A 2-dimensional small-angle X-ray scattering study of the microphase-separated morphology exhibited by thermoplastic polyurethanes and its response to deformation

Laity, Peter R.; Taylor, Jennifer E.; Wong, Suet‐Ping; Khunkamchoo, Peck; Norris, Keith C.; Cable, M.; Andrews, Geoffrey T.; Johnson, A. F.; Cameron, Ruth E.

doi:10.1016/j.polymer.2004.05.032

Cited by 41 publications

(53 citation statements)

References 56 publications

(54 reference statements)

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“…This has been reported previously [38,41] and is consistent with the material being quenched from a homogeneous melt to a single glassy phase at room temperature. As discussed elsewhere, [37,40] this was consistent with globular scattering bodies distributed on a deformable statistical lattice. This was consistent with crazing.…”

Section: P R Laity Et Al 278supporting

confidence: 82%

“…[53] Considerably stronger segmental demixing is expected for more strongly immiscible SS, such as those described in work by Bengtson et al [7] or Serrano et al [54] Limited demixing may also be favored by the distribution of HS lengths that arose from the stoichiometries used in the formulations, which were considerably shorter than those in the materials described recently by Saiani et al [55,56] Moreover, as further validation, analysis of SAXS data using these models provided plausible interpretations of the morphological changes in TPUs undergoing uniaxial strain [37,40] or during heating. Evidence for interactions of this type is found in Fourier-transform infrared (FTIR) studies by Zharkov and coworkers.…”

Section: Morphological Studiesmentioning

confidence: 60%

“…[61,62] By contrast, the annealed samples initially exhibited a circular ring of high SAXS intensity, which intensified in the strain direction and decreased in the transverse direction during deformation. This was previously attributed to microdomain fragmentation, [37] whereby the fragments bisect the expected distances between the original scatterers. Curve fitting the Zernike-Prins model to meridional and equatorial scans from the sequence of 2-D-SAXS data revealed information on the morphological response to deformation.…”

Section: P R Laity Et Al 278mentioning

confidence: 81%

“…However, it was found that R varied with scattering direction in deformed samples, [37] which suggested that the scatterers became elongated in the strain direction, probably by rotation of anisometric HS microdomains. R was independent of scattering direction in unstrained samples, consistent with isotropic morphologies and spherical or randomly oriented anisometric scatterers.…”

Section: Morphological Studiesmentioning

confidence: 99%

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The Effect of Polyurethane Composition and Processing History on Mechanical Properties

Laity

Taylor

Wong

et al. 2005

Journal of Macromolecular Science, Part B

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Uniaxial stress-strain behavior of a wide range of polyurethane elastomers was compared with current models of rubber-like elasticity. Although the data could be described well by a semi-empirical model, a systematic discrepancy was observed with more theoretically based models. This took the form of an additional energy term during deformation, which depended on the polyurethane composition. Microdomain fragmentation may provide a possible explanation. Alternatively, it may be due to the effects of segmental interactions on the relaxation of polymer chain entanglements during deformation.This combination of useful mechanical properties and ease of processing has led to the use of TPUs in many diverse applications, such as conveyer belts, rollers, solid tires, upholstery, elastomeric textile fibers, and shoe soles. [8 -11] Moreover, many TPUs exhibit good biocompatibility, making them promising candidates for medical and surgical applications such as gloves, catheters, arterial stents, and replacement heart valves. [12,13] Uniaxial tensile stress-strain curves of TPUs generally exhibit sigmoidal shapes characteristic of rubber-like elastomers. A relatively steep increase in stress (s) at low strain (1) is followed by a gradual decrease in slope (i.e., strain-softening), a less steep section of curve at intermediate strain and a second region of increased slope (i.e., strain-hardening) at higher strain. [1 -7,9] Young's modulus (E) generally increases with HS content, which has been attributed to HS microdomains acting as reinforcing filler, [1 -9] while the pronounced strain-softening behavior, mechanical hysteresis, and "tensile set" (i.e., the relaxed sample is elongated, compared with its original unstrained length) observed with some formulations may be caused by microdomain fragmentation. Strain hardening has been attributed to strain-induced crystallization; [2,3,7 -9] however, observations of similar behavior with cross-linked rubbers and other elastomers [14] suggest that alternative mechanisms may be possible in some cases.The work presented here investgated the mechanical properties of thermoplastic poly(ether-urethane) (PEU) and poly(carbonate-urethane) (PCU) copolymers at moderate strain. In particular, the effects of composition, processing history, and morphology on Young's modulus and the stress-strain behavior were studied. This forms part of an ongoing project to develop polyurethanes with improved characteristics and performance for medical applications. Rubber-like ElasticityRubber-like elasticity was discussed extensively by Heinrich et al., [15] Treloar, [16] and Dušek and Prins. [17] Recent developments in theory were reviewed by Mark. [14] and Beda and Chevallier. [18] Therefore, only a few key points need be discussed here.The stress-strain relationship of a rubber-like elastomer in uniaxial extension at low strain (i.e., before strain hardening is observed) can generally be described by the semiempirical equation derived by Mooney [19] and Rivlin: [20]

