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

这项赠款提供资金，以支持实验和计算研究的现象？流动诱导聚合物结晶？指的是加工流程对固化速率的深刻影响。这项工作的实验部分利用新的能力，在定义明确的单轴拉伸流动，涉及纯拉伸变形，没有叠加剪切的聚合物结构的X射线散射研究。 X射线散射实验将在阿贡国家实验室的高级光子源中进行，利用高亮度辐射和快速探测器监测几种半结晶聚烯烃（如聚乙烯、聚丙烯和聚（1-丁烯））中结晶度和微晶取向度随温度和流动条件（变形速率和总施加应变）的变化。实验计划还将包括在注塑过程中聚合物结晶的探索性研究。在计算部分的工作，这些数据将被用来测试和指导现有模型的流动增强成核和结晶的改进。 如果成功的话，这项研究的结果将提高合理预测半结晶聚合物在拉伸变形起重要作用的流动中的加工能力。 这些包括大批量工艺，如纤维纺丝、薄膜吹塑和吹塑。 通过比较拉伸和剪切流动中流动诱导结晶的性质，这项工作也将提供深入了解的基本分子过程，在流动过程中加速聚合物结晶的基础。 例如，一类模型是建立在这样的假设，即由分子流变学模型预测的流动诱导的链拉伸是控制加速成核的关键变量。 该假设将通过设计剪切流和拉伸流协议来直接测试，以使用非常不同的流类型来产生类似的分子拉伸。 最后，这项工作作为一个原型，如何强大的材料加工原位实验研究可以密切配合过程建模。

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.