Brigitte Hartmann

Remote Structural Correlation in the Sequence Reactor Powder–Gel–Fiber in Polyethylenes

A series of gels originated from ultra-high-molecular-weight polyethylene reactor powders, differing in morphology due to their different synthesis prehistory, were utilized for obtaining oriented fibers through the gel technology. The source powders, gels, and drawn fibers were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and low-frequency Raman spectroscopy. A comparison of the SEM images of powders with their straight chain segment (SCS) length distributions derived from the Raman spectra showed that the samples with pronounced fibrous morphology exhibited bimodal distribution functions, whereas the granular morphological pattern was specified by the unimodal SCS length distribution. Some remnant features of the ordered structure inherent in the powders were revealed in the gels. The drawability of gel-derived fibers was found to be dependent on the SCS length distributions in the gels and, indirectly, on the morphology of the reactor powders.

Crystalline Phase in Gelled UHMWPE Reactor Powder

A dried gel (xerogel) prepared from ultrahigh molecular weight polyethylene was characterized using X-ray and low-frequency Raman scattering techniques, which evidence the presence of stacked lamellar crystals in the material. The architecture of these entities is similar to a sequence of alternating crystalline and amorphous regions in oriented semicrystalline polymers but in the case of isotropic material the stacks exhibit equal “long periods” in meridional and equatorial directions. The stack-like nature of crystalline entanglements in the gel network is concluded.