Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 8Citation - Scopus: 9Polymeric Thermal Analysis of C+h and C+h+ar Ion Implanted Uhmwpe Samples(Elsevier Ltd., 2007) Kaya, N.; Öztarhan, Ahmet M.; Urkaç, Emel Sokullu; Ila, D.; Budak, S.; Oks, E.; Tıhmınlıoğlu, Funda; Muntele, C.Chemical surface characterization of C + H hybrid ion implanted UHMWPE samples were carried out using DSC (differential scanning calorimeter) and TGA (thermal gravimetric analysis) techniques. Samples were implanted with a fluence of 10(17) ion/cm(2) and an extraction voltage of 30 kV. The study of TGA and DSC curves showed that: (1) Polymeric decomposition temperature increased, (2) T-m, Delta C-p and Delta H-m values changed while Delta C-p and Delta H-m increased. T-g value could not be measured, because of some experimental limitations. However, the increase in Delta H-m values showed that T-g values increased, (3) the branch density which indicated the increase in number of cross-link (M-c) decreased in ion implanted samples and (4) increase in Delta H-m values indicated increase in crystallinity of implanted surface of UHMWPE samples.Article Citation - WoS: 54Citation - Scopus: 64Bioactive Fish Scale Incorporated Chitosan Biocomposite Scaffolds for Bone Tissue Engineering(Elsevier Ltd., 2019) Kara, Aylin; Tamburacı, Sedef; Tıhmınlıoğlu, Funda; Havıtçıoğlu, HasanRecently, biologically active natural macromolecules have come into prominence to be used as potential materials in scaffold design due to their unique characteristics which can mimic the human tissue structure with their physical and chemical similarity. Among them, fish scale (FS) is a biologically active material with its structural similarity to bone tissue due to including type I collagen and hydroxyapatite and also have distinctive collagen arrangement. In the present study, it is aimed to design a novel composite scaffold with FS incorporation into chitosan (CH) matrix for bone tissue regeneration. Therefore, two biological macromolecules, fish scale and chitosan, were combined to produce bio-composite scaffold. First, FS were decellularized with the chemical method and disrupted physically as microparticles (100 in), followed by dispersal in CH with ultrasonic homogenisation, CH/FS scaffolds were fabricated by lyophilization technique. Scaffolds were characterized physically, chemically, mechanically, and morphologically. SEM and porosity results showed that CH/FS scaffolds have uniform pore structure showing high porosity. Mechanical properties and degradation rate are enhanced with increasing FS content. In vitro cytotoxicity, proliferation and osteogenic activity of the scaffolds were evaluated with SaOS-2 cell line. CH/FS scaffolds did not show any cytotoxicity effect and the cells were gradually proliferated during culture period. Cell viability results showed that, FS microparticles had a proliferative effect on SaOS-2 cells when compared to control group. ALP activity and biomineralization studies indicated that FS micro particle reinforcement increased osteogenic activity during culture period. As a biological macromolecule with unique characteristics, FS was found as cytocompatible and provided promising effects as reinforcement agents for polymeric scaffolds. In conclusion, fabricated CH/FS bio-composites showed potential for bone tissue engineering applications. (C) 2019 Elsevier B.V. All rights reserved.Article Citation - WoS: 20Citation - Scopus: 21Long Term Stability of Biodegradable Polymers on Building Limestone(Elsevier Ltd., 2019) Kaplan, Zişan; Böke, Hasan; Sofuoğlu, Aysun; İpekoğlu, BaşakSynthetic polymers can be replaced by biodegradable ones as adhesives, water repellents and consolidants on the stone surfaces and facades of the historic buildings in their conservation to minimize future deterioration. In this study, the long-term stability of two biodegradable polymers, polyhydroxybutyrate (PHB) and poly-L-lactide (PLA), and an acrylic polymer (Paraloid B72) which is commonly used in conservation works of artefacts, were evaluated on limestone using a UV lamp-weathering chamber (up to 104 days) for future protection studies. Chemical and morphological changes induced by an accelerated weathering test were examined by Fourier Transform Infrared spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM) analyses. Protection efficiency of the polymers was determined by the changes in color, capillary water absorption, static contact angle on limestone. Paraloid B72, PHB, and PLA coatings significantly increased hydrophobicity while decreasing capillarity water absorption and caused negligible change in the color of the limestone. Protection efficiencies of PLA and PHB polymers were almost the same as that of Paraloid B72, a widely used acrylic polymer. However, PLA and PHB seemed to be favorable polymers as protective agents due to their reversibility and biodegradability, low chromatic changes, good hydrophobic behavior and good stability to weathering in reducing the effects of outdoor exposure on limestone surfaces.Article Citation - WoS: 25Citation - Scopus: 26Lowering the Sintering Temperature of Solid Oxide Fuel Cell Electrolytes by Infiltration(Elsevier Ltd., 