Step 1: Purification of cellulose:
• Spruce tress are cut into timber, their barks are removed and then
cut into small pieces.
• these pieces are treated with solution of calcium bisulphite [Ca
(HSO3)2] and cooked with steam under pressure for 14 hrs. The
cellulsoe is unaffected by this treatment but the lignin which is
present in the wood is converted into its soluble sulphonated
compound which is soluble in water and is washed off by purifying
the remaining cellulose.
• after cooking wood with calcium bisulphite a large amount of
water is added, when cellulose pulp is floats, it is sucked through
the slots; about 0.2 mm wide. A slurry containing about 30 %
cellulose is made which is then treated with bleaching agent and
finally converted into paper boards or sheets. Thjs is wood pulp
which is normally purchased by manufacturing.
Step 2: conditioning of wood pulp
The flat, bleached sulphite wood pulp sheets, containing 90 – 94%
cellulose are kept in a room at definite temp and humidity for a
sufficient time. This is called conditioning . The temperature is
maintained by air ventilation at 30 °C.

Step 3: Steeping process
The conditioned sheets are treated with caustic soda solution (17.5%).
This is called steeping process. Uniform impregnation of material
with solution is essential . Sheets are allowed to sock until they
become dark brown in colour. It takes about 1-14 hours. Now the
degree of polymerization of wood cellulose is about 1000. this
cellulose contain about 8-10% hemicelluloses which dissolve in
caustic soda solution used in steeping process. The excess caustic
soda solution and hemicelluloses dissolved in it is removed by
pressing sheets in hydraulic press. The sheet are then transformed
to a shredding machine for next opertaion. 100 kg of sulphite pulp
gives about 310 kg of soda cellulose containg some caustic soda
liquor.

Step 4: Shredding process
The soda cellulose falls into shredding machine
which contain two arms, bearing toothed
wings which cut the pulp sheet into small bits.
Thus they convert into fluffy snow like masses
of alkali cellulose. In 2-3 hours the sheets are
broken into fine crumbs.
 Step 5: Ageing process
During this process the DP is decreased from 1000
to about 300 by the oxygen present in the air,
contained in the drum. The soda cellulose is
kept in steel drums at 23°C for 48 hrs.


Step 6: churning process
This process is also called xanthation or sulphidising process. After
ageing the crumbs are transferred to rotating, air-tight hexagonal
churners which are similar to cement mixtures. Carbon disulphide
(10% of the weight of the crumbs) is added to the mixture and
churn together for 3 hrs by rotating the mixture at slow speed of 2
rev/min. sodium cellulose xanthate is formed during this process
and colour of the product changes from white to light yellow, to
deep yellow and then to reddish orange. After churning is over,
the ill-smelling vapors of carbon disulphide is removed by applying
vacuum.

Step 7: Mixing or dissolving process
The orange product from churner is in the form of small balls. They fall
into vessel, a dil solution of caustic soda is also added and the
contents are stirred for 4-5 hrs. the sodium cellulose xenthate
dissolve to give a clear brown thick viscose liquor called viscose. It
contains about 6.5% caustic soda, 7.5 % cellulose. Viscose from eight
different vissolvers are mixed together in one big mixer and
undissolve fibres are removed through filtration.
Step 8: ripening process
The viscose solution require to ripen to give the best solution for spinning.
Ripening is carried out by storing the viscose solution for 2-5 days at 10 to
18°C. During this period the viscosity drops and then rise back to the
original value due to sedimentation. The viscose solution is again filtered
and now its ready for spinning.

Step 8: spinning process
In spinning viscose solution is forced through the spinneret by compressed
air (40 – 75 lb/in pressure). The spinneret have many fine holes (0.05 -0.1
mm) and it submerge into a solution containing the following chemicals;
10%
sulphuric acid
18%
sodium sulphate
1%
Zinc sulphate
2%
glucose
69%
water
Temperature is kept at 40-45°C. sodium sulphate precipitates the dissolve d
sodium sulphate xanthate and sulphuric acid converts the xanthate into
cellulose, carbon disulphide and sodium sulphate. Glucose gives softness
and pliability to filaments. While zinc sulphate gives added strength.
The remaining process include washing with water to remove chemicals
followed by washing with sodium sulphide solution (25-30 gm/liter) at
65°C to free filaments from residual sulphur, the process is called
desulphurizing.

Macro-structure of viscose
Viscose is a fine regular filament or staple fibre (crimped
confrigation). The length of staple fibre cut from
viscose filaments depends upon the required end-use.
Usually they are cut into lengths similar to cotton, flex
and wool. Viscose fibre dia ranges form 12 μm to 22
μm, depending upon fibre end use. This gives fibre to
breath ration in excess of 2000:1, ensuring even the
shorter fibre will spin satisfactorily into yarn.
The colour of the filaments tends to be slightly off-white.
This is attributed to their translucency which permits
some light to pass through the filaments before it is
reflected.
Viscose filaments have many longitudinal striations (tiny
groove) which give them their characteristic
appearance. They are responsible for irregular
perimeter of their nearly round to oval cross-section.
Such skin feels more comfortable than the much more
intimate contact of non-striated fibres.

The polymer system
The polymer system is similar to cotton. However
the viscose polymer does not have spiral
configuration of the cotton polymer.
The viscose polymer is very amorphous, being about
35-40%
crystalline
and about 60-65%
amorphous. Its short polymer chains make its
difficult to achieve a more crystalline polymer
system.
Tenacity:
Polymer system of viscose is very amorphous and
filament s and fibers are weak. When wet, viscose is
only half as strong as when dry.

Elastic plastic nature:
It is limp handling fiber. Polymer system not
sufficiently long so hydrogen bonds formation is
restricted due to which viscose fiber has crisper
handle. When filament is put under strain, the
polymer do not come to original position. so the
filaments disarranged and will become stretched,
wrinkled and distorted.

Hygroscopic nature:
The polymer system is very absorbent due to
amorphous region and polar polymers.
Static electricity property is same as cotton.
 Chemical properties:
With regard to dyeing and printing, the
regenerated cellulose fibers will generally color
more brightly, even when delutered, than even
their mercerized cotton . This is due to greater
amount of incident light reflected by viscose,
even when delustered.
