DIFFUSION OF COPPER IN WOOD CELL-WALLS FOLLOWING VACUUM TREATMENT

The rate and extent of copper redistribution in the wood structure of red pine (Pinus resinosa Ait.) and trembling aspen (Populus tremuloide s Michx.) sapwood samples vacuum-treated with alkaline copper solution s were monitored using an expressing technique. Diffusion coefficients (D) for copper movement into the cell-wall substrate were determined from the rate of change of copper concentration in the cell lumens, us ing a finite bath model for unsteady state Fickian diffusion. D values were in the range of 0.1-165 X 10(-10) cm(2)/s, depending on the wood species and treating conditions. These D values are about 1/10 to 1/1 0,000 those for bound water diffusion. Equalization times were much lo nger for aspen than for red pine, partly as a result of the greater av erage diffusion distances in aspen; however, estimated D values were m ore than 100 times lower for aspen even with correction for the differ ent diffusion path lengths. There was no significant species effect on the concentration of copper in the cell walls at equilibrium. Dependi ng on the solution pH, the cell walls retained from 2 to 4 mg Cu per g dry wood with higher retentions for high pH treatments. The rate of d iffusion increased with temperature, while wood moisture content had n o consistent effect, ammoniacal and monoethanolamine copper solutions at similar initial pH had similar rates of copper diffusion and equili brium adsorption. Arsenate anions formulated with copper in ammoniacal copper arsenate solutions were initially excluded from the cell-wall substrate but eventually penetrated into the cell wall, but to a lesse r degree than copper.