electrospn 17 yalcinkaya-full

The International Istanbul Textile Congress 2013 May 30th to June 1th 2013, Istanbul, Turkey

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RELATION BETWEEN NUMBER OF TAYLOR CONE AND LIFE OF JET ON THE ROLLER ELECTROSPINNING

B. YALCINKAYA1, F. YENER1, F. Cengiz-CALLIOGLU2, and O. JIRSAK1

1Nonwoven Department of Textile Engineering Faculty, Technical University of Liberec, Studentska 2, 46117, Czech Republic

2Suleyman Demirel University, Engineering Faculty, Department of Textile Engineering, Cunur, Isparta.

[email protected] Abstract: Electrospinning is one the unique method to procure nanofibers at submicron. Roller electrospinning and needle electrospinning are most common way to obtain nanofiber based layers. It is possible to produce large scale nanofibers on roller electrospinning compared with needle electrospinning. Based on productivity of roller electrospinning, Taylor cone and life of jet which are the most important dependent parameters were studied. Polyvinyl alcohol and polyurethane and their salty solutions were used to investigate of Taylor cone structure on roller surface. As a result, while Taylor cone number was increasing life of jet decreased. However the salty solutions of PVA showed different behaviour. By adding salt firstly it was observed that life of jet decresed, however, increasing salt concentration more than 0.3%, life of jet started to increase. The results were correlated with solution thickness onto roller surface. Results show that solution thickness has important effect on the life of jet. Keywords: Roller electrospinning, nanofibers, Taylor cone, life of jet, solution thickness. 1. Introduction

The phenomenon of electrospinning is an issue of a tug of war solution between electrostatic and capillary forces. When a small volume of conductive liquid exposed to an electric field, the shape of liquid starts to deform from the shape caused by surface tension alone. As the voltage is increased the electrostatic force starts to over comes the surface tension and a cone shape begins to form with convex sides and a rounded tip. This approaches the shape of cone called as Taylor cone [1].

Recently, a new technology has been developed by Jirsak [2] that is based on highly productive jet creation from free liquid surfaces by self-organisation. This technology is called roller electrospinning under the brand name of Nanospider. The cylinder rotates in a polymer solution tank. The electrostatic field organised between the cylinder and a grounded collector enables the self-organisation of jets along the upper surface of the cylinder and, hence, fibers collect on the supporting material. There are lots of parameters that affect the electrospinning process. These can be divided as system and process parameters. Viscosity, concentration, net charge density (conductivity), surface tension of the polymer fluid and molecular weight can be shown as system parameters. Applied voltage, flow rate of polymer solution, distance between capillary end and collector, ambient parameters and motion of collector can be shown as process parameters [3].

In this work firstly effect of concentration and additives on the number of cones was investigated. Then number of Taylor cone was associated with life time of a cone. Poly(vinly alcohol) PVA was used as polymer and effects of dependent parameters such as number of Taylor cones and life of jet were observed.

1.1 Materials Poly (vinyl alcohol) (MWD 70.000) was used in liquid form and produced by novaky, Slovakia. The solvent, distilled water and the salt, sodium chloride (NaCl) which was purchased from Fluka, were used. Polyurethane (PU) polymer, molecular weight is 2000g/mol was used as a polymer and dimethylformamide used as a solvent. Salt, tetraethyleneammonium bromide (TEAB) was purchased from Fluka. 1.2 Preparation of solution blending of polymer PVA was used in different concentrations (8 – 10 – 12 – 14 wt. %) as the material for the experiment. The % 12 PVA water solution was used to prepare various concentrations of the solutions proportional to sodium


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chloride (12 wt % PVA + 0.1 – 0.2 – 0.3 – 0.5 – 0.7 – 1.0 wt % NaCl) as the conductive additive and distilled water as solvent. On the other hand PU solutions were prepared at various concentrations such as 15-17.5-20 wt % PU and TEAB salt was added in different concentrations such as 0-0.4-0.8-1.27 wt %. The polymer with different concentration of PVA and PU were blend under constant stirring about 1 day. 1.3 Methods Solution properties were determined, ere electrospining process. Conductivities were determined by a conductivity meter (Radelkis, OK-102/1). Rheological properties of solutions were measured using Rheometer HAAKE RotoVisco 1. Figure 1 show the image of the system used to measure thickness of the layer of the solutions onto the roller surface. Number (1) is the rotating roller with a diameter of 20.0 mm, driven by the electrical motor, (2) is the pan filled with polymer solution, (3) is the micrometer and (4) is the supporting stand [4].

