Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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Language: search.filters.language.enSubject: search.filters.subject.Nanofibers

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Now showing 1 - 4 of 4
  • Doctoral Thesis
    Toughening of Carbon Fiber Based Composites With Electrospun Fabric Layers
    (Izmir Institute of Technology, 2017) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, Engin
    The objective of this PhD thesis is to investigate interlaminar Mode-I fracture toughness of carbon fiber/epoxy composites interleaved by micro and/or nano scaled PA66 nonwoven veils. Also, the effects of electrospun PVA nanofibers on the mechanical performance of these composites were investigated. Additionally, this thesis also deals with the effects of aramid nonwoven veils on the mechanical properties of CF/EP composites. The produced nanofibers produced by electrospinning were directly deposited on carbon fiber fabrics. Then, reference and nano-modified laminates were manufactured by vacuum infusion method. A series of mechanical tests such as tensile, compression, three point bending, Charpy-impact, interlaminar shear strength and open hole tensile tests (OHT) were carried out on the prepared specimens. Double cantilever beam (DCB) tests were conducted on reference and interleaf-modified laminates. The effect of PA 66 nanofiber areal weight density was also evaluated with varying electrospinning time. Scanning electron microscopy (SEM) was used to investigate the fiber morphology and to understand the toughening mechanisms. Dynamic mechanic analysis (DMA) was used to investigate the thermo-mechanical behavior of reference and interleaf-modified composite specimens. Differential scanning calorimetry (DSC) was used to determine the thermal properties of micro and electrospun PA66 nonwoven veils. Comparing the mechanical test results, the most effective nonwoven interleaving system was determined in terms of higher delamination resistance and in-plane mechanical properties. Finite element method (FEM) was used to evaluate the effects of electrospun PA66 nonwoven veils on the CF/EP composites. Numerical simulations of Mode-I fracture toughness tests were carried out using ANSYS Workbench. The results showed that the most effective material was electrospun PA66 nonwovens considering the higher delamination resistance. Additionally, the electrospun PA 66 nonwovens also improved Charpy-impact and interlaminar shear strength of the reference CF/EP composites. Numerical results showed good agreement with the experimental ones.
  • Doctoral Thesis
    Development of Carbon Nanotube Embedded Polyacrilonitrile/Polypyrrole Electrospun Nanofibrous Scaffolds
    (Izmir Institute of Technology, 2017) İnce Yardımcı, Atike; Yılmaz, Selahattin
    In this study, electrospun polyacrilonitrile (PAN)/ polypyrrole (PPy) nanofibers containing different PPy content (10, 25, and 50 wt%) were prepared. Different carbon nanotube (CNT) amounts (1, 2, 3, and 4 wt%) were embedded into PAN/PPy nanofibers to improve their mechanical and electrical properties. CNT functionalization was carried out to solve agglomeration problem and functional CNTs effects on PAN/PPy nanofiber morphology was examined. Alignment of nanofibers was studied to improve mechanical properties of nanofibers. Obtained PAN/PPy and PAN/PPy/CNT nanofibers were utilized as kerotinocytes scaffold. PAN/PPy/CNT and aligned and randomly oriented PAN/PPy nanofibers were examined for bone marrow osteogenic differentiation of mesenchymal stem cells (MSCs). 10 wt% PPy content was optimum in terms of mechanical properties and usage with CNTs. Higher strain was observed for 10 wt% PPy content which was 23.3 %. When as-grown MWCNTs were added into PAN/PPy, disordered nanofibers were formed. To improve interficial properties of these composites, as-grown CNTs were functionalized with H2SO4/HNO3/HCl solution. Upon functionalization, formation of hydroxylic and carboxylic groups were detected on the CNT surfaces. TEM examination of the nanofibers obtained with these CNTs showed decrease in beads formation. The functionalized CNTs were well dispersed within the electrospun nanofibers and aligned along the direction of nanofibers. The electroactivity of the fibers indicated that these nanofibers could be used as electrochemical actuator in acidic solutions. PAN/PPy and PAN/PPy/CNT nanofibers supported the attachment and proliferation of keratinocytes and osteogenic differentiation of MSCs. It was found that these nanofibers could be utilized as scaffolds for both cell types.
  • Doctoral Thesis
    Preparation and Characterization of Wound Dressing Contact Layer
    (Izmir Institute of Technology, 2015) Erdoğan, İpek; Bayraktar, Oğuz; Atabey, Atay; Başal Bayraktar, Güldemet
    Wound dressings provide therapeutic and protective features and promotes natural healing process when applied to a wound area. Being non-toxic and immunologically inert, natural biopolymers have potential in fabrication of wound dressings. Growth factors and antibiotics can also be used in functionalization of wound dressings as well as plant extracts. Olive leaf extract has gained attraction due to its dual antimicrobial and antioxidant effect. By clearing pathogenic microorganisms and scavenging against increased amount of reactive oxygen species in the wound area, it has high potential in wound healing. In this study, olive leaf extract incorporated zein fibers were prepared as a model of wound dressing contact layer. In this regard, crude olive leaf extract was fractionated and characterized in terms of antioxidant capacity, total phenol content and antimicrobial activity. Crude extract and its fractions were also subjected to wound scratch assay in the presence of hydrogen peroxide. Oleuropein, as the most abundant component in crude extract, was found to promote cell migration better and close the wound area at a higher rate than other components. On the other hand, crude olive leaf extract exhibited higher percentage of wound closure than its fractions within the same time period, which may be attributed to synergistic effect of unidentified phenolics. Crude olive leaf extract also provided crosslinking effect when incorporated into zein fibers, as well as promoting cell spreading behaviour.
  • Doctoral Thesis
    Applications of Electrospun Nanofibers in Filtration Processe
    (Izmir Institute of Technology, 2013) Horzum Polat, Nesrin; Elçi, Latif
    Electrospinning is a simple and versatile method to fabricate ultrathin fibrous mats from a wide variety of organic and/or inorganic materials. Since it allows fabricating fiber diameter and surface/internal structures by solution and instrumental parameters, electrospun fibers provide much enhanced functionalities, which can not be obtained by bulk materials. This thesis examines the filtration, sensing and catalytical applications associated with the remarkable features of electrospun nanofibers. The systems studied are reported herein; (i) The first part of this dissertation deals with the filtration applications of electrospun nanofibrous membranes.  Nano-sized chitosan fibers were utilized for sorption of Fe(III), Cu(II), Ag(I), and Cd(II) ions from aqueous solutions.  The surface of chitosan fibers were further functionalized by monodisperse nano zero-valent iron (nZVI) particles for the removal of inorganic arsenic species.  Sorption of radioactive U(VI) ions from aqueous systems via column sorption under continuous flow was performed using amidoximated polyacrylonitrile fibers. (ii) The second part of this dissertation presents sensing applications of ceramic fibers.  Humidity sensing properties of electrospun ZnO fiber mats were investigated by quartz crystal microbalance (QCM) method and electrical measurements.  Electrospinning technique was used as coating process for deposition of CeO2/ZnO and ZnO based nanofibers on the electrode of QCM. The fiber-coated QCM sensors were used for the detection of volatile organic compounds (VOCs). (iii) The last part of this dissertation describes an approach to fabricate hierarchically structured composite nanofibers. The nanostructured materials prepared by the simultaneous electrospinning of CeO2 and LiCoO2 precursors and SiO2 nanoparticles were used for the photocatalytic degradation of Rhodamine B.