Some practical implications from recent research on the fixation of CCA preservatives
The mechanism of fixation of CCA preservatives is briefly described. If the temperature is increased during the primary fixation period, the formation of intermediate fixation compounds is less extensive. The length of the primary fixation period is of practical interest. It is determined by preservative composition and concentration, temperature and wood species. Diagrams are given for Pinus sylvestris. Light exposure and drying during the primary fixation period cause variability in colour intensity of CCA treated wood. Disproportionation of preservative elements with penetration depth is explained by the fixation mechanism. Conversion of intermediate fixation compounds into stable ones occurs even below the fibre saturation point, as long as the moisture ratio is sufficiently high to allow ion transport. Conversion reactions are very slow. A correlation was found between the final pH of treated timber and leachability in fresh water of copper and arsenic. The final pH depends on preservative composition and concentration, wood species and to some degree of drying and storage conditions. An electrolyte such as sodium sulfate does not affect the leachability. In saline waters leachability is increased by complex formation of Cu(II) and Cr(III) with chloride and hydroxide and the salt effect on activity coefficients. The leaching of arsenic is delayed.