Melt spinning of continuous filaments by cold air attenuation
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Traditionally ultrafine fibers below 1 dpf are produced by extrusion followed by mechanical drawing. A modified melt spinning apparatus with high-speed air nozzle was designed and fabricated to produce continuous polypropylene filaments by cold air drawing only. With this setup, the fiber is quenched and simultaneously attenuated by a symmetric cold air jet. Since the formation of fiber structure is highly dependent on the processing conditions, the new process will provide a unique operation window to study fiber attenuation and structural formation under high-speed cold air drawing. Based on computational fluid dynamics simulation results, a parametric study was carried out under different process conditions which include processing temperature, air velocity and polymer volume flow rate. Effects of changes in processing variables on the fiber diameter, molecular orientation, crystallinity, tensile strength and other properties were studied. Furthermore, a theoretical model was developed to analyze the non-isothermal fiber attenuation mechanisms. The new knowledge obtained in this study would likely yield a new process for producing innovative fiber products.