**3.1 Production of filament type microfibers**

#### **3.1.1 Direct spinning**

In this method microfiber is directly manufactured by melt spinning (Purane & Panigrahi, 2007). With this method, the fineness of the microfibers produced is limited to 0.1 dtex because of the tendency of the individual filaments to stick together. Improvements in processing conditions and finishing, such as more accurate spinnerets and strictly controlled cooling conditions after extrusion, together with lower polymer viscosity, can however make the production of microfiber yarns possible (Rupp & Yonenaga, 2000).

#### **3.1.2 Conjugate spinning**

The technical problems in direct spinning can be solved by conjugate spinning, which yields homogenous ultra-fine fibers. Okamoto et al. and Matsui et al. investigated the extrusion of conjugate fibers with a cross section consisting of highly dispersed conjugate components by modifying the spinneret structure. Conjugate spinning is classified into two types from technical viewpoint: the islands in a sea type and separation or splitting type. In either case, the microfiberization is performed in the form of fabrics. No special technical problems arise in later processing, compared with conventional spinning (Okamoto, 2000).

#### **3.1.2.1 Islands in a sea type**

In islands in a sea method, a number of continuous very fine filaments are extruded in a matrix of another polymer. In the spinneret a number of bi-component sheath-core polymer flows are combined into a single flow and extruded. The islands in the sea fiber is then quenched and drawn in the usual way (Richards, 2005). Polyester, nylon, polypropylene,

normal fibers to attain a given shade depth (Jerg & Baumann, 1990; Anonymous, 2000;

There are various methods of producing microfibers. All three conventional spinning methods, namely melt spinning, wet spinning, and dry spinning can be employed to manufacture microfibers (Purane & Panigrahi, 2007). Although, it is possible to produce microfibers through conventional melt spinning, to create such fine filaments requires very strict process controls and a uniformly high quality of polymer (Tortora & Collier, 1997).

Ultra-fine fibers are classified into two types: filament type, and staple type. Recent developments in the field of ultra-fine fibers have focused on the filament type (Okamoto,

In this method microfiber is directly manufactured by melt spinning (Purane & Panigrahi, 2007). With this method, the fineness of the microfibers produced is limited to 0.1 dtex because of the tendency of the individual filaments to stick together. Improvements in processing conditions and finishing, such as more accurate spinnerets and strictly controlled cooling conditions after extrusion, together with lower polymer viscosity, can however

The technical problems in direct spinning can be solved by conjugate spinning, which yields homogenous ultra-fine fibers. Okamoto et al. and Matsui et al. investigated the extrusion of conjugate fibers with a cross section consisting of highly dispersed conjugate components by modifying the spinneret structure. Conjugate spinning is classified into two types from technical viewpoint: the islands in a sea type and separation or splitting type. In either case, the microfiberization is performed in the form of fabrics. No special technical problems arise

In islands in a sea method, a number of continuous very fine filaments are extruded in a matrix of another polymer. In the spinneret a number of bi-component sheath-core polymer flows are combined into a single flow and extruded. The islands in the sea fiber is then quenched and drawn in the usual way (Richards, 2005). Polyester, nylon, polypropylene,

Ultra fine fiber of the filament type is produced by the methods including:

make the production of microfiber yarns possible (Rupp & Yonenaga, 2000).

in later processing, compared with conventional spinning (Okamoto, 2000).

Falkai, 1991).

2000).

**3. Production of microfibers** 

1. Direct spinning (conventional extrusion)

**3.1 Production of filament type microfibers** 

2. Conjugate spinning

**3.1.1 Direct spinning** 

**3.1.2 Conjugate spinning** 

**3.1.2.1 Islands in a sea type** 

a. Islands in a sea type b. Separation or splitting type c. Multi-layer type (Okamoto, 2000). polyethylene and polyphenylene sulfide are the polymers employed as island components (Okamoto, 2000). The various combinations of polymers to form fibers by this method successfully are polystyrene/polyamide and polystyrene/polyester (Purane & Panigrahi, 2007). The sea component is removed by dissolving it in a solvent after conventional processing into woven, knitted or nonwoven fabrics. This technology provided a means of industrial production of suede type artificial leather, silk like fabrics, wiping cloths and fine filters. Since the ultra fine filaments (the island component) are sheathed by the sea component, they are protected from damage during later processing (Okamoto, 2000).

Three component spinning can be carried out with two island components by designing a three component spinneret assembly. The sea component can be reduced to 2-10% of the total components, but the space between the ultra fine filaments is also reduced and this may lead to poorer handle of the products. When the sea component is small in amount and not miscible with the island component, the splitting can be carried our mechanically (Okamoto, 2000).
