Development of texture in poly(ethylene terephthalate) by plane-strain compression

Abstract

Morphological alterations induced by plane-strain compression of semicrystalline poly(ethylene terephthalate) (PET) at 190°C were studied using small-angle and wide-angle X-ray diffraction techniques, polarized light microscopy and differential scanning calorimetry. Based on the observations, a scheme of texture development is outlined. An initially spherulitic morphology transforms into one that comprises stacks of fragmented crystalline lamellae with lamellar normals oriented towards the flow direction. After some initial deformation by interlamellar sliding in the amorphous material (100)[001] chain slip operated throughout the remainder of the deformation. Up to a compression ratio of 2.6 the (100)[001] chain slip mechanism orients lamellar normals towards the compression axis. Further deformation caused fragmentation of the thinned-out lamellae and subsequent reorientation of lamellar normals towards the flow direction. Pole figure analysis indicated cooperative activity of the (100)[001] chain slip and (100)[010] transverse slip during the later stages of texture development. The (100)[010] transverse slip mechanism controlled the orientation of the crystal structure in a plane orthogonal to the flow direction. There was no evidence of (010)[001] chain slip during texture development. At a compression ratio of 3.3 pole figure analysis revealed the existence of a dual unit cell orientation that renders an overall orthotropic symmetry to plane-strain compressed PET.