Multiscale synchrotron scattering studies of the temperature-dependent changes in the structure and deformation response of a thermoplastic polyurethane elastomer (original) (raw)
Related papers
Synchrotron Radiation Study of the Relation between Structure and Strain in Polyurethane Elastomers
Journal of Synchrotron Radiation, 1997
This paper describes a system for the study of the relation between structure and applied strain in thermoplastic polyurethane elastomers using the Australian National Beamline Facility at the Photon Factory, KEK, T~ukuba, Japan. The system uses the sagittal focusing monochromator at beamline 20B to provide a high-intensity focused beam which then falls on the specimen mounted in a miniature tensometer mounted in the unique vacuum diffractometer (BIGDIFF). Imaging plates were used to record simultaneously SAXS and WAXS patterns from the specimen at a particular strain. The change in SAXS and WAXS patterns with loading and unloading was recorded using a ten-plate imaging-plate changer.
Real time SAXS/stress–strain studies of thermoplastic polyurethanes at large strains
Polymer, 2002
Simultaneous small angle X-ray scattering (SAXS) and force measurements have been recorded during tensile deformation of two contrasting polyurethane elastomers. The elastomers comprise the same hard and soft chemical segments; in Sample A, the length of the hard blocks is randomised while in Sample B the hard blocks are monodisperse. During deformation of Sample A, the SAXS halo from the mesophase structure deforms to an ellipse with intensification on the meridian. In Sample B, the halo transforms into a four point pattern. The ellipse patterns of A are interpreted in terms of a model based on particles located on a statistical lattice which is subjected to an affine deformation scheme. According to this model, the SAXS patterns of A are consistent with the hard phase regions behaving as embedded particles which separate from each other in an affine manner and which are not impeded by interconnections during the mechanical yield process. In B, the interconnection of the hard phase prevents affine deformation of the structure and involves the formation of a four point 'lattice' structure which then subsequently deforms in an affine manner. The differences in behaviour are linked with the segment sequencing which result in the phase regions of Sample A having a lower volume fraction and are consistent with variation in applied stress. q
Procedia Engineering, 2011
A study was made of how aspects of the mechanical and thermal responses of thermoplastic polyurethane elastomers vary with composition: the hard segment, soft segment and chain extender were varied systematically with the aim of improving understanding of the relationship between molecular/supramolecular architecture at the nm-scale and macroscopic mechanical properties in such systems. Two hard segments were compared, generated from 4,4'-methylene bis(phenyl isocyanate) (MDI), or 4,4'-dibenzyldiisocyanate (DBDI). Rotation around the-CH 2-CH 2-bridge in DBDI allows alignment of aromatic rings and crystallization within the hard phase, which is not available with MDI. The physical structures were characterized by dynamic mechanical analysis (DMA) and by X-ray scattering (SAXS and WAXS) revealing signi cant variations in degree of phase separation and degree of crystallinity, especially in the DBDI-based polymers. The presence of DBDI hard segments instead of MDI led systematically to increases in: the input strain energy to a given elongation, hysteresis and residual strain under cyclic loading, and stress relaxation. Stress-strain cycles reflect the resistance to plastic deformation occurring in the hard domains. This was enhanced by more pronounced hydrogen bonding achieved in the more mobile DBDI than in MDI. These differences between DBDI and MDI could be attributed to the greater flexibility of DBDI allowing a higher tendency to self-associate by hydrogen bonding. The degrees of hysteresis and stress relaxation were found to be greatly enhanced by hard-phase crystallinity, through its effect of increasing the flow stress. The results provide new insight into the physical origin of inelastic effects in reinforced elastomers.
Polymer, 2010
Cyclic tensile responses of fourteen polyurethane elastomers were studied, with respect to their chemical composition and physical structure. Hard segment, soft segment and chain extender were varied, while keeping the hard segment fraction at ca 40% and soft segment molar mass at 2000 g/mol. Hard segments were generated from 4,4 0-methylene bis(phenyl di-isocyanate) (MDI), or 4,4 0-dibenzyl di-isocyanate (DBDI). Physical structure was characterized by X-ray scattering (SAXS and WAXS), revealing significant variations in degree of phase separation and degree of crystallinity, especially in the DBDI-based polymers. Large differences were found in the mechanical responses during first loading to a given strain. Tensile modulus and work input increased significantly with degree of hard phase crystallinity, but were independent of degree of phase separation. First cycle hysteresis was found to increase with reduced phase separation and with replacement of MDI by DBDI. In second and subsequent load cycles, however, in which the Mullins effect was observed, a remarkable degree of uniformity of response was discovered. A unique linear relation was obtained between second cycle hysteresis and second cycle work input, for all strain levels, and for all materials except for two (with highest phase separation) which showed slightly lower second cycle hysteresis. The results can be explained in terms of pull-out of segments from the hard phase on the first cycle, to form a new series-coupled soft phase, whose constitutive response then appears almost independent of chemical and physical structure.
