Macromolecular order in spin‐oriented nylon 6 (polycaproamide) fibers

Abstract Wide‐angle x‐ray scattering (WAXS) has been used to characterize the ordered phases of spin‐oriented nylon 6 fibers wound at speeds ranging from 5000 to 8000 m/min. Quantitative analysis of the radial diffractometer scans by a computerized curve‐fitting procedure reveals that the unit‐cell geometry of both the α and γ crystalline morphologies are highly dependent on winding speed and on annealing conditions. At 800° m/min, there is a particularly large reduction in the intermolecular distance along the van der Waals forces of the α unit cell, which is accompanied by substantial crystal growth in the hydrogen‐bond direction. Similar increases in the width and perfection of the α crystals result from water annealing and steam treatment. The perfection of the γ crystals increases with winding speed and after annealing in water, but steam treatment increases the intermolecular distance along the hydrogen bonds while reducing it along the van der Waals forces. Using bulk density measurements and the experimentally determined crystalline density p c for each sample, the volume‐fraction crystallinity (VFC) is shown to pass through a maximum at ca. 6500 m/min. This maximum arises from a decrease in α crystallinity with increasing winding speed together with an increase in γ crystallinity, which levels off above ca. 7000 m/min. It is demonstrated that the determination of VFC assuming constants p c would lead to large errors. The orientation of the α crystals is found to be much less than that of the γ crystals, but it increases quite rapidly with winding speed. Water and steam treatments cause increases in α orientation and decreases in γ orientation.