WOVEN FABRIC CREATED BY NANOFIBROUS YARNS Jiří Chvojka a, Martina Pokorná b, David Lukáš a a Technical University of Liberec, Faculty of Textile Engineering, Department of Nonwovens, Studentska 2., 461 17 Liberec, Czech Republic, jiri.chvojka@tul.cz b Technical University of Liberec, Faculty of Textile Engineering, Department of textile technology, Studentska 2., 461 17 Liberec, Czech Republic, martina.pokorna@tul.cz Abstract The first reference about electrospinning is more than 100 years old. Inventor Cooley and his patent deal with apparatus for electrically dispersing fluids. This topic will refer about electrospinning, preparing nanofibrous layers, making nanoyarns and weaving fabric. Electrospinning is the process for preparing nanofibers from polymer solution or polymer melts. Electrostatic field created between two electrodes draws polymer stream from polymer solutions or polymer melts. This stream is elongated; solvent is evaporated between two electrodes. The nanofibers are deposited on opposite electrode, it is called collector. This special collector consists of conductive material. Collector is compound from two parallel rows, each row consists of cuprum combs. Nanofibrous layer is deposited on the top of combs. Polymer polyvinyl alcohol - PVA was used for preparing oriented layer. This layer is oriented in same direction as collector. Final nanofibrous layer is taken off from the collector and this layer is twisted by force of electromotor. The twisted layers are called nanoyarns and made as fabric. The final area of nanofibrous fabric is 2x2 cm. This fabric from nanoyarns can be suitable to use as reinforcement in composites materials, in electrotechnics, biomedicine as a scaffold. Keywords: electrospinning, nanofibers, nanoyarn 1. INTRODUCTION Cooley patented his first experiment about dispersal fluids in electrostatic field in the 1902. The title was Apparatus for electrically dispersing fluids [1]. Zeleny introduced his work on The electrical discharge from liquid points, and a hydrostatic method of measuring the electric intensity at their surface [2] few years later in 1914. Electrospinning process uses electrostatic field to produce nanofibers. Nanofibers are fibers with diameters about 100 500 nm. Basic process of electrospinning Fig. 1 uses high voltage and electrostatic field between two electrodes. The first one is roller in a polymer solution and on opposite side electrode is collector. Taylor s cone are generated from the roller surface [3]. From this cones polymer jets are formed. These jets are in electrostatic field draw and solvents are evaporated [4]. Drawing and evaporation is very intensive process. When nanofibers are dry they are collected on second electrode (collector). Fibers are collected randomly, when the common plate collector is used. It is possible to organize nanofibrous layer if special collector is used [5]. These ultra fine fibers have large surface area. Applications are filtration and medical use as a scaffold.
Fig.1. Nanospider TM, roller in polymer solution and collector. 2. TECHNOLOGY Electrospinning is the process for preparing nanofibers from polymer solution. Many parameters can an effect the main process. Polymer solution and his spinability depends on viscosity, conductivity and surface tension. The main role is played by electric parameters like distance between spinning electrode and collector, electric potential and a material used for collector (conductivity). Ambient parameters are humidity and temperature. These parameters are possible to transform with air conditioning [6]. Some types of polymers need higher temperature of polymer solution and prescribed humidity. 2.1 Nanospider TM All experiments were made using Nanospider TM. This machine is shown in Fig. 2. Fig. 2: NANOSPIDER TM technology: 1- high voltage source, 2 engine to motion roller, 3 ground, 4 basin with polymer solution and roller, 5 polymer nanofibers, 6 grounded collector, 7 frame with distance / position regulation.
The idea of Nanospider TM is based on a slowly rotating roller in a polymer solution. The polymer solution is yield on surface of the roller. On the top, Taylor s cones [3] rise from this roller and form polymer jets and later on nanofibers. Between electrodes is a very strong field electro static field. That causes drawing of polymer jets. From polymer jet the solvent evaporates and nanofibers rise. Nanofibers are collected on the grounded collector. 2.2 Special collector Nanofibers are deposited on collector having a form of a metal plate. The shape can be circle or square. Electric charge is homogenously distributed on this collector. Therefore nanofibers are randomly deposited. Special collector was used for experiments Fig. 3. This collector has inhomogeneously distributed electric charge. On the top of special collector is higher intensity of electric field [7]. Therefore nanofibers are preferencialy deposited on these places. Nanofibers are oriented along the collector. Fig. 3. Special collector with nanofibrous layer on the top. Size of special collector is 50 cm. 2.3 Used polymer and processing parameters For experiment was used water soluble polymer, particularly polyvinylalkohol (PVA) of 16wt% from Chemické závody Nováky (Slovakia). This polymer was diluted to concentration 12wt%. Experiments were made with Nanospider TM. The distance between roller and the collector was 120 mm and with used voltage of 45 kv. The duration of the experiment was 15 minutes, under at ambient humidity about 40%. 2.4 Vibrodyn 400 For these experiments five samples of yarns with different fineness were used. Clamping length for each sample was 1cm. Individual yarns were measured on the device VIBRODYN 400. Apparatus for measuring the of fibers VIBRODYN 400 works on the principle of the dynamometer with a constant deformation increment. The device is connected to the instrument for measuring the fineness of fibers VIBROSKOP 400, which operates on the principle of vibration of the fibers. According to the oscillation frequency and bias fibers automatically have a predetermined linear density (denier). Both devices are connected to a computer. The software allows statistical evaluation of fineness,, tenacity and the.
