Microstructural investigation of high-speed melt-spun nylon 6 fibers produced with variable spinning speeds

The structural details of high-speed melt-spun nylon 6 fibers at spinning s peeds ranging from 4500 to 6100 m/min were investigated by solid-state prot on nuclear magnetic resonance (H-1 NMR) spectroscopy, density and birefring ence measurements, differential scanning calorimetry (DSC), and X-ray diffr action (XRD). The analyses of the proton spin-lattice relaxation times in t he rotating frame and correlation times confirmed the existence of three di fferent phases, the immobile crystalline, intermediate rigid amorphous, and mobile amorphous regions, in the fiber sample. At spinning speeds lower th an 5200 m/min, the portion of the crystalline phase increased at the expens e of the rigid amorphous region and then reached a plateau afterward, from which the mobile amorphous portion increased. Combined analyses of density and birefringence measurements, DSC, and XRD in conjunction with NMR result s indicated that the formation of the gamma crystal became predominant comp ared to that of the ct crystal. The orientation factor of the crystalline p hase increased slightly with increasing spinning speed, whereas the amorpho us orientation factor decreased because of the increase of the purely amorp hous region. (C) 2000 John Wiley & Sons, Inc.