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

Abstract

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 catalyst and a Ziegler–Natta catalyst, respectively, were produced by a high-speed melt-spinning method in the range of take-up velocity from 1 to 6 km/min. The change of the fiber structure and physical properties with increasing 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 take-up velocity and that of LLDPE(45) was higher than that of LLDPE(50). With increasing take-up velocity, the crystal orientation of LLDPE transformed the a-axis orientation into a c-axis orientation. In the dynamic viscoelastic 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 decreased with increasing take-up velocity. LLDPE(45) fibers were preferred to LLDPE(50) in mechanical properties owing to the increase of crystal and amorphous orientation factor. The change of birefringence with take-up velocity affected both the initial modulus and the tenacity uniformly. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1195–1206, 2000