Morphological Changes under Strain for Different Thermoplastic Polyurethanes Monitored by SAXS Related to Strain at Break

Abstract

Abstract. In tensile tests of 6 different handcast thermoplastic polyurethanes (TPU) with a hard-segment content HSC=0.51 the volume fraction of hard domains (VH) has been tracked. The materials exhibit a linear increase up to a strain of approx. 0.5 (strain-induced phase separation). Thereafter a linear decrease of VH is indicated. When stretched by 100% about 25% of the initially present hard domains are destroyed. The extrapolation to VH=0 is close to the elongation at break. Characteristic materials parameters are suggested by the found relation.The tests (maximum strain: 3) are monitored by small-angle X-ray scattering (SAXS). The morphology is closer to particle scattering than that of machine-processed material. Therefore the longitudinal scattering appears fittable by a one-dimensional statistical model that separates the weak discrete scattering from the height distribution of hard domains, whose weight returns the variation of VH with the strain. All TPUs are based on 4,4'-methylene diphenyl diisocyanate (MDI). The other raw components are systematically varied.Two MDI units determine the height of the average hard domain. The variation of VH with strain is described by a tensile augmentation (in analogy to the tensile strength) which is realized at an end-of-growth strain. The following hard domain destruction is governed by a consumption factor. Deviations between extrapolated and measured strain at break may be related to the TPU composition.

Microstructural and mechanical property evolutions of shape memory polyurethane during a thermodynamic cycle

“…Also, it is found that the azimuthal intensity of programmed SMPU is obviously higher than those of original and recovered samples as shown in Figure (b). This suggests that the molecular crimpness is decreased in the horizontal stretching direction according to the reciprocity relationship …”

Investigation of Temperature Dependency of Morphological Properties of Thermoplastic Polyurethane using WAXS and SAXS Monitoring

“…He observed broad peaks at 2-theta of 20° with small sharp peaks at the top in the case of ester homourethanes based on EG and DBDI. Stribeck, et al [1] also observed broad peaks in the case of ether based TPU. Precise WAXS measurements make it possible to determine the exact 2-theta values and FWHM of the peak.…”

“…As the hard and soft chain segments are thermodynamically *Corresponding author: Steffen Thomas Witzleben, professor, research fields: chemistry, material science, X-ray-methods. incompatible, the resulting domains are rich in either soft or hard segments [1].…”

Melting, Solidification, and Crystallization of a Thermoplastic Polyurethane as a Function of Hard Segment Content

“…In analogy to previous work on TPU materials, the SAXS is analyzed quantitatively with respect to its information concerning the evolution of the two‐phase morphology. The isotropic scattering curves are transformed into two fundamentally different real‐space representations of the morphology, g 1 ( r ) and g ( r ).…”

“…In analogy, a ( T ) v duo is an approximate measure of the volume fraction of the arranged domains which generate the SAXS long period. Related to the parameters directly defined in the model function, with W i being the weight parameters of the fit . The “diameter” is, in fact, the number‐average chord length of a hard domain.…”