Interpretation of microfibril angle distributions in wood using microdiffraction experiments on single cells

Partially crystalline cellulose microfibrils are wound helically around the longitudinal axis of the wood cell. Microfibril angle distributions were determined using x-rays from single cells and slices of wood. Differences in results are discussed using model calculations, which are based on diffraction conditions. Microfibril angle distributions (MFA) in single wood cells were measured through a bordered pit using microbeam produced by capillary optics and synchrotron radiation. For all cells measured, the MFA distribution was asymmetric and narrow with full-width at half-maximum around 18 degrees. The mean MFA distributions of slices of wood were determined using a conventional sealed x-ray tube. MFA distributions of single cells differed from those determined from slices of wood. On the basis of model calculations the differences were attributed to the variation in MFA distributions of different cells of the wood sample, in the orientation of the cells, and in the cross-sectional shape of the cells. These factors are hard to take into account in data analysis, thus microdiffraction experiments offer a unique means for studies of the detailed structure of single wood cells.