Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Conference Object Citation - Scopus: 1Yapay Sindirim Sıvısında Doğal Zeolitlerde Meydana Gelen Morfolojik Değişmeler(Institute of Electrical and Electronics Engineers Inc., 2009) Demirbüker Kavak, Dilek; Özçelik, Serdar; Ülkü, SemraDoğal zeolitler biyoaktif maddelerdir. Doğal zeolitlerin hayvanlarda biyokütle arttırıcı besi katkı maddesi, insanlarda ülser tedavisinde mide asitliğini tamponlayıcı, asitliği düşürücü ilaç gibi değişik kullanım alanları mevcuttur. Değişik sağlık alanlarında kullanımlarından dolayı, zeolitlerin yapısal stabilitesinin sindirim sırasında belirlenmesi; olası olumlu veya olumsuz etkileşimleri anlamak açısından önem taşımaktadır. Gerçekleştirilen araştırmada, yapay sindirim sırasında zeolitte meydana gelebilecek olası morfolojik değişimlerin incelenmesi hedeflenmiştir. Bu amaçla zeolitin ABTS ile radikal sönümleme kapasitesi araştırılmış, yapay sindirim denemeleri gerçekleştirilerek de uygulama süreci sonrası yapıda olası değişimler ve adsorpsiyonlar taramalı elektron mikroskobu, FTIR, XRD analizleri ile incelenmiştir. 3g/100ml zeolitin ABTS radikalini %45 inhibe ettiği bulunmuştur. Taramalı elektron mikroskobu deneyleri sonucunda yapay sindirilmiş örneklerin yüzey morfolojisinde değişim gözlenmemiştir. Element analizleri yapısal kaybın olmadığını, Al ve Si elementlerinin ağırlıkça yüzdelerinin, kontrol örnekleriyle (Al:8.1; Si: 39) sindirilmiş örneklerde (Al:8.2; Si: 38.3) yaklaşık aynı olduğunu göstermiştir. Infrared spektrum (IR) ve X-ray ışını kırınımı analizleri sonuçları ise bu bulguları doğrulamıştır. Ayrıca taramalı elektron mikroskobu ve IR spektrum sonuçları yapay sindirim ortamındaki maddelerin, zeolit yüzeyinde adsorplanmadıklarıını göstermektedir. Sonuç olarak doğal zeolitler, yapay sindirim sırasında yapısal stabilitelerini kaybetmemektedirler.Article Citation - WoS: 3Citation - Scopus: 2Adsorption of No in Clinoptilolite-Rich Zeolitic Mineral by Concentration Pulse Chromatography Method(Elsevier Ltd., 2016) Narin, Güler; Ülkü, SemraThe equilibrium and kinetic parameters for NO adsorption in a clinoptilolite-rich natural zeolitic material from Turkey were determined using the concentration pulse chromatography method. Under the experimental conditions (carrier gas velocities and adsorption temperatures) the micropore diffusion resistance was found to be the mass transfer controlling step. Matching the first moment of the response peaks to the mathematical model the Henry's Law constants and heat of adsorption at zero loading were determined. The axial dispersion, external film, macropore and micropore diffusion coefficients, and activation energy for diffusion of NO in the micropores were calculated from the analysis of the second moments of the response peaks. For successive NO pulses without regeneration between the pulses, the retention times of the response peaks decreased and peak areas increased with the injection number indicating irreversible adsorption. The reversibly adsorbed NO could be desorbed by purging with an inert gas at the adsorption pressure and temperature. Temperature programmed desorption profile obtained by heating the NO saturated adsorbent to 400 °C under inert flow revealed presence of multiple irreversibly adsorbed species in NZ with different thermal stabilities. Desorption of these species was not achieved during the heating up to 400 °C which makes the natural zeolitic materıal suitable for NO storage rather than for cyclic adsorptive separation processes.Article Citation - WoS: 17Citation - Scopus: 20Preparation and Characterization of Antibacterial Cobalt-Exchanged Natural Zeolite/Poly(vinyl Alcohol) Hydrogels(Springer Verlag, 2014) Narin, Güler; Bulut Albayrak, Çisem; Ülkü, SemraIn the present study, potential application of the local clinoptilolite-rich natural zeolite in formulation of antibacterial hydrogels was investigated. The zeolite powder exchanged with cobalt(II) ions was used in preparation of the zeolite/poly(vinyl alcohol) hydrogel films in different amounts. The films were physically crosslinked by the freezing-thawing method and characterized for their crystallinity, surface and cross