Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
Browse
9 results
Search Results
Master Thesis Recovery of Lithium From Aqueous System Using Manganese Oxide Adsorbent With Developed Electrospun Mat Substrate(01. Izmir Institute of Technology, 2023) Akgün, Berk; Ebil, Özgenç; Demir, Mustafa MuammerLithium is used in many fields due to its high energy density and unique electrochemical properties. Recently, there has been a strong increase in demand for lithium, so the extraction of lithium from natural water resources has become a remarkable research topic. One of the most effective methods of separating lithium from natural water sources is adsorption using lithium ion-sieve adsorbents. However, the powdered nature of the adsorbents makes them challenging to process and less recyclable. Recent studies have focused on developing adsorbents using different polymeric materials as substrates or binders. In the thesis, as a new approach, flexible and free-standing polyurethane electrospun mat substrates were produced and combined with λ-MnO2 to extract lithium from aqueous systems, and their lithium removal performance was investigated. After the fabricated mats and λ-MnO2 powder were characterized, the deposition process was performed, and filtration studies were carried out in synthetic lithium solution. Optimum conditions for lithium removal were found as an adsorbent amount of 200 mg, and 200 ppm initial [Li+], and pH 12. In addition, lithium removal performances have been improved by stacking mats and multi-stage filtration processes. Lithium removal reached 76.6% when a 400 ppm lithium solution and an 8-step filtration were used. Lithium removal experiments were performed with salt-lake brine containing high concentrations of various ions and showed that these ions reduced the lithium removal. In the study, PU electrospun mats for λ-MnO2 powder were found to be a promising substrate for lithium removal from aqueous systems.Master Thesis Improving Mechanical Properties of Adhesive Joints in Carbon Fiber Reinforced Polymer Composites by Incorporation of Graphene Added Electrospun Polymeric Nanofibers(01. Izmir Institute of Technology, 2023) Yeke, Melisa; Tanoğlu, MetinSince composites joined with mechanical fasteners cause severe delamination damage, stress concentration in the joint area, and weight increase, joining composite materials with innovative methods have recently gained more importance. These joining methods prevent delamination damage, provide a uniform distribution of stress, and do not cause considerable weight increases. However, modifying the surface of composite parts joined by innovative methods is critical. In this study, the bonding surface was modified by coating carbon/epoxy prepregs with electrospun nanofibers with 10% wt/v ratio of PA 66 and 1%, 2% and 3% wt/v ratio of rGO added. Composite parts were joined in the hot press by the secondary bonding method using 3 plies of FM 300K film adhesive. The morphological structure of nanofibers and the dispersion of rGO were analyzed by SEM. The thermal properties of nanofibers were analyzed by DSC. The contact angle measurement device was used to determine the hydrophilic and hydrophobic properties of the unmodified prepreg and nanofiber-modified prepreg surface. The most hydrophilic surface was observed on the nanofiber-coated surface with 2% rGO added. Single Lap Joints (SLJ), and Charpy Impact tests were performed to examine the mechanical properties of modified and unmodified composite plates. According to the SLJ and Charpy Impact results, an improvement of 17.89% and 30.59% was observed in carbon/epoxy composite plates whose surface was modified with 2% rGO, respectively.Master Thesis Fabrication of Colorimetric Ph Indicator Films by Electrospinning(Izmir Institute of Technology, 2022) Erez, Elif; Bayramoğlu, Beste; Eroğlu, Ahmet EminThe trend in the food packaging industry evolves towards innovative packaging materials as biosensors, which record the status of the product and can warn the consumer. The logic behind the colorimetric pH biosensor is that they provide the essential information about food visually by detecting change in pH. Anthocyanins are natural color pigments susceptible to pH change. Purple basil is rich in anthocyanins. In this study, ultrasound-assisted extraction was used for the extraction of dry purple basil. The processing conditions were optimized by response surface methodology (RSM) in terms of the total monomeric anthocyanin content and the increase in green intensity with pH. Electrospinning is a nanofiber fabrication operation used to encapsulate sensitive bioactive compounds for the production of intelligent sensing system. Polycaprolactone (PCL) films incorporating different purple basil extract (PBE) concentrations were fabricated by electrospinning procedure for the usage of colorimetric pH-indicator films as intelligent packaging. The most beadles and uniform nanofibrous mats were obtained when the spinning conditions were V=20 kV and Q=0.4 mL h-1for 10% (w v-1) PCLsolutions containing 0.4% and 0.6% (w v-1) PBE. The average fiber diameters in these films were 178.59±52.92 nm and 235.39±92.46 nm, respectively. The films gave promising results with regards to their use as colorimetric pH-indicator films. The time required to observe a visible color change (ΔE) in these films was only 4-5 s. The ΔE values between all successive pH’s were higher than 2, which is detectable by an inexperienced observer. Keywords: Anthocyanin, Purple Basil, Ultrasound-Assisted Extraction, Response Surface Methodology (RSM), Electrospinning, Colorimetric pH-indicator Films.Master Thesis Improving Joining Performance of Composites by Electro-Spinning of Nano Fibers(01. Izmir Institute of Technology, 2021) Esenoğlu, Gözde; Tanoğlu, MetinMechanical