Topic 08
MAN-MADE FIBRE
Iffat Ara Anannya , Lecturer , DTE, AUST
Regenerated Cellulosic Fibre
Regenerated cellulosic fibres are simply regenerated from wood pulp or cotton linters, without any
change in chemical constitution of the polymer. But there is only a certain variation in degree of
polymerization and has modified physical properties.
Regenerated cellulose fibres: Viscose fibre, Cuprammonium fibre, Lyocell fibre, Acetate and Triacetate
fibres. Special regenerated cellulose fibres called Modal fibres (Polynosic and HWM).
The raw materials are deconstructed into fluffy white cellulose and then turned into a viscous resin (by
dissolving/by melting/by chemical reaction), which is forced through spinnerets and then hardened as
a fibre.
Raw materials:
 Linters (fuzz of cotton seeds): Pure cellulose

Wood (Beech/Pine)

Straw (Wheat/ Rye)
Must undergo an opening process. Non-cellulosic components such as
lignin, pectin, hemicellulose etc. (can be as high as 60%) must be removed.
Viscose Rayon
Basic concept:
i.
Viscose rayon is a regenerated cellulose fibre. The cellulose comes from wood.
ii.
It is purified and treated with caustic soda
iii.
Soda cellulose is then treated with carbon disulphide
which converts it into soda cellulose.
which converts it into sodium
cellulose xanthate.
iv.
Sodium cellulose xanthate is dissolved in dilute caustic soda solution.
v.
This solution is then ripened and spun into an acid coagulating bath, which precipitates
cellulose in the form of a viscose filament.
Chemical Nature
The cellulose which constitutes viscose rayon differs chemically from the original cellulose
of the wood in only one respect – the very long cellulose molecules of the wood have
been partly hydrolysed and have been broken down into shorter molecules. In wood
cellulose the molecules contains about 1000 of the glucose residues. Whereas in viscose,
the cellulose molecules contains about 270.
Apart from the fact that viscose cellulose molecules are shorter from wood cellulose
molecules, they are similar. Viscose yarn is chemically same as wood cellulose.
There is a difference in the packing of the molecules between original and regenerated
cellulose.
Chemical reaction for manufacture
The chemical reactions that are involved in the manufacture of viscose are as follows:
1.
The cellulose is treated with a 17.5%
solution of caustic soda which converts
it into soda cellulose.
2.
The soda cellulose is then reacted with
carbon disulphide producing
cellulose xanthate.
sodium
(Cont…)
Each glucose residue in the cellulose polymer chain reacts in the following manner:
3. After the ripening of the sodium
cellulose xanthate solution, it is
spun into a coagulating bath of
sulphuric acid which completes
the conversion of the sodium
cellulose xanthate to cellulose.
+ CS2 + ½ Na2SO4
+ ½ H2SO4
Viscose
The complete series of chemical reactions by which viscose is made essentially consists of the following stages:
1. Wood cellulose and concentrated caustic soda reacts to form soda cellulose.
2. The soda cellulose reacts with carbon disulphide to form sodium cellulose xanthate.
3. The sodium cellulose xanthate is dissolved in dilute caustic soda to give a viscose solution.
4. The solution is ripened.
5. It is extruded into sulphuric acid which regenerates the cellulose, now in the form of long filaments
of viscose rayon.
Flow chart for Manufacturing
Preparation of wood pulp
Steeping and pressing (1-4 hr, 17.5% NaOH, formation of soda cellulose, press-out the excess alkali)
Recovery of caustic soda
alkali)
Shredding (consists of a drum with rotating blades with serrated edges. In 2-3 hrs the boards are
broken into crumbs)
Ageing (3½ days at 22°C the crumbs are kept in galvanized vessel. DP falls from 800 to 350 due
to oxidation)
Churning (xanthation) (10% on the wt. of crumbs CS2 is added- A deep orange color gelatinous sodium
cellulose xanthate is produced)
Mixing (Dilute NaOH)
Ripening (10-18°C, 4-5 days, DP fall 350 to 270)
Spinning
Manufacturing process of Viscose rayon
Properties of viscose rayon
1. Tenacity and elongation: Ordinary viscose rayon is reasonably strong. Its tenacity is 2.6 g/denier.
The wet strength is about 1.4 g/denier. The elongation at break (dry) is about 15% and (wet) about
25%.
2. Moisture content: Under standard conditions (65% RH and 70°F) the moisture content is 12-13%.
The lower the humidity the lower is the moisture content and vice versa.
3. Creep: The elasticity of viscose rayon is not so high. If stretched and released from strain it does
not quite return to its original length, although after some time it continues to shrink, but not
completely to its original length. This is described as “delayed elasticity” or “creep” or “plasticity”.
4. Density: The Specific gravity of viscose rayon is 1.52.
5. Electrical properties: Owing to its high moisture content it is not used for insulation purposes.
When dry it is quite good insulator. Viscose is not liable to develop static electricity.
6. Resistance to light: On exposure to light, photocellulose is formed and weakening takes place.
7. Resistance to heat: Ironing property is satisfactory, although on lengthy exposure to high
temperature it turns yellow.
(cont…)
Chemical properties: Acids attack viscose more quickly than cotton. Cold solutions of acids
and short time treatment do not usually cause tendering. At high temperatures acids
carbonize viscose.
9. Biological resistance: Moulds and mildew discolor and weaken viscose rayon. Moth larvae will
eat viscose mixed with wool; they do not attack all viscose fabrics.
10. Susceptibility to bleach: Sodium hypochlorite, neutral, is most satisfactory. Potassium
permanganate followed by a clearing solution of sodium bisulphite may be used. H2O2 can be
used at temperature not more than 550C.
11. Actions of solvents: Dry cleaning solvents do not attack viscose.
12. Morphology: under the microscope the longitudinal view is that of a striated cylinder, while
the cross-section is highly serrated.
8.
Uses
Viscose rayon is suitable for all normal textile needs, including apparel, but are not
suitable for sea-ropes, fishing lines and nets, insect netting or materials subject to
chemical contacts. Typically used for- curtains, chair covering, transport furnishings, tablecloths, cushions, bed covers, quilt covers, lace, fine fabrics, day and afternoon dresses,
beach and sports wear and underwears.
Synthetic Fibre
Synthetic fibres are derived from substances that are not present in nature, but
instead created through chemical reactions (synthesis) from petrochemical products.
True synthetic fibres are non-cellulosic. Examples are polyamide (nylon),
polyester, acrylic, modacrylic, polyurethane (spandex), polyethylene, polypropylene etc.
True synthetic polymer fibres are products of the polymerization of smaller
chemical units into long chain molecular polymers.
Polyester
Polyester
Polyester
Polymer Production:
I.
Transesterification:
II. Direct Esterification
(Cont…)
Polycondensation:
Polyester
Polyester Fibre Characteristics
Properties of Polyester
Uses & Behaviour of Polyester-based Textiles
Polyester
Polyamide (Nylon)
Nylon 6.6 & Nylon 6
Properties of Nylon
Uses and Behaviour of Nylon-based Textiles
Acrylic
Acrylic Fibre
Properties of Acrylic
Acrylic Fibre Characteristics