Çözeltiden üfleme tekniği ile yeni tip filtre ve membranların geliştirilmesi

Abstract

Bu tez çalışmasında elektroüretim işlemine göre yüksek üretim hızı ve nispeten düşük maliyetiyle öne çıkan çözeltiden üfleme işlemi ile nanolif filtrelerin üretimi araştırılmıştır. Bu doğrultuda makina tasarım ve imalatı yapılmış, üretilen ürünlerin fotokatalitik hava ve su filtrasyonu performansları incelenmiştir. Çalışmalarım sonucunda görülmüştür ki, çözeltiden üfleme yöntemi elektroüretim yöntemine göre oldukça ucuz ve hızlı bir yöntemdir. İş güvenliği açısından yüksek elektrik alan gerektiren elektroüretime göre yine avantajlıdır. Bu yenilikçi yöntem ile ön çalışmalar yapılarak fotokatalitik membran üretilebileceği görülmüştür. Çözeltiden üfleme sistemi için düze tasarımı SolidWorks ortamında gerçekleştirilmiştir. Deney düzeneği kurularak nanolif yapılı membran üretilmiştir. Üretim parametrelerine bağlı olarak bu yöntemin lif çapına ve morfolojisine etkisi incelenmiştir. Elektroüretim yönteminde yüksek güç kaynağı kullanarak polimerik lif üretilmektedir. Bu yöntemde bir iğne içerisinden beslenen polimer çözeltisi yüksek voltaja tabi tutulur ve çözelti topraklanmış toplayıcı yüzeye doğru hızla fırlatılır. Çözücünün uzaklaşmasıyla oluşan polimerik lifler toplayıcı yüzey üzerinde birikerek dokusuz kumaş oluşturur. Bu yöntem halihazırda çok sık kullanılan bir yöntemdir [1]. Çözeltiden üfleme yöntemi için eş merkezli çift kanaldan oluşan bir sistem tasarlanmıştır. Bu kanallardan iç tarafta olandan polimer çözeltisi, dış tarafta olandan ise basınçlı hava beslenmektedir. Dış kanaldan gelen basınçlı hava polimer çözeltisiyle karşılaşınca çözeltiyi püskürtmektedir. Püskürtülen çözelti toplayıcı yüzeye ulaşana kadar çözeltideki çözücü uzaklaşmaktadır ve polimerik lifler toplayıcı yüzeye yapışıp dokusuz kumaş oluşturmaktadır. Bu liflerin çapı, işlem ve malzeme parametreleri değiştirilerek optimize edilmiş ve nano boyutta lif üretimi gerçekleştirilmiştir. Membran üretiminde kullanılan malzemeler termoplastik poliüretan (TPU), polivinil alkol (PVA), polivinil piroliden (PVP), poliviniliden florid (PVDF) ve poliakrilonitril (PAN) çözeltileridir. Bu çözeltiler ile elektroüretim işlemiyle nanolif üretilebilmektedir. Aynı malzemelerle çözeltiden üfleme yöntemiyle de nanolif üretimi için deneyler yapılmıştır ve bu deneylerin karakterizasyonları SEM ile incelenmiştir. Membran yapının üretilebildiği görüldükten sonra büyük ölçekte filtre kağıdı üretebilmek amacıyla konveyör sistemi tasarımı yapılmış ve kurulumu gerçekleştirilmiştir. Bu sistemle TPU membranlar için üretim parametreleri optimize edilerek membran üretimi gerçekleştirilmiştir. Optimize edilen TPU membrana fotokatalitik etkinlik kazandırmak için katalizör olarak Titanya (TiO2) kullanılmıştır ve membran üzerine kaplama yapılmıştır. Kaplama işlemi elektrosprey yöntemiyle yapılmıştır. TiO2 metanol içerisinde çözülerek elektrosprey işlemine tabi tutulmuştur ve fotokatalitik su ve gaz filtresi üretilmiştir. Elde edilen filtrenin su filtrasyon verimliliğini ölçmek için metilen mavisi kullanılmıştır. Fotokatalitik su filtresi seyreltilmiş metilen mavisi içerisine daldırılmıştır ve UV ışık altında belirli bir süre bekletilmiştir. Bu bekletmeden sonra metilen mavisinin UV vis spektrometresinde bozunma miktarı incelenmiştir ve bu verilere göre performansı değerlendirilmiştir. Yine aynı filtrenin gaz filtrasyonu verimliliğini ölçmek için ise kuru hava ile seyreltilmiş etanol UV ışık altındaki numuneye tabi tutulmuştur. Etanol 1 lt/dk hızda reaktöre gönderilerek test gerçekleştirilmiştir ve sonuç değerlendirilmiştir.

