Browsing by Author "Gulec, Haci Ali"

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Improvement of Interfacial Adhesion of Glass Fiber/Epoxy Composite by Using Plasma Polymerized Glass Fibers
(Taylor & Francis Ltd, 2010) Sever, Kutlay; Sarikanat, Mehmet; Seki, Yoldas; Gulec, Haci Ali; Mutlu, Mehmet; Tavman, Ismail Hakki
This study intends to produce plasma polymer thin films of -glycidoxypropyltrimethoxysilane (-GPS) on glass fibers in order to improve interfacial adhesion of glass fiber-reinforced epoxy composites. A low frequency (LF) plasma generator was used for the plasma polymerization of -GPS on the surface of glass fibers at different plasma powers and exposure times. X-ray photoelectron spectroscopy (XPS) and SEM analyses of plasma polymerized glass fibers were conducted to obtain some information about surface properties of glass fibers. Interlaminar shear strength (ILSS) values and interfacial shear strength (IFSS) of composites reinforced with plasma polymerized glass fiber were evaluated. The ILSS and IFSS values of non-plasma polymerized glass fiber-reinforced epoxy composite were increased 110 and 53%, respectively, after plasma polymerization of -GPS at a plasma power of 60W for 30min. The improvement of interfacial adhesion was also confirmed by SEM observations of fractured surface of the composites.
Modification of Cellulose Acetate Membrane Via Low-Pressure Plasma Polymerization for Sugar Separation Applications: Part I. Membrane Development and Characterization
(Elsevier Science Bv, 2010) Gulec, Haci Ali; Topacli, Arzu; Topacli, Cafer; Albayrak, Nedim; Mutlu, Mehmet
The aim of this study is to illustrate the low-pressure plasma modified cellulose acetate (CA) membranes can display a fractionation capability that can be of major importance for the operation of continuous enzymatic membrane reactors. For this purpose, low-frequency (LF) and/or radio-frequency (RF) excitations were applied to coat ethylenediamine (EDA) monomer to alter physico-chemical characteristics of surface as well as narrowing pore size of CA type common ultrafiltration membrane. Membrane characteristics were evaluated using various physical and chemical techniques including contact angle, Fourier Transform Infrared Spectroscopy with Horizontal Attenuated Total Reflection attachment and scanning electron microscopy. Membrane performance based on efficient monosaccharide removal was tested by using a diffusion cell. The contact angle results showed that the grafted amino groups caused great increase on the polar nature of the CA membranes studied. A complete and permanent hydrophilic modification of a CA was achieved by LF plasma treatment. From the fractionation point of view, 120 W and 10 min seemed to be a better plasma condition for membrane modification using LF plasma system. Very high retention (>94%) was obtained with the LF/PIzP-modified CA membrane for disaccharides, while the retention for monosaccharides was rather low (<73%) at the same reaction time. (C) 2010 Elsevier B.V. All rights reserved.
Modification of Food-Contacting Surfaces by Plasma Polymerization Technique: Reducing the Biofouling of Microorganisms on Stainless Steel Surface
(Springer, 2012) Sen, Yasin; Bagci, Ufuk; Gulec, Haci Ali; Mutlu, Mehmet
In this study, the prevention of the attachment of test microorganism Enterobacter sakazakii onto stainless steel (SS 316) surfaces by radio frequency (RF) plasma polymerization (PlzP) technique using several hydrophilic monomers as precursors was reported. Different plasma conditions (RF discharge power of 20-80 W with exposure time of 10 min) were employed during the modifications. PlzP-modified surfaces were characterized in detail by static contact angle measurements in order to state the change of surface hydrophilicity. The surface topology of unmodified and PlzP [ethylenediamine (EDA)]-modified SS 316 plates was characterized by atomic force microscopy. The attachment of the model microorganism on the SS 316 surface modified by plasma using EDA at 45 W and 10 min was reduced by 99.74% in comparison to the unmodified control surface. For equilibrium adsorption behavior, Freundlich and Langmuir models were attempted and model parameters for Freundlich (K (F) and 1/n) and for Langmuir (a and b) were obtained. The values of the K (F) and 1/n were 5.6 and 0.58 and 0.9 and 0.39, respectively; the values of a and b were 25 x 10(4) and 1.82 x 10(-8) and 0.3 x 10(4) and 7.96 x 10(-8), for bare and PlzP-EDA-modified SS 316 surfaces, respectively. As a result, PlzP technique was found to be an alternative simple method to decrease the microbial attachment and create bacterial anti-fouling surfaces.