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Discovery of the beta-form crystal structure in electrospun nanofibers of bio-based poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] and its implication on properties.

紀錄類型:	書目-語言資料,手稿 : Monograph/item
正題名/作者:	Discovery of the beta-form crystal structure in electrospun nanofibers of bio-based poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] and its implication on properties./
作者:	Gong, Liang.
面頁冊數:	1 online resource (163 pages)
附註:	Source: Dissertation Abstracts International, Volume: 78-08(E), Section: B.
標題:	Materials science. -
電子資源:	click for full text (PQDT)
ISBN:	9781369681246

Discovery of the beta-form crystal structure in electrospun nanofibers of bio-based poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] and its implication on properties.
Gong, Liang.

Discovery of the beta-form crystal structure in electrospun nanofibers of bio-based poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] and its implication on properties. - 1 online resource (163 pages)

Source: Dissertation Abstracts International, Volume: 78-08(E), Section: B.

Thesis (Ph.D.)--University of Delaware, 2017.

Includes bibliographical references

Bacterially produced poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHBHx) is a new type of bioplastic which not only inherits the excellent biodegradability and biocompatibility of its parent homopolymer, polyhydroxybutyrate (PHB), but also overcomes PHB's brittleness and stiffness with the incorporation of 3-hydroxyhexanoate (Hx) comonomer units with medium-chain-length (mcl) side chains. The tough and ductile PHBHx, with a much lower crystallinity and melting temperature, is well-suited for many practical applications. Efforts have been made to broaden the application range of PHBHx by introducing the beta-form crystalline structure, where the molecular chains adopt a planar zig-zag conformation. However, it is extremely difficult to produce this beta-form in PHBHx due to its much lower crystallinity and much more flexible molecular chains. In this study, we report an approach using the technique of electrospinning. The strain-induced metastable beta-form crystalline structure was successfully introduced in PHBHx by collecting the macroscopically aligned electrospun PHBHx nanofibers across the air gap on a piece of aluminum foil and on the tapered edge of a high-speed rotary disk. The presence of the beta-form crystal structure in electrospun fiber mats was confirmed by wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR), with molecular orientation of the polymer chains along the fiber axis revealed by polarized FTIR. Selected area electron diffraction (SAED) and AFM-IR were utilized to investigate the morphological and structural details of individual PHBHx nanofibers. The results demonstrated a coexistence of the thermodynamically stable alpha-form crystalline structure, where molecular chains adopt a left-handed 21 helical conformation, and the beta-form in single fibers. The molecular orientation level and the relative amounts of the two crystalline polymorphs were found to be highly dependent on fiber collection methods and fiber diameter. Moreover, the alpha and beta-form were revealed to be spatially distributed as a core-shell structure consisting of an alpha-form-rich core and a beta-form-rich shell, with the thickness of the shell remaining constant despite the variation of fiber diameter. According to these observations, a possible mechanism for the generation of the beta-form was proposed. The effects of electrospinning parameters on the formation of the beta-form were systematically investigated. The results indicated that more beta-crystals can be produced when 1) a higher fiber take-up is used, so that the polymer chains are further stretched before fiber solidification; 2) an optimal solution concentration is chosen, so that a balance between polymer chain deformation and relaxation is maintained throughout the whole electrospinning process; and 3) a more volatile solvent is used, so that more planar zig-zag chains are kinetically frozen in the fibers without being converted to the helical conformation as the fibers solidify. These experimental results indicate that the beta-content in PHBHx nanofibers can be easily regulated by modifying the electrospinning conditions. Finally, the influence of the presence of the beta-form on the piezoelectric response of the electrospun PHBHx nanofibers was studied. It was observed that the fibers containing the beta-form exhibited an obvious piezoelectric response to the applied pressure, possibly due to the planar zig-zag conformation of the chains which gives rise to a significant dipole moment change when subjected to mechanical deformation. In addition, the sensitivity of the piezoelectric PHBHx nanofibers to mechanical pressure was measured to be 7.46 mV/kPa. These preliminary investigations indicate that the piezoelectric performance of PHBHx can be largely improved by increasing the concentration of the piezoelectric-active beta-form crystalline structure. The piezoelectric PHBHx distinguishes itself from all the other piezoelectric polymers with its excellent biodegradability and biocompatibility, environmental-friendliness and most importantly, low manufacturing cost. It is a promising piezoelectric polymer which can be applied in advanced areas including portable/foldable electronic devices, artificial electronic skins and implantable sensors.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2018

