**2. Synthesis of carbon nanofibers**

*Nanofibers - Synthesis, Properties and Applications*

less, tasteless, and soluble in water [13].

were continuous [15, 16].

materials [8, 10].

The type of nanofibers that is currently developing very rapidly in the field of research, material synthesis systems and product applications is carbon nanofibers (CNF). Carbon nanofibers (CNF) has applications as a promising material and has great potential in various fields, in the chemical field, carbon nanofibers (CNF) have been widely applied to gas and water membranes, by utilizing the advantages of CNF in porosity, surface area high as well as good higher chemical resistance [8]. In the field of physics, the good thermal and electrical conductivity properties make CNF very potential to be applied to electrical devices, batteries in the electrode material, energy storage and as a sensor [9]. While in the field of materials science, CNF has been applied to the strengthening of composites and supercapacitor

The precursor for forming carbon nanofibers consists of Polyvinyl Alcohol (PVA) and Carbon, PVA is a polymer that has flexible properties, can form hydrogel bonds, is easily broken down naturally and is often used in the formation of nanofibers [11]. The chemical structure of PVA is shown in **Figure 1**, the degree of hydrolysis of PVA is around 98.5% so that it can dissolve in water with a temperature of 70 ° C [12]. In addition, PVA has optical properties, a quite good load storage capacity but poor conductivity values. Therefore, to overcome the bad conductivity properties can be done by means of doping. The nature of PVA is colorless, odour-

Because PVA has biodegradable properties, this is what makes this polymer widely used for its applications in the medical, food industry and electronics. The physical properties of PVA are presented in **Table 1** below [6]. Anita and Harsojo, in their research, explained that the morphological results of PVA fabrication using electrospinning owned by nanofibers which were formed at a concentration of 10%

Carbon is a material that has various advantages in terms of physical and chemical properties, so many researchers have developed it today. This advantage of carbon makes it a material with the extensive application. The performance of this carbon is influenced by morphology. This morphological difference will result in the wide application of the carbon, such as catalyst supports, adsorbents, gas storage, separation technology, battery electrodes, porous template materials, fuel cells, and biological cells. In addition, several carbon particles with certain morphologies will have different applications [17], besides carbon material is also an amorphous

**Character Value** Density (1.19–1.31) gr/cm3 Melting point 180–240 °C Boiling point 228 °C Decomposition temp 180 °C

**40**

**Table 1.**

**Figure 1.**

*PVA Chemical Structure.*

*Physical Properties of PVA [14].*

This section discusses the process of obtaining carbon nanofibers or the synthesis process to obtain carbon nanofibers which can be done, such as electrospinning (plate and drum collector), drawing methods and template methods. Each of these carbon nanofibers synthesis methods has its own advantages and disadvantages of the resulting material.

### **2.1 Preparation of carbon nanofibers (CNF)**

The polymer solution in this study was made from polyvinyl alcohol (PVA), distilled water and carbon powder precursors with a size of 500 mesh. In the process of forming a polymer synthesis preparation material, PVA (molecular weight 60000, Merck Co) and carbon as a solute and distilled water as a solvent. The process scheme in making polymer solutions is by determining the concentration of the solution. The concentration of PVA solution that can be used in this study is 13 wt% with the solvent, and 2% wt carbon with distilled water as a solvent. After being measured, PVA and distilled water were mixed in one beaker. Then the magnetic stirrer is inserted into the reaction glass, then it is placed on the magnetic stirrer hotplate which has been activated. The temperature is set to reach 90 °C. After the temperature is right, this stirring process is carried out for one hour. Then the carbon and distilled water are mixed in one beaker glass, with the same steps as the PVA solution, the carbon and the solvent are placed on a hotplate magnetic stirrer which has been activated and the temperature is set to 30 After the temperature has been adjusted, the stirrer is turned on and the stirring process is carried out for one hour after the two solutions have dissolved well then, the PVA and carbon solutions are mixed with a volume ratio of PVA and carbon 2:1, then sonication is carried out by ultrasonic bath for 5 hours later. Stirred back at 30 °C for one hour.

#### **2.2 Electrospinning**

The electrospinning technique is a technology for making nano-sized fiber materials derived from materials in the form of solutions or liquids, as well as an efficient nanofibers manufacturing system by utilizing the influence of electrostatics in producing a solution (jet) of electrically charged polymer solutions or melts [20]. The electrostatic effect is generated by using a high voltage source. The voltage source that can be done in the use of electrospinning is between 7 kV to 32 kV [21]. Apart from the high voltage, the other important parts controlling the process are a

**Figure 2.** *The forces that appear in the electrospinning process.*

syringe pump as a solution sprayer with a precise flow rate, and a collector as a place to collect the nanofibers that are formed [22]. When a high voltage is applied to the needle tip and collector, an electric field is formed around it. The positive pole is connected to the needle, the negative pole is connected to the collector. As the electric field around the needle increases, the hemisphere of the solution droplets at the tip of the needle will expand further and form a cone (also known as Taylor cone). When a high voltage is applied to the needle tip, the electric field will affect the surface tension of the solution droplet. Due to the influence of the electric charge on the needle tip on the solution, the solution is polarized and attracted towards the collector [23]. On the way from the tip of the needle to the collector, the solution undergoes thinning and evaporation of fibers or fibers that form and collect on the collector surface [21].

