**2.2 Preparation of as-spun solutions**

Observations while electrospinning the fiber mats and yarns showed different fiber diameters were obtained for the two processes likely due to variations in setup geometries and electric field strengths. By trial and error in varying solution concentrations, appropriate solution concentrations for the two processes were determined to produce fibers with diameters of 1200 nm for both processes. The comparisons of charges and properties discussed in the experiments below were obtained for fibers with these diameters.. Electrospinning solutions for producing fiber mats were prepared with 18%wt PVDF polymer by mixing the polymer with 50:50 wt.% blended DMF and Acetone solvents. The PVDF powder was added to mixture of solvents and heat-stirred for half an hour at 70 °C to attain a clear homogenous mixture. For production of fiber yarns, a 13 wt% PVDF polymer solution was prepared by mixing Acetone and N, N-Dimethylformamide (DMF) solvents at 1:1 ratio. This mixture was heated on a hot plate at 70 °C for 20 min to attain a clear homogenous mixture.

#### **2.3 Electrospinning set-ups and mechanism**

The fiber mats were synthesized by using a typical single-needle electrospinning setup as shown in **Figure 2.** The polymer solutions were loaded into 5 ml plastic syringes and fed by syringe pump (NE-1000, New Era Pump Systems, Inc., Farmingdale, NY). The metallic needles were charged by high voltage power supplies (ES30P-5 W, Gamma High Voltage Research, Ormond Beach, FL) to generate potential differences between the collector and the needle. The fiber mats were collected on rotating cylindrical drum collectors covered with 30 cm × 30 cm sheets of grounded aluminum foil. The fiber mats were electrospun for varying times to create mats of basis weights of 10, 20, 30, 40 and 50 g/m2 . In the experiments involving stacked layers of mats, all of the layers were formed of mats of 20 g/m2 basis weights. The electrospinning conditions are listed in **Table 3**.

**Figure 3** shows the experimental setup used to generate the electrospun yarn and is similar to setups reported in literature [28, 30]. The setup consisted of fiber spinning and yarn winding sections. In the fiber spinning section, a metallic conical-shaped funnel collector was connected to the motor and controller. The syringe pump and power supply were used to electrospin the polymer solution at a flowrate of 4 - 5 ml/hr. A potential difference of 10 – 20KV was applied between the

**199**

**Figure 3.**

*Illustration of fiber yarn setup.*

**Figure 2.**

**PVDF (wt.%)**

**Table 3.**

*Schematic of electrospinning set-up.*

**DMF – Acetone mass ratio**

*Electrospinning conditions and fiber diameter data.*

**Tip to Collector Distance (cm)**

**Applied Potential (kV)**

**Flow Rate (ml/hr)**

18 1:1 20 27 5 1139 654 30

**Avg. Fiber Diameter (nm)**

**Standard Deviation (nm)**

**Drum Rotation Rate (rpm)**

*Polarization of Electrospun PVDF Fiber Mats and Fiber Yarns*

*DOI: http://dx.doi.org/10.5772/intechopen.96305*

*Polarization of Electrospun PVDF Fiber Mats and Fiber Yarns DOI: http://dx.doi.org/10.5772/intechopen.96305*

#### **Figure 2.**

*Nanofibers - Synthesis, Properties and Applications*

pun mats.

**2.1 Materials**

**2. Materials and methods**

and density of 1.78 g/m3

tions without further purification.

**2.2 Preparation of as-spun solutions**

attain a clear homogenous mixture.

**2.3 Electrospinning set-ups and mechanism**

to create mats of basis weights of 10, 20, 30, 40 and 50 g/m2

basis weights. The electrospinning conditions are listed in **Table 3**.

a spool, which differs from typical electrospinning equipment that collect the fiber mats on a solid grounded surface. The resulting yarns had lengths up to tens of meters long and exhibited mechanical properties different from the electros-

Electrospinning solutions were prepared by dissolving PVDF powder (Arkema Inc., Exton, PA, USA, Kynar® 761 grade resin with molecular weight of 500,000 g/gmol

(Sigma Aldrich, St. Louis, MO, USA). These materials were used in making the solu-

Observations while electrospinning the fiber mats and yarns showed different fiber diameters were obtained for the two processes likely due to variations in setup geometries and electric field strengths. By trial and error in varying solution concentrations, appropriate solution concentrations for the two processes were determined to produce fibers with diameters of 1200 nm for both processes. The comparisons of charges and properties discussed in the experiments below were obtained for fibers with these diameters.. Electrospinning solutions for producing fiber mats were prepared with 18%wt PVDF polymer by mixing the polymer with 50:50 wt.% blended DMF and Acetone solvents. The PVDF powder was added to mixture of solvents and heat-stirred for half an hour at 70 °C to attain a clear homogenous mixture. For production of fiber yarns, a 13 wt% PVDF polymer solution was prepared by mixing Acetone and N, N-Dimethylformamide (DMF) solvents at 1:1 ratio. This mixture was heated on a hot plate at 70 °C for 20 min to

The fiber mats were synthesized by using a typical single-needle electrospinning setup as shown in **Figure 2.** The polymer solutions were loaded into 5 ml plastic syringes and fed by syringe pump (NE-1000, New Era Pump Systems, Inc., Farmingdale, NY). The metallic needles were charged by high voltage power supplies (ES30P-5 W, Gamma High Voltage Research, Ormond Beach, FL) to generate potential differences between the collector and the needle. The fiber mats were collected on rotating cylindrical drum collectors covered with 30 cm × 30 cm sheets of grounded aluminum foil. The fiber mats were electrospun for varying times

involving stacked layers of mats, all of the layers were formed of mats of 20 g/m2

**Figure 3** shows the experimental setup used to generate the electrospun yarn and is similar to setups reported in literature [28, 30]. The setup consisted of fiber spinning and yarn winding sections. In the fiber spinning section, a metallic conical-shaped funnel collector was connected to the motor and controller. The syringe pump and power supply were used to electrospin the polymer solution at a flowrate of 4 - 5 ml/hr. A potential difference of 10 – 20KV was applied between the

. In the experiments

) in co-solvents N-N-Dimethylformamide (DMF) and acetone

**198**

*Schematic of electrospinning set-up.*


#### **Table 3.**

*Electrospinning conditions and fiber diameter data.*

**Figure 3.** *Illustration of fiber yarn setup.*

metal needles and the collector with an 8 cm distance between the needles and the edge of the collector.

Charged polymer jets launched from drops of polymer solution at the tips of the needles and followed the electric field gradient towards the wide neck of the conical-shaped collector. Once a substantial mat of fibers collected over the open end of the collector, the center of mat was hooked onto a wire and pulled to stretch the mat into the shape of an inverted cone.

The metal collector was rotated by the motor to twist the fiber structure into a twisted continuous yarn. The yarn gradually increased in length and was stretched and attached to the take-up reel for collection onto a spool. The rotation speeds of the metal collector and the take-up reel were adjusted by trial and error to produced yarns of uniform twist and uniform outer diameter.

In the case of electrospun mats, replicate samples were obtained at consistent basis weights by adjusting the time of fiber accumulation on the mats, so that the resulting fiber mat had uniform thickness and mass over the area of the sample. But in the case of fiber yarns a suitable length of sample was considered from each replicate run and compared for consistency by comparing the mass to length ratio of each sample. Results showed ±3% variation in mass/length for each of sample used in these experiments.