Colloid & Polymer Science, 1993
The scattering behavior of undrawn and drawn annealed bristles of thermoplastic elastomers with conventional and higher molecular weight based on poly(butylene terephthalate) as hard segments and poly(ethylene glycol) as soft segments in a ratio of 49/51wt.% is studied. Small-angle x-ray scattering (SAXS) measurements with an area detector are carried out on single bristles under or without applied stress and with deformations up to 300%. At low macrodeformations (8 _< 30-40%) the morphology of the predrawn samples represents assemblies of parallel crystalline lamellae positioned perpendicular to the stretching direction. These morphological characteristics remain unchanged within the entire deformation range (up to 5 = 300%) for the predrawn samples of lower molecular weight. For the initially undrawn sample of larger molecular weight reversible orientation and disorientation of the crystallites (microdomains) is established in the same deformation range. Common morphological features are found for the predrawn and undrawn samples with increased molecular weight at medium (5 = 50-150%) and high (5 = 150-300%) deformation ranges. For both samples in an unloaded relaxed state the x-ray patterns can be explained by a zigzag arrangement of crystalline lamellae, i.e., the microdomains are inclined to the stretching direction. After loading, the microdomains transform to a position perpendicular to the stretching direction. This observed morphological transition is found to be reversible and becomes more pronounced with progressing deformation. It is suspected to contribute to reversible macrodeformations of thermoplastic elastomers in many cases and may be related to the large amount of tie-molecules created during solid-state reactions in those materials.
Multiple-length-scale deformation analysis in a thermoplastic polyurethane
Nature communications, 2015
Thermoplastic polyurethane elastomers enjoy an exceptionally wide range of applications due to their remarkable versatility. These block co-polymers are used here as an example of a structurally inhomogeneous composite containing nano-scale gradients, whose internal strain differs depending on the length scale of consideration. Here we present a combined experimental and modelling approach to the hierarchical characterization of block co-polymer deformation. Synchrotron-based small-and wide-angle X-ray scattering and radiography are used for strain evaluation across the scales. Transmission electron microscopy image-based finite element modelling and fast Fourier transform analysis are used to develop a multi-phase numerical model that achieves agreement with the combined experimental data using a minimal number of adjustable structural parameters. The results highlight the importance of fuzzy interfaces, that is, regions of nanometre-scale structure and property gradients, in determining the mechanical properties of hierarchical composites across the scales. De tec tor tra ns lat ion De tec tor tra ns lat ion x ax is 4, 35 8. 47 m m 12 8. 72 m m ARTICLE NATURE COMMUNICATIONS |
Journal of Polymer Science Part B: Polymer Physics, 2010
The mechanical behavior of polymer materials is strongly dependent on polymer structure and morphology of the material. The latter is determined mainly by processing and thermal history. Temperature-dependent on-line X-ray scattering during deformation enables the investigation of deformation processes, fatigue and failure of polymers. As an example, investigations on polypropylene are presented. By on-line X-ray scattering with synchrotron radiation, a time resolution in the order of seconds and a spatial resolution in the order of microns can be achieved. The characterization of the crystalline and amorphous phases as well as the study of cavitation processes were performed by simultaneous SAXS and WAXS. The results of scattering experiments are complemented by DSC measurements and SEM investigations.
2008
A study was made of a family of polyurethane copolymers, in which the chemical components were: a hard segment (giving, on phase separation, hard nano-scale reinforcing particles); a soft segment (giving, on phase separation, an elastomeric matrix), and a diol chain extender. The chemical compositions of all three components were varied systematically and independently, and their mechanical responses were measured in cyclic tensile tests at room temperature, up to stretches in the range 5-6. Particular attention was paid to characterizing the inelastic features – hysteresis, and stress relaxation in interrupted tests – and their variations between the materials. The same materials were also studied by wide-angle X-ray scattering (WAXS), to determine levels of crystallinity. Results showed that hysteresis was increased by increasing hard phase crystallinity. This was the case for polyurethanes based on the novel diisocyanate 4,4’-dibenzyl diiscyanate (DBDI). The extent of stress rela...
Macromolecules, 1997
The deformation behavior of poly(ether ester) is studied by means of small-and wide-angle X-ray scattering (SAXS and WAXS). The material under investigation represents a polyblock thermoplastic elastomer of poly(ether ester) (PEE) type. It comprises poly(butylene terephthalate) (PBT) as hard segments and polyethylene glycol (PEG) as soft segments in a ratio of 57/43 wt %. Isotropic PEE bristles are drawn to five times of their initial length and subsequently annealed with fixed ends for 6 h at 170°C in vacuum. The WAXS patterns were registered by a pinhole camera and a 2D area gas detector. These measurements were performed both under stress and during the subsequent relaxation in the absence of stress. The deformation was increased stepwise up to the breaking point of the sample (ca. 185%). SAXS patterns were obtained in the same deformation range by means of monochromatic X-ray radiation in the beamline A2 of the synchrotron DESY in Hamburg, Germany. SAXS patterns were registered by means of a 2D "Image-plate" detector. Five deformation intervals were revealed by SAXS. In the first one ( ) 0-50%) an ensemble of uncorrelated strained microfibrils exists and the corresponding layer line small-angle pattern is observed. These microfibrils scatter independently. In the second interval ( ) 50-80%) interactions between neighboring microfibrils develop, a microfibrillar network is observed, and the layer line pattern transforms into a four-point diagram. In the third interval ( ) 80-100%) two additional reflections show up and an unique six-point pattern is seen. Pull-out of tie molecules from crystallites begins to fibrillate the network. This pull-out mechanism is independently proved by WAXS. In the fourth interval ( ) 100-130%) the mean long period of the four-point pattern decreases and the pattern itself vanishes. At last the fiber is completely fibrillated and only a two-point pattern remains visible. In the second, third, and fourth intervals, the microfibrils correlate in the transverse direction, which allows determination of the interfibrillar distance (so-called transverse long period). It decreases gradually with the progress of deformation in both the strained and relaxed state. In the fifth interval ( > 130%) the long period of the two point pattern remains constant, but its intensity decreases until the fiber breaks. Only a few microfibrils are simultaneously carrying the load. They are destroyed one by one, until the fiber breaks as a whole.