Quantitative Investigation of the X-Ray Diffraction Picture of Some Typical Rayon Specimens

The X-ray diffraction pictures of some typical specimens of highly orientated rayon are studied quantitatively using a dirfractometer technique with Geiger counter detection and strictly monochromatized radiation. The results allow of a more reliable separation between crystalline interferences and background than heretofore possible. The background of orientated rayons is aniso tropic and has a complicated intensity distribution. It has maxima at about 2θ = 21° on the equator and at about 2θ = 35° on the meridian. Evaluation of the intensities of the principal paratropic and diatropic interferences reveals about the same relative differences in crystallinity between the rayons investigated as those given by the method of crystallinity determination employed earlier. Absolute values of the crystalline fraction could not, however, be derived from the present work. The relative intensities of the principal crystalline interferences are measured and found to be in reasonable agreement with those calculated for the Andress lattice struc ture. Some typical deviations are specified. The crystallinity of tire cord rayon was found to be somewhat lower than that of textile rayon and the crystallites in the former somewhat smaller in lateral dimension according to measurements of line width. In the series of specimens investigated there is a correlation between crystallinity and line width. It seems that higher crystallinity tends to go parallel with larger or more perfectly ordered crystallites, a correlation which is also reported to have been observed in other polymers. It is shown that orientation derived from the azimuthal spread of either the diatropic or the paratropic interferences leads to equal results. This is in support of the method developed earlier for quantitative determination of orientation from the paratropic lines in simple exposures on flat film. The outcome of this kind of orientation measurement is but little, almost negligibly, affected by the error involved in assuming the background maximum to lie at the mini mum between the A ₀ and A ₃ peaks and thus at a lower angle and at a slightly higher intensity than the true values.