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

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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.