FIBER SPINNING


Fiber spinning is used to make synthetic fibers for use in many industries.There are three main types of fiber spinning methods: melt, solution, and reaction spinning. In fiber spinning a liquid polymer is extruded through small holes in a spinneret to form thin filaments, as shown below. Upon leaving the spinneret the filaments solidify. After solidification, filaments can be combined to make threads and/or drawn to change the filaments' properties.



The processes governing the three types of fiber spinning differ mainly in the way the polymer is liquefied and solidified.



(Copyright Morningstar Fiber, Apple Creek, OH)

MELT SPINNING


GENERAL INFORMATION

Melt spinning is the most widely used form of fiber spinning. In melt spinning either molten polymer is used or polymer pellets are melted down. Once the filaments are extruded they are cooled in a fluid medium such as air, gas, or even water.


EQUIPMENT DESIGN

In melt spinning, as shown below, the molten or melted polymer is pushed vertically downwards through the spinneret. When the filaments emerge from the spinneret they are cooled by a gas, usually air, which flows either perpendicularly across, cocurrently, or countercurrently to the filaments.



(Copyright American Fiber Manufacturers Association, Inc.)

The filaments can then be brought together and/or twisted together to form a thread. Before winding the thread on the bobbin, it is often treated with water or a wetting agent and then a lubricant. Later, the wound thread may be dyed and drawn on other machines.


Spinneret design, such as those shown below, is dependent on the type of spinning and desired cross sectional shape of the filament. The cross sectional shape determines different features the filament will exhibit, such as how it will reflect light, the ability to insulate, and how easily it shows dirt.


(Copyright American Fiber Manufacturers Association, Inc.)

Spin plates and spinnerets may have as many as 80,000 bores spaced less than one millimeter apart. Some spinnerets have superfine capillaries 50 micrometers in diameter. These tiny bores and capillaries are very sensitive to impurities and corrosion; this is one reason why spinnerets are often made of high-grade steel or other metals that can be easily cleaned.


USAGE EXAMPLES

Some common fibers produced using melt spinning are: polypropylene, polyester, and nylon which is shown below and to the right. Nylon was the world's first synthetic fiber discovered and was initially used for tooth brush bristles before being used to produce women's stockings during the 1940's.



(Copyright Explainthatstuff.com)

ADVANTAGES

DISADVANTAGES

  • Ablility to run at high line speeds.
  • Requires no solvent that must be recovered later.
  • Necessary high temperatures may damage some polymers.


SOLUTION SPINNING


Solution spinning is used when the desired polymer does not form a stable melt. These polymers are dissolved in a solution to liquefy them rather than melting them. The two main types of solution spinning are dry and wet spinning.


DRY SPINNING


In dry spinning the polymer is dissolved in a volatile solvent. Once dissolved, the polymer solution is extruded through the spinneret which is in an enclosed drying tower. The solution goes through a drying process in this tower, where the solvent is evaporated.


By courtesy of Encyclopaedia Britannica, Inc., copyright 1997; used with permission.


EQUIPMENT DESIGN

The spinning solution is often filtered many times to remove foreign materials that might cause thread defects or clogging in the machine. The solution is extruded into the drying tower through which hot air or other gases pass. The concentration of the polymer increases as the solvent evaporates, leaving a solid polymer filament behind. The solvent is later recovered from the gas by condensation or absorption and is then recycled.


Solvent selection is very important, and is based on boiling point, latent heat of vaporization, thermal stability, toxicity, and inertness. Non-polar solvents are often preferred because of their low boiling points and heats of vaporization. However, non-polar solvents are prone to build-ups of electrostatic charge, which can be very dangerous.



ADVANTAGES

DISADVANTAGES

  • Better than melt spinning for temperature-sensitive polymers.
  • Faster production rates than melt and wet spinning.
  • Solvent recovery is costly.

WET SPINNING


In wet spinning the polymer is dissolved in a non-volatile solvent. The spinneret is located in a coagulating bath that causes the fiber to precipitate out.


By courtesy of Encyclopaedia Britannica, Inc., copyright 1997; used with permission.


EQUIPMENT DESIGN

The liquid in the coagulating bath is chosen so that the solvent is readily soluble in the liquid but the polymer is not. This will cause the polymer to precipitate out and form the desired solid filaments.The solvent can later be recovered by treating the wastewater in the bath.


The drag on the filament by the viscous liquid in the coagulating bath significantly reduces the production speed of the process. This makes wet spinning a slower process than melt or dry spinning.



ADVANTAGES

DISADVANTAGES

  • Better than melt and dry spinning for temperature sensitive polymers.
  • Lower production rates than melt or dry spinning due to viscous drag.
  • Solvent recovery is costly.

USAGE EXAMPLES

The synthetic fibers produced by solution spinning are made into threads which are woven into fabric for everything from clothes and carpets to airbags and windsails. In addition, sterilized synthetic fibers are used in the medical industry as sutures, dressings, and operating room drapes, face masks, caps and overshoes. Many synthetic fibers can be cut into tiny pieces called flock . Flock is used to make velvet or suede-like materials or added to plastics or papers for a decorative finish.


(Copyright Morningstar Fiber, Apple Creek, OH)

REACTION SPINNING


Reaction spinning involves cross-linking monomers or pre-polymers to create a new polymer with desirable characteristics using simultaneous chain extension reactions.


EQUIPMENT DESIGN

Reaction spinning is similar to dry spinning, but with an additional polymerization step. During polymerization the shorter monomer chains react to make the longer connected polymer chains. It is during this step that the cross-linking of the monomers takes place to form the new enhanced polymer fiber.


USAGE EXAMPLES

Reaction spinning is not very widely used for fiber spinning, but its most common product is spandex. Reaction spinning is used to crosslink a flexible and a stiff pre-polymer. The resulting enhanced fiber is the strong, durable, stretchy, material we know as spandex.




ADVANTAGES

DISADVANTAGES

  • Creates enhanced fibers with unique qualities.
  • Limited by reaction conditions.
  • Not commonly used in industry so generally more expensive.

ACKNOWLEDGEMENTS


Explainthatstuff.com

American Fiber Manufacturers Association, Arlington, VA

Morningstar Fiber, Apple Creek, OH


REFERENCES


Brody, H. Synthetic Fibre Materials. New York: John Wiley & Sons, Inc., 1994.

Hill, Rowland. Fibres from Synthetic Polymers. Amsterdam, The Netherlands: Elsevier      Publishing Co., 1953.

Kricheldorf, Hans Rytger, O. Nuyken, and Graham Swift. Handbook of Polymer Synthesis. 2nd      ed. New York: Marcel Dekker, 2005.

MacKetta, John J. Encyclopedia of Chemical Processing and Design. Vol. 21. New York u.a.:      Dekker, 1984.

Mark, H. F., S. M. Altas and E. Cernia. Man-Made Fibers Science and Technology. New York:      John Wiley & Sons, 1967.

Moncrieff, R. W. Artificial Fibres. New York: John Wiley & Sons, Inc., 1954.

Zhang, Xiangwu. Fundamentals of Fiber Science. Lancaster, Pa.: Destech Publications, Inc.,      2014


DEVELOPERS


Amber Ratliff

Joseph Palazzolo

Henry Chen

Jackie Priestley


Return to Top