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首页> 外文期刊>Journal of Macromolecular Science. Pure and Applied Chemistry >Improvement of hardening stiffness test as an indicator of environmental stress cracking resistance of polyethylene
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Improvement of hardening stiffness test as an indicator of environmental stress cracking resistance of polyethylene

机译：改善硬化刚度试验，作为聚乙烯耐环境应力开裂的指标

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Long term mechanical behavior of polyethylene (PE) is of great importance especially in cases where structural integrity is required. In order to predict characteristics of the mechanical behavior of PE, it is necessary to fully understand the molecular structure of the employed resins. In this study, evaluation of several micromolecular properties of PE is conducted. These properties influence an important performance indicator of PE for structural applications, namely, the environmental stress cracking resistance (ESCR). ESCR in PE resins occurs through a slow crack growth mechanism under low applied stresses and long periods of time. This property is usually assessed by unreliable and time consuming testing methods such as the notch constant load test (NCLT) on notched PE specimens in the presence of an aggressive fluid at elevated temperatures. In the work presented herein, relationships between molecular structure and material response characteristics, mainly between molecular weight properties and short chain branching content in relation to strain hardening behavior of PE resins, were investigated based on results from tensile experiments. Inter-lamellar entanglements are believed to be the main feature controlling slow crack growth of PE. Extent of entanglements and entanglement efficiency has been investigated by monitoring the strain hardening behavior of PE resins in solid state through a uniaxial tensile test. The hardening stiffness (HS) test for prediction of ESCR was refined and improved to cover a broader range of PE resins, along with easier sample preparation, and faster testing. The improved test offers a more reliable and consistent ESCR picture without the drawbacks of the subjective notching process and ad-hoc presence of aggressive fluids.
机译：聚乙烯（PE）的长期机械性能非常重要，特别是在需要结构完整性的情况下。为了预测PE的机械性能特征，必须充分了解所用树脂的分子结构。在这项研究中，对PE的几种微分子性质进行了评估。这些性能影响PE在结构应用中的重要性能指标，即耐环境应力开裂性（ESCR）。 PE树脂中的ESCR通过缓慢的裂纹扩展机制在低施加应力和长时间下发生。通常通过不可靠且耗时的测试方法（例如在高温下存在侵蚀性流体的情况下，对带缺口的PE试样进行的缺口恒负荷测试（NCLT））来评估此属性。在本文提出的工作中，基于拉伸实验的结果，研究了分子结构与材料响应特性之间的关系，主要是与PE树脂的应变硬化行为相关的分子量特性和短链支化含量之间的关系。层间缠结被认为是控制PE缓慢裂纹扩展的主要特征。通过单轴拉伸试验监测固态PE树脂的应变硬化行为，研究了纠缠程度和纠缠效率。改进和改进了用于预测ESCR的硬化刚度（HS）测试，以涵盖更广泛的PE树脂，以及更容易的样品制备和更快的测试。改进后的测试提供了更可靠，更一致的ESCR图像，而没有主观刻槽过程和侵蚀性流体临时存在的缺点。

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