Thermoplastic polyurethanes (TPUs) are a class of urethane elastomers which flow at elevated temperatures, enabling a diverse set of processing techniques including industrial-scale extrusion and injection molding. Due to variations in the relative content of hard and soft segments within the polymer chains, as well as block lengths and chemistries, this material exhibits a wide range of viscoelastic properties depending on the synthetic process and thermal history. Numerous manufacturers produce their own proprietary brands of TPU, thus creating a diverse market for a product whose processability varies depending on the supplier. Lot dependent undesirable characteristics may be observed during melt extrusion, including degradation at process-relevant temperatures, increases in viscosity over time, and buildup of solid-like particulates during extrusion. This manuscript implements a combination of chemorheological, spectroscopic, solubility, light scattering, and calorimetric techniques to understand the formation of this solid particulate phase during extrusion. The presence of endothermic transitions, large degrees of branching, rapidly changing viscoelastic properties, and poor dissolution capabilities were correlated with the worst performing lots of TPU in terms of extrudability. These findings suggest that solidification is caused by physical crosslinking through hard phase aggregation, which is attributed to differences in polymer branching architecture, high chain mobility, and strain under extrusion conditions. The strong association between polymer branching and solidification during extrusion highlights the capability for these characterization techniques to rapidly screen for extrusion-related performance of TPUs prior to processing.

中文翻译：

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预测热塑性聚氨酯批次挤出性能的表征方法

热塑性聚氨酯 (TPU) 是一类在高温下流动的聚氨酯弹性体，可实现多种加工技术，包括工业规模的挤出和注塑成型。由于聚合物链内硬链段和软链段的相对含量以及嵌段长度和化学性质的变化，这种材料根据合成过程和热历史表现出广泛的粘弹性能。许多制造商生产自己的专有品牌 TPU，从而为加工性能因供应商而异的产品创造了多样化的市场。在熔体挤出过程中可能会观察到与批次相关的不良特性，包括在工艺相关温度下的降解、粘度随时间的增加以及挤出过程中固体状颗粒的堆积。该手稿结合了化学流变学、光谱学、溶解度、光散射和量热技术来了解挤出过程中这种固体颗粒相的形成。吸热转变的存在、大程度的支化、快速变化的粘弹性和较差的溶解能力与挤出性方面表现最差的 TPU 批次相关。这些发现表明，固化是通过硬相聚集进行物理交联引起的，这归因于聚合物支化结构、高链迁移率和挤出条件下应变的差异。挤出过程中聚合物支化和固化之间的密切关联凸显了这些表征技术在加工前快速筛选 TPU 挤出相关性能的能力。