Copper precipitation of Cu-monoethanolamine preservative in wood

Copper precipitation is one of the important Cu fixation mechanisms of Cu-amine-treated wood. In the present work, possible pathways of Cu precipitation have been investigated via in vitro and in situ studies focusing on effects of pH and temperature and Cu species formed in Cu-monoethanolamine (Cu-Mea)-treated wood. Higher-concentration Cu-Mea solutions required a lower pH and higher amounts of acid for the precipitation because of the higher amount of free Mea in the preservative-wood system. For this reason, Cu fixation during wet conditioning of wood treated to high Cu retention (2.0% treating solution) resulted in only a slight pH decrease and low Cu fixation. When lower-concentration solutions (0.67% and 0.2%) were applied, the pH decreased enough for Cu precipitation, and the much higher Cu fixation rate was driven by both chemisorption and precipitation. Evaluation of leaching after wet conditioning and drying showed that additional Cu precipitation could occur during drying. Wet conditioning of Cu-Mea-treated wood at 50°C showed outwardly faster and higher Cu fixation, but resulted in higher Cu leaching. According to X-ray diffraction analysis, the in vitro precipitated Cu was a mixture of azurite and malachite, and possibly, Cu2O formed as a result of Cu-Mea decomposition.