WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 18Citation - Scopus: 17Cnt Incorporated Polyacrilonitrile/Polypyrrole Nanofibers as Keratinocytes Scaffold(Trans Tech Publications, 2019) İnce Yardımcı, Atike; Aypek, Hande; Öztürk, Özgür; Yılmaz, Selahattin; Özçivici, Engin; Meşe, Gülistan; Selamet, YusufPolypyrrole (PPy) is an attractive scaffold material for tissue engineering with its non-toxic and electrically conductive properties. There has not been enough information about PPy usage in skin tissue engineering. The aim of this study is to investigate biocompatibility of polyacrilonitrile (PAN)/PPy nanofibrous scaffold for human keratinocytes. PAN/PPy bicomponent nanofibers were prepared by electrospinning, in various PPy concentrations and with carbon nanotube (CNT) incorporation. The average diameter of electrospun nanofibers decreased with increasing PPy concentration. Further, agglomerated CNTs caused beads and disordered parts on the surface of nanofibers. Biocompatibility of these PAN/PPy and PAN/PPy/CNT scaffolds were analyzed in vitro. Both scaffolds provided adhesion and proliferation of keratinocytes. Nanofiber diameter did not significantly influence the morphology of cells. However, with increasing number of cells, cells stayed among nanofibers and this affected their shape and size. In this study, we demonstrated that PAN/PPy and PAN/PPy/CNT scaffolds enabled the growth of keratinocytes, showing their biocompatibility.Article Citation - WoS: 2Citation - Scopus: 1Stabilizing Effect of Biobased Additives on the Thermal Degradation of Pvc(Trans Tech Publications, 2010) Egbuchunam, Theresa Obuajulu; Okieimen, Felix Ebhodaghe; Balköse, DevrimNovel biobased additives prepared from rubber seed oil were evaluated as thermal stabilizer for PVC. Divalent metal (barium and cadmium) soaps of rubber seed oil were prepared by metathesis in aqueous alcohol and characterized by thermal methods (differential scanning calorimetry and thermogravimetry). The stabilizing effect of the soaps and their admixtures on the thermal degradation of PVC powder and plasticized PVC was examined by dynamic thermogravimetry and dehydrochlorination studies at 160°C using the Thermomat equipment. The metal soaps showed multiple decomposition endotherms but were generally stable (with weight loss less than 5%) within the temperature range (180-220°C) frequently used in the processing of PVC. Using the Broido model, values of apparent activation energy of decomposition of between 50 and 200 kJmol-1 were obtained for the soaps. The biobased additives were found to be relatively effective in stabilizing PVC in powder and plasticized forms against thermal degradation. Using inhibition/retardation time, temperature of incipient decomposition, and temperature at which various extents of decomposition was attained as indices of thermal stabilization, the results from this study indicate a potential for the application of the biobased additives as thermal stabilizer for PVC in rigid and flexible formulations. © (2010) Trans Tech Publications, Switzerland.Conference Object Citation - WoS: 2Citation - Scopus: 2Studies in the Utilization of Biobased Additives as Thermal Stabilizer for Plasticized Pvc(Trans Tech Publications, 2009) Okieimen, Felix Ebhodaghe; Egbuchunam, Theresa Obuajulu; Balköse, DevrimDivalent metal (barium, cadmium, calcium and zinc) soaps of rubber seed oil and their binary mixtures (BaJCd and CaJZn) and epoxidized rubber seed oil (4.5% epoxide content) and its admixtures with the single divalent metal soaps were evaluated as thermal stabilizer for dioctylphthalate plasticized PVC using changes in discolouration indices (yellowness index and UV absorption at 360nm) and initial rates of dehydrochlorination measured at 140 and 160°C. The results obtained showed that the divalent metal soaps were relatively effective in stabilizing the dioctylphthalate plasticized PVC against thermal degradation and that the binary soap mixtures enhanced the heat stabilizing effectiveness: marked reduction in the values of the discolouration indices; longer dehydrochiorination induction period and smaller values of rate constant of initial rate of dehydrochlorination. It was found that epoxidized rubber seed oil was less effective in comparison with the divalent metal soaps in stabilizing plasticized PVC against thermal degradation. These results show that the bio-based additives are compatible with dioctylphthalate plasticized PVC, stable to heat within the range of temperature used in the processing of plasticized PVC, inhibitlretard dehydrochlorination and reduce the extent of degradation.Conference Object Citation - WoS: 2Citation - Scopus: 2Investigation of the Permeability of Pure Gases in Sol-Gel Derived Al 2o 3 Membrane(Trans Tech Publications, 2004) Topuz, Berna; Çiftçioğlu, Muhsin; Özkan, FehimeThe preparation, characterization and pure gas permeation of sol-gel derived alumina membranes were investigated in this work. The effects of acid concentration/type and water content on the particle size in the sols and pore size distributions of the unsupported membrane were investigated by N 2 adsorption/desorption isotherms and Dynamic Light Scattering. Increasing the H +/Al 3+ mole ratio from 0.1 to 0.25 caused the hydrodynamic sol particle size and BJH pore size to decrease from 65 to 30 nm and 3.6 to 2.9 nm, respectively. The pore size increased from 2.8 nm to 3 nm upon increasing the calcination temperature from 500 to 600°C. Unsupported membranes were heat treated in the 200 to 1200 °C range for the characterization of the phase structure. Pinhole and crack free alumina membranes about 3 μm (2-layer) in thickness was observed from the SEM pictures with insignificant infiltration. The CO 2 permeability through the double layer γ-Al 2O 3 membrane calcined at 600 °C was 2.25*10 -7 mol/m 2.s.Pa, and had a slight pressure dependence indicating Knudsen Diffusion and Laminar Flow being the effective transport mechanisms. Upon the calcination of a similar 2-layer alumina membrane at 500°C, the CO 2 permeability decreased to 1.51 *10 -8 mol/m 2.s.Pa. without pressure dependence.Conference Object Citation - Scopus: 1Microstructural Characterization of Industrial Chromite and Spinel Cement Kiln Refractories With Emphasis on the Iron-Rich Rims(Trans Tech Publications, 2004) Mercanköşk, Y.; Akkurt, Sedat; Çiftçioğlu, MuhsinMagnesia-chromite (MgO + MgO·Cr2O3) and magnesia-spinel (MgO + MgO·Al2O3) refractory bricks that are used in the high temperature zones of rotary cement kilns are investigated for their microstructural characteristics. Their microstructures are important because the size, shape and distribution of periclase grains, chromites and the quality of their bonding phases significantly affect their service performances. The purpose of this study was to characterize the microstructures of industrial brick samples to develop a protocol to compare different products e.g. for evaluation as replacement bricks. In some of the chromite containing bricks iron-rich rims were observed, while a domestic brick with similar chemistry had no such feature. These iron-rich rims were examined using SEM-EDS. It was found that the counter-diffusion of Fe+3 and Cr+3 were responsible for their formation. Exsolved chrome-spinel was widely observed in the microstructures of chromite bricks. Magnesia-spinel bricks were found to contain low melting calcium aluminates as bond phases in the microstructure, posing a threat to service performance. Portmortem microanalysis of industrially used bricks revealed alkali attack in addition to creep as main destruction mechanisms for brick. Traces of elements like Mo, S and alkalies were observed and thought to originate from the use of waste derived fuels.Conference Object Citation - WoS: 8Citation - Scopus: 12Mechanical Properties of Hydroxyapatite Composites Reinforced With Hydroxyapatite Whiskers(Trans Tech Publications, 2004) Şimşek, Deniz; Çiftçioğlu, Rukiye; Güden, Mustafa; Çiftçioğlu, Muhsin; Harsa, Hayriye ŞebnemSintering and mechanical behavior of pure and hydroxyapatite (HA) whisker reinforced HA composites were investigated in this work. Pure and composite samples were prepared by using a commercial powder and whiskers prepared by molten salt synthesis. The dry-pressed samples were sintered in the 800 and 1300°C range. The effect of whisker-addition on the mechanical properties of HA was investigated through compression and hardness testing. Compressive strength and fracture strain were observed to increase by the addition of whiskers.Conference Object Citation - WoS: 10Citation - Scopus: 13Preparation and Characterization of Polylactide-Hydroxyapatite Biocomposites(Trans Tech Publications, 2004) Gültekin, Naz; Tıhmınlıoğlu, Funda; Çiftçioğlu, Rukiye; Çiftçioğlu, Muhsin; Harsa, Hayriye ŞebnemIn the present study, the preparation and characterization of polylactide-Hydroxyapatite(HA) composite films for biomedical applications have been studied. The effects of number of parameters such as polymer type, HA loading, surface modification and its concentration on the mechanical and microstructural properties of the composites were investigated. Poly-L-Lactide and 96/4 Poly(L-Lactide co D-Lactide) copolymer-HA composites containing 10-40 wt% HA particles have been prepared by solvent casting technique. The HA