Morphology‐property relationships in oriented PET films: A role of in‐plane crystalline orientation distribution on the film properties

The role of in‐plane crystalline, amorphous, and overall molecular orientation on various properties in the plane of the films was investigated using a variety of techniques. It is shown that for a fixed value of crystallinity the in‐plane crystalline orientation and the nature of the constraint imposed by the crystallites on the molecules play an important role in obtaining isotropic in‐plane expansion or shrinkage properties. Achievement of in‐plane isotropic tensile strength and elongation at the break are found to depend entirely upon an isotropic distribution of the amorphous orientation; the orientation of crystallites plays no detectable role. Furthermore, the deformation mechanisms of sequential and simultaneous biaxial stretching processes have been investigated and compared. The simulteneous stretching process is considered to be a more controlled film‐fabricating method compared to sequential stretching in achieving balanced, in‐plane film properties.