Viscose rayon is a textile synthetic fiber.

1. Viscose Rayon
Introduction:
1. Produced from natural and renewable raw material e.g. wood pulp, linters(the short, useless
fibers from cotton ball)
2. It is the first successful manmade fiber.
3. Viscose process discovered in 1891 and commercial production of fiber started in 1905.
4. Named after the nature of spinning solution.
5. Produced by wet spinning method.
Viscose fiber production

2. process:
1. Preparation of wood pulp: Trees are cut into pieces and treated with calcium or sodium
bisulfite solution. Chips are cooked with steam for 14 hours to convert into pulp.It is bleached
and washed with NaOCl and converted into pulp sheet like blotting paper.(Pupls contains 94%
cellulose)
2. Steeping and pressing: The cellulose pulp sheets are immersed (steeped) in warm 18% NaOH
solution for 1-4 hours to allow swelling and form alkali solution. Then Alkali cellulose sheets
are squeezed (pressed) mechanically to remove excess NaOH.
3. Shredding: Alkali cellulose is cut into very small pieces by a pair of blades to increase their
surface area and to facilitate the chemical reaction in the next process. These pieces are
called White Crumbs.
4. Ageing: White crumbs are allowed to stand in contact with the oxygen for 1-3 days to get the

3. desired DP. During ageing depolymerization takes place and the DP falls from 850 to 350.
(Cellulose molecules broken up to some extent into shorter molecules.).
5. Xanthation: The aged white crumbs are placed in a rotating hexagonal churn to react with CS2
for 3 hours to form yellow crumb and the color changes into reddish orange.
6. 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. 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.
8. 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.
9. 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.
10. 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.
11. 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.
Physical properties of viscose rayon:
1. Low strength (cN/tex) :22-26(dry), 10-15 (wet)
2. High elongation : 25% (dry),30% (wet)
3. Specific gravity :1.52
4. Moisture regain: 13%
Chemical Properties of viscose rayon
1. Acids : Damaged by strong acids, moderate resistance against weak acids.

4. 2. Alkali : Good resistance to weak alkali but strong alkali cause damage.
3. Bleaching : Strong oxidizing agents damage the fiber.
4. Organic solvants: good resistance to solvants.
5. Dyes: direct ,vat and sulfur dyes.
End use:
∙ Mainly used in apparel and technical textiles area.
∙ In most apparel uses it is blended with other fibers.
∙ High absorbency made it suitable for hygienic disposables.
∙ Because of thermal stability ,the HT versions is the main product used in Europe to reinforce
high speed tries.
Lyocell Fiber
Introduction:
∙ Lyocell is a new generation cellulosic fiber.
∙ Fiber is made by solvent spinning i. g. dissolving and spinning without formation of derivative.
∙ Although direct solvent N-methylmopholine-N-oxide(NMMO) for cellulose was discovered in
1939, commercial production of Lyocell fiber started in 1988 by Courtaulds.
Chemistry of Lyocell fiber:

5. Lyocell fibre production :
∙ The pulp is shredded and mixed with dilute aqueous NMMO to penetrate the pulp fully.
∙ Excess water is removed and the solution is heated under vacuum at 90-120⁰C.
∙ Fibers are formed by spinning into air gap and then coagulating in a water ?NMMO bath.

6. ∙ Fibers are washed and dried.
∙ The wash liquors are removed, purified ,concentrated and then recycled.
Fibers are crimped and made in tow or filament forms.
Physical Properties:
∙ Similar to viscose fiber but exhibits enhanced properties in terms of softness ,drapability and
dimensional stability.
∙ Higher absorbancy than cotton (MR,11%)
∙ Strongest celluiosic fiber at dry and wet states.
∙ Can be made fibrillated or non fibrillated.
Chemical properties:
Susceptible to damage by mildew and silverfish.
End uses:
· Apparel ,home textiles and technical textiles.
· Soft, luxurious men and women dresses.
· Undergarments, hosiery and sportswear.