Fatma Yalcinkaya

Preparation of antibacterial nanofibre/nanoparticle covered composite yarns

The antibacterial efficiency of nanofibre composite yarns with an immobilized antibacterial agent was tested. This novel type of nanofibrous composite material combines the good mechanical properties of the core yarn with the high specific surface of the nanofibre shell to gain specific targeted qualities. The main advantages of nanofibre covered composite yarns over the standard planar nanofibre membranes include high tensile strength, a high production rate, and their ability to be processed by standard textile techniques. The presented paper describes a study of the immobilization of an antibacterial agent and its interaction with two types of bacterial colonies. The aim of the study is to assess the applicability of the new composite nanomaterial in antibacterial filtration. During the experimental tests copper(II) oxide particles were immobilized in the polyurethane and polyvinyl butyral nanofibre components of a composite yarn. The antibacterial efficiency was evaluated by using both Gram-negative Escherichia coli and Gram-positive Staphylococcus gallinarum bacteria. The results showed that the composite yarn with polyvinyl butyral nanofibres incorporating copper(II) oxide nanoparticles exhibited better antibacterial efficiency compared to the yarn containing the polyurethane nanofibres. The nanofibre/nanoparticle covered composite yarns displayed good antibacterial activity against a number of bacteria.

Surface Modification of Electrospun PVDF/PAN Nanofibrous Layers by Low Vacuum Plasma Treatment

Nanofibres are very promising for water remediation due to their high porosity and small pore size. Mechanical properties of nanofibres restrict the application of pressure needed water treatments. Various PAN, PVDF, and PVDF/PAN nanofibre layers were produced, and mechanical properties were improved via a lamination process. Low vacuum plasma treatment was applied for the surfacemodification of nanofibres. Atmospheric air was used to improve hydrophilicity while sulphur hexafluoride gas was used to improve hydrophobicity of membranes. Hydrophilic membranes showed higher affinity to attach plasma particles compared to hydrophobic membranes.

Influence of salts on electrospinning of aqueous and nonaqueous polymer solutions

A roller electrospinning system was used to produce nanofibres by using different solution systems. Although the process of electrospinning has been known for over half a century, knowledge about spinning behaviour is still lacking. In this work, we investigated the effects of salt for two solution systems on spinning performance, fibre diameter, and web structure. Polyurethane (PU) and polyethylene oxide (PEO) were used as polymer, and tetraethylammonium bromide and lithium chloride were used as salt. Both polymer and salt concentrations had a noteworthy influence on the spinning performance, morphology, and diameter of the nanofibres. Results indicated that adding salt increased the spinnability of PU. Salt created complex bonding with dimethylformamide solvent and PU polymer. Salt added to PEO solution decreased the spinning performance of fibres while creating thin nanofibres, as explained by the leaky dielectric model.

Preparation of Fouling-Resistant Nanofibrous Composite Membranes for Separation of Oily Wastewater

A facile and low-cost method has been developed for separation of oily wastewater. Polyvinylidene fluoride/polyacrylonitrile (PVDF/PAN) nanofibers laminated on a supporting layer were tested. In order to create highly permeable and fouling-resistant membranes, surface modifications of both fibers were conducted. The results of oily wastewater separation showed that, after low vacuum microwave plasma treatment with Argon (Ar) and chemical modification with sodium hydroxide (NaOH), the membranes had excellent hydrophilicity, due to the formation of active carboxylic groups. However, the membrane performance failed during the cleaning procedures. Titanium dioxide (TiO2) was grafted onto the surface of membranes to give them highly permeable and fouling-resistance properties. The results of the self-cleaning experiment indicated that grafting of TiO2 on the surface of the membranes after their pre-treatment with Ar plasma and NaOH increased the permeability and the anti-fouling properties. A new surface modification method using a combination of plasma and chemical treatment was introduced.

Thin Film Nanofibrous Composite Membrane for Dead-End Seawater Desalination

The aim of the study was to prepare a thin film nanofibrous composite membrane utilized for nanofiltration technologies. The composite membrane consists of a three-layer system including a nonwoven part as the supporting material, a nanofibrous scaffold as the porous surface, and an active layer. The nonwoven part and the nanofibrous scaffold were laminated together to improve the mechanical properties of the complete membrane. Active layer formations were done successfully via interfacial polymerization. A filtration test was carried out using solutions of MgSO4, NaCl, Na2SO4, CaCl2, and real seawater using the dead-end filtration method. The results indicated that the piperazine-based membrane exhibited higher rejection of divalent salt ions (>98%) with high flux. In addition, the m-phenylenediamine-based membrane exhibited higher rejection of divalent and monovalent salt ions (>98% divalent and >96% monovalent) with reasonable flux. The desalination of real seawater results showed that thin film nanofibrous composite membranes were able to retain 98% of salt ions from highly saline seawater without showing any fouling. The electrospun nanofibrous materials proved to be an alternative functional supporting material instead of the polymeric phase-inverted support layer in liquid filtration.

