Assessing Crystallite Orientation in PPTA Fibres: A Comparison of Yarn and Filament Scale using WAXS Measurements

Abstract. Wide-angle X-ray scattering (WAXS) is frequently used to characterize the structure of high-performance aramid fibres, with measurements commonly performed at the yarn level. However, the extent to which yarn structural parameters represent filament-level structure has not been systematically investigated. In this study, WAXS measurements were performed on four Twaron® aramid samples using laboratory-based yarn measurements and synchrotron-based filament measurements. Structural information was extracted from the 110 and 200 reflections through radial and azimuthal profiles of the scattering patterns. Azimuthal full width half maximum (FWHM), φ values exhibited highly consistent trends across the sample series. Strong linear relationships were obtained between yarn and filament derived φ values, yielding coefficients of determination (R2) of 0.987 for both 110 and 200 reflectionsh, documenting that orientation distributions derived from yarn measurements are a reliable estimate of the true crystallite orientations. Furthermore, yarn and filament derived orientation parameters showed comparable relationships with normalized breaking tenacity, chord modulus and elongation at break. These results demonstrate that yarn-based WAXS measurements preserve the relative structural differences and structure-property relationships observed at the filament level, supporting their use for comparative characterization of aramid materials.