Rayon Manufacture Process_ppt-1.pdf

rayon manufacturing process

1. Manufacture of Rayon
Cellulose -plant cell wall
◦Abundant
◦Inexpensive
◦Renewable /biodegradable
Excellent source of textile fibres-RAYON
Industrial fiber –Tire cord
Cellulose molecules have strong intermolecular bond
◦Does not easily melt or dissolve
Chemists dissolve cellulose and further processed
Viscose process,
where cellulose converted into sodium cellulose xanthate, which
was soluble in a caustic solution, making it possible to wet-spin the
polymer into a fiber or film.
Consists of multiple steps and causes pollution
Many alternative methods like cuprammoniumor cellulose acetate
process was evolved to manufacture Rayon by dissolving cellulose
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2. Process of manufacturing viscose
rayon
Steeping
Shredding
Ageing
Xanthation
Dissolving
Filtering
Ripening
Spinning
Washing
Bleaching.
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3. Steps in manufacture process
Steeping:
Pulp sheets measuring 2 ×3 ft are placed
between perforated metal plates in the
trough or steeping press.
Around 20 sheets are arranged like a book
in the trough (steeping press)
Caustic soda (18-20% sodium hydroxide) is
added from bottom.
The pulp is allowed to soak (steep) in the
sodium hydroxide for about 20 min to 1 h
depending upon type of material produced.
Soaking will dissolve hemi cellulose and
make fibers to swell and converts the
cellulose to sodium cellulosate, commonly
called alkali celluloseor white crumb.
After steeping, the swollen mass is
compressed until its weight is brought
down to approximately three times its
original weight.
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4. Steps in manufacture process
Shredding:
Pulp sheets are shredded
mechanically in the shredder,
Pulp sheets are shredded into
finely divided fluffy particles
called ‘crumbs’.
The crumbs to provide
adequate surface area for
subsequent reactions.
Shredder resembling a bread
mixer, that rotate against a
serrated saddle bar to
disintegrate the pulp sheets.
In this operation fibers are
loosened and became uniform.
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5. Steps in manufacture process
Ageing:
The alkali cellulose is aged under controlled
condition of time and temperature (18˚ to 30˚ C)
in order to depolymerise the cellulose to the
desired degree of polymerization.
Aging also affects the processing characteristics of
viscose.
In addition, catalysts such as salts of manganese
and cobalt are added to the pulp sheets and the
steeping liquor to accelerate the aging.
During ageing average molecular weight of the
original pulp is reduced by a factor of two to
three.
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6. Steps in manufacture process
Xanthation:
Depolimerizedcellulose oxdized
Carbon disulfide is added crumbs to form
sodium cellulose xanthateat
temperature of 20˚ to 30˚ C.
This step is called xanthation,
Crumbs become yellow to orange crumb
and are easily dissolved in dilute sodium
hydroxide to yield a viscous orange
coloured solution called viscose.
Process is carried out in churn.
The churn is a hexagonal, jacketed vessel
with mixer blades and a hollow perforated
shaft through the center.
It has a centertube to admitting CS
2.
Xanthationreaction is exothermic and
must be controlled by chilled water running
through the jacket.
The reaction continues for a period of 30
min to hour.
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7. Steps in manufacture process
Dissolving:
Orange coloured cellulose xanthateis
discharged into tank called dissolver,
Further mixed and blended with sodium
hydroxide, water and sodium sulphite to
obtain uniform orange coloured solution
called “viscose”.
Forms the basisfor the manufacturing
process.
In the dissolver Xanthatecrumbs are forced
in the sides of the vessels in a draft tube and
then flows down the centerand through the
propeller blades continuously and
temperature is maintained to 16˚ to 17˚ C
for proper dissolving and complete
dissolving operation
2 to 3 hours at this stage.
The viscose solution is then filtered (to get
out the insoluble fiber material) and solution
is passed to ripening room or blender to
produce more viscose.
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8. Steps in manufacture process
Ripening:
From the blenders or dissolver,
the viscose enters the ripening
tank,
Viscose is stored for a period of
96 hours at definite
temperature for ripening
(storage time depends upon
type of viscose).
At this tank the viscose will
coagulates and ready to fit for
spinning.
During ripening the viscose is
filtered for at least three times
or more to remove solid
impurities, undissolvedor
partially undissolvedxanthate
or any other foreign material
which are liable to choke the
spinner jets during subsequent
spinning.
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10. Degassing or deaeration:
The bubble of air entrapped in the viscose is
removed in degassing operation prior to
spinning in ripening tank.
This is done by continuously by exposing a
thin film of viscose to relatively high vacuum
(28–29 in.Hg) immediately prior to pumping.
If not, it will form break in the continuity of
rayon filament.
This degassing operation is done in ripening
tank itself.
Once the viscose liquid attains adequate
consistence, then it is ready for feeding
spinning machine.
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11. Spinning
A spinning machine-several components
1.Metering pump that delivers viscose to the
spinneretteor jet
2.Troughs contain the spin-bath and other
processing baths as needed
3.Means to propel the filament bundle
through the machine and a mechanism for
collecting the fibers.
4.Spinnerette
Spinneretteis thimble-shaped and made of
corrosion-resistant metal, such as platinum or
gold, or glass.
They range in diameter from 0.5 in. to several
inches
Contain 1,000 to more than 20,000 holes of
precisely controlled size and configuration.
Holes are round and the number of holes,
and the degree to which the filaments are
stretched determine the filament denier
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12. Spinnerette
Filament Denier and Tow Size is determined
by
Rate at which viscose is delivered to the
spinnerette,
Number of holes, and
Degree to which the filaments are stretched.
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15. Spin-bath basically consists of
1.8-10% sulfuricacid (to acidify sodium
cellulose xanthate),
2.14-21% sodium sulphate (to impart a high
salt content to the bath which is useful in
rapid coagulation of viscose),
3.1% zinc sulfate,
4.Surfactant & water where it coagulate.
Coagulation of the filaments occurs
immediately upon neutralizing and acidifying
the cellulose xanthatefollowed by
simultaneous controlled stretching and
decomposition of the cellulose xanthateto
cellulose.
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16. At the prescribed distance from the
spinnerette, the fiber bundle is drawn
around a rotating wheel (godet), which
may serve as a holding point for
application of stretch.
A second wheel, or several wheels driven
at a higher speed, provides the stretching
tension.
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17. Washing:
The freshly regenerated rayon
contains many salts and other
water soluble impurities which
need to be removed by washing
with water and yarn is passed
through heated dryers.