Analysis of the effects of rotating roller speed on a roller electrospinning system

The complexity of the free surface electrospinning process makes empirical determination of the effects of parameters very difficult. The parameters of the free surface-roller electrospinning process have not been fully defined. In this paper, new electrospinning parameters were suggested and studied. The relationship between rotating roller speed as a dependent parameter and independent parameter was investigated. The effects of rotating roller speed on electrospun nanofiber diameters and the quality of a nano web are determined experimentally. The velocity of the spinning roller and the content of salts in the solutions were selected as independent process parameters. The results show that the velocity of the rotating roller, which is related to the flow rate/feed rate of a solution on the surface of the rotating roller, affects the spinning performance as well as the quality of the fibers. Moreover, the spinnability and spinning behavior of polyurethane and polyethylene oxide solutions mainly depend on the salt content, viscosity and rotating roller speed. The high speed of the rotating roller caused a thick fiber diameter for the polyurethane solutions and polyethylene oxide, while the slow motion of the rotating roller caused low spinning performance. The diameters and diameter distribution of the electrospun nanofibers and quality of the nano web were most significantly affected by the speed of the rotating roller.

Effect of Laminating Pressure on Polymeric Multilayer Nanofibrous Membranes for Liquid Filtration

In the new century, electrospun nanofibrous webs are widely employed in various applications due to their specific surface area and porous structure with narrow pore size. The mechanical properties have a major influence on the applications of nanofiber webs. Lamination technology is an important method for improving the mechanical strength of nanofiber webs. In this study, the influence of laminating pressure on the properties of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) nanofibers/laminate was investigated. Heat-press lamination was carried out at three different pressures, and the surface morphologies of the multilayer nanofibrous membranes were observed under an optical microscope. In addition, air permeability, water filtration, and contact angle experiments were performed to examine the effect of laminating pressure on the breathability, water permeability and surface wettability of multilayer nanofibrous membranes. A bursting strength test was developed and applied to measure the maximum bursting pressure of the nanofibers from the laminated surface. A water filtration test was performed using a cross-flow unit. Based on the results of the tests, the optimum laminating pressure was determined for both PAN and PVDF multilayer nanofibrous membranes to prepare suitable microfilters for liquid filtration.

Surface modification of electrospun nanofibrous membranes for oily wastewater separation

This paper presents a method for producing nanofibrous composite membranes for the separation of a vegetable oil–water mixture. Neat polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN) nanofibres and PVDF/PAN mixtures were used to prepare the membranes. Argon plasma treatment, followed by a chemical surface modification, was applied to alter the hydrophilicity and oleophobicity of the membranes. The obtained results showed that the membranes change their surface character (hydrophilicity and oleophilicity) in relation to the mixing ratio of the PVDF/PAN nanofibres and the surface modification parameters. These results can extend the application of PVDF, PAN and PVDF/PAN nanofibrous membranes to the treatment of oily water.

Experimental study on electrospun polyvinyl butyral nanofibers using a non-solvent system

The effect of the non-solvent spinning performance of nanofibers has not yet been clearly explained. To clarify this, nanofiber membranes were prepared using the roller electrospinning technique from polyvinyl butyral (PVB) solutions containing ethanol as a solvent and water as a non-solvent. A Hansen solubility graph was drawn to evaluate the non-solvent and solvent systems. The relationships among the presence of non-solvent additives, the properties of spinning solutions (viscosity, conductivity, and surface tension), current per one Taylor cone, spinning performance of fiber membranes and fiber morphology were studied. The experimental results of this work showed that the non-solvent system had positive effects on fiber diameter and web surface, resulting in a low diameter and bead-free surface, while also decreasing spinning performance.

Preparation of various nanofibrous composite membranes using wire electrospinning for oil-water separation

Due to growing demand for production of safe water a search of new materials for water purification is of critical issue. Their production should be of low cost and offers easily scalable manufacturing protocol. In this study, we have described preparation and properties of hydrophilic/oleophobic microfiltration membranes produced by means of wire electrospinning. Selective separation of oil or water was tested for oil-water emulsion by using a dead-end filtration unit. The obtained data allowed us to claim membranes as excellent separators for splitting emulsions.