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

Abstract

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

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

“…Above the transition, the system remains disordered and liquid‐like while below this temperature the material remains solid. Similar results were recorded for TPUs with a transition characterized by the passage through a critical gel state, albeit at much lower temperatures . A sharp increase in storage modulus was observed, which is consistent with behavior expected from a material experiencing an increase in crystallinity or restructuring to a more mechanically robust state.…”

“…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 . Recently, it was shown that investigating the evolution of the viscoelastic moduli allows significant insights to be gained into the kinetics of phase transition in a commercial TPU . 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.…”

“…[24][25][26]41 ] Most of the studies that investigate the phase transition behavior of TPUs were conducted by DSC, small angle X-ray scattering (SAXS) wide angle X-ray scattering (WAXS), infrared spectroscopy, and atomic force microcopy (AFM). [27][28][29][30][31][32][33][34] While the understanding of phase transition behaviors are important to understanding thermal postprocessing conditions, these techniques leave a gap in the relationship between exposure conditions and the physical performance of the system.…”

“…[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. The thermal history that the TPU was exposed to directly relates to the microstructure at the critical gel point; an increase in HS content induces the shift of phase transition kinetics to higher temperatures, due to an enhancement in the tendency of phase mixing to occur during the phase transition of the TPU.…”

Thermal stability and thermal oxidation kinetics of PU/CA‐MMT composites

“…Therefore, improving anti‐aging property of PU‐based materials will be of great magnificence . To this end, a lot of works have been done to focus on the improvement of anti‐aging property of PU‐based materials by incorporating fillers, such as clay, glass, carbon nanotubes, and graphene, and so forth. Among these fillers, clays, due to their inexpensiveness, have been extensively utilized to improve materials' physical and mechanical properties .…”