Figure 1. Cylinder immersed into the polymer solution. Roller electrospinning system was used to create nanofibers. In this method, there is a roller which is connected to high voltage supplier and top of the roller there is a collector which was grounded. When high voltage suppliers turns on the Taylor cones are created on the roller surface towards to collector (Figure 2).

Figure 2. Schematic of roller electrospinning system[3]

Digital camera was used to observe these Taylor cones and life of jet on the roller surface in course of spinning (Figure 3). In the picture of roller, every Taylor cones are looked like bright dot onto roller surface.

Figure 3. A view of the Taylor cone and solution jets onto roller surface Optimum process parameters such as roller speed, roller length, distance between the electrodes, voltage etc. were kept as stable during the spinning process of PVA solution (Table 1). Spinning conditions of electropspinning of PU solution were arranged differently [3].


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Table 1: Process parameters of roller electrospinning

Mechanical Parameters Process

Parameters Environmental

Parameters

Roller Length (cm)

Roller Diameter

(cm)

Roller Speed (rpm)

Supporting Material Speed

(cm/min)

Distance Between Electrode

(cm)

Applied Voltage

(kV)

Humidity (%)

Temperature (0C)

14,5 2 2,5 10 12 55 30 26,4

2. Results It is well known that PVA concentration has important effect on the viscosity of solutions however different concentration of NaCl salt have no effect on the viscosity of the solution of constant PVA concentration. Other side increases of NaCl salt was played significant role on the solution conductivity [4, 5]. The same results were observed during investigation of solution properties (Figure 4).

Viscosity of PVA solutions Viscosity of 12% PVA + NaCl solutions

Conductivity of PVA solutions Conductivity of 12% PVA + NaCl solutions

Figure 4. Properties of PVA solutions

It was observed that concentration of PU and TEAB were effected viscosity and conductivity of solution. Increases of concentration of PU and TEAB were increased viscosity and conductivity [3]. According to viscosity of solutions, thickness of solution layer onto roller surface was shown an alteration. It is given in the Figure 5 that increasing of PVA concentration yields to increase the thickness of solution layer ordinarily. However NaCl salt concentration was presented the vagaries. On the contrary, there were no significant changes on the viscosity while increasing NaCl concentration (Figure 4), thickness of solution layer was changed irregularly onto roller surface. It observed that firstly thickness of solution layer was decreased by adding salt then it increased by adding more salt (Figure 5). This value was calculated after repeating 10 times same experiment. Then the average values were taken [5].


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Thickness of PVA solutions layer Thickness of 12% PVA + NaCl solutions layer

Figure 5. Thickness of PVA solutions onto roller surface

Various concentration of PVA was used to intention of the increasing the spinning performance on the roller electrospinning method. It is well know justice from researchers that increasing concentration of PVA is increased spinning performance because of the high number of Taylor cones [4, 5]. However increasing of NaCl salt concentration was decreasing number of Taylor cones together with spinning performance (Figure 6). It has been note that low concentration of PVA solution was created wet-fibers, in this way 8 % PVA solution were accepted as an unsung polymer solution for calculating of Number of Taylor cone and life of jet.

Number of Taylor cone of PVA solutions Number of Taylor cone of 12% PVA + NaCl solutions

Figure 6. Number of Taylor cone of PVA solutions

Contrary to PVA solutions, PU and their salty solutions’ Taylor cone number increased together with increment of both polymer and salt concentrations. Hence, it is obvious that additive of salt in the polymer solution of PU and PVA did not has the same effect on the spinning performance. Figure 7 was involved life of PVA solutions jets. It is observed that in the case of PVA solutions without salt, the life of jet decreased when the number of Taylor cone increased. The same results were observed with PU solutions [3]. Increment of Taylor cones onto roller surface were decreased life of jet. However salty solutions of PVA polymer were indicated different behaviour.

