Synchrotron Studies and Computational Modeling of Flow-Induced Polymer Crystallization in Shear and Extensional Flow

此奖助金提供经费，以支持对？流动诱导聚合物结晶？，指的是加工流程对凝固速度的深刻影响。这项工作的实验部分利用x射线散射研究聚合物结构的新能力，在明确的单轴拉伸流中，涉及纯拉伸变形，没有叠加剪切。x射线散射实验将在阿贡国家实验室的先进光子源上进行，利用高亮度辐射和快速探测器来监测几种半结晶聚烯烃（如聚乙烯、聚丙烯和聚1-丁烯）的结晶度和结晶取向程度作为温度和流动条件（变形率和总施加应变）的函数。实验项目还将包括对注射成型过程中聚合物结晶的探索性研究。在计算部分的工作中，这些数据将用于测试和指导现有的流动增强成核和结晶模型的改进。如果成功，这项研究的结果将导致提高的能力，合理预测半结晶聚合物的加工流动，其中拉伸（拉伸）变形起重要作用。这些包括高容量工艺，如纤维纺丝，吹膜和吹塑。通过比较拉伸流动和剪切流动中流动诱导结晶的性质，这项工作还将深入了解流动过程中加速聚合物结晶的基本分子过程。例如，一类模型是建立在由分子流变模型预测的流动诱导链拉伸是控制加速成核的关键变量的假设之上的。这一假设将通过设计剪切和拉伸流动方案来直接验证，以使用非常不同的流动类型产生相似的分子拉伸。最后，这项工作为材料加工的原位实验研究如何与过程建模密切协调提供了一个原型。

This grant provides funding to support an experimental and computational study of the phenomenon of ?flow-induced polymer crystallization?, referring to the profound impact of processing flows on the rate of solidification. The experimental portion of this work utilizes new capabilities for x-ray scattering studies of polymer structure in well-defined uniaxial extensional flows which involve pure stretching deformations with no superimposed shear. X-ray scattering experiments will be performed at the Advanced Photon Source at Argonne National Laboratory, taking advantage of high brilliance radiation and fast detectors to monitor development of crystallinity and the degree of crystallite orientation as a function of temperature and flow conditions (deformation rate and total applied strain) in several semi-crystalline polyolefins, such as polyethylene, polypropylene and poly(1-butene). The experimental program will also include exploratory studies of polymer crystallization during injection molding. In the computational portion of the work, these data will be used to test and guide refinements of existing models of flow-enhanced nucleation and crystallization. If successful, the results of this research will lead to improved ability to rationally predict the processing of semi-crystalline polymers in flows where extensional (stretching) deformations play an important role. These include high volume processes such as fiber spinning, film blowing and blow molding. By comparing the nature of flow-induced crystallization in both extensional and shearing flows, this work will also provide insights into the fundamental molecular processes that underlie accelerated polymer crystallization during flow. For instance, one class of models is built upon the assumption that flow-induced chain stretch, predicted by molecular rheological models, is the crucial variable governing accelerated nucleation. This hypothesis will be tested directly by designing shear and extensional flow protocols to produce similar molecular stretch using very dissimilar flow types. Finally, this work serves as a prototype for how powerful in situ experimental studies of materials processing may be closely coordinated with process modeling.