2019) Sındıraç, Can; Çakırlar, Seda; Büyükaksoy, Aligül; Akkurt, SedatA dense electrolyte with a relative density of over 95% is vital to prevent gas leakage and thus the achievement of high open circuit voltage in solid oxide fuel cells (SOFCs). The densification process of ceria based electrolyte requires high temperatures heat treatment (i.e. 1400-1500 degrees C). Thus, the minimum co-sintering temperatures of the anode-electrode bilayers are fixed at these values, resulting in coarse anode microstructures and consequently poor performance. The main purpose of this study is to densify gadolinia doped ceria (GDC), a common SOFC electrolyte, at temperatures lower than 1400 degrees C. By this aim, an approach involving the infiltration of polymeric precursors into porous electrolyte scaffolds, a method commonly used for composite SOFC electrodes, is proposed. By infiltrating polymeric precursors of GDC into porous GDC scaffolds, a reduction in the sintering temperature by at least 200 degrees C is achieved with no additives that might affect the electrical properties. Energy dispersive x-ray spectroscopy line scan analyses performed on porous GDC scaffolds infiltrated by a marker solution (polymeric FeOx precursor in this case) reveals a homogeneous infiltrated phase distribution, demonstrating the effectiveness of polymeric precursors.Article Citation - WoS: 24Citation - Scopus: 26Self-Assembly Behavior of the Keratose Proteins Extracted From Oxidized Ovis Aries Wool Fibers(Elsevier Ltd., 2019) Pakkaner, Efecan; Yalçın, Damla; Uysal, Berk; Top, AybenWater soluble keratose proteins were obtained from an Ovis Aries wool using peracetic acid oxidation. The wool samples and the extracted keratose proteins were characterized by using FTIR, XRD, SEM and TGA techniques. Fractions of alpha-keratose (MW = 43-53 kDa) along with protein species with molecular weights between 23 kDa and 33 kDa were identified in the SDS-PAGE analysis result of the extracted protein mixture. DLS and AFM experiments indicated that self-assembled globular nanoparticles with diameters between 15 nm and 100 nm formed at 5 mg/ml keratose concentration. On the other hand, upon incubation of 10 w % keratose solutions at 37 degrees C and 50 degrees C, interconnected keratose hydrogels with respective storage modulus (G') values of 0.17 +/- 0.03 kPa and 3.7 +/- 0.5 kPa were obtained. It was shown that the keratose hydrogel prepared at 37 degrees C supported L929 mouse fibroblast cell proliferation which suggested that these keratose hydrogels could be promising candidates in soft tissue engineering applications. (C) 2018 Elsevier B.V. All rights reserved.Article Citation - WoS: 23Citation - Scopus: 24Investigation of Kinetics of Supercritical Drying of Alginate Alcogel Particles(Elsevier Ltd., 2019) Şahin, İbrahim; Uzunlar, Erdal; Erkey, CanSpherical calcium alginate gel particles were synthesized by dripping method. The effects of temperature, pressure, particle size and CO2 flow rate on kinetics of supercritical drying of alginate gel particles in a packed bed were investigated. Increase in CO2 flow rate, increase in temperature and decrease in particle size increased the drying rate and decreased the drying time. A mathematical model based on (i) the diffusion of the solvent inside the pores of gel particles, (ii) external mass transfer of the solvent from the surface of the gel particles into the flowing fluid stream, and (iii) convection and axial dispersion of the solvent in the flowing fluid stream was developed. A correlation for predicting external mass transfer coefficients for supercritical drying of alcogel particles was developed by fitting the model to experimental data. A good agreement between the experimental data and model results was achieved using the developed correlation.Article Citation - WoS: 27Citation - Scopus: 31Fluoroacrylate-Aromatic Acrylate Copolymers for Viscosity Enhancement of Carbon Dioxide(Elsevier Ltd., 2019) Kılıç, Sevgi; Enick, Robert M.; Beckman, Eric J.The effect of the structure of aromatic acrylate-fluoroacrylate copolymers on CO2 viscosity at elevated pressures was investigated. These copolymers were all found to be miscible with CO2 at pressures between 10-15 MPa (295 K) and induce an increase in the viscosity to some degree. It appears that stacking of aromatic rings is the key factor in viscosity enhancement. The results showed that viscosity of the solution increases with the increasing content of the aromatic acrylate unit in the copolymer, but a point is reached beyond which additional comonomer causes the relative viscosity to drop, suggesting that the aromatic rings associate through intramolecular rather than intermolecular interactions beyond the optimum value. The most effective CO2 thickener identified in this study was the 29% phenyl acrylate-71% fluoroacrylate copolymer. However, the presence of a spacer (methyl or ethyl) between the backbone and the aromatic group substantially diminished the viscosity enhancement.Article Citation - WoS: 15Citation - Scopus: 19Brominated Flame Retardants in a Computer Technical Service: Indoor Air Gas Phase, Submicron (pm1) and Coarse (pm10) Particles, Associated Inhalation Exposure, and