Mode of access: World Wide Web

ISBN: 9781369681246Subjects--Topical Terms:

557839
Materials science.
Index Terms--Genre/Form:

554714
Electronic books.

Discovery of the beta-form crystal structure in electrospun nanofibers of bio-based poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] and its implication on properties.
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520 $a Bacterially produced poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHBHx) is a new type of bioplastic which not only inherits the excellent biodegradability and biocompatibility of its parent homopolymer, polyhydroxybutyrate (PHB), but also overcomes PHB's brittleness and stiffness with the incorporation of 3-hydroxyhexanoate (Hx) comonomer units with medium-chain-length (mcl) side chains. The tough and ductile PHBHx, with a much lower crystallinity and melting temperature, is well-suited for many practical applications. Efforts have been made to broaden the application range of PHBHx by introducing the beta-form crystalline structure, where the molecular chains adopt a planar zig-zag conformation. However, it is extremely difficult to produce this beta-form in PHBHx due to its much lower crystallinity and much more flexible molecular chains. In this study, we report an approach using the technique of electrospinning. The strain-induced metastable beta-form crystalline structure was successfully introduced in PHBHx by collecting the macroscopically aligned electrospun PHBHx nanofibers across the air gap on a piece of aluminum foil and on the tapered edge of a high-speed rotary disk. The presence of the beta-form crystal structure in electrospun fiber mats was confirmed by wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR), with molecular orientation of the polymer chains along the fiber axis revealed by polarized FTIR. Selected area electron diffraction (SAED) and AFM-IR were utilized to investigate the morphological and structural details of individual PHBHx nanofibers. The results demonstrated a coexistence of the thermodynamically stable alpha-form crystalline structure, where molecular chains adopt a left-handed 21 helical conformation, and the beta-form in single fibers. The molecular orientation level and the relative amounts of the two crystalline polymorphs were found to be highly dependent on fiber collection methods and fiber diameter. Moreover, the alpha and beta-form were revealed to be spatially distributed as a core-shell structure consisting of an alpha-form-rich core and a beta-form-rich shell, with the thickness of the shell remaining constant despite the variation of fiber diameter. According to these observations, a possible mechanism for the generation of the beta-form was proposed. The effects of electrospinning parameters on the formation of the beta-form were systematically investigated. The results indicated that more beta-crystals can be produced when 1) a higher fiber take-up is used, so that the polymer chains are further stretched before fiber solidification; 2) an optimal solution concentration is chosen, so that a balance between polymer chain deformation and relaxation is maintained throughout the whole electrospinning process; and 3) a more volatile solvent is used, so that more planar zig-zag chains are kinetically frozen in the fibers without being converted to the helical conformation as the fibers solidify. These experimental results indicate that the beta-content in PHBHx nanofibers can be easily regulated by modifying the electrospinning conditions. Finally, the influence of the presence of the beta-form on the piezoelectric response of the electrospun PHBHx nanofibers was studied. It was observed that the fibers containing the beta-form exhibited an obvious piezoelectric response to the applied pressure, possibly due to the planar zig-zag conformation of the chains which gives rise to a significant dipole moment change when subjected to mechanical deformation. In addition, the sensitivity of the piezoelectric PHBHx nanofibers to mechanical pressure was measured to be 7.46 mV/kPa. These preliminary investigations indicate that the piezoelectric performance of PHBHx can be largely improved by increasing the concentration of the piezoelectric-active beta-form crystalline structure. The piezoelectric PHBHx distinguishes itself from all the other piezoelectric polymers with its excellent biodegradability and biocompatibility, environmental-friendliness and most importantly, low manufacturing cost. It is a promising piezoelectric polymer which can be applied in advanced areas including portable/foldable electronic devices, artificial electronic skins and implantable sensors.
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