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'''Viscose''' is a [[Semisynthesis|semi-synthetic]] fiber. "Viscose" is several separate things:
'''Viscose''' is a [[Semisynthesis|semi-synthetic]] fiber. "Viscose" is several separate things:

大身
* a viscous solution of cellulose, which can be made into rayon or cellophane
* a viscous solution of cellulose, which can be made into rayon or cellophane
* a synonym for [[rayon]]
* a synonym for [[rayon]]

Revision as of 09:20, 11 August 2017

Not to be confused with viscous.

Viscose is a semi-synthetic fiber. "Viscose" is several separate things:

  • a viscous solution of cellulose, which can be made into rayon or cellophane
  • a synonym for rayon
  • a specific term for viscose rayon, which is rayon made using the viscose (cellulose xanthate) process.

Workers can be seriously harmed by the carbon disulfide used to make viscose.[1]

The viscose process dissolves pulp with aqueous sodium hydroxide and carbon disulfide. This produces a viscous solution. This solution was the first thing to bear the name "viscose". The cellulose solution is used to spin the viscose rayon fiber, which may also be called viscose.

Byproducts of the production process include sodium thiocarbonate, sodium carbonate, and sodium sulfide.[2]

Viscose rayon fiber is a soft fiber commonly used in dresses, linings, shirts, shorts, coats, jackets, and other outerwear. It is also used in industrial yarns (tyre cord), upholstery and carpets, and in the casting of Cellophane. When Viscose is made, the cellulose is made of wood pulp.

Manufacture

Cellulose is treated with alkali and carbon disulfide to yield viscose.
Rayon fiber is produced from the ripened viscose solutions by treatment with a mineral acid, such as sulfuric acid.[3]

Viscose rayon is a fiber of regenerated cellulose; it is structurally similar to cotton but may be produced from a variety of plants such as soy, bamboo, and sugar cane. Cellulose is a linear polymer of β-D-glucose units with the empirical formula (C6H10O5)n.[4] To prepare viscose, dissolving pulp is treated with aqueous sodium hydroxide (typically 16-19% w/w) to form "alkali cellulose," which has the approximate formula [C6H9O4-ONa]n. The alkali cellulose is then treated with carbon disulfide to form sodium cellulose xanthate.[5]

[C6H9O4-ONa]n + nCS2 → [C6H9O4-OCS2Na]n

The higher the ratio of cellulose to combined sulfur, the lower the solubility of the cellulose xanthate. The xanthate is dissolved in aqueous sodium hydroxide (typically 2-5% w/w) and allowed to depolymerize to a desired extent, indicated by the solution's viscosity. The rate of depolymerization (ripening or maturing) depends on temperature and is affected by the presence of various inorganic and organic additives, such as metal oxides and hydroxides.[5] Air also affects the ripening process since oxygen causes depolymerization.[6]

Rayon fiber is produced from the ripened solutions by treatment with a mineral acid, such as sulfuric acid. In this step, the xanthate groups are hydrolyzed to regenerate cellulose and release dithiocarbonic acid that later decomposes to carbon disulfide and water:[2]

[C6H9O4-OCS2Na]2n + nH2SO4 → [C6H9O4-OH]2n +2nCS2 + nNa2SO4
H2COS2 → H2O + CS2

Aside from regenerated cellulose, acidification gives hydrogen sulfide, sulfur, and carbon disulfide. The thread made from the regenerated cellulose is washed to remove residual acid. The sulfur is then removed by the addition of sodium sulfide solution and impurities are oxidized by bleaching with sodium hypochlorite solution.[5]

Pollution and harm to workers

See also Rayon#Manufacturing health hazards

Highly toxic carbon disulfide is used in the production of viscose. It is released into the air during production. Workers breathing it in suffer serious neurological, cardiovascular, and liver problems, burns, and blindness.[1]

Studies from the 1930s show that 30% of American rayon workers suffered severe effects. Rates of disability in modern factories (mainly in China, Indonesia and India) are unknown.[1] The production of rayon poses a serious health risk to unprotected factory workers.[7]

It is more harmful to produce rayon blends than pure rayon, as the threads are pulled from the vat still dripping carbon disulfide. While it is possible to protect workers from the CS2, legal limits for occupational exposure, even in the US, are still far higher than recommended by medical researchers.[1]

The carbon disulfide is lost before the rayon gets to the consumer; the rayon itself is basically plain cellulose.[8]

The use of viscose is declining, in part because of the environmental costs of its production. Instead, rayon may be manufactured using the Lyocell process, which uses N-Methylmorpholine N-oxide as the solvent and produces little waste product, making it relatively eco-friendly.[9]

History

See also: Rayon § Viscose method

French scientist and industrialist Hilaire de Chardonnet (1838–1924)—who invented the first artificial textile fiber, artificial silk—created viscose.[10] British scientists Charles Frederick Cross and Edward John Bevan took out British patent no. 8,700, "Improvements in Dissolving Cellulose and Allied Compounds" in May, 1892.[11] In 1893 they formed the Viscose Syndicate to grant licences, and in 1896 formed the British Viscoid Co. Ltd. to exploit the process.[10]

Products made from viscose

References

  1. ^ a b c d http://www.abc.net.au/radionational/programs/healthreport/the-health-burden-of-viscose-rayon/8286870
  2. ^ a b Wyss, George de (1 October 1925). "The Ripening of Viscose". Industrial & Engineering Chemistry. 17 (10): 1043–1045. doi:10.1021/ie50190a018.
  3. ^ Siegfried Hauptmann: Organische Chemie, 2. durchgesehene Auflage, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, S. 652, ISBN 3-342-00280-8.
  4. ^ Booth, Gerald (2000). Dyes, General Survey. Wiley-VCH. doi:10.1002/14356007.a09_073.
  5. ^ a b c Wheeler, Edward (1928). The Manufacture of Artificial Silk With Special Reference to the Viscose Process. New York: D. Van Nostrand company.
  6. ^ Bartell, F. E.; Cowling, Hale (1 May 1942). "Depolymermiation of Cellulose in Viscose Production". Industrial & Engineering Chemistry. 34 (5): 607–612. doi:10.1021/ie50389a017.
  7. ^ Monosson, Emily (2016). "Toxic textiles". Science. 354 (6315): 977. doi:10.1126/science.aak9834.
  8. ^ 1951-, Blanc, Paul D.,. Fake silk : the lethal history of viscose rayon. ISBN 978-0-300-20466-7. OCLC 961828769. {{cite book}}: |last= has numeric name (help)CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  9. ^ Dawson, Tim (2011). "Progress towards a greener textile industry". Coloration Technology. 128: 1–8. doi:10.1111/j.1478-4408.2011.00346.x.
  10. ^ a b Woodings, Calvin R. "A Brief History of Regenerated Cellulosic Fibres". WOODINGS CONSULTING LTD. Retrieved 26 May 2012.
  11. ^ Day, Lance; Ian McNeil (1998). Biographical Dictionary of the History of Technology. Taylor & Francis. p. 113. ISBN 0-415-19399-0.

https://www.barnhardtcotton.net/blog/q-and-a-what-is-viscose/

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