The forces acting on the electrospinning process can be described as in **Figure 2** which shows the modelling of the forces acting on the electrospinning process. From this figure, it can be written the equation of the forces acting on the electrospinning process as follows,

$$
\overline{F}\gamma - \overline{F}\_{\mathbb{C}} + \overline{F}\_{H} = \mathbf{0} \tag{1}
$$

**43**

**Figure 4.**

*the fibers are formed only in the center of the collector.*

**Figure 3.**

*Fabrication of PVA/Carbon-Based Nanofibers Using Electrospinning*

the solution will be attracted towards the collector.

*Schematic illustration of an electrospinning system using a plate collector type.*

*SEM images of fabricated CNF using an electrospinning system with a stationary plate collector and most of* 

the schemes used here use electrospinning with a stationary plate collector and a

As shown in **Figure 3**, is an electrospinning scheme with a syringe containing a polymer solution that includes a spinneret (needle), a direct current (DC) highvoltage power generator and a stationary collector plate. In the electrospinning method, a high voltage over a certain range is applied between two electrodes to obtain the desired type and quality of carbon nanofibers. The positive electrode is made in contact with the PVA + carbon fluid via a spinneret to produce a charged liquid when subjected to an external electric field, and the negative electrode is attached to a collector which acts as a fiber collector. Due to the electrostatic force,

Although such a simple plate-collector electrospinning scheme is sufficient to obtain fibers, it does not produce a homogeneous and evenly distributed CNF layer, as more CNF collects in the center of the collector, resulting in variations in thickness through the layers, which can also affect fiber morphology, as well as carbon nanofibers the resulting system tends to easily form beads as shown in

*DOI: http://dx.doi.org/10.5772/intechopen.96175*

rolling drum collector.

when *F*γ is the surface tension force of the solution, *FC* is the Coulomb force that arises because of the electric field, and *FH* is the hydrodynamic force that occurs when the solution is pushed/pressed by the syringe pump [24].

#### **2.3 Electrospinning with a plate collector**

PVA and Carbon precursor solutions that have gone through the preparation stage will then be fabricated using an electrospinning system to produce carbon nanofibers, the electrospinning system used can be done with various schemes, but

### *Fabrication of PVA/Carbon-Based Nanofibers Using Electrospinning DOI: http://dx.doi.org/10.5772/intechopen.96175*

the schemes used here use electrospinning with a stationary plate collector and a rolling drum collector.

As shown in **Figure 3**, is an electrospinning scheme with a syringe containing a polymer solution that includes a spinneret (needle), a direct current (DC) highvoltage power generator and a stationary collector plate. In the electrospinning method, a high voltage over a certain range is applied between two electrodes to obtain the desired type and quality of carbon nanofibers. The positive electrode is made in contact with the PVA + carbon fluid via a spinneret to produce a charged liquid when subjected to an external electric field, and the negative electrode is attached to a collector which acts as a fiber collector. Due to the electrostatic force, the solution will be attracted towards the collector.

Although such a simple plate-collector electrospinning scheme is sufficient to obtain fibers, it does not produce a homogeneous and evenly distributed CNF layer, as more CNF collects in the center of the collector, resulting in variations in thickness through the layers, which can also affect fiber morphology, as well as carbon nanofibers the resulting system tends to easily form beads as shown in

#### **Figure 3.**

*Nanofibers - Synthesis, Properties and Applications*

syringe pump as a solution sprayer with a precise flow rate, and a collector as a place to collect the nanofibers that are formed [22]. When a high voltage is applied to the needle tip and collector, an electric field is formed around it. The positive pole is connected to the needle, the negative pole is connected to the collector. As the electric field around the needle increases, the hemisphere of the solution droplets at the tip of the needle will expand further and form a cone (also known as Taylor cone). When a high voltage is applied to the needle tip, the electric field will affect the surface tension of the solution droplet. Due to the influence of the electric charge on the needle tip on the solution, the solution is polarized and attracted towards the collector [23]. On the way from the tip of the needle to the collector, the solution undergoes thinning and evaporation of fibers or fibers that form and collect on the

The forces acting on the electrospinning process can be described as in **Figure 2** which shows the modelling of the forces acting on the electrospinning process. From this figure, it can be written the equation of the forces acting on the

> *F FF C H* γ

that arises because of the electric field, and *FH* is the hydrodynamic force that

PVA and Carbon precursor solutions that have gone through the preparation stage will then be fabricated using an electrospinning system to produce carbon nanofibers, the electrospinning system used can be done with various schemes, but

occurs when the solution is pushed/pressed by the syringe pump [24].

is the surface tension force of the solution, *FC* is the Coulomb force

−+ = 0 (1)

**42**

collector surface [21].

