Molecular structure and orientation of gel‐spun polyethylene fibers

Abstract

Characterization of molecular structure and orientation of six commercially available gel-spun polyethylene fibers have been carried out using infra-red and Raman spectroscopy, thermal and X-ray diffraction analysis, together with optical microscopy techniques. Thermal and X-ray diffraction analysis revealed the existence of highly oriented orthorhombic and monoclinic crystallites together with a highly oriented intermediate phase known as pseudohexagonal mesophase structure. The results suggest the existence of a three-phase structure consisting, at room temperature, of orthorhombic and monoclinic polymorphic crystallites, oriented noncrystalline and un-oriented noncrystalline (amorphous) phases, respectively. The crystallinity measurements have been carried out using density, thermal and X-ray diffraction analysis together with infra-red and Raman spectroscopy techniques whereas the molecular orientation measurements have been carried out using birefringence and polarized IR spectroscopy, respectively. The results obtained from density, thermal analysis, and Raman spectroscopy based on a simple two-phase modeling approach lead to the overestimated amorphous fractions and appears to ignore the presence of an intermediate phase known as oriented noncrystalline structure. X-ray analysis has also been used for the measurement of the apparent crystallite sizes. The birefringence values have been used to determine the overall orientation parameters whereas the dichroic measurements of IR bands have been used to determine the crystalline and oriented noncrystalline orientation parameters. The results show that the orthorhombic and monoclinic phases are more highly oriented than the oriented pseudohexagonally packed noncrystalline chains.

Influence of Crystal Thickness and Topological Constraints on Chain Diffusion in Linear Polyethylene

“…thickness L 0 %12 nm, the annealed sample with L 0 %24 nm as determined by small-angle X-ray scattering, longitudinal acoustic mode Raman spectroscopy as well as transmission electron microscopy, [5] and a solution spun Dyneema 1 fibre with extended crystalline regions. [12] For the annealed sample in the solid state, it is stated that topological constraints due to entanglements in the noncrystalline regions do not change, provided there is no change in the draw ratio. [13] The decay of the crystalline signal in these samples is displayed in Figure 2 and compared to a hypothetic exponential decay of the 13 C magnetization due to T 1 relaxation with T 1 ¼ 1 500 s. As noted before, [10,14] the data do not follow a relaxation curve.…”

The influence of annealing treatment on the molecular structure and the mechanical properties of isotactic polypropylene fibers

“…Characterization of crystallinity is usually carried out using density, 41 enthalpy of fusion through DSC, 42 X-ray diffraction, NMR, and vibrational spectroscopy (infra-red 43 and Raman 44 techniques), whereas the orientation is usually characterized using polarized infrared 45 and Raman spectroscopy, 46 X-ray diffraction 45 and optical birefringence measurements. 47 These methods provide information at different levels, with their own limitations and advantages. For example, the use of optical birefringence provides an average molecular orientation of crystalline and amorphous phase in terms of the second order orientation averages, whereas X-ray diffraction is only accessible to paracrystalline and crystalline phases and can not detect the presence of totally disordered amorphous phase.…”

Amorphous orientation and its relationship to processing stages of blended polypropylene/polyethylene fibers

“…For each sample, every scan was resolved into its crystalline and amorphous peaks. The number and initial position of the peaks were assigned according to those found in the literature 26–28. The full diffraction pattern of each sample contained 11 crystalline Bragg reflections and two amorphous reflections.…”