*2.3.3. Nanofiber*

In fiber diameter, the range from 0.1 to 1 nm is of angstrom size, that from 1 to 10 nm is of nano size, that from 100 to 1000 nm is of sub-micron size, and that from 1000 to 10 000 nm is of micron size. Fibers with an angstrom size diameter are effectively the molecular chain. Nanometer size and sub-micron size fibers can be classed as nanofiber. A micron-size fiber is called a micro-fiber. Fibers with a diameter more than a few micrometers are the conventional fibers, including those with millimeter, centimeter, or meter-order diameter [35].

The nonwoven industry generally considers nanofibers as having a diameter of less than 1µm, although the National Science Foundation (NSF) defines nanofibers as having at least one dimension of 100 nm or less. The name derives from the nanometer, a scientific measurement unit representing a billionth of an ammeter, or there to four atoms wide.

**Figure 5.** Schematic Diagram of Electrospinning Process [14]

Generally, polymeric nanofibers are produced by an electrospinning process. A schematic diagram of electrospinning is shown in Figure 5. Electrospinning is a process that spins fibers of diameter ranging from 10 mm to several hundred nanometers. This method has been known since 1934 when the first patent on electrospinning was filed. The process makes use of electrostatic and mechanical forces to spin fibers from the tip of affine orifice or spinneret. The spinneret is maintained at positive or negative charge by a DC power supply. When electro‐ static repelling force overcomes the surface tension force of the polymer solution, the liquid spills out of the spinneret and forms an extremely fine continuous filament. These filaments are collected onto a rotating or stationary collector with an electrode beneath the opposite charge to that of the spinneret where they accumulate and bond to form a nanofiber fabric [36].

In this method, polymer and solvents are used. Nanofibers in the range of 10-2000 nm diameter can be achieved by choosing the appropriate polymer solvent system. Table 4 gives a list of some of the polymer solvent systems used in electrospinning [14,37].


**Table 4.** Polymer solvent systems for electrospinning [14]

Nanofibers exhibit special properties mainly due to extremely high surface to weight ratio compared to conventional nonwovens. Nonwoven products such as aerosol filters, facemasks, and protective clothing are used mostly in filtration applications because of low density, large surface area to mass, high pore volume, and tight pore size. At present, military fabrics under development designed for chemical and biological protection have been enhanced by lami‐ nating a layer of nanofiber between the body side layer and carbon fibers. Nanofibers are also used in medical applications, which include drug and gene delivery, artificial blood vessels, artificial organs, and medical face masks. For example, carbon fiber hollow nano-tubes, smaller than blood cells, have potential to carry drugs into blood cells [14].

### *2.3.4. Bicomponent*

*2.3.3. Nanofiber*

16 Non-woven Fabrics

In fiber diameter, the range from 0.1 to 1 nm is of angstrom size, that from 1 to 10 nm is of nano size, that from 100 to 1000 nm is of sub-micron size, and that from 1000 to 10 000 nm is of micron size. Fibers with an angstrom size diameter are effectively the molecular chain. Nanometer size and sub-micron size fibers can be classed as nanofiber. A micron-size fiber is called a micro-fiber. Fibers with a diameter more than a few micrometers are the conventional

The nonwoven industry generally considers nanofibers as having a diameter of less than 1µm, although the National Science Foundation (NSF) defines nanofibers as having at least one dimension of 100 nm or less. The name derives from the nanometer, a scientific measurement

Generally, polymeric nanofibers are produced by an electrospinning process. A schematic diagram of electrospinning is shown in Figure 5. Electrospinning is a process that spins fibers of diameter ranging from 10 mm to several hundred nanometers. This method has been known since 1934 when the first patent on electrospinning was filed. The process makes use of electrostatic and mechanical forces to spin fibers from the tip of affine orifice or spinneret. The spinneret is maintained at positive or negative charge by a DC power supply. When electro‐ static repelling force overcomes the surface tension force of the polymer solution, the liquid

fibers, including those with millimeter, centimeter, or meter-order diameter [35].

unit representing a billionth of an ammeter, or there to four atoms wide.

**Figure 5.** Schematic Diagram of Electrospinning Process [14]

There has been a trend in the polymer industry since the midsixties to apply polymer blends and mixtures for the modification of material properties. In the man-made fiber industry, this trend is realized in the manufacture of fibers consisting of two or more components [38].

Bicomponent fibers can be defined as "extruding two polymers from the same spinneret with both polymers contained within the same filament." A close relative is "co-spun fiber," which is a group of filaments of different polymers, but a single component per filament, spun from the same spinneret [39]. Bicomponent fibers are commonly classified by the structure of their cross-section as side-by-side (S/S), sheath core, island in the sea, or segmented pie. Of these, the side-by-side and sheath core arrangements are relevant for thermal bonding applications [40].
