2. Introduction
It is the first successful manmade fiber.
C.F Cross, Bevan and Beadle in England in 1892, who
found that they could dissolve cellulose with caustic soda ,
then with CS2 then the product dissolved with dilute
caustic soda. This viscose liquid is called viscose.
Viscose process discovered in 1891 and commercial
production of fiber started in 1905.
The main raw material is cotton linters or wood pulp
derived from such timber as northern surpuce, western
hemlock, eucalyptus.
4. Types of Viscose Fibers
There are many types of viscose fiber. Main viscose fibers
are
1.Viscose Rayon
2.Layocell fiber.(New generation Fiber)
3.Modal Fiber.
The production process of this fibers almost same. Some
changes occur during production.
5. Production Process of Viscose Rayon
Steeping: Cellulose pulp is immersed in 17-20% aqueous sodium
hydroxide (NaOH) at a temperature in the range of 18 to 25°C in order to
swell the cellulose fibres and to convert cellulose to alkali cellulose.
(C6H10O5)n + nNaOH ---> (C6H9O4ONa)n + nH2O
Pressing: The swollen alkali cellulose mass is pressed to a wet weight
equivalent of 2.5 to 3.0 times the original pulp weight to obtain an
accurate ratio of alkali to cellulose.
Shredding: The pressed alkali cellulose is shredded mechanically to yield
finely divided, fluffy particles called "crumbs".
Aging: The alkali cellulose is aged under controlled conditions of time
and temperature (between 18 and 30° C) in order to depolymerize the
cellulose to the desired degree of polymerization.
6. Production Process of Viscose Rayon
Xanthation: In this step the aged alkali cellulose crumbs are placed in vats
and are allowed to react with carbon disulphide under controlled
temperature (20 to 30°C) to form cellulose xanthate.
(C6H9O4ONa)n + nCS2 ----> (C6H9O4O-SC-SNa)n
Mixing and dissolving: The yellow crumb is mixed with 3% NaOH
solution for 4-5 hours to give an orange color viscose solution called
viscose. The large xanthate substituents on the cellulose force the chain
apart, reducing the intermolecular hydrogen bonds and allowing water
molecules to solvate and separate chains, leading to solution of cellulose
molecules.
7. Production Process of Viscose Rayon
Ripening and blending : The viscose solution is allowed to store for 4-5 days
under vacuum to achieve a stable viscosity. The redistribution of xanthate groups
take place and viscosity of the xanthate groups take place and viscosity of the
solution falls and then rises. Different batches of solution are blended and
pigmentsdelustrants are added if required.
Filtration and Deaeration : Filtration and deaeration of spinning must be done
prior to spinning to remove any fine solid particles or air bubbles that might
disrupt the spinning of process.
Wet spinning and stretching : Extruded through the spinneret into a bath
containing 18% Na2SO4(Coagulant) , 10% H2SO4(regenerating agent) , 1% ZnSO4
(modifier) , 2% glucose (plasticizer)and 69% water at 40-55⁰C where cellulose is
regenerated in fiber form. The filaments are stretched up to 200% while they are
still wet to improve strength
8. Production Process of Viscose Rayon
Washing and purification : Fiber contains salts and water soluble impurities. In
batch process, the filaments are wound into topham box. The cakes are washed ,
desulfurized with Na2S blached with NaOCl and again washed with water. In
continuous process ,the filaments are passed through advancing rolls and washed
with spray.
Drying and packing : The washed and purified filaments obtained in the batch
process are dried, wound onto bobbins and packed. In case of continuous process,
purification and bleaching of fiber are performed later during the wet processing
stage. Fibers are made in filament or staple form.
10. Lyocell
Lyocell is a new generation cellulosic fiber.
The cellulose fibers produced by direct dissolution or solvent spinning have the
generic name of lyocell.
Although direct solvent N-methylmopholine-N-oxide(NMMO) for cellulose was
discovered in 1939, commercial production of Lyocell fiber started in 1988 by
Courtaulds.
13. HWM Modal fiber
Modal is a Cellulose regenerated fiber of the
high wet modulus type.
The fiber is manufactured according to a special viscose spinning process from
high quality wood pulp.
Fibers made of Modal display a silky gloss, which produces a shine similar to
mercerization when blended with cotton, a pleasant soft touch and drape and
excellent wear properties.
14. Production Process of Modal
Soda cellulose is produced by steeping the cellulose in caustic soda.
Pressing and shredding
In xanthation the quantity of CS2 is less than regular viscose production at 20⁰ c
then raised at 25⁰ c.
Sodium cellulose xanthate is dissolved in water to provide a solution containing 6%
cellulose and 2.8% sodium hydroxide.
The solution spun by extrusion in abath of very dilute 1% sulphuric acid at 25c .The
filaments are stretched three times their spun length,
The degredation of cellulose is held to a minimum by omission of ageing and
ripening stages.
15. Production Process of Modal
The regeneration and coagulation of cellulose takes place slowly and gently in a
dilute acid of spinning bath,which contains a little or no salt.this permits to allow
the molecules to assume a high degree of orientation and crystallization.The
filament produce is more uniform and the cross section is round.
The degree of polymerization is about 500,about twice than ordinary viscose.
17. General Properties Of Viscose
Viscose rayon-Low strength,Weak and weaker when wet.
Modal and Lyocell-higher strength than viscose rayon.
Low abrasion resistance, especially when wet.
High flexibility, excellent drape.
Poor wrinkle resistance.
Poor elastic recovery and resiliancy .
Viscose rayon- poor dimensional stability.
Modal and lyocell- good dimensional stability.
18. General Properties Of Viscose
Excellent moisture absorbance, hydrophilic.
Does not irritate skin.
Bio degradable.
Damaged by prolonged exposure to light.
Burns.
19. Care
Care varies considerably.
Easily stained by water soluble fluids.
Viscose rayon-dry clean
Modal and lyocell- machine wash.
Iron using the appropriate setting.
Damaged by acidic materials.
Susceptible to mildew and silverfish.
20. End Uses
Apparel
1.Women’sdresses, blouses,jackets and suits.
2.Men’s causal shirts pants and suits.
3. Lyocell lingerie, children’s cothing and dresses
4.Modal lingerie , sleepwear , knitwear and socks.
Textiles for interiors
Bedspreads, draperies, upholstery. Throw cushions.
21. End Uses
Household and Institutional Textiles
1.Table linen
3.Bed linen
3.Modal and mosal/cotton blends- towels and bath mats.
Technical Textiles
1.Viscose- disposable and limited use item.
2.Fire retardant rayon- Protection against radiant hear,electeic aircs and
molten metals.
3.high tenacity rayon – reinforcement of tires and firehouses.
