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Mapping the Microstructure of Single-Site Ethylene/1- Hexene Copolymers Using Response Surface Methods
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- Author / Creator
- Hegde,Venugopal
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Polyolefins are a commercially important class of polymers made only of carbon and hydrogen atoms. Polyethylene accounts for a sizable fraction of commercial polyolefins, covering applications from packaging films, water tanks, biomedical equipment, bulletproof vests, and adhesives. The use of a wide variety of catalysts and multimodal molecular weight distribution (MWD) are some routes to modify the microstructure of polyethylene and its application properties. Polyolefins with multimodal MWD are commonly produced by polymerizing ethylene and 1-olefins in reactor cascades or using a single reactor with more than one catalyst type.
Designing polyethylene resins involves optimizing multiple microstructural distributions that result in targeted end-use properties. The end-use (secondary) properties are connected to the resin microstructure (primary property) by empirical equations called structure-property relationships. The goal of a polymer reaction engineer is to find polymerization conditions that achieve all or most of the properties in this wish list. The conventional solution to this problem is to develop fundamental polymerization kinetics models, estimate their parameters, and validate the model predictions vis-à-vis experimental data. However, the conventional route is a time consuming and expensive process. An alternative solution is to use response surface models, in which polymerizations are performed according to an optimal experimental design to develop statistically significant empirical models at a fraction of time and experimental effort required by phenomenological models.
In this thesis, response surface models were applied to quantify the microstructure of ethylene/1-hexene copolymers made with a single site metallocene catalyst in solution polymerization. The molar weight averages and distributions, short chain branching (1-hexene content), and melting temperatures of these copolymers were modeled and predicted. The response surface models developed were subjected to acceptance criteria based on statistical significance tests. Explanatory validation on the effect of factors confirmed the validity of models. The forward process of predicting MWD for a given set of polymerization conditions was reversed to test the utility to reverse-engineer to find the reactor conditions for a defined resin microstructure.
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- Graduation date
- Spring 2022
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.