A real-time drawing study on solution-crystallized UHMW-polyethylene — comparison with conventional x-ray results

Abstract

Solution-crystallized ultra-high molecular weight polyethylene (UHMW-PE) can be drawn in the solid state to very high draw ratios, leading to materials with excellent mechanical properties. Very recently, the drawing process has been studied via different x-ray techniques, on the basis of which a deformation mechanism was proposed which could satisfactorily explain all observations. However, like most deformation studies performed in the past, the measuring conditions were quite different from the actual drawing conditions. Cooling drawn samples to room temperature as well as relieving the stretching force may give rise to the introduction of artefacts, leading to misinterpretation of the results. In order to exclude this possibility an x-ray study was performed on solutioncrystallized UHMW-PE in real time, i. e., duringthe deformation process, using the benefits of synchrotron facilities. Comparison of these results with x-ray results obtained via the conventional method shows that the latter method can be used without any problems for a qualitative study on the solid state drawing of ultradrawable UHMW-PE. One of the major advantages of the real-time method is the possibility to study the initial elastic deformation region.

13C Solid State NMR Characterization of Structure and Orientation Development in the Narrow and Broad Molar Mass Disentangled UHMWPE

“…Wide angle X-ray diffraction (WAXD) is widely used to determine chain orientation and crystallinity in the ultradrawn fibers due to its good resolution to detect the ordered structures. − However, partially ordered and disordered structures possess much smaller correlation length compared to the perfectly ordered structures making it difficult to monitor using WAXD technique. − Moreover, the information on spatial correlation of the observed structural components cannot be elucidated by WAXD, which hinders the understanding of stress transfer mechanism and its relation to the mechanical properties in the fibers. ,, In this work, solid-state NMR technique is used to reveal structural changes and orientation development during uniaxial deformation of the solution-cast films of the ultrahigh molecular weight polyethylenes (UHMW-PEs) having narrow and broad molar mass distribution. First, with the help of 13 C isotropic chemical shift in the 13 C spectra structural differences in the crystalline region such as orthorhombic, monoclinic, crystal defects induced on shearing of orthorhombic crystals, and in the noncrystalline region such as the mobile amorphous domains mainly away from the crystalline region and the rigid amorphous domains near the crystalline region, are identified.…”