A rheological study of the phase transition in thermoplastic polyurethanes. Critical gel behavior and microstructure development

Cossar, Silvia; Nichetti, Dario; Grizzuti, Nino

doi:10.1122/1.1687789

Cited by 27 publications

(32 citation statements)

References 15 publications

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“…The phase transition behavior and the microstructure modification of the final solid state of the investigated thermoplastic polyurethane have been explored by measuring thermal and rheological properties during the phase transition at different annealing times and temperatures. For the sake of completeness we briefly report the main findings.…”

Section: Resultsmentioning

confidence: 99%

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Constraints and thermal expansion of the free volume in a micro-phase separated poly(ester-adipate)urethane

Consolati

Nichetti²,

Quasso

2016

J. Polym. Sci. Part B: Polym. Phys.

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The free volume behavior of a thermoplastic polyesterurethane (TPU) versus temperature is investigated by positron annihilation lifetime spectroscopy and dilatometry. A discrepancy with the free volume predicted by the lattice-hole theory is found. The agreement is restored by assuming anisotropic expansion of the free volume holes, which in fact results in expansion mainly in two dimensions. This finding is perfectly compatible with a polymer structure based on rheological, thermal, and TEM data which envisage TPU as formed by short soft segments limited in their movements by chain connectivity and confined by physical crosslinks due to the hard segments

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Section: Resultsmentioning

confidence: 99%

“…DSC measurements show a structural organization of the hard segments during the early stage of the phase transition . In the course of isothermal annealing of the TPU, the system undergoes a transition from a liquid‐like to a solid‐like behavior on passing through a critical gel state.…”

Section: Resultsmentioning

confidence: 99%

Constraints and thermal expansion of the free volume in a micro-phase separated poly(ester-adipate)urethane

Consolati

Nichetti²,

Quasso

2016

J. Polym. Sci. Part B: Polym. Phys.

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“…In order to further understand the physical implications of phase transitions, rheological measurements can also be used as an experimental tool to monitor the behavior. [35][36][37] Recently, it was shown that investigating the evolution of the viscoelastic moduli allows signifi cant insights to be gained into the kinetics of phase transition in a commercial TPU. [ 33 ] The micro-phase separation between HS and SS and the crystallization of hard phase domains originates at a solution to gel (sol-to-gel) transition.…”

Section: Introductionmentioning

confidence: 99%

Effect of Soft‐to‐Hard Segment Ratio on Viscoelastic Behavior of Model Thermoplastic Polyurethanes during Phase Transitions

Gadley

Andrade

Maia

2016

Macro Materials & Eng

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Model thermoplastic polyurethanes (TPUs) are prepared with the aim of investigating the effect of soft‐to‐hard segment ratio on the phase transition and the resulting structure that forms upon isothermal exposure to temperatures near their phase transition temperature. The dynamic rheological properties of TPUs before exposure to these isothermal conditions show a phase transition at high temperatures that is directly related to the content of hard segments. The extensional viscosity data indicate a strain‐hardening behavior that becomes less pronounced with the increase of hard segments. After isothermal treatment, the DSC results show that the high‐temperature endotherm peak narrows and shifts to higher temperatures, suggesting a transition in structure. Small angle X‐ray scattering, wide angle X‐ray scattering, and atomic force microcopy results indicate a phase‐separated system in which the hard domain sizes and crystallinity change during this process. The rheological data collected after recrystallization show a significant increase in both moduli, transitioning from viscoelastic fluid‐like to glassy behavior. Concurrently, the uniaxial elongation viscosity presents a significant increase in absolute values, but with a shift from strain‐hardening to strain‐softening behavior for all strain rates. A transition from traditional phase separated viscoelastic melt behavior to more brittle rupture is also observed, marking a significant fundamental difference in properties before and after recrystallization.

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“…As such, the physical and mechanical properties of TPUs depend on several factors, including the chemistry and compatibility of soft and hard segments, the ratio of soft and hard blocks, the average block lengths used and their molecular weight distribution. Thermal as well as flow histories can greatly affect the micro-aggregation structure and properties of TPUs [2][3][4][5][6]. Much effort has been spent on investigating thermal transitions and morphological changes in TPUs using different experimental techniques such as differential scanning calorimetry (DSC) [2,4,5,[7][8][9], infrared spectroscopy [2,10], X-ray scattering [7,[10][11][12][13][14], and nuclear magnetic resonance spectroscopy [2,5,13].…”

Section: Introductionmentioning

confidence: 99%

The influence of thermo-mechanical history on structure development of elastomeric and amorphous glass thermoplastic polyurethanes

Silva

Meltzer²,

Liu

et al. 2013

Polym Eng Sci

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In this work, the effect of processing and subsequent thermal treatment on the rheological behavior and microstructure aggregation of two different types of thermoplastic polyurethanes (TPUs) are investigated. Elastomeric TPUs, which are segmented block copolymers composed of alternating soft and hard segments, and amorphous glassy TPU, predominantly composed of hard segments, were subjected to heating/cooling cycles after extrusion. All materials show rheological hystereses after the first thermal cycle; in amorphous glassy TPUs, there is an increase in dynamic moduli but the loss tangent remains unchanged, whereas in the elastomeric TPUs, there are both decreases in dynamic moduli and hystereses in the loss tangent. The changes in molecular weight during the thermal cycle were tracked by gel permeation chromatography and shown not to be responsible for the rheological hystereses. For both elastomeric and amorphous glassy TPUs, fourier transform infrared spectroscopy results indicate that an increase in dynamic moduli, especially G′, is associated with a higher degree of hydrogen bonding. These results combined with X‐ray data indicate that upon extrusion the elastomeric TPUs form a network in which hydrogen bonding plays an important role. This structure can be disrupted upon subsequent heating and cooling. POLYM. ENG. SCI., 54:1383–1393, 2014. © 2013 Society of Plastics Engineers

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A rheological study of the phase transition in thermoplastic polyurethanes. Critical gel behavior and microstructure development

Cited by 27 publications

References 15 publications

Constraints and thermal expansion of the free volume in a micro-phase separated poly(ester-adipate)urethane

Constraints and thermal expansion of the free volume in a micro-phase separated poly(ester-adipate)urethane

Effect of Soft‐to‐Hard Segment Ratio on Viscoelastic Behavior of Model Thermoplastic Polyurethanes during Phase Transitions

The influence of thermo-mechanical history on structure development of elastomeric and amorphous glass thermoplastic polyurethanes

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