Composition effects of thermoplastic segmented polyurethanes on their nanostructuring kinetics with or without preshear

Abstract

In this work, the structuring mechanism from the molten state of various thermoplastic polyurethanes was analyzed with respect to their composition [polyether or polyester soft segments (SSs), aromatic or aliphatic hard segments (HSs)]. As a preliminary study, the molar mass evolution of the materials with the temperature was quantified. Then, based on rheological experiments and in situ rheo‐small angle X‐ray scattering (SAXS) measurements, the structuring was examined at different temperatures and, particularly, the effect of a preshear treatment was analyzed. The temperature effect can be accounted by an Arrhenius‐like law with an activation energy depending mainly on the HS nature. Moreover, the shear induced structuring phenomenon is highlighted for all the studied thermoplastic segmented polyurethanes. Nevertheless, for the studied range of shear treatments, the SAXS analyses did not reveal any specific orientation. Finally, arguments based on the modification of the quench depth (ΔT = TODT − T) by the shear are given to explain the shear induced structuring phenomenon. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

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

“…The higher level of hydrogen bonding of extruded elastomeric TPUs, as compared with subsequent thermal treated material, should be attributed to the thermalmechanical history during extrusion that involves fast cooling under flow. In fact, as said above, some authors [6,11] have reported recently that flow strongly affects the structure development of TPUs. An eventual change in the distribution of hard block length could also play a role on the decrease of hydrogen bonding upon thermal treatment.…”

“…However, the microstructural changes occurring during the annealing or heating/cooling are not as yet well‐understood. There are also indications that a strain, applied during or just before the structuring process, clearly modifies the kinetics of this structuring and possibly, the resulting morphology . In particular, Mourier et al , studying TPUs with different chemical compositions, reported that a preshear treatment largely diminishes the structuring time.…”

“…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]. Some relatively recent studies [4] have shown that rheology is also a very sensitive tool to investigate the microstructural changes taking place during the phase transition stages.…”

Aliphatic polycarbonate‐based polyurethane elastomers and nanocomposites. I. The influence of hard‐segment content and macrodiol‐constitution on bottom‐up self‐assembly

“…TPU elastomers thus exhibit the rubber‐like behavior; however (unlike conventional rubbers) they can be processed and recycled like thermoplastics. Even though the interest of scientists and manufacturers in TPUs covers the period of almost 70 years, TPU, their nanocomposites, and blends are still attractive not only for industrial and practical applications, but also from the academic point of view 3, 5, 11, 14–18…”

“…As mentioned, polycarbonate‐based polyurethane (PC‐PU) elastomers belong to a relatively new and promising group of TPUs 7–13, 19–26. Aromatic di‐ and polyisocyanates based on 4,4′‐diphenylmethane diisocyanate are the mostly used in TPUs,3, 4, 7–12, 14–17, 19, 21, 26 but aliphatic, mainly hexamethylene diisocyanate (HDI),5, 6, 13, 15, 18, 20, 22–25 started to be more and more popular in current polyurethane formulations. The main disadvantage of PC‐PUs as compared with “classical” polyether‐ or polyester‐based PUs is their high cost, but their superior mechanical, biological, heat‐, oxidative‐, hydrolysis‐ and UV‐light resistant properties8, 9, 21, 25, 27 usually compensate the cost drawback.…”