Morphologies, methods biaxial orientation

In terms of macrostructure, studies on the deformation of spherulites during biaxial orientation elucidated that spherulitic break-up occurs not only at their boundaries, but also at their centers. In either case and preferentially at higher temperatures, a fibrillar morphology was observed to develop at higher levels of stretching. Less data are available on direct methods to quantify the behavior of amorphous segments as they take part in these deformations. 

The polymer is subjected to a biaxial stretching, which creates orientation both in the crystalline and in the amorphous phases. As in fiber spinning, many studies have been dedicated to orientation characterization, especially in the crystalline phase, but biaxial orientation requires more sophisticated methods. More recently, much effort has been devoted to the description of the morphology at the lamellar scale, for example, by electron microscopy. 

The orientation and properties of polyethylene films produeed by the blown-film technique have been studied by many researehes in literature [2-6]. The correlation between orientation and morphology of oriented polyethylene (mostly blown film) has been studied thoroughly as well [7-10]. Mechanieal and viseoelastic properties of biaxially oriented films produeed by double bubble method were also investigated [11-13]. 

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