powder was synthesized by precipitation technique. Interfacial interactions between HA and polylactide polymer were modified to improve filler compatibility and mechanical properties of the composites by surface treatment of the HA with two different silane coupling agents; 3-aminopropyltriemoxysilane (AMPTES) and 3-mercaptopropyltrimethoxysilane (MPTMS) at three different concentrations(0.5-2 wt%). Silane treatment indicated improvements in the mechanical properties of the composites compared to the untreated HA loaded polylactide composites. Tensile test results showed that the maximum improvement in the mechanical properties of the composites was obtained for PLA composites containing 1 wt% aminofunctional silane treated HA and 0.5-wt% mercaptopropyltrimethoxy silane treated HA for PDLA composites. Scanning electron microscopy studies also revealed better dispersion of silane treated HA particles in the polymer matrix.Conference Object Citation - WoS: 8Citation - Scopus: 8Low Temperature Synthesis of Spinel Powders by Mechanical Grinding(Trans Tech Publications, 2004) Yalamaç, Emre; Akkurt, Sedat; Çiftçioğlu, MuhsinLow temperature synthesis of spinel powder via intense mechanical grinding was performed. A dramatic decrease in the synthesis temperatures of ground powders was achieved. We were able to produce partially crystallized spinel at room temperature via a 110 minute grinding. Characterization of the synthesized powders was performed using SEM, XRD and DTA. Each stage of synthesis was analyzed using these techniques. Mixtures of Mg(OH)2 and Al(OH) 3 were used for synthesis. Temperatures as low as 800°C were able to produce bumps in the XRD patterns of ground powders at the 2θ angles for spinel crystals.Conference Object Citation - WoS: 5Citation - Scopus: 5Preparation of Ceramic Composite Membranes for Protein Separation(Trans Tech Publications, 2004) Erdem, İlker; Çiftçioğlu, Muhsin; Harsa, Hayriye ŞebnemCeramic supports were prepared from fine alumina and zirconia powders by dry-pressing and slip-casting. These supports were heat treated in the 1100° - 1200°C temperature range and dip-coated with ceramic sols prepared from alkoxides by using sol-gel methods. The average sol particle sizes were measured as 3-7 nm for zirconia and 30-40 nm for alumina by laser scattering technique. The optimum heat treatment temperature range was determined as 500°-600°C for dip-coated membranes by using TGA (thermo gravimetric analysis) results. The microstructure of the ceramic composite membranes was investigated by SEM (Scanning electron microscope). The clean water permeability (CWP) of the membranes was tested by using deionized water in a filtration set-up. Separation experiments were performed with bovine serum albumin (BSA, Stokes diameter: 7 nm) solution and whey to determine the protein separation capacity of the composite membranes. The CWP of the dry pressed alumina supports heat treated at 1100°C was found to be higher than the permeability of the slip-casted zirconia supports heat treated at 1200°C. The protein retention of the slip-casted zirconia support was determined as 60% by using UV-Vis spectrophotometer (Abs. at 280nm). A protein retention value of 96% was achieved for whey after the modification of the support with dip-coating. The permeate flux was 40 L/m2hour for dry-pressed alumina support dip-coated with zirconia sol calcined at 500°C.Conference Object Citation - Scopus: 1Effects of Processing on the Properties and Permeability of Pure Gases Through Sol-Gel Silica Membranes(Trans Tech Publications, 2004) Topuz, Berna; Çiftçioğlu, Muhsin; Özkan, FehimeN2, O2 and CO2 pure gas permeation through sol-gel derived silica membranes were determined and the effects of processing parameters on the microstructure of the membrane was investigated. Silica sols were prepared in an alcoholic solution by hydrolysis and condensation of TEOS as a function of acid content. The thickness of the silica membranes was determined to be about 2μm and significant infiltration into the support was observed from the SEM pictures. The supported membranes were heat treated in the 50-400°C. The N2 permeabilities of silica membranes varied in the 2.2*10-10-2.7*10-8 mol/m2.s.Pa range for single layer membranes dipped for 10s. in the sol. The CO2 permeability of these membranes varied in the 1.2*10-9-6.95 *10-8 mol/m2.s.Pa range. The sols became viscous and gelled at 50°C in 16 hours. The O2 permeability increased with aging time. The optimum dipping time during processing was determined to be 10 seconds. The increase in the acid content of the sols were observed to increase permeabilities of the membranes significantly.