4. Introduction
The production of regenerated cellulose fibers as early as The
1930s resulted in the generation of a new class of fibers. For
several decades, the production of regenerated cellulose fibers
such as viscose, rayon, and cuprammonium rayon was
extensively done. These fibers were considered ideal substitutes
for natural cellulose fibers. Traditionally, regenerated cellulose
fibers were produced using wood as a source of cellulose.
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5. Lyocell
Lyocell (lyo from Greek: lyein = dissolve, cell from
cellulose)
Man-made cellulosic fibres
Produced by regenerating cellulose into fibre form out
of
A solution (solvent spinning) of cellulose in an organic
Solvent
‘Organic solvent ’ - mixture of organic chemicals and
water
‘Solvent spinning’ means dissolving and spinning
without the formation of a derivative
Lenzing AG. is currently (2013) the only major
producer
of lyocell fibres
Tencel is the brand name of Lyocell 5
6. Raw Materials
Cellulose
Most abundant natural resource on earth.
• It is obtained from wood pulp.
• Trees like Eucalyptus, bamboo, and pine tree are used.
• Eucalyptus is primarily used to produce the Tencel fiber.
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7. NMMO (N-methyl morpholine oxide)
Chemically produced from N methyl morpholine and hydrogen peroxide
• Cyclic amine oxides such as N-methyl morpholine oxide have the
capacity to dissolve cellulose in large capacities
• NMMO exists in several degrees of hydration.
• At room temperature, it is a crystalline mono-hydrate and melts at 72
degrees
• When heated at 100 C, mono hydrate NMMO is able to dissolve
readily several percentages of high molecular weight cellulose
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8. Cellulose dissolution in NMMO is found to depend on:
– The temperature of the solution
– The water content of the mixtures
– The concentration and the degree of Polymerisation of the cellulose
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9. Manufacturing and Processing
Preparing Wood Pulp
• Hardwood trees are harvested, and logs are
taken to the mill.
• Wood is cut into the small chip and fed into
chemical digesters which remove lignin and
soften them into wet wood pulp.
• It is then washed with water, bleached, and
dried into huge sheets of cellulose and
rolled onto spools.
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10. Dissolving Cellulose
• Spools of cellulose are unrolled and broken
into one square inch.
• It is then loaded into a heated pressurized
vessel containing N-methyl morpholine N-
oxide.
• Cellulose dissolves into a clear solution.
Pulp/Wood pulp
NMMO Mixing
Dissolution
Filtration
Spin/Stretch
Washing
drying
Stable Fiber or
tow 10
12. FIltering
• In an Amine Oxide solvent, cellulose is dissolved into a clear solution.
• It is then pumped out and filtered.
Spinning
• Cellulose is forced through the spinnerets and long strands of fiber come
out.
• These fibers are then dissolved in a dilute Amine Oxide solution and are
later washed with water.
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13. Drying And Finishing
• Fibre is passed through the drying area.
• In the drying area, water is evaporated, and lubricant is applied
which may be soap, silicone, or another agent.
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14. Solvent Recovery
• After the spinning and drying process, the dilute solution is taken and passed
through the evaporator where water is removed, and amine oxide solvent is fed
back to the dissolving process.
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15. Properties
• Soft, strong, absorbent
• Fibrillated during wet processing to produce special textures
• It has high wet and dry strength, and it is stronger than Cotton and Wool.
• Wrinkle resistant
• Very versatile fabric, dyeable to vibrant colours, with a variety of effects and
textures.
• Can be hand washable
• Simulates silk, suede, or leather touch
• Biodegradable
• Fine yarn counts can be spun 15
16. Comfort
• Soft, smooth fiber.
• Ideal for apparel that contacts the skin.
• Thermal retention is poor.
Appearance Retention
• Resiliency is moderate- Wrinkles but not as severely as rayon.
• It Shrinks, but not progressively.
• May have problems with fuzziness or piling.
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17. Aesthetics
• Lustre, length, and diameter can be changed depending upon end use.
• Processed to produce a range of surface effects.
• Offers unusual combinations of strength, opacity, and absorbency.
Durability
• Performs more like cotton than rayon.
• Strongest cellulosic fibers.
• Unique combination of soft hand and good durability, produces
comfortable, long-lasting textiles for apparel and interiors.
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18. Care
• Either gently machine- Washable or dry-cleaned.
• Sensitive to acids.
• Resistant to mild alkalis.
• Sensitive to mildew and some insects.
• High dye affinity.
• High inherent whiteness- Bleaching is not necessary.
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19. The physical structure is a more rounded cross-
section & smoother longitudinal appearance
than rayon.
Since in the case of Lyocell we are just
dissolving cellulose in NMMO and not making
any cellulose derivatives, it has a different
molecular structure than other regenerated
cellulosic fibers.
The structure is ‘Homogeneous’ and ‘Dense’.
Physical Properties
Cross section
Longitudinal section
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20. Applications
• Professional business wear.
