Direct evidence of radial and tangential morphology of high‐modulus aromatic polyamide fibres

SUMMARY Previous work, at foreign laboratories, essentially based on electron microscopy of longitudinal sections, has suggested a radial morphology for the aromatic poly‐amide high modulus fibres; the present paper gives direct evidence of such a morphology, thanks to a special preparation technique which allows a great improvement in the quality of the cross‐sections of these fibres. This is demonstrated for both a commercial ‘Du Pont de Nemours’ yarn sample ‘Kevlar 29’, and an experimental high modulus aramid RPT (Rhǒne Poulenc Textile) yarn. In the first case, Ag 2 S insertion technique was used and permitted one to see, on the cross‐sections, an alternation of dark and clear radial bands, again with a tendency towards tangential splitting. In the second case the fibres were included into an amorphous polymer, a sample preparation technique which greatly enhances the quality of the cross‐sections; optical microscopy showed the radial morphology fairly well; dark‐field transmission electron microscopy—using the equatorial doublet of the electron diffraction pattern—allowed satisfactory resolution: both the radial, and occasionally the tangential, splitting, and the size of the cross‐sectioned crystallites were easily revealed: these crystallites appear as isodiametric bright particles c. 15 nm in lateral size.