Regenerated Cellulosic Fibers/ Rayon
Rayon is the first regenerated cellulose fiber. Normally rayon is made from wood pulp. Those
wood pulp are turned into a liquid substance of cellulose. This liquid substance is forced through
a nozzle about the size of a thimble. This nozzle is known as spinneret. This spinneret is usually
made of a platinum-rhodium alloy because that metal is not affected by acids or alkalies.
Generally, there are 2 types of methods to produce rayon. 1. Viscose method and 2. High wet
modulus method.
Viscose Rayon
Viscose rayon is usually made from wood pulp mainly obtained from spruce, hemlock, and pine
trees.
Description of Viscose Rayon Manufacturing:
1. Preparation of the wood pulp: Viscose rayon is produced from special variety of wood.
But wood contains lignin other than cellulose. There the first stage for producing viscose
rayon is to purify cellulose from wood. Firstly, the barks are removed and Woods are
chipped into pieces & treated with Calcium Bisulfite [Ca(HSO3)2]. Then these treated
chips are cooked with steam under pressure for 14 hours.
2. Steeping & pressing: This prepared wood pulps contain about 90 to 94% of pure cellulose.
They are first conditioned by storing in a room at a definite humidity and temperature. The
pulps are then soaked in a 17.5% solution of NaOH for 1 to 4 hrs.
3. Shredding: The shredding m/c consists of a drum inside which revolve a pair of blades
with serrated edges. In 2 or 3 hrs. they break it up into fine ‘crumbs’ (break into very small
pieces).
4. Ageing: After shredding, the crumbs are aged. They are contained in a galvanized vessel
with a lid and through oxidation with atmospheric oxygen, degradative changes set in.
some depolymerization occurs and the degree of polymerization falls from about 5000 to
350 in this process. The higher the temp. the more rapidly does ageing.
5. Churning: After ageing, the soda cellulose crumbs are introduced into rotating air-tight
hexagonal churns. About 10% of their own (crumbs) weight of CS2 is added and the
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crumbs and CS2 are churned up together. As a result, a deep orange gelatinous sodium
cellulose xanthate is formed.
6. Mixing: In the mixers, the sodium cellulose xanthate is stirred with dilute caustic soda
(NaOH) solution for 4 to 5 yrs., the vessel being cooled. The xanthate dissolves to a clearbrown viscous liquid similar in appearance to honey. This liquid is known as viscose but
is still too impure, too young to spin.
7. Ripening: The sodium cellulose xanthate reacts with H2SO4 & form regenerated
cellulose. The viscose solution is stored for 4 to 5 days at 10-18®C and during storage it
ripens. During the ripening the viscosity at first falls and then rises, so that by the time the
solution is ready to spin, the viscosity has risen almost to its original value.
8. Spinning: when the viscose solution is ripe, it is forced to be fed in the spinneret of a
spinning unit with additives to form viscose.
Bamboo
Bamboo is bast fiber like jute, flax, ramie etc.
Chemical Composition
Cellulose: (70-74) %
Hemicellulose: (12-14) %
Lignin: (10-12) %
Protein, Pectin, Wax etc.: (2-3) %
Fig 1: Polymeric Structure of Bamboo
Microscopic Appearance
Fig 2: Longitudinal View
Fig 3: Cross-Sectional View
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Manufacturing Process
There are two methods to manufacture bamboo.

Chemical Method

Mechanical Method
Chemical Method: For making bamboo two chemical method is followed. One is viscose rayon
method and other is lyocell processing method. In Viscose rayon method, many chemicals are
used which is harmful to environment but still it is the easiest method to produce bamboo fiber.
Also, molecular structure of the bamboo changes if produced using this method. On the other hand,
Lyocell method is eco-friendly and also don’t alter the structure of the bamboo.
Mechanical Method: Bamboo fabric of the highest quality is made with production practices that
do not extract cellulose. Instead, a natural enzyme is used on crushed bamboo wood fibers, and
these fibers are then washed and spun into yarn. This yarn usually has a silky texture, and the fabric
made by this process is sometimes called bamboo linen. It is actually true natural bamboo fiber
processing.
Advantages of Bamboo Fiber:
1. Green and eco-friendly: As it is 100% cellulosic it is bio degradable in nature
2. Soft & Breathable: Cross section of bamboo fibers are filled with micro gaps and micro
pores. So, it has better moisture absorption and ventilation
3. Natural Anti-bacterial Property
4. UV Protection Property
Lyocell
Lyocell is also regenerated cellulosic fiber like viscose but it is produced in a different method
than viscose. In viscose production, normally CS2 (Carbon disulfide) is used which is harmful for
environment. But in case of Lyocell, carbon disulfide is not used. So, it is much more sustainable
than viscose.
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Manufacturing Process
Preparing the wood pulp
The hardwood trees grown for lyocell production are harvested by loggers and trucked to the mill.
At the mill, the trees are cut to 20 ft (6.1m) lengths and debarked by high-pressure jets of water.
Next, the logs are fed into a chipper, a machine that chops them into squares little bigger than
postage stamps. Mill workers load the chips into a vat of chemical digesters that soften them into
a wet pulp. This pulp is washed with water, and may be bleached. Then, it is dried in a huge sheet,
and mill workers roll it onto spools. The sheet of cellulose has the consistency of thick posterboard
paper. The roll of cellulose is enormous, weighing some 500 lb (227 kg).
Dissolving the cellulose
At the lyocell mill, workers unroll several spools of cellulose and break them into one-inch squares.
The workers then load these squares into a heated, pressurized vessel filled with amine oxide.
Filtering
After a short time soaking in the solvent, the cellulose dissolves into a clear solution. It is pumped
out through a filter, to insure that all the chips are dissolved.
Spinning
Next, the solution is pumped through spinnerets. These are devices used with a variety of manmade
fibers. Something like a showerhead, the spinneret is pierced with small holes, and when the
cellulose is forced through it, long strands of fiber come out. The fibers are then immersed in
another solution of amine oxide, diluted this time. This sets the fiber strands. Then, they are washed
with de-mineralized water.
Drying and finishing
The lyocell fiber next passes to a drying area, where the water is evaporated from it. The strands
at this point pass to a finishing area, where a lubricant is applied. This may be a soap or silicone
or other agent, depending on the future use of the fiber. This step is basically a detangler, making
the future steps of carding and spinning into yarn easier.
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Final steps
The dried, finished fibers are at this stage in a form called tow. Tow is a large untwisted bundle of
continuous length filaments. The bundles of tow are taken to a crimper, a machine which
compresses the fiber, giving it texture and bulk. The crimped fiber is carded by mechanical carders,
which perform an action like combing, to separate and order the strands. The carded strands are
cut and baled for shipment to a fabric mill. The entire manufacturing process, from unrolling the
raw cellulose to baling the fiber, takes only about two hours. After this, the lyocell may be
processed in a wide assortment of ways. It may be spun with another fiber, such as cotton or wool.
The yarn can be woven or knit like any other fabric, and given a variety of finishes, from soft and
suede-like to silky.
Recovery of the solvent
The amine oxide used to dissolve the cellulose and set the fiber after spinning is recovered and reused in the manufacturing process. The dilute solution is evaporated, removing the water, and the
amine oxide is routed for re-use in the pressurized vessel in step 2. Ninety-nine percent of the
amine oxide is recoverable in the typical lyocell manufacturing process.
Brand
Lyocell was trademarked as “Tencel” in 1982. Other than Tencel, Lyocell has different trademark
names. Such as

Lenzing Lyocell (Lenzing)

Newcell(Akzo Nobel)

Seacell (Zimmer AG)

Excel (Birla)
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