Settled Dust(Elsevier Ltd., 2019) Genişoğlu, Mesut; Sofuoğlu, Aysun; Kurt Karakuş, Perihan Binnur; Birgül, Aşkın; Sofuoğlu, Sait CemilBrominated flame retardants (BFRs) are found in multi-media indoors, therefore, may pose serious risks to human health. This study investigated the occurrence of BFRs in particulate matter (PM1 and PM10) and gas phase by active and passive sampling, and settled dust to estimate potential exposure in a computer technical service. Polybrominated diphenyl ethers (PBDEs) and their alternatives (novel BFRs, NBFRs) were studied. PM and gas phase were collected on glass fiber filters and polyurethane foam plugs, respectively, and analyzed with a GC/MS after extraction, clean-up, and concentration. Inhalation exposure of the staff was estimated based on the measured concentrations using Monte Carlo simulation. BDE-209 was the dominating PBDE congener in all media while bis(2-ethylhexyl)-3,4,5,6-tetrabromophthalate and 1,2-bis(2,4,6-tribromophenoxy)ethane were those of NBFRs. Submicron particulate matter (PM1) BFR levels constituted about one half of the PM10-associated concentrations, while average PM10 mass concentration (69.9 μg m−3) was nine times that of PM1 (7.73 μg m−3). Calculated log10 dust-gas and PM-gas partitioning coefficients ranged from −5.03 to −2.10, −2.21 to −0.55, and −2.26 to −1.04 for settled dust, PM10, and PM1, respectively. The indoor/outdoor concentration ratios were >1 for all compounds indicating the strength of indoor sources in the service. The estimated potential inhalation exposures, for future chronic-toxic and carcinogenic risk assessments, indicated that the levels of gas-phase and PM1-associated exposures were similar at approximately one half of PM10-associated levels. Results of this study indicate that the occurrence of BFRs in all studied media should be taken into consideration for occupational health mitigation efforts.Article Citation - WoS: 34Citation - Scopus: 35Development of High Flux Nanofiltration Membranes Through Single Bilayer Polyethyleneimine/Alginate Deposition(Elsevier Ltd., 2019) Tekinalp, Önder; Alsoy Altınkaya, SacideThe aim of this study is to prepare high flux, stable, antifouling nanofiltration membranes through single bilayer polyelectrolyte deposition. To this end, a tight ultrafiltration support membrane was prepared from a polysulfone/sulfonated polyethersulfone blend. Deposition of a polyethyleneimine and alginate pair on this support has reduced the molecular weight cut off from 6 kDa to below 1 kDa. The pure water permeability and polyethylene glycol 1000 rejection of the coated membrane were found to be 15.5 ± 0.3 L/m2·h·bar and 90 ± 0.6%, respectively, by setting the deposition pH for each layer to 8 and the ionic strengths to 0.5 M and 0 M. This membrane has exhibited significantly higher permeability than commercial membranes with the same molecular weight cut off, retaining 98% of the initial flux during 15 h filtration of bovine serum albumine. In addition, the membrane has been able to completely remove anionic dyes from aqueous solution by showing 99.9% retentions to Reactive red 141, Brilliant blue G and Congo red with a 2 bar transmembrane pressure. High flux and membrane stability in acidic and salty environments have been achieved when deposition conditions favor high adsorption levels for the first layer and strong ionic cross-linking between the carboxyl group on the alginate and the amine groups on the polyethyleneimineArticle Citation - WoS: 49Citation - Scopus: 55A Facile Approach for Preparation of Positively Charged Nanofiltration Membranes by In-Situ Crosslinking Between Polyamide-Imide and Polyethylenimine(Elsevier Ltd., 2018) Cihanoğlu, Aydın; Alsoy Altınkaya, SacidePolyamide-imides (PAI) are attractive materials for membrane formation due to their high chemical and thermal stability. In this study, we report a facile approach for preparing positively charged nanofiltration (NF) membranes using a one-step process. Polyethylenimine (PEI) was dissolved in a coagulation bath and formed in-situ ionic crosslinking with PAI during phase inversion. The membranes were characterized by attenuated total reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), contact angle and zeta potential measurements. The most positively charged membrane was obtained when the pH of the coagulation bath was adjusted to 10. This membrane showed a significant decrease in contact angle and surface roughness and increase in the pure water permeability (PWP) compared to the plain PAI membrane. The salt rejection performance of the crosslinked PAI membrane was measured using MgCl2, CaCl2, NaCl and Na2SO4 salts. The rejection of Mg2+ and Ca2+ ions was found to be 95.6% and 90.2%, respectively. The crosslinked membrane showed excellent chemical stability when stored in HCl solution at pH 3 up to 7 days. Antifouling behaviour of the optimized membrane was tested using bovine serum albumin (BSA) and flux recovery ratio of the membrane was found to be 92.2% at the end of 3 h filtration. The results suggest that the positively charged PAI membranes crosslinked with PEI may have a potential in recovering valuable cationic metals from acid mine wastewater.