Fine-structure and physical properties of polyethylene fibers in high-speed spinning. I. Effect of melt-flow rate in the high-density polyethylene

High-density polyethylene (HDPE) fibers, obtained from a melt-flow rate (g/10 min) of II and 28, was produced by a high-speed melt-spinning method in the range of take-up velocity from I to 8 km/min and from 1 to 6 km/min, respectively. The change of 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. With an increase in take-up velocity, the birefringence showed a sigmoidal increase, which has distinct changes in the range of 1-5 km/min. Throughout the whole take-up velocities, the birefringence of HDPE(11) was higher than that of HDPE(28). With increasing take-up velocity, the crystalline orientation was transformed from a-axis orientation to c-axis orientation. These crystalline relaxations are confirmed by the tan 6 peak of high-speed spun HDPE fibers. The intensity of the crystalline relaxation peak decreases with increasing take-up velocity in both HDPE(11) and HDPE(28). As above, the crystalline relaxation peaks shift to lower temperature with increasing take-up velocity. With increasing take-up velocity, the ultimate strain decreases while both specific stress and the initial modulus increase. The mechanical behavior may be closely related to, as investigated by birefringence, orientation of the amorphous region, etc., the take-up velocity. (C) 2000 John Wiley & Sons, Inc.