Fine structure and physical properties of polyethylene fibers in high-speed spinning. II. Effect of catalyst systems in linear low-density polyethylene

Linear low-density polyethylene (LLDPE) fibers, obtained from the melt-flow rate (g/10 min) of 45 and 50, which were polymerized by a metallocene cata lyst and a Ziegler-Natta catalyst, respectively, were produced by a high-sp eed melt-spinning method in the range of take-up velocity from 1 to 6 km/mi n. The change of the fiber structure and physical properties with increasin g take-up velocity was investigated through birefringence, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), a Rheovibron, and a Fafegraph-M. The birefringence increased linearly with increasing ta ke-up velocity and that of LLDPE(45) was higher than that of LLDPE(SO). Wit h increasing take-up velocity, the crystal orientation of LLDPE transformed the a-axis orientation into a c-axis orientation. In the dynamic viscoelas tic behavior of LLDPE(45) fibers with high-speed spinning, the intensity of the crystalline relaxation peak was decreased and the temperature of that was shifted lower. But that of LLDPE(50) could not be observed. The tensile strength and initial modulus were increased and the elongation was decreas ed with increasing take-up velocity. LLDPE(45) fibers were preferred to LLD PE(50) in mechanical properties owing to the increase of crystal and amorph ous orientation factor. The change of birefringence with take-up velocity a ffected both the initial modulus and the tenacity uniformly. (C) 2000 John Wiley & Sons, Inc.