CRYSTAL AND MOLECULAR DEFORMATION IN STRAINED HIGH-PERFORMANCE POLYETHYLENE FIBERS STUDIED BY WIDE-ANGLE X-RAY-SCATTERING AND RAMAN-SPECTROSCOPY

Wide-angle x-ray scattering (WAXS) and Raman spectroscopic data show that on both the crystal and molecular levels, a bimodal stress distribution exists in strained high-performance polyethylene fibers. In part of the crystalline PE the microscopic strain level is high (ca. 70% of macroscopic strain); in the remainder, the microscopic strain level is low (independent of macroscopic strain, ca. 0.4%). During stress relaxation the fraction of highly strained PE decreases with time. WAXS revealed no indication of a change in the a and b unit-cell dimensions. Furthermore, no indications for stress-induced formation of monoclinic and/or hexagonal PE and for crystal breaking were found. From the latter it can be deduced that all chains within one crystal are equally strained. The WAXS results are used to calibrate the stress-induced frequency shifts of Raman bands.