Structure and Properties of Fatigued Segmented Poly(urethaneurea) I. Segment Orientation Mechanism due to Fatigue

Abstract

Changes of structure and properties of segmented poly(urethaneura) (SPUU) subjected to a sinusoidal strain were studied as a function of the duration of the load (the fatigue time). Mechanical experiments as well as infrared dichroism experiments indicate that destruction of hard segment domains and phase mixing between hard and soft segment domains proceed with increasing fatigue time. Infrared dichroism shows that the hard segments orient negatively, then positively, with increasing elongation. Negative orientation results from the behavior of the hard segment domain as a filler having an anisotropic shape (“domain orientation”). Subsequent positive orientation is explained by the hard segment orientation coupled with fragmentation of the hard segment domains (“segment orientation”). In the fatigue process, on the other hand, proceeding of phase mixing is dominant followed by phase demixing related to rearrangement and reorientation of the hard segments, which would finally lead to fracture. It is found that the fatigue process consists of three stages; the domain orientation stage, the phase-mixing stage, and the segment orientation stage.