joints traditionally used in composite materials (screws, rivets, etc.) not only increase weight but also act as a stress collector, causing serious delamination problems. At the same time, the development of alternative joining techniques has become an important issue in the composite industry due to its sensitivity to corrosion, electromagnetic properties/radar absorption properties, labor cost and adverse effects on the manufacturing process. In this master's thesis, the effects on the mechanical properties of two different prepreg composites (UD and woven) coated with polyamide 66 (PA 66) nanofibers in the joint region were investigated. In addition, the fiber structures of the produced PA66 nanofibers were investigated. The produced nanofibers were directly coated on the bond zone layer (top surface) of the carbon prepregs. The reference and nanofiber doped prepregs were cured by the hot press method, and then they were combined with the secondary bonding method using FM300K film adhesive in the hot press. Tensile, compression, bending, shear, Charpy-impact and double cantilever beam (DCB) tests were performed on the produced samples. The effect of homogeneity and areal weight density (AWD) of PA66 nanofibers on mechanical performance was investigated. The morphology and post-test deformations of the nanofibers were investigated by scanning electron microscopy (SEM). The thermal properties of PA66 nanofibers were investigated by the differential scanning calorimetry (DSC) method. By comparing the SEM images and the lap shear test results, the most efficient parameters for the mechanical performance of the composites were determined. The results showed that PA66 nanofibers produced with a 10% wt solution ratio and 10 min coating time were the most efficient on composites. The addition of PA66 nanofibers to the junction region with the electro-spinning technique has been proven to increase the junction region performance of the materials and outputs have been obtained.Master Thesis A Novel Approach for Fabrication of Free-Standing Conductive Network: Pedot: Pss Based Bendable Chemo and Photoresistor(Izmir Institute of Technology, 2019) Mutlu, Mustafa Umut; Yıldız, Ümit Hakan; Demir, Mustafa MuammerElectrospinning is a simple and versatile technique for the fabrication of polymeric nanofibrous substrate with high surface to volume ratio. Besides high surface to volume ratio, their dimensional stability and flexibility make it a perfect candidate for conductive network for various sensor applications. Free-Standing conductive network can be fabricated by deposition of PEDOT:PSS or MWCNT through bendable nanofibrous substrate. As a simple example for sensor applications, the moving object has been sensed through the electrostatic interactions between fibers and object. The sensing range has been found to be 1-5 cm above the surface of fabric. By the controlled combination of conductive polymers and electrospun polymer nanofibers effective device miniaturization has been provided without loss of performance. The noncontact motion sensor platform has unique flexibility and light weight holding a potential for wearable sensor technology. For another application as a wearable electronics, the controlled combination of conductive network and light-matter interaction provides opportunities to fabricate photo-resistor exhibits broad band response 400 to 1600 nm that holding promises for ultra-thin sensors used in telecommunication. As a final example, we report the effect of gold and iron oxide nanoparticles on the selectivity and sensitivity of MWCNT or PEDOT:PSS based chemiresistor responsive to VOCs. The interplay between conductive layer by gold and iron oxide nanoparticles resulted a significant conductivity improvement that affecting selectivity which is governed by the interaction between electron-donating VOCs and NP doped conductive layer due to variation in charge carrier densities in conductive layer lattice.Master Thesis Polymer Based Extracellular Matrix Mimetics for 3d Cell Culture(Izmir Institute of Technology, 2018) Türker, Esra; Arslan Yıldız, AhuTissue engineering combines engineering principles and knowledge of life sciences to improve biological substituents. Three dimensional (3D) supporting structures, namely scaffolds obtained from biomaterials to mimic extracellular matrix (ECM) that provides suitable microenvironment for cell proliferation, migration and differentiation. In this study, poly (L-lactide-co-ε-caprolactone) (PLLCL) and collagen type I was used to fabricate scaffold by electrospinning method. In literature, collagen was often dissolved in toxic and harmful solvents that creates the major problem for cell culture applications. To overcome this problem “co-spinning” methodology is utilized for the formation of non-toxic collagen-based ECM mimetic scaffold. Collagen mixed with water-soluble carrier materials which is either polyvinylpyrrolidone (PVP) or polyvinyl alcohol (PVA) and co-electrospinning is carried out with PLLCL. Fabricated scaffolds were immersed into water to remove co-spinning agent; PVA or PVP, so only PLLCL/Collagen remained. PLLCL has homogeneous fibers in a diameter of 1.312 ± 0.22μm. The contact angle of PLLCL (136.6° ± 2.6) proved hydrophobic behavior of PLLCL material. The contact angle of the scaffold decreased up to 86.7° ± 0.1 confirming that hydrophobic behavior is decreased with the addition of collagen. Also, collagen-containing scaffolds were saturated at lower amount of protein than PLLCL, PLLCL/PVA and PLLCL/PVP scaffolds. Cytotoxicity analysis of scaffolds showed that PVA containing scaffolds had lower viability than PVP containing scaffolds; so most of the cell studies were carried out with PLLCL/ Collagen scaffolds fabricated by