Ultra small-angle X-ray scattering studies on structural changes in micrometers upon uniaxial stretching of segmented polyurethaneureas

Ultra small-angle X-ray scattering (USAXS) experiments were conducted in order to examine structural changes in micrometers upon uniaxial stretching of elastomeric segmented polyurethaneureas at room temperature. It was possible to stretch the sample film up to α = 7.5 without break, where α designates the stretching ratio. Around α = 6.5 the sample became turbid, while it recovered transparency when the stress was removed. To understand this curious phenomenon, we conducted the USAXS experiments for the structural analyses in micrometers. Although a set of streaks appeared in the direction parallel to the stretching direction (SD) when the sample became turbid (around α = 7.2), more interesting result is that a set of streaks appeared in the direction perpendicular to SD much earlier around α = 5.0. Close examination of the scattering intensity profile revealed evolution of multiple interference peaks, which could be ascribed to the form factor of a lamellar particle. Since the streaks disappeared upon the removal of the stress, “lamellar particles” are considered to be crazes, which develop further into cracks in a subsequent stage. From the results of USAXS measurements, it is suggested that the lamellar-shaped crazes appeared around α = 5.0 being oriented parallel to SD, and further stretching created other lamellar-shaped crazes being oriented perpendicular to SD, which are co-existing with the preceding parallel crazes.