• Hosiery
• Casual wear
• Window-treatment fabrics
• Filters
• Printers’ blankets
• Specialty papers
• Medical dressings
• Conveyer belts for strength & softness
• Botanic Tencel bed
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22. Linen
Introduction:
• This fiber is obtained from the stem of the
flax plant, which is an animal plant
growing a maximum of about 40 inches.
• Linen is a cellulosic fiber derived from
the stem of the flax plant. Much stronger
and more lustrous than Cotton.
• One of the oldest and most expensive
textiles in the world.
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23. Characteristics
• Comfortable to wear.
• Has good strength; twice as strong as cotton.
• Hand washable or dry cleanable.
• Well absorbent of dyes and prints.
• Varies from light weight to heavy weight.
• Has no static or pilling problems.
• In hot weather, it lowers the body temperature up to 3-4 %.
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24. Chemical Properties
Effects of Acids: Linen fiber is damaged by highly densified acids but
low dense acids do not affect if wash instantly after application of
acids.
Effects of Alkali: Linen has excellent resistance to alkalis. It does not
affected by the strong alkalis.
Effects of Organic solvents: Linen fiber has high resistance to normal
organic solvents.
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26. Viscose Rayon
Introduction:
Viscose Rayon is the oldest commercial man-made fiber. Viscose
rayon is a naturally regenerated cellulosic fiber that can be made from
naturally occurring cellulosic-based material. (such as cotton linters,
wood pulp, etc).
It can be found in cotton-like end uses as well as silk-like end uses.
Due to its fine silk-like properties, it is also known as “Artificial Silk”.
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27. Chemical Structure
The chemical structure of viscose is the same as that of cotton i.e.
Cellulose, But the polymer chains are much shorter. The degree of
polymerization value of rayon is 400 – 700 while that of cotton is 5000.
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28. Manufacturing
The process of manufacturing
viscose rayon consists of the
following steps mentioned, in the
order that they are carried out:
Steeping,
Shredding,
Aging,
Xanthation,
Dissolving,
Ripening,
Filtering,
Degassing,
Spinning,
Drawing.
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29. 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 fibers and to convert cellulose to alkali cellulose.
(C6H10O5)n + nNaOH —> (C6H9O4ONa)n + nH2O
2. Shredding:
The pressed alkali cellulose is shredded mechanically to yield finely
divided fluffy particles called “crumbs”. This step provides an increased
surface area of the alkali cellulose, thereby increasing its ability to react
in the steps that follow. 29
30. Ageing:
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. In this step, the average molecular weight of the original pulp is
reduced by a factor of two to three. Reduction of the cellulose is done to get a viscose
solution of the right viscosity and cellulose concentration.
Xanthation:
In this step, the aged alkali cellulose crumbs are placed in vats and are allowed to
react with carbon disulfide under controlled temperature (20 to 30°C) to form
cellulose xanthate.
(C6H9O4ONa)n + nCS2 —-> (C6H9O4O-SC-SNa)nAging 30
31. Dissolving:
The yellow crumbs of cellulose xanthate are dissolved in an aqueous caustic
solution. Because the cellulose xanthate solution (or more accurately,
suspension) has a very high viscosity, it has been termed “viscose”.
Ripening:
The viscose is allowed to stand for a period of time to “ripen”. Two important
processes occur during ripening: Redistribution and loss of xanthate groups.
The reversible xanthation reaction allows some of the xanthate groups to revert
to cellulosic hydroxyls and free CS2. This free CS2 can then escape or react
with another hydroxyl on other portions of the cellulose chain. In this way, the
ordered, or crystalline, regions are gradually broken down and a more
complete solution is achieved. The CS2 that is lost reduces the solubility of the
cellulose and facilitates the regeneration of the cellulose after it is formed into
a filament.
(C6H9O4O-SC-SNa)n + nH2O —> (C6H10O5)n + nCS2 + nNaOH
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33. Chemical Properties
Viscose rayon consists of cellulose of lower DP than cotton cellulose. Also, the
amorphous region of Viscose rayon is present to a greater extent, therefore, Viscose rayon
reacts faster than cotton with chemicals.
1. Acids like H2SO4 HCL breaks the cellulose into nitrocellulose.
2. Oxidising agents like Na(OCl)2, Bleaching powder, K2Cr2O7, KMnO4 form
oxycellulose.
3. Cold acid solutions for a short time do not attack viscose rayon.
4. Action of Solvents: Textile solvents can be used on Viscose rayon without any
Deteriorating effect. Viscose rayon dissolves in a cuprammonium hydroxide solution.
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34. 5. Effect of Iron: Contact with iron in the form of ferrous hydroxide
weakens viscose rayon yarns. Therefore staining, marking or touching of
rayon to iron or iron surface should be avoided.
6. Action of Microorganisms: Microorganisms (moulds, mildew,
fungus, bacteria) affect the colour, strength, dyeing properties and lustre
of rayon. Clean and dry viscose rayon is rarely attacked by moulds and
mildew.
7. Action of Soaps: Ordinary soaps in the usual textile concentration
have no direct effect on regenerated cellulose materials. Improper use of
soap or use of poorly made soap results in rancidity and odour in rayon. 34
