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

Abstract

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.

Wood capillarity and deacetylation during eucalyptus alkaline impregnation. Sulphidity effects and comparison between transverse directions

“…As ECCSA A seems to have the same relation for any temperature and pH, it can be considered that the acetyl group content is the determinant for the ECCSA A . This fi nding is in agreement with the previous results (Inalbon and Zanuttini 2008 ), for which, less variables were available.…”

“…For the determination of the ECCSA, a laboratory conductivity cell and an especially designed frame were used (Inalbon and Zanuttini 2008 ). In the procedure, the wood slice is mounted to the frame to keep it fl at and equidistant from the electrodes.…”

“…In a previous work, an enhanced method was described which allows following the evolution of ECCSA of wood while it is under the action of an alkaline treatment. For eucalyptus wood, ECCSA dependence on alkalinity, temperature and chemical reaction degree has been experimentally determined (Inalbon and Zanuttini 2008 ).…”

Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose

“…Introducing cracks to chips may also shorten the transportation path of cooking chemicals with all the beneficial effects (Sainio 2000). The diffusion rate of chemicals increases with increasing temperature (Inalbon and Zanuttini 2008). The viscosity of the impregnation liquor decreases at higher temperatures, which contributes to the impregnation efficiency.…”

Profiles of alkali concentration and galactoglucomannan degradation in kraft impregnation of Scots pine wood: Experimental observations and modeling

“…It was shown that the ECCSAvalue is not reduced when alkali is removed by washing. As discussed in previous studies, for eucalyptus wood, it depends on the deacetylation degree (Inalbon and Zanuttini 2008) and for pine wood, it depends on both the deacetylation and GGM degradation degree .…”