#Introduction:-
●Regenerated fibres are manufactured from a natural polymer, cellulose, which is obtained from wood.
●Cellulose is reacted chemically so as to make viscos solution which can be extruded to make viscose fibres. These fibres are chemically similar to cotton and share their desirable properties of moisture absorbancy.
●The first regenerated fibre, called rayon, which was originally intended to be a substitute for silk.
●Viscose rayon is a regenerated cellulosic fibre and cellulose is the raw material for producing this fibre.
●It is obtained by the process viscose. The name viscose was derived from the liquid state of the spinning solution as the spinning solution is thick and flow like honey.
●Chemical formula of viscose rayon:-
●Chemical formula of viscose rayon:-
Manufacturing steps of Viscose Rayon:-
1. Purification of Cellulose:-
•The Spruce trees are cut into timber. Removed their barks and cut into pieces measuring 7/8" x 1/2" x 1/4".
•The Spruce trees are cut into timber. Removed their barks and cut into pieces measuring 7/8" x 1/2" x 1/4".
•These pieces are treated with a solution of calcium bisulphite and cooked with steam under pressure for about 14 hours.
•The cellulosic component of the wood is not affected by this treatment.
•But the cementing material of wood called lignin, is converted into its sulphonated compound which is soluble in water.
•This can be washed off, thereby purifying the remaining cellulose.
• This cellulose is treated with excess of water. After this it is treated with a bleaching agent (sodium hypochlorite) and finally converted into sheets or wood pulp.
2. Conditioning of Wood Pulp: -
•The pulp sheets are kept in a special room where temperature is maintained at 30℃.
•The pulp sheets are kept in a special room where temperature is maintained at 30℃.
•Air moves freely among the divisors by means of ventilatorys. In this way the desired moisture content can be had.
3.Steeping Process:
•It is also called mercerising.
•It is also called mercerising.
•The conditioned wood pulp sheets are soaked in steeping tank with 17-18% caustic soda(NaoH) solution for 30-60min at temperature 18℃.
•The high DP(degree of polymerization) cellulose (1000) is converted into soda cellulose.
•After steeping, sheets of cellulose are pressed to remove the excess alkali.
4. Shredding or cutting process:
•The wet, soft sheets of soda cellulose are passed through a shredding machine which cuts them into small bits.
•The wet, soft sheets of soda cellulose are passed through a shredding machine which cuts them into small bits.
•In 2-3 hours the sheets are broken into fine crumbs.
5. Ageing Process:
•This is depolymerization step in presence of oxygen.
•This is depolymerization step in presence of oxygen.
•Here the degree of polymerization of soda cellulose is decreased from 1000 to about 300.
•During this process the soda cellulose is stored in rectangular galvanised steel drums for about 24-72hours at 25-30℃ covered with lids.
6. Churning Process or Xanthation:
•After ageing, the crumbs of soda cellulose are transferred to rotating, air tight, hexagonal churners or mixers.
•After ageing, the crumbs of soda cellulose are transferred to rotating, air tight, hexagonal churners or mixers.
•Carbon disulphide ( 10% of the weight of the crumbs) is added to the mixer and churned together for 3 hours by rotating the mixers at a slow speed of 2-4 revolution per minutes.
•During this process and the colors of the product changes from white to yellow, yellow to deep yellow and then to reddish orange.
7. Mixing or dissolving Process:
•The orange product i.e. sod.cell.xanthate is in the form of small balls.
•The orange product i.e. sod.cell.xanthate is in the form of small balls.
•These fall into a mixer called dissover which is provided with a stirrer.
•A dilute solution of caustic soda is added, and the contents are stirred for 4-5 hours and at the same time, the dissovler is cooled.
The sod.cell.xan. dissovles to give a clear brown thick liquor, similar to honey. This is called 'viscose' and it contains about 6.5% caustic soda and 7.5% cellulose.
8. Ripening Process:
This viscose solution requires to be ripened to give a solution having best spinning qualities.
This viscose solution requires to be ripened to give a solution having best spinning qualities.
•Ripening is carried by storing the viscose solution for 4-5 days at 15 to 25 ℃.
•The viscosity of the solution first decreases and then rises to its original value. The ripened solutoin is filtered carefully and is now ready for spinning to produce viscose rayon filaments.
9. Spinning Process:
•The viscose solution is forced through a spinnerette, having many fine holes ( 0.05-0.1mm) diameter.
•The spinnerette is submerged into a solution containing the following chemicals.
H2SO4 8-10%
Na2SO4. 16-24%
Glucose. 2%
ZnSO4. 1-2%
H2O. 69%
H2SO4 8-10%
Na2SO4. 16-24%
Glucose. 2%
ZnSO4. 1-2%
H2O. 69%
•The spinning solution is kept at 40-45 deg celcius.
•Sodium sulphate precipitates the dissoved sod. cell.xanthate.
•Sulphuric Acid converts xanthate into cellulose,Carbon disulphide and sod. sulphate.
•The glucose is supposed to give softness and pliability to the filaments whereas zinc sulphate gives added strength.
# Properties
(A) Physical properties
(i) Degree of polymerization -175-240 celluboise(ii) Amorphous region - 60 65%
(iii) Crystalline region - 35 - 40%
(iv) Moisture regain - 11-12℅
(v) Tenacity - 14 - 45 g/tex (dry)
50% of the dry (wet)
(vi) Specific gravity - 1.49 g/cm3
(B) Chemical properties
●Chemical properties of the viscose rayon are similar to cotton being cellulosic fibrė.
●Chemical properties of the viscose rayon are similar to cotton being cellulosic fibrė.
●Shorter polymer and very amorphous region are responsible for greater sensitivity to acids, alkalis, bleaches, sunlight and weather in comparison to cotton.
#Uses
●The role of viscose rayon in the field of man-made fibres is similar to that of cotton in natural fibres.
●Rayon is relatively cheap and has a wide range of applications.
●Its lustre is high but it can be appropriately delustred.
●Viscose rayon conducts heat more readily than silk, the most lustrous natural fibre, and rayon has a cooler feel against the skin.
●The loss of strength that viscose undergoes under wet conditions can be controlled and brought to a minimum by modern resin finishes.
●Rayon staple is quite largely used in this fashion.
●Rayon imparts its unique moisture absorption character and some other 'cellulosic' features to its blends with stronger, lighter and less moisture absorbing fibres.
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