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Section: P R Laity Et Al 278supporting

confidence: 82%

Section: Morphological Studiesmentioning

confidence: 60%

Section: P R Laity Et Al 278mentioning

confidence: 81%

Section: Morphological Studiesmentioning

confidence: 99%

See 2 more Smart Citations

The Effect of Polyurethane Composition and Processing History on Mechanical Properties

Laity

Taylor

Wong

et al. 2005

Journal of Macromolecular Science, Part B

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“…[14][15][16] Segments in the soft phase (soft segments and dissolved hard segments) will first become oriented in the deformation direction due to the lower modulus of the soft phase and stress will be ultimately be exerted on the hard domains. If anisotropic in shape, the hard domains are expected to align with their long axis in the deformation direction.…”

mentioning

confidence: 99%

Dynamics of Uniaxially Oriented Elastomers Using Broadband Dielectric Spectroscopy

et al. 2010

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The molecular mobility of chemically cross-linked and thermoplastic elastomers is of utmost importance in establishing physical properties for uses ranging from automotive tires and shoe soles to more sophisticated aerospace and biomedical applications. In many of these applications, network chain dynamics under external stresses/strains are critical for determining ultimate performance. It is well established that T g (or T R , the dynamic T g ) and the breadth of the segmental (R) relaxation time distribution increase with increasing cross-link density for chemically cross-linked polymers. For elastomers, there are considered to be two contributions important in determining the change in T R upon uniaxial extension: a reduction in conformational entropy, encouraging an increase in T R , and a volume increase on uniaxial deformation, leading to a reduction in T R (nonideal networks are compressible to some degree). 1,2Considering the importance of mechanical deformation in elastomer applications, there have been relatively few previous investigations of mechanical strain on chain dynamics, e.g., 3,4 even fewer using broadband dielectric spectroscopy, and none on thermoplastic elastomers. [5][6][7][8] This is despite the fact that modern broadband dielectric spectroscopy is a powerful tool for the investigation of material dynamics over very wide frequency and temperature ranges.In this Communication, we report the findings of our initial dielectric spectroscopy investigation of the role of uniaxial extension on the relaxation behavior of cross-linked polyisoprene and segmented polyurethane elastomers. A Novocontrol GmbH Concept 40 broadband dielectric spectrometer was used to measure dielectric permittivity and loss over a broad range of temperatures and frequencies.Synthetic polyisoprene [PI, NIPOL-IR2200 (Zeon Chemicals), 98.5% cis-1,4 content] was cross-linked with dicumyl peroxide (Sigma-Aldrich) at 180°C for 4 min in an aerated oven. Crosslink density was determined by measuring the swelling ratio in toluene and the Flory-Rehner equation.9 A poly(tetramethylene oxide) (PTMO, MW ∼ 1000) soft segment polyurethane (PU) with 32.5 wt % of hard segments [4,4 0 -diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO)] was supplied by AorTech Biomaterials (Scoresby, QLD, Australia) in film form.For the uniaxial deformation experiments, the stretching rig shown in Figure 1 was developed in order to allow convenient loading of deformed specimens directly into the dielectric spectrometer. This rig has three essential parts: sample clamper, electrode, and stretching knob. A sample strip (10 mm Â 80 mm) was placed along the groove on the rig and drawn to a specific extension ratio (λ). An electrode was positioned in the middle of the strained sample and clamped. The strained sample-electrode assembly was then separated from the rig and dried in vacuum for 24 h before measurement.The influence of uniaxial extension on the dynamics of the cross-linked PI (cross-link density = 6.1 Â 10 -5 mol/cm 3 ) is displayed in Fi...

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Wide‐Angle X‐ray Diffraction and Small‐Angle X‐ray Scattering Studies of Rubber Nanocomposites

Causin

2010

Rubber Nanocomposites

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A 2-dimensional small-angle X-ray scattering study of the microphase-separated morphology exhibited by thermoplastic polyurethanes and its response to deformation

Cited by 41 publications

References 56 publications

The Effect of Polyurethane Composition and Processing History on Mechanical Properties

The Effect of Polyurethane Composition and Processing History on Mechanical Properties

Dynamics of Uniaxially Oriented Elastomers Using Broadband Dielectric Spectroscopy

Wide‐Angle X‐ray Diffraction and Small‐Angle X‐ray Scattering Studies of Rubber Nanocomposites

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