The morphology of semi-crystalline LLDPE blown films is surprisingly difficult to determine. The difficulty stems from apparently incompatible data obtained by different experimental techniques. For example SAXS and WAXS frequently report incompatible orientations; from DSC one expects the existence of extremely thick crystals which are not detected by any other technique. While controversy like this is typically resolved by direct visualization using electron microscopy, accurate real space assessment LLDPE crystal size and orientation is challenging as well due to the dynamic range of crystal size including a population of exceptionally small crystals that are difficult to assess.<br/>In this talk we present our latest electron microscopy experiments that have allowed us to improve visualization of structure in in LLDPE blown film. We find that a surprising majority of our films are spherulitic with spherulites losing their symmetry as stretching on the film production line increases. Evaluation of spherulite structure in TEM and Polarized Light Microscope reveal enough details to provide new insight into the crystallization process and final structure of the films. For example, the major structural elements in spherulites are lamellae radiating from the spherulite center.  They bend into S shape and C shapes along the a-axis and twist around the b-axis. We also observe a second population of lamellae oriented tangentially. This arrangement is very similar to cross hatched structures frequently observed in polypropylene but, to our knowledge, not reported for polyethylene.  <br/>Based on microscopy observation we develop a model of film crystallization that explains some of the inconsistencies between data obtained by different characterization techniques.<br/>

Crossing lamellae morphology in LLDPE

256th National Meeting (2018)

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