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Composites of TPU (Elastollan 685A by BASF) and 0−0.5 wt % 3-aminopropyltriethoxysilane functionalized silica spheres (diameter 14 nm) are strained and subjected to load cycling. Tests are monitored by SAXS which is analyzed by the chord distribution function (CDF) method. Extensibility of the soft phase is limited. Macroscopic strain is accomplished by failure of single soft domains. Broken entities comprise the overstretched soft domain, sandwiched between two hard domains. Macroscopic strain at failure determines the most probable thickness of the sandwich. Failure propagates from disordered regions into well-arranged ensembles (WAE) of domains. The higher the nanosphere content, the earlier the WAE are affected. Outbursts of local failure happen at strains of 100% and 200%. They relieve WAEs. Load cycling does not induce failure of pure TPU but of the nanocomposites. Here failure spreads in the material. The fraction of material that is not affected is a function of the nanosphere content. Extrapolation yields 1.25 wt % when all the material would be affected. Relaxed samples contain sandwiches.

Thermoplastic polyurethanes (TPUs) molded at 205, 215, and 235 ° C are monitored by SAXS and WAXS during straining. A non-affi ne nanostructure deformation and related evolution mechanisms are found. DSC and microscopy are applied. DSC shows two melting endotherms. The results indicate that melts kept below the second peak stay phase-separated. The orientation parameter f ( ε ) and d f /d ε from WAXS are related to chain orientation mechanisms (strain ε ). SAXS shows hard domains that are only correlated to a next neighbor ("sandwich"). Thick sandwiches lengthen more than thin ones. Thin-layer sandwiches feature a strain limit. Some are converted into thick-layer sandwiches. Two materials have tough hard domains. Material processed at 235 ° C is soft and contains weak hard domains that fail for ε > 0.75. of the material. Block copolymers synthesized by living polymerization are characterized by uniform block lengths. Processing of such compounds may result in lattice-like nanostructures or even in photonic crystals, in which the soft and the hard blocks reside completely in different domains. This is different with thermoplastic polyurethanes (TPU). Along with their chains a mixed sequence of soft segments and hard segments is found. Thus, even optimum process control only leads to domains of very diverse shape and size, the arrangement of which can rarely lead to lattice-like correlation. Moreover, soft domains may contain several hard segments. Consequently, the chemistry [ 1 ] and the processing conditions [2][3][4][5] defi ne the nanostructure that, in turn, determines the material's mechanical properties. The hard domains form physical cross-links and make the material behave rubber elastic. Because the hard domains are permanent only to a fi rst approximation, the stressstrain behavior of TPUs is subject to "strong hysteresis, time dependence and cyclic softening". [ 6 ] Thus maturing or aging may become a problem, if longer time elapses between investigations with different methods, because in this case the results may not be combined.

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.