A Study of Structure-Process-Property Relationships in BlownPolymeric Films

本研究的长期目标是建立高密度聚乙烯(HDPE)和低密度聚乙烯(LDPE)吹塑薄膜的结构-工艺-性能关系。结晶动力学和薄膜形态作为分子结构和工艺参数的函数将使用物理模型和过程的数值模拟来研究。这项研究将包括为所吹制的聚合物的流变学和结晶度开发合适的本构模型。在商用吹膜装置上进行实验，对本构模型进行评价，确定合适的边界条件和初始条件，对吹膜过程进行数值模拟。建立了该过程的暂态、非轴对称和非线性有限元模型。该计算模型还将用于研究非轴对称环境中的坍塌和不稳定性。由于他们在理论和计算力学、聚合物结构和机械性能表征以及聚合物加工和流变学方面的背景，这三位主要研究人员具有成功开展这项研究的唯一资格。稳定的吹膜过程需要气泡内的超压、树脂挤出速度、薄膜卷绕速度和冷却速度之间的微妙平衡。由于熔体强度和结晶度略有不同，这些参数因聚合物的不同而有很大差异。在实践中，生产高质量薄膜所需的工艺变量的最佳组合是通过一系列反复尝试的步骤来实现的，这些步骤会导致聚合物树脂的大规模浪费和工时。至少有三个原因，计算机模拟薄膜吹制过程提供了一个有吸引力的替代方案。首先，计算机模拟可以帮助回答有关特定工艺变量如何影响气泡稳定性的基本问题。其次，模拟将有助于确定哪些树脂性能在决定薄膜吹塑过程中的性能时最重要。第三，如果分子取向与聚合物结晶度之间的本构关系表述得当，就可以确定最终薄膜性能与工艺条件之间的关系。这三个因素加在一起，应该会显著减少优化新型聚合物树脂商业吹膜工艺所需的实验次数。这项研究调查的是本质上跨学科的现象。相变、结晶和表面流动现象是各种制造工艺和科学问题的研究热点。研究将在学生的帮助下进行，他们将接受培训，开发理论公式、有限元模型以及对数值结果的解释和关联，还将培训学生操作吹膜设备并收集数据，以辅助和关联数值模拟。这种培养学生思考和理解基本知识以及实践方面的能力，被认为是与研究成果同样重要的贡献。

This research has the long term objective of establishing the structure-process-property relationships in both high density polyethylene (HDPE) and low density polyethylene (LDPE) blown films. Crystallization kinetics and film morphology as a function of both molecular architecture and processing parameters will be investigated using physical models and numerical simulation of the process. The research will include the development of suitable constitutive models for the theology and crystallinity of the polymer being blown. Experiments based on commercial scale film blowing apparatus will be used to evaluate Constitutive models and determine appropriate boundary and initial conditions for the numerical simulation of the film blowing process. A transient, non- axisymmetric, and nonlinear finite element model of the process will be developed. The computational model will also be used to study collapse and instability in a non-axisymmetric setting. The three principal investigators are uniquely qualified, because of their background in theoretical and computational mechanics,polymer structure and mechanical property characterizations, and polymer processing and theology, to successfully carry out the research. A stable film blowing process requires a delicate balance between the excess pressure inside the bubble, the resin extrusion rate, the film wind-up speed, and the cooling rate. These parameters vary considerably from polymer to polymer due to slight differences in melt strength and crystallinity. In practice, the best combinations of process variables required to produce good quality film is achieved through a series of trial-and-error steps that results in large-scale wastage of polymer resin and person hours. Computer simulations of film blowing process offers an attractive alternative for at least three reasons. First, computer simulations can help answer basic questions about how specific process variables influence bubble stability. Second, simulations will help identify which resin Properties are most important in determining performance in film blowing processes. Third, if the constitutive relationship between molecular orientation and polymer crystallinity is properly formulated, the connection between the ultimate film properties and process conditions can be identified. Together-, these three factors should significantly reduce the number of experiments needed to optimize commercial film blowing processes for new polymer resins. The research investigates phenomena that are interdisciplinary in nature. Phase change, crystallization and surface flow phenomena are of interest to various manufacturing processes and scientific problems. The research will be carried with the help of students, who will be trained to develop theoretical formulations, finite element model, and interpretation and correlation of the numerical results, and the students will also be trained to run the film blowing equipment and collect data to assist and correlate numerical simulations. This training of students to think and understand the fundamental, as well practical aspects, is considered as important contribution as the results of the research.