Deformation and Transformation Mechanisms of Polybutene and Poly(vinylidene Fluoride)
Hsu, Tsuey-Chen
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https://hdl.handle.net/2142/71847
Description
Title
Deformation and Transformation Mechanisms of Polybutene and Poly(vinylidene Fluoride)
Author(s)
Hsu, Tsuey-Chen
Issue Date
1987
Doctoral Committee Chair(s)
Geil, Phillip H.
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Abstract
The deformation of thin films of polybutene (PB) and poly(vinylidene fluoride) (PVF$\sb2$) occurs by micronecking. Finite blocks are drawn off the edge of the microneck depending upon the orientation of the original crystalline lamellae comprising the spherulites with respect to the draw direction. Deformation of fresh PB thin film is accompanied by a transformation of tetragonal form to hexagonal form. Potassium permanganate etching and dark field microscopy of fresh thick and thin films reveal that the lateral crystal size of the tetragonal form crystals in the fresh film is significantly reduced upon transformation to the hexagonal crystals during aging. Dark field microscopy and electron diffraction patterns of the deformed PB thin films indicate that the majority of tetragonal crystalline segments transformed into the stable hexagonal crystals while still incorporated in the original lamellae, i.e. during tilt and slip of molecules within the blocks. Morphology of deformed thick films indicates the deformation behavior of thick films is more coherent than that of thin films.
Similar studies of the deformation of PVF$\sb2$, which is accompanied by a phase transformation of anti-polar $\alpha$-phase to the polar $\beta$-phase are also described. In contrast to the transformation behavior of PB thin film, in PVF$\sb2$, based on the bright field microscopy and electron diffraction patterns of deformed PVF$\sb2$ thin films, the transformation appears to occur only during or after the molecules are stripped off the blocks and fibrils are formed. Wide angle and small angle x-ray diffraction patterns indicate that the transformation from $\alpha$ to $\beta$ phase in the deformed thick films is strongly dependent on the temperature at which the deformation occurs. At natural draw ratio (ca. 300%) transformation is more complete in the cold drawn (82$\sp\circ$C) samples than in the hot drawn (130$\sp\circ$C) samples; $\alpha$-phase crystals tend to be oriented rather than transform into $\beta$-phase crystals in the hot drawn (130$\sp\circ$C) samples.
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