Rayon
Rayon is a manufactured regenerated cellulose fiber. It is made from purified cellulose, primarily from wood pulp, which is chemically converted into a soluble compound. It is then dissolved and forced through a spinneret to produce filaments which are chemically solidified, resulting in synthetic fibers of nearly pure cellulose. Because rayon is manufactured from naturally occurring polymers, it is considered a semi-synthetic fiber. Specific types of rayon include viscose, modal and lyocell, each of which differs in manufacturing process and properties of the finished product.
Reaction of cellulose with carbon disulfide and a base gives "viscose", a soluble polymer that can be converted into Rayon.
History
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" in about 1855, but his method was impractical for commercial use. Commercial production started in 1891, but the result was flammable and more expensive than acetate or cuprammonium rayon. Because of this, production was stopped before World War I. It was briefly known as "mother-in-law silk."[3] Frank Hastings Griffin invented the double-godet, a special stretch-spinning process that changed artificial silk to rayon, rendering it usable in many industrial products such as tire cords and clothing. Nathan Rosenstein invented the spunize process by which he turned rayon from a hard fiber to a fabric. This allowed rayon to become a popular raw material in textiles.
Acetate method
Paul Schützenberger discovered that cellulose could be reacted with acetic anhydride to form cellulose acetate. The triacetate is only[citation needed] soluble in chloroform making the method expensive. The discovery that hydrolyzed cellulose acetate is soluble in more polar solvents, like acetone, made production of cellulose acetate fibers cheap and efficient.
Cuprammonium method
The Swiss chemist Matthias Eduard Schweizer (1818–1860) discovered that tetraaminecopper dihydroxide could dissolve cellulose. Max Fremery and Johann Urban developed a method to produce carbon fibers for use in light bulbs in 1897. Production of cuprammonium rayon for textiles started in 1899 in the Vereinigte Glanzstoff Fabriken AG in Oberbruch. Improvement by the J. P. Bemberg AG in 1904 made the artificial silk a product comparable to real silk.
Viscose method
A device for spinning Viscose Rayon dating from 1901.Finally, in 1894, English chemist Charles Frederick Cross, and his collaborators 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. The first commercial viscose rayon was produced by the UK company Courtaulds Fibers in 1905. Courtaulds formed an American division, American Viscose, (later known as Avtex Fibers) to produce their formulation in the United States in 1910. 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. Research in the UK was centred on the government-funded British Rayon Research Association.
Major fiber properties
Rayon is a versatile fiber and is widely claimed to have the same comfort properties as natural fibers, although the drape and slipperiness of rayon textiles are often more like nylon. 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, although also making their handfeel cool and sometimes almost slimy to the touch.
The durability and appearance retention of regular viscose rayon are low, especially when wet; also, rayon has the lowest elastic recovery of any fiber. However, HWM rayon (high-wet-modulus rayon) is much stronger and exhibits higher durability and appearance retention. Recommended care for regular viscose rayon is dry-cleaning only. HWM rayon can be machine washed.
Industrial applications of rayon emerged around 1935. Substituting cotton fiber in tires and belts, industrial types of rayon developed a totally different set of properties, amongst which tensile strength (elasticity) was paramount. Outperforming polyester, industrial yarns are still produced for high performance tires (e.g. Cordenka, Germany).
Gallery of textures
Physical structure
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.
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:
Cellulose: Production begins with processed cellulose
Immersion: The cellulose is dissolved in caustic soda: (C6H10O5)n + nNaOH → (C6H9O4ONa)n + nH2O
Pressing: The solution is then pressed between rollers to remove excess liquid
White Crumb: The pressed sheets are crumbled or shredded to produce what is known as "white crumb"
Aging: The "white crumb" is aged through exposure to oxygen
Xanthation: The aged "white crumb" is mixed with carbon disulfide in a process known as Xanthation, the aged alkali cellulose crumbs are placed in vats and are allowed to react with carbon disulfide under controlled temperature (20 to 30 °C) to form cellulose xanthate: (C6H9O4ONa)n + nCS2 → (C6H9O4O-SC-SNa)n
Yellow Crumb: Xanthation changes the chemical makeup of the cellulose mixture and the resulting product is now called "yellow crumb"
Viscose: The "yellow crumb" is dissolved in a caustic solution to form viscose
Ripening: The viscose is set to stand for a period of time, allowing it to ripen: (C6H9O4O-SC-SNa)n + nH2O → (C6H10O5)n + nCS2 + nNaOH
Filtering: After ripening, the viscose is filtered to remove any undissolved particles
Degassing: Any bubbles of air are pressed from the viscose in a degassing process
Extruding: The viscose solution is extruded through a spinneret, which resembles a shower head with many small holes
Acid Bath: As the viscose exits the spinneret, it lands in a bath of sulfuric acid, resulting in the formation of rayon filaments: (C6H9O4O-SC-SNa)n + ½nH2SO4 → (C6H10O5)n + nCS2 + ½nNa2SO4
Drawing: The rayon filaments are stretched, known as drawing, to straighten out the fibers
Washing: The fibers are then washed to remove any residual chemicals
Cutting: If filament fibers are desired the process ends here. The filaments are cut down when producing staple fibers.
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"[clarification needed] or can be identified by the trade name Modal.
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.
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.
Disposal and biodegradability
The biodegradability of fibers in soil burial and sewage sludge was evaluated by Korean researchers, and are listed here in order of decreasing biodegradability: rayon, cotton, acetate. The more water-repellent the rayon-based fabric is, the more slowly it will decompose. Silverfish can eat rayon.
Alternative to cotton
Rising cotton prices in 2010 led clothing makers to begin replacing cotton with rayon in their fabrics. As demand for rayon increases, companies such as Fortress Paper have been investing in pulp mills to increase production. Rayon now sells for as much as $2.70 per pound, which has led to an increase in the retail price of clothing made with rayon, yet rayon has a price advantage over cotton.
Controversies
In early 2010, the U.S. Federal Trade Commission warned several retailers that six major manufacturers were falsely labeling rayon products as "bamboo", in order to appeal to environmentally conscious consumers. While rayon may be produced from bamboo as a raw material, and both rayon and bamboo may be used for similar fabrics (though natural bamboo is not as smooth), rayon is so far removed from bamboo by chemical processing that the two are entirely separate.
Producers
Trade names are used within the rayon industry to label the type of rayon in the product. Viscose Rayon was first produced in Coventry England in 1905 by Courtaulds.
Bemberg, is a trade name for cupramonium rayon developed by J. P. Bemberg. It performs much like viscose but has a smaller diameter and comes closest to silk in feel. Bemberg is now only produced in Italy due to United States Environmental Protection Agency regulations in the US. The fibers are finer than viscose rayon and
Modal and Tencel are widely used forms of rayon produced by Lenzing AG. Tencel, generic name lyocell, is made by a slightly different solvent recovery process, and is considered a different fiber by the US FTC. Tencel lyocell was first produced commercially by Courtaulds at Grimsby in England. The process which dissolves cellulose directly in amine oxide was developed by Courtaulds Research in Coventry.
Galaxy, Danufil, and Viloft are rayon brands produced by Kelheim Fibres.
Acordis was a major manufacturer of cellulose based fibers and yarns. Production facilities can be found throughout Europe, the U.S. and Brazil.
Visil rayon is a flame retardant form of viscose which has silica embedded in the fiber during manufacturing.
North American Rayon Corporation of Tennessee produced viscose rayon until its closure in the year 2000.
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, as well as joint ventures in Canada, Laos and China.
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