Rayon

Rayon is a manufactured regenerated cellulosic fiber. Rayon is produced from naturally occurring polymers and therefore it is not a truly synthetic fiber, nor is it a natural fiber. It is known by the names viscose rayon and art silk in the textile industry.

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History

Nitrocellulose

The fact that nitrocellulose is soluble in organic solvents such as ether and acetone, made it possible for Georges Audemars to develop the first "artificial silk" about 1855, but his method was impractical for commercial use. Hilaire de Charbonnet, Comte de Chardonnay, patented "Chardonnay silk" in 1884. The commercial production started 1891, but it was flammable, and more expensive than acetate or cuprammonium rayon. Because of this, production was stopped before World War I, for example 1912 in Germany.

Acetate method

Paul Schützenberger discovered that cellulose can be reacted with acetic acid anhydride to form cellulose acetate. The triacetate is only soluble in chloroform making the method expensive. The discovery that hydrolyzed cellulose acetate is soluble in less polar solvents, like acetone, made production of cellulose acetate fibers cheap and efficient.

Cuprammonium method

The German chemist Eduard Schweizer discovered that tetraamminecopper dihydroxide could dissolve cellulose. Max Fremery and Johann Urban developed a method to produce carbon fibers for use in light bulbs in 1892. Production of rayon for textiles started in 1899 in the Vereinigte Glanzstofffabriken AG in Oberbruch. Improvement by the J.P. Bemberg AG in 1901 made the artificial silk a product comparable to real silk.

Viscose method

Finally, in 1894, Charles Frederick Cross, Edward John Bevan, and Clayton Beadle patented their artificial silk, which they named "viscose", because the reaction product of carbon disulfide and cellulose in basic conditions gave a highly viscous solution of xanthate. Avtex Fibers Incorporated began selling their formulation in 1910 in the United States. The name "rayon" was adopted in 1924, with "viscose" being used for the viscous organic liquid used to make both rayon and cellophane. In Europe, though, the fabric itself became known as "viscose," which has been ruled an acceptable alternative term for rayon by the U.S. Federal Trade Commission. The method is able to use wood (cellulose and lignin) as a source of cellulose while the other methods need lignin-free cellulose as starting material. This makes it cheaper and therefore it was used on a larger scale than the other methods.

Contamination of the waste water by carbon disulfide, lignin and the xanthates made this process detrimental to the environment. Rayon was only produced as a filament fiber until the 1930s when it was discovered that broken waste rayon could be used in staple fiber.

The physical properties of rayon were unchanged until the development of high-tenacity rayon in the 1940s. Further research and development led to the creation of high-wet-modulus rayon (HWM rayon) in the 1950s ^[1].

Major fiber properties

Rayon is a very versatile fiber and has the same comfort properties as natural fibers. It can imitate the feel and texture of silk, wool, cotton and linen. The fibers are easily dyed in a wide range of colors. Rayon fabrics are soft, smooth, cool, comfortable, and highly absorbent, but they do not insulate body heat, making them ideal for use in hot and humid climates ^[2].

The durability and appearance retention of regular rayon are low, especially when wet; also, rayon has the lowest elastic recovery of any fiber. However, HWM rayon is much stronger and exhibits higher durability and appearance retention. Recommended care for regular rayon is dry-cleaning only; HWM rayon can also be machine washed ^[1].

Gallery of textures

Physical structure of rayon

Regular rayon has lengthwise lines called striations and its cross-section is an indented circular shape. The cross-sections of HWM and cupra rayon are rounder. Filament rayon yarns vary from 80 to 980 filaments per yarn and vary in size from 40 to 5000 denier. Staple fibers range from 1.5 to 15 denier and are mechanically or chemically crimped. Rayon fibers are naturally very bright, but the addition of delustering pigments cuts down on this natural brightness ^[1].

Production method

Regular rayon (or viscose) is the most widely produced form of rayon. This method of rayon production has been utilized since the early 1900s and it has the ability to produce either filament or staple fibers. The process is as follows:

1. Cellulose: Production begins with processed cellulose
2. Immersion: The cellulose is dissolved in caustic soda
3. Pressing: The solution is then pressed between rollers to remove excess liquid
4. White Crumb: The pressed sheets are crumbled or shredded to produce what is known as "white crumb"
5. Aging: The "white crumb" aged through exposure to oxygen
6. Xanthation: The aged "white crumb" is mixed with carbon disulfide in a process known as Xanthation
7. Yellow Crumb: Xanthation changes the chemical makeup of the cellulose mixture and the resulting product is now called "yellow crumb"
8. Viscose: The "yellow crumb" is dissolved in a caustic solution to form viscose
9. Ripening: The viscose is set to stand for a period of time, allowing it to ripen
10. Filtering: After ripening, the viscose is filtered to remove any undissolved particles
11. Degassing: Any bubbles of air are pressed from the viscose in a degassing process
12. Extruding: The viscose solution is extruded through a spinneret, which resembles a shower head with many small holes
13. Acid Bath: As the viscose exits the spinneret, it lands in a bath of sulfuric acid resulting in the formation of rayon filaments
14. Drawing: The rayon filaments are stretched, known as drawing, to straighten out the fibers
15. Washing: The fibers are then washed to remove any residual chemicals
16. Cutting: If filament fibers are desired the process ends here. The filaments are cut down when producing staple fibers ^[3].

High Wet Modulus rayon (HWM) is a modified version of viscose that has a greater strength when wet. It also has the ability to be mercerized like cotton. HWM rayons are also known as "polynosic" or can be identified by the trade name MODAL ^[4].

High Tenacity rayon is another modified version of viscose that has almost twice the strength of HWM. This type of rayon is typically used for industrial purposes such as tire cord ^[4].

Cupramonium rayon has properties similar to viscose but during production, the cellulose is combined with copper and ammonia (Schweizer's reagent). Due to the environmental effects of this production method, cupramonium rayon is no longer produced in the United States ^[4].

Producers

Trade names are used within the rayon industry to determine the type of rayon used.

Bemberg, for example, is a trade name for cupramonium rayon developed by J.P. Bemberg that is now only produced in Italy due to EPA regulations in the US ^[5].

Modal and Tencel are widely used forms of rayon produced by Lenzing Fibers Corp. which is based in northern Austria ^[6].

Galaxy, Danufil, and Viloft are rayon brands produced by Kelheim Fibres, a German manufacturer. ^[7]

Acordis is a major manufacturer of cellulose based fibers and yarns. Production facilities can be found throughout Europe, the U.S. and Brazil ^[8].

Visil rayon is a flame retardant form of viscose which has silica embedded in the fiber during manufacturing. ^[9].

North American Rayon Corp of Tennessee produced viscose rayon until its closure in the year 2000. ^[10].

Grasim of India is the largest producer of rayon in the world (claiming 24% market share). It has plants in Nagda, Kharach and Harihar - all in India. ^[11].

Uses of rayon

Some major rayon fiber uses include apparel (e.g. blouses, dresses, jackets, lingerie, linings, scarves, suits, ties), furnishings (e.g. bedspreads, blankets, window treatments, upholstery, slipcovers), industrial uses (e.g. medical surgery products, non-woven products, tire cord), and other uses (e.g. yarn, feminine hygiene products) ^[3].

See also

• Art silk (artificial silk)

• Modal_(textile)

References

• History of Viscose Rayon and Artificial Silk
• Cellulose Based Plastics: Celluloid and Rayon