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{{Short description|Rayon produced using a cellulose xanthate solution}} |
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{{Distinguish|Viscous}} |
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{{merge to|Rayon|discuss=Talk:Rayon#Merger proposal|date=August 2020}} |
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'''Viscose''' is a type of [[rayon]] fiber that is made from cellulose that are regenerated as [[cellulose fiber]]. The molecular structure of natural cellulose is preserved in the process. The many types and grades of viscose fibers can imitate the feel and texture of [[Natural fiber|natural fibers]] such as [[silk]], [[wool]], [[cotton]], and [[linen]]. The types that resemble silk are often called [[Art silk|artificial silk]]. The fibre is used to make textiles for clothing and other purposes.<ref name=Ull/> |
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Viscose can mean: |
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* A viscous solution of cellulose |
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* A synonym of [[rayon]] |
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* A specific term for viscose rayon — rayon made using the viscose ([[cellulose xanthate]]) process |
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== Manufacture == |
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[[File:Xanthation.png|thumb|center|520px|Simplified view of the xanthation of cellulose.<ref name=Ull>{{Ullmann | first1=Hans | last1=Krässig | first2=Josef | last2=Schurz | first3=Robert G. | last3=Steadman | first4=Karl | last4=Schliefer | first5= Wilhelm |last5=Albrecht|first6=Marc | last6=Mohring | first7=Harald | last7=Schlosser | title=Cellulose | year=2002 | doi=10.1002/14356007.a05_375.pub2}}</ref>]] |
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The molecular structure of rayon is that of cellulose, i.e., a linear polymer of β-D-glucose units with the empirical formula (C<sub>6</sub>H<sub>10</sub>O<sub>5</sub>)<sub>{{mvar|n}}</sub>. To prepare viscose, pulp is treated with aqueous sodium hydroxide (typically 16-19% [[w/w]]) to form "alkali cellulose", which has the approximate formula [C<sub>6</sub>H<sub>9</sub>O<sub>4</sub>-ONa]<sub>{{mvar|n}}</sub>. This material is allowed to depolymerize to an extent. The rate of depolymerization (ripening or maturing) depends on temperature and is affected by the presence of various inorganic additives, such as metal oxides and hydroxides. Air also affects the ripening process since oxygen causes depolymerization. The alkali cellulose is then treated with [[carbon disulfide]] to form sodium cellulose [[xanthate]].<ref name=Ull/> |
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:[C<sub>6</sub>H<sub>5</sub>(OH)<sub>4</sub>-ONa]<sub>{{mvar|n}}</sub> + {{mvar|n}}[[Carbon disulfide|CS<sub>2</sub>]] → [C<sub>6</sub>H<sub>5</sub>(OH)<sub>4</sub>-OCS<sub>2</sub>Na]<sub>{{mvar|n}}</sub> |
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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). The solution's viscosity is determined by the extent of depolymerization of the alkali cellulose. |
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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 carbon disulfide. |
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:[C<sub>6</sub>H<sub>5</sub>(OH)<sub>4</sub>-OCS<sub>2</sub>Na]<sub>2{{mvar|n}}</sub> + {{mvar|n}}H<sub>2</sub>SO<sub>4</sub> → [C<sub>6</sub>H<sub>5</sub>(OH)<sub>4</sub>-OH]<sub>2{{mvar|n}}</sub> +2{{mvar|n}}CS<sub>2</sub> + {{mvar|n}}Na<sub>2</sub>SO<sub>4</sub> |
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Aside from regenerated cellulose, acidification gives hydrogen sulfide (H<sub>2</sub>S), 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 or hydrogen peroxide solution.<ref name="Wheeler 1928" /> |
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=== Pollution=== |
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{{See also|Rayon#Environment and sustainability}} |
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Because [[carbon disulfide]] is highly toxic, its use on a large scale demands care. Historically, however, several incidents have resulted in many poisonings. With production facilities often located in developing countries, concerns for worker safety continue.<ref name="FakeSilk">{{cite book|author=Paul David Blanc|title=Fake Silk The Lethal History of Viscose Rayon|publisher=Yale University Press|year=2016|pages=325|isbn=9780300204667}}</ref> Newer control technologies have enabled improved collection of carbon disulfide and reuse of it, resulting in a lower emissions of carbon disulfide.<ref name=Ull/> |
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Viscose or rayon may also be manufactured using the [[Lyocell]] process, which uses [[N-Methylmorpholine N-oxide|N-methylmorpholine N-oxide]] (NMO) as the solvent to dissolve the cellulose. NMO is more expensive that carbon disulfide, such that losses during processing must be minimized. |
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== History == |
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{{See also|Rayon#Viscose method}} |
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French scientist and industrialist [[Hilaire de Chardonnet]] (1838–1924), inventor of the first artificial textile fiber, ''artificial silk'', created viscose.<ref name="crw-bhrcf" /> 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.<ref name=bdht>{{Cite book|last=Day|first=Lance|title=Biographical Dictionary of the History of Technology|year=1998|publisher=Taylor & Francis|isbn=0-415-19399-0|pages=113|author2=Ian McNeil}}</ref> In 1893 they formed the Viscose Syndicate to grant licences, and in 1896 formed the British Viscoid Co. Ltd. to exploit the process.<ref name=crw-bhrcf>{{Cite web|last=Woodings|first=Calvin R.|title=A Brief History of Regenerated Cellulosic Fibres|url=http://www.nonwoven.co.uk/reports/History%20of%20Cellulosics.html|publisher=Woodings Consulting Ltd.|access-date=26 May 2012}}</ref><ref name="Wheeler 1928">{{cite book|last=Wheeler|first=Edward|title=The Manufacture of Artificial Silk With Special Reference to the Viscose Process|year=1928|publisher=D. Van Nostrand company|location=New York}}</ref> |
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== Products made from viscose == |
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* [[Art silk]] |
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* [[Cellophane]] |
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* [[Casing_(sausage)#Cellulose|Sausage casings]]<!--Fact. I might be able to dig up at least one UK and one US company that makes/made them.--> |
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* [[Velvet|Synthetic velvet]] |
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== References == |
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{{Reflist|2}} |
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== External links == |
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{{Sister project links||b=no|commons=Category:Viscose |d= Q182045|m=no |mw=no |n=no |q=no|s=no |species=no |species_author=no |v=no |voy=no |wikt=viscose}} |
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* {{Cite web| title=Viscose| url=http://www.plastiquarian.com/viscose.htm | archiveurl=https://web.archive.org/web/20080625080322/http://www.plastiquarian.com/viscose.htm | work=Plastiquarian.com | archivedate=2008-06-25}} |
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* [https://www.barnhardtcotton.net/blog/q-and-a-what-is-viscose/ What Is Viscose? from Barnhardt Natural Fibers] |
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*[https://www.textiletrick.com/2020/04/viscose-yarn-manufacturing-process.html viscose fibre] |
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[[Category:Synthetic fibers]] |
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[[Category:Cellulose]] |
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Latest revision as of 23:46, 13 August 2020
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