Optimization of filtration and separation properties of centrifugally spun bicomponent nanofibrous webs

Nanofibers are widely investigated nanomaterials because of their high surface area, scalable porosity and versatility. It is mainly used in advanced technologies such as filtration, composite, energy, biomedical, and electronics. Since it has an important position in modern technology, studies on production methods are widening day by day. One of the widely known techniques, electrospinning has disadvantages due to use of electric field, occupational safety problems and low production speeds. Phase separation, as another technique, has material limitations and processing difficulties, which limits its use. Although melt blowing method has high production rate, it is not preferred in nanofiber production because of the need of high temperature compressed air and limitations to reach ultrafine fiber production. Centrifugal spinning and solution blowing methods which have high production rate seems to have overcome the mentioned limits by the use of centrifugal forces and compressed air instead of electric field, respectively. According to the operating principle of the centrifugal system, the syringe pump is first fed to the polymer solution in the syringe. Then the spinner is rotated at a certain speed. When the angular velocity exceeds a critical value, the liquid jets are extended and collected collectively on the collecting surface. Nanofiber media are currently widely used in filters and membranes. Promising results have been achieved from the aspects of filtration which showed advantages compared to traditionally produced filters. The advantages of nanofiber fabrics are shown in several studies compared to the parameters of installation, operating time and yield of conventional filters. Due to the small fiber diameter, nanofiber filters are able to hold smaller particles and do not affect the pressure change much. The small difference in pressure between the two sides of the fabric causes the typical air flow through the nanofibers to change with the reduction of the fiber diameters. This positively affects the pressure change. On the other hand, nanofibers are used in membrane structures. In the past, waterproof and breathable structures were produced with densely woven fabrics made from natural fibers. Nowadays, with the natural water repellent properties of polymers and new production techniques, waterproof and breathable fabrics are started to be produced at higher quality. The physical and chemical properties of polymers, especially in nanofiber fabrics, make nanofiber studies more attactive. Nanofiber production systems are constantly evolving and new systems have been discovered, while old systems have been developed and fiber surfaces suitable for desired properties have become available. One of the oldest systems of electrospinning is used in many studies. In recent years, new production systems related to the elimination of the deficiencies of electrospinning system have been accelerated and new systems have been introduced to the literature. One of them is solution blowing system, where 10 times more production capacity can be observed compared to electrospinning technique. Even, 30 times the production rate of electrospinning can be achieved via centrifugal spinning systems. The fibers come out of the orifices through the effect of centrifugal force and become a fiber by the force applied at the end of a certain distance. Various modifications can be made to this system for better gathering of the collecting surface and fibers. In this study, nanofibers was produced by centrifugal system. The mixture of PVDF and TPU polymers solutions at various ratios (1:0, 2: 1, 1: 2 and 0:1) were used. While preparing the solutions, DMF and acetone at different ratios (100:0, 75:25 and 50:50) were used as a solvent. The fiber solution was subjected to a spin speed of 6000 rpm and fiber production was carried out. The effects of each of solution parameters on fiber quality, filter performance, membrane properties and mechanical properties were investigated. A decrease in viscosity and surface tension values was observed with the addition of acetone. In this way, less droplet fibers are formed from the polymer solution, which becomes easier to produce fiber with reduced surface tension The effect of acetone on fiber diameters and smoothness is clearly seen. In acetone added samples, fiber diameter has increased but no droplets are seen in the fibers. Acetone also allows to obtain solutions that can be produced more easily by lowering the solution concentrations. The elemental analysis was applied to determine the content of the formed fibers. In this analysis, it was observed that each fiber (1.3, 2.3 and 3.3) contained C, O, N and F as a result of data from 3 different points. Thus it was determined that the fibers contain elements in the two polymers without being linked to the solvent. In two-component (TPU-PVDF) solutions, the properties of the two polymers were reflected on all samples. Use of TPU resulted with more elastic properties, while PVDF caused more rigid properties. In this way, the resistance shown against the elongation with the PVDF / TPU mixture is reduced while at the same time strength is given to the fibers. The produced nanofibrous mats were subjected to the filtration tests. Due to that reason, tests were carried out in several layers of nanofibers. The particle capture performances were improved for thicker fabrics, which also caused larger pressure drops. However nanofiber fabrics were successfully obtained from the all blend solutions in the desired range were obtained. On the other hand, the effect of acetone as a solvent on the PVDF polymer caused the change on fiber count and the air permeability decreased. The obtained nanofiber fabrics were also subjected to the membrane tests. Water repellent properties of PVDF polymer were investigated on fabrics. Surface contact angles increased according to PVDF concentration. Water permeability tests showed increased water repellency for larger PVDF contents, however all the produced nanofibrous mats exhibited good breathablity which is important for textile membranes. Also rise in contact angle of samples was seen with increasing amount of TPU. Therefore, an increase in the hydrophobicity of the samples was observed. After this parametric study, a general road map was drawn to obtain larger productivity, which provides better membrane structure and filtration performances as well as better mechanical performances. The mechanical strength of the PVDF polymer and the flexibility of the TPU polymer were combined to meet the expected results where both flexible and durable fabrics are made. PVDF exhibited better results in the overall parameters which used in our study. In the solutions prepared with PVDF, it is better to examine only the amounts of acetone and to make new studies by changing the other parameters.