Phd Degree / Doktora

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  • Doctoral Thesis
    Performance Improvement of Composite Materials Used as Hydrogen Storage Tanks by Microstructural Modifications
    (Izmir Institute of Technology, 2020) Ay, Zeynep; Tanoğlu, Metin
    The goal of this Ph.D. thesis is to improve the performance of the cylindrical composites manufactured by filament winding method by using the toughened matrix resin with nano-sized filler (noncovalently functionalized with ethoxylated alcohol chemical-vapor-deposition-grown SWCNTs). The effect of SWCNT concentration on the mechanical performance of these composites was investigated and discussed. One of the main focus of this thesis is to examine the effect of nano-sized filler type and filler concentration on the performance of the epoxy-based composites. For this purpose, epoxy-based nanocomposites with different nano-sized filler types (SWCNT, TEGO, and HNT) at varying concentrations were developed by a calendaring (3-roll-mill) method. A series of mechanical tests were performed for reference composite and developed nanocomposites. The scanning electron microscopy (SEM) was used to reveal the morphology and toughening mechanisms by examining the fractured surface of nanocomposites. The rheological behaviors and contact angle measurements with glass fiber of the selected filler (SWCNT) incorporated epoxy suspensions were investigated to determine the suitability of suspensions for the filament winding process. The reference and SWCNT modified glass fiber (GF)-based cylindrical fiber-reinforced polymeric composites (CFRPCs) with an inner diameter of 60 and 275 mm were manufactured by the filament winding method. The split-disk and three-point bending tests were performed for GF-based CFRPCs. The double cantilever beam (DCB) test was also carried out for the reference and SWCNT modified GF-based CFRPCs to investigate the effect of SWCNT existence on the interlaminar fracture toughness of CFRPCs. The fractured surfaces after the DCB test were analyzed under the SEM to comprehend the toughening mechanisms, and micro-and nano-sized filler morphologies. Consequently, it was revealed that blending and hence toughening the epoxy resin with SWCNT improves the interlaminar properties of the GF-based composites.
  • Doctoral Thesis
    Development of Multi and Double Walled Carbon Nanotubes (cnts) / Vinylester Nanocomposites
    (Izmir Institute of Technology, 2008) Seyhan, Abdullah Tuğrul; Tanoğlu, Metin
    This study focuses on development and characterization of thermosetting resin based nanocomposites containing multi and double walled carbon nanotubes with and without amine functional groups (MWCNT, DWCNTs, MWCNT-NH2 and DWCNTNH2).A novel 3-roll milling technique was conducted to prepare the resin suspensions with carbon nanotubes (CNTs). Rheological measurements performed on the resin suspensions showed that addition of very low contents (0.05, 0.1 and 0.3 wt. %) of MWCNTs and MWCNT-NH2 affected the flow characteristic of the resin, significantly.Further, the curing behavior of a vinylester-polyester hybrid resin suspensions containing 0.3 wt % of MWCNTs and MWCNT-NH2 was intensively studied. It was found that regardless of amine groups, presence of CNTs affected the polymerization of the hybrid matrix resin. Final individual fractional conversion rates of styrene and vinylester monomers were found to be vastly dependent on the type of CNTs. Glass transition temperature (Tg) values of the nanocomposites with MWCNTs and MWCNTNH2 were found to increase with filler content. Moreover, nanocomposites containing MWCNTs and MWCNT-NH2 were found to possess higher tensile strength, elastic modulus as well as fracture toughness and fracture energy as compared to the neat hybrid resin. On the other hand, electrical properties of the nanocomposites were also investigated and it was found that nanocomposites with MWCNTs exhibited the lowest percolation threshold value. In addition, nanocomposites with amino functionalized CNTs were found to exhibit lower electrical conductivity as compared to those with untreated CNTs. Nanocomposites with AC electric field induced aligned CNTs were also prepared. Finally, based on the findings obtained for CNT/ resin suspensions, as a case study, electrically conductive glass fiber reinforced composite laminates were successfully produced, using the CNT modified resin suspensions as matrix material, via Vacuum Assisted Resin Transfer Molding (VARTM) and Resin Transfer Molding (RTM) methods.
  • Doctoral Thesis
    Enhancement of Thermal, Electrical and Optical Properties of Zinc Oxide Filled Polymer Matrix Nano Composites
    (Izmir Institute of Technology, 2009) Özmıhçı, Filiz; Balköse, Devrim
    The purpose of this study is to enhance the electrical, thermal and optical properties of polyethylene and polypropylene by the addition of zinc oxide (ZnO) filler.Embedding ZnO in a polymeric matrix could make an economic, weight saving, chemically resistive, optical, flexible and conductive materials which possesses the properties of zinc oxide.Composites with higher electrical and thermal conductivity having luminescence properties were prepared using commercial and hydrothermally synthesized ZnO powders with different particle size and conductivity. Effect of ZnO loading and surface treatment on composite properties was investigated. Luminescence effects in green and blue regions were detected in all powders due to the defects on the structure of ZnO.The powders were found to be moderately conductive materials, as well. Un-homogenously dispersed composites were prepared using rheomixer since especially nano powders tended to be agglomerated in the composite. On the other hand, different surface properties of powder and polymer caused adhesion and wetting problems. Microvoids were detected in the interphase, as well.Composites can be used as an electrostatic dissipation and moderate electrical conductive applications in the field of electrical conductivity, as a heat sink in the field of thermal conductivity and as a solid state lamp due to luminescence properties. Stiffness of the composites was very high compared to neat polymer and can be properly used as an engineering material.