Crystallinity and crystallite size measurement in polyamide and polyester fibres

X-ray diffraction methods for evaluating crystallinity and crystallite size in fibres generally neglect the possibility of peak overlap, and separate peaks and background by arbitrary procedures. The method described here is based on the resolution of normalized diffraction peaks in terms of combined Gaussian-Cauchy profiles for each peak, together with a polynomial background. Peak area crystallinity is then measured as the total area under the resolved peaks over a defined range. Measurements of apparent crystallite size are obtained from the widths of the resolved peaks. Application of this method to high tenacity nylon-6, nylon-6,6, and PET fibres after annealing, indicates that peak area crystallinity is about 100% for the polyamides and 85% for the polyester. The increase in apparent crystallite size is considered to be due to both an increase in the true mean size and to improvements in local lattice order.