1. Effect Of Applied High Voltage And Flow Rate Parameters On Nanofibers Diameter Determined From Electrospininng Technique
Assist .Prof . Dr. Akram R. Jabur,
Assist .Prof . Dr. Laith Q.Al-haidary,
MSc.Student Safa M Muhi Aldain
University of Technology, Department of Materials Engineering, Baghdad, IRAQ
28/10/2014

2. The process of electrospinning, well known for many years in the textile industry and in organic polymer science , has recently re-emerged as a novel tool for generating biopolymer scaffolding for tissue engineering . Specifically, electrospinning provides a mechanism to produce nanofibrous scaffolds from a variety of polymer materials, including synthetic polymers and natural proteins. Fibers with diameters in the range from several micrometers down to less than 100 nm have a very high surface area to mass ratio, and can be electrospun into 3-D scaffolds with very high porosity .

3. To date, electrospinning has been applied for the fabrication of nanofibrous scaffolds from numerous biodegradable polymers, such as poly(caprolactone) (PCL), poly(lactic acid) (PLA), poly(glycolic acid) (PGA), and the copolymer poly(lactide-co-glycolide) (PLGA) and PVA(Polyvinyl alcohol) [3]. These biodegradable polymers have been used to electrospin engineered scaffolds for bone tissue and cardiac grafts. Similarly,poly(L-lactide-co-caprolactone) [P(LLA-CL)] has been electrospun into nanofibrous scaffolds for engineering blood vessel substitutes [3]. Polyurethane (PU) nanofibrous membranes have been used as wound dressings [4]. Polyvinyl alcohol(PVA) nanofibrous membranes have been used as air filter.

4. The electrospinning method is based on fi­bre formation, as the effect of a reaction of a polymer solution drop on the forces of an electric field. Transformation from a drop to a stream in an electric field is known as a Taylor cone [8-11]. Taylor proved in 1964 [10,11] that for a given kind of liq­uid, a critical value of the applied voltage exists, at which the liquid drop, flowing out from the nozzle, is transformed into a cone under the influence of the electric field. The electric charges, which diffuse in the liquid influenced by the electric field, cause strong deformation of the liquid’s surface and minimise the total system energy. Within the region of the maximum field strength and the maxi­mum charge density, the electric forces exceed the forces of surface tension, and theliquid creates a cone at the nozzle out­let. A thin stream of liquid particles is torn off from the end of the cone.

5. Materials and Methods
Characteristics of Polyvinyl alcohol (PVA)
Polyvinyl alcohol (PVA) is the world’s largest volume, synthetic, water soluble polymer. PVA is nonhazardous and is used in many adhesives, a polymer with a repeating vinyl alcohol unit and its molecular weight 80,000, Preparation of Polyvinyl Alcohol Density1.31 g/cm3 from Sinopharm chemical Reagent Co. (:100 ml of PVA[10%]water solution] (10 gm of PVA – 90ml of distilled water )as shown in fig(1). Important test for prepared PVA polymer solution before spinning process, carried with Electrical conductivity (Used Cand 7110 inolab), Viscosity(usingViscometer (DV-II+Pro ) Brook field) and Surface Tensiometer Model (JYW -200A LARYEE TECHNOLOGY CO,)

6. Electrospinning process An experimental laboratory stand for manufacturing nonwoven materials by means of the electrospinning technique was designed and constructed. a photograph of its main parts and a photograph of the electrically driven bending instability of the jet, are presented in Figure 2.

7. Electrospinning was carried out according to the procedure essentially as detailed by [4]. Briefly, polymeric solutions were loaded into 10 ml plastic syringes (BD Biosciences) equipped with blunt 18 gauge needles(orifice size 0.6 mm) were then placed in a syringe pump ( Scientific Double-Syringe Infusion Pump, Fisher Scientifics) and the needles of connected to the earthen output of a high voltage power supply (Fibers were electrospun onto aluminum grounded target (20cm×20cm) . The flow rates were tested at a range of (0.2,0.4,0.8.1 and10 ml/hr.). Electrospinning(using Nano tech Chaina) was carried out with the high voltage power supply set at 25 kV with an air gap distance(needle tip to collector distance ) D of 8 cm. The concentrations of Polyvinyl alcohol (PVA) solution were 10% .Second steps by varying the applied high voltage to (5,10,15,20,25KV) at flow rate constant flow rate of 0 .2 ml/hr and D=8 cm.

8. Experimental Results
Characteristics of Polyvinyl alcohol (PVA)
Testing the PVA water solution properties , Electrical conductivity (Used Cand 7110 inolab) obtained 1222 (µS\cm) and Viscosity(usingViscometer (DV-II+Pro ) Brook field) obtained 2014 (Cp)at 19 °C temperature and surface tension 44 mN/m2.

9. 5KV
10KV
15KV
20KV
25KV
Figure (3 a,b,c,d and d) SEM images and histogram of PVA electrospun nanofiers with various Applied Voltages (Distance=10cm, Flow rate = 0.2 ml/hr ,Temperature = 25 C°) Voltages a) 5 KV; b) 10 KV ; c) 15 KV ; d) 20 KV ; e) 25 KV respectively .

10. 0.2ml/hr
0.5ml/hr
0.8ml/hr
0.8ml/hr
1ml/hr
10ml/hr
Figure (5) SEM images of PVA electrospun nanofiers with various Rates (Voltage =15 cm, Distance = 12 cm, Temperature = 25 C°) Flow rates a) 0.2 ml/hr; b) 0.5 ml/hr ; c) 0.8 ml/hr ; d) 1 ml/hr ; e) 10 ml/hr .

11. Figure (4) Distribution of Nanofiber with various Voltages.
Figure (6) Distribution of Nanofiber with various Flow rates.

12. conclusion
1-As high voltage applied increased fibers diameter decrease.
2-The diameter of PVA electrospun fibers decreases with increasing electric field due to the electrostatic force in the polymer jet become large enough to overcome the cohesive force within the jet, then the spiral motion and elongation of the polymer jet in process with higher electric field strength become more active.