Effect of crystal modification and superstructure on the static and dynamic creep properties of isotactic polypropylene

晶体改性和超结构对等规聚丙烯静态和动态蠕变性能的影响

• 批准号: 442568249
• 负责人: Professor Dr.-Ing. Volker Altstädt
• 金额: --
• 依托单位: Lehrstuhl für Polymere Werkstoffe
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/442568249?language=en
• 关键词: Effect; crystal; modification; superstructure; static

Creep describes a significant phenomenon for materials like metals, concretes or polymers. This phenomenon occurs in most of the applications where they are exposed to a permanent load and a harsh environment. These external influences result in a deterioration in mechanical properties, a decrease in life time of materials and may even lead to premature failure. Static creep is defined as the time dependent, irreversible deformation by molecular rearrangement of polymers when they are subjected to stress. Dynamic creep describes a much more severe failure mechanism compared to static creep because of the applied stress containing a vibrational component. Good examples for vibrational stress loaded applications are underground drainages and sewerage pipes. Fundamental understanding of static and dynamic creep and predicting the life time of materials is crucial to develop materials, withstanding a significant level of stress and vibrations for extended periods of time. Isotactic polypropylene (i-PP) is a promising candidate to meet the requirements due to its low failure rate and superior mechanical properties. It is a polymorphic material showing various crystal modifications, such as alpha and beta, and crystal superstructures, such as spherulite and shish-kebab. The crystal structures are influenced by processing conditions and nucleating agents (NA) etc. We already reported on the influence of the crystal modification and superstructure of i-PP, nucleated by supramolecular nucleating agents on the toughness, tensile strength and fatigue crack propagation resistance. To the best of our knowledge, the influence of microstructure on static creep has been studied only to a limited extent in literature. Many research has been focused on improving static creep resistance of i-PP by using fillers and fibers such as glass fibers, carbon nanotubes and clay. However, a fundamental understanding of the correlation of creep resistance and the microstructure (crystal modification and superstructure) is completely missing. Therefore, the static creep behavior of i-PP with different microstructures will be analyzed at three different stress levels and temperatures. Furthermore, to best of our knowledge, no research has been done on the dynamic creep resistance of i-PP. Therefore, the objective of the research proposal is to establish structure-property relationships between microstructure and creep behavior of i-PP nucleated by commercially available supramolecular nucleating agents. The aim of the dynamic creep experiments is to investigate the effect of the i-PP crystal structure by additional superposition of a stress amplitude on the mean stress taken from the static experiments.

蠕变描述了金属，混凝土或聚合物等材料的重要现象。这种现象发生在大多数应用中，即它们暴露于永久负载和苛刻的环境中。这些外部影响会导致机械性能恶化，材料寿命的减少，甚至可能导致过早失败。静态蠕变定义为在聚合物承受应力时通过分子重排的时间依赖性，不可逆的变形。与静态蠕变相比，动态蠕变描述了更严重的失败机制，因为含有振动成分的施加应力。振动应力加载应用的好例子是地下排水管和污水管道。对静态和动态蠕变的基本理解，并预测材料的寿命对于开发材料至关重要，在长时间内承受着很大的压力和振动水平。同骨聚丙烯（I-PP）是有前途的候选人，由于其低故障率和优异的机械性能，可以满足要求。它是一种呈现各种晶体修饰的多态性材料，例如α和β，以及晶体上层建筑，例如球形和shish-kebab。晶体结构受加工条件和成核剂（NA）等的影响。我们已经报告了I-PP的晶体修饰和上部结构的影响，I-PP的影响是由超分子成核剂对韧性，拉伸强度和疲劳裂纹裂纹抗性的成核。据我们所知，在文献中仅研究了微观结构对静态蠕变的影响。通过使用填充剂和纤维（例如玻璃纤维，碳纳米管和粘土），许多研究都集中在提高I-PP的静态蠕变耐药性上。但是，完全缺少对蠕变抗性与微结构（晶体修饰和上层建筑）的基本理解。因此，将在三种不同的应力水平和温度下分析具有不同微结构的I-PP的静态蠕变行为。此外，据我们所知，尚未对I-PP的动态蠕变抗性进行研究。因此，研究建议的目的是建立由市售超分子成核剂成核I-PP的微观结构与蠕变行为之间的结构 - 质地关系。动态蠕变实验的目的是通过将应力振幅的额外叠加对静态实验取的平均应力进行额外叠加来研究I-PP晶体结构的影响。