PVP cospinning. Cell proliferation on PLLCL/Collagen scaffolds found to be more favorable than PLLCL and PLLCL/PVP scaffolds.Master Thesis Development of Natural Compound-Loaded Nanofibers by Electrospinning(Izmir Institute of Technology, 2010) Balta, Ali Bora; Bayraktar, OğuzIn this study, the crude silk which is obtained from silkworm was turned into a silk solution after a serial procedure. Then, regenerated silk (foam) was obtained. The regenerated silk was dissolved in formic acid and polymer solution was prepared. After, nanofibers were produced by electrospinning. On the other hand, the content and antimicrobial activities of some plants were analyzed. Then all three forms of silk was absorbed with the olive leaf extract and extract desorption tests were done. As the first step of the study, the analyses of extracts which were obtained from four different plants were done. For this, total phenolic content and antioxidant capacity were found. In addition, minimum inhibition concentration (MIC) test and disc diffusion test were made for all extracts to Escherichia coli, Staphylococcus epidermidis, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa bacteria and Candida albicans fungi in order to determine their antimicrobial activity. While producing nanofibers from silk polymer with electrospinning method, different parameters such as concentration, voltage and distance were examined. Morphological characterization of nanofibers was done by scanning electron microscope (SEM). According to the results, the nanofiber with an optimum value which has a suitable diameter and structure was selected. With this nanofiber, the absorption and desorption tests of natural compound were made. The results were obtained by High pressure liquid chromatography (HPLC). Same adsorption and desorption tests were done also with the microfiber silk and regenerated silk (foam). As a result, it was shown by the controlled experiments that nanofibers were better for adsorption and desorption of natural compound when compared to microfiber silk and regenerated silk. In conclusion, nano-sized silk fibroin structures can be adsorbed with natural compounds in order to gain functionality. Using this kind of biofunctional products as medical textile and wound dressing material will be more advantageous when compared to current wound dressing materials.Master Thesis Preparation of Electrospun Composite Fibers Based on Ps-pi-ps/Cdsxse1-x Nanoparticles(Izmir Institute of Technology, 2011) Aşkın, Görkem; Demir, Mustafa Muammer; Özçelik, SerdarPolymeric fibrous films were prepared based on polystyrene-b-polyisoprene-bpolystyrene triblock copolymer (SIS) and CdSxSe1-x nanoparticles by electrospinning process. SIS with 14 wt % Styrene (14% PS-SIS) and 22 wt % Styrene (22% PS-SIS) triblock copolymers were employed. Both of them undergo microphase separation. While the former shows cylinder-like morphology, the latter exhibits the lamellae one. CdSxSe1-x partciles were stabilized by two different surfactant molecules: i) n-trioctylphosphine oxide (TOPO) and ii) oleic acid (OA). When the particles were blended with 22% PS-SIS, particles capped with TOPO preferentially filled to PS domain whereas particles capped with OA loaded into the PI domain. Composite electrospun fibers were prepared with a diameter of 1.5 mm on average. Electrospinning parameters (potential difference, solution concentration, flow rate) were investigated on fiber morphology. The films are colorless under day light and have strong green emission under UV light.Master Thesis Investigation on Emission Features of Ttbc Aggregates in Pva Fiber Mats by Electrospinning(Izmir Institute of Technology, 2010) Özen, Bengisu; Demir, Mustafa Muammer1,1’,3,3’-tetraethyl-5,5’,6,6’ -tetrachlorobenzimidazolocarbocyanine (TTBC) is a frequently used cyanine dye that undergoes two different types of molecular aggregate (J and H-type). Dye molecules, in general, come into aggregation in ionic solutions and solid surfaces without control over the type and orientation of the resulting aggregate. In this research, we focused on electrospinning of aqueous poly(vinyl alcohol) (PVA)/TTBC solutions and investigated whether the aggregate formation could be controlled by solution and instrumental parameters of this process. Initially, TTBC was molecularly dispersed in aqueous PVA solution with a weight fraction of 0.001- 0.65 % and the precursor solution was subjected to electrospinning under electrical field ranging from 0.95-1.81 kV/cm. A stationary horizontal electrospinning set-up was used including two parallel-positioned metal strips as counter electrode. Both randomlydeposited and uniaxially aligned fibers were achieved. For the reason of comparison, reference films were prepared by spin-coating and film casting. Photoluminescence and polarized FTIR spectroscopy techniques were employed to examine spectral properties of the fibers. While H- and J-type aggregates coexist within spin-coated films and only J-aggregates exist within cast films, only H-type aggregates were observed within the fibers regardless of their alignment. A strong polarized emission was obtained from the unaxially aligned fibers due to the orientation of H-aggregates along the fibers. Consequently, electrospinning was found to be an alternative method to bring individually dispersed dye molecules into oriented H-type aggregates within submicron diameter fibers. Similar experimentation was also applied to TTBC/PS and Pyrene/Polystyrene(PS) systems to investigate aggregation behavior of dye molecules. TTBC exhibited similar behavior in PS/Dimethylformamide (DMF) system observed in PVA/H2O system. However, electrospinning has no remarkable influence on aggregation of pyrene in excimers. It slightly disassemble excimer structure.