative solutions some wood species: Douglas fir, Ponderosa pine and to a lesser degree Southern yellow pine, showed unexpectedly high As leachability, while on doubling the concentration normal leachability data were obtained. The study included three commercial CCA preservatives: Boliden K33, Celcure AP and Tanalith C, and one experimental variety of Celcure AP without sodium sulfate.