sectional morphology, chemical composition, thermal behaviour, mechanical properties, swelling and dissolution behaviours, and antibacterial activities against a Gram-negative bacteria. The films with 0.48 wt% and higher cobalt-exchanged zeolite contents showed antibacterial activity. Addition of the zeolite powder in the formulations did not cause significant changes in the other properties of the films.Article Citation - WoS: 51Citation - Scopus: 58Effect of Additives on Flexible Pvc Foam Formation(Elsevier Ltd., 2008) Demir, Hasan; Sipahioğlu, Muzaffer; Balköse, Devrim; Ülkü, SemraIn this study, effects of Ca/Zn stearate and organotin heat stabilizers and zeolite, CaCO3, cellulose and luffa flours fillers, and their concentrations (2.5, 5, 10 and 20% by weight) on production of flexible PVC foams by chemical blowing agent, azodicarbonamide were investigated. Foam morphology, foam density, compressive mechanical properties and water uptake capacities of samples were determined. Morphology of the sample without any filler showed that employment of Ca stearate and Zn stearate heat stabilizers instead of organotin stabilizers increases foam formation and decreases pore sizes and regularity in pore size distribution. Foams having organotin stabilizer were more resistant to heat than the ones with Ca/Zn stearate for long heating periods. Foams, including organotin-based heat stabilizers, have compact structure. It was observed that, samples containing zeolite, CaCO3, cellulose or luffa flour had lower pore volume but higher Young's modulus and stress values compared to unfilled samples.Article Citation - WoS: 39Citation - Scopus: 46Synergistic Effect of Metal Soaps and Natural Zeolite on Poly(vinyl Chloride) Thermal Stability(John Wiley and Sons Inc., 2005) Atakul, Sevdiye; Balköse, Devrim; Ülkü, SemraThe synergistic effect of metal soaps (zinc stearate and calcium stearate) and/or natural zeolite (clinoptilolite) on PVC thermal stability was investigated. For this purpose, PVC plastisol was prepared by mixing poly(vinyl chloride) (PVC) and dioctyl phthalate (DOP) and stabilized with different amounts of metal soaps and zeolite. Kinetic studies of dehydrochlorination at 140 and 160°C were done for unstabilized and stabilized PVC plastigels using 763 PVC Thermomat equipment. The stabilizing effect of zeolite on the increase in the induction period of the sample was considered to result from the absorption of HCl, a property that was thought to reduce the autocatalytic effect of HCl evolved at the initial stages of dehydrochlorination. Since the induction time of the sample having 0.53% of zinc stearate and 0.53% of zeolite was higher than those of the PVC plastigels having only zinc stearate or zeolite, the synergistic effect on thermal stability was observed at low leveles of these additives.Article Citation - WoS: 42Citation - Scopus: 42Natural Zeolite Polypropylene Composite Film Preparation and Characterization(John Wiley and Sons Inc., 2001) Özmıhçı, Filiz; Balköse, Devrim; Ülkü, SemraIn this research, the preparation and characterization of polypropylene (PP) and natural zeolite composites were studied. Natural zeolite mined in Gördes, Turkey was used as an alternative filler to CaCO3. Films were prepared by the extrusion of PP, and surface-modified zeolite was made by polyethylene glycol 4000 with 2-4% zeolite. Zeolite-filled composites had densities between 0.73 and 0.83 g/cm3 and had void fractions of 0.07-0.20. Although the permeability of water vapour through 2% zeolite-filled composites was very small, 4% zeolite-filled films had very high permeabilities. The yield stresses of 2-4% zeolite-containing films were around 26-27 N/mm2 and were lower than that of PP, which indicated no adhesion between PP and zeolite. The effect of zeolite on the thermal degradation behaviour in air and in a N2 atmosphere was also studied. In air, zeolites did not cause the oxidation of PP. In a N2 atmosphere, although the start of the thermal degradation of PP was retarded by zeolite, composites degraded at a faster rate than PP once the degradation started. At a processing temperature of 200°C, zeolites had no effect on the degradation of PP.