Life of jet of PVA solutions Life of jet of 12 % PVA + NaCl solutions


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Figure 7. Life of jet of PVA solutions For this reason, it is investigated that what kind of parameters was effective on number of Taylor cone. Firstly it is accepted that the main parameter was number of Taylor cone onto roller surface because all Taylor cone needs polymer solution to supply onto roller surface. Hence if high number of Taylor cones occurs onto roller, solution on the surface finishes swiftly and as a result cones finish. If low numbers of cones occur onto roller surface, there will be sufficient polymer solution supply on the roller and their durability was longer. Figure 8 is shown that electrospinning of different PVA solutions and different Taylor cone numbers.

12 % PVA solution 12 % PVA + 0.5 % NaCl solution

Figure 8. Electrospinning of different concentration of PVA solutions

Secondly it is believed that the thickness of solution layers are played also important role on the life of jet. If the thickness of layer and life of jet of salty solution of PVA were compared, the effect of thickness of layer is more clear (Figure 9).

Figure 9. Comparing with thickness of layer and life of jet As mentioned above it was expected that decreasing of the spinning performance or number of Taylor cone together with NaCl salt concentration would increase life of jet continually. However the thickness of layer were play second role on the life of jet and as seen Figure 9, life of jet was changed similarly with thickness of solution layer. We observed that the life of jet which is the dependent parameter on the roller electrospinning method was affected by number of Taylor cones and thickness of layer. Both of them were affected by concentration of PVA polymers and NaCl salt. As a result number of Taylor cone and life of jet affected respectively spinning performance and nanofibers morphology. Figure 10 is shown that spinning performance of PVA solution and the behaviours of spinning performance was change in the same direction with number of Taylor cone.


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Spinning performance of PVA solutions Spinning performance of 12 % PVA + NaCl solutions

Figure 10. Spinning performance of PVA solutions

On the other side it is believed that life of jet affects nanofibers morphology such as fibers diameter and non-fibrous area. In the all electrospining methods, solution jets need a specific time and enough distance between electrodes to form stable jet. Dry and uniform nanofibers form in an optimum distance between electrodes. It is possible to mention that low quality of nanofibers are achieved with short life of jet and Table 2 proves this justice.

Table 2: Morphology of PVA nanofibers

Concentration of PVA (%) 8 10 12 14 Concentarion of NaCl (%) - - - 0.1 0.2 0.3 0.5 0.7 1.0 -

Fiber diameter (nm) 145 187 227 314 324 303 289 274 251 332 Non-fibrous area (%) 1.74 0.09 0 0.32 0.29 0.22 0.2 0.19 0.11 0.6

3. Conclusion Electrospinning of PVA and PU solutions were done using roller electrospinning. Concentrations of PVA polymer and NaCl salt have impact effect on dependent parameters. Two dependent parameters such as number of Taylor cone and life of jet were observed. Concentrations of additives affected number of Taylor cone and cones were directly affected life of jet. It is indicated that both parameters have significance on the production of nanofiber based fabric. Hereby number of Taylor cones and life of jet have a role on the respectively spinning performance and nanofibers mophlogy. References [1] Taylor, S.; Proc. Roy. Soc. London. Ser. A, 1964, 280 (1382): 383. [2] Jirsak O.; Sanetrik F.; Lukas D.; Kotek V.; Martinova L.; Chaloupek J., European Patent: EP 1 (673

493), 2004. [3] Yalcinkaya, B.; Yener, F.; Cengiz-Callioglu, F.; Jirsak, O.; Effect of Concentration and Salt Additive on

Taylor Cone Structure. NanoCon, Czech Republic, 2012 [4] Tuan, D. A., The role of rheological properties of polymer solutions in needleless electrostatic

spinning.Liberec Technical University, Dissertation, 114p,Czech Republic. 2010. [5] Mduduzi B, K., The study of roller electrospinning with regard to roller movement, Liberec Technical

University, Diploma thesis, 64p, Czech Republic. 2012.

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