Tejas Upasani

Abstract

This thesis describes the effect of casting conditions on the crystallization and resulting morphology in compatibilized and uncompatibilized blends of poly(ethylene oxide) and poly (vinylidene fluoride). Two systems based on grades of PVDF were used: Kynar 301, pure PVDF, and Kynar7201, a 80:20 copolymer of PVDF and hexafluoro propylene. Poly (methyl methacrylate) and poly (vinyl acetate) were used as compatibilizers. Acetonitrile and tetrahydrofuran were used as common solvents to prepare the polymer blends. Two casting conditions were employed. In the first, hot polymer solutions were precipitated in cold hexane. In the second, the hot solutions were cast on aluminum pans. The precipitates from hexane, upon filtration, and the films obtained from casting on aluminum pans were dried in a vacuum oven at 80C for 24 hours. To study the crystallization of PEO and PVDF and the resulting morphology, the powder/films were then characterized by differential scanning calorimetry and polarized optical microscope.

In most mixtures, when THF was used as the casting solvent, the heterogeneous nucleation in PEO crystallization was suppressed. Prominent peaks characteristic of homogeneous nucleation of PEO crystallization were observed in the DSC thermograms. On the other hand, when acetonitrile was used as the casting solvent, large peaks characteristic of heterogeneous nucleation in PEO crystallization were visible at ~ 40C along with peak at 0C due to homogeneous nucleation in some systems. The peaks for heterogeneous nucleation in acetonitrile systems arise from large PEO domains dispersed in PVDF matrix. Consequently, prominent PEO structures were observed in the corresponding optical micrographs. THF systems exhibited broader peaks due to homogeneous nucleation of PEO crystallization arising from fine dispersion of small PEO domains in PVDF matrix. These results were valid for uncompatibilized as well as compatibilized blends. Crystallization of PVDF was not appreciably affected in either of the systems. Among the compatibilizers, PMMA tends to suppress PEO crystallization to a greater extent than does PVAc.

Towards application of these blends, an exploratory work was carried out where PEO fraction from the blend was extracted using solvent extraction techniques. Methanol-water mixture was used as a solvent to extract PEO. The DSC thermograms reveal that significant extraction of PEO has occurred. The morphology developed upon extraction is examined by optical microscope. The images show differences in structure, before and after extraction of PEO. Though optical microscopy is not the best technique to examine the morphology for PEO extracted samples, it creates a basis for further investigation.

Library of Congress Subject Headings

Polymers; Crystallization

Publication Date

2005

Document Type

Thesis

Student Type

Graduate

Degree Name

Materials Science and Engineering (MS)

Department, Program, or Center

Center for Materials Science and Engineering

Advisor

Andreas Langner

Advisor/Committee Member

KSV Santhanam

Comments

Physical copy available from RIT's Wallace Library at TA455.P58 U62 2005

Campus

RIT – Main Campus

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