**Figure 2.**

when *F*γ

electrospinning process as follows,

*The forces that appear in the electrospinning process.*

**2.3 Electrospinning with a plate collector**

*Schematic illustration of an electrospinning system using a plate collector type.*

#### **Figure 4.**

*SEM images of fabricated CNF using an electrospinning system with a stationary plate collector and most of the fibers are formed only in the center of the collector.*

#### **Figure 5.**

*Schematic illustration of an electrospinning system that uses a rotating drum collector type, with more complex controls and parameters.*

#### **Figure 6.**

*(a) SEM image results, and (b) size distribution of CNFs from electrospinning fabrication results with rotating drum collectors, with a rotation speed of 130 rpm, a given high DC voltage of 10 kV and a relative humidity of about 30%.*

**45**

*Fabrication of PVA/Carbon-Based Nanofibers Using Electrospinning*

**2.4 Electrospinning with a rolling drum collector**

**Figure 4**. The results were not homogeneous, and beads appeared on the CNF because the plate collector was used in a stationary or stationary position so that the effect of spinning fibers after the Taylor cone and jet polymer processes was

In this regard, electrospinning with a rotating drum collector has been developed to allow the formation of carbon nanofibers homogeneously and thoroughly to all areas on the drum surface, resulting in a CNF of uniform thickness as shown in **Figure 5.** When the drum collector rotates, the fibers will be attracted towards the collector and subjected to a spinning effect on the rotating drum, then the spinneret moves right and left, as well as the influence of the electric field between the needle and the collector which causes the CNF to form evenly throughout and

Carbon nanofibers (CNF) formed with this system has an interesting material morphology as shown in **Figure 6** which is attractive in the sense that no beads are formed on the CNF, and the fibers are evenly distributed with a homogeneous thickness. The fiber that is formed enters the nanometer scale area, from direct measurements the diameter of the CNF formed is at 262 nm, as we all know that the limitations of fiber or composite materials are said to be in the nanoscale if they

The electrospinning method has many parameters that must be controlled to produce nanofibers. The parameters that influence are high voltage, field, electricity, nozzle to collector distance, solution concentration, and humidity. The formation of jet polymer in the electrospinning method results in the morphological shape of the nanofibers. The polymer jet itself is influenced by environmental conditions, one of which is humidity. Humidity parameters greatly affect the diameter of the nanofibers, at high humidity, the fiber diameter will increase (Medeiros et al., 2018). The application of high voltage to electrospinning is very important in influencing the diameter and morphology of the nanofibers. The increase in high voltage causes an increase in the electric field as well as this affects the decrease in the diameter of the nanofibers and shortens the time of the solution from the tip of the needle to the collector. The flow rate in electrospinning is the flow of fluid from the syringe pump to the collector. The rate of solution (flowrate) affects the formation of fiber diameter and morphology. This process affects the material transfer rate and jet speed. The diameter of the fiber will increase as the

Viscosity is the thickness of a solution; this viscosity is influenced by the concentration of the solution. High viscosity is difficult to force the solution out of the syringe so that the control on the needle is unstable, the higher the viscosity, the higher the fiber diameter. The diameter and morphology of the nanofibers are basically influenced by the distance between the needle tip and the collector. Distance affects fiber diameter and morphology because distance can determine the deposition time, evaporation rate, and polymer jet instability [26]. Therefore, an optimum nozzle to collector distance is needed to form carbon nanofibers with the desired diameter and fiber morphology. Several studies have studied the effect of the nozzle to collector distance and concluded that increasing the distance makes the fiber

diameter decrease but the polymer jet instability increases [25].

*DOI: http://dx.doi.org/10.5772/intechopen.96175*

formless beads in the layer collector.

have a size of 50 nm to 500 nm.

rate of solution used increases [25].

**3. Electrospinning control parameters**

very weak.

*Nanofibers - Synthesis, Properties and Applications*

**44**

**Figure 6.**

**Figure 5.**

*controls and parameters.*

*about 30%.*

*(a) SEM image results, and (b) size distribution of CNFs from electrospinning fabrication results with rotating drum collectors, with a rotation speed of 130 rpm, a given high DC voltage of 10 kV and a relative humidity of* 

*Schematic illustration of an electrospinning system that uses a rotating drum collector type, with more complex* 

**Figure 4**. The results were not homogeneous, and beads appeared on the CNF because the plate collector was used in a stationary or stationary position so that the effect of spinning fibers after the Taylor cone and jet polymer processes was very weak.
