MORPHOLOGICAL CHARACTERIZATION DURING DEFORMATION OF A POLY(ETHER ESTER) THERMOPLASTIC ELASTOMER BY SMALL-ANGLE X-RAY-SCATTERING

The scattering behavior of pre-drawn and annealed bristles of a highly deformable poly(ether ester) thermoplastic elastomer based on poly(bu tylene terephthalate) as hard segments and poly(ethylene glycol) as so ft segments in a ratio of 57/43 wt.-% is studied. Small-angle x-ray sc attering measurements with an area detector are carried out on bristle s with and without application of stress up to 195% relative deformati on. Two-dimensional scattering patterns are used for morphological cha racterization of the sample. At small deformations one morphology peak is found, corresponding to a periodicity that changes affinely with d eformation. The morphology of the sample represents assemblies of mutu ally parallel crystalline lamellae, positioned perpendicular to the st retching direction both under and without stress. When macrodeformatio n increases a second peak appears, and a four-point pattern is observe d in the relaxed state. In this intermediate deformation range coexist ing morphologies contribute to the scattering. Additional contribution s arise from lamellae, which are inclined to the stretching direction, as well as from lamellae, which are again perpendicular to the stretc hing direction, as a result of microfibril relaxation and loss of inte rfibrillar contacts. At large deformations the latter morphology domin ates and the 2D-scattering pattern again shows a two-point character. A morphological model for this behaviour is discussed, where the break of interfibrillar contacts during deformation and the inhomogeneous s tress field in the sample play an important role.