Mechanical deformation of polyurethanes

The mechanical properties of thermoplastic polyurethanes (TPU) depend upon their composition and the complex two-phase morphologies, which originate from microphase separation of chains segments. In the present work, poly(ether-urethanes) were prepared with hard segment contents from 36% to 71% by weight, by systematically varying the length of the soft-segment macrodiol. Samples were prepared by hot pressing or solvent casting, and the resulting hard- and soft-segment morphologies were characterized by using small-angle x-ray scattering (SAXS) and transmission electron microscopy (TEM). Environmental scanning electron microscopy (ESEM) was used to study the fracture surfaces of TPU samples. The deformation behavior of the morphology was studied in real time, by using 2-dimensional SAXS (2D-SAXS) at the Daresbury synchrotron radiation source. Two distinct mechanisms were identified, with the dominant mechanism in a given material dependent on the copolymer composition and the extent of microphase separation, which developed during processing.