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数值模拟的过程进行研究。该研究将包括开发合适的本构模型的流变学和结晶度的聚合物被吹。 基于商业规模的吹膜装置的实验将用于评估本构模型，并确定吹膜过程的数值模拟的适当的边界和初始条件。一个瞬态的，非轴对称的，非线性有限元模型的过程将被开发。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。 这三位主要研究人员具有独特的资格，因为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，能够成功地进行研究。 稳定的吹膜工艺需要在气泡内的过压、树脂挤出速率、薄膜卷绕速度和冷却速率之间保持微妙的平衡。 由于熔体强度和结晶度的微小差异，这些参数在聚合物之间变化很大。在实践中，生产优质薄膜所需的工艺变量的最佳组合是通过一系列试错步骤实现的，这导致了聚合物树脂和工时的大规模浪费。吹膜过程的计算机模拟提供了一个有吸引力的替代方案，至少有三个原因。首先，计算机模拟可以帮助回答有关特定过程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工艺中的性能方面最重要。第三，如果分子取向和聚合物结晶度之间的本构关系被适当地公式化，则可以识别最终膜性质和工艺条件之间的连接。 总之，这三个因素应显着减少优化新聚合物树脂的商业薄膜吹塑工艺所需的实验数量。 这项研究调查的现象是跨学科的性质。相变、结晶和表面流动现象对各种制造工艺和科学问题都很有意义。研究将在学生的帮助下进行，他们将接受培训，以开发理论公式，有限元模型，以及数值结果的解释和相关性，学生还将接受培训，以运行吹膜设备并收集数据，以协助和关联数值模拟。这种训练学生思考和理解的基本，以及实际方面，被认为是重要的贡献，作为研究的结果。

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.