Viscose Rayon

Viscose is a man made, natural polymer, cellulosic or regenerated cellulose filament or staple fiber. According to U.S. Federal Trade Commission “Rayon is a manufactured fiber composed of regenerated cellulose in which substituent’s have replaced not more than 15% of the hydrogen’s of the hydroxyl groups”.

Types of Regenerated cellulose fiber: Regenerated cellulose fibers are three types. They are:

1. Viscose.
2. Cuprammonium/ Cupro.
3. Polynosic/Modal.

Chemical reaction for viscose rayon production: Regeneration reaction:

1. The cellulose is treated with 17.5% solution of NaOH which converts into soda-cellulose.

Cell-OH+ NaOH → Cell-OHa+ H₂O

 Cellulose                    Soad-cellulose

2. The soda cellulose reacts with carbon disulphide to form sodium cellulose xanthate.

Cell-ONa+ CS₂ → Cell-O-CS-SNa

3. Then it is dissolved in a dilute solution of caustic soda. It is extruded into H₂SO₄ which regenerates the cellulose. Now in the form of long filaments.

Cell-O-CS-SNa+ H₂SO₄ → Cell-OH+ Na₂SO₄

                                                Regenerated cellulose

Flow chart of viscose rayon:

Cellulose pulp

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Steeped in warm caustic soda for an hour

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Pressed to remove excess solution

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Powdery Crumbs

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Aged for up to a day (formation of soda cellulose)

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Mixed with carbon disulphide (formation of sodium cellulose xanthade)

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Mix into a dilute caustic soda solution (to give a viscose solution)

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Ripening for up to a day (Regenerated cellulose)

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Spinning

Physical properties of Viscose Rayon:

1. Moisture absorption: Viscose rayon absorbs moisture more than cotton. Viscose rayon moisture content 13% at 65% relative humidity.
2. Tensile strength: Less tensile strength than cotton in wet condition.
3. Elasticity: Less elasticity than cotton, about 2-3% less.
4. Abrasion resistance: Low.
5. Flammability: Like as cotton.
6. Melting temp: Do not decompose at 176ºC to 204ºC.

Chemical properties of viscose rayon:

1. Effect of acid: Acid like H₂SO₄ or HCl, break down the macromolecules of viscose and produce hydro-cellulose. Dilute acid for short time do not attack.
2. Effect of alkali: Concentrated alkali causes swelling and reduces strength. But week alkali does not damage.
3. Effect of bleaching: Viscose can withstand both oxidizing and reducing bleaches.
4. Biological agent: mildew, bacteria etc affect the color, strength and luster of rayon.
5. Dye affinity: Better affinity for dyes than cotton.
6. Flammability: Burns rapidly.

End uses of viscose rayon:

1. It is used in making umbrella cloths and protective cloths.
2. It is used as sewing embroidery threads.
3. Viscose + cotton, this blend is used for reducing cost.
4. Viscose + polyester, this blend is used for comfort strength and absorbency.
5. Uses in curtains, cushions, beach and sports wear.
6. Fire fabrics and evening gowns.