HIGH SPEED MELT SPINNING OF NYLON 12

Abstract

Nylon 66 fibers have been produced by high speed melt spinning method in the range of take-up velocity 500 to 8, 000m/min. Physical properties of as-spun nylon 66 fibers strongly depend on the passage of time after spinning, as shown in the case of nylon 6. Fibers spun in the range of 500-3000m/min exhibit spontaneous elongation with the passage of time and those spun above 4, 000 m/min contract immediately after removal from the take-up bobbin. Fibers elongate during the time conditioning in the atmosphere, 25°C and RH=50%, for 24 hours and crystallization of the fibers can be easily induced by water, which can penetrate the fiber surface. Maximum elongation of the conditioned fibers is found at a take-up speed of ca. 2, 000m/min and contraction starts at 4, 000 m/min.Birefringence of the conditioned fibers largely increases with take-up speed up to 2, 000m/min but small changes in birefringence are found from this take-up speed onwards. On the other hand, an increase density of the fibers starts at the take-up speed of 3, 000m/min. At spinning speeds above 4, 000m/min, the fibers show a definitive x-ray crystalline diffraction pattern and are constructed with well developed fiber structure based on high crystalline orientation, high crystalline perfection and large crystallite sizes. In such fiber structure, amorphous chains are stretched and frozen between the lamellar crystals. The stretched molecules, taut tie molecules, cause a superheating behavior on DSC thermogram and strongly affect mechanical properties.Fibers spun at speeds below 3, 000m/min exhibit spontaneous increase in tenacity and Young's modulus but they show levelling-off in the range of 3, 000-5, 000m/min and then increase again from these spinning speeds onwards. On annealing, Young's modulus of the fibers spun at take-up speeds above 4, 000-5, 000m/min decrease. This is caused by relaxation of the constrained molecules. On the other hand, an increase in Young's modulus is observed when fibers spun at speeds below 4, 000-5, 000m/min are annealed. This is attributed to the effect of increasing crystallinity which compensates that of relaxation of the oriented molecules.