Modeling of crystallization in polymers /
Crystallization and solidification in polymers is a problem of great importance to the polymer processing industry. In these processes the melt is subjected to deformation while being cooled into the desired shape. The properties of the final product are strongly influenced by the deformation and th...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1999.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=731686731&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Crystallization and solidification in polymers is a problem of great importance to the polymer processing industry. In these processes the melt is subjected to deformation while being cooled into the desired shape. The properties of the final product are strongly influenced by the deformation and thermal histories and the final solid is invariably anisotropic. The focus of this dissertation is on developing continuum models in a general thermo-mechanical setting to capture the effects taking place during solidification and crystallization in polymers. The frame-work has been developed using the idea of multiple natural configurations that was introduced recently to study a variety of non-linear dissipating responses of materials undergoing phase transitions. Using this framework a consistent method is developed to model the transition from a fluid like behavior to a solid like behavior. A novel way is presented of incorporating the formation of an anisotropic crystalline phase in the melt. The anisotropy of the crystalline phase and consequently that of the final solid depends on the deformation in the melt at the instant of crystallization, a fact that has been known for a long time and has been exploited in polymer processing. Particular models are generated by choosing specific forms for the internal energy, entropy and the rate of dissipation. Equations governing the evolution of the natural configurations and also the rate of crystallization are obtained by maximizing the rate of dissipation. The initiation criterion, marking the onset of crystallization, arises naturally in this setting in terms of the thermodynamic functions. It is demonstrated that the proposed models are applicable to polymer crystallization by solving a variety of problems. Firstly, the predictions of the theory are tested by studying three halogenous deformations in a purely mechanical setting. Next, a specific model is developed to study strain induced crystallization in polyethylene terephthalate. The model developed is used to simulate the stretching of polyethylene terephthalate films under conditions of constant extension rate and constant force. The results of the simulation is compared with experimental data. Then, a model is developed to capture the crystallization kinetics in polymers like polyethylene. The model is applied to the study of crystallization in quiescent polyethylene subject to rapid cooling, similar to conditions commonly encountered in polymer processing. The results are compared with data published in the literature. Finally, the crystallization kinetics developed for polyethylene are incorporated in a model to study the film blowing process. The results of the simulation are compared qualitatively with published data obtained from the film blowing process. It is anticipated that the present research will aid in the development of better constitutive equations for crystallizing polymeric systems which in turn will help to accurately model manufacturing processes such as film blowing, fiber spinning and injection molding. This should result in an improved understanding of the effect processing conditions and melt rheology have on the final properties of the material. |
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| Item Description: | Vita. "Major Subject: Mechanical Engineering". |
| Physical Description: | xiii, 161 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 150-160). |