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(butylene terephthalate) as hard segments and poly(ethylene glycol) as soft segments in a ratio of 57/43 wt.-% is studied. Small-angle x-ray scattering measurements with an area detector are carried out on bristles with and without application of stress up to 195% relative deformation. Two-dimensional scattering patterns are used for morphological characterization of the sample. At small deformations one morphology peak is found, corresponding to a periodicity that changes affinely with deformation. The morphology of the sample represents assemblies of mutually parallel crystalline lamellae, positioned perpendicular to the stretching direction both under and without stress. When macrodeformation increases a second peak appears, and a four-point pattern is observed in the relaxed state. In this intermediate deformation range coexisting morphologies contribute to the scattering. Additional contributions arise from lamellae, which are inclined to the stretching direction, as well as from lamellae, which are again perpendicular to the stretching direction, as a result of microfibril relaxation and loss of interfibrillar contacts. At large deformations the latter morphology dominates 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 stress field in the sample play an important role.