The Percentage Composition of Rayon Fabric
A disease that threatened to destroy the French silk industry in the late 19th century inspired scientists to successfully develop artificial silk. The French Count of Chardonnay patented a viable process using regenerated cellulose in 1884 and the manufacture of this first artificial (but highly flammable) fiber began in 1889. English chemists C.F. Cross, E. J. Bevan and Clayton Beadle discovered the viscose process of making a safer rayon in 1891. Does this Spark an idea?
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What Is Rayon?
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The U.S. Federal Trade Commission designates rayon as the generic term describing artificial fiber, yarn and fabric made of regenerated purified cellulose, which is the same long-chain polymer found in cotton. Rayon's cellulose comes from wood pulp, bamboo and/or cotton linters, the fibers that stick to the seeds of cotton bolls.
Manufacturers use viscose, cuprammonium and modal (polynosic) methods to create rayon. The FTC also considers output from the newer lyocell process a rayon subgroup. Rayon, with its composition of 99 percent cellulose by weight, can be dyed, spun and processed to look, feel and act like cotton, silk, wool or linen.
Manufacturing Viscose Rayon
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The viscose process is the least expensive method of creating rayon. Immersing purified cellulose in 17 to 20 per cent aqueous sodium hydroxide solution swells the cellulose and converts it to alkali cellulose. The mass is pressed to remove excess liquid, shredded into "crumbs" and aged under controlled temperature and humidity to reach the proper concentration of cellulose and viscosity.
The aged crumbs react with carbon disulphide to form cellulose xanthate, which is further processed and degassed to remove air bubbles that might weaken the filament created when the final viscose solution is extruded through a platinum spinneret into a dilute sodium hydroxide solution that decomposes the xanthate and regenerates the cellulose. Final steps include stretching and removing salts left by the chemical processes.
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Other Rayon Processes
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Cuprammonium or "cupro" rayon delivers silk-like softness, breathability and good colorfastness. The manufacturing process involves dissolving the cellulose in a cuprammonium hydroxide solution in a nitrogen atmosphere at low temperatures. This mixture is extruded into a sulphuric acid bath to decompose it back to cellulose. More expensive than the viscose process, the fiber produced exhibits an almost-round cross-section.
The polynosic or modal rayon process features enhanced stretching -- as much as 300 per cent -- to create a fiber with a low elongation of 8 percent to 11 percent, which retains its shape and remains strong whether wet or dry.
The Newest Rayon
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Lyocell, a cellulose fiber designated a rayon by the U.S. Federal Trade Commission and marketed in the U.S. under the trademarked name Tencel, is produced by a solution-spun method developed in 1992. This process mixes and heats wood pulp from farmed trees and amine oxide until the cellulose dissolves. Extruding this solution into a dilute amine oxide bath causes the cellulose to precipitate as fiber. After washing the fiber in water, it can be finished into yarn and fabric which also can be hand washed. Lyocell manufacturing uses less energy than other rayons and its dissolving agent is nontoxic and recycled.
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