HYDRATION DEPENDENCE OF THE WOOD-CELL WALL STRUCTURE IN PICEA-ABIES -A SMALL-ANGLE X-RAY-SCATTERING STUDY

Hydration dependent structural changes at the nanometer level were inv estigated in the natural wood cell of Picea abies. Using the technique of small-angle X-ray scattering (SAXS), it was possible to investigat e the same specimens at different degrees of hydration, x, in a nondes tructive way, which allowed us to separate the scattering from pores f rom the scattering of the cell wall itself. For specimens dried below the fiber saturation point, x(F), the scattering from pores and other cavities dominated and considerable changes of the cell-wall structure occurred. In the native state (for x > x(F)), however, the structure of the cell wall was independent of the hydration. The structure funct ion describing the relative arrangement of the cellulose fibrils was o btained for the native cell wall. It was in quantitative agreement wit h the prediction from a hard-disk model with packing density 0.3, corr esponding to a typical spacing between fibril centers of about 40 Angs trom.