Nylon-12 fibers have been produced by high speed melt spinning method in the range of take-up velocity 500-6, 000m/min. Physical properties of as-spun nylon 12 fibers depended on the passage of time after spinning, but they did not change so much as in the cases of nylon 6 and nylon 66. Birefringence (
Δn) of the conditioned (in the atmosphere 25°C and 50% RH) fibers largely increased with take-up speed up to 2, 000m/min, and at above this take-up speed showed very small change. On the other hand, an increase in density (ρ) of the fibers started at the take-up speed of 3, 000m/min. The take-up speed dependence of
Δn and ρ were similar to those for nylon 6 and nylon 66. Wide-angle x-ray pattern of the conditioned fibers showed pseudohexagonal form. On annealing the fibers at 150°C, the reflections became sharp but the α and the γ type crystal modifications did not obtained. The different orders of the (0k0) reflections yielded different values. Its difference became large with a decrease of take-up speed. This is caused by the fact that the dimension of the crystallites along the chain direction is very small. In fact, the crystal sizes along the chain axis of the fibers spun at speeds below 2, 000m/min were formed with less than two monomeric units. The crystal sizes, the degree of lattice perfection, and melting point all increased with an increase of take-up speed. Young's modulus, tenacity and yield stress showed maxima at a take-up speed of 5, 000m/min. This is explained in terms of the heterogeneity in the cross section of the filaments. This heterogeneity also caused the decrease of amorphous orientation and the development of lower melting peak.
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