Until the advent of the novel Enders catalysts, the nonlinear rheological characterization of polyethylene (PE) blends, containing up to 50 wt. % of ultra-high molecular weight PE (UHMWPE, with weight average molecular weight M_w > 10⁶ g/mol) was unattainable. In this study, by melt blending of a commercially available high-density PE (polymer matrix) and PE-reactor-blends (RBs), multimodal PE blends were prepared, and their nonlinear viscoelastic properties were investigated. The experiments revealed how extraordinarily high amount of UHMWPE content and ultra-broad molecular weight distribution characterized by well separated molecular weight modes influence the nonlinear viscoelasticity. Furthermore, in order to evaluate the strain hardening ability of the multimodal PE, an approach was proposed allowing to objectively analyze and quantify the nonlinear response of the investigated samples. Analyzing the “state diagram” of the extended specimens, which captures the melt behavior and flow instabilities during uniaxial extensional measurements, unveiled that the observed SH of multimodal PE blends, at temperatures notably higher than their melting temperature, is controlled by the stretched chains of the 2nd well separated UHMWPE molecular weight mode. Moreover, it was found that, in order to highly stretch the PE chains, a characteristic strain must be applied.

中文翻译：

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具有大量UHMWPE的多峰线性PE的拉伸硬化

直到新型Enders催化剂问世，聚乙烯（PE）共混物的非线性流变学表征，其含量高达50 wt％。超高分子量PE（UHMWPE，重均分子量M _w  > 10 ^6的百分比）g / mol）是无法达到的。在这项研究中，通过将市售的高密度PE（聚合物基质）和PE-反应器共混物（RB）熔融共混，制备了多峰PE共混物，并研究了其非线性粘弹性。实验表明，UHMWPE含量过高以及分子量模式分开的超宽分子量分布如何影响非线性粘弹性。此外，为了评估多峰PE的应变硬化能力，提出了一种方法，可以客观地分析和量化研究样品的非线性响应。分析扩展样本的“状态图”，以捕获单轴拉伸测量过程中的熔体行为和流动不稳定性，据揭示，在明显高于其熔融温度的温度下，观察到的多峰PE共混物的SH受第二分离良好的UHMWPE分子量模式的拉伸链控制。此外，已经发现，为了高度拉伸PE链，必须施加特征应变。