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Synthesis, characterization and applications of new types of fiberous structures
Hromádko, Luděk ; Kočí,, Kamila (oponent) ; Pekař, Miloslav (oponent) ; Macák, Jan (vedoucí práce)
This thesis presents a comprehensive investigation of centrifugal spinning and in particular the novel synthetic approaches for nano- and microfibers by this highly interesting technology. New types of polymeric fibers and also inorganic (ceramic) fibers are presented, along with their characterization and their use in various applications. In the first section, many available techniques for fibers preparation are introduced and explained. Their advantages and drawbacks are described and discussed. A comparably large attention is given to electrostatic spinning and centrifugal spinning, which belong between mostly used techniques for industrial production of the fibers. The sub-section on applications describes the main applications of the fibers, for example air/water filtration, tissue engineering, drug delivery and Li-ion battery separators. The second section presents a large experimental and comparative study of the two most used techniques for fiber preparation, the electrospinning and centrifugal spinning. Polyvinyl pyrrolidone (PVP) and polyvinyl acolhol (PVA), as some of the mostly used polymers for fibers preparation, were used for comparison of these techniques. Many parameters (air temperature, humidity, rotations etc.) were exploited and their influence on the fibers´ quality was investigated. Such a large comparatiove study of electrospinning and centrifugal spinning has not yet been conducted before us and this particular effort. The third section presents the preparation of WO3 fibers by centrifugal spinning. New, simple and green recipe of the spinning solution based on the ammonium metatungstate (NH4)6H2W12O40.xH2O and polyvinyl pyrrolidone (PVP) is demonstrated. Influence of variations of the concetration of the polymer and precursor on the properties of resulting fibers is shown. The resulting fibers with the best photocatalytic performance is compared with the fibers prepared by electrospinning and commercialy available nanoparticles. The centrifugal spun fibers showed the 1.4 up to 4 time higher photocatalytic activity. The centrifugaly spun fibers also has higher specific surface (SBET = 22.3 m2/g) compared to electrospun fibers (SBET = 7.4 m2/g) and nanoparticles (SBET = 6.4 m2/g). The fourth section shows the preparation of the amorphous SiO2 fibers. The new recipe for centrifugal spinning has been developed. The spinning solution was based on the tetraethyl orthosilicate (TEOS) and polyvinyl pyrrolidone (PVP). The calcination profile has been tuned to reach the SiO2 fibers with 824 m2/g of specific surface. The prepared SiO2 fibers had pore size distribution in 2 – 10 nm and volume of pores 0.547 cm3/g. The prepared fibers possessed superior adsorption capacity of the water comparing to silicagel of the same textural type. The fifth section presents the preparation of the ZrO2 fibers with addition of yttrium (Y). Two different precursors were used to prepare ZrO2 fibers. The use of pure Zr precursor led to fibers containing the mixture of monoclinic and tetragonal structure. The addition of about 3 mol.% of yttrium led to fibers that consist of tetragonal single phase, which is stabilized by Y. The yttrium addition also led to smaller crystallite size comparing to pure ZrO2 fibers.
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