Microfibril angle variation by scanning x-ray diffractometry

The variation in microfibril angle (MFA) in an 18-year-old Eucalyptus nitens tree was determined by scanning x-ray diffractometry (XRD) on SilviScan-2. Radial MFA profiles were measured at 0.2 mm resolution for samples taken from eleven heights and the four cardinal directions (north, south, east, west). Maps of growth-ring-average density and MFA were produced, together with whole-tree distributions as a function of tree age. MFA, which varied by up to a factor of two within some growth rings, was inversely correlated with density at the local scale. The effect was particularly strong in the outerwood. A diffraction integration method for rapidly scanning increment cores was shown to give results consistent with those obtained at high resolution, and it was concluded that more than fifty cores could be processed per day at 10 mm resolution.