TIT# Nanostructure Evolution of Oriented High-Pressure Injection-Molded
     Polyethylene during Heating
AUT# Stribeck, Norbert; Bayer, Rüdiger; von Krosigk, Gebhardt; Gehrke, Rainer;
SOU# Polymer (2002), 43(13), 3779-3784
LOC# xv070
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ABS# High-pressure injection-molded polyethylene (PE) rods are studied by
     ultra small-angle X-ray scattering from synchrotron during the heating
     of the polymer. Injection of a cool melt into a cold mold yields highly
     oriented PE rods with a coreshell structure. Samples from both the core
     and the shell material are studied. The two-dimensional scattering
     patterns are evaluated utilizing the multi-dimensional chord distribution
     function (CDF) analysis. From the obvious evolution of the nanostructure
     during successive crystallite melting, the sequence of processes
     occurring during crystallization is elucidated. First, nuclei form
     one-dimensional lattices with short-range order along the fiber axis.
     From this row structure, lamellae grow with wide lateral extension. An
     indication of an intermediate block structure is observed. Finally two
     steps of insertion crystallization result in two long period halvings.
     Increase of the mold pressure increases the lateral extension of the
     inserted lamellae in the shell material. In the core material a uniform
     row structure is absent. Extended primary lamellae form stacks with
     decreasing long periods before insertion crystallization takes over. But
     crystallites inserted in the core material do not form extended lamellae.
     Each of these steps leaves its footprint in the nanostructure and the
     corresponding scattering pattern. After CDF interpretation of the heating
     series, the room temperature pattern can be explained. The strong
     two-point pattern is associated with the primary lamellae and the
     intensity ridge extending along the meridian results from irregular
     insertion of lamellae. When the row structure is observed in the CDF,
     the fiber pattern exhibits equatorial scattering. Domain roughness
     generates a strong background scattering, which cannot be separated in
     one step. For the presented material it is shown that iterative
     background subtraction eliminates the scattering effects of the imperfect
     (i.e. inserted) lamellae.