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 investigated in the natural wood cell of Picea abies. Using the technique of small-angle X-ray scattering (SAXS), it was possible to investigate the same specimens at different degrees of hydration, x, in a nondestructive way, which allowed us to separate the scattering from pores from 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 function describing the relative arrangement of the cellulose fibrils was obtained for the native cell wall. It was in quantitative agreement with the prediction from a hard-disk model with packing density 0.3, corresponding to a typical spacing between fibril centers of about 40 Angstrom.