Bleaching:
The yarn is dull yellowish in
colour and to obtain white yarn,
it is bleached with dilute
hypochlorite solution, later
subjected to wash and drying.
The viscose rayon is also used in
manufacture of transparent film
(cellophane) and pneumatic
types.
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18. Continuous filament is collected either in a
rapidly rotating centrifugal pot machine, on
a bobbin (spool or roller) on the bobbin
machine, or on a spool or reel on the
continuous machine.
Finishing (addition of lubricant and antistat),
drying (11%), and winding onto a cone.
Bales are ready for shipment
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21. Mechanical Properties of Viscose
Rayon
Medium-weight fiber
Not as strong as cotton
Abrades more easily than cotton
Weaker wet than dry strength
Not dimensionally stable
Tends to shrink progressively when laundered
Poor elastic recovery
Poor resilience (pliable or flexible)
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22. Chemical Properties of Viscose
Rayon
Very absorbent
◦Comfortable to wear
◦Dyes readily in rich vibrant colours
Burns like cotton
Conducts electricity –no static buildup
◦Catches fire when exposed to open flame.
◦Continues to burn when flame is removed.
◦Smells like burning paper
Acids and alkalis degrade it
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23. Uses of rayon
Apparel: Accessories, dresses, jackets, lingerie, linings,
millinery, slacks, sport shirts, sportswear, suits, ties, work
clothes
Home Furnishings: Bedspreads, blankets, curtains,
draperies, sheets, slipcovers, tablecloths, upholstery
Industrial Uses: Industrial products, medical surgical
products, nonwoven products
Other Uses: Hygiene products such as diapers, sanitary
pads etc.
Industrial yarns: Rayon strength is doubled by viscose
modifier, hence rayon is reinforced with rubber articles
to form tire cord, conveyor belt and hoses.
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