Following table Tab. 1.show the value of, and of various yarn fineness. Tab. 1. Elongation, and of various yarn fineness. Yarn fineness 221 tex Yarn fineness 505 tex 28,2 318,5 1,441 16,6 420,8 0,833 37,9 224,3 1,015 30,7 541,6 1,072 51 284,8 1,289 60,2 666 1,319 30,7 301,5 1,364 88,4 572 1,133 42,9 233,5 1,057 102,8 665,9 1,319 38,14 272,52 1,233 59,74 573,26 1,135 Yarn fineness 229 tex Yarn fineness 539 tex 40,4 338,2 1,477 28,5 683 1,267 61,7 370,8 1,619 66,6 624,6 1,159 55,2 219,6 0,959 45,2 655,6 1,216 47,3 475,6 2,077 46,767 654,4 1,214 58,7 370,7 1,619 52,66 354,98 1,55 Yarn fineness 474 tex 67,5 542,4 1,144 72,1 671,7 1,417 42 674,4 1,423 69,1 476,3 1,004 53 665,9 1,405 23,7 434 0,916 54,567 577,45 1,218 3. EXPERIMENTAL An oriented nanofibrous layer was produced using the equipment depicted in Fig.3. This oriented nanofibrous layer was twisted and subjected to next observation on the scanning electron microscope (SEM). Created nanoyarns are introduced in Fig.5 and Fig. 6.
12. - 14. 10. 2010, Olomouc, Czech Republic, EU Fig.5 Fractured part of Nanoyarn. Fig.6 Detail view on twisted nanoyarns. The detailed picture of this nanoyarn is also depicted in Fig.5 and Fig.6. From these nanoyarns was created woven fabric. This fabric was man made and it was plain weave Fig.7. Fig.7 Plain weave made from nanoyarns 4. CONCLUSION This paper presents our results obtained with special collectors. On this collector is enabled to produce oriented nanofibrous layers. These special collectors used electrostatic charge for deposition. These electrostatic charges are not homogeneously distributed on a surface of the collector and hence it is possible oriented nanofibrous layer. The lengths were around 50 cm before twisting. After twisting the final lengths were shorter, around 45 cm. Twist was given using engine with rotation speed around 750 rpm, time duration was 1 minute. From nanoyarns were prepared fabric with plain weave Fig.7. Used polymer was PVA for this experiment. It is possible to prepare biodegradable materials for tissue engineering when biodegradable
polymer is used. Next use can be in filtration. For better filtration properties on this fabric can be placed nanofibrous layer. 5. ACKNOWLEDGEMENT The authors thank to, Jitka Färberová for SEM pictures, "Advanced Remediation Technologies and Processes Center" 1M0554 - Programme of Research Centers supported by Ministry of Education and Research grant GAČR 102/08/H081 for financial support of their work. 6. LITERATURE [1] Cooley, J. F. Apparatus for electrically dispersing fluids. United states patent office. US: 692631, (4. Februar 1902). [2] Zeleny, J. The electrical discharge from liquid points, and a hydrostatic method of measuring the electric intensity at their surface, Physical Review, 3, 69-91 (1914). [3] Taylor, G. F. Van Dyke, M.D. Electrically driven jets, Proc. Roy. Soc. A, 313, 453-475 (1969). [4] Reneker, D. F., Yarin, A.L., Electrospinning jets and polymer nanofibers, Polymer 49, 2008, 2387-2425 [5] Carnell L. S., Siochi E. J., Wincheski R. A., Holloway N.M., Clark R.L., Electric field effects on fiber alignment using an auxiliary electrode during electrospinning, Scripta Materialia 60, 2009, 359-361 [6] DOSHI, J, RENECKER, DH.Electrospinning process and applications of electrospun fibers. Journal of Electrostatic. 1995;35(2-3):151-60 [7] Lukáš, D., Sarkar, A., Martinová, L., Vodseďálková, K., Lubasová, D., Chaloupek, J., Pokorný, P., Mikeš, P., Chvojka, J. and Komárek, M., 2009. Physical Principles of electrospinning (Electrospinning as a Nano-scale Technology of the 21 st Century. Textile Progress, 41 (2), pp. 95-105.