Today nearly 1.5 billion people breathe polluted air every day. It is estimated by World Health Organizations (WHO) that 2.4 million people die because of indoor air pollution. A recent study showed that outdoor air pollution was examined to cause 3.7 million premature deaths worldwide per year; which is due to exposure to small particles below 10 microns [2]. According to researchers, there are 20 million Europeans suffering from respiratory problems every day. Besides, there happened 10 influenza pandemics in the past century, which increased the awareness on filtration products. Nowadays, the need for the high performance air filter with reasonable price is more than ever in the history. In this study novel nanohybrid filters were developed via solution blowing process. Solution blowing is an innovative process to overcome the drawbacks of electrospinning. The advantages might be summarized as lower cost, scalability into industrial systems and safety compared to widely investigated electrospinning. Electrospinning is based on attenuation of fibers under high electric field which is applied between a simple nozzle and collecting mesh While the jet is forwarded to the collector, the solvent of polymer evaporates and leaves nanofibers on the collector. Fibers attenuate underelectrical forces, while moving to the grounded collector. Nanofibers can be produced with various types of materials by using electrospinning method up to now and it is indicated that the diameter of fibers are decreased up to 5 nm [3]. According to Luo et al., parameters which are effective on the fiber geometry and morphology can be divided in two groups; material parameters and process parameters as shown in Table 1. Applied voltage, volumetric flow rate, distance between nozzle and collector, nozzle design and geometry of collector are process parameters and molecular chain length, concentration of solution, presence of additives, viscosity of solution, surface tension, conductivity, solvent boiling point, dielectric constant, molecular weight and solubility are material parameters [4]. At the present time, although the electrospinning is one of the most investigated method, it has some disadvantages such as low production ratefor mass production and being laborious process. Moreover, in this system high voltage power source is used, so extra safety concerns must be considered The screw extruders are used to prepare industrial polymer melts. The combination of electrospinning and extrusion process is a way for mass production with nanofibers. But it is risky to connect high voltage supply to the extruder, since it consist of lots of metals which are electrically conductive. Accordingly, well designed electrical insulation is essential for this combination. Otherwise, this system will be hazardous for operators [5] [6]. Unlike the electrospinning process, solution blowing that is used to produce nanofibers using high speed gas flow as a driving force is suitable for industrial applications. Production rate in solution blowing process is several times higher than electrospinning process because of high solution feeding rate. The electric field is not necessary in this innovative method which is another advantageous of the solution blowing process compared to electrospinning process [7]. Solution blowing system is composed of a coaxial nozzle with proper geometry, a compressor to provide high velocity air and a collector preferably with a suction unit. Solution blowing process is an alternative to electrospinning process for production of nano – micro fibers. In this method, compressed air jet is used instead of electrostatic force to convey the solution to the collector and make polymeric fibers on the surface of collector. In this new system, high velocity gas is used as driving force. The pressure and temperature of used air are significant parameters. If the temperature of air is higher, the evaporation of solvent will be faster. In comparison to electrospinning, high voltage equipment is not necessary in this system, so many nozzles can be used for die assembly without considering electric field problems. Also, this method is suitable to be commercial like melt blowing method. Both solution blowing and melt blowing processes are used to produce fibers by using air jet. In solution blowing process, air jet is applied to polymer solution, while it is applying to polymer melt in melt blowing process. Melt blowing is the traditional method which can produce fibers in the range of 0.5 – 5 µm diameter in one step [8]. In this study custom made nozzles were designed using SolidWorks 3D drawing program. After preliminary studies about the air flow with air gun, the nozzle design was modified to obtain uniformly distributed fibers. A nozzle with coaxial channels was used. The inner channel of nozzle is used to feed polymer solution and the outer one for pressurized air. Polymer jet is attenuated towards collector under the guidance of high velocity air jet, where solvent evaporates and leaves a dry fibrous web on the collector. Parameters effective on the process might be categorized into 3 groups: material parameters, process parameters and system parameters. Material parameters are concentration and viscosity of polymer solution. Air pressure, solution flowrate and nozzle-collector distance are process parameters, where nozzle geometry and collector type are system parameters. In this study, after realization of preliminary studies with a lab scale system, parametric studies were performed Then a scale up conveyor system is designed via SolidWorks program and installed at TEMAG Labs. After this step, a parametric study was realized to examine the effects of parameters. According to this study, air pressure, polymer solution flowrate, nozzle-colllector distance and concentration of solution are the most important effect on morphology of fiber. Especially nozzle-collector distance has vital importance on the structure of membrane. The characterization of the fibers were realized by using Zeiss EVO MA10 scanning electron microscope. After the optimization of system average fiber diameter and fiber diameter distribution were calculated. It was observed that the mean fiber diameter is closed to electrospun fibers which was measured 213 nm. In the second step of my study, solution blown nanofibrous webs were functionalized with photocatalytic titania (TiO2) nanoparticles. Nowadays, photocatalytic method is one of the most used one with many advantageous such as low cost, environmentally friendly and sustainable technology in wastewater industry. This advanced oxidation technology is used to separate the microorganisms and persistent organic compounds in water [9]. Titania particles were dispersed in methanol and then electrosprayed over the solution blown webs. After the electrospraying process, under the illumination of UV light titania was activated to induce oxidative and reductive rections. If the photon energy is higher than bandgap energy of titania, electron at the outermost orbital of titania moves to conduction band. During these rections electron-hole pairs occures with the irradiation of titania. With the continuity of these reactions pollutants are decomposed to by products with oxidation reaction [9]. Photocatalytic oxidation performance of the produced nanohybrid filters were also analyzed. In this study, thermoplastic polyurethane (TPU), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP) and polyvinylidene fluoride (PVDF) were among the polymers investigated. For the photocatalytic water filtration 10-7 M methylene blue aqueous solution was prepared. The functionalized solution blown membrane were dipped into methylene blue aqueous solution for a specific time. Decomposition rate was watched via analyzing sample waters under UV visible spectrometry. The experimental set up consist of three petri dishes for three photocatalytic water filter samples, a UV lamp and a closed cabin were used. The UV light was turned on simultaneously to activate the titania degredation in the cabin that is surrounding the system. Methylene blue degratation was tested by UV-Vis spectroscopy, and the results were evaluated with the change in the amount of methylene blue which were subjected to UV light in a period of time. For the photocatalytic gas filtration ethanol was diluted with dry airand send through solutoin blown/electroprayed filters in a closed reactor. During this process UV light also applied to photocatalytic filter media. Decrease of the amount of ethanol were measured. The activity of filter were measured and compared.