Dynamics of the effective capillary cross-sectional area during the alkaline impregnation of eucalyptus wood

Wood diffusion is strongly affected by the effective capillary cross-sectional area (ECCSA), which is the area of paths available for diffusion. The ECCSA varies dynamically according to the conditions and progress of the alkaline action. The alkali diffusion in natural wood is a complex process in the course of which the local transport properties are modified by chemical reactions and swelling. A method was developed which allows the fast determination of ECCSA as a result of the dynamic process. It is based on measurements of the relative electrical conductivity through thin wood slices. It is assumed that restrictions in diffusion of thin slices can be neglected regardless of alkali action. The evolution of ECCSA was determined in transverse directions of eucalyptus wood. The influence of temperature, alkali concentration and time was established. As demonstrated earlier, alkalinity had a strong effect on the ECCSA at room temperature, which is dramatically increased when the pH is elevated from 12.5 to 13.5. At high temperatures, the steep increase in the ECCSA appears at pH 10.5. It was also demonstrated that the degree of the chemical action - indicated by the deacetylation level - is also very relevant, being even higher than the temperature effect.