SAXS Investigations on Uniaxially Drawn Fibers Obtained from Polyethylene Reactor Powder

The polyethylene powders studied were synthesized by both slurry and gas-phase processes at temperatures ranging between 30 and 85 °C. Fibers were drawn from these nascent powders under identical processing conditions. The maximum achievable draw ratio was found to be strongly dependent on synthesis conditions. Highest ductilities are obtained for samples synthesized by a slurry process at 85 °C. Small-angle X-ray scattering (SAXS) measurements were performed on fibers coextruded from reactor powders at a draw ratio of 6. No interferential effects were detected in the equatorial profiles. In contrast, the meridional SAXS patterns display interference peaks whose intensities bear definite relationships to both ductility and synthesis conditions. Fibers obtained from samples synthesized by a slurry process at 85 °C display a well-defined interference peak along the meridional direction. Fibers obtained from samples synthesized in the other conditions show only an ill-defined broad shoulder. Results of peak profile analysis show that higher peak intensities and larger peak widths are obtained for most ductile samples. According to the Peterlin model for draw, these trends are ascribed to different contents of taut tie molecules. Changes in the crystallization dynamics produced by different synthesis conditions are discussed for their effect on the amount of taut tie molecules.