Different Types of Spinning Methods for Polymer Filaments

Last Updated on 30/01/2022

What is Spinning?
The textile industry uses the term spinning for two different processes: the spinning of a yarn, which incorporates staple fibers in a twisting or spinning process to help the fibers stay together so the yarn can form. This process is distinct from the spinning process used in the manufacture of man made fibers whereby a polymer solution is melted and pushed through a spinneret to produce filament fibers. Polymer filaments and fibers are very important part of the textile industry. There are various types of spinning for polymer.

Spinning is manufacturing process for creating polymer fibers. It is a specialized form of extrusion that uses a spinneret to form multiple continuous filaments. There are four types of spinning for polymer; wet, dry, melt, and gel spinning.

First, the polymer being spun must be converted into a fluid state. If the polymer is a thermoplastic then it is just melted, if not then it may be dissolved in a solvent or chemically treated to form soluble or thermoplastic derivatives. The fluid polymer is then forced through the spinneret, where the polymer cools to a rubbery state, and then a solidified state.

Different Types of Spinning Methods for Polymer Filaments:
There are different types of spinning for polymer. Such as:

  1. Dry Spinning
  2. Wet Spinning
  3. Melt Spinning
  4. Gel Spinning

Now they are described below:

1. Dry spinning:
Dry spinning is also used for fiber-forming substances in solution. However, instead of precipitating the polymer by dilution or chemical reaction, solidification is achieved by evaporating the solvent in a stream of air or inert gas.

The filaments do not come in contact with a precipitating liquid, eliminating the need for drying and easing solvent recovery. This process may be used for the production of acetate, triacetate, some acrylic, modacrylic, PBI, spandex, and vinyon (PVC, PVA) fibers.

2. Wet spinning:
Wet spinning is the oldest process. It is used for fiber-forming substances that have been dissolved in a solvent. The spinnerets are submerged in a chemical bath and as the filaments emerge they precipitate from solution and solidify.

wet spinning process
Figure 1: Wet spinning process

Because the solution is extruded directly into the precipitating liquid, this process for making fibers is called wet spinning. Wet spinning is the most often used for viscose rayon production. Besides, acrylic, aramid, modacrylic, lyocell, alginate and spandex can be produced by this process.

3. Melt spinning:
In melt spinning, the fiber-forming substance is melted for extrusion through the spinneret and then directly solidified by cooling. Melt spinning is used for the production of polyester, nylon, olefin, saran, sulfur fiber and glass fiber.

In melt spinning (Figure 2), the spinning compound is spun into a cold-air quench duct. Because in this process no solvents are released, the recycling of by-products is not necessary. Polyamide and polyester are produced according to this method.

melt spinning process
Figure 2: Melt spinning process

Melt spun fibers can be extruded from the spinneret in different cross-sectional shapes (round, trilobal, pentagonal, octagonal, and others). Trilobal-shaped fibers reflect more light and give an attractive sparkle to textiles.

Pentagonal-shaped and hollow fibers, when used in carpet, show less soil and dirt. Octagonal-shaped fibers offer glitter-free effects. Hollow fibers trap air, creating insulation and provide loft characteristics equal to, or better than, down.

4. Gel spinning:
Gel spinning is a special process used to obtain high strength or other special fiber properties. The polymer is not in a true liquid state during extrusion. Not completely separated, as they would be in a true solution, the polymer chains are bound together at various points in liquid crystal form.

This produces strong inter-chain forces in the resulting filaments that can significantly increase the tensile strength of the fibers. In addition, the liquid crystals are aligned along the fiber axis by the shear forces during extrusion. The filaments emerge with an unusually high degree of orientation relative to each other, further enhancing strength. The process can also be described as dry-wet spinning, since the filaments first pass through air and then are cooled further in a liquid bath. Some high-strength polyethylene and aramid fibers are produced by gel spinning.

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