• Meylan, B.A.
  Physics and Engineering Laboratory, Lowe Hutt, New Zealand
  

The measurement of the mean microfibril angle (commonly called spiral angle) in a sample of wood can be determined quickly and easily using X-ray diffraction, in contrast to the use of direct methods that are very tedious.

A new method for making an objective estimate of the angle from the spread of the (002) arcs in the X-ray diffraction diagram is proposed. This is based on the shape of the intensity distribution and is independent of the peak intensity.

Using about 60 samples of Pinus radiata, covering a wide range of microfibril angles, the width of the arc as assessed by this method is compared with the angle measured by a variety of direct methods. The relation between these, although not one-to-one, is highly linear and shows good agreement with the theoretical predictions of Cave (5). This relationship can be used to determine the mean microfibril angle with a very high degree of confidence.

It is commonly assumed that half the width of the (002) arc at 40 percent of its peak height is equal to the mean microfibril angle. The relation between these two, however, is shown to be nonlinear and the assumption that they are equal leads to quite large errors at large microfibril angles.